Method for dual protocol for mobility enhancement and user equipment thereof

Abstract

Apparatuses and methods are provided to reduce mobility interruption time by dual protocol stack for mobility enhancement. In novel aspects, a UE configures a target protocol stack for a target gNB upon receiving a reconfiguration message from a source gNB, performs a random access procedure and establishes an RRC connection with the target gNB through the target protocol stack while maintaining data transmission and reception with the source gNB, releases the source RRC connection with the source gNB upon detecting one or more predefined release trigger events, and performs data transmission and reception with the target gNB. In one embodiment, the target protocol stack includes a PHY layer, a MAC layer and RLC layer, a PDCP layer, and an optional SDAP layer. In one embodiment, the UE enables PDCP reordering, wherein the PDCP reordering is performed on PDCP protocol data units received from the source protocol stack and the target protocol stack. The present invention utilizes dual protocol stack to achieve the beneficial effect of reducing mobility interruption time.

Description

[0001] Cross-references

[0002] This application is filed under 35 U.SC §111(a) and claims priority under 35 U.SC §120 and §365(c) for the following international application, filed on June 27, 2018, with application number PCT / CN2018 / 093142, entitled “Apparatus and Methods to support dual-protocol for mobility enhancement”, the invention of which is incorporated herein by reference. Technical Field

[0003] The embodiments of the present invention are generally related to wireless communication, and more specifically, to reducing mobility interruption time through a dual protocol stack for mobility enhancement. Background Technology

[0004] 5G radio access technology will be a key component of modern access networks. It will address the high traffic growth and increasing demand for high-bandwidth connectivity. It will also support a large number of connected devices, meeting the real-time, high-reliability communication requirements of mission-critical applications. Both standalone new radio (NR) deployments and non-standalone NR deployments combined with Long Term Evolution (LTE) or Enhanced LTE (eLTE) will be considered. To improve the user experience, it is necessary to reduce mobility interruption time during handover. Mobility interruption time refers to the shortest duration during which a user terminal cannot exchange user plane data packets with any base station during the transition period. The target for mobility interruption time should be 0 milliseconds (ms), which applies to both intra-frequency and inter-frequency mobility within NR. In current LTE networks, the latency during handover from step 7 (receiving RRC connection reconfiguration) to step 11 (RRC connection reconfiguration complete) is close to 50 ms. This latency does not meet the mobility interruption requirements of NR networks. An alternative solution, make-before-break, is used to reduce mobility disruptions. While this reduces latency, disruptions due to random access (RA) acquiring and transmitting RRC connection reconfiguration complete messages are unavoidable. Improvements are needed to reduce mobility disruptions during handover. Summary of the Invention

[0005] Apparatus and methods are provided to reduce mobility downtime using a dual protocol stack for mobility enhancement. In one novel aspect, when a UE receives a reconfiguration message from a source gNB in ​​a wireless network, it configures a target protocol stack for a target gNB, wherein the UE performs data transmission and reception with the source gNB via the source protocol stack, performs a random access (RA) process, establishes an RRC connection with the target gNB via the target protocol stack, maintains data transmission and reception with the source gNB, and releases the RRC connection with the source gNB and performs data transmission and reception with the target gNB upon detection of one or more predefined release trigger events. In one embodiment, the target protocol stack includes a PHY layer, a MAC layer, and an RLC layer. In another embodiment, the target protocol stack further includes at least one upper layer of: a Packet Data Convergence Protocol (PDCP) layer and a Service Data Adaptation Protocol (SDAP) layer. In one embodiment, the reconfiguration message instructs the UE to maintain the RRC connection with the source gNB and the source protocol stack. In another embodiment, the reconfiguration message indicates the establishment of a new data radio bearer (DRB) for the target gNB. In yet another embodiment, the reconfiguration message indicates that the target gNB should continue data packet transmission using the existing source DRB. In one embodiment, the UE sends a reconfiguration response message to the target gNB when establishing an RRC connection with the target gNB, and simultaneously performs data transmission and reception with both the source and target gNBs. In another embodiment, the UE enables PDCP reordering, wherein PDCP reordering is performed on PDCP protocol data units (PDUs) received from the source and target protocol stacks.

[0006] In other embodiments, one or more release triggering events include: receiving an RRC connection release message from a source gNB, receiving an RRC connection release message from a target gNB, receiving an RRC connection release message in response to an RRC connection release request sent by the UE upon detection of a radio link failure (RLF) at the source gNB, and receiving an RRC connection release message in response to an RRC connection release request sent by the UE, wherein the UE indicates an RLF to the target gNB. In yet another embodiment, the UE triggers a PDCP status report when releasing the source RRC connection.

