Quasi-co-located source selection and indication on sidelinks

Abstract

Certain aspects of the present disclosure provide techniques for selecting and indicating a quasi-co-located (QCL) source signal for sidelink (SL) communications. For example, a scheduling node may select a signal from multiple candidates for a first user equipment (UE) to use as a spatial QCL source for a receive (RX) or transmit (TX) beam for communicating with a second UE over a SL interface. The scheduling node may then signal an indication of the selection of the signal to the first UE.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Application No. 17 / 137,083, filed on December 29, 2020, which in turn claims priority to U.S. Provisional Patent Application No. 62 / 955,587, filed on December 31, 2019, all of which are hereby expressly incorporated by reference in their entirety. Technical Field

[0003]

[0004] Generally speaking, aspects of the present disclosure relate to wireless communication systems and, more particularly, to techniques for selecting and indicating a quasi-co-sited (QCL) source signal for sidelink (SL) communications. Background Art

[0004] Wireless communication systems are widely deployed to provide various telecommunication services such as telephony, video, data, messaging, broadcast, and the like. These wireless communication systems may employ multiple-access technologies capable of supporting communication with multiple users by sharing available system resources (e.g., bandwidth, transmit power, etc.). Examples of such multiple-access systems include 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) systems, LTE-Advanced (LTE-A) systems, Code Division Multiple Access (CDMA) systems, Time Division Multiple Access (TDMA) systems, Frequency Division Multiple Access (FDMA) systems, Orthogonal Frequency Division Multiple Access (OFDMA) systems, Single Carrier Frequency Division Multiple Access (SC-FDMA) systems, and Time Division Synchronous Code Division Multiple Access (TD-SCDMA) systems, to name a few.

[0005] In some examples, a wireless multiple access communication system may include multiple base stations (BSs), each BS capable of simultaneously supporting communications for multiple communication devices (or user equipment (UE)). In an LTE or LTE-A network, a set of one or more base stations may define an eNodeB (eNB). In other examples (e.g., in next generation, new radio (NR) or 5G networks), a wireless multiple access communication system may include multiple distributed units (DUs) (e.g., edge units (EUs), edge nodes (ENs), radio heads (RHs), smart radio heads (SRHs), transmit receive points (TRPs), etc.) communicating with multiple central units (CUs) (e.g., central nodes (CNs), access node controllers (ANCs), etc.), where a set of one or more DUs communicating with a CU may define an access node (e.g., which may be referred to as a BS, 5G NB, next generation Node B (gNB or gNodeB), transmit receive point (TRP), etc.). A BS or DU may communicate with a group of UEs on downlink (DL) channels (eg, for transmission from the BS or DU to the UEs) and uplink (UL) channels (eg, for transmission from the UEs to the BS or DU).

[0006] These multiple access technologies have been adopted in various telecommunication standards to provide a common protocol that enables different wireless devices to communicate at a city, country, region, or even global level. NR (e.g., New Radio or 5G) is an example of an emerging telecommunication standard. NR is a set of enhancements to the LTE mobile standard released by 3GPP. NR is designed to better support mobile broadband internet access by improving spectral efficiency, reducing costs, improving services, utilizing new spectrum, and better integrating with other open standards using OFDMA with cyclic prefix (CP) on both the DL and UL. To this end, NR supports beamforming, multiple-input multiple-output (MIMO) antenna technology, and carrier aggregation.

[0007] However, as demand for mobile broadband access continues to increase, there is a need to further improve NR and LTE technologies. Preferably, these improvements can also be applied to other multi-access technologies and the telecommunication standards that adopt these technologies. Summary of the Invention

[0008] The systems, methods, and devices of the present disclosure each have several aspects, no single one of which is solely responsible for its desirable attributes. Without limiting the scope of the present disclosure as indicated by the claims that follow, some features will now be briefly discussed. After considering this discussion, and particularly after reading the section entitled "Detailed Description," those skilled in the art will understand how the features of this disclosure provide advantages, including improved communication between access points and stations in a wireless network.

[0009] Certain aspects provide a method for wireless communications by a scheduling node. The method generally includes selecting, based on one or more criteria, a signal from a plurality of candidates for use by a first user equipment (UE) as a spatially quasi-co-located (QCL) source for a receive (RX) beam or a transmit (TX) beam for communicating with a second UE on a sidelink (SL) interface; and signaling an indication of the selection to the first UE.

[0010] Certain aspects provide a method for wireless communication by a first UE. The method generally includes: receiving signaling from a scheduling node indicating selection of a signal from a plurality of candidates based on one or more criteria for the first UE to use as a QCL source for an RX beam or a TX beam for communicating with a second UE over a SL interface; and communicating with the second UE over the SL interface using the RX beam or the TX beam determined based on the indicated selection.

[0011] Certain aspects provide means, devices, and / or computer-readable media having computer-executable code stored thereon for performing the techniques described herein.

[0012] To accomplish the foregoing and related ends, one or more aspects include the features fully described below and particularly pointed out in the claims. The following description and accompanying drawings describe in detail certain exemplary features of one or more aspects. However, these features are indicative of only some of the various ways in which the basic principles of the various aspects can be employed. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order that the above-described features of the present disclosure may be understood in detail, a more particular description of what has been briefly summarized above may be had by reference to various aspects, some of which are illustrated in the accompanying drawings. It should be noted, however, that the drawings illustrate only certain typical aspects of the disclosure and are not to be considered limiting of its scope, as the description may admit to other equally effective aspects.

[0014] Figure 1 is a block diagram conceptually illustrating an example telecommunications system in accordance with certain aspects of the present disclosure.

[0015] Figure 2 is a block diagram conceptually illustrating designs of example base stations (BSs) and user equipment (UEs) in accordance with certain aspects of the present disclosure.

[0016] Figure 3 An example of a frame format for a telecommunications system is shown, in accordance with certain aspects of the present disclosure.

[0017] Figure 4 An example beam management process is shown in accordance with certain aspects of the present disclosure.

[0018] Figure 5A and Figure 5B A diagrammatic representation of an example vehicle-to-everything (V2X) system is shown, in accordance with certain aspects of the present disclosure.

[0019] Figure 6 An example sidelink (SL) communication mode is shown in accordance with certain aspects of the present disclosure.

[0020] Figure 7 Examples of transmission configuration indicator (TCI) state information for signaling quasi co-location (QCL) information are shown, in accordance with certain aspects of the present disclosure.

[0021] Figure 8 An example QCL relationship between source and target reference signals is graphically illustrated, in accordance with certain aspects of the present disclosure.

[0022] Figure 9 An overview of beam indication for a cellular interface is shown, in accordance with certain aspects of the present disclosure.

[0023] Figure 10 is a flow diagram illustrating example operations that may be performed by a scheduling node in accordance with certain aspects of the present disclosure.

[0024] Figure 11 is a flow diagram illustrating example operations that may be performed by a UE in accordance with certain aspects of the present disclosure.

[0025] Figure 12 Examples of possible spatial QCL sources for SL interfaces according to certain aspects of the present disclosure are shown.

[0026] Figure 13 A communication device according to aspects of the present disclosure is shown that may include various components configured to perform operations for the techniques disclosed herein.

[0027] Figure 14A communication device according to aspects of the present disclosure is shown that may include various components configured to perform operations for the techniques disclosed herein.

[0028] To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one aspect may be beneficially applied to other aspects without specific recitation. DETAILED DESCRIPTION

[0029] Various aspects of the present disclosure relate to wireless communications, and more particularly, to techniques for selecting and indicating a quasi-co-located (QCL) source signal for sidelink (SL) communications. The QCL source signal indication can allow a user equipment (UE) to determine the receive (RX) beam or transmit (TX) beam to be used for reception or transmission on the SL interface. The techniques can be applied to new radio (NR) access technology or fifth generation (5G) technology.

[0030] The following description provides examples of QCL source signal selection and indication for SL communication, but is not intended to limit the scope, applicability, or examples set forth in the claims. The functions and arrangements of the elements discussed may be changed without departing from the scope of the present disclosure. Various examples may omit, substitute, or add various processes or components as needed. For example, the methods described may be performed in an order different from that described, and various steps may be added, omitted, or combined. In addition, features described with respect to some examples may be combined in other examples. For example, an apparatus may be implemented or a method may be implemented using any number of the aspects set forth herein. In addition, the scope of the present disclosure is intended to cover such an apparatus or method implemented using other structures, functions, or structures and functions in addition to or different from the various aspects of the disclosure set forth herein. It should be understood that any aspect of the disclosure disclosed herein may be embodied by one or more elements of the claims. The word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any aspect described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other aspects.

[0031] The techniques described herein can be used for various wireless communication technologies, such as Long Term Evolution (LTE), Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Orthogonal Frequency Division Multiple Access (OFDMA), Single Carrier Frequency Division Multiple Access (SC-FDMA), and other networks. The terms "network" and "system" are often used interchangeably. A CDMA network can implement radio technologies such as Universal Terrestrial Radio Access (UTRA), CDMA 2000, and the like. UTRA includes Wideband CDMA (WCDMA) and other variants of CDMA. CDMA 2000 covers IS-2000, IS-95, and IS-856 standards. A TDMA network can implement radio technologies such as Global System for Mobile Communications (GSM). An OFDMA network may implement a radio technology such as NR (e.g., 5G RA), Evolved UTRA (E-UTRA), Ultra Mobile Broadband (UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDMA, etc. UTRA and E-UTRA are part of the Universal Mobile Telecommunications System (UMTS).

[0032] NR is an emerging wireless communication technology under development in conjunction with the 5G Technology Forum (5GTF). 3GPP LTE and Advanced LTE (LTE-A) are versions of UMTS that use E-UTRA. UTRA, E-UTRA, UMTS, LTE, LTE-A, and GSM are described in documents from an organization named "3rd Generation Partnership Project" (3GPP). CDMA2000 and UMBS are described in documents from an organization named "3rd Generation Partnership Project 2" (3GPP2). The techniques described herein can be used for the wireless networks and radio technologies mentioned above, as well as other wireless networks and radio technologies. For clarity, although terms commonly associated with 3G and / or 4G wireless technologies are used herein to describe various aspects, various aspects of the present disclosure may also be applied to communication systems based on other generations (such as 5G and later versions, including NR technology).

