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Title:
CROSS-CARRIER HYBRID AUTOMATIC REPEAT REQUEST
Document Type and Number:
WIPO Patent Application WO/2019/240937
Kind Code:
A1
Abstract:
This document describes using cross-carrier Hybrid Automatic Repeat Request (HARQ) transmission in a Fifth Generation New Radio (5G NR) radio system that can perform retransmissions of data from a base station (121) to a user equipment (110) on a second carrier different than a first carrier used for a previous transmission for a same HARQ process. The techniques described are useful in providing deterministic operation and low-latency operation using unlicensed radio spectrum where regulations require Clear Channel (CCA), also known as listen-before-talk (LBT), operations to promote coexistence between users of the unlicensed spectrum. With cross-carrier HARQ transmission techniques, retransmissions of downlink data can be switched among different carriers to provide determinism and low-latency.

Inventors:
MENG LING-SAN (US)
Application Number:
PCT/US2019/034166
Publication Date:
December 19, 2019
Filing Date:
May 28, 2019
Export Citation:
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Assignee:
GOOGLE LLC (US)
International Classes:
H04L1/18; H04L5/00
Foreign References:
EP3086499A12016-10-26
Other References:
ZTE: "Control signalling and HARQ related issues for Licensed-assisted access using LTE", vol. RAN WG1, no. Fukuoka, Japan; 20150525 - 20150529, 24 May 2015 (2015-05-24), XP050972502, Retrieved from the Internet [retrieved on 20150524]
Attorney, Agent or Firm:
JOHNSON, Matthew (US)
Download PDF:
Claims:
CLAIMS

What is claimed is:

1. A method for communicating downlink data by a base station to a user equipment, the method comprising:

generating a first downlink control information including a first carrier identifier for a first carrier;

transmitting the first downlink control information in a first search space to the user equipment on the first carrier in a first slot, the first search space being determined by at least the first carrier identifier;

transmitting a first data associated with the first downlink control information to the user equipment and on the first carrier;

receiving a Hybrid Automatic Repeat Request Acknowledgement/Negative Acknowledgement feedback message corresponding to the first data;

generating a second downlink control information including the first carrier identifier;

transmitting the second downlink control information in a second search space to the user equipment on a second carrier in a second slot, the second search space being determined by at least a second carrier identifier for the second carrier; and

transmitting a second data associated with the second downlink control information to the user equipment on the second carrier, the second data being a Hybrid Automatic Repeat Request retransmission of the first data.

2. The method of claim 1, wherein the first downlink control information includes a first cross-Hybrid Automatic Repeat Request indicator field indicating that the first data is not a cross-Hybrid Automatic Repeat Request transmission, and wherein the second downlink control information includes a second cross-Hybrid Automatic Repeat Request indicator field indicating that the second data is a cross-Hybrid Automatic Repeat Request transmission that is continued on the second carrier.

3. The method of claim 1 or claim 2, wherein the second downlink control information including the first carrier identifier is generated in response to a Hybrid Automatic Repeat Request Acknowledgement/Negative Acknowledgement feedback message indicating that the transmission of the first data on the first carrier has failed.

4. The method of claim 3, wherein the second data is a different redundancy version of the first data.

5. The method of any one of the preceding claims, further comprising:

transmitting a message configuring cross-carrier scheduling to the user equipment.

6. The method of any of the preceding claims, further comprising:

transmitting a second message configuring a third carrier to be cross-scheduled by the first carrier;

generating a third downlink control information including a third carrier identifier for the third carrier, and a third cross-Hybrid Automatic Repeat Request indicator field indicating a third data associated with the third downlink control information is not a cross-Hybrid Automatic Repeat Request transmission;

transmitting the third downlink control information in a third search space to the user equipment on the first carrier, the third search space being determined by at least the third carrier identifier; and

transmitting the third data to the user equipment on the third carrier.

7. The method of any of the preceding claims, further comprising:

generating a fourth downlink control information and a fourth data associated with the fourth downlink control information, the fourth data being a retransmission of the first data; and

transmitting the fourth downlink control information to the user equipment on a fourth carrier in the second slot.

8. The method of claim 7, wherein the fourth downlink control information includes a third Hybrid Automatic Repeat Request process identifier having same value as a first Hybrid Automatic Repeat Request process identifier.

9. The method of claim 7 or 8, wherein the second downlink control information includes a first counter downlink assignment index, and wherein the fourth downlink control information includes a second counter downlink assignment index having same value as in the first counter downlink assignment index.

10. The method of any one of claims 7 to 9, wherein the fourth data is a different redundancy version of the first data.

11. A method for a user equipment to communicate with a base station, the method comprising:

receiving a first downlink control information in a first search space from the base station on a first carrier in a first slot, the first downlink control information including a first carrier identifier for the first carrier, the first search space being determined by at least the first carrier identifier;

receiving a first data on the first carrier using the first downlink control information;

generating a first decoding result by using the first data;

based on the generating the first decoding result, transmitting a Hybrid Automatic Repeat Request Acknowledgement/Negative Acknowledgement feedback message to the base station;

receiving a second downlink control information in a second search space on a second carrier in a second slot, the second downlink control information including the first carrier identifier, the second search space being determined by at least a second carrier identifier for the second carrier;

receiving a second data on the second carrier using the second downlink control information, the second data being a retransmission of the first data;

generating a second decoding result by using at least the first data and the second data; and

based on the generating the second decoding result, transmitting a second Hybrid Automatic Repeat Request Acknowledgement/Negative Acknowledgement feedback message to the base station.

12. The method of claim 11, wherein the first downlink control information includes a first cross-Hybrid Automatic Repeat Request indicator field indicating that the first data is not a cross-Hybrid Automatic Repeat Request transmission, and wherein the second downlink control information includes a second cross-Hybrid Automatic Repeat Request indicator field indicating that the second data is a cross-Hybrid Automatic Repeat Request transmission that is continued on the second carrier.

