Data transmission method and device

Abstract

The invention provides a data transmission method and device. The method is applied to UE and comprises the following steps: receiving an RRC connection reconfiguration message sent by a source gNB when determining that the UE needs to be switched from a source cell to a target cell through an RRC entity in the UE; if it is judged that an uplink PDCP state report corresponding to a target DRB in the AM is carried in the RRC connection reconfiguration message through a sending PDCP entity in the RRC connection reconfiguration message, determining a first uplink PDCP SDU needing to be discarded and a second uplink PDCP SDU needing to be transmitted; a first uplink PDCP SDU cached by UE is discarded through a sending PDCP entity, and after an RRC connection reconfiguration completion message is sent to a target gNB to which a target cell belongs through an RRC entity, a second uplink PDCP SDU is transmitted to the target gNB based on a target DRB through the sending PDCP entity. According to the invention, the data transmission time delay can be shortened.

Description

Technical Field

[0001] The present application relates to the field of communication technology, and in particular to a data transmission method and device. Background Art

[0002] When a user equipment (UE) switches from a source cell to a target cell, the UE needs to disconnect from the source 5G base station (gNodeB, gNB for short) to which the source cell belongs, and then reconnect to the gNB to which the target cell belongs.

[0003] When the UE needs to send an uplink packet data convergence protocol (PDCP) service data unit (SDU) to the target gNB, it may need to wait for the uplink PDCP status report (Status Reporting) sent by the target gNB before sending the uplink PDCP SDU, which results in a longer transmission delay of the uplink PDCP SDU.

[0004] Here, the uplink PDCP status report is sent to the UE by the target gNB after receiving the Radio Resource Control (RRC) connection reconfiguration completion message sent by the UE.

[0005] When the target gNB needs to send a downlink PDCP SDU to the UE, it may need to wait for the downlink PDCP status report sent by the UE before sending the downlink PDCP SDU, which results in a longer transmission delay of the downlink PDCP SDU.

[0006] Here, the downlink PDCP status report is sent by the UE to the target gNB after sending the RRC reconfiguration completion message to the target gNB. Summary of the invention

[0007] In order to overcome the problems existing in the related art, the present application provides a data transmission method and device. According to a first aspect of an embodiment of the present application, a data transmission method is provided, the method is applied to a UE, and the method includes:

[0008] Receiving, through the RRC entity in itself, an RRC connection reconfiguration message sent by the source gNB to which the source cell to which it accesses belongs when determining that the UE needs to be switched from the source cell to the target cell;

[0009] If it is determined by the sending PDCP entity in itself that the RRC connection reconfiguration message carries an uplink PDCP status report corresponding to a target data radio bearer (DRB) in an acknowledged mode (AM), the sending PDCP entity determines, according to the uplink PDCP status report, a first uplink PDCP SDU to be discarded and a second uplink PDCP SDU to be transmitted;

[0010] The sending PDCP entity discards the first uplink PDCP SDU cached by the UE, and after sending an RRC connection reconfiguration completion message to the target gNB to which the target cell belongs through the RRC entity, the sending PDCP entity transmits the second uplink PDCP SDU to the target gNB based on the target DRB.

[0011] According to a second aspect of an embodiment of the present application, a data transmission method is provided, the method being applied to a UE, the method comprising:

[0012] Receiving, through the RRC entity in itself, an RRC connection reconfiguration message sent by the source gNB to which the source cell to which it accesses belongs when determining that the UE needs to be switched from the source cell to the target cell;

[0013] If a downlink PDCP SDU sent by the source gNB based on the target DRB in AM is received through the sending PDCP entity in itself, a downlink PDCP status report for the target DRB is sent to the source gNB through the sending PDCP entity, so that the source gNB determines the first downlink PDCP SDU to be discarded and the second downlink PDCP SDU to be transmitted according to the downlink PDCP status report when receiving the downlink PDCP status report, and discards the first downlink PDCP SDU. When the source gNB and the target gNB to which the target cell belongs are the same gNB, the second downlink PDCP SDU is cached to the sending MAC entity in the target distributed unit (DU) in the source gNB that communicates with the UE through the sending PDCP entity in the centralized unit (CU) of the source gNB. After monitoring that the UE completes the random access process, the sending MAC entity transmits the downlink MAC SDU associated with the second downlink PDCP SDU to the UE based on the target DRB, or, when the source gNB and the target gNB are different gNBs, the second downlink PDCP SDU is cached to the sending MAC entity in the target distributed unit (DU) of the source gNB that communicates with the UE. The SDU is synchronized to the target gNB so that when the target gNB receives the second downlink PDCP SDU through the sending PDCP entity in its own CU, it caches it to the sending MAC entity in the DU that communicates with the UE in the target gNB, and after monitoring that the UE completes the random access process, the sending MAC entity transmits the downlink MAC SDU associated with the second downlink PDCP SDU to the UE based on the target DRB.

[0014] According to a third aspect of an embodiment of the present application, a data transmission method is provided, where the method is applied to a gNB, and the method includes:

[0015] When it is determined that the target UE needs to switch from the currently accessed source cell to the target cell, and an uplink PDCP SDU sent by the target UE based on the target DRB in AM has been received, an RRC connection reconfiguration message carrying an uplink PDCP status report corresponding to the target DRB is generated;

[0016] The RRC connection reconfiguration message is sent to the target UE, so that the target UE receives the RRC connection reconfiguration message through the RRC entity in itself, and when the sending PDCP entity in itself determines that the RRC connection reconfiguration message carries the uplink PDCP status report, the first uplink PDCP SDU that needs to be discarded and the second uplink PDCP SDU that needs to be transmitted are determined according to the uplink PDCP status report, the first uplink PDCP SDU cached by the UE is discarded, and after sending an RRC connection reconfiguration completion message to the target gNB through the RRC entity, the second uplink PDCP SDU is transmitted to the target gNB through the sending PDCP entity based on the target DRB.

