Multicast and Broadcast Service (MBS) mobility with service continuity in connected state

Abstract

The present invention describes techniques for improving service continuity of multicast and broadcast service (MBS) communications during handover. Techniques are included for supporting lossless handover and data forwarding during handover for point-to-multipoint (PTM) MBS transmissions. Lossless handover can be achieved in part by a user equipment (UE) providing an indication to a target base station of the next packet of an MBS session to be received after an RRC reconfiguration message, and an indication provided by a source base station before the RRC reconfiguration message of any MBS packets that were not correctly received by the UE. If the MBS session was not configured on the target base station before the handover, data forwarding can be performed from the source base station to the target base station. If the MBS session was configured on the target base station before the handover, data forwarding can be omitted.

Description

Technical Field

[0001] The present application relates to wireless communications, and more particularly, to systems, apparatuses, and methods for improving service continuity for Multicast and Broadcast Service (MBS) communications.

[0002] Related technical description

[0003] The use of wireless communication systems is growing rapidly. In recent years, wireless devices such as smartphones and tablets have become increasingly sophisticated. In addition to supporting phone calls, many mobile devices (i.e., user equipment devices or UEs) now also provide access to the Internet, email, text messaging and navigation using the Global Positioning System (GPS), and are capable of operating sophisticated applications that utilize these capabilities. In addition, there are many different wireless communication technologies and wireless communication standards. Some examples of wireless communication standards include GSM, UMTS (e.g., associated with WCDMA or TD-SCDMA air interfaces), LTE, LTE-Advanced (LTE-A), NR, HSPA, 3GPP2 CDMA2000 (e.g., 1xRTT, 1xEV-DO, HRPD, eHRPD), IEEE 802.11 (WLAN or Wi-Fi), BLUETOOTH TM wait.

[0004] One aspect of cellular communication systems relates to Multicast and Broadcast Service (MBS) communications.Improvements in the art are desired. Summary of the Invention

[0005] Embodiments of apparatus, systems, and methods for improving Multicast and Broadcast Service (MBS) communications through service continuity during handover are presented herein.

[0006] A method for performing communication for a multicast and broadcast service (MBS) session is disclosed. According to the method, a target base station of a wireless communication network may receive a request from a remote base station of the wireless communication network to initiate handover of an MBS session for a user equipment (UE) from a source base station to the target base station. The target base station may receive an indication of a next protocol data unit (PDU) of the MBS session to be received by the UE. The target base station may transmit a peer-to-peer (PTP) message to the UE including the next PDU of the MBS session, wherein the next PDU of the MBS session was previously transmitted by the source base station via a point-to-multipoint (PTM) message following the request to initiate handover.

[0007] In some scenarios, the target base station may receive an indication of discarded PDUs for the MBS session from the UE, where the discarded PDUs were transmitted by the source base station but were not correctly received by the UE. The target base station may transmit a peer-to-peer message including the discarded PDUs to the UE.

[0008] In some scenarios, an indication of the next PDU and an indication of the discarded PDUs may be received from the UE in a Packet Data Convergence Protocol (PDCP) status report.

[0009] In some cases, an indication of the next PDU may be received from the source base station.

[0010] In some scenarios, the target base station may determine whether to transmit subsequent PDUs for the MBS session via peer-to-peer messaging or point-to-multipoint messaging based at least in part on the number of UEs subscribed to the MBS session served by the target base station.

[0011] In some scenarios, the target base station may establish an MBS session with a core network element of the wireless communication network in response to receiving a request to initiate a handover. The target base station may receive at least one PDU for the MBS session from the source base station to be forwarded to the UE, the at least one PDU including a next PDU for the MBS session. After receiving the next PDU, the target base station may receive subsequent PDUs for the MBS session from the core network element.

[0012] In some scenarios, the target base station may receive an indication from the UE that the MBS handover reconfiguration at the UE is complete. In response to receiving the indication from the UE that the MBS handover reconfiguration is complete, 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 forwarding PDUs for the MBS session.

[0013] In some scenarios, the target base station may forward each of the at least one PDU of the MBS session received from the source base station to the UE via at least one PTP message before receiving an indication of MBS handover reconfiguration completion at the UE.

[0014] In some scenarios, the target base station may establish an MBS session with a core network element of the wireless communication network, wherein the MBS session is established before receiving the request to initiate the handover.

[0015] In some scenarios, the target base station may receive an indication of a sequence number to be assigned to a designated PDU for the MBS session from a core network element of the wireless communication network.The target base station may assign sequential sequence numbers to PDUs subsequent to the designated PDU.

[0016] In some scenarios, a target base station may receive an MBS packet including MBS payload data for an MBS session from a core network element of a wireless communication network, the MBS packet having a packet sequence number. The target base station may transmit the packet including the MBS payload data to a 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.

[0017] A method for performing communications for a multicast and broadcast service (MBS) session is described. According to the method, a wireless communication device may receive a multicast transmission including at least one data packet for the multicast session from a first base station of the wireless network. The wireless communication device may receive an instruction from the first base station to perform a handover 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, the unicast transmission including a next sequential data packet for the multicast session following a last data packet for the multicast session received from the first base station, wherein 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.

[0018] In some scenarios, the wireless communication device may transmit an identifier of a next sequential packet to the second base station before receiving the unicast transmission.

[0019] In some scenarios, the wireless communication device may receive a unicast transmission from the second base station that includes discarded data packets for the multicast session, where the discarded data packets were included in the multicast transmission from the first base station before the instruction to perform the handover but were not properly received by the UE.

[0020] In some scenarios, the wireless communication device may transmit an identifier of the discarded data packet to the second base station before receiving the unicast transmission including the discarded data packet.

[0021] In some scenarios, the wireless communication device may receive a multicast transmission including at least one data packet for a multicast session from a second base station.

[0022] In some scenarios, the instructions for performing a handover to the second base station may include configuration information for establishing a connection with the second base station for multicast transmission.

[0023] A method for performing communications for a multicast and broadcast service (MBS) session is described. According to the method, a first base station of a wireless communication network may transmit a multicast transmission including at least one data packet for the multicast session to a user equipment (UE). In response to determining to initiate a handover procedure to handover the UE to a second base station of the wireless communication network, the first base station may transmit an instruction to the UE to perform the handover. After transmitting the instruction, the first base station may transmit an indication of a next packet of the MBS session to be transmitted to the UE to the second base station. After transmitting the instruction, the first base station may begin forwarding packets of the MBS session to be transmitted to the UE to the second base station, the forwarded packets of the MBS session including the next packet. The first base station may stop forwarding packets of the MBS session in response to receiving an indication from the second base station that the handover is complete.

[0024] In some scenarios, the first base station may provide a handover request including information about the MBS session to the second base station.

[0025] In some scenarios, the first base station may receive a handover request confirmation message from the second base station indicating the MBS session configuration information of the second base station. The first base station may include the MBS session configuration information of the second base station in the instruction for performing the handover.

[0026] Also disclosed are devices, apparatuses, and systems for performing any of the aforementioned methods.