[0007] This paper proposes a dual-protocol method for mobility enhancement and its user equipment, which utilizes a dual-protocol stack to achieve the beneficial effect of reducing mobility interruption time.

[0008] This invention is not intended to define the invention; the invention is defined by the claims. Attached Figure Description

[0009] The accompanying drawings illustrate embodiments of the invention, wherein the same numbers indicate the same components.

[0010] Figure 1 This is an exemplary system schematic diagram illustrating an example wireless communication network with a dual protocol stack for mobility enhancement, according to an embodiment of the present invention.

[0011] Figure 2 An example NR wireless system with a centralized upper layer and an NR radio interface stack is shown in an embodiment of the present invention.

[0012] Figure 3 An example NR wireless system supporting inter-gNB mobility scenarios is illustrated according to an embodiment of the present invention.

[0013] Figure 4 An example NR wireless system using E-UTRA for intra-system RAT handover is illustrated according to an embodiment of the present invention.

[0014] Figure 5 An exemplary mobility process using a dual protocol stack between two gNBs having a common central unit is illustrated according to an embodiment of the present invention.

[0015] Figure 6 An exemplary mobility process using a dual protocol stack between two gNBs using different central units is illustrated in an embodiment of the present invention.

[0016] Figure 7A An exemplary message diagram illustrating the release of a 0ms mobility interruption implemented using a dual protocol stack, based on an embodiment of the present invention, is shown.

[0017] Figure 7B An exemplary message diagram illustrating a 0ms mobility interruption using a dual protocol stack and a release triggered by an RLF according to an embodiment of the present invention is shown.

[0018] Figure 8 An exemplary dual protocol stack is illustrated in an embodiment of the present invention.

[0019] Figure 9 An exemplary dual-protocol stack processing method using PDCP reordering is illustrated in an embodiment of the present invention.

[0020] Figure 10 An exemplary dual-protocol stack processing method using PDCP reordering is illustrated in an embodiment of the present invention.

[0021] Figure 11An exemplary flowchart for implementing a 0ms mobility interruption during protocol stack attachment during inter-gNB HO is shown in an embodiment of the present invention.

[0022] Figure 12 An exemplary flowchart for handling different security keys during HO between gNBs to achieve 0ms mobility interruption is shown in an embodiment of the present invention.

[0023] Figure 13 An exemplary flowchart for removing the protocol stack during an inter-gNB HO period to achieve a 0ms mobility interruption is shown in an embodiment of the present invention.

[0024] Figure 14 An exemplary flowchart for triggering a PDCP status report when the protocol stack is removed during an inter-gNB HO is provided in an embodiment of the present invention.

[0025] Figure 15 An exemplary flowchart for a UE to perform data transmission using a dual protocol stack to reduce interruptions is shown in an embodiment of the present invention. Detailed Implementation

[0026] Reference is now made to some embodiments of the present invention, examples of which are described in the accompanying drawings.

[0027] Figure 1 This is an exemplary system schematic diagram illustrating an example wireless communication network 100 with a dual protocol stack for mobility enhancement according to an embodiment of the present invention. The wireless communication network 100 includes one or more fixed infrastructure units forming a network distributed across a geographical area. The infrastructure unit may also be referred to as an access point, access terminal, base station, Node B, evolved Node B (eNB), next-generation Node B (gNB), or other terms used in the art. As an example, a base station serves multiple mobile stations within a service area (e.g., a cell) or a cell sector. In some systems, one or more base stations are coupled to a controller, forming an access network coupled to one or more core networks. gNB 101 and gNB 102 are base stations in an NR network whose service areas may overlap or not overlap. For example, UE 105 or mobile station 105 is only in the service area of ​​gNB 101 and connected to gNB 101. UE 105 is only connected to gNB 101. Similarly, UE 106 is only in the service area of ​​gNB 102 and connected to gNB 102. UE 106 connects only to gNB 102. gNB 101 connects to gNB 102 via Xnr interface 109. UE 103 is located in the overlapping service area of ​​gNB 101 and gNB 102. In one embodiment, UE 103 is configured with a dual protocol stack and can connect to both gNB 101 and gNB 102 simultaneously.

