Enhancement for user equipment-based timing advance acquisition capability

Abstract

Embodiments disclose enhancements for user equipment-based timing advance acquisition capabilities. A user equipment (UE) receives a higher layer message having group information for estimating timing advance (TA) values of a plurality of target cells. After estimating the TA value for the first target cell, the UE can re-use the estimated TA value for the second target cell to which it is handed over if the first target cell and the second target cell share the same TA value. As a result, the UE switches to the second target cell using the estimated TA value of the first target cell, and avoids performing the UE-based TA acquisition on the second target cell. Handover to the second target cell does not occur if the UE must experience a random access channel procedure, and this minimizes the risk that the UE experiences an interrupt when switching the cell.

Description

Technical Field

[0001] Various example embodiments of the present disclosure relate to the field of telecommunications, and more particularly to enhancements to user equipment-based timing advance acquisition capabilities. Background Art

[0002] Certain abbreviations that may be found in the specification and / or drawings are defined herein as follows. 5G NR Fifth Generation New Radio CSC cell switching command CU Central Unit DU Distributed Unit eNB Evolved Node B gNB Next Generation Node B LTM Lower layer triggered handover or layer 1 / layer 2 triggered mobility MAC Media Access Control RSTD Reference Signal Time Difference S-DU Source Distribution Unit SSB Synchronous Signal Block TA Timing Advance T-DU Target Distributed Unit UE User Equipment UL Uplink

[0003] 3GPP (3rd Generation Partnership Project) Release 18 (Rel-18) introduces Layer 1 (L1) or Layer 2 (L2) mobility, also known as Lower Layer Triggered Mobility (LTM), to reduce latency, overhead, and disruption time associated with UEs moving between different cells. In LTM, mobility is triggered by L1 (physical layer (PHY)) and L2 (media access control (MAC)).

[0004] In the case of LTM, when the UE estimates the timing advance (TA) (i.e., UE-based TA estimation), the UE is able to estimate the TA of the target cell without having to go through any random access channel (RACH) procedures. This helps prevent the UE from experiencing any interruptions that would otherwise be caused as a result of going through the RACH procedure. However, currently, UE-based TA estimation is limited by the capabilities of the UE, where the capabilities of the UE are defined by the following items: (i) the number of configurations that the UE receives for UE-based TA estimation; and (ii) the number of candidate cells for which the UE is able to perform UE-based TA estimation (based on the received configuration). For example, if the UE is configured with up to 8 candidate cells, the UE may receive a UE-based TA estimation configuration for only 4 candidate cells. However, despite receiving a configuration for 4 candidate cells, the UE may only be able to estimate TA for 2 candidate cells and only maintain TA for 2 candidate cells at a time. In other words, there is currently a limitation in the UE-based TA estimation capability, where UE-based TA estimation cannot be performed for any candidate cell, but can only be performed for a subset of the configured LTM candidate cells. Summary of the invention

[0005] According to some aspects, the subject matter of the independent claims is provided. Some embodiments are defined in the dependent claims.

[0006] In a first aspect of the present disclosure, a user equipment (UE) is provided. The user equipment includes: at least one memory; and at least one processor. The at least one processor is operatively coupled to the at least one memory, wherein the at least one processor is configured to: obtain group information for a group of target cells from a first network node; perform measurements of the group of target cells; estimate the timing advance TA value of a first target cell in the group of target cells based on the group information and the measurements of the group of target cells; and reuse the estimated TA of the first target cell to switch to another target cell in the group of target cells.

[0007] In a second aspect of the present disclosure, a method performed by a user equipment (UE) is provided. The method includes: obtaining group information for a group of target cells from a first network node; performing measurements of the group of target cells; estimating a timing advance TA value of a first target cell in the group of target cells based on the group information and the measurements of the group of target cells; and reusing the estimated TA of the first target cell to switch to another target cell in the group of target cells. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] In the following, various exemplary embodiments will be described in more detail with reference to the accompanying drawings, in which:

[0009] Figure 1A message sequence chart for the LTM procedure between the UE and the gNB is shown;

[0010] Figure 2 shows a detailed message sequence chart for the LTM process between the UE, S-DU, T-DU and CU;

[0011] Figure 3 A flow chart depicting a manner of performing UE-based TA acquisition is shown;

[0012] Figure 4 A message sequence chart depicting a first solution for enhancing UE-based TA acquisition capability according to an example embodiment disclosed herein is shown;

[0013] Figure 5 A message sequence chart depicting a second solution for enhancing UE-based TA acquisition capability according to an example embodiment disclosed herein is shown;

[0014] Figure 6 A flowchart depicting steps performed by a user equipment for performing an overall solution for enhancing UE-based TA acquisition capabilities according to example embodiments disclosed herein is shown; and

[0015] Figure 7 A device suitable for implementing an example embodiment of the present disclosure is shown. DETAILED DESCRIPTION

[0016] Example embodiments will now be described with reference to the accompanying drawings. However, the present invention may be implemented in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that the present invention will be thorough and complete and its scope will be fully conveyed to those skilled in the art. The terms used in the detailed description of the example embodiments shown in the accompanying drawings are not intended to be limiting. In the accompanying drawings, the same numerals represent the same elements.

