WO2024065439A1

WO2024065439A1 - Methods and apparatus to support dual stack based inter-du inter-cell beam management with mobility

Info

Publication number: WO2024065439A1
Application number: PCT/CN2022/122765
Authority: WO
Inventors: Xiaonan Zhang; Yuanyuan Zhang
Original assignee: MediaTek Singapore Pte Ltd
Current assignee: MediaTek Singapore Pte Ltd
Priority date: 2022-09-29
Filing date: 2022-09-29
Publication date: 2024-04-04
Anticipated expiration: 2025-03-29

Abstract

This disclosure describes methods and apparatus of user plane handling for the network and UE to support dual stack based L1/L2 Inter-Cell Beam Management and switching between a first cell and a second cell, further comprising the step of performing the source cell and target cell handling; control the ToS timer to measure the ToS of the cell switch and control the behavior for the source protocol stack, handle the source protocol stack according to the states of the ToS timer.

Description

METHODS AND APPARATUS TO SUPPORT DUAL STACK BASED INTER-DU INTER-CELL BEAM MANAGEMENT WITH MOBILITY

FIELD

The present disclosure relates generally to communication systems, and more particularly, the method to support dual stack based L1/L2 Inter-Cell Beam Management with Mobility.

BACKGROUND

In conventional network of 3rd generation partnership project (3GPP) 5G new radio (NR) , when the UE moves from the coverage area of one cell to another cell, at some point a serving cell change needs to be performed. Currently serving cell change is triggered by L3 measurements and is done by RRC signaling triggered by reconfiguration with synchronization for change of PCell and PSCell, as well as release/add for SCells when applicable. All cases involve complete L2 (and L1) resets, leading to longer latency, larger overhead and longer interruption time than beam switch mobility. In order to reduce the latency, overhead and interruption time during UE mobility, the mobility mechanism can be enhanced to enable a serving cell to change via beam management with L1/L2 signaling. The L1/L2 based inter-cell mobility with beam management should support the different scenarios, including intra-DU/inter-DU inter-cell cell change, FR1/FR2, intra-frequency/inter-frequency, and source and target cells may be synchronized or non-synchronized.

In legacy HO design controlled by a series of L3 procedures including RRM measurement and RRC Reconfiguration, ping-pong effects should be avoided with relatively long ToS (time of stay) in order to reduce the occurrences of HOs, accompanied with which is the reduce of signaling overhead and interruption during the overall lifetime of RRC connection. However, the drawback is that UE can’t achieve the optimized instantaneous throughput if the best beam is not belonging to the serving cell. For L1/L2 based inter-cell mobility with beam management, the network can take advantage of ping-pong effects, i.e., cell switch back and forth between the source and target cells with relatively short ToS, to select the best beams among a wider area including both the source cell and target cell for throughput boosting during UE mobility. L1/L2 based inter-cell mobility is more proper for the scenarios of intra-DU and inter-DU cell change. Ping-pong effect is not concerned in those scenarios. For intra-DU cell change, there is no additional signaling/latency needed at the network side; for inter-DU cell change, the F1 interface between DU and CU can support high data rate with short latency (inter-DU) . L1/L2 based inter- cell mobility is supportable considering the F1 latency is 5ms.

During L1/L2 based inter-cell mobility, DL synchronization and UL time alignment are required with the corresponding serving cell. By default, DL synchronization and UL time alignment are preformed after the handover command is received. Considering the performance requirement of inter-cell beam management, A method to perform DL synchronization and UL time alignment before beam management is introduced to reduce the DIT (Data Interruption Time) during inter-cell beam management. For the scenario UE switches back and forth between cells, a method to control TA maintenance is further introduced to reduce the DIT during inter-cell beam management.

In this invention, apparatus and mechanisms are sought to optimize inter-DU inter-cell mobility scenarios and support dual stack based L1/L2 Inter-Cell Beam Management with Mobility.

SUMMARY

The following presents a simplified summary of one or more aspects in order to provide a basic understanding of such aspects. This summary is not an extensive overview of all contemplated aspects, and is intended to neither identify key or critical elements of all aspects nor delineate the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form as a prelude to the more detailed description that is presented later.

