WO2023283828A1

WO2023283828A1 - Methods and apparatuses for handover

Info

Publication number: WO2023283828A1
Application number: PCT/CN2021/106267
Authority: WO
Inventors: Mingzeng Dai; Hyung-Nam Choi; Lianhai WU; Prateek Basu Mallick; Congchi ZHANG; Le Yan; Yibin ZHUO
Original assignee: Lenovo (Beijing) Limited
Priority date: 2021-07-14
Filing date: 2021-07-14
Publication date: 2023-01-19

Abstract

Embodiments of the present application relate to methods and apparatuses for handover. According to an embodiment of the present application, a method may include: receiving configuration information of a multicast radio bearer (MRB) associated with a multicast and broadcast services (MBS) session from a first base station that supports MBS; and receiving at least one configuration message associated with from the first base station before or during a handover procedure from the first base station to a second base station, wherein the at least one configuration message includes related data radio bearer (DRB) information that is associated with the MRB to provide continuity of the MBS session after the handover procedure from the first base station to the second base station, in the event that the second base station does not support MBS. Embodiments of the present application can minimize the data loss or support no data loss during handover from a base station (BS) supporting MBS to a BS not supporting MBS.

Description

METHODS AND APPARATUSES FOR HANDOVER

TECHNICAL FIELD

Embodiments of the present application generally relate to wireless communication technology, and especially to methods and apparatuses for handover.

BACKGROUND

In new radio (NR) , service and system aspects working group 2 (SA2) of 3rd generation partnership project (3GPP) agreed to support that a user equipment (UE moves between a next generation radio access network (NG-RAN) node (e.g., a base station (BS) ) that supports multicast and broadcast services (MBS) and a NG-RAN node that does not support MBS.

From radio access network (RAN) 's point of view, during handover from a source BS supporting MBS to a target BS not supporting MBS, the source BS may transmit all radio resource control (RRC) configuration including MBS related configuration to the target BS. Since the target BS does not support MBS, the target BS may have to issue a full configuration to the UE. After receiving the full configuration, the UE may release all multicast radio bearers (MRBs) and data radio bearers (DRBs) configured by the source BS and establish new DRBs configured by the target BS. During such a process, the data loss may happen.

Given the above, the industry desires an improved technology for handover, so as to minimize the data loss or even support achieve no data loss during a handover from a BS supporting MBS to a BS not supporting MBS.

SUMMARY OF THE DISCLOSURE

Embodiments of the present application at least provide a technical solution for handover, especially for handover from a BS supporting MBS to a BS not supporting MBS.

According to some embodiments of the present application, a method for wireless communication may include: receiving configuration information of MRB associated with an MBS session from a first base station that supports MBS; and receiving at least one configuration message associated with from the first base station before or during a handover procedure from the first base station to a second base station, wherein the at least one configuration message includes related DRB information that is associated with the MRB to provide continuity of the MBS session after the handover procedure from the first base station to the second base station, in the event that the second base station does not support MBS.

In some embodiments of the present application, the configuration information of the MRB may include at least one of: an identity (ID) of the MRB; service data adaptation protocol (SDAP) configuration information of a SDAP layer for the MRB; packet data convergence protocol (PDCP) configuration information of a PDCP layer for the MRB; radio link control (RLC) bearer configuration information for a point to multipoint (PTM) leg of the MRB; and radio link control (RLC) bearer configuration information for a point to point (PTP) leg of the MRB.

In some embodiments of the present application, wherein the related DRB information includes configuration information of a DRB and a mapping between the MRB and the DRB, and wherein the configuration information of the DRB includes at least one of: an ID of the DRB; and RLC bearer configuration information of the DRB.

In some embodiments of the present application, wherein the related DRB information includes an MRB presence indication which indicates whether to continue to use the MRB for data reception of the MBS session in a handover procedure, and wherein the MRB presence indication is received together with the configuration information of the MRB.

In an embodiment of the present application, in the case that the at least one configuration message includes delta configuration information of the DRB, the method further includes at least one of: inheriting at least one of the following for the DRB: SDAP entity and corresponding SDAP configuration information of the MRB, and PDCP entity and corresponding PDCP configuration information of the MRB; performing PDCP reestablishment; releasing lower layer entities and lower layer configuration information of the MRB; applying lower layer configuration information in the configuration information of the DRB and the delta configuration information of the DRB; and establishing lower layer entities of the DRB.

In another embodiment of the present application, the related DRB information is received together with the MRB configuration of the MRB, while the delta configuration information of the DRB is received in an RRC message of the at least one configuration message, wherein the RRC message is a handover command or conditional handover (CHO) configuration information.

In yet another embodiment of the present application, the related DRB information is received together with the delta configuration information of the DRB in an RRC message of the at least one configuration message, wherein the RRC message is a RRC reconfiguration message including a handover command or CHO configuration information.

In yet another embodiment of the present application, in the case that the handover is a CHO, the configuration information of the DRB is associated with at least one candidate cell.

In some embodiments of the present application, the related DRB information includes an ID of a DRB associated with the MRB, and wherein the ID of the DRB associated with the MRB is received together with the configuration information of the MRB.

In an embodiment of the present application, in the case that the at least one configuration message includes a handover command including the ID of the DRB and delta configuration information of a PTP leg of the MRB, the method includes at least one of: inheriting at least one of the following for the DRB: SDAP entity and corresponding SDAP configuration information of the MRB, and PDCP entity and corresponding PDCP configuration information of the MRB; performing PDCP reestablishment; releasing lower layer entities and lower layer configuration information of a PTM leg of the MRB; inheriting lower layer entities and lower layer configuration information of the PTP leg of the MRB as lower layer entities and lower layer configuration information of the DRB; and applying the delta configuration information.

In some embodiments of the present application, in the case that the at least one configuration message includes a handover command including delta configuration information of a PTP leg of the MRB without the MRB presence indication, the method includes at least one of: inheriting at least one of the following for the DRB: SDAP entity and corresponding SDAP configuration information of the MRB, and PDCP entity and corresponding PDCP configuration information of the MRB; performing PDCP reestablishment; releasing lower layer entities and lower layer configuration information of a PTM leg of the MRB; inheriting lower layer entities and lower layer configuration information of the PTP leg of the MRB as lower layer entities and lower layer configuration information of the DRB; and applying the delta configuration information.

In some other embodiments of the present application, the method may further include: receiving the at least one configuration message via RRC; and determining whether to reconfigure the MRB to a DRB based on the at least one configuration message.

In some embodiments of the present application, the method further includes: in the case that the related DRB information includes an ID of a DRB, reconfiguring the MRB to the DRB, which includes at least one of: replacing an ID of the MRB with the ID of the DRB; inheriting at least one of the following for the DRB: SDAP entity and corresponding SDAP configuration information of the MRB, and PDCP entity and corresponding PDCP configuration information of the MRB; performing PDCP reestablishment; releasing lower layer entities and lower layer configuration information of a PTM leg of the MRB; inheriting lower layer entities and lower layer configuration information of a PTP leg of the MRB for the DRB; and changing an MBS session ID in the SDAP configuration information to a PDU session ID.

In some embodiments of the present application, the method further includes: in the case the related DRB information does not include an MRB presence indication which indicates whether to continue to use the MRB for data reception of the MBS session, reconfiguring the MRB to the DRB, which includes at least one of: inheriting at least one of the following for the DRB: SDAP entity and corresponding SDAP configuration information of the MRB, and PDCP entity and corresponding PDCP configuration information of the MRB; performing PDCP reestablishment; releasing lower layer entities and lower layer configuration information of a PTM leg of the MRB; and inheriting lower layer entities and lower layer configuration information of a PTP leg of the MRB for the DRB.

In some embodiments of the present application, the method further includes: in the case the related DRB information includes configuration information of the DRB, reconfiguring the MRB to the DRB, which includes at least one of: inheriting at least one of the following for the DRB: SDAP entity and corresponding SDAP configuration information of the MRB, and PDCP entity and corresponding PDCP configuration information of the MRB; performing PDCP reestablishment; establishing lower layer entities based on the configuration information of the DRB; and changing an MBS session ID in the SDAP configuration information to a PDU session ID.

In an embodiment of the present application, the information of at least one of SDAP entity and PDCP entity for the DRB is an ID of the MRB.

In some embodiments of the present application, the method further includes: triggering a PDCP status reporting in the case that the MRB is reconfigured to the DRB.