[0028] Figure 1 A simplified block diagram of gNB 102 and mobile station or UE 103 is further shown according to the present invention. gNB 102 has an antenna 156 that transmits and receives radio signals. An RF transceiver module 153 is coupled to the antenna 156, receives RF signals from the antenna 156, converts the RF signals into baseband signals, and sends the baseband signals to a processor 152. The RF transceiver module 153 also converts the baseband signals received from the processor 152, converting the baseband signals into RF signals, and sends them to the antenna 156. The processor 152 processes the received baseband signals and invokes different functional modules to perform features in gNB 102. Memory 151 stores program instructions and data 154 to control the operation of gNB 102. gNB 102 has a protocol stack 161. gNB 102 also includes a set of control modules 155 that perform functional tasks to communicate with the mobile station. Control modules 155 may include a measurement module, a mobility controller, a protocol stack controller, and a security processor. The measurement module controls RRM measurements via RRC configuration and receives measurement reports from the UE. The mobility controller determines the target gNB for mobility. The mobility controller coordinates with other candidate gNBs via the Xnr interface, makes a handover (HO) decision, and sends an HO command to the UE. The protocol stack controller manages the processes of attaching or removing protocol stacks associated with the source and target gNBs. The security processor generates a security key corresponding to the gNB. The protocol stack includes SDAP, PDCP, RLC, MAC, and PHY layers. In one embodiment, the SDAP layer is optionally configured.

[0029] UE 103 has an antenna 135 that transmits and receives radio signals. An RF transceiver module 137 is coupled to the antenna 135, receives RF signals from the antenna 135, converts the RF signals into baseband signals, and sends the baseband signals to the processor 132. In one embodiment, the RF transceiver module 137 may include two RF modules (not shown). A first RF module is used for high-frequency transmission and reception, and another RF module, different from the high-frequency transceiver, is used for transmission and reception in a different frequency band. The RF transceiver module 137 also converts the baseband signals received from the processor 132 into RF signals and sends them to the antenna 136. The processor 132 processes the received baseband signals and calls different functional modules to perform features in UE 103. Memory 131 stores program instructions and data 138 to control the operation of UE 103. Antenna 135 transmits uplink transmissions to antenna 156 of gNB 102 and receives downlink transmissions from gNB 102.

[0030] Mobile station 103 also includes a set of control modules that perform functional tasks. Measurement module 191 controls RRM measurements according to the network configuration. Mobility controller 192 receives RRC messages for mobility, such as HO commands, and sends response messages for HO commands. Protocol stack controller 193 manages the processes of attaching or removing protocol stacks associated with the source gNB and the destination gNB. Security processor 194 associates different security keys with the corresponding gNBs. Dual protocol stacks are enabled for UE 103. Protocol stack 1 133 and protocol stack 2 134 are respectively configured with a PHY layer, a MAC layer, an RLC layer, a PDCP layer, and an SDAP layer. In one embodiment, the SDAP layer is optional. In one embodiment, a PDCP reordering function is present, which receives PDCP PDUs from the destination gNB and the source gNB, reorders these PDCP PDUs based on sequence number (SN) / count, and transmits PDCP service data units (SDUs) to the upper layer in sequence. In one embodiment, PDCP reordering is enabled when an HO command is received. In one embodiment, PDCP reordering is performed by the PDCP layer; in another embodiment, PDCP reordering is performed by the SDAP layer. Note that... Figure 1 The modules can be implemented via circuits.

[0031] Figure 2 An example NR wireless system with a centralized upper layer and an NR radio interface stack is illustrated according to an embodiment of the present invention. Different protocol partitioning options exist between the central unit and the lower layers of the gNB node. The functional partitioning between the central unit and the lower layers of the gNB node may depend on the transport layer. Since higher-level protocol layers have lower performance requirements for the transport layer in terms of bandwidth, latency, synchronization, and jitter, low-performance transmission between the central unit and the lower layers of the gNB node allows the higher-level protocol layers of the NR radio stack to be supported in the central unit. In one embodiment, the SDAP and PDCP layers are located in the central unit, while the RLC, MAC, and PHY layers are located in the distributed units. The core unit 201 is connected to the central unit 211, which has a gNB upper layer 252. In one embodiment, the gNB upper layer 252 includes a PDCP layer and optionally an SDAP layer. The central unit 211 is connected to distributed units 221, 222, and 223. Distributed units 221, 222, and 223 correspond to cells 231, 232, and 233, respectively. Distributed units 221, 222, and 223 include the gNB lower layer 251. In one embodiment, the lower layer 251 of the gNB includes a PHY, a MAC, and an RLC layer.

[0032] Figure 3An example NR radio system supporting inter-gNB mobility scenarios is illustrated according to embodiments of the present invention. 5G intra-RAT handover is typically based on Xn handover. HO is performed between gNBs connected to the NR core network via the Xn interface. Each gNB has a protocol stack including SDAP, PDCP, RLC, MAC, and PHY layers. gNB 311 and gNB 312 are 5G gNBs with protocol stacks 351 and 352, respectively. gNB 311 and gNB 312 are connected to core 301 via NG. gNB 311 and gNB 312 are interconnected via the Xn interface. Protocol stacks 351 and 352 include PHY, MAC, RLC, PDCP, and optional SDAP.