[0017] The specification can refer to "one", "one" or "some" (multiple) embodiments in several positions. This does not necessarily mean that each such reference is for the same embodiment, or the feature is only applied to a single embodiment. The single features of different embodiments can also be combined to provide other embodiments. As used herein, unless otherwise clearly stated or understood based on the context, the singular forms "one", "one" and "the" are also intended to include plural forms. It should also be understood that when used in this specification, the terms "comprise", "include", "include" and / or "include" specify the existence of the features, integers, steps, operations, elements and / or components, but do not exclude the existence or addition of one or more other features, integers, steps, operations, elements, components and / or their groups. In other words, the terms "comprise", "include", "include" and / or "include" should be understood as open. As used herein, whenever the phrase "at least one of the following" is before the element list, wherein the element is connected by "and" or "or", which means that there is at least any one element or at least all elements. As used herein, the term "and / or" includes any and all combinations and permutations of one or more of the associated listed items.

[0018] Conditional language, such as "may" or "can", unless otherwise expressly stated or otherwise understood within the context of use, is generally intended to convey that certain embodiments may include certain features, elements, and / or steps, while other embodiments may not include certain features, elements, and / or steps. Therefore, such conditional language is generally not intended to imply that features, elements, and / or steps are required in any way for one or more embodiments. It should be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element, or there can be intervening elements. In addition, "connected" or "coupled" as used herein can include wirelessly connected or coupled.

[0019] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention belongs. It will be further understood that terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant art, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0020] The accompanying drawings depict simplified structures, showing only some elements and functional entities, all of which are logical units, the implementation of which may be different from that shown. The connections shown are logical connections; the actual physical connections may be different. In addition, all logical units described and depicted in the accompanying drawings include software and / or hardware components required for the unit to function. Further, each unit may include one or more components that are implicitly understood within itself. These components may be operably coupled to each other and configured to communicate with each other to perform the functions of the unit.

[0021] As used herein, the term "circuitry" may refer to at least one of the following: a) hardware circuit implementation only (such as implementation in analog and / or digital circuits only); b) a combination of hardware circuitry and software, such as (where applicable): (i) a combination of analog and / or digital hardware circuitry and software / firmware and (ii) any portion of a hardware processor(s) with software (including digital signal processor(s), software and memory(s) that work together to enable a device (such as a mobile phone or server) to perform various functions); or c) Hardware circuits and / or processor(s), such as microprocessor(s) or portions of microprocessor(s), that require software (e.g., firmware) to operate, but which may not be present when the software is not required to operate.

[0022] The definition of circuitry applies to all uses of the term in this application, including any claims. As yet another example, as used in this application, the term circuitry also covers an implementation of only a hardware circuit or processor (or multiple processors) or a portion of a hardware circuit or processor and its (or their) accompanying software and / or firmware. The term circuitry also covers, for example (and if applicable to a particular claim element), a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in a server, cellular network device, or other computing or network device.

[0023] Before explaining example embodiments of the present disclosure in detail, certain general principles of wireless communication systems and mobile communication devices are briefly explained to help understand the technology behind the described examples.

[0024] In the following, as examples of communication networks to which examples of embodiments may be applied, different exemplary embodiments will be described using a communication network architecture based on a 3GPP standard for communication networks (such as 5G NR), without however limiting the embodiments to such architecture. It will be apparent to those skilled in the art that the embodiments may also be applied to other types of communication networks in which mobile communication principles are integrated with D2D (device to device) or V2X (vehicle to everything) configurations (such as SL (side link)), such as Wi-Fi, Worldwide Interoperability for Microwave Access (Wi MAX), Bluetooth, Personal Communications Service, ZigBee, Wideband Code Division Multiple Access (WCDMA), systems using ultra-wideband (UWB) technology, mobile ad hoc networks (MANET), wired access, and the like. In addition, without loss of generality, the description of some examples of the embodiments relates to mobile communication networks, but the principles of the present disclosure may be extended and applied to any other type of communication network, such as a wired communication network.

[0025] A basic system architecture of a (telecommunication) communication network including a mobile communication system, wherein some of the example embodiments are applicable to a basic system architecture that may include an architecture of one or more communication networks including (multiple) radio access network subsystems and (multiple) core networks. Such an architecture may include one or more communication network control elements or functions, access network elements, radio access network elements, access service network gateways or network nodes, such as base stations (BS), access points (AP), node Bs (NBs), eNBs or gNBs, distributed units (DUs) or centralized / central units (CUs), which control the corresponding coverage area or (multiple) cells, and which communicate with one or more communication stations (such as communication elements or functions), such as user equipment or terminal equipment, such as user equipment (UE), or another device with similar functionality, such as a modern chipset, chip, module, etc., which may also be a station, element, function or application capable of communication (such as a UE), an element or function applicable in a machine-to-machine communication architecture, or attached as a separate element to such an element, a function or application capable of communication, etc., capable of communicating via one or more communication beams via one or more channels for transmitting several types of data in multiple access domains. Furthermore, core network elements or network functions may be included, such as gateway network elements / functions, mobility management entities, mobile switching centers, servers, databases, etc.

