Method for reducing invalid scheduling of source cell in 5G NR switching

Abstract

The invention discloses a method for reducing invalid scheduling of a source cell in 5G NR switching, which comprises the following steps that: after a source base station issues a switching command to user equipment (UE), corresponding operation is executed according to the type fed back by a hybrid automatic repeat request (HARQ) of the switching command; if the type fed back by the hybrid automatic repeat request (HARQ) is negative acknowledgement (NACK), carrying out HARQ retransmission on the switching command; if the type fed back by the hybrid automatic repeat request (HARQ) is acknowledgement (ACK) or discontinuous transmission (DTX), executing a detection operation to judge whether the user equipment (UE) leaves the source cell or not; and if it is determined that the UE leaves the source cell, stopping downlink scheduling of the UE in the source cell. Compared with the prior art, the invention can quickly identify the user equipment leaving the source cell in the 5G NR switching process, timely stop invalid downlink scheduling and retransmission, and effectively improve the utilization rate of air interface resources.

Description

Technical Field

[0001] This invention relates to the field of wireless communication technology, and in particular to a method for reducing invalid scheduling of source cells during 5G NR handover. Background Technology

[0002] In a 5G NR system, when a user equipment (UE) needs to switch from the serving cell of one base station (called the source base station) to the serving cell of another base station (the target base station), the source base station sends a handover command to the UE. According to the 3GPP protocol, after receiving the handover command, the UE can directly initiate a random access procedure to the target cell and perform the handover without sending an ACK message for the Hybrid Automatic Repeat Request (HARQ) to the source base station or sending a status acknowledgment packet at the Radio Link Control (RLC) layer.

[0003] This mechanism causes the Distributed Unit (DU) of the source base station to continuously initiate HARQ retransmission and RLC retransmission procedures because it has not received a HARQ ACK from the MAC layer or a status ACK from the RLC layer. It attempts to repeatedly send handover command packets that the UE has already received but has not acknowledged or that are no longer needed. During this period, the source base station still maintains the user context for the UE and continues to allocate downlink resources for it in its scheduling queue. Since the UE has actually left or is leaving the source cell, these retransmissions and scheduling are completely ineffective, wasting air interface resources and baseband processing resources, and reducing the overall resource utilization and scheduling efficiency of the cell.

[0004] A search revealed Chinese Patent Publication No. CN104244345A, which discloses a method and a WTRU for performing handover from a source cell to a target cell. This method optimizes the timing of the user equipment (UE) receiving and processing system information from the target cell to shorten handover interruption time and accelerate the UE's access process in the target cell. However, this solution focuses on UE-side behavior optimization, aiming to solve latency and synchronization efficiency issues during handover. It does not address the resource management problem at the base station side, where the UE may not provide HARQ confirmation, leading to continuous invalid retransmissions and scheduling of already handed-over users, resulting in long-term occupation and waste of air interface resources.

[0005] Therefore, how to enable the source cell base station during the 5G NR handover process to determine in a timely and accurate manner whether the user equipment has successfully handed over to the target cell, so as to avoid ineffective downlink retransmission scheduling for the user equipment that has been handed over, is a technical problem that needs to be solved. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a method for reducing invalid scheduling of source cells during 5G NR handover.

[0007] The objective of this invention can be achieved through the following technical solutions: According to a first aspect of the present invention, a method for reducing invalid scheduling of source cells during 5G NR handover is provided, the method comprising: After the source base station sends a handover command to the user equipment (UE), it performs corresponding operations according to the type of the Hybrid Automatic Repeat Request (HARQ) feedback of the handover command. If the type of the HARQ feedback of the Hybrid Automatic Repeat Request is Negative Acknowledgment (NACK), then the switching command is retransmitted via HARQ. If the type of the Hybrid Automatic Repeat Request (HARQ) feedback is ACK or Discontinuous Transmission (DTX), then a probe operation is performed to determine whether the User Equipment (UE) has left the source cell. If it is determined that the user equipment (UE) has left the source cell, then downlink scheduling of the UE in the source cell is stopped.