13. The method of claims 11 or 12, further comprising:

receiving a message configuring cross-carrier scheduling.

14. The method of any of claims 11 to 13, further comprising:

receiving a second message configuring a third carrier to be cross-scheduled by the first carrier;

receiving a third downlink control information in a third search space on the first carrier, the third downlink control information including a third carrier identifier for the third carrier, a third cross-Hybrid Automatic Repeat Request indicator field indicating a third data associated with the third downlink control information is not a cross-Hybrid Automatic Repeat Request transmission, and the third search space being determined by at least the third carrier identifier; and

receiving the third data on the third carrier using the third downlink control information.

15. The method of any of claims 11 to 14, further comprising:

receiving a fourth downlink control information on a fourth carrier in the second slot;

receiving a fourth data using the fourth downlink control information, the fourth data being a retransmission of the first data; and

generating the second decoding result by using the fourth data in addition to the first data and the second data.

16. The method of claim 15, wherein the fourth data is a different redundancy version of the first data.

17. The method of claim 15 or 16, wherein the second downlink control information includes a first counter downlink assignment index, and wherein the fourth downlink control information includes a second counter downlink assignment index having the same value as the first counter downlink assignment index.

18. A base station comprising:

a processor; and

a memory comprising instructions executable by the processor to configure the base station to:

generate a first downlink control information including a first carrier identifier for a first carrier;

transmit the first downlink control information in a first search space to a user equipment on the first carrier in a first slot, the first search space being determined by at least the first carrier identifier;

transmit a first data associated with the first downlink control information to the user equipment and on the first carrier;

receive a Hybrid Automatic Repeat Request Acknowledgement/Negative Acknowledgement feedback message corresponding to the first data;

generate a second downlink control information including the first carrier identifier;

transmit the second downlink control information in a second search space to the user equipment on a second carrier in a second slot, the second search space being determined by at least a second carrier identifier for the second carrier; and

transmit a second data associated with the second downlink control information to the user equipment on the second carrier, the second data being a Hybrid Automatic Repeat Request retransmission of the first data.

19. A user equipment comprising:

a processor; and

a memory comprising instructions executable by the processor to configure the user equipment to:

receive a first downlink control information in a first search space from a base station on a first carrier in a first slot, the first downlink control information including a first carrier identifier for the first carrier, the first search space being determined by at least the first carrier identifier;

receive a first data on the first carrier using the first downlink control information;

generate a first decoding result by using the first data;

based on the generation of the first decoding result, transmit a Hybrid Automatic Repeat Request Acknowledgement/Negative Acknowledgement feedback message to the base station;

receive a second downlink control information in a second search space on a second carrier in a second slot, the second downlink control information including the first carrier identifier, the second search space being determined by at least a second carrier identifier for the second carrier;

receive a second data on the second carrier using the second downlink control information, the second data being a retransmission of the first data; generate a second decoding result by using at least the first data and the second data; and

based on the generation of the second decoding result, transmit a second Hybrid Automatic Repeat Request Acknowledgement/Negative Acknowledgement feedback message to the base station.

Description:
CROSS-CARRIER HYBRID AUTOMATIC REPEAT REQUEST

BACKGROUND

[0001] A unified air interface, which utilizes licensed, unlicensed, and shared license radio spectrum, in multiple frequency bands, is one aspect of enabling the capabilities of fifth generation new radio (5G NR) communication systems. Some 5GNR systems that operate in unlicensed radio spectrum share the unlicensed radio spectrum with other radio systems and operate under regulations that require access techniques to fairly share the radio spectrum between different users.

[0002] Unlike resources in licensed radio spectrum that can be scheduled to support deterministic operation for communications that require low or guaranteed latency, operations under spectrum-sharing regulations for unlicensed radio spectrum can create uncertainty about when particular resources will be available or become unavailable. A communication device may not be able to transmit on a desired carrier in a timely fashion if that carrier is in use by another wireless transmitting device.

[0003] In fourth generation (4G) Long Term Evolution (LTE) systems, there is at least one licensed carrier available so that downlink communications requiring low latency can be transmitted on licensed carriers for deterministic operation. Some 5G NR systems are targeted to operate exclusively using unlicensed radio spectrum, generally in a standalone mode that lacks licensed channels. Therefore, these 5G NR systems lack the ability to provide radio resources to support deterministic behavior for communications that require low or guaranteed latency. SUMMARY

[0004] This summary is provided to introduce simplified concepts of cross- carrier hybrid automatic repeat request. The simplified concepts are further described below in the Detailed Description. This summary is not intended to identify essential features of the claimed subj ect matter, nor is it intended for use in determining the scope of the claimed subject matter.

[0005] In some aspects, methods, devices, systems, and means for communicating downlink data by a base station to a user equipment are described in which the base station generates a first downlink control information (DCI) including a first carrier identifier (ID) for a first carrier. The base station transmits the first DCI in a first search space to the user equipment on the first carrier in a first slot, the first search space being determined by at least the first carrier ID, and transmits a first data associated with the first DCI to the user equipment and on the first carrier. The base station receives a Hybrid Automatic Repeat Request feedback message, ( e.g ., a Hybrid Automatic Repeat Request Acknowledgement/Negative Acknowledgement (HARQ- ACK/NACK) feedback message), corresponding to the first data, generates a second DCI including the first carrier ID, transmits the second DCI in a second search space to the user equipment on a second carrier in a second slot, the second search space being determined by at least a second carrier ID for the second carrier, and transmits a second data associated with the second DCI to the user equipment on the second carrier, the second data being a Hybrid Automatic Repeat Request (HARQ) retransmission of the first data.