[0026] A UE may be any device capable of sending and receiving radio signals. Non-limiting examples of a UE include a mobile station (MS) or mobile device (such as a mobile phone or so-called "smart phone"), a computer provided with a wireless interface card or other wireless interface facility (e.g., a USB dongle), a personal data assistant (PDA) or a tablet computer provided with wireless communication capabilities, a machine type device, or any combination of these devices, etc.

[0027] A network node, an example of which is a base station such as an eNodeB (eNB) or gNodeB (gNB), may include a processor and associated circuitry to execute or direct the execution of computer-readable instructions to perform operations such as those further described herein. In short, the network node may retrieve and execute software from a storage device, which may include a disk drive, a flash drive, memory circuitry, or some other memory device, and may be locally or remotely accessible. The software may include a computer program, firmware, or some other form of machine-readable instructions, and may include an operating system, a utility, a driver, a network interface, an application, or some other type of software, including combinations thereof. Further, the network node may receive instructions and other inputs at a user interface.

[0028] gNB can be divided into gNB central / centralized unit and gNB distributed unit.

[0029] The gNB Central Unit (gNB-CU) includes, for example, a logical node, hosting protocols such as Radio Resource Control (RRC), Service Data Adaptation Protocol (SDAP), and Packet Data Convergence Protocol (PDCP) of the gNB, or RRC and PDCP protocols of the en-GNB, which controls the operation of one or more gNB-DUs (gNB Distributed Units). The gNB-CU terminates the F1 interface connected to the gNB-DU. For simplicity, and because the embodiments disclosed herein may be applicable to evolved systems after the 5G NR system, the gNB-CU may be referred to as a CU.

[0030] The gNB distributed unit (gNB-DU) includes, for example, a logical node that hosts, for example, the radio link control (RLC), media access control (MAC), and physical (PHY) layers of a gNB or en-gNB, and whose operation is partially controlled by the gNB-CU. One gNB-DU supports one or more cells. One cell is supported by only one gNB-DU. The gNB-DU terminates the F1 interface connected to the gNB-CU. The gNB-DU can support one or more cells and can therefore be used as, for example, a serving cell for a UE. The gNB CU and gNB DU parts can, for example, be co-located or physically separated. For simplicity, and because the embodiments disclosed herein may be applicable to evolved systems after the 5G NR system, the gNB-DU may be referred to as a source DU or a target DU.

[0031] In this specification, a cell may refer to a component carrier having coverage of a signal transmitted from a transmission / reception point (TRP) or coverage of a signal transmitted from a transmission / reception point.

[0032] In this specification, candidate cell and target cell may be used synonymously. Source cell and serving cell may be used synonymously. Source network node and serving network node may be used synonymously.

[0033] Figure 1 The message sequence diagram for the LTM process between the UE and the gNB is shown. At steps 1 to 3, as Figure 1 As shown, the following steps occur: a) The gNB-CU (also referred to herein as “CU”) prepares candidate cells for LTM based on Layer 3 (Radio Resource Control (RRC)) measurement reports sent by the UE; b) Then, the CU provides the UE with the prepared LTM configuration of the candidate cell; and c) The CU configures the UE with the L1 measurement reports required for LTM execution.

[0034] At step 4, the UE performs early UL / DL synchronization with the candidate cell to minimize the interruption during LTM execution. This is an advantage of LTM over conventional handover procedures, where in LTM, the interruption time caused by synchronization with the candidate cell during handover is minimized with the help of the early synchronization procedure.

[0035] At step 5, the UE prepares and sends an L1 (PHY) measurement report to the gNB, where the measurement report includes measurements of the beam from the prepared candidate cell to the source cell.

[0036] At step 6, based on the L1 measurement report, the gNB decides the target cell (among the prepared candidate cells) to which the UE should switch, and accordingly, sends a cell switching command to the UE in the form of a media access control (MAC) control element (CE), causing the UE to switch to the target cell.

[0037] At step 7, during the handover procedure, the UE initiates a Random Access Channel (RACH) procedure with the target cell. If the Timing Advance (TA) from step 4 is still valid, the RACH procedure can be skipped.

[0038] Figure 2 A detailed message sequence diagram for the LTM process between UE, S-DU, T-DU and CU is shown. At step 1, the UE generates an L3 measurement report of at least one candidate cell and transmits it to the source DU. The at least one candidate cell includes the target cell to which the UE is switched through the S-DU.

[0039] At step 2, the source DU forwards the L3 measurement report to the CU via uplink RRC messaging. At step 3, the CU prepares at least one candidate cell for LTM based on the L3 measurement report.

[0040] At steps 4 and 5, the CU initiates a preparation process for at least one candidate cell under the DU, where the T-DU may also be an S-DU (ie, the source cell and the target cell belong to the same DU).

[0041] At steps 6 and 7, the CU and S-DU proceed with the UE Context Modification procedure for collecting further configuration details for the LTM preparation procedure by the CU.