[0033] NR access (e.g., 5G technology) can support various wireless communication services, such as enhanced mobile broadband (eMBB) targeting wide bandwidth (e.g., 80 MHz or above), millimeter wave (mmW) targeting high carrier frequency (e.g., 25 GHz or above), massive machine type communication MTC (mMTC) targeting non-backward compatible MTC technology, and / or mission-critical services targeting ultra-reliable low-latency communication (URLLC). These services may include latency and reliability requirements. These services may also have different transmission time intervals (TTIs) to meet corresponding quality of service (QoS) requirements. In addition, these services can coexist in the same subframe.

[0034] Example Wireless Communication System

[0035] Figure 1 An example wireless communication network 100 is shown in which aspects of the present disclosure may be implemented. For example, Figure 1 The user equipment (UE) 120 and / or base station (BS) 110 may be configured to perform the following reference Figure 10 and / or Figure 11 Operations are described to select and instruct a quasi-co-located (QCL) source for sidelink (SL) communications.

[0036] like Figure 1 As shown in FIG, a wireless communication network 100 may include multiple base stations (BSs) 110 and other network entities. A BS may be a station that communicates with a user equipment (UE). Each BS 110 may provide communication coverage for a specific geographic area. In 3GPP, the term "cell" may refer to the coverage area of ​​a Node B (NB) and / or the NB subsystem serving that coverage area, depending on the context in which the term is used. In NR systems, the term "cell" and next-generation Node B (gNB or gNodeB), NR BS, 5G NB, access point (AP), or transmit / receive point (TRP) may be interchangeable. In some examples, a cell may not necessarily be stationary, and the geographic area of ​​a cell may move depending on the location of a mobile BS. In some examples, base stations may interconnect with each other and / or with one or more other base stations or network nodes (not shown) in the wireless communication network 100 using any suitable transport network via various types of backhaul interfaces (e.g., direct physical connections, wireless connections, virtual networks, etc.).

[0037] In general, any number of wireless networks can be deployed in a given geographic area. Each wireless network can support a specific radio access technology (RAT) or can operate on one or more frequencies. RAT can also be referred to as radio technology, air interface, etc. Frequency can also be referred to as carrier, subcarrier, frequency channel, tone, subband, etc. Each frequency can support a single RAT in a given geographic area to avoid interference between wireless networks of different RATs. In some cases, NR or 5G RAT networks can be deployed.

[0038] A BS may provide communication coverage for macro cells, pico cells, femto cells, and / or other types of cells. A macro cell may cover a relatively large geographic area (e.g., a radius of several kilometers) and may allow unrestricted access by UEs with service subscriptions. A pico cell may cover a relatively small geographic area and may allow unrestricted access by UEs with service subscriptions. A femto cell may cover a relatively small geographic area (e.g., a residence) and may allow restricted access by UEs associated with the femto cell (e.g., UEs in a closed subscriber group (CSG), UEs for users in a home, etc.). A BS for a macro cell may be referred to as a macro BS. A BS for a pico cell may be referred to as a pico BS. A BS for a femto cell may be referred to as a femto BS or a home BS. In Figure 1 In the illustrated example, BSs 110a, 110b, and 110c may be macro BSs for macrocells 102a, 102b, and 102c, respectively. BS 110x may be a pico BS for picocell 102x. BSs 110y and 110z may be femto BSs for femtocells 102y and 102z, respectively. A BS may support one or more (e.g., three) cells.

[0039] The wireless communication network 100 may also include a relay station. A relay station is a station that receives transmissions of data and / or other information from an upstream station (e.g., a BS or a UE) and sends transmissions of data and / or other information to a downstream station (e.g., a UE or a BS). A relay station may also be a UE that relays transmissions for other UEs. Figure 1 In the illustrated example, a relay station 110r may communicate with a BS 110a and a UE 120r to facilitate communication between the BS 110a and the UE 120r. A relay station may also be referred to as a relay BS, a relay, or the like.

[0040] The wireless communication network 100 may be a heterogeneous network including different types of BSs (e.g., macro BSs, pico BSs, femto BSs, relays, etc.). These different types of BSs may have different transmit power levels, different coverage areas, and different impacts on interference in the wireless communication network 100. For example, a macro BS may have a high transmit power level (e.g., 20 watts), while a pico BS, a femto BS, and a relay may have a lower transmit power level (e.g., 1 watt).

[0041] The wireless communication network 100 can support synchronous or asynchronous operation. For synchronous operation, the BSs can have similar frame timing, and transmissions from different BSs can be approximately aligned in time. For asynchronous operation, the BSs can have different frame timing, and transmissions from different BSs can be misaligned in time. The techniques described herein can be used for both synchronous and asynchronous operation.

[0042] The network controller 130 may be coupled to a group of BSs and provide coordination and control for these BSs. The network controller 130 may communicate with the BSs 110 via a backhaul. The BSs 110 may also communicate with each other via a wireless backhaul or a wired backhaul (eg, directly or indirectly).

[0043] UEs 120 (e.g., UE 120x, UE 120y, etc.) may be dispersed throughout the wireless communication network 100, and each UE may be stationary or mobile. A UE may also be referred to as a mobile station, terminal, access terminal, subscriber unit, station, customer premises equipment (CPE), cellular phone, smart phone, personal digital assistant (PDA), wireless modem, wireless communication device, handheld device, laptop computer, cordless phone, wireless local loop (WLL) station, tablet computer, camera, gaming device, netbook, smartbook, ultrabook, appliance, medical device or medical apparatus, biosensor / device, wearable device such as smart watch, smart clothing, smart glasses, smart wristband, smart jewelry (e.g., smart wristband, smart bracelet, etc.), entertainment device (e.g., music device, video device, satellite radio unit, etc.), vehicle component or sensor, smart meter / sensor, industrial manufacturing equipment, global positioning system device, or any other suitable device configured to communicate via wireless or wired medium. Some UEs may be considered machine type communication (MTC) devices or evolved MTC (eMTC) devices. For example, MTC and eMTC UEs include robots, drones, remote devices, sensors, meters, monitors, location tags, and the like that can communicate with a BS, another device (e.g., a remote device), or some other entity. A wireless node may provide connectivity to or to a network (e.g., a wide area network such as the Internet or a cellular network) via, for example, a wired or wireless communication link. Some UEs may be considered Internet of Things (IoT) devices, which may be narrowband IoT (NB-IoT) devices.

[0044] Some wireless networks (e.g., LTE) utilize orthogonal frequency division multiplexing (OFDM) on the downlink (DL) and single-carrier frequency division multiplexing (SC-FDM) on the uplink (UL). OFDM and SC-FDM divide the system bandwidth into multiple (K) orthogonal subcarriers, also commonly referred to as tones, bins, etc. Each subcarrier can be modulated with data. Typically, modulation symbols are sent in the frequency domain with OFDM and in the time domain with SC-FDM. The spacing between adjacent subcarriers can be fixed, and the total number of subcarriers (K) can depend on the system bandwidth. For example, the subcarrier spacing can be 15 kHz, and the minimum resource allocation (called a "resource block" (RB)) can be 12 subcarriers (or 180 kHz). Therefore, for system bandwidths of 1.25, 2.5, 5, 10, or 20 megahertz (MHz), the nominal fast Fourier transform (FFT) size can be equal to 128, 256, 512, 1024, or 2048, respectively. The system bandwidth may also be partitioned into subbands. For example, a subband may cover 1.08 MHz (ie, 6 resource blocks), and there may be 1, 2, 4, 8, or 16 subbands for system bandwidths of 1.25, 2.5, 5, 10, or 20 MHz, respectively.

[0045] While aspects of the examples described herein may be associated with LTE technology, aspects of the present disclosure may be applicable to other wireless communication systems, such as NR. NR can utilize OFDM with CP on both the UL and DL, and includes support for half-duplex operation using TDD. Beamforming can be supported, and the beam direction can be dynamically configured. MIMO transmission with precoding can also be supported. MIMO configurations in the DL can support up to 8 transmit antennas with up to 8 streams and multi-layer DL transmission of up to 2 streams per UE. Multi-layer transmission of up to 2 streams per UE can be supported. Aggregation of multiple cells up to 8 serving cells can be supported.

[0046] In some examples, access to the air interface can be scheduled. A scheduling entity (e.g., BS) allocates resources for communications between some or all devices and equipment within its service area or cell. A scheduling entity can be responsible for scheduling, allocating, reconfiguring, and releasing resources for one or more subordinate entities. That is, for scheduled communications, subordinate entities utilize resources allocated by the scheduling entity. A base station is not the only entity that can act as a scheduling entity. In some examples, a UE can act as a scheduling entity and can schedule resources for one or more subordinate entities (e.g., one or more other UEs), and other UEs can utilize the resources scheduled by the UE for wireless communications. In some examples, a UE can act as a scheduling entity in a peer-to-peer (P2P) network and / or a mesh network. In the mesh network example, in addition to communicating with the scheduling entity, UEs can also communicate directly with each other.

[0047] exist Figure 1 , a solid line with double arrows indicates desired transmissions between a UE and a serving BS, which is a BS designated to serve the UE on DL and / or UL. A thin dashed line with double arrows indicates interfering transmissions between the UE and the BS.

[0048] Figure 2 Shown (for example, in Figure 1 1 and 2. Example components of a BS 110a and a UE 120a in a wireless communication network 100 of FIG.

[0049] At BS 110, transmit processor 220 may receive data from data source 212 and control information from controller / processor 240. The control information may be for a physical broadcast channel (PBCH), a physical control format indicator channel (PCFICH), a physical hybrid ARQ indicator channel (PHICH), a physical downlink control channel (PDCCH), a group common PDCCH (GC PDCCH), etc. Data may be for a physical downlink shared channel (PDSCH), etc. A medium access control (MAC) control element (MAC-CE) is a MAC layer communication structure that may be used for the exchange of control commands between wireless nodes. A MAC-CE may be carried on a shared channel such as a physical downlink shared channel (PDSCH), a physical uplink shared channel (PUSCH), or a physical sidelink shared channel (PSSCH).