[0006] In other aspects, methods, devices, systems, and means for communicating by a user equipment to a base station are described in which the user equipment receives a first downlink control information (DCI) in a first search space from the base station on a first carrier in a first slot, the first DCI including a first carrier identifier (ID) for the first carrier and the first search space being determined by at least the first carrier ID. The user equipment receives a first data on the first carrier using the first DCI. The user equipment generates a first decoding result by using the first data and, based on the generation of the first decoding result, transmits a Hybrid Automatic Repeat Request feedback message, ( e.g ., a Hybrid Automatic Repeat Request Acknowledgement/Negative Acknowledgement (HARQ-ACK/NACK) feedback message) to the base station. Further, the user equipment receives a second DCI in a second search space on a second carrier in a second slot, the second DCI including the first carrier ID, the second search space being determined by at least a second carrier ID for the second carrier. The user equipment receives a second data on the second carrier using the second DCI, the second data being a retransmission of the first data. The user equipment generates a second decoding result by using at least the first data and the second data and, based on the generation of the second decoding result, transmits a second HARQ-ACK/NACK feedback message to the base station.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Aspects of techniques for, and apparatuses configured to enable, cross- carrier hybrid automatic repeat requests are described with reference to the following drawings. The same numbers are used throughout the drawings to reference like features and components:

FIG. 1 illustrates an example wireless network system in which various aspects of cross-carrier hybrid automatic repeat request can be implemented.

FIG. 2 illustrates an example device diagram of devices that can implement various aspects of cross-carrier hybrid automatic repeat request. FIG. 3 illustrates an example method of cross-carrier hybrid automatic repeat request as generally related to a base station in accordance with aspects of the techniques described herein.

FIG. 4 illustrates an example method of cross-carrier hybrid automatic repeat request as generally related to a user equipment in accordance with aspects of the techniques described herein.

DETAILED DESCRIPTION

[0008] This document describes using cross-carrier Hybrid Automatic Repeat Request (HARQ) transmission in a Fifth Generation New Radio (5G R) radio system that can perform retransmissions of data from a base station to a user equipment on a second carrier different from a first carrier used for a previous transmission for a same HARQ process. The techniques described are useful in providing deterministic operation and low-latency operation using unlicensed radio spectrum where regulations require Clear Channel (CCA), also known as listen-before-talk (LBT), operations to promote coexistence between users of the unlicensed spectrum. With cross-carrier HARQ transmission techniques, retransmissions of downlink data can be switched among different carriers to provide determinism and low-latency.

[0009] The rapid uptake of 4G LTE in different regions of the world shows both that demand for wireless broadband data is increasing and that 4G LTE is an extremely successful platform to meet that demand. For International Mobile Telecommunications (IMT) systems, existing and new spectrum licensed for exclusive use by IMT technologies will remain important for providing seamless coverage, achieving high spectral efficiency, and ensuring high reliability of cellular networks through careful planning and deployment of network equipment and devices. All of these qualities cannot be achieved with unlicensed spectrum that can be accessed by a variety of wireless devices.

[0010] However, the use of unlicensed spectrum is increasingly being considered by cellular operators to augment their service offerings and solutions provided on licensed spectrum. Efficient use of unlicensed spectrum as a complement to licensed spectrum is potentially valuable to service providers and the wireless industry as a whole. Given the widespread deployment and usage of other technologies in unlicensed spectrum for wireless communications, it is necessary for 4G LTE and 5GNR to coexist with incumbent systems in this shared, unlicensed spectrum.

[0011] One approach to coexistence is determining if a radio channel is in use by another device before beginning a transmission. Clear channel assessment (CCA) is a technique used by wireless devices to assess the channel status using energy detection before attempting to perform a transmission. A wireless device measures the energy in a wireless channel to determine if the detected energy is above a threshold which indicates that another device is transmitting on the channel. When the CCA detects energy above the threshold, the wireless device postpones transmitting on the channel or moves to another channel to transmit.

[0012] Hybrid Automatic Repeat Request (HARQ) is a physical layer transmission technique in modern communication systems where retransmissions are requested by the receiver in the case of a decoding failure. The retransmissions are combined with failed previous transmissions to enable a user equipment to determine whether there is still useful information embedded in the previous failed transmissions. Error control coding is commonly applied to implement HARQ. In LTE systems, tail- biting convolutional coding (TBCC) and turbo coding with incremental redundancy (IR) are used. In 5G NR systems, low density parity checking (LDPC) coding is used. To appropriately operate using HARQ, a receiver has to be aware of the existence of a transmission in advance, even if the transmission itself fails to be correctly decoded, so that the failed transmission can be retained and combined with later retransmissions. In 4G LTE and 5G NR systems, the base station issues explicit downlink control information (DCI) to a user device (e.g., user equipment or UE) along with the associated downlink data. After receiving the DCI, the user equipment can then configure itself to receive the downlink data and buffers the downlink data if the decoding fails. The user equipment transmits a HARQ ACK/NACK (Acknowledgement/Negative Acknowledgement) feedback message to the base station based on the decoding result for the downlink data. In the case of receiving a NACK, the base station retransmits a different redundancy version (RV) of the downlink data to the user equipment. Multiple stop-and-wait (SW) HARQ processes can occur in a pipeline, so that one HARQ process can begin before obtaining the HARQ ACK/NACK associated with a previous HARQ process. Each HARQ process is given a unique identification number (ID), which is carried in the DCI.