According to some embodiments of the present application, a method for wireless communication may include: transmitting configuration information of MRB associated with an MBS session from a first base station that supports MBS; transmitting at least one configuration message associated with from the first base station before or during a handover procedure from the first base station to a second base station, wherein the at least one configuration message includes related DRB information that is associated with the MRB to provide continuity of the MBS session after the handover procedure from the first base station to the second base station, in the event that the second base station does not support MBS.

In some embodiments of the present application, the configuration information of the MRB may include at least one of: an ID of the MRB; SDAP configuration information of a SDAP layer for the MRB; PDCP configuration information of a PDCP layer for the MRB; RLC bearer configuration information for a PTM leg of the MRB; and RLC bearer configuration information for a PTP leg of the MRB.

In some embodiments of the present application, wherein the related DRB information includes an MRB presence indication which indicates whether to continue to use the MRB for data reception of the MBS session, and wherein the MRB presence indication is transmitted together with the configuration information of the MRB.

In some embodiments of the present application, the method further includes: transmitting a handover request message including: RRC context of the DRB associated with the MRB; and PDU session context; and receiving a handover response message in response to the handover request message, wherein the handover response message includes delta configuration information of the DRB.

In an embodiment of the present application, the RRC context of the DRB includes at least one of: SDAP configuration information of a SDAP layer for the DRB; PDCP configuration information of a PDCP layer for the DRB; RLC bearer configuration information of the DRB; and a mapping between the ID of the DRB and unicast quality of service (QoS) flow IDs which are associated with multicast QoS flow IDs of the MBS session.

In an embodiment of the present application, the PDU session context includes at least one of: security indication for the MBS session; unicast QoS flow IDs which are associated with multicast QoS flow IDs of the MBS session; and PDU session ID associated with the MBS session ID of the MBS session.

In an embodiment of the present application, wherein the handover request message includes a CHO request message, and the handover response message includes a CHO response message.

In some embodiments of the present application, wherein the at least one configuration message includes delta configuration information of the DRB.

In an embodiment of the present application, at least one configuration message is transmitted together with the MRB configuration of the MRB, while the delta configuration information of the DRB is transmitted in an RRC message of the at least one configuration message, wherein the RRC message is a handover command or CHO configuration information.

In another embodiment of the present application, of the at least one configuration message is transmitted together with the delta configuration information of the DRB in an RRC message of the at least one configuration message, wherein the RRC message is a RRC reconfiguration message including a handover command or CHO configuration information.

In some embodiments of the present application, the related DRB information includes an ID of a DRB associated with the MRB, and wherein the ID of the DRB associated with the MRB is transmitted together with the configuration information of the MRB.

In an embodiment of the present application, wherein the at least one configuration message includesa handover command including the ID of the DRB and delta configuration information of a PTP leg of the MRB.

In some embodiments of the present application, wherein at least one configuration message includes a handover command including delta configuration information of a PTP leg of the MRB without the MRB presence indication.

In some embodiments of the present application, the method further includes: transmitting a handover request message including: RRC context of a PTP leg of the MRB; and PDU session context; and receiving a handover response message in response to the handover request message, wherein the handover response message includes delta configuration information of the DRB.

In an embodiment of the present application, the RRC context of the PTP leg of the MRB includes at least one of: SDAP configuration information of a SDAP layer of the PTP leg of the MRB; PDCP configuration information of a PDCP layer of the PTP leg of the MRB; RLC bearer configuration information of the PTP leg of the MRB; and a mapping between the ID of the DRB and unicast QoS flow IDs which are associated with multicast QoS flow IDs of the MBS session.

In some embodiments of the present application, the related DRB information includes an ID of a DRB.

In some embodiments of the present application, the related DRB informationincludes configuration information of the DRB and information of at least one of SDAP entity and PDCP entity for the DRB.

Some embodiments of the present application also provide a user equipment, including: a processor; and a transceiver coupled to the processor, wherein the processor is configured to receive configuration information of an MRB associated with an MBS session from a first base station that supports MBS; and to receive at least one configuration message from the first base station before or during a handover procedure from the first base station to a second base station, wherein the at least one configuration message comprises related DRB information that is associated with the MRB to provide continuity of the MBS session after the handover procedure from the first base station to the second base station, in the event that the second base station does not support MBS.

Some other embodiments of the present application also provide a base station configured to support MBS, the base station comprising: a processor; and a transceiver coupled to the processor, wherein the processor is configured to transmit configuration information of a multicast radio bearer (MRB) associated with an MBS session to a user equipment (UE) ; and to transmit at least one configuration message from the base station before or during a handover procedure from the base station to another base station, wherein the at least one configuration message comprises related data radio bearer (DRB) information that is associated with the MRB to provide continuity of the MBS session after the handover procedure from the base station to the other base station, in the event that the other base station does not support MBS.

Embodiments of the present application provide a technical solution for handover, which can avoid full configuration during a handover from a BS supporting MBS to a BS not supporting MBS, and minimize data loss and even support lossless handover.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to describe the manner in which advantages and features of the application can be obtained, a description of the application is rendered by reference to specific embodiments thereof, which are illustrated in the appended drawings. These drawings depict only example embodiments of the application and are not therefore to be considered limiting of its scope.

FIG. 1 is a schematic diagram illustrating an exemplary wireless communication system according to some embodiments of the present application;

FIG. 2 is a schematic diagram illustrating a handover from an MBS supporting node to an MBS non-supporting node according to some embodiments of the present application;

FIG. 3 is a flow chart illustrating a method for handover according to some embodiments of the present application;

FIG. 4 illustrates an exemplary handover procedure according to some embodiments of the present application;

FIG. 5 illustrates an exemplary procedure of activating a preconfigured DRB and releasing a corresponding MRB according to some embodiments of the present application;

FIG. 6 illustrates an exemplary protocol stack of an MRB and a DRB according to some other embodiments of the present application;

FIG. 7 illustrates an exemplary handover procedure according to some other embodiments of the present application;

FIG. 8 illustrates an exemplary handover procedure according to some other embodiments of the present application;

FIG. 9 illustrates an exemplary procedure of switching the PTP leg of the MRB to DRB according to some embodiments of the present application;

FIG. 10 illustrates an exemplary handover procedure according to some other embodiments of the present application;

FIG. 11 is a flow chart illustrating a method for reconfiguring an MRB to DRB according to some embodiments of the present application; and

FIG. 12 illustrates a simplified block diagram of an apparatus for handover according to some embodiments of the present application.

DETAILED DESCRIPTION

The detailed description of the appended drawings is intended as a description of the currently preferred embodiments of the present application and is not intended to represent the only form in which the present application may be practiced. It is to be understood that the same or equivalent functions may be accomplished by different embodiments that are intended to be encompassed within the spirit and scope of the present application.

Reference will now be made in detail to some embodiments of the present application, examples of which are illustrated in the accompanying drawings. To facilitate understanding, embodiments are provided under specific network architecture and new service scenarios, such as 3GPP 5G (i.e., NR) , 3GPP long term evolution (LTE) Release 8 and so on. Persons skilled in the art know very well that, with the development of network architecture and new service scenarios, the embodiments in the present application are also applicable to similar technical problems; and moreover, the terminologies recited in the present application may change, which should not affect the principle of the present application.

FIG. 1 is a schematic diagram illustrating an exemplary wireless communication system 100 according to some embodiments of the present application.

As shown in FIG. 1, the wireless communication system 100 includes at least one base station (BS) 101 and at least one UE 102. In particular, the wireless communication system 100 includes one BS 101 and two UEs 102 (e.g., a UE 102a and a UE 102b) for illustrative purpose. Although a specific number of BS 101 and UEs 102 are depicted in FIG. 1, it is contemplated that any number of BSs 101 and UEs 102 may be included in the wireless communication system 100.

The wireless communication system 100 is compatible with any type of network that is capable of sending and receiving wireless communication signals. For example, the wireless communication system 100 is compatible with a wireless communication network, a cellular telephone network, a time division multiple access (TDMA) -based network, a code division multiple access (CDMA) -based network, an orthogonal frequency division multiple access (OFDMA) -based network, an LTE network, a 3GPP-based network, a 3GPP 5G network, a satellite communications network, a high altitude platform network, and/or other communications networks.

The BS 101 may also be referred to as a NG-RAN node, a RAN node, an access point, an access terminal, a base, a macro cell, a node-B, an enhanced node B (eNB) , a gNB, a home node-B, a relay node, or a device, or described using other terminology used in the art. The BS 101 is generally part of a radio access network that may include a controller communicably coupled to the BS 101.

According to some embodiments of the present application, the UE (s) 102 may include computing devices, such as desktop computers, laptop computers, personal digital assistants (PDAs) , tablet computers, smart televisions (e.g., televisions connected to the Internet) , set-top boxes, game consoles, security systems (including security cameras) , vehicle on-board computers, network devices (e.g., routers, switches, and modems) , or the like.

