WO2022077341A1

WO2022077341A1 - User equipment, source base station, target base station, and handover method for multicast/broadcast service

Info

Publication number: WO2022077341A1
Application number: PCT/CN2020/121164
Authority: WO
Inventors: Ahmed MOHAMMED MIKAEIL; Jia SHENG
Original assignee: JRD Communication (Shenzhen) Ltd.
Priority date: 2020-10-15
Filing date: 2020-10-15
Publication date: 2022-04-21
Also published as: CN116349301A

Abstract

A user equipment (UE), a source base station, a target base station, and handover methods for multicast/broadcast service (MBS) are provided. The method is partially performed by the source base station includes exchanging MBS service and/or Quality-of-Service (QoS) related information between a source base station and at least a UE as a part of a handover measurement message and/or a target base station as a part of handover request message, and partially performed by the target base station includes exchanging of MBS scheduling information and timing information when the target base station starts/stops PDCP SN allocation and/or data forwarding to at least the source base station via handover acknowledgement message and/or UE via handover command message, and further includes deciding based on handover measurement and/or handover request messages to be performed and/or configured by the source or target base stations to support optimal MBS mobility for the given UE.

Description

USER EQUIPMENT, SOURCE BASE STATION, TARGET BASE STATION, AND HANDOVER METHOD FOR MULTICAST/BROADCAST SERVICE

BACKGROUND OF DISCLOSURE

1. Field of the Disclosure

The present disclosure relates to the field of communication systems, and more particularly, to a user equipment (UE) , a source base station, a target base station, and handover (HO) methods for multicast/broadcast service (MBS) , which can provide a good communication performance and/or provide high reliability.

2. Description of the Related Art

A wireless communication network may include a base station that can support communication for user equipments (UEs) . A UE may communicate with the base station via downlink and uplink. The downlink refers to a communication link from the base station to the UE, and the uplink refers to a communication link from the UE to the base station.

In a 3rd generation partnership project (3GPP) cellular network, broadcast and multicast services may be transported via a transport service called multimedia broadcast/multicast service (MBMS) . A broadcast multicast service center (BM-SC) server is responsible to disseminate a media content to a group of subscribers. When a UE moves out of a network coverage, the UE may be unable to use the MBMS because uplink and downlink connections to the BM-SC server are no longer available. MBMS is a point-to-multipoint (PTM) interface specification designed to provide efficient delivery of broadcast and multicast services within 3GPP cellular networks. Examples of MBMS interface specifications include those described in universal mobile telecommunication system (UMTS) and long term evolution (LTE) communication specifications. For broadcast transmission across multiple cells, the specifications define transmission over single-frequency network configurations. Intended applications include mobile TV, news, radio broadcasting, file delivery, emergency alerts, and others. When services are broadcasted by MBMS, all cells inside a multimedia broadcast/multicast service single frequency network (MBSFN) area transmit the same MBMS service.

Users access these services and obtain the MBMS content through wireless communication devices such as cellular phones, tablets, laptops, and other devices with wireless transceivers that communicate with the base station within the communication system. The base station provides wireless service to the wireless communication devices, sometimes referred to as mobile devices or UEs, within cells.

A user can access at least some multimedia services through a UE using either a point-to-point (PTP) connection or a PTM transmission. In 3GPP systems, PTP services can be provided using unicast techniques and PTM transmissions can be provided using MBMS communication, transmitted over an MBSFN or single cell point to multipoint (SC-PTM) communication. In systems operating in accordance with a revision of 3GPP long term evolution (LTE) communication specification, MBMS is provided using eMBMS. Accordingly, an MBMS service can be provided using either unicast service, MBSFN, or SC-PTM in an LTE system. In radio access network (RAN) meeting #88-e held during June 29, 2020 to July 3, 2020, a new working item was approved to target a RAN support of multicast/broadcast services (MBS) in 5G. Aims of this working item is to provide the support in RAN to enable general MBS services over 5GS to support different MBS services such as public safety and mission critical, V2X applications, transparent IPv4/IPv6 multicast delivery, IPTV, software delivery over wireless, group communications, and IoT applications. One of key objectives of this RAN working item is to study and specify the support for basic mobility with service continuity for 5G new radio (NR) multicast/broadcast services (MBS) .

During 3GPP RAN2 #111-e meeting, there was a considerable discussion on NR MBS mobility, with a lot of companies’ proposeing to consider NR legacy handover with lossless features as a baseline for NR MBS mobility due to its high reliability requirement of some NR MBS services. On the other hand, some companies have proposed additional enhancements on lossless handover targeting the packet data convergence protocol (PDCP) sequence number (SN) allocation issue, PDCP count value misalignment, and data-gap issue due to miss-synchronization between the source and the target gNBs during handover. Also, during this meeting some others companies have proposed to adopt NR dual active protocols stacks (DAPS) handover to minimize the service interruption time during NR MBS mobility; while , others have proposed to deprioritize DAPS HO due to its huge amount of signaling at UE side. DAPS is essential for NR MBS mobility due to the fact that some NR MBS services such as V2X and industrial applications (e.g., motion sensors and actuators) requiring very low service interruption delay during mobility but some modifications are needed to the current DAPS or a new handover procedures is required to support low-latency MBS mobility. In addition to this, there are many MBS mobility related issues in NR such as the signaling nested during handover and the type of information to be exchanged within the signaling, and the QoS handling issue have not yet addressed during 3GPP RAN2 #111-e meetings.

Therefore, this report proposes a new handover procedure to support MBS mobility with service continuity while guaranteeing both the reliability and the latency requirement of different MBS services targeted in 5G, and tries to address some of NR MBS mobility related issues mentioned above while keeping UE signaling complexity and processing cost as low as possible.

SUMMARY

An object of the present disclosure is to propose a user equipment (UE) , a source base station, a target base station, and handover methods for multicast/broadcast service (MBS) , which can solve issues in the prior art, address latency and reliability requirements during MBS mobility process, reduce UE signalling complexity, reduce processing cost, support service continuity, provide a good communication performance, and/or provide high reliability.

In a first aspect of the present disclosure, a handover method for a multicast/broadcast service (MBS) performed by a user equipment (UE) comprises determining, by the UE, an MBS service and/or a Quality-of-Service (QoS) related information as a part of a handover measurement report and exchanging the MBS service and/or the QoS related information as the part of the handover measurement report between at least two of the UE, a source base station, and a target base station, wherein a handover to be performed and/or configured for UE MBS mobility is made based on the part of the handover measurement report.

In an embodiment of the present disclosure, a selection of a type of the handover to be performed and/or configured for UE MBS mobility is made based on at least one of the followings: an indication of the UE comprising the MBS service and/or the QoS related information; an internal configuration of the source base station; or an indication of a core network.

In an embodiment of the present disclosure, the MBS service and/or the QoS related information comprises a UE identity (ID) , an MBS service ID, a QoS flow ID, or a session ID association.

In an embodiment of the present disclosure, the internal configuration of the source base station comprises a UE ID, an MBS service ID, a QoS flow ID, or a session ID association.

In an embodiment of the present disclosure, the indication of the core network comprises a UE MBS context message, a UE ID, an MBS service ID, a QoS flow ID, or a session ID association.

In an embodiment of the present disclosure, determining, by the UE, the MBS service and/or the QoS related information as the part of the handover measurement report comprises receiving, by the UE, the MBS service and/or the QoS related information from a core network via multicast radio bearers (MRBs) or unicast data radio bearers (DRBs) .

In an embodiment of the present disclosure, exchanging the MBS service and/or the QoS related information between the at least two of the UE, the source base station, and the target base station comprises indicating, by the UE, the MBS service and/or the QoS related information as the part of the handover measurement report to the source base station.

In an embodiment of the present disclosure, exchanging the MBS service and/or the QoS related information between the at least two of the UE, the source base station, and the target base station comprises forwarding, by the source base station, the MBS service and/or the QoS related information received from the UE, as the part of a handover request to the target base station.

In an embodiment of the present disclosure, forwarding, by the source base station from the UE, the MBS service and/or the QoS related information as the part of the handover measurement report to the target base station is indicated within a handover request signaling.

In an embodiment of the present disclosure, the selection of the type of the handover to be performed and/or configured for UE MBS mobility comprises a lossless handover or a lossless and low-latency handover.

In an embodiment of the present disclosure, the selection of the type of the handover to be performed and/or configured for UE MBS mobility comprises the lossless handover or the lossless and low-latency handover according to UE MBS service reliability and latency level requirements.

In an embodiment of the present disclosure, the handover method further comprises receiving, by the UE, configurations from the source base station, wherein the configurations comprise at least one of the followings: an agreed time of start/stop packet data convergence protocol (PDCP) sequence number (SN) allocation and/or data forwarding by the source base station and the target base station; a target pre-allocated grant; an uplink time advance command; a downlink synchronization information; or MBS bearers scheduling/forwarding configuration.

In an embodiment of the present disclosure, the configurations are forwarded by the source base station from the target base station to the UE.

In an embodiment of the present disclosure, the configurations are forwarded by the source base station from the target base station to the UE in a handover initiation/command message.

In an embodiment of the present disclosure, when the UE receives the configurations from the source base station, the UE performs at least one of the followings: synchronizing to a target cell based on downlink sync timing and uplink time advance information provided by the source base station from the target base station; configuring a separate entity of a medium access control (MAC) configuration, a PDCP configuration, and/or a radio link control (RLC) configuration for the target base station and the source base station; stopping receiving from the source base station after timing information given in a radio resource control (RRC) configuration while keeping a source MAC, a PDCP, and/or a MAC entity until receiving a first packet from the target base station; stopping sending an uplink (UL) layer 1 channel state information (CSI) feedback, a hybrid automatic repeat request (HARQ) feedback, a layer 2 RLC feedback, a robust header compression (ROHC) feedback, a HARQ data re-transmission, and/or an RLC data re-transmission to the source base station; sending a handover complete message or a handover radio link failure on a pre-allocated grant by the source base station and/or the target base station; omitting sending the handover complete message and utilizing the pre-allocated grant for uplink data transmission toward the target base station; or releasing the MAC configuration, the PDCP configuration, and/or the RLC configuration for the source base station.

In a second aspect of the present disclosure, a handover method for a multicast/broadcast service (MBS) performed by a source base station comprises exchanging an MBS service and/or a Quality-of-Service (QoS) related information between the source base station and at least a user equipment (UE) as a part of a handover measurement message and/or a target base station as a part of a handover request message and performing a handover for UE MBS mobility based on the UE QoS information within the handover measurement report or the handover request message.

In an embodiment of the present disclosure, exchanging the MBS service and/or the QoS related information between the at least two of the UE, the source base station, and the target base station comprises receiving , by the source base station, the MBS service and/or the QoS related information as the part of the handover measurement report from the UE.

In an embodiment of the present disclosure, exchanging the MBS service and/or the QoS related information between the at least two of the UE, the source base station, and the target base station comprises forwarding, by the source base station the MBS service and/or the QoS related information received from the UE as the part of the measurement report to the target base station.

In an embodiment of the present disclosure, the handover method further comprises receiving, by the source base station, a handover request acknowledgment in response to the handover request signaling from the target base station.

In an embodiment of the present disclosure, the handover request acknowledgment comprises configurations, and the configurations comprise at least one of the followings: an agreed time of start/stop packet data convergence protocol (PDCP) sequence number (SN) allocation and/or data forwarding by the source base station and the target base station; a target pre-allocated grant; an uplink time advance command; a downlink synchronization information; or MBS bearers scheduling/forwarding configuration.

In an embodiment of the present disclosure, when the source base station receives the handover request acknowledgment, the source base station performs at least one of the followings: performing a PDCP SN assigning PDCP service data unit (SDU) data forwarding if a low-latency and lossless handover is selected and/or configured for UE MBS mobility; or sending a SN status transfer message to the target base station to convey an uplink PDCP SN receiver status and a downlink PDCP SN transmitter status for which PDCP status preservation applies.

In an embodiment of the present disclosure, the uplink PDCP SN receiver status comprises at least one of the followings: a PDCP SN of a first missing UL PDCP SDU; or a bit map of a receive status of out of sequence UL PDCP SDUs that the UE needs to retransmit in a target cell.

In an embodiment of the present disclosure, the downlink PDCP SN transmitter status indicates a next PDCP SN that the target base station assigns to new PDCP SDUs, not having a PDCP SN yet if a lossless handover is configured.

In an embodiment of the present disclosure, the handover method further comprises transmitting, by the source base station, the configurations to the UE.

In a third aspect of the present disclosure, a handover method for a multicast/broadcast service (MBS) performed by a target base station comprises exchanging of MBS scheduling information and timing information when the target base station starts/stops the PDCP SN allocation and/or a the MBS data forwarding to at least the source base station via a handover acknowledgement message and/or the UE via a handover command message.

In an embodiment of the present disclosure, exchanging the MBS service and/or the QoS related information between the at least two of the UE, the source base station, and the target base station comprises forwarding, by the source base station the MBS service and/or the QoS related information received from the UE, as the part of the handover measurement report to the target base station.

In an embodiment of the present disclosure, when the target base station receives the handover request signaling, the target base station performs at least one of the followings: performing admission control on the UE MBS mobility and performing the selection of the type of the handover to be performed and/or configured for UE MBS mobility if the selection of the type of the handover to be performed and/or configured for UE MBS mobility is not performed by the source base station; determining and/or deciding based on configurations received in the handover request, time to start a PDCP SN allocation and/or data forwarding toward the UE with respect to a time reference provided by the source base station; initiating a UE MSB session join if an MBS session/service/temporary mobile group identity (TMGI) that the UE receiving is existed at the target base station or initiating a session establishment request toward the core network if an MBS session that the UE receiving does not exist at the target base station; switching the UE to a new radio bearer if required, and striving to provide the same QoS flow to a radio bearer mapping and scheduling configuration/forwarding treatment for MBS bearers as indicated by the source base station; determining a timing configuration requiring synchronizing with the UE and providing a time advice command and a pre-allocated grant for the UE; or starting forwarding a copy MBS downlink data forwarded from the source base station to as starting the PDCP SN allocation toward the UE.