[0013] Carrier aggregation (CA) was first introduced in LTE- Advanced (3 GPP Release 10) in order to increase bandwidth, thereby increasing the bit rate for data transmission. Each carrier in a carrier aggregation is referred to as a component carrier (CC). In 5G NR, a maximum of 16 component carriers can be aggregated. Carrier aggregation with at least one secondary cell (SCell) operating in unlicensed spectrum is referred to as Li censed- Assisted Access (LAA) in LTE/LTE-A systems. In 5G NR, operations in unlicensed spectrum are termed NR-U. Conventionally, downlink data transmission on a particular carrier can only be scheduled on the same carrier. In other words, the base station can only transmit a DCI and associated downlink data on the same carrier. Cross-carrier scheduling (CCS) removes the limitation of scheduling on a single carrier. In cross-carrier scheduling, each carrier is given a unique ID which is carried in the DCI to indicate which carrier is associated with the downlink DCI. [0014] The user equipment receives DCIs using blind decoding. A certain set of time-frequency resources, which the base station can potentially use to transmit a DCI to the user equipment, is known in advance to both the user equipment and the base station. Such a set of time-frequency resources is called a search space. The user equipment blindly performs detection of a DCI over all valid positions in the search space to receive DCIs sent from the base station. Using cross-carrier scheduling, a carrier can have more than one search space, with each search space determined by the ID of the scheduled carrier.

[0015] Due to the uncertainty created by listen-before-talk (LBT) operations in NR-U systems, a transmitter might not be able to perform retransmissions on the same carrier in a timely fashion, since that the carrier could become occupied by another wireless transmitting device between the time of the original transmission and the time of the retransmission. This results in a lack of determinism for devices and applications having stringent latency requirements in NR-U systems. In 4G LTE, there is at least one licensed carrier available so that downlink data requiring low latency can be transmitted on a licensed carrier, if needed. However, an NR-U base station can operate solely with unlicensed carriers and requires a solution to support deterministic and low- latency operations in unlicensed radio bands.

[0016] In aspects, by using cross-carrier HARQ transmission, a NR-U base station can perform retransmissions on a second carrier different than a first carrier used for a previous transmission of the same HARQ process. To coexist with the mechanism of cross-carrier scheduling, a cross-HARQ indicator field is included in the DCI. If the cross-HARQ indicator field is set to OFF, the existing carrier indicator field (CIF) (e.g, carrier identifier) functions as before, i.e., a CIF pointing to another carrier indicates that there is downlink data (e.g, first data) scheduled for the user equipment on that carrier. [0017] If the cross-HARQ indicator field is set to ON, the CIF indicates which carrier is targeted for the downlink data. For example, a DCI transmitted on a first carrier including a CIF pointing to a second carrier means the associated downlink data is to be transmitted on the first carrier, but the continuation of the HARQ process for the downlink data occurs on the second carrier. In other words, the transmission of the downlink data is conceptually moved from the first carrier to the second carrier. This solves the problem when the first carrier is temporarily unavailable for retransmission due to an LBT failure.

[0018] In another aspect, the base station can send different redundancy versions of the same downlink data on different carriers in the same slot. This can be accomplished by transmitting multiple DCIs on separate component carriers with the DCIs all having the same CIF and the cross-HARQ indicator being set to ON. The user equipment would then be able to determine that all the DCIs and their associated copies of the downlink data originate from a same data, and the copies of downlink data are simply different redundancy versions. In case there are multiple HARQ processes, a HARQ process ID is also carried in the DCI to further distinguish among different HARQ processes. For example, the base station can configure a third carrier to be cross-scheduled by the first carrier to transmit additional data. The base station transmits a second message configuring the third carrier and generates a third DCI including a third carrier identifier for the third carrier, and a third cross-Hybrid Automatic Repeat Request indicator field indicating a third data (additional data) associated with the third DCI is not a cross-Hybrid Automatic Repeat Request transmission. In a further example, to transmit a different redundancy version of the first data, the base station can configure a fourth carrier to transmit the a second (different) redundancy version of the first data. The base station generates a fourth DCI and a fourth data associated with the fourth DCI, the fourth data being a retransmission of the first data. The base station transmits the fourth downlink control information to the user equipment on a fourth carrier in the second slot. The fourth DCI includes a third HARQ process identifier having same value as the first Hybrid Automatic Repeat Request process identifier. The fourth DCI includes a second counter downlink assignment index having same value as in the first counter downlink assignment index indicating that the fourth data is a second redundancy version of the first data.

Example Environment

[0019] FIG. 1 illustrates an example environment 100 which includes a user equipment 110 (UE 110) that can communicate with base stations 120 (illustrated as base stations 121 and 122) through wireless communication links 130 (wireless link 130), illustrated as wireless links 131 and 132. For simplicity, the UE 110 is implemented as a smartphone but may be implemented as any suitable computing or electronic device, such as a mobile communication device, modem, cellular phone, gaming device, navigation device, media device, laptop computer, desktop computer, tablet computer, smart appliance, vehicle-based communication system, or an Internet- of-Things (IoT) device such as a sensor or an actuator. The base stations 120 (e.g, an Evolved Universal Terrestrial Radio Access Network Node B, E-UTRAN Node B, evolved Node B, eNodeB, eNB, Next Generation Node B, gNode B, gNB, or the like) may be implemented in a macrocell, microcell, small cell, picocell, and the like, or any combination thereof.

[0020] The base stations 120 communicate with the user equipment 110 using the wireless links 131 and 132, which may be implemented as any suitable type of wireless link. The wireless links 131 and 132 include control and data communication, such as downlink of data and control information communicated from the base stations

120 to the user equipment 110, uplink of other data and control information communicated from the user equipment 110 to the base stations 120, or both. The wireless links 130 may include one or more wireless links ( e.g ., radio links) or bearers implemented using any suitable communication protocol or standard, or combination of communication protocols or standards, such as 3rd Generation Partnership Project Long-Term Evolution (3GPP LTE), Fifth Generation New Radio (5G NR), and so forth. Multiple wireless links 130 may be aggregated in a carrier aggregation to provide a higher data rate for the LIE 110. Multiple wireless links 130 from multiple base stations 120 may be configured for Coordinated Multipoint (CoMP) communication with the UE 110.