[0008] As a preferred technical solution, the detection operation includes: Send a probe signaling message to the user equipment (UE); Based on whether the user equipment (UE) has received a response to the probe signaling, it is determined whether the UE has left the source cell.

[0009] As a preferred technical solution, if no response is received from the user equipment (UE) to the probe signaling, it is determined that the user equipment (UE) has left the source cell.

[0010] As a preferred technical solution, if a response from the user equipment (UE) to the probe signaling is received, it is determined that the UE is still camped in the source cell, and the handover command continues to be scheduled.

[0011] As a preferred technical solution, the detection signaling is a signal used to trigger the user equipment (UE) to initiate random access.

[0012] As a preferred technical solution, the probe signaling includes a dedicated random access preamble resource indication issued through the downlink control channel command PDCCH ORDER.

[0013] As a preferred technical solution, the execution of the detection operation specifically includes: Apply for a dedicated preamble identifier for the user equipment (UE); The dedicated preamble identifier is scheduled to the user equipment (UE) via the downlink control channel command PDCCH ORDER.

[0014] As a preferred technical solution, the step of determining whether a response to the probe signaling is received from the user equipment (UE) includes: If no random access preamble identifier corresponding to the dedicated preamble identifier is detected within the preset time window, it is determined that no response has been received. If a random access preamble identifier corresponding to the dedicated preamble identifier is detected within a preset time window, it is determined that a response has been received.

[0015] As a preferred technical solution, the corresponding operation is performed according to the type of the Hybrid Automatic Repeat Request (HARQ) feedback, which is triggered at the time point indicated by the timing of the Hybrid Automatic Repeat Request (HARQ) feedback corresponding to the switching command.

[0016] As a preferred technical solution, stopping downlink scheduling for the user equipment (UE) includes: releasing the air interface resources and scheduling authorization allocated to the UE.

[0017] Compared with the prior art, the present invention has the following advantages: 1. This invention provides a differentiated processing and active detection mechanism based on HARQ feedback type, which can accurately and quickly determine whether the UE has left the source cell during the handover process, solve the problem of long-term invalid scheduling and retransmission caused by UE context release delay, and reduce the waste of air interface and scheduling resources.

[0018] 2. By identifying and stopping the scheduling of switched UEs in advance, this invention can immediately release the occupied time and frequency resources, HARQ processes and scheduling authorizations, and redistribute them to other active users, thereby effectively improving the overall resource utilization and system capacity of the cell.

[0019] 3. The implementation of this invention is based on the HARQ feedback, PDCCH ORDER and dedicated preamble process defined in the existing 3GPP protocol. It does not require any modification to UE behavior or core network signaling, has good backward compatibility, and is easy to deploy and upgrade in the existing network.

[0020] 4. The core judgment and execution logic of this invention is concentrated on the base station side, and the implementation scheme is simple and efficient. It mainly involves the logic enhancement of the scheduler and MAC layer, with little modification to the existing system architecture and low development and maintenance costs. Attached Figure Description

[0021] Figure 1 This is a flowchart of the method of the present invention; Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0023] Example 1: like Figure 1 As shown, the core of this invention is that after the source base station issues a handover command to the UE, it does not passively wait for higher-layer signaling to release the UE context, but actively and based on real-time feedback from the physical layer / MAC layer, i.e., HARQ feedback, to quickly detect the actual state of the UE.

[0024] Specifically, after the source base station issues a handover command, it listens for HARQ feedback information in response to the handover command at a specific time point according to the HARQ feedback timing relationship defined in the protocol. Based on the different types of received HARQ feedback (ACK, NACK, or DTX), this invention triggers differentiated subsequent operation logic: If a NACK is received, it indicates that the UE clearly stated that it did not receive the handover command correctly, and HARQ retransmission will be performed according to the normal procedure. If an ACK or DTX is received, there is a probability that the UE may have left the source cell. In this case, the source base station will initiate a lightweight active detection process to determine whether the UE is still in the current cell. If the detection result indicates that the UE has left, all downlink scheduling for that UE will be stopped immediately, and resources will be released in advance.

