CROSS REFERENCE

[0001] The present Application for Patent claims priority to U.S. Patent Application No. 17/096,101 by TAKEDA et al., entitled “MULTICAST FEEDBACK BASED ON ACKNOWLEDGEMENT TRANSMISSIONS” filed November 12, 2020, which claims the benefit of U.S. Provisional Patent Application No. 62/935,838 by TAKEDA et al., entitled “MULTICAST FEEDBACK BASED ON ACKNOWLEDGMENT TRANSMISSIONS,” filed November 15, 2019, assigned to the assignee hereof.

FIELD OF TECHNOLOGY

[0002] The following relates generally to wireless communications and more specifically to techniques for reporting multicast feedback based on acknowledgment transmissions.

BACKGROUND

[0003] Wireless communications systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems may be capable of supporting communication with multiple users by sharing the available system resources (e.g., time, frequency, and power). Examples of such multiple- access systems include fourth generation (4G) systems such as Long Term Evolution (LTE) systems, LTE-Advanced (LTE-A) systems, or LTE-A Pro systems, and fifth generation (5G) systems which may be referred to as New Radio (NR) systems. These systems may employ technologies such as code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal frequency division multiple access (OFDMA), or discrete Fourier transform spread orthogonal frequency division multiplexing (DFT-S-OFDM).

[0004] A wireless multiple-access communications system may include one or more base stations or one or more network access nodes, each simultaneously supporting communication for multiple communication devices, which may be otherwise known as user equipment (UE). In some cases, a base station may perform a transmission that carries one or more sets of data that are each intended for a respective UE. Such a transmission may be referred to as a unicast transmission. Additionally, or alternatively, a base station may perform a transmission that carries a set of data that is intended for multiple UEs. Such a transmission may be referred to as a multicast transmission.

SUMMARY

[0005] The described techniques relate to improved methods, systems, devices, and apparatuses that support reporting multicast feedback based on acknowledgment transmissions. In some cases, a set of uplink communication resources may be shared among multicast-enabled user equipments (UEs), where each uplink communication resource may be configured to be associated with particular set(s) of channel state information. Based on the association, a UE may indicate channel state information measured by the UE by transmitting over an uplink communication resource that is associated with the measured channel state information.

[0006] For example, a set of uplink control channel communication resources configured for acknowledgment feedback may be shared among multicast-enabled UEs or multicast- configured UEs, and each uplink control channel communication resource may be configured to be associated with a particular set of channel state information. The multicast-enabled UEs or multicast-configured UEs may transmit acknowledgment feedback over the shared set of uplink control channel communication resources based on channel state information determined by the multicast-enabled or configured UEs. For example, after determining a set of channel state information, a multicast-enabled or configured UE may select an uplink control channel communication resource that is associated with the channel state information. In some cases, the uplink control channel communication resource may be associated with (e.g., logically assigned to) the same set of channel state information determined by the multicast-enabled or configured UE. In other cases, the uplink control channel communication resource may be associated with (e.g., logically assigned to) multiple sets of channel state information that include the set of channel state information determined by the multicast-enabled or configured UE. After selecting the uplink control channel communication resource, the multicast-enabled or configured UE may transmit an acknowledgment message over the selected uplink control channel resource. The acknowledgment message may be a negative acknowledgment message.

[0007] A method of wireless communications at a UE is described. The method may include receiving an indication of uplink control channel resources for reporting acknowledgement feedback by the UE for multicast communications, the uplink control channel resources to be shared by UEs associated with the multicast communications, measuring one or more multicast channels or one or more signals monitored by the UE to determine a set of channel state information for UE receipt of the multicast communications, selecting one of the uplink control channel resources based on an association between the set of channel state information and the one of the uplink control channel resources, and transmitting an acknowledgement feedback message over the one of the uplink control channel resources.

[0008] An apparatus for wireless communications at a UE is described. The apparatus may include a processor, memory coupled with the processor, and instructions stored in the memory. The instructions may be executable by the processor to cause the apparatus to receive an indication of uplink control channel resources for reporting acknowledgement feedback by the UE for multicast communications, the uplink control channel resources to be shared by UEs associated with the multicast communications, measure one or more multicast channels or one or more signals monitored by the UE to determine a set of channel state information for UE receipt of the multicast communications, select one of the uplink control channel resources based on an association between the set of channel state information and the one of the uplink control channel resources, and transmit an acknowledgement feedback message over the one of the uplink control channel resources.

[0009] Another apparatus for wireless communications at a UE is described. The apparatus may include means for receiving an indication of uplink control channel resources for reporting acknowledgement feedback by the UE for multicast communications, the uplink control channel resources to be shared by UEs associated with the multicast communications, measuring one or more multicast channels or one or more signals monitored by the UE to determine a set of channel state information for UE receipt of the multicast communications, selecting one of the uplink control channel resources based on an association between the set of channel state information and the one of the uplink control channel resources, and transmitting an acknowledgement feedback message over the one of the uplink control channel resources.

[0010] A non-transitory computer-readable medium storing code for wireless communications at a UE is described. The code may include instructions executable by a processor to receive an indication of uplink control channel resources for reporting acknowledgement feedback by the UE for multicast communications, the uplink control channel resources to be shared by UEs associated with the multicast communications, measure one or more multicast channels or one or more signals monitored by the UE to determine a set of channel state information for UE receipt of the multicast communications, select one of the uplink control channel resources based on an association between the set of channel state information and the one of the uplink control channel resources, and transmit an acknowledgement feedback message over the one of the uplink control channel resources.

[0011] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, the selecting may include operations, features, means, or instructions for identifying the one of the uplink control channel resources based on the set of channel state information determined by the UE.

[0012] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for determining that the set of channel state information includes a channel state information (CSI)-reference signal index, a precoding matrix index, and a channel quality index, and identifying the one of the uplink control channel resources as being associated with the CSI- reference signal index, the precoding matrix index, and the channel quality index.

[0013] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for identifying a set of the uplink control channel resources that may be associated with one or more CSI-reference signal indices, where the one of the uplink control channel resources may be selected from the set of the uplink control channel resources.

[0014] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for identifying a set of the uplink control channel resources that may be associated with one or more precoding matrix indices, where the one of the uplink control channel resources may be selected from the set of the uplink control channel resources.

[0015] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for identifying a set of the uplink control channel resources that may be associated with one or more channel quality indices, where the one of the uplink control channel resources may be selected from the set of the uplink control channel resources.

[0016] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for determining that the set of channel state information includes a CSI-reference signal index, and identifying a set of the uplink control channel resources that may be associated with the CSI-reference signal index, where the one of the uplink control channel resources may be selected from the set of the uplink control channel resources.

[0017] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for determining that the set of channel state information includes a precoding matrix index, and identifying, from the set of the uplink control channel resources, a subset of the uplink control channel resources that may be associated with a first set of precoding matrix indices including the precoding matrix index, where the one of the uplink control channel resources may be selected from the subset of the uplink control channel resources.

[0018] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for determining that the set of channel state information includes a channel quality index, and identifying, from the subset of the uplink control channel resources, a first uplink control channel resource that may be associated with a first set of channel quality indices including the channel quality index, where the first uplink control channel resource may be selected as the one of the uplink control channel resources.

[0019] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for identifying, from the subset of the uplink control channel resources, a second uplink control channel resource that may be associated with a second set of channel quality indices including the channel quality index, where the first uplink control channel resource or the second uplink control channel resource may be selected as the one of the uplink control channel resources.

[0020] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for determining that a condition of the one or more multicast channels may have changed by a threshold amount, where the UE may be associated with a second group of UEs based on the condition changing by the threshold amount, and selecting a different uplink control channel resource of the uplink control channel resources based on being associated with the second group of UEs.

[0021] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving a first multicast transmission using a first set of transmission parameters, where transmitting the acknowledgement feedback message includes transmitting a negative acknowledgment feedback message for the first multicast transmission, and receiving, based on transmitting the negative acknowledgement feedback message, a second multicast transmission that may be transmitted based on the association between the set of channel state information and the one of the uplink control channel resources.

[0022] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, the receiving may include operations, features, means, or instructions for receiving the second multicast transmission over a transmission beam indicated by the association between the set of channel state information and the one of the uplink control channel resources.

[0023] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, the receiving may include operations, features, means, or instructions for receiving the second multicast transmission using a modulation and coding scheme indicated by the association between the set of channel state information and the one of the uplink control channel resources.

[0024] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, the second multicast transmission includes a retransmission of data included in the first multicast transmission.

[0025] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for determining associations between each of the uplink control channel resources and sets of channel state information, where the one of the uplink control channel resources may be selected based on the associations. [0026] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, determining the associations may include operations, features, means, or instructions for a first set of the uplink control channel resources may be associated with a first CSI-reference signal index, a second set of the uplink control channel resources may be associated with a second CSI-reference signal index, a first subset of the first set of the uplink control channel resources may be associated with a first set of precoding matrix indices, a second subset of the first set of the uplink control channel resources may be associated with a second set of precoding matrix indices, a first uplink control channel resource of the first subset of the first set of the uplink control channel resources may be associated with a first set of channel quality indices, and a second uplink control channel resource of the first subset of the first set of the uplink control channel resources may be associated with a second set of channel quality indices.

[0027] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, the first set of the uplink control channel resources corresponds to a first group of UEs based on the first CSI-reference signal index indicating a first transmission beam, and the second set of the uplink control channel resources corresponds to a second group of UEs based on the second CSI-reference signal index indicating a second transmission beam.

[0028] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving an indication of the associations in a radio resource control message or a physical downlink control channel message.

[0029] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for measuring one or more CSI-reference signals transmitted over the one or more multicast channels, and determining the set of channel state information based on the one or more CSI- reference signals.

[0030] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving, from a base station, an indication of the one or more CSI-reference signals to measure. [0031] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for determining, by the UE, a quantity of CSI-reference signals to measure, and selecting the one or more CSI-reference signals based on the determining, the one or more CSI-reference signals including the quantity of CSI-reference signals.

[0032] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving, from a base station, an indication of the quantity of CSI-reference signals for the UE to measure; or, and transmitting, to the base station, the indication of the quantity of CSI- reference signals measured by the UE.

[0033] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for measuring a set of demodulation reference signals transmitted over the one or more multicast channels, the set of demodulation reference signals being associated with a set of precoding resource block groups, and determining the set of channel state information based on the set of demodulation reference signals.

[0034] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for determining that a demodulation reference signal of the set of demodulation reference signals may have a highest signal-to-noise ratio based on the measuring, the demodulation reference signal being associated with a precoding resource block group, and identifying a set of the uplink control channel resources that may be associated with the precoding resource block group based on the determining, where the one of the uplink control channel resources may be selected from the set of the uplink control channel resources.

[0035] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for determining, for the set of channel state information, a precoding matrix indicator, channel quality indicator, or channel state information-reference signal resource indicator, or any combination thereof, based on measuring the one or more multicast channels or the one or more signals monitored by the UE. [0036] A method of wireless communications at a base station is described. The method may include transmitting, over one or more multicast channels, an indication of uplink control channel resources for reporting acknowledgement feedback for multicast communications, the uplink control channel resources to be shared by UEs associated with the multicast communications, receiving, from a UE, an acknowledgement feedback message over one of the uplink control channel resources, the one of the uplink control channel resources being associated with a set of channel state information, and transmitting, over the one or more multicast channels, multicast data based on an association between the set of channel state information and the one of the uplink control channel resources.

[0037] An apparatus for wireless communications at a base station is described. The apparatus may include a processor, memory coupled with the processor, and instructions stored in the memory. The instructions may be executable by the processor to cause the apparatus to transmit, over one or more multicast channels, an indication of uplink control channel resources for reporting acknowledgement feedback for multicast communications, the uplink control channel resources to be shared by UEs associated with the multicast communications, receive, from a UE, an acknowledgement feedback message over one of the uplink control channel resources, the one of the uplink control channel resources being associated with a set of channel state information, and transmit, over the one or more multicast channels, multicast data based on an association between the set of channel state information and the one of the uplink control channel resources.

[0038] Another apparatus for wireless communications at a base station is described. The apparatus may include means for transmitting, over one or more multicast channels, an indication of uplink control channel resources for reporting acknowledgement feedback for multicast communications, the uplink control channel resources to be shared by UEs associated with the multicast communications, receiving, from a UE, an acknowledgement feedback message over one of the uplink control channel resources, the one of the uplink control channel resources being associated with a set of channel state information, and transmitting, over the one or more multicast channels, multicast data based on an association between the set of channel state information and the one of the uplink control channel resources. [0039] A non-transitory computer-readable medium storing code for wireless communications at a base station is described. The code may include instructions executable by a processor to transmit, over one or more multicast channels, an indication of uplink control channel resources for reporting acknowledgement feedback for multicast communications, the uplink control channel resources to be shared by UEs associated with the multicast communications, receive, from a UE, an acknowledgement feedback message over one of the uplink control channel resources, the one of the uplink control channel resources being associated with a set of channel state information, and transmit, over the one or more multicast channels, multicast data based on an association between the set of channel state information and the one of the uplink control channel resources.

[0040] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for determining a set of transmission parameters for transmitting the multicast data based on the set of channel state information.

[0041] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving, from a second UE, a second acknowledgement feedback message over another one of the uplink control channel resources and concurrently with the acknowledgement feedback message, the other one of the uplink control channel resources being associated with a second set of channel state information, and determining a set of transmission parameters for transmitting the multicast data based on the set of channel state information and the second set of channel state information.

[0042] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving, from a second UE after transmitting the multicast data, a second acknowledgement feedback message for the multicast data transmission over another one of the uplink control channel resources, the other one of the uplink control channel resources being associated with a second set of channel state information, determining a second set of transmission parameters for transmitting second multicast data based on the second set of channel state information, and transmitting the second multicast data using the second set of transmission parameters based on the determining. [0043] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving, from a set of UE after transmitting the multicast data, a set of acknowledgement feedback messages over a set of the uplink control channel resources, the set of the uplink control channel resources being associated with a set of sets of channel state information, and determining a set of transmission parameters for transmitting second multicast data independent of the set of sets of channel state information based on the set of sets of channel state information including different CSI-reference signal indices.

[0044] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for transmitting an indication of associations between the uplink control channel resources and sets of channel state information.

[0045] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for transmitting an indication of a set of CSI-reference signals for the UE to measure or a quantity of CSI-reference signals for the UE to measure.

[0046] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving an indication of a quantity of CSI-reference signals measured by the UE.

[0047] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, the uplink control channel resources includes a first set of uplink control channel resources associated with a first precoding resource block group and a second set of uplink control channel resources associated with a second precoding resource block group, and receiving the acknowledgement feedback message may include operations, features, means, or instructions for receiving the acknowledgement feedback message over the first set of uplink control channel resources associated with the first precoding resource block group, the first precoding resource block group being associated with the set of channel state information.

[0048] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for determining a precoding matrix for transmitting the multicast data based on receiving the acknowledgment feedback message over the first set of uplink control channel resources associated with the first precoding resource block group.

BRIEF DESCRIPTION OF THE DRAWINGS

[0049] FIG. 1 illustrates an example of a wireless communications system that supports reporting multicast feedback based on acknowledgment transmissions in accordance with aspects of the present disclosure.

[0050] FIG. 2 illustrates an example of a wireless communications system that supports reporting multicast feedback based on acknowledgment transmissions in accordance with aspects of the present disclosure.

[0051] FIG. 3 illustrates an example of an association between control channel resources and channel state information for reporting multicast feedback based on acknowledgment transmissions in accordance with aspects of the present disclosure.

[0052] FIG. 4 illustrates an example process flow for reporting multicast feedback based on acknowledgment transmissions in accordance with aspects of the present disclosure.

[0053] FIG. 5 shows a block diagram of a device that supports reporting multicast feedback based on acknowledgment transmissions in accordance with aspects of the present disclosure.

[0054] FIG. 6 shows a block diagram of a communications manager that supports reporting multicast feedback based on acknowledgment transmissions in accordance with aspects of the present disclosure.

[0055] FIG. 7 shows a diagram of a system including a device that supports reporting multicast feedback based on acknowledgment transmissions in accordance with aspects of the present disclosure.

[0056] FIG. 8 shows a block diagram of a device that supports reporting multicast feedback based on acknowledgment transmissions in accordance with aspects of the present disclosure.

[0057] FIG. 9 shows a block diagram of a communications manager that supports reporting multicast feedback based on acknowledgment transmissions in accordance with aspects of the present disclosure. [0058] FIG. 10 shows a diagram of a system including a device that supports reporting multicast feedback based on acknowledgment transmissions in accordance with aspects of the present disclosure.

[0059] FIGs. 11 and 12 show flowcharts illustrating methods that support multicast feedback based on acknowledgment transmissions in accordance with aspects of the present disclosure.

