WO2025166703A1

WO2025166703A1 - Multi-transceiver user equipment (ue) assisted transmission reception point (trp) synchronization

Info

Publication number: WO2025166703A1
Application number: PCT/CN2024/076844
Authority: WO
Inventors: Jing Dai; Xiaoxia Zhang; Mostafa KHOSHNEVISAN; Peter Gaal; Shaozhen GUO
Original assignee: Qualcomm Inc
Current assignee: Qualcomm Inc
Priority date: 2024-02-08
Filing date: 2024-02-08
Publication date: 2025-08-14
Anticipated expiration: 2026-08-08

Abstract

A method for wireless communication by a user equipment (UE) includes transmitting, from each transceiver of a group of transceivers of the UE to each transmission reception point (TRP) of a group of TRPs, a respective group of sounding reference signals (SRSs). The method also includes receiving, from each TRP of the group of TRPs, a respective group of downlink reference signals (DL-RSs) in accordance with transmitting the group of SRSs, each transceiver of the group of transceivers being associated with a respective DL-RS of the respective group of DL-RSs. The method further includes transmitting, to a TRP the group of TRPs, a message indicating one or more TRP-relative timing alignment errors (TAEs) and one or more phase offsets for one or more pairs of TRPs of the group of TRPs in accordance with receiving the respective group of DL-RSs at each one of the group of transceivers.

Description

MULTI-TRANSCEIVER USER EQUIPMENT (UE) ASSISTED TRANSMISSION RECEPTION POINT (TRP) SYNCHRONIZATION

FIELD OF THE DISCLOSURE

The present disclosure relates generally to wireless communications, and more specifically to using a multi-transceiver user equipment (UE) to assist in synchronizing a group of transmission reception points (TRPs) .

BACKGROUND

Wireless communications systems are widely deployed to provide various telecommunications services such as telephony, video, data, messaging, and broadcasts. Typical wireless communications systems may employ multiple-access technologies capable of supporting communications with multiple users by sharing available system resources (for example, bandwidth, transmit power, and/or the like) . Examples of such multiple-access technologies include 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, time division synchronous code division multiple access (TD-SCDMA) systems, and long term evolution (LTE) . LTE/LTE-Advanced is a set of enhancements to the universal mobile telecommunications system (UMTS) mobile standard promulgated by the Third Generation Partnership Project (3GPP) . Narrowband (NB) -Internet of things (IoT) and enhanced machine-type communications (eMTC) are a set of enhancements to LTE for machine type communications.

A wireless communications network may include a number of base stations (BSs) that can support communications for a number of user equipment (UEs) . A user equipment (UE) may communicate with a base station (BS) via the downlink and uplink. The downlink (or forward link) refers to the communication link from the BS to the UE, and the uplink (or reverse link) refers to the communication link from the UE to the BS. As will be described in more detail, a BS may be referred to as a Node B, an evolved Node B (eNB) , a gNB, an access point (AP) , a radio head, a transmission reception point (TRP) , a new radio (NR) BS, a 5G Node B, and/or the like.

The above multiple access technologies have been adopted in various telecommunications standards to provide a common protocol that enables different user equipment to communicate on a municipal, national, regional, and even global level. New radio, which may also be referred to as 5G, is a set of enhancements to the LTE mobile standard promulgated by the Third Generation Partnership Project (3GPP) . NR is designed to better support mobile broadband Internet access by improving spectral efficiency, lowering costs, improving services, making use of new spectrum, and better integrating with other open standards using orthogonal frequency division multiplexing (OFDM) with a cyclic prefix (CP) (CP-OFDM) on the downlink (DL) , using CP-OFDM and/or SC-FDM (for example, also known as discrete Fourier transform spread OFDM (DFT-s-OFDM) ) on the uplink (UL) , as well as supporting beamforming, multiple-input multiple-output (MIMO) antenna technology, and carrier aggregation.

Some wireless communication systems are time division duplexing (TDD) systems in which transmissions and receptions occur at different times in a same frequency spectrum, allowing for a single frequency band to be used for both uplink and downlink transmissions. Sounding reference signals (SRSs) transmitted in uplink may be used in TDD systems for downlink channel measurements. These channel measurements may indicate one or more channel conditions, such as precoder (precoding matrix) for a downlink transmission, path loss, interference, or signal strength. The SRSs may be used for channel measurements due to uplink (UL) and downlink (DL) reciprocity in TDD systems. UL/DL reciprocity assumes a DL channel is a transpose of a UL channel within a reciprocal medium. Phase coherence across ports of a network node is required to maintain UL/DL reciprocity. The phase coherence ensures that a phase of a signal remains consistent over time, such that signals, for example SRSs, may be combined across multiple transmission and reception paths.

SUMMARY

In one aspect of the present disclosure, a method for wireless communication by a UE includes transmitting, from each transceiver of a group of transceivers of the UE to each transmission reception point (TRP) of a group of TRPs, a respective group of sounding reference signals (SRSs) . The method further includes receiving, from each TRP of the group of TRPs, a respective group of downlink reference signals (DL-RSs) in accordance with transmitting the group of SRSs. Each transceiver of the group of transceivers may be associated with a respective DL-RS of the respective group of DL-RSs. The method also includes transmitting, to a TRP the group of TRPs, a message indicating one or more TRP-relative timing alignment errors (TAEs) and one or more phase offsets for one or more pairs of TRPs of the group of TRPs in accordance with receiving the respective group of DL-RSs at each one of the group of transceivers.

Another aspect of the present disclosure is directed to an apparatus including means for transmitting, from each transceiver of a group of transceivers of the UE to each TRP of a group of TRPs, a respective group of SRSs. The apparatus further includes means for receiving, from each TRP of the group of TRPs, a respective group of DL-RSs in accordance with transmitting the group of SRSs. Each transceiver of the group of transceivers may be associated with a respective DL-RS of the respective group of DL-RSs. The apparatus further includes means for transmitting, to a TRP the group of TRPs, a message indicating one or more TRP-relative TAEs and one or more phase offsets for one or more pairs of TRPs of the group of TRPs in accordance with receiving the respective group of DL-RSs at each one of the group of transceivers.

In another aspect of the present disclosure, a non-transitory computer-readable medium with non-transitory program code recorded thereon is disclosed. The program code is executed by a processor and includes program code to transmit, from each transceiver of a group of transceivers of the UE to each TRP of a group of TRPs, a respective group of SRSs. The program code still further includes program code to receive, from each TRP of the group of TRPs, a respective group of DL-RSs in accordance with transmitting the group of SRSs. Each transceiver of the group of transceivers may be associated with a respective DL-RS of the respective group of DL-RSs. The program code also includes program code to transmit, to a TRP the group of TRPs, a message indicating one or more TRP-relative TAEs and one or more phase offsets for one or more pairs of TRPs of the group of TRPs in accordance with receiving the respective group of DL-RSs at each one of the group of transceivers.

Another aspect of the present disclosure is directed to an apparatus having one or more processors, and one or more memories coupled with the one or more processors and storing instructions operable, when executed by the one or more processors, to cause the apparatus to transmit, from each transceiver of a group of transceivers of the UE to each TRP of a group of TRPs, a respective group of SRSs. Execution of the instructions further cause the apparatus to receive, from each TRP of the group of TRPs, a respective group of DL-RSs in accordance with transmitting the group of SRSs. Each transceiver of the group of transceivers may be associated with a respective DL-RS of the respective group of DL-RSs. Execution of the instructions also cause the apparatus to transmit, to a TRP the group of TRPs, a message indicating one or more TRP-relative TAEs and one or more phase offsets for one or more pairs of TRPs of the group of TRPs in accordance with receiving the respective group of DL-RSs at each one of the group of transceivers.

Aspects generally include a method, apparatus, system, computer program product, non-transitory computer-readable medium, user equipment, base station, wireless communication device, and processing system as substantially described with reference to and as illustrated by the accompanying drawings and specification.

The foregoing has outlined rather broadly the features and technical advantages of examples according to the disclosure in order that the detailed description that follows may be better understood. Additional features and advantages will be described. The conception and specific examples disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present disclosure. Such equivalent constructions do not depart from the scope of the appended claims. Characteristics of the concepts disclosed, both their organization and method of operation, together with associated advantages will be better understood from the following description when considered in connection with the accompanying figures. Each of the figures is provided for the purposes of illustration and description, and not as a definition of the limits of the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

So that features of the present disclosure can be understood in detail, a particular description may be had by reference to aspects, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only certain aspects of this disclosure and are therefore not to be considered limiting of its scope, for the description may admit to other equally effective aspects. The same reference numbers in different drawings may identify the same or similar elements.

Figure 1 is a block diagram conceptually illustrating an example of a wireless communications network, in accordance with various aspects of the present disclosure.

Figure 2 is a block diagram conceptually illustrating an example of a base station in communication with a user equipment (UE) in a wireless communications network, in accordance with various aspects of the present disclosure.

Figure 3 is a block diagram illustrating an example disaggregated base station architecture, in accordance with various aspects of the present disclosure.

Figure 4 is a timing diagram illustrating an example of a network node determining a timing alignment error (TAE) and a phase offset based on assistance from a single antenna UE.

Figure 5 is a block diagram illustrating an example of a UE with multiple transceivers, in accordance with various aspects of the present disclosure.

Figure 6 is a timing diagram illustrating an example of a UE with multiple transceivers determining a TAE and a phase offset for multiple transmission reception points (TRPs) , in accordance with various aspects of the present disclosure.

Figure 7 is a diagram illustrating an example of TRPs and with multiple transmit receive units (TXRUs) , in accordance with various aspects of the present disclosure.

Figure 8 is a block diagram illustrating an example of downlink reference signals (DL-RSs) associated with sounding reference signals (SRSs) , in accordance with various aspects of the present disclosure.

Figure 9 is a block diagram illustrating an example wireless communication device that supports synchronizing TRPs, in accordance with various aspects of the present disclosure.

Figure 10 is a flow diagram illustrating an example of a process for synchronizing TRPs, by a UE, in accordance with various aspects of the present disclosure.

Figure 11 is a block diagram illustrating an example wireless communication device that supports UE-assisted synchronization, in accordance with various aspects of the present disclosure.

Figure 12 is a flow diagram illustrating an example of a process for synchronizing TRPs, by a network node, in accordance with various aspects of the present disclosure.

DETAILED DESCRIPTION

Various aspects of the disclosure are described more fully below with reference to the accompanying drawings. This disclosure may, however, be embodied in many different forms and should not be construed as limited to any specific structure or function presented throughout this disclosure. Rather, these aspects are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Based on the teachings, one skilled in the art should appreciate that the scope of the disclosure is intended to cover any aspect of the disclosure, whether implemented independently of or combined with any other aspect of the disclosure. For example, an apparatus may be implemented or a method may be practiced using any number of the aspects set forth. In addition, the scope of the disclosure is intended to cover such an apparatus or method, which is practiced using other structure, functionality, or structure and functionality in addition to or other than the various aspects of the disclosure set forth. It should be understood that any aspect of the disclosure disclosed may be embodied by one or more elements of a claim.

