WO2023231001A1

WO2023231001A1 - Methods and apparatus to improve ue experience during inter-du inter-cell beam management

Info

Publication number: WO2023231001A1
Application number: PCT/CN2022/096896
Authority: WO
Inventors: Yuanyuan Zhang; Xiaonan Zhang
Original assignee: Mediatek Singapore Pte. Ltd.
Priority date: 2022-06-02
Filing date: 2022-06-02
Publication date: 2023-12-07
Also published as: CN117177256A

Abstract

This disclosure describes methods and apparatus to perform inter-DU inter-cell beam management with mobility. To support fast cell switching, the cell switch command is transmitted through lower layer signaling, i.e., MAC CE or PDCCH. Upon reception of the cell switch command, UE performs RLC re-establishment, MAC reset for L1/L2 cell switch and PDCP handling. In one novel aspect, the PDCP entity triggers PDCP status report in UL for DL data transfer upon reception of the cell switch command. In another novel aspect, the PDCP entity performs PDCP retransmission for UL data transfer according to the PDCP status report received from the network to minimize the data loss especially for the UM DRBs after reception of cell switch command. In another novel aspect, the RLC entity copies the RLC SDUs, RLC SDU segments, RLC data PDUs that are pending for initial transmission and indicates to PDCP entity that those RLC SDUs are not successfully delivered when the RLC entity is requested to be re-established. The PDCP entity performs PDCP retransmission based on the indications from the RLC entity.

Description

METHODS AND APPARATUS TO IMPROVE UE EXPERIENCE DURING INTER-DU INTER-CELL BEAM MANAGEMENT

FIELD

The present disclosure relates generally to communication systems, and more particularly, the method of TA maintenance and acquisition for mobility with inter-DU inter-cell beam management.

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.

In this invention, apparatus and mechanisms are sought to handle both AM and UM RBs to improve User experience for inter-DU 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. To support fast cell switching, the cell switch command is transmitted through lower layer signaling, i.e., MAC CE or PDCCH. Upon reception of the cell switch command, UE performs RLC re-establishment, MAC reset for L1/L2 cell switch and PDCP handling. In one novel aspect, the PDCP entity triggers PDCP status report in UL for DL data transfer upon reception of the cell switch command. In another novel aspect, the PDCP entity performs PDCP retransmission for UL data transfer according to the PDCP status report received from the network to minimize the data loss especially for the UM DRBs after reception of cell switch command. In one embodiment, UE needs to identify the PDCP PDUs which are not successfully delivered or not transmitted to the source cell before performing RLC reestablishment when receiving a cell switch command. In one embodiment, the RLC entity identify the information. In another embodiment, UE sends the RLC SDUs, RLC SDU segments, RLC data PDUs that are pending for initial transmission back to the PDCP entity and the PDCP entity identifies which PDCP PDUs are not successfully delivered or not transmitted to the source cell. The PDCP entity performs PDCP retransmission to the target cell. In one embodiment, UE triggers, compiles and sends PDCP status report to the target cell.

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 1A illustrates HOF of legacy HO and L1/L2 based inter-cell mobility with beam management.

Figure 1B illustrates Ping-pong of legacy HO and L1/L2 based inter-cell mobility with beam management.

Figure 1C illustrates ToS of legacy HO and L1/L2 based inter-cell mobility with beam management.

Figure 1D illustrates a schematic system diagram illustrating an exemplary wireless 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 illustrate an exemplary process for UP handling for inter-DU inter-cell beam management in accordance with embodiments of the current invention.

Figure 6 illustrate an exemplary process for inter-DU inter-cell beam management with mobility from both network and the UE side in accordance with embodiments of the current invention.

Figure 7A-7B illustrates an exemplary interaction between different layers at the UE side to initiate UP process upon reception of the cell switch command in accordance with embodiments of the current invention.

Figure 8 illustrate an exemplary process of DL data transfer for inter-DU inter-cell beam management with mobility from both network and the UE side in accordance with embodiments of the current invention.

Figure 9 illustrate an exemplary process of UL data transfer for inter-DU inter-cell beam management with mobility from both network and the UE side in accordance with embodiments of the current invention.

Figure 10 illustrate an exemplary process of UP handling at the UE side for inter-DU inter-cell beam management with mobility from in accordance with embodiments of the current invention.

Figure 11 illustrate an exemplary process of DL data transfer at the network side for inter-DU inter-cell beam management with mobility from in accordance with embodiments of the current invention.

DETAILED DESCRIPTION

Figure 1A illustrates HOF of legacy HO and L1/L2 based inter-cell mobility with beam management. We run system level simulation to compare the mobility performance in terms of handover failure (HOF) rate, radio link failure (RLF) rate, handover interruption time (HIT) , PingPong rate and time of stay (ToS) .

