Multicast-broadcast service (MBS) mobility with service continuity in connected state

Abstract

To provide a method for enhancing service continuity with respect to a multicast-broadcast service (MBS) communication under handover.SOLUTION: A request to start handover to a target base station of a MBS session with respect to user equipment (UE) is received from a source base station by the target base station. An instruction of a next protocol data unit (PDU) of the MBS session that the UE should receive is received. After the request to start the handover is received, a peer-to-peer (PTP) message including the next PDU of the MBS session which is previously transmitted via a peer-to-multiple (PTM) message by the source base station is transmitted to the UE.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] This application relates to wireless communication, and more specifically, to a system, apparatus, and method for improving service continuity for Multicast and Broadcast Services (MBS) communication.

Background Art

[0002] The use of wireless communication systems has been increasing rapidly. In recent years, wireless devices such as smartphones and tablet computers have been becoming more and more high-performance. Currently, many mobile devices (i.e., user equipment devices, or UEs) not only support telephone calls, but also provide access to the Internet, email, text messaging, and navigation using the Global Positioning System (GPS), and can operate high-performance applications that utilize these functions. In addition, there are numerous different wireless communication technologies and standards. Some examples of wireless communication standards include GSM, UMTS (associated with, for example, the WCDMA or TD-SCDMA air interface), LTE, LTE Advanced (LTE-A), NR, HSPA, 3GPP2 CDMA2000 (e.g., 1xRTT, 1xEV-DO, HRPD, eHRPD), IEEE802.11 (WLAN or Wi-Fi), BLUETOOTH (trademark), and the like.

[0003] One aspect of cellular communication systems involves Multicast and Broadcast Services (MBS) communication. Therefore, improvements in this field are desired.

Summary of the Invention

[0004] This specification presents embodiments of an apparatus, system, and method for improving Multicast and Broadcast Services (MBS) communication by service continuity during handover.

[0005] Disclosed is a method for performing communication of a multicast broadcast service (MBS) session. According to this method, a request to initiate a handover of an MBS session from a source base station to a target base station for a certain user equipment (UE) may be received by the target base station of the radio communication network from a remote base station of the radio communication network. The target base station may receive an indication of the next protocol data unit (PDU) of the MBS session to be received by that UE. The target base station may transmit a peer-to-peer (PTP) message including the next PDU of the MBS session to that UE, and the next PDU of the MBS session was previously transmitted by the source base station via a point-to-multiple (PTM) message after the request to initiate the handover.

[0006] In some scenarios, the target base station may receive an indication of a dropped PDU of the MBS session from the UE, and the dropped PDU was transmitted by the source base station but not properly received by the UE. The target base station may transmit a peer-to-peer message including the dropped PDU to the UE.

[0007] In some scenarios, the indication of the next PDU and the indication of the dropped PDU may be received from the UE in a packet data convergence protocol (PDCP) status report.

[0008] In some scenarios, the indication of the next PDU may be received from the source base station.

[0009] In some scenarios, the target base station may determine whether to transmit subsequent PDUs of the MBS session via peer-to-peer messages or via point-to-multiple messages based at least in part on the number of UEs served by the target base station that are participating in the MBS session.

[0010] In some scenarios, the target base station may establish its MBS session with a core network element of the radio communication network in response to receiving a request to initiate a handover. The target base station may receive at least one PDU of the MBS session to be transferred to the UE from the source base station, and this at least one PDU includes the next PDU of the MBS session. After receiving the next PDU, the target base station may subsequently receive subsequent PDUs of the MBS session from the core network element.

[0011] In some scenarios, the target base station may receive an indication from the UE that the MBS handover reconfiguration at the UE has been completed. In response to receiving the indication that the MBS handover reconfiguration at the UE has been completed and after establishing the MBS session with the core network element, the target base station may provide an instruction to the source base station to stop the transfer of PDUs of the MBS session.

[0012] In some scenarios, the target base station may transfer each PDU of at least one PDU of the MBS session received from the source base station before receiving the indication that the MBS handover reconfiguration at the UE has been completed, to the UE via at least one PTP message.

[0013] In some scenarios, the target base station may establish its MBS session with a core network element of the radio communication network, and the MBS session is established before receiving a request to initiate a handover.

[0014] In some scenarios, the target base station may receive an indication of the sequence number to be assigned to a specified PDU of its MBS session from a core network element of the radio communication network. The target base station may sequentially assign sequence numbers to subsequent PDUs of the specified PDU.

[0015] In some scenarios, the target base station may receive from a certain core network element of the wireless communication network an MBS packet containing MBS payload data for its MBS session, and this MBS packet has a packet sequence number. The target base station may transmit a packet containing its MBS payload data to the UE, and the packet sequence number of this MBS packet is used as the downlink (DL) packet data convergence protocol (PDCP) sequence number of the transmitted packet.

[0016] A method for performing communication of a multicast broadcast service (MBS) session is described. According to this method, a wireless communication device may receive a multicast transmission including at least one data packet of a multicast session from a first base station of a wireless network. The wireless communication device may receive an instruction to perform a handover from the first base station to a second base station of the wireless network. In response to receiving the instruction, the wireless communication device may stop receiving transmissions from the first base station and establish a connection with the second base station. The wireless communication device may receive a unicast transmission from the second base station including the next sequential data packet of the multicast session following the last data packet of the multicast session received from the first base station, where the next sequential data packet was previously included in the multicast transmission from the first base station after the wireless communication device stopped receiving transmissions from the first base station.

[0017] In some scenarios, the wireless communication device may transmit an identifier of the next sequential packet to the second base station before receiving the unicast transmission.

[0018] In some scenarios, the wireless communication device may receive a unicast transmission from a second base station that includes dropped data packets of a multicast session, where the dropped data packets were included in a multicast transmission from a first base station prior to an instruction to perform a handover, but were not properly received by the UE.

[0019] In some scenarios, the wireless communication device may transmit an identifier of the dropped data packet to the second base station before receiving a unicast transmission that includes the dropped data packet.

[0020] In some scenarios, the wireless communication device may receive a multicast transmission from the second base station that includes at least one data packet of a multicast session.

[0021] In some scenarios, an instruction to perform a handover to the second base station may include configuration information for establishing a connection with the second base station for multicast transmission.

[0022] A method for performing communication of a Multicast Broadcast Service (MBS) session is described. According to this method, a first base station of a wireless communication network may transmit a multicast transmission including at least one data packet of a multicast session to a user equipment (UE). In response to determining to initiate a handover procedure for handing over the UE to a second base station of the wireless communication network, the first base station may transmit an instruction to execute the handover to the UE. Subsequently after transmitting the instruction, the first base station may transmit an indication of the next packet of the MBS session to the second base station, which is to be transmitted to the UE. Subsequently after transmitting the instruction, the first base station may start transferring the packets of the MBS session to the second base station, which are to be transmitted to the UE, and the packets of the MBS session to be transferred include the next packet. The first base station may stop transferring the packets of the MBS session in response to receiving an indication from the second base station that the handover has been completed.

[0023] In some scenarios, the first base station may provide a handover request including information regarding the MBS session to the second base station.

[0024] In some scenarios, the first base station may receive a handover request positive response message from the second base station indicating the MBS session configuration information for the second base station. The first base station may include the second base station MBS session configuration information in the instruction to execute the handover.

[0025] Devices, apparatuses, and systems for performing any of the above-described methods are also disclosed.

[0026] Note that the technology described herein may be implemented in and / or used with a number of different types of devices, including but not limited to base stations, access points, cellular telephones, portable media players, tablet computers, wearable devices, drones, drone controllers, automobiles and / or motor vehicles, and various other computing devices.

[0027] The summary of this invention is intended to provide some brief overviews of the subject matter described in this document. Thus, it should be understood that the above features are merely examples and should not be construed as narrowing the scope or spirit of the subject matter described in this document. Other features, aspects, and advantages of the subject matter described in this document will become apparent from the following detailed description, drawings, and claims.

Brief Description of the Drawings

[0028] A better understanding of the subject matter can be obtained when the following detailed description of various embodiments is considered in conjunction with the following drawings.