[0017] According to a fourth aspect of an embodiment of the present application, a data transmission method is provided, where the method is applied to a gNB, and the method includes:

[0018] If it is the source gNB to which the source cell accessed by the target UE belongs, when it is determined that the target UE needs to be switched from the source cell to the target cell, an RRC connection reconfiguration message is sent to the target UE;

[0019] If a downlink PDCP status report for a target DRB in AM sent by the target UE is received, determining, according to the downlink PDCP status report, a first downlink PDCP SDU to be discarded and a second downlink PDCP SDU to be transmitted;

[0020] discarding the first downlink PDCP SDU;

[0021] When the source gNB and the target gNB to which the target cell belongs are the same gNB, the second downlink PDCP SDU is cached to the sending MAC entity in the target DU in the source gNB that communicates with the target UE through the sending PDCP entity in the CU of the source gNB, and after monitoring that the target UE completes the random access process, the sending MAC entity transmits the downlink MAC SDU associated with the second downlink PDCP SDU to the target UE based on the target DRB; or,

[0022] When the source gNB and the target gNB are different gNBs, the second downlink PDCP SDU is synchronized to the target gNB, so that when the target gNB receives the second downlink PDCP SDU through the sending PDCP entity in its own CU, it caches it to the sending MAC entity in the DU that communicates with the target UE in the target gNB, and after monitoring that the target UE completes the random access process, the sending MAC entity transmits the downlink MAC SDU associated with the second downlink PDCP SDU to the target UE based on the target DRB.

[0023] According to a fifth aspect of an embodiment of the present application, a data transmission device is provided, where the device is applied to a UE, and the device includes:

[0024] A receiving module, configured to receive, through an RRC entity in itself, an RRC connection reconfiguration message sent by a source gNB to which a source cell to which the source gNB itself accesses belongs when determining that the UE needs to be switched from the source cell to a target cell;

[0025] A determination module, configured to determine, through the sending PDCP entity in itself, a first uplink PDCP SDU to be discarded and a second uplink PDCP SDU to be transmitted according to the uplink PDCP status report if it is determined that the RRC connection reconfiguration message carries an uplink PDCP status report corresponding to the target DRB in AM;

[0026] A transmission module is used to discard the first uplink PDCP SDU cached by the UE through the sending PDCP entity, and after sending an RRC connection reconfiguration completion message to the target gNB to which the target cell belongs through the RRC entity, transmit the second uplink PDCP SDU to the target gNB based on the target DRB through the sending PDCP entity.

[0027] According to a sixth aspect of an embodiment of the present application, a data transmission device is provided, where the device is applied to a UE, and the device includes:

[0028] A receiving module, configured to receive, through an RRC entity in itself, an RRC connection reconfiguration message sent by a source gNB to which a source cell to which the source gNB itself accesses belongs when determining that the UE needs to be switched from the source cell to a target cell;

[0029] a transmission module, configured to send a downlink PDCP status report for the target DRB to the source gNB through the sending PDCP entity if the downlink PDCP SDU sent by the source gNB based on the target DRB in AM is received through the sending PDCP entity in the source gNB, so that the source gNB determines the first downlink PDCP SDU to be discarded and the second downlink PDCP SDU to be transmitted according to the downlink PDCP status report when receiving the downlink PDCP status report, and discards the first downlink PDCP SDU; when the source gNB and the target gNB to which the target cell belongs are the same gNB, the second downlink PDCP SDU is cached to the sending MAC entity in the target DU in the source gNB that communicates with the UE through the sending PDCP entity in the CU of the source gNB; after monitoring that the UE completes the random access process, the sending MAC entity transmits the downlink MAC SDU associated with the second downlink PDCP SDU to the UE based on the target DRB, or, when the source gNB and the target gNB are different gNBs, the second downlink PDCP SDU is cached to the sending MAC entity in the target DU in the source gNB that communicates with the UE. The SDU is synchronized to the target gNB so that when the target gNB receives the second downlink PDCP SDU through the sending PDCP entity in its own CU, it caches it to the sending MAC entity in the DU that communicates with the UE in the target gNB. After monitoring that the UE has completed the random access process, the sending MAC entity transmits the downlink MAC SDU associated with the second downlink PDCP SDU to the UE based on the target DRB.

[0030] According to a seventh aspect of an embodiment of the present application, a data transmission device is provided, where the device is applied to a gNB, and the device includes:

[0031] A generating module, configured to generate a radio resource control RRC connection reconfiguration message carrying an uplink PDCP status report corresponding to the target DRB when it is determined that the target UE needs to switch from the currently accessed source cell to the target cell and has received an uplink PDCP SDU sent by the target UE based on the target DRB in AM;

[0032] A transmission module is used to send the RRC connection reconfiguration message to the target UE, so that the target UE receives the RRC connection reconfiguration message through the RRC entity in itself, and when the sending PDCP entity in itself determines that the RRC connection reconfiguration message carries the uplink PDCP status report, determines the first uplink PDCP SDU that needs to be discarded and the second uplink PDCP SDU that needs to be transmitted according to the uplink PDCP status report, discards the first uplink PDCP SDU cached by the UE, and after sending the RRC connection reconfiguration completion message to the target gNB through the RRC entity, transmits the second uplink PDCP SDU to the target gNB based on the target DRB through the sending PDCP entity.

[0033] According to an eighth aspect of an embodiment of the present application, a data transmission device is provided, where the device is applied to a gNB, and the device includes:

[0034] A first transmission module is configured to send an RRC connection reconfiguration message to the target UE when it is determined that the target UE needs to be switched from the source cell to the target cell if the source gNB itself is the source gNB to which the source cell accessed by the target UE belongs;

[0035] a determination module, configured to determine, if a downlink PDCP status report for a target DRB in AM sent by the target UE is received, a first downlink PDCP SDU to be discarded and a second downlink PDCP SDU to be transmitted according to the downlink PDCP status report;

[0036] A discarding module, configured to discard the first downlink PDCP SDU;

[0037] A second transmission module is configured to cache the second downlink PDCP SDU to a sending MAC entity in a target DU in the source gNB that communicates with the target UE when the source gNB and the target gNB to which the target cell belongs are the same gNB, through a sending PDCP entity in a CU in the source gNB, and after the sending MAC entity monitors that the target UE completes a random access procedure, transmits the downlink MAC SDU associated with the second downlink PDCP SDU to the target UE based on the target DRB; or

[0038] A synchronization module is used for synchronizing the second downlink PDCP SDU to the target gNB when the source gNB and the target gNB are different gNBs, so that when the target gNB receives the second downlink PDCP SDU through the sending PDCP entity in its own CU, it caches it to the sending MAC entity in the DU that communicates with the target UE in the target gNB, and after monitoring that the target UE completes the random access process, the sending MAC entity transmits the downlink MAC SDU associated with the second downlink PDCP SDU to the target UE based on the target DRB.