[0033] Figure 4 An example NR wireless system supporting intra-system RAT handover using E-UTRA is illustrated according to an embodiment of the present invention. Intra-system RAT handover is typically based on Xn handover. HO is performed between the gNB and eLTE / eNB via the Xn interface, which is connected to the NR core network. The gNB has a protocol stack including SDAP, PDCP, RLC, MAC, and PHY layers, while the eLTE / eNB has a protocol stack including PDCP, RLC, MAC, and PHY layers. gNB 411 is a 5G gNB with protocol stack 451. Base station 412 is an LTE / eLTE eNB with protocol stack 452. gNB 411 and eNB 412 are connected to core 401 via NG. gNB 411 and eNB 412 are interconnected via the Xn interface. Protocol stack 451 includes PHY, MAC, RLC, PDCP, and optional SDAP. Protocol stack 452 includes PHY, MAC, RLC, and PDCP.

[0034] Figure 5An exemplary mobility process using dual protocol stacks between two gNBs with a common central unit (CU) is illustrated according to an embodiment of the present invention. Cells 501 and 502 are controlled by different gNBs with a common central unit (CU), which includes a PDCP layer and an optional SDAP layer. The UE moves between different distributed units (DUs) including PHY, MAC, and RLC layers. The SDAP and PDCP layers are common to all DUs and are located in the CU. Each DU has RLC, MAC, and PHY layers. Cell 501 is covered by DU1, and cell 502 is covered by DU2. At time T1 511, the UE connects to DU1 configured with a protocol stack 521. A UE protocol stack 531 including SDAP, PDCP, RLC, MAC, and PHY layers is established on the UE side, and the UE protocol stack 531 has a peer layer on the network side. At time T2 512, the UE moves to the cell edge. The CU determines that the UE performs a HO (House of Occurrence) from cell 501 to cell 502. To minimize mobility disruption, simultaneous data transmission and reception with cells 501 and 502 should be supported. A target protocol stack with RLC, MAC, and PHY layers is established for DU2. The gNB protocol stack 522 includes a source protocol stack and a target protocol stack. The HO command instructs the establishment of RLC and the creation of the MAC layer on the UE side without rebuilding PDCP, for example, by attaching via RLC bearer. The UE establishes a dual protocol stack 532 with a target DU layer including PHY, MAC, and RLC. The target DU stack is inactive at time T2 512. At time T3 513, after the protocol stack is established for the target cell, the PDCP reordering function is enabled. PDCPPDUs of the data radio bearer (DRB) are transmitted through the two RLC entities located in DU1 and DU2, respectively. The common PDCP entity on the UE side performs PDCP reordering on the PDCP PDUs received from the two RLC entities. The network protocol stack 523 has both the source DU stack and the target DU stack connected to the CU stack in an active state. UE protocol stack 533 has a source DU stack and a target DU stack with a pre-configured common PDCP layer and an optional common SDAP layer. At time T4 514, when the UE moves out of the source cell's coverage area, the radio link with the source cell becomes unreliable for data packet transmission, for example, due to a radio link failure (RLF). The CU stops data transmission via DU1. The UE's source DU in protocol stack 534 is not activated when the target DU stack is activated. The UE only receives PDCP PDUs from the RLC entity corresponding to the target cell. The gNB also deactivates the source DU in protocol stack 524.At time T515, the source cell's protocol stack is removed, for example, via RLC bearer removal. UE protocol stack 535 and gNB protocol stack 525 are activated only as the target protocol stack.