[0029]

Figure 1

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[0039] The features described herein are capable of various modifications and alternative forms. However, specific embodiments are shown in the drawings and described in detail herein. It should be understood, however, that the drawings and their detailed description are not intended to limit to the specific forms disclosed, but rather are intended to cover all modifications, equivalents, and alternatives within the spirit and scope of the subject matter defined by the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

[0040] Acronyms Various acronyms are generally used throughout the present disclosure. The definitions of the most prominently used acronyms that may appear throughout the present disclosure are as follows. ● BS: Base Station ● CN: Core Network ● DL: Downlink ● GPRS: General Packet Radio Service ● GSM: Global System for Mobile Communications ● GTP: GPRS Tunneling Protocol ● IE: Information Element ● LTE: Long Term Evolution ● MBS: Multicast Broadcast Service ● NR: New Radio ● PDCP: Packet Data Convergence Protocol ● PDU: Protocol Data Unit ● PTM: Peer-to-Multiple ● PTP: Peer-to-Peer ● RACH: Random Access Channel ● RAT: Radio Access Technology ● RF: Radio Frequency ● RX: Receive / Receiving ● TX: Transmit / Transmitting ● UE: User Equipment ● UL: Uplink ● UMTS: Universal Mobile Telecommunications System ● UPF: User Plane Function Term The following is an explanation of terms that may appear in the present disclosure.

[0041] Memory medium - Any of various types of non-transitory memory devices or storage devices. The term "memory medium" is intended to include, for example, installation media such as CD-ROMs, floppy disks, or tape devices; computer system memories or random access memories such as DRAM, DDR RAM, SRAM, EDO RAM, Rambus RAM; magnetic media such as hard drives, or non-volatile memories such as optical storage, flash, registers, or other similar types of memory elements. The storage medium may include other types of non-transitory memory, or combinations thereof. Additionally, the memory medium may be located in a first computer system on which the program is executed, or may be located in a second different computer system connected to the first computer system via a network such as the Internet. In the latter case, the second computer system can provide program instructions for execution to the first computer system. The term "memory medium" may include two or more memory media that can exist in different locations, for example, in different computer systems connected via a network. The memory medium may store program instructions executable by one or more processors (e.g., embodied as a computer program).

[0042] Carrier medium - A memory medium as described above, as well as physical transmission media such as buses, networks, and / or other physical transmission media that transmit signals such as electrical signals, electromagnetic signals, or digital signals.

[0043] Computer system (or computer) - any of various types of computing systems or processing systems, including a personal computer system (PC), mainframe computer system, workstation, network device, Internet appliance, personal digital assistant (PDA), television system, grid computing system, or other device or combination of devices. In general, the term "computer system" may be broadly defined to include any device (or combination of devices) having at least one processor that executes instructions from a memory medium.

[0044] User equipment (UE) (or "UE device") - any of various types of computer systems or devices that are mobile or portable and perform wireless communication. Examples of UE devices include mobile phones or smartphones (e.g., iPhone (trademark), Android (trademark)-based phones), tablet computers (e.g., iPad (trademark), Samsung Galaxy (trademark)), portable game devices (e.g., Nintendo DS (trademark), PlayStation Portable (trademark), Gameboy Advance (trademark), iPhone (trademark)), wearable devices (e.g., smartwatches, smart glasses), laptops, PDAs, portable Internet devices, music players, data storage devices, other handheld devices, automobiles and / or motor vehicles, unmanned aerial vehicles (UAVs) (e.g., drones), UAV controllers (unmanned aerial controllers, UAC), etc. In general, the terms "UE" or "UE device" may be broadly defined to include any electronic device, computing device, and / or telecommunication device (or combination of devices) that can be easily carried by a user and is capable of wireless communication.

[0045] Wireless device - Any of various types of computer systems or devices that perform wireless communication. The wireless device can be portable (or mobile), or may be stationary or fixed in a location. A UE is an example of a wireless device.

[0046] Communication device - Any of various types of computer systems or devices that perform communication, where the communication can be wired or wireless. The communication device may be portable (or mobile), or may be stationary or fixed in a particular location. A wireless device is an example of a communication device. A UE is another example of a communication device.

[0047] Base station (BS) - The term "base station" has all of its ordinary meanings and includes, at a minimum, a radio communication station installed in a fixed location and used to communicate as part of a radiotelephone system or wireless system.

[0048] Processing element (or processor) - Refers to various elements or combinations of elements capable of performing functions within a device, e.g., within a user equipment device or within a cellular network device. The processing element can include, for example, a processor and associated memory, a portion or circuit of an individual processor core, an entire processor core, a processor array, a circuit such as an Application Specific Integrated Circuit (ASIC), a programmable hardware element such as a Field Programmable Gate Array (FPGA), and any of various combinations of the above.

[0049] The Wi-Fi term "Wi-Fi" has its full ordinary meaning and includes at least a wireless communication network or RAT that is served by wireless LAN (WLAN) access points and provides connectivity to the Internet through these access points. The latest Wi-Fi networks (or WLAN networks) are based on the IEEE 802.11 standard and are commercially available under the name "Wi-Fi". Wi-Fi (WLAN) networks are different from cellular networks.

[0050] Automatically - where user input does not directly specify or execute an action or operation, but rather the computer system (e.g., software executed by a computer system) or device (e.g., circuit mechanism, programmable hardware element, ASIC, etc.) performs those actions or operations. Thus, the term "automatically" is in contrast to actions that are manually performed or specified by the user, where the user provides input to directly execute the action. An automatic procedure can be initiated by input provided by the user, but subsequent actions that are "automatically" performed are not specified by the user. That is, each action performed is not "manually" specified by the user. For example, when a user fills out an electronic form by selecting each field and providing input to specify information (e.g., by typing information, selecting a checkbox, making radio selections, etc.), the computer system must update the form in response to the user action, but this is considered filling out the form manually. The form may be filled out automatically by the computer system, where the computer system (e.g., software executed on a computer system) analyzes the fields of the form and fills out the form without user input specifying responses to the fields. As described above, the user can initiate the automatic filling of the form but is not involved in the actual filling of the form (e.g., the user does not manually specify responses to the fields; rather, the responses are automatically completed). This specification provides various examples of actions that are automatically performed in response to actions taken by the user.

[0051] configured to - Various components can be described as being "configured to" perform a task. In such a context, "configured to" is a broad description generally meaning "having a structure" that performs the task or tasks during operation. Thus, a component may be configured to perform a task even when the component is not currently performing the task (e.g., a set of conductors may be configured to electrically connect a module to another module even when the two modules are not connected). In some contexts, "configured to" may be a broad description of a structure generally meaning "having a circuit" that performs the task or tasks during operation. Thus, a component may be configured to perform a task even when the component is not currently on. Generally, a circuit forming the structure corresponding to "configured to" may include a hardware circuit.

[0052] In the description of this specification, for convenience, various components can be described as performing a task or tasks. Such descriptions should be construed to include the phrase "configured to". It is clearly intended that the description of a component configured to perform one or more tasks is not applicable to the interpretation of that component under paragraph 6 of 35 U.S.C. 112. FIG. 1 and FIG. 2 - Exemplary Communication Systems

[0053] FIG. 1 shows an exemplary (and simplified) wireless communication system in which aspects of the present disclosure may be implemented, according to some embodiments. Note that the system of FIG. 1 is merely an example of a possible system, and embodiments may be implemented in various systems as desired.

[0054] As shown, an exemplary wireless communication system includes a base station 102 that communicates with one or more (e.g., any number of) user devices 106A, 106B, etc., up to 106N via a transmission medium. In this specification, each of the user devices may be referred to as a "user equipment" (UE) or UE device. Thus, user device 106 is referred to as a UE or UE device.

[0055] Base station 102 may be a base transceiver station (BTS) or a cell site and may include hardware and / or software that enables wireless communication with UEs 106A - 106N. When base station 102 is implemented in the context of LTE, it may alternatively be referred to as an "eNodeB" or "eNB". When base station 102 is implemented in the context of 5G NR, it may alternatively be referred to as a "gNodeB" or "gNB". Also, base station 102 may be equipped to communicate with network 100 (e.g., among various possibilities, the core network of a cellular service provider, a telecommunications network such as the public switched telephone network (PSTN), and / or the Internet). Thus, base station 102 can facilitate communication between user devices and / or between a user device and network 100. The communication area (or coverage area) of a base station may be referred to as a "cell". Also, as used in this specification, from the perspective of a UE, the base station may be considered to represent the network insofar as the uplink and downlink communications of the UE are concerned. Thus, a UE that communicates with one or more base stations in a network may be interpreted as a UE that communicates with the network.

