Method for Implementing Cell Switching Procedure and User Equipment

Abstract

PURPOSE: To provide a method for implementing a cell switch procedure and user equipment UE.SOLUTION: A method includes: receiving a cell switch configuration for a cell switch procedure from a source cell, wherein the cell switch configuration comprises an early-uplink synchronization (EUS) configuration for an EUS procedure; performing the EUS procedure based on the EUS configuration to obtain a timing advance (TA) value associated with a target cell and a cell switch command from the source cell; in response to receiving the cell switch command, performing the cell switch procedure to the target cell based on the TA value; and transmitting cell switch complete information to the target cell after completing the cell switch procedure.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates generally to communication mechanisms, and more particularly to a method and user equipment (UE) for performing a cell switching procedure. [Background technology]

[0002] In the new radio (NR) standard, the protocol stack can be understood as an L1 / L2 / L3 structure, where L1 includes the physical (PHY) layer, L2 includes the medium access control (MAC), radio link control (RLC), and packet data convergence protocol (PDCP) layers, and L3 includes the radio resource control (RRC) layer.

[0003] Currently, the serving cell change procedure is triggered by L3 measurements and by L3 signaling triggered mobility. However, the current serving cell change procedure involves a full L2 (and L1) reset, which can lead to high overhead and long interruption times.

[0004] Therefore, to improve the efficiency of the serving cell change procedure, "L1 / L2 triggered mobility" has been proposed for reducing mobility latency.

[0005] Referring to Figures 1A and 1B, Figure 1A illustrates a flow diagram of a serving cell change procedure based on L1 / L2 triggered mobility, and Figure 1B illustrates a timing diagram related to Figure 1A.

[0006] In step S101, the UE receives a candidate target cell configuration (e.g., an RRC message) from a primary cell (PCell), and the UE can measure the signal quality of the candidate target cell. In step S102, the UE provides a measurement report (e.g., an L1 measurement report) to the PCell, where the measurement report can include the measured signal quality of the candidate target cell.

[0007] In this case, the PCell may determine whether there is a suitable target cell to serve the UE based on the received measurement report, and if so, the PCell may send a cell switch command (e.g., L2 signaling (e.g., MAC control element, CE)) to the UE in step S103, requesting the UE to switch to the target cell.

[0008] In FIG. 1B, in response to the cell switch command (indicating the target cell), the UE needs to perform downlink (DL) synchronization and uplink (UL) synchronization, where UL synchronization includes transmitting a random access preamble of a random access (RA) procedure to the target cell. In response to the random access preamble from the UE, the target cell provides a random access response (RAR) to the UE, where the RAR can carry a timing advance (TA) value so that the UE can transmit its UL data to the target cell accordingly.

[0009] As can be seen from Figure 1B, the period from when the UE receives the cell switch command until when the UE transmits the first UL data is called the interruption time, which is the period required for the UE to complete the handover procedure to the target cell.

[0010] To reduce the interruption time, the concept of early RA has been proposed, which is implemented by controlling the UE to perform an RA before receiving a cell switch command.

[0011] Referring to Figures 2A and 2B, Figure 2A shows a flow of a serving cell change procedure based on early RA, and Figure 2B shows a timing diagram of early RA. As can be seen from Figures 2A and 2B, the interruption time of early RA is short compared with that of Figure 1B, but a scheduling gap is also introduced. Here, the scheduling gap is a period during which the serving cell cannot schedule the UE. Summary of the Invention [Problem to be solved by the invention]

[0012] Therefore, it is beneficial for engineers in the field to design a mechanism that can apply early RA and at the same time shorten the scheduling gap. [Means for solving the problem]

[0013] Therefore, the present invention relates to a method for implementing a cell switching procedure and a UE that can be used to solve the above technical problems.

[0014] An embodiment of the present invention is applied to a user equipment (UE) and provides a method for performing a cell switch procedure, including: receiving, by the UE, a cell switch configuration for a cell switch procedure from a source cell, where the cell switch configuration includes an EUS configuration for an early-uplink synchronization (EUS) procedure; performing, by the UE, the EUS procedure based on the EUS configuration to obtain a Timing Advance (TA) value related to a target cell and a cell switch command from the source cell; when receiving the cell switch command, in response thereto, performing, by the UE, the cell switch procedure to the target cell based on the TA value; and after completing the cell switch procedure, sending, by the UE, cell switch completion information to the target cell.

[0015] An embodiment of the present invention provides a user equipment (UE) including a transceiver and a processor, the processor is coupled to the transceiver and controls the transceiver to receive a cell switch configuration for a cell switch procedure from a source cell, the cell switch configuration including an EUS configuration for an Early Uplink Synchronization (EUS) procedure, perform the EUS procedure based on the EUS configuration to obtain a Timing Advance (TA) value related to a target cell and a cell switch command from the source cell, when receiving the cell switch command, in response thereto, perform a cell switch procedure to the target cell based on the TA value, and control the transceiver to send cell switch completion information to the target cell after completing the cell switch procedure.

[0016] An embodiment of the present invention is applied to a source cell and provides a method for performing a cell switch procedure, including: sending, by the source cell, a cell switch configuration for the cell switch procedure to a user equipment (UE), where the cell switch configuration includes an EUS configuration for the UE to perform an early uplink synchronization (EUS) procedure; and, in response to determining that a target cell has provided a timing advance (TA) value during the EUS procedure, sending, by the source cell, a cell switch command to the UE, where the cell switch command controls the UE to perform a cell switch procedure to the target cell based on the TA value provided by the target cell in the EUS procedure. Effect of the Invention

[0017] Therefore, embodiments of the present invention can be used to shorten the scheduling gap and reduce latency. [Brief description of the drawings]

[0018] The accompanying drawings are included to provide a further understanding of the principles of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