In an aspect of the disclosure, a method, a computer-readable medium, and an apparatus are provided. The apparatus may be a UE.

For the user plane handling of dual stack based L1/L2 Inter-Cell Beam Management, when the network indicates UE to switch the cell, the source protocol stacks (also called protocol stack 1) for the network and UE are deactivated, then the target protocol stacks (also called protocol stack 2) for target cell are established and activated. The RLC and MAC entities of the source protocol stacks for network and UE may be suspended. The L1/L2 Inter-Cell Beam Management may also be referred to as the cell switch procedure, or the handover procedure used in the art. The L1/L2 signaling used to indicate cell switch may also be referred to as the cell switch command, or cell switch signaling used in the art. The source cell may also be referred to as the cell 1, or the first cell used in the art. The target cell may also be referred to as the cell 2, or the second cell used in the art.

When the target protocol stacks for the target cell are established and activated, the Downlink Data Delivery Status frame may not be sent at once and the transmitting side may not retransmit the PDUs which are not successfully decoded by the receiving side of the source protocol stack. A ToS timer is defined and started to measure the ToS of the UE.

In one embodiment, when UE switches back to the cell 1 and the ToS is relatively short (i.e., the ToS timer is still running) , the transmitting side of the protocol stack 1 continues to transmit the previous PDUs which are not successfully decoded by the receiving side of the protocol stack 1. In one embodiment, the lost packets are retransmitted by RLC ARQ. In one embodiment, the lost packets are retransmitted by HARQ. The protocol stack 2 for the network and UE are deactivated, and the transmitting side of protocol stack 1 will not retransmit the PDUs which are not successfully decoded by the receiving side of the protocol stack 2. In one embodiment, the ToS timer is restarted after cell switch.

In one embodiment, when the ToS timer expires before UE switches back to the cell 1 (i.e., the ToS is relatively long) , the Downlink Data Delivery Status frame is sent to notify PDCP of the PDUs which are not successfully decoded by the receiving side of the source protocol stack. In one embodiment, the PDCP data recovery is triggered and the lost PDUs are retransmitted by the target protocol stack. In one embodiment, the RLC entity and the MAC entity for the source protocol stack are re-established and reset.

To the accomplishment of the foregoing and related ends, the one or more aspects comprise the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative features of the one or more aspects. These features are indicative, however, of but a few of the various ways in which the principles of various aspects may be employed, and this description is intended to include all such aspects and their equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates an schematic system diagram illustrating an exemplary 5G new radio network in accordance with embodiments of the current invention.

Figure 2 illustrates an exemplary NR wireless system with centralization of the upper layers of the NR radio stacks in accordance with embodiments of the current invention.

Figure 3 illustrates an exemplary deployment scenario for intra-DU inter-cell beam management in accordance with embodiments of the current invention.

Figure 4 illustrates an exemplary deployment scenario for inter-DU inter-cell beam management in accordance with embodiments of the current invention.

Figure 5 illustrates an exemplary process of user plane handling for network and UE to perform dual stack based inter-cell beam management when UE receiving the cell switch command after the pre-configuration in accordance with embodiments of the current invention.

Figure 6 illustrates an exemplary time chart of a new defined ToS timer to measure the ToS and control the behavior of the source protocol stack after cell switch for dual stack based inter-cell beam management in accordance with embodiments of the current invention.

Figure 7 illustrates an exemplary process of user plane handling for network and UE when UE switch back to the source cell with short ToS behavior for dual stack based inter-cell beam management in accordance with embodiments of the current invention.

Figure 8 illustrates an exemplary process of user plane handling for network and UE when ToS timer expires while UE did not switch back to the source cell with long ToS behavior for dual stack based inter-cell beam management in accordance with embodiments of the current invention.

Figure 9 illustrates exemplary processes when cell switch is triggered for dual stack based Inter cell beam management in accordance with embodiments of the current invention.

Figure 10 illustrates exemplary processes after UE performs cell switch procedure for dual stack based Inter cell beam management in accordance with embodiments of the current invention.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appended drawings is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well known structures and components are shown in block diagram form in order to avoid obscuring such concepts.