[0056] The base station 102 and the user device may be configured to communicate over a transmission medium using any of a variety of radio access technologies (RATs), also referred to as wireless communication technologies, or remote communication standards such as GSM, UMTS (WCDMA), LTE, LTE-Advanced (LTE-A), LAA / LTE-U, 5G NR, 3GPP2 CDMA2000 (e.g., 1xRTT, 1xEV-DO, HRPD, eHRPD), Wi-Fi, etc.

[0057] Accordingly, other similar base stations operating according to the same or different cellular communication standards as the base station 102 may be provided as one or more networks of cells that provide continuous or substantially continuous overlapping services to the UE106 and similar devices across a geographic area via one or more cellular communication standards.

[0058] Note that the UE106 may be capable of communicating using multiple wireless communication standards. For example, the UE106 may be configured to communicate using either or both of the 3GPP cellular communication standards or the 3GPP2 cellular communication standards. In some embodiments, the UE106 may be configured to perform techniques that support service continuity during MBS handover, such as according to the various methods described herein. The UE106 may further or alternatively be configured to communicate using, for example, WLAN, BLUETOOTH (trademark), one or more global navigation satellite systems (GNSS, e.g., GPS or GLONASS), one and / or more mobile television broadcast standards (e.g., ATSC-M / H), etc. Other combinations of wireless communication standards (including three or more wireless communication standards) are also possible.

[0059] Figure 2 shows an exemplary user equipment 106 (e.g., one of devices 106A - 106N) in communication with base station 102 according to some embodiments. UE 106 may be a device having wireless network connectivity, such as a mobile phone, a handheld device, a wearable device, a computer or tablet, an unmanned aerial vehicle (UAV), an unmanned aircraft controller (UAC), or substantially any type of wireless device. UE 106 may include a processor (processing element) configured to execute program instructions stored in a memory. By executing such stored instructions, UE 106 can execute any of the method embodiments described herein. Alternatively or in addition, UE 106 may include a field programmable gate array (FPGA), an integrated circuit, and / or any of various other possible hardware components configured to execute any of the method embodiments described herein, or any portion of any of the method embodiments described herein (e.g., individually or in combination), such as programmable hardware elements. UE 106 may be configured to communicate using any of a plurality of wireless communication protocols. For example, UE 106 may be configured to communicate using two or more of CDMA2000, LTE, LTE - A, 5G NR, WLAN, or GNSS. Other combinations of wireless communication standards are possible.

[0060] UE106 may include one or more antennas for communicating using one or more of the wireless communication protocols according to one or more RAT standards. In some embodiments, UE106 may share one or more portions of the receive chain and / or transmit chain among multiple wireless communication standards. The shared radio may include a single antenna for performing wireless communication, or may include multiple antennas (e.g., for MIMO). Generally, the radio may include any combination of a baseband processor, analog RF signal processing circuitry (including, e.g., filters, mixers, oscillators, amplifiers, etc.), or digital processing circuitry (e.g., for digital modulation and other digital processing). Similarly, the radio may execute one or more receive and transmit chains using the above hardware.

[0061] In some embodiments, UE106 may include separate transmit and / or receive chains (including, e.g., separate antennas and other radio components) for each of the wireless communication protocols that UE106 is configured to communicate therewith. As a further possibility, UE106 may include one or more radios shared among multiple wireless communication protocols, and one or more radios exclusively used by a single wireless communication protocol. For example, UE106 may include a shared radio for communicating using either LTE or CDMA2000 1xRTT (or LTE or NR or LTE or GSM), and individual radios for communicating using each of Wi-Fi and BLUETOOTH (trademark). Other configurations are possible. Figure 3 - Block diagram of an exemplary UE device

[0062] FIG. 3 shows a block diagram of an exemplary UE 106 according to some embodiments. As shown, UE 106 may include a system-on-chip (SOC) 300, which may include portions for various purposes. For example, as shown in the figure, SOC 300 may include a processor(s) 302 that can execute program instructions for UE 106, and a display circuit 304 that can perform graphic processing and supply a display signal to a display 360. SOC 300 may also include a sensor circuit 370 that may include components for sensing or measuring any of various possible characteristics or parameters of UE 106. For example, sensor circuit 370 may include a motion sensing circuit configured to detect the motion of UE 106 using, for example, any of a gyroscope, an accelerometer, and / or various other motion sensing components. As another possibility, sensor circuit 370 may include, for example, one or more antenna panels and / or one or more temperature sensing components for measuring the temperature of each of the other components of UE 106. Optionally, any of various other possible types of sensor circuits may be included additionally or alternatively in UE 106. Processor(s) 302 may be coupled to a memory management unit (MMU) 340, which may receive addresses from processor(s) 302 and translate those addresses to locations within a memory (e.g., memory 306, read-only memory (ROM) 350, NAND flash memory 310) and / or couple to other circuits or devices such as display circuit 304, radio circuit 330, connector interface (I / F) 320, and / or display 360. MMU 340 may be configured to perform memory protection and page table translation or setup. In some embodiments, MMU 340 may be included as part of processor(s) 302.

[0063] As shown in the figure, the SOC 300 may be coupled to various other circuits of the UE 106. For example, the UE 106 may include various types of memories (e.g., including NAND flash 310), a connector interface 320 (e.g., for coupling to a computer system, dock, charging station, etc.), a display 360, and a radio circuit 330 (e.g., for LTE, LTE-A, NR, CDMA2000, BLUETOOTH™, Wi-Fi, GPS, etc.). The UE device 106 may include at least one antenna (e.g., 335a) for performing wireless communication with a base station and / or other devices, and optionally, a plurality of antennas (e.g., exemplified by antennas 335a and 335b). Antennas 335a and 335b are shown as an example, and the UE device 106 may include fewer or more antennas. Generally, those one or more antennas are collectively referred to as antenna 335. For example, the UE device 106 may use the antenna 335 and the radio circuit 330 to perform wireless communication. As described above, in some embodiments, the UE may be configured to wirelessly communicate using multiple wireless communication standards.

[0064] UE 106 may include hardware and software components for implementing a method for executing techniques that support service continuity during a multicast broadcast service (MBS) handover, such as further description later in this specification. The processor(s) 302 of the UE device 106 may be configured to execute some or all of the methods described herein, for example, by executing program instructions stored in a memory medium (e.g., a non-transitory computer-readable memory medium). In other embodiments, the processor(s) 302 may be configured as a programmable hardware element such as a field programmable gate array (FPGA), or as an application specific integrated circuit (ASIC). Further, the processor(s) 302 may be coupled to or interact with other components to execute techniques that support service continuity during a multicast broadcast service (MBS) handover according to various embodiments disclosed herein, as shown in FIG. 3. The processor(s) 302 may also implement various other applications and / or end-user applications operating on the UE 106.

[0065] In some embodiments, the radio circuitry 330 may include separate dedicated controllers for controlling communications for each of the various RAT standards. For example, as shown in FIG. 3, the radio circuitry 330 may include a Wi-Fi controller 352, a cellular controller (e.g., an LTE-A and / or NR controller) 354, and a BLUETOOTH™ controller 356, and in at least some embodiments, one or more or all of these controllers may be implemented as respective integrated circuits (abbreviated as ICs or chips) that are in communication with each other and with the SOC 300 (more specifically, with the processor(s) 302). For example, the Wi-Fi controller 352 may communicate with the cellular controller 354 via a cell-ISM link or a WCI interface, and / or the BLUETOOTH™ controller 356 may communicate with the cellular controller 354 via a cell-ISM link or the like. Although three separate controllers are shown within the radio circuitry 330, other embodiments may have fewer or more similar controllers for the various different RATs that can be implemented in the UE device 106. In some embodiments, the cellular controller 354 may include a baseband processor configured to implement one or more or a portion of the procedures disclosed herein, or configured to cause the UE 106 to implement them. FIG. 4 - Block Diagram of an Exemplary Base Station

[0066] FIG. 4 shows a block diagram of an exemplary base station 102, according to some embodiments. Note that the base station of FIG. 4 is only an example of a possible base station. As shown, the base station 102 includes a processor(s) 404 that can execute program instructions for the base station 102. The processor(s) 404 may also be coupled to a memory management unit (MMU) 440, which may be configured to receive addresses from the processor(s) 404 and translate those addresses to locations within a memory (e.g., memory 460 and read-only memory (ROM) 450), or to other circuits or devices.

[0067] The base station 102 may include at least one network port 470. The network port 470 may be configured to couple to a telephone network and provide access to the telephone network to a plurality of devices such as the UE device 106 as described in FIGS. 1 and 2 above. The network port 470 (or an additional network port) may also or alternatively be configured to couple to a cellular network such as, for example, the core network of a cellular service provider. The core network may be able to provide mobility-related services and / or other services to a plurality of devices such as the UE device 106. In some cases, the network port 470 may couple to the telephone network via the core network and / or the core network may provide the telephone network (e.g., between other UE devices that are the service targets of a cellular service provider).