According to some other embodiments of the present application, the UE (s) 102 may include a portable wireless communication device, a smart phone, a cellular telephone, a flip phone, a device having a subscriber identity module, a personal computer, a selective call receiver, or any other device that is capable of sending and receiving communication signals on a wireless network.

According to some other embodiments of the present application, the UE (s) 102 may include wearable devices, such as smart watches, fitness bands, optical head-mounted displays, or the like.

Moreover, the UE (s) 102 may be referred to as a subscriber unit, a mobile, a mobile station, a user, a terminal, a mobile terminal, a wireless terminal, a fixed terminal, a subscriber station, a user terminal, or a device, or described using other terminology used in the art.

Both the UE 102a and the UE 102b in the embodiments of FIG. 1 may transmit information to the BS 101 and receive control information from the BS 101, for example, via LTE or new radio (NR) Uu interface.

In NR Release 17, MBS was introduced to focus on a small area mixed mode multicast. MBS traffic needs to be delivered from a single data source (e.g., an application service provider) to multiple UEs. Depending on many factors, multiple delivery methods may be used to deliver MBS traffic in the 5G system (5GS) .

From the viewpoint of 5G core network (CN) , two delivery methods are possible for MBS multicast service:

- 5G core network (5GC) individual MBS traffic delivery method. In this method, the 5G CN receives a single copy of MBS data packets and delivers separate copies of those MBS data packets to individual UEs via per-UE PDU sessions. Therefore, for each UE, one PDU session is required to be associated with a multicast session.

- 5GC shared MBS traffic delivery method. In this method, the 5G CN receives a single copy of MBS data packets and delivers a single copy of those MBS packets packet to a RAN node, which then delivers them to one or multiple UEs.

In the case that the 5GC shared MBS traffic delivery method is used for MBS traffic, from the viewpoint of RAN, two delivery methods or modes are available for the transmission of MBS packet flows over radio:

- PTP delivery method (also referred to as PTP mode or PTP leg) : a RAN node delivers separate copies of MBS data packets over radio to individual UEs.

- PTM delivery method (also referred to as PTM mode or PTM leg) : a RAN node delivers a single copy of MBS data packets over radio to a set of UEs.

Accordingly, a RAN node may use the PTP delivery method, the PTM delivery method, or a combination of the PTP delivery method and PTM delivery method to deliver an MBS packet to UEs.

In NR, it has been agreed that a UE may move from a network node, e.g., a BS which supports MBS (also referred to as MBS supporting node or BS) to another network node e.g., another BS which does not support MBS (also referred to as MBS non-supporting node or BS) . FIG. 2 is a schematic diagram illustrating a handover from MBS supporting node to MBS non-supporting node according to some embodiments of the present application.

Referring to FIG. 2, BS 201a may support MBS and BS 202b may not support MBS. For the MBS traffic transmitted from MBS server 204, CN 203 may receive a single copy of MBS data packets and delivers a single copy of those MBS packets to BS 201a via an MBS session, and then BS 201a may transmit those MBS packets via an MRB to UEs severed by BS 201a. CN 203 may also delivers separate copies of those MBS data packets to BS 201b via per-UE unicast PDU sessions, and then BS 201b may transmit those MBS packets via per-UE unicast DRB to UEs severed by BS 201b.

A UE (e.g., UE 202a) may move from BS 201a to BS 201b (i.e., framed by the dotted line in FIG. 2) , wherein BS 201a is referred to as the source BS of UE 202a and BS 201b is referred to as the target BS of UE 202a. To support a handover from the source BS 201a that supports MBS to the target BS 201b that does not support MBS, as defined TS 23.247, the following operation may be performed:

- mapping information about unicast QoS flows and the associated multicast QoS flows are provided to the NG-RAN node. This is already performed during the PDU session modification procedure for the PDU session associated with the MBS session when the UE joins into the MBS Session;

- during the handover procedure, the delivery method is switched from 5GC shared MBS traffic delivery method to 5GC individual MBS traffic delivery method, i.e. the N3 tunnel of the PDU Session for 5GC individual MBS traffic delivery needs to be activated towards the target NG-RAN node. The session management function (SMF) realizes that the target NG-RAN node does not support 5GC shared MBS traffic delivery method.

- the SMF and the multicast/broadcast session management function (MB-SMF) shall also activate the general packet radio service (GPRS) tunneling protocol (GTP) tunnel between the user plane function (UPF) and the multicast/broadcast user plane function (MB-UPF) for 5GC individual MBS traffic delivery method, if needed.

In addition, during RAN2#113e meeting, it was agreed that mobility from a source BS supporting MBS to a target BS not supporting MBS can be achieved by switching the traffic from delivery via MRB to delivery via DRB either before or during the handover. That is, from RAN's point of view, before or during the handover from an MBS supporting BS to an MBS non-supporting BS, the MRB should be switched to unicast DRB. However, during the handover, the source BS may transmit all RRC configurations including MBS related configuration to the target BS. Since the target BS does not support MBS, the target BS may have to issue a full configuration to the UE. After receiving the full configuration, the UE may release all MRBs and DRBs configured by the source BS and establish new DRBs configured by the target BS. During such a process, the data loss may happen. Accordingly, how to minimize the data loss or even support data lossless during the handover from a BS supporting MBS to a BS not supporting MBS should be addressed.

Embodiments of the present application at least consider the following two aspects. First, how to avoid full configuration in which the data loss may happen, because in the case of full configuration, the DRB is totally new established and the MRB is released, which may cause the data loss. Second, how to inherit common PDCP entity from MRB to DRB. The PDCP entity (and/or SDAP) inherited from MRB (from a source node) to DRB (to a target node) provides continuous PDCP (and/or SDAP) sequence number (SN) , which supports service continuity and can support lossless handover.

Given this, embodiments of the present application provides a technical solution for handover, which avoids full configuration and inherits common PDCP entity from MRB (asource node supporting MBS) to DRB (atarget node not supporting MBS) , and accordingly can minimize the data loss and even can achieve data lossless during the handover from a node supporting MBS to a node not supporting MBS. More details on embodiments of the present application will be illustrated in the following text in combination with the appended drawings.

According to some embodiments of the present application, the mobility from the source BS supporting MBS to target BS not supporting MBS can be achieved by switching the traffic from delivery via MRB to delivery via DRB during the handover. In such embodiments, the source BS may configure or indicate a DRB to which the MRB to be switched, and then the UE may switch the MRB to the DRB in response to receiving a message associated with handover.

For example, FIG. 3 is a flow chart illustrating a method for handover according to some embodiments of the present application. Although the method is illustrated in a system level by a UE (e.g., the UE 202a in FIG. 2) and a source BS which supports MBS (e.g., the source BS 201a in FIG. 2) , persons skilled in the art can understand that the method implemented in the UE and that implemented in the source BS can be separately implemented and incorporated in other apparatus with the like functions.

In the exemplary method shown in FIG. 3, in step 301, the source BS (e.g., a first BS 201a) may transmit configuration information of an MRB associated with an MBS session to the UE. Consequently, in step 302, the UE may receive the configuration information of the MRB from the BS. The MRB may also be referred to as a multicast data radio bearer (M-DRB) .

In step 303, the source BS may transmit at least one configuration message before or during a handover procedure from the source BS to a target BS (e.g., a second BS 201b) . The at least one configuration message may include related DRB information that is associated with the MRB to provide continuity of the MBS session after the handover procedure from the source BS to the target BS. The target BS may not support MBS. Consequently, in step 304, the UE may receive at least one configuration message from the source before or during a handover procedure from the source BS to the target BS.

According to some embodiments of the present application, the related DRB information may include configuration information of a DRB (also referred to as a virtual DRB or a preconfigured DRB, which has been configured but has not been activated) , and may include a mapping between the MRB and the DRB to the UE. The preconfigured DRB may also be named as unicast data radio bearer (U-DRB) . The preconfigured DRB may be activated based on the RRC message associated with handover and then is used for data transmission between the UE and the target BS (e.g., the BS 201b in FIG. 2) .

In an embodiment of the present application, the related DRB information may be transmitted together with the configuration information of the MRB, e.g., in one configuration message of the at least one configuration. For example, FIG. 4 illustrates an exemplary handover procedure according to some embodiments of the present application, in which the related DRB information may be transmitted together with the configuration information of the MRB.

Referring to FIG. 4, in step 401, the 5GC may transmit a PDU session setup request to the source BS. The PDU session setup request may include an MBS context of an MBS session and unicast QoS flow information associated with the MBS session.

