CN116896780A

CN116896780A - Method for timing advance acquisition and maintenance and user equipment

Info

Publication number: CN116896780A
Application number: CN202310263532.3A
Authority: CN
Inventors: 张晓楠; 张园园
Original assignee: MediaTek Singapore Pte Ltd
Current assignee: MediaTek Singapore Pte Ltd
Priority date: 2022-04-01
Filing date: 2023-03-10
Publication date: 2023-10-17
Also published as: WO2023184476A1

Abstract

The invention provides a method for acquiring and maintaining timing advance and user equipment, wherein the method comprises the following steps: maintaining, by the user equipment, a plurality of timing advance groups, TAGs, wherein each TAG is associated with a cell and a timing advance timer, TAT; receiving an inter-cell beam management indication to switch from a first cell to a second cell, wherein the user equipment is connected to the first cell by a first cell TAG associated with the first cell; determining, upon receipt of the inter-cell beam management indication indicating handover, whether a TAG associated with the second cell is valid; and when the user equipment determines that a second cell TAG associated with the second cell is valid, the user equipment performs a cell handover to the second cell skipping a random access RA procedure. By utilizing the invention, TA acquisition and maintenance can be better performed.

Description

Method for timing advance acquisition and maintenance and user equipment

Technical Field

The present invention relates to wireless communications, and more particularly to Timing Advance (TA) maintenance and acquisition for mobility through inter-cell beam management (ICBM).

Background

In a legacy network of the third generation partnership project (3rd generation partnership project,3GPP) 5G New Radio (NR), a serving cell change needs to be performed at some point when a User Equipment (UE) moves from the coverage area of one cell to another. The current serving cell change is triggered by layer 3 (L3) measurements and is done by radio resource control (radio resource control, RRC) reconfiguration signaling, including simultaneous change of primary cell (PCell) and primary secondary cell (primary and secondary cell, PSCell) and release/addition of secondary cell (SCell) when applicable. The cell switching procedure involves a full L2 (and L1) reset, which results in longer delays, more overhead and longer interruption times than during beam switching movements. To reduce delay, overhead, and outage time during UE movement, a movement mechanism may be enhanced to allow modification of serving cells through beam management via L1/L2 signaling. L1/L2 based inter-cell mobility with beam management should support different scenarios, such as intra-unit (DU)/inter-DU (inter-cell) change, FR1/FR2 and intra-frequency/inter-frequency, the source and target cells may be synchronized or unsynchronized.

In a conventional Handover (HO) design controlled by a series of L3 procedures including radio resource management (radio resource management, RRM) measurements and RRC reconfiguration, ping-pong effects with relatively long time of stay (ToS) should be avoided to mitigate the occurrence of HO, with consequent reduction of signaling overhead and interruption throughout the life of the RRC connection. However, a disadvantage is that the UE cannot achieve an optimized instantaneous throughput if the best beam does not belong to the serving cell. With the development of L1/L2 based inter-cell mobility with beam management, cell handover can take advantage of the ping-pong effect to further improve system performance.

There is a need to improve and enhance TA maintenance and acquisition for mobility under ICBM to take advantage of cell handover.

Disclosure of Invention

An embodiment of the present invention provides a method for timing advance acquisition and maintenance, including: maintaining, by the user equipment, a plurality of timing advance groups, TAGs, wherein each TAG is associated with a cell and a timing advance timer, TAT; receiving an inter-cell beam management indication to switch from a first cell to a second cell, wherein the user equipment is connected to the first cell by a first cell TAG associated with the first cell; determining, upon receipt of the inter-cell beam management indication indicating handover, whether a TAG associated with the second cell is valid; and when the user equipment determines that a second cell TAG associated with the second cell is valid, the user equipment performs a cell handover to the second cell skipping a random access RA procedure.

Another embodiment of the present invention provides a user equipment, including: a transceiver for transmitting and receiving radio frequency signals in a wireless network; a timing advance group TAG recording module for maintaining a plurality of TAGs, wherein each TAG is associated with a cell and a timing advance timer TAT; an inter-cell management module configured to receive an inter-cell beam management indication to switch from a first cell to a second cell, wherein the user equipment is connected to the first cell by a first cell TAG associated with the first cell; a TAG control module for determining, upon receipt of the inter-cell beam management indication indicating handover, whether a TAG associated with the second cell is valid; and a cell handover controller for performing a cell handover to the second cell by the user equipment skipping a random access RA procedure when the user equipment determines that a second cell TAG associated with the second cell is valid.