[0019] [Figure 1A] 1 illustrates a flow chart of a serving cell change procedure based on L1 / L2 triggered mobility. [Figure 1B] 1B shows a timing diagram related to FIG. 1A. [Figure 2A] 1 shows a flow chart of a serving cell change procedure based on early RA. [Figure 2B] A timing diagram of early RA is shown. [Diagram 3] 1 is a functional block diagram of a communication device according to an embodiment of the present invention; [Figure 4] 1 shows a schematic diagram of an EUS procedure according to an embodiment of the present invention. [Diagram 5] 2 illustrates a flowchart of a method for performing a cell switching procedure according to an embodiment of the present invention. [Figure 6A] 1 illustrates a flow chart of a method for implementing a cell switching procedure according to an embodiment of the present invention. [Figure 6B] 6B illustrates a method flow for implementing a cell switching procedure based on FIG. 6A. [Figure 7A] 4 illustrates different scenarios when an EUS failure (EUSF) timer is applied by a source cell according to an embodiment of the present invention. [Figure 7B] 4 illustrates different scenarios when an EUS failure (EUSF) timer is applied by a source cell according to an embodiment of the present invention. [Figure 7C] 4 illustrates different scenarios when an EUS failure (EUSF) timer is applied by a source cell according to an embodiment of the present invention. [Figure 8A] 4 illustrates different scenarios when an EUSF timer is applied by a UE according to an embodiment of the present invention. [Figure 8B] 4 illustrates different scenarios when an EUSF timer is applied by a UE according to an embodiment of the present invention. [Figure 8C] 4 illustrates different scenarios when an EUSF timer is applied by a UE according to an embodiment of the present invention. [Figure 9] 2 illustrates a flowchart of a method for performing a cell switching procedure according to an embodiment of the present invention. [Figure 10] 1 illustrates a scenario when an EUS timer according to an embodiment of the present invention is applied. [Figure 11] 13 illustrates a flowchart for verifying a TA value before performing a cell switching procedure according to an embodiment of the present invention. [Figure 12] 2 illustrates a flowchart of a method for performing a cell switching procedure according to an embodiment of the present invention. [Figure 13]13 illustrates a flowchart for verifying a TA value before performing a cell switching procedure according to an embodiment of the present invention. [Figure 14] 2 illustrates a flowchart of a method for performing a cell switching procedure according to an embodiment of the present invention. [Figure 15] 2 illustrates a flowchart of a method for performing a cell switching procedure according to an embodiment of the present invention. [Figure 16] 2 illustrates a flowchart of a method for performing a cell switching procedure according to an embodiment of the present invention. [Figure 17A] 1 illustrates a scenario in which CTCG information is implicit according to an embodiment of the present invention. [Figure 17B] 1 illustrates a scenario in which CTCG information is explicitly indicated according to an embodiment of the present invention. [Figure 18] 2 illustrates a flowchart of a method for performing a cell switching procedure according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings, in which the same reference numerals are used to refer to the same or similar elements throughout the various drawings.

[0021] Please refer to FIG. 3, which shows a functional block diagram of a communication device according to an embodiment of the present invention.

[0022] In FIG. 3, the communication device 300 includes a transceiver 302 and a processor 304. The transceiver 302 can be configured to transmit and receive signals from other devices within its coverage area. The transceiver 302 can perform analog to digital signal conversion (ADC), digital to analog signal conversion (DAC), modulation, demodulation, signal amplification, low-pass filtering, and band-pass filtering. For example, the transceiver 302 is configured to provide information of the received signal to the processor 304, modulate the data received from the processor 304 into a modulated signal, and transmit the modulated signal to other devices.

[0023] In some embodiments, the communications device 300 may further include other components, such as an antenna module, for performing the above-described functions of the transceiver 302 and the processor 304.

[0024] The processor 304 may be coupled to the transceiver 302 and may be, for example, a general purpose processor, a specialized processor, a conventional processor, a digital signal processor (DSP), multiple microprocessors, one or more microprocessors in conjunction with a DSP core, a controller, a microcontroller, Application Specific Integrated Circuits (ASIC), Field Programmable Gate Array (FPGA) circuitry, any other type of integrated circuit (IC), state machine, etc.

[0025] In an embodiment of the present invention, the communication device 300 can be used to implement a device such as a UE and / or a communication node. In some embodiments, the communication node in the present invention can include a source cell, a target cell, etc., and the meaning of each communication node can refer to the specifications of related communication standards (e.g., 3GPP Rel-17 / Rel-18), but the present invention is not limited thereto.

[0026] In an embodiment of the present invention, a mechanism named "Early UL Synchronization (EUS)" procedure is proposed to implement an early RA concept, for example, by a UE to acquire the TA value of a target cell before receiving a cell switch command from the serving cell.

[0027] Referring to Fig. 4, Fig. 4 illustrates a schematic diagram of an EUS procedure according to an embodiment of the present invention. In Fig. 4, the EUS procedure performed by at least one of the UE 410, the source cell 420, and the target cell 430 may illustratively include two stages: (1) an EUS initial stage, and (2) an EUS execution stage.

[0028] In one embodiment, the source cell 420 may be a PCell or a Primary Secondary cell (PSCell) serving the UE 410, and the target cell 430 may be a candidate cell determined to be suitable for handover to the UE 410, but the present invention is not limited thereto.

[0029] In one embodiment, the EUS procedure can be applied to intra-frequency and inter-frequency cell switching cases.

[0030] In one embodiment, the EUS initial stage may be used to configure an EUS procedure for the UE 410 by a source cell 420 (e.g., a PCell or a PSCell). In one embodiment, in the EUS initial stage, the UE 410 may be configured with at least one candidate target cell (CTC) configuration (CTCC) by a CTCC message from the source cell 420.

[0031] In one embodiment, the CTCC may include at least one of the following information for each CTC: (1) MAC, RLC, PHY configuration for each CTC, (2) EUS configuration for each CTC or CTC group (CTCG). In this embodiment, the EUS configuration may include at least one of the following types of information: (1) EUS resource configuration, (2) EUS procedure configuration.