[0021] The base stations 120 are collectively a Radio Access Network 140 (e.g., RAN, Evolved Universal Terrestrial Radio Access Network, E-UTRAN, 5G NR RAN or NR RAN). The base stations 121 and 122 in the RAN 140 are connected to a core network 150. The base stations 121 and 122 connect, at 102 and 104 respectively, to the core network 150 through an NG2 interface for control -plane signaling and using an NG3 interface for user-plane data communications when connecting to a 5G core network, or using an Sl interface for control-plane signaling and user-plane data communications when connecting to an Evolved Packet Core (EPC) network. The base stations 121 and 122 can communicate using an Xn Application Protocol (XnAP) through an Xn interface, or using an X2 Application Protocol (X2AP) through an X2 interface, at 106, to exchange user-plane and control -plane data. The user equipment 110 may connect, via the core network 150, to public networks, such as the Internet 160 to interact with a remote service 170.

Example Devices

[0022] FIG. 2 illustrates an example device diagram 200 of the user equipment 110 and the base stations 120. The user equipment 110 and the base stations 120 may include additional functions and interfaces that are omitted from FIG. 2 for the sake of clarity. The user equipment 110 includes antennas 202, a radio frequency front end 204 (RF front end 204), an LTE transceiver 206, and a 5GNR transceiver 208 for communicating with base stations 120 in the RAN 140. The RF front end 204 of the user equipment 110 can couple or connect the LTE transceiver 206, and the 5G R transceiver 208 to the antennas 202 to facilitate various types of wireless communication. The antennas 202 of the user equipment 110 may include an array of multiple antennas that are configured similar to or differently from each other. The antennas 202 and the RF front end 204 can be tuned to, and/or be tunable to, one or more frequency bands defined by the 3GPP LTE and 5G NR communication standards and implemented by the LTE transceiver 206, and/or the 5GNR transceiver 208. Additionally, the antennas 202, the RF front end 204, the LTE transceiver 206, and/or the 5GNR transceiver 208 may be configured to support beamforming for the transmission and reception of communications with the base stations 120. By way of example and not limitation, the antennas 202 and the RF front end 204 can be implemented for operation in sub-gigahertz bands, sub-6 GHZ bands, and/or above 6 GHz bands that are defined by the 3GPP LTE and 5G NR communication standards.

[0023] The user equipment 110 also includes processor(s) 210 and computer- readable storage media 212 (CRM 212). The processor 210 may be a single core processor or a multiple core processor composed of a variety of materials, such as silicon, polysilicon, high-K dielectric, copper, and so on. The computer-readable storage media described herein excludes propagating signals. CRM 212 may include any suitable memory or storage device such as random-access memory (RAM), static RAM (SRAM), dynamic RAM (DRAM), non-volatile RAM (NVRAM), read-only memory (ROM), or Flash memory useable to store device data 214 of the user equipment 110. The device data 214 includes user data, multimedia data, beamforming codebooks, applications, and/or an operating system of the user equipment 110, which are executable by processor(s) 210 to enable user-plane communication, control-plane signaling, and user interaction with the user equipment 110.

[0024] In some implementations, the CRM 212 may also include a data decoder 216. Alternately or additionally, the data decoder 216 may be implemented in whole or part as hardware logic or circuitry integrated with or separate from other components of the user equipment 110. The data decoder 216 can communicate with the antennas 202, the RF front end 204, the LTE transceiver 206, and/or the 5G NR. transceiver 208 to implement techniques for cross-carrier hybrid automatic repeat request described herein.

[0025] The device diagram for the base stations 120, shown in FIG. 2, includes a single network node ( e.g . , a gNode B). The functionality of the base stations 120 may be distributed across multiple network nodes or devices and may be distributed in any fashion suitable to perform the functions described herein. The base stations 120 include antennas 252, a radio frequency front end 254 (RF front end 254), one or more LTE transceivers 256, and/or one or more 5G NR. transceivers 258 for communicating with the TIE 110. The RF front end 254 of the base stations 120 can couple or connect the LTE transceivers 256 and the 5G NR. transceivers 258 to the antennas 252 to facilitate various types of wireless communication. The antennas 252 of the base stations 120 may include an array of multiple antennas that are configured similar to or differently from each other. The antennas 252 and the RF front end 254 can be tuned to, and/or be tunable to, one or more frequency band defined by the 3GPP LTE and 5G NR. communication standards, and implemented by the LTE transceivers 256, and/or the 5G NR. transceivers 258. Additionally, the antennas 252, the RF front end 254, the LTE transceivers 256, and/or the 5G NR. transceivers 258 may be configured to support beamforming, such as Massive-MIMO, for the transmission and reception of communications with the UE 110.

[0026] The base stations 120 also include processor(s) 260 and computer- readable storage media 262 (CRM 262). The processor 260 may be a single core processor or a multiple core processor composed of a variety of materials, such as silicon, polysilicon, high-K dielectric, copper, and so on. CRM 262 may include any suitable memory or storage device such as random-access memory (RAM), static RAM (SRAM), dynamic RAM (DRAM), non-volatile RAM (NVRAM), read-only memory (ROM), or Flash memory useable to store device data 264 of the base stations 120. The device data 264 includes network scheduling data, radio resource management data, beamforming codebooks, applications, and/or an operating system of the base stations 120, which are executable by processor(s) 260 to enable communication with the user equipment 110.