In an embodiment of the present disclosure, the handover method further comprises transmitting, by the target base station, a handover request acknowledgment (ACK) in response to the handover request signaling to the source base station.

In a fourth aspect of the present disclosure, a user equipment (UE) for a multicast/broadcast service (MBS) comprises a memory, a transceiver, and a processor coupled to the memory and the transceiver. The processor is configured to determine an MBS service and/or a Quality-of-Service (QoS) related information as a part of a handover measurement report and exchange the MBS service and/or the QoS related information as the part of the handover measurement report between at least two of the UE, a source base station, and a target base station, wherein a handover to be performed and/or configured for UE MBS mobility is made based on the part of the handover measurement report.

In an embodiment of the present disclosure, determining, by the processor, the MBS service and/or the QoS related information as the part of the handover measurement report comprises receiving, by the transceiver, the MBS service and/or the QoS related information from a core network via multicast radio bearers (MRBs) or unicast data radio bearers (DRBs) .

In an embodiment of the present disclosure, exchanging the MBS service and/or the QoS related information between the at least two of the UE, the source base station, and the target base station comprises indicating, by the processor, the MBS service and/or the QoS related information as the part of the handover measurement report to the source base station.

In an embodiment of the present disclosure, exchanging the MBS service and/or the QoS related information between the at least two of the UE, the source base station, and the target base station comprises forwarding, by the source base station from the transceiver, the MBS service and/or the QoS related information as the part of the handover measurement report to the target base station.

In an embodiment of the present disclosure, forwarding, by the source base station from the transceiver, the MBS service and/or the QoS related information as the part of the handover measurement report to the target base station is indicated within a handover request signaling.

In an embodiment of the present disclosure, the transceiver is configured to receive configurations from the source base station, wherein the configurations comprise at least one of the followings: an agreed time of start/stop packet data convergence protocol (PDCP) sequence number (SN) allocation and/or data forwarding by the source base station and the target base station; a target pre-allocated grant; an uplink time advance command; a downlink synchronization information; or MBS bearers scheduling/forwarding configuration.

In an embodiment of the present disclosure, the configurations are forwarded by the source base station from the target base station to the transceiver.

In an embodiment of the present disclosure, the configurations are forwarded by the source base station from the target base station to the transceiver in a handover initiation/command message.

In an embodiment of the present disclosure, when the transceiver receives the configurations from the source base station, the processor performs at least one of the followings: synchronizing to a target cell based on downlink sync timing and uplink time advance information provided by the source base station from the target base station; configuring a separate entity of a medium access control (MAC) configuration, a PDCP configuration, and/or a radio link control (RLC) configuration for the target base station and the source base station; stopping receiving from the source base station after timing information given in a radio resource control (RRC) configuration while keeping a source MAC, a PDCP, and/or a MAC entity until receiving a first packet from the target base station; stopping sending an uplink (UL) layer 1 channel state information (CSI) feedback, a hybrid automatic repeat request (HARQ) feedback, a layer 2 RLC feedback, a robust header compression (ROHC) feedback, a HARQ data re-transmission, and/or an RLC data re-transmission to the source base station; sending a handover complete message or a handover radio link failure on a pre-allocated grant by the source base station and/or the target base station; omitting sending the handover complete message and utilizing the pre-allocated grant for uplink data transmission toward the target base station; or releasing the MAC configuration, the PDCP configuration, and/or the RLC configuration for the source base station.

In a fifth aspect of the present disclosure, a source base station for a multicast/broadcast service (MBS) comprises a memory, a transceiver, and a processor coupled to the memory and the transceiver. The processor is configured to exchange an MBS service and/or a Quality-of-Service (QoS) related information between the source base station 20 and at least a user equipment (UE) 10 as a part of a handover measurement message and/or a target base station 30 as a part of a handover request message and performs a handover to be performed and/or configured for UE MBS mobility based on the part of the handover measurement report.

In an embodiment of the present disclosure, exchanging the MBS service and/or the QoS related information between the at least two of the UE, the source base station, and the target base station comprises determining, by the processor, the MBS service and/or the QoS related information as the part of the handover measurement report from the UE.

In an embodiment of the present disclosure, exchanging the MBS service and/or the QoS related information between the at least two of the UE, the source base station, and the target base station comprises forwarding, by the transceiver from the UE, the MBS service and/or the QoS related information as the part of the handover measurement report to the target base station via the source base station .

In an embodiment of the present disclosure, forwarding, by the transceiver from the UE, the MBS service and/or the QoS related information as the part of the handover measurement report to the target base station is indicated within a handover request signaling.

In an embodiment of the present disclosure, the transceiver is configured to receive a handover request acknowledgment in response to the handover request signaling from the target base station.

In an embodiment of the present disclosure, when the transceiver receives the handover request acknowledgment, the processor performs at least one of the followings: performing a PDCP SN assigning PDCP service data unit (SDU) data forwarding if a low-latency and lossless handover is selected and/or configured for UE MBS mobility; or sending a SN status transfer message to the target base station to convey an uplink PDCP SN receiver status and a downlink PDCP SN transmitter status for which PDCP status preservation applies.

In an embodiment of the present disclosure, the transceiver is configured to transmit the configurations to the UE.

In an embodiment of the present disclosure, the configurations are forwarded by the transceiver from the target base station to the UE.

In an embodiment of the present disclosure, the configurations are forwarded by the transceiver from the target base station to the UE in a handover initiation/command message.

In a sixth aspect of the present disclosure, a target base station for a multicast/broadcast service (MBS) comprises a memory, a transceiver, and a processor coupled to the memory and the transceiver. The processor is configured to exchange an MBS service and/or a Quality-of-Service (QoS) related information as a part of a handover measurement report between at least two of a user equipment (UE) , a source base station, and the target base station and exchange of MBS scheduling information and timing information when the target base station 30 starts/stops a PDCP SN allocation and/or a data forwarding to at least the source base station 20 via a handover acknowledgement message and/or the UE 10 via a handover command message..

In an embodiment of the present disclosure, exchanging the MBS service and/or the QoS related information between the at least two of the UE, the source base station, and the target base station comprises forwarding, by the source base station from the UE, the MBS service and/or the QoS related information as the part of the handover measurement report to the transceiver.

In an embodiment of the present disclosure, forwarding, by the source base station from the UE, the MBS service and/or the QoS related information as the part of the handover measurement report to the transceiver is indicated within a handover request signaling.

In an embodiment of the present disclosure, the transceiver is configured to transmit a handover request acknowledgment in response to the handover request signaling to the source base station.

In an embodiment of the present disclosure, the configurations are forwarded by the source base station from the transceiver to the UE.

In an embodiment of the present disclosure, the configurations are forwarded by the source base station from the transceiver to the UE in a handover initiation/command message.

In a seventh aspect of the present disclosure, a non-transitory machine-readable storage medium has stored thereon instructions that, when executed by a computer, cause the computer to perform the above method.

In an eighth aspect of the present disclosure, a chip includes a processor, configured to call and run a computer program stored in a memory, to cause a device in which the chip is installed to execute the above method.

In a ninth aspect of the present disclosure, a computer readable storage medium, in which a computer program is stored, causes a computer to execute the above method.

In a tenth aspect of the present disclosure, a computer program product includes a computer program, and the computer program causes a computer to execute the above method.

In an eleventh aspect of the present disclosure, a computer program causes a computer to execute the above method.

BRIEF DESCRIPTION OF DRAWINGS

In order to illustrate the embodiments of the present disclosure or related art more clearly, the following figures will be described in the embodiments are briefly introduced. It is obvious that the drawings are merely some embodiments of the present disclosure, a person having ordinary skill in this field can obtain other figures according to these figures without paying the premise.

FIG. 1 is a block diagram of a user equipment (UE) , a source base station, and a target base station of communication in a communication network system according to an embodiment of the present disclosure.

FIG. 2 is a flowchart illustrating a handover method for a multicast/broadcast service (MBS) performed by a user equipment (UE) in a communication network system according to an embodiment of the present disclosure.

FIG. 3 is a flowchart illustrating a handover method for a multicast/broadcast service (MBS) performed by a source base station in a communication network system according to an embodiment of the present disclosure.

FIG. 4 is a flowchart illustrating a handover method for a multicast/broadcast service (MBS) performed by a target base station in a communication network system according to an embodiment of the present disclosure.

FIG. 5 is a schematic diagram illustrating a 5G NR baseline handover procedure according to an embodiment of the present disclosure.

FIG. 6 is a schematic diagram illustrating a handover of MBS capable UE from one NG-RAN to another NG-RAN according to an embodiment of the present disclosure.

FIG. 7 is a schematic diagram illustrating a proposed handover to support low-latency and reliable MBS mobility according to an embodiment of the present disclosure.

FIG. 8 is a block diagram of a system for wireless communication according to an embodiment of the present disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

Embodiments of the present disclosure are described in detail with the technical matters, structural features, achieved objects, and effects with reference to the accompanying drawings as follows. Specifically, the terminologies in the embodiments of the present disclosure are merely for describing the purpose of the certain embodiment, but not to limit the disclosure.

Some embodiments of the present disclosure are related to wireless communication, more specifically to a mobility issue for multicast/broadcast service (MBS) in NR system. MBS is a point-to-multipoint (PTM) interface designed to provide efficient delivery of broadcast and multicast services in 3GPP cellular networks.

As discussed per [RP-201308] 3GPP document, there is a clear requirement to support basic mobility with service continuity for NR MBS. Although, in the recent 3GPP meeting, there is a wide discussion on MBS mobility, but there are many MBS mobility related technical gaps that are still uncovered or still open for further discussion in upcoming meetings such as QoS requirement handling during the MBS mobility, the service interruption delay during MBS mobility, the selection types of handover to be performed/configured to support MBS mobility, the signaling nested during handover and the type of information that is exchanged within the signaling during the handover. The major objectives of some embodiments of the present disclosure are to address some of these technical gaps. Therefore, some embodiments of the present disclosure propose a novel handover method with modified handover signaling and procedures to support seamless MBS mobility with service continuity while considering the difference in QoS requirements for different MBS use-cases during the mobility.

In a framework of NR MBS mobility, most of the proposals submitted to the recent 3GPP RAN2 meetings have focused on legacy NR unicast handover (HO) with lossless feature as a potential candidate for MBS mobility in NR. The legacy NR unicast HO with lossless features can effectively resolve the reliability issues during MBS mobility. However, lossless HO can cause additional (from 25 ms to 40 ms) service interruption time. Given the fact that some MBS use cases targeted in NR that may involve MBS reception during mobility such as V2X and industrial applications (e.g., motion sensors and actuators) require very low service interruption delay on the top of their reliability requirements, a mechanism to handle both the latency and reliability issue is very essential for efficient MBS mobility. Although, some companies have proposed to adopt DAPS for low latency MBS mobility, but DAPS can also introduce huge amount of signalling to UE due to simultaneous reception from the source and target handover gNB.

In some embodiments of the present disclosure, a QoS aware reliable and low latency handover method is proposed to support MBS mobility with service continuity and to guarantee the difference in MBS service QoS requirements during the UE handover process. In this method, we propose to exchange MBS service and/or QoS related information between the UE, the source base station such as a source gNB, and the target base station such as a target gNB to decide the type of handover to configure for UE MBS mobility. In addition, we propose several enhancements to current NR handovers including some modifications on HO signalling and procedures such as introducing of new type of information to be exchanged during handover procedures (e.g., a timing related information between UE, source and target gNB) to reduce service interruption time while keeping UE signalling complexity, processing cost, and power consumption as low as possible (as suggested per [RP-201308] i.e., to facilitate implementation and deployment of the NR MBS features, UE complexity should be minimized and device hardware impact should be avoided) .

The major advantages of some embodiments of the present disclosure compared to the prior art provide a handover method that capable of addressing both the latency and reliability requirements during MBS mobility process, minimizing UE signalling complexity and processing cost as low as possible.

Other advantages of some embodiments of the present disclosure include at least one of the followings.

UE side advantages:

The new method exchanges the target gNB MBS data forwarding timing to the UE in handover command, the UE can clearly know when it will expect to start receiving MBS DL data from the target gNB. Given such information in addition to other information related to MBS scheduling within handover command, the UE can prepares the optimal reception configuration for MBS data in advance and decides when to stop receiving DL data from source and when to release the source configuration (i.e. avoiding the need to continue the MBS downlink data reception from both source and target gNBs until the source gNB connection is released by an explicit release command from the target gNB as in DAPS) . Such a procedures can relatively reduce UE signaling complexity, processing cost and minimize UE power consumption

The new method introduces idea of exchanging of target gNB timing advance and downlink sync info to the source gNB and UE. Such information can help UE to avoid the need of random access (RACH) procedure during handover execution period which could result in reducing the handover interruption time (and help in relaxing UE processing and signaling complexity) .

The new method l introduces the idea of pre-allocating uplink grants from source and target gNB which is new and could help in relatively improving the UE resiliency against the handover failure (i.e. UE can send the handover failure indication or re-connection request to either the source or target gNB.

The new method introduces the procedure of sending or start forwarding the MBS DL data by target gNB earlier (without of waiting to receiving the handover complete message as in DAPS) to the UE which can relatively help in reducing the UE handover interruption time.

Network side advantages:

The method introduces new type of information to be exchanged between the source gNB and the target gNB within the handover request message such as the agreed timing information when the target NB will start forwarding data toward UE sending with the respect to a specific downlink/uplink frame sent/received by the source gNB toward/from UE. Such timing information could help in overcoming several issues at network side such as the followings.

PDCP SN allocation and count value misalignment issues: The PDCP SN allocation and count value maintenance can be straightforwardly done at the source gNB and the target gNB individually and according to the agreed timing when each node will start/stop the downlink /uplink transmission toward UE/user plane function (UPF) . For example, the source gNB may start allocating PDCP SN from the time it receives HANDOVER ACK message from the target gNB until the starting time of PDCP SN is allocation by the target gNB that is provided within HANDOVER ACK message. This can help in maintaining a logical connectivity (PDCP level) between the source and the target gNBs during the handover and minimizes MBS data loss at UE side.