[0032] The EUS resource configuration may include at least one of the following types of information: RACH resource configuration, or sounding reference signal (SRS) resource configuration. The EUS procedure configuration may include at least one of the following types of information: enable EUS configuration, TA validity timer, EUS failure (EUSF) timer, EUS timer, or EUS failure handling configuration (but the invention is not limited thereto).

[0033] In one embodiment, the UE 410 may obtain a TA value associated with the target cell 430 during the EUS execution phase.

[0034] Please refer to FIG. 5, which illustrates a flowchart of a method for implementing a cell switching procedure according to an embodiment of the present invention.

[0035] In step S510, the UE 410 receives a cell switch configuration for a cell switch procedure from the source cell. In step S520, the UE 410 performs an EUS procedure based on the EUS configuration, and obtains a Timing Advance (TA) value related to the target cell and a cell switch command from the source cell 420. In step S530, in response to receiving the cell switch command, the UE 410 performs a cell switch procedure to the target cell 430 based on the TA value. In step S540, the UE 410 transmits cell switch completion information to the target cell 430 after completing the cell switch procedure.

[0036] In various embodiments, the EUS procedure of step S520 may be performed in different ways, the relevant details of which will be described later.

[0037] Please refer to FIG. 6A, which illustrates a flow diagram of a method for implementing a cell switching procedure according to one embodiment of the present invention.

[0038] 6A, in the EUS initial stage, in step S510, the UE 410 can receive a cell switch configuration from the source cell 420. In this case, the cell switch configuration can be carried in a CTCC message from the source cell 420, but the present invention is not limited thereto.

[0039] After obtaining the CTCC from the CTCC message, the UE 410 may perform associated measurements and provide measurement reports to the source cell 420 accordingly.

[0040] In one embodiment, the source cell 420 can determine, based on the measurement report, whether there is a suitable target cell for the UE 410 to perform the cell switch procedure, and if so, the source cell 420 can decide to trigger the EUS execution phase of the EUS procedure.

[0041] In this embodiment, the source cell 420 may send an EUS request to the UE 410 in step S611, where the EUS request includes a candidate configuration index associated with the target cell 430.

[0042] In one embodiment, the EUS request can be used to trigger the UE 410 to perform an EUS procedure to the indicated target cell. The EUS request can include at least ID information of the target cell 430 that is also the target of the EUS procedure. The EUS request can also include uplink resources (e.g., uplink grant) for transmitting the cell switch completion information. The EUS request message can be, but is not limited to, a modified physical DL control channel (PDCCH) command, a new MAC CE, or a newly defined RRC message.

[0043] In an embodiment using a modified PDCCH order to implement an EUS request, a DL control information (DCI) format 1_0 with a cyclic redundancy check (CRC) scrambled by a cell radio network temporary identifier (C-RNTI) may be used for the EUS request. The modified PDCCH order used for the EUS request may carry candidate target cell information that is the target of the EUS procedure.

[0044] In an embodiment where a new MAC CE is used to implement the EUS request, a new logical channel ID (LCID) can be reserved for the EUS request MAC CE. The new MAC CE used in the EUS request can carry candidate target cell information that is the target of the EUS procedure, but the present invention is not limited thereto.

[0045] After receiving an EUS request from the source cell 420 in step S611, the UE 410 may transmit a preamble (e.g., an RA preamble and / or an SRS) to the target cell 430 in step S612 based on resources configured to transmit the preamble.

[0046] After transmitting the preamble, the UE 410 may return to the source cell 420. That is, the UE 410 does not need to wait for a TA value from the target cell 430 after transmitting the preamble.

[0047] In this embodiment, the resource configured to transmit the preamble can be included in the EUS configuration of the CTCC message, but the present invention is not limited thereto. In another embodiment, the resource configured to transmit the preamble can be included in the EUS request (described in FIG. 6B).

[0048] In FIG. 6A, the target cell 430 may determine a TA value associated with the target cell 430 based on the preamble and provide the TA value to the source cell 420 in step S613.

[0049] In one embodiment, if the source cell 420 does not have a CTC EUS resource configuration (e.g., a resource configured to transmit a preamble), the scheduling gap ends after receiving a TA value from the target cell in step S613. In another embodiment, if the source cell 420 has a CTC EUS resource configuration, the scheduling gap ends after the UE transmits a preamble to the target cell 430 in step S612. These two aspects of the scheduling gap can be observed in FIG. 6A.

[0050] After obtaining the TA value from the target cell 430 in step S613, in step S614, the source cell 420 can send a cell switch command (which may carry the TA value associated with the target cell 430) and obtain the TA value associated with the target cell 430 from the cell switch command.

[0051] Depending on the TA value associated with the target cell 430, the UE 410 may accordingly execute step S530. Specifically, the UE 410 may execute step S530 without TA acquisition. The UE 410 may then execute step S540.

[0052] In one embodiment, the UE 410 can obtain an uplink grant from a cell switch configuration or a cell switch command, and send cell switch completion information to the target cell 430 after completing the cell switch procedure based on the uplink grant, but the present invention is not limited thereto.

[0053] Specifically, when the UE 410 executes step S530 without executing TA acquisition, the target cell 430 may not know when the UE 410 has completed the cell switching procedure. Therefore, the UE 410 may transmit cell switching completion information to the target cell 430 to notify the target cell 430 that the UE 410 has completed the cell switching procedure, but the present invention is not limited thereto.

[0054] Referring to Figure 6B, Figure 6B illustrates a flow of a method for implementing a cell switching procedure based on Figure 6A. Different from Figure 6A, when the source cell 420 in Figure 6B decides to trigger the EUS execution phase of the EUS procedure, the source cell 420 can inform the target cell 430 that the EUS execution phase of the EUS procedure has started. In this case, the target cell 430 can reserve an EUS resource as a resource configured to transmit a preamble, and provide an EUS response to the source cell 420. Here, the EUS response can carry the EUS resource.