[0027] CRM 262 also includes a data encoder 266. Alternately or additionally, the data encoder 266 may be implemented in whole or part as hardware logic or circuitry integrated with or separate from other components of the base stations 120. In at least some aspects, the data encoder 266 configures the LTE transceivers 256 and the 5G R transceivers 258 for communication with the user equipment 110, as well as communication with a core network, such as the core network 150.

[0028] The base stations 120 include an inter-base station interface 268, such as an Xn and/or X2 interface, which the data encoder 266 configures to exchange user- plane and control -plane data between other base stations 120, to manage the communication of the base stations 120 with the user equipment 110. The base stations 120 include a core network interface 270 that the data encoder 266 configures to exchange user-plane and control-plane data with core network functions and/or entities. Example Methods

[0029] Example methods 300 and 400 are described with reference to FIGs. 3 and 4 in accordance with one or more aspects of cross-carrier hybrid automatic repeat request. The order in which the method blocks are described are not intended to be construed as a limitation, and any number of the described method blocks can be skipped or combined in any order to implement a method or an alternate method. Generally, any of the components, modules, methods, and operations described herein can be implemented using software, firmware, hardware ( e.g ., fixed logic circuitry), manual processing, or any combination thereof. Some operations of the example methods may be described in the general context of executable instructions stored on computer-readable storage memory that is local and/or remote to a computer processing system, and implementations can include software applications, programs, functions, and the like. Alternatively or in addition, any of the functionality described herein can be performed, at least in part, by one or more hardware logic components, such as, and without limitation, Field-programmable Gate Arrays (FPGAs), Application-specific Integrated Circuits (ASICs), Application-specific Standard Products (ASSPs), System- on-a-chip systems (SoCs), Complex Programmable Logic Devices (CPLDs), and the like.

[0030] FIG. 3 illustrates example method(s) 300 of cross-carrier hybrid automatic repeat request as generally related to communications by the base station 121. At block 302, a base station performs a clear channel assessment procedure. For example, the base station 121 performs a clear channel assessment by detecting an amount of energy on a radio channel to determine if the detected energy is above a threshold which indicates that another device is transmitting on the channel.

[0031] At block 304, the base station generates a first downlink control information (DCI) including a first carrier identifier (ID) for a first carrier. For example, the base station 121 generates a first downlink control information (DCI) including a first carrier identifier (ID) for a first carrier. The DCI includes a cross- HARQ indicator field to enable the HARQ transmission and/or retransmission to move to another carrier on another channel if the channel of the first carrier becomes unavailable to the base station.

[0032] At block 306, the base station transmits the first DCI in a first search space to the user equipment on the first carrier in a first slot, the first search space being determined by at least the first carrier ID. For example, the base station 121 transmits the first DCI in a first search space to the user equipment 110 on the first carrier in a first slot, the first search space being determined by at least the first carrier ID.

[0033] At block 308, the base station transmits a first data associated with the first DCI to the user equipment and on the first carrier. For example, the base station 121 transmits a first data associated with the first DCI to the user equipment 110 and on the first carrier.

[0034] At block 310, the base station receives a Hybrid Automatic Repeat Request Acknowledgement/Negative Acknowledgement (HARQ-ACK/NACK) feedback message corresponding to the first data. For example, the base station 121 receives a Hybrid Automatic Repeat Request Acknowledgement/Negative Acknowledgement (HARQ-ACK/NACK) feedback message corresponding to the first data from the user equipment 110.

[0035] At block 312, the base station generates a second DCI including the first carrier ID. For example, the base station 121 generates a second DCI including the first carrier ID that indicates that a continuation of the HARQ process for the first data occurs on the second carrier.

[0036] At block 314, the base station transmits the second DCI in a second search space to the user equipment on a second carrier in a second slot, the second search space being determined by at least a second carrier ID for the second carrier. For example, the base station 121 transmits the second DCI in a second search space to the user equipment 110 on a second carrier in a second slot, the second search space being determined by at least a second carrier ID for the second carrier.

[0037] At block 316, the base station transmits a second data associated with the second DCI to the user equipment on the second carrier, the second data being a Hybrid Automatic Repeat Request (HARQ) retransmission of the first data. For example, the base station 121 transmits a second data associated with the second DCI to the user equipment 110 on the second carrier, the second data being a Hybrid Automatic Repeat Request (HARQ) retransmission of the first data.

[0038] FIG. 4 illustrates example method(s) 400 of cross-carrier hybrid automatic repeat request as generally related to the user equipment 110. At block 402, a user equipment performs a clear channel assessment procedure. For example, the user equipment 110 performs a clear channel assessment by detecting an amount of energy on a radio channel.

[0039] At block 404, the user equipment receives a first downlink control information (DCI) in a first search space from the base station on a first carrier in a first slot, the first DCI including a first carrier identifier (ID) for the first carrier, the first search space being determined by at least the first carrier ID. For example, the user equipment 110 receives a first downlink control information (DCI) in a first search space from the base station 121 on a first carrier in a first slot, the first DCI including a first carrier identifier (ID) for the first carrier, the first search space being determined by at least the first carrier ID. After receiving the first DCI, the user equipment then configures itself to receive the first data and buffers the first data if the decoding of the first data fails. [0040] At block 406, the user equipment receives a first data on the first carrier using the first DCI. For example, the user equipment 110 receives a first data on the first carrier using the first DCI from the base station 121.

[0041] At block 408, the user equipment generates a first decoding result by using the first data. For example, the data decoder 216 of the user equipment 110 generates a first decoding result by using the first data.

[0042] At block 410, based on the first decoding result, the user equipment transmits a Hybrid Automatic Repeat Request Acknowledgement/Negative Acknowledgement (HARQ-ACK/NACK) feedback message to the base station. For example, based on the first decoding result, the user equipment 110 transmits a Hybrid Automatic Repeat Request Acknowledgement/Negative Acknowledgement (HARQ- ACK/NACK) feedback message to the base station 121 indicating that the first data was successfully decoded or that the decoding failed.