[0027] Note that the techniques described herein may be implemented and / or used with a number of different types of devices, including but not limited to base stations, access points, mobile phones, portable media players, tablet computers, wearable devices, unmanned aerial vehicles, unmanned flight controllers, automobiles and / or motor vehicles, and various other computing devices.

[0028] This summary is intended to provide a brief overview of some of the subject matter described in this document. Therefore, it should be understood that the above-described features are merely examples and should not be construed as narrowing the scope or spirit of the subject matter described herein in any way. Other features, aspects, and advantages of the subject matter described herein will become apparent from the following detailed description, accompanying drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] A better understanding of the present subject matter may be obtained when the following detailed description of various embodiments is considered in conjunction with the following drawings, in which:

[0030] Figure 1 An exemplary (and simplified) wireless communication system is shown in accordance with some embodiments.

[0031] Figure 2 An exemplary base station in communication with an exemplary wireless user equipment (UE) device is shown in accordance with some embodiments.

[0032] Figure 3 An exemplary block diagram of a UE according to some embodiments is illustrated.

[0033] Figure 4 An exemplary block diagram of a base station according to some embodiments is shown.

[0034] Figure 5 A block diagram illustrating an MBS architecture and delivery method according to some embodiments is shown.

[0035] Figure 6 is a signal flow diagram illustrating a conventional handover process according to some embodiments.

[0036] Figure 7 is a signal flow diagram illustrating a conventional MBS handover procedure according to some embodiments.

[0037] Figure 8 A signal flow diagram is shown for lossless switching of MBS transmissions according to some embodiments.

[0038] Figure 9 A signal flow diagram is shown for data forwarding from a source base station to a target base station during MBS handover for an MBS session previously enabled on both base stations, according to some embodiments.

[0039] Figure 10 A signal flow diagram is shown for data forwarding from a source base station to a target base station during an MBS handover for an MBS session not previously enabled on the target base station, according to some embodiments.

[0040] While the features described herein are susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the drawings and detailed description thereof are not intended to limit this disclosure to the specific forms disclosed, but on the contrary, are intended to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the subject matter as defined by the appended claims. DETAILED DESCRIPTION

[0041] Acronyms

[0042] Various acronyms are used throughout this disclosure. The definitions of the most prominent acronyms used that may appear throughout this disclosure are as follows:

[0043] BS: Base Station

[0044] CN: Core Network

[0045] DL: Downlink

[0046] GPRS: General Packet Radio Service

[0047] GSM: Global System for Mobile Communications

[0048] GTP: GPRS Tunneling Protocol

[0049] IE: Information Element

[0050] LTE: Long Term Evolution

[0051] MBS: Multicast and Broadcast Service

[0052] NR: New Radio

[0053] ●PDCP: Packet Data Convergence Protocol

[0054] PDU: Protocol Data Unit

[0055] PTM: Point-to-Multipoint

[0056] PTP: peer-to-peer

[0057] RACH: Random Access Channel

[0058] RAT: Radio Access Technology

[0059] RF: Radio Frequency

[0060] RX: Receive

[0061] TX: Transmit

[0062] UE: User Equipment

[0063] UL: Uplink

[0064] UMTS: Universal Mobile Telecommunications System

[0065] UPF: User Plane Function

[0066] the term

[0067] The following is a glossary of terms that will appear in this disclosure:

[0068] Memory medium—any of various types of non-transitory memory devices or storage devices. The term "memory medium" is intended to include installation media, such as CD-ROMs, floppy disks, or tape devices; computer system memory or random access memory such as DRAM, DDR RAM, SRAM, EDO RAM, Rambus RAM, etc.; non-volatile memory such as flash memory, magnetic media, for example, hard drives or optical storage devices; registers or other similar types of memory elements, etc. The memory medium may also include other types of non-transitory memory or a combination thereof. In addition, the memory medium may be located in the first computer system executing the program, or may be located in a different second computer system connected to the first computer system via a network such as the Internet. In the latter example, the second computer system may provide program instructions to the first computer system for execution. The term "memory medium" may include two or more memory media that may reside in different locations in different computer systems connected, for example, via a network. The memory medium may store program instructions (e.g., represented as a computer program) that may be executed by one or more processors.

[0069] Carrier Media—storage media as described above, and physical transmission media such as a bus, network, and / or other physical transmission media that carry signals such as electrical, electromagnetic, or digital signals.

[0070] Computer system (or computer)—any of various types of computing or processing systems, including a personal computer system (PC), a mainframe computer system, a workstation, a network appliance, an Internet appliance, a personal digital assistant (PDA), a television system, a grid computing system, or other devices or combinations of devices. In general, the term "computer system" can be broadly defined as any device (or combination of devices) that includes at least one processor that executes instructions from a memory medium.

[0071] User Equipment (UE) (or "UE device") - any of various types of computer systems or devices that are mobile or portable and that perform wireless communication. Examples of UE devices include mobile phones or smartphones (e.g., iPhones, TM , based on Android TM phones), tablet computers (e.g., iPad TM 、Samsung Galaxy TM ), portable gaming devices (e.g., Nintendo DS TM PlayStation Portable TM 、Gameboy Advance TM , iPhone TM ), wearable devices (e.g., smart watches, smart glasses), laptops, PDAs, portable Internet devices, music players, data storage devices, other handheld devices, cars and / or motor vehicles, unmanned aerial vehicles (UAVs) (e.g., drones), UAV controllers (UACs), etc. In general, the term "UE" or "UE device" can be broadly defined to cover any electronic device, computing device, and / or telecommunication device (or combination of these devices) that is easily transportable by a user and capable of wireless communication.

[0072] Wireless Device—Any of various types of computer systems or devices that perform wireless communications. A wireless device may be portable (or mobile), or may be stationary or fixed in place. A UE is an example of a wireless device.

[0073] Communication Device—Any of various types of computer systems or devices that perform communication, where the communication may be wired or wireless. A communication device may be portable (or mobile), or may be stationary or fixed in place. A wireless device is one example of a communication device. A UE is another example of a communication device.

[0074] Base Station (BS)—The term “base station” has the full breadth of its ordinary meaning and includes at least a wireless communication station installed at a fixed location and used to communicate as part of a wireless telephone system or radio system.

[0075] Processing element (or processor)—refers to any element or combination of elements capable of performing functions in a device (e.g., a user equipment device or a cellular network device). A processing element may include, for example, a processor and associated memory, portions or circuits of individual processor cores, entire processor cores, processor arrays, circuits such as ASICs (application-specific integrated circuits), programmable hardware elements such as field-programmable gate arrays (FPGAs), and any combination thereof.

[0076] Wi-Fi—The term "Wi-Fi" has the full scope of its ordinary meaning and includes at least wireless communication networks, or RATs, that are served by wireless LAN (WLAN) access points and provide connectivity to the Internet through those access points. Most modern Wi-Fi networks (or WLAN networks) are based on the IEEE 802.11 standard and are marketed under the name "Wi-Fi." Wi-Fi (WLAN) networks are distinct from cellular networks.