[0055] Next, the source cell 420 can convey the EUS resources using the EUS request in step S611, so that the UE 410 can transmit a preamble using the EUS resources in step S612, although the present invention is not limited thereto.

[0056] In an embodiment of the present invention, steps S611, S612, and S614 can be understood as belonging to the EUS procedure performed by the UE 410 in step S520, but the present invention is not limited thereto.

[0057] Referring to FIGS. 7A-7C, FIGS. 7A-7C illustrate different scenarios when an EUS failure (EUSF) timer is applied by a source cell according to an embodiment of the present invention.

[0058] In FIG. 7A, the source cell 420 may start an EUS failure (EUSF) timer in response to sending an EUS request in step S711, and may stop the EUSF timer in response to receiving a TA value from the target cell 430 in step S712.

[0059] In this embodiment, if the EUSF timer does not expire before the source cell 420 receives the TA value from the target cell 430, this can indicate that the EUS procedure was successful, and the source cell 420 can then perform step S614 described above.

[0060] On the other hand, if the EUSF timer expires before the source cell 420 receives the TA value from the target cell 430, it may indicate that the EUS procedure has failed. In this case, the source cell 420 may send another EUS request to the UE 410 as shown in Figure 7B, or may send another cell switch command to control the UE 410 to perform a normal cell switch procedure as shown in Figure 7C, but the invention is not limited thereto.

[0061] 8A to 8C, which illustrate different scenarios when an EUSF timer is applied by a UE according to an embodiment of the present invention. In FIG. 8A, the UE 410 can start an EUSF timer in response to receiving an EUS request in step S811, and can stop the EUSF timer in response to receiving a cell switch command from the source cell 420 in step S812.

[0062] In this embodiment, if the EUSF timer does not expire before the UE 410 receives a cell switch command from the source cell 420, this can indicate that the EUS procedure was successful, and the UE 410 can then perform step S530 described above.

[0063] On the other hand, if the EUSF timer expires before the UE 410 receives a cell switch command from the source cell 420, it may indicate that the EUS procedure has failed. In this case, the UE 410 may trigger a connection re-establishment procedure as shown in Figure 8B, or may provide failure information to the source cell 420 as shown in Figure 8C, but the present invention is not limited thereto.

[0064] In an embodiment of the present invention, the EUS execution phase of the EUS procedure in Figures 6A-8C may be understood as being triggered by the source cell 420. In the following embodiment, the EUS execution phase of the EUS procedure may be understood as being triggered by the UE 410, a detailed description of which is provided below.

[0065] Referring to FIG. 9, FIG. 9 illustrates a flowchart of a method for implementing a cell switching procedure according to an embodiment of the present invention.

[0066] 9, in the EUS initial stage, the UE 410 can receive a cell switch configuration from the source cell 420 in step S510. In this case, the cell switch configuration can be carried in a CTCC message from the source cell 420, but the present invention is not limited thereto.

[0067] After obtaining the CTCCs from the CTCC messages, the UE 410 may perform related measurements and determine accordingly whether any of the CTCs meets the EUS conditions.

[0068] In this embodiment, the EUS condition may be included in the EUS configuration, and the EUS condition may be a condition under which the UE 410 can perform an EUS procedure. For example, the UE 410 may determine whether there is a CTC whose measured signal quality is better than a signal quality threshold. If there is, the UE 410 may determine that the CTC meets the EUS condition, but the present invention is not limited thereto.

[0069] From another perspective, the UE 410 may determine a signal quality of each of the at least one target cell. When determining that the signal quality of a first target cell of the at least one target cell satisfies the EUS condition, in response, the UE 410 may determine that the first target cell is the target cell 430 that satisfies the EUS condition, but the present invention is not limited thereto.

[0070] In step S911, the UE 410 may determine that the target cell 430 satisfies the EUS condition. In step S912, in response to determining that the target cell 430 satisfies the EUS condition, the UE 410 may send an EUS indicator to the source cell 420. Here, the EUS indicator may indicate that an EUS procedure has been triggered by the UE 410.

[0071] In one embodiment, the EUS indicator may be used to inform the source cell that the UE 410 will perform EUS to a CTC (e.g., a target cell 430). In some embodiments, the EUS indicator may include an identifier of the target cell 430 that satisfies the EUS condition.

[0072] In one embodiment, the UL resources for transmitting the EUS indicator may be pre-configured by the CTC configuration. In one embodiment, the source cell 420 should not schedule the UE 410 after receiving the EUS indicator.

[0073] In step S913, the UE 410 transmits a preamble (eg, an RA preamble or an SRS) to the target cell 430 that satisfies the EUS condition.

[0074] In step S914, the UE 410 obtains a TA value associated with the target cell 430. In different embodiments, the UE 410 may receive the TA value from the target cell 430 or from the source cell 420, the related details of which will be described later.

[0075] In an embodiment in which the UE 410 receives the TA value from the target cell 430, the UE 410 may further perform step S915 to send an EUS termination indicator to the source cell 420 after receiving the TA value from the target cell 430. Here, the EUS termination indicator indicates that the EUS procedure has ended. Thus, when determining that the EUS termination indicator has been received from the UE 410, in response, the source cell 420 may determine that the target cell 430 has provided a TA value during the EUS procedure. Here, the EUS termination indicator indicates that the EUS procedure has ended. In this case, the source cell 420 should start scheduling the UE 410 after receiving the EUS termination indicator.

[0076] In an embodiment in which the UE 410 receives the TA value from the source cell 420, the UE 410 may not need to send an EUS termination indicator after obtaining the TA value, although related details will be described later.

[0077] In step S916, the UE 410 may receive a cell switch command from the source cell 420. In one embodiment, in an embodiment in which the UE 410 receives a TA value from the target cell 430 in step S914, the cell switch command may not include a TA value. In another embodiment in which the UE 410 receives a TA value from the source cell 420 in step S914, the cell switch command may or may not include a TA value.

[0078] After step S916, steps S530 and S540 can be performed. For related details, reference can be made to the above-mentioned embodiments.