[0039] The technical solution provided by the embodiments of the present application may have the following beneficial effects:

[0040] In an embodiment of the present application, the source gNB carries the uplink PDCP status report corresponding to the target DRB in AM for the UE in the RRC connection reconfiguration message, so that the UE can process the uplink PDCP status report in time, and after sending the RRC connection reconfiguration completion message to the target gNB to which the target cell belongs through the RRC entity, transmit the relevant uplink PDCP SDU in time to shorten the transmission delay of the uplink PDCP SDU.

[0041] In addition, when the UE receives the RRC connection reconfiguration message sent by the source gNB through its own RRC entity and receives the downlink PDCP SDU sent by the source gNB based on the relevant DRB in AM through its own sending PDCP entity, the UE sends a downlink PDCP status report for the relevant DRB to the source gNB through the sending PDCP entity, so that the source gNB can process the downlink PDCP status report in time, and when the source gNB and the target gNB are the same gNB, the downlink PDCP SDU to be transmitted is cached in the sending MAC entity in the DU in the source gNB that communicates with the UE through the sending PDCP entity in the CU of the source gNB. After monitoring that the UE has completed the random access process, the sending MAC entity transmits the downlink MAC SDU associated with the downlink PDCP SDU to be transmitted to the UE based on the relevant DRB, so as to shorten the transmission delay of the downlink PDCP SDU.

[0042] Alternatively, when the source gNB and the target gNB are different gNBs, the source gNB synchronizes the downlink PDCP SDU to be transmitted to the target gNB, and when the target gNB receives the downlink PDCP SDU to be transmitted through the sending PDCP entity in its own CU, it caches it to the sending MAC entity in the target DU in the target gNB that communicates with the UE. After monitoring that the UE has completed the random access process, the sending MAC entity transmits the downlink MAC SDU associated with the downlink PDCP SDU to be transmitted to the UE based on the relevant DRB, so as to shorten the transmission delay of the downlink PDCP SDU.

[0043] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The accompanying drawings, which are incorporated in the specification and constitute a part of this application, illustrate embodiments consistent with the application and, together with the description, serve to explain the principles of the application.

[0045] Figure 1 One of the flowcharts of a data transmission method provided in an embodiment of the present application;

[0046] Figure 2 A second flowchart of a data transmission method provided in an embodiment of the present application;

[0047] Figure 3 A third flowchart of a data transmission method provided in an embodiment of the present application;

[0048] Figure 4 A fourth flowchart of a data transmission method provided in an embodiment of the present application;

[0049] Figure 5 A fifth flowchart of a data transmission method provided in an embodiment of the present application;

[0050] Figure 6 A sixth flowchart of a data transmission method provided in an embodiment of the present application;

[0051] Figure 7 One of the structural schematic diagrams of a data transmission device provided in an embodiment of the present application;

[0052] Figure 8 A second structural diagram of a data transmission device provided in an embodiment of the present application;

[0053] Fig. 9 A third structural diagram of a data transmission device provided in an embodiment of the present application;

[0054] Fig.10 A fourth structural diagram of a data transmission device provided in an embodiment of the present application. DETAILED DESCRIPTION

[0055] Exemplary embodiments will be described in detail herein, examples of which are shown in the accompanying drawings. When the following description refers to the drawings, the same numbers in different drawings represent the same or similar elements unless otherwise indicated. The implementations described in the following exemplary embodiments do not represent all implementations consistent with the present application. Instead, they are merely examples of devices and methods consistent with some aspects of the present application as detailed in the appended claims.

[0056] The terms used in this application are for the purpose of describing specific embodiments only and are not intended to limit this application. The singular forms of "a", "said" and "the" used in this application and the appended claims are also intended to include plural forms unless the context clearly indicates other meanings. It should also be understood that the term "and / or" used herein refers to and includes any or all possible combinations of one or more associated listed items.

[0057] It should be understood that, although the terms first, second, third, etc. may be used in the present application to describe various information, these information should not be limited to these terms. These terms are only used to distinguish the same type of information from each other. For example, without departing from the scope of the present application, the first information may also be referred to as the second information, and similarly, the second information may also be referred to as the first information. Depending on the context, the words "if" or "if" as used herein may be interpreted as "at the time of" or "when...".

[0058] Next, the embodiments of the present application are described in detail.

[0059] The present application embodiment provides a data transmission method, which is applied to a UE, such as Figure 1 As shown, the method may include the following steps:

[0060] S11. Receive, through the RRC entity in itself, an RRC connection reconfiguration message sent by the source gNB to which the source cell to which it accesses belongs when it determines that the UE needs to switch from the source cell to the target cell.

[0061] S12. If the sending PDCP entity determines that the RRC connection reconfiguration message carries an uplink PDCP status report corresponding to the target DRB in AM, the sending PDCP entity determines the first uplink PDCP SDU that needs to be discarded and the second uplink PDCP SDU that needs to be transmitted based on the uplink PDCP status report.

[0062] S13. After discarding the first uplink PDCP SDU cached by the UE through the sending PDCP entity, and sending an RRC connection reconfiguration completion message to the target gNB to which the target cell belongs through the RRC entity, the second uplink PDCP SDU is transmitted to the target gNB based on the target DRB through the sending PDCP entity.

[0063] By executing steps S11 to S13, the UE does not need to wait for the target gNB to send an uplink PDCP status report, and can promptly process and transmit relevant uplink PDCP SDU based on the uplink PDCP status report carried in the RRC connection reconfiguration message sent by the source gNB, thereby greatly shortening the transmission delay of the uplink PDCP SDU.

[0064] It should be noted that the above-mentioned source gNB and the above-mentioned target gNB can be the same gNB or different gNBs.

[0065] It should be further explained that, for the UE, the specific determination process of determining the first uplink PDCP SDU to be discarded and the second uplink PDCP SDU to be transmitted is detailed in the determination process described in Section 5.4.2 of 3GPP TS38.323, which will not be described in detail here.

[0066] In addition, the specific transmission process of the UE transmitting the second uplink PDCP SDU to the target gNB through the sending PDCP entity is detailed in the relevant chapters of 3GPP TS38.323 and will not be described in detail here.

[0067] The above content is the data transmission method described on the UE side. The following describes the corresponding data transmission method on the gNB side.