Several aspects of telecommunication systems will now be presented with reference to various apparatus and methods. These apparatus and methods will be described in the following detailed description and illustrated in the accompanying drawings by various blocks, components, circuits, processes, algorithms, etc. (collectively referred to as “elements” ) . These elements may be implemented using electronic hardware, computer software, or any combination thereof. Whether such elements are implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system.

Aspects of the present disclosure provide methods, apparatus, processing systems, and computer readable mediums for NR (new radio access technology, or 5G technology) or other radio access technology. NR may support various wireless communication services. These services may have different quality of service (QoS) requirements e.g., latency and reliability requirements.

Figure 1 illustrates a schematic system diagram illustrating an exemplary wireless network in accordance with embodiments of the current invention. Wireless system includes one or more fixed base infrastructure units forming a network distributed over a geographical region. The base unit may also be referred to as an access point, an access terminal, a base station, a Node-B, an eNode-B, a gNB, or by other terminology used in the art. As an example, base stations serve a number of mobile stations within a serving area, for example, a cell, or within a cell sector. In some systems, one or more base stations are coupled to a controller forming an access network that is coupled to one or more core networks. gNB 1and gNB 2 are base stations in NR, the serving area of which may or may not overlap with each other. As an example, UE1 or mobile station is only in the service area of gNB 1 and connected with gNB1. UE1 is connected with gNB1 only, gNB1 is connected with gNB 1 and 2 via Xn interface. UE2 is in the overlapping service area of gNB1 and gNB2.

Figure 1 further illustrates simplified block diagrams for UE2 and gNB2, respectively. UE has an antenna, which transmits and receives radio signals. A RF transceiver, coupled with the antenna, receives RF signals from antenna, converts them to baseband signal, and sends them to processor. In one embodiment, the RF transceiver may comprise two RF modules (not shown) . A first RF module is used for transmitting and receiving on one frequency band, and the other RF module is used for different frequency bands transmitting and receiving which is different from the first transmitting and receiving. RF transceiver also converts received baseband signals from processor, converts them to RF signals, and sends out to antenna. Processor processes the received baseband signals and invokes different functional modules to perform features in UE. Memory stores program instructions and data to control the operations of mobile station. UE also includes multiple function modules that carry out different tasks in accordance with embodiments of the current invention.

A pre-config controller, which stores the pre-configuration and control UE to apply the configuration and perform RF/baseband retuning for the target cell or one or multiple candidate cells. A mobility controller, which controls the mobility procedure based on different scenario of cell switch. A protocol stack controller, which manage to add, modify or remove the protocol stack for the DRB. The protocol Stack includes SDAP, PDCP, RLC, MAC and PHY layers.

In one embodiment, the SDAP layer supports the functions of transfer of data, mapping between a QoS flow and a DRB, marking QoS flow ID, reflective QoS flow to DRB mapping for the UL SDAP data PDUs, etc.

In one embodiment, the PDCP layer supports the functions of transfer of data, maintenance of PDCP SN, header compression and decompression using the ROHC protocol, ciphering and deciphering, integrity protection and integrity verification, timer based SDU discard, routing for split bearer, duplication, re-ordering and in-order delivery; out of order delivery and duplication discarding.

In one embodiment, the RLC layer supports the functions of error correction through ARQ, segmentation and reassembly, re-segmentation, duplication detection, re-establishment, etc. In one embodiment, a new procedure for RLC reconfiguration is performed, which can reconfigure the RLC entity to associated to one or two logical channels.

In one embodiment, the MAC layer supports the following functions: mapping between logical channels and transport channels, multiplexing/demultiplexing, HARQ, radio resource selection, etc. In one embodiment, there is one MAC entity to support L1/L2 inter-cell mobility with beam management. In one embodiment, the MAC entity controls two TAGs associated to the first cell and the second cell respectively. In one embodiment, the two TAGs are pTAGs. In one embodiment, the first cell is the source cell and the second cell is the target cell. In one embodiment, UE is switched back-and-forth between the first and second cell. If UE is switched back from the second cell to the first cell, the second cell is considered as source cell and the first cell is considered as the target cell. The UL time alignment status of the first and the second cell is controlled by the TAT of the associated TAG. In one embodiment, multiple candidate cells belonging to multiple TAGs are configured for the UE. UE maintains the UL time alignment of the TAGs for the candidate cells configured.