[0079] In an embodiment of the present invention, steps S912, S913, S914 (and S915) can be understood as belonging to the EUS procedure performed by the UE 410 in step S520, but the present invention is not limited thereto.

[0080] Referring to Fig. 10, Fig. 10 illustrates a scenario when applying an EUS timer according to one embodiment of the present invention. In this embodiment, it is assumed that the UE 410 receives a TA value directly from the target cell 430 in step S914a. In one embodiment, step S914a can be understood as a means for implementing step S914, but the present invention is not limited thereto.

[0081] In step S1011, the UE 410 may start an EUS timer in response to sending an EUS indicator to the source cell 420 in step S913, and may stop the EUS timer in response to obtaining a TA value from the target cell 430 in step S1012.

[0082] In this embodiment, an EUS timer is maintained in the UE 410 and is used to detect whether the EUS procedure has failed.

[0083] In one embodiment, when the EUS timer expires or is stopped, the UE 410 returns to the source cell 420 and sends an EUS end indicator to the source cell 420.

[0084] In this embodiment, if the EUS timer does not expire before the UE 410 receives the TA value from the target cell 430, it may indicate that the EUS procedure is successful. In this case, the UE 410 may assist the source cell 420 in selecting the target cell 430 by including the information of the target cell 430 in the EUS termination indicator.

[0085] On the other hand, if the EUS timer expires before the UE 410 receives the TA value from the target cell 430, it may indicate that the EUS procedure has failed. In this case, the UE 410 may indicate that the EUS procedure has failed without including information about the target cell 430 in the EUS termination indicator, but the present invention is not limited thereto.

[0086] In one embodiment, the UE 410 may determine whether the TA value is valid before performing a cell switch procedure to the target cell 430. In response to determining that the TA value is valid, the UE 410 may perform a cell switch procedure to the target cell 430 based on the TA value.

[0087] In one embodiment, when the UE 410 obtains the TA value in step S1013, the UE 410 may responsively start a TA validity timer and determine whether the TA validity timer has expired before performing a cell switch procedure to the target cell 430 based on the TA value.

[0088] In one embodiment, in response to determining that the TA validity timer has not expired prior to performing a cell switch procedure to the target cell 430 based on the TA value, the UE 410 may determine that the TA value is valid and, accordingly, perform a cell switch procedure to the target cell 430 based on the TA value. On the other hand, in response to determining that the TA validity timer has expired prior to performing a cell switch procedure to the target cell 430 based on the TA value, the UE 410 may determine that the TA value is invalid and not perform a cell switch procedure to the target cell 430 based on the TA value.

[0089] In another embodiment, the UE 410 may obtain the TA value and then determine whether the signal quality variation of the target cell 430 exceeds a threshold. In one embodiment, in response to determining that the signal quality variation of the target cell 430 does not exceed a threshold at the time the TA value is obtained, the UE 410 may determine that the TA value is valid and, accordingly, perform a cell switch procedure to the target cell 430 based on the TA value. On the other hand, in response to determining that the signal quality variation of the target cell 430 exceeds a threshold at the time the TA value is obtained, the UE 410 may determine that the TA value is invalid and not perform a cell switch procedure to the target cell 430 based on the TA value.

[0090] In one embodiment, the TA value from the target cell 430 may be carried by the RAR or the new MAC CE. After receiving the TA value, the UE 410 may perform at least one of the following actions: (1) return to the source cell 420, (2) send an EUS termination indicator to the source cell 420, (3) save the TA value, (4) stop the EUS timer, and (5) start the TA validity timer.

[0091] In one embodiment, the UE 410 may also include TA validity timer information in the EUS termination indicator to assist the source cell 420 in verifying the TA validity of the target cell 430, although the present invention is not limited thereto.

[0092] Referring to FIG. 11, FIG. 11 illustrates a flow chart of verifying the TA value before performing a cell switching procedure according to one embodiment of the present invention.

[0093] In Figure 11, after performing steps S914 and S916, the UE 410 can determine whether the TA value is valid in step S1111 based on the above-mentioned mechanism, and determine whether to perform a cell switching procedure accordingly. For details, refer to the above-mentioned embodiments.

[0094] Please refer to FIG. 12, which shows a flowchart of a method for implementing a cell switching procedure according to one embodiment of the present invention.

[0095] 12, in the EUS initial stage, the UE 410 can receive a cell switch configuration from the source cell 420 in step S510. In this case, the cell switch configuration can be carried in a CTCC message from the source cell 420, but the present invention is not limited thereto.

[0096] After obtaining the CTCCs from the CTCC messages, the UE 410 may perform related measurements and determine accordingly whether any of the CTCs meets the EUS conditions.

[0097] Then, steps S911 to S913 can be executed. For related details, reference can be made to the above-mentioned embodiments.

[0098] In this embodiment, it is assumed that the UE 410 receives a TA value associated with the target cell 430 from the source cell 420 in step S914b, where the TA value associated with the target cell 430 is provided by the target cell 430 to the source cell 420 in response to the target cell 430 receiving the preamble in step S1211. In one embodiment, step S914b can be understood as a means for implementing step S914, but the present invention is not limited thereto.

[0099] In this case, after transmitting the preamble, the UE 410 may return to the source cell 420. That is, the UE 410 does not wait for the TA value from the target cell after transmitting the preamble.

[0100] In this embodiment, the source cell 420 may use the new MAC CE to provide the TA value to the UE 410. In one embodiment, the UE 410 may store the TA value after receiving it from the source cell 420.

[0101] In one embodiment, upon determining that a TA value has been received from the target cell 430, in response the source cell 420 may determine that the target cell 430 provided a TA value during the EUS procedure and may provide the TA value to the UE 410 in step S914b.

[0102] 12, when the UE 410 obtains the TA value in step S1013, the UE 410 starts a TA validity timer in response thereto, and determines whether the TA validity timer expires before performing a cell switching procedure to the target cell 430 based on the TA value. For related details, reference may be made to the above-mentioned embodiments.