[0043] At block 412, the user equipment receives a second DCI in a second search space on a second carrier in a second slot, the second DCI including the first carrier ID, the second search space being determined by at least a second carrier ID for the second carrier. For example, the user equipment 110 receives, from the base station 121, a second DCI in a second search space on a second carrier in a second slot, the second DCI including the first carrier ID, the second search space being determined by at least a second carrier ID for the second carrier.

[0044] At block 414, the user equipment receives a second data on the second carrier using the second DCI, the second data being a retransmission of the first data. For example, the user equipment 110 receives, from the base station 121, a second data on the second carrier using the second DCI, the second data being a retransmission of the first data. [0045] At block 416, the user equipment generates a second decoding result by using at least the first data and the second data. For example, the data decoder 216 of the user equipment 110 generates a second decoding result by using at least the first data, buffered by the user equipment, and the second data.

[0046] At block 418, based on the second decoding result, the user equipment transmits a second HARQ-ACK/NACK feedback message to the base station. For example, based on the second decoding result, the user equipment 110 transmits a second HARQ-ACK/NACK feedback message to the base station 121 indicating that the first data and second data was successfully decoded or that the decoding failed.

[0047] In the following some examples are described- Example 1 : A method for communicating downlink data by a base station to a user equipment, the method comprising:

generating a first downlink control information including a first carrier identifier for a first carrier;

transmitting the first downlink control information in a first search space to the user equipment on the first carrier in a first slot, the first search space being determined by at least the first carrier identifier;

transmitting a first data associated with the first downlink control information to the user equipment and on the first carrier;

receiving a Hybrid Automatic Repeat Request Acknowledgement/Negative Acknowledgement feedback message corresponding to the first data;

generating a second downlink control information including the first carrier identifier;

transmitting the second downlink control information in a second search space to the user equipment on a second carrier in a second slot, the second search space being determined by at least a second carrier identifier for the second carrier; and

transmitting a second data associated with the second downlink control information to the user equipment on the second carrier, the second data being a Hybrid Automatic Repeat Request retransmission of the first data.

Example 2: The method of example 1, wherein the first downlink control information includes a first cross-Hybrid Automatic Repeat Request indicator field indicating that the first data is not a cross-Hybrid Automatic Repeat Request transmission, and wherein the second downlink control information includes a second cross-Hybrid Automatic Repeat Request indicator field indicating that the second data is a cross-Hybrid Automatic Repeat Request transmission that is continued on the second carrier.

Example 3 : The method of example 1 or example 2, wherein the second downlink control information including the first carrier identifier is generated in response to a Hybrid Automatic Repeat Request Acknowledgement/Negative Acknowledgement feedback message indicating that the transmittal of the first data on the first carrier has failed.

Example 4: The method of example 3, wherein the second data is a different redundancy version of the first data.

Example 5: The method of any one of the preceding examples, further comprising: transmitting a message configuring cross-carrier scheduling to the user equipment.

Example 6: The method of any of the preceding examples, further comprising: transmitting a second message configuring a third carrier to be cross-scheduled by the first carrier;

generating a third downlink control information including a third carrier identifier for the third carrier, and a third cross-Hybrid Automatic Repeat Request indicator field indicating a third data associated with the third downlink control information is not a cross-Hybrid Automatic Repeat Request transmission; transmitting the third downlink control information in a third search space to the user equipment on the first carrier, the third search space being determined by at least the third carrier identifier; and

transmitting the third data to the user equipment on the third carrier.

Example 7: The method of any of the preceding examples, further comprising: generating a fourth downlink control information and a fourth data associated with the fourth downlink control information, the fourth data being a retransmission of the first data; and

transmitting the fourth downlink control information to the user equipment on a fourth carrier in the second slot.

Example 8: The method of example 7, wherein the fourth downlink control information includes a third Hybrid Automatic Repeat Request process identifier having same value as a first Hybrid Automatic Repeat Request process identifier.

Example 9: The method of example 7 or 8, wherein the second downlink control information includes a first counter downlink assignment index, and wherein the fourth downlink control information includes a second counter downlink assignment index having same value as in the first counter downlink assignment index.

Example 10: The method of any one of examples 7 to 9, wherein the fourth data is a different redundancy version of the first data.

Example 11 : The method of any of the preceding examples, wherein the first downlink control information includes a first Hybrid Automatic Repeat Request process identifier, and wherein the second downlink control information includes a second Hybrid Automatic Repeat Request process identifier having the same value as the first Hybrid Automatic Repeat Request process identifier.

Example 12: The method of any of the preceding examples, further comprising: transmitting, to the user equipment, a third message configuring cross-Hybrid Automatic Repeat Request transmission.

Example 13: The method of any of the preceding examples, wherein the second data is a different redundancy version of the first data.

Example 14: The method of any of the preceding examples, wherein the base station and the user equipment communicate in an unlicensed frequency band.

Example 15: The method of any of the preceding examples, wherein the base station and the user equipment communicate using a carrier aggregation.

Example 16: The method of any of the preceding examples, further comprising: performing, by the base station, a clear channel assessment procedure.