For a given MBS session, the source BS may configure one or more MRBs for data transmission of the MBS session. The MRB is used for delivery of MBS data packets using the following methods:

- PTP delivery method (also referred to as PTP mode) : the BS individually delivers separate copies of MBS data packets to each UE independently, i.e. the BS uses UE-specific physical downlink control channel (PDCCH) with cyclic redundancy check (CRC) scrambled by UE-specific radio network temporary identity (RNTI) (e.g., cell-radio network temporary identifier (C-RNTI) ) to schedule UE-specific physical downlink shared channel (PDSCH) which is scrambled with the same UE-specific RNTI.

- PTM delivery method (also referred to as PTM mode) : the BS delivers a single copy of MBS data packets to a set of UEs, e.g., BS uses group-common PDCCH with CRC scrambled by group-common RNTI to schedule group-common PDSCH which is scrambled with the same group-common RNTI.

Then, for an MRB associated with an MBS session, in step 402, the source BS may transmit configuration information of an MRB associated with an MBS session to the UE.

The configuration information of the MRB may include at least one of: an ID of the MRB which is used to identify the MRB; SDAP configuration information (e.g., SDAP-Config as specified in 3GPP standard documents) of a SDAP layer for the MRB which is used to set the configurable parameters of the SDAP layer for the MRB; PDCP configuration information of a PDCP layer for the MRB (e.g., pdcp-Config as specified in 3GPP standard documents) which is used to set the configurable parameters of the PDCP layer for the MRB; RLC bearer configuration information for a PTM leg of the MRB (e.g., RLC-BearerConfig-PTM as specified in 3GPP standard documents) ; and RLC bearer configuration information (e.g., RLC-BearerConfig-PTP as specified in 3GPP standard documents) for a PTP leg of the MRB.

In step 402, the source BS may also transmit the related DRB information to the UE together with the configuration information of the MRB. For example, the related DRB information and the configuration information of the MRB may be transmitted in one configuration message of the at least one configuration message.

In some embodiments of the present application, the related DRB information may include configuration information of a DRB and a mapping between the MRB and the DRB. The configuration information of the DRB may include at least one of: an ID of the DRB which is used to identify the DRB; and RLC bearer configuration information of the DRB (e.g., RLC-BearerConfig-DRB as specified in 3GPP standard documents) . The mapping between the MRB and the DRB may be implemented by several methods. In an embodiment of the present application, the mapping between the MRB and the DRB may be implemented by including the ID of the MRB in the configuration information of the DRB. In another embodiment of the present application, the mapping between the MRB and the DRB may be implemented by including the ID of the DRB in the configuration information of the MRB. In yet another embodiment of the present application, the mapping between the MRB and the DRB may be implemented by a list including the ID of the MRB and the ID of the DRB associated with the MRB.

After receiving the configuration information of the DRB and the mapping between the MRB and the DRB together with the MRB configuration of the MRB, the UE may only store the configuration information of the DRB but not use the DRB for data transmission and reception.

In some embodiments of the present application, the related DRB information may include an MRB presence indication. The MRB presence indication may indicate whether the UE continues to use the MRB for data reception of the MBS session in the handover procedure. For example, if the MRB presence indication is present in a configuration message, e.g., a RRC message the UE may use the MRB for data reception of the MBS session in the handover procedure. In another example, if the MRB presence indication is present in a configuration message, the UE continues to use the MRB for data reception of the MBS session after the handover procedure. In yet another example, if the MRB presence indication is not present in a configuration message, the UE may use the preconfigured DRB for data reception of the MBS session in the handover procedure. In yet another example, if the MRB presence indication is not present in the configuration message, e.g., not in a RRC message associated with handover, the UE uses the preconfigured DRB for data reception of the MBS session after the handover procedure and releases the MRB or part of MRB. The MRB presence indication may be implicitly indicated by whether the full configuration information or a part of configuration information the MRB is present or not. That is, if the full configuration information or a part of configuration information of the MRB is present in a configuration message, e.g., in the RRC message associated with handover, the UE may use the MRB for data reception of the MBS session in the handover procedure or after the handover procedure. If the full configuration information or a part of configuration information of the MRB is not present in a configuration message, the UE may use the preconfigured DRB for data reception of the MBS session in the handover procedure or after the handover procedure.

Then, the 5GC may use a shared MBS traffic delivery method to transmit the MBS data to the source BS and the source BS may use MRB to transmit the MBS data to the UE.

When the source BS decides that the UE may perform a handover to a target BS (e.g., BS 201b) which is an MBS non-supporting BS, in step 403, the source BS may transmit a handover request message to the target BS. The handover request message may include at least one of: RRC context of the DRB associated with the MRB; and PDU session context.

The RRC context of the DRB may include at least one of: SDAP configuration information of a SDAP layer for the DRB; PDCP configuration information of a PDCP layer for the DRB; RLC bearer configuration information of the DRB; and a mapping between the ID of the DRB and unicast QoS flow IDs which are associated with multicast QoS flow IDs of the MBS session.

The PDU session context may include at least one of: security indication for the MBS session; unicast QoS flow IDs which are associated with multicast QoS flow IDs of the MBS session; and PDU session ID associated with the MBS session ID of the MBS session. In some embodiments of the present application, security indication for the MBS session may include at least one of: an integrity protection indication set as "not needed" by the source BS; and a confidentiality protection indication set as "not needed" by the source BS.

In step 403, the source BS does not include any MRB related or MBS session related parameters (i.e., configuration information of the MRB) in the handover request message to avoid a full configuration transmitted from the target BS.

In the embodiments of FIG. 4, there is no sequence restriction between

step

402 and 403. The step 402 may be performed before, after, or simultaneously with step 403. In some embodiments of the present application, after the step 402, it is also possible that the source BS reconfigures the preconfigured DRB according to its implementation.

After receiving the handover request message, according to the RRC context of the DRB and PDU session context, the target BS may provide delta configuration of the DRB for the UE. The delta configuration information may not include all the configuration information of the DRB, but only include the configuration information of the DRB needed to be changed or updated.

Then, in step 404, the target BS may transmit a handover response message in response to the handover request message to the source BS. The handover response message may include delta configuration information of the DRB.

After receiving the delta configuration information of the DRB, in step 405, the source BS may transmit another configuration message (e.g., a RRC message associated with handover) of the at least one configuration message to the UE. The RRC message associated with handover may include the delta configuration information of the DRB. In the embodiments of FIG. 4, the RRC message associated with handover may be a handover command including the delta configuration information of the DRB.

After receiving the RRC message including the delta configuration information of the DRB, the UE may activate the preconfigured DRB, that is, turn the virtual DRB to a real or activated DRB. For example, after receiving the RRC message including the delta configuration information of the DRB, in step 406, the UE may perform at least one of:

● inheriting at least one of the following for the DRB: SDAP entity and corresponding SDAP configuration information of the MRB, and PDCP entity and corresponding PDCP configuration information of the MRB.

● performing PDCP reestablishment. During the PDCP reestablishment, the SN of the PDCP packet may be retained.

● releasing lower layer entities and lower layer configuration information of the MRB. The lower layer may be a layer lower than the PDCP layer. The lower layer entities for the MRB may include at least one of: RLC entity for the MRB, MAC entity for the MRB, and physical (PHY) entity for the MRB. The lower layer configuration information of the MRB may include at least one of: RLC bearer configuration information for the PTM leg of the MRB; RLC bearer configuration information for the PTP leg of the MRB; MAC configuration information of the MAC layer for the MRB; and PHY configuration information of the PHY layer for the MRB.

● applying the lower layer configuration information of the DRB and the delta configuration information of the DRB. The lower layer configuration information of the DRB may include at least one of: RLC bearer configuration information of the DRB included in the configuration information of the DRB; MAC configuration information of the MAC layer for the DRB; and PHY configuration information of the PHY layer for the DRB. The delta configuration information of the DRB may be used to reconfigure the parameters of the DRB.

● establishing lower layer entities of the DRB. The lower layer entities of the DRB may include at least one of: RLC entity of the DRB, MAC entity of the DRB, and PHY entity of the DRB.

In some embodiments of the present application, the above operation may be performed in response to implicit information, e.g., if the full or a part of configuration information of the MRB are not included in the handover command or if the MRB presence indication is not included in the handover command, the UE may perform the above operations, e.g., releasing the lower layers configurations of the MRB and activating the lower layers configurations of the DRB.

Then, the 5GC may use an individual MBS traffic delivery method to transmit the MBS data to the target BS and the BS may use the DRB to transmit the MBS data to the UE.