DETAILED DESCRIPTION

[0060] In some cases, a wireless communications system may support both unicast and multicast transmissions for communication between devices (e.g., a base station and user equipment (UE)). Unicast transmissions may involve transmitting sets of data that are intended for individual UEs. Multicast transmissions may involve transmitting a set of data that is intended for multiple UEs. In some cases, while performing unicast transmissions, a base station may be provided with channel information (e.g., location information, channel condition information, etc.) for each UE that receives or is scheduled to receive a unicast transmission. By contrast, a base station performing multicast transmissions may not be provided with channel information for UEs that receive a multicast transmission — e.g., the UEs may autonomously access multicast communication resources without coordination with the base station.

[0061] In some cases, signaling and reporting techniques (e.g., UE-specific reference signal transmissions, channel state information (CSI) reporting, hybrid automatic repeat request (HARQ) feedback reporting, etc.) for improving the reliability or efficiency of unicast communications may not be used to improve multicast communications. For example, using the unicast signaling and reporting techniques in a multicast environment may result in excessive signaling overhead. In another example, the unicast signaling and reporting techniques may not be used for multicast communication because the unicast techniques may not be supported in a multicast environment. That is, certain unicast techniques may rely on a base station being provided with channel information for individual UEs, enabling a base station to use tailored transmission parameters for subsequent transmissions to the individual UEs. [0062] Failing to utilize the unicast signaling and reporting techniques may result in multicast communications having decreased reliability and/or efficiency. For example, a failure to support the reporting of channel information for multicast communications may prevent a base station from determining channel conditions for UEs that are receiving a multicast transmission. Thus, a base station performing multicast communications may be unable to customize (e.g., by beamforming, identifying a modified modulation and coding scheme (MCS), identifying a modified transmission parameter, etc.) multicast transmissions for the UEs that are actually receiving the multicast transmission. Also, a failure to support HARQ feedback reporting for multicast communications may prevent a base station from performing HARQ retransmissions to UEs that failed to receive an initial data transmission.

In some cases, the UE may perform soft-combining between the initial data transmission and retransmission. In other cases, the UE may not perform soft-combining between the initial data transmission and retransmission. If, however, HARQ feedback reporting is supported for multicast communication, a failure to support the reporting of channel information may prevent a base station from performing HARQ retransmissions that are adapted to the UEs that actually failed to receive an initial HARQ transmission.

[0063] To increase the reliability and/or efficiency of multicast transmissions, signaling and reporting techniques used to determine multicast channel information for UEs operating in a multicast environment may be implemented.

[0064] In some examples, adaptive multicast retransmissions may be supported by configuring a set of uplink control channel resources configured for HARQ feedback (which may also be referred to as “HARQ resources”) so that each HARQ resource is associated with a particular set of CSI. The set of HARQ resources may be shared by multicast-enabled UEs, and the UEs that fail to receive a multicast transmission may transmit a negative acknowledgment (NACK) message over a particular shared HARQ resource based on individual channel estimates determined by the UEs. Thus, a base station may determine channel information for the UEs — e.g., based on averaging the CSI indicated by the occupied shared HARQ resources — and thus, may determine characteristics of a multicast channel between the base station and the UEs that failed to receive an initial multicast transmission. After determining the multicast channel information, the base station may adapt a multicast retransmission to conform to the determined multicast channel. [0065] In some examples, adaptive multicast retransmissions may be supported by configuring multiple sets of shared HARQ resources so that each HARQ resource is associated with a particular precoding matrix resource block group (PRG). Each PRG may be associated with a particular set of CSI. In such examples, a base station may be configured to transmit a multicast transmission over multiple sets of downlink resources using multiple PRGs. And multicast-enabled UEs may be configured to transmit a NACK indication over a set of the shared HARQ resources corresponding to a particular PRG based on individual channel estimates determined by the UEs. Thus, a base station may determine channel information for the UEs — e.g., based on averaging the CSI indicated by the occupied shared HARQ resources — and thus, may determine characteristics of a multicast channel between the base station and the UEs that failed to receive an initial multicast transmission. After determining the multicast channel information, the base station may adapt a multicast retransmission to conform to the determined multicast channel.

[0066] Aspects of the disclosure are initially described in the context of wireless communications systems. Aspects of the disclosure are further illustrated by and described with reference to apparatus diagrams, system diagrams, and flowcharts that relate to techniques for implicit channel state information reporting for multicast.

[0067] FIG. 1 illustrates an example of a wireless communications system 100 that supports techniques for reporting multicast feedback based on acknowledgment transmissions in accordance with aspects of the present disclosure. The wireless communications system 100 may include one or more base stations 105, one or more UEs 115, and a core network 130. In some examples, the wireless communications system 100 may be a Long Term Evolution (LTE) network, an LTE- Advanced (LTE-A) network, an LTE-A Pro network, or a New Radio (NR) network. In some examples, the wireless communications system 100 may support enhanced broadband communications, ultra-reliable (e.g., mission critical) communications, low latency communications, communications with low-cost and low- complexity devices, or any combination thereof.

[0068] The base stations 105 may be dispersed throughout a geographic area to form the wireless communications system 100 and may be devices in different forms or having different capabilities. The base stations 105 and the UEs 115 may wirelessly communicate via one or more communication links 125. Each base station 105 may provide a coverage area 110 over which the UEs 115 and the base station 105 may establish one or more communication links 125. The coverage area 110 may be an example of a geographic area over which a base station 105 and a UE 115 may support the communication of signals according to one or more radio access technologies.

[0069] The UEs 115 may be dispersed throughout a coverage area 110 of the wireless communications system 100, and each UE 115 may be stationary, or mobile, or both at different times. The UEs 115 may be devices in different forms or having different capabilities. Some example UEs 115 are illustrated in FIG. 1. The UEs 115 described herein may be able to communicate with various types of devices, such as other UEs 115, the base stations 105, or network equipment (e.g., core network nodes, relay devices, integrated access and backhaul (IAB) nodes, or another network equipment), as shown in FIG. 1.

[0070] The base stations 105 may communicate with the core network 130, or with one another, or both. For example, the base stations 105 may interface with the core network 130 through one or more backhaul links 120 (e.g., via an SI, N2, N3, or another interface). The base stations 105 may communicate with one another over the backhaul links 120 (e.g., via an X2, Xn, or other interface) either directly (e.g., directly between base stations 105), or indirectly (e.g., via core network 130), or both. In some examples, the backhaul links 120 may be or include one or more wireless links.

[0071] One or more of the base stations 105 described herein may include or may be referred to by a person having ordinary skill in the art as a base transceiver station, a radio base station, an access point, a radio transceiver, a NodeB, an eNodeB (eNB), a next- generation NodeB or a giga-NodeB (either of which may be referred to as a gNB), a Home NodeB, a Home eNodeB, or other suitable terminology.

[0072] A UE 115 may include or may be referred to as a mobile device, a wireless device, a remote device, a handheld device, or a subscriber device, or some other suitable terminology, where the “device” may also be referred to as a unit, a station, a terminal, or a client, among other examples. A UE 115 may also include or may be referred to as a personal electronic device such as a cellular phone, a personal digital assistant (PDA), a tablet computer, a laptop computer, or a personal computer. In some examples, a UE 115 may include or be referred to as a wireless local loop (WLL) station, an Internet of Things (IoT) device, an Internet of Everything (IoE) device, or a machine type communications (MTC) device, among other examples, which may be implemented in various objects such as appliances, or vehicles, meters, among other examples.

[0073] The UEs 115 described herein may be able to communicate with various types of devices, such as other UEs 115 that may sometimes act as relays as well as the base stations 105 and the network equipment including macro eNBs or gNBs, small cell eNBs or gNBs, or relay base stations, among other examples, as shown in FIG. 1.

[0074] The UEs 115 and the base stations 105 may wirelessly communicate with one another via one or more communication links 125 over one or more carriers. The term “carrier” may refer to a set of radio frequency spectrum resources having a defined physical layer structure for supporting the communication links 125. For example, a carrier used for a communication link 125 may include a portion of a radio frequency spectrum band (e.g., a bandwidth part (BWP)) that is operated according to one or more physical layer channels for a given radio access technology (e.g., LTE, LTE-A, LTE-A Pro, NR). Each physical layer channel may carry acquisition signaling (e.g., synchronization signals, system information), control signaling that coordinates operation for the carrier, user data, or other signaling. The wireless communications system 100 may support communication with a UE 115 using carrier aggregation or multi-carrier operation. A UE 115 may be configured with multiple downlink component carriers and one or more uplink component carriers according to a carrier aggregation configuration. Carrier aggregation may be used with both frequency division duplexing (FDD) and time division duplexing (TDD) component carriers.

[0075] Signal waveforms transmitted over a carrier may be made up of multiple subcarriers (e.g., using multi-carrier modulation (MCM) techniques such as orthogonal frequency division multiplexing (OFDM) or discrete Fourier transform spread OFDM (DFT- S-OFDM)). In a system employing MCM techniques, a resource element may consist of one symbol period (e.g., a duration of one modulation symbol) and one subcarrier, where the symbol period and subcarrier spacing are inversely related. The number of bits carried by each resource element may depend on the modulation scheme (e.g., the order of the modulation scheme, the coding rate of the modulation scheme, or both). Thus, the more resource elements that a UE 115 receives and the higher the order of the modulation scheme, the higher the data rate may be for the UE 115. A wireless communications resource may refer to a combination of a radio frequency spectrum resource, a time resource, and a spatial resource (e.g., spatial layers or beams), and the use of multiple spatial layers may further increase the data rate or data integrity for communications with a UE 115.

[0076] The time intervals for the base stations 105 or the UEs 115 may be expressed in multiples of a basic time unit which may, for example, refer to a sampling period of T _s =

1 /{ f _{max '} Nf) seconds, where A/ _ma may represent the maximum supported subcarrier spacing, and JV- may represent the maximum supported discrete Fourier transform (DFT) size. Time intervals of a communications resource may be organized according to radio frames each having a specified duration (e.g., 10 milliseconds (ms)). Each radio frame may be identified by a system frame number (SFN) (e.g., ranging from 0 to 1023).

[0077] Each frame may include multiple consecutively numbered subframes or slots, and each subframe or slot may have the same duration. In some examples, a frame may be divided (e.g., in the time domain) into subframes, and each subframe may be further divided into a number of slots. Alternatively, each frame may include a variable number of slots, and the number of slots may depend on subcarrier spacing. Each slot may include a number of symbol periods (e.g., depending on the length of the cyclic prefix prepended to each symbol period). In some wireless communications systems 100, a slot may further be divided into multiple mini-slots containing one or more symbols. Excluding the cyclic prefix, each symbol period may contain one or more (e.g., Nf) sampling periods. The duration of a symbol period may depend on the subcarrier spacing or frequency band of operation.

[0078] A subframe, a slot, a mini-slot, or a symbol may be the smallest scheduling unit (e.g., in the time domain) of the wireless communications system 100 and may be referred to as a transmission time interval (TTI). In some examples, the TTI duration (e.g., the number of symbol periods in a TTI) may be variable. Additionally, or alternatively, the smallest scheduling unit of the wireless communications system 100 may be dynamically selected (e.g., in bursts of shortened TTIs (sTTIs)).

[0079] Physical channels may be multiplexed on a carrier according to various techniques. A physical control channel and a physical data channel may be multiplexed on a downlink carrier, for example, using one or more of time division multiplexing (TDM) techniques, frequency division multiplexing (FDM) techniques, or hybrid TDM-FDM techniques. A control region (e.g., a control resource set (CORESET)) for a physical control channel may be defined by a number of symbol periods and may extend across the system bandwidth or a subset of the system bandwidth of the carrier. One or more control regions (e.g., CORESETs) may be configured for a set of the UEs 115. For example, one or more of the UEs 115 may monitor or search control regions for control information according to one or more search space sets, and each search space set may include one or multiple control channel candidates in one or more aggregation levels arranged in a cascaded manner. An aggregation level for a control channel candidate may refer to a number of control channel resources (e.g., control channel elements (CCEs)) associated with encoded information for a control information format having a given payload size. Search space sets may include common search space sets configured for sending control information to multiple UEs 115 and UE-specific search space sets for sending control information to a specific UE 115.

[0080] In some examples, a base station 105 may be movable and therefore provide communication coverage for a moving geographic coverage area 110. In some examples, different geographic coverage areas 110 associated with different technologies may overlap, but the different geographic coverage areas 110 may be supported by the same base station 105. In other examples, the overlapping geographic coverage areas 110 associated with different technologies may be supported by different base stations 105. The wireless communications system 100 may include, for example, a heterogeneous network in which different types of the base stations 105 provide coverage for various geographic coverage areas 110 using the same or different radio access technologies.

[0081] The wireless communications system 100 may be configured to support ultra reliable communications or low-latency communications, or various combinations thereof. For example, the wireless communications system 100 may be configured to support ultra reliable low-latency communications (URLLC) or mission critical communications. The UEs 115 may be designed to support ultra-reliable, low-latency, or critical functions (e.g., mission critical functions). Ultra-reliable communications may include private communication or group communication and may be supported by one or more mission critical services such as mission critical push-to-talk (MCPTT), mission critical video (MCVideo), or mission critical data (MCData). Support for mission critical functions may include prioritization of services, and mission critical services may be used for public safety or general commercial applications. The terms ultra-reliable, low-latency, mission critical, and ultra-reliable low- latency may be used interchangeably herein. [0082] In some examples, a UE 115 may also be able to communicate directly with other UEs 115 over a device-to-device (D2D) communication link 135 (e.g., using a peer-to-peer (P2P) or D2D protocol). One or more UEs 115 utilizing D2D communications may be within the geographic coverage area 110 of a base station 105. Other UEs 115 in such a group may be outside the geographic coverage area 110 of a base station 105 or be otherwise unable to receive transmissions from a base station 105. In some examples, groups of the UEs 115 communicating via D2D communications may utilize a one-to-many (1 :M) system in which each UE 115 transmits to every other UE 115 in the group. In some examples, a base station 105 facilitates the scheduling of resources for D2D communications. In other cases, D2D communications are carried out between the UEs 115 without the involvement of a base station 105.

[0083] The core network 130 may provide user authentication, access authorization, tracking, Internet Protocol (IP) connectivity, and other access, routing, or mobility functions. The core network 130 may be an evolved packet core (EPC) or 5G core (5GC), which may include at least one control plane entity that manages access and mobility (e.g., a mobility management entity (MME), an access and mobility management function (AMF)) and at least one user plane entity that routes packets or interconnects to external networks (e.g., a serving gateway (S-GW), a Packet Data Network (PDN) gateway (P-GW), or a user plane function (UPF)). The control plane entity may manage non-access stratum (NAS) functions such as mobility, authentication, and bearer management for the UEs 115 served by the base stations 105 associated with the core network 130. User IP packets may be transferred through the user plane entity, which may provide IP address allocation as well as other functions. The user plane entity may be connected to the network operators IP services 150. The operators IP services 150 may include access to the Internet, Intranet(s), an IP Multimedia Subsystem (IMS), or a Packet- Switched Streaming Service.

[0084] Some of the network devices, such as a base station 105, may include subcomponents such as an access network entity 140, which may be an example of an access node controller (ANC). Each access network entity 140 may communicate with the UEs 115 through one or more other access network transmission entities 145, which may be referred to as radio heads, smart radio heads, or transmission/reception points (TRPs). Each access network transmission entity 145 may include one or more antenna panels. In some configurations, various functions of each access network entity 140 or base station 105 may be distributed across various network devices (e.g., radio heads and ANCs) or consolidated into a single network device (e.g., a base station 105).

[0085] The wireless communications system 100 may operate using one or more frequency bands, typically in the range of 300 megahertz (MHz) to 300 gigahertz (GHz). Generally, the region from 300 MHz to 3 GHz is known as the ultra-high frequency (UHF) region or decimeter band because the wavelengths range from approximately one decimeter to one meter in length. The UHF waves may be blocked or redirected by buildings and environmental features, but the waves may penetrate structures sufficiently for a macro cell to provide service to the UEs 115 located indoors. The transmission of UHF waves may be associated with smaller antennas and shorter ranges (e.g., less than 100 kilometers) compared to transmission using the smaller frequencies and longer waves of the high frequency (HF) or very high frequency (VHF) portion of the spectrum below 300 MHz.