[0103] Referring to FIG. 13, FIG. 13 illustrates a flow chart of verifying the TA value before performing a cell switching procedure according to one embodiment of the present invention.

[0104] In Fig. 13, after performing steps S911-S913, S914b, and S916, the UE 410 can determine whether the TA value is valid in step S1111 based on the above-mentioned mechanism, and determine whether to perform a cell switching procedure accordingly. For details, refer to the above-mentioned embodiments.

[0105] Referring to Figure 14, Figure 14 illustrates a flowchart of a method for implementing a cell switch procedure according to one embodiment of the present invention. In this embodiment, after the source cell 420 receives a TA value from the target cell 430 in step S1211, the source cell 420 can send a cell switch command to the UE 410 in step S916. Here, the cell switch command can carry a TA value associated with the target cell 430. That is, the UE 410 can obtain the TA value associated with the target cell 430 from the cell switch command.

[0106] Then, the UE 410 can perform steps S530 and S540. For related details, reference can be made to the above-mentioned embodiments.

[0107] In one embodiment, the mechanism by which the UE 410 receives the TA value from the target cell 430 or the source cell 420 may be configured by a waiting flag maintained by the UE 410.

[0108] In one embodiment, in response to determining that the wait flag is enabled, the UE 410 may receive a TA value from the target cell 430. Furthermore, in the event that the wait flag is enabled, in response to determining that the UE 410 has received a TA value from the target cell 430, the UE 410 may notify the source cell 420 that the EUS procedure has ended. For example, the UE 410 may notify the source cell 420 that the EUS procedure has ended by using the EUS end indicator described above, although the present invention is not limited thereto.

[0109] In another embodiment, in response to determining that the wait flag is disabled, the UE 410 may receive a TA value from the source cell 420.

[0110] From another perspective, when the wait flag is enabled, the UE 410 can operate based on the embodiments of Figures 10 and 11. When the wait flag is disabled, the UE 410 can operate based on the embodiments of Figures 12 to 14, but the present invention is not limited thereto.

[0111] Please refer to FIG. 15, which illustrates a flowchart of a method for implementing a cell switching procedure according to one embodiment of the present invention.

[0112] In this embodiment, when the source cell 420 receives the EUS indicator from the UE 410 in step S912, the source cell 420 may notify the target cell 430 that the EUS execution phase of the EUS procedure has begun. In this case, the target cell 430 may reserve EUS resources as resources configured to transmit the preamble, and provide an EUS response to the source cell 420. Here, the EUS response may carry the EUS resources.

[0113] Then, the source cell 420 can carry the EUS resource using the EUS request in step S611, so that the UE 410 can transmit the preamble using the EUS resource in step S913, but the present invention is not limited thereto. After step S913, steps S914 to S916 (step S915 is selectively performed according to whether the UE 410 receives a TA value from the target cell 430) and steps S530 and S540 can be performed. For related details, reference can be made to the above-mentioned embodiments.

[0114] Please refer to FIG. 16, which illustrates a flowchart of a method for implementing a cell switching procedure according to one embodiment of the present invention.

[0115] In this embodiment, if multiple CTCs share the same TA value, these CTCs can be considered to belong to the same CTCG.

[0116] In FIG. 16 , it is assumed that the first target cell 431 and the second target cell 432 belong to the same CTCG, and the UE 410 obtains the TA value associated with the first target cell 431 after transmitting a preamble to the first target cell 431 .

[0117] In this embodiment, when a cell switch command from the source cell 420 controls the UE 410 to perform a cell switch procedure to the second target cell 432, since the first target cell 431 and the second target cell 432 share the same TA value, the UE 410 can perform the cell switch procedure to the second target cell 432 based on the TA value.

[0118] In other words, the UE 410 can perform a cell switching procedure to the second target cell 432 based on the TA value associated with the first target cell 431 without needing to additionally obtain a TA value associated with the second target cell 432, although the present invention is not limited thereto.

[0119] In different embodiments, the information in the CTCG may be indicated explicitly or implicitly.

[0120] Referring to FIG. 17A, FIG. 17A illustrates a scenario in which CTCG information is implicit according to one embodiment of the present invention.

[0121] 17A, the source cell 420 can send a CTCC message to the UE 410 in the EUS initial phase. Here, the CTCC message does not include information of the CTCG. That is, the UE 410 cannot know from the CTCC message which CTCs belong to the same CTCG.

[0122] In this embodiment, if the source cell 420 determines that the first target cell 431 meets the EUS conditions, the source cell 420 can send an EUS request to the UE 410 in step S1711, and the UE 410 can accordingly perform step S1712 and send a preamble to the first target cell 431.

[0123] In response to the preamble, the first target cell 431 may provide the source cell 420 with a TA value associated with the first target cell 431 in step S1713.

[0124] In this embodiment, assuming that after receiving the TA value in step S1713, the source cell 420 decides for some reason to request the UE 410 to perform a cell switch procedure to the second target cell 432 (which belongs to the same CTCG as the first target cell 431), the source cell 420 may send a cell switch command to the UE 410 in step S1714. Here, the cell switch command may request the UE 410 to perform a cell switch procedure to the second target cell 432 based on the TA value associated with the first target cell 431.

[0125] Then, the UE 410 can perform steps S530 and S540. Specifically, in step S530, the UE 410 can perform a cell switching procedure to the second target cell 432 based on a TA value associated with the first target cell 431, but the present invention is not limited thereto.

[0126] In other words, even if UE 410 does not know the CTCG information, since the target cells 430 indicated in the EUS request and the cell switching command are different, UE 410 can implicitly know that the first target cell 431 and the second target cell 432 belong to the same CTCG, but the present invention is not limited to this.

[0127] Referring to FIG. 17B, FIG. 17B illustrates a scenario in which CTCG information is explicitly indicated according to one embodiment of the present invention.