[0050] The transmit processor 220 can process the data and control information (e.g., encode and symbol map) to obtain data symbols and control symbols, respectively. The transmit processor 220 can also generate reference symbols, such as for the primary synchronization signal (PSS), the secondary synchronization signal (SSS), and the cell-specific reference signal (CRS). The transmit multiple-input multiple-output (MIMO) processor 230 can perform spatial processing (e.g., precoding) on ​​the data symbols, control symbols, or reference symbols (if applicable) and provide output symbol streams to the modulators (MODs) in transceivers 232a-232t. Each MOD in transceiver 232 can process a corresponding output symbol stream (e.g., for OFDM, etc.) to obtain an output sample stream. Each MOD in transceiver 232 can further process (e.g., convert to analog, amplify, filter, and upconvert) the output sample stream to obtain a DL signal. The DL signals from the MODs in transceivers 232a-232t can be transmitted via antennas 234a-234t, respectively.

[0051] At UE 120, antennas 252a-252r may receive downlink signals from BS 110 and provide received signals to demodulators (DEMODs) in transceivers 254a-254r, respectively. Each DEMOD in transceiver 254 may condition (e.g., filter, amplify, downconvert, and digitize) a corresponding received signal to obtain input samples. Each DEMOD in the transceiver may further process the input samples (e.g., for OFDM, etc.) to obtain received symbols. A MIMO detector 256 may obtain received symbols from all DEMODs in transceivers 254a-254r, perform MIMO detection on the received symbols (if applicable), and provide detected symbols. A receive processor 258 may process (e.g., demodulate, deinterleave, and decode) the detected symbols, provide decoded data for UE 120a to a data sink 260, and provide decoded control information to a controller / processor 280.

[0052] On the UL, at the UE 120, a transmit processor 264 may receive and process data from a data source 262 (e.g., for a physical uplink shared channel (PUSCH)) and control information from a controller / processor 280 (e.g., for a physical uplink control channel (PUCCH)). The transmit processor 264 may also generate reference symbols for reference signals (e.g., for a sounding reference signal (SRS)). The symbols from the transmit processor 264 may be precoded by a transmit MIMO processor 266 (if applicable), further processed by a DEMOD in transceivers 254a-254r (e.g., for SC-FDM, etc.), and transmitted to the BS 110. At the BS 110, the UL signal from the UE 120 may be received by the antenna 234, processed by the MOD in the transceiver 232, detected by the MIMO detector 236 (if applicable), and further processed by the receive processor 238 to obtain decoded data and control information transmitted by the UE 120. The receive processor 238 may provide decoded data to a data sink 239 and decoded control information to a controller / processor 240 .

[0053] Memories 242 and 282 may store data and program codes for BS 110 and UE 120, respectively. Scheduler 244 may schedule UEs for data transmission on the DL or UL.

[0054] The antennas 252, processors 266, 258, 264, and / or controller / processor 280 of the UE 120a and / or the antennas 234, processors 220, 230, 238, and / or controller / processor 240 of the BS 110a may be used to perform the various techniques and methods described herein. Figure 2 As shown in FIG, the controller / processor 240 of BS 110a may be configured to perform Figure 10 The operations shown in , and other operations disclosed herein. Figure 2 As shown in FIG, the controller / processor 280 of the UE 120a may be configured to perform Figure 10 and Figure 11 Although shown at the controller / processor level, other components of the UE 120a and BS 110a may also be used to perform the operations described herein.

[0055] Figure 33 is a diagram showing an example of a frame format 300 for NR. The transmission timeline for each of DL and UL can be divided into units of radio frames. Each radio frame can have a predetermined duration (e.g., 10 ms) and can be divided into 10 subframes indexed from 0 to 9, each subframe being 1 ms. Each subframe can include a variable number of slots depending on the subcarrier spacing. Each slot can include a variable number of symbol periods (e.g., 7 or 14 symbols) depending on the subcarrier spacing. The symbol periods in each slot can be assigned indices. A microslot, which can be referred to as a subslot structure, refers to a transmission time interval whose duration is less than a slot (e.g., 2, 3, or 4 symbols).

[0056] Each symbol in a slot may indicate the link direction (e.g., DL, UL, or flexible) used for data transmission, and the link direction used for each subframe may be dynamically switched. The link direction may be based on the slot format. Each slot may include DL / UL data and DL / UL control information.

[0057] In NR, a synchronization signal (SS) block is sent. The SS block includes PSS, SSS, and two symbols of PBCH. It can be sent at a fixed time slot position (such as Figure 3 SS blocks are transmitted on the physical downlink shared channel (PDSCH) in certain subframes, for example, up to 64 different beam directions for mmW. Up to 64 transmissions of SS blocks are called SS burst sets. The SS blocks in a SS burst set are transmitted in the same frequency region, while the SS blocks in different SS burst sets may be transmitted at different frequency positions.

[0058] Example Beam Management Process

[0059] In fifth generation (5G) New Radio (NR), various beamforming and management procedures may be used to determine and maintain beam pair links (BPLs).

[0060] For example, Figure 4An example process is shown, which is referred to as a P1 process. A base station (BS) 410 (such as BS 110a) may send a measurement request to a user equipment (UE) 420 (such as UE 120a), and may subsequently send one or more signals for measurement (sometimes referred to as "P1 signals") to UE 420. In the P1 process, BS 410 transmits a signal with beamforming in different spatial directions (corresponding to transmit beams (TX beams) 411, 412, ..., 417) in each symbol, so as to reach several (e.g., most or all) relevant spatial locations of the cell of BS 410. In this way, BS 410 transmits signals using different TX beams in different directions over time. In some examples, a synchronization signal block (SSB) is used as the P1 signal. In some examples, a channel state information reference signal (CSI-RS), a demodulation reference signal (DMRS), or another downlink (DL) signal may be used as the P1 signal.

[0061] During the P1 process, in order to successfully receive at least one symbol of the P1 signal, the UE 420 searches for (e.g., determines / selects) an appropriate receive beam (RX beam) (421, 422, ..., 426). For a given signal index (e.g., SSB index) corresponding to a given time period, signals (e.g., SSBs) from multiple BSs can be measured simultaneously. The UE 420 can apply a different RX beam during each occurrence (e.g., each symbol) of the P1 signal. Once the UE 420 successfully receives a symbol of the P1 signal, the UE 420 and the BS 410 have found the BPL (i.e., the UE RX beam for receiving the P1 signal in the symbol, and the BS TX beam for transmitting the P1 signal in the symbol). In some cases, the UE 420 does not search all possible UE RX beams before it finds the best UE RX beam, as this results in additional latency. Alternatively, once the RX beam is "good enough" (e.g., has a quality (e.g., signal-to-noise ratio (SNR) or signal-to-interference-plus-noise ratio (SINR)) that meets a threshold (e.g., a predefined threshold), the UE 420 can select the RX beam. The UE 420 may not know which beam the BS 410 is using to transmit the P1 signal in the symbol; however, the UE 420 can report to the BS 410 the time when it observed the signal. For example, the UE 420 can report to the BS 410 the symbol index in which the P1 signal was successfully received. The BS 410 can receive the report and determine which BS TX beam the BS 410 used at the indicated time. In some examples, the UE 420 measures the signal quality of the P1 signal, such as reference signal received power (RSRP) or another signal quality parameter (e.g., SNR, channel flatness, etc.). The UE 420 can report the measured signal quality (e.g., RSRP) along with the symbol index to the BS 410. In some cases, the UE 420 may report a plurality of symbol indices corresponding to a plurality of BS TX beams to BS 410 .

[0062] As part of the beam management process, the BPL used between the UE 420 and the BS 110 may be refined / changed. For example, the BPL may be periodically refined to adapt to changing channel conditions (e.g., due to movement of the UE 420 or other objects, fading due to Doppler spread, etc.). The UE 420 may monitor the quality of the BPL (e.g., the BPL found / selected in the P1 process and / or the previously refined BPL) to refine the BPL when the quality degrades (e.g., when the BPL quality drops below a threshold or another BPL has higher quality). In 5G NR, the beam management process for BPL beam refinement may be referred to as the P2 and P3 processes to refine the BS beam and UE beam of a single BPL, respectively.

[0063] like Figure 4 As shown in , for the P2 process, BS 410 transmits symbols of a signal using different BS beams (e.g., TX beams 415, 414, 413) that are spatially close to the BS beam of the current BPL. For example, BS 410 transmits signals in different symbols using adjacent TX beams around the TX beam of the current BPL (e.g., beam scanning). Figure 4 As shown in , the TX beam used by BS 410 for the P2 process may be different from the TX beam used by BS 410 for the P1 process. For example, the TX beam used by BS 410 for the P2 process may be spaced closer together and / or may be more focused (e.g., narrower) than the TX beam used by BS 410 for the P1 process. During the P2 process, UE 420 maintains its RX beam (e.g., RX beam 424) constant. UE 420 may measure the signal quality (e.g., RSRP) of the signal in different symbols and indicate the symbol in which the highest signal quality was measured. Based on the indication, BS 410 may determine the strongest (e.g., best, or associated with the highest signal quality) TX beam (i.e., the TX beam used in the indicated symbol). The BPL may be refined accordingly to use the indicated TX beam.

[0064] like Figure 4 As shown in FIG, for the P3 process, BS 420 maintains a constant TX beam (e.g., the TX beam of the current BPL) and uses a constant TX beam (e.g., TX beam 414) to transmit symbols of the signal. During the P3 process, UE 420 uses different RX beams (e.g., RX beams 423, 424, 425) in different symbols to scan for signals. For example, UE 420 may perform scanning using an RX beam adjacent to the RX beam in the current BPL (i.e., the BPL being refined). UE 420 may measure the signal quality (e.g., RSRP) of the signal for each RX beam and identify the strongest UE RX beam. UE 420 may use the identified RX beam for the BPL. UE 420 may report the signal quality to BS 410.

[0065] Example Sidelink Scenario

[0066] In some cases, two or more slave entities (e.g., user equipment (UE)) may communicate with each other using sidelink (SL) signals. Practical applications of such SL communications may include public safety, proximity services, UE-to-network relay, vehicle-to-vehicle (V2V) communications, Internet of Everything (IoE) communications, Internet of Things (IoT) communications, mission-critical grids, and / or various other appropriate applications. Generally, an SL signal may refer to a signal that is transmitted from one slave entity (e.g., UE1) to another slave entity (e.g., UE2) without relaying the communication through a scheduling entity (e.g., UE or BS), although the scheduling entity may be used for scheduling and / or control purposes. In some examples, licensed spectrum may be used to transmit SL signals (unlike wireless local area networks that typically use unlicensed spectrum).