[0025] The method of this invention effectively reduces invalid retransmissions and resource consumption by enabling the source base station to make intelligent decisions based on the received HARQ feedback type during 5G NR handover.

[0026] The steps of the method of the present invention are described in detail below, taking the source base station as the execution subject. Issue the switchover command: The source base station generates a handover command at the Radio Resource Control (RRC) layer and schedules it to be sent to the target UE via the Downlink Shared Channel (PDSCH). Corresponding to this downlink transmission, the base station will listen for HARQ feedback on a specific Physical Downlink Control Channel (PDCCH) resource. Receive and determine the feedback type at the HARQ feedback time: At the HARQ feedback moment corresponding to the downlink transmission, the source base station attempts to receive HARQ-ACK information from the UE. The reception result can be divided into three categories: ACK, NACK, or DTX (i.e., no valid feedback is detected).

[0027] Scenario 1: Received HARQ NACK When the base station determines that it has received a NACK, it means that the UE has clearly indicated that it has failed to decode the handover command, and then HARQ retransmission is performed. The base station retransmits the handover command data packet during a subsequent scheduling opportunity, following the standard HARQ retransmission mechanism. Afterward, it continues to wait for the next HARQ feedback and repeats the above judgment process.

[0028] Scenario 2: Receive HARQ ACK or DTX When the base station determines that it has received an ACK or DTX, it triggers the core detection process of this invention. ACK indicates that the UE's physical layer has successfully received the signal, while DTX may mean that the UE has not received the PDCCH scheduling instruction or has left without responding. In both cases, the UE may have already initiated a handover to the target cell. At this time, a dedicated random access preamble resource is requested. The base station requests a dedicated preamble ID from the random access resource management module for the UE. This dedicated preamble is different from the preamble used in contention-based random access and is used to uniquely identify the probe request of this specific UE.

[0029] Special preamble for scheduling via PDCCH ORDER: The base station generates a PDCCH ORDER instruction using Downlink Control Information (DCI) format 1_0 (whose Cyclic Redundancy Check (CRC) is scrambled by the Cell Radio Network Temporary Identifier (C-RNTI). This instruction carries the requested dedicated preamble identifier and instructs the UE to initiate contention-free random access on the designated Random Access Channel (PRACH) resource.

[0030] The base station schedules and sends out this PDCCH ORDER instruction. After transmission, the base station starts a timer (or listens for the uplink random access channel within a preset time window).

[0031] Listen to the UE's random access response: The base station checks the uplink PRACH resources for the existence of a preamble sequence corresponding to the scheduled dedicated preamble identifier.

[0032] 1. No response received from the probe. If the base station does not detect the dedicated preamble within the preset time window, it determines that no response has been received from the UE. This result indicates that the UE has most likely successfully received the handover command and left the source cell, and is undergoing the handover process in the target cell. Therefore, it cannot respond to the PDCCH ORDER of the source cell. Based on this determination, the source base station can safely consider that the UE no longer belongs to its cell.

[0033] Release UE resources and stop downlink scheduling: The source base station immediately stops any new downlink data scheduling for this UE (including further retransmission of handover commands). Simultaneously, it can notify the MAC layer and scheduler to release air interface resources reserved or allocated for this UE (such as time-frequency resources, HARQ processes, queues in the scheduler, etc.), thereby quickly reclaiming these resources for serving other UEs. At this point, the process for this UE ends.

[0034] 2. The probe received a response. If the base station detects the dedicated preamble within the preset time window, it determines that it has received a response from the UE. This result indicates that the UE is still camped on the source cell and can successfully receive and execute the source cell's PDCCH ORDER command. For cases where ACK was previously received, it may mean that although the UE successfully decoded at the physical layer, higher-layer processing was not yet complete or the handover had not been performed. For cases where DTX was previously received, it means that the UE may have failed to send HARQ feedback due to signal quality issues, but is still actually online.

[0035] Continue normal UE scheduling (including possible handover command retransmission). Since the UE is confirmed to still be in the source cell, the base station continues to treat the UE as a normal user in this cell and maintains its scheduling status. For scenarios where DTX feedback was previously received, the base station should continue to execute the HARQ retransmission procedure for the original handover command to ensure that the UE eventually receives the handover command. Afterward, wait for the next HARQ feedback, which may trigger this probe procedure again, until the UE successfully hands over or the connection fails.

[0036] Other solutions in this invention embodiment: The probe signaling is not limited to the dedicated preamble for PDCCH ORDER scheduling. In other embodiments, other types of downlink signaling that require an immediate response from the UE at the physical layer can also be used for probe, such as downlink reference signals of a specific format, which are detected by detecting the corresponding uplink probe reference signal (SRS) or channel state information (CSI) feedback from the UE to determine their presence. The action to stop scheduling can be an immediate hard stop or a gradual soft stop, such as first stopping new data transmission but maintaining the transmission of control signaling for a period of time to ensure reliability. The length of the time window for determining whether a response has not been received can be adaptively adjusted based on factors such as network configuration and cell radius.

[0037] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for reducing invalid scheduling of source cells during 5G NR handover, characterized in that, include: After the source base station sends a handover command to the user equipment (UE), it performs corresponding operations according to the type of the Hybrid Automatic Repeat Request (HARQ) feedback of the handover command. If the type of the HARQ feedback of the Hybrid Automatic Repeat Request is Negative Acknowledgment (NACK), then the switching command is retransmitted via HARQ. If the type of the Hybrid Automatic Repeat Request (HARQ) feedback is ACK or Discontinuous Transmission (DTX), then a probe operation is performed to determine whether the User Equipment (UE) has left the source cell. If it is determined that the user equipment (UE) has left the source cell, then downlink scheduling of the UE in the source cell is stopped.

2. The method for reducing invalid scheduling of source cells during 5G NR handover according to claim 1, characterized in that, The detection operation includes: Send a probe signaling message to the user equipment (UE); Based on whether the user equipment (UE) has received a response to the probe signaling, it is determined whether the UE has left the source cell.

3. A method for reducing invalid scheduling of source cells during 5G NR handover according to claim 2, characterized in that, If no response to the probe signaling is received from the user equipment (UE), it is determined that the user equipment (UE) has left the source cell.

4. A method for reducing invalid scheduling of source cells during 5G NR handover according to claim 2, characterized in that, If a response to the probe signaling is received from the user equipment (UE), it is determined that the UE is still camped in the source cell, and the handover command continues to be scheduled.

5. A method for reducing invalid scheduling of source cells during 5G NR handover according to claim 2, characterized in that, The detection signaling is a signal used to trigger the user equipment (UE) to initiate random access.

6. A method for reducing invalid scheduling of source cells during 5G NR handover according to claim 5, characterized in that, The probe signaling includes a dedicated random access preamble resource indication issued via the downlink control channel command PDCCH ORDER.

7. A method for reducing invalid scheduling of source cells during 5G NR handover according to claim 6, characterized in that, The specific steps of performing the detection operation include: Apply for a dedicated preamble identifier for the user equipment (UE); The dedicated preamble identifier is scheduled to the user equipment (UE) via the downlink control channel command PDCCH ORDER.

8. A method for reducing invalid scheduling of source cells during 5G NR handover according to claim 7, characterized in that, The step of determining whether a response to the probe signaling is received from the user equipment (UE) includes: If no random access preamble identifier corresponding to the dedicated preamble identifier is detected within the preset time window, it is determined that no response has been received. If a random access preamble identifier corresponding to the dedicated preamble identifier is detected within a preset time window, it is determined that a response has been received.

9. A method for reducing invalid scheduling of source cells during 5G NR handover according to claim 1, characterized in that, The corresponding operation is performed according to the type of the Hybrid Automatic Repeat Request (HARQ) feedback, and is triggered at the time point indicated by the timing of the HARQ feedback corresponding to the switching command.

10. A method for reducing invalid scheduling of source cells during 5G NR handover according to claim 1, characterized in that, The step of stopping downlink scheduling for the user equipment (UE) includes: releasing the air interface resources and scheduling authorization allocated to the UE.

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