FIG. 5 illustrates an exemplary procedure of activating preconfigured DRB and releasing MRB according to some embodiments of the present application. Referring to FIG. 5, after receiving the handover command, the UE may inherit the PDCP entity and corresponding PDCP configuration information of the MRB for the DRB, perform PDCP reestablishment, release lower layer entities and lower layer configuration information of the MRB (e.g., release RLC entity and RLC bearer configuration information for the PTM leg and the PTP leg of the MRB) , and activate the lower layer configuration information of the preconfigured DRB (e.g., activate the RLC bearer configuration of the DRB include in the configuration information of the DRB) . By doing so, the preconfigured DRB is turned to an activated DRB.

FIG. 6 illustrates an exemplary protocol stack of MRB and DRB according to some other embodiments of the present application. Referring to FIG. 6, after turning the preconfigured DRB to an activated DRB, the activated DRB may have a common PDCP entity with the MRB, but have its own RLC entity different from the MRB. In the embodiments of FIG. 6 or the like, the DRB may have the common MAC entity with the MRB but have the different PHY entity from the MRB. The MRB may be scrambled by a group radio network temporary identifier (G-RNTI) in at least one cell, while the DRB may be scrambled by a C-RNTI of the UE.

Although the above embodiments of the present application are illustrated in view of FIG. 4, which illustrates preconfiguring a DRB (also referred to as a preconfigured DRB) associated with the MRB and activating the DRB in response to the handover command in a legacy handover procedure, In some other embodiments of the present application, similar technical solution can also be implemented in a CHO procedure.

The CHO is defined as a handover that is executed by the UE when one or more handover execution conditions are met. During the handover procedure, the UE may start evaluating the execution condition (s) upon receiving the CHO configuration, and may stop evaluating the execution condition (s) once a handover is executed (including a legacy handover or a conditional handover) . For simplicity, only exemplary steps concerned on the technical solution of the present application are illustrated.

In the CHO, step 401 and step 402 may also be performed. Different from the legacy handover, the CHO may prepare one or more CHO candidate cells. Among the one or more CHO candidate cells, at least one CHO candidate cell may be an MBS supporting cell (corresponding to an MBS supporting node or BS) and the remaining candidate cell (s) may be MBS non-supporting cell (s) (corresponding to MBS non-supporting node (s) or BS (s) ) . Then, different from step 403 in FIG. 4, during the CHO procedure, the source BS may transmit a CHO request message to each of the one or more CHO candidate cells. If the candidate cell supports MBS, the source BS may not provide the RRC context of the DRB to the candidate cell. If the candidate cell does not support MBS, the source BS may provide the RRC context of the DRB to the candidate cell. That is, for each candidate cell which does not support MBS, the CHO request message transmitted by the source BS may include the same information as that included in the handover request message transmitted by the source BS in step 403.

After receiving the CHO request message, according to the RRC context of the DRB and PDU session context, the candidate cell may provide delta configuration of the DRB for the UE.

Then, similar to step 404, the candidate cell may transmit a CHO response message in response to the CHO request message to the source BS. The CHO response message may include delta configuration information of the DRB.

The source BS may receive one or more CHO response messages from the one or more candidate cells. At least one CHO response message from at least one candidate cell may include the delta configuration information of the DRB and the remaining response messages of the one more CHO response messages may not include the delta configuration information of the DRB. Then, the source BS may transmit a RRC message associated handover to the UE. In the CHO procedure, the RRC message associated with handover is CHO configuration information including delta configuration information of the DRB from the at least one candidate cell which supports MBS. For example, the CHO configuration information may indicate one or more candidate cells, in which at least one candidate cell is MBS supporting cell, and thus each of the at least one candidate cell is associated with corresponding delta configuration information of the DRB. That is, the configuration information of the DRB is associated with the at least one candidate cell.

When the UE receives the CHO configuration information from the source BS, the UE needs to know which candidate cell (s) needs to apply the configuration information of the DRB and which candidate cell (s) does not need to apply the configuration information of the DRB. In other words, the UE needs to know that the DRB is associated with the at least one candidate cell, which may be implemented by several methods.

In some embodiments of the present application, the source BS may transmit an indication to the UE to indicate that the at least one candidate cell is associated the configuration information of the DRB.

In some other embodiments of the present application, the UE may identify that the at least one candidate cell is associated the configuration information of the DRB by an implicit way. For example, for each candidate cell which supports MBS, the CHO configuration information may include the candidate cell and the corresponding delta configuration information of the DRB associated with the candidate cell. Accordingly, if the UE receives the candidate cell with the corresponding delta configuration information of the DRB, the UE may know the candidate cell is associated with the DRB. In another example, if the full configuration information of the MRB or a part of configuration information of the MRB for a candidate cell are not included in the CHO configuration information or if the MRB presence indication for a candidate cell is not included in the CHO configuration information, the UE may know the candidate cell is associated with the DRB.

After receiving the CHO configuration information, for the MBS supporting candidate cell which is selected as a target cell, the UE may apply the configuration information of the DRB, and perform the same operation as that performed in step 406; while for the MBS non-supporting candidate cell which is selected as a target cell, the UE may not apply the configuration information of the DRB.

In another embodiment of the present application, the related DRB information may be transmitted together with the delta configuration information of the DRB in the RRC message. For example, FIG. 7 illustrates an exemplary handover procedure according to some other embodiments of the present application, in which the related DRB information may be transmitted together with the delta configuration information of the DRB in the RRC message.

Referring to FIG. 7,

step

701, 703, and 704 may be the same as

step

401, 403, 404, respectively.

The difference between step 702 and step 402 is that, in step 702, the source BS merely transmits configuration information of an MRB associated with an MBS session to the UE. The configuration information of the MRB is the same as that in step 402.

The difference between

step

705 and 405 is that, in step 705, the BS may transmit the configuration information of a DRB and a mapping between the MRB and the DRB together with the delta configuration information of the DRB in the RRC message. For example, in step 705, the BS may transmit a configuration message (e.g., a RRC message associated with handover) to the UE. The RRC message may be a RRC reconfiguration message including a handover command, the configuration information of the DRB, and a mapping between the MRB and the DRB. The handover command may include the delta configuration information of the DRB. The information included in the configuration information of the DRB, the delta configuration information of the DRB, and the methods for indicating the mapping between the DRB and the MRB may be the same as those in FIG. 4.

After receiving the RRC message including the configuration information of the DRB, the mapping between the DRB and the MRB, and the delta configuration information of the DRB, in step 706, the UE may apply the configuration information of the DRB firstly, which enables to switch MRB to DRB. Then, the UE may apply the DRB delta configuration, which is provided by the target BS, as a part of the handover procedure. For example, after receiving the RRC message, the UE may perform at least one of:

● releasing lower layer entities and lower layer configuration information of the MRB. The lower layer may be a layer lower than the PDCP layer. The lower layer entities for the MRB may include at least one of: RLC entity for the MRB, MAC entity for the MRB, and PHY entity for the MRB. The lower layer configuration information of the MRB may include at least one of: RLC bearer configuration information for the PTM leg of the MRB; RLC bearer configuration information for the PTP leg of the MRB; MAC configuration information of the MAC layer for the MRB; and PHY configuration information of the PHY layer for the MRB.

● applying the lower layer configuration information of the DRB. The lower layer configuration information of the DRB may include at least one of: RLC bearer configuration information of the DRB included in the configuration information of the DRB; MAC configuration information of the MAC layer for the DRB; and PHY configuration information of the PHY layer for the DRB.

● applying the delta configuration information of the DRB. Applying the delta configuration information of the DRB may be performed after applying the lower layer configuration information of the DRB.

In some embodiments of the present application, the above operations may be performed in response to implicit information, e.g., if full configuration information of the MRB or a part of configuration information of MRB are not included in the handover command or if the MRB presence indication is not included in the handover command, the UE may perform the above operation, e.g., releasing the lower layers configurations of the MRB and activating the lower layers configurations of the DRB.

Similarly, although the above embodiments of the present application are illustrated in view of FIG. 7, which illustrates providing a DRB (also referred to as a preconfigured DRB) configuration together with the handover command in a legacy handover procedure. In some other embodiments of the present application, providing a DRB configuration in a RRC message associated with handover may also be implemented in a CHO procedure. For simplicity, only exemplary steps concerned on the technical solution of the present application are illustrated.