[0067] Figure 5A and Figure 5B A diagrammatic representation of an example vehicle-to-everything (V2X) system is shown in accordance with certain aspects of the present disclosure. For example, Figure 5A and Figure 5B The vehicles shown in can communicate via a sidelink channel and can perform SL channel state information (CSI) reporting as described herein.

[0068] Figure 5A and Figure 5B The V2X system described in [1] provides two complementary transmission modes. The first transmission mode (based on Figure 5A The second transmission mode (shown by way of example in FIG. 1 ) involves direct communication (e.g. also referred to as sidelink communication) between participants that are close to each other in a local area. Figure 5B ) involves network communication through a network, which may be implemented through a Uu interface (e.g., a wireless communication interface between a radio access network (RAN) and a UE).

[0069] refer to Figure 5A , a V2X system 500 (e.g., including V2V communications) is shown with two vehicles 502, 504. A first transmission mode allows direct communication between different participants in a given geographic location. As shown, the vehicles can have a wireless communication link 506 (V2P) with an individual through a PC5 interface (e.g., via a UE). Communication between vehicles 502 and 504 can also occur through a PC5 interface 508. In a similar manner, communication (V2I) can occur from vehicle 502 to other highway components (e.g., highway component 510) such as traffic signals or signs through a PC5 interface 512. Figure 5AEach communication link shown in can enable bidirectional communication between elements, so each element can be both a transmitter and a receiver of information. The V2X system 500 can be a self-managed system implemented without the assistance of a network entity. Because no network service interruption occurs during handover operations of a moving vehicle, the self-managed system can achieve improved spectrum efficiency, reduced costs, and increased reliability. The V2X system 500 can be configured to operate in a licensed or unlicensed spectrum, so any vehicle equipped with the system can access common frequencies and share information. Such coordinated / shared spectrum operation allows for safe and reliable operation.

[0070] Figure 5B A V2X system 550 is shown for communicating between vehicle 552 and vehicle 554 via network entity 556. These network communications can occur through discrete nodes, such as base stations (BSs) (e.g., eNBs or gNBs), which send and receive information to and from vehicles 552, 554 (e.g., relay information between them). Network communications via vehicle-to-network (V2N) links 558 and 510 can be used, for example, for long-distance communications between vehicles 552, 554, such as for communicating a car accident some distance ahead along a road or highway. Other types of communications can be sent by the nodes to vehicles 552, 554, such as traffic flow conditions, road hazard warnings, environmental / weather reports, and service station availability. Such data can be obtained from cloud-based sharing services.

[0071] In some cases, two or more slave entities (e.g., UEs) may communicate with each other using SL signals. As described above, V2V and V2X communications are examples of communications that may be transmitted via SL. Other applications of SL communications may include public safety or service announcement communications, communications for proximity services, communications for UE to network relay, device to device (D2D) communications, IoE communications, IoT communications, mission-critical mesh communications, and other suitable applications. Generally, SL may refer to a direct link between one slave entity (e.g., UE1) and another slave entity (e.g., UE2). In this way, SL may be used to send and receive communications (also referred to herein as "SL signals") without relaying the communications through a scheduling entity (e.g., BS), even though the scheduling entity may be used for scheduling or control purposes. In some examples, licensed spectrum may be used to transmit SL signals (unlike wireless local area networks that typically use unlicensed spectrum).

[0072] Various SL channels can be used for SL communication, including the physical sidelink discovery channel (PSDCH), the physical sidelink control channel (PSCCH), the physical sidelink shared channel (PSSCH), and the physical sidelink feedback channel (PSFCH). The PSDCH can carry discovery expressions that enable neighboring devices to discover each other. The PSCCH can carry control signaling (such as sidelink resource configuration and other parameters for data transmission), and the PSSCH can carry data transmission.

[0073] For operations on the PSSCH, the UE performs transmission or reception in a slot on a carrier. For the UE, New Radio (NR) SL supports a case where all symbols in a slot are available for SL, and another case where only a subset of consecutive symbols in a slot are available for SL.

[0074] The PSFCH can carry feedback, such as CSI related to the SL channel quality. A sequence-based PSFCH format with one symbol (excluding the automatic gain control (AGC) training period) can be supported. The following formats are possible: a PSFCH format based on PUCCH format 2 and a PSFCH format that spans all available symbols for the SL in a time slot.

[0075] Figure 6 Provides an overview of SL communication (broadcast and multicast device-to-device or D2D) between UEs. As noted above, reference Figure 5A and Figure 5B ,SL usually refers to a link between two users or user ,relays and can be used in different scenarios and different ,applications.

[0076] For example, for applications with in-coverage operation, two users are within the coverage of a gNodeB (gNB) but communicate directly. In-coverage operation can be assumed to enable some gaming applications. For applications with partial-coverage operation, one UE is within coverage and acts as a relay to extend the coverage of other users. For applications with out-of-coverage operation, users are outside the coverage of the gNB but still need to communicate. Out-of-coverage operation is important for mission-critical applications such as V2X and public safety.

[0077] like Figure 6 As shown in , resource allocation for SL communication can be done in different ways. In a first mode, such as Mode 1, the gNB schedules the SL resources to be used by the UE for SL transmission.

[0078] For the second mode, such as Mode 2, the UE determines the SL resources (the gNB does not schedule SL transmission resources within the SL resources configured by the gNB / network). The UE autonomously selects SL resources for transmission. The UE can assist in SL resource selection for other UEs. The UE can be configured with an NR Configuration Grant (CG) for SL transmission, and the UE can schedule SL transmission for other UEs.

[0079] Example Quasi Co-location (QCL) Signaling

[0080] In many cases, it is important for a user equipment (UE) to know which assumptions the UE can make about the channels corresponding to different transmissions. For example, the UE may need to know which reference signals (RS) the UE can use to estimate the channel in order to decode a transmitted signal, such as the physical downlink control channel (PDCCH) or the physical downlink shared channel (PDSCH). It may also be important for the UE to be able to report relevant channel state information (CSI) to the base station (BS) (e.g., gNB) for scheduling, link adaptation, and / or beam management purposes. In New Radio (NR), information about these assumptions is conveyed using the concepts of Quasi Co-location (QCL) and Transmission Configuration Indicator (TCI) states.

[0081] The QCL assumption is typically defined based on channel characteristics. According to 3GPP TS 38.214, "Two antenna ports are said to be quasi-co-located if the characteristics of the channel over which the symbols on one antenna port are transmitted can be inferred from the channel over which the symbols on the other antenna port are transmitted." Different reference signals are considered to be quasi-co-located ("QCL'd") if a receiver (e.g., a UE) can apply the channel characteristics determined by detecting the first reference signal to help detect the second reference signal. The TCI state typically includes configurations such as the QCL relationship, for example, the QCL relationship between the downlink (DL) RS and the PDSCH demodulation RS (DMRS) ports in one channel state information RS CSI-RS set.

[0082] In some cases, a UE can be configured with up to M TCI states. The configuration of the M TCI states can be achieved through higher layer signaling, and the UE can be signaled to decode the PDSCH based on the detected PDCCH (which has downlink control information (DCI) indicating one of the TCI states). For example, a specific TCI state can be indicated by an N-bit DCI field for the PDSCH. Each configured TCI state can include an RS set TCI-RS-SetConfig, which indicates different QCL assumptions between certain source and target signals.

[0083] In some deployments, in scenarios involving multiple cells (e.g., coordinated multi-point (CoMP) scenarios where multiple transmit receive points (TRPs) or integrated access backhaul (IAB) nodes each have their own cell ID), techniques are used to provide QCL signaling for RSs and channels.

[0084] Figure 7 An example of how RS associated with a TCI state can be configured via radio resource control (RRC) signaling is shown. In some cases, the QCL information and / or type may be dependent on or based on other information. For example, the QCL type indicated to the UE may be based on a higher layer parameter QCL-Type and may be one of the following types or a combination thereof:

[0085] QCL-TypeA: {Doppler shift, Doppler spread, average delay, delay spread},

[0086] QCL-TypeB: {Doppler shift, Doppler spread},

[0087] QCL-TypeC: {average delay, Doppler shift}, and

[0088] QCL-TypeD: {spatial reception parameters},

[0089] A spatial QCL assumption (QCL-Type D) may be used to help the UE select an analog receive (Rx) beam (e.g., during a beam management procedure). For example, a synchronization signal (SS) block resource indicator may indicate that the same beam used for a previous reference signal should be used for subsequent transmissions.

[0090] like Figure 7 As shown in , the TCI state can indicate which RSs are QCL and the QCL type. The TCI state can also indicate the ServCellIndex, which is a short identifier used to identify the serving cell, such as the primary cell (PCell) or secondary cell (Scell) in a carrier aggregation (CA) deployment. A value of 0 for this field can indicate the PCell, while a previously assigned SCellIndex can be applied to the SCell.

[0091] Figure 8 An example of association of a DL RS with a corresponding QCL type that can be indicated through TCI-RS-SetConfig is shown.

[0092] exist Figure 8In the example of , the source RS is indicated in the top block and is associated with the target signal indicated in the bottom block. In this context, the target signal refers to a signal for which the channel properties of the associated source signal can be inferred by measuring those channel properties. As noted above, the UE can use the source RS to determine various channel parameters (depending on the associated QCL type) and use those various channel characteristics (determined based on the source RS) to process the target signal. The target RS does not necessarily need to be the DMRS of the PDSCH, to be precise, it can be any other RS: physical uplink shared channel (PUSCH) DMRS, CSI-RS, tracking RS (TRS) and sounding RS (SRS).

[0093] As shown, each TCI-RS-SetConfig contains some parameters. For example, these parameters can configure the QCL relationship between the RSs in the RS set and the DM-RS port group of the PDSCH. The RS set contains references to one or two DL RSs and the associated QCL-Type for each DL RS, which is configured by the higher-layer parameter QCL-Type.

[0094] like Figure 8 As shown in , for the case of two DL RSs, the QCL type can be arranged in multiple ways. For example, the QCL type can be different whether the reference is to the same DL RS or different DL RSs. In the example shown, the SSB is associated with Type C QCL for P-TRS, while the CSI-RS for beam management (CSIRS-BM) is associated with Type D QCL.

