PRIORITY CLAIM

[0001] This application claims priority to and the benefit of non-provisional patent application no. 16/181,231 filed in the United States Patent and Trademark Office on November 5, 2018 and provisional patent application no. 62/584,024 filed in the United States Patent Office on November 9, 2017, the entire contents of which are incorporated herein by reference as if fully set forth below in their entirety and for all applicable purposes.

TECHNICAL FHCLD

[0002] The technology discussed below relates generally to wireless communication systems, and more particularly, to wireless communication using device-to-device communication across different cells.

INTRODUCTION

[0003] Some wireless communication systems employ multiple-access technologies capable of supporting communication with multiple users by sharing available system resources. Some examples of system resources are bandwidth, subcarriers, time slots, transmit power, antennas, etc. In a shared resource network, a user equipment (UE) may transmit data using a request-grant method (also known as grant-based method) in that the UE requests a permission or grant from the network prior to transmitting data, and a base station or scheduling entity decides when and how the UE may transmit its information/data using granted or scheduled network resources (e.g., time, spatial, and/or frequency resources).

[0004] When a UE transmits data without first requesting a grant of network resources from a base station or scheduling entity, such data transmission may be called grant-less or grant-free traffic in this disclosure. In some wireless communication systems, a cellular network enables wireless devices (e.g., UEs) to communicate with each other via a nearby base station or cell. In some networks, wireless devices may communicate with one another directly, rather than via an intermediary base station, scheduling entity, or cell. This type of direct communication between UEs may be called device-to-device (D2D), peer-to-peer (P2P), or sidelink communication. When D2D connections use grant-less resources for communication, interference between the D2D connections and/or interference between a D2D connection and an uplink/downlink connection may occur.

BRIEF SUMMARY OF SOME EXAMPLES

[0005] The following presents a simplified summary of one or more aspects of the present disclosure, in order to provide a basic understanding of such aspects. This summary is not an extensive overview of all contemplated features of the disclosure, and is intended neither to identify key or critical elements of all aspects of the disclosure nor to delineate the scope of any or all aspects of the disclosure. Its sole purpose is to present some concepts of one or more aspects of the disclosure in a simplified form as a prelude to the more detailed description that is presented later.

[0006] One aspect of the present disclosure provides a method of wireless communication. A scheduling entity requests a plurality of user equipments (UEs) in a cell to transmit a reference signal in turn in a first rotation. The scheduling entity receives a measurement report from each UE of the plurality of UEs. The measurement report includes measurements of the reference signal received from different UEs, and the measurements respectively correspond to a plurality of device-to-device (D2D) connections that are potentially established between the plurality of UEs. The scheduling entity groups the D2D connections into a plurality of clusters based on the measurement reports such that an interference between D2D connections of different clusters is below a predetermined threshold. The scheduling entity requests the UEs of each cluster to transmit the reference signal in turn according to a second rotation such that two or more UEs corresponding to different clusters transmit the reference signal using a same network resource.

[0007] Another aspect of the present disclosure provides an apparatus for wireless communication. The apparatus includes a communication interface, a memory, and a processor operatively coupled to the communication interface and the memory. The processor is configured to request a plurality of user equipments (UEs) in a cell to transmit a reference signal in turn in a first rotation. The processor is further configured to receive a measurement report from each UE of the plurality of UEs. The measurement report includes measurements of the reference signal received from different UEs. The measurements respectively correspond to a plurality of device-to- device (D2D) connections that are potentially established between the plurality of UEs. The processor is further configured to group the D2D connections into a plurality of clusters based on the measurement reports such that an interference between D2D connections of different clusters is below a predetermined threshold. The processor is further configured to request the UEs corresponding to each cluster to transmit the reference signal in turn according to a second rotation such that two or more UEs corresponding to different clusters transmit the reference signal using a same network resource.

[0008] Another aspect of the present disclosure provides a method of wireless communication at a first user equipment (UE) in a cell including the first UE and a plurality of second UEs. The first UE receives a request from a scheduling entity of the cell to transmit a reference signal. The first UE transmits the reference signal in a first rotation including the first UE and the plurality of second UEs transmitting the reference signal in turn. The first UE measures the reference signal received from each UE of the plurality of second UEs. The first UE transmits a measurement report to the scheduling entity, and the measurement report includes one or more measurements of the reference signal transmitted by the plurality of second UEs. The measurements respectively correspond to a plurality of device-to-device (D2D) connections that are potentially established between first UE and the plurality of second UEs. The first UE transmits the reference signal in a second rotation including the first UE and a subset of the plurality of second UEs trammitting the reference signal in turn. The first UE and the plurality of second UEs are grouped by the scheduling entity into different clusters based on the measurement report.

[0009] Another aspect of the present disclosure provides a user equipment (UE) for wireless communication. The UE includes a communication interface, a memory, and a processor operatively coupled to the communication interface and the memory. The processor is configured to receive a request from a scheduling entity of a cell to transmit a reference signal. The processor is further configured to transmit the reference signal in a first rotation including the UE and a plurality of other UEs transmitting the reference signal in turn. The processor is further configured to measure the reference signal received from each of the plurality of other UEs. The processor is further configured to transmit a measurement report to the scheduling entity, and the measurement report includes one or more measurements of the reference signal transmitted by the plurality of other UEs. The measurements respectively correspond to a plurality of device-to- device (D2D) connections between UE and the plurality of other UEs. The processor is further configured to transmit the reference signal in a second rotation including the UE and a subset of the plurality of other UEs transmitting the reference signal in turn. The UE and the plurality of other UEs are grouped by the scheduling entity into different clusters based on the measurement report.

[0010] These and other aspects of the invention will become more fully understood upon a review of the detailed description, which follows. Other aspects, features, and embodiments of the present invention will become apparent to those of ordinary skill in the art, upon reviewing the following description of specific, exemplary embodiments of the present invention in conjunction with the accompanying figures. While features of the present invention may be discussed relative to certain embodiments and figures below, all embodiments of the present invention can include one or more of the advantageous features discussed herein. In other words, while one or more embodiments may be discussed as having certain advantageous features, one or more of such features may also be used in accordance with the various embodiments of the invention discussed herein. In similar fashion, while exemplary embodiments may be discussed below as device, system, or method embodiments it should be understood that such exemplary embodiments can be implemented in various devices, systems, and methods.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG. 1 is a schematic illustration of a wireless communication system.

[0012] FIG. 2 is a conceptual illustration of an example of a radio access network.

[0013] FIG. 3 is a schematic illustration of an organization of wireless resources in an air interface utilizing orthogonal frequency divisional multiplexing (OFDM),

[0014] I FIG. 4 is a block diagram conceptually illustrating an example of a hardware implementation for a scheduling entity according to some aspects of the disclosure.

[0015] I FIG. 5 is a block diagram conceptually illustrating an example of a hardware implementation for a scheduled entity according to some aspects of the disclosure.

[0016] I FIG. 6 is a diagram illustrating an example of device-to-device (D2D) communication in a wireless cell according to some aspects of the disclosure.

[0017] I FIG. 7 is diagram illustrating an exemplary D2D channel measurement process according to some aspects of the disclosure. [0018] FIG. 8 is a diagram illustrating an intra-cell interference management process for facilitating network resources reuse among D2D connections according to some aspects of the disclosure.

[0019] FIG. 9 is a diagram illustrating a process of grouping D2D connections into clusters based on reference signal measurements.

[0020] FIG. 10 is a diagram illustrating two exemplary D2D connection clusters.

[0021] FIG. 11 is a diagram illustrating an exemplary timeline of cell-wide sounding reference signal (SRS) measurements and cluster-wide SRS measurements.

[0022] FIG. 12 is a flow chart illustrating an exemplary process for managing intra-cell

D2D connection interference according to some aspects of the disclosure.

[0023] FIG. 13 is a flow chart illustrating another exemplary process for managing intra-cell D2D connection interference according to some aspects of the present disclosure.

DETAILED DESCRIPTION

[0024] The detailed description set forth below in connection with the appended drawings is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well known structures and components are shown in block diagram form in order to avoid obscuring such concepts.