[0068] The embodiment of the present application also provides a data transmission method, which is applied to a gNB, such as Figure 2 As shown, the method may include the following steps:

[0069] S21. When it is determined that the target UE needs to switch from the currently accessed source cell to the target cell and an uplink PDCP SDU is received from the target UE based on the target DRB in AM, an RRC connection reconfiguration message carrying an uplink PDCP status report corresponding to the target DRB is generated.

[0070] S22. Send the RRC connection reconfiguration message to the target UE, so that the target UE receives the RRC connection reconfiguration message through the RRC entity in itself, and when the sending PDCP entity in itself determines that the RRC connection reconfiguration message carries an uplink PDCP status report, determines the first uplink PDCP SDU that needs to be discarded and the second uplink PDCP SDU that needs to be transmitted according to the uplink PDCP status report, discards the first uplink PDCP SDU cached by the UE, and after sending the RRC connection reconfiguration completion message to the target gNB through the RRC entity, transmits the second uplink PDCP SDU to the target gNB based on the target DRB through the sending PDCP entity.

[0071] The gNB, as the source gNB of the UE, executes the above steps S21 to S22, so that the UE does not need to wait for the target gNB to send an uplink PDCP status report. Based on the uplink PDCP status report carried in the RRC connection reconfiguration message sent by the source gNB, the UE can promptly process and transmit the relevant uplink PDCP SDU, thereby greatly shortening the transmission delay of the uplink PDCP SDU.

[0072] It should be noted that the above-mentioned source gNB and the above-mentioned target gNB can be the same gNB or different gNBs.

[0073] It should be further explained that, for the UE, the specific process of determining the first uplink PDCP SDU that needs to be discarded and the second uplink PDCP SDU that needs to be transmitted, as well as the specific transmission process of transmitting the second uplink PDCP SDU have been described on the UE side and will not be described in detail here.

[0074] For example, Figure 3 As shown, assuming that the gNB (called the source gNB) to which the cell 1 (called the source cell) currently accessed by UE1 belongs is gNB1, assuming that UE1 sends uplink PDCP SDUs with sequence numbers 1 to 6 to gNB1 based on DRB1 in AM, but UE1 does not receive a confirmation message for the uplink PDCP SDUs with sequence numbers 3 to 4; and assuming that at time 1, gNB1 determines that UE1 needs to switch from cell 1 to cell 2. At this time, gNB1 sends an RRC connection reconfiguration message 1 carrying an uplink PDCP status report 1 corresponding to DRB1 to UE1.

[0075] UE1 determines that the RRC connection reconfiguration message 1 carries the uplink PDCP status report 1 through the sending PDCP entity in itself. At this time, UE1 determines the first uplink PDCP SDU that needs to be discarded (for example, the uplink PDCP SDU with sequence numbers 1 to 6) and the second uplink PDCP SDU that needs to be transmitted (for example, the uplink PDCP SDU with sequence number 7) through the sending PDCP entity according to the uplink PDCP status report 1.

[0076] UE1 discards the uplink PDCP SDUs with sequence numbers 1 to 6 cached by UE1 through the sending PDCP entity, and after sending the RRC connection reconfiguration completion message 1 to the gNB (referred to as the target gNB, for example, gNB2) to which cell 2 belongs through the RRC entity, the sending PDCP entity transmits the second uplink PDCP SDU (i.e., the uplink PDCP SDU with sequence number 7) to gNB2 based on DRB1.

[0077] The embodiment of the present application also provides a data transmission method, which is applied to a UE, such as Figure 4 As shown, the method may include the following steps:

[0078] S41. Receive, through the RRC entity in itself, the RRC connection reconfiguration message sent by the source gNB to which the source cell to which it accesses belongs when it determines that the UE needs to switch from the source cell to the target cell.

[0079] S42. If a downlink PDCP SDU sent by the source gNB based on the target DRB in AM is received through the sending PDCP entity in itself, a downlink PDCP status report for the target DRB is sent to the source gNB through the sending PDCP entity, so that when the source gNB receives the downlink PDCP status report, it determines the first downlink PDCP SDU to be discarded and the second downlink PDCP SDU to be transmitted according to the downlink PDCP status report, and discards the first downlink PDCP SDU. When the source gNB and the target gNB to which the target cell belongs are the same gNB, the second downlink PDCP SDU is cached to the sending MAC entity in the target distributed unit DU in the source gNB that communicates with the UE through the sending PDCP entity in the centralized unit CU in the source gNB. After monitoring that the UE completes the random access process, the sending MAC entity transmits the downlink MAC SDU associated with the second downlink PDCP SDU to the UE based on the target DRB, or, when the source gNB and the target gNB are different gNBs, the second downlink PDCP SDU is synchronized to the target gNB, so that the target gNB receives the second downlink PDCP SDU through the sending PDCP entity in the CU in itself. When a downlink PDCP SDU is received, it is cached in the sending MAC entity in the DU that communicates with the UE in the target gNB. After monitoring that the UE has completed the random access process, the sending MAC entity transmits the downlink MAC SDU associated with the second downlink PDCP SDU to the UE based on the target DRB.

[0080] The UE executes steps S41 to S42 so that the source gNB can process the downlink PDCP status report in a timely manner, and when the source gNB and the target gNB are the same gNB, the UE caches the downlink PDCP SDU to be transmitted to the sending MAC entity in the DU that communicates with the UE in the source gNB through the sending PDCP entity in the CU of the source gNB. After monitoring that the UE has completed the random access process, the sending MAC entity transmits the downlink MAC SDU associated with the downlink PDCP SDU to be transmitted to the UE based on the relevant DRB, so as to shorten the transmission delay of the downlink PDCP SDU.

[0081] Alternatively, when the source gNB and the target gNB are different gNBs, the source gNB synchronizes the downlink PDCP SDU to be transmitted to the target gNB, and when the target gNB receives the downlink PDCP SDU to be transmitted through the sending PDCP entity in its own CU, it caches it to the sending MAC entity in the target DU in the target gNB that communicates with the UE. After monitoring that the UE has completed the random access process, the sending MAC entity transmits the downlink MAC SDU associated with the downlink PDCP SDU to be transmitted to the UE based on the relevant DRB, so as to shorten the transmission delay of the downlink PDCP SDU.

[0082] It should be noted that, for the source gNB, the specific process of determining the first downlink PDCP SDU to be discarded and the second downlink PDCP SDU to be transmitted is detailed in the relevant chapters of 3GPP TS38.323 and will not be described in detail here.

[0083] It should be further explained that, for the target gNB, after obtaining the second downlink PDCP SDU to be transmitted, if it receives a downlink PDCP status report sent by the UE again, it will no longer process the downlink PDCP status report received again.