[0035] Figure 6 An exemplary mobility process using dual protocol stacks between two gNBs with different central units is illustrated according to an embodiment of the present invention. Cells 601 and 602 are controlled by different gNBs with different CUs, and the central unit includes a PDCP layer and an optional SDAP layer. Each gNB has a protocol stack including SDAP, PDCP, RLC, MAC, and PHY layers. At time T1 611, the UE connects to gNB1 via protocol stack 631. A peer layer of gNB1 protocol stack 621 is established on the UE side, including SDAP, PDCP, RLC, MAC, and PHY layers. At time T2 612, the UE moves to the cell edge. gNB1 determines to perform a HO (House of Origin) from the UE to gNB2. To minimize mobility interruption, simultaneous data transmission and reception with gNB1 and gNB2 should be supported. A target protocol stack with SDAP, PDCP, RLC, MAC, and PHY layers is established for gNB2. gNB protocol stack 622 has a source protocol stack and a target protocol stack, and data transmission is performed through the source protocol stack. The HO command instructs the establishment of SDAP, PDCP, RLC, and the creation of the MAC layer on the UE side. Similarly, the UE protocol stack 632 has a source protocol stack and a target protocol stack. At time T3 613, after the protocol stack is established for the target gNB, the PDCP reordering function is activated. The DRB's PDCP PDUs are transmitted through two PDCP entities located in gNB1 and gNB2, respectively. The gNB protocol stack 623 includes the source protocol stack of gNB1 and the target protocol stack of gNB2. The PDCP reordering function on the UE side performs PDCP reordering on the PDCP PDUs received from the two PDCP entities. The UE protocol stack 633 also has both an active source protocol stack and an active target protocol stack. At time T4 614, when the UE moves out of the coverage area of ​​the source cell, the radio link with the source cell is not reliable enough for data packet transmission, for example, due to RLF. gNB1 stops data transmission. The gNB protocol stack 624 deactivates the source protocol stack of gNB1 and activates the target protocol stack of gNB2. The UE receives PDCP PDUs from gNB2 only through protocol stack 634, where the source protocol stack of protocol stack 634 is deactivated and the target protocol stack is activated. At time T5 615, the protocol stack of gNB1 is removed. UE protocol stack 635 contains only the target protocol stack. gNB protocol stack 625 contains only the target protocol stack.

[0036] Figure 7AThis invention illustrates an exemplary message diagram of a network-initiated release of a 0ms mobility interruption implemented using a dual protocol stack, according to an embodiment of the present invention. UE 701 is connected to gNB 702, which is the source gNB. gNB 703 is the handover target gNB for UE 701. In step 711, the UE sends a measurement report to gNB 702. In step 712, the source gNB 701 initiates a handover and sends a handover request to the target gNB 703 based on the Xn interface. In step 713, the target gNB 703 performs admission control. In step 714, the target gNB 703 provides RRC configuration as part of the handover confirmation. In step 715, the source gNB 702 provides RRC configuration to UE 701 in an HO command. The HO command instructs to maintain RRC connectivity and protocol stack with the source gNB 702. Upon receiving the HO command, in step 721, UE 701 maintains an RRC connection and a protocol stack including SDAP, PDCP, RLC, MAC, and PHY with the source gNB, and continues data packet transmission and reception with the source gNB. To support simultaneous transmission, in step 722, the source gNB 702 maintains multiple PDCP SDUs and forwards other PDCP SDUs to the target gNB 703. In step 731, UE 701 continues data packet transmission and reception with the source gNB 702. Furthermore, in step 732, the source gNB 702 reserves multiple sequence numbers (SNs) for unsent PDCP SDUs and forwards the SN status to the target gNB 703. In step 734, the target gNB 703 buffers the source packet data received from the source gNB 702. Then, in step 733, UE 701 synchronizes with target gNB 703 and performs random access to target gNB 703, while continuing data packet transmission simultaneously with the source gNB. In step 741, UE 701 establishes an RRC connection to target gNB 703 and replies that the handover is complete. Then, data packet transmission is performed simultaneously through two protocol stacks for source gNB 701 (step 752) and target gNB 703 (step 751). In this case, the HO mechanism triggered by RRC requires the UE not to reset the MAC entity, not to rebuild the RLC, and not to rebuild the PDCP. Handover managed by RRC is supported with and without PDCP entity rebuild. When the target gNB uses the same DRB configuration as the source gNB, data forwarding, in-order delivery, and duplication avoidance during handover can be guaranteed. Finally, the connection with the source gNB is released when one or more predefined trigger events occur. In one embodiment, the protocol stack and RRC connection with the source gNB are released when all data buffered from the source gNB is successfully transmitted. In step 761, the UE automatically releases the connection with the source gNB 702.In another embodiment, as shown in step 771, the connection is released by an explicit RRC message sent by either the source gNB 702 or the target gNB 703. In yet another embodiment, in step 772, the RRC connection release message may optionally originate from the source gNB 702.

[0037] Figure 7B This invention illustrates an exemplary message diagram demonstrating a 0ms mobility interruption using a dual-protocol stack with a release triggered by an RLF. UE 701 is connected to gNB 702, which is the source gNB. gNB 703 is the handover target gNB for UE 701. Figure 7A As shown, when the handover from source gNB 702 to target gNB 703 is completed, the UE uses a dual protocol stack for handover to achieve interrupt enhancement from steps 711 to 751 and 752, while exchanging data with both source gNB 702 and target gNB 703. In one embodiment, when an RLF occurs or the measurement result of the radio link with the source gNB is below a threshold, the UE automatically releases the protocol stack and RRC connection with the source gNB. In one embodiment, in step 791, the connection is released via an explicit RRC message sent by the target gNB 703, which is a response message to the RLF report (step 781) from the UE side. In another embodiment, in step 792, the connection is released via an explicit RRC message sent by the source gNB 702, which is a response message to the RLF report from the UE side.

