CN118474818A

CN118474818A - Method, user equipment and storage medium for cell change in wireless network

Info

Publication number: CN118474818A
Application number: CN202410102729.3A
Authority: CN
Inventors: 王苗; 余仓纬
Original assignee: MediaTek Singapore Pte Ltd
Current assignee: MediaTek Singapore Pte Ltd
Priority date: 2023-02-08
Filing date: 2024-01-24
Publication date: 2024-08-09
Also published as: WO2024164185A1

Abstract

The embodiment of the invention provides a method, user equipment and storage medium for cell change in a wireless network, wherein the method comprises the following steps: receiving, by a user equipment, a cell change command from the wireless network, wherein the cell change command indicates a handover from a source cell to a target cell; performing downlink synchronization for the target cell prior to performing one or more of user equipment layer 1/layer 2/layer 3 processing procedures, wherein the user equipment layer 1/layer 2/layer 3 processing procedures include layer 2 reconfiguration, layer 3 reconfiguration, radio frequency retuning, baseband retuning, and security updates; and switching to the target cell after performing one or more of the user equipment layer 1/layer 2/layer 3 processing procedures. By utilizing the invention, the cell change process can be enhanced.

Description

Method, user equipment and storage medium for cell change in wireless network

[ Field of technology ]

The present invention relates to wireless communications, and more particularly to a cell change procedure.

[ Background Art ]

In a wireless communication system, mobility performance is a very important indicator. Researchers are striving to reduce handoff delays and interruptions. The shorter the delay and interruption, the less data is lost. In order to reduce the handover delay, mobility of layer 1 (layer 1, L1)/L2 triggers is designed. In L1/L2 triggered mobility, cell handover delay and data interruption time can be reduced by pre-synchronizing a target cell Downlink (DL). In the current process, after receiving a handover command or a cell handover command, a User Equipment (UE) L1/L2/L3 process is first performed, including L2/L3 reconfiguration, radio frequency retuning (RF retuning,), baseband retuning (baseband retuning), security update (if needed), and the like. The UE will then perform downlink synchronization on the target cell if needed. Next, uplink (UL) synchronization is performed on the target cell, if necessary. The interrupt starts with the UE L1/L2/L3 processing. Although the UE will pre-synchronize the downlink of the target cell for L1/L2 trigger based mobility, the UE may still need to perform downlink synchronization on the target cell before data reception due to mobility of the UE and channel condition variation. The data interrupt starts when the UE performs L1/L2/L3 processing. The data interruption time includes a time of waiting for a reference signal for downlink synchronization.

Cell change procedures require improvement and enhancement.

[ Invention ]

The embodiment of the invention provides a method for changing a cell in a wireless network, which comprises the following steps: receiving, by a user equipment, a cell change command from the wireless network, wherein the cell change command indicates a handover from a source cell to a target cell; performing downlink synchronization for the target cell prior to performing one or more of user equipment layer 1/layer 2/layer 3 processing procedures, wherein the user equipment layer 1/layer 2/layer 3 processing procedures include layer 2 reconfiguration, layer 3 reconfiguration, radio frequency retuning, baseband retuning, and security updates; and switching to the target cell after performing one or more of the user equipment layer 1/layer 2/layer 3 processing procedures.

The embodiment of the invention provides user equipment, which comprises the following steps: a transceiver for transmitting and receiving radio frequency signals in a wireless network; a command module for receiving a cell change command from the wireless network, wherein the cell change command indicates a handover from a source cell to a target cell; a process controller for performing downlink synchronization for the target cell prior to performing one or more of a user equipment layer 1/layer 2/layer 3 processing process, wherein the user equipment layer 1/layer 2/layer 3 processing process includes layer 2 reconfiguration, layer 3 reconfiguration, radio frequency retuning, baseband retuning, and security update; and a cell switching module for switching to the target cell after performing one or more of the ue layer 1/layer 2/layer 3 processing procedures.

An embodiment of the present application provides a storage medium storing a program that, when executed, causes an apparatus to perform the steps of the present application of performing a method for cell change in a wireless network.

This summary is not intended to define the invention. The invention is defined by the claims.

[ Description of the drawings ]

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

Fig. 1A is a system diagram of an exemplary wireless network with an enhanced cell change procedure in accordance with an embodiment of the present invention.