[0068] The base station 102 may include at least one antenna 434, and possibly a plurality of antennas. The antenna(s) 434 may be configured to operate as a radio transceiver and may be further configured to communicate with the UE device 106 by the radio 430. The antenna(s) 434 communicate with the radio 430 via a communication chain 432. The communication chain 432 may be a receive chain, a transmit chain, or both. The radio 430 may be designed to communicate via various radio communication standards including, but not limited to, NR, LTE, LTE-A, WCDMA, CDMA2000, etc. The processor 404 of the base station 102 may be configured to implement and / or support the implementation of some or all of the methods described herein, for example, by executing program instructions stored in a memory medium (e.g., a non-transitory computer-readable memory medium). Alternatively, the processor 404 may be configured as a programmable hardware element such as an FPGA (Field Programmable Gate Array), or as an ASIC (Application Specific Integrated Circuit), or as a combination thereof. For a given RAT, such as Wi-Fi, the base station 102 may be designed as an access point (AP), in which case the network port 470 may be implemented to provide access to a wide area network and / or a local area network(s), for example, may include at least one Ethernet port, and the radio 430 may be designed to communicate according to the Wi-Fi standard. MBS Mobility with Service Continuity

[0069] As the density of cellular spectrum usage increases, multicast broadcast service (MBS) is becoming increasingly popular as a solution to improve resource efficiency when a base station has information to transmit to multiple UEs. In some scenarios, UEs that are members of an MBS session may be served by multiple different base stations and may also move between cells. In legacy systems such as LTE, as a result of inter-cell MBS communication handovers, MBS packets may be dropped and / or missed. However, with the spread of MBS, an improvement in the reliability of MBS communication is desired, which can be partially achieved by providing service continuity during handovers.

[0070] Unicast communication represents an example of peer-to-peer (PTP) communication from a base station, such as base station 102, to a single UE, such as UE 106. In contrast, MBS communication represents an example of peer-to-multiple (PTM) communication between a base station, such as base station 102, communicating with a plurality of UEs, such as UEs 106A to 106N. In some MBS scenarios, base station 102 may broadcast a message to all UEs capable of receiving the message. In other MBS scenarios, base station 102 may multicast the communication by addressing the communication to a group of multiple or defined UEs, such as a group of UEs that are members of the corresponding MBS session.

[0071] FIG. 5 shows a block diagram of an MBS architecture and delivery method, such as used in NR, according to some embodiments. As shown, a core network (CN) 502 of a wireless communication network (e.g., a cellular provider network) may receive MBS traffic, for example, from a content source. CN 502 may duplicate the MBS traffic for delivery to appropriate UEs, such as UEs that are subscribed to an MBS session in which the MBS traffic is involved. As shown, the duplicated MBS traffic may be delivered via a RAN 504, which may include one or more base stations, such as base station 102. In some cases, the MBS traffic may be delivered to the UE via PTP communication, such as a conventional protocol data unit (PDU) session, such as PDU sessions 506A and 506B, between the CN and the UE. In other scenarios, CN 502 may provide the MBS traffic to be delivered to multiple UEs to the RAN 504 (e.g., to the base stations of the RAN 504) via a shared transport 506C. When a base station receives MBS traffic via the shared transport, it may determine whether to deliver the MBS traffic to each UE via multiple PTP communications or to deliver the MBS traffic to multiple UEs via MBS messages. The base station may make this determination based on, for example, the number of UEs to receive the MBS traffic, the reception quality, and / or various other factors.

[0072] For the handover procedure for MBS communication, existing procedures for PTP communication, such as a conventional PDU session, can also be utilized. However, these existing procedures are insufficient by themselves and need to be improved to support MBS communication.

[0073] Figure 6 shows a signal flow diagram for a conventional unicast handover procedure according to some embodiments. A detailed description of this procedure is provided in 3GPP TS 38.300 version 16.3.0, section 9.2.3.2, which is hereby incorporated by reference in its entirety as if fully set forth herein. An overview is provided below.

[0074] Figure 6 shows the signal flow between a UE (such as UE 106), a source base station and a target base station (such as base station 102), an access and mobility management function (AMF) of the core network, and one or more user plane functions (UPF) of the core network.

[0075] Initially, the UE may be connected to the source base station and may exchange user data with the source base station. The source base station may also exchange user data with the UPF on the network side.

[0076] At 602, the AMF may provide mobility control information to the source base station and / or the target base station.

[0077] At 604, the source base station and the UE may exchange messages related to measurement control and reporting.

[0078] At 606, the source base station may determine to initiate a handover of the UE to the target base station.

[0079] Between 608 and 612, the source base station and the target base station may perform handover preparation. Specifically, as shown in the figure, at 608, the source base station may transmit a handover request to the target base station, for example, via the Xn interface. In response, the target base station may perform admission control at 610 and may transmit a handover request positive response message to the source base station at 612. The handover request positive response message may include new RRC configuration.

[0080] At 614, the source base station and the UE may exchange one or more messages to initiate a RAN handover. For example, the source base station may provide new RRC configuration to the UE. At 618, the UE may respond by moving the RRC connection to the target base station. When these steps are completed, at 628, the UE may provide an indication to the target base station that the RAN handover is completed. For example, the UE synchronizes with the target base station and transmits an RRC reconfiguration complete message.

[0081] On the other hand, at 616, the source base station may deliver buffered data and new data from the UPF(s). At 620, the source base station may transmit an early state transfer message to the target base station for a dedicated radio bearer (DRB) configured with, for example, dual active protocol stacks (DAPS). At 622, the source base station may transmit a sequence number (SN) state transfer message to the target base station for a DRB not configured with DAPS, for example.

[0082] At 624, the source base station may receive user data for the UE from the UPF(s) and may transfer the user data to the target base station during the progress of the handover. At 626, the target base station may buffer the user data received from the source base station until the handover is completed.

[0083] At 628, after the target base station receives an indication that the RAN handover has been completed, at 630, the target base station may send a handover success message to the source base station. The source base station may respond by sending an SN state transfer message, which may include information such as the UL PDCP SN receiver state and the DL PDCP SN transmitter state.

[0084] At 634, the source base station may subsequently receive user data for the UE from the UPF(s), and may transfer the user data to the target base station. Since the handover reconfiguration is completed at the UE at this stage, at 636, the target base station may transfer the user data to the UE and receive user data from the UE. At 638, the target base station may deliver the user data from the UE to the UPF(s).

[0085] At 640, the target base station may send a path switch request message to the AMF to trigger the core network to, for example, switch the DL data path towards the target base station and establish an NG-C interface instance towards the target base station.

[0086] Accordingly, the core network may switch the DL data path towards the target base station at 642. The UPF(s) may send one or more "end marker" packets on the old path to the source base station for each PDU session / tunnel, and may then release the U plane / TNL resources towards the source gNB if available. The source base station may transfer the end marker packets to the target base station.

[0087] Thereafter, as shown at 646, the target base station may receive user data for the UE directly from the UPF(s).

[0088] At 648, the AMF may confirm the path switch request message of 640 using a path switch request positive response message. Upon receiving the path switch request positive response message from the AMF, at 650, the target base station may send a UE context release message to notify the source base station of the success of the handover. The source base station may then release the radio and C-plane related resources associated with the UE context. An ongoing data transfer may be continued if there is any.

[0089] In the current context, two sections of this procedure may be of particular note. First, during the execution of a basic handover, the UE may stop transmitting and receiving data to / from the network within the Uu interface between 614 and 628. The UE may then resume data transmission when uplink synchronization to the target cell via the RACH procedure is completed. However, during a DAPS handover, the UE may continue receiving data in the DL between the source cell and the target cell during the window of 614 to 628.

[0090] Second, as described above, upon receiving a handover, at 640, the target base station may initiate a path switch. Before the path switch is completed, the CN transfers UE-specific data to the source base station, and the source base station transfers the packets to the target base station via the Xn interface. When the path switch is completed, the CN may send an end marker to the source base station and transfer user data to the source base station. Upon receiving the end marker, the target base station may stop receiving data from the source base station and may consider all data received directly from the CN to be located after the data transferred from the source base station.