Option

1, 2, 3 are different options for L1/L2 based inter-cell mobility with beam management, which have different latency to perform handover or cell switch from the source cell to the target cell. The cell switch latency of

option

1, 2 and 3 is 45ms, 25ms and 5ms. The baseline is the normal handover procedure, which is performed through a sequency of L3 procedures. The handover latency is 75ms in the typical case in FR2. In Figure 1A, it can be observed that HOF can be reduced dramatically by L1/L2 based inter-cell mobility with beam management. The shorter the latency, the better of HOF rate.

But on the other hand, L1/L2 based inter-cell mobility with beam management can result in high ping-pong rate (increased from 55.77%in legacy handover to 74%) , just as illustrated in Figure 1B. Figure 1B illustrates Ping-pong of legacy HO and L1/L2 based inter-cell mobility with beam management. The consequence of the high Pingpong rate is the short ToS. Figure 1C illustrates ToS of legacy HO and L1/L2 based inter-cell mobility with beam management. In Figure 1C, the average ToS can be reduced to 200ms. For the mechanism of 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, 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 changes. 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.

For the scenario of inter-DU handover, legacy handover procedure always triggers RLC re-establishment and MAC reset. All the packets in RLC and MAC which are not successfully delivered before handover execution are discarded. Since lossless data transmission should be guaranteed for AM DRBs, those PDCP PDUs which are not successfully delivered will be retransmitted after handover to target cell. For UM DRBs, data loss is allowed during handover and the PDCP PDUs which are not successfully delivered will not be retransmitted after handover and considered as lost. However, for inter-DU inter-cell beam management with mobility, the existing UP handling method through RLC re-establishment and MAC reset will cause serious problems. Due to high ping-pong rate and short ToS, frequency user plane (UP) reset will result frequent data retransmission for AM DRBs and large number of data loss for UM DRBs, which will finally impair User experience.

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 1D 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 1D 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 RRC State controller, which controls UE RRC state according to network’s command and UE conditions. RRC supports the following states, RRC_IDLE, RRC_CONNECTED and RRC_INACTIVE.

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 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, UE triggers PDCP status report in the UL upon reception of the cell switch command from the network. In one embodiment, the PDCP status report is for RLC UM DRBs. In one embodiment, UE performs PDCP data recovery upon reception of the cell switch command from the network. In one embodiment, UE performs PDCP data recovery for RLC UM DRBs. In one embodiment, UE performs retransmission of all the PDCP Data PDUs previously submitted to re-established or released UM RLC entities in ascending order of the associated COUNT values for which the successful delivery has not been confirmed by lower layers. In one embodiment, UE performs retransmission of all the PDCP Data PDUs previously submitted to re-established or released UM RLC entities in ascending order of the associated COUNT values for which has not been transmitted by lower layer. In one embodiment, UE receives PDCP status report from the target cell and performs retransmission of all the PDCP Data PDUs in ascending order of the associated COUNT values, which are indicated as missing.

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, the transmitting side of RLC AM entity or the transmitting RLC UM entity sends the RLC SDUs, RLC SDU segments or RLC PDUs back to the PDCP entity, which are to be discarded upon request of RLC re-establishment. In one embodiment, the RLC entities identifies the PDCP PDUs which are not successfully delivered or not transmitted by lower layers and send indications to PDCP layers.

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 MAC entity controls two beamFailureDetectionTimer associated to the first cell and the second cell respectively. 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, UE performs MAC reset upon reception of the cell switch command from the network. In one embodiment, a particular MAC reset procedure is performed for cell switch. In the MAC reset procedure, UE keeps the timeAlignmentTimers of the TAG associated with the source cell running, i.e., stops (if running) all timers, except timeAlignmentTimers of the TAG associated with the source cell. In one embodiment, UE further keeps beamFailureDetectionTimer associated with the source cell running. In one embodiment, UE stops (if running) all timers, except beamFailureDetectionTimer and timeAlignmentTimers associated to the source cell.

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 TAGs are pTAGs. In one embodiment, the MAC entity controls two beamFailureDetectionTimer associated to the first cell and the second cell respectively.

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 (CU) and lower layers of gNB nodes may depend on the transport layer. Low performance transport between the CU and lower layers of gNB nodes can enable the higher protocol layers of the NR radio stacks to be supported in the CU, 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 CU, while RLC, MAC and PHY layers are located in the distributed unit (DU) .

Figure 3 illustrates an exemplary deployment scenario for intra-DU inter-cell beam management in accordance with embodiments of the current invention. A CU is connected to two DUs 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 HO reliability and the throughput of the 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 is connected to two DUs 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. Each DU owns its own low layer user plane (RLC, MAC) 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 HO reliability and the throughput 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 5 illustrate an exemplary process for UP handling for inter-DU inter-cell beam management in accordance with embodiments of the current invention. UE receives the cell switch command from the network during mobility. In one embodiment, the cell switch command is sent by MAC CE. In one embodiment, the cell switch command is sent together with beam management indication by MAC CE. In one embodiment, the cell switch command is sent by RRC message. In one embodiment, the cell switch command is sent by PDCCH. Upon reception of the cell switch command, UE re-establishes the RLC entity for each RB, reset MAC and performs PDCP handling.