Several aspects of telecommunications systems will now be presented with reference to various apparatuses and techniques. These apparatuses and techniques will be described in the following detailed description and illustrated in the accompanying drawings by various blocks, modules, components, circuits, steps, processes, algorithms, and/or the like (collectively referred to as “elements” ) . These elements may be implemented using hardware, software, or combinations thereof. Whether such elements are implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system.

It should be noted that while aspects may be described using terminology commonly associated with 5G and later wireless technologies, aspects of the present disclosure can be applied in other generation-based communications systems, such as and including 3G and/or 4G technologies.

As discussed, some wireless communication systems are time division duplexing (TDD) systems that allow the use of a single frequency band for uplink and downlink transmissions. In TDD systems, sounding reference signals (SRSs) may be used for channel measurements due to uplink (UL) and downlink (DL) reciprocity. UL/DL reciprocity assumes a DL channel is a transpose of a UL channel within a reciprocal medium. Phase coherence across ports of a network node is required to maintain UL/DL reciprocity. The phase coherence ensures that a phase of a signal remains consistent over time, such that signals, for example SRSs, may be combined across multiple transmission and reception paths.

In coordinated joint transmission (CJT) systems with distributed transmission reception points (TRPs) , phase coherence between ports of different TRPs may not be guaranteed. Phase coherence may ensure that signals from different TRPs arrive at a user equipment (UE) in a synchronized manner. In some cases, phase coherence errors may be due to unsynchronized clocks at each TRP. Additionally, or alternatively, phase coherence errors may be due to the variability in distributed circuitries, such as phased-locked loops (PLLs) , of the respective ports. Therefore, CJT systems with distributed TRPs may fail to establish DL/UL reciprocity. The lack of DL/UL reciprocity may lead to inaccurate channel measurements and degrade overall network functionality.

In some cases, to mitigate phase coherence errors, a UE may assist in estimating a phase offset and timing alignment error (TAE) between TRPs. The TAE, also referred to as a timing offset, is a measure of the temporal misalignment in transmissions from the TRPs. In some such cases, the phase offset and the TAE may be determined at a network node, such as one of the TRPs. In other such cases, the phase offset and the TAE may be determined at the UE. The TRPs may then be synchronized in accordance with the phase offset and the TAE. Synchronizing the TRPs may cure DL/UL reciprocity errors.

In some cases, a UE is configured with multiple transceivers and phase coherence errors may not be uniform across the transceivers. In some conventional systems, one transceiver may be used to avoid phase coherence errors. However, in such conventional systems, the transmit power-and consequently the signal-to-noise ratio (SNR) -may be effectively reduced. For example, in a two-transceiver UE, using a single-transceiver for uplink transmissions may result in a 3 dB loss in power, as the available power is halved. This reduction in uplink transmission power may impact a quality of the transmitted signal and/or reduce overall system performance.

A UE may operate multiple transceivers in a coordinated manner when the multiple transceivers are coherent. The coherence allows the UE to use the combined power of the multiple transceivers without introducing phase errors. Various aspects of the present disclosure are directed to synchronizing a TAE and phase offset of the multiple TRPs to achieve coherence at the transceivers of the UE. The multiple transceivers may also be referred to as a group of transceivers, hereinafter used interchangeably. In some examples, the UE transmits, from each transceiver of a group of transceivers of the UE to each TRP of a group of TRPs, a respective group of sounding reference signals (SRSs) . The UE may then receive, from each TRP, a respective group of downlink reference signals (DL-RSs) in accordance with transmitting the group of SRSs to the TRP. Each transceiver of the group of transceivers may receive a respective DL-RS of each group of DL-RSs such that each transceiver receives a DL-RS from each of the group of TRPs. Each group of DL-RSs may be precoded by the respective TRP in accordance with the group of SRSs. In such examples, the UE may determine, for the group of transceivers, a group of self-terms and a group of cross-terms in accordance with each transceiver of the group of transceivers receiving a respective DL-RS from each TRP. Each self-term represents a signal component of a signal received from one TRP of the group of TRPs, in which the antenna index is the same at the TRP and the transceiver. Each cross-term represents a signal component of another signal received from one TRP of the group of TRPs, in which the antenna index at the TRP is different than an antenna index of the transceiver. A TRP-relative TAE and a phase offset of the group of TRPs may be derived from the group of self-terms and the group of cross-terms. The UE may then transmit, to one or more of the group of TRPs, a message indicating the TRP-relative TAE and the phase offset. The group of TRPs may be synchronized in accordance with transmitting the message indicating the TRP-relative TAE and the phase offset.

Particular aspects of the subject matter described in this disclosure can be implemented to realize one or more of the following potential advantages. In some examples, the described techniques for synchronizing the group of TRPs may increase spectrum utilization and enable coherence at the group of transceivers. By enabling coherence, the group of transceivers may operate in a coordinated manner, thereby increasing a combined power for uplink transmissions without phase errors. The increase in uplink transmission power may improve a quality of transmitted signals, thereby reducing communication errors and improving overall network performance.

Figure 1 is a diagram illustrating a network 100 in which aspects of the present disclosure may be practiced. The network 100 may be a 5G or NR network or some other wireless network, such as an LTE network. The wireless network 100 may include a number of BSs 110 (shown as BS 110a, BS 110b, BS 110c, and BS 110d) and other network entities. A BS is an entity that communicates with user equipment (UEs) and may also be referred to as a base station, an NR BS, a Node B, a gNB, a 5G Node B, an access point, a TRP, a network node, a network entity, and/or the like. A base station can be implemented as an aggregated base station, as a disaggregated base station, an integrated access and backhaul (IAB) node, a relay node, a sidelink node, etc. The base station can be implemented in an aggregated or monolithic base station architecture, or alternatively, in a disaggregated base station architecture, and may include one or more of a central unit (CU) , a distributed unit (DU) , a radio unit (RU) , a near-real time (near-RT) RAN intelligent controller (RIC) , or a non-real time (non-RT) RIC.

Each BS may provide communications coverage for a particular geographic area. In 3GPP, the term “cell” can refer to a coverage area of a BS and/or a BS subsystem serving this coverage area, depending on the context in which the term is used.

A BS may provide communications coverage for a macro cell, a pico cell, a femto cell, and/or another type of cell. A macro cell may cover a relatively large geographic area (for example, several kilometers in radius) and may allow unrestricted access by UEs with service subscription. A pico cell may cover a relatively small geographic area and may allow unrestricted access by UEs with service subscription. A femto cell may cover a relatively small geographic area (for example, a home) and may allow restricted access by UEs having association with the femto cell (for example, UEs in a closed subscriber group (CSG) ) . 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 the example shown in Figure 1, a BS 110a may be a macro BS for a macro cell 102a, a BS 110b may be a pico BS for a pico cell 102b, and a BS 110c may be a femto BS for a femto cell 102c. A BS may support one or multiple (for example, three) cells. The terms “eNB, ” “base station, ” “NR BS, ” “gNB, ” “AP, ” “Node B, ” “5G Node B, ” “TRP, ” and “cell” may be used interchangeably.

In some aspects, a cell may not necessarily be stationary, and the geographic area of the cell may move according to the location of a mobile BS. In some aspects, the BSs may be interconnected to one another and/or to one or more other BSs or network nodes (not shown) in the wireless network 100 through various types of backhaul interfaces such as a direct physical connection, a virtual network, and/or the like using any suitable transport network.

The wireless network 100 may also include relay stations. A relay station is an entity that can receive a transmission of data from an upstream station (for example, a BS or a UE) and send a transmission of the data to a downstream station (for example, a UE or a BS) . A relay station may also be a UE that can relay transmissions for other UEs. In the example shown in Figure 1, a relay station 110d may communicate with macro BS 110a and a UE 120d in order to facilitate communications between the BS 110a and UE 120d. A relay station may also be referred to as a relay BS, a relay base station, a relay, and/or the like.

The wireless network 100 may be a heterogeneous network that includes BSs of different types (for example, macro BSs, pico BSs, femto BSs, relay BSs, and/or the like) . These different types of BSs may have different transmit power levels, different coverage areas, and different impact on interference in the wireless network 100. For example, macro BSs may have a high transmit power level (for example, 5 to 40 watts) whereas pico BSs, femto BSs, and relay BSs may have lower transmit power levels (for example, 0.1 to 2 watts) .

As an example, the BSs 110 (shown as BS 110a, BS 110b, BS 110c, and BS 110d) and the core network 130 may exchange communications via backhaul links 132 (for example, S1, etc. ) . Base stations 110 may communicate with one another over other backhaul links (for example, X2, etc. ) either directly or indirectly (for example, through core network 130) .

The core network 130 may be an evolved packet core (EPC) , which may include at least one mobility management entity (MME) , at least one serving gateway (S-GW) , and at least one packet data network (PDN) gateway (P-GW) . The MME may be the control node that processes the signaling between the UEs 120 and the EPC. All user IP packets may be transferred through the S-GW, which itself may be connected to the P-GW. The P-GW may provide IP address allocation as well as other functions. The P-GW may be connected to the network operator's IP services. The operator's IP services may include the Internet, the Intranet, an IP multimedia subsystem (IMS) , and a packet-switched (PS) streaming service.

The core network 130 may provide user authentication, access authorization, tracking, IP connectivity, and other access, routing, or mobility functions. One or more of the base stations 110 or access node controllers (ANCs) may interface with the core network 130 through backhaul links 132 (for example, S1, S2, etc. ) and may perform radio configuration and scheduling for communications with the UEs 120. In some configurations, various functions of each access network entity or base station 110 may be distributed across various network devices (for example, radio heads and access network controllers) or consolidated into a single network device (for example, a base station 110) .

UEs 120 (for example, 120a, 120b, 120c) may be dispersed throughout the wireless network 100, and each UE may be stationary or mobile. A UE may also be referred to as an access terminal, a terminal, a mobile station, a subscriber unit, a station, and/or the like. A UE may be a cellular phone (for example, a smart phone) , a personal digital assistant (PDA) , a wireless modem, a wireless communication device, a handheld device, a laptop computer, a cordless phone, a wireless local loop (WLL) station, a tablet, a camera, a gaming device, a netbook, a smartbook, an ultrabook, a medical device or equipment, biometric sensors/devices, wearable devices (smart watches, smart clothing, smart glasses, smart wrist bands, smart jewelry (for example, smart ring, smart bracelet) ) , an entertainment device (for example, a music or video device, or a satellite radio) , a vehicular component or sensor, smart meters/sensors, industrial manufacturing equipment, a global positioning system device, or any other suitable device that is configured to communicate via a wireless or wired medium.

