MULTIPLE TIMING MAINTENANCE AND ESTIMATION OF TIMING ERROR BETWEEN MULTIPLE RUS/TRPS/CELLS

BACKGROUND
Field

The present disclosure relates generally to communication systems, and more particularly, to techniques of determining clock errors between a first access node and a second access node.

Background

The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

Wireless communication systems are widely deployed to provide various telecommunication services such as telephony, video, data, messaging, and broadcasts. Typical wireless communication systems may employ multiple-access technologies capable of supporting communication with multiple users by sharing available system resources. 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, and time division synchronous code division multiple access (TD-SCDMA) systems.

These multiple access technologies have been adopted in various telecommunication standards to provide a common protocol that enables different wireless devices to communicate on a municipal, national, regional, and even global level. An example telecommunication standard is 5G New Radio (NR). 5G NR is part of a continuous mobile broadband evolution promulgated by Third Generation Partnership Project (3GPP) to meet new requirements associated with latency, reliability, security, scalability (e.g., with Internet of Things (IoT)), and other requirements. Some aspects of 5G NR may be based on the 4G Long Term Evolution (LTE) standard. There exists a need for further improvements in 5G NR technology. These improvements may also be applicable to other multi-access technologies and the telecommunication standards that employ these technologies.

SUMMARY

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

In an aspect of the disclosure, a method, a computer-readable medium, and an apparatus are provided. The apparatus may be a UE. The UE receives first downlink signals from a first access node. The UE determines a first downlink timing of the first access node based on the first downlink signals. The UE transmits a first preamble to a second access node based on the first downlink timing of the first access node. The UE receives second downlink signals from the second access node. The UE determines a second downlink timing of the second access node based on the second downlink signals. The UE transmits a second preamble to the second access node based on the second downlink timing of the second access node.

In another aspect of the disclosure, a method, a computer-readable medium, and an apparatus are provided. The apparatus may be a UE. The UE receives first downlink signals from a first access node and second downlink signals from a second access node. The UE determines a first downlink timing based on the first downlink signals and a second downlink timing based on the second downlink signals. The UE transmits a first preamble to the second access node based on the first downlink timing. The UE estimates a downlink timing difference between the first downlink timing and the second downlink timing. The UE transmits a report of the estimated downlink timing difference to at least one of the first access node and second access node.

To the accomplishment of the foregoing and related ends, the one or more aspects comprise the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative features of the one or more aspects. These features are indicative, however, of but a few of the various ways in which the principles of various aspects may be employed, and this description is intended to include all such aspects and their equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of a wireless communications system and an access network.

FIG. 2 is a diagram illustrating a base station in communication with a UE in an access network.

FIG. 3 illustrates an example logical architecture of a distributed access network.

FIG. 4 illustrates an example physical architecture of a distributed access network.

FIG. 5 is a diagram showing an example of a DL-centric slot.

FIG. 6 is a diagram showing an example of an UL-centric slot.

FIG. 7 is a diagram illustrating a communication system.

FIG. 8 is a sequence diagram illustrating interactions among a UE, a source node, and a target node according to a first technique to determine a clock error between the source node and the target node.

FIG. 9 is a diagram illustrating timing of transmissions and receptions at the UE, the source node, and the target node according to the first technique.

FIG. 10 is a sequence diagram illustrating interactions among a UE, a source node, and a target node according to a second technique to determine a clock error between the source node and the target node.

FIG. 11 is a diagram illustrating timing of transmissions and receptions at the UE, the source node, and the target node according to the second technique.

FIG. 12 is a flow chart of a first method (process) for assisting determination of a clock error between two access nodes.

FIG. 13 is a flow chart of a second method (process) for assisting determination of a clock error between two access nodes.

DETAILED DESCRIPTION

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

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

By way of example, an element, or any portion of an element, or any combination of elements may be implemented as a “processing system” that includes one or more processors. Examples of processors include microprocessors, microcontrollers, graphics processing units (GPUs), central processing units (CPUs), application processors, digital signal processors (DSPs), reduced instruction set computing (RISC) processors, systems on a chip (SoC), baseband processors, field programmable gate arrays (FPGAs), programmable logic devices (PLDs), state machines, gated logic, discrete hardware circuits, and other suitable hardware configured to perform the various functionality described throughout this disclosure. One or more processors in the processing system may execute software. Software shall be construed broadly to mean instructions, instruction sets, code, code segments, program code, programs, subprograms, software components, applications, software applications, software packages, routines, subroutines, objects, executables, threads of execution, procedures, functions, etc., whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise.

Accordingly, in one or more example aspects, the functions described may be implemented in hardware, software, or any combination thereof. If implemented in software, the functions may be stored on or encoded as one or more instructions or code on a computer-readable medium. Computer-readable media includes computer storage media. Storage media may be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can comprise a random-access memory (RAM), a read-only memory (ROM), an electrically erasable programmable ROM (EEPROM), optical disk storage, magnetic disk storage, other magnetic storage devices, combinations of the aforementioned types of computer-readable media, or any other medium that can be used to store computer executable code in the form of instructions or data structures that can be accessed by a computer.

FIG. 1 is a diagram illustrating an example of a wireless communications system and an access network 100. The wireless communications system (also referred to as a wireless wide area network (WWAN)) includes base stations 102, UEs 104, an Evolved Packet Core (EPC) 160, and another core network 190 (e.g., a 5G Core (5GC)). The base stations 102 may include macrocells (high power cellular base station) and/or small cells (low power cellular base station). The macrocells include base stations. The small cells include femtocells, picocells, and microcells.