Data forwarding and data gap issue: all MBS packet (PDCP SDUs) received from core network (UPF) by the source gNB during the UE switching time (i.e. the time agreed by the source and target gNBs to stop/start serving the UE) is forwarded to the target gNB then to the UE which ensures that MBS packet loss will not occur at UE side.

PDCP re-ordering and duplication issue: the UE may stop downlink either as specified the HANDOVER INITIATION command (i.e., the agreed time when the target gNB will start forwarding data toward the UE) or immediately after receiving a first packet from the target gNB. This procedure simplifies network implementation since the duplication check and in-sequence delivery to the 5G core is done either in the source gNB (i.e., until the agreed time or until receiving a first packet from the target gNB or in the target gNB) apposing to the current DAPS procedure in which a common re-ordering and duplication function (for the source gNB and the target gNB) is required in a single PDCP entity. FIG. 1 illustrates that, in some embodiments, a user equipment (UE) 10, a source base station 20, and a target base station 30 of communication in a communication network system 40 according to an embodiment of the present disclosure are provided. The communication network system 40 includes the UE 10, the source base station 20, and the target base station 30. The UE 10 may include a memory 12, a transceiver 13, and a processor 11 coupled to the memory 12 and the transceiver 13. The source base station 20 may include network nodes such as a next generation radio access network (NG-RAN node, an access and mobility management function (AMF) node, a session data management function (SMF) node, a network exposure function (NEF) /policy control function (PCF) node, a user plane function (UPF) node, and an application function (AF) node. The source base station 20 may include a memory 22, a transceiver 23, and a processor 21 coupled to the memory 22 and the transceiver 23. The target base station 30 may include network nodes such as a next generation radio access network (NG-RAN node, an access and mobility management function (AMF) node, a session data management function (SMF) node, a network exposure function (NEF) /policy control function (PCF) node, a user plane function (UPF) node, and an application function (AF) node. The target base station 30 may include a memory 32, a transceiver 33, and a processor 31 coupled to the memory 32 and the transceiver 33. The

processor

11 or 21 or 31 may be configured to implement proposed functions, procedures and/or methods described in this description. Layers of radio interface protocol may be implemented in the

processor

11 or 21 or 31. The

memory

12 or 22 or 32 is operatively coupled with the

processor

11 or 21 or 31 and stores a variety of information to operate the

processor

11 or 21 or 31. The

transceiver

13 or 23 or 33 is operatively coupled with the

processor

11 or 21 or 31, and the

transceiver

13 or 23 or 33transmits and/or receives a radio signal.

The

processor

11 or 21 or 31 may include application-specific integrated circuit (ASIC) , other chipset, logic circuit and/or data processing device. The

memory

12 or 22 or 32 may include read-only memory (ROM) , random access memory (RAM) , flash memory, memory card, storage medium and/or other storage device. The

transceiver

13 or 23 or 33 may include baseband circuitry to process radio frequency signals. When the embodiments are implemented in software, the techniques described herein can be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. The modules can be stored in the

memory

12 or 22 or 32 and executed by the

processor

11 or 21 or 31. The

memory

12 or 22 or 32 can be implemented within the

processor

11 or 21 or 31 or external to the

processor

11 or 21 or 31 in which case those can be communicatively coupled to the

processor

11 or 21 or 31 via various means as is known in the art.

In some embodiments, the processor 11 is configured to determine an MBS service and/or a Quality-of-Service (QoS) related information as a part of a handover measurement report and exchange the MBS service and/or the QoS related information as the part of the handover measurement report between at least two of the UE 10, the source base station 20, and the target base station 30, wherein a handover to be performed and/or configured for UE MBS mobility is made based on the part of the handover measurement report.

In some embodiments, the processor 21 is configured to exchange an MBS service and/or a Quality-of-Service (QoS) related information between the source base station 20 and at least a user equipment (UE) 10 as a part of a handover measurement message and/or a target base station 30 as a part of a handover request message and to perform a handover to be performed and/or configured for UE MBS mobility based on the part of the handover measurement report.

In some embodiments, the processor 31 is configured to exchange an MBS service and/or a Quality-of-Service (QoS) related information as a part of a handover measurement report between at least two of the user equipment (UE) 10, the source base station 20, and the target base station 30 and exchange of MBS scheduling information and timing information when the target base station 30 starts/stops a PDCP SN allocation and/or a data forwarding to at least the source base station 20 via a handover acknowledgement message and/or the UE 10 via a handover command message. This can solve issues in the prior art, address latency and reliability requirements during MBS mobility process, reduce UE signalling complexity, reduce processing cost, support service continuity, provide a good communication performance, and/or provide high reliability.

FIG. 2 illustrates a handover method 200 for a multicast/broadcast service (MBS) performed by a user equipment (UE) in a communication network system according to an embodiment of the present disclosure. In some embodiments, the handover method 200 includes: a block 202, determining, by the UE, an MBS service and/or a Quality-of-Service (QoS) related information as a part of a handover measurement report, and a block 204, exchanging the MBS service and/or the QoS related information as the part of the handover measurement report between at least two of the UE, a source base station, and a target base station, wherein a handover to be performed and/or configured for UE MBS mobility is made based on the part of the handover measurement report, and a block 206: receiving by the UE from the source base station a handover command containing the target downlink/uplink sync information, MBS scheduling info and MBS data forwarding timing information, and a block 208: preparing by the UE optimal reception configuration for MBS data in advance and deciding when to stop receiving DL data from the source gNB and when to release the source gNB configuration and avoiding the need to continue the MBS downlink data reception from both source and target gNBs until the source gNB connection is released by an explicit release command from the target gNB. Such a procedures can relatively reduce UE signaling complexity, processing cost and minimize UE power consumption.

In an embodiment of the present disclosure, a selection of a type of the handover to be performed and/or configured for UE MBS mobility is made based on at least one of the followings: an indication of the UE comprising the MBS service and/or the QoS related information; an internal configuration of the source base station; or an indication of a core network. In an embodiment of the present disclosure, the MBS service and/or the QoS related information comprises a UE identity (ID) , an MBS service ID, a QoS flow ID, or a session ID association. In an embodiment of the present disclosure, the internal configuration of the source base station comprises a UE ID, an MBS service ID, a QoS flow ID, or a session ID association. In an embodiment of the present disclosure, the indication of the core network comprises a UE MBS context message, a UE ID, an MBS service ID, a QoS flow ID, or a session ID association. In an embodiment of the present disclosure, determining, by the UE, the MBS service and/or the QoS related information as the part of the handover measurement report comprises receiving, by the UE, the MBS service and/or the QoS related information from a core network via multicast radio bearers (MRBs) or unicast data radio bearers (DRBs) .

In an embodiment of the present disclosure, exchanging the MBS service and/or the QoS related information between the at least two of the UE, the source base station, and the target base station comprises indicating, by the UE, the MBS service and/or the QoS related information as the part of the handover measurement report to the source base station. In an embodiment of the present disclosure, exchanging the MBS service and/or the QoS related information between the at least two of the UE, the source base station, and the target base station comprises forwarding, by the source base station from the UE, the MBS service and/or the QoS related information as the part of the handover measurement report to the target base station. In an embodiment of the present disclosure, forwarding, by the source base station from the UE, the MBS service and/or the QoS related information as the part of the handover measurement report to the target base station is indicated within a handover request signaling. In an embodiment of the present disclosure, the selection of the type of the handover to be performed and/or configured for UE MBS mobility comprises a lossless handover or a lossless and low-latency handover.

In an embodiment of the present disclosure, the selection of the type of the handover to be performed and/or configured for UE MBS mobility comprises the lossless handover or the lossless and low-latency handover according to UE MBS service reliability and latency level requirements. In an embodiment of the present disclosure, the handover method further comprises receiving, by the UE, configurations from the source base station, wherein the configurations comprise at least one of the followings: an agreed time of start/stop packet data convergence protocol (PDCP) sequence number (SN) allocation and/or data forwarding by the source base station and the target base station; a target pre-allocated grant; an uplink time advance command; a downlink synchronization information; or MBS bearers scheduling/forwarding configuration. In an embodiment of the present disclosure, the configurations are forwarded by the source base station from the target base station to the UE.

In an embodiment of the present disclosure, the configurations are forwarded by the source base station from the target base station to the UE in a handover initiation/command message. In an embodiment of the present disclosure, when the UE receives the configurations from the source base station, the UE performs at least one of the followings: synchronizing to a target cell based on downlink sync timing and uplink time advance information provided by the source base station from the target base station; configuring a separate entity of a medium access control (MAC) configuration, a PDCP configuration, and/or a radio link control (RLC) configuration for the target base station and the source base station; stopping receiving from the source base station after timing information given in a radio resource control (RRC) configuration while keeping a source MAC, a PDCP, and/or a MAC entity until receiving a first packet from the target base station; stopping sending an uplink (UL) layer 1 channel state information (CSI) feedback, a hybrid automatic repeat request (HARQ) feedback, a layer 2 RLC feedback, a robust header compression (ROHC) feedback, a HARQ data re-transmission, and/or an RLC data re-transmission to the source base station; sending a handover complete message or a handover radio link failure on a pre-allocated grant by the source base station and/or the target base station; omitting sending the handover complete message and utilizing the pre-allocated grant for uplink data transmission toward the target base station; or releasing the MAC configuration, the PDCP configuration, and/or the RLC configuration for the source base station.

FIG. 3 illustrates a handover method 300 for a multicast/broadcast service (MBS) performed by a source base station in a communication network system according to an embodiment of the present disclosure. In some embodiments, the handover method 300 includes: a block 302, exchanging an MBS service and/or a Quality-of-Service (QoS) related information between the source base station and at least a user equipment (UE) as a part of a handover measurement message and/or a target base station as a part of a handover request message., and a block 304, performing a handover to be performed and/or configured for UE MBS mobility based on the part of the handover measurement report.

In an embodiment of the present disclosure, the MBS service and/or the QoS related information comprises a UE identity (ID) , an MBS service ID, a QoS flow ID, or a session ID association. In an embodiment of the present disclosure, the internal configuration of the source base station comprises a UE ID, an MBS service ID, a QoS flow ID, or a session ID association. In an embodiment of the present disclosure, the indication of the core network comprises a UE MBS context message, a UE ID, an MBS service ID, a QoS flow ID, or a session ID association. In an embodiment of the present disclosure, exchanging the MBS service and/or the Quality-of-Service (QoS) related information between the source base station and at least the user equipment (UE) as the part of the handover measurement message and/or the target base station as the part of the handover request message comprises determining, by the source base station, the MBS service and/or the QoS related information as the part of the handover measurement report from the UE. In an embodiment of the present disclosure, exchanging the MBS service and/or the Quality-of-Service (QoS) related information between the source base station and at least the user equipment (UE) as the part of the handover measurement message and/or the target base station as the part of the handover request message comprises forwarding, by the source base station from the UE, the MBS service and/or the QoS related information as the part of the handover measurement report to the target base station.

In an embodiment of the present disclosure, forwarding, by the source base station from the UE, the MBS service and/or the QoS related information as the part of the handover measurement report to the target base station is indicated within a handover request signaling. In an embodiment of the present disclosure, the selection of the type of the handover to be performed and/or configured for UE MBS mobility comprises a lossless handover or a lossless and low-latency handover. In an embodiment of the present disclosure, the selection of the type of the handover to be performed and/or configured for UE MBS mobility comprises the lossless handover or the lossless and low-latency handover according to UE MBS service reliability and latency level requirements. In an embodiment of the present disclosure, the handover method further comprises receiving, by the source base station, a handover request acknowledgment in response to the handover request signaling from the target base station. In an embodiment of the present disclosure, the handover request acknowledgment comprises configurations, and the configurations comprise at least one of the followings: an agreed time of start/stop packet data convergence protocol (PDCP) sequence number (SN) allocation and/or data forwarding by the source base station and the target base station; a target pre-allocated grant; an uplink time advance command; a downlink synchronization information; or MBS bearers scheduling/forwarding configuration.

In an embodiment of the present disclosure, when the source base station receives the handover request acknowledgment, the source base station performs at least one of the followings: performing a PDCP SN assigning PDCP service data unit (SDU) data forwarding if a low-latency and lossless handover is selected and/or configured for UE MBS mobility; or sending a SN status transfer message to the target base station to convey an uplink PDCP SN receiver status and a downlink PDCP SN transmitter status for which PDCP status preservation applies. In an embodiment of the present disclosure, the uplink PDCP SN receiver status comprises at least one of the followings: a PDCP SN of a first missing UL PDCP SDU; or a bit map of a receive status of out of sequence UL PDCP SDUs that the UE needs to retransmit in a target cell. In an embodiment of the present disclosure, the downlink PDCP SN transmitter status indicates a next PDCP SN that the target base station assigns to new PDCP SDUs, not having a PDCP SN yet if a lossless handover is configured. In an embodiment of the present disclosure, the handover method further comprises transmitting, by the source base station, the configurations to the UE. In an embodiment of the present disclosure, the configurations are forwarded by the source base station from the target base station to the UE. In an embodiment of the present disclosure, the configurations are forwarded by the source base station from the target base station to the UE in a handover initiation/command message.

FIG. 4 illustrates a handover method 400 for a multicast/broadcast service (MBS) performed by a target base station in a communication network system according to an embodiment of the present disclosure. In some embodiments, the handover method 400 includes: a block 402, exchanging an MBS service and/or a Quality-of-Service (QoS) related information as a part of a handover measurement report between at least two of a user equipment (UE) , a source base station, and the target base station, and a block 404, exchanging of MBS scheduling information and timing information when the target base station starts/stops a PDCP SN allocation and/or a data forwarding to at least the source base station via a handover acknowledgement message and/or the UE via a handover command message. This can solve issues in the prior art, address latency and reliability requirements during MBS mobility process, reduce UE signalling complexity, reduce processing cost, support service continuity, provide a good communication performance, and/or provide high reliability.