[0042] At step 8, the CU generates an RRC reconfiguration for at least one candidate cell prepared for LTM. The RRC reconfiguration may include measurement and reporting configuration information of at least one candidate cell and the RRC reconfiguration of at least one candidate cell to be applied on the UE when a cell change to a target cell is triggered.

[0043] At steps 9 to 12, the CU sends an RRC message to the UE via the S-DU, where the message includes the TA acquisition criteria and the cell switching criteria and the necessary configuration. The trigger criteria for TA acquisition and cell switching may be similar to the measurement event report trigger conditions, such as A3, A4 or A5 conditions or the validity of the acquired TA. The trigger configuration may be a filter configuration (for L1 measurement), a trigger offset, a cell individual offset, etc. The UE notifies the S-DU about the completion of the RRC reconfiguration, and the S-DU initiates ULRRC message transmission to the CU.

[0044] At step 13, the UE reports L1 measurements of at least one candidate for LTM configuration to the S-DU.

[0045] At steps 14 and 15, based on the L1 measurement report, the S-DU decides to trigger TA acquisition of the T-DU (target cell) so that the UE can synchronize with the T-DU, and accordingly, the S-DU sends a TA acquisition command to the UE.

[0046] At step 16, the UE sends a random access preamble to the T-DU so that the T-DU can estimate the TA between the UE and the T-DU.

[0047] At step 17, the S-DU receives a random access response (RAR) indirectly (via the CU).

[0048] At step 18, the UE sends L1 beam measurements of at least one candidate cell, and at step 19, based on the L1 beam measurements, the S-DU decides to which target cell (among the at least one candidate cell) the UE should be handed over.

[0049] At step 17, if the RAR is not received indirectly, then at step 20, the S-DU provides the UE with the acquired TA of the target cell via a MAC CE command, which triggers a cell change (from the source cell to the target cell).

[0050] If the TA of the target cell is still valid (received in step 17), the UE skips the RACH procedure in step 21 when performing HO.

[0051] At steps 22 to 25, the UE and the network proceed with the completion of the LTM procedure.

[0052] It should be noted that the phrases "TA acquisition" and "TA estimation" as used herein are synonymous with each other.

[0053] Figure 3A flow chart depicting the manner in which UE-based TA acquisition is performed for a second transmit receive point (TRP2) is shown. Timing alignment error (TAE) represents the relative difference in the timing of transmissions between any pair of two TRPs, i.e., TRP downlink transmission (TRP DLTX) of TRP 1 and TRP DL TX of TRP 2. TAE is defined in 3GPP Technical Specification (TS) 38.104 Section 6.5.3 in the context of MIMO transmissions from TRPs, with a maximum value not exceeding 3000ns and with extensions to the definition for LTM under discussion in 3GPP. A similar quantity is defined in Section 7.4 of 38.133, referred to as cell phase synchronization accuracy, with respect to transmissions from a pair of cells. Cell phase synchronization accuracy for time division duplex (TDD) is defined as the maximum absolute deviation in frame start timing between any pair of cells on the same frequency with overlapping coverage areas, and should be better than 3000ns.

[0054] Furthermore, in the context of DL positioning, TX timing error is defined in 3GPP TS 38.305 Section 3.1 as the result of the TX time delay involved in the transmission of the signal, which in turn is defined as the time delay between the time when the digital signal is generated at the baseband to the time when the RF signal is transmitted from the Tx antenna. Furthermore, in 3GPP TS 37.355, the information element NR-RTD-Info is used by the location server to provide time synchronization information between the reference TRP and the list of neighboring TRPs. These definitions, information elements and related mechanisms in this specification allow the UE to be aware of timing misalignments in transmissions from different TRPs and take these into account in the position estimate. The reference time difference (RTD) represents the time difference between the UE's DL reception (UE DL RX) of the UL TX of TRP 1 and the UE's DL RX of the UL TX of TRP 2. D1 represents the time difference between TRP 1 and the UE's TX and RX towards each other, and D2 represents the time difference between TRP 2 and the UE's TX and RX towards each other.

[0055] The timing advance TA2 for the second TRP 2 is equal to: TA2=TA1+2RTD-2Realized(TAE)–OtherEstError, Wherein, OtherEstError refers to any error that may be caused by UL / DL reciprocity or estimator implementation / method error.

[0056] The overall solution for enhancing the UE-based TA acquisition capability and thereby solving the above-mentioned (multiple) problems enables the UE to reuse the UE-based TA acquisition for multiple target cells for cells sharing the same TA value. In other words, when there are multiple target cells sharing the same TA value, the UE only needs to estimate the TA value for one of the target cells and reuse it for any other target cells, rather than performing the TA estimation process for the other target cells. This helps to overcome the capability limitations of the UE for performing TA acquisition for a limited number of target cells. By providing a grouping mechanism for UE-based TA estimation for target cells, the UE is enabled to reuse the UE-based TA acquisition of multiple target cells for those target cells sharing the same TA value. The CU requests information related to multiple target cells and related TAs from the target DU (serving multiple target cells) and forwards the information to the UE. The UE then estimates the TA for multiple target cells based on the received information (by estimating the TA value for one of the multiple target cells) and transmits the TA value to the S-DU. It can be said that two target cells share the same TA value in the following scenarios: (1) The TA values ​​of the two target cells are exactly the same; or (2) The TA value of one target cell can be used for other target cells.