[0077] Automatic—refers to an action or operation being performed by a computer system (e.g., software executed by the computer system) or a device (e.g., a circuit, a programmable hardware element, an ASIC, etc.) without requiring user input to directly specify or execute the action or operation. Thus, the term "automatically" is in contrast to an action being manually performed or specified by a user, where the user provides input to directly perform the action. An automatic process may be initiated by user-provided input, but the subsequent actions performed "automatically" are not specified by the user, i.e., they are not performed "manually," where the user specifies each action to be performed. For example, a user filling out an electronic form by selecting each field and providing input specifying information (e.g., by typing information, selecting checkboxes, radio selections, etc.) is not manually filling out the form, even though the computer system must update the form in response to the user's actions. The form can be automatically filled out by a computer system, where the computer system (e.g., software executing on the computer system) analyzes the fields of the form and fills it out without requiring any user input to specify the answers to the fields. As indicated above, a user can invoke the automatic filling of a form without participating in the actual filling out of the form (e.g., the user does not manually specify the answers to the fields; they are automatically completed). This specification provides various examples of operations that are automatically performed in response to actions that a user has taken.

[0078] Configured to—Various components may be described as being “configured to” perform one or more tasks. In such contexts, “configured to” is a broad statement that generally means “having the structure” to perform one or more tasks during operation. Thus, a component can be configured to perform a task even when the component is not currently performing the task (e.g., a set of electrical conductors can be configured to electrically connect a module to another module even when the two modules are not connected). In some contexts, “configured to” can be a broad statement that generally means “having the circuitry” to perform one or more tasks during operation. Thus, a component can be configured to perform a task even when the component is not currently turned on. Generally, the circuitry that forms the structure corresponding to “configured to” may include hardware circuitry.

[0079] For ease of description, various components may be described as performing one or more tasks. Such descriptions should be interpreted as including the phrase "configured to." Representing a component as being configured to perform one or more tasks expressly does not invoke the sixth paragraph of section 112 of title 35 of the United States Code for that component.

[0080] Figure 1 and Figure 2 -Exemplary Communication System

[0081] Figure 1 An exemplary (and simplified) wireless communication system is shown in which various aspects of the present disclosure may be implemented according to some embodiments. Figure 1 The system is only one example of a possible system, and the embodiment may be implemented in any of a variety of systems as desired.

[0082] As shown, the exemplary wireless communication system includes a base station 102 that communicates with one or more (e.g., any number) user devices 106A, 106B, and so on through 106N via a transmission medium. Each user device may be referred to herein as a "user equipment" (UE) or a UE device. Accordingly, user device 106 is referred to as a UE or a UE device.

[0083] Base station 102 may be a base transceiver station (BTS) or a cell site and may include hardware and / or software that enables wireless communications with UEs 106A to 106N. If base station 102 is implemented in the context of LTE, it may be referred to as an "eNodeB" or "eNB." If base station 102 is implemented in the context of 5G NR, it may alternatively be referred to as a "gNodeB" or "gNB." Base station 102 may also be equipped to communicate with network 100 (e.g., a cellular service provider's core network, a telecommunications network such as the Public Switched Telephone Network (PSTN), and / or the Internet, among various other possible networks). Thus, base station 102 may facilitate communications between user devices and / or between user devices and network 100. The communication area (or coverage area) of a base station may be referred to as a "cell." Also as used herein, with respect to a UE, a base station may sometimes be considered to represent the network, taking into account the UE's uplink and downlink communications. Thus, a UE communicating with one or more base stations in a network may also be understood as a UE communicating with the network.

[0084] The base station 102 and the user equipment may be configured to communicate over a transmission medium using any of a variety of radio access technologies (RATs), also known as wireless communication technologies or telecommunication standards, such as GSM, UMTS (WCDMA), LTE, Advanced LTE (LTE-A), LAA / LTE-U, 5G NR, 3GPP2, CDMA2000 (e.g., 1xRTT, 1xEV-DO, HRPD, eHRPD), Wi-Fi, and the like.

[0085] Base station 102 and other similar base stations operating according to the same or different cellular communication standards may thus be provided as one or more cell networks that may provide continuous or nearly continuous overlapping service to UE 106 and similar devices over a geographic area via one or more cellular communication standards.

[0086] Note that the UE 106 is capable of communicating using multiple wireless communication standards. For example, the UE 106 may be configured to communicate using either or both of the 3GPP cellular communication standard or the 3GPP2 cellular communication standard. In some embodiments, the UE 106 may be configured to perform techniques for supporting service continuity during MBS handover, such as according to the various methods described herein. The UE 106 may also or alternatively be configured to use WLAN, BLUETOOTH, or other similar communication methods. TM, one or more global navigation satellite systems (GNSS, such as GPS or GLONASS), one and / or more mobile television broadcast standards (e.g., ATSC-M / H), etc. Other combinations of wireless communication standards (including more than two wireless communication standards) are also possible.

[0087] Figure 2 An exemplary user equipment 106 (e.g., one of devices 106A to 106N) in communication with a base station 102 according to some embodiments is shown. UE 106 can be a device with 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 flight controller (UAC), a car, or virtually any type of wireless device. UE 106 may include a processor (processing element) configured to execute program instructions stored in a memory. UE 106 can execute any of the method embodiments described herein by executing such stored instructions. Alternatively or in addition, UE 106 may include a programmable hardware element, such as an FPGA (field programmable gate array), an integrated circuit, and / or any of various other possible hardware components configured to execute (e.g., individually or in combination) any one of the method embodiments described herein or any part of any one of the method embodiments described herein. UE 106 can be configured to communicate using any one 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 also possible.

[0088] UE 106 may include one or more antennas for communicating using one or more wireless communication protocols according to one or more RAT standards. In some embodiments, UE 106 may share one or more portions of a receive chain and / or transmit chain between multiple wireless communication standards. The shared radio components may include a single antenna, or may include multiple antennas for performing wireless communication (e.g., for MIMO). Typically, the radio components may include any combination of a baseband processor, analog radio frequency (RF) signal processing circuits (e.g., including filters, mixers, oscillators, amplifiers, etc.), or digital processing circuits (e.g., for digital modulation and other digital processing). Similarly, the radio components may implement one or more receive chains and transmit chains using the aforementioned hardware.

[0089] In some embodiments, the UE 106 may include a separate transmit chain and / or receive chain (e.g., including separate antennas and other radio components) for each wireless communication protocol with which it is configured to communicate. As another possibility, the UE 106 may include one or more radio components shared between multiple wireless communication protocols, and one or more radio components used uniquely by a single wireless communication protocol. For example, the UE 106 may include shared radio components for communicating using any of LTE or CDMA2000 1xRTT (or LTE or NR, or LTE or GSM), and shared radio components for communicating using Wi-Fi and BLUETOOTH. TM Each of the radio components communicates independently. Other configurations are also possible.