In an embodiment of the present disclosure, a selection of a type of the handover to be performed and/or configured for UE MBS mobility is made based on at least one of the followings: an indication of the UE comprising the MBS service and/or the QoS related information; an internal configuration of the source base station; or an indication of a core network. In an embodiment of the present disclosure, the MBS service and/or the QoS related information comprises a UE identity (ID) , an MBS service ID, a QoS flow ID, or a session ID association. In an embodiment of the present disclosure, the internal configuration of the source base station comprises a UE ID, an MBS service ID, a QoS flow ID, or a session ID association. In an embodiment of the present disclosure, the indication of the core network comprises a UE MBS context message, a UE ID, an MBS service ID, a QoS flow ID, or a session ID association. In an embodiment of the present disclosure, exchanging the MBS service and/or the QoS related information between the at least two of the UE, the source base station, and the target base station comprises forwarding, by the source base station from the UE, the MBS service and/or the QoS related information as the part of the handover measurement report to the target base station.

In an embodiment of the present disclosure, forwarding, by the source base station from the UE, the MBS service and/or the QoS related information as the part of the handover measurement report to the target base station is indicated within a handover request signaling. In an embodiment of the present disclosure, the selection of the type of the handover to be performed and/or configured for UE MBS mobility comprises a lossless handover or a lossless and low-latency handover. In an embodiment of the present disclosure, the selection of the type of the handover to be performed and/or configured for UE MBS mobility comprises the lossless handover or the lossless and low-latency handover according to UE MBS service reliability and latency level requirements.

In an embodiment of the present disclosure, the handover method further comprises transmitting, by the target base station, a handover request acknowledgment in response to the handover request signaling to the source base station. In an embodiment of the present disclosure, the handover request acknowledgment comprises configurations, and the configurations comprise at least one of the followings: an agreed time of start/stop packet data convergence protocol (PDCP) sequence number (SN) allocation and/or data forwarding by the source base station and the target base station; a target pre-allocated grant; an uplink time advance command; a downlink synchronization information; or MBS bearers scheduling/forwarding configuration. In an embodiment of the present disclosure, the configurations are forwarded by the source base station from the target base station to the UE. In an embodiment of the present disclosure, the configurations are forwarded by the source base station from the target base station to the UE in a handover initiation/command message.

In some embodiments, we will start this section by reviewing currently standardized legacy or baseline NR handover and discussing how the minimization of data loss and service interruption delay is achieved for NR unicast services. We will mainly focus on discussing the features targeting the reduction of data loss during handover such as lossless handover features, and the procedures targeting the minimization of service interruption time such as DAPS procedures. Then we will point out to the limitations and drawbacks of the above-mentioned handover procedures in addressing the MBS mobility requirements in NR. Finally, we will introduce our proposed handover procedure to overcome these drawbacks and limitations.

Review of NR baseline handover:

FIG. 5 illustrates a 5G NR baseline handover procedure according to an embodiment of the present disclosure. FIG. 5 illustrates that, in some embodiments, a NR baseline handover procedure for a UE receiving unicast service moving from a source gNB to a target gNB is illustrated in FIG. 5. The major steps of control plane (CP) handling of baseline handover include; a) handover preparation phase (step 0 to step 5) , b) Handover execution phase (step 6 to step 8) , and 3) Handover completion phase (step 8a to12) . These steps are detailed as follows:

Step 0: The UE context within the source gNB contains information regarding roaming and access restrictions which are provided either at connection establishment or at the last tracking area (TA) update.

Step 1: The source gNB configures the UE measurement procedures and the UE reports according to the measurement configuration.

Step 2: The source gNB decides to handover the UE based on MeasurementReport and radio resource management (RRM) information.

Step 3: The source gNB issues a Handover Request message to the target gNB passing a transparent RRC container with necessary information to prepare the handover at the target side. The information includes at least the target cell ID, KgNB*, cell radio network temporary Identifier (C-RNTI) of the UE in the source gNB, RRM-configuration including UE inactive time, basic AS (access stratum) -configuration including antenna information and downlink (DL) carrier frequency, the current QoS flow to data radio bearer (DRB) mapping rules applied to the UE, system information block 1 (SIB1) from the source gNB, UE capabilities for different radio access technologies (RATs) , plane packet data unit (PDU) session related information, and can include the UE reported measurement information including beam-related information if available. The PDU session related information includes slice information and QoS flow level QoS profile (s) . The source gNB may also request a DAPS Handover for some DRBs.

Step 4: Admission control may be performed by the target gNB. Slice-aware admission control shall be performed if the slice information is sent to the target gNB. If the PDU sessions are associated with non-supported slices, the target gNB shall reject such PDU sessions.

Step 5: The target gNB prepares the handover with L1/L2 and sends the HANDOVER REQUEST ACKNOWLEDGMENT to the source gNB, which includes a transparent container to be sent to the UE as an RRC message to perform the handover.

Step 6: The source gNB triggers a Uu handover by sending an RRCReconfiguration message to the UE, containing the information required to access the target cell: at least the target cell ID, the new C-RNTI, the target gNB security algorithm identifiers for the selected security algorithms. It can also include a set of dedicated random access channel (RACH) resources, the association between RACH resources and synchronization signal block (S) (SSB (s) ) , the association between RACH resources and UE-specific channel state information-reference signal (CSI-RS) configuration (s) , common RACH resources, and system information of the target cell, etc.

Step 7: The source gNB sends a SN STATUS TRANSFER message to the target gNB to convey an uplink PDCP SN receiver status and a downlink PDCP SN transmitter status of DRBs for which PDCP status preservation applies (i.e. for RLC AM) . The uplink PDCP SN receiver status includes at least the PDCP SN of the first missing UL PDCP SDU and may include a bit map of the receive status of the out of sequence UL PDCP SDUs that the UE needs to retransmit in the target cell, if any. The downlink PDCP SN transmitter status indicates the next PDCP SN that the target gNB shall assign to new PDCP SDUs, not having a PDCP SN yet.

Step 8: The UE synchronizes to the target cell and completes the RRC handover procedure by sending RRCReconfigurationComplete message to the target gNB.

Step 9: The target gNB sends a PATH SWITCH REQUEST message to an access and mobility management function (AMF) to trigger 5GC to switch the DL data path towards the target gNB and to establish an NG-C interface instance towards the target gNB.

Step 10: 5GC switches the DL data path towards the target gNB. The user plane function (UPF) sends one or more "end marker" packets on the old path to the source gNB per PDU session/tunnel and then can release any U-plane/TNL resources towards the source gNB.

Step 11: The AMF confirms the PATH SWITCH REQUEST message with the PATH SWITCH REQUEST ACKNOWLEDGMENT message.

Step 12: Upon reception of the PATH SWITCH REQUEST ACKNOWLEDGMENT message from the AMF, the target gNB sends a UE CONTEXT RELEASE to inform the source gNB about the success of the handover.

Baseline handover user plane handling:

For user plane handling the following is apply; during handover preparation phase, a user plane tunnels can be established between the source gNB and the target gNB; and during handover execution phase, user data can be forwarded from the source gNB to the target gNB as follows. The forwarding should take place in order as long as packets are received at the source gNB from the UPF or the source gNB buffer has not been emptied.

While during the handover completion phase: The target gNB sends a path switch request message to the AMF to inform that the UE has gained access and the AMF then triggers path switch related 5GC internal signalling and actual path switch of the source gNB to the target gNB in UPF. The source gNB continues forwarding data if packets are received at the source gNB from the UPF or the source gNB buffer has not been emptied. For end marker packets handling, the source gNB receives one or several GTP-U end marker packets per PDU session from the UPF and replicates the end marker packets into each data forwarding tunnel when no more user data packets are to be forwarded over that tunnel. (as illustrated in the step10. )

For user plane bearers configure with radio link control-unacknowledged mode (RLC-UM) mode, PDCP entities including header compression contexts are reset, and COUNT values are set to zero. As a new key is anyway generated at handover, there is no security reason to keep the COUNT values. On UE side, all the PDCP SDUs that have not been transmitted yet will be sent to the target cell after handover. PDCP SDUs for which the transmission has not been started can be forwarded via Xn-AP interface towards the target gNB. While, unacknowledged PDCP SDUs will be lost. This minimizes handover complexity because no context (i.e. configuration information) has to be transferred between the source and the target gNB. For radio link control-acknowledged mode (RLC-AM) configured user plane bearers, the user plane handling follow the procedure described in lossless handover section.

Lossless procedures: For lossless handover control plane (CP) is handled as specified in the step 7 above. As for user plane handling, the header compression protocol is reset at UE side because its context is not forwarded from the source eNB to the target eNB, but the PDCP SDUs’ sequence numbers and the COUNT values are not reset. To ensure lossless handover in the uplink, the PDCP PDUs stored in the PDCP retransmission buffer are retransmitted by the RLC protocol based on the PDCP SNs which are maintained during the handover and deliver them to the gateway in the correct sequence. In order to ensure lossless handover in the downlink, the source eNodeB forwards the uncompressed PDCP SDUs for which reception has not yet been acknowledgment by the UE to the target eNodeB for retransmission in the downlink.

DAPS procedures: For DAPS handover the CP is handled as the followings.

Step 7a: For DRBs configured with DAPS, the source gNB sends an EARLY STATUS TRANSFER message. A DL COUNT value conveyed in the EARLY STATUS TRANSFER message indicates PDCP SN and hyperframe number (HFN) of the first PDCP SDU that the source gNB forwards to the target gNB. The source gNB does not stop assigning SNs to downlink PDCP SDUs until it sends the SN STATUS TRANSFER message to the target gNB in step 8b.

Step 8: In case of DAPS HO, the UE does not detach from the source cell upon receiving the RRCReconfiguration message. The UE releases the source SRB resources, security configuration of the source cell and stops DL/UL reception/transmission with the source upon receiving an explicit release from the target node.

Step 8a/8b: In case of DAPS Handover, the target gNB sends a HANDOVER SUCCESS message to the source gNB to inform that the UE has successfully accessed the target cell. In return, the source gNB sends a SN STATUS TRANSFER message for DRBs configured with DAPS for which, and the normal data forwarding occurs as the followings.

The downlink PDCP SDUs are forwarded with SN assigned by the source gNB, until SN assignment is handed over to the target gNB in step 8b, and the source gNB does not stop transmitting downlink packets until it receives the HANDOVER SUCCESS message from the target gNB in the step 8a. The source gNB may additionally send the EARLY STATUS TRANSFER message (s) between the step 7 and the step 8b, to inform discarding of already forwarded PDCP SDUs. The target gNB does not transmit forwarded downlink PDCP SDUs to the UE, whose COUNT is less than the conveyed DL COUNT value and discards them if transmission has not been attempted already. The uplink PDCP SN receiver status and the downlink PDCP SN transmitter status are also conveyed for DRBs with RLC-UM in the SN STATUS TRANSFER message in the step 8b, if configured with DAPS.

For DRBs configured with DAPS for which duplication avoidance is required (i.e. RLC-AM) , the source gNB does not stop delivering uplink QoS flows to the UPF until it sends the SN STATUS TRANSFER message in the step 8b. The target gNB does not forward QoS flows of the uplink PDCP SDUs successfully received in-sequence to the UPF until it receives the SN STATUS TRANSFER message, in which UL HFN and the first missing SN in the uplink PDCP SN receiver status indicates the start of uplink PDCP SDUs to be delivered to the UPF. The target gNB does not deliver any uplink PDCP SDUs which has an UL COUNT lower than the provided. The source gNB may omit sending the SN STATUS TRANSFER message if none of DRBs is configured with DAPS or shall be treated with PDCP status preservation.

For User plane handling of RLC-AM bearers configured with DAPS:

For downlink the following principles are applied: During HO preparation, a forwarding tunnel is always established. The source gNB is responsible for allocating downlink PDCP SNs until the SN assignment is handed over to the target gNB and data forwarding takes place. That is, the source gNB does not stop assigning PDCP SNs to downlink packets until it receives the HANDOVER SUCCESS message and sends the SN STATUS TRANSFER message to the target gNB. Upon allocation of downlink PDCP SNs by the source gNB, it starts scheduling downlink data on the source radio link and starts forwarding downlink PDCP SDUs along with assigned PDCP SNs to the target gNB. For security synchronization, ciphering and integrity protection HFN and PDCP SN are maintained after the SN assignment is handed over to the target gNB. The SN STATUS TRANSFER message indicates the next DL PDCP SN to allocate to a packet which does not have a PDCP sequence number yet, even for RLC-UM. During handover execution period, the source and target gNBs separately perform ROHC header compression, ciphering, and adding PDCP header. During handover execution period, the UE continues to receive downlink data from both source and target gNBs until the source gNB connection is released by an explicit release command from the target gNB. The UE configured with DAPS PDCP maintains separate security and ROHC header decompression associated with each gNB, while maintaining common reordering function, duplicate detection, discard function, and PDCP SDUs in-sequence delivery to upper layers. PDCP SN continuity is supported for both RLC AM and UM DRBs configured with DAPS.

For Uplink: The UE transmits UL data to the source gNB until the random access procedure toward the target gNB has been successfully completed. Afterwards the UE switches its UL data transmission to the target gNB. Even after switching its UL data transmissions, the UE continues to send UL layer 1 CSI feedback, HARQ feedback, layer 2 RLC feedback, ROHC feedback, HARQ data re-transmissions, and RLC data re-transmission to the source gNB. During handover execution period, the UE maintains separate security context and ROHC header compressor context for uplink transmissions towards the source and target gNBs. The UE maintains common UL PDCP SN allocation. PDCP SN continuity is supported for both RLC AM and UM DRBs configured with DAPS. During handover execution period, the source and target gNBs maintain their own security and ROHC header decompressor contexts to process UL data received from the UE. The establishment of a forwarding tunnel is optional. HFN and PDCP SN are maintained in the target gNB. The SN STATUS TRANSFER message indicates the first missing UL COUNT that the target should start delivering to the 5GC, even for RLC-UM.