[0086] The wireless communications system 100 may utilize both licensed and unlicensed radio frequency spectrum bands. For example, the wireless communications system 100 may employ License Assisted Access (LAA), LTE-Unlicensed (LTE-U) radio access technology, or NR technology in an unlicensed band such as the 5 GHz industrial, scientific, and medical (ISM) band. When operating in unlicensed radio frequency spectrum bands, devices such as the base stations 105 and the UEs 115 may employ carrier sensing for collision detection and avoidance. In some examples, operations in unlicensed bands may be based on a carrier aggregation configuration in conjunction with component carriers operating in a licensed band (e.g., LAA). Operations in unlicensed spectrum may include downlink transmissions, uplink transmissions, P2P transmissions, or D2D transmissions, among other examples.

[0087] A base station 105 or a UE 115 may be equipped with multiple antennas, which may be used to employ techniques such as transmit diversity, receive diversity, multiple-input multiple-output (MIMO) communications, or beamforming. The antennas of a base station 105 or a UE 115 may be located within one or more antenna arrays or antenna panels, which may support MIMO operations or transmit or receive beamforming. For example, one or more base station antennas or antenna arrays may be co-located at an antenna assembly, such as an antenna tower. In some examples, antennas or antenna arrays associated with a base station 105 may be located in diverse geographic locations. A base station 105 may have an antenna array with a number of rows and columns of antenna ports that the base station 105 may use to support beamforming of communications with a UE 115. Likewise, a UE 115 may have one or more antenna arrays that may support various MIMO or beamforming operations. Additionally, or alternatively, an antenna panel may support radio frequency beamforming for a signal transmitted via an antenna port.

[0088] The base stations 105 or the EEs 115 may use MIMO communications to exploit multipath signal propagation and increase the spectral efficiency by transmitting or receiving multiple signals via different spatial layers. Such techniques may be referred to as spatial multiplexing. The multiple signals may, for example, be transmitted by the transmitting device via different antennas or different combinations of antennas. Likewise, the multiple signals may be received by the receiving device via different antennas or different combinations of antennas. Each of the multiple signals may be referred to as a separate spatial stream and may carry bits associated with the same data stream (e.g., the same codeword) or different data streams (e.g., different codewords). Different spatial layers may be associated with different antenna ports used for channel measurement and reporting. MIMO techniques include single-user MIMO (SU-MIMO), where multiple spatial layers are transmitted to the same receiving device, and multiple-user MIMO (MU-MIMO), where multiple spatial layers are transmitted to multiple devices.

[0089] Beamforming, which may also be referred to as spatial filtering, directional transmission, or directional reception, is a signal processing technique that may be used at a transmitting device or a receiving device (e.g., a base station 105, a UE 115) to shape or steer an antenna beam (e.g., a transmit beam, a receive beam) along a spatial path between the transmitting device and the receiving device. Beamforming may be achieved by combining the signals communicated via antenna elements of an antenna array such that some signals propagating at particular orientations with respect to an antenna array experience constructive interference while others experience destructive interference. The adjustment of signals communicated via the antenna elements may include a transmitting device or a receiving device applying amplitude offsets, phase offsets, or both to signals carried via the antenna elements associated with the device. The adjustments associated with each of the antenna elements may be defined by a beamforming weight set associated with a particular orientation (e.g., with respect to the antenna array of the transmitting device or receiving device, or with respect to some other orientation). [0090] A base station 105 or a UE 115 may use beam sweeping techniques as part of beam forming operations. For example, a base station 105 may use multiple antennas or antenna arrays (e.g., antenna panels) to conduct beamforming operations for directional communications with aUE 115. Some signals (e.g., synchronization signals, reference signals, beam selection signals, or other control signals) may be transmitted by a base station 105 multiple times in different directions. For example, the base station 105 may transmit a signal according to different beamforming weight sets associated with different directions of transmission. Transmissions in different beam directions may be used to identify (e.g., by a transmitting device, such as a base station 105, or by a receiving device, such as a UE 115) a beam direction for later transmission or reception by the base station 105.

[0091] Some signals, such as data signals associated with a particular receiving device, may be transmitted by a base station 105 in a single beam direction (e.g., a direction associated with the receiving device, such as a UE 115). In some examples, the beam direction associated with transmissions along a single beam direction may be determined based on a signal that was transmitted in one or more beam directions. For example, a UE 115 may receive one or more of the signals transmitted by the base station 105 in different directions and may report to the base station 105 an indication of the signal that the UE 115 received with a highest signal quality or an otherwise acceptable signal quality.

[0092] In some examples, transmissions by a device (e.g., by a base station 105 or a UE 115) may be performed using multiple beam directions, and the device may use a combination of digital precoding or radio frequency beamforming to generate a combined beam for transmission (e.g., from a base station 105 to a UE 115). The UE 115 may report feedback that indicates precoding weights for one or more beam directions, and the feedback may correspond to a configured number of beams across a system bandwidth or one or more sub-bands. The base station 105 may transmit a reference signal (e.g., a cell-specific reference signal (CRS), a channel state information reference signal (CSI-RS)), which may be precoded or unprecoded. The UE 115 may provide feedback for beam selection, which may be a precoding matrix indicator (PMI) or codebook-based feedback (e.g., a multi-panel type codebook, a linear combination type codebook, a port selection type codebook). Although these techniques are described with reference to signals transmitted in one or more directions by a base station 105, a UE 115 may employ similar techniques for transmitting signals multiple times in different directions (e.g., for identifying a beam direction for subsequent transmission or reception by the UE 115) or for transmitting a signal in a single direction (e.g., for transmitting data to a receiving device).

[0093] A receiving device (e.g., a UE 115) may try multiple receive configurations (e.g., directional listening) when receiving various signals from the base station 105, such as synchronization signals, reference signals, beam selection signals, or other control signals. For example, a receiving device may try multiple receive directions by receiving via different antenna subarrays, by processing received signals according to different antenna subarrays, by receiving according to different receive beamforming weight sets (e.g., different directional listening weight sets) applied to signals received at multiple antenna elements of an antenna array, or by processing received signals according to different receive beamforming weight sets applied to signals received at multiple antenna elements of an antenna array, any of which may be referred to as “listening” according to different receive configurations or receive directions. In some examples, a receiving device may use a single receive configuration to receive along a single beam direction (e.g., when receiving a data signal). The single receive configuration may be aligned in a beam direction determined based on listening according to different receive configuration directions (e.g., a beam direction determined to have a highest signal strength, highest signal-to-noise ratio (SNR), or otherwise acceptable signal quality based on listening according to multiple beam directions).

[0094] The UEs 115 and the base stations 105 may support retransmissions of data to increase the likelihood that data is received successfully. Hybrid automatic repeat request (HARQ) feedback is one technique for increasing the likelihood that data is received correctly over a communication link 125. HARQ may include a combination of error detection (e.g., using a cyclic redundancy check (CRC)), forward error correction (FEC), and retransmission (e.g., automatic repeat request (ARQ)). HARQ may improve throughput at the medium access control (MAC) layer in poor radio conditions (e.g., low signal-to-noise conditions). In some examples, a device may support same-slot HARQ feedback, where the device may provide HARQ feedback in a specific slot for data received in a previous symbol in the slot. In other cases, the device may provide HARQ feedback in a subsequent slot, or according to some other time interval.

[0095] In some cases, a wireless communications system 100 may be configured to perform multiple transmissions each individual transmission carrying data for a particular UE 115. Such transmissions may be referred to as unicast transmissions. For example, a base station 105 may perform a first transmission that conveys first data to a first UE 115 located within a coverage area 110 over a first set of communication resources and a second transmission that conveys second data to a second UE 115 located within the coverage area 110 over a second set of communication resources. In some cases, transmissions between a base station 105 and a UE 115 may fail — e.g., a receiving device may fail to detect and/or decode a transmission from a transmitting device. In some cases, transmission failures may be due to characteristics of a channel between the base station 105 and the UE 115 — e.g., the channel may excessively delay or shift the phase of a transmission. In some cases, transmission failures may be due to interference on a channel between the base station 105 and the UE 115 — e.g., nearby transmissions or physical objects may interfere with the channel.

[0096] To increase the reliability of wireless unicast communications, a wireless communications system 100 may use reference signals that indicate characteristics (or a state) of a channel between a transmitting and receiving device. In some examples, a receiving device may use reference signals to estimate a state of a channel between the transmitting and receiving device. After estimating a channel between itself and a transmitting device, a wireless device may update parameters for receiving signals (or “receiver parameters”) to account for properties of the channel. Also, a receiving device (e.g., a UE 115) may report information about the estimated channel to a transmitting device (e.g., a base station 105) — e.g., in a CSI report). A transmitting device that receives a CSI report may use the included channel information to modify transmission parameters to conform the transmission to the channel. Reference signals used by a wireless communications system 100 may include CSI- RS, demodulation reference signals (DMRS), and sounding reference signals (SRS).

[0097] A base station 105 may transmit CSI-RSs to UEs within a coverage area 110 of base station 105 using scheduled downlink communication resources. In some cases, a common set of CSI-RSs is transmitted across a coverage area 110 of a base station 105. In some cases, the base station 105 may transmit multiple sets of common CSI-RSs across a coverage area 110 using multiple transmission beams. In some cases, a UE may be configured to monitor a particular quantity of CSI-RSs within a time period. [0098] A UE 115 that receives CSI-RSs may use the CSI-RSs to estimate a channel between the UE 115 and the base station 105. To estimate the channel, the UE may measure aspects of the received CSI-RSs (including a SNR, signal-to-interference-to noise ratio (SINR), and phase of the received CSI-RS) and compare the measured aspects with transmission parameters used for transmitting the CSI-RSs. In some cases, the UE 115 may be provided with the transmission parameters prior to the transmission of the CSI-RSs — e.g., in an initial setup message, such as a radio resource control (RRC) message. In some cases, the UE 115 may determine multiple channel estimates based on received CSI-RSs — e.g., one channel estimate for each transmission beam used to transmit the CSI-RSs.

[0099] After determining the channel estimate(s), the UE 115 may determine a quality of the channel, a desired precoding matrix for the channel, and/or a desired transmission beam for receiving subsequent transmissions from a base station 105. In some cases, the UE 115 may determine the quality of the channel by mapping a measured SNR value to a channel quality index included in a list of channel quality indices — e.g., the UE 115 may map a measured SNR value of 6dB to a second channel quality indicator (CQI) index (or CQI 2). In some cases, the UE 115 determines the desired precoding matrix using a codebook that maps the measured channel characteristics to a precoding matrix that is adapted for the channel. In some examples, the determined precoding matrix corresponds to a precoding matrix index. And in some cases, the UE 115 determines the desired transmission beam based on determining the CSI-RSs with the highest SNR and the transmission beam that corresponds to the CSI-RS(s) with the highest SNR. In some cases, the determined transmission beam corresponds to a transmission beam index.

[0100] After determining a channel quality index, a precoding matrix index, and/or a transmission beam index, the UE 115 may report the channel quality index, the precoding matrix index, and/or the transmission beam index to the base station in a CSI report — e.g., using CQI field, PMI field, and a CSI-RS resource indicator (CRI) field. A CSI report may also be referred to as CSI feedback. In some cases, the UE 115 may send an explicit indication of the CSI report over physical uplink control channel (PUCCH) resources that are allocated to the UE 115. After receiving a CSI report, a base station 105 may adapt subsequent transmissions to a UE 115 based on the indices indicated in the CQI, PMI, and CRI fields. For example, in a subsequent transmission, the base station may use an MCS corresponding to the CQI index, a precoding matrix corresponding to the PMI index, and a transmission beam corresponding to the CRI index.

[0101] A base station 105 may also transmit DMRSs to UEs 115. In some cases, a set of DMRSs may be configured for a particular UE 115 and may be transmitted using, or alongside, physical downlink shared channel (PDSCH) resources that are allocated to the UE 115 — e.g., DMRS resources may be interleaved with PDSCH resources for a UE 115. In some cases, DMRSs may be transmitted over a particular transmission beam — e.g., a same transmission beam as the transmission beam used for a data transmission to a UE. A UE 115 that receives DMRSs may use the DMRSs to estimate a channel between the UE 115 and the base station 105, as similarly discussed with reference to CSI-RS. In some cases, DMRSs are used to determine an instantaneous SINR for a channel. Unlike CSI-RSs, a UE 115 may use DMRSs to decode a received downlink data transmission instead of using the DMRSs to report channel information.

[0102] In some cases, a UE 115 may transmit reference signals to a base station 105 to assist the base station 105 with channel estimation. For example, a UE 115 may send an uplink SRS over the system bandwidth so that a base station 105 can select optimal frequencies for communication with the UE 115. For instance, the base station 105 may measure the SRS to determine the received signal power across the system bandwidth and then use the information to implement frequency dependent scheduling of the UE 115. In some examples, a UE 115 may transmit SRSs in SRS resources (e.g., uplink communication resources scheduled for SRS) that occur periodically. For example, the SRS resources (which may also be referred to as SRS transmission occasions) may occur in every nth subframe. In some examples, the SRS resources are located in the last symbol of an uplink subframe. However, other locations of SRS are possible. In some examples, multiple UEs 115 are configured to transmit SRSs over different (e.g., non-overlapping) sets of communication resources — e.g., to prevent interference between SRS transmissions.

[0103] To further increase the reliability of wireless unicast communications, a wireless communications system 100 may be configured to support the retransmission of failed transmissions (e.g., the wireless communications system 100 may support HARQ operation). In some cases, to support retransmissions, UEs 115 may report whether a received transmission (which may be an initial transmission) was successfully decoded or an expected transmission was not received (or detected). For example, a UE 115 may report to a base station 105 that a transmission was successfully received and decoded by transmitting a positive acknowledgment (ACK) message. Alternatively, the UE 115 may report to a base station 105 that a transmission was not received or was unsuccessfully decoded by transmitting a negative acknowledgment (NACK) message. In some cases, each UE 115 may be configured with uplink control channel resources (e.g., PUCCH resources) for transmitting acknowledgement feedback. After receiving a NACK message, a base station 105 may retransmit data included in the failed transmission to the UE 115. In some cases, the UE 115 may transmit the acknowledgment feedback over a PUCCH resources that is allocated to the UE 115 for reporting acknowledgment feedback.

[0104] In some cases, the base station 105 may retransmit the data using the same transmission parameters that were used for the failed transmission. But using the same transmission parameters may result in a failure of the retransmission — e.g., if long-term interference caused the previous transmission to fail. In other cases, the base station 105 may perform the retransmission using different transmission parameters (e.g., a lower MCS, a higher transmit power, etc.) than the transmission parameters used for the failed transmission. Performing retransmissions using modified transmission parameters may be referred to as adaptive retransmission, adaptive HARQ operation, and the like. In some cases, the base station 105 selects the transmission parameters for the retransmission based on channel information reported by a UE 115 that also reports a failed transmission. For example, the base station 105 may perform the retransmission using an MCS that corresponds to a reported CQI index, a precoding matrix that corresponds to a reported PMI index, and a transmission beam that corresponds to a reported CRI index.

[0105] In some cases, to increase the reliability of wireless unicast communications, a wireless communications system 100 may perform data transmission over multiple precoding resource block groups (PRGs) — e.g., to mitigate the effects of interference on one of the PRGs. In some examples, a base station 105 may transmit data over a first set of PDSCH resources using a first precoding matrix and/or beamforming (a first PRG), a second set of PDSCH resources using a second precoding matrix and/or beamforming (a second PRG), and a third set of PDSCH resources using a third precoding matrix and/or beamforming (a third PRG). In some cases, a DMRS may be included in each of the sets of PDSCH resources. In some cases, a UE 115 may receive the data transmission over one or more of the PRGs and be configured to report HARQ feedback for the data transmission over multiple sets of PUCCH resources — e.g., the UE 115 may be configured to report feedback for the portion of the data transmission using the first PRG over a first set of PUCCH resources, the portion of the data transmission using the second PRG over a second set of PUCCH resources, and so on. In some cases, the UE 115 receives each portion of the data transmission based on the corresponding DMRSs included in the corresponding sets of PDSCH resources.

[0106] In some cases, a wireless communications system 100 may be configured to perform a single transmission carrying a set of data that is intended for multiple UEs 115. Such a transmission may be referred to as a multicast transmission. For example, a base station 105 may perform a multicast transmission that reaches (or is detectable) across a coverage area 110. That is, a multicast transmission may be received by any authorized UE 115 within the coverage area 110. In some cases, a multicast transmission includes data for a live broadcast to be simultaneously received and displayed to individual users that have tuned into the multicast transmission. In some cases, the UEs 115 receiving the multicast transmission may be distributed throughout the coverage area 110 and implicitly arranged into groups — e.g., based on different regions of the coverage area 110. In some cases, one or more UEs 115 may fail to receive a multicast transmission while other UEs 115 may successfully receive the multicast transmission — e.g., due to localized interference on a channel between the base station 105 and the one or more UEs 115.