[0090] Figure 3 - Block diagram of an exemplary UE device

[0091] Figure 3 A block diagram of an exemplary UE 106 according to some embodiments is shown. As shown, the UE 106 may include a system on a chip (SOC) 300, which may include components for various purposes. For example, as shown, the SOC 300 may include a processor 302 that can execute program instructions for the UE 106, and a display circuit 304 that can perform graphics processing and provide display signals to a display 360. The SOC 300 may also include sensor circuitry 370, which may include components for sensing or measuring any of various possible characteristics or parameters of the UE 106. For example, the sensor circuitry 370 may include motion sensing circuitry configured to detect the motion of the UE 106, for example, using a gyroscope, an accelerometer, and / or any of various other motion sensing components. As another possibility, the sensor circuitry 370 may include one or more temperature sensing components, for example, for measuring the temperature of each of one or more antenna panels and / or other components of the UE 106. Any of various other possible types of sensor circuitry may also or alternatively be included in the UE 106, as desired. Processor 302 may also be coupled to a memory management unit (MMU) 340, which may be configured to receive addresses from processor 302 and translate those addresses into locations in memory (e.g., memory 306, read-only memory (ROM) 350, NAND flash memory 310) and / or other circuits or devices, such as display circuitry 304, radio circuitry 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 302.

[0092] As shown, the SOC 300 may be coupled to various other circuits of the UE 106. For example, the UE 106 may include various types of memory (e.g., including NAND flash memory 310), a connector interface 320 (e.g., for coupling to a computer system, a docking station, a charging station, etc.), a display 360, and radio circuitry 330 (e.g., for LTE, LTE-A, NR, CDMA2000, BLUETOOTH, etc.). TM , Wi-Fi, GPS, UWB, etc.). The UE device 106 may include at least one antenna (e.g., 335a), and may include multiple antennas (e.g., as shown by antennas 335a and 335b), for performing wireless communications with base stations and / or other devices. Antennas 335a and 335b are shown by way of example, and the UE device 106 may include fewer or more antennas. In general, one or more antennas are collectively referred to as antennas 335. For example, the UE device 106 may use antennas 335 with the aid of radio circuitry 330 to perform wireless communications. As described above, in some embodiments, the UE may be configured to perform wireless communications using multiple wireless communication standards.

[0093] The UE 106 may include hardware and software components for implementing the UE 106 to perform methods such as the techniques for supporting service continuity during multicast and broadcast service (MBS) handovers described further below herein. The processor 302 of the UE device 106 may be configured to implement part or all of the methods described herein, for example, by executing program instructions stored on a memory medium (e.g., a non-transitory computer-readable memory medium). In other embodiments, the processor 302 may be configured as a programmable hardware element, such as an FPGA (field programmable gate array) or as an ASIC (application-specific integrated circuit). In addition, the processor 302 may be coupled to a processor such as a processor 102 or a processor 103. Figure 3 Other components are shown and / or may interoperate with other components to perform techniques for supporting service continuity during MBS handover according to various embodiments disclosed herein. Processor 302 may also implement various other applications and / or end-user applications running on UE 106.

[0094] In some embodiments, the radio circuitry 330 may include separate controllers dedicated to controlling communications for various corresponding RAT standards. Figure 3 As shown, the radio circuit 330 may include a Wi-Fi controller 352, a cellular controller (e.g., LTE-A and / or NR controller) 354, and a BLUETOOTH controller. TMController 356 and in at least some embodiments, one or more or all of these controllers may be implemented as respective integrated circuits (ICs or chips) that communicate with each other and with SOC 300 (more specifically, with processor 302). For example, Wi-Fi controller 352 may communicate with cellular controller 354 via a cell-ISM link or WCI interface, and / or BLUETOOTH controller 354 may communicate with the cellular controller 354 via a cell-ISM link or WCI interface. TM The controller 356 may communicate with the cellular controller 354 via a cell-ISM link, etc. Although three separate controllers are shown within the radio circuitry 330, other embodiments with fewer or more similar controllers for various different RATs may be implemented in the UE device 106. In some embodiments, the cellular controller 354 may include a baseband processor configured to implement or cause the UE 106 to implement one or more of the processes disclosed herein, or portions thereof.

[0095] Figure 4 - Block diagram of an exemplary base station

[0096] Figure 4 1 shows a block diagram of an exemplary base station 102 according to some embodiments. Note that Figure 4 The base station 102 is only one example of a possible base station. As shown, the base station 102 may include a processor 404 that may execute program instructions for the base station 102. The processor 404 may also be coupled to a memory management unit (MMU) 440 or other circuit or device that may be configured to receive addresses from the processor 404 and translate those addresses into locations in memory (e.g., memory 460 and read-only memory (ROM) 450).

[0097] 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 as described above. Figure 1 and Figure 2 The network port 470 may be configured to couple to a plurality of devices such as the UE device 106 to the telephone network described in the embodiment of the present invention. The network port 470 (or an additional network port) may also or alternatively be configured to couple to a cellular network, such as a core network of a cellular service provider. The core network may 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 be coupled to the telephone network via the core network, and / or the core network may provide the telephone network (e.g., in other UE devices served by the cellular service provider).

[0098] The base station 102 may include at least one antenna 434 and possibly multiple antennas. One or more antennas 434 may be configured to operate as a wireless transceiver and may be further configured to communicate with the UE device 106 via the radio component 430. The antenna 434 communicates with the radio component 430 via a communication chain 432. The communication chain 432 may be a receive chain, a transmit chain, or both. The radio component 430 may be designed to communicate via various wireless telecommunication 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 implementation of part or all of the methods described herein, for example, by executing program instructions stored on 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 a combination thereof. In the case of certain RATs (e.g., 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 one or more local area networks, for example, it may include at least one Ethernet port, and the radio component 430 may be designed to communicate according to the Wi-Fi standard.

[0099] MBS mobility with service continuity

[0100] As cellular spectrum usage becomes increasingly dense, Multicast and Broadcast Services (MBS) are becoming a more popular solution for improving resource efficiency when a base station has information to convey to multiple UEs. In some scenarios, UEs subscribed to an MBS session may be served by different base stations and may travel between cells. In traditional systems such as LTE, handover of MBS communications between cells may result in dropped and / or lost MBS packets. However, as MBS becomes more prevalent, it is desirable to improve the reliability of MBS communications, which can be achieved in part by providing service continuity during handovers.

[0101] Unicast communication represents an example of peer-to-peer (PTP) communication, e.g., directed 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 point-to-multipoint (PTM) communication, e.g., a base station (such as base station 102) communicating with multiple UEs (such as UEs 106A-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 a communication by addressing the communication to multiple or a limited group of UEs (such as a group of UEs subscribed to an applicable MBS session).