[0128] In Fig. 17B, the source cell 420 can include CTCG information in the CTCC message sent in the EUS initial stage. For example, if the first target cell 431 and the second target cell 432 belong to the same CTCG, the source cell 420 can provide the CTCG identifier in the CTCC message. In this case, the UE 410 can know which CTCs belong to the same CTCG from the CTCC message, but the present invention is not limited thereto.

[0129] In this embodiment, after step S911, the UE 410 may send an EUS indicator to the source cell 420 in step S912, where the EUS indicator may include an identifier of the first target cell 431 and / or an identifier of the CTCG to which the target cell 430 belongs.

[0130] In this case, assuming that the source cell 420 decides for some reason to request the UE 410 to perform a cell switch procedure to the second target cell 432 (belonging to the same CTCG as the first target cell 431) after receiving the EUS end indicator in step S915 or after receiving the TA value from the first target cell 431, the source cell 420 may send a cell switch command to the UE 410 in step S916. Here, the cell switch command may request the UE 410 to perform a cell switch procedure to the second target cell 432 based on the TA value associated with the first target cell 431.

[0131] Then, the UE 410 can perform steps S530 and S540. Specifically, in step S530, the UE 410 can perform a cell switching procedure to the second target cell 432 based on a TA value associated with the first target cell 431, but the present invention is not limited thereto.

[0132] In one embodiment, after the UE 410 receives the cell switch command in step S916, the UE 410 may further perform step S1111 in Fig. 11 to determine whether the TA value is valid. For related details, reference may be made to the above-mentioned embodiments.

[0133] Please refer to FIG. 18, which shows a flowchart of a method for implementing a cell switching procedure according to one embodiment of the present invention.

[0134] In step S1810, the source cell 420 sends a cell switch configuration for a cell switch procedure to the UE, where the cell switch configuration includes an EUS configuration for the UE to perform an EUS procedure.

[0135] In response to determining in step S1820 that the target cell has provided a TA value during the EUS procedure, the source cell 420 transmits a cell switch command to the UE, where the cell switch command controls the UE to perform a cell switch procedure to the target cell based on the TA value provided by the target cell in the EUS procedure.

[0136] For details of each step in FIG. 18, reference can be made to the above-mentioned embodiment, and therefore a repeated description will not be given here.

[0137] As described above, the embodiments of the present invention provide several technical solutions for implementing the concept of early RA, which can be used to shorten the scheduling gap and reduce latency.

[0138] It will be appreciated by those of ordinary skill in the art that various modifications and variations may be made to the disclosed embodiments without departing from the scope or spirit of the invention. In view of this, it is intended that the present invention cover modifications and variations that come within the scope of the following claims and their equivalents. [Industrial Applicability]

[0139] The method for implementing a cell switching procedure and the UE of the present invention can be applied in a communication system. [Explanation of symbols]

[0140] S101-S103, S510-S540, S611-S614, S711, S712, S811, S812, S911-S916, S914a, S914b, S1011-S1013, S1111, S1211, S1711-S1714, S1810, S1820 Steps 300 Communication Devices 302 Transceiver 304 Processor 410 User Equipment (UE) 420 Source Cell 430 Target Cell 431 First Target Cell 432 Second Target Cell

Claims

1. A method for performing a cell switching procedure applied to a user equipment (UE), comprising: receiving, by the UE, a cell switch configuration for the cell switch procedure from a source cell, the cell switch configuration including an Early Uplink Synchronization (EUS) configuration for an EUS procedure; performing, by the UE, the EUS procedure based on the EUS configuration to obtain a Timing Advance (TA) value associated with a target cell and a cell switch command from the source cell; performing, by the UE, upon receiving the cell switch command, in response thereto, the cell switch procedure to the target cell based on the TA value; After completing the cell switching procedure, sending cell switching completion information to the target cell by the UE; The method includes:

2. The EUS procedure comprises: receiving an EUS request from the source cell, the EUS request including a candidate configuration index associated with the target cell; transmitting the preamble to the target cell based on resources configured to transmit the preamble; receiving the cell switch command from the source cell, the cell switch command carrying the TA value; obtaining the TA value associated with the target cell from the cell switch command; 2. The method of claim 1, comprising:

3. The method of claim 2 , wherein the resource configured to transmit the preamble is included in at least one of the EUS configuration and the EUS request.

4. The EUS procedure further comprises: initiating an EUS Failure (EUSF) timer in response to receiving the EUS request; stopping the EUSF timer in response to receiving the cell switch command from the source cell; 3. The method of claim 2 comprising:

5. 5. The method of claim 4, further comprising, in response to determining that the EUS procedure has failed when the EUSF timer has expired, triggering a connection re-establishment procedure or providing failure information to the source cell.

6. The EUS setting includes an EUS condition, and the EUS procedure includes: sending an EUS indicator to the source cell in response to the target cell determining that the EUS condition is satisfied; and transmitting a preamble to the target cell that satisfies the EUS condition; obtaining the TA value associated with the target cell; receiving the cell switch command from the source cell; 2. The method of claim 1, comprising:

7. determining a signal quality of each of the at least one target cell; in response to determining that a signal quality of a first target cell among the at least one target cell satisfies the EUS condition, determining that the first target cell is the target cell that satisfies the EUS condition; The method of claim 6 further comprising:

8. The method of claim 6 , wherein the step of obtaining the TA value associated with the target cell comprises receiving the TA value from the target cell or receiving the TA value from the source cell.

9. The EUS procedure further comprises:

9. The method of claim 8, comprising sending an EUS termination indicator to the source cell after receiving the TA value from the target cell, the EUS termination indicator indicating that the EUS procedure has terminated.

10. 7. The method of claim 6, wherein the cell switch command carries the TA value, and the step of obtaining the TA value associated with the target cell includes obtaining the TA value associated with the target cell from the cell switch command.