[0091] In the case of a DRB that is configured without DAPS, the source base station may send an SN status transfer message 622 to the target base station to transfer the uplink PDCP SN receiver state and the downlink PDCP SN transmitter state of the DRB for which PDCP state preservation applies (i.e., for RLC AM). The uplink PDCP SN receiver state may include at least the PDCP SN of the first missed UL PDCP SDU, and may include a bitmap of the reception status of out-of-order UL PDCP SDUs that the UE needs to retransmit within the target cell. The downlink PDCP SN transmitter state may indicate the next PDCP SN that the target base station should allocate to a new PDCP SDU that does not yet have a PDCP SN. In particular, the UE may indicate both UL and DL SN information for each DRB to the target cell / gNB.

[0092] Table 1 defines the fields of the SN STATUS TRANSFER (622) as defined by 3GPP TS 38.423 version 16.3.0, section 9.1.1.4. TIFF2025106318000002.tif70166

[0093] Table 2 defines the fields of the information element (IE) "list of DRBs for state transfer" shown in Table 1. TIFF2025106318000003.tif251170

[0094] FIG. 7 shows a signal flow diagram of a conventional MBS handover procedure according to some embodiments. FIG. 7 shows the signal flow between a UE (such as UE106), a source base station and a target base station (such as base station 102), the AMF of the core network, and one or more UPF(s) of the core network.

[0095] Initially, the UE may be connected to the source base station and may receive MBS data from the source base station either as PTP transmission or PTM transmission. The source base station may receive MBS multicast data from the UPF(s) on the network side. As shown in the figure, in some scenarios, the target base station may also receive MBS multicast data from the UPF(s).

[0096] At 702, the UE may send a measurement report to the source base station. Accordingly, at 704, the source base station may determine to initiate an MBS handover to the target base station.

[0097] At 706 - 710, the source base station and the target base station may perform MBS handover preparation. Specifically, as shown in the figure, at 706, the source base station may send a handover request to the target base station, and this handover request may include the MBS context about the UE, such as information about the MBS session(s) the UE is subscribed to. Accordingly, if the target base station currently does not have an established MBS session with the corresponding CN, at 708, the target base station may establish an MBS session via the AMF. At 710, the target base station may send a handover request positive response message to the source base station, and this handover request positive response message may include the MBS configuration information about the target base station.

[0098] At 712, the source base station may transfer an RRC reconfiguration message including MBS configuration information to the UE. At 714, the source base station may also send an SN status report message to the target base station.

[0099] The UE may move the RRC connection to the target base station according to the RRC reconfiguration message at 712, and at 716, may provide an indication to the target base station that the RAN handover is completed. For example, the UE synchronizes with the target base station and sends an RRC reconfiguration complete message.

[0100] At that point, the target base station may start transmitting MBS data to the UE as either PTP transmission or PTM transmission at 718. As shown at 720, the target base station may receive BMS multicast data from the UPF(s).

[0101] After receiving an indication that the RAN handover has been completed at 716, the target base station may negotiate with the AMF on a path switching procedure at 722 to, for example, switch the DL data path towards the target base station and to trigger the core network to establish an NG-C interface instance towards the target base station. This path switching procedure may include steps similar to those shown in 640-648 of FIG. 6.

[0102] When the path switching procedure is completed, the target base station may send a UE context release message at 724 to notify the source base station of the success of the handover. The source base station may then release the resources associated with the UE context.

[0103] In some scenarios, until the handover is completed, the source base station may continue to transmit MBS communication for the UE, for example, at 716 or 724. However, similar to the scenario shown in FIG. 6, the UE may stop receiving MBS communication from the source base station when it receives an RRC reconfiguration message at 712.

[0104] At 726, the UE may send a PDCP status report indicating the PDU(s) lost, for example, during PTP / PTM transmission at 718, to the target base station. In response, at 728, the target base station may re - transmit the lost PDU(s) to the UE via a unicast (PTP) message. However, there is no measure in the procedure of FIG. 7 to identify the PDU(s) lost before 712 or for re - transmission via the target base station. The procedure of FIG. 7 also has no measure to identify the PDU(s) missed during handover or for re - transmission via the target base station. Figure 8 - Seamless handover for MBS transmission

[0105] FIG. 8 shows a signal flow diagram for seamless handover for MBS transmission according to some embodiments. Specifically, in the example scenario of FIG. 8, the NW performs re - transmission of missed MBS packets via PTP communication within the target cell. New data transmission for the same MBS session / MBS DRB within the target cell may be transmitted via either PTM communication or PTP communication. The PDU information for re - transmission may be based on the UE PDCP status report after the UE accesses the target cell. FIG. 8 shows a specific scenario of the MBS handover procedure similar to the procedure shown in FIG. 7.

[0106] In FIG. 8, it should be understood that a part of the signal flow is simplified for clarity in focusing on the details of this example. However, in some implementations, the wide arrows shown in FIG. 8 may represent multiple communications similar to the multiple communications shown at similar points in FIG. 7.

[0107] FIG. 8 shows the signal flow between a UE (such as UE106) and a source base station and a target base station (such as base station 102).

[0108] As shown in FIG. 8, at 802, the UE may establish an RRC connection with the source base station. At 806, the source base station may transmit one or more MBS PTM communications for the MBS session to that UE (and to other UEs subscribed to the MBS session). Specifically, in the example of FIG. 8, the MBS PTM communication may include four PDUs having sequence numbers 1 to 4. In this example, PDUs 1, 2, and 4 are successfully received, but PDU 3 is dropped (e.g., due to interference, insufficient signal strength, etc.).

[0109] At 812, the source base station and the target base station may perform MBS handover preparation. In some scenarios, this may include steps similar to 706 - 710 of FIG. 7.

[0110] At 816, the source base station may transmit an RRC reconfiguration message to the UE together with synchronization parameters. For example, the RRC reconfiguration message may include a handover command and may further include configuration information regarding PTP and / or PTM communications.

[0111] The UE may move the RRC connection to the target base station in response to the RRC reconfiguration message at 816, and at 824, may send an indication to the target base station that the RAN handover is complete. For example, the UE synchronizes with the target base station and transmits an RRC reconfiguration complete message. Since the UE moves the RRC connection to the target base station, the UE may stop receiving MBS communications from the source base station in response to the RRC reconfiguration message at 816.

[0112] Transmission at 824 may also include a PDCP status report. For example, the PDCP status report may include the SN (e.g., DL PDCP SN) or other indication of the dropped or missed PDU(s) of the MBS session, such as the PDU3 in the scenario of FIG. 8. As another example, the PDCP status report may include the SN or other indication of the next PDU of the MBS session to be received by the UE, such as the PDU5 in the scenario of FIG. 8. For example, the PDCP status report may include the SN immediately following the SN of the last PDU (e.g., PDU4) of the MBS session received by the UE before 816.

[0113] When RRC reconfiguration is completed at the UE, the target base station may start transmitting communication for the MBS session to the UE. FIG. 8 shows two possible scenarios, one shown by 828 and the other shown by 830 - 832.

[0114] As shown by 828, the target base station may transmit one or more PTP communications for the MBS session to the UE. The PTP communication may include the dropped PDU identified by the UE at 824. The PTP communication may also include the next PDU of the MBS session identified by the UE at 824, along with the subsequent PDU transmitted by the source base station during handover, i.e., the PDU not received by the UE because it was transmitted by the source base station after 816. The PTP communication may also include the subsequent PDU of the MBS session received by the target base station from the core network.

[0115] In the second example, the target base station may provide continuous support for the MBS session using PTM communication. As shown in 830, similar to the scenario of 828, the target base station may first send one or more PTP communications for the MBS session to the UE, including the dropped PDU identified by the UE at 824, along with the next PDU of the MBS session and subsequent PDUs transmitted by the source base station during handover. However, at 832, the target base station may send subsequent PDUs for the MBS session to that UE (and other UEs subscribed to the MBS session) via PTM transmission.