The base stations 102 configured for 4G LTE (collectively referred to as Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (E-UTRAN)) may interface with the EPC 160 through backhaul links 132 (e.g., SI interface). The base stations 102 configured for 5G NR (collectively referred to as Next Generation RAN (NG-RAN)) may interface with core network 190 through backhaul links 184. In addition to other functions, the base stations 102 may perform one or more of the following functions: transfer of user data, radio channel ciphering and deciphering, integrity protection, header compression, mobility control functions (e.g., handover, dual connectivity), inter cell interference coordination, connection setup and release, load balancing, distribution for non-access stratum (NAS) messages, NAS node selection, synchronization, radio access network (RAN) sharing, multimedia broadcast multicast service (MBMS), subscriber and equipment trace, RAN information management (RIM), paging, positioning, and delivery of warning messages. The base stations 102 may communicate directly or indirectly (e.g., through the EPC 160 or core network 190) with each other over backhaul links 134 (e.g., X2 interface). The backhaul links 134 may be wired or wireless.

The base stations 102 may wirelessly communicate with the UEs 104. Each of the base stations 102 may provide communication coverage for a respective geographic coverage area 110. There may be overlapping geographic coverage areas 110. For example, the small cell 102′ may have a coverage area 110′ that overlaps the coverage area 110 of one or more macro base stations 102. A network that includes both small cell and macrocells may be known as a heterogeneous network. A heterogeneous network may also include Home Evolved Node Bs (eNBs) (HeNBs), which may provide service to a restricted group known as a closed subscriber group (CSG). The communication links 120 between the base stations 102 and the UEs 104 may include uplink (UL) (also referred to as reverse link) transmissions from a UE 104 to a base station 102 and/or downlink (DL) (also referred to as forward link) transmissions from a base station 102 to a UE 104. The communication links 120 may use multiple-input and multiple-output (MIMO) antenna technology, including spatial multiplexing, beamforming, and/or transmit diversity. The communication links may be through one or more carriers. The base stations 102/UEs 104 may use spectrum up to X MHz (e.g., 5, 10, 15, 20, 100, 400, etc. MHz) bandwidth per carrier allocated in a carrier aggregation of up to a total of Yx MHz (x component carriers) used for transmission in each direction. The carriers may or may not be adjacent to each other. Allocation of carriers may be asymmetric with respect to DL and UL (e.g., more or fewer carriers may be allocated for DL than for UL). The component carriers may include a primary component carrier and one or more secondary component carriers. A primary component carrier may be referred to as a primary cell (PCell) and a secondary component carrier may be referred to as a secondary cell (SCell).

Certain UEs 104 may communicate with each other using device-to-device (D2D) communication link 158. The D2D communication link 158 may use the DL/UL WWAN spectrum. The D2D communication link 158 may use one or more sidelink channels, such as a physical sidelink broadcast channel (PSBCH), a physical sidelink discovery channel (PSDCH), a physical sidelink shared channel (PSSCH), and a physical sidelink control channel (PSCCH). D2D communication may be through a variety of wireless D2D communications systems, such as for example, FlashLinQ, WiMedia, Bluetooth, ZigBee, Wi-Fi based on the IEEE 802.11 standard, LTE, or NR.

The wireless communications system may further include a Wi-Fi access point (AP) 150 in communication with Wi-Fi stations (STAs) 152 via communication links 154 in a 5 GHz unlicensed frequency spectrum. When communicating in an unlicensed frequency spectrum, the STAs 152/AP 150 may perform a clear channel assessment (CCA) prior to communicating in order to determine whether the channel is available.

The small cell 102′ may operate in a licensed and/or an unlicensed frequency spectrum. When operating in an unlicensed frequency spectrum, the small cell 102′ may employ NR and use the same 5 GHz unlicensed frequency spectrum as used by the Wi-Fi AP 150. The small cell 102′, employing NR in an unlicensed frequency spectrum, may boost coverage to and/or increase capacity of the access network.

A base station 102, whether a small cell 102′ or a large cell (e.g., macro base station), may include an eNB, gNodeB (gNB), or another type of base station. Some base stations, such as gNB 180 may operate in a traditional sub 6 GHz spectrum, in millimeter wave (mmW) frequencies, and/or near mmW frequencies in communication with the UE 104. When the gNB 180 operates in mmW or near mmW frequencies, the gNB 180 may be referred to as an mmW base station. Extremely high frequency (EHF) is part of the RF in the electromagnetic spectrum. EHF has a range of 30 GHz to 300 GHz and a wavelength between 1 millimeter and 10 millimeters. Radio waves in the band may be referred to as a millimeter wave. Near mmW may extend down to a frequency of 3 GHz with a wavelength of 100 millimeters. The super high frequency (SHF) band extends between 3 GHz and 30 GHz, also referred to as centimeter wave. Communications using the mmW/near mmW radio frequency band (e.g., 3 GHZ-300 GHz) has extremely high path loss and a short range. The mmW base station 180 may utilize beamforming 182 with the UE 104 to compensate for the extremely high path loss and short range.

The base station 180 may transmit a beamformed signal to the UE 104 in one or more transmit directions 108a. The UE 104 may receive the beamformed signal from the base station 180 in one or more receive directions 108b. The UE 104 may also transmit a beamformed signal to the base station 180 in one or more transmit directions. The base station 180 may receive the beamformed signal from the UE 104 in one or more receive directions. The base station 180/UE 104 may perform beam training to determine the best receive and transmit directions for each of the base station 180/UE 104. The transmit and receive directions for the base station 180 may or may not be the same. The transmit and receive directions for the UE 104 may or may not be the same.

The EPC 160 may include a Mobility Management Entity (MME) 162, other MMEs 164, a Serving Gateway 166, a Multimedia Broadcast Multicast Service (MBMS) Gateway 168, a Broadcast Multicast Service Center (BM-SC) 170, and a Packet Data Network (PDN) Gateway 172. The MME 162 may be in communication with a Home Subscriber Server (HSS) 174. The MME 162 is the control node that processes the signaling between the UEs 104 and the EPC 160. Generally, the MME 162 provides bearer and connection management. All user Internet protocol (IP) packets are transferred through the Serving Gateway 166, which itself is connected to the PDN Gateway 172. The PDN Gateway 172 provides UE IP address allocation as well as other functions. The PDN Gateway 172 and the BM-SC 170 are connected to the IP Services 176. The IP Services 176 may include the Internet, an intranet, an IP Multimedia Subsystem (IMS), a PS Streaming Service, and/or other IP services. The BM-SC 170 may provide functions for MBMS user service provisioning and delivery. The BM-SC 170 may serve as an entry point for content provider MBMS transmission, may be used to authorize and initiate MBMS Bearer Services within a public land mobile network (PLMN), and may be used to schedule MBMS transmissions. The MBMS Gateway 168 may be used to distribute MBMS traffic to the base stations 102 belonging to a Multicast Broadcast Single Frequency Network (MBSFN) area broadcasting a particular service, and may be responsible for session management (start/stop) and for collecting eMBMS related charging information.

The core network 190 may include a Access and Mobility Management Function (AMF) 192, other AMFs 193, a location management function (LMF) 198, a Session Management Function (SMF) 194, and a User Plane Function (UPF) 195. The AMF 192 may be in communication with a Unified Data Management (UDM) 196. The AMF 192 is the control node that processes the signaling between the UEs 104 and the core network 190. Generally, the SMF 194 provides QoS flow and session management. All user Internet protocol (IP) packets are transferred through the UPF 195. The UPF 195 provides UE IP address allocation as well as other functions. The UPF 195 is connected to the IP Services 197. The IP Services 197 may include the Internet, an intranet, an IP Multimedia Subsystem (IMS), a PS Streaming Service, and/or other IP services.

The base station may also be referred to as a gNB, Node B, evolved Node B (eNB), an access point, a base transceiver station, a radio base station, a radio transceiver, a transceiver function, a basic service set (BSS), an extended service set (ESS), a transmit reception point (TRP), or some other suitable terminology. The base station 102 provides an access point to the EPC 160 or core network 190 for a UE 104. Examples of UEs 104 include a cellular phone, a smart phone, a session initiation protocol (SIP) phone, a laptop, a personal digital assistant (PDA), a satellite radio, a global positioning system, a multimedia device, a video device, a digital audio player (e.g., MP3 player), a camera, a game console, a tablet, a smart device, a wearable device, a vehicle, an electric meter, a gas pump, a large or small kitchen appliance, a healthcare device, an implant, a sensor/actuator, a display, or any other similar functioning device. Some of the UEs 104 may be referred to as IoT devices (e.g., parking meter, gas pump, toaster, vehicles, heart monitor, etc.). The UE 104 may also be referred to as a station, a mobile station, a subscriber station, a mobile unit, a subscriber unit, a wireless unit, a remote unit, a mobile device, a wireless device, a wireless communications device, a remote device, a mobile subscriber station, an access terminal, a mobile terminal, a wireless terminal, a remote terminal, a handset, a user agent, a mobile client, a client, or some other suitable terminology.

Although the present disclosure may reference 5G New Radio (NR), the present disclosure may be applicable to other similar areas, such as LTE, LTE-Advanced (LTE-A), Code Division Multiple Access (CDMA), Global System for Mobile communications (GSM), or other wireless/radio access technologies.

FIG. 2 is a block diagram of a base station 210 in communication with a UE 250 in an access network. In the DL, IP packets from the EPC 160 may be provided to a controller/processor 275. The controller/processor 275 implements layer 3 and layer 2 functionality. Layer 3 includes a radio resource control (RRC) layer, and layer 2 includes a packet data convergence protocol (PDCP) layer, a radio link control (RLC) layer, and a medium access control (MAC) layer. The controller/processor 275 provides RRC layer functionality associated with broadcasting of system information (e.g., MIB, SIBs), RRC connection control (e.g., RRC connection paging, RRC connection establishment, RRC connection modification, and RRC connection release), inter radio access technology (RAT) mobility, and measurement configuration for UE measurement reporting; PDCP layer functionality associated with header compression/decompression, security (ciphering, deciphering, integrity protection, integrity verification), and handover support functions; RLC layer functionality associated with the transfer of upper layer packet data units (PDUs), error correction through ARQ, concatenation, segmentation, and reassembly of RLC service data units (SDUs), re-segmentation of RLC data PDUs, and reordering of RLC data PDUs; and MAC layer functionality associated with mapping between logical channels and transport channels, multiplexing of MAC SDUs onto transport blocks (TBs), demultiplexing of MAC SDUs from TBs, scheduling information reporting, error correction through HARQ, priority handling, and logical channel prioritization.

The transmit (TX) processor 216 and the receive (RX) processor 270 implement layer 1 functionality associated with various signal processing functions. Layer 1, which includes a physical (PHY) layer, may include error detection on the transport channels, forward error correction (FEC) coding/decoding of the transport channels, interleaving, rate matching, mapping onto physical channels, modulation/demodulation of physical channels, and MIMO antenna processing. The TX processor 216 handles mapping to signal constellations based on various modulation schemes (e.g., binary phase-shift keying (BPSK), quadrature phase-shift keying (QPSK), M-phase-shift keying (M-PSK), M-quadrature amplitude modulation (M-QAM)). The coded and modulated symbols may then be split into parallel streams. Each stream may then be mapped to an OFDM subcarrier, multiplexed with a reference signal (e.g., pilot) in the time and/or frequency domain, and then combined together using an Inverse Fast Fourier Transform (IFFT) to produce a physical channel carrying a time domain OFDM symbol stream. The OFDM stream is spatially precoded to produce multiple spatial streams. Channel estimates from a channel estimator 274 may be used to determine the coding and modulation scheme, as well as for spatial processing. The channel estimate may be derived from a reference signal and/or channel condition feedback transmitted by the UE 250. Each spatial stream may then be provided to a different antenna 220 via a separate transmitter 218TX. Each transmitter 218TX may modulate an RF carrier with a respective spatial stream for transmission.

At the UE 250, each receiver 254RX receives a signal through its respective antenna 252. Each receiver 254RX recovers information modulated onto an RF carrier and provides the information to the receive (RX) processor 256. The TX processor 268 and the RX processor 256 implement layer 1 functionality associated with various signal processing functions. The RX processor 256 may perform spatial processing on the information to recover any spatial streams destined for the UE 250. If multiple spatial streams are destined for the UE 250, they may be combined by the RX processor 256 into a single OFDM symbol stream. The RX processor 256 then converts the OFDM symbol stream from the time-domain to the frequency domain using a Fast Fourier Transform (FFT). The frequency domain signal comprises a separate OFDM symbol stream for each subcarrier of the OFDM signal. The symbols on each subcarrier, and the reference signal, are recovered and demodulated by determining the most likely signal constellation points transmitted by the base station 210. These soft decisions may be based on channel estimates computed by the channel estimator 258. The soft decisions are then decoded and deinterleaved to recover the data and control signals that were originally transmitted by the base station 210 on the physical channel. The data and control signals are then provided to the controller/processor 259, which implements layer 3 and layer 2 functionality.

The controller/processor 259 can be associated with a memory 260 that stores program codes and data. The memory 260 may be referred to as a computer-readable medium. In the UL, the controller/processor 259 provides demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, and control signal processing to recover IP packets from the EPC 160. The controller/processor 259 is also responsible for error detection using an ACK and/or NACK protocol to support HARQ operations.

Similar to the functionality described in connection with the DL transmission by the base station 210, the controller/processor 259 provides RRC layer functionality associated with system information (e.g., MIB, SIBs) acquisition, RRC connections, and measurement reporting; PDCP layer functionality associated with header compression/decompression, and security (ciphering, deciphering, integrity protection, integrity verification); RLC layer functionality associated with the transfer of upper layer PDUs, error correction through ARQ, concatenation, segmentation, and reassembly of RLC SDUs, re-segmentation of RLC data PDUs, and reordering of RLC data PDUs; and MAC layer functionality associated with mapping between logical channels and transport channels, multiplexing of MAC SDUs onto TBs, demultiplexing of MAC SDUs from TBs, scheduling information reporting, error correction through HARQ, priority handling, and logical channel prioritization.

Channel estimates derived by a channel estimator 258 from a reference signal or feedback transmitted by the base station 210 may be used by the TX processor 268 to select the appropriate coding and modulation schemes, and to facilitate spatial processing. The spatial streams generated by the TX processor 268 may be provided to different antenna 252 via separate transmitters 254TX. Each transmitter 254TX may modulate an RF carrier with a respective spatial stream for transmission. The UL transmission is processed at the base station 210 in a manner similar to that described in connection with the receiver function at the UE 250. Each receiver 218RX receives a signal through its respective antenna 220. Each receiver 218RX recovers information modulated onto an RF carrier and provides the information to a RX processor 270.

The controller/processor 275 can be associated with a memory 276 that stores program codes and data. The memory 276 may be referred to as a computer-readable medium. In the UL, the controller/processor 275 provides demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, control signal processing to recover IP packets from the UE 250. IP packets from the controller/processor 275 may be provided to the EPC 160. The controller/processor 275 is also responsible for error detection using an ACK and/or NACK protocol to support HARQ operations.

New radio (NR) may refer to radios configured to operate according to a new air interface (e.g., other than Orthogonal Frequency Divisional Multiple Access (OFDMA)-based air interfaces) or fixed transport layer (e.g., other than Internet Protocol (IP)). NR may utilize OFDM with a cyclic prefix (CP) on the uplink and downlink and may include support for half-duplex operation using time division duplexing (TDD). NR may include Enhanced Mobile Broadband (eMBB) service targeting wide bandwidth (e.g., 80 MHz beyond), millimeter wave (mmW) targeting high carrier frequency (e.g., 60 GHz), massive MTC (mMTC) targeting non-backward compatible MTC techniques, and/or mission critical targeting ultra-reliable low latency communications (URLLC) service.

A single component carrier bandwidth of 100 MHz may be supported. In one example, NR resource blocks (RBs) may span 12 sub-carriers for each RB with a sub-carrier spacing (SCS) of 60 kHz over a 0.25 ms duration or a SCS of 30 kHz over a 0.5 ms duration (similarly, 15 kHz SCS over a 1 ms duration). Each radio frame may consist of 10 subframes (10, 20, 40 or 80 NR slots) with a length of 10 ms. Each slot may indicate a link direction (i.e., DL or UL) for data transmission and the link direction for each slot may be dynamically switched. Each slot may include DL/UL data as well as DL/UL control data. UL and DL slots for NR may be as described in more detail below with respect to FIGS. 5 and 6.

The NR RAN may include a central unit (CU) and distributed units (DUs). A NR BS (e.g., gNB, 5G Node B, Node B, transmission reception point (TRP), access point (AP)) may correspond to one or multiple BSs. NR cells can be configured as access cells (ACells) or data only cells (DCells). For example, the RAN (e.g., a central unit or distributed unit) can configure the cells. DCells may be cells used for carrier aggregation or dual connectivity and may not be used for initial access, cell selection/reselection, or handover. In some cases DCells may not transmit synchronization signals (SS) in some cases DCells may transmit SS. NR BSs may transmit downlink signals to UEs indicating the cell type. Based on the cell type indication, the UE may communicate with the NR BS. For example, the UE may determine NR BSs to consider for cell selection, access, handover, and/or measurement based on the indicated cell type.

FIG. 3 illustrates an example logical architecture of a distributed RAN 300, according to aspects of the present disclosure. A 5G access node 306 may include an access node controller (ANC) 302. The ANC may be a central unit (CU) of the distributed RAN. The backhaul interface to the next generation core network (NG-CN) 304 may terminate at the ANC. The backhaul interface to neighboring next generation access nodes (NG-ANs) 310 may terminate at the ANC. The ANC may include one or more TRPs 308 (which may also be referred to as BSs, NR BSs, Node Bs, 5G NBs, APs, or some other term). As described above, a TRP may be used interchangeably with “cell.”

The TRPs 308 may be a distributed unit (DU). The TRPs may be connected to one ANC (ANC 302) or more than one ANC (not illustrated). For example, for RAN sharing, radio as a service (RaaS), and service specific ANC deployments, the TRP may be connected to more than one ANC. A TRP may include one or more antenna ports. The TRPs may be configured to individually (e.g., dynamic selection) or jointly (e.g., joint transmission) serve traffic to a UE.

The local architecture of the distributed RAN 300 may be used to illustrate fronthaul definition. The architecture may be defined that support fronthauling solutions across different deployment types. For example, the architecture may be based on transmit network capabilities (e.g., bandwidth, latency, and/or jitter). The architecture may share features and/or components with LTE. According to aspects, the next generation AN (NG-AN) 310 may support dual connectivity with NR. The NG-AN may share a common fronthaul for LTE and NR.

The architecture may enable cooperation between and among TRPs 308. For example, cooperation may be preset within a TRP and/or across TRPs via the ANC 302. According to aspects, no inter-TRP interface may be needed/present.

According to aspects, a dynamic configuration of split logical functions may be present within the architecture of the distributed RAN 300. The PDCP, RLC, MAC protocol may be adaptably placed at the ANC or TRP.

FIG. 4 illustrates an example physical architecture of a distributed RAN 400, according to aspects of the present disclosure. A centralized core network unit (C-CU) 402 may host core network functions. The C-CU may be centrally deployed. C-CU functionality may be offloaded (e.g., to advanced wireless services (AWS)), in an effort to handle peak capacity. A centralized RAN unit (C-RU) 404 may host one or more ANC functions. Optionally, the C-RU may host core network functions locally. The C-RU may have distributed deployment. The C-RU may be closer to the network edge. A distributed unit (DU) 406 may host one or more TRPs. The DU may be located at edges of the network with radio frequency (RF) functionality.

FIG. 5 is a diagram 500 showing an example of a DL-centric slot. The DL-centric slot may include a control portion 502. The control portion 502 may exist in the initial or beginning portion of the DL-centric slot. The control portion 502 may include various scheduling information and/or control information corresponding to various portions of the DL-centric slot. In some configurations, the control portion 502 may be a physical DL control channel (PDCCH), as indicated in FIG. 5. The DL-centric slot may also include a DL data portion 504. The DL data portion 504 may sometimes be referred to as the payload of the DL-centric slot. The DL data portion 504 may include the communication resources utilized to communicate DL data from the scheduling entity (e.g., UE or BS) to the subordinate entity (e.g., UE). In some configurations, the DL data portion 504 may be a physical DL shared channel (PDSCH).

The DL-centric slot may also include a common UL portion 506. The common UL portion 506 may sometimes be referred to as an UL burst, a common UL burst, and/or various other suitable terms. The common UL portion 506 may include feedback information corresponding to various other portions of the DL-centric slot. For example, the common UL portion 506 may include feedback information corresponding to the control portion 502. Non-limiting examples of feedback information may include an ACK signal, a NACK signal, a HARQ indicator, and/or various other suitable types of information. The common UL portion 506 may include additional or alternative information, such as information pertaining to random access channel (RACH) procedures, scheduling requests (SRs), and various other suitable types of information.

As illustrated in FIG. 5, the end of the DL data portion 504 may be separated in time from the beginning of the common UL portion 506. This time separation may sometimes be referred to as a gap, a guard period, a guard interval, and/or various other suitable terms. This separation provides time for the switch-over from DL communication (e.g., reception operation by the subordinate entity (e.g., UE)) to UL communication (e.g., transmission by the subordinate entity (e.g., UE)). One of ordinary skill in the art will understand that the foregoing is merely one example of a DL-centric slot and alternative structures having similar features may exist without necessarily deviating from the aspects described herein.

FIG. 6 is a diagram 600 showing an example of an UL-centric slot. The UL-centric slot may include a control portion 602. The control portion 602 may exist in the initial or beginning portion of the UL-centric slot. The control portion 602 in FIG. 6 may be similar to the control portion 502 described above with reference to FIG. 5. The UL-centric slot may also include an UL data portion 604. The UL data portion 604 may sometimes be referred to as the pay load of the UL-centric slot. The UL portion may refer to the communication resources utilized to communicate UL data from the subordinate entity (e.g., UE) to the scheduling entity (e.g., UE or BS). In some configurations, the control portion 602 may be a physical DL control channel (PDCCH).

As illustrated in FIG. 6, the end of the control portion 602 may be separated in time from the beginning of the UL data portion 604. This time separation may sometimes be referred to as a gap, guard period, guard interval, and/or various other suitable terms. This separation provides time for the switch-over from DL communication (e.g., reception operation by the scheduling entity) to UL communication (e.g., transmission by the scheduling entity). The UL-centric slot may also include a common UL portion 606. The common UL portion 606 in FIG. 6 may be similar to the common UL portion 506 described above with reference to FIG. 5. The common UL portion 606 may additionally or alternatively include information pertaining to channel quality indicator (CQI), sounding reference signals (SRSs), and various other suitable types of information. One of ordinary skill in the art will understand that the foregoing is merely one example of an UL-centric slot and alternative structures having similar features may exist without necessarily deviating from the aspects described herein.

In some circumstances, two or more subordinate entities (e.g., UEs) may communicate with each other using sidelink signals. Real-world applications of such sidelink communications may include public safety, proximity services, UE-to-network relaying, vehicle-to-vehicle (V2V) communications, Internet of Everything (IoE) communications, IoT communications, mission-critical mesh, and/or various other suitable applications. Generally, a sidelink signal may refer to a signal communicated from one subordinate entity (e.g., UE1) to another subordinate entity (e.g., UE2) without relaying that communication through the scheduling entity (e.g., UE or BS), even though the scheduling entity may be utilized for scheduling and/or control purposes. In some examples, the sidelink signals may be communicated using a licensed spectrum (unlike wireless local area networks, which typically use an unlicensed spectrum).

FIG. 7 is a diagram 700 illustrating a communication system. A UE 704 is in communication with an access node 716 and a access node 718. Each of the access node 716 and the access node 718 may be a radio unit (RU), a transmission reception point (TRP), or a base station (cell). The access node 716 and the access node 718 are in communication with and are under the control of control entity 702. The control entity 702 may include a distributed unit (DU), a centralized unit (CU), a base station, and/or a network implementing various functions. In certain configurations RUs are radio hardware that transmits and receives radio signals to/from the UE. It handles functions like modulation/demodulation, amplifying, encoding/decoding etc. A DU controls the RUs connected to it. It handles certain lower layer functions like scheduling, radio resource control, encoding/decoding packets etc. A CU is the main unit that controls multiple DUs. It handles higher layer functions like radio resource management, mobility management, QoS management etc.

The access node 716 has a coverage 722, and the access node 718 has a coverage 724. In this example, initially the UE 704 is at a location 772 only under the coverage 722. The UE 704 is connected with the access node 716. Subsequently, the UE 704 moves from the location 772 to a location 774 that is under both the coverage 722 and the coverage 724. The UE 704 measures signals transmitted from both the access node 716 and the access node 718 and reports the measurements to the control entity 702. The control entity 702 may determine that the signal quality of the access node 718 is better for the UE 704 and that the access node 716 should handover the UE 704 to the access node 718. In this handover procedure, the node 716 is a source node and the access node 718 is a target node.

In certain scenarios, a clock error y exists between the source node and the target node. The clock error y refers to the timing difference between the source node (e.g., source RU/TRP/Cell) and the target node (e.g., target RU/TRP/Cell). The clock error y exists because the source and target nodes may not be perfectly synchronized in time. For example, their local oscillators/clocks may operate at slightly different frequencies, leading to a drift in their timing over time.

When the clock error y, representing downlink timing mismatch becomes, too large, it may exceed the cyclic prefix (CP) length. This will cause inter-symbol interference as the CP can no longer absorb the timing mismatch. In this example, the signals transmitted from the access node 716 and the signals transmitted from the access node 718 may interfere with each other when received by the UE 704 at the location 774. The inter-symbol interference caused by the timing mismatch can lead to errors in downlink decoding at the UE. The UE may not be able to properly decode the downlink signal. Further, in multi-TRP/distributed MIMO systems, proper pre-coding requires the downlink signals from multiple TRPs to be synchronized at the UE. The timing mismatch may lose these MIMO gains.

FIG. 8 is a sequence diagram 800 illustrating interactions among the UE 704, the access node 716, and the access node 718 according to a first technique to determine the clock error y between the access node 716 and the access node 718. FIG. 9 is a diagram 900 illustrating timing of transmissions and receptions at the UE 704, the access node 716, and the access node 718 according to the first technique.

In procedure 802, the UE 704 may receive, from the access node 716, a PDCCH order instructing the UE 704 to conduct a random access procedure. The UE 704 further receives, from the access node 716, downlink reference signals including SSBs. The UE 704 have also received from access node 716 also RO configurations. Based on the SSBs, the UE 704 can determine timing of the access node 716, including a slot boundary at time point T.

In this example, the access node 716 transmits DL signals to the UE 704 at time point T in a transmission 902. Due to propagation delay time duration t_s, the UE 704 receives the DL signals at time point T+t_sin a reception 904.

In procedure 804, the UE 704 selects a RO at the time point T+t_s, and transmit a PRACH preamble to the access node 716 at the RO in a transmission 906. Due to propagation delay time duration t_s, the access node 716 receives the PRACH preamble from the UE 704 at a time point T+2·t_sin a reception 908. Further, the access node 716 reports the timing of the transmission 906 and the reception 908 to the control entity 702. Accordingly, the control entity 702 can determine the time duration t_s.

In procedure 806, the access node 716 may send a timing advance command (TAC) to the UE 704, informing the UE 704 about a timing advance (TA) based on the time duration t_s. The control entity 702 may decide to request the UE 704 to transmit PRACH preambles to the access node 718.

In procedure 808, the access node 716 transmits to the UE 704 a command (e.g., a PDCCH order), instructing the UE 704 to transmit PRACH preambles to the access node 718. The command includes an identifier (e.g., a cell ID) of the access node 718.

In procedure 812, the UE 704 may receive, from the access node 718, downlink reference signals including SSBs. The UE 704 have also received from access node 718 RO configurations for transmitting PRACH preambles to the access node 718. Based on the SSBs, the UE 704 can determine timing of the access node 716, including a slot boundary at time point T+y, where time point T is the slot boundary of the access node 716 and the time duration y is the clock error between the access node 716 and the access node 718 as described supra.

In this example, the access node 718 transmits DL signals to the UE 704 at time point T+y in a transmission 912. Due to propagation delay time duration t_tfrom the access node 718 to the UE 704, the UE 704 receives the DL signals from the access node 718 at time point T+y+t_tin a reception 914.

Further, in procedure 814, the UE 704 selects an RO at time point T+t_sof the access node 716, and transmits a PRACH preamble A to the access node 718 in a transmission 916. Due to propagation delay time duration t_s, the access node 718 receives the PRACH preamble A from the UE 704 at a time point T+t_s+t_tin a reception 917.

In procedure 816, the UE 704 selects an RO at the time point T+y+t_tof the access node 718, and transmits a PRACH preamble to the access node 718 at the RO in a transmission 918. Due to propagation delay time duration t_t, the access node 718 receives the PRACH preamble B from the UE 704 at a time point T+y+2·t_tin a reception 919.

Further, in procedure 818, the access node 718 reports the timing of the transmission 918 (i.e., T+y+t_t) and the timing of the reception 919 (i.e., T+y+2·t_t) to the control entity 702. Accordingly, the control entity 702 can determine the time duration ty. Furthermore, the access node 718 reports the timing of the transmission 916 (i.e., T+t_s) and the timing of the reception 917 (i.e., T+t_s+t_t) to the control entity 702.

In procedure 820, the control entity 702 may calculate a TA_{target_first}, which is the difference between the slot boundary of the access node 718 and the timing of the reception 917, as follows:

$T A_{target_first} = (T + t_{s} + t_{t}) - (T + y) = t_{s} + t_{t} - y$

The values of the time duration t_sand the time duration t_tare known to the control entity 702. Accordingly, the control entity 702 can calculate y as y=t_s+t_t-TA_{target_first}

As such, the control entity 702 may derive the value of the clock error y. In procedure 822, the control entity 702 may signal the access node 716 to compensate the clock error y. In procedure 824, the control entity 702 may signal the access node 718 to compensate the clock error y. Accordingly, the access node 716 and the access node 718 may be adjusted such that the clock error y is less than a threshold value (e.g., half cyclic prefix length).

FIG. 10 is a sequence diagram 1000 illustrating interactions among the UE 704, the access node 716, and the access node 718 according to a second technique to determine the clock error y between the access node 716 and the access node 718. FIG. 11 is a diagram 1100 illustrating timing of transmissions and receptions at the UE 704, the access node 716, and the access node 718 according to the second technique.

In this second technique, the UE 704, the access node 716, and/or the access node 718 perform procedures 1002, 1004, 1006, 1008, 1012, and 1014 that are the same as the procedures 802, 804, 806, 1008, 812, and 814 of the first technique, respectively. The UE 704, the access node 716, and/or the access node 718 perform transmissions or receptions 1102, 1104, 1106, 1108, 1112, 1114, 1116, and 1117 that are the same as the transmissions or receptions 902, 904, 906, 908, 912, 914, 916, and 917 of the first technique, respectively. The UE 704, the access node 716, and/or the access node 718 do not perform procedures 816, transmission 918, or reception 919 of the first technique.

In this second technique, in procedure 1014, the UE 704 may transmit a PRACH preamble to the access node 718 based on the timing reference of the access node 716 in transmission 1116, as described in procedure 814. Specifically, the UE 704 transmits the PRACH preamble to the access node 718 at time T+t_s, based on the downlink timing T of the access node 716 and the known propagation delay t_sbetween the UE 704 and the access node 716. The access node 718 receives this PRACH preamble in reception 1117 at time point T+t_s+t_tand reports the timing to the control entity 702.

In procedure 1016, the UE 704 may estimate the downlink timing difference between the access node 716 and the access node 718. Let t_targetdenote the downlink timing of the access node 718 at the UE 704, and t_sourcedenote the downlink timing of the access node 716 at the UE 704. Then the UE 704 may estimate:

$Δ t = t_{target} - t_{s o u r c e} = (T + y + t_{t}) - (T + t_{s}) = y + t_{t} - t_{s}$

Here, y is the unknown clock error between the access node 716 and the access node 718. The UE 704 can measure t_targetand t_sourcebased on receiving downlink signals from the access nodes 716 and 718 in the reception 1104 and the reception 1114, respectively. Next, in procedure 1018, the UE 704 reports the estimated timing difference Δt to the control entity 702 through the access node 716.

In procedure 1020, the control entity 702 can then calculate TA_targetwhich is the difference between the downlink timing of the access node 718 (which is T+y) and the timing of reception 1117 (which is T+t_s+t_t).

$T A_{target} = (T + t_{s} + t_{t}) - (T + y) = t_{s} + t_{t} - y$

Further, upon receiving the timing difference report, the control entity 702 can derive the clock error y as:

$y = \frac{(Δ t - T A_{t a r g e t}) + 2 \cdot t_{s}}{2} = \frac{(y + t_{t} - t_{s}) - (t_{s} + t_{t} - y) + 2 \cdot t_{s}}{2}$

As such, the control entity 702 may obtain the value of the clock error y.

In procedure 1022, the control entity 702 may signal the access node 716 to compensate the clock error y. In procedure 1024, the control entity 702 may signal the access node 718 to compensate the clock error y. Accordingly, the access node 716 and the access node 718 may be adjusted such that the clock error y is less than a threshold value (e.g., half cyclic prefix length).

In this second technique, the UE 704 estimates the downlink timing difference Δt between a source node (e.g., the access node 716) and a target node (e.g., the access node 718). To calculate Δt, the UE determines the downlink timing t_targetof the target node and the downlink timing t_sourceof the source node based on receiving downlink signals from the two nodes. The downlink timings t_targetand t_sourcecorrespond to the times when the UE receives downlink signals from the target node and source node respectively. Then, the UE calculates the timing difference:

$Δ t = t_{target} - t_{s o u r c e} .$

In certain configurations, the target node is indicated to the UE 704 by the network (e.g., the control entity 702). For example, the network may configure the UE to measure and report the timing difference between a source node and a specific target node. In certain configurations, the UE 704 autonomously selects the source and target nodes to measure the timing difference. For example, the UE may select the source node as its serving cell and select the target node as a neighboring cell.

After calculating Δt, the UE reports the timing difference to the network. The report may include identity of the source node, e.g., source cell ID, source TCI state, or source SSB index, identity of the target node, e.g., target cell ID, target TCI state, or target SSB index, and the estimated timing difference Δt. This allows the network to obtain information about the downlink timing mismatch between the source and target nodes from the UE's perspective. The network can then adjust the nodes to compensate for the timing difference.

FIG. 12 is a flow chart 1200 of a first method (process) for assisting determination of a clock error between two access nodes. The method may be performed by a UE (e.g., the UE 704, the UE 250). In operation 1202, the UE receives, from a first access node, first downlink signals. In operation 1204, the UE determines, based on the first downlink signals, a first downlink timing of the first access node.

In certain configurations, in operation 1206, the UE transmits, to a first access node, a third preamble. In operation 1208, the UE receives, from the first access node, timing advance information with respect to the first access node based on the third preamble.

In certain configurations, in operation 1210, the UE receives, from the first access node, a command instructing the UE to transmit the first preamble and the second preamble to the second access node. The command may include an identifier of the second access node. In operation 1212, the UE transmits, to a second access node, a first preamble based on the first downlink timing of the first access node. In operation 1214, the UE receives, from the second access node, second downlink signals. In operation 1216, the UE determines, based on the second downlink signals, a second downlink timing of the second access node. In operation 1218, the UE transmits, to the second access node, a second preamble based on the second downlink timing of the second access node.

In certain configurations, the first downlink signals comprise first synchronization signal blocks and the second downlink signals comprise second synchronization signal blocks. In certain configurations, the first preamble and the second preamble are physical random access channel (PRACH) preambles. In certain configurations, the first access node is a source node and the second access node is a target node during handover of the UE from the first access node to the second access node.

In certain configurations, to transmit the first preamble comprises, the UE selects a first random access occasion configured by the first access node, and transmits the first preamble in the first random access occasion. To transmit the second preamble, the UE selects a second random access occasion configured by the second access node, and transmits the second preamble in the second random access occasion.

FIG. 13 is a flow chart 1300 of a second method (process) for assisting determination of a clock error between two access nodes. The method may be performed by a UE (e.g., the UE 704, the UE 250). In operation 1302, the UE receives first downlink signals from a first access node and second downlink signals from a second access node. In certain configurations, the first downlink signals include first synchronization signal blocks from the first access node and the second downlink signals comprise second synchronization signal blocks from the second access node.

In operation 1304, the UE determines a first downlink timing based on the first downlink signals and a second downlink timing based on the second downlink signals. In operation 1305, the UE transmits, to the first access node, a third preamble based on the first downlink timing. In operation 1306, the UE receives, from the first access node, timing advance information with respect to the first access node based on the third preamble.

In certain configurations, in operation 1308, the UE receives, from the first access node, a command instructing the UE to transmit the first preamble to the second access node. The command includes an identifier of the second access node. In certain configurations, the first access node is a source node and the second access node is a target node during handover of the UE from the first access node to the second access node.

In operation 1310, the UE transmits the first preamble to the second access node based on the first downlink timing. In certain configurations, the first preamble is a physical random access channel (PRACH) preamble. In certain configurations, to transmit the first preamble, the UE selects a first random access occasion configured by the first access node, and transmits the first preamble in the first random access occasion.

In operation 1312, the UE estimates a downlink timing difference between the first downlink timing and the second downlink timing. In certain configurations, to estimate the downlink timing difference, the UE determines a first time of reception of the first downlink signals, determine a second time of reception of the second downlink signals, and calculate a difference between the first time of reception and the second time of reception.

In operation 1314, the UE transmits a report of the estimated downlink timing difference to at least one of the first access node and second access node. In certain configurations, the report includes an identifier of the first access node, an identifier of the second access node, and the estimated downlink timing difference.

It is understood that the specific order or hierarchy of blocks in the processes/flowcharts disclosed is an illustration of exemplary approaches. Based upon design preferences, it is understood that the specific order or hierarchy of blocks in the processes/flowcharts may be rearranged. Further, some blocks may be combined or omitted. The accompanying method claims present elements of the various blocks in a sample order, and are not meant to be limited to the specific order or hierarchy presented.

The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but is to be accorded the full scope consistent with the language claims, wherein reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more.” The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any aspect described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects. Unless specifically stated otherwise, the term “some” refers to one or more. Combinations such as “at least one of A, B, or C,” “one or more of A, B, or C,” “at least one of A, B, and C,” “one or more of A, B, and C,” and “A, B, C, or any combination thereof” include any combination of A, B, and/or C, and may include multiples of A, multiples of B, or multiples of C. Specifically, combinations such as “at least one of A, B, or C,” “one or more of A, B, or C,” “at least one of A, B, and C,” “one or more of A, B, and C,” and “A, B, C, or any combination thereof” may be A only, B only, C only, A and B, A and C, B and C, or A and B and C, where any such combinations may contain one or more member or members of A, B, or C. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. The words “module,” “mechanism,” “element,” “device,” and the like may not be a substitute for the word “means.” As such, no claim element is to be construed as a means plus function unless the element is expressly recited using the phrase “means for.”

	Number	Date	Country
	63377056	Sep 2022	US
	63377743	Sep 2022	US

MULTIPLE TIMING MAINTENANCE AND ESTIMATION OF TIMING ERROR BETWEEN MULTIPLE RUS/TRPS/CELLS

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