[0095] Example QCL source selection and indication on the sidelink

[0096] Aspects of the present disclosure relate to wireless communications and, more particularly, to techniques for selecting and indicating a quasi-co-located (QCL) source signal for sidelink (SL) communications. As noted above, the QCL source indication may allow a user equipment (UE) to determine a receive beam (RX beam) or transmit beam (TX beam) for reception or transmission on a SL interface.

[0097] Figure 9The possible QCL sources for beam indication for the New Radio (NR) cellular (Uu) interface are summarized. As shown, according to the first option, the beam indication for some transmissions can be trained directly, which means that the beams can be instructed by signals in the same direction (for example, the RX beam can be trained directly using the downlink (DL) signal, while the TX beam can be trained directly using the uplink (UL) signal). According to the second option ("vice versa"), the beam in one direction can be trained using the signal in the other direction (for example, the RX beam can be trained using the UL signal, while the TX beam can be trained using the DL signal).

[0098] As shown, for reception (DL RX), the physical downlink control channel (PDCCH) and the physical downlink shared channel (PDSCH) can be indicated via the transmission configuration indicator (TCI) state configuration as being spatially QCLed ("QCL-D") with signals including synchronization signal blocks (SSBs) and channel state information reference signals (CSI-RSs). In other words, this QCL indication means that the UE can receive the PDCCH and / or PDSCH using the same RX beam it uses for SSBs and / or CSI-RSs.

[0099] For UL transmission (UL TX), signals such as the physical uplink control channel (PUCCH), physical uplink shared channel (PUSCH), and / or sounding reference signal (SRS) may be indicated as being QCL-D with respect to SSB and / or CSI-RS (e.g., assuming channel reciprocity) or SRS (configured via signalSpatialRelationInfo). In other words, this QCL indication means that the UE may transmit PUCCH, PUSCH, or SRS using the same RX beam used for receiving SSB or CSI-RS or using the same TX beam used for SRS transmission.

[0100] like Figure 9 As shown in

[15] , reciprocity-based “reverse” training of beams in one direction based on signals in the other direction may have limited applicability in Uu applications. This may be due to differences in transmission characteristics between the gNB and UE (e.g., different transmit powers and different knowledge of transmission scheduling).

[0101] Various aspects of the present disclosure provide mechanisms for signaling spatial QCL sources that can be used as beam indicators for SL communications. In some cases, these mechanisms can exploit the relative similarities and / or differences between UEs communicating via SL (such as when a UE is performing or has performed beam scanning).

[0102] Figure 10is a flow diagram illustrating example operations 1000 that may be performed by a scheduling node in accordance with certain aspects of the present disclosure. Operations 1000 may be performed by any node that performs scheduling functions, such as a gNB (e.g., Figure 1 or Figure 2 10a) or a SL node (e.g., it actually participates in the corresponding SL communication with another SL node). The SL node may be a UE (e.g., such as Figure 1 or Figure 2 UE 120a in.

[0103] Operations 1000 begin at 1002 by selecting a signal from a plurality of candidates based on one or more criteria for use by a first UE as a spatial QCL source for a receive beam or a transmit beam for communicating with a second UE over a SL interface.

[0104] At 1004, the scheduling node signals an indication of the selection to the first UE.

[0105] Figure 11 1 is a flow chart illustrating example operations 1100 that may be performed by a first UE (e.g., a SL node) according to certain aspects of the present disclosure. Operation 1100 may be considered to be in addition to operation 1000. For example, operation 1100 may be performed by the SL node to determine a beam to be used for SL communications scheduled by a scheduling node performing operation 1000. The SL node may be a UE (e.g., such as Figure 1 or Figure 2 UE 120a in.

[0106] Operations 1100 begin at 1102 by receiving signaling from a scheduling node indicating selection of a signal from a plurality of candidates based on one or more criteria for a first UE to use as a spatial QCL source for an RX beam or a TX beam for communicating with a second UE over a SL interface.

[0107] At 1104, the first UE communicates with the second UE on the SL interface using the RX beam or the TX beam determined based on the indicated selection.

[0108] In some cases, a UE (e.g. Figure 12 The SL reception (SL Rx) of the UE2 in FIG. 1 may be indicated based on any other SL signal that the UE must receive (e.g., similar to the SL for Figure 9 In other cases, the SL RX beam may be indicated based on another SL signal sent by the UE (e.g., similar to that shown for option 1 of the Uu table). Figure 9 "vice versa" case of Option 2 of the Uu table).

[0109] In some cases, the SL transmit (SL TX) beam for UE2 may also be based on another TX channel from UE2 (similar to the "direct training" case for Uu, i.e. option 1 in the table) or based on the SL RX beam of UE2 (similar to the "vice versa" case for Uu, i.e. option 2 in the table).

[0110] Refer to using UE2 as a reference point for SL RX and SL TX beams Figure 12 To explain the mechanism proposed in this paper for indicating spatial QCL (QCL-D) sources. Figure 12 The left side of the figure shows an example of Uu signaling between the gNB and UE2, where the gNB provides QCL indications. As indicated by the dashed line, for DL ​​RX beam indications, the DL signal can be used as the QCL source. For UL TX beam indications, as indicated by the two dashed lines, either the UL signal (according to option 1) or the DL signal (according to option 2) can be used as the QCL source.

[0111] Figure 12 The right side of FIG shows an example of SL signaling between two UEs (UE1 and UE2). As shown by the two dotted lines, for SL RX beam indication, a signal sent from UE1 to UE2 or a signal sent from UE2 to UE1 can be used as a QCL source. Similarly, for SL TX beam indication, as shown by the two dotted lines, a UL signal (according to option 1) or a DL signal (according to option 2) can be used as a QCL source.

[0112] In some cases, spatial QCL source information signaling can be transmitted (by the scheduling node) in a similar manner to Uu, using TCI state information for DL ​​or spatial relation information for UL, but with adaptation for SL (SL does not have the concept of UL and DL). As noted above, the scheduling node can be a gNB or one of the UEs participating in SL communication (e.g., UE1 or UE2).

[0113] Reference again Figure 12 For SL RX beams, in the case where UE2 receives from UE1, the beam indication may have multiple QCL-D candidate sources. The first candidate QCL source may be a signal sent from UE1 to UE2 (e.g., a channel or reference signal). The second candidate QCL source may be a signal sent from UE2 to UE1 (e.g., similar to Figure 9 and vice versa for option 2). There is currently no similar Uu DL option for this candidate option, as there is currently no mechanism for the DL RX beam to be indicated based on the UL TX beam.

[0114] For SL TX beam, in case UE2 transmits to UE1, the beam indication may also have multiple QCL-D source candidates. The third candidate QCL source may be a signal sent from UE1 to UE2 (similar to Figure 9 Uu Option 2). There is currently no similar option for Uu DL because there is currently no signaling mechanism for indicating the DL Tx beam based on the UL RX beam. A fourth candidate QCL source can be a signal sent from UE2 to UE1 (e.g., similar to Uu Option 1).

[0115] The selection (by the scheduling node) of which candidate spatial QCL source may be based on one or more selection criteria.In the case of SL, the UL / DL beam correspondence may be based on channel reciprocity and similar transmission characteristics of the UEs.

[0116] In some cases, one or more criteria can be applied so that candidate QCL sources are selected based on relative channel quality from the perspective of one UE to another. For example, the criteria can be designed so that the second or fourth candidate spatial QCL source is selected when UE1 is able to receive from UE2 with high quality (UE1 can "hear UE2's Tx" with high quality), and the first or third candidate spatial QCL source is selected when UE2 is able to receive from UE1 with high quality. An example of a UE being able to receive from another UE with higher quality than the opposite is when one UE has a higher TX power capability than the other UE.

[0117] One process for implementing the various signaling mechanism options described herein is as follows. First, the UE may be configured to send a measurement-enabling signal such that selection criteria are applied. For example, UE1 and / or UE2 may be configured to periodically transmit their reference signals (e.g., SSB or CSI-RS). The scheduling node may dynamically select between various options for RX / TX beam indication.

[0118] As noted above, UE1, UE2, or a gNB (serving UE1 or UE2) can act as a scheduler. For example, if UE1 is the scheduler, UE1 dynamically selects a candidate spatial QCL source based on recent measurements (e.g., based on a comparison of the most recent UE1-to-UE2 reference signal quality reported from UE2 relative to the UE2-to-UE1 reference signal quality measured at UE1).

[0119] UE1 may then signal the scheduling options / selected candidates to UE2 (on the QCL-D source) for RX / TX beam indication.

[0120] Another option for the selection criteria can be designed to try and save beam training resources. For example, if a UE has already scanned (or recently scanned) its wide beam on the SL (e.g. similar to the reference Figure 4 If the Uu P1 process described in the previous section is used, the selected QCL source can be a signal / channel that has already been scanned (most recently scanned) from the UE, so as to save beam training work. In this case, dynamic scheduling may not be required.

[0121] In some cases, instead of using the signal between UE1 and UE2 as the spatial QCL reference source, a signal to / from some type of reference node (e.g., Node X) can be used. For example, the signal between Node X and UE2 can be used as the spatial QCL source for the SL transmission between UE1 and UE2. For example, Node X can be another UE or gNB (e.g., the serving gNB for UE1 or UE2 or both). In this case, some type of additional ("side") information can be used (e.g., based on the relative positions of Node X, UE1, and UE2) to infer that the beam between Node X and UE2 will also benefit communication between UE1 and UE2. In this case, the QCL indication may also come from Node X to save beam training work.

[0122] Various types of signaling can be used to implement the spatial QCL source signaling mechanism described herein. For example, if a gNB is involved, Uu signaling of the measurement results can be sent to the scheduling node via radio resource control (RRC), medium access control (MAC) control element (CE), PUCCH, or PUSCH. Equivalent (or similar) SL signaling mechanisms (e.g., PSCCH, PSSCH) of RRC / MAC-CE / PUCCH / PUSCH / PDSCH can be used to transmit measurement results between UEs.