[0025] While aspects and embodiments are described in this application by illustration to some examples, those skilled in the art will understand that additional implementations and use cases may come about in many different arrangements and scenarios. Innovations described herein may be implemented across many differing platform types, devices, systems, shapes, sizes, packaging arrangements. For example, embodiments and/or uses may come about via integrated chip embodiments and other non-module-component based devices (e.g., end-user devices, vehicles, communication devices, computing devices, industrial equipment, retail/purchasing devices, medical devices, AI-enabled devices, etc.). While some examples may or may not be specifically directed to use cases or applications, a wide assortment of applicability of described innovations may occur. Implementations may range a spectrum from chip-level or modular components to non-modular, non-chip-level implementations and further to aggregate, distributed, or OEM devices or systems incorporating one or more aspects of the described innovations. In some practical settings, devices incorporating described aspects and features may also necessarily include additional components and features for implementation and practice of claimed and described embodiments. For example, transmission and reception of wireless signals necessarily includes a number of components for analog and digital purposes (e.g., hardware components including antenna, RF-chains, power amplifiers, modulators, buffer, processors), interleaver, adders/summers, etc.). It is intended that innovations described herein may be practiced in a wide variety of devices, chip-level components, systems, distributed arrangements, end-user devices, etc. of varying sizes, shapes and constitution.

[0026] In cellular communication networks, wireless devices generally communicate with each other via one or more network entities such as a base station or scheduling entity. Some networks may additionally or alternatively support device-to-device (D2D) communication that enables discovery of, and communication with nearby devices using a direct D2D link between the devices (i.e., without passing through a base station, scheduling, relay, or other node). D2D communication can enable mesh networks and device-to-network relay functionality. Some examples of D2D technology include Bluetooth, Wi-Fi Direct, Miracast, and LTE Direct. D2D communication may also be called point-to-point (P2P), sidelink communication, or the like.

[0027] D2D communication may be implemented using licensed or unlicensed frequency bands. Using D2D communication can avoid the overhead involving the routing to and from the base station or scheduling entity. Therefore, D2D communication may provide better throughput, lower latency, and/or higher energy efficiency. MuLTEFire is an example of Long-term Evolution (LTE) network that supports D2D communication using unlicensed frequency bands. MuLTEFire is a 3 ^rd Generation Partnership Project (3 GPP) specification that defines how LTE operates in unlicensed and shared spectrum while ensuring fair sharing of spectrum with other users and technologies. For example, MuLTEFire may be used in any unlicensed spectrum where there is contention for use of the spectrum. MuLTEFire implements a listen- before-talk (LBT) strategy for coexistence management.

[0028] Aspects of the present disclosure provide methods and apparatuses for intra-cell interference management of D2D communication using grant-free uplink (GUL) resources. When a user equipment (UE) transmits data without first requesting a grant of certain network resources from a base station or scheduling entity, such data transmission may be called grant-less or grant-free traffic in this disclosure. In some wireless networks, a base station may allocate certain GUL resources for each UE to transmit D2D traffic. In some aspects of the disclosure, GUL resources may be reused to improve resource utilization in a network.

[0029] The various concepts presented throughout this disclosure may be implemented across a broad variety of telecommunication systems, network architectures, and communication standards. Referring now to FIG. 1, as an illustrative example without limitation, various aspects of the present disclosure are illustrated with reference to a wireless communication system 100. The wireless communication system 100 includes three interacting domains: a core network 102, a radio access network (RAN) 104, and a user equipment (UE) 106. By virtue of the wireless communication system 100, the UE 106 may be enabled to carry out data communication with an external data network 110, such as (but not limited to) the Internet.

[0030] The RAN 104 may implement any suitable wireless communication technology or technologies to provide radio access to the UE 106. As one example, the RAN 104 may operate according to 3 ^rd Generation Partnership Project (3 GPP) New Radio (NR) specifications, often referred to as 5G. As another example, the RAN 104 may operate under a hybrid of 5G NR and Evolved Universal Terrestrial Radio Access Network (eUTRAN) standards, often referred to as LTE. The 3GPP refers to this hybrid RAN as a next-generation RAN, or NG-RAN. Of course, many other examples may be utilized within the scope of the present disclosure.

[0031] As illustrated, the RAN 104 includes a plurality of base stations 108. Broadly, a base station is a network element in a radio access network responsible for radio transmission and reception in one or more cells to or from a UE. In different technologies, standards, or contexts, a base station may variously be referred to by those skilled in the art as a base transceiver station (BTS), a radio base station, a radio transceiver, a transceiver function, a basic service set (BSS), an extended service set (ESS), an access point (AP), a Node B (NB), an eNode B (eNB), a gNode B (gNB), or some other suitable terminology.

[0032] The radio access network 104 is further illustrated supporting wireless communication for multiple mobile apparatuses. A mobile apparatus may be referred to as user equipment (UE) in 3GPP standards, but may also be referred to by those skilled in the art as a mobile station (MS), a subscriber station, a mobile unit, a subscriber unit, a wireless unit, a remote unit, a mobile device, a wireless device, a wireless communications device, a remote device, a mobile subscriber station, an access terminal (AT), a mobile terminal, a wireless terminal, a remote terminal, a handset, a terminal, a user agent, a mobile client, a client, or some other suitable terminology. A UE may be an apparatus that provides a user with access to network services.

[0033] Within the present document, a "mobile" apparatus need not necessarily have a capability to move, and may be stationary. The term mobile apparatus or mobile device broadly refers to a diverse array of devices and technologies. UEs may include a number of hardware structural components sized, shaped, and arranged to help in communication; such components can include antennas, antenna arrays, RF chains, amplifiers, one or more processors, etc. electrically coupled to each other. For example, some non-limiting examples of a mobile apparatus include a mobile, a cellular (cell) phone, a smart phone, a session initiation protocol (SIP) phone, a laptop, a personal computer (PC), a notebook, a netbook, a smartbook, a tablet, a personal digital assistant (PDA), and a broad array of embedded systems, e.g., corresponding to an "Internet of things" (IoT). A mobile apparatus may additionally be an automotive or other transportation vehicle, a remote sensor or actuator, a robot or robotics device, a satellite radio, a global positioning system (GPS) device, an object tracking device, a drone, a multi-copter, a quad-copter, a remote control device, a consumer and/or wearable device, such as eyewear, a wearable camera, a virtual reality device, a smart watch, a health or fitness tracker, a digital audio player (e.g., MP3 player), a camera, a game console, etc. A mobile apparatus may additionally be a digital home or smart home device such as a home audio, video, and/or multimedia device, an appliance, a vending machine, intelligent lighting, a home security system, a smart meter, etc. A mobile apparatus may additionally be a smart energy device, a security device, a solar panel or solar array, a municipal infrastructure device controlling electric power (e.g., a smart grid), lighting, water, etc.; an industrial automation and enterprise device; a logistics controller; agricultural equipment; military defense equipment, vehicles, aircraft, ships, and weaponry, etc. Still further, a mobile apparatus may provide for connected medicine or telemedicine support, e.g., health care at a distance. Telehealth devices may include telehealth monitoring devices and telehealth administration devices, whose communication may be given preferential treatment or prioritized access over other types of information, e.g., in terms of prioritized access for transport of critical service data, and/or relevant QoS for transport of critical service data.

[0034] Wireless communication between a RAN 104 and a UE 106 may be described as utilizing an air interface. Transmissions over the air interface from a base station (e.g., base station 108) to one or more UEs or scheduled entities (e.g., UE 106) may be referred to as downlink (DL) transmission. In accordance with certain aspects of the present disclosure, the term downlink may refer to a point-to-multipoint transmission originating at a scheduling entity (described further below; e.g., base station 108). Another way to describe this scheme may be to use the term broadcast channel multiplexing. Transmissions from a UE (e.g., UE 106) to a base station (e.g., base station 108) may be referred to as uplink (UL) transmissions. In accordance with further aspects of the present disclosure, the term uplink may refer to a point-to-point transmission originating at a scheduled entity (described further below; e.g., UE 106). Some UEs 106 may communicate with each other using D2D communication.