One or more UEs 120 may establish a protocol data unit (PDU) session for a network slice. In some cases, the UE 120 may select a network slice based on an application or subscription service. By having different network slices serving different applications or subscriptions, the UE 120 may improve its resource utilization in the wireless network 100, while also satisfying performance specifications of individual applications of the UE 120. In some cases, the network slices used by UE 120 may be served by an AMF (not shown in Figure 1) associated with one or both of the base station 110 or core network 130. In addition, session management of the network slices may be performed by an access and mobility management function (AMF) .

The UEs 120 may include a timing module 140. For brevity, only one UE 120d is shown as including the timing module 140. The timing module 140 may perform one or more operations, such as one or more operations of the process 1000 described with respect to Figure 10.

Some UEs may be considered machine-type communications (MTC) or evolved or enhanced machine-type communications (eMTC) UEs. MTC and eMTC UEs include, for example, robots, drones, remote devices, sensors, meters, monitors, location tags, and/or the like, that may communicate with a base station, another device (for example, remote device) , or some other entity. A wireless node may provide, for example, connectivity for or to a network (for example, a wide area network such as Internet or a cellular network) via a wired or wireless communication link. Some UEs may be considered Internet of things (IoT) devices, and/or may be implemented as NB-IoT (narrowband Internet of things) devices. Some UEs may be considered a customer premises equipment (CPE) . UE 120 may be included inside a housing that houses components of UE 120, such as processor components, memory components, and/or the like.

In general, any number of wireless networks may be deployed in a given geographic area. Each wireless network may support a particular radio access technology (RAT) and may operate on one or more frequencies. A RAT may also be referred to as a radio technology, an air interface, and/or the like. A frequency may also be referred to as a carrier, a frequency channel, and/or the like. Each frequency may support a single RAT in a given geographic area in order to avoid interference between wireless networks of different RATs. In some cases, NR or 5G RAT networks may be deployed.

In some aspects, two or more UEs 120 (for example, shown as UE 120a and UE 120e) may communicate directly using one or more sidelink channels (for example, without using a base station 110 as an intermediary to communicate with one another) . For example, the UEs 120 may communicate using peer-to-peer (P2P) communications, device-to-device (D2D) communications, a vehicle-to-everything (V2X) protocol (for example, which may include a vehicle-to-vehicle (V2V) protocol, a vehicle-to-infrastructure (V2I) protocol, and/or the like) , a mesh network, and/or the like. In this case, the UE 120 may perform scheduling operations, resource selection operations, and/or other operations described elsewhere as being performed by the base station 110. For example, the base station 110 may configure a UE 120 via downlink control information (DCI) , radio resource control (RRC) signaling, a media access control-control element (MAC-CE) or via system information (for example, a system information block (SIB) .

As indicated above, Figure 1 is provided merely as an example. Other examples may differ from what is described with regard to Figure 1.

Figure 2 shows a block diagram of a design 200 of the base station 110 and UE 120, which may be one of the base stations and one of the UEs in Figure 1. The base station 110 may be equipped with T antennas 234a through 234t, and UE 120 may be equipped with R antennas 252a through 252r, where in general T ≥ 1 and R ≥ 1.

At the base station 110, a transmit processor 220 may receive data from a data source 212 for one or more UEs, select one or more modulation and coding schemes (MCS) for each UE based at least in part on channel quality indicators (CQIs) received from the UE, process (for example, encode and modulate) the data for each UE based at least in part on the MCS (s) selected for the UE, and provide data symbols for all UEs. Decreasing the MCS lowers throughput but increases reliability of the transmission. The transmit processor 220 may also process system information (for example, for semi-static resource partitioning information (SRPI) and/or the like) and control information (for example, CQI requests, grants, upper layer signaling, and/or the like) and provide overhead symbols and control symbols. The transmit processor 220 may also generate reference symbols for reference signals (for example, the cell-specific reference signal (CRS) ) and synchronization signals (for example, the primary synchronization signal (PSS) and secondary synchronization signal (SSS) ) . A transmit (TX) multiple-input multiple-output (MIMO) processor 230 may perform spatial processing (for example, precoding) on the data symbols, the control symbols, the overhead symbols, and/or the reference symbols, if applicable, and may provide T output symbol streams to T modulators (MODs) 232a through 232t. Each modulator 232 may process a respective output symbol stream (for example, for orthogonal frequency division multiplexing (OFDM) and/or the like) to obtain an output sample stream. Each modulator 232 may further process (for example, convert to analog, amplify, filter, and upconvert) the output sample stream to obtain a downlink signal. T downlink signals from modulators 232a through 232t may be transmitted via T antennas 234a through 234t, respectively. According to various aspects described in more detail below, the synchronization signals can be generated with location encoding to convey additional information.

At the UE 120, antennas 252a through 252r may receive the downlink signals from the base station 110 and/or other base stations and may provide received signals to demodulators (DEMODs) 254a through 254r, respectively. Each demodulator 254 may condition (for example, filter, amplify, downconvert, and digitize) a received signal to obtain input samples. Each demodulator 254 may further process the input samples (for example, for OFDM and/or the like) to obtain received symbols. A MIMO detector 256 may obtain received symbols from all R demodulators 254a through 254r, perform MIMO detection on the received symbols if applicable, and provide detected symbols. A receive processor 258 may process (for example, demodulate and decode) the detected symbols, provide decoded data for the UE 120 to a data sink 260, and provide decoded control information and system information to a controller/processor 280. A channel processor may determine reference signal received power (RSRP) , received signal strength indicator (RSSI) , reference signal received quality (RSRQ) , channel quality indicator (CQI) , and/or the like. In some aspects, one or more components of the UE 120 may be included in a housing.

On the uplink, at the UE 120, a transmit processor 264 may receive and process data from a data source 262 and control information (for example, for reports comprising RSRP, RSSI, RSRQ, CQI, and/or the like) from the controller/processor 280. Transmit processor 264 may also generate reference symbols for one or more reference signals. The symbols from the transmit processor 264 may be precoded by a TX MIMO processor 266 if applicable, further processed by modulators 254a through 254r (for example, for discrete Fourier transform spread OFDM (DFT-s-OFDM) , CP-OFDM, and/or the like) , and transmitted to the base station 110. At the base station 110, the uplink signals from the UE 120 and other UEs may be received by the antennas 234, processed by the demodulators 254, detected by a MIMO detector 236 if applicable, and further processed by a receive processor 238 to obtain decoded data and control information sent by the UE 120. The receive processor 238 may provide the decoded data to a data sink 239 and the decoded control information to a controller/processor 240. The base station 110 may include communications unit 244 and communicate to the core network 130 via the communications unit 244. The core network 130 may include a communications unit 294, a controller/processor 290, and a memory 292.

The controller/processor 240 of the base station 110, the controller/processor 280 of the UE 120, and/or any other component (s) of Figure 2 may perform one or more techniques associated with UE-assisted TRP synchronization as described in more detail elsewhere. For example, the controller/processor 240 of the base station 110, the controller/processor 280 of the UE 120, and/or any other component (s) of Figure 2 may perform or direct operations of, for example, the processes of Figure 10 and/or other processes as described. Memories 242 and 282 may store data and program codes for the base station 110 and UE 120, respectively. A scheduler 246 may schedule UEs for data transmission on the downlink and/or uplink.

In some aspects, the UE 120 may include means for receiving, means for transmitting, and means for determining. Such means may include one or more components of the UE 120 described in connection with FIGURE 2.

Deployment of communication systems, such as 5G new radio (NR) systems, may be arranged in multiple manners with various components or constituent parts. In a 5G NR system, or network, a network node, a network entity, a mobility element of a network, a radio access network (RAN) node, a core network node, a network element, or a network equipment, such as a base station (BS) , or one or more units (or one or more components) performing base station functionality, may be implemented in an aggregated or disaggregated architecture. For example, a BS (such as a Node B, an evolved Node B (eNB) , an NR BS, 5G Node B, an access point (AP) , a TRP, or a cell, etc. ) may be implemented as an aggregated base station (also known as a standalone BS or a monolithic BS) or a disaggregated base station.

An aggregated base station may be configured to utilize a radio protocol stack that is physically or logically integrated within a single RAN node. A disaggregated base station may be configured to utilize a protocol stack that is physically or logically distributed among two or more units (such as one or more central or centralized units (CUs) , one or more distributed units (DUs) , or one or more radio units (RUs) ) . In some aspects, a CU may be implemented within a RAN node, and one or more DUs may be co-located with the CU, or alternatively, may be geographically or virtually distributed throughout one or multiple other RAN nodes. The DUs may be implemented to communicate with one or more RUs. Each of the CU, DU, and RU also can be implemented as virtual units (for example, a virtual central unit (VCU) , a virtual distributed unit (VDU) , or a virtual radio unit (VRU) ) .

Base station-type operations or network designs may consider aggregation characteristics of base station functionality. For example, disaggregated base stations may be utilized in an integrated access backhaul (IAB) network, an open radio access network (O-RAN (such as the network configuration sponsored by the O-RAN Alliance) ) , or a virtualized radio access network (vRAN, also known as a cloud radio access network (C-RAN) ) . Disaggregation may include distributing functionality across two or more units at various physical locations, as well as distributing functionality for at least one unit virtually, which can enable flexibility in network design. The various units of the disaggregated base station, or disaggregated RAN architecture, can be configured for wired or wireless communication with at least one other unit.

In some cases, different types of devices supporting different types of applications and/or services may coexist in a cell. Examples of different types of devices include UE handsets, customer premises equipment (CPEs) , vehicles, Internet of things (IoT) devices, and/or the like. Examples of different types of applications include ultra-reliable low-latency communications (URLLC) applications, massive machine-type communications (mMTC) applications, enhanced mobile broadband (eMBB) applications, vehicle-to-anything (V2X) applications, and/or the like. Furthermore, in some cases, a single device may support different applications or services simultaneously.

Figure 3 shows a diagram illustrating an example disaggregated base station 300 architecture. The disaggregated base station 300 architecture may include one or more central units (CUs) 310 that can communicate directly with a core network 320 via a backhaul link, or indirectly with the core network 320 through one or more disaggregated base station units (such as a near-real time (near-RT) RAN intelligent controller (RIC) 325 via an E2 link, or a non-real time (non-RT) RIC 315 associated with a service management and orchestration (SMO) framework 305, or both) . A CU 310 may communicate with one or more distributed units (DUs) 330 via respective midhaul links, such as an F1 interface. The DUs 330 may communicate with one or more radio units (RUs) 340 via respective fronthaul links. The RUs 340 may communicate with respective UEs 120 via one or more radio frequency (RF) access links. In some implementations, the UE 120 may be simultaneously served by multiple RUs 340.