[0057] In scenario 2, when the difference between the TA values ​​of the two target cells is negligible, the TA value of one target cell may be used for the other target cell (ie, the TA values ​​of the two target cells may be used interchangeably).

[0058] Figure 4 A message sequence chart depicting a first solution for enhancing UE-based TA acquisition capability according to an example embodiment of the present disclosure is shown. In the first solution, UE-based TA estimation configurations of target cells will be grouped into one configuration for target cells sharing the same TA. Therefore, the UE receives a smaller number of configurations and can reuse one TA estimation for multiple target cells.

[0059] At step 1, the UE sends an L3 measurement report to the CU via the S-DU, which triggers the preparation of multiple target cells. The L3 measurement report may include measured details (e.g., signal strength) of the target cells served by the target network node (e.g., T-DU-1 and / or T-DU-2).

[0060] At steps 2 to 3, the CU initiates the preparation of cell 1.1 and cell 1.2 from T-DU-1 and the preparation of cell 2.1 and cell 2.2 from T-DU-2 via the UE context setup request message. The CU also requests the configuration required for UE-based TA estimation for the prepared target cells at the UE. In one embodiment, the CU may indicate for which target cell among multiple target cells it requests UE-based TA estimation configuration. The selection of which target cell to request UE-based TA estimation configuration may be based on measurements in the L3 measurement report.

[0061] At steps 4 to 5, the T-DU (T-DU-1 and / or T-DU-2) responds to the CU's request by indicating that the cell requested by the CU is ready, and transmits group UE-based TA acquisition to the CU via a UE context setup response message. Each T-DU (1) groups its corresponding target cells (as requested by the CU) and their beams, and (2) provides a list of groups to the CU. Each group of target cells includes the following information for each target cell in the group: (i) physical cell identity (PCI), (ii) cell frequency, and (iii) synchronization signal block (SSB) index, where each target cell in the group shares the same timing advance (TA) value. The group may also be provided with a group identifier (ID) to help identify them. Those target cells that are requested and do not share any TA with other target cells (i.e., those target cells with unique TAs) may be provided with separate UE-based TA acquisition configurations by their corresponding T-DUs.

[0062] At step 6, the CU also proceeds with the S-DU with the UE context modification procedure before generating an RRC reconfiguration message carrying the LTM candidate configuration (for LTM switching) and its related configuration (eg, reporting configuration, etc.).

[0063] At step 7, if necessary, the CU may regroup the UE-based TA acquisition configurations configured for all T-DUs, i.e., if the cells between the T-DUs share the same TA, the CU may organize the configurations so that the UE-based TA acquisition configurations of the cells from different T-DUs are grouped into the same configuration. For example, in the case where the CU requests a UE-based TA acquisition configuration for the target cells served by T-DU-1 and T-DU-2, the CU may initially receive a group UE-based TA acquisition configuration for each of T-DU-1 and T-DU-2. Subsequently, if there are any target cells from T-DU-1 that share the same TA value as the target cells from T-DU-2, the group UE-based TA acquisition configurations are regrouped so that the target cells from T-DU-1 and T-DU-2 that share the same TA value are classified under the same group UE-based TA acquisition configuration. In some embodiments, target cells from the same T-DU may be regrouped into different groups despite having the same TA value.

[0064] At step 8, the CU provides the LTM candidate configuration to the UE via the S-DU in the RRC reconfiguration message. The CU also provides the UE with the group UE-based TA acquisition configuration via the RRC reconfiguration message. The CU also notifies the S-DU of (multiple) group UE-based TA acquisition configurations.

[0065] At step 9, after successfully decoding the received configuration, the UE responds with an RRCReconfigurationComplete message.

[0066] At step 10, the UE may start L1 measurement reporting, which contains L1 measurements of the serving cell and the target cell (in the group), so that the S-DU can monitor the quality of both the source cell and the target cell (i.e., the prepared target cell) before triggering TA estimation or cell handover. The reporting may be periodic, and the period is configured in RRCReconfiguration.

[0067] At step 11, UE-based TA acquisition may be triggered by the UE itself or by the network. In the case of network triggering, the S-DU triggers the UE to initiate UE-based TA acquisition. The S-DU may also indicate the target cell for which the UE should evaluate its TA, or the UE itself may evaluate which target cell's TA should be estimated. In either case, the criteria for the target cell for TA estimation may be based on the signal strength of the target cell, i.e., the selected target cell has the highest signal strength and has a valid UE-based TA acquisition configuration. As an example, cell 1.1 may be selected for UE-based TA estimation because cell 1.1 may be the strongest target cell at that point in time. In one embodiment, the S-DU may indicate the group ID of the group UE-based TA acquisition configuration instead of the cell ID to inform the UE which group UE-based TA acquisition configuration it should use for UE-based TA estimation.