In the CHO, step 701 and step 702 may also be performed. Different from the legacy handover, the CHO may prepare one or more CHO candidate cells. Among the one or more CHO candidate cells, at least one CHO candidate cell may be an MBS supporting cell (corresponding to an MBS supporting node or BS) and the remaining candidate cell (s) may be MBS non-supporting cell (s) (corresponding to MBS non-supporting node (s) or BS (s) ) . Then, different from step 703 in FIG. 7, during the CHO procedure, the source BS may transmit a CHO request message to each of the one or more CHO candidate cells. If the candidate cell supports MBS, the source BS may not provide the RRC context of the DRB to the candidate cell. If the candidate cell does not support MBS, the source BS may provide the RRC context of the DRB to the candidate cell. That is, for each candidate cell which does not support MBS, the CHO request message transmitted by the source BS may include the same information as that included in the handover request message transmitted by the source BS in step 703.

Then, similar to step 704, the candidate cell may transmit a CHO response message in response to the CHO request message to the source BS. The CHO response message may include delta configuration information of the DRB.

The source BS may receive one or more CHO response messages from the one or more candidate cells. At least one CHO response message from at least one candidate cell may include the delta configuration information of the DRB and the remaining response messages of the one more CHO response messages may not include the delta configuration information of the DRB.

Then, the source BS may transmit a RRC message associated handover to the UE. In the CHO procedure, the RRC message associated with handover may be a RRC reconfiguration information including the configuration information of the DRB, the mapping between the MRB and the DRB, and CHO configuration information including delta configuration information of the DRB from the at least one candidate cell which support MBS. For example, the CHO configuration information may indicate one or more candidate cells, in which at least one candidate cell is MBS supporting cell, and thus each of the at least one candidate cell is associated with corresponding delta configuration information of the DRB. That is, the configuration information of the DRB is associated with the at least one candidate cell.

In some other embodiments of the present application, the UE may identity that the at least one candidate cell is associated the configuration information of the DRB by an implicit way. For example, for each candidate cell which supports MBS, the CHO configuration information may include the candidate cell and the corresponding delta configuration information of the DRB. Accordingly, if the UE receives the candidate cell with the corresponding delta configuration information of the DRB, the UE may know the candidate cell is associated with the DRB. In another example, if the full configuration information of the MRB or a part of configuration information of MRB for a candidate cell is not included in the CHO configuration information or if the MRB presence indication for a candidate cell is not included in the CHO configuration information, the UE may know the candidate cell is associated with the DRB.

After receiving the CHO configuration information, for the MBS supporting candidate cell which is selected as a target cell, the UE may apply the configuration information of the DRB, and perform the same operation as that performed in step 706, while for the MBS non-supporting candidate cell which is selected as a target cell, the UE may not apply the configuration information of the DRB.

According to some other embodiments of the present application, the PTP leg of MRB may be switched to unicast DRB during the handover from an MBS supporting BS to an MBS non-supporting BS.

FIG. 8 illustrates an exemplary handover procedure according to some other embodiments of the present application.

Referring to FIG. 8, step 801 may be the same as step 401 in FIG. 4.

For a given MBS session, the source BS (e.g., BS 201a in FIG. 2) may configure one or more MRBs for data transmission of the MBS session. The MRB is used for delivery of MBS data packets using at least one of PTP delivery method and PTM delivery method. Then, in step 802, the source BS may transmit configuration information of an MRB associated with an MBS session to the UE. The configuration information of the MRB may be the same as that in FIG. 4.

In step 802, the source BS may also transmit the related DRB information together with the configuration information of the MRB to the UE. For example, the related DRB information together with the configuration information of the MRB may be transmitted in one configuration message of the at least one configuration message. The related DRB information in step 802 may include an ID of a DRB associated with the MRB. In some embodiments of the present application, the ID of the MRB may be different from the ID of the MRB.

When the source BS decides that the UE may perform the handover to a target BS (e.g., BS 201b) that is an MBS non-supporting BS, in step 803, the source BS may transmit a handover request message to the target BS. The handover request message may include at least one of: RRC context of a PTP leg (e.g., PTP mode) of the MRB; and PDU session context.

The RRC context of the PTP leg of the MRB may include at least one of: SDAP configuration information of a SDAP layer of the PTP leg of the MRB; PDCP configuration information of a PDCP layer the PTP leg of the MRB; RLC bearer configuration information of the PTP leg of the MRB; and a mapping between the ID of the DRB and unicast QoS flow IDs which are associated with multicast QoS flow IDs of the MBS session.

In step 803, the source BS does not include any PTM transmission or MBS session related parameters (i.e., configuration information of the MRB) in the handover request message to avoid a full configuration transmitted to the UE from the target BS.

In the embodiments of FIG. 8, there is no sequence restriction between

step

802 and 803. The step 802 may be performed before, after, or simultaneously with step 803.

After receiving the handover request message, according to the RRC context of the PTP leg of the MRB and PDU session context, the target BS provides delta configuration of the PTP leg of the MRB for the UE. The delta configuration information may not include all the configuration information of the PTP leg of the MRB, but only include the configuration information of the PTP leg of the MRB needed to be changed or updated.

Then, in step 804, the target BS may transmit a handover response message in response to the handover request message to the source BS. The handover response message may include delta configuration information of the PTP leg of the MRB.

After receiving the delta configuration information of the PTP leg of the MRB in step 805, the source BS may transmit another configuration message (e.g., a RRC message associated with handover) of the at least one configuration message to the UE. The RRC message associated with handover may include the delta configuration information of the PTP leg of the MRB and the ID of the DRB. In the embodiments of FIG. 8 or the like, the RRC message associated with handover may be a handover command.

After receiving the RRC message including the delta configuration information of the PTP leg of the MRB, the UE may switch the PTP leg of the MRB to the DRB. For example, after receiving the RRC message including the delta configuration information of the PTP leg of the MRB, in step 806, the UE may perform at least one of:

● rereleasing lower layer entities and lower layer configuration information of the PTM leg of the MRB. The lower layer may be a layer lower than the PDCP layer. The lower layer entities of the PTM leg of the MRB may include at least one of: RLC entity of the PTM leg of the MRB, MAC entity of the PTM leg of the MRB, and PHY entity of the PTM leg of the MRB. The lower layer configuration information of the PTM leg of the MRB may include at least one of: RLC bearer configuration information for the PTM leg of the MRB, MAC configuration information of the MAC layer of the PTM leg of the MRB, and PHY configuration information of the PHY layer of the PTM leg of the MRB.

● inheriting lower layer entities and lower layer configuration information of the PTP leg of the MRB for the DRB. The lower layer entities of the PTP leg of the MRB may include at least one of: RLC entity of the PTP leg of the MRB, MAC entity of the PTP leg of the MRB, and PHY entity of the PTP leg of the MRB. The lower layer configuration information of the PTP leg of the MRB may include at least one of: RLC bearer configuration information for the PTP leg of the MRB, MAC configuration information of the MAC layer of the PTP leg of the MRB, and PHY configuration information of the PHY layer of the PTP leg of the MRB.

● applying the delta configuration information. The UE may use the delta configuration information to reconfigure the parameters of the DRB.

FIG. 9 illustrates an exemplary procedure of switching the PTP leg of the MRB to DRB according to some embodiments of the present application.

Referring to FIG. 9, after receiving the handover command, the UE may inherit the PDCP entities and corresponding PDCP configuration information of the MRB for the DRB, perform PDCP reestablishment, release lower layer entities and lower layer configuration information of the PTM leg of the MRB (e.g., release RLC entity and RLC bearer configuration information of the PTM leg of the MRB) , and inherit the lower layer entices and configuration information of the PTP leg of the MRB (e.g., inherit the RLC entity and the RLC bearer configuration for the PTP leg of the MRB) . By doing so, the PTP leg of the MRB is switched to a DRB.

The embodiments in FIG. 8 use an ID of the DRB to indicate switching from the PTP leg of the MRB to the DRB. In the embodiments of FIG. 10 or the like, an MRB presence indication is used to indicate switching from the PTP leg of the MRB to the DRB. Specifically, FIG. 10 illustrates an exemplary handover procedure according to some other embodiments of the present application. In some embodiments of the FIG. 10, the ID of the DRB may be the same as the ID of the MRB.

Referring to FIG. 10, step 1001 may be the same as step 801 in FIG. 8.

For a given MBS session, the source BS (e.g., BS 201a in FIG. 2) may configure one or more MRBs for data transmission of the MBS session. The MRB is used for delivery of MBS data packets using at least one of the PTP delivery method and PTM delivery method. Then, in step 1002, the source BS may transmit configuration information of an MRB associated with an MBS session to the UE. The configuration information of the MRB may be the same as that in FIG. 8.