Problem Statement:

NR MBS use cases include public safety and mission critical, vehicle-to-anything (V2X) applications, transparent internet protocol version 4 (IPv4) /internet protocol version 6 (IPv6) multicast delivery, internet protocol television (IPTV) , software delivery over wireless, group communications, and internet of things (IoT) applications. Most of these use cases involve MBS service reception during inter-node mobility, e.g. public safety, V2X applications and so on. As illustrated in Table 1 (R1-2007001) , it is obviously that most of the above use cases require high reliability, for example, V2X applications require up to 99.9999%reliability, public safety, and mission critical push to talk (MCPTT) service also requires up to 99.9999%reliability. In addition, some of MBS use-cases such as V2X and industry application e.g., motion related sensor such as industrial actuators may involve MBS service reception during inter-node mobility which require service interruption time due to their very strict delay requirement which could ranging from 5ms to 0.5ms (See also Table 1) . While most of MBS mobility proposals discussed in latest 3GPP meeting suggesting to adopt legacy and/or lossless handovers for supporting MBS mobility in NR, it is clear that adopting such handovers can only guarantee the requirements of MBS reliability-sensitive service application and use-cases for the other time-sensitive use cases the requirement of an alternative handover techniques is quite obvious. Although, there are some proposals suggesting to adopt DAPS handover for MBS, which can guarantee very low service interruption delay for MBS applications. However, considering the amount of complexity brought to UE when performing DAPS handover (i.e. due to simultaneous downlink and uplink transmission form both the source and target gNBs during DAPS HO) , current standardized DAPS HO procedure may need to be improved to better support MBS services. To address these technical limitations and drawbacks, some embodiments of the present disclosure propose a new handover method involving several changes in the handover procedures such as a changing in the handover signaling, the information nested within the handover signaling as well as some handover procedures at both source and target gNBs.

Table 2: Requirements for different MBS use cases

MBS use cases	Latency	Reliability
V2X	5-100 ms variable	90%to 99.9999%
Live Video	150 ms	99.9%
IoT, Software update	Latency Tolerant	Higher reliability is beneficial
Industry applications	0.5 ms	99.9999%

In some embodiments of the present disclosure, the description of the detailed handover procedures and signalling changes is illustrated in the followings.

Proposed Solutions:

Summary of the proposed methods: Some embodiments of the present disclosure provide a method for a handover procedure to support a UE mobility while receiving a service that requires low interruption delay and/or high degree of reliability e.g., 5g MBS. FIG. 6 illustrates a handover of MBS capable UE from one NG-RAN to another NG-RAN according to an embodiment of the present disclosure. FIG. 6 illustrates that, in some embodiments, the method considers a scenario where an MBS capable UE receiving a service that requires low interruption time and/or high degree of reliability MBS service form 5g core network via either multicast radio bearers (MRB) or unicast data radio bearers (DRBs) in a source NG-RAN and move to another NG-RAN (i.e. target NG-RAN) which is supporting/not-supporting the service provided for the given UE as illustrated in FIG. 6.

FIG. 7 illustrates a proposed handover to support low-latency and reliable MBS mobility according to an embodiment of the present disclosure. FIG. 6 and FIG. 7 illustrate that, in some embodiments, in this method, a UE may indicate its MBS service interest (i.e., the identity (ID) or the type of the MBS service or the QoS requirement of the MBS service) to the source gNB as part of a HANDOVER MEASUREMENT report. In return, the source gNB may decide a handover based on the part of a HANDOVER MEASUREMENT report and may select the type of handover to be performed/configured for the given UE MBS radio bearer (MRB/DRB) based on one of the followings.

The UE indication (service interest information e.g., service QoS requirement such as target delay and/or reliably level ) , and/or the source gNB internal configuration which may contain UE and MBS service ID or QoS flow ID or session ID association, and/or the core network indication e.g. UE MBS context message from AMF or SMF containing and UE identity and MBS service ID/QoS flow ID/session ID association.

In an alternative way, the selection of handover type to be configured for UE MBS bearers could to be performed by the target gNB; In this case, the UE interested service related IDs and/or UE and QoS flow or session association related information shall be indicated within HANDOVER REQUEST signaling that is forwarded by the source gNB to the target gNB (i.e., via Xn-AP interface) . The type of handovers options to be selected/configured for UE MBS bearers by the source target gNB node or target gNB node may include lossless handover or lossless and low-latency handover according to UE MBS service reliability and latency level requirement as illustrated in Table 2. The detail of procedures and signalling applicable in case of lossless and low-latency handover compared to the existing unicast DAPS and lossless handover is given as described in observation and proposals section.

Table 2: Handover type based on UE MBS use cases

MBS use cases	Latency	Reliability	Type of Handover (HO)
V2X	5-100ms variable	90%to 99.9999%	Low-latency and Lossless HO
Live Video	150 ms	99.9%	Lossless HO
IoT, Software update	Latency Tolerant	Higher reliability is beneficial	Lossless HO
Industry applications	0.5 ms	99.9999%	Low-latency and Lossless HO

After deciding handover (e.g., by the source gNB) , a HANDOVER REQUEST message can be forwarded form the source gNB to the target gNB. The handover message may comprise at least one the following information according to selected/configured handover. The handover message may comprise a UE measurement report, UE MRB/DRB service/QoS information, UE and MBS service/QoS/session association information, the decided/configured handover type by the source gNB, if low–latency handover is selected/configured, a request to target gNB to suggest it will start allocating PDCP SN and/or start forwarding data, time to the UE with the reference to X, where X is for example, a time reference when a specific downlink/uplink frame is forwarded/received toward/from UE by the gNB source, the downlink and/or uplink timing advance of the given UE with reference X or to a scheduled downlink/uplink frame by the source, the MBS current delivery mode (i.e., MRB/DRB) , and/or QoS flow to MRB/DRB mapping of UE MBS bearer at the source and the L1, L2 and/or L3 scheduling information/forwarding treatment for given UE MBS bearers.

In some embodiments, upon the reception of the HANDOVER REQUEST message by the target gNB, the target gNB may perform at least one of the followings.

The target gNB may preform admission control on the handed-over MBS bearers (MRB/DRB) and may decide/configure the type of handover type to be performed for the given MBS bearers if not decided/configured by the source gNB.

The target gNB may determine/decide based on the configuration received in the HANDOVER REQUEST, the exact the time to start PDCP SN allocation and start data forwarding toward UE with respect to time reference X provided the source gNB (or if low-latency handover feature is selected/configured in the HANDOVER REQUEST ACK, or locally. )

The target gNB may prepares based on the configuration received in the HANDOVER REQUEST, the synchronization/timing information (e.g., the radio network temporary identifier (RNTI) assignment i.e. g-RNTI for MBS reception over MRB or C-RNTI for MBS reception over DRB, UE pre-allocated grant assignment and the downlink and uplink timing advance with respect to X) .

The target gNB may initiate a UE MSB session join if the MBS session/service/TMGI that UE receiving is existed in the target gNB or initiate a session establishment request toward the core network if MABS session that UE receiving does not exist at the target gNB.

The target gNB may switch the UE to a new radio bearer (MRB/DRB) if required, and may strive to provide the same QoS flow to MRB/DRB mapping and prepares the scheduling configuration/forwarding treatment for the given MBS bearers as indicated by the source gNB.

The target gNB may determine the timing configuration required synchronize with the given UE and may provide a time advice command and a pre-allocated grant for the given UE (or if low-latency handover feature is selected/configured in the HANDOVER REQUEST ACK, or locally. )

The target gNB may start forwarding a copy of MBS downlink data forwarded from source gNB to as soon as it starts PDCP SN allocation toward UE (i.e. without the need to waiting to receive the handover complete message from UE) to reduce the UE handover interruption time. (If low-latency handover feature is selected/configured in the HANDOVER REQUEST ACK, or locally at the target gNB) .

In some embodiments, after the target gNB preparing all the above configuration, the target gNB will prepare the handover with L1, L2 and L3 configuration, and will send a HANDOVER REQUEST ACKNOWLEDGMENT to the source gNB. The request comprises a transparent container to be sent to the UE as an RRC message (containing the above configurations, the uplink time advance command, and/or downlink sync information) to perform the handover. In return, the source gNB may perform at least one of the followings.

The source gNB may perform PDCP SN assigning PDCP SDU data forwarding as given in the above embodiments (or if low-latency and lossless feature is selected/configured for MBS bearers. )

The source gNB may send the SN STATUS TRANSFER message to the target gNB to convey the uplink PDCP SN receiver status and the downlink PDCP SN transmitter status of DRBs for which PDCP status preservation applies (i.e. for RLC AM) . The uplink PDCP SN receiver status includes at least the PDCP SN of the first missing UL PDCP SDU and may include a bit map of the receive status of the out of sequence UL PDCP SDUs that the UE needs to retransmit in the target cell, if any. The downlink PDCP SN transmitter status indicates the next PDCP SN that the target gNB shall assign to new PDCP SDUs, not having a PDCP SN yet (or if lossless handover is configured. )

In some embodiments, upon the reception of HANDOVER REQUEST ACKNOWLEDGMENT by the source gNB containing the configurations forwarded by the target gNB, the source gNB transmits a HANDOVER INITIATION/COMMAND message toward the UE containing the provided configurations by the target gNB. The provided configurations comprise for example, the agreed time of source and target start/stop PDCP SN allocation and/or data forwarding, target pre-allocated grant, uplink time advance command, downlink sync information, and/or MBS bearers scheduling/forwarding configuration. When the UE receives the configuration from the source gNB, the UE may perform at least one of the followings.

The UE may synchronize to a target cell based on the synchronization/timing information provided by the target gNB (i.e., the downlink sync timing and the uplink time advance information provided by the source gNB from the target gNB in the handover command container) .

The UE may configure a separate entity of MAC configuration, PDCP configuration, and/or RLC configuration for the target gNB and the source gNB.

The UE may start receiving MBS data after from the target gNB after synchronizing and connecting to the target gNB.

The UE may stop receiving from source gNB after as specified by the timing information given in the Handover command RRC message (i.e. base on the agreed time by the source and target gNBs to stop/start forwarding downlink data toward UE) ) while it may keep the release of the configured MAC RLC and PDCP, entities configuration of the source gNB until receiving first MBS packet from target gNB) .

The UE may stop sending UL layer 1 CSI feedback, HARQ feedback, layer 2 RLC feedback, ROHC feedback, HARQ data re-transmissions, and/or RLC data re-transmission to the source gNB.

The UE may send handover complete message or handover radio link failure on the pre-allocated grant by the source/target gNB.

The UE may omit sending the handover complete message and utilize the pre-allocated grant for uplink data transmission toward the target gNB.

The UE may release the MAC configuration, PDCP configuration, and/or RLC configuration for the source gNB.

Low-latency and Lossless features proposals:

PDCP SN allocation and misalignment:

In current DAPS procedures, the downlink PDCP SNs allocation is carried out by the source gNB until the SN assignment is handed over to the target gNB and the data forwarding is started . That is, the source gNB does not stop assigning PDCP SNs to downlink packets until it receives the HANDOVER SUCCESS message and sends the SN STATUS TRANSFER message to the target gNB. Such a process could result in loading the gNB buffer of target gNB . Because the time when to stop PDCP SN allocation and to start data forwarding by the source is totally depends on the reception of the HANDOVER SUCCESS message from the target gNB which could take very long time because this message is also triggered by the target after the reception of a HANDOVER COMPLETION message from the UE.

Example: In some embodiments of the present disclosure, in the new proposed low-latency and lossless handover procedure, the source gNB and target gNB allocate PDCP SN and maintain count value separately and straightforwardly based on to the agreed timing when each node will start/stop the downlink /uplink transmission toward UE/UPF (e.g., the source gNB may start allocating PDCP SN from the time it receives HANDOVER ACK message from the target gNB until will the starting time of PDCP SN allocation by the target gNB which is provided within HANDOVER ACK message) . Such procedure can help on reducing dependency of handover procedures (the source gNB) on the UE related signalling (i.e. HANDOVER COMPLETION message) because it allows the source gNB to start and stop PDCP SN allocations STATUS transfer (as agreed by the target gNB) and start data forwarding (of low-latency handover) without the need for waiting of a HANDOVER SUCCESS message from the target gNB which depends on the reception of a HANDOVER completion from the UE. This could also help in reducing the handover delay and allows for omitting some handover signalling (e.g., the UE may send handover completion signalling in some case and omit it if not needed and used the pre-allocated grant for uplink data transmission. )

PDCP re-ordering and duplication:

In current DAPS configuration, the UE will receive downlink user data simultaneously from both the source gNB and the target gNB. Therefore, the PDCP layer is reconfigured to a common PDCP entity for the source and target user plane protocol stacks. To secure in-sequence delivery of DL user data, PDCP (SN) continuation is maintained during the handover procedure. For this reason, a common re-ordering and duplication function (for source and target gNB) is required in a single PDCP entity.

Example l: In some embodiments of the present disclosure, in the new proposed low-latency and Lossless handover MBS procedure, the UE may stop downlink either as specified the HANDOVER INITIATION command (i.e. the agreed time when the target will start forwarding data toward UE) or immediately after receiving a first packet from the target. This procedure can simplify UE and network implementation since the duplication check and in-sequence delivery to the 5G Core is done by either the source gNB (i.e., until the agreed time or until receiving a first packet from the target) or by the target gNB. Compared to current DAPS procedure in which a common re-ordering and duplication function (for the source gNB and target gNB) is required in a single PDCP entity.