[0107] Unlike unicast operation, a base station 105 performing multicast operations may be unable to use reference signals to determine a channel between the base station 105 and the UEs 115 receiving multicast transmissions. That is, during multicast operation, a base station 105 may not be provided with, or determine, information related to which UEs 115 are currently receiving a multicast transmission. Similarly, the base station 105 may not be provided with, or determine, a location, or general location, of the UEs 115 that are receiving the multicast transmission. Without such UE-specific information, the base station 105 may not support UE-specific transmission techniques during multicast operations. For example, a base station 105 performing multicast operations may not support CSI reporting or the transmission of UE-specific reference signals (e.g., DMRS or SRS).

[0108] In some cases, an inability of a base station 105 to determine a location of the UEs 115 that are receiving multicast transmissions may result in reduced reliability transmissions for a majority (or all) of the UEs 115 receiving the multicast transmissions. For example, if a majority (or all) of the UEs 115 receiving multicast transmissions are located in one region of a coverage area 110, a base station 105 performing multicast operations may transmit a multicast transmission that is spread across the entire coverage area 110 rather than a multicast transmission that is adapted for the region where the UEs 115 are located. Also, an inability of a base station 105 to determine channel information for UEs 115 that are receiving multicast transmissions may result in decreased reliability transmissions to a majority (or all) of the UEs 115 receiving the multicast transmissions. That is, a base station 105 performing multicast transmissions may be unable to determine a state of a channel between the base station 105 and the UEs 115 that are receiving the multicast transmissions. Thus, the base station may be prevented from modifying transmission parameters in subsequent transmissions to conform to the channel, and thus the base station is prevented from better serving those UEs 115. Similarly, an inability of a base station 105 to determine a location and/or channel information of the UEs 115 may result in inefficient multicast transmissions. That is, in some cases, a base station 105 may perform a multicast transmission that is sufficient to reach all of the UEs 115 in a coverage area 110 when the base station may perform an equally effective multicast transmission by directing a lower- power multicast transmission to the location of a majority (or all) of the UEs 115.

[0109] To increase the reliability and/or efficiency of multicast wireless communications, a base station performing multicast operations may be configured to support the retransmission of failed multicast transmissions — e.g., multicast transmissions that are not detected and/or decoded by at least one UE 115 that is currently monitoring a multicast channel. In some cases, to support multicast retransmissions, a base station 105 may configure a multicast uplink PUCCH resource for multicast HARQ feedback for each UE 115 that is authorized to receive a multicast transmission. But allocating a dedicated multicast PUCCH resource to each UE 115 may increase overhead and decrease a throughput of a wireless communications system 100.

[0110] In other cases, to support multicast retransmissions, a base station may configure a multicast PUCCH resource for multicast HARQ feedback that is shared by multiple UEs 115. In such examples, any UE 115 within the coverage area 110 may be permitted to transmit a NACK message over the multicast PUCCH resources after failing to receive and/or unsuccessfully decoding an initial multicast transmission. In some cases, if a base station 105 receives a NACK message from at least one UE 115 over the multicast PUCCH resources, the base station 105 may retransmit the failed multicast transmission to all of the UEs 115 within the coverage area 110 using the same transmission parameters. In some examples, the base station 105 may use the same transmission parameters for the multicast retransmission because, without UE-specific channel reporting, the base station 105 may be unable to determine improved transmission parameters for the UE(s) 115 that failed to receive the initial multicast transmission. However, multicast retransmissions that use the same transmission parameters as an initial multicast transmission may fail for the same reasons as the initial multicast transmission. For example, if a long-term blockage (e.g., a physical obstruction) interferes with multicast transmissions to UEs 115 in a particular region of a coverage area 110, both an initial multicast transmission and multicast retransmission may be disrupted by the long-term blockage.

[0111] To support adaptive multicast transmissions, techniques for indicating location and/or channel information for UEs 115 that are actually receiving multicast transmissions may be utilized. For example, to support indicating a location of UEs receiving multicast transmissions, shared SRS resources may be configured so that different subsets of the shared resources indicate different locations of the UEs. Similarly, to support indicating channel information for UEs 115 receiving multicast transmissions, the shared SRS resources may be configured to indicate particular sets of CSI.

[0112] To support adaptive multicast retransmissions, techniques for indicating locations and/or channel information for UEs 115 that fail to successfully process multicast transmissions may be utilized. For example, to support indicating a location of UEs (which may correspond to a long-term channel property) that failed to successfully process multicast transmissions, shared uplink resources (e.g., shared SRS resources or shared PUCCH resources for HARQ feedback) may be configured so that different subsets of the shared resources indicate different locations of the UEs. In some cases, shared PUCCH resources for HARQ feedback may be referred to as “shared HARQ resources”). Similarly, to support indicating channel information for UEs that fail to successfully process multicast transmissions, the shared uplink resources may be configured to indicate particular sets of CSI. [0113] FIG. 2 illustrates an example of a wireless communications system 200 that supports reporting multicast feedback based on acknowledgment transmissions in accordance with aspects of the present disclosure. Wireless communications system 200 may include transmission points 205-a, 205-b, and 205-c, which may be examples of transmission/reception points of a base station 105 as described with reference to FIG. 1. For instance, a transmission point 205 may be an example of an access network transmission entity 145 as described with reference to FIG. 1. Wireless communications system 200 may also include UE 215-a through UE 215 -f, which may be examples of a UE 115 as described with reference to FIG. 1. The UEs 215 may use reference signals, such as SRS, or feedback information, such as HARQ NACKs, to implicitly communicate location information and/or channel information to a base station associated with the transmission points 205.

[0114] The transmission points 205 may support a mixed-mode environment in which they work cooperatively to transmit unicast data to a single UE 215 or multicast data to multiple UEs 215. The unicast or multicast data may originate from a base station coupled, co-located, or otherwise associated with the transmission points 205.

[0115] When the transmission points 205 transmit unicast data to a UE 215 (e.g., UE 215-a), the reliability of the transmissions may be improved by transmitting SRSs, reporting CSI, and/or initializing HARQ processes, as described above. For example, an initial unicast transmission to UE 215-a may occur over frequencies that are optimal for UE 215-a as determined by a base station measuring SRSs from UE 215-a. Also, the transmission parameters (e.g., beam, precoding matrix, MCS, etc. used for the transmission of the unicast data) may be tailored to the location of UE 215-a and the channel conditions experienced by UE 215-a as indicated by channel information reported by UE 215-a. Further, HARQ feedback from UE 215-a can increase the likelihood that UE 215-a receives the unicast data by prompting a re-transmission of the unicast data when UE 215-a fails to decode the initial transmission. Used collectively, these techniques increase the reliability and efficiency of unicast communications by allowing a base station to 1) use appropriate transmission parameters for initial unicast transmissions and 2) implement adaptive retransmissions.

[0116] However, such techniques may not be supported for multicast transmissions, and thus the reliability and efficiency of multicast communications may be inferior relative to that of unicast communications. For example, if wireless communications system 200 does not perform SRS transmissions for multicast, the base station may be unable to determine optimal frequencies for the UEs 215. So, the base station may make uninformed selections of transmission frequencies for the UEs 215, which may result in the multicast transmissions experiencing various negative conditions such as interference, noise, etc. Thus, the reliability of multicast communications may suffer when a base station operates without using SRSs.

[0117] As another example, consider a transmission of multicast data by transmission points 205-a, 205-b, and 205-c. If wireless communications system 200 is not informed of which UEs 215 are receiving a multicast transmission and/or does not support CSI reporting for multicast, the base station may be ignorant of the location and channel conditions of the UEs 215. Thus, the base station may attempt to reach as many UEs 215 as possible with the transmission by selecting transmission parameters so that the transmission covers a wide geographic area (e.g., is unidirectional) and is robust enough to overcome the worst channel conditions expected by the base station. But a transmission that covers a wide geographic may be unnecessary if the UEs 215 are closely grouped, and a robust transmission may be unneeded if the UEs 215 are experiencing good channel conditions. Thus, various resources (e.g., processing resources, communication resources, etc.) may be wasted when a multicast transmission is performed independent of location and/or channel information.

[0118] If wireless communications system 200 does not support HARQ processes for multicast, the base station may be unaware when the initial multicast transmission is unsuccessfully decoded. And if failed multicast transmissions go undetected, the base station may not perform re-transmissions when needed, leading to a loss of information. Thus, the reliability of multicast communications may suffer when HARQ processes are unsupported for multicast. It should be appreciated that even if HARQ processes for multicast are enabled, a base station may still be unable to perform adaptive re-transmissions without enablement of CSI reporting (and vice versa). For example, enabling HARQ processes without CSI reporting may result in multicast data being retransmitted in the same manner as the initial transmission (e.g. unidirectionally) even though only UEs in a particular location (e.g., UEs 215-a and 215-b) failed to decode the initial transmission.

[0119] So, it may be desirable for wireless communications system 200 to support CSI reporting, SRS transmissions, and/or HARQ processes for multicast. But implementing CSI reporting, SRS transmissions, and HARQ processes for multicast communications in the same manner as for unicast communications may be undesirable for efficiency and complexity reasons. This is because, for unicast communications, the resources for conveying information and signals related to these processes are assigned on a per-UE basis, meaning that each UE 215 is assigned its own resources for CSI reporting, sending SRS, and transmitting HARQ feedback, respectively. When many EEs 215 are in the multicast environment, such an implementation may increase signaling, resource consumption, and complexity to undesirable levels.

[0120] According to the techniques described herein, wireless communications system 200, while operating in a multicast mode, may implement SRS transmissions and channel feedback reporting for multicast to determine location and/or channel information for EEs 215 and support adaptive multicast transmissions. For example, wireless communications system 200 may implement joint SRS and CSI reporting for multicast by assigning shared SRS resources to multicast UEs and associating each SRS resource with a particular set of CSI. When a UE 215 sends an SRS on an SRS resource that is associated with CSI determined by that UE 215, a base station may update multicast transmission parameters based on the determined CSI. Thus, the base station may perform a subsequent multicast transmission that is directed to UEs in the same area as the reporting UE 215 and tailored to the channel conditions experienced by those UEs.

[0121] As an example, the UEs 215 may be divided into logical groups based on their location and/or channel information. For instance, the UEs 215 may be conceptually divided into group 210-a, group 210-b, and group 210-c. Each group 210 may have a set of transmission parameters that is distinct from the transmission parameters of the other groups 210. For instance, group 210-a may be associated with a first transmission beam in the direction of UE 215-a and UE 215-b, group 210-b may be associated with a second transmission beam in the direction of UE 215-c and UE 215-d, and group 210-c may be associated with a third transmission beam in the direction of UE 215-e and UE 215-f.

[0122] The transmission beam and other preferred transmission parameters (e.g., precoding matrix, carrier frequency, MCS, etc.) for a group of UEs 215 may be indicated by a UE 215 in the group 210 transmitting an SRS over an SRS resource that maps to a set of CSI associated with the transmission parameters. For example, UE 215-a may transmit an SRS on an SRS resource that maps to a particular set of CRI, PMI, and CQI determined by UE 215-a. After determining this set of CSI based on the SRS resource, the base station may select multicast transmission parameters for the group 210 in accordance with the CSI. For example, the base station may select the multicast transmission parameters so that a transmission beam indicated by the CRI is used, a precoding matrix indicated by the PMI is used, and an MCS associated with the channel quality indicated by the CQI is used. Thus, a sounding reference signal transmission may be implemented in a multicast environment such that CSI reporting occurs in an implicit manner.

[0123] According to the techniques described herein, wireless communications system 200, while operating in a multicast mode, may support adaptive retransmissions by implementing SRS transmissions, channel feedback reporting, and/or HARQ operation for multicast to determine location and/or channel information for UEs 215 that fail to receive an initial multicast transmission. For example, to support adaptive multicast retransmissions, wireless communications system 200 may implement joint HARQ feedback and CSI reporting for multicast by assigning shared HARQ resources to UEs 215 and associating each PUCCH resource with a particular set of CSI.

[0124] In some cases, to support indicating a location of UEs 215 that failed to receive multicast transmissions, a set of shared HARQ resources may be grouped into subsets of HARQ resources. In some cases, each subset of HARQ resources may be associated with a group of UEs 215 located within a coverage area. For example, a first subset of the HARQ resources may be associated with group 210-a of UEs 215, a second subset of the uplink communication resources may be associated with group 210-b of UEs 215, and a third subset of the uplink communication resources may be associated with group 210-c of UEs 215. In some cases, the first, second, and third subsets of the HARQ resources include consecutive HARQ resources.

[0125] In some examples, after failing to receive or decode a multicast transmission, UE 215-a may transmit a NACK message over a HARQ feedback resource of a subset of the HARQ resources that is associated with group 210-a of UEs 215. After receiving the NACK message over the subset of the HARQ resources, a base station may determine that a UE 215 within group 210-a failed to receive a multicast transmission and may perform a retransmission that is adapted for group 210-a. For example, after receiving the NACK message over the first subset of the HARQ resources, the base station may perform a multicast retransmission using transmission parameters that are adapted for group 210-a — e.g., using a transmission beam that is formed in the direction of group 210-a.

[0126] Additionally, or alternatively, to support indicating CSI for UEs 215 that fail to receive multicast transmissions, each resource of a shared set of HARQ resources may be configured to correspond to a particular set of CSI. For example, a first HARQ feedback resource may correspond to a first CRI index, a first set of PMI indices, and a first set of CQI indices. And a second HARQ feedback resource may correspond to a first CRI index, a second set of PMI indices, and the first set of CQI indices. In some cases, sets of CSI are assigned to the shared HARQ resources based on a grouping of UEs 215 within a coverage area. For example, CSI indices that are associated with a first group of UEs (e.g., group 210- a) may be assigned to a first subset of consecutive HARQ resources (e.g., by assigning a first CRI index to the first subset of consecutive HARQ resources), CSI indices that are associated with a second group of UEs (e.g., group 210-b) may be assigned to a first subset of consecutive HARQ resources (e.g., by assigning a second CRI index to the second subset of consecutive HARQ resources), and so on. In some cases, a first CRI index may be associated with a first transmission beam that is directed toward group 210-a; a second CRI index may be associated with a second transmission beam that is directed toward group 210-b; and a third CRI index may be associated with a third transmission beam that is directed toward group 210-c.

[0127] In some cases, after failing to receive or decode a multicast transmission, first UE 215-a may transmit a NACK message over a HARQ feedback resource that is associated with group 210-a and reflects CSI feedback determined by first UE 215-a. For example, after determining a preferred transmission beam, a preferred precoding matrix, and a CQI index for a received multicast transmission — e.g., based on a CQI-RS measurement — first UE 215- a may transmit the NACK message over a HARQ feedback resource that is mapped to a first CRI index, a first set of precoding matrices that includes the precoding matrix, and a set of CQI indices that includes the CQI index. After receiving the NACK message over a HARQ resource, a base station may determine that a UE within group 210-a failed to receive a multicast transmission — e.g., based on determining that the HARQ feedback resource is associated with a first transmission beam. In some cases, the base station may also determine CSI associated with group 210-a — e.g., based on determining that the HARQ feedback resource is associated with a first set of precoding matrices and a first set of channel qualities. After determining that a UE within group 210-a failed to receive the multicast transmission and a set of CSI for group 210-a, the base station may perform a retransmission that is adapted for group 210-a based on the determined set of CSI.

[0128] In some examples, to support adaptive multicast retransmissions, wireless communications system 200 may implement joint HARQ feedback and CSI reporting for multicast by using shared SRS resources where each SRS resource is associated with a particular set of CSI and received SRS transmissions are interpreted as NACK messages. In such cases, UEs 215 may be configured to transmit an SRS over shared SRS resources only after failing to decode an initial multicast transmission.

[0129] For example, UEs 215 may be configured with a shared set of SRS resources. After failing to receive a multicast transmission, first UE 215-a may transmit an SRS over a shared SRS resource that is associated with a set of CSI determined by first UE 215-a. A base station may receive the SRS transmission and determine that a UE from group 210-a failed to receive a multicast transmission as well as CSI for group 210-a based on a set of CSI associated with the shared SRS resource. After determining that a UE in group 210-a failed to receive the multicast transmission, the base station may perform a multicast retransmission using transmission parameters that are tailored to group 210-a.

[0130] In some cases, the UEs 215 may determine CSI for a multicast channel based on CSI-RSs that are associated with the multicast channel — e.g., using CSI-RS that are located within the multicast channel and/or quasi-colocated with the multicast channel. In some cases, a base station configures UEs 215 to measure a particular set of CSI-RS resources to determine CSI for a multicast channel. For example, the base station may indicate K CSI-RS resources for UEs 215 to measure. In other cases, each UE 215 may autonomously select f CSI-RS resources to measure. In some examples, the network (e.g., a base station) sends a message to UEs 215 indicating the quantity (K) of CSI-RS resources to measure. In other examples, UE 215 independently determines the quantity (K) of CSI-RS resources to measure and indicates the chosen quantity to the network. In some cases, UEs 215 may use CSI-RS resources used for estimating a unicast channel separately from CSI-RS resources used for estimating a multicast channel.