Similarly, gNB2 has an antenna, which transmits and receives radio signals. A RF transceiver, coupled with the antenna, receives RF signals from antenna, converts them to baseband signals, and sends them to processor. RF transceiver also converts received baseband signals from processor, converts them to RF signals, and sends out to antenna. Processor processes the received baseband signals and invokes different functional modules to perform features in gNB2. Memory stores program instructions and data to control the operations of gNB2. gNB2 also includes multiple function modules that carry out different tasks in accordance with embodiments of the current invention.

A RRC State controller, which performs access control for the UE.

A DRB controller, which controls to establish/add, reconfigure/modify and release/remove a DRB based on different sets of conditions for DRB establishment, reconfiguration and release. A protocol stack controller, which manage to add, modify or remove the protocol stack for the DRB. The protocol Stack includes RLC, MAC and PHY layers. In one embodiment, the MAC entity controls two TAGs associated to the first cell and the second cell respectively. In one embodiment the MAC entity controls multiple TAGs associated to multiple candidate cells. In one embodiment, the TAGs are pTAGs.

Figure 2 illustrates an exemplary NR wireless system with centralization of the upper layers of the NR radio stacks in accordance with embodiments of the current invention. Different protocol split options between Central Unit and lower layers of gNB nodes may be possible. The functional split between the Central Unit and lower layers of gNB nodes may depend on the transport layer. Low performance transport between the Central Unit and lower layers of gNB nodes can enable the higher protocol layers of the NR radio stacks to be supported in the Central Unit, since the higher protocol layers have lower performance requirements on the transport layer in terms of bandwidth, delay, synchronization and jitter. In one embodiment, SDAP and PDCP layer are located in the central unit, while RLC, MAC and PHY layers are located in the distributed unit.

Figure 3 illustrates an exemplary deployment scenario for intra-DU inter-cell beam management in accordance with embodiments of the current invention. A CU (Central Unit) is connected to two DUs (Distributed Unit) through the F1 interface, and two DUs are connected to multiple RUs respectively. A cell may consist of a range covered by one or more RUs under the same DU. In this scenario, a UE is moving from the edge of one cell to another cell, which two belong to the same DU and share a common protocol stack. Intra-DU inter-cell beam management can be used in this scenario to replace the legacy handover process to reduce the interruption and improve the throughput and handover reliability in terms of handover failure rate of UE. In one embodiment, single protocol stack at the UE side (common RLC/MAC) is used to handle L1/L2 inter-cell beam management with mobility.

Figure 4 illustrates an exemplary deployment scenario for inter-DU inter-cell beam management in accordance with embodiments of the current invention. A CU (Central Unit) is connected to two DUs (Distributed Unit) through the F1 interface, and two DUs are connected to multiple RUs respectively. A cell may consist of a range covered by one or more RUs under the same DU. In this scenario, a UE is moving from the edge of one cell to another cell, which two belong to different DUs and share a common CU. The low layer user plane (RLC, MAC) is different in two DUs while high layer (PDCP) remains the same. Inter-DU inter-cell beam management can be used in this scenario to replace the legacy handover process to reduce the interruption and improve the throughput and handover reliability in terms of handover failure rate of UE. In one embodiment, single protocol stack at the UE side (common RLC/MAC) is used to handle L1/L2 inter-cell beam management with mobility. In one embodiment, dual protocol stack at the network and UE side are used to handle L1/L2 inter-cell beam management with mobility.

Figure 5 illustrates an exemplary process of user plane handling for network and UE to perform dual stack based inter-cell beam management when UE receiving the cell switch command after the pre-configuration in accordance with embodiments of the current invention. When the pre-configuration is done and UE does not receive the cell switch command, UE receives data PDUs from the source protocol stack. The downlink scenario described in this contribution also applies to uplink scenario. As shown in Fig 5, the data PDUs with

PDCP SN

1, 2, 3 is successfully decoded by the receiving side while PDUs with SN=4, 5 are still in progress. These two PDUs may be being transmitted or retransmitted by HARQ/RLC ARQ.