In step 1002, the source BS may also transmit the related DRB information together with the configuration information of the MRB to the UE. For example, the related DRB information together with the configuration information of the MRB may be transmitted in one configuration message of the at least one configuration message. The related DRB information in step 1002 may include an MRB presence indication. The MRB presence indication may indicate whether to continue to use the MRB for data reception of the MBS session in the handover procedure.

Step 1003 and step 1004 may be the same as

step

803 and 804, respectively.

After receiving the delta configuration information of the PTP leg of the MRB, in step 1005, the source BS may transmit another configuration message (e.g., an RRC message associated with handover) of the at least one configuration message to the UE. The RRC message associated with handover may be a handover command. The difference between step 1005 and step 805 is that: in step 1005, the handover command may include the delta configuration information of the PTP leg of the MRB without the MRB presence indication.

After receiving the RRC message including the delta configuration information of the PTP leg of the MRB, the UE may switch the PTP leg of the MRB to the DRB. In step 1006, the UE may perform the same operation as those performed in step 806 to switch the PTP leg of the MRB to the DRB.

According to some embodiments of the present application, the MRB presence indication in FIG. 10 may be an implicit indication. For example, if the full configuration information of the MRB or a part of configuration information of the MRB is not included in the handover command, the UE may switch the PTP leg of the MRB to the DRB. In another example, if the full configuration information of the MRB or a part of configuration information of the MRB is included in step 1002, the UE may continue to use the MRB for data reception.

The embodiments of FIG. 3 to FIG. 10 illustrate switching or turning the MRB to DRB during the handover procedure. According to some other embodiments of the present application, the source BS may reconfigure the MRB to DRB before the handover procedure. In such embodiments, it is assumed that the value ranges of the ID of the MRB and the ID of the DRB are independent, i.e., separate value ranges for IDs of the MRB and DRB are allocated.

FIG. 11 is a flow chart illustrating a method for reconfiguring an MRB to a DRB according to some embodiments of the present application. Although the method is illustrated in a system level by a UE (e.g., UE 202a in FIG. 2) and a source BS which supports the MBS (e.g., BS 201a in FIG. 2) , persons skilled in the art can understand that the method implemented in the UE and that implemented in the source BS can be separately implemented and incorporated in other apparatus with the like functions.

In the exemplary method shown in FIG. 11, in step 1101, the source BS (e.g., the first BS 201a) may transmit configuration information of an MRB associated with an MBS session to the UE. The configuration information of the MRB may be the same as that in FIG. 4. Consequently, the UE may receive the configuration information of the MRB from the source BS.

In step 1102, the source BS may transmit at least one configuration message before a handover procedure of the UE from the source BS to the target BS (e.g., the second BS 201b) . Consequently, the UE may receive the at least one configuration message from the source BS. The target BS may not support MBS. In some embodiments, the at least one configuration message may be transmitted or received via RRC. For example, the at least one configuration message may include a RRC message to the UE. The RRC message may indicate whether to reconfigure the MRB to a DRB. Then, the UE may determine whether to reconfigure the MRB to a DRB based on the received RRC message.

According to some embodiments of the present application, the at least one configuration message (e.g., a RRC message) may include related DRB information. The related DRB information may include an ID of the DRB. Then, after recceing the RRC message including the ID of the DRB, the UE may reconfigure the MRB to the DRB. Reconfiguring the MRB to the DRB may include performing at least one of:

● replacing an ID of the MRB with the ID of the DRB. The UE may replace the ID of the MRB with the DRB ID in the RLC-BearerConfig or in the DRBtoAddMod information element (IE) as specified in 3GPP standard documents.

● inheriting at least one of the following for the DRB: SDAP entity and corresponding SDAP configuration information of the MRB, and PDCP entity and corresponding configuration information of the MRB;

● performing PDCP reestablishment. In the PDCP reestablishment, the ID of the MRB is changed to the ID of the DRB, the SN of the PDCP packet may be retained;

● rereleasing lower layer entities and lower layer configuration information of the PTM leg of the MRB. The lower layer entities of the PTM leg of the MRB may include at least one of: RLC entity of the PTM leg of the MRB, MAC entity of the PTM leg of the MRB, and PHY entity of the PTM leg of the MRB. The lower layer configuration information of the PTM leg of the MRB may include at least one of: RLC bearer configuration information for the PTM leg of the MRB, MAC configuration information of the MAC layer of the PTM leg of the MRB, and PHY configuration information of the PHY layer of the PTM leg of the MRB.

● changing an MBS session ID in the SDAP configuration information to a PDU session ID.

According to some other embodiments of the present application, the at least one configuration message (e.g., a RRC message) may include related DRB information. The related DRB information may include configuration information of the DRB and information of at least one of SDAP entity and PDCP entity for the DRB. In an embodiment of the present application, the configuration information of the DRB may be the same as that in FIG. 4. In an embodiment of the present application, the information of at least one of SDAP entity and PDCP entity for the DRB is an ID of the MRB.

Then, after recceing the RRC message including the above information, the UE may reconfigure the MRB to the DRB. Reconfiguring the MRB to the DRB may include performing at least one of:

● inheriting at least one of the following for the DRB: SDAP entity and corresponding SDAP configuration information of the MRB, and PDCP entity and corresponding PDCP configuration information of the MRB;

● establishing lower layer entities based on the configuration information of the DRB. The lower layer entities of the DRB may include at least one of: RLC entity of the DRB, MAC entity of the DRB, and PHY entity of the DRB;

According to some other embodiments of the present application, the at least one configuration message (e.g., a RRC message) may include related DRB information. The related DRB information may not include the MRB presence indication, which indicates whether to continue to use the MRB for data reception of the MBS session. In some embodiments of the present application, the related DRB information may include all or a part of configurations for the DRB. In an embodiment of the present application, the related DRB information may include the configuration information of the PTP leg of the MRB. In another embodiment of the present application, the related DRB information may include the delta configuration information of the PTP leg of the MRB.

Then, after receiving the related DRB information not including the MRB presence indication, the UE may reconfigure the MRB to the DRB. Reconfiguring the MRB to the DRB may include performing at least one of:

● inheriting at least one of the following for the DRB: SDAP entity and corresponding SDAP configuration information of the MRB, and PDCP entity and corresponding configuration information of the MRB.

● performing PDCP reestablishment.

Then, in the case that the MRB is reconfigured to the DRB, the UE may trigger a PDCP status reporting.

FIG. 12 illustrates a simplified block diagram of an exemplary apparatus 1200 for handover according to some embodiments of the present application. The apparatus 1200 may include a UE (e.g., UE 202a) or a BS (e.g., BS 201a or 201b as shown in FIG. 2) .

Referring to FIG. 12, the apparatus 1200 may include at least one processor 1204 and at least one transceiver 1202 coupled to the processor 1204.

Although in this figure, elements such as the at least one transceiver 1202 and processor 1204 are described in the singular, the plural is contemplated unless a limitation to the singular is explicitly stated. In some embodiments of the present application, the transceiver 1202 may be divided into two devices, such as a receiving circuitry and a transmitting circuitry. In some embodiments of the present application, the apparatus 1200 may further include an input device, a memory, and/or other components.

In some embodiments of the present application, the apparatus 1200 may be a UE. The processor 1204 may be configured to receive configuration information of an MRB associated with a MBS session from a first base station that supports MBS; and configured to receive at least one configuration message from the first base station before or during a handover procedure from the first base station to a second base station, wherein the at least one configuration message comprises related DRB information that is associated with the MRB to provide continuity of the MBS session after the handover procedure from the first base station to the second base station, in the event that the second base station does not support MBS.

In some embodiments of the present application, the apparatus 1200 may be a base station. The processor 1204 may be configured to transmit configuration information of an MRB associated with an MBS session to a UE; and configured to transmit at least one configuration message from the base station before or during a handover procedure from the base station to another base station, wherein the at least one configuration message comprises related DRB information that is associated with the MRB to provide continuity of the MBS session after the handover procedure from the base station to the other base station, in the event that the other base station does not support MBS.

In some embodiments of the present application, the apparatus 1200 may further include at least one non-transitory computer-readable medium. In some embodiments of the present disclosure, the non-transitory computer-readable medium may have stored thereon computer-executable instructions to cause a processor to implement the method with respect to a UE or a BS as described above. For example, the computer-executable instructions, when executed, cause the processor 1204 interacting with transceiver 1202, so as to perform operations of the methods, e.g., as described in view of any of FIGS. 3-11.