[0035] In some examples, access to the air interface may be scheduled, wherein a scheduling entity (e.g., a base station 108) allocates resources for communication among some or all devices and equipment within its service area or cell. Within the present disclosure, as discussed further below, the scheduling entity may be responsible for scheduling, assigning, reconfiguring, and releasing resources for one or more scheduled entities. The scheduling entity may allocate certain GUL resources to UEs for D2D communication. Once allocated the GUL resources, the UEs can communicate using D2D communication without involving the scheduling entity. That is, for scheduled communication, UEs 106, which may be scheduled entities, may utilize resources allocated by the scheduling entity 108.

[0036] Base stations 108 are not the only entities that may function as scheduling entities. That is, in some examples, a UE may function as a scheduling entity, scheduling resources for one or more scheduled entities (e.g., one or more other UEs).

[0037] As illustrated in FIG. 1, a scheduling entity 108 may broadcast downlink traffic

112 to one or more scheduled entities 106, Broadly, the scheduling entity 108 is a node or device responsible for scheduling traffic in a wireless communication network, including the downlink traffic 112 and, in some examples, uplink traffic 116 from one or more scheduled entities 106 to the scheduling entity 108. On the other hand, the scheduled entity 106 is a node or device that receives downlink control information 114, including but not limited to scheduling information (e.g., a grant), synchronization or timing information, or other control information from another entity in the wireless communication network such as the scheduling entity 108.

[0038] In general, base stations 108 may include a backhaul interface for communication with a backhaul portion 120 of the wireless communication system. The backhaul 120 may provide a link between a base station 108 and the core network 102. Further, in some examples, a backhaul network may provide interconnection between the respective base stations 108. Various types of backhaul interfaces may be employed, such as a direct physical connection, a virtual network, or the like using any suitable transport network.

[0039] The core network 102 may be a part of the wireless communication system 100, and may be independent of the radio access technology used in the RAN 104. In some examples, the core network 102 may be configured according to 5G standards (e.g., 5GC). In other examples, the core network 102 may be configured according to a 4G evolved packet core (EPC), or any other suitable standard or configuration.

[0040] Referring now to FIG. 2, by way of example and without limitation, a schematic illustration of a RAN 200 is provided. In some examples, the RAN 200 may be the same as the RAN 104 described above and illustrated in FIG. 1. The geographic area covered by the RAN 200 may be divided into cellular regions (cells) that can be uniquely identified by a user equipment (UE) based on an identification broadcasted from one access point or base station. FIG. 2 illustrates macrocells 202, 204, and 206, and a small cell 208, each of which may include one or more sectors (not shown). A sector is a sub- area of a cell. All sectors within one cell are served by the same base station. A radio link within a sector can be identified by a single logical identification belonging to that sector. In a cell that is divided into sectors, the multiple sectors within a cell can be formed by groups of antennas with each antenna responsible for communication with UEs in a portion of the cell.

[0041 ] In FIG. 2, two base stations 210 and 212 are shown in cells 202 and 204; and a third base station 214 is shown controlling a remote radio head (RRH) 216 in cell 206. That is, a base station can have an integrated antenna or can be connected to an antenna or RRH by feeder cables. In the illustrated example, the cells 202, 204, and 126 may be referred to as macrocells, as the base stations 210, 212, and 214 support cells having a large size. Further, a base station 218 is shown in the small cell 208 (e.g., a microcell, picocell, femtocell, home base station, home Node B, home eNode B, etc.) which may overlap with one or more macrocells. In this example, the cell 208 may be referred to as a small cell, as the base station 218 supports a cell having a relatively small size. Cell sizing can be done according to system design as well as component constraints.

[0042] It is to be understood that the radio access network 200 may include any number of wireless base stations and cells. Further, a relay node may be deployed to extend the size or coverage area of a given cell. The base stations 210, 212, 214, 218 provide wireless access points to a core network for any number of mobile apparatuses. In some examples, the base stations 210, 212, 214, and/or 218 may be the same as the base station/scheduling entity 108 described above and illustrated in FIG. 1.

[0043] FIG. 2 further includes a quadcopter or drone 220, which may be configured to function as a base station. That is, in some examples, a cell may not necessarily be stationary, and the geographic area of the cell may move according to the location of a mobile base station such as the quadcopter 220.

[0044] Within the RAN 200, the cells may include UEs that may be in communication with one or more sectors of each cell. Further, each base station 210, 212, 214, 218, and 220 may be configured to provide an access point to a core network 102 (see FIG. 1) for all the UEs in the respective cells. For example, UEs 222 and 224 may be in communication with base station 210; UEs 226 and 228 may be in communication with base station 212; UEs 230 and 232 may be in communication with base station 214 by way of RRH 216; UE 234 may be in communication with base station 218; and UE 236 may be in communication with mobile base station 220. In some examples, the UEs 222, 224, 226, 228, 230, 232, 234, 236, 238, 240, and/or 242 may be the same as the UE/scheduled entity 106 described above and illustrated in FIG. 1.

[0045] In some examples, a mobile network node (e.g., quadcopter 220) may be configured to function as a UE. For example, the quadcopter 220 may operate within cell 202 by communicating with base station 210.

[0046] In a further aspect of the RAN 200, sidelink signals or D2D traffic may be used between UEs without necessarily relying on scheduling or control information from a base station. For example, two or more UEs (e.g., UEs 226 and 228) may communicate with each other using peer to peer (P2P), D2D, or sidelink signals 227 without relaying that communication through a base station (e.g., base station 212). In a further example, UE 238 is illustrated communicating with UEs 240 and 242. Here, the UE 238 may function as a scheduling entity or a primary sidelink device, and UEs 240 and 242 may function as a scheduled entity or a non-primary (e.g., secondary) sidelink device. In still another example, a UE may function as a scheduling entity in a device-to-device (D2D), peer-to-peer (P2P), or vehicle-to-vehicle (V2V) network, and/or in a mesh network. In a mesh network example, UEs 240 and 242 may optionally communicate directly with one another in addition to communicating with the scheduling entity 238. Thus, in a wireless communication system with scheduled access to time-frequency resources and having a cellular configuration, a P2P configuration, or a mesh configuration, a scheduling entity and one or more scheduled entities may communicate utilizing the scheduled resources.

10047] In the radio access network 200, the ability for a UE to communicate while moving, independent of its location, is referred to as mobility. The various physical channels between the UE and the radio access network are generally set up, maintained, and released under the control of an access and mobility management function (AMF, not illustrated, part of the core network 102 in FIG. 1), which may include a security context management function (SCMF) that manages the security context for both the control plane and the user plane functionality, and a security anchor function (SEAF) that performs authentication.

[0048] In various aspects of the disclosure, a radio access network 200 may utilize DL- based mobility or UL-based mobility to enable mobility and handovers (i.e., the transfer of a UE's connection from one radio channel to another). In a network configured for DL-based mobility, during a call with a scheduling entity, or at any other time, a UE may monitor various parameters of the signal from its serving cell as well as various parameters of neighboring cells. Depending on the quality of these parameters, the UE may maintain communication with one or more of the neighboring cells. During this time, if the UE moves from one cell to another, or if signal quality from a neighboring cell exceeds that from the serving cell for a given amount of time, the UE may undertake a handoff or handover from the serving cell to the neighboring (target) cell. For example, UE 224 (illustrated as a vehicle, although any suitable form of UE may be used) may move from the geographic area corresponding to its serving cell 202 to the geographic area corresponding to a neighbor cell 206. When the signal strength or quality from the neighbor cell 206 exceeds that of its serving cell 202 for a given amount of time, the UE 224 may transmit a reporting message to its serving base station 210 indicating this condition. In response, the UE 224 may receive a handover command, and the UE may undergo a handover to the cell 206.