Data forwarding and data gap:

In case of DAPS handover, the UE continues to receive downlink data from both source and target gNBs until the source gNB connection is released by an explicit release command from the target gNB. The release of the resources at the source gNB during the handover completion phase is triggered by the target gNB upon the reception of HANDOVER COMPLETION message from the UE. Such a procedure may increase UE reception complexity processing cost and power consumption. In addition, the UE will also continue to transmit UL data to the source gNB until the random access procedure toward the target gNB has been successfully completed; then, switches the UL data transmission to the target gNB. This will also increase signaling UE complexity, processing cost and power consumption.

Example-1: In some embodiments of the present disclosure, in the new proposed low-latency and lossless handover MBS procedure, the source gNB may forward all of the MBS packet (PDCP SDUs) received from a core network (UPF) during the agreed timing (transmission switching period) between the source gNB and the target gNB to the target gNB and then to the UE to ensure packet loss will not occur at the UE side. By doing so, the UE does not need to wait until the release command to be sent by the target gNB to the source gNB. The UE can stop receiving MBS data from the source gNB as specified the RRC HANDOVER INITIATION command (i.e. the agreed time when the target gNB will start forwarding data toward the UE) without to worry about MBS data loss since all data within that agreed time will be transferred from the source gNB to the target gNB, and the target gNB can start sending a copy of this data toward the UE as early as possible (i.e. prior or in parallel to the reception of HANDOVER INITIATION command by the UE. ) Alliteratively, the UE may stop reception from the source gNB immediately after receiving first packet from the target gNB. Such a procedure could help in avoiding packet loss and relaxing UE processing power and reduce power consumption.

Example-2: In some embodiments of the present disclosure, the source gNB may forward within the HANDOVER COMMAND message including the target gNB timing advance information and uplink pre-allocation grant. The source gNB may also pre-allocate an uplink grant for the UE, to allow the UE to adjust its uplink timing to the target gNB (at the time when switching to the target gNB. ) This could allow UE to avoid/omit the RACH process which could relatively reduce the handover delay and relax UE handover signalling complexity.

Some embodiments of the present disclosure provide a method for reliable and low-latency handover for multicast/broadcast service mobility with service continuity in 5G NR. The major innovative aspects of the method include the followings.

1. Introducing the idea of exchanging the MBS service and/or QoS related information between the UE, the source gNB, and the target gNB for propose of deciding the type of handover to be configured for UE MBS mobility.

2. Introducing of a new type of information to be exchanged within the handover request message between the source gNB and the target gNB during the handover, such as timing related information which helps both source gNB and target gNB in overcoming the PDCP allocation, PDCP count value miss-alignment, and data gap issues.

3. Introducing of the exchange of UE and MBS service, QoS flow, and/or session identity association information between the UE, the source gNB, and the target gNB, which can allows the target gNB to strive to provide the same QoS flow to MRB/DRB mapping and scheduling configuration/forwarding treatment for MBS bearers similar to the configuration at the source gNB. Given such scheduling configuration information and the timing information when the source gNB and the target gNB will start and stop sending the data toward the UE for the give MBS service, the UE can able to prepare an optimal reception configuration of the target configured MBS bearers.

4. Introducing the idea of combining the PDCP SN allocation and data forwarding can in a single signalling that could help on saving the handover signalling between the source gNB and target gNB.

5. Introducing the idea of forwarding a copy downlink data forwarded from the target gNB as soon as it starts PDCP SN allocation toward the UE (i.e. prior or in parallel to the reception of HANDOVER INITIATION command by the UE from the source gNB) to help the UE avoiding packet loss and relaxing UE processing power and reduce power consumption.

6. Introducing the idea of omitting some handover signalling (e.g. UE may send handover completion signalling in some cases and omit it if not needed and used the pre-allocated grant for uplink data transmission. )

7. Introducing the idea of pre-allocating uplink grant from the source gNB and/or the target gNB which could help in increasing the UE resiliency against handover failure (i.e. by allowing the UE to send the handover failure to either the source gNB or the target gNB. )

In summary, in some embodiments of the present disclosure, a QoS aware reliable and low latency handover method is proposed to support MBS mobility with service continuity and to guarantee the difference in MBS service QoS requirements during the UE handover process. In this method, we propose to exchange MBS service and/or QoS related information between the UE, the source base station such as a source gNB, and the target base station such as a target gNB to decide the type of handover to configure for UE MBS mobility. In addition, we propose several enhancements to current NR handovers including some modifications on HO signalling and procedures such as introducing of new type of information to be exchanged during handover procedures (e.g., a timing related information between UE, source and target gNB) to reduce service interruption time while keeping UE signalling complexity, processing cost, and power consumption as low as possible.

The major advantages of some embodiments of the present disclosure compared to the prior art provide a handover method that capable of addressing both the latency and reliability requirements during MBS mobility process, and minimizing UE signalling complexity and processing cost as low as possible.

UE side advantages:

1. Compared prior proposals to address the service interruption delay issue for MBS mobility such as DAPS handover in which a huge amount of signalling is imposed to UE due to reception of MBS service from both target and source gNB until the target gNB indicates a handover success toward gNB source. The new method provides UE with a target gNB timing information that allow UE to stop receiving MBS service from the source at any point (as specified in the agreed timing within the handover command or decided by UE locally) without to worry about losing MBS data since all of the MBS data within the agreed timing will be forwarded from the source gNB to the target gNB and from the target to UE as early as possible. Such a procedure could help in relaxing UE processing power and UE reducing UE power consumption (i.e. UE does not need to simultaneously receive/transmit from/to both source and target gNBs to receive MBS mobility with low service interruption time) .

2. The new method exchanges the target gNB timing advance information to UE and provides pre-allocated uplink grant from either the source or the target gNB or both to UE, which allows UE to avoid/omit imitating a RACH process toward target gNB. Such a process which relatively reduces UE handover delay and reduce UE signalling complexity. The pre-allocated uplink grant provided from the source gNB and/or target gNB could also help in increasing UE resiliency against the handover failure UE handover failure (i.e. by allowing UE to be become capable of sending a handover failure to either the source or target gNB the target gNB.

Network side advantages:

PDCP SN allocation and count value misalignment issues: The PDCP SN allocation and count value maintenance can be straightforwardly done at the source gNB and the target gNB individually and according to the agreed timing when each node will start/stop the downlink /uplink transmission toward UE/UPF. For example, the source gNB may start allocating PDCP SN from the time it receives HANDOVER ACK message from the target gNB until the starting time of PDCP SN is allocation by the target gNB which is provided within HANDOVER ACK message.

Data forwarding and data gap issue: all of the received MBS packet (PDCP SDUs) from core network (UPF) by the source gNB during the agreed handover timing by the source gNB and the target gNB can be forwarded to the target gNB and then to the UE to ensure that packet loss will not occur at UE side.

PDCP re-ordering and duplication issue: the UE may stop downlink either as specified the HANDOVER INITIATION command (i.e., the agreed time when the target gNB will start forwarding data toward the UE) or immediately after receiving a first packet from the target gNB. This procedure simplifies network implementation since the duplication check and in-sequence delivery to the 5G core is done either in the source gNB (i.e., until the agreed time or until receiving a first packet from the target gNB or in the target gNB) apposing to the current DAPS procedure in which a common re-ordering and duplication function (for the source gNB and the target gNB) is required in a single PDCP entity.

In summary, in some embodiments, a user equipment (UE) , a source base station, a target base station, and handover methods for multicast/broadcast service (MBS) are provided. The handover method for MBS is partially performed by the source base station includes exchanging an MBS service and/or a Quality-of-Service (QoS) related information between a source base station and at least a user equipment (UE) as a part of a handover measurement message and/or a target base station as a part of a handover request message, and partially performed by the target base station include exchanging of the MBS scheduling information and the timing information about the when the target base station starts/stops the PDCP SN allocation and/or the data forwarding to the at least the source base station via handover acknowledgement message and/or a UE via handover command message , and furtherly include deciding based on the handover measurement and/or the handover request messages the handover to be performed and/or configured by the source or the target base station to support optimal MBS mobility for the given UE. This can solve issues in the prior art, address UE latency and reliability requirements during MBS mobility process, reduce UE signaling complexity, reduce UE processing cost, support service continuity, provide a good communication performance, and/or provide high reliability.

Commercial interests for some embodiments are as follows. 1. Solving issues in the prior art. 2. Addressing latency and reliability requirements during MBS mobility process. 3. Reducing UE signalling complexity. 4. Reducing processing cost. 5. Supporting service continuity 6. Providing a good communication performance. 7. Providing a high reliability. 8. Some embodiments of the present disclosure are used by 5G-NR chipset vendors, V2X communication system development vendors, automakers including cars, trains, trucks, buses, bicycles, moto-bikes, helmets, and etc., drones (unmanned aerial vehicles) , smartphone makers, communication devices for public safety use, AR/VR device maker for example gaming, conference/seminar, education purposes. Some embodiments of the present disclosure are a combination of “techniques/processes” that can be adopted in 3GPP specification to create an end product. Some embodiments of the present disclosure propose technical mechanisms.

FIG. 8 is a block diagram of an example system 700 for wireless communication according to an embodiment of the present disclosure. Embodiments described herein may be implemented into the system using any suitably configured hardware and/or software. FIG. 8 illustrates the system 700 including a radio frequency (RF) circuitry 710, a baseband circuitry 720, an application circuitry 730, a memory/storage 740, a display 750, a camera 760, a sensor 770, and an input/output (I/O) interface 780, coupled with each other at least as illustrated. The application circuitry 730 may include a circuitry such as, but not limited to, one or more single-core or multi-core processors. The processors may include any combination of general-purpose processors and dedicated processors, such as graphics processors, application processors. The processors may be coupled with the memory/storage and configured to execute instructions stored in the memory/storage to enable various applications and/or operating systems running on the system.

The baseband circuitry 720 may include circuitry such as, but not limited to, one or more single-core or multi-core processors. The processors may include a baseband processor. The baseband circuitry may handle various radio control functions that enables communication with one or more radio networks via the RF circuitry. The radio control functions may include, but are not limited to, signal modulation, encoding, decoding, radio frequency shifting, etc. In some embodiments, the baseband circuitry may provide for communication compatible with one or more radio technologies. For example, in some embodiments, the baseband circuitry may support communication with an evolved universal terrestrial radio access network (EUTRAN) and/or other wireless metropolitan area networks (WMAN) , a wireless local area network (WLAN) , a wireless personal area network (WPAN) . Embodiments in which the baseband circuitry is configured to support radio communications of more than one wireless protocol may be referred to as multi-mode baseband circuitry.

In various embodiments, the baseband circuitry 720 may include circuitry to operate with signals that are not strictly considered as being in a baseband frequency. For example, in some embodiments, baseband circuitry may include circuitry to operate with signals having an intermediate frequency, which is between a baseband frequency and a radio frequency. The RF circuitry 710 may enable communication with wireless networks using modulated electromagnetic radiation through a non-solid medium. In various embodiments, the RF circuitry may include switches, filters, amplifiers, etc. to facilitate the communication with the wireless network. In various embodiments, the RF circuitry 710 may include circuitry to operate with signals that are not strictly considered as being in a radio frequency. For example, in some embodiments, RF circuitry may include circuitry to operate with signals having an intermediate frequency, which is between a baseband frequency and a radio frequency.

In various embodiments, the transmitter circuitry, control circuitry, or receiver circuitry discussed above with respect to the user equipment, eNB, or gNB may be embodied in whole or in part in one or more of the RF circuitry, the baseband circuitry, and/or the application circuitry. As used herein, “circuitry” may refer to, be part of, or include an Application Specific Integrated Circuit (ASIC) , an electronic circuit, a processor (shared, dedicated, or group) , and/or a memory (shared, dedicated, or group) that execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable hardware components that provide the described functionality. In some embodiments, the electronic device circuitry may be implemented in, or functions associated with the circuitry may be implemented by, one or more software or firmware modules. In some embodiments, some or all of the constituent components of the baseband circuitry, the application circuitry, and/or the memory/storage may be implemented together on a system on a chip (SOC) . The memory/storage 740 may be used to load and store data and/or instructions, for example, for system. The memory/storage for one embodiment may include any combination of suitable volatile memory, such as dynamic random access memory (DRAM) ) , and/or non-volatile memory, such as flash memory.

In various embodiments, the I/O interface 780 may include one or more user interfaces designed to enable user interaction with the system and/or peripheral component interfaces designed to enable peripheral component interaction with the system. User interfaces may include, but are not limited to a physical keyboard or keypad, a touchpad, a speaker, a microphone, etc. Peripheral component interfaces may include, but are not limited to, a non-volatile memory port, a universal serial bus (USB) port, an audio jack, and a power supply interface. In various embodiments, the sensor 770 may include one or more sensing devices to determine environmental conditions and/or location information related to the system. In some embodiments, the sensors may include, but are not limited to, a gyro sensor, an accelerometer, a proximity sensor, an ambient light sensor, and a positioning unit. The positioning unit may also be part of, or interact with, the baseband circuitry and/or RF circuitry to communicate with components of a positioning network, e.g., a global positioning system (GPS) satellite.

In various embodiments, the display 750 may include a display, such as a liquid crystal display and a touch screen display. In various embodiments, the system 700 may be a mobile computing device such as, but not limited to, a laptop computing device, a tablet computing device, a netbook, an ultrabook, a smartphone, a AR/VR glasses, etc. In various embodiments, system may have more or less components, and/or different architectures. Where appropriate, methods described herein may be implemented as a computer program. The computer program may be stored on a storage medium, such as a non-transitory storage medium.

A person having ordinary skill in the art understands that each of the units, algorithm, and steps described and disclosed in the embodiments of the present disclosure are realized using electronic hardware or combinations of software for computers and electronic hardware. Whether the functions run in hardware or software depends on the condition of application and design requirement for a technical plan. A person having ordinary skill in the art can use different ways to realize the function for each specific application while such realizations should not go beyond the scope of the present disclosure. It is understood by a person having ordinary skill in the art that he/she can refer to the working processes of the system, device, and unit in the above-mentioned embodiment since the working processes of the above-mentioned system, device, and unit are basically the same. For easy description and simplicity, these working processes will not be detailed.