Fig. 1B is a diagram of an exemplary UE and base station for enhancing cell change in accordance with an embodiment of the present invention.

Fig. 2 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. 3 is an exemplary deployment scenario for intra-DU inter-cell beam management according to an embodiment of the present invention.

Fig. 4 is 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 conventional cell change procedure based on a random access channel.

Fig. 6 is an exemplary diagram of a RACH-based cell change procedure performed after UE processing according to an embodiment of the present invention.

Fig. 7 is an exemplary diagram of a RACH-based cell change procedure performed by RACH prior to UE processing in accordance with an embodiment of the present invention.

Fig. 8 is an exemplary diagram of a conventional cell change procedure without RACH.

Fig. 9 is an exemplary diagram of an enhanced RACH-free cell handover procedure according to an embodiment of the present invention.

Fig. 10 is an exemplary flow chart of an enhanced cell handover procedure according to an embodiment of the invention.

[ Detailed description ] of the invention

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

Fig. 1A is a system diagram of an exemplary wireless network with an enhanced cell change procedure in accordance with an embodiment of the present 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, the UE or mobile station 112 is located only in the service area of the gNB 101 and is connected with the gNB 101.UE 112 connects only to 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 gnbs 101, 102, and 103 are connected to the network through NG connections (e.g., 136, 137, and 138), respectively, through network entities (e.g., network entity 106). Xn connections 131 and 132 connect non-collocated receive base units. Xn connection 131 connects gNB 101 and gNB 102.Xn connection 132 connects gNB 102 and gNB 103. These Xn/NG connections may be ideal or non-ideal.

In an example, the enhanced cell change procedure, the UE processing procedure is performed after the downlink synchronization procedure. Fig. 170 illustrates an exemplary conventional cell change procedure. In step 171, the ue receives an RRC reconfiguration message including the candidate cell. The UE processes the RRC message for a time T _RRC, about 10ms. In step 172, the ue transmits an L1 measurement report based on the pre-configuration message. In step 175, the ue receives a cell handover command. The time for the UE to process the cell switch command is T _cmd, which typically is approximately T _HARQ +3ms, where T _HARQ is the time between the cell switch command and the acknowledgement of receipt of the command to the network. In the current system, after receiving the cell handover command, the UE performs the UE processing procedure for a period of about 20ms, which is T _processing. The UE processing procedure begins with an interrupt. Furthermore, although the UE may perform downlink synchronization including time frequency (T/F) tracking (tracking) before the cell handover command, the UE needs to perform T/F tracking again after receiving the cell handover command, which is T _Δ+T_MARGIN, where T _Δ is about 20ms and T _MARGIN is about 2ms. Before random access is performed in step 176, UL synchronization is performed for a time T _IU, which is approximately 15ms. For the exemplary legacy cell change procedure, the interrupt time 178 is the sum of T _PROCESSING、T_Δ+T_MARGIN and T _IU.

In one example, downlink synchronization is performed prior to the UE processing procedure to reduce interruption time. Fig. 180 illustrates an exemplary timeline for an enhanced cell change procedure. In step 181, the ue receives an RRC reconfiguration message including the candidate cell. The UE processes the RRC message for a time T _RRC, about 10ms. In step 182, the ue transmits an L1 measurement report based on the pre-configuration message. In step 185, the ue receives a cell handover command. The time for the UE to process the cell handover command is T _cmd, about 3ms. After receiving the cell switch command, the UE first performs a downlink synchronization procedure, including T/F tracking, for a time T _Δ+T_MARGIN. Subsequently, the UE processing procedure is started with an interrupt. Before random access is performed in step 186, UL synchronization is performed for a time T _IU, which is approximately 15ms. For the exemplary enhanced cell change procedure, the interrupt time 188 is the sum of T _PROCESSING and T _IU.

Fig. 1B is a diagram of an exemplary UE and base station for enhancing cell change in accordance with an embodiment of the present invention. Fig. 150 is an exemplary simplified block diagram of a base station/gNB. The base station has an antenna 156 which 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 signal and invokes different functional modules to perform functional features in the base station. Memory 151 stores program instructions and data 154 to control the operation of the base station. The base station also includes a set of control modules 155 for performing functional tasks to communicate with the mobile station.

Fig. 160 is a simplified block diagram of a mobile device/UE for enhancing cell change. The UE has an antenna 165 to send and receive 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) for transmission and reception of different frequency bands. 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. Memory 161 stores program instructions and data 164 to control the operation of the UE. The antenna 165 sends uplink transmissions to the base station's antenna 156 and receives downlink transmissions from the base station's antenna 156.

The UE 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 command module 191 receives a command for a cell change from the wireless network, wherein the command for the cell change indicates a handover from a source cell to a target cell. The process controller 192 performs downlink synchronization on the target cell and then performs one or more of the UE L1/L2/L3 processing procedures including L2 reconfiguration, L3 reconfiguration, radio frequency retuning, baseband retuning, and security updates. The cell switching module 193 is configured to switch to the target cell after performing one or more of the UE L1/L2/L3 processing procedures.

Fig. 2 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. Different protocol split options are possible between Central Units (CUs) and Distributed Units (DUs) of the gNB node. 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 service data adaptation protocol (SERVICE DATA adaptation protocol, SDAP) and packet data convergence protocol (PACKET DATA convergence protocol, PDCP) layers are located at the central unit, while the radio link control (radio link control, RLC), medium access control (medium access control, MAC) layer and Physical (PHY) layer are located at the distributed units. 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 one embodiment, the gNB lower layer 251 includes Physical (PHY), MAC and RLC layers.

Fig. 3 is an exemplary deployment scenario for intra-DU inter-cell beam management according to an embodiment of the present invention. CU 302 is connected to two DUs 303 and 304 through an F1 interface. CU 302 includes a protocol stack PDCP layer 321. The DU 303 includes a protocol stack RLC layer 331 and a MAC layer 332. The DU 304 includes a protocol stack RLC layer 341 and a MAC layer 342.DU 303 and DU 304 are respectively connected to a plurality of Radio Units (RUs). A 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 with DU 304. In this scenario, UE 301 moves from the edge of one cell served by the gNB 382 to another cell served by the gNB 381, both belonging to the same DU and sharing a common protocol stack. In this scenario, intra-DU inter-cell beam management may be used instead of traditional handover procedures, thereby reducing disruption and improving UE throughput and handover reliability (which may be measured by the UE's handover failure rate). In an embodiment, a single protocol stack (common RLC/MAC) on the UE side is used to handle L1/L2 inter-cell beam management with mobility.

Fig. 4 is an exemplary deployment scenario for inter-DU inter-cell beam management according to an embodiment of the present invention. CU 402 is connected to two DUs through the F1 interface: DU 403 and DU 404.CU 402 includes a protocol stack PDCP layer 421. The DU 403 includes a protocol stack RLC layer 431 and a MAC layer 432. The DU 404 includes a protocol stack RLC layer 441 and a MAC layer 442.DU 403 and DU 404 are connected to the plurality of RUs, respectively. A 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 the edge of one cell served by the gNB 481 to another cell served by the gNB 491, which belong to different DUs: DU 403 and DU 404, and share a common CU 402. The lower layer user plane (RLC, MAC) in the two DUs is different while the higher layer (PDCP) remains the same. In this scenario, inter-DU inter-cell beam management may be used instead of traditional handover procedures, thereby reducing outage and improving UE throughput and handover reliability (which may be measured by the UE's handover failure rate). In an embodiment, a single protocol stack (common RLC/MAC) on the UE side is used to handle L1/L2 inter-cell beam management with mobility. In an embodiment, a dual protocol stack (separate RLC/MAC) on the UE side is used to handle L1/L2 inter-cell beam management with mobility.

Fig. 5 is an exemplary diagram of a conventional cell change procedure based on a Random Access Channel (RACH) ACCESS CHANNEL. In step 511, the ue receives a command for a cell change. After some necessary decoding of the command, the UE performs one or more L1/L2/L3 processing procedures, including L2 and/or L3 reconfiguration, and/or radio frequency retuning, and/or baseband retuning, and/or security updates, etc., at step 521. In step 522, the ue performs downlink synchronization on the target cell and then transmits PRACH to the target cell, if necessary. The interruption time starts from step 521, i.e. the UE performs one or more L1/L2/L3 processing procedures, and ends at step 523, i.e. the UE transmits PRACH to the target cell. In step 531, the ue receives a random access response (random access response, RAR). As shown, the conventional cell change procedure has a long interruption time including UE processing time, downlink synchronization time, and PRACH transmission time.

Fig. 6 is an exemplary diagram of a RACH-based cell change procedure performed after UE processing according to an embodiment of the present invention. The UE receives a command for a cell change. In one embodiment 611, the command for a cell change is a cell switch command. In one embodiment, the cell switch command is received through a MAC Control Element (CE). In another embodiment 615, the UE receives a conditional handover command at step 616. At step 617, at least one condition is satisfied. When at least one condition is met, a command for a cell change is triggered in step 617. After some necessary processing of the decode command or detection condition, the UE first performs downlink synchronization to the target cell in step 612. No interruption is generated when the downlink synchronization process starts. Upon receiving the reference signal (REFERENCE SIGNAL, RS) for downlink synchronization, an interrupt 618 may occur. In step 621, the UE performs one or more L1/L2/L3 processing procedures. The L1/L2/L3 processing process 650 includes an L2 reconfiguration 651, and/or an L3 reconfiguration 652, and/or a radio frequency retuning 653, and/or a baseband retuning 654, and/or a security update 655, etc. In step 622, the UE transmits the PRACH to the target cell, if needed. The interrupt time 601 begins at step 621, i.e., the UE performs one or more L1/L2/L3 processing procedures, and ends at step 622, i.e., the UE transmits the PRACH to the target cell.

Fig. 7 is an exemplary diagram of a RACH-based cell change procedure performed by RACH prior to UE processing in accordance with an embodiment of the present invention. The UE receives a command for a cell change. In an embodiment 711, the command for a cell change is a cell handover command. In an embodiment, the cell switch command is received by the MAC CE. In another embodiment 715, the UE receives the conditional handover command in step 716. At step 717, at least one condition is satisfied. When at least one condition is met, a command for a cell change is triggered in step 717. After some necessary processing of the decode command or detection condition, the UE first performs downlink synchronization to the target cell at step 712. Upon receiving the RS for downlink synchronization, a break 718 may occur. In step 713, the UE transmits the PRACH to the target cell, if necessary. An interrupt 719 may occur due to the transmission of the PRACH. In step 721, the ue performs one or more of L1/L2/L3 processing procedures, wherein the L1/L2/L3 processing procedures include L2 reconfiguration, L3 reconfiguration, radio frequency retuning, baseband retuning, security updates, and the like. The interrupt time 701 starts from step 721, i.e. the UE performs one or more of the L1/L2/L3 processing procedures, and ends at step 731, i.e. the UE starts RAR reception.

Fig. 8 is an exemplary diagram of a conventional cell change procedure without RACH (RACH-less). In step 811, the ue receives a command for a cell change. After some necessary processing to decode the command, the ue performs one or more L1/L2/L3 processing procedures including one or more of L2 reconfiguration, L3 reconfiguration, radio frequency retuning, baseband retuning, security update, etc., at step 812. In step 813, the ue performs downlink synchronization to the target cell. The interrupt time 801 starts when the UE performs one or more L1/L2/L3 processing procedures, step 812, and ends before the target cell transceives, step 813, after the UE completes downlink synchronization for the target cell. In step 814, the ue starts transceiving in the target cell.

Fig. 9 is an exemplary diagram of an enhanced RACH-free cell handover procedure according to an embodiment of the present invention. The UE receives a command for a cell change. In an embodiment 911, the command for a cell change is a cell handover command. In an embodiment, the cell switch command is received by the MAC CE. In another embodiment 915, the UE receives a conditional handover command at step 916. At step 917, at least one condition is satisfied. When at least one condition is met, a cell change is triggered in step 917. In step 912, the ue first performs downlink synchronization on the target cell after performing some necessary decoding process on the command. In step 921, the ue performs one or more L1/L2/L3 processing procedures including one or more of L2 reconfiguration, L3 reconfiguration, radio frequency retuning, baseband retuning, security updates, and the like. The interrupt time 901 starts in step 912, i.e. the UE performs one or more L1/L2/L3 processing procedures, and ends before the target cell transceives after the UE completes processing. There may also be some interruption 918 in step 912 due to receiving the downlink synchronization reference signal of the target cell.