[0049] In a network configured for UL-based mobility, UL reference signals from each

UE may be utilized by the network to select a serving cell for each UE. In some examples, the base stations 210, 212, and 214/216 may broadcast unified synchronization signals (e.g., unified Primary Synchronization Signals (PSSs), unified Secondary Synchronization Signals (SSSs) and unified Physical Broadcast Channels (PBCH)). The UEs 222, 224, 226, 228, 230, and 232 may receive the unified synchronization signals, derive the carrier frequency and slot timing from the synchronization signals, and in response to deriving timing, transmit an uplink pilot or reference signal. The uplink pilot signal transmitted by a UE (e.g., UE 224) may be concurrently received by two or more cells (e.g., base stations 210 and 214/216) within the radio access network 200. Each of the cells may measure a strength of the pilot signal, and the radio access network (e.g., one or more of the base stations 210 and 214/216 and/or a central node within the core network) may determine a serving cell for the UE 224. As the UE 224 moves through the radio access network 200, the network may continue to monitor the uplink pilot signal transmitted by the UE 224. When the signal strength or quality of the pilot signal measured by a neighboring cell exceeds that of the signal strength or quality measured by the serving cell, the network 200 may handover the UE 224 from the serving cell to the neighboring cell, with or without informing the UE 224.

[0050] Although the synchronization signal transmitted by the base stations 210, 212, and 214/216 may be unified, the synchronization signal may not identify a particular cell, but rather may identify a zone of multiple cells operating on the same frequency and/or with the same timing. The use of zones in 5G networks or other next generation communication networks enables the uplink-based mobility framework and improves the efficiency of both the UE and the network, since the number of mobility messages that need to be exchanged between the UE and the network may be reduced.

[0051] In various implementations, the air interface in the radio access network 200 may utilize licensed spectrum, unlicensed spectrum, or shared spectrum. Licensed spectrum provides for exclusive use of a portion of the spectrum, generally by virtue of a mobile network operator purchasing a license from a government regulatory body. Unlicensed spectrum provides for shared use of a portion of the spectrum without need for a government-granted license. While compliance with some technical rules is generally still required to access unlicensed spectrum, generally, any operator or device may gain access. Shared spectrum may fall between licensed and unlicensed spectrum, wherein technical rules or limitations may be required to access the spectrum, but the spectrum may still be shared by multiple operators and/or multiple RATs. For example, the holder of a license for a portion of licensed spectrum may provide licensed shared access (LSA) to share that spectrum with other parties, e.g., with suitable licensee- determined conditions to gain access. In one example, the radio access network 200 may support MuLTEFire using licensed or unlicensed spectrum.

[0052] In order for transmissions over the radio access network 200 to obtain a low block error rate (BLER) while still achieving very high data rates, channel coding may be used. That is, wireless communication may generally utilize a suitable error correcting block code. In a typical block code, an information message or sequence is split up into code blocks (CBs), and an encoder (e.g., a CODEC) at the transmitting device then mathematically adds redundancy to the information message. Exploitation of this redundancy in the encoded information message can improve the reliability of the message, enabling correction for any bit errors that may occur due to the noise.

[0053] In some aspects of the disclosure, user data may be coded using quasi-cyclic low-density parity check (LDPC) with two different base graphs: one base graph is used for large code blocks and/or high code rates, while the other base graph is used otherwise. Control information and the physical broadcast channel (PBCH) are coded using Polar coding, based on nested sequences. For these channels, puncturing, shortening, and repetition are used for rate matching.

[0054] However, those of ordinary skill in the art will understand that aspects of the present disclosure may be implemented utilizing any suitable channel code. Various implementations of scheduling entities 108 and scheduled entities 106 may include suitable hardware and capabilities (e.g., an encoder, a decoder, and/or a CODEC) to utilize one or more of these channel codes for wireless communication.

[0055] The air interface in the radio access network 200 may utilize one or more multiplexing and multiple access algorithms to enable simultaneous communication of the various devices. For example, 5G NR specifications provide multiple access for UL transmissions from UEs 222 and 224 to base station 210, and for multiplexing for DL transmissions from base station 210 to one or more UEs 222 and 224, utilizing orthogonal frequency division multiplexing (OFDM) with a cyclic prefix (CP). In addition, for UL transmissions, 5G NR specifications provide support for discrete Fourier transform-spread-OFDM (DFT-s-OFDM) with a CP (also referred to as single- carrier FDMA (SC-FDMA)). However, within the scope of the present disclosure, multiplexing and multiple access are not limited to the above schemes, and may be provided utilizing time division multiple access (TDMA), code division multiple access (CDMA), frequency division multiple access (FDMA), sparse code multiple access (SCMA), resource spread multiple access (RSMA), or other suitable multiple access schemes. Further, multiplexing DL transmissions from the base station 210 to UEs 222 and 224 may be provided utilizing time division multiplexing (TDM), code division multiplexing (CDM), frequency division multiplexing (FDM), orthogonal frequency division multiplexing (OFDM), sparse code multiplexing (SCM), or other suitable multiplexing schemes.

[0056] Various aspects of the present disclosure will be described with reference to an OFDM waveform, schematically illustrated in FIG. 3. It should be understood by those of ordinary skill in the art that the various aspects of the present disclosure may be applied to a DFT-s-OFDMA waveform in substantially the same way as described herein below. That is, while some examples of the present disclosure may focus on an OFDM link for clarity, it should be understood that the same principles may be applied as well to DFT-s-OFDMA waveforms.

10057] Within the present disclosure, a frame refers to a predetermined duration of time

(e.g., 10 ms) for wireless transmissions, with each frame consisting of a predetermined number of subframes (e.g., 10 subframes of 1 ms each). On a given carrier, there may be one set of frames in the UL, and another set of frames in the DL. Referring now to FIG. 3, an expanded view of an exemplary subframe 302 is illustrated, showing an OFDM resource grid 304. However, as those skilled in the art will readily appreciate, the PHY transmission structure for any particular application may vary from the example described here, depending on any number of factors. Here, time is in the horizontal direction with units of OFDM symbols; and frequency is in the vertical direction with units of subcarriers or tones.

[0058] The resource grid 304 may be used to schematically represent time-frequency resources for wireless communication. The resource grid 304 is divided into multiple resource elements (REs) 306. An RE, which is 1 subcarrier x 1 symbol, is the smallest discrete part of the time-frequency grid, and contains a single complex value representing data from a physical channel or signal. Depending on the modulation utilized in a particular implementation, each RE may represent one or more bits of information. In some examples, a block of REs may be referred to as a physical resource block (PRB) or more simply a resource block (RB) 308, which contains any suitable number of consecutive subcarriers in the frequency domain. In one example, an RB may include 12 subcarriers, a number independent of the numerology used. In some examples, depending on the numerology, an RB may include any suitable number of consecutive OFDM symbols in the time domain. Within the present disclosure, it is assumed that a single RB such as the RB 308 entirely corresponds to a single direction of communication (either transmission or reception for a given device).

[0059] A UE generally utilizes only a subset of the resource grid 304. An RB may be the smallest unit of resources that can be allocated to a UE. Thus, the more RBs scheduled for a UE, and the higher the modulation scheme chosen for the air interface, the higher the data rate for the UE. In some examples, some RBs may be GUL resources that may be used for D2D communication.

[0060] In this illustration, the RB 308 is shown as occupying less than the entire bandwidth of the subframe 302, with some subcarriers illustrated above and below the RB 308. In a given implementation, the subframe 302 may have a bandwidth corresponding to any number of one or more RBs 308. Further, in this illustration, the RB 308 is shown as occupying less than the entire duration of the subframe 302, although this is merely one possible example.

[0061] Each subframe (e.g., 1 ms subframe 302) may consist of one or multiple adjacent slots. In the example shown in FIG. 3, one subframe 302 includes four slots 310, as an illustrative example. An expanded view of one of the slots 310 illustrates the slot 310 including a control region 312 and a data region 314. In general, the control region 312 may carry control channels (e.g., PDCCH or PUCCH), and the data region 314 may carry data channels (e.g., PDSCH or PUSCH). Of course, a slot may contain all DL, all UL, or at least one DL portion and at least one UL portion. The simple structure illustrated in FIG. 3 is merely exemplary in nature, and different slot structures may be utilized, and may include one or more of each of the control region(s) and data region(s).