It is understood that the disclosed system, device, and method in the embodiments of the present disclosure can be realized with other ways. The above-mentioned embodiments are exemplary only. The division of the units is merely based on logical functions while other divisions exist in realization. It is possible that a plurality of units or components are combined or integrated in another system. It is also possible that some characteristics are omitted or skipped. On the other hand, the displayed or discussed mutual coupling, direct coupling, or communicative coupling operate through some ports, devices, or units whether indirectly or communicatively by ways of electrical, mechanical, or other kinds of forms. The units as separating components for explanation are or are not physically separated. The units for display are or are not physical units, that is, located in one place or distributed on a plurality of network units. Some or all of the units are used according to the purposes of the embodiments. Moreover, each of the functional units in each of the embodiments can be integrated in one processing unit, physically independent, or integrated in one processing unit with two or more than two units.

If the software function unit is realized and used and sold as a product, it can be stored in a readable storage medium in a computer. Based on this understanding, the technical plan proposed by the present disclosure can be essentially or partially realized as the form of a software product. Or, one part of the technical plan beneficial to the conventional technology can be realized as the form of a software product. The software product in the computer is stored in a storage medium, including a plurality of commands for a computational device (such as a personal computer, a server, or a network device) to run all or some of the steps disclosed by the embodiments of the present disclosure. The storage medium includes a USB disk, a mobile hard disk, a read-only memory (ROM) , a random access memory (RAM) , a floppy disk, or other kinds of media capable of storing program codes.

While the present disclosure has been described in connection with what is considered the most practical and preferred embodiments, it is understood that the present disclosure is not limited to the disclosed embodiments but is intended to cover various arrangements made without departing from the scope of the broadest interpretation of the appended claims.

Claims

A handover method for a multicast/broadcast service (MBS) performed by a user equipment (UE) , comprising:

determining, by the UE, an MBS service and/or a Quality-of-Service (QoS) related information as a part of a handover measurement report; and

exchanging the MBS service and/or the QoS related information as the part of the handover measurement report between at least two of the UE, a source base station, and a target base station, wherein a handover to be performed and/or configured for UE MBS mobility is made based on the part of the handover measurement report.
The handover method of claim 1, wherein a selection of a type of the handover to be performed and/or configured for UE MBS mobility is made based on at least one of the followings:

an indication of the UE comprising the MBS service and/or the QoS related information;

an internal configuration of the source base station; or

an indication of a core network.
The handover method of claim 1 or 2, wherein the MBS service and/or the QoS related information comprises a UE identity (ID) , an MBS service ID, a QoS flow ID, or a session ID association.
The handover method of claim 2 or 3, wherein the internal configuration of the source base station comprises a UE ID, an MBS service ID, a QoS flow ID, or a session ID association.
The handover method of any one of claims 2 to 4, wherein the indication of the core network comprises a UE MBS context message, a UE ID, an MBS service ID, a QoS flow ID, or a session ID association.
The handover method of any one of claims 1 to 5, wherein determining, by the UE, the MBS service and/or the QoS related information as the part of the handover measurement report comprises receiving, by the UE, the MBS service and/or the QoS related information from a core network via multicast radio bearers (MRBs) or unicast data radio bearers (DRBs) .
The handover method of any one of claims 1 to 6, wherein exchanging the MBS service and/or the QoS related information between the at least two of the UE, the source base station, and the target base station comprises indicating, by the UE, the MBS service and/or the QoS related information as the part of the handover measurement report to the source base station.
The handover method of claim 7, wherein exchanging the MBS service and/or the QoS related information between the at least two of the UE, the source base station, and the target base station comprises forwarding, by the source base station from the UE, the MBS service and/or the QoS related information as the part of the handover measurement report to the target base station.
The handover method of claim 8, wherein forwarding, by the source base station from the UE, the MBS service and/or the QoS related information as the part of the handover measurement report to the target base station is indicated within a handover request signaling.
The handover method of any one of claims 2 to 9, wherein the selection of the type of the handover to be performed and/or configured for UE MBS mobility comprises a lossless handover or a lossless and low-latency handover.
The handover method of claim 10, wherein the selection of the type of the handover to be performed and/or configured for UE MBS mobility comprises the lossless handover or the lossless and low-latency handover according to UE MBS service reliability and latency level requirements.
The handover method of any one of claims 1 to 11, further comprising receiving, by the UE, configurations from the source base station, wherein the configurations comprise at least one of the followings:

an agreed time of start/stop packet data convergence protocol (PDCP) sequence number (SN) allocation and/or data forwarding by the source base station and the target base station;

a target pre-allocated grant;

an uplink time advance command;

a downlink synchronization information; or

MBS bearers scheduling/forwarding configuration; and/or;

the method further comprising receiving by the UE from the source base station a handover command containing a target downlink/uplink sync information, MBS scheduling information, and MBS data forwarding timing information; and/or

preparing by a UE optimal reception configuration for MBS data in advance and deciding when to stop receiving downlink data from the source base station and when to release a source base station configuration and releasing the source base station configuration accordingly.
The handover method of claim 12, wherein the configurations are forwarded by the source base station from the target base station to the UE.
The handover method of claim 12 or 13, wherein the configurations are forwarded by the source base station from the target base station to the UE in a handover initiation/command message.
The handover method of ant one of claims 12 to 14, wherein when the UE receives the configurations from the source base station, the UE performs at least one of the followings:

synchronizing to a target cell based on downlink sync timing and uplink time advance information provided by the source base station from the target base station;

configuring a separate entity of a medium access control (MAC) configuration, a PDCP configuration, and/or a radio link control (RLC) configuration for the target base station and the source base station;

stopping receiving from the source base station after timing information given in a radio resource control (RRC) configuration while keeping a source MAC, a PDCP, and/or a MAC entity until receiving a first packet from the target base station;

stopping sending an uplink (UL) layer 1 channel state information (CSI) feedback, a hybrid automatic repeat request (HARQ) feedback, a layer 2 RLC feedback, a robust header compression (ROHC) feedback, a HARQ data re-transmission, and/or an RLC data re-transmission to the source base station;

sending a handover complete message or a handover radio link failure on a pre-allocated grant by the source base station and/or the target base station;

omitting sending the handover complete message and utilizing the pre-allocated grant for uplink data transmission toward the target base station; or

releasing the MAC configuration, the PDCP configuration, and/or the RLC configuration for the source base station.
A handover method for a multicast/broadcast service (MBS) performed by a source base station, comprising:

exchanging an MBS service and/or a Quality-of-Service (QoS) related information between the source base station and at least a user equipment (UE) as a part of a handover measurement message and/or a target base station as a part of a handover request message; and

performing a handover to be performed and/or configured for UE MBS mobility based on the part of the handover measurement report.
The handover method of claim 16, wherein a selection of a type of the handover to be performed and/or configured for UE MBS mobility is made based on at least one of the followings:

an indication of the UE comprising the MBS service and/or the QoS related information;

an internal configuration of the source base station; or

an indication of a core network.
The handover method of claim 16 or 17, wherein the MBS service and/or the QoS related information comprises a UE identity (ID) , an MBS service ID, a QoS flow ID, or a session ID association.
The handover method of claim 17 or 18, wherein the internal configuration of the source base station comprises a UE ID, an MBS service ID, a QoS flow ID, or a session ID association.
The handover method of any one of claims 17 to 19, wherein the indication of the core network comprises a UE MBS context message, a UE ID, an MBS service ID, a QoS flow ID, or a session ID association.
The handover method of any one of claims 16 to 20, wherein exchanging the MBS service and/or the Quality-of-Service (QoS) related information between the source base station and at least the user equipment (UE) as the part of the handover measurement message and/or the target base station as the part of the handover request message comprises determining, by the source base station, the MBS service and/or the QoS related information as the part of the handover measurement report from the UE.
The handover method of claim 21, wherein exchanging the MBS service and/or the Quality-of-Service (QoS) related information between the source base station and at least the user equipment (UE) as the part of the handover measurement message and/or the target base station as the part of the handover request message comprises forwarding, by the source base station from the UE, the MBS service and/or the QoS related information as the part of the handover measurement report to the target base station.
The handover method of claim 22, wherein forwarding, by the source base station from the UE, the MBS service and/or the QoS related information as the part of the handover measurement report to the target base station is indicated within a handover request signaling.
The handover method of any one of claims 17 to 23, wherein the selection of the type of the handover to be performed and/or configured for UE MBS mobility comprises a lossless handover or a lossless and low-latency handover.
The handover method of claim 24, wherein the selection of the type of the handover to be performed and/or configured for UE MBS mobility comprises the lossless handover or the lossless and low-latency handover according to UE MBS service reliability and latency level requirements.
The handover method of any one of claims 23 to 25, further comprising receiving, by the source base station, a handover request acknowledgment in response to the handover request signaling from the target base station.
The handover method of claim 26, wherein the handover request acknowledgment comprises configurations, and the configurations comprise at least one of the followings:

an agreed time of start/stop packet data convergence protocol (PDCP) sequence number (SN) allocation and/or data forwarding by the source base station and the target base station;

a target pre-allocated grant;

an uplink time advance command;

a downlink synchronization information; or

MBS bearers scheduling/forwarding configuration.
The handover method of claim 26 or 27, wherein when the source base station receives the handover request acknowledgment, the source base station performs at least one of the followings:

performing a PDCP SN assigning PDCP service data unit (SDU) data forwarding if a low-latency and lossless handover is selected and/or configured for UE MBS mobility; or

sending a SN status transfer message to the target base station to convey an uplink PDCP SN receiver status and a downlink PDCP SN transmitter status for which PDCP status preservation applies.
The handover method of claim 28, wherein the uplink PDCP SN receiver status comprises at least one of the followings:

a PDCP SN of a first missing UL PDCP SDU; or

a bit map of a receive status of out of sequence UL PDCP SDUs that the UE needs to retransmit in a target cell.
The handover method of claim 28 or 29, wherein the downlink PDCP SN transmitter status indicates a next PDCP SN that the target base station assigns to new PDCP SDUs, not having a PDCP SN yet if a lossless handover is configured.
The handover method of any one of claims 27 to 30, further comprising transmitting, by the source base station, the configurations to the UE.
The handover method of claim 31, wherein the configurations are forwarded by the source base station from the target base station to the UE.
The handover method of claim 31 or 32, wherein the configurations are forwarded by the source base station from the target base station to the UE in a handover initiation/command message.
A handover method for a multicast/broadcast service (MBS) performed by a target base station, comprising:

exchanging an MBS service and/or a Quality-of-Service (QoS) related information as a part of a handover measurement report between at least two of a user equipment (UE) , a source base station, and the target base station; and

exchanging of MBS scheduling information and timing information when the target base station starts/stops a PDCP SN allocation and/or a data forwarding to at least the source base station via a handover acknowledgement message and/or the UE via a handover command message.
The handover method of claim 34, wherein a selection of a type of the handover to be performed and/or configured for UE MBS mobility is made based on at least one of the followings:

an indication of the UE comprising the MBS service and/or the QoS related information;

an internal configuration of the source base station; or

an indication of a core network.
The handover method of claim 34 or 35, wherein the MBS service and/or the QoS related information comprises a UE identity (ID) , an MBS service ID, a QoS flow ID, or a session ID association.
The handover method of claim 35 or 36, wherein the internal configuration of the source base station comprises a UE ID, an MBS service ID, a QoS flow ID, or a session ID association.
The handover method of any one of claims 35 to 37, wherein the indication of the core network comprises a UE MBS context message, a UE ID, an MBS service ID, a QoS flow ID, or a session ID association.
The handover method of claim 38, wherein exchanging the MBS service and/or the QoS related information between the at least two of the UE, the source base station, and the target base station comprises forwarding, by the source base station from the UE, the MBS service and/or the QoS related information as the part of the handover measurement report to the target base station.
The handover method of claim 39, wherein forwarding, by the source base station from the UE, the MBS service and/or the QoS related information as the part of the handover measurement report to the target base station is indicated within a handover request signaling.
The handover method of any one of claims 35 to 40, wherein the selection of the type of the handover to be performed and/or configured for UE MBS mobility comprises a lossless handover or a lossless and low-latency handover.
The handover method of claim 41, wherein the selection of the type of the handover to be performed and/or configured for UE MBS mobility comprises the lossless handover or the lossless and low-latency handover according to UE MBS service reliability and latency level requirements.
The handover method of any one of claims 40 to 42, wherein when the target base station receives the handover request signaling, the target base station performs at least one of the followings:

performing admission control on the UE MBS mobility and performing the selection of the type of the handover to be performed and/or configured for UE MBS mobility if the selection of the type of the handover to be performed and/or configured for UE MBS mobility is not performed by the source base station;

determining and/or deciding based on configurations received in the handover request, time to start a PDCP SN allocation and/or data forwarding toward the UE with respect to a time reference provided by the source base station;

initiating a UE MSB session join if an MBS session/service/temporary mobile group identity (TMGI) that the UE receiving is existed at the target base station or initiating a session establishment request toward the core network if an MBS session that the UE receiving does not exist at the target base station;

switching the UE to a new radio bearer if required, and striving to provide the same QoS flow to a radio bearer mapping and scheduling configuration/forwarding treatment for MBS bearers as indicated by the source base station;

determining a timing configuration requiring synchronizing with the UE and providing a time advice command and a pre-allocated grant for the UE; or

starting forwarding a copy MBS downlink data forwarded from the source base station to as starting the PDCP SN allocation toward the UE.
The handover method of any one of claims 40 to 43, further comprising transmitting, by the target base station, a handover request acknowledgment in response to the handover request signaling to the source base station.
The handover method of claim 44, wherein the handover request acknowledgment comprises configurations, and the configurations comprise at least one of the followings:

an agreed time of start/stop packet data convergence protocol (PDCP) sequence number (SN) allocation and/or data forwarding by the source base station and the target base station;

a target pre-allocated grant;

an uplink time advance command;