[0068] At step 12, the UE estimates the TA of the group-1 configuration for the target cells included in the group. In this context, the estimation will be based on the cell 1.1 measurements, which provide the TA for all cells of group-1. In other words, by performing TA estimation based on measurements of a single cell within the group of target cells (to which the group-based UE's TA acquisition configuration applies), the UE is able to subsequently estimate the TA of the group configuration (and the remaining target cells in the group configuration) because the estimated target cells and the group configuration share the same group identity (because they share the same TA value).

[0069] At step 13, the UE may report to the S-DU that it has estimated the TA of group-1 (by estimating the TA of cell 1.1 belonging to group-1).

[0070] At steps 14 to 15, after receiving further measurement reports from the UE, the S-DU may determine that cell-1.2 is a more suitable cell for handover than cell-1.1 (due to signal quality, load balancing, etc.). Since both cell-1.1 and cell-1.2 belong to the same configuration group (i.e., group-1), the S-DU does not trigger any early TA-based acquisition procedure for cell-1.2, because the UE can reuse its estimated TA for cell-1.1. In other words, since cell-1.1 and cell-1.2 share the same TA value and therefore have the same UE-based TA acquisition configuration, the UE may avoid estimating the TA value for cell-1.2 and instead use the estimated TA value of cell-1.1 to handover to cell-1.2.

[0071] At step 16, the S-DU decides to trigger a cell change towards cell-1.2. The S-DU checks whether cell-1.2 belongs to the group configuration for which the UE has confirmed the UE-based TA estimation. Since cell-1.1 and cell-1.2 belong to the same group configuration, i.e., group-1, the S-DU decides to trigger an LTM cell change without RACH.

[0072] At step 17, the S-DU sends a MAC CE cell switching command (i.e., LTM cell switching command) to trigger the LTM cell change. The S-DU also instructs to acquire the configured group-ID based on the UE's TA so that the UE will use the configured TA and perform a RACH-free cell switching to the target cell-1.2.

[0073] In one embodiment, the S-DU may indicate (in the MAC CE Cell Switch Command) the identity of Cell-1.2 instead of its Group-ID, and the UE infers the Group-ID of Cell-1.2 and accordingly determines the applicable TA value to perform a RACH-less LTM cell change.

[0074] At steps 18 to 21, the UE continues with the No RACH procedure and completes the LTM cell change towards cell-1.2.

[0075] Figure 5 FIG. 1 is a message sequence diagram depicting a second solution for enhancing UE-based TA acquisition capability according to an example embodiment disclosed herein. Figure 5 Also exists in Figure 4 The description of the steps in are omitted.

[0076] At steps 4 to 5, the T-DUs (T-DU1 and T-DU2) provide a group of cells that share the same TA. There may be multiple groups that (1) contain cells that share the same TA within the group and (2) contain cells that do not share the same TA between cells in other groups.

[0077] At step 7, the CU may regroup the set of target cells that share the same TA between T-DUs. In some embodiments, target cells from the same T-DU may be regrouped into different groups despite having the same TA value.

[0078] At step 8, the CU provides the target cell grouping information to the S-DU and the UE. In one embodiment, the CU explicitly provides the group of cells, with the cell list as a separate group. In another embodiment, the CU also provides a group ID for each group of cells. In another embodiment, the CU provides a group ID for each cell, rather than providing a group ID for each group of cells.

[0079] At step 11, if network-triggered UE-based TA acquisition is considered, the S-DU indicates the group ID of cells for which UE-based TA estimation should be performed.

[0080] At step 12, the UE will select a suitable cell from the set of cells with UE-based TA acquisition configuration. As an example, if cell-1.1 is a suitable cell, the UE performs UE-based TA acquisition based on the configuration of cell-1.1. The UE estimates the TA value for cell-1.1 (based on the measurement of cell-1.1) and thus estimates the TA of the set of cells that share the same TA value with cell-1.1.

[0081] At step 13, the UE indicates to the S-DU the group ID of cells used for TA acquisition based on the UE and the estimated TA values ​​of the group of cells.

[0082] At steps 14 to 15, if the cell belongs to: a) the group indicated by the S-DU to the UE for UE-based TA estimation; or b) The group for UE-based TA estimation indicated by the UE to the S-DU, and if the cell becomes stronger (e.g., cell-1.2 becomes stronger than cell-1.1) during the L1 measurement report, the S-DU does not trigger the UE to perform any UE-based TA acquisition procedure for that cell (i.e., cell-1.2). Similarly, the UE does not perform UE-based TA estimation for any other cells in the same group, because the UE can reuse the same TA value estimated at step 12.

[0083] The S-DU decides to trigger an LTM cell change without RACH towards the target cell-1.2 at step 16. The reason for no RACH is that cell-1.2 belongs to the same group ID triggered by the S-DU or reported by the UE.

[0084] At step 17, the S-DU indicates the cell group ID of its TA that the UE should use when performing a RACH-less LTM cell change towards cell-1.2.

[0085] At step 18, in one embodiment, the UE uses the group ID indicated in the LTM Cell Switch Command (CSC) to identify which TA value to use.