Each of the units (for example, the CUs 310, the DUs 330, the RUs 340, as well as the near-RT RICs 325, the non-RT RICs 315, and the SMO framework 305) may include one or more interfaces or be coupled to one or more interfaces configured to receive or transmit signals, data, or information (collectively, signals) via a wired or wireless transmission medium. Each of the units, or an associated processor or controller providing instructions to the communication interfaces of the units, can be configured to communicate with one or more of the other units via the transmission medium. For example, the units can include a wired interface configured to receive or transmit signals over a wired transmission medium to one or more of the other units. Additionally, the units can include a wireless interface, which may include a receiver, a transmitter or transceiver (such as a radio frequency (RF) transceiver) , configured to receive or transmit signals, or both, over a wireless transmission medium to one or more of the other units.

In some aspects, the CU 310 may host one or more higher layer control functions. Such control functions can include radio resource control (RRC) , packet data convergence protocol (PDCP) , service data adaptation protocol (SDAP) , or the like. Each control function can be implemented with an interface configured to communicate signals with other control functions hosted by the CU 310. The CU 310 may be configured to handle user plane functionality (for example, central unit –user plane (CU-UP) ) , control plane functionality (for example, central unit –control Plane (CU-CP) ) , or a combination thereof. In some implementations, the CU 310 can be logically split into one or more CU-UP units and one or more CU-CP units. The CU-UP unit can communicate bi-directionally with the CU-CP unit via an interface, such as the E1 interface when implemented in an O-RAN configuration. The CU 310 can be implemented to communicate with the DU 330, as necessary, for network control and signaling.

The DU 330 may correspond to a logical unit that includes one or more base station functions to control the operation of one or more RUs 340. In some aspects, the DU 330 may host one or more of a radio link control (RLC) layer, a medium access control (MAC) layer, and one or more high physical (PHY) layers (such as modules for forward error correction (FEC) encoding and decoding, scrambling, modulation and demodulation, or the like) depending, at least in part, on a functional split, such as those defined by the Third Generation Partnership Project (3GPP) . In some aspects, the DU 330 may further host one or more low PHY layers. Each layer (or module) can be implemented with an interface configured to communicate signals with other layers (and modules) hosted by the DU 330, or with the control functions hosted by the CU 310.

Lower-layer functionality can be implemented by one or more RUs 340. In some deployments, an RU 340, controlled by a DU 330, may correspond to a logical node that hosts RF processing functions, or low-PHY layer functions (such as performing fast Fourier transform (FFT) , inverse FFT (iFFT) , digital beamforming, physical random access channel (PRACH) extraction and filtering, or the like) , or both, based at least in part on the functional split, such as a lower layer functional split. In such an architecture, the RU (s) 340 can be implemented to handle over the air (OTA) communication with one or more UEs 120. In some implementations, real-time and non-real-time aspects of control and user plane communication with the RU (s) 340 can be controlled by the corresponding DU 330. In some scenarios, this configuration can enable the DU (s) 330 and the CU 310 to be implemented in a cloud-based RAN architecture, such as a vRAN architecture.

The SMO framework 305 may be configured to support RAN deployment and provisioning of non-virtualized and virtualized network elements. For non-virtualized network elements, the SMO framework 305 may be configured to support the deployment of dedicated physical resources for RAN coverage requirements, which may be managed via an operations and maintenance interface (such as an O1 interface) . For virtualized network elements, the SMO framework 305 may be configured to interact with a cloud computing platform (such as an open cloud (O-cloud) 390) to perform network element life cycle management (such as to instantiate virtualized network elements) via a cloud computing platform interface (such as an O2 interface) . Such virtualized network elements can include, but are not limited to, CUs 310, DUs 330, RUs 340, and near-RT RICs 325. In some implementations, the SMO framework 305 can communicate with a hardware aspect of a 4G RAN, such as an open eNB (O-eNB) 311, via an O1 interface. Additionally, in some implementations, the SMO framework 305 can communicate directly with one or more RUs 340 via an O1 interface. The SMO framework 305 also may include a non-RT RIC 315 configured to support functionality of the SMO framework 305.

The non-RT RIC 315 may be configured to include a logical function that enables non-real-time control and optimization of RAN elements and resources, artificial intelligence/machine learning (AI/ML) workflows including model training and updates, or policy-based guidance of applications/features in the near-RT RIC 325. The non-RT RIC 315 may be coupled to or communicate with (such as via an A1 interface) the near-RT RIC 325. The near-RT RIC 325 may be configured to include a logical function that enables near-real-time control and optimization of RAN elements and resources via data collection and actions over an interface (such as via an E2 interface) connecting one or more CUs 310, one or more DUs 330, or both, as well as the O-eNB 311, with the near-RT RIC 325.

In some implementations, to generate AI/ML models to be deployed in the near-RT RIC 325, the non-RT RIC 315 may receive parameters or external enrichment information from external servers. Such information may be utilized by the near-RT RIC 325 and may be received at the SMO framework 305 or the non-RT RIC 315 from non-network data sources or from network functions. In some examples, the non-RT RIC 315 or the near-RT RIC 325 may be configured to tune RAN behavior or performance. For example, the non-RT RIC 315 may monitor long-term trends and patterns for performance and employ AI/ML models to perform corrective actions through the SMO framework 305 (such as reconfiguration via O1) or via creation of RAN management policies (such as A1 policies) .

In TDD systems, sounding reference signals (SRSs) may be used for channel measurements due to UL and DL reciprocity (also referred to as TDD reciprocity) . UL/DL reciprocity assumes a DL channel is a transpose of a UL channel within a reciprocal medium. UL/DL reciprocity may be expressed as H^DL= (H^UL) ^T, where H represents a channel matrix and T represents a transpose function. The channel gain from an i^th antenna at the UE to a j^th port at a TRP in the uplink is equal to the channel gain from the j^th port at the TRP to the i^th antenna at the UE in the downlink. The notationrepresents an individual entry in the channel matrix H, where A represents a number of antennas at the UE and P represents a number of ports at the TRP.

UL/DL reciprocity is predicated on phase coherence across the ports of a TRP, which includes maintaining coherence between the receiving and transmitting phases. Phase coherence ensures that a phase of a signal remains consistent over time, such that signals, for example SRSs, may be combined across multiple transmission and reception paths. UL/DL reciprocity may fail in the absence of phase coherence. It is important to note, however, that phase coherence may not extend to the UE. Within the UE, the antennas and transceivers, as well as the receiving and transmitting pathways, generally do not specify the same level of phase coherence.

In some examples, for a single antenna UE, the TAE ρ₁₂ between a first TRP (TRP1) and a second TRP (TRP2) may be determined as follows:

In equation 1, represents timing errors (for example, TAE) introduced by transmission-side clock jitters of a TRP n, represents timing errors introduced by reception-side clock jitters of the TRP n. The timing errors may cause transmission or reception phase ramp over subcarriers. These timing errors may include errors due to clock inaccuracies, processing delays, or any other factors that cause a signal to deviate from its expected timing. It may be desirable to reduce the TAE ρ₁₂ to aligning the timing between the first and second TRPs.

In some examples, for a single antenna UE, the phase offset φ₁₂ between a first TRP (TRP1) and a second TRP (TRP2) may be determined as follows:

In equation 2, represents phase uncertainty introduced by transmission-side clock jitters and a PLL of a TRP n, represents introduced by reception-side clock jitters and a PLL of the TRP n. It may be desirable to reduce the phase offset φ₁₂ to reduce the phase uncertainty between the first and second TRPs.

As discussed, in some cases, to mitigate phase coherence errors, a UE may assist in estimating a phase offset and timing alignment error (TAE) between TRPs. In some such cases, a network node, such as one of the TRPs, may determine the TAE and phase offset. Figure 4 is a timing diagram illustrating an example 400 of a network node determining a TAE and a phase offset based on assistance from a single antenna UE. In the example of Figure 4, the UE 120 is an example of a single antenna UE that may communicate with a first TRP 402, a second TRP 404, and a network node 406. The first TRP 402, second TRP 404, and the network node 406 may be examples of a base station 110 described with reference to Figures 1 and 2, or a CU 310, DU 330, or RU 340 described with reference to Figure 3. In some examples, the network node 406 may be the same as one of the first or second TRPs 402 or 404.

In the example of Figure 4, at time t1, the first TRP 402 transmits a first downlink reference signal (DL-RS) to the UE 120. The DL-RS may be an example of a single-port channel state information (CSI) RS (CSI-RS) , such as a tracking reference signal (TRS) . In the example of Figure 4, y₁ represents the signal received at the UE 120 from the first TRP 402. The signal y₁ may be represented as:

In equation 3, represents phase uncertainty contributions at the receiver of the UE 120, represents phase uncertainty contributions at the transmitter of the first TRP 402, andrepresents downlink channel coefficients from the first TRP 402 to the UE 120. These coefficients characterize the channel's behavior, including the effects of path loss, fading, and any phase shifts that occur during the signal's transmission from the first TRP 402 to the UE 120. At time t3, the UE 120 also receives a second DL-RS from the second TRP 404. In the example of Figure 4, y₂ represents the signal received at the UE 120 from the second TRP 404. The signal y₂ may be represented by an equation similar to equation 3, accounting for the second TRP 404 instead of the first TRP 402 (for example, ) .

For a receiver side, at either a TRP 402 or 404 or the UE 120, the phase uncertainty contributions ψ^Rx may be defined as ψ^Rx=exp (j2πkρ^RxΔf+jφ^Rx) , where ρ^Rx represents a timing offset at the receiver, Δf represents subcarrier spacing, φ^Rx represents a phase offset at the receiver, and k represents a subcarrier index. The exponential terms exp (j2πkρ^RxΔf) and exp (jφ^Rx) represent the phase rotation due to the timing offset and phase offset, respectively, with the parameterindicating the complex nature of the phase rotation. For a transmitter side, at either a TRP 402 or 404 or the UE 120, the phase uncertainty contributions ψ^Tx may be defined as ψ^Tx=exp (-j2πkρ^TxΔf-jφ^Tx) , where ρ^Tx represents a timing offset at the transmitter, and φ^Tx represents a phase offset at the transmitter.

At times t2 and t4, the UE 120 transmits a corresponding UL-RS, such as an SRS to each TRP 402 and 404. The UL-RS may be precoded based on the corresponding DL-RS (for example, precoded withwhich denote the conjugate of the received y₁ and y₂ respectively) received at times t1 and t3. SRS precoding cancels out timing (for example, propagation delay) and phase variations of a channel, such that the timing and phase variations do not influence the calculation of the processed reference signals z₁ and z₂ at the respective receivers (for example, the first TRP 402 and the second TRP 404) . In some examples, the reference signal z₁ transmitted at time t2 may be represented as:

In equation 4, represents phase uncertainty at a receiver of the first TRP 402, represents an uplink channel coefficient from the UE 120 to the first TRP 402, represents phase uncertainty at a transmitter of the UE 120, andrepresents the DL-RS from the first TRP. As shown in equation 3, the received signal y₁ is a product of the downlink channel coefficientand the transmitter phase uncertaintyWhen precoding the SRS, both the downlink channel coefficient and the transmitter phase uncertaintyare conjugated to negate their effects. The result iswherein a magnitude squared of the channel coefficient |h_TRP1|² remains. Still, the phase terms cancel out due to the multiplication with their respective complex conjugates. Similarly, z₂ is computed in the same way for the second TRP 404resulting in the magnitude squared of the channel coefficient |h_TRP2|² for the second TRP 404 and cancellation of the phase terms. This precoding strategy may be implemented using a single antenna (for example, single-transceiver ) UE because phase coherence between multiple UE transceivers is not guaranteed.