[0084] The above content is another data transmission method described on the UE side. The following describes the corresponding data transmission method on the gNB side.

[0085] The embodiment of the present application also provides a data transmission method, which is applied to a gNB, such as Figure 5 As shown, the method may include the following steps:

[0086] S51. If it is the source gNB to which the source cell accessed by the target UE belongs, when it is determined that the target UE needs to be switched from the source cell to the target cell, an RRC connection reconfiguration message is sent to the target UE.

[0087] S52: If a downlink PDCP status report for a target DRB in AM sent by the target UE is received, determine a first downlink PDCP SDU that needs to be discarded and a second downlink PDCP SDU that needs to be transmitted according to the downlink PDCP status report.

[0088] S53: discard the first downlink PDCP SDU.

[0089] S54. When the source gNB and the target gNB to which the target cell belongs are the same gNB, the second downlink PDCP SDU is cached in the sending MAC entity in the target DU in the source gNB that communicates with the target UE through the sending PDCP entity in the CU of the source gNB, and the sending MAC entity transmits the downlink MAC SDU associated with the second downlink PDCP SDU to the target UE based on the target DRB after monitoring that the target UE completes the random access process; or, when the source gNB and the target gNB are different gNBs, the second downlink PDCP SDU is synchronized to the target gNB, so that when the target gNB receives the second downlink PDCP SDU through the sending PDCP entity in its CU, it caches it in the sending MAC entity in the DU in the target gNB that communicates with the target UE, and the sending MAC entity transmits the downlink MAC SDU associated with the second downlink PDCP SDU to the target UE based on the target DRB after monitoring that the target UE completes the random access process.

[0090] By executing the above steps S51 to S54, the gNB can process the downlink PDCP status report in a timely manner, and when the source gNB and the target gNB are the same gNB, the gNB caches the downlink PDCP SDU to be transmitted to the sending MAC entity in the DU that communicates with the UE in the source gNB through the sending PDCP entity in the CU of the source gNB. After monitoring that the UE has completed the random access process, the sending MAC entity transmits the downlink MAC SDU associated with the downlink PDCP SDU to be transmitted to the UE based on the relevant DRB, so as to shorten the transmission delay of the downlink PDCP SDU.

[0091] Alternatively, when the source gNB and the target gNB are different gNBs, the source gNB synchronizes the downlink PDCP SDU to be transmitted to the target gNB, and when the target gNB receives the downlink PDCP SDU to be transmitted through the sending PDCP entity in its own CU, it caches it to the sending MAC entity in the target DU in the target gNB that communicates with the UE. After monitoring that the UE has completed the random access process, the sending MAC entity transmits the downlink MAC SDU associated with the downlink PDCP SDU to be transmitted to the UE based on the relevant DRB, so as to shorten the transmission delay of the downlink PDCP SDU.

[0092] It should be noted that, for the gNB, the specific process of determining the first downlink PDCP SDU to be discarded and the second downlink PDCP SDU to be transmitted is detailed in the relevant chapters of 3GPP TS38.323 and will not be described in detail here.

[0093] It should be further explained that, for the target gNB, after obtaining the second downlink PDCP SDU to be transmitted, if it receives a downlink PDCP status report sent by the UE again, it will no longer process the downlink PDCP status report received again.

[0094] For example, Figure 6 As shown, assuming that the gNB (called source gNB) to which the cell 3 (called the source cell) currently accessed by UE2 belongs is gNB3, assuming that gNB3 sends downlink PDCP SDUs with sequence numbers 11 to 16 to UE2 based on DRB2 in AM, but gNB3 does not receive a confirmation message for downlink PDCP SDUs with sequence numbers 13 to 14; and assuming that at time 2, gNB3 determines that UE2 needs to switch from cell 3 to cell 4, at this time, gNB3 sends an RRC connection reconfiguration message 2 to UE2.

[0095] After receiving the RRC connection reconfiguration message 2, UE2 sends the downlink PDCP status report 1 of DRB2 to gNB3.

[0096] After receiving the downlink PDCP status report 1, gNB3 determines, based on the downlink PDCP status report 1, the first downlink PDCP SDU that needs to be discarded (for example, the downlink PDCP SDU with sequence numbers 11 to 16) and the second downlink PDCP SDU that needs to be transmitted (for example, the downlink PDCP SDU with sequence number 7).

[0097] Next, gNB3 discards the downlink PDCP SDUs with sequence numbers 11 to 16.

[0098] Assume that the source gNB and the gNB to which cell 4 belongs (called the target gNB, for example, gNB4) are different gNBs. At this time, gNB3 synchronizes the second downlink PDCP SDU to gNB4.

[0099] When gNB4 receives the second downlink PDCP SDU through the sending PDCP entity in its own CU, it caches it to the sending MAC entity in the DU in gNB4 that communicates with UE2. After monitoring that UE2 has completed the random access process, the sending MAC entity transmits the downlink MAC SDU associated with the second downlink PDCP SDU to UE2 based on DRB2.

[0100] It can be seen from the above technical solution that in an embodiment of the present application, the source gNB carries the uplink PDCP status report corresponding to the target DRB in AM for the UE in the RRC connection reconfiguration message, so that the UE can process the uplink PDCP status report in time, and after sending the RRC connection reconfiguration completion message to the target gNB to which the target cell belongs through the RRC entity, transmit the relevant uplink PDCP SDU in time to shorten the transmission delay of the uplink PDCP SDU.

[0101] In addition, when the UE receives the RRC connection reconfiguration message sent by the source gNB through its own RRC entity and receives the downlink PDCP SDU sent by the source gNB based on the relevant DRB in AM through its own sending PDCP entity, the UE sends a downlink PDCP status report for the relevant DRB to the source gNB through the sending PDCP entity, so that the source gNB can process the downlink PDCP status report in time, and when the source gNB and the target gNB are the same gNB, the downlink PDCP SDU to be transmitted is cached in the sending MAC entity in the DU in the source gNB that communicates with the UE through the sending PDCP entity in the CU of the source gNB. After monitoring that the UE has completed the random access process, the sending MAC entity transmits the downlink MAC SDU associated with the downlink PDCP SDU to be transmitted to the UE based on the relevant DRB, so as to shorten the transmission delay of the downlink PDCP SDU.