[0116] In some implementations, the target base station may dynamically determine whether to send the continuous PDUs of the MBS session via PTP communication according to the scenario of 828 or via PTM communication according to the scenario of 832. For example, if the UE shown in Figure 8 is the only UE (or one of a small number of UEs) receiving the MBS session within the target cell, the target base station may determine to send the MBS PDU via PTP communication. However, if several UEs within the target cell are receiving the MBS session, the target base station may determine to send the MBS PDU to some of them via PTM communication. In any case, the PDUs dropped by the UE shown in Figure 8, together with the PDUs missed by that UE during handover, should be resent only to that UE, not to all UEs in the target cell receiving the MBS session. Therefore, these PDUs may be sent via PTP transmission in both the scenarios of 828 and 830. Figure 9 - Data Transfer from Source gNB with MBS Session Set to Target gNB

[0117] FIG. 9 shows a signal flow diagram for data transfer from a source base station to a target base station during an MBS handover for an MBS session that was previously activated on both base stations, according to some embodiments. FIG. 9 shows the signal flow between a UE (such as UE 106), a source base station and a target base station (such as base station 102), and one or more UPF(s) of the core network. Specifically, the procedure of FIG. 9 shows an example where the same MBS session is configured and activated at both the source base station and the target base station, according to some embodiments.

[0118] As shown in FIG. 9, at 902, the UE may establish an RRC connection with the source base station. At 904, the source base station may receive data of the MBS session from the UPF. For example, the data may include data transmitted as PDU 1-4, 1-7, or 1-10 by the source base station. In some scenarios, the source base station may receive additional data of the MBS session at other times throughout the procedure of FIG. 9.

[0119] At 906, the source base station may transmit one or more MBS PTM communications containing at least a part of the data for the MBS session received at 904 to that UE (and to other UEs subscribed to the MBS session). Specifically, in the example of FIG. 9, the MBS PTM communication may include 4 PDUs having sequence numbers 1 to 4. In this example, PDU1, 2, and 4 are successfully received, but PDU3 is dropped.

[0120] In the scenario of Figure 9, the MBS session is also set up and activated at the target base station. Therefore, the target base station may also receive the data of the MBS session at 908. In some scenarios, the data received by the target base station at 908 may be the same as the data received by the source base station at 904. However, some aspects such as UE address specification may be different between 904 and 908. At 910, the target base station may transmit at least a portion of the data received at 908 to the UEs that are members of the target cell.

[0121] At 912, the source base station and the target base station may perform MBS handover preparation. In some scenarios, this may include steps similar to 706 - 710 of Figure 7. However, note that since the MBS session is already set up and activated at the target base station, MBS session establishment (such as shown at 708) is not necessary and may be omitted (not executed).

[0122] At 916, the source base station may transmit an RRC reconfiguration message to the UE together with synchronization parameters. For example, the RRC reconfiguration message may include a handover command and MBS configuration information. In some scenarios, the RRC reconfiguration message at 916 may be similar to or equivalent to the RRC reconfiguration message at 816.

[0123] At 918, the source base station may transmit an SN state transfer message to the target base station. For example, the SN state transfer message may include the SN of the next PDU of the MBS session or other instructions to be received by the UE, such as PDU5 in the scenario of Figure 9. For example, the PDCP status report may include the SN immediately following the SN of the last PDU (e.g., PDU4) of the MBS session received by the UE before 916.

[0124] In response to the RRC reconfiguration message of 916, the UE may move the RRC connection to the target base station, and at 924, may send an indication to the target base station that the RAN handover has been completed. For example, the UE synchronizes with the target base station and sends an RRC reconfiguration complete message. Since the UE moves the RRC connection to the target base station, the UE may stop receiving MBS communication from the source base station in response to the RRC reconfiguration message of 916.

[0125] The transmission at 924 may also include a PDCP status report. For example, the PDCP status report may include the SN or other indication of the PDU(s) of the dropped or missed MBS session, such as the PDU3 in the scenario of FIG. 9.

[0126] At 926, the target base station may send a handover success message to the source base station. In some scenarios, the handover success message may be similar to the handover success message 630 in FIG. 6.

[0127] When RRC reconfiguration is completed at the UE, the target base station may start sending communication for the MBS session to the UE. FIG. 9 shows two possible scenarios that are the same as those in FIG. 8. One is shown at 928 and is equivalent to 828, and the other is shown at 930 - 932 and is equivalent to 830 - 832.

[0128] Note that since the MBS session is set up and activated before the start of the handover, there is no need for the source base station to transfer MBS data to the target base station. Instead, the target base station may send or re - send any one of MBS PDU3, 5 - 10 to the UE based on the data received from the UPF at 908. Similarly, there is no need to execute a path switching procedure such as that shown at 722 in FIG. 7. Figure 10 - Data transfer from source gNB to target gNB when the MBS session is not set up

[0129] FIG. 10 shows a signal flow diagram for data transfer from a source base station to a target base station during an MBS handover for an MBS session that was not previously activated on the target base station, according to some embodiments. FIG. 10 shows the signal flow among a UE (such as UE106), a source base station and a target base station (such as base station 102), and one or more UPF(s) of the core network. Specifically, the procedure of FIG. 10 shows an example where the MBS session in which the UE is subscribed in the source cell is not configured and not activated at the target base station, according to some embodiments.

[0130] As shown in FIG. 10, at 1002, the UE may establish an RRC connection with the source base station. At 1004, the source base station may receive data of the MBS session from the UPF. For example, the data may include data transmitted as PDU1-4, 1-7 by the source base station. In some scenarios, the source base station may receive additional data of the MBS session at other times throughout the procedure of FIG. 10.

[0131] At 1006, the source base station may transmit one or more MBS PTM communications to that UE (and other UEs subscribed to the MBS session) including at least a part of the data for the MBS session received at 1004. Specifically, in the example of FIG. 10, the MBS PTM communication may include four PDUs having sequence numbers 1 to 4. In this example, PDUs 1, 2, and 4 are successfully received, but PDU3 is dropped.

[0132] In some scenarios, the signals shown at 1002-1006 may be similar to or the same as those shown at 902-906 in FIG. 9. However, in the scenario of FIG. 10, the MBS session is not configured or activated at the target base station.

[0133] At 1012, the source base station and the target base station may perform MBS handover preparation. In some scenarios, this may include steps similar to 706 - 710 in FIG. 7. Specifically, since the MBS session is not yet configured and activated at the target base station, MBS session establishment (such as shown in 708) may be performed in response to a handover request message such as that shown in 706, for example.

[0134] At 1016, the source base station may send an RRC reconfiguration message to the UE along with synchronization parameters. For example, the RRC reconfiguration message may include a handover command and MBS configuration information. In some scenarios, the RRC reconfiguration message at 1016 may be similar to or equivalent to the RRC reconfiguration message at 816.

[0135] At 1018, the source base station may send an SN state transition message to the target base station. For example, the SN state transition message may include the SN of the next PDU of the MBS session or other instructions to be received by the UE, such as PDU5 in the scenario of FIG. 10. For example, the PDCP status report may include the SN immediately following the SN of the last PDU (e.g., PDU4) of the MBS session received by the UE before 1016.

[0136] As described in the previous example, in response to the RRC reconfiguration message at 1016, the UE may stop receiving transmissions from the source base station and move the RRC connection to the target base station. Therefore, these PDUs may be resent to the UE following the completion of the handover. However, since the MBS session establishment was performed during handover preparation, the target base station has not received MBS data such as PDU1 - 7 transmitted before that point from the UPF. Thus, at 1020, the source base station may transfer MBS PDUs (or corresponding MBS data) transmitted by the source base station following the RRC reconfiguration message at 1016, such as PDU5 - 7 in the example of FIG. 10, to the target base station.

[0137] In addition, at 1022, the target base station may receive subsequent data for the MBS session, such as PDU 8-10 in the example of FIG. 10, from the UPF. The UPF may send data at least partially in response to the establishment of the MBS session at 1014.

[0138] When RRC reconfiguration is completed in the UE, at 1024, the UE may send an indication to the target base station that the RAN handover has been completed. For example, the UE synchronizes with the target base station and sends an RRC reconfiguration complete message.

[0139] The transmission at 1024 may also include a PDCP status report. For example, the PDCP status report may include the SN or other indication of the dropped or missed PDU(s) of the MBS session, such as PDU 3 in the scenario of FIG. 10.

[0140] At 1026, the target base station may send a handover success message to the source base station. In some scenarios, the handover success message may be similar to the handover success message 630 in FIG. 6. In some scenarios, the handover success message 1026 may include an instruction or indication to stop the transfer of MBS data to the source base station. The handover success message may be at least partially in response to the RRC reconfiguration complete message 1024, and may also be at least partially in response to receiving data for the MBS session at 1022.