Another embodiment of the present invention provides a storage medium storing a program which, when executed, causes a user equipment to perform the steps of the method of timing advance acquisition and maintenance of the present invention.

By utilizing the invention, TA acquisition and maintenance can be better performed.

Drawings

The drawings illustrate embodiments of the invention, wherein like numerals indicate like components.

Fig. 1 is a system diagram of an exemplary wireless network for TA maintenance and acquisition for mobility during ICBM according to an embodiment of the invention.

Fig. 2A is a schematic diagram of an exemplary NR wireless system with a centralized upper layer of NR radio interface stacks according to an embodiment of the present invention.

Fig. 2B is an exemplary diagram of inter-cell beam management with TA maintenance according to an embodiment of the present invention.

Fig. 3 is a schematic diagram of an exemplary deployment scenario for intra-DU inter-cell beam management according to an embodiment of the present invention.

Fig. 4 is a schematic diagram of an exemplary deployment scenario for inter-DU inter-cell beam management according to an embodiment of the present invention.

Fig. 5 is an exemplary diagram of a procedure in which a UE partially resets a MAC entity and maintains TAG from a source cell when the UE side uses a single stack according to an embodiment of the present invention.

Fig. 6 is an exemplary diagram of a process in which a UE establishes a new MAC entity and maintains a source MAC entity when the UE side uses dual stacks according to an embodiment of the present invention.

Fig. 7 is an exemplary diagram of a UE retaining TAG of a source cell and performing RA when accessing a target cell for the first time, and skipping RA procedure when switching back to the source cell and switching to the target cell again, according to an embodiment of the present invention.

Fig. 8 is an exemplary overall flow diagram of inter-cell beam management according to an embodiment of the present invention.

Fig. 9 is an exemplary flow diagram for inter-cell beam management by a UE over single and dual stacks in accordance with an embodiment of the present invention.

Fig. 10 is an exemplary flow chart of TA acquisition and maintenance for mobility under inter-cell beam management in accordance with an embodiment of the present invention.

Detailed Description

Reference will now be made in detail to some embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

Fig. 1 is a system diagram of an exemplary wireless network for TA maintenance and acquisition for mobility during ICBM according to an embodiment of the invention. The wireless system 100 includes one or more fixed infrastructure elements forming a network distributed over a geographic area. For example, base stations/gNBs 101, 102, and 103 serve multiple mobile stations, such as UEs 111, 112, and 113, within a certain service area (e.g., cell or cell sector). In some systems, one or more base stations are coupled to a controller through a network entity, such as network entity 106, to form an access network, where the access network is coupled to one or more core networks. The gnbs 101, 102, and 103 are base stations in NR whose service areas may or may not overlap. For example, UE 112 is connected only with gNB 101. UE 111 is located in an overlapping service area of gNB 101 and gNB 102 and may switch back and forth between gNB 101 and gNB 102. UE 113 is located in an overlapping service area of gNB 102 and gNB 103 and may switch back and forth between gNB 102 and gNB 103. Base stations such as gNB 101, 102, and 103 are connected to the network through links 136, 137, and 138, respectively, through a network entity (e.g., network entity 106). Backhaul connections (e.g., xn connections 131 and 132) connect non-collocated receiving base station units. Xn connection 131 connects gNB 101 and gNB 102.Xn connection 132 connects gNB 102 and gNB 103. These backhaul connections may be ideal or non-ideal.

When a UE (e.g., UE 111) is located in the overlap region, L1/L2-based inter-cell mobility may be performed. For L1/L2 based inter-cell mobility with beam management, the network may take advantage of the ping-pong effect (i.e., cell-to-cell handover back and forth between the source cell and the target cell) to select the best beam in a wider area including the source cell and the target cell to improve throughput during UE movement. Inter-cell mobility based on L1/L2 is more suitable for scenarios of intra-DU and inter-DU cell change, in which the ping-pong effect is not important. No additional signaling/delay is needed on the network side for cell change within the DU. For inter-DU cell change, the F1 interface between the DU and a Central Unit (CU) may support high data rates and short delays. Considering that the F1 delay is 5 ms, L1/L2 based inter-cell mobility can be supported. UL time alignment with the corresponding serving cell is required during L1/L2 based inter-cell movement. By default, the UE needs to perform a Random Access (RA) procedure on the cell to which the UE accesses. Considering that a UE may switch back and forth between different cells, it is complicated and power consuming if the UE always performs an RA procedure to the cell to which the UE is handed over.