[0123] RRC / MAC-CE / DCI / PDSCH can be used to transmit spatial QCL sources for beam indication (on Uu). Similarly, SL signaling similar to RRC / MAC-CE / DCI / PUCCH / PUSCH / PDSCH (e.g., PSCCH or PSSCH) can be used to transmit QCL source equivalents (over SL).

[0124] Figure 13 A communication device 1300 is shown that may include various components (eg, corresponding to functional unit components) configured to perform operations for the techniques disclosed herein, such as Figure 10. The communication device 1300 includes a processing system 1302 coupled to a transceiver 1308 (e.g., a transmitter and / or a receiver). The transceiver 1308 is configured to transmit and receive signals for the communication device 1300, such as the various signals described herein, via an antenna 1310. The processing system 1302 is configured to perform processing functions for the communication device 1300, including processing signals to be received and / or transmitted by the communication device 1300.

[0125] The processing system 1302 includes a processor 1304 coupled to a computer-readable medium / memory 1312 via a bus 1306. In some aspects, the computer-readable medium / memory 1312 is configured to store instructions (e.g., computer-executable code) that, when executed by the processor 1304, cause the processor 1304 to perform Figure 10 , or other operations for performing the various techniques discussed herein. In certain aspects, the computer-readable medium / memory 1312 stores code for selecting 1314 and code for signaling 1316. The code for selecting 1314 may include code for selecting a signal from a plurality of candidates based on one or more criteria for the first UE to use as a spatial source for an RX beam or a TX beam for communicating with a second UE over the SL interface. The code for signaling 1316 may include code for signaling an indication of the selection to the first UE.

[0126] Processor 1304 may include circuitry configured to implement code stored in computer-readable medium / memory 1312, such as for executing Figure 10 , and other operations for performing the various techniques discussed herein. For example, processor 1304 includes circuitry for selecting 1318 and circuitry for signaling 1320. Circuitry for selecting 1318 may include circuitry for selecting a signal from a plurality of candidates based on one or more criteria for the first UE to use as a spatial source for an RX beam or a TX beam for communicating with a second UE over the SL interface. Circuitry for signaling 1320 may include circuitry for signaling an indication of the selection to the first UE.

[0127] Figure 14 A communication device 1400 is shown that may include various components (eg, corresponding to functional unit components) configured to perform operations for the techniques disclosed herein, such as Figure 11. The communication device 1400 includes a processing system 1402 coupled to a transceiver 1408 (e.g., a transmitter and / or a receiver). The transceiver 1408 is configured to transmit and receive signals for the communication device 1400, such as the various signals described herein, via an antenna 1410. The processing system 1402 is configured to perform processing functions for the communication device 1400, including processing signals to be received and / or transmitted by the communication device 1400.

[0128] The processing system 1402 includes a processor 1404 coupled to a computer-readable medium / memory 1412 via a bus 1406. In some aspects, the computer-readable medium / memory 1412 is configured to store instructions (e.g., computer-executable code) that, when executed by the processor 1404, cause the processor 1404 to perform Figure 11 , or other operations for performing the various techniques discussed herein. In certain aspects, the computer-readable medium / memory 1412 stores code 1414 for receiving and code 1416 for communicating. The code 1414 for receiving may include code for receiving signaling from a scheduling node indicating selection of a signal from a plurality of candidates based on one or more criteria for the first UE to use as a spatial QCL source for an RX beam or a TX beam for communicating with a second UE on a SL interface. The code 1416 for communicating may include code for communicating with the second UE on the SL interface using the RX beam or the TX beam determined based on the indicated selection.

[0129] Processor 1404 may include circuitry configured to implement code stored in computer-readable medium / memory 1412, such as for executing Figure 11 , and other operations for performing the various techniques discussed herein. For example, processor 1404 includes circuitry 1418 for receiving and circuitry 1420 for communicating. Circuitry 1418 for receiving may include circuitry for receiving signaling from a scheduling node indicating selection of a signal from a plurality of candidates based on one or more criteria for the first UE to use as a spatial QCL source for an RX beam or a TX beam for communicating with a second UE over a SL interface. Circuitry 1420 for communicating may include circuitry for communicating with the second UE over the SL interface using the RX beam or the TX beam determined based on the indicated selection.

[0130] Example aspects

[0131] In a first aspect, a method for wireless communication performed by a scheduling node comprises: selecting a signal from a plurality of candidates based on one or more criteria for a first user equipment (UE) to use as a spatial quasi-co-site (QCL) source for a receive beam or a transmit beam for communicating with a second UE on a sidelink interface; and signaling an indication of the selection to the first UE.

[0132] In a second aspect, alone or in combination with the first aspect, the scheduling node further signals an indication of the selection to the second UE.

[0133] In a third aspect, alone or in combination with one or more of the first and second aspects, the signal selected for use by the first UE as a spatial QCL source comprises a reference signal or channel.

[0134] In the fourth aspect, alone or in combination with one or more aspects of the first to third aspects, the candidate includes at least one of the following: a first candidate, which is used for the first UE to use a signal sent from the first UE to the second UE as a QCL source for a receive beam for receiving transmissions from the second UE; or a second candidate, which is used for the first UE to use a signal sent from the second UE to the first UE as a QCL source for a transmit beam for sending transmissions to the second UE.

[0135] In the fifth aspect, alone or in combination with one or more aspects from the first to the fourth aspects, the candidate includes at least one of the following: a first candidate for the first UE to use a signal sent from the second UE to the first UE as a QCL source for a receive beam for receiving transmissions from the second UE; or a second candidate for the first UE to use a signal sent from the first UE to the second UE as a QCL source for a transmit beam for sending transmissions to the second UE.

[0136] In a sixth aspect, alone or in combination with one or more of the first to fifth aspects, the scheduling node includes a second UE or a base station.

[0137] In the seventh aspect, either alone or in combination with one or more of aspects 1 to 6, at least one of the standards relates to differences in: a first sidelink channel quality measured based on a signal sent from a first UE to a second UE; and a second sidelink channel quality measured based on a signal sent from the second UE to the first UE.

[0138] In the eighth aspect, alone or in combination with one or more aspects from the first to the seventh aspects, the scheduling node: indicates that if the first sidelink channel quality is greater than the second sidelink channel quality, the first UE should use the signal sent from the first UE to the second UE as the spatial QCL source; or indicates that if the second sidelink channel quality is greater than the first sidelink channel quality, the first UE should use the signal sent from the second UE to the first UE as the spatial QCL source.

[0139] In a ninth aspect, either alone or in combination with one or more of aspects 1 to 8, at least one of the criteria considers whether the first UE or the second UE is currently performing or has recently completed a beam scanning transmission on the sidelink.

[0140] In the tenth aspect, alone or in combination with one or more aspects from the first to the ninth aspect, the scheduling node: indicates that if the first UE is currently performing or has recently completed a beam scanning transmission on the sidelink, the first UE should use the signal sent from the first UE to the second UE as the spatial QCL source; or indicates that if the second UE is currently performing or has recently completed a beam scanning transmission on the sidelink, the first UE should use the signal sent from the second UE to the first UE as the spatial QCL source.

[0141] In the eleventh aspect, alone or in combination with one or more aspects from the first to the tenth aspect, the candidates include: at least one candidate for a first UE to use a signal transmitted between the first UE and a reference node different from the second UE as a QCL source for a receive beam or a transmit beam for communicating with the second UE.

[0142] In a twelfth aspect, alone or in combination with one or more of the first to eleventh aspects, at least one of the criteria considers relative positions of a reference node, the first UE, and the second UE.

[0143] In a thirteenth aspect, alone or in combination with one or more of the first to twelfth aspects, the scheduling node includes a second UE or a reference node.

[0144] In the fourteenth aspect, alone or in combination with one or more of the first to thirteenth aspects, the scheduling node makes a selection based on measurement results received by the scheduling node via: if forwarded via a cellular interface, then at least one of RRC signaling, MAC CE, PUCCH or PUSCH; or if forwarded via a sidelink interface, then at least one of a sidelink equivalent or signaling mechanism similar to RRC signaling and MAC CE, PSCCH and PSSCH.

[0145] In the fifteenth aspect, alone or in combination with one or more aspects from the first to the fourteenth aspect, the scheduling node signals an indication of the selected option to the first UE via: if received via a cellular interface, at least one of RRC signaling, MAC CE, DCI or PDSCH; or if received via a sidelink interface, at least one of a sidelink equivalent or signaling mechanism similar to RRC signaling and MAC CE, PSCCH and PSSCH.

[0146] In a sixteenth aspect, a method for wireless communication performed by a first UE comprises: receiving signaling from a scheduling node, the signaling indicating selection of a signal from a plurality of candidates based on one or more criteria for the first user equipment (UE) to be used as a spatial quasi-co-site (QCL) source for a receive beam or a transmit beam for communicating with a second UE on a sidelink interface; and communicating with the second UE on the sidelink interface using the receive beam or the transmit beam determined based on the indicated selection.

[0147] In a seventeenth aspect, alone or in combination with the sixteenth aspect, the signal selected for use by the first UE as a spatial QCL source comprises a reference signal or channel.

[0148] In an eighteenth aspect, alone or in combination with one or more of the sixteenth and seventeenth aspects, the scheduling node includes a second UE or a base station.

[0149] In the nineteenth aspect, alone or in combination with one or more aspects from the sixteenth to the eighteenth aspect, the signaling: indicates that the first UE should use a signal sent from the first UE to the second UE as a spatial QCL source; or indicates that the first UE should use a signal sent from the second UE to the first UE as a spatial QCL source.

[0150] In aspect 20, alone or in combination with one or more of aspects 16 to 19, the candidate includes at least one of: a first candidate for the first UE to use a signal sent from the first UE to the second UE as a QCL source for a receive beam for receiving transmissions from the second UE; or a second candidate for the first UE to use a signal sent from the second UE to the first UE as a QCL source for a transmit beam for sending transmissions to the second UE.

[0151] In aspect 21, alone or in combination with one or more aspects from aspects 16 to 20, the candidate includes at least one of the following: a first candidate for the first UE to use a signal sent from the second UE to the first UE as a QCL source for a receive beam for receiving transmissions from the second UE; or a second candidate for the first UE to use a signal sent from the first UE to the second UE as a QCL source for a transmit beam for sending transmissions to the second UE.