[0062] Although not illustrated in FIG. 3, the various REs 306 within a RB 308 may be scheduled to carry one or more physical channels, including control channels, shared channels, data channels, etc. Other REs 306 within the RB 308 may also carry pilots or reference signals, including but not limited to a demodulation reference signal (DMRS) a control reference signal (CRS), or a sounding reference signal (SRS). These pilots or reference signals may provide for a receiving device to perform channel estimation of the corresponding channel, which may enable coherent demodulation/detection of the control and/or data channels within the RB 308. Some REs or RBs may be used or reserved for grant-free traffic, for example, D2D or sidelink communication. [0063] In a DL transmission, the transmitting device (e.g., the scheduling entity 108) may allocate one or more REs 306 (e.g., within a control region 312) to carry DL control information 114 including one or more DL control channels that generally carry information originating from higher layers, such as a physical broadcast channel (PBCH), a physical downlink control channel (PDCCH), etc., to one or more scheduled entities 106. In addition, DL REs may be allocated to carry DL physical signals that generally do not carry information originating from higher layers. These DL physical signals may include a primary synchronization signal (PSS); a secondary synchronization signal (SSS); demodulation reference signals (DM-RS); phase-tracking reference signals (PT-RS); channel-state information reference signals (CSI-RS); etc. The PDCCH may carry downlink control information (DCI) for one or more UEs in a cell, including but not limited to power control commands, scheduling information, a grant, and/or an assignment of REs for DL and UL transmissions or D2D traffic.

[0064] In an UL transmission, the transmitting device (e.g., the scheduled entity 106) may utilize one or more REs 306 to carry UL control information 118 originating from higher layers via one or more UL control channels, such as a physical uplink control channel (PUCCH) or short PUCCH, a physical random access channel (PRACII), etc., to the scheduling entity 108. A sPUCCH generally has fewer symbols than a PUCCH. Further, UL REs may carry UL physical signals that generally do not cany information originating from higher layers, such as demodulation reference signals (DM-RS), phase- tracking reference signals (PT-RS), sounding reference signals (SRS), etc. In addition to control information, one or more REs 306 (e.g., within the data region 314) may be allocated for user data or traffic data. Such traffic may be carried on one or more traffic channels, such as, for a DL transmission, a physical downlink shared channel (PDSCH), for an UL transmission, a physical uplink shared channel (PUSCH), or D2D communication or sidelink data between UEs.

[0065] Thus, in a wireless communication network with scheduled access to time- frequency resources (e.g., REs 306) and having a cellular configuration, a D2D configuration, a P2P configuration, or a mesh configuration, a scheduling entity and one or more scheduled entities may communicate utilizing the scheduled resources. The network 200 may also provide grant-free uplink (GUL) access to the UEs. GUL resources (e.g., RB 308) may be allocated to the UEs in the frequency domain, time domain, and/or spatial domain for regular UL access and/or D2D communication. In some examples, the base station may allocate certain subframes or slots in which GUL traffic is allowed. Different UEs may be allocated different GUL subframes or slots to avoid collision or interference. In some examples, the base station may allocate certain frequency bands or subcarriers in which grant-free traffic is allowed. In some examples, the base station may allocate certain MIMO or spatial layer(s) in which grant- free traffic is allowed. The base station may activate or release GUL resources using semi-static control (e.g., RRC signaling or higher protocol layer messages) or dynamic control (e.g., downlink control information (DCI) in a downlink control channel). When a UE needs to transmit GUL data, the UE may use a listen-before-talk (LBT) procedure to determine that the GUL channel or resource is available.

[0066] The channels or carriers described above and illustrated in FIGs. 1 and 3 are not necessarily all the channels or carriers that may be utilized between a scheduling entity 108 and scheduled entities 106, and those of ordinary skill in the art will recognize that other channels or carriers may be utilized in addition to those illustrated, such as other traffic, control, and feedback channels.

10067] These physical channels described above are generally multiplexed and mapped to transport channels for handling at the medium access control (MAC) layer. Transport channels carry blocks of information called transport blocks (TB). The transport block size (TBS), which may correspond to a number of bits of information, may be a controlled parameter, based on the modulation and coding scheme (MCS) and the number of RBs in a given transmission.

[0068] FIG. 4 is a block diagram illustrating an example of a hardware implementation for a scheduling entity 400 employing a processing system 414. For example, the scheduling entity 400 may be a user equipment (UE) as illustrated in any one or more of FIGs. 1, 2, 6, 7, 8, and/or 10. In another example, the scheduling entity 400 may be a base station as illustrated in any one or more of FIGs. 1, 2, 6, 7, 8, and/or 10.

[0069] The scheduling entity 400 may be implemented with a processing system 414 that includes one or more processors 404. Examples of processors 404 include microprocessors, microcontrollers, digital signal processors (DSPs), field programmable gate arrays (FPGAs), programmable logic devices (PLDs), state machines, gated logic, discrete hardware circuits, and other suitable hardware configured to perform the various functionality described throughout this disclosure. In various examples, the scheduling entity 400 may be configured to perform any one or more of the functions described herein. That is, the processor 404, as utilized in a scheduling entity 400, may be used to implement any one or more of the processes and procedures described below and illustrated in FIGs. 6-13.

[0070] In this example, the processing system 414 may be implemented with a bus architecture, represented generally by the bus 402. The bus 402 may include any number of interconnecting buses and bridges depending on the specific application of the processing system 414 and the overall design constraints. The bus 402 communicatively couples together various circuits including one or more processors (represented generally by the processor 404), a memory 405, and computer-readable media (represented generally by the computer-readable medium 406). The bus 402 may also link various other circuits such as timing sources, peripherals, voltage regulators, and power management circuits, which are well known in the art, and therefore, will not be described any further. A bus interface 408 provides an interface between the bus 402 and a transceiver 410. The transceiver 410 provides a communication interface or means for communicating with various other apparatus over a transmission medium. Depending upon the nature of the apparatus, a user interface 412 (e.g., keypad, display, speaker, microphone, joystick) may also be provided. Of course, such a user interface 412 is optional, and may be omitted in some examples, such as a base station.

[0071] In some aspects of the disclosure, the processor 404 may include circuitry configured for various functions, including, for example, functions for configuring and performing D2D communication using GUL resources. For example, the circuitry may be configured to implement one or more of the functions described in relation to FIGs. 6-13. The processor 404 may include, for example, a processing circuit 440, a UL/DL communication circuit 442, and a D2D communication circuit 444. The processing circuit 440 may be configured to perform various data processing and logic functions that may be used in wireless communication. The UL/DL communication circuit 442 may be configured to perform various functions used in UL and DL communications, for example, encoding / decoding, resource mapping, data packet encapsulation / decapsulation, interlacing / deinterlacing, interleaving / deinterleaving, multiplexing / demultiplexing, etc. The D2D communication circuit 444 may be configured to perform various functions used in D2D communication, for example, D2D channel measurements, D2D communication resource allocation, D2D channel configuration D2D channels grouping, etc. In some examples, the UL/DL communication 442 and D2D communication circuit 444 may be included in a communication circuit. [0072] The processor 404 is responsible for managing the bus 402 and general processing, including the execution of software stored on the computer-readable medium 406. The software, when executed by the processor 404, causes the processing system 414 to perform the various functions described below for any particular apparatus. The computer-readable medium 406 and the memory 405 may also be used for storing data that is manipulated by the processor 404 when executing software.

[0073] One or more processors 404 in the processing system may execute software.

Software shall be construed broadly to mean instructions, instruction sets, code, code segments, program code, programs, subprograms, software modules, applications, software applications, software packages, routines, subroutines, objects, executables, threads of execution, procedures, functions, etc., whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise. The software may reside on a computer-readable medium 406. The computer-readable medium 406 may be a non-transitory computer-readable medium. A non-transitory computer-readable medium includes, by way of example, a magnetic storage device (e.g., hard disk, floppy disk, magnetic strip), an optical disk (e.g., a compact disc (CD) or a digital versatile disc (DVD)), a smart card, a flash memory device (e.g., a card, a stick, or a key drive), a random access memory (RAM), a read only memory (ROM), a programmable ROM (PROM), an erasable PROM (EPROM), an electrically erasable PROM (EEPROM), a register, a removable disk, and any other suitable medium for storing software and/or instructions that may be accessed and read by a computer. The computer-readable medium 406 may reside in the processing system 414, external to the processing system 414, or distributed across multiple entities including the processing system 414. The computer-readable medium 406 may be embodied in a computer program product. By way of example, a computer program product may include a computer-readable medium in packaging materials. Those skilled in the art will recognize how best to implement the described functionality presented throughout this disclosure depending on the particular application and the overall design constraints imposed on the overall system.