[0131] In some examples, to support adaptive multicast retransmissions, wireless communications system 200 may implement joint CSI reporting and HARQ feedback (or joint CSI reporting and SRS transmissions) for multicast by using shared uplink PRG resources, where each uplink PRG resource is associated with a particular set of CSI. In some cases, UEs 215 may receive a multicast transmission over multiple downlink PRG resources that are each associated with different precoding matrices and/or beamforming. In some cases, the downlink PRG resources may also be associated with respective uplink PRG resources. In some cases, UEs 215 may also receive DMRSs in each of the downlink PRG resources. UEs 215 may use the received DMRSs to perform instantaneous multicast channel estimates for the different downlink PRG resources. If one or more of UEs 215 fail to receive the multicast transmission, the one or more UEs 215 may transmit a NACK message over an uplink PRG resource that corresponds to the downlink PRG resource having the highest SNR. In some cases, a base station that receives a NACK message over an uplink PRG resource may perform a retransmission using a precoding matrix and/or beamforming associated with the PRG resource. Alternatively, one or more UEs 215 may transmit an SRS over an uplink PRG resource that corresponds to the downlink PRG resource having the highest SNR. In some cases, a base station that receives an SRS over an uplink PRG resource may perform a retransmission using a precoding matrix and/or beamforming associated with the PRG resource.

[0132] In some examples, UE 215-a receives a multicast transmission that is transmitted over a first downlink PRG resources using a first beamforming and first precoding matrix, a second downlink PRG resources using a second beamforming and second precoding matrix, and a third downlink PRG resources using a third beamforming and third precoding matrix. UE 215-a may also receive a first DMRS in the first downlink PRG resource, a second DMRS in the second downlink PRG resource, and a third DMRS in the third downlink PRG resource. In some examples, UE 215-a may determine instantaneous SNR values for the first, second, and third downlink PRG resources based on the first, second, and third DMRSs and determine that signals received over the third downlink PRG resource have the highest SNR.

[0133] In some cases, UE 215-a may fail to decode the multicast transmission and transmit a NACK indication (e.g., a NACK message or SRS-based NACK transmission) over a third uplink PRG resource that corresponds to the third downlink PRG resource. A base station may receive the NACK indication over the third uplink PRG resource and perform a multicast retransmission over a subsequent instance of the third downlink PRG resources — e.g., using the precoding matrix and/or beamforming associated with the third downlink PRG resources. Alternatively, UE 215-a may transmit an SRS over the third uplink PRG resource that corresponds to the third downlink PRG resource. A base station may receive the SRS over the third uplink PRG resource and perform a multicast retransmission over a subsequent instance of the third downlink PRG resources — e.g., using the precoding matrix and/or beamforming associated with the third downlink PRG resources.

[0134] In some cases, a base station may configure UEs 215 to use one or more of the above techniques for reporting channel state and/or HARQ information. In some cases, the base station may switch between joint CSI and HARQ reporting techniques and joint CSI and SRS reporting techniques — e.g., based on an expected level of multicast traffic and/or available multicast resources. For ease of reference, the joint CSI and HARQ reporting techniques may be referred to herein as HARQ-based CSI reporting, or a variation thereof, and the joint CSI and SRS reporting techniques may be referred to herein as SRS-based CSI reporting, or a variation thereof. In general, features and aspects described with respect to one type of CSI reporting (e.g., HARQ-based or SRS-based) may be imputed to the other type of CSI reporting.

[0135] FIG. 3 illustrates an example of an association 300 between acknowledgement resources 310 and channel state information for reporting multicast feedback based on acknowledgment transmissions in accordance with aspects of the present disclosure. Each acknowledgment resource 310 may be associated with (e.g., correspond to, map to) a set of channel state information so that transmission of an acknowledgment message (e.g., a NACK message) on an acknowledgment resource 310 implies a particular set of channel state information.

[0136] A base station may configure (e.g., reserve, schedule, allocate, etc.) the acknowledgment resources 310 for transmission of acknowledgment messages by UEs 115 in a multicast environment. For example, the base station may configure acknowledgment resources 310 for acknowledgment messages from UEs 115 that are recipients of a multicast transmission by the base station. In some cases, the acknowledgment resources 310 may be configured to occur a predetermined duration (e.g., N subframes) after a multicast downlink transmission is performed by a base station. As described below, each acknowledgment resource 310 may be associated with a set of channel state information. For example, each acknowledgment resource 310 may be associated with a unique combination of CRI, PMI(s), and CQI(s). As described herein, the CRI may indicate a transmission beam preferred by a UE, the PMI may indicate a precoding matrix preferred by the UE, and the CQI may indicate the channel quality and, indirectly, the MCS preferred by the EE. Although described with reference to CRI, PMI, and CQI, other types of channel state information are contemplated, as are other hierarchical structures for associating acknowledgment resources with channel state information.

[0137] At the highest level, the acknowledgment resources 310 may be divided into sets that are associated with different CRI. For example, the acknowledgment resources 310 may include set 315-a, set 315-b, and set 315-c, which may be associated with CRI #0, CRI #1, and CRI #2, respectively. Due to the relationship between CRI and transmission beams, the sets 315 may correspond to different groups of UEs. For instance, the acknowledgment resources in set 315-a may correspond to a group of UEs by virtue of the UEs sharing a preferred transmission beam as indicated by CRI #0. Referring to FIG. 2 as an illustration, set 315-a may correspond to UEs in group 210-a, set 315-b may correspond to UEs in group 210-b, and set 315-c may correspond to UEs in group 210-c. In some cases, the UEs in a group may be in close proximity with each other as illustrated in FIG. 2. In other cases, the UEs may be dispersed yet still share a preferred transmission beam due to reflections in the multicast environment.

[0138] To indicate additional channel state information, the acknowledgment resources 310 may be further divided into subsets 320 that are associated with different sets of PMI.

For example, referring to set 315-a, subset 320-a-l be associated with PMI set #0 and subset 320-a-2 may be associated with PMI set #1. The PMI sets may be preconfigured at a UE or dynamically configured by RRC signaling. Because there may be many PMIs (e.g., sixteen) supported by a base station, the PMIs may be grouped into sets to reduce the quantity of acknowledgment resources 310 used to indicate PMI. For example, given a range of PMIs 0 through 15, PMI set #0 may include PMIs 0 through 7 and PMI set #1 may include PMIs 8 through 15.

[0139] To indicate more channel state information, each subset 320 of acknowledgment resources 310 may be further divided into individual acknowledgment resources that are associated with different sets of CQI. For example, referring to subset 320-a, acknowledgment resource 310-a may be associated with CQI set #0 and acknowledgment resource 310-b may be associated with CQI set #1. Because there may be many CQIs supported by a base station, the CQIs may be grouped into sets that are to reduce the quantity of acknowledgment resources used to indicate CQI. For example, given a range of CQIs 0 through 30, CQI set #0 may include CQIs 0 through 15 and CQI set #1 may include CQIs 16 through 30. In some cases, each acknowledgment resource 310 may be associated with a relatively high CQI value or a relatively low CQI value (instead of sets of CQI).

[0140] Because the associations between acknowledgment resources 310 and channel state information are known to both a UE and a base station, the UE may implicitly indicate channel state information by transmitting an acknowledgment message in the acknowledgment resource 310 associated with the channel state information. For example, a UE that determines a set of channel state information that includes CRI #1, a precoding matrix index that is included in PMI set #1, and a channel quality index that is included in CQI set #1 may transmit an acknowledgment message in acknowledgment resource 310-h. That is, the UE may select acknowledgment resources 310-h by determining that set 315-b is associated with CRI # 1, determining that subset 320-b-2 is associated with PMI set #1, and determining that acknowledgment resource 310-h is associated with CQI #1. In some cases, the UE may refer to a set of rules or a table to determine the acknowledgment resource 310 that is associated with a given set of channel state information. In some cases, the set of rules or table may be indicated to the UE in a message from the base station. In other cases, the set of rules or table may be preprogrammed at the UE. In some cases, multiple UEs may simultaneously transmit acknowledgment messages over a same acknowledgment resource 310 — the acknowledgment message may coherently combine with one another.

[0141] Given that the base station also knows the associations between acknowledgment resources 310 and sets of channel state information, the base station may infer channel state information for a group of UEs based on the acknowledgment message(s) being included in acknowledgment resource 310-h. For example, based on receiving an acknowledgment message over acknowledgment resource 310-h, the base station may determine that one or more multicast-enabled UEs are located in a coverage area region associated with a direction of a transmission beam that indicated by CRI#1. The base station may then select transmission parameters for an upcoming multicast communications based on a set of channel state information that is associated with acknowledgment resource 310-h. For example, the base station may use a precoding matrix indicated by the set of channel state information (e.g., a precoding matrix indicated by PMI set #1) to transmit multicast data over a particular transmission beam indicated by the channel state information (e.g., a transmission beam indicated by CRI #1). The base station may also use an MCS indicated by the set of channel state information (e.g., an MCS corresponding to a CQI indicated by CQI set #1).

[0142] The transmission parameters selected by the base station may be used for an initial transmission of multicast data or a retransmission of multicast data. Because the multicast transmission is over a particular transmission beam, the group of UEs in the direction of that transmission beam may receive the updated multicast transmission even if only a single UE in the group reports channel state information. So, the techniques for implicit channel state information reporting described herein may be used to adapt multicast transmissions for groups of UEs.

[0143] In some cases, a UE may determine that channel state information has changed since the UE last transmitted an acknowledgment message. For example, the UE may move to a different region of a coverage area, resulting in new channel conditions and thus new channel state information (e.g., new values for CRI, PMI, and/or CQI). After determining the new channel state information and failing to receive or decode another multicast transmission, the UE may indicate the new set of channel state information by transmitting another acknowledgment message in a different acknowledgment resource 310 than was used for the last acknowledgment message. For example, if the UE previously transmitted an acknowledgment message in acknowledgment resource 310-h, the UE may transmit another acknowledgment message in acknowledgment resource 310-c to indicate that the channel state information now includes CRI #0, PMI set #1, and CQI set #0. If the channel state information changes and the UE fails to receive or decode a multicast transmission again, the UE may indicate the change by transmitting an additional acknowledgment message in yet another acknowledgment resource 310. For example, the UE may transmit an acknowledgment message in subset 320-a-2 to indicate that the latest channel state information includes CRI #2, PMI set #1, and CQI set #1.

[0144] In some cases, a base station may receive multiple acknowledgment messages in a single set 315. Put another way, the base station may receive multiple acknowledgment messages on acknowledgment resources 310 that are each associated with the same CRI. For example, the base station may receive acknowledgment messages on acknowledgment resources 310-a and 310-c. In such cases, the base station may determine that multiple UEs that failed to receive a multicast transmission are in a particular location (or at least, prefer a same transmission beam). However, there may be a discrepancy in the precoding matrices preferred by the UEs (e.g., one UE may prefer a precoding matrix included in PMI set #0 and the other UE may prefer a precoding matrix included in PMI set #1). In such a scenario, the base station may select for use the PMI previously used for the indicated CRI (e.g., CRI #0).

[0145] In some cases, a base station may receive multiple acknowledgment messages in different sets 315. Put another way, the base station may receive multiple acknowledgement messages on acknowledgment resources 310 that are each associated with different CRI. For example, the base station may receive a first acknowledgment message on acknowledgment resource 310-b and a second acknowledgment message on acknowledgment resource 310-f.

In such a scenario, the base station may determine that there are UEs in two different areas (or at least, UEs that prefer different transmission beams). Accordingly, the base station may use transmission parameters that are based on channel state information associated with the multiple acknowledgment resources 310 (e.g., 310-b and 310-f) conveying the acknowledgment messages.

[0146] In another example of receiving multiple acknowledgment messages, the base station may receive acknowledgment messages in three different sets 315. For example, the base station may receive acknowledgment messages on acknowledgment resource 310-b, acknowledgment resource 310-f, and acknowledgment resource 310-j. In such a scenario, the base station may determine that there are UEs in three different areas (or at least, three UEs that prefer different transmission beams). Because there are too many UEs with varying channel conditions for the channel state information to be meaningfully applied, the base station may ignore the indicated sets of channel state information and use transmission parameters that are selected to reach as many UEs as possible.

[0147] As described above and illustrated in FIG. 3, the association between an acknowledgment resource 310 and a set of channel state information may be one-to-one. That is, each acknowledgment resource 310 may be associated with a unique set of channel state information. However, in some examples the mapping between acknowledgment resources 310 and sets of channel state information may be one-to-many or many-to-one. As an example of one-to-many mapping, a single acknowledgment resource 310 may be associated with two sets of channel state information. As an example of many-to-one mapping, multiple acknowledgment resources 310 may be associated with the same set of channel information. When a set of channel state information is associated with multiple acknowledgment resources 310, the UE reporting the channel state information may select one of the associated acknowledgment resources 310 according to its configuration or to provide one or more advantages.

[0148] In some examples, a UE may determine a set of channel state information that is not associated with an acknowledgment resource 310. For instance, the UE may determine a set of channel state information that includes CRI #0, PMI subset #0, and an intermediate CQI that is not included in either CQI set. In such a scenario, the UE may identify the acknowledgment resources 310 associated with the channel information closest to the set of channel information determined by the UE and transmit an acknowledgment message on one of those acknowledgment resources 310. Continuing the foregoing example, the UE may identify acknowledgment resources 310-a and 310-b and transmit an acknowledgment message over one of those acknowledgment resources 310 — e.g., based on determining that one of the acknowledgment resources will cause a base station to transmit a more robust transmission.

[0149] In some examples, the acknowledgment resources 310 may be associated with other aspects of a wireless communications system. For example, each acknowledgment resource 310 may be associated with a physical resource block group (PRG), which may be a collection of physical resource blocks (PRBs) that are applied with the same precoding matrix. In such examples, a base station may transmit a DMRS within a multicast PDSCH that spans multiple PRGs applied with different precoding matrices (e.g., the base station may use a different precoding matrix for each PRG). A UE that receives the multicast PDSCH may measure the DMRS to determine the PRG with the highest SINR, then transmit an acknowledgment message in the acknowledgment resource 310 that is associated with the PRG. Upon receiving the acknowledgment message in the acknowledgment resource 310, the base station may determine that the preferred precoding matrix for communications with the UE is the precoding matrix that was used for the PRG associated with the acknowledgment resource 310. Accordingly, the base station may use that precoding matrix for the next multicast transmission to the UE. Because associating acknowledgment resources 310 with PRGs allows for implicit indication of the preferred precoding matrix for a UE, in some examples the association between acknowledgment resources 310 and PRGs may replace the association between acknowledgment resources 310 and PMI sets.

[0150] In an additional or alternative example, shared reference signal resources may be similarly configured to be associated with channel state information. In such cases, a UE may similarly transmit an SRS over a particular shared reference signal resource based on a set of channel state information determined by the UE. And a base station may similarly determine and use information about a multicast channel based on receiving one or more SRSs over the shared reference signal resources to adapt subsequent multicast transmissions or retransmissions. In some cases, a base station may configure a UE or set of UEs to use one or both of the above techniques for joint HARQ feedback and CSI reporting (e.g., the base station may configure the UE or set of UEs to use HARQ-based CSI reporting and/or SRS- based CSI reporting). In some examples, the base station may switch between the different CSI reporting techniques — e.g., based on measured multicast channel conditions.

[0151] FIG. 4 illustrates an example of a process flow 400 for reporting multicast feedback based on acknowledgment transmissions in accordance with aspects of the present disclosure.

[0152] Process flow 400 may be performed by base station 405 which may be an example of a base station described herein, including with reference to FIGs. 1, 2 and 4. Process flow 400 may also be performed by UE 410, which may be an example of a UE described herein, including with reference to FIGs. 1 and 2. In some examples, base station 405 and UE 410 are part of a multicast or mixed mode wireless communications system. In some examples, process flow 400 illustrates a technique for implicitly indicating a set of channel state information in a multicast environment using shared acknowledgment resources.

[0153] In the following description of the process flow 400, the operations between base station 405 and UE 410 may occur in a different order than the exemplary order shown, or the operations performed by the devices may be performed in different orders or at different times. Certain operations may also be left out of the process flow 400, or other operations may be added to the process flow 400.