a downlink synchronization information; or

MBS bearers scheduling/forwarding configuration.
The handover method of claim 45, wherein the configurations are forwarded by the source base station from the target base station to the UE.
The handover method of claim 45 or 46, wherein the configurations are forwarded by the source base station from the target base station to the UE in a handover initiation/command message and/or the target base station prepares based on the configuration received in a handover request, synchronization/timing information, UE pre-allocated grant assignment, and the downlink and uplink timing advance.
A user equipment (UE) for a multicast/broadcast service (MBS) , comprising:

a memory;

a transceiver; and

a processor coupled to the memory and the transceiver;

wherein the processor is configured to:

determine an MBS service and/or a Quality-of-Service (QoS) related information as a part of a handover measurement report; and

exchange the MBS service and/or the QoS related information as the part of the handover measurement report between at least two of the UE, a source base station, and a target base station, wherein a handover to be performed and/or configured for UE MBS mobility is made based on the part of the handover measurement report.
The UE of claim 48, wherein a selection of a type of the handover to be performed and/or configured for UE MBS mobility is made based on at least one of the followings:

an indication of the UE comprising the MBS service and/or the QoS related information;

an internal configuration of the source base station; or

an indication of a core network.
The UE of claim 48 or 49, wherein the MBS service and/or the QoS related information comprises a UE identity (ID) , an MBS service ID, a QoS flow ID, or a session ID association.
The UE of claim 49 or 50, wherein the internal configuration of the source base station comprises a UE ID, an MBS service ID, a QoS flow ID, or a session ID association.
The UE of any one of claims 49 to 51, wherein the indication of the core network comprises a UE MBS context message, a UE ID, an MBS service ID, a QoS flow ID, or a session ID association.
The UE of any one of claims 48 to 52, wherein determining, by the processor, the MBS service and/or the QoS related information as the part of the handover measurement report comprises receiving, by the transceiver, the MBS service and/or the QoS related information from a core network via multicast radio bearers (MRBs) or unicast data radio bearers (DRBs) .
The UE of any one of claims 48 to 53, wherein exchanging the MBS service and/or the QoS related information between the at least two of the UE, the source base station, and the target base station comprises indicating, by the processor, the MBS service and/or the QoS related information as the part of the handover measurement report to the source base station.
The UE of claim 54, wherein exchanging the MBS service and/or the QoS related information between the at least two of the UE, the source base station, and the target base station comprises forwarding, by the source base station from the transceiver, the MBS service and/or the QoS related information as the part of the handover measurement report to the target base station.
The UE of claim 55, wherein forwarding, by the source base station from the transceiver, the MBS service and/or the QoS related information as the part of the handover measurement report to the target base station is indicated within a handover request signaling.
The UE of any one of claims 49 to 56, wherein the selection of the type of the handover to be performed and/or configured for UE MBS mobility comprises a lossless handover or a lossless and low-latency handover.
The UE of claim 57, wherein the selection of the type of the handover to be performed and/or configured for UE MBS mobility comprises the lossless handover or the lossless and low-latency handover according to UE MBS service reliability and latency level requirements.
The UE of any one of claims 48 to 58, wherein the transceiver is configured to receive configurations from the source base station, wherein the configurations comprise at least one of the followings:

an agreed time of start/stop packet data convergence protocol (PDCP) sequence number (SN) allocation and/or data forwarding by the source base station and the target base station;

a target pre-allocated grant;

an uplink time advance command;

a downlink synchronization information; or

MBS bearers scheduling/forwarding configuration; and/or

wherein the transceiver is configured to receive, from the source base station, a handover command containing a target downlink/uplink sync information, MBS scheduling information, and MBS data forwarding timing information; and/or

wherein the processor is configured to prepare optimal reception configuration for MBS data in advance and deciding when to stop receiving downlink data from the source base station and when to release a source base station configuration and releasing the source base station configuration accordingly.
The UE of claim 59, wherein the configurations are forwarded by the source base station from the target base station to the transceiver.
The UE of claim 59 or 60, wherein the configurations are forwarded by the source base station from the target base station to the transceiver in a handover initiation/command message.
The UE of ant one of claims 59 to 61, wherein when the transceiver receives the configurations from the source base station, the processor performs at least one of the followings:

synchronizing to a target cell based on downlink sync timing and uplink time advance information provided by the source base station from the target base station;

configuring a separate entity of a medium access control (MAC) configuration, a PDCP configuration, and/or a radio link control (RLC) configuration for the target base station and the source base station;

stopping receiving from the source base station after timing information given in a radio resource control (RRC) configuration while keeping a source MAC, a PDCP, and/or a MAC entity until receiving a first packet from the target base station;

stopping sending an uplink (UL) layer 1 channel state information (CSI) feedback, a hybrid automatic repeat request (HARQ) feedback, a layer 2 RLC feedback, a robust header compression (ROHC) feedback, a HARQ data re-transmission, and/or an RLC data re-transmission to the source base station;

sending a handover complete message or a handover radio link failure on a pre-allocated grant by the source base station and/or the target base station;

omitting sending the handover complete message and utilizing the pre-allocated grant for uplink data transmission toward the target base station; or

releasing the MAC configuration, the PDCP configuration, and/or the RLC configuration for the source base station.
A source base station for a multicast/broadcast service (MBS) , comprising:

a memory;

a transceiver; and

a processor coupled to the memory and the transceiver;

wherein the processor is configured to:

exchanging an MBS service and/or a Quality-of-Service (QoS) related information between the source base station and at least a user equipment (UE) as a part of a handover measurement message and/or a target base station as a part of a handover request message; and

perform a handover to be performed and/or configured for UE MBS mobility based on the part of the handover measurement report.
The source base station of claim 63, wherein a selection of a type of the handover to be performed and/or configured for UE MBS mobility is made based on at least one of the followings:

an indication of the UE comprising the MBS service and/or the QoS related information;

an internal configuration of the source base station; or

an indication of a core network.
The source base station of claim 63 or 64, wherein the MBS service and/or the QoS related information comprises a UE identity (ID) , an MBS service ID, a QoS flow ID, or a session ID association.
The source base station of claim 64 or 65, wherein the internal configuration of the source base station comprises a UE ID, an MBS service ID, a QoS flow ID, or a session ID association.
The source base station of any one of claims 64 to 66, wherein the indication of the core network comprises a UE MBS context message, a UE ID, an MBS service ID, a QoS flow ID, or a session ID association.
The source base station of any one of claims 63 to 67, wherein exchanging the MBS service and/or the Quality-of-Service (QoS) related information between the source base station and at least the user equipment (UE) as the part of the handover measurement message and/or the target base station as the part of the handover request message comprises determining, by the processor, the MBS service and/or the QoS related information as the part of the handover measurement report from the UE.
The source base station of claim 68, wherein exchanging the MBS service and/or the Quality-of-Service (QoS) related information between the source base station and at least the user equipment (UE) as the part of the handover measurement message and/or the target base station as the part of the handover request message comprises forwarding, by the transceiver from the UE, the MBS service and/or the QoS related information as the part of the handover measurement report to the target base station.
The source base station of claim 69, wherein forwarding, by the transceiver from the UE, the MBS service and/or the QoS related information as the part of the handover measurement report to the target base station is indicated within a handover request signaling.
The source base station of any one of claims 64 to 70, wherein the selection of the type of the handover to be performed and/or configured for UE MBS mobility comprises a lossless handover or a lossless and low-latency handover.
The source base station of claim 71, wherein the selection of the type of the handover to be performed and/or configured for UE MBS mobility comprises the lossless handover or the lossless and low-latency handover according to UE MBS service reliability and latency level requirements.
The source base station of any one of claims 70 to 72, wherein the transceiver is configured to receive a handover request acknowledgment in response to the handover request signaling from the target base station.
The source base station of claim 73, wherein the handover request acknowledgment comprises configurations, and the configurations comprise at least one of the followings:

an agreed time of start/stop packet data convergence protocol (PDCP) sequence number (SN) allocation and/or data forwarding by the source base station and the target base station;

a target pre-allocated grant;

an uplink time advance command;

a downlink synchronization information; or

MBS bearers scheduling/forwarding configuration.
The source base station of claim 73 or 74, wherein when the transceiver receives the handover request acknowledgment, the processor performs at least one of the followings:

performing a PDCP SN assigning PDCP service data unit (SDU) data forwarding if a low-latency and lossless handover is selected and/or configured for UE MBS mobility; or

sending a SN status transfer message to the target base station to convey an uplink PDCP SN receiver status and a downlink PDCP SN transmitter status for which PDCP status preservation applies.
The source base station of claim 75, wherein the uplink PDCP SN receiver status comprises at least one of the followings:

a PDCP SN of a first missing UL PDCP SDU; or

a bit map of a receive status of out of sequence UL PDCP SDUs that the UE needs to retransmit in a target cell.
The source base station of claim 75 or 76, wherein the downlink PDCP SN transmitter status indicates a next PDCP SN that the target base station assigns to new PDCP SDUs, not having a PDCP SN yet if a lossless handover is configured.
The source base station of any one of claims 74 to 77, wherein the transceiver is configured to transmit the configurations to the UE.
The source base station of claim 78, wherein the configurations are forwarded by the transceiver from the target base station to the UE.
The source base station of claim 78 or 79, wherein the configurations are forwarded by the transceiver from the target base station to the UE in a handover initiation/command message.
A target base station for a multicast/broadcast service (MBS) , comprising:

a memory;

a transceiver; and

a processor coupled to the memory and the transceiver;

wherein the processor is configured to:

exchange an MBS service and/or a Quality-of-Service (QoS) related information as a part of a handover measurement report between at least two of a user equipment (UE) , a source base station, and the target base station; and

exchange of MBS scheduling information and timing information when the target base station starts/stops a PDCP SN allocation and/or a data forwarding to at least the source base station via a handover acknowledgement message and/or the UE via a handover command message.
The target base station of claim 81, wherein a selection of a type of the handover to be performed and/or configured for UE MBS mobility is made based on at least one of the followings:

an indication of the UE comprising the MBS service and/or the QoS related information;

an internal configuration of the source base station; or

an indication of a core network.
The target base station of claim 81 or 82, wherein the MBS service and/or the QoS related information comprises a UE identity (ID) , an MBS service ID, a QoS flow ID, or a session ID association.
The target base station of claim 82 or 83, wherein the internal configuration of the source base station comprises a UE ID, an MBS service ID, a QoS flow ID, or a session ID association.
The target base station of any one of claims 82 to 84, wherein the indication of the core network comprises a UE MBS context message, a UE ID, an MBS service ID, a QoS flow ID, or a session ID association.
The target base station of claim 85, wherein exchanging the MBS service and/or the QoS related information between the at least two of the UE, the source base station, and the target base station comprises forwarding, by the source base station from the UE, the MBS service and/or the QoS related information as the part of the handover measurement report to the transceiver.
The target base station of claim 86, wherein forwarding, by the source base station from the UE, the MBS service and/or the QoS related information as the part of the handover measurement report to the transceiver is indicated within a handover request signaling.
The target base station of any one of claims 82 to 87, wherein the selection of the type of the handover to be performed and/or configured for UE MBS mobility comprises a lossless handover or a lossless and low-latency handover.
The target base station of claim 88, wherein the selection of the type of the handover to be performed and/or configured for UE MBS mobility comprises the lossless handover or the lossless and low-latency handover according to UE MBS service reliability and latency level requirements.
The target base station of any one of claims 87 to 89, wherein when the target base station receives the handover request signaling, the target base station performs at least one of the followings:

performing admission control on the UE MBS mobility and performing the selection of the type of the handover to be performed and/or configured for UE MBS mobility if the selection of the type of the handover to be performed and/or configured for UE MBS mobility is not performed by the source base station;

determining and/or deciding based on configurations received in the handover request, time to start a PDCP SN allocation and/or data forwarding toward the UE with respect to a time reference provided by the source base station;

initiating a UE MSB session join if an MBS session/service/temporary mobile group identity (TMGI) that the UE receiving is existed at the target base station or initiating a session establishment request toward the core network if an MBS session that the UE receiving does not exist at the target base station;

switching the UE to a new radio bearer if required, and striving to provide the same QoS flow to a radio bearer mapping and scheduling configuration/forwarding treatment for MBS bearers as indicated by the source base station;

determining a timing configuration requiring synchronizing with the UE and providing a time advice command and a pre-allocated grant for the UE; or

starting forwarding a copy MBS downlink data forwarded from the source base station to as starting the PDCP SN allocation toward the UE.
The target base station of any one of claims 87 to 90, wherein the transceiver is configured to transmit a handover request acknowledgment in response to the handover request signaling to the source base station.
The target base station of claim 91, wherein the handover request acknowledgment comprises configurations, and the configurations comprise at least one of the followings:

an agreed time of start/stop packet data convergence protocol (PDCP) sequence number (SN) allocation and/or data forwarding by the source base station and the target base station;

a target pre-allocated grant;

an uplink time advance command;

a downlink synchronization information; or

MBS bearers scheduling/forwarding configuration.
The target base station of claim 92, wherein the configurations are forwarded by the source base station from the transceiver to the UE.
The target base station of claim 92 or 93, wherein the configurations are forwarded by the source base station from the transceiver to the UE in a handover initiation/command message and/or the target base station prepares based on the configuration received in a handover request, synchronization/timing information, UE pre-allocated grant assignment, and the downlink and uplink timing advance.
A non-transitory machine-readable storage medium having stored thereon instructions that, when executed by a computer, cause the computer to perform the handover method of any one of claims 1 to 47.
A chip, comprising:

a processor, configured to call and run a computer program stored in a memory, to cause a device in which the chip is installed to execute the handover method of any one of claims 1 to 47.
A computer readable storage medium, in which a computer program is stored, wherein the computer program causes a computer to execute the handover method of any one of claims 1 to 47.
A computer program product, comprising a computer program, wherein the computer program causes a computer to execute the handover method of any one of claims 1 to 47.
A computer program, wherein the computer program causes a computer to execute the handover method of any one of claims 1 to 47.