[0152] In aspect 22, alone or in combination with one or more aspects from aspects 16 to 21, the candidates include: at least one candidate for a first UE to use a reference signal transmitted between the first UE and a reference node different from the second UE as a QCL source for a receive beam or a transmit beam for communicating with the second UE.

[0153] In aspect 23, alone or in combination with one or more of aspects 16 to 22, the scheduling node makes a selection based on measurement results sent from the first UE via: if forwarded via a cellular interface, then via at least one of RRC signaling, MAC CE, PUCCH or PUSCH; or if forwarded via a sidelink interface, then via at least one of a sidelink equivalent or signaling mechanism similar to RRC signaling and MAC CE, PSCCH and PSSCH.

[0154] In aspect 24, alone or in combination with one or more of aspects 16 to 22, the signaling indicating the selection from the scheduling node is received via: if received via a cellular interface, at least one of RRC signaling, MAC CE, DCI or PDSCH; or if received via a sidelink interface, at least one of a sidelink equivalent or signaling mechanism similar to RRC signaling and MAC CE, PSCCH and PSSCH.

[0155] In aspect twenty-fifth, an apparatus for wireless communication performed by a scheduling node comprises at least one processor and a memory, configured to: select a signal from a plurality of candidates based on one or more criteria for a first user equipment (UE) to use as a spatial quasi-co-site (QCL) source for a receive beam or a transmit beam for communicating with a second UE on a sidelink interface; and signal an indication of the selection to the first UE.

[0156] In aspect 26, alone or in combination with aspect 25, the candidate includes at least one of: a first candidate for the first UE to use a signal sent from the first UE to the second UE as a QCL source for a receive beam for receiving transmissions from the second UE; or a second candidate for the first UE to use a signal sent from the second UE to the first UE as a QCL source for a transmit beam for sending transmissions to the second UE.

[0157] In aspect 27, alone or in combination with one or more aspects of aspect 25 and aspect 26, the candidate includes at least one of the following: a first candidate for the first UE to use a signal sent from the second UE to the first UE as a QCL source for a receive beam for receiving transmissions from the second UE; or a second candidate for the first UE to use a signal sent from the first UE to the second UE as a QCL source for a transmit beam for sending transmissions to the second UE.

[0158] In aspect 28, an apparatus for wireless communication performed by a first user equipment (UE) includes at least one processor and a memory, configured to: receive signaling from a scheduling node, the signaling indicating selection of a signal from a plurality of candidates based on one or more criteria for the first UE to use as a spatial quasi-co-site (QCL) source for a receive beam or a transmit beam for communicating with a second UE on a sidelink interface; and communicate with the second UE on the sidelink interface using the receive beam or the transmit beam determined based on the indicated selection.

[0159] In aspect 29, alone or in combination with aspect 28, the candidate includes at least one of: a first candidate for the first UE to use a signal sent from the first UE to the second UE as a QCL source for a receive beam for receiving transmissions from the second UE; or a second candidate for the first UE to use a signal sent from the second UE to the first UE as a QCL source for a transmit beam for sending transmissions to the second UE.

[0160] In aspect 30, alone or in combination with one or more of aspects 28 and 29, the candidate includes at least one of: a first candidate for the first UE to use a signal sent from the second UE to the first UE as a QCL source for a receive beam for receiving transmissions from the second UE; or a second candidate for the first UE to use a signal sent from the first UE to the second UE as a QCL source for a transmit beam for sending transmissions to the second UE.

[0161] Additional considerations

[0162] The methods disclosed herein include one or more steps or actions for implementing the methods. Method steps and / or actions may be interchanged without departing from the scope of the claims. In other words, unless a specific order of steps or actions is specified, the order and / or use of specific steps and / or actions may be modified without departing from the scope of the claims.

[0163] As used herein, a phrase referring to "at least one of" a list of items refers to any combination of those items, including single members. For example, "at least one of a, b, or c" is intended to cover: a, b, c, ab, ac, bc, and abc, as well as any combination with multiples of the same elements (e.g., aa, aaa, aab, aac, abb, acc, bb, bbb, bbc, cc, and ccc, or any other ordering of a, b, and c).

[0164] As used herein, the term "determine" encompasses a wide variety of actions. For example, "determine" may include calculating, computing, processing, deriving, investigating, searching (e.g., searching in a table, database, or other data structure), ascertaining, and the like. Furthermore, "determine" may also include receiving (e.g., receiving information), accessing (e.g., accessing data in a memory), and the like. Furthermore, "determine" may also include resolving, selecting, choosing, establishing, and the like.

[0165] The previous description is provided to enable those skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be apparent to those skilled in the art, and the overall principles defined herein may be applied to other aspects. Therefore, the claims are not intended to be limited to the various aspects shown herein, but are to be given the full scope consistent with the language of the claims, wherein, unless specifically stated otherwise, references to singular elements are not intended to mean "one and only one," but rather "one or more." Unless otherwise specifically stated, the term "some" refers to one or more. All structural and functional equivalents of the elements throughout the various aspects described in this disclosure are expressly incorporated herein by reference and are intended to be covered by the claims, and these structural and functional equivalents are or will become known to those skilled in the art. In addition, the content disclosed herein is not intended to be dedicated to the public, regardless of whether such disclosure is explicitly stated in the claims. No claim is to be interpreted under the terms of 35 U.S.C. § 112(f) unless the element is explicitly stated using the phrase "unit for..." or, in the case of a method claim, the element is stated using the phrase "step for..."

[0166] The various operations of the methods described above may be performed by any appropriate units capable of performing the corresponding functions. These units may include various hardware and / or software components and / or modules, including but not limited to circuits, application specific integrated circuits (ASICs), or processors. Generally, where operations are shown in the accompanying drawings, these operations may have corresponding paired functional module components. For example, Figure 10 and Figure 11 The various operations shown in Figure 2 The various processors of the BS 110 and / or UE 120 shown in FIG. 1 are executed.

[0167] The various illustrative logic blocks, modules, and circuits described in conjunction with the present disclosure may be implemented or executed using a general-purpose processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA) or other programmable logic device (PLD), discrete gate or transistor logic, discrete hardware components, or any combination thereof, designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any commercially available processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, for example, a combination of a DSP and a microprocessor, a plurality of microprocessors, a combination of one or more microprocessors and a DSP core, or any other such configuration.

[0168] When implemented in hardware, an example hardware configuration may include a processing system in a wireless node. The processing system may be implemented using a bus architecture. Depending on the specific application and overall design constraints of the processing system, the bus may include any number of interconnected buses and bridges. The bus may link together various circuits including a processor, a machine-readable medium, and a bus interface. The bus interface may be used to connect a network adapter, etc., to the processing system via the bus. The network adapter may be used to implement the signal processing functions of the PHY layer. In the user terminal 120 (see Figure 1 ), a user interface (e.g., keyboard, display, mouse, joystick, etc.) may also be connected to the bus. The bus also links various other circuits, such as clock sources, peripherals, voltage regulators, power management circuits, etc., which are well known in the art and therefore will not be described in any further detail. The processor may be implemented using one or more general-purpose processors and / or special-purpose processors. Examples include microprocessors, microcontrollers, DSP processors, and other circuits capable of executing software. Those skilled in the art will recognize how to best implement the described functionality for the processing system depending on the specific application and the overall design constraints imposed on the entire system.

[0169] When implemented in software, the functions may be stored as one or more instructions or codes on a computer-readable medium or transmitted via a computer-readable medium. Whether referred to as software, firmware, middleware, microcode, hardware description language, or other terms, software should be broadly interpreted to mean instructions, data, or any combination thereof. Computer-readable media include both computer storage media and communication media, including any medium that facilitates the transfer of computer programs from one place to another. The processor may be responsible for managing the bus and general processing, including executing software stored on a machine-readable storage medium. The computer-readable storage medium may be coupled to the processor so that the processor can read information from the storage medium and write information to the storage medium. In an alternative embodiment, the storage medium may be part of the processor. For example, the machine-readable medium may include a transmission line, a carrier modulated by data, and / or a computer-readable storage medium having instructions stored thereon that is separate from the wireless node, all of which can be accessed by the processor via a bus interface. Alternatively or additionally, the machine-readable medium or any portion thereof may be integrated into the processor, such as in the case of a cache and / or general register file. For example, examples of machine-readable storage media may include RAM (random access memory), flash memory, ROM (read-only memory), PROM (programmable read-only memory), EPROM (erasable programmable read-only memory), EEPROM (electrically erasable programmable read-only memory), registers, magnetic disks, optical disks, hard disks, or any other suitable storage media, or any combination thereof. Machine-readable media may be embodied in a computer program product.

[0170] A software module may include a single instruction or many instructions and may be distributed across several different code segments, among different programs, and across multiple storage media. A computer-readable medium may include multiple software modules. A software module includes instructions that, when executed by a device such as a processor, cause a processing system to perform various functions. A software module may include a transmission module and a reception module. Each software module may be located in a single storage device or distributed across multiple storage devices. For example, when a triggering event occurs, a software module may be loaded from a hard disk into RAM. During execution of the software module, the processor may load some of these instructions into a cache to increase access speed. Subsequently, one or more cache lines may be loaded into a general register file for execution by the processor. When reference is made to the functions of a software module below, it will be understood that such functions are implemented by the processor when executing instructions from the software module.

[0171] Furthermore, any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared (IR), radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. As used herein, disk and disc include compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk, and Blu-ray Optical disks, where magnetic disks typically reproduce data magnetically, and optical disks use lasers to reproduce data optically. Thus, in some aspects, computer-readable media may include non-transitory computer-readable media (e.g., tangible media). Furthermore, for other aspects, computer-readable media may include transitory computer-readable media (e.g., signals). Combinations of the above should also be included within the scope of computer-readable media.

[0172] Thus, certain aspects may include a computer program product for performing the operations presented herein. For example, such a computer program product may include a computer-readable medium having instructions stored (and / or encoded) thereon, the instructions being executable by one or more processors to perform the operations described herein. For example, a computer program product for performing the operations described herein and in Figure 10 and Figure 11 Instructions for the operations shown in .