[0141] When RRC reconfiguration is completed in the UE, the target base station may start sending communications for the MBS session to the UE. FIG. 10 shows two possible scenarios, the same as in FIG. 8. One is shown at 1028 and is equivalent to 828, and the other is shown at 1030-1032 and is equivalent to 830-832. PDCP SN Synchronization

[0142] In each of the examples of FIGS. 8 to 10, the source base station may communicate to the target base station the SN (e.g., DL PDCP SN) of the dropped packet and / or the next MBS PDU to be transmitted to the UE. The source base station may synchronize the PDCP SN assignment with the target base station so that the SN provided by the source base station is meaningful to the target base station. This may be achieved, for example, by configuring each base station to assign a PDCP SN to each PDU based on information received from the UPF during MBS session establishment or in MBS session data transmission.

[0143] As a first example, when transmitting a PDU carrying MBS data, the base station may assign a PDCP SN according to the SN in the MBS packet in which the MBS data is received from the UPF. For example, the base station may set the PDCP SN to be equal to (or based on) the PDU header of the MBS packet. Alternatively, the base station may set the PDCP SN to be equal to (or based on) the GTP-U header of the MBS packet. In either example, the UPF may use the same SN to transmit a given MBS packet to both the source base station and the target base station. As a result, since the source base station and the target base station assign the same PDCP SN to the packet, the source base station can identify the packet to the target base station by referring to its own PDCP SN.

[0144] As another example, the base station may assign PDCP SNs according to the received packet order, for example, by sequentially increasing the SN. In some scenarios, the UPF may provide a starting number for each base station. For example, the UPF may indicate to the source base station the PDCP SN to be used for the first MBS packet transmitted to the source base station in the MBS session. The PDCP SN may be indicated, for example, during MBS session establishment, or may be indicated within the header of the first MBS packet transmitted to the source base station in the MBS session (e.g., within a spare field of the PDU header). Then, both the UPF and the source base station may increment the PDCP SN for each subsequent PDU. Similarly, the UPF may indicate to the target base station the PDCP SN to be used for the first MBS packet to be transmitted to the target base station, and the PDCP SN to be used may match the PDCP SN numbering indicated to the source gNB. For example, the PDCP SN to be used is the PDCP SN obtained from the numbering of the PDU after the first MBS packet has been transmitted to the source base station in the MBS session. As a result, the target base station assigns the PDCP SN specified by the UPF, which is the same as the PDCP SN assigned by the source base station to its packet based on the sequential number of the PDU. Following the first PDU, the target base station also increments the PDCP SN for each subsequent PDU. Also in this case, the source base station may identify each packet to the target base station by referring to its own PDCP SN. Specific embodiments

[0145] The following are specific embodiments of implementations that conform to the foregoing description. Other different embodiments are also envisioned within the entire scope of the foregoing description.

[0146] 1. In some embodiments, a method for performing communication of a multicast broadcast service (MBS) session includes a target base station of a wireless communication network receiving, from a remote base station of the wireless communication network, a request to initiate a handover of the MBS session for a user equipment (UE) from a source base station to the target base station, receiving an indication of a next protocol data unit (PDU) of the MBS session to be received by the UE, and transmitting, to the UE, a peer-to-peer (PTP) message including the next PDU of the MBS session, which was previously transmitted by the source base station via a point-to-multipoint (PTM) message after the request to initiate the handover.

[0147] 2. In some embodiments according to Example 1, the method further includes receiving, from the UE, an indication of a dropped PDU of the MBS session that was transmitted by the source base station but not properly received by the UE, and transmitting, to the UE, a peer-to-peer message including the dropped PDU.

[0148] 3. In some embodiments according to Example 2, the indication of the next PDU and the indication of the dropped PDU are received from the UE in a packet data convergence protocol (PDCP) status report.

[0149] 4. In some embodiments according to Example 1, the indication of the next PDU is received from the source base station.

[0150] 5. In some embodiments according to any of Examples 1-4, the method further includes determining, at least in part based on the number of UEs served by the target base station that are joined to the MBS session, whether to transmit subsequent PDUs of the MBS session via peer-to-peer messages or via point-to-multipoint messages.

[0151] 6. In some embodiments according to any of Examples 1 to 5, the method comprises, in response to receiving a request to initiate a handover, establishing the MBS session with a core network element of a radio communication network, receiving from a source base station at least one PDU of the MBS session to be transferred to the UE, the at least one PDU including the next PDU of the MBS session, and subsequently receiving subsequent PDUs of the MBS session from the core network element after receiving the next PDU.

[0152] 7. In some embodiments according to Example 6, the method further comprises receiving from the UE an indication that the MBS handover reconfiguration at the UE is complete, and providing an instruction to the source base station to stop transferring PDUs of the MBS session in response to receiving the indication that the MBS handover reconfiguration at the UE is complete and after establishing the MBS session with the core network element.

[0153] 8. In some embodiments according to Example 7, the method further comprises transferring each PDU of at least one PDU of the MBS session received from the source base station before receiving the indication that the MBS handover reconfiguration at the UE is complete to the UE via at least one PTP message.

[0154] 9. In some embodiments according to any of Examples 1 to 5, the method comprises establishing the MBS session with a core network element of a radio communication network, the MBS session being established before receiving a request to initiate a handover.

[0155] 10. In some embodiments according to any of Examples 1 to 9, the method further comprises receiving from a core network element of a radio communication network an indication of a sequence number to be assigned to a specified PDU of the MBS session, and sequentially assigning sequence numbers to PDUs subsequent to the specified PDU.

[0156] 11. In some embodiments according to any of Examples 1 to 9, receiving, from a core network element of a wireless communication network, an MBS packet including MBS payload data for its MBS session, the MBS packet having a packet sequence number; and transmitting, to a UE, a packet including the MBS payload data, wherein the packet sequence number of this MBS packet is used as the downlink (DL) packet data convergence protocol (PDCP) sequence number of the transmitted packet.

[0157] 12. In some embodiments, a target base station of a wireless communication network includes a wireless communication circuit and a processor circuit communicatively connected to the wireless communication circuit, the processor circuit being configured to cause the target base station to execute the steps according to any of Examples 1 to 11.

[0158] 13. In some embodiments, an apparatus includes a processor configured to cause a target base station to execute the steps according to any of Examples 1 to 11.

[0159] 14. In some embodiments, an apparatus comprises means for executing the method according to any of Examples 1 to 11.

[0160] 15. In some embodiments, a method for performing communication of a multicast broadcast service (MBS) session includes a wireless communication device receiving, from a first base station of a wireless network, a multicast transmission including at least one data packet of a multicast session; and receiving, from the first base station, an instruction to perform a handover to a second base station of the wireless network. In response to receiving the command, stop receiving transmissions from the first base station, establish a connection with the second base station, and receive from the second base station a unicast transmission that includes the next sequential data packet of the multicast session following the last data packet of the multicast session received from the first base station, where the next sequential data packet is the one that was previously included in the multicast transmission from the first base station after the wireless communication device stopped receiving transmissions from the first base station.

[0161] 16. In some embodiments according to embodiment 15, the method further includes transmitting an identifier of the next sequential packet to the second base station before receiving the unicast transmission.

[0162] 17. In some embodiments according to any of embodiments 15 - 16, the method further includes receiving from the second base station a unicast transmission that includes dropped data packets of the multicast session that were included in the multicast transmission from the first base station before the command to perform the handover but were not properly received by the UE.

[0163] 18. In some embodiments according to embodiment 17, the method further includes transmitting an identifier of the dropped data packet to the second base station before receiving the unicast transmission that includes the dropped data packet.

[0164] 19. In some embodiments according to any of embodiments 15 - 18, the method further includes receiving from the second base station a multicast transmission that includes at least one data packet of the multicast session.

[0165] 20. In some embodiments according to any of embodiments 15 - 19, the command to perform the handover to the second base station includes configuration information for establishing a connection with the second base station for multicast transmission.

[0166] 21. In some embodiments, a wireless communication device operating within a wireless communication network includes a wireless communication circuit and a processor circuit communicatively coupled to the wireless communication circuit, the processor circuit configured to cause the wireless communication device to perform the steps according to any of Examples 15 to 20.

[0167] 22. In some embodiments, the apparatus includes a processor configured to cause a wireless communication device to perform the steps according to any of Examples 15 to 20.

[0168] 23. In some embodiments, the apparatus comprises means for performing the method according to any of Examples 15 to 20.

[0169] 24. In some embodiments, a method for performing communication of a multicast broadcast service (MBS) session includes: a first base station of a wireless communication network transmitting a multicast transmission including at least one data packet of a multicast session to a user equipment (UE); transmitting, in response to determining to initiate a handover procedure for handing over the UE to a second base station of the wireless communication network, an instruction to the UE to perform the handover; providing, after transmitting the instruction, to the second base station an indication of a next packet of the MBS session to be transmitted to the UE; starting, after transmitting the instruction, a transfer of packets of the MBS session, including the next packet, to the second base station; and stopping, in response to receiving an indication from the second base station that the handover is complete, the transfer of packets of the MBS session.