Figure 6 illustrate an exemplary process for inter-DU inter-cell beam management with mobility from both network and the UE side in accordance with embodiments of the current invention. At the very beginning, UE is connected to the source cell. When UE moves towards the target cell, the preconfiguration for a list of candidate cells or the target cell is provided, which contains at least the cell identity, the physical resource configurations e.g., PRACH resource, the MAC configuration, etc. for the candidate cells or the target cell. When UE moves at the edge of the source cell, the network decides to perform cell switch and change the serving cell from the source cell to the target cell. Then network sends cell switch command to the UE. UE performs RLC re-establishment and MAC reset for cell switch. The PDCP handling is enhanced to avoid data loss during the L1/L2 cell switch.

Figure 7A-7B illustrates an exemplary interaction between different layers at the UE side to initiate UP process upon reception of the cell switch command in accordance with embodiments of the current invention. In one embodiment, the cell switch command is received through MAC CE or PDCCH. In Figure7A, upon reception of the cell switch command, the MAC entity sends the indication of cell switch to RRC layer. RRC layer sends request to the RLC to perform RLC re-establishment, so the RLC entity perform RLC reestablishment upon requested by RRC. RRC layer sends the indication of cell switch to the PDCP entity to trigger PDCP handling, so the PDCP entity initiates PDCP handling when RRC request cell switch. In one embodiment, RRC may further request the MAC to perform MAC reset for cell switch. In Figure 7B, upon reception of the cell switch command, the MAC entity sends the indication of cell switch to the RLC entity, so the RLC entity perform RLC reestablishment upon requested by MAC. The MAC entity also sends the indication of cell switch to the PDCP entity, so the PDCP initiates PDCP handling when MAC requests cell switch. In one embodiment, the MAC entity initiates and performs MAC reset for cell switch.

Figure 8 illustrate an exemplary process of DL data transfer for inter-DU inter-cell beam management with mobility from both network and the UE side in accordance with embodiments of the current invention. When the network decides to perform cell switch from the source DU to the target DU, the PDCP PDUs with SN 7, 8, 9, 10 are not successfully delivered or transmitted to the UE. After cell switch, those PDCP PDUs with SN 7, 8, 9, 10 are retransmitted to the UE by the target cell. For AM RBs, the successfully delivery means the RLC ACK for those PDCP PDUs has been received. For UM RBs, in one embodiment if those RLC SDUs or RLC SDU segments have not yet been included in an RLC data PDU, or RLC data PDUs that are pending for initial transmission, the associated PDCP PDUs are considered as not transmitted. In another embodiment for UM RBs, if no HARQ ACK feedbacks are not received for those RLC data PDUs which have been transmitted by lower layer, the associated PDCP PDUs are considered not successfully delivered. In one embodiment, upon reception of the cell switch command, the PDCP entity of UE triggers, compiles, and sends PDCP Status report to inform the target DU which PDCP PDUs are considered as missing. The target DU retransmits the PDCP PDUs which are reported as missing in the PDCP status report.

Figure 9 illustrate an exemplary process of UL data transfer for inter-DU inter-cell beam management with mobility from both network and the UE side in accordance with embodiments of the current invention. When the UE receives the cell switch command to perform cell switch from the source DU to the target DU, the PDCP PDUs with SN 7, 8, 9, 10 have not been successfully delivered or transmitted to the source DU. After cell switch, UE retransmits the PDCP PDUs with SN 7, 8, 9, 10 to the target cell. In one embodiment, the target DU sends PDCP status report to the UE providing the information which PDCP PDUs are considered as missing. In one embodiment, the UE itself figures out which PDCP PDUs are not successfully delivered or not transmitted to the source cell. For AM RBs, the successfully delivery means the RLC ACK for those PDCP PDUs has been received. For UM RBs, in one embodiment if those RLC SDUs or RLC SDU segments have not yet been included in an RLC data PDU, or RLC data PDUs that are pending for initial transmission, the associated PDCP PDUs are considered not transmitted. In another embodiment for UM RBs, if no HARQ ACK feedbacks are not received for those RLC data PDUs which have been transmitted by lower layer, the associated PDCP PDUs are considered not successfully delivered.