In an example, the UE performs TA maintenance and acquisition of multiple TA groups (TAGs) to enable Ll/L2 based inter-cell mobility with beam management. In an embodiment, a source cell TAG with an associated source TA timer (TAT) is acquired and maintained during HO. The source TAT continues to operate after the UE switches to a new target cell. When the UE performs cell handover, the UE determines whether there is a valid TAG for the target cell. If the target TAG is valid, the UE skips the RA procedure and switches to the target cell. When the UE finds that the TAG of the target cell is present and the TAT associated with the TAG of the target cell has not expired, the target TAG is valid.

Fig. 1 further shows a simplified block schematic diagram of a base station and mobile device/UE for TA maintenance and acquisition. The gNB 102 has an antenna 156 that transmits and receives radio signals. RF transceiver circuitry 153 coupled to the antenna receives RF signals from antenna 156, converts the RF signals to baseband signals, and sends the baseband signals to processor 152. The RF transceiver 153 also converts baseband signals received from the processor 152 into RF signals and sends to the antenna 156. The processor 152 processes the received baseband signals and invokes different functional modules to perform the functional features in the gNB 102. Memory 151 stores program instructions and data 154 to control the operation of gNB 102. The gNB 102 also includes a set of control modules 155 for performing the functional tasks to communicate with the mobile station. The RRC state controller 181 performs access control to the UE. The data radio bearer (data radio bearer, DRB) controller 182 establishes/adds, reconfigures/modifies and releases/removes DRBs based on the different sets of conditions for DRB establishment, reconfiguration and release. The protocol stack controller 183 may add, modify or remove the protocol stack of the DRB. The protocol stack includes a Physical (PHY) layer 189, a medium access control (medium access control, MAC) layer 188, a radio link control (radio link control, RLC) layer 187, a packet data convergence protocol (packet data convergence protocol, PDCP) layer 186, and a service data adaptation protocol (service data adaptation protocol, SDAP) layer 185. In an embodiment, the MAC entity 188 controls two TAGs associated with the first cell and the second cell, respectively. In an embodiment, the MAC entity 188 controls one TAG associated with the first cell or the second cell. In an embodiment, the MAC entity 188 controls a plurality of TAGs associated with a plurality of candidate cells. In an embodiment, the UL TAs of the different cell TAGs are maintained independently. In one embodiment, the TAG is the master TAG (primary TAG).

UE 111 has an antenna 165 that transmits and receives radio signals. An RF transceiver circuit 163 coupled to the antenna receives RF signals from the antenna 165, converts the RF signals to baseband signals, and sends the baseband signals to the processor 162. In one embodiment, the RF transceiver may include two RF modules (not shown). The first RF module is used for High Frequency (HF) transmission and reception, and the other RF module is used for transmission and reception of a different frequency band than the HF transceiver. The RF transceiver 163 also converts the baseband signal received from the processor 162 into an RF signal and transmits to the antenna 165. The processor 162 processes the received baseband signals and invokes different functional modules to perform functional features in the UE 111. Memory 161 stores program instructions and data 164 to control the operation of UE 111. Antenna 165 sends uplink transmissions to antenna 156 of gNB 102 and receives downlink transmissions from antenna 156 of gNB 102.