[0086] In another embodiment, the UE will identify that cell-1.1 and cell-1.2 belong to the same target cell group and use the TA of that group to perform LTM without RACH towards cell-1.2.

[0087] Figure 6A flow chart 600 is shown depicting steps performed by a user equipment (UE) to implement an overall solution for enhancing UE-based TA acquisition capabilities according to example embodiments disclosed herein.

[0088] At step 602, the UE obtains group information for a set of target cells from a first network node (e.g., a centralized unit (CU)). The CU may transmit the group information to the UE after transmitting a request for the group information for the set of target cells to a target network node (e.g., a target distributed unit). Each target cell in the set of target cells may share the same TA value. The CU may transmit a request for the group information via a UE context setup request message. The target network node responds to the CU's request with the group information via a UE context setup response message. The UE obtains the group information from the CU via a radio resource control (RRC) reconfiguration message. The group information helps the UE perform TA estimation for any target cell in the set of target cells. The RRC reconfiguration message may also include LTM configuration information.

[0089] At step 604, the UE performs measurements on the set of target cells. The measurements (e.g., signal strengths of the target cells) may be compiled in a measurement report that is transmitted to the second network node (e.g., the source distributed unit). Based on the measurements, the second network node may decide which target cell should be used for handover.

[0090] At step 606, the UE estimates a timing advance (TA) value of a first target cell within the group of target cells based on the group information and the measurements of the group of target cells. Because each cell in the group of target cells shares the same TA value, by estimating the TA value of the first target cell, the UE has estimated the TA values ​​of the remaining target cells in the group. The UE reports to the second network node that the TA value of the group of target cells is the same as the TA value of the first target cell.

[0091] In step 608, the UE reuses the estimated TA value of the first target cell to switch to another target cell in the group of target cells. Since the UE has already acquired the TA value of the other target cell, the UE does not have to undertake the TA acquisition process for the other target cell. The UE switches to the other target cell based on a lower layer triggered mobility (LTM) cell switching command (CSC) that directs the UE to switch to the other target cell. The LTM CSC can be based on a measurement report. The handover to the other target cell does not have to occur under the condition of undergoing a random access channel (RACH) process, and it is not necessary to perform a UE-based TA acquisition process for the other target cell.

[0092] As stated previously herein, the TA value of the first target cell need not be exactly the same as the TA value of any remaining target cell in the group; rather, the difference in TA values ​​between the first target cell and any other target cell may be ignored such that the TA value of the first target cell may be used for any other target cell in the same group.

[0093] Figure 6 The method depicted in the may include other steps not shown and / or may omit certain steps, and therefore, this should not be construed as limiting the scope of the present disclosure. In addition, Figure 6 The steps in the description may not necessarily occur in the same order as presented herein.

[0094] Figure 7 700 is a simplified block diagram of an apparatus 700 for implementing an example embodiment of the present disclosure. The apparatus 700 is an example of an apparatus that can be configured to implement the various methods and processes described herein. The apparatus 700 can be a network device (e.g., a source network node / source DU / CU / target DU) or a terminal device (e.g., a UE).

[0095] The device 700 includes a processor 704 that can control the operation of the device. The processor 704 may also be referred to as a central processing unit (CPU). The memory 702, which may include both a read-only memory (ROM) and a random access memory (RAM), may provide instructions and data to the processor 704. The memory 1502 and the processor 704 may be operatively coupled. The memory 702 may store computer-readable instructions / computer program codes. The computer-readable instructions / computer program codes may be pre-stored to the memory 702, or alternatively or additionally, they may be received by the device 700 via an electromagnetic carrier signal and / or may be copied from a physical entity (such as a computer program product). The execution of the computer-readable instructions by the processor 704 may enable the device 700 to implement the example embodiments described herein.

[0096] In the context of this document, "memory" (also referred to as "computer-readable medium") can be any non-transitory medium or component that can contain, store, communicate, propagate or transmit instructions for use by or in conjunction with an instruction execution system, apparatus or device (such as a computer). As used herein, the term "non-transitory" is a limitation of the medium itself (i.e., tangible rather than a signal), not a limitation on data storage persistence (e.g., RAM vs. ROM).

[0097] Transmitter / receiver (TX / RX) circuitry 706 may include a transmitter 710 and a receiver 712, which may enable device 700 to transmit or receive data. Device 700 may include (not shown) multiple antennas, transmitters, and receivers.

[0098] In some example embodiments, the device 700 may include a Figure 6 The component may be implemented in any suitable form. For example, the component may be implemented in a circuit system (e.g., memory 702 and processor 704) or a software module.

[0099] According to an exemplary embodiment of the present disclosure, a user equipment UE is provided, comprising: at least one memory; and at least one processor, the at least one processor being operatively coupled to the at least one memory, wherein the at least one processor is configured to: obtain group information for a group of target cells from a first network node; perform measurements of a group of target cells; estimate a timing advance TA value of a first target cell in the group of target cells based on the group information and the measurements of the group of target cells; and reuse the estimated TA value of the first target cell to switch to another target cell in the group of target cells.