The method according to embodiments of the present application can also be implemented on a programmed processor. However, the controllers, flowcharts, and modules may also be implemented on a general purpose or special purpose computer, a programmed microprocessor or microcontroller and peripheral integrated circuit elements, an integrated circuit, a hardware electronic or logic circuit such as a discrete element circuit, a programmable logic device, or the like. In general, any device on which resides a finite state machine capable of implementing the flowcharts shown in the figures may be used to implement the processor functions of this application. For example, an embodiment of the present application provides an apparatus for handover, including a processor and a memory. Computer programmable instructions for implementing a method for handover are stored in the memory, and the processor is configured to perform the computer programmable instructions to implement the method for handover. The method may be a method as stated above or other method according to an embodiment of the present application.

An alternative embodiment preferably implements the methods according to embodiments of the present application in a non-transitory, computer-readable storage medium storing computer programmable instructions. The instructions are preferably executed by computer-executable components preferably integrated with a network security system. The non-transitory, computer-readable storage medium may be stored on any suitable computer readable media such as RAMs, ROMs, flash memory, EEPROMs, optical storage devices (CD or DVD) , hard drives, floppy drives, or any suitable device. The computer-executable component is preferably a processor but the instructions may alternatively or additionally be executed by any suitable dedicated hardware device. For example, an embodiment of the present application provides a non-transitory, computer-readable storage medium having computer programmable instructions stored therein. The computer programmable instructions are configured to implement a method for MBS as stated above or other method according to an embodiment of the present application.

While this application has been described with specific embodiments thereof, it is evident that many alternatives, modifications, and variations may be apparent to those skilled in the art. For example, various components of the embodiments may be interchanged, added, or substituted in the other embodiments. Also, all of the elements of each figure are not necessary for operation of the disclosed embodiments. For example, one of ordinary skills in the art would be enabled to make and use the teachings of the application by simply employing the elements of the independent claims. Accordingly, embodiments of the application as set forth herein are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the application.

Claims

A method for wireless communication, comprising:

receiving configuration information of a multicast radio bearer (MRB) associated with a multicast and broadcast services (MBS) session from a first base station that supports MBS; and

receiving at least one configuration message from the first base station before or during a handover procedure from the first base station to a second base station, wherein the at least one configuration message comprises related data radio bearer (DRB) information that is associated with the MRB to provide continuity of the MBS session after the handover procedure from the first base station to the second base station, in the event that the second base station does not support MBS.
The method of Claim 1, wherein the configuration information of the MRB comprises at least one of:

an identity (ID) of the MRB;

service data adaptation protocol (SDAP) configuration information of a SDAP layer for the MRB;

packet data convergence protocol (PDCP) configuration information of a PDCP layer for the MRB;

radio link control (RLC) bearer configuration information for a point to multipoint (PTM) leg of the MRB; and

radio link control (RLC) bearer configuration information for a point to point (PTP) leg of the MRB.
The method of Claim 1, wherein the related DRB information comprises an MRB presence indication which indicates whether to continue to use the MRB for data reception of the MBS session, and wherein the MRB presence indication is received together with the configuration information of the MRB.
The method of Claim 1, wherein in the case that the at least one configuration message comprises delta configuration information of the DRB, the method further comprises at least one of:

inheriting at least one of the following for the DRB: service data adaptation protocol (SDAP) entity and corresponding SDAP configuration information of the MRB, and packet data convergence protocol (PDCP) entity and corresponding PDCP configuration information of the MRB;

performing PDCP reestablishment;

releasing lower layer entities and lower layer configuration information of the MRB;

applying lower layer configuration information in the configuration information of the DRB and the delta configuration information of the DRB; and

establishing lower layer entities of the DRB.
The method of Claim 1, wherein the related DRB information comprises an identity (ID) of a DRB associated with the MRB, and wherein the ID of the DRB associated with the MRB is received together with the configuration information of the MRB.
The method of Claim 5, wherein in the case that the at least one configuration message comprises a handover command comprising the ID of the DRB and delta configuration information of a point to point (PTP) leg of the MRB, the method comprises at least one of:

inheriting at least one of the following for the DRB: service data adaptation protocol (SDAP) entity and corresponding SDAP configuration information of the MRB, and packet data convergence protocol (PDCP) entity and corresponding PDCP configuration information of the MRB;

performing PDCP reestablishment;

releasing lower layer entities and lower layer configuration information of a point to multipoint (PTM) leg of the MRB;

inheriting lower layer entities and lower layer configuration information of the PTP leg of the MRB as lower layer entities and lower layer configuration information of the DRB; and

applying the delta configuration information.
The method of Claim 1, comprising:

receiving the at least one configuration message via radio resource control (RRC) ; and

determining whether to reconfigure the MRB to a DRB based on the at least one configuration message.
The method of Claim 1, further comprising: in the case that the related DRB information comprises an identity (ID) of a DRB, reconfiguring the MRB to the DRB, which comprises at least one of:

replacing an ID of the MRB with the ID of the DRB;

inheriting at least one of the following for the DRB: service data adaptation protocol (SDAP) entity and corresponding SDAP configuration information of the MRB, and packet data convergence protocol (PDCP) entity and corresponding PDCP configuration information of the MRB;

performing PDCP reestablishment;

releasing lower layer entities and lower layer configuration information of a point to multipoint (PTM) leg of the MRB;

inheriting lower layer entities and lower layer configuration information of a point to point (PTP) leg of the MRB for the DRB; and

changing a MBS session ID in the SDAP configuration information to a protocol data unit (PDU) session ID.
The method of Claim 1, further comprising: in the case that the related DRB information does not include an MRB presence indication which indicates whether to continue to use the MRB for data reception of the MBS session, reconfiguring the MRB to the DRB, which comprises at least one of:

inheriting at least one of the following for the DRB: service data adaptation protocol (SDAP) entity and corresponding SDAP configuration information of the MRB, and packet data convergence protocol (PDCP) entity and corresponding PDCP configuration information of the MRB;

performing PDCP reestablishment;

releasing lower layer entities and lower layer configuration information of a point to multipoint (PTM) leg of the MRB; and

inheriting lower layer entities and lower layer configuration information of a point to point (PTP) leg of the MRB for the DRB.
A method for wireless communication, comprising:

transmitting configuration information of a multicast radio bearer (MRB) associated with a multicast and broadcast services (MBS) session from a first base station that supports MBS; and

transmitting at least one configuration message from the first base station before or during a handover procedure from the first base station to a second base station, wherein the at least one configuration message comprises related data radio bearer (DRB) information that is associated with the MRB to provide continuity of the MBS session after the handover procedure from the first base station to the second base station, in the event that the second base station does not support MBS.
The method of Claim 10, wherein the configuration information of the MRB comprises at least one of:

an identity (ID) of the MRB;

service data adaptation protocol (SDAP) configuration information of a SDAP layer for the MRB;

packet data convergence protocol (PDCP) configuration information of a PDCP layer for the MRB;

radio link control (RLC) bearer configuration information for a point to multipoint (PTM) leg of the MRB; and

radio link control (RLC) bearer configuration information for a point to point (PTP) leg of the MRB.
The method of Claim 10, further comprising:

transmitting a handover request message comprising:

radio resource control (RRC) context of the DRB associated with the MRB; and

protocol data unit (PDU) session context; and

receiving a handover response message in response to the handover request message, wherein the handover response message comprises delta configuration information of the DRB.
The method of Claim 12, wherein the RRC context of the DRB comprises at least one of:

service data adaptation protocol (SDAP) configuration information of a SDAP layer for the DRB;

packet data convergence protocol (PDCP) configuration information of a PDCP layer for the DRB;

radio link control (RLC) bearer configuration information of the DRB; and

a mapping between the ID of the DRB and unicast quality of service (QoS) flow IDs which are associated with multicast QoS flow IDs of the MBS session.
A user equipment, comprising:

a processor; and

a transceiver coupled to the processor, wherein the processor is configured

to receive configuration information of a multicast radio bearer (MRB) associated with a multicast and broadcast services (MBS) session from a first base station that supports MBS; and

to receive at least one configuration message from the first base station before or during a handover procedure from the first base station to a second base station, wherein the at least one configuration message comprises related data radio bearer (DRB) information that is associated with the MRB to provide continuity of the MBS session after the handover procedure from the first base station to the second base station, in the event that the second base station does not support MBS.
A base station configured to support multicast and broadcast services (MBS) , the base station comprising:

a processor; and

a transceiver coupled to the processor, wherein the processor is configured

to transmit configuration information of a multicast radio bearer (MRB) associated with an MBS session to a user equipment (UE) ; and

to transmit at least one configuration message from the base station before or during a handover procedure from the base station to another base station, wherein the at least one configuration message comprises related data radio bearer (DRB) information that is associated with the MRB to provide continuity of the MBS session after the handover procedure from the base station to the other base station, in the event that the other base station does not support MBS.