[0074] In one or more examples, the computer-readable storage medium 406 may include software configured for various functions, including, for example, functions for configuring and performing D2D communication using GUL resources. For example, the software may be configured to implement one or more of the functions described in relation to FIGs. 6-13. The software may include processing instructions 452, UL/DL communication instructions 454, and D2D communication instructions 456. The processing instructions 452 may configure the processing system 414 to perform various data processing and logic functions that may be used in wireless communication. The UL/DL communication instructions 454 may configure the processing system 414 to perform various functions used in UL and DL communications, for example, encoding / decoding, resource mapping, data packet encapsulation / decapsulation, interlacing / deinterlacing, interleaving / deinterleaving, multiplexing / demultiplexing, etc. The D2D communication instructions 456 may configure the processing system 414 to perform various functions used in D2D communication, for example, D2D channel measurements, D2D communication resource allocation, D2D channel configuration, D2D channel grouping, etc.

[0075] FIG. 5 is a conceptual diagram illustrating an example of a hardware implementation for an exemplary scheduled entity 500 employing a processing system 514. In accordance with various aspects of the disclosure, an element, or any portion of an element, or any combination of elements may be implemented with a processing system 514 that includes one or more processors 504. For example, the scheduled entity 500 may be a user equipment (UE) as illustrated in any one or more of FIGs. 1, 2, 6, 7, 8, and/or 10.

[0076] The processing system 514 may be substantially the same as the processing system 414 illustrated in FIG. 4, including a bus interface 508, a bus 502, memory 505, a processor 504, and a computer-readable medium 506. Furthermore, the scheduled entity 500 may include a user interface 512 and a transceiver 510 substantially similar to those described above in FIG. 4. That is, the processor 504, as utilized in a scheduled entity 500, may be used to implement any one or more of the processes described and illustrated in FIGs. 6-13.

[0077] In some aspects of the disclosure, the processor 504 may include circuitry configured for various functions, including, for example, functions for configuring and performing D2D communication using GUL resources. For example, the circuitry may be configured to implement one or more of the functions described in relation to FIGs. 6-13. The processor 504 may include a processing circuit 540, a UL/DL communication circuit 542, and a D2D communication circuit 544. The processing circuit 540 may be configured to perform various data processing and logic functions that may be used in wireless communication. The UL/DL communication circuit 542 may be configured to perform various functions used in UL and DL communications, for example, encoding / decoding, resource mapping, data packet encapsulation / decapsulation, interlacing / deinterlacing, interleaving / deinterleaving, multiplexing / demultiplexing, etc. The D2D communication circuit 544 may be configured to perform various functions used in D2D communication, for example, D2D channel measurements, D2D communication resource allocation, D2D channel configuration, D2D channel grouping, etc.

[0078] In one or more examples, the computer-readable storage medium 506 may include software configured for various functions, including, for example, functions for configuring and performing D2D communication using GUL resources. For example, the software may be configured to implement one or more of the functions described in relation to FIGs. 6-13. The software may include processing instructions 552, UL/DL communication instructions 554, and D2D communication instructions 556. The processing instructions 552 may configure the processing system 514 to perform various data processing and logic functions that may be used in wireless communication. The UL/DL communication instructions 554 may configure the processing system 514 to perform various functions used in UL and DL communications, for example, encoding / decoding, resource mapping, data packet encapsulation / decapsulation, interlacing / deinterlacing, interleaving / deinterleaving, multiplexing / demultiplexing, etc. The D2D communication instructions 556 may configure the processing system 514 to perform various functions used in D2D communication, for example, D2D channel measurements, D2D communication resource allocation, D2D channel configuration, D2D channel grouping, etc.

10079] FIG. 6 is a diagram illustrating an example of D2D communication in a wireless cell 600 according to some aspects of the present disclosure. The wireless cell 600 may be one of the cells illustrated in FIG. 2. In some examples, the wireless cell 600 may support D2D communication between UEs using grant-free uplink (GUL) resources. For example, UE A 602 may communicate with UE B 604 using a D2D connection 605, and UE C 606 may communicate with UE D 608 using a D2D connection 609. In other examples, the UEs may communicate with each other using different D2D connections not shown in FIG. 6. A scheduling entity (e.g., base station 610) sets up and configures the D2D connections, for example, by scheduling GUL resources to the UEs for use during D2D communication. To that end, the base station 610 uses D2D-channel measurements to facilitate and support D2D connection setup, interference management between D2D connections, and mobility. In some aspects of the disclosure, D2D- channel measurements may be performed based on UL sounding reference signal (SRS) transmitted by the UEs.

[0080] FIG. 7 is a diagram illustrating an exemplary D2D channel measurement process according to some aspects of the present disclosure. A scheduling entity may use this D2D channel measurement process to facilitate D2D connection communication. In some examples, a UE may transmit an SRS aperiodically (e.g., on request from a base station, eNB, or gNB) either in a PUCCH, a short PUCCH (sPUCCH), or a physical uplink shared channel (PUSCH). A sPUCCH may have fewer symbols than a PUCCH, The sPUCCH may be used for smaller payload. A UE can measure the SRS transmitted by another UE to measure one or more characteristics of a D2D channel, if configured, between the UEs.

[0081] Referring to FIG. 7, the base station 610 may tansmit an SRS request 702 that requests a specific UE (e.g., UE A) to transmit an aperiodic SRS in an upcoming sPUCCH. For example, the base station may transmit the SRS request 702 in a PDCCH DCI flag. UE A may transmit an SRS 704 in a PUCCH/sPUCCH. If UE A is already transmitting UL traffic, UE A may transmit an SRS in its PUSCH. In addition, the base station 610 transmits an SRS measurement request 706 to other UEs (e.g., UE B, UE D, UE C) in an expected neighborhood to monitor UE A's SRS in the upcoming PUCCH/sPUCCH PUSCH when UE A transmits the SRS, and report the measurements back to the base station. In response to the SRS measurement request 706, at block 708, the UEs (e.g., UE B) measures the SRS transmitted by UE A. In some examples, the SRS measurements may include signal strength, signal quality, signal-to-noise ratio (SNR), etc. For example, UE B measures the SRS transmitted by UE A. If the SNR of the measured SRS is greater and 10 dB, it means that the channel between UE A and UE B can be used for D2D communication.

[0082] To facilitate D2D channel measurements, the base station provides UE A's SRS parameters (e.g., network resources allocation information) to the other UEs to avoid transmission-reception conflicts among the UEs. For example, the SRS measurement request 706 may include UE A's SRS parameters. In some aspects of the disclosure, the base station 610 may rotate SRS transmission among the UEs to perform the D2D channel measurements for each D2D connection or channel among the UEs. In that case, the UEs take turn transmitting their respective SRS in response to a corresponding SRS request. In some examples, the base station may schedule the UEs to transmit the SRS using GUL resources that may be the same resources used for D2D communication.

[0083] FIG. 8 is a diagram illustrating an intra-cell interference management process for facilitating network resources reuse among D2D connections according to some aspects of the disclosure. FIG. 8 illustrates a base station 802 and a number of UEs 804. The base station 802 and UEs 804 may be the same as those illustrated in FIGs. 1, 2, 6, 7, and/or 10. The base station 802, at block 806, may request the UEs 804 (e.g., UE 1, UE 2, UE 3, ... UE n) in its cell or coverage area to transmit SRS in turn according to a cycle (e.g., a predetermined cycle and/or a slow timescale cycle). The base station may transmit the request to the UEs using any suitable unicast or broadcast signaling, e.g., an RRC message or DCI. The base station 802 may allocate certain GUL resources to the UEs 804 for the SRS transmission. In response, at block 808, each UE may take turns to transmit its SRS in a rotation (e.g., a cell-wide rotation) using a slow timescale. For example, the slow timescale may be in the order of minutes per rotation or any duration that is long enough to allow the UEs in a cell to transmit its SRS in turn. An example for the slow timescale may be between 100 ms to 500 ms per rotation. When one UE transmits its SRS, other UEs may measure the SRS from the transmitting UE. For example, when UE 1 transmits an SRS, UE 2 through UE n may all listen to UE l 's SRS and measure the quality of a D2D connection to UE 1 based on their respective SRS measurements. Similarly, when UE 2 transmits an SRS, all other UEs (e.g., UE 1 and UE 3 through UE n) may listen to UE 2's SRS and measure the quality of a potential D2D connection to UE 2 based on their respective SRS measurements. After this slow timescale cell- wide rotation of SRS measurements, at block 810, the base station 802 can group, arrange, or divide the D2D connections into different clusters based on the SRS measurements.