[0173] In addition, it should be understood that the modules and / or other appropriate units for performing the methods and techniques described herein can be downloaded and / or obtained on demand by the user terminal and / or base station. For example, such a device can be coupled to a server to facilitate the transmission of the units for performing the methods described herein. Alternatively, the various methods described herein can be provided via a storage unit (e.g., RAM, ROM, a physical storage medium such as a compact disc (CD) or a floppy disk, etc.) so that the user terminal and / or base station can obtain the various methods when the storage unit is coupled to the device or provided to the device. In addition, any other appropriate technology for providing the methods and techniques described herein to the device can be utilized.

[0174] It is to be understood that the claims are not limited to the precise configuration and components shown above, and that various modifications, changes, and variations may be made in the arrangement, operation, and details of the methods and apparatus described above without departing from the scope of the claims.

Claims

1. A method for wireless communication performed by a scheduling node, comprising: selecting, based on one or more criteria, a signal from a plurality of candidates for use by a first user equipment (UE) as a spatial quasi-co-location (QCL) source for a receive beam or a transmit beam for communicating with a second UE on a sidelink interface, wherein the plurality of candidates includes a first signal from the first UE to the second UE having a first signal quality and a second signal from the second UE to the first UE having a second signal quality, and wherein the one or more criteria indicate: using the first signal as the QCL source when the first signal quality is higher than the second signal quality, or using the second signal as the QCL source when the second signal quality is higher than the first signal quality; and An indication of the selection is signaled to the first UE.

2. The method according to claim 1, wherein The scheduling node also signals an indication of the selection to the second UE.

3. The method according to claim 1, wherein The signal selected for use by the first UE as a spatial QCL source comprises a reference signal or channel.

4. The method according to claim 1, wherein The candidates include at least one of the following: The first UE uses the first signal transmitted from the first UE to the second UE as a QCL source for a receive beam for receiving transmissions from the second UE; or The first UE uses the second signal sent from the second UE to the first UE as a QCL source for a transmit beam used to send a transmission to the second UE.

5. The method according to claim 1, wherein The candidates include at least one of the following: the first UE using the second signal transmitted from the second UE to the first UE as a QCL source for a receive beam for receiving transmissions from the second UE; or The first UE uses the first signal sent from the first UE to the second UE as a QCL source for a transmit beam used to send a transmission to the second UE.

6. The method according to claim 1, wherein The scheduling node includes the second UE or a base station.

7. The method according to claim 1, wherein At least one of the standards involves a difference in: a first sidelink channel quality measured based on a signal transmitted from the first UE to the second UE; and A second sidelink channel quality is measured based on a signal sent from the second UE to the first UE.

8. The method according to claim 7, wherein: The scheduling node: indicating that if the first sidelink channel quality is greater than the second sidelink channel quality, the first UE should use a signal sent from the first UE to the second UE as the spatial QCL source; or Indicates that if the second sidelink channel quality is greater than the first sidelink channel quality, the first UE should use a signal sent from the second UE to the first UE as the spatial QCL source.

9. The method according to claim 1, wherein At least one of the criteria considers whether the first UE or the second UE is currently performing or has recently completed a beam scanning transmission on the sidelink.

10. The method according to claim 9, wherein: The scheduling node: indicating that if the first UE is currently performing or has recently completed a beam sweeping transmission on the sidelink, the first UE should use a signal sent from the first UE to the second UE as the spatial QCL source; or Indicates that if the second UE is currently performing or has recently completed a beam scanning transmission on the sidelink, the first UE should use the signal sent from the second UE to the first UE as the spatial QCL source.

11. The method according to claim 1, wherein The candidates include: The first UE uses a signal transmitted between the first UE and a reference node different from the second UE as at least one candidate for a QCL source for a receive beam or a transmit beam for communicating with the second UE.

12. The method according to claim 11, wherein At least one of the criteria takes into account the relative positions of the reference node, the first UE and the second UE.

13. The method according to claim 11, wherein The scheduling node includes the second UE or the reference node.

14. The method according to claim 1, wherein The scheduling node makes the selection based on measurement results received by the scheduling node via: If forwarding is via a cellular interface, via at least one of Radio Resource Control (RRC) signaling, Medium Access Control (MAC) Control Element (CE), Physical Uplink Control Channel (PUCCH), or Physical Uplink Shared Channel (PUSCH); or If forwarding is via a sidelink interface, then via at least one of a Physical Sidelink Control Channel (PSCCH) and a Physical Sidelink Shared Channel (PSSCH).

15. The method according to claim 1, wherein The scheduling node signals an indication of the selected option to the first UE via: If received via a cellular interface, via at least one of radio resource control (RRC) signaling, a medium access control (MAC) control element (CE), downlink control information (DCI), or a physical downlink shared channel (PDSCH); or If received via the sidelink interface, then via at least one of a Physical Sidelink Control Channel (PSCCH) and a Physical Sidelink Shared Channel (PSSCH).

16. A method for wireless communication performed by a first user equipment (UE), comprising: receiving signaling from a scheduling node, the signaling indicating selection of a signal from a plurality of candidates for use by the first UE as a spatial quasi-co-location (QCL) source for a receive beam or a transmit beam for communicating with a second UE on a sidelink interface based on one or more criteria, wherein the plurality of candidates includes a first signal from the first UE to the second UE having a first signal quality and a second signal from the second UE to the first UE having a second signal quality, and wherein the one or more criteria indicate using the first signal as the QCL source when the first signal quality is higher than the second signal quality, or using the second signal as the QCL source when the second signal quality is higher than the first signal quality; and Communicate with the second UE on the sidelink interface using a receive beam or a transmit beam determined based on the indicated selection.

17. The method according to claim 16, wherein The signal selected for use by the first UE as a spatial QCL source comprises a reference signal or channel.

18. The method according to claim 16, wherein The scheduling node includes the second UE or a base station.

19. The method according to claim 16, wherein The signaling: Instructing the first UE to use the first signal transmitted from the first UE to the second UE as the spatial QCL source; or Indicate that the first UE should use the second signal sent from the second UE to the first UE as the spatial QCL source.

20. The method according to claim 19, wherein The candidates include at least one of the following: The first UE uses the first signal transmitted from the first UE to the second UE as a QCL source for a receive beam for receiving transmissions from the second UE; or The first UE uses the second signal sent from the second UE to the first UE as a QCL source for a transmit beam used to send a transmission to the second UE.

21. The method according to claim 19, wherein The candidates include at least one of the following: the first UE using the second signal transmitted from the second UE to the first UE as a QCL source for a receive beam for receiving transmissions from the second UE; or The first UE uses the first signal sent from the first UE to the second UE as a QCL source for a transmit beam used to send a transmission to the second UE.

22. The method according to claim 16, wherein The candidates include: The first UE uses a reference signal transmitted between the first UE and a reference node different from the second UE as at least one candidate for a QCL source for a receive beam or a transmit beam communicating with the second UE.

23. The method according to claim 16, wherein The scheduling node performs the selection based on a measurement result sent from the first UE via: If forwarding is via a cellular interface, via at least one of Radio Resource Control (RRC) signaling, Medium Access Control (MAC) Control Element (CE), Physical Uplink Control Channel (PUCCH), or Physical Uplink Shared Channel (PUSCH); or If forwarding is via a sidelink interface, then via at least one of a Physical Sidelink Control Channel (PSCCH) and a Physical Sidelink Shared Channel (PSSCH).

24. The method according to claim 16, wherein The signaling from the scheduling node indicating the selection is received via: If received via a cellular interface, via at least one of radio resource control (RRC) signaling, a medium access control (MAC) control element (CE), downlink control information (DCI), or a physical downlink shared channel (PDSCH); or If received via the sidelink interface, then via at least one of a Physical Sidelink Control Channel (PSCCH) and a Physical Sidelink Shared Channel (PSSCH).

25. An apparatus for wireless communication performed by a scheduling node, comprising: At least one processor and memory configured to: selecting, based on one or more criteria, a signal from a plurality of candidates for use by a first user equipment (UE) as a spatial quasi-co-location (QCL) source for a receive beam or a transmit beam for communicating with a second UE on a sidelink interface, wherein the plurality of candidates includes a first signal from the first UE to the second UE having a first signal quality and a second signal from the second UE to the first UE having a second signal quality, and wherein the one or more criteria indicate: using the first signal as the QCL source when the first signal quality is higher than the second signal quality, or using the second signal as the QCL source when the second signal quality is higher than the first signal quality; and An indication of the selection is signaled to the first UE.

26. The device according to claim 25, wherein The candidates include at least one of the following: The first UE uses the first signal transmitted from the first UE to the second UE as a QCL source for a receive beam for receiving transmissions from the second UE; or The first UE uses the second signal sent from the second UE to the first UE as a QCL source for a transmit beam used to send a transmission to the second UE.

27. The device according to claim 26, wherein The candidates include at least one of the following: the first UE using the second signal transmitted from the second UE to the first UE as a QCL source for a receive beam for receiving transmissions from the second UE; or The first UE uses the first signal sent from the first UE to the second UE as a QCL source for a transmit beam used to send a transmission to the second UE.

28. An apparatus for wireless communication performed by a first user equipment (UE), comprising: At least one processor and memory configured to: receiving signaling from a scheduling node, the signaling indicating selection of a signal from a plurality of candidates for use by the first UE as a spatial quasi-co-location (QCL) source for a receive beam or a transmit beam for communicating with a second UE on a sidelink interface based on one or more criteria, wherein the plurality of candidates includes a first signal from the first UE to the second UE having a first signal quality and a second signal from the second UE to the first UE having a second signal quality, and wherein the one or more criteria indicate using the first signal as the QCL source when the first signal quality is higher than the second signal quality, or using the second signal as the QCL source when the second signal quality is higher than the first signal quality; and Communicate with the second UE on the sidelink interface using a receive beam or a transmit beam determined based on the indicated selection.

29. The apparatus according to claim 28, wherein The candidates include at least one of the following: The first UE uses the first signal transmitted from the first UE to the second UE as a QCL source for a receive beam for receiving transmissions from the second UE; or The first UE uses the second signal sent from the second UE to the first UE as a QCL source for a transmit beam used to send a transmission to the second UE.

30. The apparatus according to claim 28, wherein The candidates include at least one of the following: the first UE using the second signal transmitted from the second UE to the first UE as a QCL source for a receive beam for receiving transmissions from the second UE; or The first UE uses the first signal sent from the first UE to the second UE as a QCL source for a transmit beam used to send a transmission to the second UE.

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