[0102] Alternatively, when the source gNB and the target gNB are different gNBs, the source gNB synchronizes the downlink PDCP SDU to be transmitted to the target gNB, and when the target gNB receives the downlink PDCP SDU to be transmitted through the sending PDCP entity in its own CU, it caches it to the sending MAC entity in the target DU in the target gNB that communicates with the UE. After monitoring that the UE has completed the random access process, the sending MAC entity transmits the downlink MAC SDU associated with the downlink PDCP SDU to be transmitted to the UE based on the relevant DRB, so as to shorten the transmission delay of the downlink PDCP SDU.

[0103] Based on the same inventive concept, the present application also provides a data transmission device, which is applied to UE, and its structural diagram is as follows: Figure 7 As shown, specifically including:

[0104] The receiving module 71 is used to receive, through the RRC entity in itself, an RRC connection reconfiguration message sent by the source gNB to which the source cell to which it accesses belongs when determining that the UE needs to be switched from the source cell to the target cell;

[0105] The determining module 72 is configured to determine, through the sending PDCP entity in itself, a first uplink PDCP SDU to be discarded and a second uplink PDCP SDU to be transmitted according to the uplink PDCP status report if it is determined that the RRC connection reconfiguration message carries an uplink PDCP status report corresponding to the target DRB in AM;

[0106] The transmission module 73 is used to discard the first uplink PDCP SDU cached by the UE through the sending PDCP entity, and after sending an RRC connection reconfiguration completion message to the target gNB to which the target cell belongs through the RRC entity, transmit the second uplink PDCP SDU to the target gNB based on the target DRB through the sending PDCP entity.

[0107] Preferably, the source gNB and the target gNB are the same gNB, or, the source gNB and the target gNB are different gNBs.

[0108] The present application also provides a data transmission device, which is applied to UE, and its structural diagram is as follows: Figure 8 As shown, specifically including:

[0109] The receiving module 81 is configured to receive, through the RRC entity in itself, an RRC connection reconfiguration message sent by the source gNB to which the source cell to which the source gNB accesses belongs when determining that the UE needs to be switched from the source cell to the target cell;

[0110] The transmission module 82 is used for sending a downlink PDCP status report for the target DRB to the source gNB through the sending PDCP entity if the downlink PDCP SDU sent by the source gNB based on the target DRB in AM is received through the sending PDCP entity in itself, so that the source gNB determines the first downlink PDCP SDU to be discarded and the second downlink PDCP SDU to be transmitted according to the downlink PDCP status report when receiving the downlink PDCP status report, and discards the first downlink PDCP SDU. When the source gNB and the target gNB to which the target cell belongs are the same gNB, the second downlink PDCP SDU is cached to the sending MAC entity in the target DU in the source gNB that communicates with the UE through the sending PDCP entity in the CU of the source gNB. After monitoring that the UE completes the random access process, the sending MAC entity transmits the downlink MAC SDU associated with the second downlink PDCP SDU to the UE based on the target DRB, or, when the source gNB and the target gNB are different gNBs, the second downlink PDCP SDU is cached to the sending MAC entity in the target DU in the source gNB that communicates with the UE. The SDU is synchronized to the target gNB so that when the target gNB receives the second downlink PDCP SDU through the sending PDCP entity in its own CU, it caches it to the sending MAC entity in the DU that communicates with the UE in the target gNB. After monitoring that the UE has completed the random access process, the sending MAC entity transmits the downlink MAC SDU associated with the second downlink PDCP SDU to the UE based on the target DRB.

[0111] The present application also provides a data transmission device, which is applied to a gNB, and its structural diagram is as follows: Fig. 9 As shown, specifically including:

[0112] A generating module 91 is used to generate a radio resource control RRC connection reconfiguration message carrying an uplink PDCP status report corresponding to the target DRB when it is determined that the target UE needs to switch from the currently accessed source cell to the target cell and has received an uplink PDCP SDU sent by the target UE based on the target DRB in AM;

[0113] The transmission module 92 is used to send the RRC connection reconfiguration message to the target UE so that the target UE receives the RRC connection reconfiguration message through the RRC entity in itself, and when the sending PDCP entity in itself determines that the RRC connection reconfiguration message carries the uplink PDCP status report, the first uplink PDCP SDU that needs to be discarded and the second uplink PDCP SDU that needs to be transmitted are determined according to the uplink PDCP status report, and the first uplink PDCP SDU cached by the UE is discarded. After sending the RRC connection reconfiguration completion message to the target gNB through the RRC entity, the second uplink PDCP SDU is transmitted to the target gNB through the sending PDCP entity based on the target DRB.

[0114] Preferably, the source gNB and the target gNB are the same gNB, or, the source gNB and the target gNB are different gNBs.

[0115] The present application also provides a data transmission device, which is applied to a gNB, and its structural diagram is as follows: Fig.10 As shown, specifically including:

[0116] The first transmission module 101 is configured to send an RRC connection reconfiguration message to the target UE when it is determined that the target UE needs to be switched from the source cell to the target cell if the source gNB itself is the source gNB to which the source cell accessed by the target UE belongs;

[0117] The determination module 102 is configured to determine, if a downlink PDCP status report for a target DRB in AM sent by the target UE is received, a first downlink PDCP SDU to be discarded and a second downlink PDCP SDU to be transmitted according to the downlink PDCP status report;

[0118] A discarding module 103, configured to discard the first downlink PDCP SDU;

[0119] The second transmission module 104 is used for caching the second downlink PDCP SDU to the sending MAC entity in the target DU communicating with the target UE in the source gNB through the sending PDCP entity in the CU of the source gNB when the source gNB and the target gNB to which the target cell belongs are the same gNB, and the sending MAC entity transmits the downlink MAC SDU associated with the second downlink PDCP SDU to the target UE based on the target DRB after monitoring that the target UE completes the random access process; or

[0120] The synchronization module 105 is used to synchronize the second downlink PDCP SDU to the target gNB when the source gNB and the target gNB are different gNBs, so that when the target gNB receives the second downlink PDCP SDU through the sending PDCP entity in its own CU, it caches it to the sending MAC entity in the DU that communicates with the target UE in the target gNB, and after monitoring that the target UE completes the random access process, the sending MAC entity transmits the downlink MAC SDU associated with the second downlink PDCP SDU to the target UE based on the target DRB.