[0038] Figure 8 An exemplary dual-protocol stack is illustrated according to an embodiment of the present invention. In one embodiment, a new DRB is established at the target gNB. In this case, different DRBs are sent from the source gNB and the target gNB using different protocol stacks. PDCP reordering is not required. UE 801 connects to gNB 802 using protocol stack 811 and protocol stack 821. A DRB is established between UE 801 and the source gNB 802. When switching to the target gNB 803, UE 801 also establishes a DRB with the target gNB 803 using protocol stack 831. Reordering is not required for this configuration. The source gNB 802 connects to the target gNB 803 via Xn interface 841.

[0039] Figure 9An exemplary dual-stack processing method using PDCP reordering is illustrated in an embodiment of the present invention. UE 901 establishes a connection with source gNB 902 using protocol stack 911 and source protocol stack 931. Upon receiving a HO command instructing the establishment of a new protocol stack for target gNB 903, the UE establishes SDAP, PDCP, RLC, and creates a MAC entity using protocol stack 921. Simultaneously, the PDCP reordering function is enabled. Source gNB 902 reserves a range of SNs (e.g., 0–499) for PDCP SDU transmission via the source gNB and forwards the remaining PDCP SDUs #500 and above to target gNB 903. Furthermore, source gNB 902 sends the SN status to target gNB 903, for example, the initial SN is 500. Source gNB 902 connects to target gNB 903 via Xn interface 941. The UE then receives PDCP PDUs from the two PDCP entities corresponding to the source and target gNBs. For example, PDCP PDU#0 and PDCP PDU#1 are received from the source gNB, while PDCP PDU#500 and PDCP PDU#501 are received from the destination gNB. Since PDCP PDUs are received out of order, a PDCP reordering function is used to ensure sequential transmission and avoid duplication. When a PDCP PDU with an SN of 2 to 499 is received, all stored PDCP SDUs will be transmitted to the upper layer.

[0040] Figure 10An exemplary dual-stack processing method using PDCP reordering is illustrated in an embodiment of the present invention. A UE 1001 with protocol stack 1011 is connected to a source gNB 1002 with protocol stack 1021. PDCP PDUs #0 and #1 are received from the source gNB 1002, while PDCP PDUs #500 and #501 are received from the target gNB 1003 using protocol stack 1031. Since PDCP PDUs are received out of order, the PDCP reordering function ensures sequential delivery and avoids duplication. All stored PDCP SDUs are only transmitted to the upper layer when PDCP PDUs with SNs from 2 to 499 are received. In one embodiment, the UE has a source PDCP layer and a target PDCP layer in protocol stack 1011. In another embodiment, the UE has a single PDCP layer for both the source and target gNBs. The reordering process and security-critical features are performed by a common PDCP layer. In one embodiment, all resource PDCP SDUs on the source gNB may be successfully transmitted to the UE. In this case, the RRC connection and protocol stack 1021 of the source gNB are explicitly released by either the source gNB or the target gNB via an RRC Connection Release message. Upon receiving the RRC Connection Release message, the UE releases the RRC connection with the source gNB 1002 and releases the protocol stack 1021. In one embodiment, an RLF may occur before all reserved PDCP SDUs are successfully transmitted to the UE. In one example, all PDCP SDUs with SNs up to #300 are successfully transmitted to the UE. PDCP SDUs with SNs less than or equal to #300 are transmitted to the upper layer. The remaining PDCP SDUs with SNs from #301 to #499 cannot be sent by the source gNB. Therefore, these PDCP SDUs with updated SN states are forwarded to the target gNB. The source gNB 1002 is connected to the target gNB 1003 via the Xn interface 1041. In one embodiment, the UE sends an RLF report from the source gNB to the target gNB. The target gNB responds to the UE with an RRC connection release message to release the RRC connection with the source gNB 1002. In another embodiment, the UE 1001 automatically releases the RRC connection with the source gNB 1002 after sending an RLF report to the target gNB 1003.