[0154] At block 415, base station 405 may select a channel state information reporting scheme for multicast UEs. For example, base station 405 may select a HARQ-based CSI reporting scheme in which HARQ resources carrying NACKs are associated with sets of channel state information. Alternatively, base station 405 may select an SRS-based CSI reporting scheme in which reference signal resources carrying SRSs are associated with sets of channel state information. In some examples, base station 405 may select an SRS-based CSI reporting scheme that uses SRSs to indicate a multicast transmission failure (e.g., that uses an SRS as a pseudo-NACK message, which may also be referred to as an SRS-NACK).

[0155] In the example illustrated in process flow 400, base station 405 may select a HARQ-based CSI reporting scheme. After selecting the CSI reporting scheme, base station 405 may, at arrow 420, transmit an indication of the reporting scheme to UE 410. In some examples, the indication is included in an RRC message that is part of multicast transmission. In other examples, the indication is included in downlink control information that is part of a multicast transmission.

[0156] At block 425, base station 405 may identify HARQ resources to be shared by UEs that receive multicast communications. A set of resources is shared by UEs if multiple UEs are permitted to transmit over the resources. The shared HARQ resources may be allocated for HARQ feedback transmissions and may include time and frequency resources like the acknowledgment resources 310 described with reference to FIG. 3. In cases where an SRS-based CSI reporting scheme is used to convey HARQ information, base station 405 may identify shared SRS resources.

[0157] At block 430, base station 405 may determine the associations between the shared HARQ (or SRS) resources and sets of channel state information. In some examples, base station 405 may reference one or more sets of rules or tables to determine the associations. The sets of rules or tables may be preconfigured (e.g., hardcoded) at base station 405 or configured at base station 405 by the network. Alternatively, base station 405 may autonomously determine the associations. The association between the HARQ resources and sets of channel state information may be one-to-one, as illustrated in FIG. 3, one-to-many, or many-to-one.

[0158] At arrow 435, base station 405 may transmit, and UE 410 may receive, an indication of the shared HARQ (or SRS) resources. The indication may be included in an RRC message or downlink control information (DCI) message that is part of a multicast communication. In some cases, the indication of the HARQ resources may indicate to UE 410 a duration between a multicast downlink transmission and the HARQ resources. [0159] At arrow 440, base station 405 may transmit, and UE 410 may receive, an indication of the associations between the shared HARQ (or SRS) resources and sets of channel state information. In some examples, the indication of associations may be included in an RRC message or DCI message that is part of a multicast communication. In some examples, the indication of associations may be included in the message that conveys the reporting scheme indication. In some cases, the indication may convey the table or set of rules used by base station 405 to determine the associations or the indication may indicate a table or set of rules already configured at UE 410, among other alternatives. In some cases, the indication may include an index that is associated with a particular association between HARQ resources and sets of channel state information. In some cases, the indication may indicate the CRI values that are assigned to the different sets of HARQ resources.

[0160] At block 445, UE 410 may determine the shared HARQ resources that it is to use for multicast operations. UE 410 may determine the shared HARQ resources based on information from base station 405 (e.g., based on the resource indication at 435 and/or the reporting scheme indication at 420). In some examples, UE 410 may determine that the shared HARQ resources are configured to occur a predetermined or indicated number of subframes after an end of a multicast downlink transmission. In cases where an SRS-based CSI reporting scheme is used to convey HARQ information, UE 410 may determine that the shared SRS resources are configured to occur periodically and/or when multicast PDSCH transmissions occur. In some cases, UE 410 may determine that the shared HARQ (or SRS) resources include multiple sets of shared HARQ (or SRS) resources for each PRG used for a downlink multicast transmission.

[0161] At block 450, UE 410 may determine the associations between the shared HARQ (or SRS) resources and sets of channel state information. UE 410 may determine the associations based on information received from base station 405 (e.g., based on the association indication at 440 and/or the reporting scheme indication as 420). In some examples, the associations determined by UE 410 may be consolidated into a table or set of rules that UE 410 can later reference. In other examples, UE 410 may determine the associations by identifying a table or set of rules configured at UE 410 that represents the associations. [0162] At block 455, base station 405 may determine a set of transmission parameters for an initial multicast transmission. For example, base station 405 may determine a transmission beam, precoding matrix, MCS, and/or frequency for the initial multicast transmission. In some cases, the set of transmission parameters may be selected to reach as many UEs as possible. At arrow 460, base station 405 may transmit multicast data (e.g., in a multicast PDSCH) using the transmission parameters determined at block 455. In some cases, the multicast data transmission may be an initial transmission for a HARQ process. Accordingly, UE 410 may receive the multicast PDSCH at arrow 460 and attempt to decode the multicast data. In some cases, UE 410 may fail to detect and/or decode the transmission including the multicast data. After failing to detect or decode the transmission, UE 410 may prepare a NACK message or SRS-based NACK indication for transmission to base station 405.

[0163] At block 465, UE 410 may determine channel state information for a multicast channel between UE 410 and base station 405. The channel state information may be determined by measuring the multicast channel, which may involve one or more measurements of reference signals transmitted over the multicast channel. In some cases, the channel state information may also be based on the transmission of multicast data at arrow 460.

[0164] In a first example, UE 410 may determine the channel state information based on measurements of CSI-reference signals transmitted by base station 405. The CSI-reference signals may be transmitted over different beams and, from the perspective of UE 410, may be separate from CSI-reference signals transmitted for unicast. In one example, UE 410 may measure K CSI-reference signals to determine the CRI, PMI, and/or CQI for the multicast channel. The quantity of measured CSI-reference signals may be less than the quantity of CSI-reference signals transmitted by base station 405.

[0165] In some cases, base station 405 may determine the quantity K and indicate the quantity to UE 410 (e.g., via RRC signaling, MAC signaling, or physical layer signaling). In such cases, base station 405 may also indicate the CSI-reference signals that UE 410 is expected to measure. In some cases, UE 410 may autonomously determine the quantity K and indicate the quantity to base station 405. Because UE 410 can measure a limited number of CSI-reference signals, UE 410 may indicate the quantity K so that base station 405 knows how many CSI-reference signal computational processes are occupied with the multicast measurements. This way, base station 405 can determine how many CSI-reference signals UE 410 is able to measure for unicast and operate accordingly.

[0166] In a second example, UE 410 may determine the channel state information based on measurements of DMRSs transmitted by base station 405. The base station 405 may transmit the DMRSs in a PDSCH that spans multiples PRGs, each of which is applied with a different precoding matrix. Upon receipt of the PDSCH, UE 410 may measure the DMRSs to determine the SINR for each PRG. UE 410 may then determine the PRG with the highest SINR. The PRG with the highest SINR may serve as a basis for selecting a HARQ resource at 470. For example, UE 410 may select, for transmission of an acknowledgment message, the HARQ resource associated with the PRG with the highest SINR. In such a scenario, base station 405 may determine the precoding matrix to use for a subsequent multicast transmission based on the HARQ resource used to convey the acknowledgment message. For example, base station 405 may determine that the HARQ resource is associated with a particular PRG and select the precoding matrix used for that PRG as the precoding matrix for the subsequent multicast transmission.

[0167] At block 470, UE 410 may select a shared HARQ (or SRS) resource for transmission of an acknowledgment message. UE 410 may select the HARQ resource based on the channel state information determined at block 465 and based on the associations determined at block 450. For example, UE 410 may select the HARQ resource based on the HARQ resource being mapped to channel state information that matches (or includes) the channel state information determined by UE 410 at block 465. As an example, if at block 465 UE 410 determines that the channel state information for the multicast channel includes CRI #x, PMI #y, and CQI #z, at block 470, UE 410 may select the HARQ resource that maps to CRI #x, PMI #y (or PRG #y), and CQI #z.

[0168] At arrow 475, UE 410 may transmit an acknowledgment message in the shared HARQ (or SRS) resource selected at block 470. In some examples, UE 410 may transmit the acknowledgment message or indication based on failing to receive or decode the transmission of multicast data (e.g., the multicast data transmitted at arrow 460). When base station 405 selects an SRS-based CSI reporting scheme to report HARQ feedback, UE 410 may transmit an SRS-NACK during periodically scheduled reference SRS resources or aperiodically in response to a trigger received from base station 405. In one example, the trigger may be a control element (e.g., a MAC-CE) that is included in a multicast PDSCH transmission (e.g., the multicast PDSCH transmission at arrow 460). In another example, the trigger may be a DCI format that schedules a multicast PDSCH transmission. In some examples, the SRS may be a single-port SRS that is transmitted without precoding.

[0169] At block 480, base station 405 may determine channel state information for UE 410 or a group of UEs that includes UE 410 based on the NACK message or SRS-NACK received at arrow 475. For example, base station 405 may identify the HARQ resource used to convey the NACK (or SRS-NACK) and refer to the associations determined at block 430 to determine the channel state information that maps to the received acknowledgment message or signal. Thus, base station 405 may determine that the channel state information for UE 410 or a group of UEs that includes UE 410 includes CRI #x, PMI #y (or PRG #y), and CQI #z.

[0170] At block 485, base station 405 may update the transmission parameters for multicast communications. For example, base station 405 may select a transmission beam that corresponds to CRI #x, a precoding matrix that corresponds to PMI #y (or PRG #y), and an MCS that corresponds to CQI #z. At 490, base station 405 may transmit multicast data using the transmission parameters selected at block 485. In some examples, the multicast data may be the same as the multicast data transmitted at arrow 460. Thus, the transmission at arrow 490 may be an adaptive retransmission.

[0171] FIG. 5 shows a block diagram 500 of a device 505 that supports reporting multicast feedback based on acknowledgment transmissions in accordance with aspects of the present disclosure. The device 505 may be an example of aspects of a UE 115 as described herein. The device 505 may include a receiver 510, a communications manager 515, and a transmitter 520. The device 505 may also include a processor. Each of these components may be in communication with one another (e.g., via one or more buses).

[0172] The receiver 510 may receive information such as packets, user data, or control information associated with various information channels (e.g., control channels, data channels, and information related to multicast feedback based on acknowledgment transmissions, etc.). Information may be passed on to other components of the device 505. The receiver 510 may be an example of aspects of the transceiver 720 described with reference to FIG. 7. The receiver 510 may utilize a single antenna or a set of antennas. [0173] The communications manager 515 may receive an indication of uplink control channel resources for reporting acknowledgment feedback by the UE for multicast communications, the uplink control channel resources to be shared by UEs associated with multicast communications, measure one or more multicast channels or one or more signals monitored by the UE to determine a set of channel state information for UE receipt of the multicast communications. The communications manager 515 may also select one of the uplink control channel resources based on an association between the set of channel state information and the one of the uplink control channel resources. The communications manager 515 may also transmit an acknowledgment feedback message over the one of the uplink control channel resources. The communications manager 515 may be an example of aspects of the communications manager 710 described herein.

[0174] The communications manager 515, or its sub-components, may be implemented in hardware, code (e.g., software or firmware) executed by a processor, or any combination thereof. If implemented in code executed by a processor, the functions of the communications manager 515, or its sub-components may be executed by a general-purpose processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described in the present disclosure.

[0175] The communications manager 515, or its sub-components, may be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations by one or more physical components. In some examples, the communications manager 515, or its sub-components, may be a separate and distinct component in accordance with various aspects of the present disclosure. In some examples, the communications manager 515, or its sub-components, may be combined with one or more other hardware components, including but not limited to an input/output (I/O) component, a transceiver, a network server, another computing device, one or more other components described in the present disclosure, or a combination thereof in accordance with various aspects of the present disclosure.

[0176] The transmitter 520 may transmit signals generated by other components of the device 505. In some examples, the transmitter 520 may be collocated with a receiver 510 in a transceiver module. For example, the transmitter 520 may be an example of aspects of the transceiver 720 described with reference to FIG. 7. The transmitter 520 may utilize a single antenna or a set of antennas.

[0177] FIG. 6 shows a block diagram 600 of a communications manager 605 that supports reporting multicast feedback based on acknowledgment transmissions in accordance with aspects of the present disclosure. The communications manager 605 may be an example of aspects of a communications manager 515 or a communications manager 710 described herein. The communications manager 605 may include control information component 610, channel estimation component 615, uplink resource selector 620, uplink transmission manager 625, and multicast reception manager 630. Each of these modules may communicate, directly or indirectly, with one another (e.g., via one or more buses).

[0178] Control information component 610 may receive an indication of uplink control channel resources for reporting acknowledgment feedback by the UE for multicast communications, the uplink control channel resources to be shared by UEs associated with multicast communications.

[0179] Channel estimation component 615 may measure one or more multicast channels or one or more signals monitored by the UE to determine a set of channel state information for UE receipt of the multicast communications.

[0180] Uplink resource selector 620 may select one of the uplink control channel resources based on an association between the set of channel state information and the one of the uplink control channel resources.

[0181] Uplink transmission manager 625 may transmit an acknowledgment feedback message over the one of the uplink control channel resources.

[0182] In some cases, channel estimation component 615 may measure one or more channel state information (CSI)-reference signals transmitted over the one or more multicast channels and determine the set of channel state information based on the one or more CSI- RSs. In some cases, channel estimation component 615 may receive, from a base station, an indication of one or more CSI-RSs to measure. In some cases, channel estimation component 615 may determine a quantity of CSI-RSs to measure and select the one or more CSI-RSs based on the determining, where the one or more CSI-RSs include the quantity of CSI-RSs. In some cases, channel estimation component 615 may receive, from a base station, an indication of the quantity of CSI-RSs for the UE to measure. In other cases, channel estimation component 615 may transmit, to the base station, the indication of the quantity of CSI-RSs measured by the UE.

[0183] In some cases, channel estimation component 615 may measure a plurality of DMRSs transmitted over the one or more multicast channels and determine the set of channel state information based on the plurality of DMRSs. In some cases, the plurality of DMRSs are associated with a plurality of precoding resource block groups. In some cases, channel estimation component 615 may determine that a DMRS of the plurality of DMRSs has a highest signal-to-noise ratio based on the measuring. In some cases, the DMRS with the highest signal-to-noise ration may be associated with a precoding resource block group.

[0184] In some cases, channel estimation component 615 may determine, for the set of channel state information, a precoding matrix indicator, channel quality indicator, or channel state information-reference signal resource indicator, or any combination thereof, based on measuring the one or more multicast channels.

[0185] In some cases, uplink resource selector 620 may determine associations between each of the uplink control channel resources and sets of channel state information, where the one of the uplink control channel resources may be selected based on the associations. In some cases, control information component 610 may receive an indication of the associations in a radio resource control message or a physical downlink control channel message. In some cases, uplink resource selector 620 may determine that a first set of the uplink control channel resources is associated with a first CSI-RS index and a second set of the uplink control channel resources is associated with a second CSI-RS index. Uplink resource selector 620 may also determine that a first subset of the first set of the uplink control channel resources is associated with a first set of precoding matrix indices and a second subset of the first set of the uplink control channel resources is associated with a second set of precoding matrix indices. Uplink resource selector 620 may additionally determine a first uplink control channel resource of the first subset of the first set of the uplink control channel resources is associated with a first set of channel quality indices and a second uplink control channel resource of the first subset of the first set of the uplink control channel resources is associated with a second set of channel quality indices. In some cases, the first set of the uplink control channel resources corresponds to a first group of UEs based on the first CSI-RS index indicating a first transmission beam, and the second set of the uplink control channel resources corresponds to a second group of UEs based on the second CSI-RS index indicating a second transmission beam.

[0186] In some cases, uplink resource selector 620 may identify the one of the uplink control channel resources based on the set of channel state information determined by the UE. In some cases, uplink resource selector 620 may identify a set of the uplink control channel resources that is associated with the precoding resource block group based on the determining, wherein the one of the uplink control channel resources is selected from the set of the uplink control channel resources. In some cases, uplink resource selector 620 may identify a set of control channel resources that is associated with one or more CSI-RS indices, where the one of the control channel resources may be selected from the set of control channel resources. In some cases, uplink resource selector 620 may identify a set of control channel resources that is associated with one or more precoding matrix indices, where the one of the control channel resources is selected from the set of control channel resources. In some cases, uplink resource selector 620 may identify a set of control channel resources that is associated with one or more channel quality indices, where the one of the control channel resources is selected from the set of control channel resources.

[0187] In some cases, channel estimation component 615 may determine that the set of channel state information includes a channel state information (CSI)-reference signal index, a precoding matrix index, and a channel quality index. And uplink resource selector 620 may identify the one of the uplink control channel resources as being associated with the CSI-RS index, the precoding matrix index, and the channel quality index.

[0188] In some cases, channel estimation component 615 may determine that the set of channel state information includes a channel state information (CSI)-reference signal index, and uplink resource selector 620 may identify a set of the uplink control channel resources that is associated with the CSI-RS index. Uplink resource selector 620 may select the one of the uplink control channel resources from the set of the uplink control channel resources. In some cases, channel estimation component 615 may determine that the set of channel state information includes a precoding matrix index, and uplink resource selector 620 may identify, from the set of the uplink control channel resources, a subset of the uplink control channel resources that is associated with a first set of precoding matrix indices including the precoding matrix index. Uplink resource selector 620 may select the one of the uplink control channel resources from the subset of the uplink control channel resources.