As shown in the example of Figure 4, at times t5 and t6, each TRP 402 and 404 may transmit raw data associated with the respective SRSs to the network node

406. At time t7, based on the raw data associated with the respective SRSs, the network node 406 may determine the TAE and/or phase offset between the first TRP 402 and the second TRP 404. The TAE and phase offset may be based on a product of the first precoded SRS z₁ and the complex conjugate of the second precoded SRS z₂, denoted as This product cancels out UE receiving phase uncertaintyand UE transmitting phase uncertaintyand isolates specific phase and timing error characteristics between the first TRP 402 and the second TRP 404. Specifically, the network node 406 calculates:

By using the product of the precoded SRSs, the network node 406 ensures that phase errors introduced by a receive-transmit (Rx-Tx) mismatch of the UE 120 is canceled out, and the only remaining phase is the relative TAE ρ₁₂ and phase offset φ₁₂between the TRPs 402 and 404, where

The relative TAE and phase offset between the two TRPs 402 and 404 (ρ₁₂, φ₁₂) are estimated by observationacross multiple subcarriers. At time t8, the estimated TAE ρ₁₂ and phase offset φ₁₂ may be transmitted to one of the TRPs, such as the second TRP 404. The TAE ρ₁₂ and phase offset φ₁₂ may be used by the TRPs, such as the second TRP 404, to synchronize to the other TRP, such as the first TRP 402.

In some examples, the UE 120 may determine the TAE ρ₁₂ and the phase offset φ₁₂. In such examples, the UE 120 transmits a UL-RS, such as a first SRS z₁, to the first TRP 402 and a UL-RS, such as a second SRS z₂, to the second TRP 404. The first SRS z₁ may be expressed asThe second SRS z₂ may be expressed asAs previously discussed, for a receiver side, ψ^Rx=exp(j2πkρ^RxΔf+jφ^Rx) , and for a transmitter side, ψ^Tx=exp (-j2πkρ^TxΔf-jφ^Tx) . The SRS should be transmitted from a single antenna (for example, single-transceiver) UE because phase coherence between multiple UE transceivers may not be guaranteed.

In response to the SRS, each TRP 402 and 404 may transmit a corresponding DL-RS (such as a single-port CSI-RS) to the UE 120. Each DL-RS may be precoded based on the corresponding received SRSDL-RS precoding ensures that timing (propagation delay) and phase variations of a channel do not impact a first precoded DL-RS y₁ (transmitted from the first TRP 402) and a second precoded DL-RS y₂ (transmitted from the second TRP 404) . The precoded DL-RSs may be represented as:

The UE 120 may then calculate based on the received precoded DL-RSs. Similar to the example of Figure 4, the Rx-Tx mismatch is cancelled out, and the only remaining phase is the relative TAE ρ₁₂ and phase offset φ₁₂ between the TRPs 402 and 404, where The relative TAE and phase offset between the two TRPs are estimated by observationacross multiple subcarriers. The TAE ρ₁₂ and phase offset φ₁₂ are reported to one of the TRPs, such as the second TRP 404, to synchronize to the other TRP, such as the first TRP 402.

In the example described with respect to Figure 4, the communication system used a single-transceiver UE. The use of the single-transceiver UE may be advantageous for counteracting the Rx-Tx mismatch of the single-transceiver UE. The mismatch is corrected by processing the signals (for example, ) from the first and second TRPs. For example, the producteffectively eliminates the Rx-Tx phase errors associated with the single-transceiver UE.

However, when multiple transceivers are present in the UE, the Rx-Tx mismatch could differ across the multiple transceivers because the phase errors may not be uniform. This leads to a challenge, because if only one transceiver is used for uplink transmission to avoid Rx-Tx mismatch issues, the transmit power-and consequently the signal-to-noise ratio (SNR) -is effectively reduced. For example, in a two-transceiver UE, using a single-transceiver for uplink transmissions may result in a three decibel (3 dB) loss in power, as the available power is halved. This reduction in uplink transmission power is a drawback because the reduced power may impact a quality of the transmitted signal and reduce overall system performance. Therefore, the coherent use of multiple transceivers within the UE may be desirable, even if these transceivers are not inherently phase-coherent with each other.

The coherent use of multiple transceivers enables the UE to operate multiple transceivers in a coordinated manner, thereby utilizing their combined power for UL transmission without introducing phase errors. Achieving this coherence may be challenging due to the inherent non-coherence between the UE's transceivers. Various aspects of the present disclosure are directed to synchronizing a TAE and phase offset of the multiple TRPs to utilize the multiple transceivers of the UE in a coordinated manner.

Figure 5 is a block diagram illustrating an example of a UE 120 with multiple transceivers, in accordance with various aspects of the present disclosure. In the example of Figure 5, the UE 120 may include a first transceiver 252a and a second transceiver 252b. Each transceiver may communicate with a first TRP 402 and a second TRP 404. The signals between the transceivers 252a and 252b and the TRPs 402 and 404 are represented as h_TRPn, _UE _(m) , where n represents a TRP index and m represents a transceiver index.

In the context of signal processing, z_TRP1←UE ₍₁₎ and z_TRP1←UE ₍₂₎ represent signals received at the first TRP 402 from the first transceiver 252a and the second transceiver 252b, respectively. These signals may be affected by the phase uncertainty at a receiver of the first TRP 402, the channel from the first TRP 402 to the first transceiver 252a and the second transceiver 252b (h_TRP1, _UE ₍₁₎ and h_TRP1, _UE ₍₂₎ , respectively) , and the phase uncertainty at the UE's transmittersSpecifically,

Self-terms refer to the components of the signals that are the direct result of the transmission from a TRP 402 or 404 to a corresponding transceiver 252a or 252b. For example, the self-terms from the first TRP 402 may be represented as:

In equations 10 and 11, each self-term is computed by multiplying a received signal (for example, ) with the conjugate of the corresponding precoded signal z (for example, ) . In equations 10 and 11, [1] and [2] represent an orthogonal signal index, such as the orthogonal DL-RS precoded based on respectively. A magnitude squared of the channel coefficient (|h_TRP1, _UE ₍₁₎ |² and |h_TRP1, _UE ₍₂₎ |²) reflects a power of the channel, and the phase terms are designed to cancel out, leaving only the magnitude of the channel.

Cross-terms occur when a signal from one TRP antenna is mixed with the signal received by a different UE antenna. The cross-terms are calculated similarly to the self-terms but involve the channel coefficients from different paths. A channel phase may be cancelled out when a first cross-term y_UE ₍₁₎ _←TRP1 _[2] is multiplied by a second cross-term y_UE ₍₂₎ _←TRP1 _[1] .

The cross-terms may be represented as:

The cancelled out channel phase may be represented as:

A similar computation may be performed for signals associated with the second TRP 404 and the UE 120, yielding similar self-terms and cross-terms.

A Rx-Tx mismatch, which refers to the difference in phase between signals received and transmitted at the UE 120, may be eliminated by combining the self-terms and cross-terms associated with the first and second TRPs 402 and 404. Specifically, the self-terms and cross-terms associated with the first TRP 402 may be multiplied by the self-terms and cross-terms associated with the second TRP 404 (for example, (y_UE ₍₁₎ _←TRP1 _[1] × y_UE ₍₂₎ _←TRP1 _[1] × y_UE ₍₁₎ _←TRP1 _[2] y_UE ₍₂₎ _←TRP1 _[1] ) × (y_UE ₍₁₎ _←TRP2 _[1] × y_UE ₍₂₎ _←TRP2 _[1] × y_UE ₍₁₎ _←TRP2 _[2] y_UE ₍₂₎ _←TRP2 _[1] ) ) . This results in a network node (for example, one of the TRPs 402 or 404) or the UE 120 extracting four TAEs (4ρ₁₂) and four phase offsets (4φ₁₂) .

This process described with respect to equations 10-14 and the corresponding equations for the second TRP 404 is an example of a coherent function for determining the relative TAE and phase offset by observing the combined terms across multiple subcarriers. The relative TAE and phase offset may be used to synchronize the TRPs 402 and 404. Aspects of the present disclosure are not limited to the coherent function described above, as other functions may be implemented based on UE implementation.

Figure 6 is a timing diagram illustrating an example 600 of a UE 120 with multiple transceivers determining a TAE and a phase offset for multiple TRPs 402 and 404, in accordance with various aspects of the present disclosure. As shown in the example of Figure 6, the UE 120 may include multiple transceivers, labeled 1 to A, where A is greater than one. At time t1a, the UE 120 may transmit an SRS to each TRP 402 and 404 via a first transceiver (index 1) , such that the UE 120 transmits A>1 SRSs. At time t1b, the UE 120 may transmit an SRS to each TRP 402 and 404 via an A^th transceiver (index A) , such that the UE 120 transmits A>1 SRSs. Alternatively, the UE 120 may transmit A>1 SRSs to each TRP 402 and 404 via one or more ports of each transceiver. In the example of Figure 6, an SRS transmitted by the first transceiver to the second TRP 404 is represented as z_TRP2←UE ₍₁₎ and an SRS transmitted by the A^th transceiver to the second TRP 404 is represented as z_TRP2←UE _(A) . Similar representations may be used for the SRSs transmitted from the respective transceivers of the UE 120 to the first TRP 402.

At time t2a, in response to receiving the SRSs at time t1a from the first transceiver, the first TRP 402 transmits a precoded DL-RS, such as a single-port CSI-RS, to each transceiver (1 to A) of the UE 120. Each DL-RS at time t2a may be precoded in accordance with a corresponding SRS (z_TRP1←UE ₍₁₎ ) . At time t2b, in response to receiving the SRSs at time t2b from the A^th transceiver, the first TRP 402 transmits a precoded DL-RS to each transceiver (1 to A) of the UE 120. Each DL-RS at time t2b may be precoded in accordance with a corresponding SRS (z_TRP1←UE _(A) ) . The UE 120 may determine a set of self-terms and cross-terms in response to receiving the DL-RSs from the first TRP 402 at times t2a and t2b.

At time t3a, in response to receiving the SRSs at time t1a from the first transceiver, the second TRP 404 transmits a precoded DL-RS, such as a single-port CSI-RS, to each transceiver (1 to A) of the UE 120. Each DL-RS at time t3a may be precoded in accordance with a corresponding SRS (z_TRP2←UE ₍₁₎ ) . At time t3b, in response to receiving the SRSs at time t1b from the A^th transceiver, the second TRP 404 transmits a precoded DL-RS to each transceiver (1 to A) of the UE 120. Each DL-RS at time t3b may be precoded in accordance with a corresponding SRS (z_TRP2←UE _(A) ) . The UE 120 may determine a set of self-terms and cross-terms in response to receiving the DL-RSs from the second TRP 404 at times t3a and t3b. Each set of DL-RSs transmitted at a time step may be orthogonal.