[0102] Figure 5 A block diagram illustrates an MBS architecture and delivery method, for example, for use 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. The CN 502 may replicate the MBS traffic for distribution to appropriate UEs, for example, UEs subscribed to the MBS session to which the MBS traffic relates. As shown, the replicated MBS traffic may be distributed 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 distributed to the UEs via PTP communications (e.g., traditional protocol data unit (PDU) sessions between the CN and the UEs, such as PDU sessions 506A and 506B). In other scenarios, the CN 502 may provide the MBS traffic to the RAN 504 (e.g., to a base station of the RAN 504) via a shared transport 506C for delivery to multiple UEs. Upon receiving the MBS traffic via the shared transport, the base station may determine whether to deliver the MBS traffic to the corresponding UE via multiple PTP communications or to deliver the MBS traffic to the multiple UEs via MBS messages. The base station may make this determination based on, for example, how many UEs should receive MBS traffic, reception quality, and / or various other factors.

[0103] The handover process for MBS communication can utilize existing processes for PTP communication, such as traditional PDU sessions. However, these existing processes are not sufficient in themselves and must be improved to accommodate MBS communication.

[0104] Figure 6 is a signal flow diagram illustrating a conventional unicast handover process according to some embodiments. A detailed description of this process can be found in 3GPP TS 38.300, version 16.3.0, section 9.2.3.2, the entire contents of which are incorporated herein by reference as if fully and completely set forth herein. A brief overview follows.

[0105] Figure 6 Signal flows are shown 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 (UPFs) of the core network.

[0106] Initially, the UE may connect to the source base station and exchange user data with it. On the network side, the source base station may also exchange user data with the UPF.

[0107] At 602, the AMF may provide mobility control information to a source base station and / or a target base station.

[0108] At 604, the source base station and the UE may exchange messages related to measurement control and reporting.

[0109] At 606, the source base station may determine to initiate a handover of the UE to the target base station.

[0110] At 608-612, 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 an Xn interface. In response, the target base station may perform admission control at 610 and may transmit a handover request confirmation message to the source base station at 612. The handover request confirmation message may include the new RRC configuration.

[0111] At 614, the source base station and the UE may exchange one or more messages initiating the RAN handover. For example, the source base station may provide the UE with a new RRC configuration. At 618, the UE may respond by moving the RRC connection to the target base station. After completing these steps, at 628, the UE may provide the target base station with an indication that the RAN handover is complete. For example, the UE may synchronize with the target base station and transmit an RRCReconfigurationComplete message.

[0112] At the same time, the source base station may deliver the buffered data and new data from the UPF at 616. At 620, the source base station may transmit an early status transfer message to the target base station, for example, for a dedicated radio bearer (DRB) configured with a dual active protocol stack (DAPS). At 622, the source base station may transmit a sequence number (SN) status transfer message to the target base station, for example, for a DRB not configured with DAPS.

[0113] At 624, the source base station may receive user data for the UE from the UPF and may forward the user data to the target base station while the handover is ongoing. At 626, the target base station may buffer the user data received from the source base station until the handover is complete.

[0114] After the target base station receives the indication of RAN handover completion at 628, the target base station may transmit a handover success message to the source base station at 630. The source base station may respond by transmitting an SN status transfer message, which may include information such as the UL PDCP SN receiver status and the DL PDCP SN transmitter status.

[0115] At 634, the source base station may continue to receive user data for the UE from the UPF and may forward the user data to the target base station. At this stage, because the handover reconfiguration is complete at the UE, the target base station may forward user data to the UE and receive user data from the UE at 636. At 638, the target base station may transfer the user data from the UE to the UPF.

[0116] At 640, the target base station may transmit a path switch request message to the AMF, for example to trigger the core network to switch the DL data path to the target base station and establish an NG-C interface instance to the target base station.

[0117] In response, at 642, the core network may switch the DL data path to the target base station. The UPF may send one or more "end marker" packets on the old path to the source gNB based on the PDU session / tunnel and may then release any U-plane / TNL resources toward the source gNB. The source gNB may forward the end marker packets to the target gNB.

[0118] Thereafter, the target base station may receive the user data of the UE directly from the UPF, as shown at 646 .

[0119] At 648, the AMF may confirm the Path Switch Request message of 640 with a Path Switch Request Acknowledge message. Upon receiving the Path Switch Request Acknowledge message from the AMF, the target base station may send a UE Context Release message at 650 to notify the source base station of the successful handover. The source base station may then release the radio and C-plane related resources associated with the UE context. Any ongoing data forwarding may continue.

[0120] In the present context, two parts of this process may be particularly noteworthy. First, during the basic handover execution, the UE may cease data transmission / reception to the network in the Uu interface from 614 to 628. The UE may then resume data transmission after completing uplink synchronization with the target cell via the RACH procedure. However, during the DAPS handover, the UE may continue data reception between the source cell and the target cell in the DL during the window from 614 to 628.

[0121] Next, as noted above, upon receiving the handover request, the target base station may initiate a path switch at 640. Prior to completing the path switch, the CN forwards UE-specific data to the source base station, which then forwards packets to the target base station via the Xn interface. After the path switch is complete, the CN may send an end marker to the source base station and forward 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 treat all data received directly from the CN as subsequent to the data forwarded from the source base station.

[0122] For DRBs not configured with DAPS, the source base station may send an SN status transfer message 622 to the target base station to convey the uplink PDCP SN receiver status and downlink PDCP SN transmitter status (i.e., for RLC AM) for the DRB to which PDCP status preservation is applied. The uplink PDCP SN receiver status may include at least the PDCP SN of the first lost UL PDCP SDU and may include a bitmap of the reception status of out-of-sequence UL PDCP SDUs that the UE needs to retransmit in the target cell, if any. The downlink PDCP SN transmitter status may indicate the next PDCP SN that the target base station should assign to new PDCP SDUs that do not yet have a PDCP SN. Notably, for each DRB, the UE may indicate both UL and DL SN information to the target cell / gNB.

[0123] Table 1 defines the fields of the SN Status Transport (622), as defined in 3GPP TS 38.423 Version 16.3.0, Section 9.1.1.4:

[0124]

[0125] Table 1

[0126] Table 2 defines the fields of the information element (IE) "DRB subject to state transfer list", as shown in Table 1:

[0127]

[0128]

[0129] Table 2

[0130] Figure 7 is a signal flow diagram illustrating a conventional MBS handover procedure according to some embodiments. Figure 7 The signal flows between a UE (such as UE 106), a source base station and a target base station (such as base station 102), an AMF of a core network, and one or more UPFs of the core network are shown.

[0131] Initially, the UE may connect to the source base station and receive MBS data from it as PTP or PTM transmission. On the network side, the source base station may receive MBS multicast data from the UPF. As shown in the figure, in some scenarios, the target base station may also receive MBS multicast data from the UPF.

[0132] At 702, the UE may transmit a measurement report to the source base station. In response, at 704, the source base station may determine to initiate an MBS handover to a target base station.

[0133] 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 transmit a handover request to the target base station, for example, via an Xn interface. The handover request may include the UE's MBS context, such as information about the MBS session to which the UE is subscribed. In response, if the target base station does not currently have a corresponding MBS session established with the CN, at 708, the target base station may establish an MBS session via the AMF. At 710, the target base station may transmit a handover request confirmation message to the source base station. The handover request confirmation message may include MBS configuration information about the target base station.