[0189] In some cases, channel estimation component 615 may determine that the set of channel state information includes a channel quality index, and uplink resource selector 620 may identify, from the subset of the uplink control channel resources, a first uplink control channel resource that is associated with a first set of channel quality indices including the channel quality index. Uplink resource selector 620 may select the first uplink control channel resource as the one of the uplink control channel resources. In other cases, uplink resource selector 620 may identify, from the subset of the uplink control channel resources, a second uplink control channel resource that is associated with a second set of channel quality indices including the channel quality index, and the first uplink control channel resource or the second uplink control channel resource is selected may be the one of the uplink control channel resources.

[0190] In some cases, the one of the uplink control channel resources is selected based on the UE being associated with a first group of UEs. After selecting the one of the uplink control channel resources, channel estimation component 615 may determine that a condition of the one or more multicast channels has changed by a threshold amount. Channel estimation component 615 may also determine that the UE is associated with a second group of UEs based on the condition changing by the threshold amount. In some cases, uplink resource selector 620 may select a different uplink control channel resource of the uplink control channel resources based on the UE being associated with the second group of UEs.

[0191] Multicast reception manager 630 may receive a first multicast transmission using a first set of transmission parameters. In some cases, uplink transmission manager 625 may transmit the acknowledgment feedback message including a negative acknowledgment for the first multicast transmission. In some cases, multicast reception manager 630 may receive, based on transmitting the negative acknowledgment, a second multicast transmission that is transmitted based on the association between the set of channel state information and the one of the uplink control channel resources. In some cases, multicast reception manager 630 may receive the second multicast transmission over a transmission beam indicated by the association between the set of channel state information and the one of the uplink control channel resources. In some cases, multicast reception manager 630 may receive the second multicast transmission using a modulation and coding scheme indicated by the association between the set of channel state information and the one of the uplink control channel resources. In some cases, the second multicast transmission includes a retransmission of data included in the first multicast transmission.

[0192] FIG. 7 shows a diagram of a system 700 including a device 705 that supports reporting multicast feedback based on acknowledgment transmissions in accordance with aspects of the present disclosure. The device 705 may be an example of or include the components of device 505 or a UE 115 as described herein. The device 705 may include components for bi-directional voice and data communications including components for transmitting and receiving communications, including a communications manager 710, an I/O controller 715, a transceiver 720, an antenna 725, memory 730, and a processor 740. These components may be coupled (e.g., in electronic communication) via one or more buses (e.g., bus 745).

[0193] The communications manager 710 may receive an indication of uplink control channel resources for reporting acknowledgment feedback by the UE for multicast communications, the uplink control channel resources to be shared by UEs associated with multicast communications, measure one or more multicast channels or one or more signals monitored by the UE to determine a set of channel state information for UE receipt of the multicast communications, select one of the uplink control channel resources based on an association between the set of channel state information and the one of the uplink control channel resources, and transmit an acknowledgment feedback message over the one of the uplink control channel resources.

[0194] The I/O controller 715 may manage input and output signals for the device 705. The I/O controller 715 may also manage peripherals not integrated into the device 705. In some cases, the I/O controller 715 may represent a physical connection or port to an external peripheral. In some cases, the I/O controller 715 may utilize an operating system such as iOS®, ANDROID®, MS-DOS®, MS-WINDOWS®, OS/2®, UNIX®, LINUX®, or another known operating system. In other cases, the I/O controller 715 may represent or interact with a modem, a keyboard, a mouse, a touchscreen, or a similar device. In some cases, the EO controller 715 may be implemented as part of a processor. In some cases, a user may interact with the device 705 via the I/O controller 715 or via hardware components controlled by the I/O controller 715.

[0195] The transceiver 720 may communicate bi-directionally, via one or more antennas, wired, or wireless links as described above. For example, the transceiver 720 may represent a wireless transceiver and may communicate bi-directionally with another wireless transceiver. The transceiver 720 may also include a modem to modulate the packets and provide the modulated packets to the antennas for transmission, and to demodulate packets received from the antennas.

[0196] In some cases, the wireless device may include a single antenna 725. However, in some cases the device may have more than one antenna 725, which may be capable of concurrently transmitting or receiving multiple wireless transmissions.

[0197] The memory 730 may include random-access memory (RAM) and read-only memory (ROM). The memory 730 may store computer-readable, computer-executable code 735 including instructions that, when executed, cause the processor to perform various functions described herein. In some cases, the memory 730 may contain, among other things, a basic input/output system (BIOS) which may control basic hardware or software operation such as the interaction with peripheral components or devices.

[0198] The processor 740 may include an intelligent hardware device, (e.g., a general- purpose processor, a DSP, a CPU, a microcontroller, an ASIC, an FPGA, a programmable logic device, a discrete gate or transistor logic component, a discrete hardware component, or any combination thereof). In some cases, the processor 740 may be configured to operate a memory array using a memory controller. In other cases, a memory controller may be integrated into the processor 740. The processor 740 may be configured to execute computer- readable instructions stored in a memory (e.g., the memory 730) to cause the device 705 to perform various functions (e.g., functions or tasks supporting multicast feedback based on acknowledgment transmissions).

[0199] The code 735 may include instructions to implement aspects of the present disclosure, including instructions to support wireless communications. The code 735 may be stored in a non-transitory computer-readable medium such as system memory or other type of memory. In some cases, the code 735 may not be directly executable by the processor 740 but may cause a computer (e.g., when compiled and executed) to perform functions described herein.

[0200] FIG. 8 shows a block diagram 800 of a device 805 that supports reporting multicast feedback based on acknowledgment transmissions in accordance with aspects of the present disclosure. The device 805 may be an example of aspects of a base station 105 as described herein. The device 805 may include a receiver 810, a communications manager 815, and a transmitter 820. The device 805 may also include a processor. Each of these components may be in communication with one another (e.g., via one or more buses).

[0201] The receiver 810 may receive information such as packets, user data, or control information associated with various information channels (e.g., control channels, data channels, and information related to multicast feedback based on acknowledgment transmissions, etc.). Information may be passed on to other components of the device 805.

The receiver 810 may be an example of aspects of the transceiver 1020 described with reference to FIG. 10. The receiver 810 may utilize a single antenna or a set of antennas.

[0202] The communications manager 815 may transmit, over a multicast channel, an indication of uplink control channel resources for reporting acknowledgment feedback for multicast communications, the uplink control channel resources to be shared by a set of user equipments (UEs) associated with multicast communication. The communications manager 815 may also receive, from a UE, an acknowledgment feedback message over one of the uplink control channel resources, the one of the uplink control channel resources associated with a set of channel state information for the UE. The communications manager 815 may also transmit, over the multicast channel, multicast data based on the set of channel state information for the UE. The communications manager 815 may be an example of aspects of the communications manager 1010 described herein.

[0203] The communications manager 815, or its sub-components, may be implemented in hardware, code (e.g., software or firmware) executed by a processor, or any combination thereof. If implemented in code executed by a processor, the functions of the communications manager 815, or its sub-components may be executed by a general-purpose processor, a DSP, an application-specific integrated circuit (ASIC), a FPGA or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described in the present disclosure. [0204] The communications manager 815, or its sub-components, may be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations by one or more physical components. In some examples, the communications manager 815, or its sub-components, may be a separate and distinct component in accordance with various aspects of the present disclosure. In some examples, the communications manager 815, or its sub-components, may be combined with one or more other hardware components, including but not limited to an input/output (I/O) component, a transceiver, a network server, another computing device, one or more other components described in the present disclosure, or a combination thereof in accordance with various aspects of the present disclosure.

[0205] The transmitter 820 may transmit signals generated by other components of the device 805. In some examples, the transmitter 820 may be collocated with a receiver 810 in a transceiver module. For example, the transmitter 820 may be an example of aspects of the transceiver 1020 described with reference to FIG. 10. The transmitter 820 may utilize a single antenna or a set of antennas.

[0206] FIG. 9 shows a block diagram 900 of a communications manager 905 that supports reporting multicast feedback based on acknowledgment transmissions in accordance with aspects of the present disclosure. The communications manager 905 may be an example of aspects of a communications manager 815 or a communications manager 1010 described herein. The communications manager 905 may include control information component 910, uplink reception manager 915, multicast transmission manager 920, and channel estimation component 925. Each of these modules may communicate, directly or indirectly, with one another (e.g., via one or more buses).

[0207] Control information component 910 may transmit, over a multicast channel, an indication of uplink control channel resources for reporting acknowledgment feedback for multicast communications, where the uplink control channel resources may be shared by a plurality of user equipments (UEs) associated with multicast communication.

[0208] Uplink reception manager 915 may receive, from a UE, an acknowledgment feedback message over one of the uplink control channel resources, where the one of the uplink control channel resources may be associated with a set of channel state information for the UE. [0209] Multicast transmission manager 920 may transmit, over the multicast channel, multicast data based on the set of channel state information for the UE.

[0210] Channel estimation component 925 may determine a set of transmission parameters for transmitting the multicast data based on the set of channel state information.

[0211] In some cases, uplink reception manager 915 may receive, from a second UE, a second acknowledgment feedback message over another one of the uplink control channel resources and concurrently with the acknowledgment feedback message, where the other one of the uplink control channel resources may be associated with a second set of channel state information. In some cases, control information component 910 may determine a set of transmission parameters for transmitting the multicast data based on the set of channel state information and the second set of channel state information.

[0212] In some cases, the multicast data may be transmitted using a first set of transmission parameters. After transmitting the multicast data, uplink reception manager 915 may receive, from a second UE, a second acknowledgement message for the multicast data transmissions over another one of the uplink control channel resources that may be associated with a second set of channel state information. In some cases, channel estimation component 925 may determine a second set of transmission parameters for transmitting second multicast data based on the second set of channel state information, and multicast transmission manager 920 may transmit the second multicast data using the second set of transmission parameters based on the determining.

[0213] In some cases, uplink reception manager 915 may receive, from a plurality of UEs after transmitting the multicast data, a plurality of acknowledgment feedback messages over a plurality of the uplink control channel resources. In some cases, the plurality of the uplink control channel resources may be associated with a plurality of sets of channel state information. In some cases, channel estimation component 925 may determine a set of transmission parameters for transmitting second multicast data independent of the plurality of sets of channel state information based on the plurality of sets of channel state information including different CSI-RS indices.

[0214] In some cases, control information component 910 may transmit an indication of associations between the uplink control channel resources and sets of channel state information. In some cases, control information component 910 may transmit an indication of a plurality of channel state information (CSI)-reference signals for the UE to measure or a quantity of CSI-RSs for the UE to measure. In some cases, control information component 910 may receive an indication of a quantity of channel state information (CSI)-reference signals measured by the UE.

[0215] In some cases, the uplink control channel resources include a first set of uplink control channel resources associated with a first precoding resource block group and a second set of uplink control channel resources associated with a second precoding resource block group. In such cases, uplink reception manager 915 may receive the acknowledgment feedback message over the first set of uplink control channel resources associated with the first precoding resource block group, the first precoding resource block group being associated with the set of channel state information. In some cases, channel estimation component 925 may determine a precoding matrix for transmitting the multicast data based on receiving the acknowledgment feedback message over the first set of uplink control channel resources associated with the first precoding resource block group.

[0216] FIG. 10 shows a diagram of a system 1000 including a device 1005 that supports reporting multicast feedback based on acknowledgment transmissions in accordance with aspects of the present disclosure. The device 1005 may be an example of or include the components of device 805 or a base station 105 as described herein. The device 1005 may include components for bi-directional voice and data communications including components for transmitting and receiving communications, including a communications manager 1010, a network communications manager 1015, a transceiver 1020, an antenna 1025, memory 1030, a processor 1040, and an inter-station communications manager 1045. These components may be coupled (e.g., in electronic communication) via one or more buses (e.g., bus 1050).

[0217] The communications manager 1010 may transmit, over a multicast channel, an indication of uplink control channel resources for reporting acknowledgment feedback for multicast communications, the uplink control channel resources to be shared by a set of user equipments (UEs) associated with multicast communication, receive, from a UE, an acknowledgment feedback message over one of the uplink control channel resources, the one of the uplink control channel resources associated with a set of channel state information for the UE, and transmit, over the multicast channel, multicast data based on the set of channel state information for the UE. [0218] The network communications manager 1015 may manage communications with the core network (e.g., via one or more wired backhaul links). For example, the network communications manager 1015 may manage the transfer of data communications for client devices, such as one or more UEs 115.

[0219] The transceiver 1020 may communicate bi-directionally, via one or more antennas, wired, or wireless links as described above. For example, the transceiver 1020 may represent a wireless transceiver and may communicate bi-directionally with another wireless transceiver. The transceiver 1020 may also include a modem to modulate the packets and provide the modulated packets to the antennas for transmission, and to demodulate packets received from the antennas.

[0220] In some cases, the wireless device may include a single antenna 1025. However, in some cases the device may have more than one antenna 1025, which may be capable of concurrently transmitting or receiving multiple wireless transmissions.

[0221] The memory 1030 may include RAM, ROM, or a combination thereof. The memory 1030 may store computer-readable code 1035 including instructions that, when executed by a processor (e.g., the processor 1040) cause the device to perform various functions described herein. In some cases, the memory 1030 may contain, among other things, a BIOS which may control basic hardware or software operation such as the interaction with peripheral components or devices.

[0222] The processor 1040 may include an intelligent hardware device, (e.g., a general- purpose processor, a DSP, a CPU, a microcontroller, an ASIC, an FPGA, a programmable logic device, a discrete gate or transistor logic component, a discrete hardware component, or any combination thereof). In some cases, the processor 1040 may be configured to operate a memory array using a memory controller. In some cases, a memory controller may be integrated into processor 1040. The processor 1040 may be configured to execute computer- readable instructions stored in a memory (e.g., the memory 1030) to cause the device 1005 to perform various functions (e.g., functions or tasks supporting multicast feedback based on acknowledgment transmissions).

[0223] The inter-station communications manager 1045 may manage communications with other base station 105 and may include a controller or scheduler for controlling communications with UEs 115 in cooperation with other base stations 105. For example, the inter-station communications manager 1045 may coordinate scheduling for transmissions to UEs 115 for various interference mitigation techniques such as beamforming or joint transmission. In some examples, the inter-station communications manager 1045 may provide an X2 interface within an LTE/LTE-A wireless communication network technology to provide communication between base stations 105.

[0224] The code 1035 may include instructions to implement aspects of the present disclosure, including instructions to support wireless communications. The code 1035 may be stored in a non-transitory computer-readable medium such as system memory or other type of memory. In some cases, the code 1035 may not be directly executable by the processor 1040 but may cause a computer (e.g., when compiled and executed) to perform functions described herein.

[0225] FIG. 11 shows a flowchart illustrating a method 1100 that supports reporting multicast feedback based on acknowledgment transmissions in accordance with aspects of the present disclosure. The operations of method 1100 may be implemented by a UE 115 or its components as described herein. For example, the operations of method 1100 may be performed by a communications manager as described with reference to FIGs. 5 through 7. In some examples, a UE may execute a set of instructions to control the functional elements of the UE to perform the functions described below. Additionally, or alternatively, a UE may perform aspects of the functions described below using special-purpose hardware.

[0226] At 1105, the UE may receive an indication of uplink control channel resources for reporting acknowledgement feedback by the UE for multicast communications, the uplink control channel resources to be shared by UEs associated with the multicast communications. The operations of 1105 may be performed according to the methods described herein. In some examples, aspects of the operations of 1105 may be performed by a control information component as described with reference to FIGs. 5 through 7.

[0227] At 1110, the UE may measure one or more multicast channels or one or more signals monitored by the UE to determine a set of channel state information for UE receipt of the multicast communications. The operations of 1110 may be performed according to the methods described herein. In some examples, aspects of the operations of 1110 may be performed by a channel estimation component as described with reference to FIGs. 5 through 7. [0228] At 1115, the UE may select one of the uplink control channel resources based at least in part on an association between the set of channel state information and the one of the uplink control channel resources. The operations of 1115 may be performed according to the methods described herein. In some examples, aspects of the operations of 1115 may be performed by an uplink resource selector as described with reference to FIGs. 5 through 7.

[0229] At 1120, the UE may transmit an acknowledgement feedback message over the one of the uplink control channel resources. The operations of 1120 may be performed according to the methods described herein. In some examples, aspects of the operations of 1120 may be performed by an uplink transmission manager as described with reference to FIGs. 5 through 7.