[0041] Figure 11An exemplary flowchart for implementing 0ms mobility interruption during a protocol stack attachment during an inter-gNB HO (Ho) operation, according to an embodiment of the present invention, is shown. In step 1101, the UE establishes an RRC connection with the source gNB. In step 1102, the UE receives a HO command instructing the UE to maintain the RRC connection and protocol stack with the source gNB while performing a HO operation with the target gNB. In step 1103, the UE establishes another RRC connection with the target gNB and establishes a protocol stack with the target gNB including SDAP, PDCP, RLC, MAC, and PHY. In step 1104, the UE simultaneously performs data transmission or reception with both the source and target gNBs. Finally, in step 1105, when one or more release trigger events are detected, the UE releases the RRC connection with the source gNB. Release triggering events include: the successful transmission of a reserved PDCP SDU, or when an RLF occurs on the radio link with the source gNB and triggers an RRC connection release (RRCConnectRelease) message from the source gNB or the target gNB, or when the source gNB or the target gNB explicitly sends an RRCConnectRelease message to the UE.

[0042] Figure 12 An exemplary flowchart for handling different security keys during an inter-gNB HO (Ho) operation to achieve a 0ms mobility interruption is shown according to an embodiment of the present invention. In step 1201, after receiving the HO command, the UE establishes a protocol stack with the target gNB. In step 1202, the UE applies a new security key associated with the target gNB and enables PDCP reordering. In step 1203, the UE begins receiving data packets from or sending data packets to both the source and target gNBs. In step 1204, the UE applies the corresponding security key. Different options exist for applying the security key. PDCP entities corresponding to different gNBs apply different keys accordingly. In one embodiment, in step 1214, if the PDCP layer is common to both the source and target gNBs, the UE checks which RLC entity each PDCP PDU was received from and applies the corresponding security key to the received PDCP PDU. In another embodiment, optionally, in step 1224, the UE determines which key to use for each PDCP PDU based on a flag in the PDCP PDU header. In step 1205, the UE performs PDCP reordering on the out-of-order received packets.

[0043] Figure 13An exemplary flowchart for removing the protocol stack during an inter-gNB HO (Hot-Off) event to achieve a 0ms mobility interruption is shown according to an embodiment of the present invention. In step 1301, the UE performs measurements on the source link and determines whether to release the connection with the source gNB. In step 1302, the UE detects an RLF (Relative Link Default) or that the measurement result of the source link is below a threshold. In step 1303, the UE sends an RRC (Release RRC Connection) request to the target gNB. In step 1304, the UE receives an RRC connection release message from the target gNB to release the RRC connection with the source gNB. In step 1305, the UE releases the source protocol stack.

[0044] Figure 14 An exemplary flowchart illustrating the triggering of a PDCP status report during protocol stack removal during an inter-gNB HO (Hospital-Hot) period is provided according to an embodiment of the present invention. Upon releasing the protocol stack of the source gNB, a PDCP status report is triggered for PDCP SDU retransmission. Unsuccessfully transmitted PDCP SDUs are retransmitted by the target gNB. The UE performs PDCP reordering to ensure that PDCP SDUs are transmitted sequentially to the upper layers. In step 1401, the UE releases the source protocol stack. In step 1402, the UE triggers a PDCP status report. In step 1403, the UE retransmits the PDCP SDU that was not successfully transmitted. In step 1404, the UE performs PDCP reordering.

[0045] Figure 15 An exemplary flowchart for a UE to perform data transmission using a dual protocol stack to reduce interruptions is shown according to an embodiment of the present invention. In step 1501, the UE receives a reconfiguration message from a source gNB in ​​the wireless network, wherein the UE performs data transmission and reception with the source gNB through the source protocol stack. In step 1502, the UE configures a target protocol stack for the target gNB based on the received reconfiguration message. In step 1503, the UE performs an RA process and establishes an RRC connection with the target gNB through the target protocol stack, while maintaining data transmission and reception with the source gNB. In step 1504, upon detecting one or more predefined release trigger events, the UE releases the RRC connection with the source gNB and performs data transmission and reception with the target gNB.

[0046] While the invention has been described in conjunction with specific embodiments for illustrative purposes, it is not limited thereto. Therefore, various modifications, adaptations, and combinations of the features of the described embodiments can be made without departing from the scope of the invention as set forth in the claims.

Claims

1. A dual-protocol method for mobility enhancement, comprising: In a wireless network, a user equipment receives a reconfiguration message from a source next-generation node B, wherein the user equipment performs data transmission and reception with the source next-generation node B through the source protocol stack; Configure the target protocol stack for the target next-generation node B based on the received reconfiguration message, wherein the target protocol stack coexists with the source protocol stack; Reconfigure the existing source data radio bearer for this target protocol stack; The random access process is executed and a radio resource control connection is established with the target next-generation node B through the target protocol stack, while maintaining the data transmission and reception with the source next-generation node B; The user equipment packet data aggregation protocol entity performs packet data aggregation protocol reordering on the packet data aggregation protocol data units received from the source protocol stack and the target protocol stack; as well as Upon detecting one or more predefined release trigger events, release the radio resource control connection with the source next-generation node B and perform data transmission and reception with the target next-generation node B.