[0134] At 712, the source base station may forward the RRC reconfiguration message including the MBS configuration information to the UE. At 714, the source base station may also transmit an SN status report message to the target base station.

[0135] In response to the RRC reconfiguration message at 712, the UE may move the RRC connection to the target base station and may provide an indication of RAN handover completion to the target base station at 716. For example, the UE may synchronize with the target base station and transmit an RRCReconfigurationComplete message.

[0136] At this point, the target base station may begin transmitting MBS data to the UE as a PTP or PTM transmission at 718. The target base station may receive BMS multicast data from the UPF, as shown at 720.

[0137] After the target base station receives the indication of RAN handover completion at 716, the target base station may negotiate a path switching procedure with the AMF at 722, for example, to trigger the core network to switch the DL data path to the target base station and establish an NG-C interface instance to the target base station. The path switching procedure may include Figure 6 The steps are similar to those shown at 640-648.

[0138] After completing the path switching process, the target base station may send a UE context release message to notify the source base station of the success of the handover at 724. The source base station may then release resources associated with the UE context.

[0139] In some scenarios, the source base station may continue to transmit MBS communications for the UE until the handover is complete, for example, at 716 or 724. However, similar to Figure 6 In the illustrated scenario, the UE may stop receiving MBS communications from the source base station upon receiving the RRC reconfiguration message at 712 .

[0140] At 726, the UE may transmit a PDCP status report to the target base station, e.g., indicating any PDUs lost during the PTP / PTM transmission at 718. In response, the target base station may retransmit any lost PDUs to the UE via a unicast (PTP) message at 728. However, Figure 7 The process does not include provisions for identifying or retransmitting any PDUs lost prior to 712 via the target base station. Figure 7 The procedure also does not include provisions for identifying or retransmitting any PDUs lost during the handover via the target base station.

[0141] Figure 8 - Lossless switching for MBS transmission

[0142] Figure 8 FIGURE 1 shows a signal flow diagram for lossless switching of MBS transmission according to some embodiments. Figure 8 In an exemplary scenario, the NW performs retransmission of lost MBS packets in the target cell via PTP communication. New data transmission for the same MBS session / MBS DRB in the target cell can be transmitted via PTM or PTP communication. The PDU information used for retransmission can be based on the UE PDCU status report after the UE accesses the target cell. Figure 8 shows a specific scenario of the MBS switching process, similar to Figure 7 The process shown.

[0143] It should be understood that in order to more clearly focus on the details related to this example, Figure 8 However, in some implementations, Figure 8 The broad arrows shown may represent multiple communications, for example, similar to Figure 7 Multiple communications are shown at similar points in FIG.

[0144] Figure 8 Signal flows between a UE (such as UE 106) and a source base station and a target base station (such as base station 102) are shown.

[0145] like Figure 8 As shown, the UE may establish an RRC connection with the source base station at 802. At 806, the source base station may transmit one or more MBS PTM communications of the MBS session to the UE (and to other UEs subscribed to the MBS session). Figure 8 In the example of , the MBS PTM communication may include 4 PDUs with sequence numbers 1 - 4. In this example, PDUs 1, 2, and 4 are successfully received, but PDU 3 is discarded (e.g., due to interference, insufficient signal strength, etc.).

[0146] At 812, the source base station and the target base station may perform MBS handover preparation. In some scenarios, this may include something like Figure 7 Steps 706-710.

[0147] At 816, the source base station may transmit an RRC reconfiguration message with synchronization parameters to the UE. For example, the RRC reconfiguration message may include a handover command and may also include configuration information related to PTP and / or PTM communications.

[0148] In response to the RRC reconfiguration message at 816, the UE may move the RRC connection to the target base station and may transmit an indication of RAN handover completion to the target base station at 824. For example, the UE may synchronize with the target base station and transmit an RRCReconfigurationComplete message. Because 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.

[0149] The transmission at 824 may also include a PDCP status report. For example, the PDCP status report may include any discarded or lost PDUs for the MBS session (such as Figure 8 For example, the PDCP status report may include the next PDU of the MBS session to be received by the UE (such as Figure 8 For example, the PDCP status report may include the SN immediately following the SN of the last PDU (eg, PDU 4) of the MBS session received by the UE before 816.

[0150] Once the RRC reconfiguration is completed at the UE, the target base station may begin transmitting communications for the MBS session to the UE. Figure 8 Two possible scenarios are shown, one scenario is shown by 828 and the other scenario is shown by 830-832.

[0151] As shown at 828, the target base station may transmit one or more PTP communications for the MBS session to the UE. The PTP communications may include any discarded PDUs identified by the UE at 824. The PTP communications may also include the next PDU for the MBS session (as identified by the UE at 824) and subsequent PDUs transmitted by the source base station during the handover (i.e., PDUs not received by the UE due to transmission by the source base station after 816). The PTP communications may also include subsequent PDUs for the MBS session received by the target base station from the core network.

[0152] In a second example, the target base station may use PTM communications to provide continued support for the MBS session. As shown at 830, the target base station may first transmit one or more PTP communications for the MBS session to the UE, including any discarded PDUs identified by the UE at 824, as well as the next PDU of the MBS session and subsequent PDUs transmitted by the source base station during the handover, as shown in the scenario of 828. However, at 832, the target base station may transmit subsequent PDUs of the MBS session to the UE (and to other UEs subscribed to the MBS session) via PTM transmission.

[0153] In some implementations, the target base station may dynamically decide whether to transmit the ongoing 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 Figure 8 If the UE shown is the only UE (or one of a small number of UEs) receiving an MBS session in the target cell, the target base station may decide to transmit the MBS PDUs via PTP communication. However, if several UEs in the target cell are receiving MBS sessions, the target base station may decide to transmit the MBS PDUs to those several UEs via PTM communication. However, in either case, Figure 8 The PDUs discarded by the UE shown and the PDUs lost by the UE during the handover should only be retransmitted to the UE, rather than to all UEs in the target cell that are receiving MBS sessions. Therefore, those PDUs can be transmitted via PTP transmission in both the scenario of 828 and the scenario of 830.

[0154] Figure 9 - Data forwarding from source gNB to target gNB configured with MBS session

[0155] Figure 9 A signal flow diagram is shown for data forwarding from a source base station to a target base station during MBS handover for an MBS session previously enabled on both base stations, according to some embodiments. Figure 9 106), a source base station and a target base station (such as base station 102), and one or more UPFs of the core network. Figure 9 The process of illustrates an example in which the same MBS session is configured and enabled in both the source base station and the target base station according to some embodiments.

[0156] like Figure 9 As shown, the UE may establish an RRC connection with the source base station at 902. At 904, the source base station may receive data for the MBS session from the UPF. For example, the data may include data to be transmitted by the source base station as PDUs 1-4, 1-7, or 1-10. In some scenarios, the source base station may Figure 9 Additional data for the MBS session is received at other times during the process.