[0084] FIG. 9 is a diagram illustrating a process of grouping D2D connections into clusters based on SRS measurements. In some examples, a UE may not establish a D2D connection with another UE when the SRS measurement is lower than a signal quality threshold (e.g., a predetermined signal strength and/or signal quality). At block 902, the base station determines interference between D2D connections based on the SRS measurements performed in the cell-wide rotation. For example, UE 1 has a D2D connection with UE 2, and UE 3 has a D2D connection with UE 4 . If UE 1 's or UE 2's SRS measured at UE 3 or UE 4 is greater than a predetermined interference threshold, the base station may determine that there is too much interference between these D2D connections.

[0085] At block 904, the base station groups certain D2D connections into a cluster when interference between the D2D connections is greater than or equal to an interference threshold (e.g., a predetermined threshold). The interference threshold may be determined by the ratio of D2D signal strength to the interference signal strength. The D2D signal strength may be the SRS signal strength. In one example, if the D2D signal to interference ratio is less than 3dB, then the interference between the D2D connections is determined to be above the interference threshold. At block 906, the base station groups certain D2D connections in different clusters when interference between the D2D connections is less than the predetermined threshold. In one example, the base station may determine the interference between two D2D connections based on the signal strength of all the SRS's reported by the UEs. The threshold may be set to a suitable value such that two UEs respectively grouped to different clusters may transmit D2D traffic using the same network resources (e.g., GUL resources) without causing significant interference between D2D connections of different clusters.

[0086] FIG. 10 is a diagram illustrating two exemplary D2D connection clusters that may be determined using the process described above in relation to FIG. 9. In this example, four UEs (e.g., UE 1, UE 2, UE5, and UE 6) are grouped into a first cluster 1002, and four other UEs (e.g., UE3, UE4, UE 7, and UE 8) are grouped into a second cluster 1004. In the first cluster 1002, the D2D connection between UE 1 and UE 2 uses different network resources (e.g., GUL resources ) from the D2D connection between UE 5 and UE 6 to reduce interference between D2D connections in the same cluster. Similarly, in the second cluster 1004, the D2D connection between UE 3 and UE 4 uses different network resources (e.g., GUL resources ) from the D2D connection between UE 7 and UE 8 to reduce interference between the D2D connections. Between different clusters, the D2D connections may reuse the same network resources. For example, the base station may allocate the same network resources to a D2D connection between UEl and UE 2 of a first cluster 1002, and a D2D connection between UE 3 and UE 4 of a second cluster 1004 (i.e., different clusters). In that case, the same network resources are reused spatially.

[0087] The above-described cell-wide SRS rotation D2D measurements may be repeated according to a predetermined cycle (e.g., slow timescale), and the base station may update the clusters to include different D2D connections/UEs after each rotation. An example of the timescale for cell-wide SRS rotation may be between 100 ms and 500 ms.

[0088] Referring back to FIG. 8, with the D2D connections grouped into clusters based on a slow timescale, the base station, at block 812, may request the UEs in each cluster to transmit an SRS in turn according to a fast timescale that is faster than the slow timescale. For example, the fast timescale may be at least multiple times faster than the slow timescale. In one example, the fast timescale may be between 10 ms to 50 ms. In some examples, the fast timescale may be one tenth or less of the slow timescale. Then, at block 814, the UEs may perform cluster- wide SRS measurements and report the measurements to the base station. In this cluster-wide SRS transmission rotation (cluster-wide rotation), the UEs may reuse SRS resources (e.g., GUL resources) spatially across the clusters. For example, referring to FIG. 10, UE 1 and UE3 from different clusters can transmit their respective SRS using the same network resources. The above-described cell-wide SRS measurement rotation is performed at a slower timescale than the cluster-wide SRS measurement rotation. Therefore, the cluster-wide SRS measurement rotation is performed more often than the cell-wide SRS measurement rotation.

[0089] FIG. 11 is a diagram illustrating an exemplary timeline of cell- wide SRS measurements and cluster-wide SRS measurements. In this example, one cell-wide SRS measurement rotation 1102 and three cluster- wide SRS measurement rotations 1104 are performed in a predetermined time period 1106 or cycle. In each rotation, the UEs in a cell or cluster take turn to transmit an SRS, and other non-transmitting UEs in the same cell or cluster measure the SRS. In both the cell-wide rotation and cluster-wide rotation, the UE may transmit an SRS at the intended D2D transmission (Tx) power for the D2D connection. Transmitting the SRS at the same power as D2D transmission allows SRS measurements to be a better measure of the D2D connection. In some aspects of the disclosure, the D2D Tx power level may be different from the regular UL SRS Tx power level. In some examples, different D2D connections may use different Tx power levels. For example, if a UE has multiple D2D connections, the UE may transmit an SRS at different Tx power levels using different network resources for different D2D connections.

[0090] Referring back to FIG. 8, at block 816, after the cluster- wide SRS measurement rotation, the base station 802 may set up D2D connections among the UEs and allocate network resources (e.g., GUL resources) to the D2D connections based on the SRS measurements. In some aspects of the disclosure, the base station may configure D2D connections in different clusters to use the same GUL resources for D2D communication. The base station may also ensure that GUL resources allocated to D2D communication do not conflict with GUL resources used for regular UL traffic or DL traffic.

[0091] FIG. 12 is a flow chart illustrating an exemplary process 1200 for managing intra-cell D2D connection interference according to some aspects of the present disclosure. As described below, some or all illustrated features may be omitted in a particular implementation within the scope of the present disclosure, and some illustrated features may not be required for implementation of all embodiments. In some examples, the process 1200 may be carried out by the scheduling entity 400 illustrated in FIG. 4. A scheduling entity may be a base station, eNB, or gNB. In some examples, the process 1200 may be carried out by any suitable apparatus or means for carrying out the functions or algorithm described below.

10092] At block 1202, a base station requests a plurality of UEs in a cell to transmit a reference signal in turn in a first rotation (e.g., cell-wide rotation). For example, the base station may utilize the UL/DL communication circuit 442 and transceiver 410 to transmit the request to the UEs. In some examples, the base station may transmit the request in an RRC message or DCI. For example, the base station may request each UE to transmit an SRS for D2D channel measurements according to a first (slow) timescale as described in relation to FIGs. 7-10. The base station may request the UEs to use GUL resources for transmitting the SRS for D2D channel measurements.

[0093] At block 1204, the base station receives a measurement report from each UE.

The measurement report includes measurements of the reference signal (e.g., SRS) received from different UEs. The base station may use the UL/DL communication circuit 442 and transceiver 410 to receive the measurement reports. In some examples, each UE may transmit its measurement report in PUCCH/sPUCCH. In each UE's report, the measurements respectively correspond to a plurality of D2D connections that are potentially established between the UE and other UEs. In some examples, a UE may have multiple D2D connections with different UEs. In that case, the UE may make multiple SRS transmission each for a corresponding D2D connection.

[0094] At block 1206, the base station groups the D2D connections into a plurality of clusters based on the measurement reports such that interference between D2D connections of different clusters is below a predetermined threshold. The base station may use the D2D communication circuit 544 to set the threshold for grouping the D2D connections. The base station may set the threshold such that the base station may allocate the same network resources for D2D connections in different clusters to achieve spatial reuse of network resources.