[0121] It can be seen from the above technical solution that in an embodiment of the present application, the source gNB carries the uplink PDCP status report corresponding to the target DRB in AM for the UE in the RRC connection reconfiguration message, so that the UE can process the uplink PDCP status report in time, and after sending the RRC connection reconfiguration completion message to the target gNB to which the target cell belongs through the RRC entity, transmit the relevant uplink PDCP SDU in time to shorten the transmission delay of the uplink PDCP SDU.

[0122] In addition, when the UE receives the RRC connection reconfiguration message sent by the source gNB through its own RRC entity and receives the downlink PDCP SDU sent by the source gNB based on the relevant DRB in AM through its own sending PDCP entity, the UE sends a downlink PDCP status report for the relevant DRB to the source gNB through the sending PDCP entity, so that the source gNB can process the downlink PDCP status report in time, and when the source gNB and the target gNB are the same gNB, the downlink PDCP SDU to be transmitted is cached in the sending MAC entity in the DU in the source gNB that communicates with the UE through the sending PDCP entity in the CU of the source gNB. After monitoring that the UE has completed the random access process, the sending MAC entity transmits the downlink MAC SDU associated with the downlink PDCP SDU to be transmitted to the UE based on the relevant DRB, so as to shorten the transmission delay of the downlink PDCP SDU.

[0123] Alternatively, when the source gNB and the target gNB are different gNBs, the source gNB synchronizes the downlink PDCP SDU to be transmitted to the target gNB, and when the target gNB receives the downlink PDCP SDU to be transmitted through the sending PDCP entity in its own CU, it caches it to the sending MAC entity in the target DU in the target gNB that communicates with the UE. After monitoring that the UE has completed the random access process, the sending MAC entity transmits the downlink MAC SDU associated with the downlink PDCP SDU to be transmitted to the UE based on the relevant DRB, so as to shorten the transmission delay of the downlink PDCP SDU.

[0124] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A data transmission method, characterized in that: The method is applied to a user equipment UE, and the method includes: Receiving, through the radio resource control RRC entity in itself, an RRC connection reconfiguration message sent by the source 5G base station gNB to which the source cell to which it accesses belongs when determining that the UE needs to be switched from the source cell to the target cell; If it is determined by the sending packet data convergence protocol PDCP entity in itself that the RRC connection reconfiguration message carries an uplink PDCP status report corresponding to the target data radio bearer DRB in the acknowledged mode AM, the sending PDCP entity determines, according to the uplink PDCP status report, a first uplink PDCP service data unit SDU to be discarded and a second uplink PDCP SDU to be transmitted; The sending PDCP entity discards the first uplink PDCP SDU cached by the UE, and after sending an RRC connection reconfiguration completion message to the target gNB to which the target cell belongs through the RRC entity, the sending PDCP entity transmits the second uplink PDCP SDU to the target gNB based on the target DRB.

2. The method according to claim 1, characterized in that The source gNB and the target gNB are the same gNB, or the source gNB and the target gNB are different gNBs.

3. A data transmission method, characterized in that: The method is applied to a user equipment UE, and the method includes: Receiving, through the radio resource control RRC entity in itself, an RRC connection reconfiguration message sent by the source 5G base station gNB to which the source cell to which it accesses belongs when determining that the UE needs to be switched from the source cell to the target cell; If a downlink PDCP service data unit SDU sent by the source gNB based on a target data radio bearer DRB in acknowledged mode AM is received through a sending packet data convergence protocol PDCP entity in the source gNB, a downlink PDCP status report for the target DRB is sent to the source gNB through the sending PDCP entity, so that the source gNB determines, when receiving the downlink PDCP status report, a first downlink PDCP SDU that needs to be discarded and a second downlink PDCP SDU that needs to be transmitted according to the downlink PDCP status report, and discards the first downlink PDCP SDU. When the source gNB and the target gNB to which the target cell belongs are the same gNB, the second downlink PDCP SDU is cached in a sending MAC entity in a target distributed unit DU in the source gNB that communicates with the UE through a sending PDCP entity in a centralized unit CU in the source gNB. After monitoring that the UE completes the random access procedure, the sending MAC entity transmits the downlink MAC SDU associated with the second downlink PDCP SDU to the UE based on the target DRB, or, when the source gNB and the target gNB are different gNBs, the second downlink PDCP SDU is cached in a sending MAC entity in a target distributed unit DU in the source gNB that communicates with the UE. The SDU is synchronized to the target gNB so that when the target gNB receives the second downlink PDCP SDU through the sending PDCP entity in its own CU, it caches it to the sending MAC entity in the DU that communicates with the UE in the target gNB, and after monitoring that the UE completes the random access process, the sending MAC entity transmits the downlink MAC SDU associated with the second downlink PDCP SDU to the UE based on the target DRB.

4. A data transmission method, characterized in that: The method is applied to a 5G base station gNB, and the method includes: When it is determined that the target user equipment UE needs to be switched from the currently accessed source cell to the target cell, and an uplink packet data convergence protocol PDCP service data unit SDU sent by the target UE based on a target data radio bearer DRB in an acknowledgement mode AM is received, a radio resource control RRC connection reconfiguration message carrying an uplink PDCP status report corresponding to the target DRB is generated; The RRC connection reconfiguration message is sent to the target UE, so that the target UE receives the RRC connection reconfiguration message through the RRC entity in itself, and when the sending PDCP entity in itself determines that the RRC connection reconfiguration message carries the uplink PDCP status report, the first uplink PDCP SDU that needs to be discarded and the second uplink PDCP SDU that needs to be transmitted are determined according to the uplink PDCP status report, the first uplink PDCP SDU cached by the UE is discarded, and after sending an RRC connection reconfiguration completion message to the target gNB through the RRC entity, the second uplink PDCP SDU is transmitted to the target gNB through the sending PDCP entity based on the target DRB.

5. The method according to claim 4, characterized in that The source gNB and the target gNB are the same gNB, or the source gNB and the target gNB are different gNBs.