The UE 101 also includes a set of control modules for performing functional tasks. These functional modules may be implemented in circuitry, software, firmware, or a combination of the above. The RRC state controller 171 controls the UE RRC state according to the network command and the UE condition. The RRC supports the following states: RRC IDLE (rrc_idle), RRC CONNECTED (rrc_connected), and RRC INACTIVE (rrc_inactive). The DRB controller 172 establishes/adds, reconfigures/modifies and releases/removes DRBs based on the different sets of conditions for DRB establishment, reconfiguration and release. The protocol stack controller 173 adds, modifies or removes the protocol stack of the DRB. The protocol stack includes an SDAP layer 175, a PDCP layer 176, an RLC layer 177, a MAC layer 178, and a PHY layer 179.TAG recording module 191 maintains a plurality of TAGs, where each TAG is associated with a cell and a TAT. The inter-cell management module 192 receives an inter-cell beam management indication to switch from a first cell to a second cell, wherein the UE is connected to the first cell by a first cell TAG associated with the first cell. The TAG control module 193, upon receiving an inter-cell beam management indication indicating a handover, determines whether a TAG associated with the second cell is valid. When the UE determines that the second cell TAG associated with the second cell is valid, the cell handover controller 194 skips the RA procedure to perform a cell handover to the second cell.

Fig. 2A is a schematic diagram of an exemplary NR wireless system with a centralized upper layer of NR radio interface stacks according to an embodiment of the present invention. There may be different protocol partitioning choices between upper layers (upper layers) of CU/gNB nodes and lower layers (lower layers) of DU/gNB nodes. The functional division between the central unit and the gNB lower layers may depend on the transport layer. The low performance transmission between the central unit and the gNB lower layers may enable the higher protocol layers of the NR radio stack to be supported in the central unit, since the higher protocol layers have lower performance requirements on the transmission layers in terms of bandwidth, delay, synchronization and jitter. In one embodiment, the SDAP and PDCP layers are located at a central unit, while the RLC, MAC and physical layers are located at a distributed unit. The core unit (core unit) 201 is connected to a central unit 211 with a gNB upper layer 252. In an embodiment, the gNB upper layer 252 includes a PDCP layer and an optional SDAP layer. The central unit 211 is connected to distributed units 221, 222, and 223, wherein the distributed units 221, 222, and 223 correspond to cells 231, 232, and 233, respectively. Distributed units 221, 222, and 223 include a gNB underlayer 251. In an embodiment, the gNB lower layer 251 includes PHY, MAC, and RLC layers.

Fig. 2B is an exemplary diagram of inter-cell beam management with TA maintenance according to an embodiment of the present invention. In step 261, the ue performs L1 measurements and sends measurement reports to the network. In step 262, the ue receives a cell handover command from the network to handover to the target cell. The cell handover may be an intra-DU cell handover, an inter-DU cell handover or an inter-cell handover. In step 271, the ue determines whether the target TAG is valid. The target TAG is valid when it is present and the TAT of the target TAG is running. If step 271 determines yes, the UE skips RA in step 281. If step 271 determines no, the UE performs RA in step 282. In step 291, after successful handover to the target cell, the UE maintains the first cell/source cell TAG by maintaining the TAG and maintaining running the TAT associated with the TAG.

Fig. 3 is a schematic diagram of an exemplary deployment scenario for intra-DU inter-cell beam management according to an embodiment of the present invention. CU 302 connects to DUs 303 and 304 through the F1 interface. CU 302 includes a protocol stack PDCP 321. The DU 303 includes the protocol stack RLC 331 and MAC 332.DU304 includes protocol stack RLC 341 and MAC 342.DU 303 and DU304 are respectively connected to a plurality of Radio Units (RUs). One cell may consist of a range covered by one or more RUs under the same DU. RU/gNB 381, 382, 383, 384 and 385 are connected to DU 303. RU/gnbs 391, 392, 393, 394 and 395 connect to DU 304. In this scenario, UE 301 moves from one cell edge served by the gNB 382 to another cell served by the gNB 381, where the two cells belong to the same DU and share a common protocol stack. This scenario may employ inter-cell beam management within the DU to replace the traditional handover procedure, thereby reducing outage and improving throughput for the UE. In an embodiment, a single protocol stack (common RLC/MAC) on the UE side may be employed to handle L1/L2 inter-cell beam management with mobility.