[0170] 25. In some embodiments according to Example 24, the method further includes providing a handover request including information regarding the MBS session to the second base station.

[0171] 26. In some embodiments according to Example 25, the method further includes receiving, from a second base station, a handover request acknowledgment message indicating MBS session setup information for the second base station, and including the MBS session setup information for the second base station in an instruction to execute a handover.

[0172] 27. In some embodiments, a first base station operating within a wireless communication network includes a wireless communication circuit and a processor circuit communicatively coupled to the wireless communication circuit, the processor circuit configured to cause the first base station to perform the steps according to any of Examples 24 - 26.

[0173] 28. In some embodiments, an apparatus includes a processor configured to cause a first base station to perform the steps according to any of Examples 24 - 26.

[0174] 29. In some embodiments, an apparatus comprises a stage of executing a method according to any of Examples 24 - 26.

[0175] It is well understood that the use of personal information should comply with privacy policies and practices generally recognized as meeting or exceeding industry or government requirements for maintaining user privacy. In particular, personal information data should be managed and handled to minimize the risk of unintended or unauthorized access or use, and the nature of authorized use should be clearly indicated to the user.

[0176] Any of the methods described herein for operating a user equipment (UE) can form the basis of a corresponding method for operating a base station by interpreting each message / signal X received by the UE on the downlink as the message / signal X transmitted by the base station, and interpreting each message / signal Y transmitted by the UE on the uplink as the message / signal Y received by the base station.

[0177] Embodiments of the present disclosure may be implemented in any of a variety of forms. For example, in some embodiments, the subject matter may be implemented as a computer-executable method, a computer-readable storage medium, or a computer system. In other embodiments, the subject matter may be implemented using one or more custom-designed hardware devices, such as an ASIC. In still other embodiments, the subject matter may be implemented using one or more programmable hardware elements, such as an FPGA.

[0178] In some embodiments, a non-transitory computer-readable memory medium (e.g., a non-transitory memory element) stores program instructions and / or data, and the program instructions, when executed by a computer system, cause the computer system to perform a method, such as any of the method embodiments described herein, or any combination of the method embodiments described herein, or any subset of the method embodiments described herein, or any combination of such subsets.

[0179] In some embodiments, a device (e.g., a UE) may be configured to include a processor (or a set of processors) and a memory medium (or a memory element), the memory medium stores program instructions, and the processor is configured to read and execute the program instructions from the memory medium, and the program instructions are executable to implement any of the various method embodiments described herein (or any combination of the method embodiments described herein, or any arbitrary subset of any of the method embodiments described herein, or any combination of such subsets). The device may be realized in any of a variety of forms.

[0180] Although the above embodiments have been described in considerable detail, many variations and modifications will become apparent to those skilled in the art once the above disclosure is fully understood. The following claims are intended to be construed to embrace all such variations and modifications.

Claims

1. A method for performing communication of a multicast broadcast service (MBS) session, comprising: receiving, by a target base station of a wireless communication network, from a remote base station of the wireless communication network, a request to initiate a handover of the MBS session for a user equipment (UE) from the source base station to the target base station; receiving an indication of a next protocol data unit (PDU) of the MBS session to be received by the UE; transmitting, to the UE, a peer-to-peer (PTP) message including the next PDU of the MBS session, which is the next PDU of the MBS session that was previously transmitted via a point-to-multipoint (PTM) message by the source base station after the request to initiate the handover; The method.

2. receiving, from the UE, an indication of a dropped PDU of the MBS session that was transmitted by the source base station but not properly received by the UE; transmitting, to the UE, a peer-to-peer message including the dropped PDU; The method according to claim 1, further comprising.

3. The method according to claim 2, wherein the indication of the next PDU and the indication of the dropped PDU are received from the UE in a packet data convergence protocol (PDCP) status report.

4. The method according to claim 1, wherein the indication of the next PDU is received from the source base station.

5. determining whether to transmit subsequent PDUs of the MBS session via peer-to-peer messages or via point-to-multipoint messages, at least in part based on the number of UEs served by the target base station that are joined to the MBS session; The method according to claim 1, further comprising.

6. establishing the MBS session with a core network element of the wireless communication network in response to receiving the request to initiate the handover; receiving, from the source base station, at least one PDU of the MBS session to be transferred to the UE, including the next PDU of the MBS session; Subsequently to receiving the next PDU, receiving subsequent PDUs of the MBS session from the core network element; The method according to claim 1, further comprising: **Claim 7** Receiving, from the UE, an indication that MBS handover reconfiguration in the UE has been completed; In response to receiving the indication that MBS handover reconfiguration in the UE has been completed, and subsequent to establishing the MBS session with the core network element, providing an instruction to the source base station to stop transferring PDUs of the MBS session; The method according to claim 6, further comprising: **Claim 8** Transferring each PDU of the at least one PDU of the MBS session, received from the source base station before receiving the indication that MBS handover reconfiguration in the UE has been completed, to the UE via at least one PTP message; The method according to claim 7, further comprising: **Claim 9** Further comprising establishing the MBS session with a core network element of the wireless communication network, the MBS session being established before receiving the request to initiate the handover; The method according to claim 1. **Claim 10** Receiving, from a core network element of the wireless communication network, an indication of a sequence number to be assigned to a designated PDU of the MBS session; Assigning sequential sequence numbers to subsequent PDUs of the designated PDU; The method according to claim 1, further comprising: **Claim 11** Receiving, from a core network element of the wireless communication network, an MBS packet comprising MBS payload data for the MBS session, the MBS packet having a packet sequence number; Transmitting the packet comprising the MBS payload data to the UE, wherein the packet sequence number of the MBS packet is used as a downlink (DL) packet data convergence protocol (PDCP) sequence number of the transmitted packet; The method according to claim 1. **Claim 12** Comprising a processor; The processor causes a wireless communication device to receive a multicast transmission comprising at least one data packet of a multicast session from a first base station of a wireless network; Cause the first base station to receive an instruction to perform a handover to a second base station of the wireless network, In response to receiving the instruction, stop receiving transmissions from the first base station and establish a connection with the second base station, From the second base station, a next sequential data packet of the multicast session following the last data packet of the multicast session received from the first base station, and after the wireless communication device stops receiving transmissions from the first base station, the next sequential data packet previously included in the multicast transmission from the first base station, and is configured to receive a unicast transmission including the next sequential data packet, Device.

13. The processor further configures the wireless communication device to, Before receiving the unicast transmission, cause the second base station to transmit an identifier of the next sequential packet, The device according to claim 12.

14. The processor further configures the wireless communication device to, From the second base station, receive a unicast transmission including a dropped data packet of the multicast session, which was included in the multicast transmission from the first base station before the instruction to perform the handover but was not properly received by the UE, The device according to claim 12.

15. Before receiving the unicast transmission including the dropped data packet, the processor further configures the wireless communication device to cause the second base station to transmit an identifier of the dropped data packet, The device according to claim 14.

16. The processor further configures the wireless communication device to, From the second base station, receive a multicast transmission including at least one data packet of the multicast session, The device according to claim 12.

17. The instruction to perform the handover to the second base station includes setting information for establishing the connection with the second base station for multicast transmission, the device according to claim 12.

18. Comprising a processor, The processor is connected to a first base station of a wireless communication network, Cause the user equipment (UE) to send a multicast transmission including at least one data packet of a multicast session, In response to determining that a handover procedure for handing over the UE to a second base station of the wireless communication network is to be started, cause the UE to send a command to execute the handover, Subsequent to sending the command, cause the second base station to provide an indication of the next packet of the MBS session to be sent to the UE, Subsequent to sending the command, cause the second base station to start transferring packets of the MBS session that are to be sent to the UE and that include the next packet, Configured to stop transferring the packets of the MBS session in response to receiving an indication that the handover has been completed from the second base station, Device.

19. The processor is further configured to cause the first base station to, Cause the second base station to provide a handover request including information regarding the MBS session, The device according to claim 18.

20. The processor is further configured to cause the first base station to, Receive, from the second base station, a handover request positive response message indicating MBS session configuration information for the second base station, Configure the command to execute the handover to include the MBS session configuration information for the second base station, The device according to claim 19.

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