[0095] At block 1208, the base station requests the UEs of each cluster to transmit the reference signal in turn according to a second rotation (e.g., cluster-wide rotation) such that two or more UEs corresponding to different clusters can transmit the reference signal using the same network resource (e.g., GUL resource). The base station may use the UL/DL communication circuit 442 and transceiver 510 to transmit the requests, for example, using RRC messages or DCI. In one example, the cluster-wide rotation may be performed according to a second (fast) timescale that is faster than the first (slow) timescale. The base station may use the D2D communication circuit 444 to determine the second timescale for the cluster-wide rotation. In response to the request, two UEs in different clusters may use the same network resources (e.g., GUL resources) to transmit their respective SRS, thus resource saving may be achieved. Because the second timescale is faster than the first timescale, the UEs perform the cluster-wide SRS measurements more often than the cell-wide SRS measurements.

[0096] FIG. 13 is a flow chart illustrating an exemplary process 1300 for managing intra-cell D2D connection interference according to some aspects of the present disclosure. As described below, some or all illustrated features may be omitted in a particular implementation within the scope of the present disclosure, and some illustrated features may not be required for implementation of all embodiments. In some examples, the process 1300 may be carried out by the scheduled entity 500 illustrated in FIG. 5. A scheduled entity may be any of UEs illustrated in FIGs. 1, 2, 6, 7, 8, and/or 10. In some examples, the process 1300 may be carried out by any suitable apparatus or means for carrying out the functions or algorithm described below.

[0097] At block 1302, a first UE of a cell receives a request from a scheduling entity of the cell to transmit a reference signal. The first UE and a plurality of second UEs (other UEs) may be located in the cell, and the scheduling entity may be a base station of the cell. The first UE may use a UL/DL communication circuit 542 and a transceiver 510 to receive the request. In some examples, the request may be included in an RRC message or DCI.

[0098] At block 1304, the first UE transmits the reference signal in a first rotation (e.g., cell-wide rotation) including the first UE and the plurality of second UEs transmitting the reference signal in turn. For example, the cell-wide rotation may be similar to that described above in relation to FIGs. 8 and 9. The first UE may use a D2D communication circuit 544 to transmit the reference signal. In some examples, each UE may transmit an SRS as the reference signal using GUL resources.

[0099] At block 1306, the first UE measures the reference signal received from each second UE. In one aspect of the disclosure, the first UE may use the D2D communication circuit 544 to measure the reference signal transmitted by each second UE during the cell-wide rotation. Some examples of measurements of the reference signal may be signal strength, signal quality, and signal-to-noise ratio.

[0100] At block 1308, the first UE transmits a measurement report to the scheduling entity. The UE may use the UL/DL communication circuit 542 to transmit the measurement report that includes one or more measurements of the reference signals transmitted by the plurality of second UEs. The measurements respectively correspond to a plurality of D2D connections between first UE and the plurality of second UEs. That is, the reference signal measurements can indicate the D2D channel quality that are potentially established between the first UE and each second UE.

[0101] At block 1310, the first UE transmits the reference signal in a second rotation

(e.g., cluster-wide) rotation including the first UE and a subset of the plurality of second UEs transmitting the reference signal in turn. The cluster-wide rotation may be similar to that described above in relation to FIGs. 8 and 9. The scheduling entity may group the first UE and the plurality of second UEs into different clusters based on the measurement report of the cell- wide rotation.

[0102] In one configuration, the apparatus 400 for wireless communication includes means for requesting a plurality of UEs in a cell to transmit a reference signal in turn in a cell-wide rotation; means for receiving a measurement report from each UE, the measurement report comprising measurements of the reference signal transmitted from different UEs, the measurements respectively corresponding to a plurality of D2D connections between the plurality of UEs; means for grouping the D2D connections into a plurality of clusters based on the measurement reports such that an interference between D2D connections of different clusters is below a predetermined threshold; and means for requesting the UEs of each cluster to transmit the reference signal in turn according to a cluster-wide rotation such that two or more UEs corresponding to different clusters transmit the reference signal using a same network resource. [0103] In one aspect, the aforementioned means may be the processor(s) 404 shown in

FIG. 4 configured to perform the functions recited by the aforementioned means. In another aspect, the aforementioned means may be a circuit or any apparatus configured to perform the functions recited by the aforementioned means.

[0104] In one configuration, the apparatus 500 for wireless communication includes means for receiving a request from a scheduling entity of a cell to transmit a reference signal; means for transmitting the reference signal in a cell-wide rotation comprising a first UE (the apparatus 500) and a plurality of second UEs transmitting the reference signal in turn; means for measuring the reference signal transmitted from each second UE; means for transmitting a measurement report to the scheduling entity, the measurement report comprising one or more measurements of the reference signal transmitted by the plurality of second UEs, the measurements respectively corresponding to a plurality of D2D connections between first UE and the plurality of second UEs; and means for transmitting the reference signal in a cluster-wide rotation comprising the first UE and a subset of the plurality of second UEs transmitting the reference signal in turn, the first UE and the plurality of second UEs grouped by the scheduling entity into different clusters based on the measurement report.

[0105] Of course, in the above examples, the circuitry included in the processor

404/504 is merely provided as an example, and other means for carrying out the described functions may be included within various aspects of the present disclosure, including but not limited to the instructions stored in the computer-readable storage medium 406/506, or any other suitable apparatus or means described in any one of the FIGs. 1, 2, 6, 7, 8, and/or 10, and utilizing, for example, the processes and/or algorithms described herein in relation to FIGs. 6-13.

[0106] Several aspects of a wireless communication network have been presented with reference to an exemplary implementation. As those skilled in the art will readily appreciate, various aspects described throughout this disclosure may be extended to other telecommunication systems, network architectures and communication standards.

[0107] By way of example, various aspects may be implemented within other systems defined by 3 GPP, such as Long-Term Evolution (LTE), the Evolved Packet System (EPS), the Universal Mobile Telecommunication System (UMTS), and/or the Global System for Mobile (GSM). Various aspects may also be extended to systems defined by the 3rd Generation Partnership Project 2 (3GPP2), such as CDMA2000 and/or Evolution-Data Optimized (EV-DO). Other examples may be implemented within systems employing IEEE 802.1 1 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Ultra- Wideband (UWB), Bluetooth, and/or other suitable systems. The actual telecommunication standard, network architecture, and/or communication standard employed will depend on the specific application and the overall design constraints imposed on the system.

[0108] Within the present disclosure, the word "exemplary" is used to mean "serving as an example, instance, or illustration." Any implementation or aspect described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other aspects of the disclosure. Likewise, the term "aspects" does not require that all aspects of the disclosure include the discussed feature, advantage or mode of operation. The term "coupled" is used herein to refer to the direct or indirect coupling between two objects. For example, if object A physically touches object B, and object B touches object C, then objects A and C may still be considered coupled to one another— even if they do not directly physically touch each other. For instance, a first object may be coupled to a second object even though the first object is never directly physically in contact with the second object. The terms "circuit" and "circuitry" are used broadly, and intended to include both hardware implementations of electrical devices and conductors that, when connected and configured, enable the performance of the functions described in the present disclosure, without limitation as to the type of electronic circuits, as well as software implementations of information and instructions that, when executed by a processor, enable the performance of the functions described in the present disclosure.

10109] One or more of the components, steps, features and/or functions illustrated in

FIGs. 1-13 may be rearranged and/or combined into a single component, step, feature or function or embodied in several components, steps, or functions. Additional elements, components, steps, and/or functions may also be added without departing from novel features disclosed herein. The apparatus, devices, and/or components illustrated in FIGs. 1-13 may be configured to perform one or more of the methods, features, or steps described herein. The novel algorithms described herein may also be efficiently implemented in software and/or embedded in hardware.

[0110] It is to be understood that the specific order or hierarchy of steps in the methods disclosed is an illustration of exemplary processes. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the methods may be rearranged. The accompanying method claims present elements of the various steps in a sample order, and are not meant to be limited to the specific order or hierarchy presented unless specifically recited therein.

[0111] The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but are to be accorded the full scope consistent with the language of the claims, wherein reference to an element in the singular is not intended to mean "one and only one" unless specifically so stated, but rather "one or more." Unless specifically stated otherwise, the term "some" refers to one or more. A phrase referring to "at least one of a list of items refers to any combination of those items, including single members. As an example, "at least one of: a, b, or c" is intended to cover: a; b; c; a and b; a and c; b and c; and a, b and c. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims.