Methods and apparatus for inter-cell cross-trp seamless mobility

Abstract

According to embodiments, a UE receives, from a source cell, a mobility preconfigured radio resource control (RRC) message for a random-access channel (RACH)-less access. The mobility preconfigured RRC message indicates target timing advance (TA) assistance information. The UE receives, from the source cell, a lower layer target access command. The lower layer target access command indicates recently updated or latest network updated time sensitive dynamic TA assistance information. The UE determines a target cell TA of a target cell according to a latest source cell TA of the source cell, a latest measured time difference between a reference signal (RS) from the source cell and a RS from the target cell, the recently updated or latest network updated time sensitive dynamic TA assistance information, and the target TA assistance information. The UE performs the RACH-less mobility access to the target cell according to the target cell TA.

Description

[0001] Cross-references to related applications

[0002] This patent application claims the benefit of U.S. Provisional Patent Application No. 63 / 396,491, filed August 9, 2022, entitled “Method and Apparatus for Intercell Cross-TRP Seamless Mobility,” and U.S. Provisional Patent Application No. 63 / 422,576, filed November 4, 2022, entitled “Method for UL RS Based TA Determination and Cell Switch Triggering,” both of which are incorporated herein by reference. Technical Field

[0003] This invention generally relates to telecommunications, and in specific embodiments to techniques and mechanisms for inter-cell mobility. Background Technology

[0004] For many wireless applications with high data rate and low latency requirements, handover (HO) latency remains a major issue, causing service interruptions and throughput loss during mobility in cell boundary areas. Specifically, in frequency range 2 (FR2) (e.g., frequencies above 24 GHz), rapidly moving UEs experience significant data throughput degradation and service interruptions during frequent HO events. Summary of the Invention

[0005] The embodiments of the present invention describe methods and apparatus for seamless inter-cell TRP mobility, and the embodiments of the present invention generally achieve technical advantages.

[0006] According to an embodiment, the UE receives a mobility pre-configured radio resource control (RRC) message from a source cell for mobility access to a target cell without a random access channel (RACH). The mobility pre-configured RRC message indicates pre-configured target timing advance (TA) assistance information. The UE receives a lower-layer target access command from the source cell. The lower-layer target access command indicates time-sensitive dynamic TA assistance information updated recently or latest from the network. The UE determines the target cell TA of the target cell based on the latest source cell TA of the source cell, the latest measured time difference between the reference signal (RS) from the source cell and the target cell, the latest or latest network-updated time-sensitive dynamic TA assistance information, and the pre-configured target TA assistance information. The UE performs RACH-free mobility access to the target cell based on the target cell TA. The lower layer is a protocol layer lower than RRC (Layer 3), and can be Layer 1 (e.g., physical layer) or Layer 2 (e.g., media access control (MAC) layer). Accordingly, the lower-level target access command can be a Layer 1 target access command or a Layer 2 target access command (e.g., a MAC control element (MAC CE)).

[0007] In some embodiments, the UE can indicate the reference signal (RS) of the target beam selected by the UE to the target cell by transmitting the corresponding sounding RS (SRS) or RS identifier (ID) in the initial message. The association between the SRS and the RS of the candidate target beam is pre-configured.

[0008] In some embodiments, the UE may maintain pre-configured mobility parameters without performing cell handover and access to candidate cells until a lower-layer target access command is received or a cell handover trigger condition is met. The UE may perform layer 1 (L1) measurements and track the time of reference signals from candidate beams by periodically measuring, updating, and storing the time deviation of candidate beams relative to the UE's local reference time based on the pre-configured mobility parameters, in order to maintain synchronization with the candidate beams. Upon receiving a mobility incremental configuration message, the UE may update new mobility configuration parameters, including target time TA (Target Time Auxiliary) information. The UE may apply new mobility configuration parameters for the target cell in response to receiving a lower-layer target access command or meeting the cell handover trigger condition.

[0009] In some embodiments, when the UE receives a lower-layer target access command or the cell handover triggering condition is met, the UE may (1) use the target cell TA based on the time of the RS of the target beam from the target cell selected by the UE, (2) use a pre-configured SRS uniquely corresponding to the RS of the target beam from the target cell, and (3) use a pre-configured grant with no RACH initiation message to transmit a no-RACH initiation message and SRS to the target cell. The pre-configured grant may be predetermined by the target cell and pre-configured to the UE based on each candidate cell. The no-RACH initiation message may include lower-layer information.

[0010] In some embodiments, the lower-layer information may include a media access control (MAC) control element (CE) indicating the ID of the RS from the target beam of the target cell. This ID may be either a synchronization signal block (SSB) ID or a channel state information (CSI) RS ID.

[0011] In some embodiments, the MAC CE may also indicate at least one of a buffer status report (BSR) or a power headroom report (PHR).

[0012] In some embodiments, a UE configured for conditional mobility can update its currently maintained latest source cell TA, source cell reference signal time, and target cell reference signal time based on the latest or most recently updated network update time-sensitive TA auxiliary information received from the source cell. Conditional mobility can be one of a conditional PSCell addition or change (CPAC) or a conditional handover (CHO) within a conditional secondary cell group. When mobility conditions are met, a UE configured for conditional mobility can trigger a target cell TA derived based on the latest source cell TA, the latest measured time difference between the source cell and target cell RS, and the latest or most recently updated network update time-sensitive TA auxiliary information.

[0013] In some embodiments, when the UE configured for CHO believes that the target cell TA determined by the UE is no longer valid after the timing alignment timer (TAT) of the most recently updated source cell TA has expired, the UE may perform conventional random access to the target cell.

[0014] According to an embodiment, the central unit (CU) determines one or more mobility candidate cells and one or more associated transmission and reception points (TRPs) based on measurement reports and additional information including predicted trajectories of user equipment (UE). The CU sends mobility preconfiguration requests to candidate cells having a subset of one or more associated TRPs. The CU receives a mobility preconfiguration response from the candidate cells, which indicates target cell timing advance (TA) assistance information. The CU sends a second mobility preconfiguration request to the source cell. The CU receives a second mobility preconfiguration response from the source cell, which indicates source assistance information. The CU sends final target TA assistance information to the source cell. The source cell transmits a mobility preconfiguration radio resource control (RRC) message to the UE for mobility access to the target cell without a random-access channel (RACH). The mobility preconfiguration RRC message indicates target TA assistance information.

[0015] In some embodiments, the mobility preconfiguration request may indicate a timestamp of the CU transmission time. Target cell TA assistance information from the candidate cell may indicate the candidate cell transmission time difference relative to the CU transmission time and one or more first DL / UL asymmetry factors of the candidate cell. Source cell TA assistance information from the source cell may include the source cell transmission time difference relative to the CU transmission time and one or more second DL / UL asymmetry factors of the source cell.

[0016] In some embodiments, a candidate cell can determine its transmission time difference with the CU based on a timestamp and a first intermediate-range delay between the CU and the candidate cell. A source cell can determine its transmission time difference with the CU based on a CU timestamp and a second intermediate-range delay between the CU and the source cell. The CU can determine the transmission time difference between the source cell and the target cell based on the source cell transmission time difference and the transmission time difference with the target cell. The CU can merge the source cell TA auxiliary information, the target cell TA auxiliary information, and the transmission time difference between the source cell and the target cell to generate final target TA auxiliary information.

[0017] In some embodiments, the source cell may send dynamic TA assistance information to the UE configured for conditional mobility, which is triggered by at least one of the following: the source node one-way delay (OWD) or the source TA change is higher than a threshold, and / or the change in the transmission time difference between the source cell and the target cell updated by the CU is higher than a time deviation threshold.

[0018] According to an embodiment, the UE measures the time deviation between the source transmission and reception point (TRP) reference signal (RS) time tracked by the UE and the target TRP RS time to obtain the most recently measured time difference between the RS from the source TRP and the target TRP. The UE transmits an uplink signal to the target TRP after the source TRP RS time tracked by the UE. The UE receives the current target TA from either the source TRP or the target TRP of the current serving cell. The current target TA is measured by the source TRP and the current serving cell of the target TRP on uplink signals aligned with the source TRP RS time tracked by the UE and received through the target TRP. The UE determines the target TRP TA of the target TRP based on the most recently measured time difference and the current target TA. The UE performs RACH-free mobility access to the target TRP based on the target TRP TA and the target TRP RS time tracked by the UE in order to perform UL transmission to the target TRP.

[0019] In some embodiments, the uplink signal may be a sounding reference signal (SRS).

[0020] In some embodiments, when the UE starts using the target TRP RS time as a local reference to perform UL transmission to the target TRP, the UE can adjust the current target TA based on the source TRP RS time tracked by the UE and the time deviation between the source TRP RS time tracked by the UE and the target TRP RS time to obtain the target TRP TA.

[0021] According to an embodiment, the serving cell receives uplink signals from the user equipment (UE) through a target transmission and reception point (TRP). The serving cell sends a current target TA to the UE through either the source TRP or the target TRP. This current target TA is measured by the serving cell on the uplink signal from the target TRP. The target TRP performs RACH-free mobility access with the UE based on the latest measured time difference between the source TRP and the target TRP's RS and the current target TA, using the target TRP's target TRP TA.

[0022] According to an embodiment, the UE receives and maintains a mobility pre-configuration message from the serving source cell. The mobility pre-configuration message indicates L1 measurement configuration information of the serving source cell, first L1 measurement configuration information of a first candidate cell, and second L1 measurement configuration information of a second candidate cell. The second candidate cell is the subsequent cell of the first candidate cell on the UE's predicted trajectory. The UE receives a first lower-layer target access command from the serving source cell to hand over to the first candidate cell as the target cell. The UE hands over to the first candidate cell, making the first candidate cell the UE's current serving cell. The UE performs a first L1 measurement based on the first L1 measurement configuration information. The UE reports the first L1 measurement results to the current serving cell based on the first L1 measurement configuration information of the current serving cell. The UE receives a second lower-layer target access command from the current serving cell to hand over to the second candidate cell. The UE performs cell handover access to the second candidate cell, which becomes the UE's new serving cell. The UE in the new serving cell performs the second L1 measurement only based on the second L1 measurement configuration information. The UE reports the second L1 measurement results to the new serving cell based on the second L1 measurement configuration information.

[0023] In some embodiments, mobility pre-configuration messages can be included in radio resource control (RRC) messages.

[0024] In some embodiments, the L1 measurement configuration information of the serving source cell may include all L1 measurement configurations of all candidate beams of the candidate cells of the serving source cell.

[0025] In some embodiments, the first L1 measurement configuration information of the first candidate cell may include all L1 measurement configurations of all candidate beams of the candidate cell of the first candidate cell. The second L1 measurement configuration information of the second candidate cell may include all L1 measurement configurations of all candidate beams of the candidate cell of the second candidate cell. The first and second L1 measurement configurations described herein are for illustrative purposes only and are not intended to diminish their generality. The number of candidate cells (and their corresponding L1 measurement configuration information) used for sequential cell handover may be greater (e.g., all candidate cells in the UE's predicted trajectory).

[0026] In some embodiments, the L1 measurement configuration information of the current serving cell or candidate cell can indicate the corresponding candidate beam scanning mode. The candidate scanning mode includes the serving beam from the current or potential serving cell and the candidate beams associated with the serving beam.

[0027] In some embodiments, the UE can select a candidate beam scanning mode based on the currently serving beam. The UE can use the currently serving beam as a reference beam to perform candidate beam scanning and candidate beam search according to the candidate beam scanning mode.

[0028] In some embodiments, the first L1 measurement configuration information and the second L1 measurement configuration information can be based on each cell.

[0029] According to an embodiment, the CU determines a sequence of mobility candidate cells based on the user equipment (UE)'s predicted trajectory and measurement reports. The CU sends the L1 measurement configuration of each cell of the current serving source cell and the candidate cells to the current serving source cell. The L1 measurement configuration of each cell includes one or more beam scanning modes in the L1 measurement configuration of each cell. The current serving source cell transmits a mobility pre-configuration message to the UE. The mobility pre-configuration message indicates the L1 measurement configuration information of the current serving source cell, the first L1 measurement configuration information of the first candidate cell, and the second L1 measurement configuration information of the second candidate cell. The second candidate cell is the subsequent cell of the first candidate cell on the UE's predicted trajectory. The current serving source cell transmits a first lower-layer target access command to the UE to hand over to the first candidate cell as the target cell. After the cell handover and after the first candidate cell becomes the UE's current serving cell, the current serving cell receives a first L1 measurement report from the UE based on the current serving cell's configuration information for the first L1 measurement. The current serving cell transmits a second lower-layer target access command to the UE so that the UE hands over to the second candidate cell. After the second candidate cell becomes the new serving cell of the UE, the new serving cell receives the second L1 measurement report from the UE according to the second L1 measurement configuration information.

[0030] In some embodiments, during the mobility preparation phase, the CU may indicate the current serving cell and one or more potential serving cells of a candidate cell to the candidate cells on the UE's predicted trajectory in the mobility request. The candidate cell may report candidate beams and the associated L1 measurement configurations corresponding to the current serving cell and each potential serving cell to the CU.

[0031] In some embodiments, the CU can merge the L1 measurement configurations of one or more candidate beams from all or more candidate cells of the current serving cell as the L1 measurement configuration of the current serving cell.

[0032] In some embodiments, the CU may combine the L1 measurement configurations of one or more candidate beams of all or more candidate cells of each potential serving cell as the L1 measurement configuration of each candidate cell, where the potential serving cell is currently a mobility candidate cell on the UE's predicted trajectory.

[0033] In some embodiments, the CU can determine the beam scanning pattern of one or more candidate beams of one or more candidate cells associated with a first potential serving beam of the current serving cell or a second potential serving beam of one or more potential serving cells based on the UE's predicted trajectory.

[0034] To gain a more complete understanding of the invention and its advantages, the following description is provided in conjunction with the accompanying drawings. In the drawings,

[0035] Figure 1A Exemplary communication systems provided in some embodiments are shown;

[0036] Figure 1B The examples illustrate scenarios of intra-cell TRP handover and inter-cell TRP handover provided by some embodiments;

[0037] Figure 2 Examples of mobility pre-configuration based on UE trajectory prediction provided by some embodiments are shown;

[0038] Figure 3 Exemplary architectures and protocols for seamless mobility solutions provided by some embodiments are illustrated;

[0039] Figure 4 Exemplary location-based TA estimations performed at the RAN are shown in some embodiments;

[0040] Figure 5 An exemplary method for determining a target TA at a UE is shown according to some embodiments;

[0041] Figure 6 Examples of DL-based seamless mobility frameworks provided by some embodiments are shown;

[0042] Figure 7 Examples of target TA determination when the source DU and target DU times are not aligned, provided by some embodiments, are shown;

[0043] Figure 8 Examples of target TA determination when there is temporal asymmetry between DL and UL in the presence of DU are shown in some embodiments;

[0044] Figure 9 Examples of DU / intra-cell TRP handover provided by some embodiments are shown;

[0045] Figure 10 Flowcharts of seamless mobility features and processes at the UE provided in some embodiments are shown;

[0046] Figure 11A and Figure 11B Flowcharts of seamless mobility capabilities and processes at the network provided in some embodiments are shown;

[0047] Figure 12 Flowcharts of conditional seamless mobility functions and procedures at the UE provided in some embodiments are shown;

[0048] Figure 13A and Figure 13B Flowcharts of conditional seamless mobility features and processes at the network provided in some embodiments are shown;

[0049] Figure 14 Examples of HO processes between DUs within a CU provided by some embodiments are shown;

[0050] Figure 15 An exemplary target access command MAC CE is shown;

[0051] Figure 16 This illustrates some embodiments of TA adjustment based on UL measurements for multiple TRPs within a DU;

[0052] Figure 17 The source beam and candidate beam of the UE at the boundary point determined by the network are shown;

[0053] Figure 18 Examples of signaling flowcharts for a UL RS-based mobility framework provided in some embodiments are shown;

[0054] Figure 19 Exemplary flowcharts of UL RS-based mobility functions and processes at the UE provided in some embodiments are shown;

[0055] Figure 20 Exemplary flowcharts of UL RS-based mobility functions and processes at the CU provided in some embodiments are shown;

[0056] Figure 21 Exemplary flowcharts of UL RS-based mobility functions and processes at candidate DU / cells provided in some embodiments are shown;

[0057] Figure 22 Examples of signaling flowcharts for a UL RS-based mobility framework provided in some embodiments are shown;

[0058] Figure 23A Examples of candidate beam search using pre-configured beam scanning modes are shown in some embodiments;

[0059] Figure 23B Examples of L1 measurement configurations and process flowcharts for sequential mobility on the UE side provided in some embodiments are shown;

[0060] Figure 23C Examples of network-side L1 measurement configurations and process flowcharts for sequential mobility provided in some embodiments are shown;

[0061] Figure 24A Flowcharts of methods performed by a UE according to some embodiments are shown;

[0062] Figure 24B Flowcharts of methods performed by one or more network nodes according to some embodiments are shown;

[0063] Figure 24C Flowcharts of methods performed by a UE according to some embodiments are shown;

[0064] Figure 24D Flowcharts of methods performed by one or more network nodes according to some embodiments are shown;

[0065] Figure 24E Flowcharts of methods performed by a UE according to some embodiments are shown;

[0066] Figure 24F Flowcharts of methods performed by one or more network nodes according to some embodiments are shown;

[0067] Figure 25 An embodiment of a communication system is shown;

[0068] Figure 26A and Figure 26B Exemplary devices are shown that can implement the methods and guidance provided by the present invention;

[0069] Figure 27 Block diagrams of computing systems provided in some embodiments that can be used to implement the devices and methods disclosed herein are shown.

[0070] Unless otherwise stated, corresponding numbers and symbols in the various figures generally refer to corresponding parts. These figures are drawn to clearly illustrate relevant aspects of the various embodiments and are not necessarily drawn to scale. Detailed Implementation

[0071] The structure and use of embodiments of the present invention are discussed in detail below. However, it should be understood that the concepts disclosed herein can be embodied in a wide variety of specific contexts, and the specific embodiments discussed herein are merely illustrative and not intended to limit the scope of the claims. Furthermore, it should be understood that various changes, substitutions, and modifications can be made without departing from the spirit and scope of the invention as defined by the appended claims.

[0072] Figure 1AAn exemplary communication system 100 provided in an embodiment is illustrated; the communication system 100 includes an access node 110 having coverage 101. Access node 110 serves user equipment (UE), such as UE 120. In a first operating mode, communication to and from the UE passes through access node 110 having coverage 101. Access node 110 is connected to backhaul network 115 for internet access and operation and management, etc. Communication between the UE and the access node pair occurs via unidirectional communication links, wherein the communication link between the UE and the access node is referred to as uplink 130, and the communication link between the access node and the UE is referred to as downlink 135.

[0073] Access nodes are also commonly referred to as Node B, evolved NodeB (eNB), next-generation (NG) NodeB (gNB), master eNB (MeNB), secondary eNB (SeNB), master gNB (MgNB), secondary gNB (SgNB), network controller, control node, base station, access point, transmission point (TP), transmission-reception point (TRP), cell, carrier, macro cell, femtocell, picocell, etc., while UEs are also commonly referred to as mobile stations, mobile phones, terminals, users, subscribers, sites, etc. Access nodes can provide wireless access according to one or more wireless communication protocols, such as Third Generation Partnership Project (3GPP) Long Term Evolution (LTE), LTE Advanced (LTE-A), 5G, 5G LTE, 5G NR, Sixth Generation (6G), High Speed ​​Packet Access (HSPA), and IEEE 802.11 series standards such as 802.11a / b / g / n / ac / ad / ax / ay / be. While it is understood that a communication system can use multiple access nodes capable of communicating with multiple UEs, for simplicity, only one access node and two UEs are shown.

[0074] During mobility HO (Hogging) operations, several steps on the time-critical path of HO introduce significant latency. One of these is using radio resource control (RRC) messages as HO commands. Prior to version 17, mobility commands, including various types of HO commands, and requests to add or change the primary cell of a secondary cell group (PSCell) in dual-connectivity (DC) secondary cell groups were all RRC reconfiguration messages.

[0075] Compared to Layer 2 (L2) media access control (MAC) control element (CE) messages, RRC reconfiguration messages introduce significantly greater latency. For example, when adding a PSCell, an RRC message takes 18ms to 22ms, while a MAC CE message takes only 6ms. If Layer 1 (L1) signaling (e.g., downlink control information (DCI)) is used, the expected latency is even lower. L1 / L2 signaling latency is much lower than RRC signaling. However, the size of one or more L1 / L2 signaling messages cannot be very large, and the control information they can carry is very limited.

[0076] Random access (RA) is another step on the time-critical path of mobility procedures, including home access (HO), secondary cell group (SCG) addition / activation, conditional HO (CHO), and conditional PSCell addition or change (CPAC) processes. These all contribute to the total HO latency. The RAN2 latency model indicates that RA typically introduces a latency of around 20ms to the target cell.

[0077] Figure 1BThis illustrates scenarios 150 (intra-cell cross-transmission and reception point (TRP) handover within cell A152) and 160 (inter-cell cross-TRP handover) when a home homing (HO) occurs from cell A162 to cell B164. Intra-cell cross-TRP handovers involve beam management and do not trigger HO. Inter-cell TRP handovers are a consequence of inter-cell HO and introduce significantly greater latency than beam management. Our goal is to minimize HO latency, thereby minimizing service interruptions and maximizing continuous data throughput during HO. To enhance mobility, we aim to achieve the same or comparable UE experience during inter-cell HO TRP handovers as intra-cell TRP handovers without HO. In principle, the solutions to the RRC and RA issues are:

[0078] Using RRC pre-configuration and L1 / L2 signaling triggering for mobility can solve the RRC latency problem.

[0079] Using RACH-free access can solve the mobility latency problem introduced by RA.

[0080] Access without RACH is access that skips at least some steps of the RACH procedure. The RACH procedure typically includes: the UE sending a random access preamble (message 1) to the base station or gNB; the UE receiving a random access response (message 2) from the base station or gNB; the UE sending a message (message 3) to the base station or gNB for scheduling transmissions; and the UE receiving a contention resolution message (message 4) from the base station or gNB. This is the four-step RACH procedure. Access without RACH can skip these four steps, thus avoiding RA delay, but currently, it only applies to the extreme scenario where the timing advance (TA) of the target cell can be determined before the HO (House Opening) in the standard.

[0081] In LTE, RACH-free access is only permitted when TA=0 (the target cell size is very small) or the source cell's TA can be reused (e.g., the source and target cells are co-located).

[0082] During R17 fast SCG activation, RACH-free access to the activated PSCell is only permitted if the Time Alignment Timer (TAT) has not expired and no SCG beam failure is detected.

[0083] Typically, initial UL time alignment and initial UL TX power may require RA. To date, UL time alignment and TA determination are the primary reasons why UEs are required to perform random access to the target cell during HO. In most mobility scenarios, RACH-free HO is not permitted due to the lack of accurate and reliable target TA estimation prior to HO.

[0084] In Rel-18 WID (RP-213565) "Further NR Mobility Enhancements," one objective is L1 / L2-based mobility, aiming to specify mechanisms and processes for L1 / L2-based inter-cell mobility to reduce mobility latency, including:

[0085] Configuring and maintaining multiple candidate cells to enable rapid application of candidate configurations.

[0086] The dynamic handover mechanism between candidate serving cells (including SpCell and SCell) is applicable to potential application scenarios (RAN2, RAN1) based on L1 / L2 signaling.

[0087] L1 enhancements, including inter-cell beam management, L1 measurement and reporting, and beam indication, are suitable for handling asynchronous scenarios managed by TA (RAN1, RAN2).

[0088] Timing lead management (RAN1, RAN2)

[0089] Central unit (CU) - distributed unit (DU) interface signaling, used to support L1 / L2 mobility (if required) (RAN3).

[0090] L1 / L2-based inter-cell mobility processes are applicable to the following scenarios:

[0091] Independent, CA, and new radio (NR)-DC scenarios; changes in serving cell within a cell group (CG); intra-DU scenarios; and intra-CU and inter-DU scenarios.

[0092] Both same frequency and different frequency,

[0093] Both frequency range 1 (FR1) and frequency range 2 (FR2)

[0094] The source cell and the target cell can be synchronized or asynchronous.

[0095] Because in Rel-18, scenarios between DUs within a CU require inter-cell HO (Hopping and Opening) operations, and the latency introduced during HO is much greater, this invention focuses on scenarios between DUs within a CU and describes them using the CU-internal architecture. In fact, the lower-level operations disclosed in this invention can also be applied to scenarios between CUs. Figure 2The strategy for achieving L1 / L2-based mobility in Rel-18 to reduce latency is illustrated. Figure 2 The corresponding high-level architecture and protocols are shown. The lower layer is a protocol layer that is relatively lower than RRC, which is layer 3, and can be layer 1 (e.g., physical layer) or layer 2 (e.g., media access control (MAC) layer).

[0096] To achieve the Rel-18 objective of configuring and maintaining multiple candidate cells so that the candidate cell configuration can be quickly applied during cell / TRP handover, one approach is for the network to predict the UE trajectory not only based on the UE radio measurement report but also on other side information (e.g., UE location, speed, highway / route traffic information, travel plan information, user travel pattern / historical information, etc.). Then, based on the UE trajectory prediction, the network performs Layer 3 (L3) pre-configuration via RRC reconfiguration messages, without interrupting L1 / L2 operations during inter-cell mobility.

[0097] One possible approach is to pre-configure candidate cells in the network before their measurement intensity exceeds a threshold, much like adding deactivated PSCells in advance, and then perform seamless PSCell activation later when triggered. Options include:

[0098] Pre-configure and establish a separate bearer with a protocol stack on the candidate cell group (similar to adding an SCG to a DC when DC is supported).

[0099] Pre-configure UE early measurement / reporting, including L1 and L3 measurements, on candidate cells / TRPs.

[0100] One or more candidate target nodes are pre-configured to begin monitoring / detecting the UE's UL signal / initial message.

[0101] Resources are reserved in advance for access to candidate cells (without RACH or with RACH).

[0102] Predict the dwell time in candidate cells / TRPs and allocate relevant resources to the UE accordingly.

[0103] Efficient HO pre-configuration relies on the network to correctly determine candidate DUs / cells based on the UE's travel time and trajectory.

[0104] After pre-configuration, the network sends L1 / L2 signaling to the UE based on one or more L1 measurement reports from the UE to activate HO access to the target DU / TRP. The pre-configuration parameters are applied quickly when activation is triggered.

[0105] Figure 3Examples of the architecture and protocols of a framework for implementing RRC pre-configuration and L1 / L2 triggering mobility schemes provided by some embodiments are illustrated. In this exemplary architecture between DUs within a CU, the pre-configuration process involves, as... Figure 3 The F1 interface 312 and Uu air interface 314 shown perform signaling exchange. During the fast activation step, the signaling exchange occurs at the Uu air interface 314. According to some embodiments, the present invention may affect both the F1 and Uu interfaces.

[0106] In mobility scenarios supported by Rel-18, a DC-based protocol structure between CU and DU should be adopted as much as possible to achieve the following objectives:

[0107] To achieve DC-based mobility,

[0108] Both DL and UL achieve 0ms interrupts.

[0109] Supports high throughput during mobility.

[0110] like Figure 3 As shown, RRC pre-configuration is used by the network for early addition and rapid activation of DU / SCGs to deactivate them when triggering conditions are met. There are three main steps in the seamless mobility framework.

[0111] In the first step 301, one or more DU / SCGs can be pre-configured to be in an inactive state via RRC messages. With the Packet Data Convergence Protocol (PDCP) 316 anchored at CU 318 unchanged, secondary node (SN) additions and changes, including changes to the master node (MN) role relative to the SN, can be performed via RRC reconfiguration without resetting radio link control (RLC) and MAC. After UE 320 receives the RRC pre-configuration message, UE 320 performs L1 measurements and reports on all configured candidate cells.

[0112] In the second step 302, the network triggers fast PSCell and SCell activation between DU / CG based on the L1 measurement report from the UE. Upon receiving L1 / L2 signaling to activate access to the target cell, the UE 320 performs RACH-free access to the target cell.

[0113] In step 303, CU 318 determines when a DU (e.g., DU 331 or 332) acting as an SN is deactivated or released. The CU notifies the relevant SN and UE. An SN can be released when the link with an SN (DU) cannot be maintained. An SN / SCG can be deactivated when the link with an SN / SCG is still good but no data needs to be transmitted; the deactivated SN / SCG can be quickly reactivated via L1 / L2 signaling when new data arrives.

[0114] In most cases, a challenge in bypassing random access during HO (Ho) is the unknown TA (Target Access Term) of uplink (UL) transmissions to the target cell. Numerous studies have suggested that networks perform target cell TA estimation before HO is triggered. For example, location-based TA estimation or TA estimation based on historical data from self-organizing networks (SONs) presents security concerns when location servers are involved. The accuracy of the network-estimated TA is also technically challenging.

[0115] Another goal under mobility enhancement is TA management. TA management goals can include initial TA identification and continuous connection TA maintenance / updates. Figure 4 An example of location-based TA estimation at the radio access network (RAN) is shown to avoid involving security servers.

[0116] In this scheme, source node 402 (or master node (MN) if DC is enabled) estimates the target node TA (e.g., source node 402 estimates the location of UE 420 and estimates the UE TA to target SN 404 / TRP 406 based on the UE location). Source node 402 measures the angle of departure (AOD) or angle of arrival (AOA) and round-trip delay (RTD) from UE 420 to source node (or MN) 402. The source node determines the UE location based on the measured AOD / AOA and RTD. Based on the UE location and the known location of target node 404 (or secondary node (SN) if DC is enabled), source node 402 determines the distance between UE 420 and target node 404. Source node 402 calculates the target node TA = RTD based on the distance from the UE to the target node. In the case of TRP406, if baseband processing is performed at target node 404 (or SN), the TRP 406 location and the forward propagation delay of the TRP target node (or SN) can be included at source node 402 (or MN) for target TA estimation.

[0117] During mobility access activation, source node 420 estimates the target TA (e.g., target TA) of target node 404 and transmits the target node's TA to the UE via a MAC CE. In the current standard, a MAC CE is defined for the TA associated with the MAC entity of the current serving node, not for the target node. A new MAC CE with a new logical channel ID can be defined for the current serving node (e.g., source node 402 or MN) to transmit the TA of a different node (e.g., target node 404 or SN) to the UE 420.

[0118] Location-based location (TA) estimation has several technical challenges. First, UE location / distance estimation based on radio measurements may not be very accurate. Furthermore, multipath channels can also lead to inaccurate location / distance-based TA estimation.

[0119] An alternative target TA estimation method is as follows: the UE determines the target TA based on the current source node TA and the reference signal time deviation (time difference) between the source node and the target node that the UE can measure. Figure 5 An exemplary scenario is shown where the CU / DU are precisely synchronized and their local reference times are precisely aligned. In this scenario, a method can be employed to determine the target TA at the UE.

[0120] exist Figure 5 In the method shown, UE 520 can determine the uplink TA of target cell 504 based on the modified current uplink TA of source cell 502. UE 520 can modify the current uplink TA of the source cell based on the difference between the downlink time measured in source cell 502 and the downlink time of target cell 504. The target TA can be expressed by the general formula: Target_TA = Source_TA + 2 * TS_Offset.

[0121] In 5G systems, the situation is likely to be much more complex in inter-cell multi-TRP environments. Figure 5 Technical issues related to the methods shown and similar methods include:

[0122] This method does not take into account the problem of inaccurate synchronization between the source node and the target node;

[0123] This method does not take into account any possible time deviations between the source baseband node and the target baseband node. The baseband node can be a CU or DU that performs baseband signal processing, or even a TRP.

[0124] This method does not take into account any possible asymmetric time deviations between UL and DL, which may be introduced by the fronthaul or configured / implemented by the operator.

[0125] Currently, inter-cell mobility commands are RRC messages, and random access is performed in most inter-cell mobility scenarios. During inter-cell TRP handover, these commands and RA procedures cause significant latency, which impacts the UE experience compared to intra-cell TRP handover.

[0126] In order to perform RACH-free HO to avoid random access delay, the UE needs to know the target TA before the HO; however, the previous scheme of estimating the target TA at the source node or UE is inaccurate, unreliable, and not suitable for most mobility scenarios in multi-cell / TRP deployments.

[0127] Current signaling and mobility procedures do not support RACH-based mobility for target node access without RACH using the target TA determined by the UE.

[0128] The embodiments of the present invention minimize the time delay on the time critical path of the HO process, so that the UE experience during the TRP handover of HO between cells is the same or equivalent to that of intra-cell TRP handover without HO.

[0129] According to some embodiments, a seamless mobility method based on L3RRC pre-configuration and L1 / L2 signaling is introduced in inter-cell multi-TRP mobility environments, targeting mobility target access triggering. A RACH-free mobility access scheme for general mobility scenarios is proposed, where the target cell TA (Target_TA) is determined at the UE. An optimal beam indication mechanism is proposed to support low-latency beam management.

[0130] When a UE receives an L1 / L2 HO access command (e.g., MAC CE), the UE determines the target_TA based on the time offset measurement between the DL reference signals from the source and target nodes, the most recently updated source node TA or DL-OWD from the HO access command, and TA assistance information from the network. The UE then performs RACH-free access to the target cell based on the determined target_TA.

[0131] Pre-configured handover information for the UE includes static TA auxiliary information. Inter-cell HO / TRP handover is triggered by the HO access command based on the L1 measurement report. Delay-sensitive TA auxiliary information is also sent to the UE via the HO access command.

[0132] The following describes in detail the structure and use of embodiments of the present invention. However, it should be understood that the present invention provides many applicable concepts that can be embodied in various specific contexts. The specific embodiments discussed are illustrative of specific ways of constructing and using the invention and do not limit the scope of the invention. These and other aspects are described in more detail below. The present invention can provide a method for applications with extremely high reliability, low latency, and low delay requirements, particularly for mobility applications in the MBB and V2X domains. Compared to various prior art, this method is highly reliable, accurate, and efficient, minimizing latency caused by mobility. This method can be used in different systems such as NR or LTE.

[0133] Figure 6 Examples of a seamless mobility framework based on DL provided by some embodiments are shown. At operation 600, UE 612 transmits a measurement report to source DU 614, which is forwarded to CU 618. At operation 601, CU 618 performs mobility prediction based on the measurement report and other UE travel information and determines to add a selected SN / SCG. At operation 602, CU 618 sends a candidate DU mobility pre-configuration (or, where DC is supported, adding an SCG) request element (IE) to target DU 616. The mobility pre-configuration IE is carried in each UE F1 message (e.g., UE_Context_modification_request) and contains the following:

[0134] The current UE SRS configuration for one or more serving cells is configured to be unique for each UE across the entire CU coverage area. The source DU and / or target DU can use the same SRS configuration, differing only in TX time. In designs where target-specific SRS configuration is not required, the SRS configuration is optional in the pre-configured IE.

[0135] The Time Deviation Reporting Request (IE) with timestamps is used in asynchronous scenarios, such as those with loose synchronization between the CU and DU. A timestamp is sent to the candidate / target DU 616 so that the CU 618 can obtain the time deviation between the CU and DU (or so that the MN can determine the time deviation between the MN and SN). The candidate / target DU 616 determines the transmission time difference with the CU and reports it to the CU 618. The candidate / target DU 616 may include the DL / UL asymmetry adjustment of the connection-associated TRP fronthaul in the candidate / target DU time deviation report.

[0136] Simultaneously, at operation 602.1, CU 618 also sends a time skew report request to source DU 614. At operation 602.2, upon receiving the time skew report request, source DU 614 determines the time skew relative to the CU reference time and reports the time skew to CU 618. Source DU 614 may also include DL / UL asymmetry adjustments for the connection-associated TRP fronthaul in the source DU time skew.

[0137] At operation 603, candidate / target DU 616 sends an acknowledgment IE to CU 618, including L1 / L2 configuration, local time offset from the CU, target C-RNTI, candidate beam, one or more target SRS corresponding to one or more candidate beams of one or more candidate cells, and the first authorization without RACH TX. For candidate beams, a list of candidate SSBs and CSI-RS for candidate TRPs is configured for UE 612. UE 612 ultimately selects a beam from the candidates as the target beam to which UE 612 HO. For candidate beam-associated SRSs, the SRS configuration corresponds to each of the candidate SSBs and CSI-RSs. The SRS used here is an example. The SRS can be any predefined and configured unique UL transmission waveform with a one-to-one configuration corresponding to the candidate SSBs and CSI-RS without loss of generality.

[0138] At operation 603.1, after receiving all mobility configurations from candidate / target DU 616, CU 618 includes all or more target configurations from one or more candidate / target DUs into a pre-configured IE and forwards the pre-configured IE to source DU 614 via each UEF1 message. CU also determines the transmission time offset between source DU 614 and candidate / target DU 616 based on time offset reports from source DU and target DU, and includes the time offset in the F1 message sent to source DU 614.

[0139] At operation 604, upon receiving an F1 message for mobility pre-configuration from the CU, the source DU sends a pre-configuration RRC message to the UE, including all target DU configurations, static TA assistance information, and pre-configuration indication or deactivation status indication.

[0140] Static TA assistance information may include nodes_Timing_Offset. This is the time offset between the source DU 614 and the target DU 616, determined by the CU 618 after issuing a pre-configuration request via F1 to both the source DU 614 and the candidate / target DU 616. Incremental changes to this offset can be updated to the UE via the Access Activation MAC CE as part of the dynamic TA assistance information.

[0141] Static TA auxiliary information may also include SourceTRP1_DL_Adjustment and TargetTRP2_DL_Adjustment. These are the source DL asymmetric adjustment factors and target DL asymmetric adjustment factors pre-measured when deploying target TRP2 and target DU2. The asymmetric adjustment factor represents the DL / UL time deviation difference caused by fiber fronthaul between the TRP and its associated DU or by intentional operator settings. It is a TRP-based factor.

[0142] New pre-configuration messages can be defined for mobility pre-configuration to distinguish them from the current RRC reconfiguration messages and conditional reconfiguration messages.

[0143] Another option is to reuse existing RRC reconfiguration messages and define new preconfiguration indications within them. For mobility preconfiguration, this is set to "true". If mobility preconfiguration enables DC, the DC activation state mechanism can be reused. In preconfigurations that add SCG, the activation state in the RRC reconfiguration message can be set to "deactivated".

[0144] At operation 605, upon receiving a pre-configured RRC message, UE 612 responds with an RRC configuration complete message to source DU 614 (source node). Source DU 614 then forwards this information to CU 618, which in turn forwards it to target DU 616 via an F1 message. UE 612 then performs L1 measurement reporting on the pre-configured candidate cells / beams.

[0145] At operation 606, the network initiates mobility access to the target cell (or SCG activation in the case of DC) based on the UE L1 measurement report. Source DU 614 sends a target cell access activation command (e.g., MAC CE) to UE 612. The newly activated MAC CE includes an indication of one or more optimal beams selected and dynamic target_TA auxiliary information.

[0146] At operation 607, upon receiving an activation command (e.g., MAC CE), UE 612 performs RACH-free access to the target node by directly transmitting a pre-authorized first message to the target DU and transmitting a pre-configured SRS corresponding to the target beam ultimately selected by the UE. UE 612 selects only the strongest beam of either the SSB or CSI-RS as the target beam for the HO.

[0147] An alternative to UE 612 indicating the optimal beam for the target cell is to use a pre-authorized first message to carry the ID (SSB_ID or CSI_ID) of the reference signal for the optimal beam. In this case, the beam-associated SRS is not required. The UE can then perform an early CSI report to the target node 616.

[0148] At operation 608, target node 616 (target DU) determines the DL beam selected by the UE for the following control signaling and data transmission based on the indication in the SRS or first message received from the UE.

[0149] One reason that determining the time offset (TA) at the UE based on the DL time deviation is complex is that, in many cases, the source and target nodes are not precisely synchronized (i.e., the reference base is unreliable). However, in most cases, the network can determine the time deviation between nodes. Figure 7 An example of inter-DU mobility within a CU is illustrated, where the two DUs (source DU and target DU) are not precisely synchronized with the CU. The CU can determine the time offset from the two DUs and provide this time offset information to the UE before handover. Based on auxiliary information from the network, the current one-way delay (OWD), or TA, the UE measures the time offset between the source DL reference signal and the target DL reference signal and determines the TA for the target cell.

[0150] Figure 7 The scenario shown illustrates a situation where the DU and CU reference times have one or more time deviations. For example... Figure 6 As shown in operations 602 and 603, CU 618 can determine the DU time offset before issuing the RRC HO command. UE 612 measures TS_offset and determines Target_TA:

[0151] TS_Offset=(DU2_Offset+OWD2)–(DU1_Offset+OWD1),

[0152] TS_Offset is the time difference between the source DU 614DL reference signal and the target DU 616 reference signal. The meaning of TS_Offset is exactly the same as the term Reference Signal Time Difference (RSTD) for the source node (DU 614) and the target node (DU 616). These two terms are used interchangeably in this invention. TS_Offset can be measured by UE 612. According to this equation, the one-way radio propagation delay from the target DU 616 to UE 612 can be calculated as follows:

[0153] OWD2=TS_Offset+OWD1+DU1_Offset–DU2_Offset

[0154] =TS_Offset+OWD1+(Source_DU_Offset–Target_DU_Offset)

[0155] Target_TA = 2 * OWD2

[0156] If there is no DL / UL asymmetry, then target_TA is the RTD between UE 612 and target DU 616, which is twice OWD2.

[0157] DU1_Offset and DU2_Offset are the time offsets between DU 614 and DU 616 and CU 618. They can be determined by CU 618 before HO. The value Nodes_Timing_Offset (=Source_DU_Offset–Target_DU_Offset) can be determined by CU 618. CU can send Nodes_Timing_Offset to source DU 614, and source DU 614 sends Nodes_Timing_Offset to UE 612 via RRC mobility preconfiguration message.

[0158] In cases where the low-cost DU and CU 618 are not precisely synchronized, where the local reference clock of CU 618 drifts rapidly (e.g., they can only meet the synchronization accuracy requirements of asynchronous DC), after mobility pre-configuration is complete, CU 618 periodically monitors the changes in Nodes_Timing_Offset and updates the latest deviation change Nodes_delta_offset to the source DU 614 if the incremental deviation change is higher than a threshold.

[0159] Source DU 614 can update Nodes_delta_offset along with other dynamic TA auxiliary information to UE 612 via MAC CE.

[0160] Another issue affecting the UE when determining the target_TA is the potential DL / UL time asymmetry. This asymmetry can be introduced when the fronthaul propagation delays of the DL and UL differ. Operators can configure / implement timing advances at the DL. However, this introduces DL / UL time asymmetry. DL / UL time asymmetry deviations can typically be measured or determined in advance at the network. Figure 8 This paper illustrates a method by which the UE uses DL / UL time asymmetry information provided by the network to determine the target_TA.

[0161] In this scenario, the DL time offset of the TRP differs from that of the UL. This could be because the DU advances its TX time, aligning the TRP DL transmission time with the DL signal from the associated DU. Another reason for the UL / DL time offset asymmetry could be the difference in fiber fronthaul propagation delay between the DL and UL. Based on the time offset between the source DU 614 and the target DU 616 reference signal measured by UE 612, the total DL time offset from the target DU2 to the UE is:

[0162] OWD2+TRP2_Offset=TS_Offset+OWD1+TRP1_Offset (1)

[0163] OWD1 and OWD2 are the one-way time delays from UE 612 to source TRP 801 and target TRP 802, respectively. TRP1_Offset and TRP2_Offset are the DL time offsets at the antennas of source TRP 801 and TRP 802 relative to source DU 614 and target DU 616.

[0164] Considering the potential time asymmetry with the DU 616 / TRP 802 fronthaul, the time-of-flight (TA) for the target DU 616 / TRP 802 can be derived as follows:

[0165] Target_TA=2*(OWD2+TRP2_Offset)+TRP2_DL_Adjustment (2)

[0166] TRPn_DL_Adjustment is associated with TRPn forward (UL time offset – DL time offset).

[0167] In equation (2), (OWD2+TRP2_Offset) can be replaced by equation (1), where (OWD1+TRP1_Offset) can be obtained at DU1:

[0168] TA_DU1 measured by DU 614 is

[0169] TA_DU1=2*OWD1+2*TRP1_UL_Front_Haul_Delay–TRP1_DL_Adjustment

[0170] OWD1+TRP1_UL_Front_Haul_Delay=1 / 2(TA_DU1+TRP1_DL_Adjustment)

[0171] (OWD1+TRP1_Offset)=OWD1+TRP1_UL_Front_Haul_Delay–TRP1_DL_Adjustment

[0172] =1 / 2(Source_TA_DU1+TRP1_DL_Adjustment)–TRP1_DL_Adjustment

[0173] =1 / 2(Source_TA_DU1–TRP1_DL_Adjustment) (3)

[0174] The value (OWD1+TRP1_Offset) equals the DL time offset from DU 614 to source TRP 801 plus the time offset from source TRP 801 to UE 612. It is based on the TA measurement at DU 614. DU 614 sends this value to UE 612 by activating MAC CE.

[0175] OWD2+TRP2_Offset=TS_Offset+OWD1+TRP1_Offset

[0176] =TS_Offset+1 / 2(Source_TA_DU1–TRP1_DL_Adjustment)

[0177] Finally, the TA for the target DU 616 / TRP 802 is:

[0178] Target_TA=2*(OWD2+TRP2_Offset)+TRP2_DL_Adjustment

[0179] =2 * TS_Offset+Source_TA_DU1–TRP1_DL_Adjustment+TRP2_DL_Adjustment(4)

[0180] In summary, in equation (4), TS_Offset is measured by UE 612 when access to the target cell is activated. Total_SourceTRP1_DLoffset is sent to UE 612 from source TRP 801 via MAC CE activation. It is based on the RTD measurement at source DU 614.

[0181] TargetTRP2_DL_Adjustment is a fixed parameter for target TRP 802. It is sent to UE 612 via an RRC reconfiguration SCG add message. Since the TRP is transparent to the upper layers, TargetTRP_DL_Adjustment is configured for all or more candidate SSBs and CSI-RS associated with target TRP 802, where target TRP 802 can be identified by the beam set ID associated with that TRP.

[0182] An alternative approach is that, upon target cell access activation, source DU 614 sends source TA_DU1 and TRP1_DL_Adjustment to UE 612 via the activated MAC CE. Based on this information, UE 612 can determine Total_SourceTRP1_DLoffset and Target_TA.

[0183] Based on the above analysis, the following general formula can be formulated for determining the target TA at the UE. This formula takes into account the synchronization inaccuracy of the baseband node, the time deviation between the source node and the target node, and the asymmetry of the forward transmission DL / UL propagation time deviation:

[0184] Target_TA=2*TS_Offset+Source_TA+2*Nodes_Timing_Offset–

[0185] SourceTRP_DL_Adjustment+TargetTRP_DL_Adjustment(5)

[0186] TS_Offset is the time deviation between the source reference signal and the target reference signal measured by the UE.

[0187] Source_TA is the TA used by the UE when transmitting UL data to the source node / cell. It is time-sensitive. When target cell access activation is triggered, the most recent Source_TA is sent to the UE via the target cell access activation command (which can be MAC CE).

[0188] Nodes_Timing_Offset = Source_DU_Offset – Target_DU_Offset: This includes the node time offset configured by RRC and the incremental offset of MAC CE updates, which can be determined by the CU and updated to the UE.

[0189] SourceTRP_DL_Adjustment is a source DL asymmetry adjustment factor that is pre-measured when deploying source TRP and source DU.

[0190] TargetTRP_DL_Adjustment is a target DL asymmetric adjustment factor that is pre-measured when deploying the target TRP and target DU.

[0191] The term 2*Nodes_Timing_Offset–SourceTRP_DL_Adjustment+TargetTRP_DL_Adjustment in equation (5) can be determined at the network and combined into a single TA adjustment factor. Here, this term can be named TA_NT_Adj_Factor without loss of generality. The network includes the TA network adjustment factor in the RRC pre-configuration message and sends this message to the UE. The final target TA equation can be simplified to:

[0192] Target_TA=2*TS_Offset+Source_TA+TA_NT_Adj_Factor(5A)

[0193] In such Figure 9 In a separate embodiment of the DU / intra-cell scenario shown, when the UE initially uses the reference signal received from TRP 901 as the local reference for the UE to transmit its SRS and UL messages, the TA (i.e., TRP1_TA) determined by DU 903 for TRP 901 is:

[0194] TRP1_TA=2*(TRP1_Offset+OWD1) (6)

[0195] TRP1_Offset is the forward propagation delay from DU 903 to TRP 901.

[0196] OWD1 is the air interface delay from TRP 901 to UE 904.

[0197] When the TRP 901 reference signal is used as the UE local reference for TRP 902 UL transmission, the TA (i.e., TRP2_TRP1-Ref_TA) determined by DU 903 for TRP 902 is:

[0198] TRP2_TRP1-Ref_TA=(TRP1_Offset+OWD1)+(TRP2_Offset+OWD2) (6),

[0199] TRP2_Offset is the forward propagation delay from DU 903 to TRP 902.

[0200] OWD2 is the air interface delay from TRP 902 to UE 904.

[0201] TRP2-TRP1-Ref_TA is the initial TA sent by DU 903 to UE 904 for UE 904 to perform UL transmission to TRP 902. However, due to mobility, UE 904 may need to use the reference signal from TRP 902 as its local reference for UL transmission to TRP 902 in certain situations. When UE 904 switches its local reference to the TRP 902 reference signal for UL transmission to TRP 902, the new TRP2_TA should be:

[0202] TRP2_TA=2*(TRP2_Offset+OWD2) (7)

[0203] From equations (6) and (7), we can conclude that:

[0204] TRP2_TA=TRP2_TRP1-Ref_TA+(TRP2_Offset+OWD2)–(TRP1_Offset+OWD1) (8)

[0205] Given that TS_Offset(RSTD) is:

[0206] TS_Offset=(TRP2_Offset+OWD2)–(TRP1_Offset+OWD1) (9)

[0207] Then, when the local reference time switches to the time of the TRP 902 reference signal, UE 904 can obtain its new TA for TRP 902 without waiting for DU 903 to update its TA due to the reference switch at UE 904. The new TRP2_TA can be obtained by adjusting the current TRP2_TRP1-Ref_TA and TS_Offset:

[0208] TRP2_TA=TRP2_TRP1-Ref_TA+TS_Offset (10)

[0209] UE 904 can distinguish the reference signals of TRP 901 and TRP 902 by the reference signal set ID associated with TRP 901 and TRP 902.

[0210] Figure 10 The functions and procedures performed at the UE during seamless inter-cell HO as provided in some embodiments are illustrated. At operation 1001, the UE performs L1 measurements on the candidate cell / TRP / beam according to the mobility preconfiguration and sends a measurement report back to the source node.

[0211] At operation 1002, the UE tracks the reference signal time for each candidate TRP beam set. Taking TRP_ID as an example, where TRP_ID is the ID of each TRP beam set, the UE can track the time by periodically measuring, updating, and storing the time of the strongest beam in the set. The most recent update time of the candidate cell / TRP beam set is used by the UE to determine the time offset between the source beam and the target beam when activating target access.

[0212] At operation 1003, the UE determines whether it has received a mobility access command (e.g., MAC CE).

[0213] If so, at operation 1004, upon receiving the L1 / L2 target access command, the UE determines the optimal beam as the HO target beam. The UE determines the target_TA based on the measured reference signal time difference (TS_Offset / RSTD) between the source beam and the target beam, as well as static and dynamic TA auxiliary information.

[0214] At operation 1005, the UE locks the reference signal time of the target beam and applies the target TA to the UL transmission. The UE performs RACH-free access to the target cell. Utilizing pre-authorized UL resources and SRS, the UE transmits the first message to the target cell at the time of target_TA, based on the reference signal time of the target beam selected by the UE in the target cell / TRP. An alternative is not to configure pre-authorized UL resources for the UE. The UE sends SRS to the target cell / TRP at the time of target_TA, based on the reference signal time of the target beam selected by the UE.

[0215] At operation 1006, after receiving the SRS at the target cell, the UE receives authorization from the target cell's PDCCH. After establishing a connection with the target cell, the UE sends messages and / or data.

[0216] An alternative to not configuring RRC pre-authorized UL resources to the UE is to transmit the first message authorization at a pre-configured time for the target PDCCH. Following mobility pre-configuration, the UE monitors the PDCCH at the pre-configured time. In the first message, the UE indicates the optimal target beam to the target cell, or transmits a pre-configured SRS associated with the selected target beam, enabling the target node to determine the optimal DL beam for PDCCH and PDSCH transmission. The UE determines the UL receive beam to optimally receive UL transmissions from the UE, particularly in FR2.

[0217] Figure 11A and Figure 11B The functions and procedures performed at the network during seamless inter-cell HO operations provided by some embodiments are illustrated. Figure 11A and Figure 11BIn the illustrated embodiment, the control node (e.g., the CU, which may be the same as the mobility source node) performs UE trajectory prediction based on measurement reports and other side information. The control node determines HO candidate cells based on the predicted UE trajectory and other information and performs mobility pre-configuration for the candidate cells. Pre-configuration includes pre-configuration of L1 measurement, TA determination, no-RACH access, target beam selection, and indication.

[0218] The control node determines the time offset between the source node and one or more target nodes. The source node determines when to send an L1 / L2 target access command (e.g., MAC CE) to the UE based on pre-configured UE L1 measurement reports for candidate cells / beams. Taking MAC CE as an example, MAC CE contains auxiliary information for the UE to calculate Target_TA, including: Source_TA (the most recently updated source TA change transmitted to the source node's UL), one or more candidate SSBs and / or one or more CSI-RSs and Nodes_delta_offset.

[0219] In MAC CE, one or more possible targets SSB and / or CSI-RS can be indicated.

[0220] The network control node sends a mobility preconfiguration request to a candidate node (e.g., the target DU) via an F1 message. This request may include a request for time offset reporting. The network control node may also request the source node (e.g., the source DU) to report its time offset.

[0221] The target node provides a pre-configured authorization for the first RACH-free transmission to the UE at the target node. For example, the authorization in the RRC configuration may include the following.

[0222] Pre-configured authorization fields Number of bits Initial message PUSCH frequency resource allocation 4 bits or any other suitable number of bits Initial message PUSCH time resource allocation 4 bits or any other suitable number of bits MCS 5 bits or any other suitable number of bits Power allocation for initial message PUSCH 2 bits or any other suitable number of bits

[0223] like Figure 11A and Figure 11B As shown, at operation 1101, the network control node (e.g., CU) predicts the UE trajectory based on measurement reports and other side information. The network control node then determines mobility candidate cells for configuration based on the predicted UE trajectory.

[0224] At operation 1102, the network control node (e.g., CU) sends a mobility configuration request to a candidate node (e.g., DU) / cell via an F1 message. This mobility configuration request may include a time offset reporting request. The network control node may also request the source node (e.g., source DU) to report its time offset.

[0225] At operation 1103, candidate nodes / cells can respond with the target cell configuration, including candidate beams, initial TX grant, and candidate beam association SRS. Candidate nodes / cells can also report their time deviations from the network control node. If requested, the source node can also report its time deviation.

[0226] At operation 1104, the network control node can forward mobility configurations from candidate nodes to source nodes. The network control node can also provide the source node with the time offset between the source node and the candidate node.

[0227] At operation 1105, the source node can send RRC pre-configuration to the UE. RRC pre-configuration may include pre-configuration indication, candidate cells / beams and corresponding SRS, L1 measurement configuration and static TA auxiliary information.

[0228] At operation 1106, the source node receives and processes the L1 measurement report from the UE.

[0229] At operation 1107, the source node determines whether any candidate L1 measurement reports meet the access triggering conditions. If so, at operation 1108, the source node sends an L1 / L2 target access command (e.g., MAC CE) to the UE. The target access command may include dynamic TA auxiliary information, such as the latest incremental time offset, the latest source TA change, or the total DL OWD.

[0230] At operation 1109, the network control node periodically sends time skew report requests to the source node and candidate nodes. The network control node determines the current time skew between the source node and the target node based on the skew reports.

[0231] At operation 1110, the network control node determines whether the incremental time deviation change exceeds a threshold. If so, at operation 1111, the network control node sends the incremental time deviation to the source node, and then the process continues to execute operation 1108 as described above.

[0232] At operation 1112, each candidate node / cell continues to transmit the SSB / CSI_RS of the proposed candidate beam. After pre-configured authorization, the candidate node / cell begins monitoring the UE's first RACH-free transmission and monitors the pre-configured SRS (if configured).

[0233] At operation 1113, each candidate node / cell determines whether any pre-authorization messages and SRS transmissions have been detected. If a candidate node / cell has detected any, then at operation 1114, the candidate node / cell becomes the target cell, decodes the UE's first message, processes the SRS, and determines the optimal beam selected by the UE.

[0234] At operation 1115, the target cell begins DL signaling and data transmission on the optimal beam selected by the UE.

[0235] It can provide conservative resource allocation (e.g., MCS, power) for the RACH-free initial message sent by the UE to the target node.

[0236] In LTE and R17, RACH-free access to targets is supported in certain scenarios, but so far no one has paid attention to the power allocation for the initial RACH-free transmission.

[0237] For initial power allocation, one possible approach is to adopt a more conservative power setting, similar to the power allocation of a random access preamble that follows open-loop PC rules.

[0238] In a separate embodiment, if no optimal target beam is indicated in the first message without RACH, the candidate node may pre-configure the SRS associated with the candidate beam of that candidate node. After the candidate node is selected as the target node, the beam-associated SRS can be used to indicate the target beam selected by the UE.

[0239] Upon receiving the initial transmission from the UE, the candidate node becomes the target node and determines the optimal beam selected by the UE by decoding the received initial message or processing the received SRS. Then, the target node performs DL transmission on the optimal beam.

[0240] This embodiment of the technology reduces latency on the time-critical path of mobility. It extends the intra-cell TRP handover experience to inter-cell TRP handover, enabling seamless mobility with minimal service interruptions and high data throughput during inter-cell mobility.

[0241] This embodiment provides a more accurate and reliable method for quickly determining the TA at the UE, enabling RACH-free access in most common mobility scenarios.

[0242] In individual embodiments, seamless mobility can also be extended to conditional HO (CHO) and conditional PSCell addition or change (CPAC). In this embodiment, similar to pre-configured RRC messages, conditional RRC messages (CHO commands or CPAC requests) also include associated TargetTRP_DL_Adjustment, Nodes_timing_offset, pre-allocation authorization for RACH-free access to the target cell, and candidate SSBs and CSI-RS for the SRS.

[0243] One difference between conditional seamless mobility and pre-configured seamless mobility lies in the target access triggering. The former is triggered by the UE, while the latter is triggered by the network. This leads to a difference in dynamic TA (Target Access Assist) information updates. In the case of network triggering, the information can be updated when target access is activated. However, in the case of conditional UE triggering, the update must occur before the condition triggering occurs. After starting CHO / CPAC via RRC reconfiguration message, in CPAC, since CPAC is under DC, the UE continues to maintain a connection with the source node (MN in CPAC). For CHO, the UE will maintain a connection with the source node for as long as possible. If the UE's connection with the source is interrupted before CHO access is triggered, if the TAT (Target Access Assist) has not timed out when CHO is triggered, the nearest source node OWD (Overhead Data) or TA maintained at the UE can still be considered valid; otherwise, the source node OWD or TA maintained by the UE cannot be considered valid, and random access to the target cell should be performed.

[0244] After the conditional RRC reconfiguration message is sent, the control node continues to monitor the time deviation between the source node and the candidate node. If the deviation changes significantly, the control node updates the incremental time deviation to the source node, and then the source node sends the incremental deviation to the UE via MAC CE. In addition, the source node continues to update the UE with the incremental OWD or incremental TA associated with the source node via MAC CE.

[0245] To improve the accuracy of the source node OWD or TA used in the UE, stricter update triggering conditions will be used to trigger OWD or TA updates more frequently at the network.

[0246] When the condition triggering conditions are met, the UE applies a pre-configured system including static and recently updated dynamic target TA auxiliary information to determine the target_TA. The UE locks the target cell reference signal time as its local reference time for UL transmission. Utilizing pre-authorized UL resources, the UE performs its first RACH-free transmission to the target cell based on the received target cell reference signal time, at a time further ahead of the target_TA.

[0247] Figure 12 Flowcharts of the functions and procedures performed at the UE during conditional seamless inter-cell mobility provided in some embodiments are shown. At operation 1201, the UE performs L1 measurements on candidate cells / beams according to mobility pre-configuration in order to trigger conditional target access.

[0248] At operation 1202, the UE tracks the reference signal time for each candidate TRP beam set. Using the TRP_ID, where TRP_ID is the ID of each TRP beam set, the UE can track the time of the strongest beam in that set to determine the time deviation between the source and target beams when target access is activated.

[0249] At operation 1203, the UE determines whether the candidate beam measurement is higher than the condition trigger condition.

[0250] If so, at operation 1204, when one or more beams meet the condition triggering condition, the UE determines the optimal beam's SSB or CSI-RS as the access target beam. The UE applies conditional configuration including static and recently updated dynamic target TA auxiliary information. The UE determines target_TA based on the measured time deviation between the source beam and the target beam, and the static and dynamic TA auxiliary information from the network.

[0251] At operation 1205, the UE locks the timing of the reference signal for the target beam and applies the target TA to UL transmission. The UE performs RACH-free access to the target cell by transmitting a first message to the target cell using pre-configured UL resources. The pre-configured UL resources can be authorized resources issued via RRC mobility pre-configuration messages. Alternatively, the authorization of the first message can be indicated by the target cell PDCCH at a pre-configured time, or the PDCCH instruction can be triggered by an SRS transmission. In the first message, the UE indicates the optimal target beam to the target cell, or transmits a pre-configured SRS associated with the selected target beam, enabling the target node to determine the optimal DL beam for PDCCH and PDSCH transmission, and the UE to determine the UL receive beam for optimal UL transmission reception from the UE, particularly in FR2.

[0252] At operation 1206, the UE begins to use the CRNTI associated with the target cell to monitor the PDCCH.

[0253] Figure 13A and Figure 13B The functions and procedures performed at the network during seamless inter-cell mobility provided by some embodiments are illustrated. Figure 13A and Figure 13B In this embodiment, the network control node (which may be a mobility source node, or an MN in a DC scenario) performs UE trajectory prediction. Based on the predicted UE trajectory and other information, the network control node determines candidate CHOs and performs conditional pre-configuration of the candidate cells. Pre-configuration includes pre-configuration of L1 measurement, TA determination, no RACH access, target beam selection, and indication.

[0254] The network control node determines the time offset between the source node and one or more target nodes and tracks changes in the time offset. The network control node provides the source node with `Nodes_timing_offset` for conditional configuration. Subsequently, whenever the time offset changes beyond a threshold, the network control node updates the source node with `Nodes_delta_offset`.

[0255] The source node performs conditional RRC configuration on the UE. The source node tracks source OWD or TA changes (whenever the change exceeds a threshold) and sends incremental source OWD or incremental TA to the UE via MAC CE. Whenever the source node receives Nodes_delta_offset, it updates it to the UE via MAC CE.

[0256] The target node provides a pre-configured authorization for the first RACH-free transmission to the UE at the target node. Resource allocation for the initial transmission, which serves as the first message of access notification, can be conservative. The pre-authorized first transmission to the target node may include a power headroom report (PHR), a buffer status report (BSR), and the selected best SSB or CSI_RS ID.

[0257] like Figure 13A and Figure 13B As shown, at operation 1301, the network control node (e.g., CU) determines mobility candidate cells for CHO / CPAC based on trajectory prediction.

[0258] At operation 1302, the network control node sends a conditional mobility request to a candidate node (e.g., DU) / cell via an F1 message. This conditional mobility request may include a time skew reporting request. The network control node may also request the source node (e.g., DU) to report its time skew.

[0259] At operation 1303, candidate nodes / cells respond with the target cell configuration, including candidate beams, initial TX grants, and candidate beam association SRS corresponding to their current serving cell and / or one or more potential serving cells. Candidate nodes / cells may also report their time offsets from the network control node. If requested, the source node also reports its time offset.

[0260] At operation 1304, the network control node forwards mobility configuration from the candidate node to the source node. The network control node can also provide the source node with the time offset between the source node and the candidate node.

[0261] At operation 1305, the source node sends RRC condition configuration to the UE. The RRC condition configuration may include candidate cells / beams and corresponding SRS and static TA auxiliary information.

[0262] At operation 1306, after the latest source TA is applied to the UE, the source node continues to monitor the current time deviation of the received signal relative to the local reference.

[0263] At operation 1307, the source node determines whether the time offset (incremental Source_TA) of the received signal is greater than a threshold. If so, at operation 1308, once an incremental time offset update is received or the incremental Source_TA is higher than the threshold, the source node updates the incremental time offset and / or incremental Source_TA (or incremental OWD) to the UE via MAC CE.

[0264] At operation 1309, the network control node periodically sends time skew report requests to the source node and candidate nodes. Based on the time skew reports, the network control node determines the current time skew change (incremental time skew) between the source and target nodes.

[0265] At operation 1310, the network control node determines whether the incremental time deviation change exceeds a threshold. If so, at operation 1311, the network control node sends the incremental time deviation to the source node, and then the process continues to execute operation 1308 as described above.

[0266] At operation 1312, each candidate node / cell continues to transmit the SSB / CSI_RS of the proposed candidate beam. After pre-configured authorization, the candidate node / cell begins monitoring the UE's first RACH-free transmission and monitors the pre-configured SRS (if configured).

[0267] At operation 1313, each candidate node / cell determines whether any pre-authorization messages and SRS transmissions have been detected. If a candidate node / cell has detected any, then at operation 1314, the candidate node / cell becomes the target cell, decodes the UE's first message, processes the SRS, and determines the optimal beam selected by the UE.

[0268] At operation 1315, the target cell begins DL signaling and data transmission on the optimal beam selected by the UE.

[0269] Figure 14 It shows the relationship with Figure 3 The signaling flow of the proposed framework for seamless mobility corresponding to the mobility architecture shown is illustrated. Operations 1400 to 1402 are similar. Figure 6 Operations 600 to 602 are performed within this process. Figure 14In the illustrated scheme, RRC mobility pre-configuration and RRC reconfiguration at operations 1403 and 1404 are performed ahead of schedule, pushing the process into the mobility preparation phase. The delay caused by the RRC message does not interrupt data transmission via the UE / source node connection. At operation 1405, target cell access activation is triggered by MAC CE. At operation 1406, RACH-free access is performed. Operation 1407 is similar. Figure 6 Operation 608. At operation 1408, source DU / cell release can be performed.

[0270] The following table shows an exemplary change in TS 38.215 regarding the DL reference signal time difference (DL RSTD).

[0271]

[0272] The changes to transmission time adjustment in TS 38.213 are as follows.

[0273] Delay common (t) is the distance between the serving satellite and the uplink time synchronization reference point at time t divided by the speed of light. The uplink time synchronization reference point is the point where the DL and UL frames are aligned, where the deviation is determined by N. TA,offset Provided.

[0274] If RACH-free mobility is configured, when mobility access to the target cell is triggered by the target access command in TS 38.321 or the conditions in TS 38.331, the UE first determines the optimal SSB or CSI-RS as the target beam for mobility access; then, the UE determines the DL RSTD between the reference signals of the source TP and the target TP, as described in Clause 5.1.19 of TS 38.215, where the source TP and the target TP are TPi and TPj, respectively. The UE further determines the timing advance of the target cell, Target_TA.

[0275] Target_TA=2*DL_RSTD+nSource_TA+TA_NT_Adj_Factor+2*Nodes_delta_offset

[0276] In TS 38.133, DL_RSTD is the time deviation between the source reference signal and the target reference signal measured by the UE, expressed in Tc. DL_RSTD can also be referred to as TS_Offset in this invention.

[0277] nSource_TA is derived from the absolute time advance Source_TA in the source cell (absolute in TA 38.321). nSource_TA is in units of Tc. When target cell access is triggered, the most recent Source_TA is sent to the UE via the target cell access command MAC CE in TA 38.321.

[0278] TA_NT_Adj_Factor is a network adjustment factor used at the UE to determine the target TA, in units of Tc. The network sends the TA network adjustment factor to the UE via RRC mobility preconfiguration messages.

[0279] Nodes_delta_offset is the change in time offset between the source node and the target node since the RRC mobility preconfiguration message was sent, in units of Tc, and can be carried by the target cell access command MAC CE.

[0280] The UE tracks the time of the SSB or CSI-RS received by the target TRP and uses this as a reference to adjust the UL transmission time in advance according to the target TA so as to perform PUSCH / SRS / PUCCH transmission on the target cell.

[0281] Figure 15 An exemplary Target Access Command (MAC) CE is shown. The DO field indicates the presence of an octet containing the Node Incremental Offset field. The CSI-RS Num field contains the number of CSI-RS IDs included in this MAC CE. The SSB Num field contains the number of SSB IDs included in this MAC CE. The SSB IDi field contains the i-th SSB ID out of the Num SSB IDs included in this MAC CE. The CSI-RS IDi field contains the i-th CSI-RS ID out of the Num CSI-RS IDs included in this MAC CE. The Source Cell TA field is a 12-bit field containing the current absolute TA or the TA change of the source cell since the last update. The Node Incremental Offset field is an octet field containing the incremental change of the time offset between the source node and the target node after the time offset is configured to the UE during mobility pre-configuration. The presence of this field is indicated by the DO field.

[0282] If RACH-free mobility is configured, the MAC entity may: (1) initiate the RACH-free target cell access procedure by receiving the target access command MAC CE as defined in Section 6.1.3.x, and the target access command has explicitly provided a list of SSBs and / or CSI-RSs; (2) select an SSB with an SS-RSRP higher than rsrp-ThresholdSSB from the list of SSBs if at least one of the listed SSBs with an SS-RSRP higher than rsrp-ThresholdSSB is available, and transmit the SRS and the first message corresponding to the selected SSB if the authorization of the first message is pre-configured; otherwise, if at least one CSI-RS with a CSI-RSRP higher than rsrp-ThresholdCSI-RS is available, the MAC entity may select a CSI-RS with a CSI-RSRP higher than rsrp-ThresholdCSI-RS from the list of CSI-RSs, and transmit the SRS and the first message corresponding to the selected CSI-RS if the authorization of the first message is pre-configured.

[0283] During mobility hoisting (HO), several steps on the time-critical path of HO introduce significant latency. RAN2 defines the latency model and the total time spent using traditional methods for L1 or L2 mobility. In the RAN2 mobility latency model, total handover latency includes L1 measurement latency, DL synchronization latency, and UL synchronization latency. High total handover latency leads to high handover failure rates, high call drop rates, and service interruptions.

[0284] After the target cell appears, it takes some time for the UE to perform L1 measurements and report them to the serving cell. The serving cell makes a cell handover decision based on the measurement report and sends a cell handover command to the UE. RAN2 considers this delay as the L1 measurement delay. The L1 measurement delay has a negative impact on handover performance. In the RAN2 mobility delay model, the total handover delay includes the L1 measurement delay, DL synchronization delay, and UL synchronization delay. A large total handover delay leads to a high handover failure rate, a high call drop rate, and service interruption. It should be noted that the delay model discussed in RAN2 assumes a mobility framework based on DL reference signal (RS) measurements (i.e., the cell handover decision is made at the source cell based on the UE's DL RS measurement report).

[0285] For early target TA acquisition, various schemes have been proposed. These schemes include: (1) RACH-based schemes (e.g., RACH indicated by PDCCH, UE-triggered RACH, RACH triggered by higher layers of the network other than L3 HO commands); (2) RACH-free schemes (e.g., SRS-based TA acquisition, such as the Rx time difference-based RACH-free mechanism in LTE, UE-based TA measurement (including UE-based TA measurement via a TAC from the serving cell)).

[0286] SRS-based TA acquisition is one of the candidate solutions. Unlike other solutions, it can be considered an example of ULRS-based mobility if the cell handover decision made by the target cell based on ULRS measurements is permitted.

[0287] Technical challenges associated with mobility based on UL reference signals (RS) include UE power consumption. The UE needs to transmit the UL RS (e.g., SRS) at sufficiently high power and frequency so that the target cell can understand the UE. In the worst-case scenario, the target TA is determined at the target cell, which then sends the TA to the source cell. The source cell then performs a cell handover based on L1 measurements. In this case, the UE needs to transmit both the SRS and L1 measurement reports simultaneously.

[0288] Technical challenges related to mobility based on the UL reference signal (RS) also include latency issues. The total latency of UL RS-based mobility includes DL measurement / beam selection, DL synchronization latency, and UL measurement / synchronization latency. Because the UL time offset at the target cell / TRP can be significant, a longer UL RS measurement time may be required to acquire the ULRS and obtain a reliable TA. If the target TA determined by the target cell is sent back to the source cell, additional backhaul latency is introduced.

[0289] Due to well-known UE power consumption and latency issues, it is impractical to send the target cell's determined TA back to the source cell via backhaul. SRS-based schemes cannot be used solely for obtaining the target TA. Mobility based entirely on UL RS, where the target cell makes cell handover decisions based on UL RS measurements, warrants further investigation. This invention addresses the model / framework issues related to UL-based mobility.

[0290] The following is an example of a known traditional mobility approach based on UL SRS. For multiple candidate cells / beams, each candidate cell / beam corresponds to a uniquely configured set of SRSs. After pre-configuration, the UE transmits SRSs to all detected candidate cells / beams. The transmission time of each SRS should follow the time of the reference signal for the corresponding candidate cell / TRP / beam in order to directly obtain the absolute TA of the target cell / TRP.

[0291] The candidate / target cell measures the absolute TA of the cell / TRP based on the received SRS from the UE and the associated SSB or CSI-RS indicated by the UE. The target cell determines that the UE is close enough to initiate a cell handover based on the SRS measurement and sends the measured TA directly to the UE in the cell handover command.

[0292] The problem with this TA (Target Acquisition) method is that, in addition to transmitting the SRS (Service Reference Signal) of its current serving cell at different transmission times corresponding to each candidate cell / TRP (Transmission Time Point), the UE must also transmit multiple candidate SRSs throughout the entire TA acquisition time. Since the UE may need to transmit multiple SRSs in parallel at high power for extended periods, power consumption is a significant issue. This can also consume substantial radio resources and generate additional signaling overhead.

[0293] The goal is to obtain a large absolute TA at one or more candidate DUs, including initial UE SRS acquisition. Obtaining a reliable and accurate TA at candidate DUs within a short timeframe is challenging and may require a longer timeframe to acquire the TA.

[0294] The UE needs to adjust the transmission time differently for different SRS transmissions. This may increase complexity and affect the serving cell transmission time in the serving cell.

[0295] Based on the SRS TX time of the candidate TRP, the UE needs to perform DL synchronization with the candidate TRP first, so the SRS transmission to the candidate will be later, which will lead to an increase in HO latency.

[0296] One related scheme is a TA adjustment scheme based on multi-TRP UL RS measurement within a DU. In this scheme, the incremental TA of the target TRP is determined at the serving DU that serves both the source TRP and the target TRP. The serving DU sends the incremental TA of the target TRP to the UE. After the UE obtains the DL reference signal of the target TRP, it can measure the RSTD at the UE, such as... Figure 16 As shown.

[0297] RSTD = Target Time Offset – Source Time Offset = TargetTRP2_Offset + OWD2 – (SourceTRP1_Offset + OWD1)

[0298] In the above equations, RSTD is the time deviation between the source reference signal and the target reference signal measured by UE 1604. SourceTRP1_Offset is the forward propagation delay from DU 1603 to source TRP 1601. OWD1 is the air interface delay from source TRP 1601 to UE 1604. TargetTRP2_Offset is the forward propagation delay from DU 1603 to target TRP 1602. OWD2 is the air interface delay from target TRP 1602 to UE 1604.

[0299] When UE 1604 uses the target TRP reference signal time as its reference for UL transmission to perform UL TX, the adjusted incremental TA should be used, and UE 1604 should adjust using the latest measured RSTD.

[0300] Adjusted_TargetdeltaTA=SourceRef_DeltaTargetTA+RSTD

[0301] In the above equation, the mobility RSTD is defined as RSTD = Target TRP Reference Signal Time – Source TRP Reference Signal Time, measured at UE 1604. SourceRef_DeltaTargetTA is the incremental TA for the SRS measurement at source time for service DU 1603. It is transmitted via a TAC that includes the TAGID associated with the target beam of target TRP 1602.

[0302] This solution can be extended to multi-TRP scenarios between DUs.

[0303] With the increasing use of travel planning applications (e.g., Google Maps) and more fully self-driving (FSD) devices, the UE's travel trajectory is often pre-scheduled and predetermined. In these cases, the UE trajectory can be considered deterministic or semi-deterministic, and can be updated by the UE or at the network over a period of time. Assuming that the UE's semi-deterministic trajectory information is available at the network, this information can be used for L1 / L2 multi-candidate pre-configuration. Figure 17 The diagram illustrates the source beam and candidate beams determined by the network based on the UE trajectory. The UE mobility boundary region points of candidate cells on the trajectory can be determined by the network. Based on the location of the boundary points and the locations of the TRPs of the source and target cells adjacent to the boundary points, one or more serving beams and one or more candidate beams for the UE at the boundary points can be predetermined. Therefore, the UE receives a beam scanning pattern associated with the serving beam and candidate beams.

[0304] Since mobility pre-configuration is based not only on measurements but also on other information (e.g., UE trajectory), initial candidate beam search and acquisition may be required when the UE performs a subsequent cell handover from a new serving source cell to a subsequent candidate cell. Typically, an exhaustive beam scan-based initial candidate beam search can take a considerable amount of time to acquire candidate beams. The aim is to reduce initial beam search time to support fast cell handovers in L1 / L2 mobility by instructing the UE to perform beam search and measurement only on candidate beams of the current serving cell. Furthermore, the UE can be instructed to perform an initial beam search on candidate beams associated with the current serving beam. This avoids searching and measuring all candidate beams of all pre-configured candidate cells, saving UE power and reducing measurement latency.

[0305] In L1 / L2 mobility, L1 measurement and beam selection delays are among the main delay components. As mentioned above, in systems with multi-beamforming enabled, initial beam selection and acquisition via beam scanning operations is time-consuming. This invention introduces a pre-configured beam scanning mode to reduce the initial beam acquisition time. This invention discloses how the beam mode is determined and how the UE actually uses the beam scanning mode.

[0306] Traditional mobility solutions based on UL RS have problems with high UE power consumption and high signaling overhead.

[0307] This invention describes a mobility scheme based on UL RS that can minimize latency on the time-critical path of the HO process, is applicable to both synchronous and asynchronous networks, and solves the problems of high UE power consumption, high radio resource consumption, high signal overhead, and low reliability of traditional mobility schemes based on UL RS.

[0308] To reduce L1 measurement latency for L1 / L2 mobility, a method for pre-configuring UE receive (RX) beam scanning modes is introduced. Based on UE trajectory prediction, the relative positions of one or more source serving beams and one or more candidate target beams can be pre-determined. A UE beam scanning mode using the serving source beam as a reference can be determined and configured to the UE via RRC configuration. After pre-configuration in the boundary area, the UE only needs to follow the beam scanning mode to perform the initial candidate beam search.

[0309] To address the issues of UE power consumption and radio resource usage in UL RS-based mobility and to minimize target access latency, this invention describes a two-stage SRS transmission scheme for target TA acquisition during DU / inter-cell handover, as shown below.

[0310] During the mobility preparation phase, the CU informs one or more candidate DUs of the configuration of one or more SRSs used by the UE in one or more source DUs / cells.

[0311] By pre-configuring, one or more SRSs corresponding to one or more candidate SSB / CSI-RS are configured to the UE.

[0312] This embodiment of the technology can perform early SRS transmission to one or more candidate cells / TRPs / beams with low additional power consumption. If the received candidate SSB or CSI-RS is strong enough (above a threshold), the UE continues to transmit the SRS of its current serving cell at the time + source_TA of the received serving source cell reference signal, with a possible reduced periodicity and continuous repetition configured for mobility.

[0313] After achieving DL synchronization with the candidate beam and meeting the high-quality target SSB / CSI-RS standard, the UE transmits the pre-configured SRS corresponding to the synchronized candidate beam at the time + source_TA of the received serving cell reference signal, according to the periodicity configured for mobility.

[0314] The candidate / target DU performs an initial SRS search for the UE based on the serving SRS configuration, including receive beam scanning with the expected receive beam and TRP, and using a wide search window to handle large time deviations. The candidate DU measures the time deviation of the target beam-associated SRS received from the candidate TRP of the candidate DU / cell. If the received SRS strength is higher than a threshold, the candidate / target DU uses the measured time deviation as the TA of the target cell / TRP / beam and issues a cell handover command to the UE including the measured TA.

[0315] The incremental TA of the target cell / TRP / beam, determined by the target DU, is the incremental time offset (denoted as SourceRef_DeltaTargetTA) obtained from the measurement of the received SRS, which is transmitted by the UE at the source RS time.

[0316] In DU / inter-cell handover scenarios, the UE adjusts the UL transmission time to the target cell based on the target beam reference signal time.

[0317] Adjusted_DeltaTargetTA=SourceRef_DeltaTargetTA+RSTD

[0318] The structure and use of embodiments of the present invention are discussed in detail below. However, it should be understood that the present invention provides many applicable inventive concepts that can be embodied in various specific contexts. The specific embodiments discussed are merely illustrative of specific ways of constructing and using the invention and do not limit the scope of the invention. These and other inventive aspects are described in more detail below. The present invention provides a general method for applications with extremely high reliability, low latency, and low delay requirements, particularly for mobility applications in the MBB and V2X domains. Compared to various prior art, this method is highly reliable, accurate, and efficient, minimizing latency caused by mobility. This method can be used in different systems such as NR and LTE.

[0319] Figure 18 An example of a UL RS-based mobility framework that affects both the air interface and the network interface is shown. At operation 1801, during the mobility preparation phase, source DU 1824 informs one or more candidate DUs 1826 via CU 1828 of the configuration of one or more SRSs used by UE 1822 in one or more serving source DUs / cells 1824.

[0320] At operation 1802, one or more SRS and RX beam scanning modes corresponding to one or more target SSB / CSI-RS are configured to UE 1822 via pre-configuration.

[0321] At operation 1803, after receiving the RRC pre-configuration, the UE sends an RRC configuration complete message back to one or more source DU / cells 1824. The source DU 1824 relays the message to CU 1828, and CU 1828 notifies one or more candidate DU / cells 1826 at operations 1803.1 and 1803.2.

[0322] At operation 1804, upon receiving the RRC configuration complete notification, candidate cell 1826 begins transmitting the DL reference signal (if any) configured for UE 1822.

[0323] At operation 1805, upon receiving an RRC reconfiguration message for L1 / L2 mobility, UE 1822 begins searching and measuring one or more SSBs and one or more CSI-RSs for candidate cells / TRPs. One or more candidate SSBs and CSI-RSs are searched according to a pre-configured RX beam scanning pattern.

[0324] At operation 1806, when the received candidate SSB or CSI-RS is sufficiently strong (above a threshold), for FR1, UE1822 begins to continue transmitting the SRS of its current serving cell at the time + source_TA of the received serving cell reference signal, according to the periodicity and repetition configured for mobility. For FR2, UE1822 begins to tune the UL TX beam toward the target cell with a power based on the received power of the target cell's SSB or CSI-RS, and transmits the SRS of its current serving cell on that beam at the time + source_TA of the received serving cell reference signal, according to the periodicity configured for mobility.

[0325] At operation 1807, if one or more SSBs or one or more CSI_RSs are sufficiently strong and stable, UE 1822 performs DL synchronization with them. UE 1822 obtains and stores their time (e.g., RSTD) or the time deviation between the candidate SSBs or CSI-RS and the UE's local reference time, as well as other synchronization information, from the broadcast channel (BCH), and begins tracking their time information by measuring, reading, and periodically updating the stored DL synchronization information of one or more tracked SSBs and CSI-RSs. UE 1822 begins monitoring for pre-configured periodic cell handover command monitoring opportunities.

[0326] At operation 1808, when UE 1822 acquires DL synchronization with a candidate SSB or CSI-RS whose quality is above a threshold, UE 1822 transmits a pre-configured SRS corresponding to the synchronized candidate SSB or CSI-RS at the time + Source_TA of the received serving cell reference signal, according to the periodicity configured for mobility. In the case of FR2, beamforming is directed to the target cell for transmitting the SRS, and its power is determined by the received power of the synchronized candidate SSB or CSI-RS.

[0327] At operation 1809, after receiving the RRC configuration complete message, the candidate DU performs an initial search of the UE SRS according to the serving SRS configuration, including receiving beam scanning through the expected receive beam and TRP, and using a wide search window to handle large time deviations. The candidate DU also begins monitoring the SRS configured for the UE associated with the candidate beam.

[0328] At operations 1810 and 1811, when a candidate DU receives and synchronizes with an SRS indicating that the UE has selected a good SSB / CSI-RS, and the SRS measurement meets the cell handover triggering criteria, the target DU 1826 determines the corresponding target SSB or CSI-RS based on the received SRS. The target DU 1826 measures the time deviation from the received SRS and determines the TA (=SourceRef_DeltaTargetTA). The target DU 1826 schedules the cell handover command MAC CE on the target beam via PDCCH and transmits the MAC CE to the UE 1822 during pre-configured monitoring opportunities. The MAC CE carries the incremental TA measured by the target DU.

[0329] At operation 1812, after UE 1822 receives the cell handover command MAC CE, UE 1822 transmits a first UL MAC CE, which may include BSR and PHR, to the target DU 1826 according to the following adjusted incremental time advance:

[0330] Adjusted_DeltaTargetTA=SourceRef_deltaTargetTA+RSTD

[0331] If UE 1822 receives more than one cell handover command from multiple candidate DUs, UE 1822 selects one as the target DU 1826 and sends an acknowledgment to it, and then sends one or more “reject” or “suspend” notifications to one or more other handover-triggered DUs.

[0332] To address the issues of UE power consumption and radio resource usage in UL RS-based mobility and to minimize target access latency, this invention provides an exemplary two-stage SRS transmission scheme.

[0333] During the mobility preparation phase, the source DU informs one or more candidate DUs of the configuration of one or more SRSs used by the UE in one or more source DUs / cells. This enables one or more candidate DUs to detect the SRS that the UE is using in the current source serving cell.

[0334] Through pre-configuration, one or more SRSs corresponding to one or more candidate target SSBs / CSI-RSs and one or more SRSs corresponding to one or more serving SSBs and CSI-RSs of candidate cells are configured to the UE. One or more candidate target SSBs and CSI-RSs, source SSBs and CSI-RSs, and their one or more associated SRSs are associated with one or more corresponding candidate DU(d) / cells to facilitate subsequent cell handover when a candidate cell becomes the new source cell. Their configuration is prepared for each candidate DU.