In the example 600, the SRS should be no less dynamic than the DL-RS. For example, if the DL-RS is periodic, the SRS may be periodic, semi-persistent, or aperiodic. Additionally, if the DL-RS is semi-persistent, the SRS may be semi-persistent or aperiodic. Finally, if the DL-RS is aperiodic, the SRS may be aperiodic.

As discussed, in some examples, each DL-RS transmitted by a TRP may be precoded based on an SRS transmitted by a transceiver of the UE. In some such examples, a network node, such as a core network node or a TRP, may configure a set of DL-RSs (for example single-port CSI-RSs or TRSs) . The set of the DL-RSs may be divided into a number of groups, where the number of groups may be equal to a number of TRPS (N_TRP) , in which N_TRP>1. Each group of DL-RSs may include A>1 DL-RSs. In each group, each DL-RS is associated to an SRS or an SRS port. In the example of Figure 5, the network node may configure two groups of DL-RSs. A first DL-RS in each group may be associated (for example, linked) with a first SRS transmitted at time t1a and a second DL-RS in each group may be associated with a second SRS transmitted at time t2b. Specifically, each DL-RS may be precoded based on a corresponding SRS or SRS port. In some examples, the set of DL-RSs may correspond to a set of SRSs (A>1) . In such examples, the SRSs may be using different symbols or be within a same symbol but on different subcarriers (for example, comb offsets) . In other examples, the set of DL-RSs may be associated with an SRS that uses more than one port. In such examples, the same SRS may be transmitted over identical time-frequency resources but distinguished by varying cyclic shifts. The ports may be associated with the set of transceivers configured at the UE 120, such that a quantity of ports is greater than one.

At time t4, the UE 120 may determine the TAE and/or phase offset based on the DL-RSs received at times t2a, t2b, t3a, and t3b. For example, the UE 120 may determine A² terms for each TRP 402 and 404. These terms include both self-terms and cross-terms, as described above with respect to equations 10-14. For example, for each TRP 402 and 404, the UE may determine A self-terms and A (A-1) cross-terms. The UE 120 may use these terms to calculate the relative TAE ρ₁₂ and phase offsetbetween the TRPs 402 and 404. Specifically, the UE 120 may determine A² multiples of TAE A²ρ₁₂ and A² multiples of phase offsetAt time t5, the UE 120 transmits the relative TAE ρ₁₂ and phase offsetto one of the TRPs 402 or 404, such as the second TRP 404, such that at time t6, the second TRP 404 synchronizes to the other TRP, for example the first TRP 402.

Aspects of the present disclosure are not limited to a UE with two transceivers, as the UE may have any quantity of transceivers, wherein a total quantity of transceivers is greater than one. For example, the UE may have three transceivers (for example, A=3) . In such an example, each TRP may receive three SRSs z from the UE. Specifically, the SRSs received at a first TRP may be expressed as:

Furthermore, the UE may determine three self-terms for each TRP. For example, the self-terms associated with the first TRP may be expressed as:

Additionally, for each TRP, the UE may determine six cross-terms (for example, A (A-1) ) . For example, the cross-terms associated with the first TRP may be expressed as:

Similar to the example for equations 10-14, the phase offset and TAE may be derived from the self-terms and cross-terms associated with the first TRP and the self-terms and cross-terms associated with the second TRP.

Aspects of the present disclosure are not limited to a TRP with a single transmit receive unit (TXRU) . The TXRU may be an example of a transceiver. In some examples, each TRP may include multiple TXRUs. Figure 7 is a diagram illustrating an example 700 of TRPs 702 and 704 with multiple TXRUs, in accordance with various aspects of the present disclosure. In the example 700 of Figure 7, each TRP 702 and 704 may be examples of a base station 110 described with reference to Figures 1 and 2, or a CU 310, DU 330, or RU 340 described with reference to Figure 3. Each TRP 702 and 704 may include P TXRUs, in which P>1 (labeled as 1 to P) . Furthermore, each TRP 702 and 704 may communicate with a UE 120 that includes multiple transceivers 252a and 252b. The respective TXRUs of each TRP 702 and 704 may be coherent. In some examples, the respective TXRUs of each TRP 702 and 704 may use the same downlink resources. Therefore, when transmitting a DL-RS, the TXRUs may be virtualized to appear as a single port.

Based on the example 700 of Figure 7, the signals (for example, SRSs) received at the first TRP may be represented asSpecifically, sized Px1, and sized Px1. Each signal may be influenced by phase uncertaintyat a receiver of the first TRP 702, a respective uplink channel matrix associated with each transceiver 252a and 252band respective phase uncertainty at each transceiver 252a and 252b

For each TRP 702 and 704, the UE 120 may determine a self-term based on a virtualized single port. For example, the self-terms (y_UE ₍₁₎ _←TRP1 _[1] and y_UE(2) _←TRP1 _[2] ) associated with the first TRP 702 may be defined as:

For each TRP 702 and 704, the UE 120 may also determine a cross-term based on a virtualized single port. For example, the cross-terms (y_UE ₍₁₎ _←TRP1 _[2] and y_UE(2) _←TRP1 _[1] ) associated with the first TRP 702 may be defined as: In this example, the termsmay be conjugate to each other.

The cross-terms and self-terms associated with transmissions from the second TRP 704 may be similar to the cross-terms and self-terms associated with transmissions from the first TRP 702. Additionally, similar to the example described with respect to equations 10-14, an Rx-Tx mismatch of a first transceiver 252a and a second transceiver 252b would be canceled by multiplying the self-terms and cross-terms associated with the first TRP 402 with the self-terms and cross-terms associated with the second TRP 404 (for example, (y_UE ₍₁₎ _←TRP1 _[1] × y_UE ₍₂₎ _←TRP1 _[1] × y_UE ₍₁₎ _←TRP1 _[2] y_UE ₍₂₎ _←TRP1 _[1] ) × (y_UE ₍₁₎ _←TRP2 _[1] × y_UE ₍₂₎ _←TRP2 _[1] × y_UE ₍₁₎ _←TRP2 _[2] y_UE ₍₂₎ _←TRP2 _[1] ) ) . This results the UE 120 extracting four TAEs (4ρ₁₂) and four phase offsets (4φ₁₂) .

In some examples, a TRP or central node may determine a TAE and phase offset. In such examples, each TRP, of a group of TRPs, may transmit a DL-RS (for example, single-port CSI-RS) to each transceiver of a set of transceivers (1 to A) of a UE, such as the UE 120 described with reference to Figures 5 and 6. In response, each transceiver may transmit a precoded UL-RS (for example, SRS) to each TRP. Each UL-RS may be precoded based on a corresponding received DL-RS on the corresponding transceiver. For example, a first set of UL-RS transmitted to a first TRP from the set of transceivers may be expressed as z_TRP1←UE ₍₁₎ to z_TRP1←UE _(A) and a second set of UL-RS transmitted to a second TRP from the set of transceivers may be expressed as z_TRP2←UE ₍₁₎ to z_TRP2←UE _(A) . In some examples, the DL-RS should not be less dynamic that the UL-RS (for example, SRS) . In such examples, if the SRS is periodic, the DL-RS may be periodic, semi-persistent, or aperiodic. Additionally, the DL-RS may be semi-persistent or aperiodic if the SRS is semi-persistent. Finally, if the SRS is aperiodic, the DL-RS may be aperiodic.

As discussed, each UL-RS, such an SRS, may be precoded based on the received DL-RS. In some examples, the network node may configure a set of SRS groups, where a number of SRS groups may correspond to the number of TRPs. Alternatively, the network node may configure a set of SRSs, where a number of SRSs in the set may correspond to the number of TRPs. Each SRS group or each SRS of the set of SRSs may be associated with a DL-RS, such that each SRS group or each SRS is precoded in accordance with the associated DL-RS. In some examples, an SRS group may be linked to a DL-RS in different symbols or a DL-RS in the same symbol with different comb offsets. In other examples, an SRS associated with a set of ports (A>1) may be associated with a DL-RS, in which the DL-RS is transmitted on the same time-frequency resources with different cyclic shifts. Accordingly, the SRSs or SRS ports may be associated with the transceivers at the UE.

In some examples, upon receiving the precoded UL-RSs, each TRP may forward the raw UL-RS data (for example, z_TRP1 and z_TRP2) to the central node. Alternatively, one TRP may forward the respective raw UL-RS data to another TRP. The network node that received the raw UL-RS data may then determine a total of A² terms for each TRP. The terms may include self-terms and cross-terms. The network node may then derive the TRP-relative TAE ρ₁₂ and the phase offsetbased on the A² terms for each TRP. The estimated TRP-relative TAE ρ₁₂ and the phase offsetmay then be used by one TRP to synchronize with another TRP.

In accordance with various aspects of the present disclosure, the DL-RSs may be transmitted within a first time period (for example, a first threshold duration) . In some examples, the first time period may be two consecutive slots that do not include a switch between downlink and uplink transmissions. This timing ensures that the UE's receiver does not experience a change in TAE and phase uncertainty while receiving signals from the TRPs. For periodic or semi-persistent CSI-RSs, which are scheduled at regular intervals, the transmission offset satisfies the first threshold duration. For aperiodic CSI-RSs, which do not follow a regular transmission pattern, a triggering offset may satisfy the first threshold duration.

Similarly, SRSs may be transmitted within a second time period (for example, a second threshold duration) . The example given is again two consecutive time slots without a DL/UL switch. In some examples, the second time period may be two consecutive slots without a downlink and uplink switch. This constraint ensures that the UE's transmitter TAE and phase uncertainty remain stable. For periodic or semi-persistent SRSs, the transmission offset may satisfy the second threshold duration. For aperiodic SRSs, the triggering offset may satisfy the second threshold duration.

Additionally, a third time period may be associated with both the DL-RSs and SRSs. Specifically, the third time period may be a sum of the first time period and the second time period. As such, the DL-RSs and SRSs should be transmitted and received within the third time period. The third time period duration may ensure that the channel's phase uncertainty does not vary during the Rx-Tx period.