Fig. 10 is an exemplary flow chart of an enhanced cell handover procedure according to an embodiment of the invention. In step 1001, the ue receives a command for a cell change from a wireless network, wherein the command for the cell change indicates a handover from a source cell to a target cell. In step 1002, the UE performs downlink synchronization on the target cell before performing one or more of the UE L1/L2/L3 processing procedures including L2 reconfiguration, L3 reconfiguration, radio frequency retuning, baseband retuning, and security updates. In step 1003, the UE switches to the target cell after performing one or more of the UE L1/L2/L3 processing procedures.

While the invention has been described with respect to preferred embodiments, it is not intended to limit the invention thereto. Various modifications, adaptations, and combinations of the features of the embodiments can be made without departing from the scope of the invention as defined in the claims.

Claims

1. A method for cell change in a wireless network, comprising:

receiving, by a user equipment, a cell change command from the wireless network, wherein the cell change command indicates a handover from a source cell to a target cell;

performing downlink synchronization for the target cell prior to performing one or more of user equipment layer 1/layer 2/layer 3 processing procedures, wherein the user equipment layer 1/layer 2/layer 3 processing procedures include layer 2 reconfiguration, layer 3 reconfiguration, radio frequency retuning, baseband retuning, and security updates; and

After performing one or more of the user equipment layer 1/layer 2/layer 3 processing procedures, a handover is made to the target cell.

2. The method for cell change in a wireless network of claim 1, wherein the cell change command is a cell handover command.

3. The method for cell change in a wireless network of claim 2, wherein the user device receives a pre-configuration of candidate cells from the wireless network before receiving the cell switch command.

4. The method for cell change in a wireless network of claim 2, wherein the user equipment performs downlink synchronization after receiving the cell switch command.

5. The method for cell change in a wireless network of claim 2, wherein the cell switch command is carried by a medium access control element.

6. The method for cell change in a wireless network of claim 1, wherein the cell change command is a conditional handover command, and wherein the user equipment performs downlink synchronization on the target cell when at least one handover condition is satisfied.

7. The method for cell change in a wireless network of claim 1, wherein the cell switch procedure is a random access channel RACH based cell switch.

8. The method for cell change in a wireless network of claim 7, wherein the user equipment transmits a physical random access channel, PRACH, on the target cell after receiving the command for cell change and before performing one or more of the user equipment layer 1/layer 2/layer 3 processing procedures.

9. The method for cell change in a wireless network of claim 7, wherein the user equipment transmits PRACH in the target cell after performing one or more of the user equipment layer 1/layer 2/layer 3 processing procedures.

10. The method for cell change in a wireless network of claim 1, wherein the cell handover procedure is a RACH-free cell handover procedure.

11. A user equipment, comprising:

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

A command module for receiving a cell change command from the wireless network, wherein the cell change command indicates a handover from a source cell to a target cell;

A process controller for performing downlink synchronization for the target cell prior to performing one or more of a user equipment layer 1/layer 2/layer 3 processing process, wherein the user equipment layer 1/layer 2/layer 3 processing process includes layer 2 reconfiguration, layer 3 reconfiguration, radio frequency retuning, baseband retuning, and security update; and

And the cell switching module is used for switching to the target cell after one or more of the user equipment layer 1/layer 2/layer 3 processing processes are executed.

12. The user equipment of claim 11 wherein the cell change command is a cell switch command.

13. The user equipment of claim 12 wherein the user equipment receives a pre-configuration of candidate cells from the wireless network prior to receiving the cell switch command.

14. The user equipment of claim 12 wherein the user equipment performs downlink synchronization after receiving the cell switch command.

15. The user equipment of claim 12 wherein the cell switch command is carried by a medium access control element.

16. The user equipment of claim 11, wherein the command for cell change is a conditional handover command, and wherein the user equipment performs downlink synchronization for the target cell when at least one handover condition is satisfied.

17. The user equipment of claim 11, wherein the cell switching procedure is a cell switching based on a random access channel RACH.

18. The user equipment of claim 17, the user equipment transmitting a physical random access channel, PRACH, on the target cell after receiving the command for the cell change and before performing one or more of the user equipment layer 1/layer 2/layer 3 processing procedures.

19. The user equipment of claim 17, wherein the user equipment transmits PRACH at the target cell after performing one or more of the user equipment layer 1/layer 2/layer 3 processing procedures.

20. The user equipment of claim 11, wherein the cell handover procedure is a RACH-free cell handover procedure.

21. A storage medium storing a program which, when executed, causes a user equipment to perform the steps of the method for cell change in a wireless network of any of claims 1-10.