11. The UE is configured with a waiting flag, and the method further comprises: receiving the TA value from the target cell in response to determining that the standby flag is enabled; and receiving the TA value from the source cell in response to determining that the wait flag has been disabled; 9. The method of claim 8, comprising:

12. 12. The method of claim 11, further comprising, in response to determining that the TA value has been received from the target cell, notifying the source cell that the EUS procedure has ended, in the event that the wait flag is enabled.

13. starting an EUS timer in response to transmitting the EUS indicator to the source cell; responsive to obtaining the TA value, stopping the EUS timer; The method of claim 6 further comprising:

14. 14. The method of claim 13, further comprising, in response to determining that the EUS procedure has failed when the EUS timer has expired, transmitting an EUS termination indicator to the source cell, the EUS termination indicator indicating that the EUS procedure has terminated.

15. determining whether the TA value is valid before performing the cell switch procedure to the target cell; performing the cell switching procedure to the target cell based on the TA value in response to determining that the TA value is valid; and The method of claim 6 further comprising:

16. initiating a TA validity timer in response to obtaining the TA value; determining that the TA value is valid in response to determining that the TA validity timer has not expired prior to performing the cell switch procedure to the target cell based on the TA value; and determining, in response to determining that the TA validity timer has expired prior to performing the cell switch procedure to the target cell based on the TA value, that the TA value is invalid; and 16. The method of claim 15 further comprising:

17. After obtaining the TA value, determining whether a signal quality fluctuation of the target cell exceeds a threshold; determining that the TA value is valid in response to determining that the signal quality fluctuation of the target cell does not exceed the threshold when the TA value is obtained; and determining, in response to determining that the signal quality fluctuation of the target cell exceeds the threshold at the time the TA value is obtained, that the TA value is invalid; 20. The method of claim 16 further comprising:

18. The method of claim 6 , wherein the EUS indicator carries an identifier of the target cell that satisfies the EUS condition.

19. receiving an EUS request from the source cell, the EUS request including resources configured to transmit the preamble; transmitting the preamble to the target cell that satisfies the EUS condition based on the resources; 20. The method of claim 18, comprising:

20. the target cells include a first target cell and a second target cell, the first target cell and the second target cell share the TA value, and the method further comprises: transmitting a preamble to the first target cell; performing the cell switch procedure to the second target cell based on the TA value; 2. The method of claim 1, comprising:

21. The step of transmitting the cell switching completion information to the target cell after completing the cell switching procedure, Obtaining an uplink grant from the cell switching configuration or the cell switching command; Sending the cell switching completion information to the target cell after completing the cell switching procedure based on the uplink grant; 2. The method of claim 1, comprising:

22. A transceiver; connected to the transceiver, controlling the transceiver to receive a cell switch configuration for a cell switch procedure from a source cell, the cell switch configuration including an Early Uplink Synchronization (EUS) configuration for an EUS procedure; performing the EUS procedure based on the EUS configuration to obtain a Timing Advance (TA) value associated with a target cell and a cell switch command from the source cell; upon receiving the cell switch command, in response thereto, performing the cell switch procedure to the target cell based on the TA value; controlling the transceiver to send cell switch completion information to the target cell after completing the cell switch procedure; A processor executing A user equipment (UE) including:

23. A method for implementing a cell switching procedure applied to a source cell, comprising the steps of: sending, by the source cell, a cell switch configuration to a user equipment (UE) for the cell switch procedure, the cell switch configuration including an early uplink synchronization (EUS) configuration for the UE to perform an EUS procedure; sending, by the source cell, a cell switch command to the UE upon determining that the target cell has provided a Timing Advance (TA) value during the EUS procedure, the cell switch command controlling the UE to perform the cell switch procedure to the target cell based on the TA value provided by the target cell in the EUS procedure; The method includes:

24. sending an EUS request to the UE during the EUS procedure, the EUS request including a candidate configuration index associated with the target cell; and in response to determining that the TA value has been received from the target cell during the EUS procedure, determining that the target cell has provided the TA value during the EUS procedure and including the TA value in the cell switch command.

24. The method of claim 23, comprising:

25. starting an EUS Failure (EUSF) timer in response to transmitting the EUS request; stopping the EUSF timer in response to receiving the TA value from the target cell; and 25. The method of claim 24, further comprising:

26. 26. The method of claim 25, further comprising, in response to determining that the EUS failure timer has expired, sending another EUS request to the UE or sending another cell switch command to control the UE to perform a normal cell switch procedure.

27. The EUS settings include EUS conditions, and the method further comprises:

24. The method of claim 23, comprising receiving an EUS indicator from the UE, the EUS indicator indicating that the EUS procedure has been triggered by the UE.

28. 24. The method of claim 23, further comprising: in response to determining that an EUS termination indicator is received from the UE, determining that the target cell has provided the TA value during the EUS procedure, the EUS termination indicator indicating that the EUS procedure has terminated.

29. 24. The method of claim 23, further comprising, in response to determining that the target cell has provided the TA value during the EUS procedure, providing the TA value to the UE upon determining that the TA value has been received from the target cell.

30. 30. The method of claim 29, wherein the TA value is conveyed in the cell switch command.

31. The EUS indicator carries an identity of the target cell that satisfies the EUS condition, and the method further comprises: obtaining resources configured to transmit a preamble from the target cell; sending an EUS request to the UE, the EUS request including the resource configured to transmit the preamble; 28. The method of claim 27, comprising:

32. the target cells include a first target cell and a second target cell, the first target cell and the second target cell share the TA value, and the method further comprises: determining, in response to determining that the first target cell has provided the TA value during the EUS procedure, that the target cell has provided the TA value during the EUS procedure; sending the cell switch command to the UE, the cell switch command controlling the UE to perform the cell switch procedure to the second target cell based on the TA value provided by the first target cell in the EUS procedure; 24. The method of claim 23, comprising:

33. 24. The method of claim 23, further comprising: sending an uplink grant to the UE, the uplink grant being included in the cell switch configuration or the cell switch command, and the UE using the uplink grant to send cell switch completion information to the target cell after completing the cell switch procedure.

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