As discussed, in some examples, the network node may associate each DL-RS of a group of DL-RSs with an SRS. Figure 8 is a block diagram illustrating an example 800 of DL-RSs associated with SRSs, in accordance with various aspects of the present disclosure. In some examples, the network node may configure a set of DL-RSs 808, and the set of DL-RSs 808 may be divided into N_TRP groups of DL-RSs (shown as groups 1 to 4 in Figure 8) , where N_TRP represents a number of TRPs. Each group may include a set of DL-RSs, where a number of DL-RSs in each set may correspond to a number of transceivers A or a number of SRS ports A, both of which correspond to a number of transceivers A at a UE. As shown in the example 800, within each group, each DL-RS 802 may be associated with an index from 1 to A. For brevity, only one DL-RS 802 is labeled in the example 800 of Figure 8. Furthermore, within each group, each DL-RS 802 may be associated with a respective SRS resource 804 of a set of SRS resources 806. For ease of explanation, each SRS resource 804 may be associated with an index from 1 to A. For example, each DL-RS 802 associated with index 1 may be associated with a first SRS resource associated with index 1. In some examples, each SRS resource 804 of the set of SRS resources 806 may be an SRS, and each SRS is transmitted on a different symbol. In other examples, each SRS resource 804 of the set of SRS resources 806 may be an SRS, and each SRS may be transmitted on a same symbol with different comb offsets. In some other examples, each SRS resource 804 may be an SRS port, such that the same SRS may be transmitted from each SRS port over the same time-frequency resources with different cyclic shifts. The set of SRS resources 806 may not be precoded. The set of DL-RSs 808 may be precoded.

Figure 9 is a block diagram illustrating an example wireless communication device that supports selectively updating a frequency-dependent subband impairment estimate, in accordance with various aspects of the present disclosure. The device 900 may be an example of aspects of a UE 120 described with reference to Figures 1, 2, 3, and 4. The wireless communications device 900 may include a receiver 910, a communications manager 905, a transmitter 920, a reference signal component 930, and a synchronization component 940, which may be in communication with one another (for example, via one or more buses) . In some examples, the wireless communications device 900 is configured to perform operations, including operations of the process 1000 described below with reference to Figure 10.

In some examples, the wireless communications device 900 can include a chip, chipset, package, or device that includes at least one processor and at least one modem (for example, a 5G modem or other cellular modem) . In some examples, the communications manager 905, or its sub-components, may be separate and distinct components. In some examples, at least some components of the communications manager 905 are implemented at least in part as software stored in a memory. For example, portions of one or more of the components of the communications manager 905 can be implemented as non-transitory code executable by the processor to perform the functions or operations of the respective component.

The receiver 910 may receive one or more of reference signals (for example, periodically configured channel state information reference signals (CSI-RSs) , aperiodically configured CSI-RSs, or multi-beam-specific reference signals) , synchronization signals (for example, synchronization signal blocks (SSBs) ) , control information and data information, such as in the form of packets, from one or more other wireless communications devices via various channels including control channels (for example, a physical downlink control channel (PDCCH) , physical uplink control channel (PUCCH) , or physical shared control channel (PSCCH) ) and data channels (for example, a physical downlink shared channel (PDSCH) , physical sidelink shared channel (PSSCH) , a physical uplink shared channel (PUSCH) ) . The other wireless communications devices may include, but are not limited to, a base station 110 described with reference to Figures 1, 2, and 4, a DU 330, an RU 340, or a CU 310 described with reference to Figure 3.

The received information may be passed on to other components of the device 900. The receiver 910 may be an example of aspects of the receive processor 258 described with reference to Figure 2. The receiver 910 may include a set of radio frequency (RF) chains that are coupled with or otherwise utilize a set of antennas (for example, the set of antennas may be an example of aspects of the antennas 252 described with reference to Figure 2) .

The transmitter 920 may transmit signals generated by the communications manager 905 or other components of the wireless communications device 900. In some examples, the transmitter 920 may be collocated with the receiver 910 in a transceiver. The transmitter 920 may be an example of aspects of the transmit processor 264 described with reference to Figure 2. The transmitter 920 may be coupled with or otherwise utilize a set of antennas (for example, the set of antennas may be an example of aspects of the antennas 252 described with reference to Figure 2) , which may be antenna elements shared with the receiver 910. In some examples, the transmitter 920 is configured to transmit control information in a PUCCH, PSCCH, or PDCCH and data in a physical uplink shared channel (PUSCH) , PSSCH, or PDSCH.

The communications manager 905 may be an example of aspects of the controller/processor 280 described with reference to Figure 2. The communications manager 905 may include the reference signal component 930 and the synchronization component 940. In some examples, working in conjunction with the transmitter 920, the reference signal component 930 transmits, from each transceiver of a group of transceivers of the UE to each TRP of a group of TRPs, a respective group of SRSs. Additionally, working in conjunction with the receiver 910, the reference signal component 930 receives, from each TRP of the group of TRPs, a respective group of DL-RSs in accordance with transmitting the group of SRSs. Each transceiver of the group of transceivers may be associated with a respective DL-RS of the respective group of DL-RSs. Finally, working in conjunction with the transmitter 920 and the reference signal component 930, the synchronization component 940 transmits, to a TRP the group of TRPs, a message indicating one or more TRP-relative TAEs and one or more phase offsets for one or more pairs of TRPs of the group of TRPs in accordance with receiving the respective group of DL-RSs at each one of the group of transceivers.

Figure 10 is a flow diagram illustrating an example process 1000 for synchronizing a group of TRPs, in accordance with various aspects of the present disclosure. The process 1000 may be performed by UE, such as a UE 120 described with reference to Figures 1, 2, 3, and 4. The example process 1000 begins at block 1002 by transmitting, from each transceiver of a group of transceivers of the UE to each TRP of a group of TRPs, a respective group of SRSs. At block 1004, the process 1000 receives, from each TRP of the group of TRPs, a respective group of DL-RSs in accordance with transmitting the group of SRSs. Each transceiver of the group of transceivers may be associated with a respective DL-RS of the respective group of DL-RSs. At block 1006, the process 1000 transmits, to a TRP the group of TRPs, a message indicating one or more TRP-relative TAEs and one or more phase offsets for one or more pairs of TRPs of the group of TRPs in accordance with receiving the respective group of DL-RSs at each one of the group of transceivers.

Figure 11 is a block diagram illustrating an example wireless communication device that supports synchronizing a group of TRPs, in accordance with various aspects of the present disclosure. The device 1100 may be an example of aspects of a UE 120 described with reference to Figures 1, 2, 3, and 4. The wireless communications device 1100 may include a receiver 1110, a communications manager 1105, a transmitter 1120, a reference signal component 1130, and a precoding component 1140, which may be in communication with one another (for example, via one or more buses) . In some examples, the wireless communications device 1100 is configured to perform operations, including operations of the process 1200 described below with reference to Figure 12.

In some examples, the wireless communications device 1100 can include a chip, chipset, package, or device that includes at least one processor and at least one modem (for example, a 5G modem or other cellular modem) . In some examples, the communications manager 1105, or its sub-components, may be separate and distinct components. In some examples, at least some components of the communications manager 1105 are implemented at least in part as software stored in a memory. For example, portions of one or more of the components of the communications manager 1105 can be implemented as non-transitory code executable by the processor to perform the functions or operations of the respective component.

The receiver 1110 may receive one or more of reference signals (for example, periodically configured CSI-RSs, aperiodically configured CSI-RSs, or multi-beam-specific reference signals) , synchronization signals (for example, synchronization signal blocks (SSBs) ) , control information and data information, such as in the form of packets, from one or more other wireless communications devices via various channels including control channels (for example, a PDCCH, PUCCH, or PSCCH) and data channels (for example, a PDSCH, PSSCH, a PUSCH) . The other wireless communications devices may include, but are not limited to, a base station 110 described with reference to Figures 1, 2, and 4, a DU 330, an RU 340, or a CU 310 described with reference to Figure 3.

The received information may be passed on to other components of the device 1100. The receiver 1110 may be an example of aspects of the receive processor 258 described with reference to Figure 2. The receiver 1110 may include a set of radio frequency (RF) chains that are coupled with or otherwise utilize a set of antennas (for example, the set of antennas may be an example of aspects of the antennas 252 described with reference to Figure 2) .

The transmitter 1120 may transmit signals generated by the communications manager 1105 or other components of the wireless communications device 1100. In some examples, the transmitter 1120 may be collocated with the receiver 1110 in a transceiver. The transmitter 1120 may be an example of aspects of the transmit processor 264 described with reference to Figure 2. The transmitter 1120 may be coupled with or otherwise utilize a set of antennas (for example, the set of antennas may be an example of aspects of the antennas 252 described with reference to Figure 2) , which may be antenna elements shared with the receiver 1110. In some examples, the transmitter 1120 is configured to transmit control information in a PUCCH, PSCCH, or PDCCH and data in a physical uplink shared channel (PUSCH) , PSSCH, or PDSCH.

The communications manager 1105 may be an example of aspects of the controller/processor 280 described with reference to Figure 2. The communications manager 905 may include the reference signal component 1130 and the precoding component 1140. In some examples, working in conjunction with the receiver 1110 the reference signal component 1130 may receive, from each TRP of a group of TRPs, a respective group of DL-RSs. Each transceiver of the group of transceivers may be associated with a respective DL-RS of the respective group of DL-RSs. Furthermore, working in conjunction with the transmitter 1120, the reference signal component 1130 may transmit, from each transceiver of a group of transceivers of the UE to each TRP of a group of TRPs, a respective group of SRS in accordance with receiving the respective group of DL-RSs from each TRP of a group of TRPs. In some examples, working in conjunction with the reference signal component 1130, the precoding component 1140 may precode the groups of SRSs in accordance with receiving the respective group of DL-RSs from each TRP of a group of TRPs.

Figure 12 is a flow diagram illustrating an example process 1200 for synchronizing TRPs, in accordance with various aspects of the present disclosure. The process 1200 may be performed by UE, such as a UE 120 described with reference to Figures 1, 2, 3, and 4. The process 1200 begins at block 1202 by receiving, from each TRP of a group of TRPs, a respective group of DL-RSs. Each transceiver of the group of transceivers may be associated with a respective DL-RS of the respective group of DL-RSs. At block 1204, the process 1200 transmits, from each transceiver of a group of transceivers of the UE to each TRP of a group of TRPs, a respective group of SRS in accordance with receiving the respective group of DL-RSs from each TRP of a group of TRPs.

Implementation examples are described in the following numbered clauses:

Clause 1. A method for wireless communication by a UE, comprising: transmitting, from each transceiver of a group of transceivers of the UE to each TRP of a group of TRPs, a respective group of SRSs; receiving, from each TRP of the group of TRPs, a respective group of DL-RSs in accordance with transmitting the group of SRSs, each transceiver of the group of transceivers being associated with a respective DL-RS of the respective group of DL-RSs; and transmitting, to a TRP the group of TRPs, a message indicating one or more TRP-relative TAEs and one or more phase offsets for one or more pairs of TRPs of the group of TRPs in accordance with receiving the respective group of DL-RSs at each one of the group of transceivers.

Clause 2. The method of Clause 1, further comprising determining, for the group of transceivers, a group of self-terms and a group of cross-terms in accordance with receiving the respective group of DL-RSs from each TRP of the group of TRPs, wherein the one or more TRP-relative TAEs and the one or more phase offsets are a function of the group of self-terms and the group of cross-terms.