Fig. 4 is a schematic diagram of an exemplary deployment scenario for inter-DU inter-cell beam management according to an embodiment of the present invention. CU 402 is connected to DU 403 and DU 404 through an F1 interface. CU 402 includes a protocol stack PDCP 421. The DU 403 includes the protocol stack RLC 431 and MAC 432. The DU 404 includes protocol stacks RLC 441 and MAC 442.DU 403 and DU 404 are connected to the plurality of RUs, respectively. One cell may consist of a range covered by one or more RUs under the same DU. RU/gNB 481, 482, 483, 484 and 485 are connected to DU 403. RU/gNB 491, 492, 493, 494 and 495 are connected to DU 404. In this scenario, UE 401 moves from one cell edge served by the gNB 481 to another cell served by the gNB 491, where the two cells belong to different DUs (DU 403 and DU 404), respectively, and share a common CU 402. The lower user plane (RLC, MAC) in the two DUs is different, while the higher layer (PDCP) remains unchanged. This scenario may employ inter-DU inter-cell beam management to replace the traditional handover procedure, thereby reducing outage and improving UE throughput. In an embodiment, a single protocol stack (common RLC/MAC) on the UE side may be employed to handle L1/L2 inter-cell beam management with mobility. In an embodiment, dual protocol stacks (separate RLC/MAC) on the UE side may be employed to handle L1/L2 inter-cell beam management with mobility.

Fig. 5 is an exemplary diagram of a procedure in which a UE partially resets a MAC entity and maintains TAG from a source cell when the UE side uses a single stack according to an embodiment of the present invention. UE 503 is connected to the gNB 501 in cell 510. The UE 503 performs inter-cell measurements for the target cell 520 served by the gNB 502. UE 503 is configured with a single protocol stack including RLC 512, MAC 511, and PDCP 530. The UE 503 establishes and maintains a cell 1tag 517 of the cell 510. In an embodiment, the cell handover is performed within the same DU. In an embodiment, the cell handover is performed in a different DU. The UE may receive an inter-cell beam management indication when approaching a neighboring cell, such as cell 520. In an embodiment, the UE employs an inter-cell beam management single stack for inter-cell beam management. In an embodiment, the inter-cell beam management indication is a MAC Control Element (CE). When the inter-cell beam management indication is received, the UE establishes a TAG for the target cell, resets the TAG of the MAC entity but retains the TAG of the source cell and maintains the associated TAT of the source cell, and re-establishes the RLC entity and switches to the target cell. After cell handover, UE 503 has a protocol stack including PDCP 530, RLC 522, and MAC 521. TAG 528 of cell 520 may be established and maintained. The TAG 527 of the source cell will be maintained and the TAT will run until it expires.

Fig. 6 is an exemplary diagram of a process in which a UE establishes a new MAC entity and maintains a source MAC entity when the UE side uses dual stacks according to an embodiment of the present invention. UE 603 is connected with a gNB 601 in cell 610. UE 603 performs inter-cell measurements for target cell 620 served by the gNB 602. UE 603 is configured with dual protocol stacks including active PDCP 631, RLC 612, and MAC 611. The UE 603 establishes and maintains a cell 1tag 617 of the cell 610. In an embodiment, cell switching is performed across different DUs. The UE may receive an inter-cell beam management indication when approaching a neighboring cell. In an embodiment, the UE employs dual stacks for inter-cell beam management. In an embodiment, the inter-cell beam management indication is a MAC CE. In an embodiment, the UE 603 establishes a new MAC entity MAC 621b for the target cell in the pre-configuration prior to the inter-cell beam management indication. Upon receiving the inter-cell beam management indication, the UE switches to the target cell with the new MAC entity 621b for data transmission/reception. After cell handover, UE 603 has a dual protocol stack including MAC 621a, RLC 622a, and PDCP 632. The dual protocol stack also includes MAC 621b, RLC 622b for cell 620. The TAG 627 of the source cell will be maintained and the TAT will run until it expires. The TAG 628 corresponding to cell 620 is also maintained in the corresponding protocol stack.

Fig. 7 is an exemplary diagram of a UE retaining TAG of a source cell and performing RA when accessing a target cell for the first time, and skipping RA procedure when switching back to the source cell and switching to the target cell again, according to an embodiment of the present invention. UE 703 is connected to the gNB 701 in cell 1 710. When the UE 703 initially accesses cell 1 710, a cell 1tag 711 is established and maintained. Neighbor cell 2720 is served by the gNB 702. When the UE 703 first accesses cell 2720, a procedure 760 is performed. Upon receiving the inter-cell beam management indication, the ue performs an RA procedure for cell 2720 in step 761. At the same time, in step 762, the TAG 711 of the source cell (cell 1) can be maintained, and the TAT of the TAG 711 remains operational. At step 763, TAG 712 of cell 2 is established after RA is successful. UE 703 is connected to cell 2720. After the RA procedure is successfully completed, cell 2720 is considered to be the source cell.