[0157] At 906, the source base station may transmit one or more MBS PTM communications to the UE (and to other UEs subscribed to the MBS session), the one or more MBS PTM communications including at least a portion of the data for the MBS session received at 904. Figure 9 In the example of , the MBS PTM communication may include 4 PDUs with sequence numbers 1 - 4. In this example, PDUs 1, 2, and 4 are successfully received, but PDU 3 is discarded.

[0158] exist Figure 9 In the scenario described above, an MBS session is also configured and enabled in the target base station. Therefore, the target base station may also receive data for 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 addressing, may differ between 904 and 908. At 910, the target base station may transmit at least a portion of the data received at 908 to a subscribed UE of the target cell.

[0159] At 912, the source base station and the target base station may perform MBS handover preparation. In some scenarios, this may include something like Figure 7 However, it should be noted that since the MBS session has already been configured and enabled in the target base station, the MBS session establishment (as shown at 708) is not necessary and may be omitted (may not be performed).

[0160] At 916, the source base station may transmit an RRC reconfiguration message with synchronization parameters to the UE. 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 identical to the RRC reconfiguration message at 816.

[0161] At 918, the source base station may transmit an SN status transmission message to the target base station. For example, the SN status transmission message may include the next PDU of the MBS session to be received by the UE (such as Figure 9 For example, the PDCP status report may include the SN immediately following the SN of the last PDU (eg, PDU 4) of the MBS session received by the UE before 916.

[0162] In response to the RRC reconfiguration message at 916, the UE may move the RRC connection to the target base station and may transmit an indication of RAN handover completion to the target base station at 924. For example, the UE may synchronize with the target base station and transmit an RRCReconfigurationComplete message. Because 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 916.

[0163] The transmission at 924 may also include a PDCP status report. For example, the PDCP status report may include any discarded or lost PDUs for the MBS session (such as Figure 9 SN or other indication of PDU 3) in the scenario.

[0164] At 926, the target base station may transmit a handover success message to the source base station. In some scenarios, the handover success message may be similar to Figure 6 The switching success message 630 is displayed.

[0165] Once the RRC reconfiguration is completed at the UE, the target base station may begin transmitting communications for the MBS session to the UE. Figure 9 Shown with Figure 8 The same two possible scenarios; one scenario is shown by 928, which is equivalent to 828, and the other scenario is shown by 930-932, which is equivalent to 830-832.

[0166] It should be noted that because the MBS session is configured and enabled before the handover begins, the source base station does not need to forward the MBS data to the target base station. Instead, the target base station may transmit or retransmit any of the MBS PDUs 3, 5-10 to the UE based on the data received from the UPF at 908. Similarly, there is no need to perform operations such as Figure 7 The path switching process shown at 722.

[0167] Figure 10 - Data forwarding from source gNB to target gNB without configured MBS session

[0168] Figure 10 A signal flow diagram is shown for data forwarding from a source base station to a target base station during an MBS handover for an MBS session not previously enabled on the target base station, according to some embodiments. Figure 10 106), a source base station and a target base station (such as base station 102), and one or more UPFs of the core network. Figure 10 The process illustrates an example in which an MBS session to which the UE is subscribed in the source cell is not configured and enabled in the target base station according to some embodiments.

[0169] like Figure 10 As shown, the UE may establish an RRC connection with the source base station at 1002. At 1004, the source base station may receive data for the MBS session from the UPF. For example, the data may include data to be transmitted by the source base station as PDUs 1-4, 1-7. In some scenarios, the source base station may Figure 10 Additional data for the MBS session is received at other times during the process.

[0170] At 1006, the source base station may transmit one or more MBS PTM communications to the UE (and to other UEs subscribed to the MBS session), the one or more MBS PTM communications including at least a portion of the data for the MBS session received at 1004. Figure 10 In the example of , the MBS PTM communication may include 4 PDUs with sequence numbers 1 - 4. In this example, PDUs 1, 2, and 4 are successfully received, but PDU 3 is discarded.

[0171] In some scenarios, the signals shown at 1002-1006 may be Figure 9 The signals shown at 902-906 are similar or identical to those shown at 902-906. Figure 10 In the scenario, the MBS session is not configured or enabled in the target base station.

[0172] At 1012, the source base station and the target base station may perform MBS handover preparation. In some scenarios, this may include something like Figure 7 Specifically, because the MBS session has not yet been configured and enabled in the target base station, the MBS session establishment (as shown at 708 ) may be performed, for example, in response to a handover request message such as shown at 706 .

[0173] At 1016, the source base station may transmit an RRC reconfiguration message with synchronization parameters to the UE. 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 identical to the RRC reconfiguration message at 816.

[0174] At 1018, the source base station may transmit an SN status transmission message to the target base station. For example, the SN status transmission message may include the next PDU of the MBS session to be received by the UE (such as Figure 10 For example, the PDCP status report may include the SN immediately following the SN of the last PDU (eg, PDU 4) of the MBS session received by the UE before 1016.

[0175] As noted in the previous example, these PDUs may be retransmitted to the UE after the handover is complete because, 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. However, because the MBS session establishment is performed during handover preparation, the target base station does not receive MBS data transmitted before that point, such as PDUs 1-7, from the UPF. Therefore, at 1020, the source base station may forward to the target base station any MBS PDUs (or applicable MBS data) transmitted by the source base station after the RRC reconfiguration message at 1016, such as Figure 10 In the example, PDUs 5-7 are shown.

[0176] Additionally, at 1022, the target base station may receive subsequent data for the MBS session from the UPF, such as Figure 10 The UPF may transmit data at least in part in response to the MBS session establishment at 1014.

[0177] Once the RRC reconfiguration is completed at the UE, the UE may transmit an indication of RAN handover completion to the target base station at 1024. For example, the UE may synchronize with the target base station and transmit an RRCReconfigurationComplete message.

[0178] The transmission at 1024 may also include a PDCP status report. For example, the PDCP status report may include any discarded or lost PDUs for the MBS session (such as Figure 10 SN or other indication of PDU 3) in the scenario.

[0179] At 1026, the target base station may transmit a handover success message to the source base station. In some scenarios, the handover success message may be similar to Figure 6 The handover success message 630 is sent. In some scenarios, the handover success message 1026 may include instructions or indications for the source base station to stop forwarding MBS data. The handover success message may be at least partially responsive to the RRC reconfiguration complete message 1024 and may also be at least partially responsive to receiving the data for the MBS session at 1022.

[0180] Once the RRC reconfiguration is completed at the UE, the target base station may begin transmitting communications for the MBS session to the UE. Figure 10 Shown with Figure 8 The same two possible scenarios; one scenario is shown by 1028, which is equivalent to 828, and the other scenario is shown by 1030-1032, which is equivalent to 830-832.