Figure 10 illustrate an exemplary process of UP handling at the UE side for inter-DU inter-cell beam management with mobility from in accordance with embodiments of the current invention. Upon reception of the cell switch command, the RLC receives the request for RLC re-establishment. Before performing RLC re-establishment, the RLC entity performs additional procedures to help to identify the PDCP PDUs which have not been successfully delivered or not transmitted to the lower layers. In one embodiment, the RLC entity sends those PDCP PDUs (RLC SDUs) which are not successfully delivered back to the PDCP entity. In one embodiment, the RLC entity sends the PDCP PDUs (RLC SDUs) which have not been transmitted to lower layers back to the PDCP entity. Then the PDCP entity figures out which PDCP PDUs are not transmitted or not successfully delivered. In another embodiment, the RLC entity figures out which PDCP PDUs which has not been successfully delivered or not transmitted and sends the indication to PDCP. Finally, the PDCP entity retransmits the PDCP PDUs to the target cell, which were not successfully delivered or not transmitted to the source DU side before cell switch. In one embodiment, upon reception of the cell switch command, the PDCP entity of UE receives the PDCP status report from the target cell after cell switch, based on which UE knows which PDCP PDUs are considered as missing. The PDCP entity retransmits the PDCP PDUs to the target cell which were reported as missing in the PDCP status report.

In one embodiment, when UE receives the cell switch command, it calculates the data volume for the PDCP PDUs which are not successfully delivered or not transmitted to lower layer. If the data volume is less than a threshold, UE doesn’t perform PDCP PDU retransmission after cell switch to the target cell. The threshold can be configured by RRC. In one embodiment, whether to perform PDCP retransmission at the target cell is configured by RRC. In one embodiment, whether to perform PDCP retransmission at the target cell is indicated together with the cell switch command.

Figure 11 illustrate an exemplary process of DL data transfer at the network side for inter-DU inter-cell beam management with mobility from in accordance with embodiments of the current invention. In one embodiment, the source DU makes the cell switch decision and sends the cell switch command to the UE.In other embodiment, the CU makes the cell switch decision and sends the cell switch command to the source DU, which sends the cell switch command to the UE. When network sends the cell switch command to the UE, the source DU sends DL DATA DELIVERY STATUS to CU. In one embodiment, the source DU informs CU which PDCP PDUs are not successfully delivered. In one embodiment, the source DU informs CU which PDCP PDUs are successfully delivered. In one embodiment for UM DRBS, the source DU informs CU the highest PDCP PDU SN successfully delivered in sequence to the UE among those NR PDCP PDUs received from CU. In one embodiment for UM DRBS, DU informs CU the highest PDCP PDU SN transmitted to the lower layers among those NR PDCP PDUs received from CU. The CU retransmits the PDCP PDUs which are not successfully delivered or not transmitted at the source DU side to the target DU. The target DU retransmits those PDCP PDUs to the UE after UE is switched to the target cell.

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 to handle DL and UL data transfer for AM and UM radio bearers when L1/L2 cell switch is performed through inter-DU inter-cell beam management, comprising the steps of:

receiving a cell switch command from the network, which switch the UE from the source cell to the target cell,

performing RLC re-establishment,

performing MAC reset for cell switch,

triggering, compiling, and sending PDCP status report in UL to the target cell indicating the PDCP PDUs which are considered as missing,

retransmitting the PDCP PDUs to the target cell, which have not been successfully delivered or not transmitted to the source cell.
The method of claim 1, wherein the cell switch command is carried by MAC CE or PDCCH.
The method of claim 2, further comprising that the MAC entity indicates the cell switch to RRC, and RRC requests RLC re-establishment, triggers PDCP status report in UL, triggers PDCP PDU retransmission and request MAC reset for cell switch.
The method of claim 2, further comprising that the MAC entity request RLC re-establishment, triggers PDCP status report in UL and triggers PDCP PDU retransmission.
The method of claim 1, wherein the MAC reset for cell switch keeping the timeAlignmentTimers of the TAG associated with the source cell running.
The method of claim 5, the MAC reset for cell switch further comprising keeping beamFailureDetectionTimer associated with the source cell running.
The method of claim 1, further comprising identifying the PDCP PDUs which are not successfully delivered or not transmitted by the lower layers before performing RLC re-establishment.
The method of claim 7, wherein the PDCP PDUs which are not successfully delivered or not transmitted by the lower layers are identified by the RLC entity, which sends the indications to the PDCP entity.
The method of claim 7, wherein the PDCP PDUs which are not successfully delivered or not transmitted by the lower layers are identified by the PDCP entity.
The method of claim 9, further comprising sending those PDCP PDUs back to the PDCP entity by the RLC entity.
The method of claim 1, further comprising determining whether to perform PDCP PDU retransmission to the target cell based on comparison of data volume of the PDCP PDUs which are not successfully delivered or transmitted to the source cell with a threshold configured by the network.
The method of claim 1, further comprising that the cell switch command also indicates whether to perform PDCP PDU retransmission to the target cell.