After the UE 703 connects to cell 2720, a procedure 770 is performed to switch back to cell 1, skipping the RA procedure and maintaining the TAG of cell 2, according to an embodiment of the present invention. The UE 703 receives an inter-cell beam management indication from the network to switch back to cell 1 according to the L1 measurement report 710. At this time, since the UE communicates with the network by way of cell 2, 720 is considered the source cell and cell 1, 710 is considered the target cell. Upon receiving the inter-cell beam management indication to switch back to cell 1, the UE 703 reserves the TAG 712 of the source cell (cell 2) 720 and checks the TAG of the target cell (cell 1) 710 in step 772. In an embodiment, the ue 703 skips the RA procedure for the target cell (cell 1) in step 771 when the associated TAT for cell 1tag 711 is running. The UE then switches to the target cell (cell 1) 710. At the same time, in step 772, the TAG 712 of the source cell (cell 2) 720 is maintained, and the TAT of the TAG 712 remains operational. In step 773, the TAG 711 of the target cell (cell 1) 710 is maintained.

After the UE switches back to cell 1 710, procedure 780 is performed to switch to cell 2 again and skip the RA procedure while preserving the TAG of cell 1. The UE 703 receives an inter-cell beam management indication from the network to switch to the cell 2720 again according to the L1 measurement report. At this time, since the UE relies on cell 1 710 to communicate with the network, cell 2720 is considered the target cell and cell 1 710 is considered the source cell. When receiving the inter-cell beam management indication for the re-handover, the UE reserves TAG 711 of the source cell (cell 1) 710 and checks TAG of the target cell (cell 2). In an embodiment, the UE 703 targets the RA procedure of the target cell (cell 2) when there is a TAG associated with the target cell (i.e., TAG 712) and the associated TAT of TAG 712 is running. The UE 703 skips the RA and switches to the target cell (cell 2) in step 718. In step 782, the ue reserves TAG 712 of cell 2720. Meanwhile, in step 783, the TAG 711 of the source cell (cell 1) 710 is maintained, and the TAT of the TAG 711 is operated as it is.

Fig. 8 is an exemplary overall flow diagram of inter-cell beam management according to an embodiment of the present invention. The UE 801 connects to a wireless network through source DUs 802 and CUs 804. The neighboring cell is served by the target DU 803. In step 811, downlink (DL) user data is transmitted to the source DU 802 and the UE 801 through the CU 804. In step 812, the ue 801 transmits Uplink (UL) user data to the DU 802 and CU 804. The network first provides a pre-configuration 860 before performing inter-cell beam management. In step 861, the ue 801 sends a measurement report to the source DU 802. In step 862, the du 802 transmits measurement reports to the CU 804 through UL RRC messaging. In step 863, the cu 804 sends a UE context setup request to the DU 802. In step 864, the DU 802 sends a UE context setup response to the CU 804. The network provides pre-configuration and prepares target/candidate cells based on UE measurements. In an embodiment, the pre-configuration is performed by an RRC reconfiguration message. In step 865, cu 804 sends a DL RRC message including RRC reconfiguration to DU 802. In step 866, the du 802 sends an RRC reconfiguration message to the UE 801. In an embodiment, the UE establishes a TAG for the target cell upon receiving the RRC configuration of the second cell. In an embodiment, the UE establishes a TAG for the target cell upon receiving the inter-cell beam management indication. In another embodiment, the UE establishes a new MAC entity for the target cell upon receiving the RRC configuration of the second cell. In step 867, the ue 801 transmits an RRC reconfiguration complete message to the DU 802.DU 802 sends UL RRC message including RRC reconfiguration complete message to CU 804.