[0335] Currently, SRS lengths range from 1 to 4 symbols. Short RACH preamble lengths range from 2 to 12 symbols. SRS enhancements can be added for UL RS-based mobility, including defining longer SRS for mobility purposes. In the first phase of SRS transmission for mobility, shorter periodicity and continuous repetition of current conventional SRS symbols can be permitted.

[0336] Two-stage SRS transmission is described for UE power saving and efficient UL synchronization.

[0337] In the first phase, after pre-configuration, the UE performs beam search and L1 measurement on candidate beams. If a candidate beam is strong enough (above a threshold), the UE continues to transmit the SRS of its current serving cell, but may do so with a shorter periodicity configured for mobility and the repetition of the current SRS symbols. The timing of the SRS transmission is consistent with the time of the received serving cell reference signal + Source_TA. In the case of FR2, the beam is tuned to the target cell for SRS transmission, and its power is determined by the received power of the candidate SSB or CSI-RS.

[0338] In the second phase, when the UE acquires DL synchronization with a candidate SSB or CSI-RS whose quality is above a threshold, the UE treats the SSB or CSI-RS as a possible target reference signal and periodically transmits the pre-configured SRS corresponding to the candidate SSB or CSI-RS synchronized with the UE, as configured for mobility. SRS transmission occurs at the time + Source_TA of the serving cell reference signal received by the UE.

[0339] In the case of FR2, the beam is directed to the target cell for transmitting SRS, and its power is determined by the received power of the candidate SSB or CSI-RS synchronized by the UE.

[0340] SRS is used to indicate the DL beam selected by the UE, indicating that the UE is synchronized with the selected beam, which helps in the final UL synchronization, thereby obtaining accurate and stable TA measurements.

[0341] The candidate / target DU performs an initial search of the UE SRS based on the serving SRS configuration, including receiving beam scanning with the expected receive beam and TRP, and using a wide search window to cope with large time deviations.

[0342] Figure 19The functions and procedures performed at the UE during inter-cell HO based on UL RS are illustrated. At operation 1901, if necessary, the UE performs an initial search and acquisition of candidate cells / TRPs / beams according to the mobility preconfiguration, and performs L1 measurements on the acquired candidate beams. If a beam scanning mode is configured, the UE performs an initial beam search on candidate beams adjacent to the current serving cell according to the beam switching mode.

[0343] At operation 1902, the UE maintains pre-configured parameters, continues L1 measurements of one or more candidate beams, and selects one or more optimal beams.

[0344] At operation 1903, the UE determines whether there are any candidate SSB or CSI-RS strengths above a reasonably good level (threshold). If so, at operation 1904, the UE continues to perform existing serving cell SRS transmissions with reduced periodicity and continuous symbol repetition of the serving cell SRS and may initiate an enhanced version (if configured).

[0345] At operation 1905, the UE determines whether a candidate SSB or CSI-RS that meets the high-quality and reliability criteria exists. If so, at operation 1906, the UE acquires the DL synchronization information (e.g., RSTD) of the selected high-quality candidate beam, and the UE begins transmitting the pre-configured SRS associated with the selected high-quality candidate beam at the time of the received serving source cell reference signal plus the source cell TA. The UE begins monitoring for cell handover commands from the target cell at the pre-configured target cell monitoring opportunity.

[0346] At operation 1907, the UE determines whether it has received a cell handover command from the target cell. If so, at operation 1908, upon receiving the cell handover command, the UE obtains the incremental TA from the received cell handover command. The UE obtains the most recently updated RSTD between the source reference signal and the selected target reference signal. The UE determines DeltaTargetTA based on the received incremental TA and RSTD measured by the target DU.

[0347] At operation 1909, the UE locks the reference signal time of the target cell / beam, applies the determined target TA to the UL transmission, performs RACH-free access to the target cell, and begins data transmission.

[0348] Figure 20 The following embodiments illustrate the functions and procedures performed at the CU during the HO (Hopping) phase of an inter-cell UL RS-based network. At operation 2001, the network CU performs UE trajectory prediction. The CU predicts the UE trajectory based on the L3 measurement report and other side information from the network. The CU determines mobility candidate cells based on the trajectory prediction for pre-configuration of UL RS-based mobility.

[0349] At operation 2002, the CU sends a mobility preconfiguration request to the candidate DU / cell based on the UE L3 measurement report, other side information, and UE trajectory prediction, and notifies the source DU via an F1 message. The mobility request to the candidate DU may include information based on the predicted UE trajectory, such as a reduced list of neighboring cells / beams for the candidate DU based on trajectory prediction, and the configuration of SRS for one or more possible source cells.

[0350] At operation 2003, after receiving all responses from candidate nodes (e.g., DUs), the CU forwards the mobility configuration container from the candidate node to the current source DU, and then the source DU sends the mobility configuration container to the UE via an RRC configuration message. The CU forwards the configuration of one or more pre-determined source cell SRSs of the candidate DU / cell to the candidate's neighboring candidates.

[0351] At operation 2004, after receiving the RRC configuration complete message from the UE via the source DU, the CU forwards the UE acknowledgment to all candidate DUs.

[0352] Figure 21 The functions and procedures performed at the candidate DU / cell during the inter-cell HO period based on UL RS are illustrated. At operation 2101, upon receiving a mobility preconfiguration request from the CU, the candidate DU / cell prepares the target cell mobility configuration for the UE and sends the UE configuration container and neighboring candidate cell configurations to the CU.

[0353] In the UE configuration container, based on traditional mobility configuration, mobility configuration may include one or more boundary area source cell serving SSB / CSI-RS, as well as one or more candidate SSB / CSI-RS of the candidate cell and one or more associated SRS, UE DL monitoring opportunities, and UE RX beam scanning mode.

[0354] Outside of the UE configuration container, mobility configuration may also include source cell service SRS configurations for one or more boundary areas of the candidate DU / cell. When the candidate DU / cell becomes a source DU / cell, this configuration helps neighboring candidate DU / cells search for and obtain source cell service SRS.

[0355] At operation 2102, the candidate DU / cell receives one or more source cell SRSs from one or more neighboring candidate DU / cells from the CU. Based on UE trajectory prediction, some of the candidate DU / cell's one or more neighboring candidate DU / cells may become source DU / cells with one or more associated source SRSs in the cell boundary area. The configuration of the potential source serving SRSs of one or more neighboring candidate DU / cells is relayed by the CU to the reference candidate DU / cell.

[0356] At operation 2103, upon receiving a notification from the CU that the RRC configuration is complete, the candidate DU / cell transmits any CSI-RS configured for the UE and begins searching for the source SRS of the source cell transmitted by the UE.

[0357] At operation 2104, when acquiring the source service SRS, the candidate DU / cell begins to perform initial UL synchronization to measure the incremental TA relative to the local reference time and begins to search for one or more SRSs associated with one or more candidate SSB / CSI-RS pre-configured for that candidate DU / cell.

[0358] At operation 2105, when acquiring one or more SRSs associated with one or more candidate SSBs / CSI-RS pre-configured with the candidate DU / cell, the DU / cell uses the SRS to perform one or more quality metric measurements and further TA measurements. The SRS instructs the candidate DU / cell that the UE considers the SRS-associated beam (SSB or CSI-RS) as a good target beam and that the UE has acquired beam synchronization.

[0359] At operation 2106, the candidate DU / cell determines whether a received candidate beam-associated SRS quality indicator and possible received source SRS indicators meet the cell handover quality criteria. If so, at operation 2107, the candidate DU / cell identifies itself as the target DU / cell for mobility. During UE monitoring opportunities, the candidate DU / cell sends a cell handover command to the UE via the DL beam indicated by the SRS, carrying the measured incremental TA.

[0360] The above-described embodiments reduce UE power consumption and latency for UL RS-based mobility. These embodiments enable seamless UL RS-based mobility with minimal service interruptions and high data throughput during inter-cell handover. They also address the issues of high UE power consumption, high radio resource consumption, high signal overhead, and low reliability in known UL RS-based mobility solutions.

[0361] This invention provides a more accurate and reliable method for rapidly determining the TA at the target DU / cell for both synchronous and asynchronous networks. It enables RACH-free access in most common mobility scenarios.

[0362] In this embodiment, the SRS transmission time is the source reference signal time + Source_TA, and the time deviation of the target cell / TRP determined by the target DU is the incremental time deviation (incremental TA) obtained by measuring the SRS at the source TX time (denoted as SourceRef_DeltaTargetTA). The incremental TA measured by the target DU can be a positive or negative value, representing the time advance or delay relative to the current UE transmission time.

[0363] Figure 22 An example is shown where UE 2224 initially uses the reference signal received from source TRP 2201 as the local reference for UE 2224 to transmit its SRS, and the TA (i.e., SourceTRP1_TA) determined by source DU 2211 for source TRP 2201 is shown below.

[0364] SourceTRP1_TA=2*(SourceTRP1_Offset+OWD1) (11)

[0365] OWD1 is the air interface delay from source TRP 2201 to the UE. There is a time offset between source DU 2211 and target DU 2212 as shown below.

[0366] DU_offset=TargetDU2_offset–SourceDU1_offset

[0367] With the source DU 2211 time as a reference, Du_offset = TargetDU2_offset is the time deviation of the target DU 2212 relative to the local reference time of the source DU 2211.

[0368] With the source DU1 time as a reference, Du_offset = TargetDU2_offset is the time deviation of the target DU 2212 relative to the local reference time of the source DU 2211.

[0369] The received UL RS time deviation measured by target DU 2212 is the increment TA of target TRP 2202, which uses TRP 2201 reference signal as UE local reference, plus the source TA as UL RS transmission time, hereinafter referred to as SourceRef_DeltaTargetTA.

[0370] SourceRef_DeltaTargetTA=(SourceTRP1_Offset+OWD1)+(TargetTRP2_Offset+OWD2)–

[0371] SourceTRP1_TA–DU_offset(12)

[0372] TargetTRP2_Offset is the forward propagation delay from target DU 2212 to target TRP 2202. OWD2 is the air interface delay from TRP 2202 to UE 2224. SourceTRP1_TA is the timing advance currently used by UE 2224 in source cell / TRP 2201. DU_offset is the time offset of target DU 2212 relative to source DU 2211. Since target TA is measured at target DU 2212 with reference to the local time of DU 2212, DU_offset is a minus sign in equation (12).

[0373] SourceRef_DeltaTargetTA is the incremental target TA of the UL RS measurement received by target DU 2212 from target TRP 2202 before cell handover. As can be seen from equation (12), the time offset DU_offset between source DU 2211 and target DU 2212, as well as the source cell TA (i.e., SourceTRP1_TA), are already included in the incremental target TA measurement at target DU 2212. When target DU 2212 decides to perform cell handover and sends a cell handover command including SourceRef_DeltaTargetTA to UE 2224, UE 2224 switches its local time reference to the target TRP 2202 reference signal upon receiving the command in order to perform UL transmission to target cell / TRP 2202. The new TargetTRP2_TA is shown below.

[0374] TargetTRP2_TA=2*(TargetTRP2_Offset+OWD2) (13)

[0375] From equations (12) and (13), we can derive the following equation (14):

[0376] (TargetTRP2_Offset+OWD2)–(SourceTRP1_Offset+OWD1)+DU_offset(14)

[0377] The time difference between the DL reference signals from the source cell / TRP 2201 and the target cell / TRP 2202 is RSTD.

[0378] RSTD=(TargetTRP2_Offset+OWD2+DU_offset)–(SourceTRP1_Offset+OWD1)(15)

[0379] Equation (15) also shows that the RSTD measured by the UE also includes DU_offset. Since the time offset introduced by the network has been measured by the target DU 2212 and UE 2224, there is no need to configure a network adjustment factor to compensate for DU_offset in this method.

[0380] Then, during cell handover, UE 2224 can obtain its new TA for target TRP 2212 by adjusting the incremental TA received from the cell handover command. The new TRP2_TA can be obtained by adjusting the received SourceRef_DeltaTargetTA using RSTD.

[0381] TargetTRP2_TA=SourceRef_DeltaTargetTA+SourceTRP1_TA+RSTD (16)

[0382] TargetTRP2_TA is the absolute TA for UL transmission to target cell / TRP 2202. When UE 2224 receives SourceRef_DeltaTargetTA via cell handover command, it can apply the adjusted incremental TA to UL transmission to target cell based on the current in-use TA of source cell / TRP 2201 (i.e., SourceTRP1_TA).

[0383] Adjusted_DeltaTargetTA=SourceRef_DeltaTargetTA+RSTD (7)

[0384] The cell handover command is sent from the target DU 2212 / TRP 2202 through the DL beam that the UE has selected and instructed to the target DU 2212.

[0385] The above embodiments describe how to adjust the incremental TA measured at the target node (e.g., target DU 2212) based on the received UL signal (whose transmission time is the source cell reference signal time locked by the UE). After cell handover, the UE needs to adjust the incremental TA received from the target DU using RSTD, and then apply the adjusted incremental target TA to the UL transmission.

[0386] If the UE transmits a UL signal after the source cell reference time obtained by the TA at the target DU / cell, the above-described embodiments provide a general method for adjusting the incremental TA received from the target DU / cell. The UL signal can be one or more preambles of a RACH-based TA scheme, one or more SRSs obtained by an SRS-based TA, or other UL signals of other TA acquisition methods.

[0387] In another embodiment, to reduce L1 measurement latency, in high-frequency scenarios (e.g., FR2), the UE RX beam scanning mode can be pre-configured to the UE based on UE trajectory prediction. Figure 23A As shown, based on the beam scanning mode suggested by the network for the current serving source cell 2312, UE 2304 performs an initial search for the candidate beams predicted by the current source cell 2312.

[0388] RAN2 has agreed to use mobility RRC pre-configuration to configure multiple candidate cells, and subsequent cell handovers between candidate cells can be performed without additional RRC configuration. Currently, mobility configuration only considers configuring candidate cells / beams to UEs (e.g., UE 2304). In L1 / L2 sequential cell handovers, cell role changes occur (i.e., a candidate cell can become a source cell, and a source cell can become a candidate cell). To support subsequent cell handovers, RRC pre-configuration can consider role changes from candidate cell to source serving cell. Cells on the UE 2304 trajectory are used to act as candidate cells and serving source cells. For example, candidate beams, serving beams, and association configurations can be configured for cells in the serving source cell role.

[0389] To support L1 measurements based on the current serving cell after cell handover and role changes, during the mobility preparation and pre-configuration phase, the network CU indicates its current serving cell and / or one or more potential serving cells to candidate cells in the F1 Mobility Request message. Upon receiving one or more identifiers of the serving cell and / or one or more potential serving cells from the CU, the candidate cell reports candidate beams and the associated L1 measurement configurations corresponding to the current serving cell and / or each potential serving cell to the CU. Based on the reports from all candidate cells, the CU merges all received L1 measurement configurations of one or more candidate beams from all one or more candidate cells of the current serving cell to form the L1 measurement configuration of the current serving cell. Similarly, the CU merges the L1 measurement configurations of one or more candidate beams from all one or more candidate cells of each potential serving cell to form the L1 measurement configuration of each current candidate cell, which is currently a mobility candidate cell on the UE trajectory. Furthermore, after a role change, the CU determines the beam scanning mode of one or more candidate beams of one or more candidate cells associated with the potential serving beams of the current serving cell and / or one or more potential serving cells based on the predicted UE trajectory.

[0390] In this specific scenario, UE mobility RX beam scanning modes are configured for each cell based on the initial RRC pre-configuration, for the current source cell (e.g., cell 2312) and each candidate cell (e.g., cell 2314 and / or cell 2316). The cell's RX beam scanning mode is used / applied by the UE only when the cell is currently the source serving cell. That is, the pre-configured beam scanning mode for the candidate cells is applied at the UE only when the candidate cell becomes the new serving source cell.

[0391] A beam scanning pattern can be associated with one or more serving beams at a mobility boundary area and pre-configured to the UE. In current conventional mobility configurations, only one or more candidate cells / beams are pre-configured to the UE. According to embodiments of the present invention, for each pre-configured candidate cell, one or more candidate beams and one or more serving beams are pre-configured to the UE. One or more serving beams and one or more candidate beams of a specific candidate cell are used by the UE to perform subsequent cell handover when that candidate cell becomes the new serving source cell. The association between one or more serving beams and candidate beams and the cell handover pattern can be defined and configured to the UE.

[0392] For example, the RX beam pattern is referenced to and numbered with the current serving beam (e.g., beam 0 in cell 2312), and the remaining beams are numbered clockwise (e.g., for a UE with 8 beams, numbered 1 to 7). If there is only one possible serving beam, then as follows... Figure 23AAs shown, the scanning mode can be indexed as [3,4] relative to the serving beam 0. The mobility serving beam ID (SSB or CSI-RS) can be associated with beam 0 and pre-configured to the UE.

[0393] If there is more than one serving beam, the beam with the higher probability of use during HO can be assigned as beam 0. Another beam can be assigned number 3 based on the relative position of the beams, etc. Based on the candidate beam position relative to beam 0 in cell 2316, the beam scanning mode is the beam indexed at [5,6] in cell 2316.

[0394] If the serving beam (ID) is the beam corresponding to beam 0, the UE can perform a beam scan with index [5,6] relative to beam 0 in a clockwise direction.

[0395] If the serving beam is the beam corresponding to beam 3, the UE can perform a beam scan clockwise relative to beam 3 [5,6].

[0396] The example of a horizontal UE receiving beam used here is to demonstrate the method of this embodiment. This embodiment's method uses the currently serving beam as a reference and performs beam scanning according to a pre-configured pattern, which can be extended to more complex scenarios. The serving beam can be considered as beam 00 or any ij, and the relative beam scanning pattern can be indexed as [kl,mn...] in the beam map, which can be pre-configured for UEs with a large number of beams in the support space. The beam scanning direction can be from a lower-numbered beam to a higher-numbered beam and then back again.

[0397] The above embodiments detail how to determine the beam pattern based on the UE trajectory and adjacent TRPs at the boundary region, and how the UE actually uses the beam scanning mode to perform the initial candidate beam search.

[0398] The above embodiments provide a method for a UE to perform beam scanning according to a pre-configured beam scanning mode for initial candidate beam search and acquisition. Using this method, the initial beam acquisition time can be significantly shortened. Therefore, beam selection and L1 measurement delays can be significantly reduced.

[0399] Figure 23BExamples of L1 measurement configurations and process flowcharts for sequential mobility on the UE side are shown in some embodiments. At operation 2321, upon receiving a mobility pre-configuration, which includes L1 measurement configurations for the current serving cell and predicted candidate cells on the UE trajectory, the UE applies the L1 measurement configuration of the current serving cell and stores the L1 measurement configuration for each cell of each predicted candidate cell. The L1 measurement configurations for candidate cells are stored by the UE and are only used by the UE when a candidate cell becomes the UE's new serving cell after a cell handover. At operation 2322, the UE performs L1 measurements only on one or more candidate beams of one or more candidate cells of the current serving cell, based on the L1 measurement configuration of the current serving cell. If a beam scanning mode is configured, the UE performs an initial beam scan / search on the candidate beams of the current serving cell according to the beam switching mode. The UE reports the measurement results to the current serving cell according to the current serving cell's configuration. At operation 2323, the UE determines whether a cell handover has been triggered. If so, then at operation 2324, upon completion of the cell handover, the candidate target cell becomes the UE's new serving cell. The UE applies the L1 measurement configuration corresponding to the new serving cell as the configuration for the new serving cell.

[0400] Figure 23CExamples of network-side L1 measurement configuration and process flowcharts for sequential mobility provided in some embodiments are shown. At operation 2331, the network central unit (CU) determines mobility candidate cells for sequential cell handover on the predicted UE trajectory based on trajectory prediction. After the cell handover, each candidate cell is also a potential future serving cell. The network CU begins mobility preparation and pre-configuration. At operation 2332, the network CU sends a mobility pre-configuration request to the candidate distributed unit (DU) / cell via an F1 interface message. The network CU indicates to the candidate DU / cell the identifiers of the candidate cell's current serving cell and / or one or more potential serving cells. At operation 2333, upon receiving the pre-configuration request, the candidate DU / cell responds to the network CU with a candidate target cell L1 measurement configuration, including one or more candidate beams of the candidate DU / cell's current serving cell and / or one or more candidate beams of each potential future serving cell. At operation 2334, the candidate DU / cell is ready for the UE to perform cell handover and initial access. After the cell handover is complete, the candidate cell becomes the UE's new serving cell and begins receiving L1 measurement reports from the UE. At operation 2335, after receiving all responses, the network CU merges the L1 measurement configurations of candidate beams from all or more candidate cells from the current serving cell to form the L1 measurement configuration of the current serving cell, and / or merges the L1 measurement configurations of candidate beams from all or more candidate cells from one or more potential serving cells to form one or more L1 measurement configurations for each potential serving cell. At operation 2336, the network CU sends a prepared sequential mobility pre-configuration to the serving source DU / cell, including the L1 measurement configurations for each cell of the current serving cell and potential serving cells (current candidate cells). The serving DU / cell sends the pre-configuration to the UE via an RRC message.

[0401] Figure 24A A flowchart of a method 2400 performed by a UE according to some embodiments is shown. The UE may include computer-readable code or instructions that execute on one or more processors of the UE. In this invention, the encoding of the software used to perform or execute method 2400 is within the scope of those skilled in the art. Method 2400 may include more or fewer operations than those shown and described, and may be performed or executed in different orders. The computer-readable code or instructions of one or more processor-executable software may be stored on a non-transitory computer-readable medium such as the memory of the UE.

[0402] Method 2400 begins with operation 2402, in which the UE receives a mobility pre-configured radio resource control (RRC) message from the source cell for access without a random-access channel (RACH). The mobility pre-configured RRC message indicates target timing advance (TA) assistance information. At operation 2404, the UE receives a lower-layer target access command from the source cell. The lower-layer target access command indicates time-sensitive dynamic TA assistance information that has been recently updated or is currently updated by the network. At operation 2406, the UE determines the target cell TA of the target cell based on the latest source cell TA of the source cell, the latest measured time difference between the reference signal (RS) from the source cell and the target cell, the recently updated or currently updated time-sensitive dynamic TA assistance information, and the target TA assistance information. At operation 2108, the UE performs RACH-free access to the target cell based on the target cell TA.

[0403] In some embodiments, the UE may indicate to the target cell the reference signal (RS) of the target beam selected by the UE by transmitting the corresponding sounding RS (SRS) or RS identifier (ID) in the initial message.

[0404] In some embodiments, the UE may maintain pre-configured mobility parameters without performing cell handover and access to candidate cells until a lower-layer target access command is received or a cell handover trigger condition is met. The UE may perform layer 1 (L1) measurements and track the time of reference signals from candidate beams by periodically measuring, updating, and storing the time deviation of candidate beams relative to the UE's local reference time based on the pre-configured mobility parameters, in order to maintain synchronization with the candidate beams. Upon receiving a mobility incremental configuration message, the UE may update new mobility configuration parameters, including target time TA (Target Time Auxiliary) information. The UE may apply new mobility configuration parameters for the target cell in response to receiving a lower-layer target access command or meeting the cell handover trigger condition.

[0405] In some embodiments, when the UE receives a lower-layer target access command or the cell handover triggering condition is met, the UE may (1) use the target cell TA based on the time of the RS of the target beam from the target cell selected by the UE, (2) use a pre-configured SRS uniquely corresponding to the RS of the target beam from the target cell, and (3) use a pre-configured grant with no RACH initiation message to transmit a no-RACH initiation message and SRS to the target cell. The pre-configured grant may be predetermined by the target cell and pre-configured to the UE based on each candidate cell. The no-RACH initiation message may include lower-layer information.

[0406] In some embodiments, the lower-layer information may include a media access control (MAC) control element (CE) indicating the ID of the RS from the target beam of the target cell. This ID may be either a synchronization signal block (SSB) ID or a channel state information (CSI) RS ID.

[0407] In some embodiments, the MAC CE may also indicate at least one of a buffer status report (BSR) or a power headroom report (PHR).

[0408] In some embodiments, a UE configured for conditional mobility can update its currently maintained latest source cell TA, source cell reference signal time, and target cell reference signal time based on the most recently updated or latest network-updated time-sensitive dynamic TA auxiliary information received from the source cell. Conditional mobility can be one of a conditional PSCell addition or change (CPAC) or a conditional handover (CHO) within a conditional secondary cell group. When mobility conditions are met, a UE configured for conditional mobility can trigger a target cell TA derived based on the latest source cell TA, the latest measured time difference between the source cell and target cell RS, and the most recently updated or latest network-updated time-sensitive dynamic TA auxiliary information.

[0409] In some embodiments, when the UE configured for CHO believes that the target cell TA determined by the UE is no longer valid after the timing alignment timer (TAT) of the latest source cell TA expires, the UE may perform conventional random access to the target cell.

[0410] Figure 24B A flowchart of a method 2410 performed by one or more network nodes according to some embodiments is shown. The one or more network nodes may include computer-readable code or instructions executable on one or more processors of the one or more network nodes. In this invention, the encoding of the software used to perform or execute method 2410 is within the scope of those skilled in the art. Method 2410 may include more or fewer operations than those shown and described, and may be performed or executed in different orders. The computer-readable code or instructions of the one or more processor-executable software may be stored on one or more non-transitory computer-readable media such as one or more memories of the one or more network nodes.

[0411] Method 2410 begins with operation 2412, in which the central unit (CU) determines one or more mobility candidate cells and one or more associated transmission and reception points (TRPs) based on measurement reports and additional information including predicted trajectories of user equipment (UE). At operation 2414, the CU sends mobility preconfiguration requests to candidate cells having a subset of one or more associated TRPs. At operation 2416, the CU receives a mobility preconfiguration response from a candidate cell, indicating target cell timing advance (TA) assistance information. At operation 2418, the CU sends a second mobility preconfiguration request to the source cell. At operation 2420, the CU receives a second mobility preconfiguration response from the source cell, indicating source assistance information. At operation 2422, the CU sends final target TA assistance information to the source cell. At operation 2424, the source cell transmits a mobility pre-configuration radio resource control (RRC) message to the UE for access without a random-access channel (RACH). The mobility pre-configuration RRC message indicates target TA assistance information.

[0412] In some embodiments, the mobility preconfiguration request may indicate a timestamp of the CU transmission time. Target cell TA assistance information from the candidate cell may indicate the candidate cell transmission time difference relative to the CU transmission time and one or more first DL / UL asymmetry factors of the candidate cell. Source cell TA assistance information from the source cell may include the source cell transmission time difference relative to the CU transmission time and one or more second DL / UL asymmetry factors of the source cell.

[0413] In some embodiments, a candidate cell can determine its transmission time difference with the CU based on a timestamp and a first intermediate-range delay between the CU and the candidate cell. A source cell can determine its transmission time difference with the CU based on a CU timestamp and a second intermediate-range delay between the CU and the source cell. The CU can determine the transmission time difference between the source cell and the target cell based on the source cell transmission time difference and the transmission time difference with the target cell. The CU can merge the source cell TA auxiliary information, the target cell TA auxiliary information, and the transmission time difference between the source cell and the target cell to generate final target TA auxiliary information.

[0414] In some embodiments, the source cell may send dynamic TA assistance information to the UE configured for conditional mobility, which is triggered by at least one of the following: the source node one-way delay (OWD) or the source TA change is higher than a threshold, and / or the change in the transmission time difference between the source cell and the target cell updated by the CU is higher than a time deviation threshold.

[0415] Figure 24C A flowchart of a method 2300 performed by a UE according to some embodiments is shown. The UE may include computer-readable code or instructions that execute on one or more processors of the UE. In this invention, the encoding of the software used to perform or execute method 2430 is within the scope of those skilled in the art. Method 2430 may include more or fewer operations than those shown and described, and may be performed or executed in different orders. The computer-readable code or instructions of one or more processor-executable software may be stored on a non-transitory computer-readable medium such as the memory of the UE.

[0416] Method 2430 begins with operation 2432, in which the UE measures the time deviation between the source transmission and reception point (TRP) reference signal (RS) time tracked by the UE and the target TRP RS time to obtain the most recently measured time difference between the RS from the source TRP and the target TRP. At operation 2434, the UE transmits an uplink signal to the target TRP after the source TRP RS time tracked by the UE. At operation 2436, the UE receives the current target TA from either the source TRP or the target TRP of the current serving cell. The current target TA is measured by the current serving cells of the source TRP and the target TRP on uplink signals aligned with the source TRP RS time tracked by the UE and received through the target TRP. At operation 2438, the UE determines the target TRP TA of the target TRP based on the most recently measured time difference and the current target TA. At operation 2439, the UE performs RACH-free access to the target TRP based on the target TRP TA and the target TRP RS time tracked by the UE, in order to perform UL transmission to the target TRP.

[0417] In some embodiments, the uplink signal may be a sounding reference signal (SRS).

[0418] In some embodiments, when the UE starts using the target TRP RS time as a local reference to perform UL transmission to the target TRP, the UE can adjust the current target TA based on the source TRP RS time tracked by the UE and the time deviation between the source TRP RS time tracked by the UE and the target TRP RS time to obtain the target TRP TA.

[0419] Figure 24D A flowchart of a method 2440 performed by one or more network nodes according to some embodiments is shown. The one or more network nodes may include computer-readable code or instructions executable on one or more processors of the one or more network nodes. In this invention, the encoding of the software used to perform or execute method 2440 is within the scope of those skilled in the art. Method 2440 may include more or fewer operations than those shown and described, and may be performed or executed in different orders. The computer-readable code or instructions of the one or more processor-executable software may be stored on one or more non-transitory computer-readable media such as one or more memories of the one or more network nodes.

[0420] Method 2440 begins with operation 2442, in which the serving cell receives uplink signals from the user equipment (UE) via the target transmission and reception point (TRP). At operation 2444, the serving cell transmits the current target TA to the UE via either the source TRP or the target TRP. This current target TA is measured by the serving cell on the uplink signal from the target TRP. At operation 2446, the target TRP performs RACH-free access with the UE based on the latest measured time difference between the source TRP and the target TRP's RS, and the current target TA, using the target TRP's target TRP TA.

[0421] Figure 24E A flowchart of a method 2450 performed by a UE according to some embodiments is shown. The UE may include computer-readable code or instructions that execute on one or more processors of the UE. In this invention, the encoding of the software used to perform or execute method 2450 is within the scope of those skilled in the art. Method 2450 may include more or fewer operations than those shown and described, and may be performed or executed in different orders. The computer-readable code or instructions of one or more processor-executable software may be stored on a non-transitory computer-readable medium such as the memory of the UE.

[0422] Method 2450 begins with operation 2452, in which the UE receives and maintains a mobility pre-configuration message from the serving source cell. The mobility pre-configuration message indicates L1 measurement configuration information of the serving source cell, first L1 measurement configuration information of a first candidate cell, and second L1 measurement configuration information of a second candidate cell. The second candidate cell is the subsequent cell of the first candidate cell on the UE's predicted trajectory. At operation 2454, the UE receives a first lower-layer target access command from the serving source cell to hand over to the first candidate cell as the target cell. At operation 2456, the UE hands over to the first candidate cell, making the first candidate cell the UE's current serving cell. At operation 2458, the UE performs a first L1 measurement based on the first L1 measurement configuration information. At operation 2460, the UE reports the first L1 measurement result to the current serving cell based on the first L1 measurement configuration information of the current serving cell. At operation 2462, the UE receives a second lower-layer target access command from the current serving cell to hand over to the second candidate cell. At operation 2464, the UE performs cell handover access to the second candidate cell as the UE's new serving cell. At operation 2466, the UE in the new serving cell performs the second L1 measurement only based on the second L1 measurement configuration information. At operation 2468, the UE reports the second L1 measurement results to the new serving cell based on the second L1 measurement configuration information.

[0423] In some embodiments, mobility pre-configuration messages can be included in radio resource control (RRC) messages.

[0424] In some embodiments, the L1 measurement configuration information of the serving source cell may include all L1 measurement configurations of all candidate beams of the candidate cells of the serving source cell.

[0425] In some embodiments, the first L1 measurement configuration information of the first candidate cell may include all L1 measurement configurations of all candidate beams of the candidate cell of the first candidate cell. The second L1 measurement configuration information of the second candidate cell may include all L1 measurement configurations of all candidate beams of the candidate cell of the second candidate cell. The first and second L1 measurement configurations described herein are for illustrative purposes only and are not intended to diminish their generality. The number of candidate cells (and their corresponding L1 measurement configuration information) used for sequential cell handover may be greater (e.g., all candidate cells in the UE's predicted trajectory).

[0426] In some embodiments, the L1 measurement configuration information of the current serving cell or candidate cell can indicate the corresponding candidate beam scanning mode. The candidate scanning mode includes the serving beam from the current or potential serving cell and the candidate beams associated with the serving beam.

[0427] In some embodiments, the UE can select a candidate beam scanning mode based on the currently serving beam. The UE can use the currently serving beam as a reference beam to perform candidate beam scanning and candidate beam search according to the candidate beam scanning mode.

[0428] In some embodiments, the first L1 measurement configuration information and the second L1 measurement configuration information can be based on each cell.

[0429] Figure 24F A flowchart of a method 2470 performed by one or more network nodes according to some embodiments is shown. The one or more network nodes may include computer-readable code or instructions that execute on one or more processors of the one or more network nodes. In this invention, the encoding of the software used to perform or execute method 2470 is within the scope of those skilled in the art. Method 2470 may include more or fewer operations than those shown and described, and may be performed or executed in different orders. The computer-readable code or instructions of the one or more processor-executable software may be stored on one or more non-transitory computer-readable media such as one or more memories of the one or more network nodes.

[0430] Method 2470 begins with operation 2472, in which the CU determines a sequence of mobility candidate cells based on the user equipment (UE)'s predicted trajectory and measurement reports. At operation 2474, the CU sends the L1 measurement configuration of each cell of the current serving source cell and the candidate cells to the current serving source cell. The L1 measurement configuration of each cell includes one or more beam scanning modes in the L1 measurement configuration of each cell. At operation 2476, the current serving source cell transmits a mobility pre-configuration message to the UE. The mobility pre-configuration message indicates the L1 measurement configuration information of the current serving source cell, the first L1 measurement configuration information of the first candidate cell, and the second L1 measurement configuration information of the second candidate cell. The second candidate cell is the subsequent cell of the first candidate cell on the UE's predicted trajectory. At operation 2478, the current serving source cell transmits a first lower-layer target access command to the UE to hand over to the first candidate cell as the target cell. At operation 2480, after cell handover and after the first candidate cell becomes the UE's current serving cell, the current serving cell receives the first L1 measurement report from the UE based on the current serving cell's configuration information for the first L1 measurement. At operation 2482, the current serving cell transmits a second lower-layer target access command to the UE so that the UE can hand over to the second candidate cell. At operation 2484, after the second candidate cell becomes the UE's new serving cell, the new serving cell receives the second L1 measurement report from the UE based on the second L1 measurement configuration information.

[0431] In some embodiments, during the mobility preparation phase, the CU may indicate the current serving cell and one or more potential serving cells of a candidate cell to the candidate cells on the UE's predicted trajectory in the mobility request. The candidate cell may report candidate beams and the associated L1 measurement configurations corresponding to the current serving cell and each potential serving cell to the CU.

[0432] In some embodiments, the CU can merge the L1 measurement configurations of one or more candidate beams from all or more candidate cells of the current serving cell as the L1 measurement configuration of the current serving cell.

[0433] In some embodiments, the CU may combine the L1 measurement configurations of one or more candidate beams of all or more candidate cells of each potential serving cell as the L1 measurement configuration of each candidate cell, where the potential serving cell is currently a mobility candidate cell on the UE's predicted trajectory.

[0434] In some embodiments, the CU can determine the beam scanning pattern of one or more candidate beams of one or more candidate cells associated with a first potential serving beam of the current serving cell or a second potential serving beam of one or more potential serving cells based on the UE's predicted trajectory.

[0435] Figure 25 An exemplary communication system 2500 is illustrated. Typically, system 2500 enables multiple wireless or wired users to send and receive data and other content. Communication system 2500 may implement one or more channel access methods, such as code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrier FDMA (SC-FDMA), or non-orthogonal multiple access (NOMA).

[0436] In this example, the communication system 2500 includes electronic devices (EDs) 2510a to 2510c, radio access networks (RANs) 2520a and 2520b, a core network 2530, a public switched telephone network (PSTN) 2540, the Internet 2550, and other networks 2560. Although a certain number of these components or elements... Figure 25 As shown, but any number of these components or elements may be included in system 2500.

[0437] ED 2510a to ED 2510c are used for operation or communication within system 2500. For example, ED 2510a to ED 2510c are used for transmitting or receiving via a wireless communication channel or a wired communication channel. Each ED 2510a to ED 2510c represents any suitable end-user equipment, which may include (or be referred to as) devices such as: user equipment (UE), wireless transmit or receive unit (WTRU), mobile station, fixed or mobile subscriber unit, cellular phone, personal digital assistant (PDA), smartphone, laptop computer, computer, touchpad, wireless sensor, or consumer electronic device, etc.

[0438] Here, RAN 2520a and RAN 2520b include base stations 2570a and 2570b, respectively. Base stations 2570a and 2570b are used to establish wireless connections with one or more of ED 2510a to ED 2510c to enable access to the core network 2530, PSTN 2540, Internet 2550, or other networks 2560. For example, base stations 2570a and 2570b may include (or may be) one or more of several known devices, such as a base transceiver station (BTS), a NodeB, an evolved NodeB (eNodeB), a Next Generation (NG) NodeB (gNB), a gNB central unit (gNB-CU), a gNB distributed unit (gNB-DU), a femtocell, a femtocell eNodeB, a site controller, an access point (AP), or a wireless router. ED 2510a to ED 2510c are used for connection and communication with Internet 2550 and can access core network 2530, PSTN 2540 or other network 2560.

[0439] exist Figure 25 In the illustrated embodiment, base station 2570a is part of RAN 2520a, which may include other base stations, components, or devices. Similarly, base station 2570b is part of RAN 2520b, which may include other base stations, components, or devices. Each base station 2570a and 2570b operates to transmit or receive radio signals within a specific geographic area (sometimes referred to as a "cell"). In some embodiments, if each cell has multiple transceivers, multiple-input multiple-output (MIMO) technology may be used.

[0440] Base stations 2570a and 2570b communicate with one or more of ED 2510a to ED 2510c via one or more air interfaces 2590 using a wireless communication link. Air interface 2590 can use any suitable wireless access technology.

[0441] It is conceivable that System 2500 can use multi-channel access capabilities, including the schemes described above. In specific embodiments, the base station and ED implement 5G New Radio (NR), LTE, LTE-A, or LTE-B. Of course, other multiple access schemes and radio protocols can also be used.

[0442] RAN 2520a and RAN 2520b communicate with core network 2530 to provide voice, data, application, Voice over Internet Protocol (VoIP), or other services to ED 2510a through ED 2510c. It is understood that RAN 2520a and RAN 2520b or core network 2530 can communicate directly or indirectly with one or more other RANs (not shown). Core network 2530 can also serve as a gateway access for other networks (e.g., PSTN 2540, Internet 2550, and other networks 2560). Furthermore, some or all of ED 2510a through ED 2510c may include the ability to communicate with different wireless networks via different wireless links using different wireless technologies or protocols. EDs may communicate with service providers or switches (not shown) and with Internet 2550 via wired communication channels, rather than wirelessly (or also wirelessly).

[0443] Although Figure 25 An example of a communication system is shown, but it is possible to... Figure 25 Various modifications can be made. For example, the communication system 2500 can include any number of EDs, base stations, networks, or other components in any suitable configuration.

[0444] Figure 26A and Figure 26B Exemplary apparatuses are shown that can implement the methods and guidance provided by this invention. Specifically, Figure 26A An exemplary ED 2610 is shown. Figure 26B An exemplary base station 2670 is shown. These components can be used in system 2500 or any other suitable system.

[0445] like Figure 26A As shown, ED 2610 includes at least one processing unit 2600. The processing unit 2600 implements various processing operations of ED 2610. For example, the processing unit 2600 may perform signal encoding, data processing, power control, input / output processing, or any other function that enables ED 2610 to operate in system 2500. The processing unit 2600 also supports the methods and guidelines described in more detail above. Each processing unit 2600 includes any suitable processing or computing device for performing one or more operations. For example, each processing unit 2600 may include a microprocessor, microcontroller, digital signal processor, field-programmable gate array, or application-specific integrated circuit.

[0446] ED 2610 also includes at least one transceiver 2602. Transceiver 2602 is used to modulate data or other content for transmission via at least one antenna or Network Interface Controller (NIC) 2604. Transceiver 2602 is also used to demodulate data or other content received via at least one antenna 2604. Each transceiver 2602 includes any suitable structure for generating signals for wireless or wired transmission or for processing signals received wirelessly or wiredly. Each antenna 2604 includes any suitable structure for transmitting or receiving wireless or wired signals. ED 2610 may use one or more transceivers 2602, and ED 2610 may use one or more antennas 2604. Although transceiver 2602 is shown as a separate functional unit, transceiver 2602 may also be implemented using at least one transmitter and at least one separate receiver.

[0447] ED 2610 also includes one or more input / output devices 2606 or interfaces (e.g., a wired interface connected to the Internet 2550). Input / output devices 2606 facilitate interaction with users or other devices on the network (network communication). Each input / output device 2606 includes any suitable structure for providing or receiving information from a user, such as a speaker, microphone, keypad, keyboard, display, or touchscreen, including network interface communication.

[0448] Additionally, ED 2610 includes at least one memory 2608. Memory 2608 stores instructions and data used, generated, or collected by ED 2610. For example, memory 2608 may store software or firmware instructions executed by one or more processing units 2600, as well as data used to reduce or eliminate interference in incoming signals. Each memory 2608 includes any suitable one or more volatile or non-volatile storage and retrieval devices. Any suitable type of memory can be used, such as random access memory (RAM), read-only memory (ROM), hard disk, optical disk, subscriber identity module (SIM) card, memory stick, or secure digital card (SD card).

[0449] like Figure 26BAs shown, base station 2670 includes at least one processing unit 2650, at least one transceiver 2652, one or more antennas 2656, at least one memory 2658, and one or more input / output devices or interfaces 2666, wherein the at least one transceiver 2652 includes transmitter and receiver functions. A scheduler, as understood by those skilled in the art, is coupled to processing unit 2650. The scheduler may be included within base station 2670 or may operate separately from base station 2670. Processing unit 2650 implements various processing operations of base station 2670, such as signal encoding, data processing, power control, input / output processing, or any other functions. Processing unit 2650 may also support the methods and instructions described in more detail above. Each processing unit 2650 includes any suitable processing or computing device for performing one or more operations. For example, each processing unit 2650 may include a microprocessor, microcontroller, digital signal processor, field-programmable gate array, or application-specific integrated circuit.

[0450] Each transceiver 2652 includes any suitable structure for generating signals for wireless or wired transmission to one or more EDs or other devices. Each transceiver 2652 also includes any suitable structure for processing signals received wirelessly or wiredly from one or more EDs or other devices. Although shown as a combined transceiver 2652, the transmitter and receiver may be separate components. Each antenna 2656 includes any suitable structure for transmitting or receiving wireless or wired signals. Although a common antenna 2656 is shown herein coupled to transceiver 2652, one or more antennas 2656 may be coupled to one or more transceivers 2652, allowing individual antennas 2656 to be coupled to the transmitter and receiver (if equipped as separate components). Each memory 2658 includes any suitable one or more volatile or non-volatile storage and retrieval devices. Each input / output device 2666 facilitates interaction with users or other devices in the network (network communication). Each input / output device 2666 includes any suitable structure for providing information to or receiving information from a user, including network interface communication.

[0451] Figure 27This is a block diagram of a computing system 2700 that can be used to implement the devices and methods disclosed herein. For example, the computing system can be any entity in a UE, access network (AN), mobility management (MM), session management (SM), user plane gateway (UPGW), or access stratum (AS). A particular device may use all or only a subset of the components shown, and the level of integration may vary from device to device. Furthermore, the device may contain multiple instances of components, such as multiple processing units, processors, memories, transmitters, receivers, etc. The computing system 2700 includes a processing unit 2702. The processing unit includes a central processing unit (CPU) 2714, memory 2708, and may also include a mass storage device 2704, a video adapter 2710, and an I / O interface 2712 connected to a bus 2720.

[0452] Bus 2720 can be one or more of any type of bus architecture, including a memory bus or memory controller, a peripheral bus, or a video bus. CPU 2714 can include any type of electronic data processor. Memory 2708 can include any type of non-transitory system memory, such as static random access memory (SRAM), dynamic random access memory (DRAM), synchronous DRAM (SDRAM), read-only memory (ROM), or any combination thereof. In one embodiment, memory 2708 can include ROM for use at startup and DRAM for storing programs and data for use during program execution.

[0453] Mass storage 2704 may include any type of non-transitory storage device for storing data, programs, and other information and making such data, programs, and other information accessible via bus 2720. Mass storage 2704 may include one or more of solid-state drives, hard disk drives, disk drives, or optical disk drives.

[0454] Video adapter 2710 and I / O interface 2712 provide interfaces for coupling external input and output devices to processing unit 2702. Examples of input and output devices, as shown, include a monitor 2718 coupled to video adapter 2710 and a mouse, keyboard, or printer 2716 coupled to I / O interface 2712. Other devices may be coupled to processing unit 2702, and additional or fewer interface cards may be used. For example, a serial interface such as Universal Serial Bus (USB) (not shown) may be used to provide interfaces for external devices.

[0455] The processing unit 2702 also includes one or more network interfaces 2706, which may include wired links such as Ethernet cables or wireless links to access nodes or different networks. The network interface 2706 enables the processing unit 2702 to communicate with remote units via a network. For example, the network interface 2706 may provide wireless communication via one or more transmitter / transmit antennas and one or more receiver / receive antennas. In one embodiment, the processing unit 2702 is coupled to a local area network 2722 or a wide area network to perform data processing and communicate with remote devices (e.g., other processing units, the Internet, or remote storage facilities).

[0456] It should be understood that one or more steps in the methods of the embodiments provided herein can be performed by corresponding units or modules. For example, a signal can be sent by a sending unit or sending module. A signal can be received by a receiving unit or receiving module. A signal can be processed by a processing unit or processing module. Other steps can be performed by an execution unit or module, a generation unit or module, an acquisition unit or module, a setting unit or module, an adjustment unit or module, an addition unit or module, a reduction unit or module, a determination unit or module, a modification unit or module, a reduction unit or module, a removal unit or module, or a selection unit or module. The corresponding units or modules can be hardware, software, or a combination thereof. For example, one or more units or modules can be integrated circuits, such as field-programmable gate arrays (FPGAs) or application-specific integrated circuits (ASICs).

[0457] Although the invention and its advantages have been described in detail, it should be understood that various changes, substitutions and modifications can be made without departing from the scope of the invention.

Claims

1. A communication method, characterized in that, include: The user equipment (UE) receives a radio resource control (RRC) message from the source cell for mobility access without a random-access channel (RACH), the RRC message indicating pre-configured timing advance (TA) assistance information; The UE receives a lower-layer target access command from the source cell at a protocol layer below the RRC layer. The lower-layer target access command indicates the time-sensitive dynamic TA auxiliary information that has been recently updated or is the latest network update. The UE determines the target cell TA of the target cell based on the most recently updated or latest source cell TA of the source cell, the latest measured time difference between the reference signal (RS) from the source cell and the reference signal from the target cell, the time-sensitive dynamic TA auxiliary information of the most recently updated or latest network update, and the pre-configured target TA auxiliary information. The UE performs RACH-free mobility access to the target cell based on the target cell TA; The method further includes: The UE maintains pre-configured mobility parameters without performing cell handover or access to candidate cells until it receives the lower-layer target access command or the cell handover triggering condition is met. The UE performs layer 1 (L1) measurements and tracks the time of the reference signal from the candidate beam by periodically measuring, updating, and storing the time deviation of the candidate beam relative to the UE's local reference time according to the pre-configured mobility parameters, in order to maintain synchronization with the candidate beam. Upon receiving the mobility incremental configuration message, the UE updates new mobility configuration parameters including the target TA assistance information; In response to receiving the lower-layer target access command or meeting the cell handover triggering condition, the UE applies the new mobility configuration parameters of the target cell.

2. The method according to claim 1, characterized in that, The most recently updated or latest source cell TA of the source cell is received by the UE through the lower-layer target access command.

3. The method according to claim 1 or 2, characterized in that, Before the UE receives the RRC message for RACH-free mobility access from the source cell, the method further includes: The UE measures the time deviation between the source transmission and reception point (TRP) RS time and the target TRP RS time tracked by the UE to obtain the latest measured time difference between the RS from the source TRP and the target TRP.

4. The method according to claim 1 or 2, characterized in that, Also includes: The UE configured for conditional mobility updates the source cell TA, source cell reference signal time, and target cell reference signal time currently maintained by the UE based on the time-sensitive dynamic TA auxiliary information received from the source cell. The conditional mobility is one of the following: conditional PSCell addition or change (CPAC) or conditional handover (CHO) in a conditional secondary cell group. When mobility conditions are met, the UE configured for the conditional mobility triggers the inference of the target cell TA at the UE based on the most recently updated or latest source cell TA, the latest measured time difference between the RS from the source cell and the target cell, and the time-sensitive dynamic TA auxiliary information of the most recently updated or latest network update.

5. The method according to claim 4, characterized in that, When the UE configured for the CHO believes that the target cell TA determined by the UE is no longer valid after the timing alignment timer (TAT) of the latest source cell TA expires, the UE performs conventional random access to the target cell.

6. A communication method, characterized in that, include: The central unit (CU) determines one or more mobility candidate cells and one or more associated transmission and reception points (TRPs) based on measurement reports and additional information including predicted trajectories of user equipment (UE). The CU sends a mobility preconfiguration request to candidate cells that have a subset of the one or more associated TRPs; The CU receives a mobility preconfiguration response from the candidate cell, the mobility preconfiguration response indicating target cell timing advance (TA) assistance information; The CU sends a second mobility preconfiguration request to the source cell; The CU receives a second mobility preconfiguration response from the source cell, the second mobility preconfiguration response indicating source assistance information; The CU sends final target TA auxiliary information to the source cell; The source cell transmits a radio resource control (RRC) message for access without a random-access channel (RACH) to the UE. The RRC message indicates pre-configured target TA assistance information, which is the final target TA assistance information.

7. The method according to claim 6, characterized in that, The mobility preconfiguration request indicates the timestamp of the CU transmission time. The target cell TA auxiliary information from the candidate cells indicates the candidate cell transmission time difference relative to the CU transmission time and one or more first DL / UL asymmetry factors of the candidate cells. The source cell TA auxiliary information from the source cell includes the source cell transmission time difference relative to the CU transmission time and one or more second DL / UL asymmetry factors of the source cell.

8. The method according to claim 7, characterized in that, Also includes: The candidate cell determines the transmission time difference with the CU based on the timestamp and the first mid-range delay between the CU and the candidate cell; The source cell determines the transmission time difference with the source cell based on the CU timestamp and the second mid-range delay between the CU and the source cell; The CU determines the transmission time difference between the source cell and the target cell based on the transmission time difference between the source cell and the target cell. The CU merges the source cell TA auxiliary information, the target cell TA auxiliary information, and the transmission time difference between the source cell and the target cell to generate the final target TA auxiliary information.

9. The method according to claim 8, characterized in that, Also includes: The source cell sends dynamic TA assist information to the UE configured for conditional mobility, which is triggered by at least one of the following: the source node one-way delay (OWD) or the source TA is higher than a threshold, or the transmission time difference between the source cell and the target cell updated by the CU is higher than a time deviation threshold.

10. A user equipment (UE), characterized in that, include: At least one processor; A non-transitory computer-readable storage medium for storing instructions that, when executed by the at least one processor, cause the UE to perform the method according to any one of claims 1 to 5.

11. A network system, characterized in that, include: Centralized unit (CU); Source Community; One or more mobility candidate cells, The network system is used to perform the method according to any one of claims 6 to 9.

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