Example 17: A base station comprising:

a radio frequency transceiver;

a processor; and

a memory comprising instructions executable by the processor to perform any method of examples 1 to 16. Example 18: A method for a user equipment to communicate with a base station, the method comprising:

receiving a first downlink control information in a first search space from the base station on a first carrier in a first slot, the first downlink control information including a first carrier identifier for the first carrier, the first search space being determined by at least the first carrier identifier;

receiving a first data on the first carrier using the first downlink control information;

generating a first decoding result by using the first data;

based on the generating the first decoding result, transmitting a Hybrid Automatic Repeat Request Acknowledgement/Negative Acknowledgement feedback message to the base station;

receiving a second downlink control information in a second search space on a second carrier in a second slot, the second downlink control information including the first carrier identifier, the second search space being determined by at least a second carrier identifier for the second carrier;

receiving a second data on the second carrier using the second downlink control information, the second data being a retransmission of the first data;

generating a second decoding result by using at least the first data and the second data; and

based on the generating the second decoding result, transmitting a second Hybrid Automatic Repeat Request Acknowledgement/Negative Acknowledgement feedback message to the base station.

Example 19: The method of example 16, wherein the first downlink control information includes a first cross-Hybrid Automatic Repeat Request indicator field indicating that the first data is not a cross-Hybrid Automatic Repeat Request transmission, and wherein the second downlink control information includes a second cross-Hybrid Automatic Repeat Request indicator field indicating that the second data is a cross-Hybrid Automatic Repeat Request transmission that is continued on the second carrier.

Example 20: The method of example 18 or 19, further comprising:

receiving a message configuring cross-carrier scheduling.

Example 21 : The method of any one of examples 18 to 20, further comprising: receiving a second message configuring a third carrier to be cross scheduled by the first carrier;

receiving a third downlink control information in a third search space on the first carrier, the third downlink control information including a third carrier identifier for the third carrier, a third cross-Hybrid Automatic Repeat Request indicator field indicating a third data associated with the third downlink control information is not a cross-Hybrid Automatic Repeat Request transmission, and the third search space being determined by at least the third carrier identifier; and

receiving the third data on the third carrier using the third downlink control information.

Example 22: The method of any one of examples 18 to 21, further comprising: receiving a fourth downlink control information on a fourth carrier in the second slot;

receiving a fourth data using the fourth downlink control information, the fourth data being a retransmission of the first data; and

generating the second decoding result by using the fourth data in addition to the first data and the second data.

Example 23 : The method of example 22, wherein the fourth data is a different redundancy version of the first data.

Example 24: The method of example 22 or 23, wherein the second downlink control information includes a first counter downlink assignment index, and wherein the fourth downlink control information includes a second counter downlink assignment index having the same value as the first counter downlink assignment index.

Example 25 : The method of any one of examples 18 to 24, wherein the first downlink control information includes a first Hybrid Automatic Repeat Request process identifier, and wherein the second downlink control information includes a second Hybrid Automatic Repeat Request process identifier having same value as the first Hybrid Automatic Repeat Request process identifier.

Example 26: The method of example 25, wherein the fourth downlink control information includes a third Hybrid Automatic Repeat Request process identifier having same value as the first Hybrid Automatic Repeat Request process identifier. Example 27: The method of any one of examples 18 to 26, further comprising: receiving a third message configuring cross-Hybrid Automatic Repeat Request transmission.

Example 28: The method of any one of examples 18 to 27, wherein the second data is a different redundancy version of the first data.

Example 29: The method of any one of examples 18 to 28, wherein the base station and the user equipment communicate in an unlicensed frequency band.

Example 30: The method of any one of examples 18 to 29, wherein the base station and the user equipment communicate using a carrier aggregation.

Example 31 : The method of any one of examples 18 to 30, the method further comprising:

performing a clear channel assessment procedure.

Example 32: A user equipment comprising:

a radio frequency transceiver;

a processor; and

a memory comprising instructions executable by the processor to perform any method of examples 18 to 31. Example 33 : A base station comprising:

a processor; and

a memory comprising instructions executable by the processor to configure the base station to:

generate a first downlink control information including a first carrier identifier for a first carrier;

transmit the first downlink control information in a first search space to the user equipment on the first carrier in a first slot, the first search space being determined by at least the first carrier identifier;

transmit a first data associated with the first downlink control information to the user equipment and on the first carrier;

receive a Hybrid Automatic Repeat Request Acknowledgement/Negative Acknowledgement feedback message corresponding to the first data;

generate a second downlink control information including the first carrier identifier;

transmit the second downlink control information in a second search space to the user equipment on a second carrier in a second slot, the second search space being determined by at least a second carrier identifier for the second carrier; and

transmit a second data associated with the second downlink control information to the user equipment on the second carrier, the second data being a Hybrid Automatic Repeat Request retransmission of the first data. Example 34: A user equipment comprising:

a processor; and

a memory comprising instructions executable by the processor to configure the user equipment to:

receive a first downlink control information in a first search space from the base station on a first carrier in a first slot, the first downlink control information including a first carrier identifier for the first carrier, the first search space being determined by at least the first carrier identifier;

receive a first data on the first carrier using the first downlink control information;

generate a first decoding result by using the first data;

based on the generation of the first decoding result, transmit a Hybrid Automatic Repeat Request Acknowledgement/Negative Acknowledgement feedback message to the base station;

receive a second downlink control information in a second search space on a second carrier in a second slot, the second downlink control information including the first carrier identifier, the second search space being determined by at least a second carrier identifier for the second carrier;

receive a second data on the second carrier using the second downlink control information, the second data being a retransmission of the first data; generate a second decoding result by using at least the first data and the second data; and

based on the generation of the second decoding result, transmit a second Hybrid Automatic Repeat Request Acknowledgement/Negative Acknowledgement feedback message to the base station. [0048] Although aspects of cross-carrier hybrid automatic repeat request have been described in language specific to features and/or methods, the subject of the appended claims is not necessarily limited to the specific features or methods described. Rather, the specific features and methods are disclosed as example implementations of cross-carrier hybrid automatic repeat request, and other equivalent features and methods are intended to be within the scope of the appended claims. Further, various different aspects are described, and it is to be appreciated that each described aspect can be implemented independently or in connection with one or more other described aspects.