After the pre-configuration, the ue 801 transmits an L1 measurement report to the network through the DU 802 in step 821. If an inter-cell beam management indication is received, the UE reserves the TAG of the source cell and checks the TAT of the TAG associated with the target cell. In an embodiment, if the TAT of the TAG associated with the target cell is not running, process 870 is performed to handover the cell to the target cell that has no valid TAG. In step 871, the source DU 802 sends a cell switch indication to the UE 801 through the MAC CE. In step 872, the DU 802 sends a DL data delivery state cell switch message to the CU 804. At step 873, cu 804 sends a cell switch indication to target DU 803. In step 874, the ue performs a random access procedure for the target cell. In step 875, the target DU 803 sends the DL data delivery state to the CU 804. In step 876, the target DU 803 sends an access success message to the CU 804.UE 801 now switches to target DU 803.

In step 817, the cu 804 transmits DL user data to the UE 801 through the DU 803. In step 818, the ue 801 transmits UL user data to the DU 803. In step 822, the ue 801 transmits an L1 measurement report to the DU 803. If the TAT of the TAG associated with the target cell is running, process 880 may skip RA execution. In step 881, the DU 803, now the source DU, sends a cell switch indication to the UE 801 through the MAC CE. Upon receiving the inter-cell beam management indication, the UE 801 skips the RA procedure and switches to the target cell served by the DU 802 if it determines that the TAG associated with the DU 802 (target cell) is valid. In step 882, the DU 803 sends the DL data delivery status to the CU 804. In step 883, cu 804 sends a cell switch indication to DU 802. In step 884, DU 802 sends the DL data delivery state to CU 804.UE 801 now switches back to DU 802. At step 891, cu 804 sends a UE context release command to DU 802. At step 892, the du 802 sends a UE context release complete message to the CU 804.

Fig. 9 is an exemplary flow diagram for inter-cell beam management by a UE over single and dual stacks in accordance with an embodiment of the present invention. In an embodiment, the cell handover is performed within the same DU. In an embodiment, cell switching is performed across different DUs. Prior to cell handover, the UE performs a pre-configuration procedure 910. For a single stack UE, the UE receives an RRC reconfiguration message indicating a cell handover for single stack based pre-configuration of inter-cell beam management in step 911. In step 912, the ue establishes a TAG for the target cell and pre-configures for cell handover. For dual stack UEs, the UE receives an RRC reconfiguration message indicating a cell handover for dual stack based pre-configuration of inter-cell beam management in step 961. In step 962, the ue establishes a MAC entity for a target cell and performs pre-configuration for cell handover.

In step 921, for a single stack UE, the UE reports L1 measurements to the network after pre-configuration. In step 922, the ue receives an inter-cell beam management indication. In step 971, for a dual stack UE, the UE reports L1 measurements to the network after pre-configuration. In step 972, the ue receives an inter-cell beam management indication. A process 970 may be performed to maintain the source TAG when performing a cell handover. For a single stack UE, in step 923, the UE performs a partial MAC reset, which maintains the TAG of the source cell and maintains the associated TAT. For dual stack UEs, the UE reserves the MAC of the source cell and the source TAG and keeps the TAT of the source TAG running in step 973. In procedure 930, the ue performs a cell handover with or without RA based on the state of the target TAG. In step 931, the ue checks the TAT of the TAG associated with the target cell. In an embodiment, in step 932, the UE performs random access for the target cell if the UE first accesses the target cell or if the TAT of the TAG associated with the target cell is not running. And after RA is successful, the UE is switched to the target cell. If the TAT of the TAG of the target cell is running, the UE skips the RA procedure and directly switches to the target cell in step 933.

Fig. 10 is an exemplary flow chart of TA acquisition and maintenance for mobility under inter-cell beam management in accordance with an embodiment of the present invention. In step 1001, the ue maintains a plurality of TAGs, wherein each TAG is associated with a cell and a TAT. In step 1002, the UE receives an inter-cell beam management indication to handover from a first cell to a second cell, wherein the UE is connected to the first cell by a first cell TAG associated with the first cell. In step 1003, upon receiving an inter-cell beam management indication indicating handover, the ue determines whether a TAG associated with the second cell is valid. In step 1004, when the UE determines that the second cell TAG associated with the second cell is valid, the UE performs cell handover to the second cell, skipping the RA procedure.