Clause 3. The method of any one of Clauses 1-2, wherein the group of TRPs are synchronized in accordance with transmitting the message indicating the one or more TRP-relative TAEs and the one or more phase offsets.

Clause 4. The method of any one of Clauses 1-3, wherein each DL-RS of each of the groups of DL-RSs received from the group of TRPs is precoded in accordance with a respective SRS of the group of SRSs.

Clause 5. The method of any one of Clauses 1-4, wherein: the group of transceivers is associated with a group of SRS ports; and each DL-RS of each of the groups of DL-RSs received from the group of TRPs is precoded in accordance with a respective SRS port of the group of SRS ports.

Clause 6. The method of any one of Clauses 1-5, wherein: each group of DL-RSs received from the group of TRPs is received within a first time period; each group of SRSs transmitted to the group of TRPs is transmitted within a second time period; and a third time period between the transmission of an initial SRS group of the transmitted groups of SRSs and the reception of a final group of DL-RS of the received groups of DL-RSs is less than or equal to a time threshold.

Clause 7. The method of any one of Clauses 1-6, wherein each DL-RS of each of the groups of DL-RSs is a single-port CSI-RS or a TRS.

Clause 8. The method of any one of Clauses 1-7, wherein: each group of SRSs transmitted to the group of TRPs is configured as an aperiodic SRS, and each DL-RS of each of the groups of DL-RSs is configured as aperiodic DL-RS; each group of SRSs transmitted to the group of TRPs is configured as a semi-persistent SRS, and each DL-RS of each of the groups of DL-RSs is configured as aperiodic or semi-persistent DL-RS; or each group of SRSs transmitted to the group of TRPs is configured as periodic SRS, and each DL-RS of each of the groups of DL-RSs is configured as aperiodic, semi-persistent or periodic DL-RS.

The foregoing disclosure provides illustration and description, but is not intended to be exhaustive or to limit the aspects to the precise form disclosed. Modifications and variations may be made in light of the above disclosure or may be acquired from practice of the aspects.

As used, the term “component” is intended to be broadly construed as hardware, firmware, and/or a combination of hardware and software. As used, a processor is implemented in hardware, firmware, and/or a combination of hardware and software.

Some aspects are described in connection with thresholds. As used, satisfying a threshold may, depending on the context, refer to a value being greater than the threshold, greater than or equal to the threshold, less than the threshold, less than or equal to the threshold, equal to the threshold, not equal to the threshold, and/or the like.

It will be apparent that systems and/or methods described may be implemented in different forms of hardware, firmware, and/or a combination of hardware and software. The actual specialized control hardware or software code used to implement these systems and/or methods is not limiting of the aspects. Thus, the operation and behavior of the systems and/or methods were described without reference to specific software code-it being understood that software and hardware can be designed to implement the systems and/or methods based, at least in part, on the description.

Even though particular combinations of features are recited in the claims and/or disclosed in the specification, these combinations are not intended to limit the disclosure of various aspects. In fact, many of these features may be combined in ways not specifically recited in the claims and/or disclosed in the specification. Although each dependent claim listed below may directly depend on only one claim, the disclosure of various aspects includes each dependent claim in combination with every other claim in the claim set. A phrase referring to “at least one of” a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover a, b, c, a-b, a-c, b-c, and a-b-c, as well as any combination with multiples of the same element (for example, a-a, a-a-a, a-a-b, a-a-c, a-b-b, a-c-c, b-b, b-b-b, b-b-c, c-c, and c-c-c or any other ordering of a, b, and c) .

No element, act, or instruction used should be construed as critical or essential unless explicitly described as such. Also, as used, the articles “a” and “an” are intended to include one or more items, and may be used interchangeably with “one or more. ” Furthermore, as used, the terms “set” and “group” are intended to include one or more items (for example, related items, unrelated items, a combination of related and unrelated items, and/or the like) , and may be used interchangeably with “one or more. ” Where only one item is intended, the phrase “only one” or similar language is used. Also, as used, the terms “has, ” “have, ” “having, ” and/or the like are intended to be open-ended terms. Further, the phrase “based on” is intended to mean “based, at least in part, on” unless explicitly stated otherwise.

Claims

A method for wireless communication by a user equipment (UE) , comprising:

transmitting, from each transceiver of a group of transceivers of the UE to each transmission reception point (TRP) of a group of TRPs, a respective group of sounding reference signals (SRSs) ;

receiving, from each TRP of the group of TRPs, a respective group of downlink reference signals (DL-RSs) in accordance with transmitting the group of SRSs, each transceiver of the group of transceivers being associated with a respective DL-RS of the respective group of DL-RSs; and

transmitting, to a TRP the group of TRPs, a message indicating one or more TRP-relative timing alignment errors (TAEs) and one or more phase offsets for one or more pairs of TRPs of the group of TRPs in accordance with receiving the respective group of DL-RSs at each one of the group of transceivers.
The method of claim 1, further comprising determining, for the group of transceivers, a group of self-terms and a group of cross-terms in accordance with receiving the respective group of DL-RSs from each TRP of the group of TRPs, wherein the one or more TRP-relative TAEs and the one or more phase offsets are a function of the group of self-terms and the group of cross-terms.
The method of claim 1, wherein the group of TRPs are synchronized in accordance with transmitting the message indicating the one or more TRP-relative TAEs and the one or more phase offsets.
The method of claim 1, wherein each DL-RS of each of the groups of DL-RSs received from the group of TRPs is precoded in accordance with a respective SRS of the group of SRSs.
The method of claim 1, wherein:

the group of transceivers is associated with a group of SRS ports; and

each DL-RS of each of the groups of DL-RSs received from the group of TRPs is precoded in accordance with a respective SRS port of the group of SRS ports.
The method of claim 1, wherein:

each group of DL-RSs received from the group of TRPs is received within a first time period;

each group of SRSs transmitted to the group of TRPs is transmitted within a second time period; and

a third time period between the transmission of an initial SRS group of the transmitted groups of SRSs and the reception of a final group of DL-RS of the received groups of DL-RSs is less than or equal to a time threshold.
The method of claim 1, wherein each DL-RS of each of the groups of DL-RSs is a single-port channel state information (CSI) -RS (CSI-RS) or a tracking reference signal (TRS) .
The method of claim 1, wherein:

each group of SRSs transmitted to the group of TRPs is configured as an aperiodic SRS, and each DL-RS of each of the groups of DL-RSs is configured as aperiodic DL-RS;

each group of SRSs transmitted to the group of TRPs is configured as a semi-persistent SRS, and each DL-RS of each of the groups of DL-RSs is configured as aperiodic or semi-persistent DL-RS;

each group of SRSs transmitted to the group of TRPs is configured as periodic SRS, and each DL-RS of each of the groups of DL-RSs is configured as aperiodic, semi-persistent or periodic DL-RS.
A user equipment (UE) , comprising:

one or more processors; and

one or more memories coupled with the one or more processors and storing instructions operable, when executed by the one or more processors, to cause the apparatus to:

transmit, from each transceiver of a group of transceivers of the UE to each transmission reception point (TRP) of a group of TRPs, a respective group of sounding reference signals (SRSs) ;

receive, from each TRP of the group of TRPs, a respective group of downlink reference signals (DL-RSs) in accordance with transmitting the group of SRSs, each transceiver of the group of transceivers being associated with a respective DL-RS of the respective group of DL-RSs; and

transmit, to a TRP the group of TRPs, a message indicating one or more TRP-relative timing alignment errors (TAEs) and one or more phase offsets for one or more pairs of TRPs of the group of TRPs in accordance with receiving the respective group of DL-RSs at each one of the group of transceivers.
The UE of claim 9, wherein execution of the instructions further cause the apparatus to determine, for the group of transceivers, a group of self-terms and a group of cross-terms in accordance with receiving the respective group of DL-RSs from each TRP of the group of TRPs, wherein the one or more TRP-relative TAEs and the one or more phase offsets are a function of the group of self-terms and the group of cross-terms.
The UE of claim 9, wherein the group of TRPs are synchronized in accordance with transmitting the message indicating the one or more TRP-relative TAEs and the one or more phase offsets.
The UE of claim 9, wherein each DL-RS of each of the groups of DL-RSs received from the group of TRPs is precoded in accordance with a respective SRS of the group of SRSs.
The UE of claim 9, wherein:

the group of transceivers is associated with a group of SRS ports; and

each DL-RS of each of the groups of DL-RSs received from the group of TRPs is precoded in accordance with a respective SRS port of the group of SRS ports.
The UE of claim 9, wherein:

each group of DL-RSs received from the group of TRPs is received within a first time period;

each group of SRSs transmitted to the group of TRPs is transmitted within a second time period; and

a third time period between the transmission of an initial SRS group of the transmitted groups of SRSs and the reception of a final group of DL-RS of the received groups of DL-RSs is less than or equal to a time threshold.
The UE of claim 9, wherein each DL-RS of each of the groups of DL-RSs is a single-port channel state information (CSI) -RS (CSI-RS) or a tracking reference signal (TRS) .
The UE of claim 9, wherein:

each group of SRSs transmitted to the group of TRPs is configured as an aperiodic SRS, and each DL-RS of each of the groups of DL-RSs is configured as aperiodic DL-RS;

each group of SRSs transmitted to the group of TRPs is configured as a semi-persistent SRS, and each DL-RS of each of the groups of DL-RSs is configured as aperiodic or semi-persistent DL-RS; or

each group of SRSs transmitted to the group of TRPs is configured as periodic SRS, and each DL-RS of each of the groups of DL-RSs is configured as aperiodic, semi-persistent or periodic DL-RS.
An apparatus for wireless communication at a user equipment (UE) , apparatus comprising:

means for transmitting, from each transceiver of a group of transceivers of the UE to each transmission reception point (TRP) of a group of TRPs, a respective group of sounding reference signals (SRSs) ;

means for receiving, from each TRP of the group of TRPs, a respective group of downlink reference signals (DL-RSs) in accordance with transmitting the group of SRSs, each transceiver of the group of transceivers being associated with a respective DL-RS of the respective group of DL-RSs; and

means for transmitting, to a TRP the group of TRPs, a message indicating one or more TRP-relative timing alignment errors (TAEs) and one or more phase offsets for one or more pairs of TRPs of the group of TRPs in accordance with receiving the respective group of DL-RSs at each one of the group of transceivers.
The apparatus of claim 17, further comprising means for determining, for the group of transceivers, a group of self-terms and a group of cross-terms in accordance with receiving the respective group of DL-RSs from each TRP of the group of TRPs, wherein the one or more TRP-relative TAEs and the one or more phase offsets are a function of the group of self-terms and the group of cross-terms.
The apparatus of claim 17, wherein the group of TRPs are synchronized in accordance with transmitting the message indicating the one or more TRP-relative TAEs and the one or more phase offsets.
The apparatus of claim 17, wherein each DL-RS of each of the groups of DL-RSs received from the group of TRPs is precoded in accordance with a respective SRS of the group of SRSs.