[0100] In some example embodiments, the UE is configured to: in response to performing measurements of a set of target cells, send a measurement report to the second network node.

[0101] In some example embodiments, the UE is configured to report to the second network node that the TA values ​​of a group of target cells are the same as the estimated TA value of the first target cell.

[0102] In some example embodiments, where the first target cell and the another target cell share the same TA value, the UE reuses the estimated TA value of the first target cell to handover to the another target cell.

[0103] In some example embodiments, the UE is configured to: in response to sending the measurement report, receive a lower layer triggered mobility (LTM) cell handover command from the second network node to handover to another target cell.

[0104] In some example embodiments, the UE is configured to: switch to another target cell without: undergoing a random access channel RACH procedure; and performing UE-based TA acquisition for the other target cell.

[0105] In some example embodiments, wherein: the first network node is a centralized unit; and the second network node is a source distributed unit.

[0106] According to an exemplary embodiment of the present disclosure, a method performed by a user equipment UE is also provided, including: obtaining group information for a group of target cells from a first network node; performing measurements of a group of target cells; estimating a timing advance TA value of a first target cell in a group of target cells based on the group information and measurements of the group of target cells; and reusing the estimated TA value of the first target cell to switch to another target cell in the group of target cells.

[0107] In some example embodiments, the method comprises, in response to performing measurements of a set of target cells, sending a measurement report to the second network node.

[0108] In some example embodiments, the method comprises reporting to the second network node that a set of target cells have TA values ​​that are the same as the estimated TA value of the first target cell.

[0109] In some example embodiments, where the first target cell and the another target cell share the same TA value, the UE reuses the estimated TA value of the first target cell to handover to the another target cell.

[0110] In some example embodiments, the method comprises, in response to sending the measurement report, receiving a Lower Layer Triggered Mobility (LTM) Cell Handover command from the second network node to handover to another target cell.

[0111] In some example embodiments, the method includes, in response to receiving the LTM cell handover command, handing over by the UE to another target cell without undergoing a random access channel (RACH) procedure and without performing UE-based TA acquisition for the other target cell.

[0112] In some example embodiments, wherein the first network node is a centralized unit; and the second network node is a source distributed unit. Technical Effects

[0113] Embodiments disclosed herein improve resource efficiency of the UE because the UE avoids utilizing resources to estimate the TA value of the second target cell by reusing the estimated TA value of the first target cell when switching to the second target cell (having the same TA value as the first target cell). Embodiments herein also improve channel quality of the UE because the UE experiences less interruption during switching by undergoing switching to the second target cell without performing a random access channel (RACH) procedure. Embodiments herein also improve the output of LTM because the UE can perform LTM on a greater number of target cells using UE-based TA acquisition.

[0114] In the drawings and specification, exemplary embodiments of the present invention have been disclosed. Although specific terms are used, they are used only in a general and descriptive sense and not for limiting purposes. It is apparent to those of ordinary skill in the art that various modifications and variations may be made to the embodiments disclosed herein without departing from the spirit and scope of the present invention. Other embodiments consistent with the present invention will become apparent from consideration of the specification and practice of the description disclosed herein.

Claims

1. A user equipment UE, comprising: at least one memory; as well as at least one processor operatively coupled to the at least one memory, wherein the at least one processor is configured to: obtaining, from the first network node, group information for a group of target cells; performing measurements of the set of target cells; estimating a timing advance (TA) value of a first target cell in the group of target cells based on the group information of the group of target cells and the measurement; as well as The estimated TA value of the first target cell is reused to perform handover to another target cell in the set of target cells.

2. The UE according to claim 1, wherein the UE is configured to: In response to performing the measurements of the set of target cells, a measurement report is sent to the second network node.

3. The UE according to claim 1, wherein the UE is configured to: The TA value of the set of target cells is reported to a second network node as being the same as the estimated TA value of the first target cell. 4 . The UE according to claim 1 , wherein since the first target cell and the another target cell share the same TA value, the UE reuses the estimated TA value of the first target cell to switch to the another target cell.

5. The UE according to claim 2, wherein the UE is configured to: In response to sending the measurement report, a Lower Layer Triggered Mobility (LTM) cell handover command is received from the second network node to handover to the another target cell.

6. The UE according to claim 5, wherein the UE is configured to: Handover to the another target cell without performing the following: undergoing a random access channel RACH procedure; and Performing UE-based TA acquisition for the another target cell.

7. The UE according to claim 2, wherein: The first network node is a centralized unit; and The second network node is a source distributed unit.

8. A method performed by a user equipment UE, comprising: obtaining, from the first network node, group information for a group of target cells; performing measurements of the set of target cells; estimating a timing advance (TA) value of a first target cell in the group of target cells based on the group information of the group of target cells and the measurement; as well as The estimated TA value of the first target cell is reused to perform handover to another target cell in the set of target cells.

9. The method according to claim 8, comprising: In response to performing the measurements of the set of target cells, a measurement report is sent to the second network node.

10. The method according to claim 8, comprising: The TA value of the set of target cells is reported to a second network node as being the same as the estimated TA value of the first target cell.

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