6. A data transmission method, characterized in that: The method is applied to a 5G base station gNB, and the method includes: If it is the source gNB to which the source cell accessed by the target user equipment UE belongs, when it is determined that the target UE needs to be switched from the source cell to the target cell, a radio resource control RRC connection reconfiguration message is sent to the target UE; If a downlink packet data convergence protocol PDCP status report for a target data radio bearer DRB in acknowledged mode AM sent by the target UE is received, determining, according to the downlink PDCP status report, a first downlink PDCP SDU that needs to be discarded and a second downlink PDCP SDU that needs to be transmitted; discarding the first downlink PDCP SDU; When the source gNB and the target gNB to which the target cell belongs are the same gNB, the second downlink PDCP SDU is cached to a sending MAC entity in a target distributed unit DU in the source gNB that communicates with the target UE through a sending PDCP entity in a centralized unit CU in the source gNB, and after monitoring that the target UE completes a random access procedure, the sending MAC entity transmits a downlink MAC SDU associated with the second downlink PDCP SDU to the target UE based on the target DRB; or, When the source gNB and the target gNB are different gNBs, the second downlink PDCP SDU is synchronized to the target gNB, so that when the target gNB receives the second downlink PDCP SDU through the sending PDCP entity in its own CU, it caches it to the sending MAC entity in the DU that communicates with the target UE in the target gNB, and after monitoring that the target UE completes the random access process, the sending MAC entity transmits the downlink MAC SDU associated with the second downlink PDCP SDU to the target UE based on the target DRB.

7. A data transmission device, characterized in that: The device is applied to a user equipment UE, and the device includes: A receiving module, configured to receive, through a radio resource control RRC entity in itself, an RRC connection reconfiguration message sent by a source 5G base station gNB to which a source cell to which the UE accesses belongs when determining that the UE needs to be switched from the source cell to a target cell; A determination module, configured to determine, through the sending PDCP entity, a first uplink PDCP service data unit SDU that needs to be discarded and a second uplink PDCP SDU that needs to be transmitted according to the uplink PDCP status report, if it is determined through the sending packet data convergence protocol PDCP entity in the RRC connection reconfiguration message that the uplink PDCP status report corresponding to the target data radio bearer DRB in the confirmation mode AM is carried; A transmission module is used to discard the first uplink PDCP SDU cached by the UE through the sending PDCP entity, and after sending an RRC connection reconfiguration completion message to the target gNB to which the target cell belongs through the RRC entity, transmit the second uplink PDCP SDU to the target gNB based on the target DRB through the sending PDCP entity.

8. A data transmission device, characterized in that: The device is applied to a user equipment UE, and the device includes: A receiving module, configured to receive, through a radio resource control RRC entity in itself, an RRC connection reconfiguration message sent by a source 5G base station gNB to which a source cell to which the UE accesses belongs when determining that the UE needs to be switched from the source cell to a target cell; a transmission module, configured to, if a downlink PDCP service data unit SDU sent by the source gNB based on a target DRB in an acknowledgement mode AM is received through a sending packet data convergence protocol PDCP entity in the transmission PDCP entity, send a downlink PDCP status report for the target DRB to the source gNB through the transmission PDCP entity, so that the source gNB, when receiving the downlink PDCP status report, determines a first downlink PDCP SDU to be discarded and a second downlink PDCP SDU to be transmitted according to the downlink PDCP status report, and discards the first downlink PDCP SDU; when the source gNB and the target gNB to which the target cell belongs are the same gNB, the second downlink PDCP SDU is cached in a sending MAC entity in a target distributed unit DU in the source gNB that communicates with the UE through a sending PDCP entity in a centralized unit CU in the source gNB; after monitoring that the UE completes a random access procedure, the sending MAC entity transmits a downlink MAC SDU associated with the second downlink PDCP SDU to the UE based on the target DRB, or, when the source gNB and the target gNB are different gNBs, the second downlink PDCP SDU is cached in a sending MAC entity in a target distributed unit DU in the source gNB that communicates with the UE. The SDU is synchronized to the target gNB so that when the target gNB receives the second downlink PDCP SDU through the sending PDCP entity in its own CU, it caches it to the sending MAC entity in the DU that communicates with the UE in the target gNB, and after monitoring that the UE completes the random access process, the sending MAC entity transmits the downlink MAC SDU associated with the second downlink PDCP SDU to the UE based on the target DRB.

9. A data transmission device, characterized in that: The device is applied to a 5G base station gNB, and the device includes: A generating module, configured to generate a radio resource control RRC connection reconfiguration message carrying an uplink PDCP status report corresponding to the target DRB when it is determined that the target user equipment UE needs to be switched from the currently accessed source cell to the target cell and an uplink packet data convergence protocol PDCP service data unit SDU sent by the target UE based on a target data radio bearer DRB in an acknowledgement mode AM is received; A transmission module is used to send the RRC connection reconfiguration message to the target UE, so that the target UE receives the RRC connection reconfiguration message through the RRC entity in itself, and when the sending PDCP entity in itself determines that the RRC connection reconfiguration message carries the uplink PDCP status report, determines the first uplink PDCP SDU that needs to be discarded and the second uplink PDCP SDU that needs to be transmitted according to the uplink PDCP status report, discards the first uplink PDCP SDU cached by the UE, and after sending the RRC connection reconfiguration completion message to the target gNB through the RRC entity, transmits the second uplink PDCP SDU to the target gNB based on the target DRB through the sending PDCP entity.

10. A data transmission device, characterized in that: The device is applied to a 5G base station gNB, and the device includes: A first transmission module is configured to send a radio resource control RRC connection reconfiguration message to the target UE when it is determined that the target UE needs to be switched from the source cell to the target cell if the source gNB itself is the source gNB to which the source cell accessed by the target user equipment UE belongs; a determination module, configured to determine, if a downlink packet data convergence protocol PDCP status report for a target DRB in the AM sent by the target UE is received, a first downlink PDCP SDU to be discarded and a second downlink PDCP SDU to be transmitted according to the downlink PDCP status report; A discarding module, configured to discard the first downlink PDCP SDU; A second transmission module is configured to cache the second downlink PDCP SDU to a sending MAC entity in a target distributed unit DU in the source gNB that communicates with the target UE when the source gNB and the target gNB to which the target cell belongs are the same gNB, through a sending PDCP entity in a centralized unit CU in the source gNB, and after the sending MAC entity monitors that the target UE completes a random access procedure, transmits the downlink MAC SDU associated with the second downlink PDCP SDU to the target UE based on the target DRB; or A synchronization module is used for synchronizing the second downlink PDCP SDU to the target gNB when the source gNB and the target gNB are different gNBs, so that when the target gNB receives the second downlink PDCP SDU through the sending PDCP entity in its own CU, it caches it to the sending MAC entity in the DU that communicates with the target UE in the target gNB, and after monitoring that the target UE completes the random access process, the sending MAC entity transmits the downlink MAC SDU associated with the second downlink PDCP SDU to the target UE based on the target DRB.

Images