When UE receives the cell switch command from the network, the source protocol stacks for the network and UE are deactivated, then the target protocol stacks for target cell are established and activated. In one embodiment, the RLC and MAC entities of the source protocol stacks for network and UE are suspended, the buffers are kept, and the timers are paused. In one embodiment, the RLC entities of the source protocol stacks for network and UE are suspended, and the MAC entities of the source protocol stacks for network and UE are reset.

In this contribution, for the case when RLC entity is suspend, the RLC entity stops data transfer functions. The RLC SDUs, RLC SDU segments and RLC PDUs are stored. The state variables for RLC entity are maintained and the timers (except the ToS timer in this contribution) are paused. For the case when MAC entity is suspend, the MAC entity stops data transfer, signaling, resource allocation and measurement functions. The MAC SDUs and MAC PDUs are stored. The timers used in MAC entity are paused and the parameters used in MAC entity are stored.

The new protocol stacks contain RLC, MAC and physical layer, and the anchor is PDCP layer. The new data PDUs are delivered from the target protocol stack, while the Downlink Data Delivery Status frame may not be sent, and the PDUs which are transmitted but not successfully decoded by the receiving side of the source protocol stack will not be retransmitted by target protocol stack. As shown in Fig 5, the new data PDUs with PDCP SN=6, 7, 8 is transmitted, while the PDUs which are not successfully decoded by the receiving side of the source protocol stack (i.e., with PDCP SN=4, 5) will not be retransmitted by target protocol stacks.

Figure 6 illustrates an exemplary time chart of a new defined ToS timer to measure the ToS and control the behavior of the source protocol stack after cell switch for dual stack based inter-cell beam management in accordance with embodiments of the current invention. The ToS timer may also be referred to as a cell switch timer used in the art. In one embodiment, the ToS timer is configured per cell. In one embodiment, the ToS timer is set to a value smaller than the t- reordering timer for PDCP entity. In one embodiment, the ToS timer starts or restarts after the cell switch procedure. When UE performs the cell switch procedure, the target protocol stacks for target cell are established and activated. The ToS timer of the source cell is started, and the behavior for source protocol stacks is controlled by the ToS timer. When the ToS timer is running, the short ToS behavior will be performed, and the source protocol stacks are deactivated. When the ToS timer expires, the long ToS behavior will be performed. The source RLC entity is re-established and the source MAC entity is reset. In one embodiment, the Downlink Data Delivery Status frame is sent to inform the PDCP of the lost data PDUs. In one embodiment, the PDCP data recovery procedure is performed to retransmit the lost PDUs by the target protocol stack.

Figure 7 illustrates an exemplary process of user plane handling for network and UE when UE switch back to the source cell (also called the first cell, or cell 1) with short ToS behavior for dual stack based inter-cell beam management in accordance with embodiments of the current invention. The steps ①～② are the same as Figure 5. After the first cell switch, UE keeps performing L1 measurements for one or multiple candidate cells and sending the measurement reports to the network. If UE receives cell switch command which indicate UE to switch back to the first cell before the ToS timer expires, the short ToS behavior will be performed. The protocol stacks for the first cell are activated, while the protocol stacks for the second cell (also called cell 2) are deactivated. The ToS timer for cell 1 is stopped, while the ToS timer for cell 2 is (re) started.

As shown in Fig 7, before UE switch back to the first cell, the PDCP PDU with SN=6, 7 is successfully delivered by the protocol stacks of cell 2, while PDCP SN=8 is still in progress. The PDU may be being transmitted or retransmitted by HARQ/RLC ARQ. The protocol stacks of cell 1 is deactivated. When UE switch back to the first cell, the new data PDUs with PDCP SN=9, 10, 11 is transmitted by the protocol stacks of cell 1, while the PDCP PDU which are not successfully delivered by the protocol stacks of cell 2 (i.e., with PDCP SN=8) will not be retransmitted by the protocol stack of cell 1. Meanwhile, the PDCP PDUs which were not successfully delivered by the protocol stacks of cell 1 (i.e., with PDCP SN=4, 5) will be continued.

In one embodiment, the RLC and MAC entities of the protocol stacks for cell 1 were suspended. When UE switch back to cell 1, the RLC ARQ/HARQ can be continued. In one embodiment, the RLC entities of the protocol stacks for cell 1 were suspended, and the MAC entities of the protocol stacks for cell 1 were reset. When UE switch back to cell 1, the HARQ entity is reset and RLC ARQ can be continued.