[0230] FIG. 12 shows a flowchart illustrating a method 1200 that supports reporting multicast feedback based on acknowledgment transmissions in accordance with aspects of the present disclosure. The operations of method 1200 may be implemented by a base station 105 or its components as described herein. For example, the operations of method 1200 may be performed by a communications manager as described with reference to FIGs. 8 through 10. In some examples, a base station may execute a set of instructions to control the functional elements of the base station to perform the functions described below. Additionally, or alternatively, a base station may perform aspects of the functions described below using special-purpose hardware.

[0231] At 1205, the base station may transmit, over one or more multicast channels, an indication of uplink control channel resources for reporting acknowledgement feedback for multicast communications, the uplink control channel resources to be shared by user equipments (UEs) associated with the multicast communications. The operations of 1205 may be performed according to the methods described herein. In some examples, aspects of the operations of 1205 may be performed by a control information component as described with reference to FIGs. 8 through 10.

[0232] At 1210, the base station may receive, from a UE, an acknowledgement feedback message over one of the uplink control channel resources, the one of the uplink control channel resources being associated with a set of channel state information. The operations of 1210 may be performed according to the methods described herein. In some examples, aspects of the operations of 1210 may be performed by an uplink reception manager as described with reference to FIGs. 8 through 10.

[0233] At 1215, the base station may transmit, from a UE, an acknowledgement feedback message over one of the uplink control channel resources, the one of the uplink control channel resources being associated with a set of channel state information. The operations of 1215 may be performed according to the methods described herein. In some examples, aspects of the operations of 1215 may be performed by a multicast transmission manager as described with reference to FIGs. 8 through 10.

[0234] It should be noted that the methods described herein describe possible implementations, and that the operations and the steps may be rearranged or otherwise modified and that other implementations are possible. Further, aspects from two or more of the methods may be combined.

[0235] The following provides an overview of aspects of the present disclosure:

[0236] Aspect 1 : A method for wireless communications at a UE, comprising: receiving an indication of uplink control channel resources for reporting acknowledgement feedback by the UE for multicast communications, the uplink control channel resources to be shared by UEs associated with the multicast communications; measuring one or more multicast channels or one or more signals monitored by the UE to determine a set of channel state information for UE receipt of the multicast communications; selecting one of the uplink control channel resources based at least in part on an association between the set of channel state information and the one of the uplink control channel resources; and transmitting an acknowledgement feedback message over the one of the uplink control channel resources.

[0237] Aspect 2: The method of aspect 1, wherein the selecting comprises: identifying the one of the uplink control channel resources based at least in part on the set of channel state information determined by the UE.

[0238] Aspect 3: The method of any of aspects 1 through 2, further comprising: determining that the set of channel state information comprises a CSI-reference signal index, a precoding matrix index, and a channel quality index; and identifying the one of the uplink control channel resources as being associated with the CSI-reference signal index, the precoding matrix index, and the channel quality index. [0239] Aspect 4: The method of any of aspects 1 through 3, further comprising: identifying a set of the uplink control channel resources that is associated with one or more CSI-reference signal indices, wherein the one of the uplink control channel resources is selected from the set of the uplink control channel resources.

[0240] Aspect 5: The method of any of aspects 1 through 4, further comprising: identifying a set of the uplink control channel resources that is associated with one or more precoding matrix indices, wherein the one of the uplink control channel resources is selected from the set of the uplink control channel resources.

[0241] Aspect 6: The method of any of aspects 1 through 5, further comprising: identifying a set of the uplink control channel resources that is associated with one or more channel quality indices, wherein the one of the uplink control channel resources is selected from the set of the uplink control channel resources.

[0242] Aspect 7: The method of any of aspects 1 through 6, further comprising: determining that the set of channel state information comprises a CSI-reference signal index; and identifying a set of the uplink control channel resources that is associated with the CSI- reference signal index, wherein the one of the uplink control channel resources is selected from the set of the uplink control channel resources.

[0243] Aspect 8: The method of aspect 7, further comprising: determining that the set of channel state information comprises a precoding matrix index; and identifying, from the set of the uplink control channel resources, a subset of the uplink control channel resources that is associated with a first set of precoding matrix indices comprising the precoding matrix index, wherein the one of the uplink control channel resources is selected from the subset of the uplink control channel resources.

[0244] Aspect 9: The method of aspect 8, further comprising: determining that the set of channel state information comprises a channel quality index; and identifying, from the subset of the uplink control channel resources, a first uplink control channel resource that is associated with a first set of channel quality indices comprising the channel quality index, wherein the first uplink control channel resource is selected as the one of the uplink control channel resources. [0245] Aspect 10: The method of aspect 9, further comprising: identifying, from the subset of the uplink control channel resources, a second uplink control channel resource that is associated with a second set of channel quality indices comprising the channel quality index, wherein the first uplink control channel resource or the second uplink control channel resource is selected as the one of the uplink control channel resources.

[0246] Aspect 11 : The method of any of aspects 1 through 10, wherein the one of the uplink control channel resources is selected based at least in part on the UE being associated with a first group of UEs, the method further comprising: determining that a condition of the one or more multicast channels has changed by a threshold amount, wherein the UE is associated with a second group of UEs based at least in part on the condition changing by the threshold amount; and selecting a different uplink control channel resource of the uplink control channel resources based at least in part on being associated with the second group of UEs.

[0247] Aspect 12: The method of any of aspects 1 through 11, further comprising: receiving a first multicast transmission using a first set of transmission parameters, wherein transmitting the acknowledgement feedback message comprises transmitting a negative acknowledgment feedback message for the first multicast transmission; and receiving, based at least in part on transmitting the negative acknowledgement feedback message, a second multicast transmission that is transmitted based at least in part on the association between the set of channel state information and the one of the uplink control channel resources.

[0248] Aspect 13: The method of aspect 12, wherein the receiving comprises: receiving the second multicast transmission over a transmission beam indicated by the association between the set of channel state information and the one of the uplink control channel resources.

[0249] Aspect 14: The method of any of aspects 12 through 13, wherein the receiving comprises: receiving the second multicast transmission using a modulation and coding scheme indicated by the association between the set of channel state information and the one of the uplink control channel resources.

[0250] Aspect 15: The method of any of aspects 12 through 14, wherein the second multicast transmission comprises a retransmission of data included in the first multicast transmission. [0251] Aspect 16: The method of any of aspects 1 through 15, further comprising: determining associations between each of the uplink control channel resources and sets of channel state information, wherein the one of the uplink control channel resources is selected based at least in part on the associations.

[0252] Aspect 17: The method of aspect 16, wherein determining the associations comprises determining that: a first set of the uplink control channel resources is associated with a first CSI-reference signal index, a second set of the uplink control channel resources is associated with a second CSI-reference signal index, a first subset of the first set of the uplink control channel resources is associated with a first set of precoding matrix indices, a second subset of the first set of the uplink control channel resources is associated with a second set of precoding matrix indices, a first uplink control channel resource of the first subset of the first set of the uplink control channel resources is associated with a first set of channel quality indices, and a second uplink control channel resource of the first subset of the first set of the uplink control channel resources is associated with a second set of channel quality indices.

[0253] Aspect 18: The method of aspect 17, wherein the first set of the uplink control channel resources corresponds to a first group of UEs based at least in part on the first CSI- reference signal index indicating a first transmission beam, and the second set of the uplink control channel resources corresponds to a second group of UEs based at least in part on the second CSI-reference signal index indicating a second transmission beam.

[0254] Aspect 19: The method of any of aspects 16 through 18, further comprising: receiving an indication of the associations in a radio resource control message or a physical downlink control channel message.

[0255] Aspect 20: The method of any of aspects 1 through 19, further comprising: measuring one or more CSI-reference signals transmitted over the one or more multicast channels; and determining the set of channel state information based at least in part on the one or more CSI-reference signals.

[0256] Aspect 21 : The method of aspect 20, further comprising: receiving, from a base station, an indication of the one or more CSI-reference signals to measure.

[0257] Aspect 22: The method of any of aspects 20 through 21, further comprising: determining, by the UE, a quantity of CSI-reference signals to measure; selecting the one or more CSI-reference signals based at least in part on the determining, the one or more CSI- reference signals comprising the quantity of CSI-reference signals.

[0258] Aspect 23: The method of aspect 22, further comprising: receiving, from a base station, an indication of the quantity of CSI-reference signals for the UE to measure; or transmitting, to the base station, the indication of the quantity of CSI-reference signals measured by the UE.

[0259] Aspect 24: The method of any of aspects 1 through 23, further comprising: measuring a plurality of demodulation reference signals transmitted over the one or more multicast channels, the plurality of demodulation reference signals being associated with a plurality of precoding resource block groups; and determining the set of channel state information based at least in part on the plurality of demodulation reference signals.

[0260] Aspect 25: The method of aspect 24, further comprising: determining that a demodulation reference signal of the plurality of demodulation reference signals has a highest signal-to-noise ratio based at least in part on the measuring, the demodulation reference signal being associated with a precoding resource block group; and identifying a set of the uplink control channel resources that is associated with the precoding resource block group based at least in part on the determining, wherein the one of the uplink control channel resources is selected from the set of the uplink control channel resources.

[0261] Aspect 26: The method of any of aspects 1 through 25, further comprising: determining, for the set of channel state information, a precoding matrix indicator, channel quality indicator, or channel state information-reference signal resource indicator, or any combination thereof, based at least in part on measuring the one or more multicast channels.

[0262] Aspect 27: A method for wireless communications at a base station, comprising: transmitting, over one or more multicast channels, an indication of uplink control channel resources for reporting acknowledgement feedback for multicast communications, the uplink control channel resources to be shared by user equipments (UEs) associated with the multicast communications; receiving, from a UE, an acknowledgement feedback message over one of the uplink control channel resources, the one of the uplink control channel resources being associated with a set of channel state information; and transmitting, over the one or more multicast channels, multicast data based at least in part on an association between the set of channel state information and the one of the uplink control channel resources.

[0263] Aspect 28: The method of aspect 27, further comprising: determining a set of transmission parameters for transmitting the multicast data based at least in part on the set of channel state information.

[0264] Aspect 29: The method of any of aspects 27 through 28, further comprising: receiving, from a second UE, a second acknowledgement feedback message over another one of the uplink control channel resources and concurrently with the acknowledgement feedback message, the other one of the uplink control channel resources being associated with a second set of channel state information; and determining a set of transmission parameters for transmitting the multicast data based at least in part on the set of channel state information and the second set of channel state information.

[0265] Aspect 30: The method of any of aspects 27 through 29, wherein the multicast data is transmitted using a first set of transmission parameters, the method further comprising: receiving, from a second UE after transmitting the multicast data, a second acknowledgement feedback message for the multicast data transmission over another one of the uplink control channel resources, the other one of the uplink control channel resources being associated with a second set of channel state information; determining a second set of transmission parameters for transmitting second multicast data based at least in part on the second set of channel state information; and transmitting the second multicast data using the second set of transmission parameters based at least in part on the determining.

[0266] Aspect 31 : The method of any of aspects 27 through 30, further comprising: receiving, from a plurality of UE after transmitting the multicast data, a plurality of acknowledgement feedback messages over a plurality of the uplink control channel resources, the plurality of the uplink control channel resources being associated with a plurality of sets of channel state information; and determining a set of transmission parameters for transmitting second multicast data independent of the plurality of sets of channel state information based at least in part on the plurality of sets of channel state information comprising different CSI-reference signal indices. [0267] Aspect 32: The method of any of aspects 27 through 31, further comprising: transmitting an indication of associations between the uplink control channel resources and sets of channel state information.

[0268] Aspect 33: The method of any of aspects 27 through 32, further comprising: transmitting an indication of a plurality of CSI-reference signals for the UE to measure or a quantity of CSI-reference signals for the UE to measure.

[0269] Aspect 34: The method of any of aspects 27 through 33, further comprising: receiving an indication of a quantity of CSI-reference signals measured by the UE.

[0270] Aspect 35: The method of any of aspects 27 through 34, wherein the uplink control channel resources comprises a first set of uplink control channel resources associated with a first precoding resource block group and a second set of uplink control channel resources associated with a second precoding resource block group, receiving the acknowledgement feedback message comprises receiving the acknowledgement feedback message over the first set of uplink control channel resources associated with the first precoding resource block group, the first precoding resource block group being associated with the set of channel state information.

[0271] Aspect 36: The method of aspect 35, further comprising: determining a precoding matrix for transmitting the multicast data based at least in part on receiving the acknowledgment feedback message over the first set of uplink control channel resources associated with the first precoding resource block group.

[0272] Aspect 37: An apparatus for wireless communications at a UE, comprising a processor; memory coupled with the processor; and instructions stored in the memory and executable by the processor to cause the apparatus to perform a method of any of aspects 1 through 26.

[0273] Aspect 38: An apparatus for wireless communications at a UE, comprising at least one means for performing a method of any of aspects 1 through 26.

[0274] Aspect 39: A non-transitory computer-readable medium storing code for wireless communications at a UE, the code comprising instructions executable by a processor to perform a method of any of aspects 1 through 26. [0275] Aspect 40: An apparatus for wireless communications at a base station, comprising a processor; memory coupled with the processor; and instructions stored in the memory and executable by the processor to cause the apparatus to perform a method of any of aspects 27 through 36.

[0276] Aspect 41 : An apparatus for wireless communications at a base station, comprising at least one means for performing a method of any of aspects 27 through 36.

[0277] Aspect 42: A non-transitory computer-readable medium storing code for wireless communications at a base station, the code comprising instructions executable by a processor to perform a method of any of aspects 27 through 36.

[0278] Although aspects of an LTE, LTE-A, LTE-A Pro, or NR system may be described for purposes of example, and LTE, LTE-A, LTE-A Pro, or NR terminology may be used in much of the description, the techniques described herein are applicable beyond LTE, LTE-A, LTE-A Pro, or NR networks. For example, the described techniques may be applicable to various other wireless communications systems such as Ultra Mobile Broadband (UMB), Institute of Electrical and Electronics Engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDM, as well as other systems and radio technologies not explicitly mentioned herein.

[0279] Information and signals described herein may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

[0280] The various illustrative blocks and components described in connection with the disclosure herein may be implemented or performed with a general-purpose processor, a DSP, an ASIC, a CPU, an FPGA or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices (e.g., a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration).

[0281] The functions described herein may be implemented in hardware, software executed by a processor, firmware, or any combination thereof. If implemented in software executed by a processor, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Other examples and implementations are within the scope of the disclosure and appended claims. For example, due to the nature of software, functions described herein may be implemented using software executed by a processor, hardware, firmware, hardwiring, or combinations of any of these. Features implementing functions may also be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations.

[0282] Computer-readable media includes both non-transitory computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A non-transitory storage medium may be any available medium that may be accessed by a general-purpose or special-purpose computer. By way of example, and not limitation, non-transitory computer-readable media may include RAM, ROM, electrically erasable programmable ROM (EEPROM), flash memory, compact disk (CD) ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other non-transitory medium that may be used to carry or store desired program code means in the form of instructions or data structures and that may be accessed by a general-purpose or special-purpose computer, or a general-purpose or special-purpose processor. Also, any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of computer-readable medium. Disk and disc, as used herein, include CD, laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above are also included within the scope of computer-readable media. [0283] As used herein, including in the claims, “or” as used in a list of items (e.g., a list of items prefaced by a phrase such as “at least one of’ or “one or more of’) indicates an inclusive list such that, for example, a list of at least one of A, B, or C means A or B or C or AB or AC or BC or ABC (i.e., A and B and C). Also, as used herein, the phrase “based on” shall not be construed as a reference to a closed set of conditions. For example, an example step that is described as “based on condition A” may be based on both a condition A and a condition B without departing from the scope of the present disclosure. In other words, as used herein, the phrase “based on” shall be construed in the same manner as the phrase “based at least in part on.”

[0284] In the appended figures, similar components or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label by a dash and a second label that distinguishes among the similar components. If just the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label, or other subsequent reference label.

[0285] The description set forth herein, in connection with the appended drawings, describes example configurations and does not represent all the examples that may be implemented or that are within the scope of the claims. The term “example” used herein means “serving as an example, instance, or illustration,” and not “preferred” or “advantageous over other examples.” The detailed description includes specific details for the purpose of providing an understanding of the described techniques. These techniques, however, may be practiced without these specific details. In some instances, known structures and devices are shown in block diagram form in order to avoid obscuring the concepts of the described examples.

[0286] The description herein is provided to enable a person having ordinary skill in the art to make or use the disclosure. Various modifications to the disclosure will be apparent to a person having ordinary skill in the art, and the generic principles defined herein may be applied to other variations without departing from the scope of the disclosure. Thus, the disclosure is not limited to the examples and designs described herein but is to be accorded the broadest scope consistent with the principles and novel features disclosed herein.