In one embodiment, a storage medium (e.g., a computer-readable storage medium) stores a program that, when executed, causes a UE to perform embodiments of the present invention.

Although the invention has been described in connection with specific embodiments for purposes of illustration, the invention is not limited thereto. Accordingly, various modifications, adaptations, and combinations of the various features of the described embodiments can be practiced without departing from the scope of the invention as set forth in the claims.

Claims

1. A method of timing advance acquisition and maintenance, comprising:

maintaining, by the user equipment, a plurality of timing advance groups, TAGs, wherein each TAG is associated with a cell and a timing advance timer, TAT;

receiving an inter-cell beam management indication to switch from a first cell to a second cell, wherein the user equipment is connected to the first cell by a first cell TAG associated with the first cell;

determining, upon receipt of the inter-cell beam management indication indicating handover, whether a TAG associated with the second cell is valid; and

when the user equipment determines that a second cell TAG associated with the second cell is valid, the user equipment performs a cell handover to the second cell, bypassing a random access RA procedure.

2. The method of timing advance acquisition and maintenance of claim 1 wherein the second cell TAG is determined to be valid when the second cell TAG is present and the TAT of the second cell TAG is running.

3. The method of timing advance acquisition and maintenance of claim 1, further comprising: RA is performed for the second cell when the user equipment determines that there is no TAG associated with the second cell or when TAT of the second cell TAG expires.

4. The method of timing advance acquisition and maintenance of claim 3, further comprising: the second cell TAG associated with the second cell is established and maintained when the RA performed for the second cell is successful.

5. The method of timing advance acquisition and maintenance of claim 1, wherein a TAG is established for the first cell when a radio resource control configuration for the first cell is received.

6. The method of timing advance acquisition and maintenance of claim 1, wherein the first cell and the second cell belong to the same cell group.

7. The method of timing advance acquisition and maintenance of claim 6, wherein performing the cell handover comprises performing a partial medium access control reset and maintaining a TAT associated with the first cell.

8. The method of timing advance acquisition and maintenance of claim 1, wherein the first cell and the second cell belong to different cell groups.

9. The method of timing advance acquisition and maintenance of claim 1, further comprising: and establishing a medium access control entity for the second cell.

10. The method of timing advance acquisition and maintenance of claim 1 wherein uplink timing advances of the first cell TAG and the second cell TAG are maintained independently.

11. A user equipment, comprising:

a transceiver for transmitting and receiving radio frequency signals in a wireless network;

a timing advance group TAG recording module for maintaining a plurality of TAGs, wherein each TAG is associated with a cell and a timing advance timer TAT;

an inter-cell management module configured to receive an inter-cell beam management indication to switch from a first cell to a second cell, wherein the user equipment is connected to the first cell by a first cell TAG associated with the first cell;

a TAG control module for determining, upon receipt of the inter-cell beam management indication indicating handover, whether a TAG associated with the second cell is valid; and

and a cell switching controller, configured to skip a random access RA procedure to perform cell switching to the second cell when the user equipment determines that a second cell TAG associated with the second cell is valid.

12. The user device of claim 11, wherein the second cell TAG is determined to be valid when the second cell TAG is present and the TAT of the second cell TAG is running.

13. The user device of claim 11, wherein the user device performs RA for the second cell when it is determined that there is no TAG associated with the second cell or when TAT for the second cell TAG expires.

14. The user device of claim 13, wherein the user device establishes and maintains the second cell TAG associated with the second cell when the RA performed for the second cell is successful.

15. The user equipment of claim 11, wherein a TAG is established for the first cell when a radio resource control configuration for the first cell is received.

16. The user device of claim 11, wherein the first cell and the second cell belong to the same cell group.

17. The user equipment of claim 16, wherein performing the cell handover comprises performing a partial medium access control reset and maintaining a TAT associated with the first cell.

18. The user device of claim 11, wherein the first cell and the second cell belong to different cell groups.

19. The user equipment of claim 11, wherein the user equipment establishes a medium access control entity for the second cell.

20. The user device of claim 11, wherein uplink timing advances for the first cell TAG and the second cell TAG are maintained independently.

21. A storage medium storing a program which, when executed, causes a user equipment to perform the steps of the method of timing advance acquisition and maintenance of any of claims 1-10.