Figure 8 illustrates an exemplary process of user plane handling for network and UE when ToS timer expires while UE did not switch back to the source cell (also called the first cell, or cell 1) with long ToS behavior for dual stack based inter-cell beam management in accordance with embodiments of the current invention. The steps ①～② are the same as Figure 5. After the first cell switch, UE keeps performing L1 measurements for one or multiple candidate cells and sending the measurement reports to the network. If the ToS timer expires but UE did not switch back to the source cell, the long ToS behavior will be performed. The RLC entity for the first cell are re-established and the MAC entity for the first cell is reset. In one embodiment, the Downlink Data Delivery Status frame is sent to inform the PDCP of the lost data PDUs. In one embodiment, the PDCP data recovery procedure is performed to retransmit the lost PDUs by the target protocol stack in cell 2 (also called the second cell, or target cell) .

As shown in Fig 8, before the ToS timer expires, the PDCP PDU with SN=6, 7 is successfully delivered by the protocol stacks of cell 2, while PDCP SN=8 is still in progress. The PDU may be being transmitted or retransmitted by HARQ/RLC ARQ. The protocol stacks of cell 1 is deactivated. When the ToS timer expires, the protocol stacks for the first cell are re-established and reset. In one embodiment, the Downlink Data Delivery Status frame is sent to inform the PDCP of the lost data PDUs in cell 1 (i.e., with PDCP SN=4, 5) , and PDCP retransmits these lost PDUs by the target protocol stack in cell 2. The new arrived data PDUs (i.e., with PDCP SN=9, 10) will be delivered by the target protocol stacks.

Figure 9 illustrates exemplary processes when cell switch is triggered for dual stack based Inter cell beam management in accordance with embodiments of the current invention. When the dual stack based Inter cell beam management is configured and cell switch is triggered by the network, the different handling procedure will be performed for the source protocol stacks of UE and network depends on different configurations. In one embodiment, the RLC and MAC entities of the source protocol stacks are suspended. In one embodiment, the RLC entities of source protocol stacks are suspended, and the MAC entities of the source protocol stacks are reset. In one embodiment, the RLC and MAC entities of the source protocol stacks are both re-established and reset, the Downlink Data Delivery Status frame is sent to gNB-CU. The target protocol stacks of network and UE are established and activated. The new arrived data will be delivered by the target protocol stacks after cell switch procedure. The ToS timer is started after the cell switch procedure.

Figure 10 illustrates exemplary processes after UE performs cell switch procedure for dual stack based Inter cell beam management in accordance with embodiments of the current invention. After UE switches to target cell, if UE receives the cell switch command to switch back to the first cell before the ToS timer expires, the short ToS behavior is performed. UE will switch back to the first cell and UE continues to receive the lost packets from the protocol stacks of the first cell. In one embodiment, retransmission will be performed in different layer (i.e., RLC or MAC) , which depends on different handling procedure for the protocol stacks of the first cell mentioned in Figure 9. If ToS timer expires and UE did not receive the cell switch command to switch back to the first cell, the long ToS behavior is performed. In one embodiment, the Downlink Data Delivery Status frame is sent to gNB-CU. In one embodiment, the PDCP data recovery is triggered and the lost packets are retransmitted by the target protocol stacks. The protocol stacks of the first cell are re-established and reset.

It is understood that the specific order or hierarchy of blocks in the processes /flowcharts disclosed is an illustration of exemplary approaches. Based upon design preferences, it is understood that the specific order or hierarchy of blocks in the processes /flowcharts may be rearranged. Further, some blocks may be combined or omitted. The accompanying method claims present elements of the various blocks in a sample order, and are not meant to be limited to the specific order or hierarchy presented.