2. The dual-protocol method for mobility enhancement according to claim 1, characterized in that, The target protocol stack includes the physical layer, the media access control layer, and the radio link control layer.

3. The dual-protocol method for mobility enhancement according to claim 1, characterized in that, The target protocol stack further includes at least one of the following upper layers: packet data aggregation protocol layer and service data adaptation protocol layer.

4. The dual-protocol method for mobility enhancement according to claim 1, characterized in that, The reconfiguration message instructs that the radio resource control connection with the source next-generation node B and the source protocol stack be maintained.

5. The dual-protocol method for mobility enhancement according to claim 1, characterized in that, Further includes: When establishing the radio resource control connection with the target next-generation node B, a reconfiguration response message is sent to the target next-generation node B; as well as Simultaneously, data transmission and reception are performed with both the source next-generation node B and the target next-generation node B.

6. The dual-protocol method for mobility enhancement according to claim 1, characterized in that, Further includes: The first security key is applied to the source protocol stack, and the second security key is applied to the target protocol stack.

7. The dual-protocol method for mobility enhancement according to claim 1, characterized in that, The one or more predefined release trigger events include: Receive the radio resource control connection release message from the next-generation node B of the source; Receive the radio resource control connection release message from point B of the next generation node of the target; Receive a Radio Resource Control Connection Release message in response to a Radio Resource Control Connection Release request sent by the User Equipment upon detection of a radio link failure in the source next-generation node B; and Receive a Radio Resource Control Connection Release message in response to a Radio Resource Control Connection Release request sent by the User Equipment, wherein the User Equipment indicates a radio link failure to the target Next Generation Node B.

8. The dual-protocol method for mobility enhancement according to claim 1, characterized in that, This further includes triggering a packet data aggregation protocol status report when releasing the radio resource control connection with the source next-generation node B.

9. A user equipment for dual protocols for enhanced mobility, comprising: Radio frequency transceivers are used to receive and transmit radio frequency signals in wireless networks; The source and destination protocol stacks that communicate with the radio frequency transceiver; Memory; as well as A processor coupled to the memory, the source protocol stack, and the target protocol stack is configured to: Receive reconfiguration messages from the source next-generation node B, wherein data transmission and reception with the source next-generation node B are performed via the source protocol stack; Based on the received reconfiguration message, configure the target protocol stack for the target next-generation node B, wherein the target protocol stack coexists with the source protocol stack; Reconfigure the existing source data radio bearer for this target protocol stack; The random access process is executed and a radio resource control connection is established with the target next-generation node B through the target protocol stack, while maintaining the data transmission and reception with the source next-generation node B; The user equipment packet data aggregation protocol entity performs packet data aggregation protocol reordering on the packet data aggregation protocol data units received from the source protocol stack and the target protocol stack; as well as Upon detecting one or more predefined release trigger events, release the radio resource control connection with the source next-generation node B and perform data transmission and reception with the target next-generation node B.

10. The user equipment according to claim 9, characterized in that, The target protocol stack includes the physical layer, the media access control layer, and the radio link control layer.

11. The user equipment according to claim 9, characterized in that, The target protocol stack further includes at least one of the following upper layers: packet data aggregation protocol layer and service data adaptation protocol layer.

12. The user equipment according to claim 9, characterized in that, The reconfiguration message instructs that the radio resource control connection with the source next-generation node B and the source protocol stack be maintained.

13. The user equipment according to claim 9, characterized in that, The processor is further configured to: send a reconfiguration response message to the target next-generation node B when establishing the radio resource control connection with the target next-generation node B; and simultaneously perform data transmission and reception with both the source next-generation node B and the target next-generation node B.

14. The user equipment according to claim 9, characterized in that, The processor is further configured to apply a first security key to the source protocol stack and a second security key to the target protocol stack.

15. The user equipment according to claim 9, characterized in that, in, The one or more predefined release trigger events include: Receive radio resource control connection release messages from the source next-generation node B and from the target next-generation node B. Receive a Radio Resource Control Connection Release message in response to a Radio Resource Control Connection Release request sent by the User Equipment upon detection of a radio link failure in the source next-generation node B; and Receive a Radio Resource Control Connection Release message in response to a Radio Resource Control Connection Release request sent by the User Equipment, wherein the User Equipment indicates a radio link failure to the target Next Generation Node B.

16. The user equipment according to claim 9, characterized in that, The processor is further configured to trigger a packet data aggregation protocol status report when the radio resource control connection with the source next-generation node B is released.

Images