The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but is to be accorded the full scope consistent with the language claims, wherein reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more. ” The word “exemplary” is used herein to mean “serving as an example, instance, or illustration. ” Any aspect described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects. Unless specifically stated otherwise, the term “some” refers to one or more. Combinations such as “at least one of A, B, or C, ” “one or more of A, B, or C, ” “at least one of A, B, and C, ” “one or more of A, B, and C, ” and “A, B, C, or any combination thereof” include any combination of A, B, and/or C, and may include multiples of A, multiples of B, or multiples of C. Specifically, combinations such as “at least one of A, B, or C, ” “one or more of A, B, or C, ” “at least one of A, B, and C, ” “one or more of A, B, and C, ” and “A, B, C, or any combination thereof” may be A only, B only, C only, A and B, A and C, B and C, or A and B and C, where any such combinations may contain one or more member or members of A, B, or C. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. The words “module, ” “mechanism, ” “element, ” “device, ” and the like may not be a substitute for the word “means. ” As such, no claim element is to be construed as a means plus function unless the element is expressly recited using the phrase “means for. ”

While aspects of the present disclosure have been described in conjunction with the specific embodiments thereof that are proposed as examples, alternatives, modifications, and variations to the examples may be made. Accordingly, embodiments as set forth herein are intended to be illustrative and not limiting. There are changes that may be made without departing from the scope of the claims set forth below.

Claims

A method of user plane handling to support dual stack based inter-DU inter-cell beam management for a UE when and after UE receives the cell switch command, comprising the steps of:

perform the source cell and target cell handling;

control the ToS timer to measure the ToS of the cell switch and control the behavior of the source protocol stack after cell switch.

handle the source protocol stack according to the states of ToS timer.
The method of claim 1, wherein the target cell handling includes establishing and activating the target protocol stack for the target cell.
The method of claim 1, wherein the source cell handlings is to suspend RLC and MAC entities.
The method of claim 1, wherein the source cell handlings is to suspend RLC entity and to reset MAC entity.
The method of claim 1, wherein the ToS timer for one cell is started when UE switches to another cell.
The method of claim 1, wherein the ToS timer for one cell is stopped when UE switches to that cell if the ToS timer is running.
The method of claim 1, further comprising UE performs short ToS behavior if UE switches back to the first cell when the ToS timer of the first cell is still running.
The method of claim 7, wherein the short ToS behavior is to resume the protocol stack of the first cell.
The method of claim 7, further comprising UE continues to receive the lost packets from the protocol stack of the first cell.
The method of claim 9, wherein the lost packets are retransmitted by RLC ARQ.
The method of claim 9, wherein the lost packets are retransmitted by HARQ procedure.
The method of claim 1, further comprising UE performs long ToS behavior when the ToS timer expires.
The method of claim 10, further comprising UE re-establishes the RLC entity and resets the MAC entity for the protocol stack of the first cell.
The method of claim 10, further comprising UE receives the lost packets from the target protocol stack.
A method of user plane handling for network to support dual stack based inter-DU inter-cell beam management, comprising the steps of:

Indicating UE of the configuration of the source cell and target cell handling;

Indicating the configuration of the ToS timer to UE;

start the ToS timer to measure the ToS of UE and control the behavior of the source protocol stack when and after cell switch;

performs different ToS behavior according to the states of ToS timer.
The method of claim 15, wherein the target cell handling includes establishing and activating the protocol stack for the target cell.
The method of claim 15, wherein the source cell handlings is to suspend RLC and MAC entities.
The method of claim 15, wherein the source cell handlings is to suspend RLC entity and to reset MAC entity.
The method of claim 15, wherein the ToS timer for one cell is started when UE switches to another cell.
The method of claim 15, wherein the ToS timer for one cell is stopped when UE switches to that cell.
The method of claim 15, further comprising network performs short ToS behavior when UE switches back to the first cell when the ToS timer of the first cell is still running.
The method of claim 21, further comprising resuming the protocol stacks of the first cell and continue to retransmit the lost packets.
The method of claim 22, wherein the lost packets are retransmitted by RLC ARQ.
The method of claim 22, wherein the lost packets are retransmitted by HARQ procedure.
The method of claim 15, further comprising network performs long ToS behavior when the ToS timer expires.
The method of claim 25, further comprising re-establish the RLC entity and reset the MAC entity of the first cell.
The method of claim 26, further comprising gNB-DU to send Downlink Data Delivery Status frame to gNB-CU.
The method of claim 25, wherein the data recovery procedure is triggered to retransmit the lost packets by PDCP.