[0181] PDCP SN synchronization

[0182] exist Figures 8 to 10 In each of the examples, the source base station may communicate to the target base station any discarded packets and / or the SN (e.g., DL PDCP SN) of the next MBS PDU to be transmitted to the UE. To make the SN provided by the source base station meaningful to the target base station, the source base station may synchronize PDCP SN allocation with the target base station. This may be achieved by configuring each base station to assign a PDCP SN to each PDU based on information received from the UPF, for example, during MBS session establishment or during MBS session data transmission.

[0183] As a first example, when transmitting a PDU carrying MBS data, the base station may assign a PDCP SN based on 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 equal to (or based on) the PDU header of the MBS packet. Alternatively, the base station may set the PDCP SN 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, the source base station and the target base station will assign the same PDCP SN to the packet, allowing the source base station to identify the packet to the target base station by reference to its PDCP SN.

[0184] As another example, the base station may assign a PDCP SN based on the order of received packets, 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 to be transmitted to the source base station in an MBS session. For example, the PDCP SN may be indicated in the header of the first MBS packet transmitted to the source base station in an MBS session (for example, in a spare field of the PDU header) during MBS session establishment or in the header of the first MBS packet transmitted to the source base station in an MBS session. Both the UPF and the source base station may then 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, where the PDCP SN to be used is consistent with the PDCP SN number indicated to the source gNB; for example, the PDCP SN to be used is the PDCP SN resulting from numbering the PDUs starting from the first MBS packet transmitted to the source base station in the MBS session. Therefore, the target base station will assign a PDCP SN assigned by the UPF based on the sequence number of the PDU, which will be the same PDCP SN assigned to the packet by the source base station. After the first PDU, the target base station will also increment the PDCP SN for each subsequent PDU. Once again, the source base station can identify each packet to the target base station by reference to its PDCP SN. Specific embodiments

[0186] The following are specific examples of specific implementations consistent with the above description. Within the full scope of the above description, other different embodiments are also envisioned.

[0187] 1. In some embodiments, a method for performing communication of a multicast and broadcast service (MBS) session includes: a target base station of a wireless communication network receiving a request to initiate handover of the MBS session for a user equipment (UE) from the source base station to the target base station from a remote base station of the wireless communication network; receiving an indication of a next protocol data unit (PDU) of the MBS session to be received by the UE; and transmitting a peer-to-peer (PTP) message including the next PDU of the MBS session to the UE, wherein the next PDU of the MBS session was previously transmitted by the source base station via a point-to-multipoint (PTM) message after the request to initiate the handover.

[0188] 2. In some embodiments according to Example 1, the method further includes: receiving an indication of a discarded PDU of the MBS session from the UE, wherein the discarded PDU was transmitted by the source base station but was not correctly received by the UE; and transmitting a peer message including the discarded PDU to the UE.

[0189] 3. In some implementations of embodiment 2, the indication of the next PDU and the indication of the discarded PDU are received from the UE in a Packet Data Convergence Protocol (PDCP) status report.

[0190] 4. In some implementations according to embodiment 1, an indication of the next PDU is received from the source base station.

[0191] 5. In some embodiments according to any one of Examples 1 to 4, the method further includes: determining whether to transmit subsequent PDUs of the MBS session via peer-to-peer messaging or point-to-multipoint messaging based at least in part on the number of UEs subscribed to the MBS session served by the target base station.

[0192] 6. In some implementations according to any one of Examples 1 to 5, the method further includes: establishing the MBS session with the core network element of the wireless communication network in response to receiving the request to initiate the handover; receiving at least one PDU of the MBS session to be forwarded to the UE from the source base station, the at least one PDU including the next PDU of the MBS session; and after receiving the next PDU, receiving a subsequent PDU of the MBS session from the core network element.

[0193] 7. In some implementation schemes according to Example 6, the method further includes: receiving an indication from the UE that the MBS switching reconfiguration at the UE is complete; and in response to receiving the indication that the MBS switching reconfiguration at the UE is complete, and after establishing the MBS session with the core network element, providing an instruction to the source base station to stop forwarding the PDU of the MBS session.

[0194] 8. In some implementations according to Example 7, the method further includes: before receiving an indication of completion of the MBS switching reconfiguration at the UE, forwarding each PDU of the at least one PDU of the MBS session received from the source base station to the UE via at least one PTP message.

[0195] 9. In some implementations of any one of Examples 1 to 5, the method further comprises: establishing the MBS session with a core network element of the wireless communication network, wherein the MBS session is established before receiving the request to initiate the handover.

[0196] 10. In some embodiments according to any one of Examples 1 to 9, the method further includes: receiving an indication of a sequence number of a designated PDU to be assigned to the MBS session from a core network element of the wireless communication network; and assigning sequential sequence numbers to PDUs following the designated PDU.

[0197] 11. In some embodiments according to any one of Examples 1 to 9: receiving an MBS packet including MBS payload data for the MBS session from a core network element of the wireless communication network, the MBS packet having a packet sequence number; and transmitting a packet including 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.

[0198] 12. In some embodiments, a target base station of a wireless communication network includes: a wireless communication circuit; and a processor circuit, the processor circuit being communicatively connected to the wireless communication circuit, the processor circuit being configured to cause the target base station to perform the steps described in any one of Examples 1 to 11.

[0199] 13. In some embodiments, an apparatus includes: a processor configured to cause a target base station to perform the steps according to any one of embodiments 1 to 11.

[0200] 14. In some embodiments, an apparatus comprises: means for performing the steps of any one of embodiments 1 to 11.

[0201] 15. In some embodiments, a method for performing communications for a multicast and broadcast service (MBS) session includes: a wireless communication device receiving a multicast transmission including at least one data packet of a multicast session from a first base station of a wireless network; receiving an instruction from the first base station to perform a switch to a second base station of the wireless network; in response to receiving the instruction, stopping receiving transmissions from the first base station and establishing a connection with the second base station; and receiving a unicast transmission from the second base station, the unicast transmission including a next sequential data packet of the multicast session after the last data packet of the multicast session received from the first base station, wherein 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.

[0202] 16. In some implementations of embodiment 15, the method further comprises: transmitting an identifier of the next sequential packet to the second base station before receiving the unicast transmission.

[0203] 17. In some embodiments according to any one of Examples 15 to 16, the method further includes: receiving a unicast transmission of discarded data packets of the multicast session from the second base station, wherein the discarded data packets were included in the multicast transmission from the first base station before the instruction for performing the switching, but were not correctly received by the UE.

[0204] 18. In some implementations of embodiment 17, the method further comprises: transmitting an identifier of the discarded data packet to the second base station before receiving the unicast transmission including the discarded data packet.

[0205] 19. In some implementations of any one of embodiments 15 to 18, the method further comprises: receiving a multicast transmission comprising at least one data packet of the multicast session from the second base station.

[0206] 20. In some embodiments of any one of embodiments 15 to 19, the instructions for performing the handover to the second base station include configuration information for establishing a connection with the second base station for multicast transmission.

[0207] 21. In some embodiments, a wireless communication device operating in a wireless communication network includes: a wireless communication circuit; and a processor circuit, the processor circuit being communicatively connected to the wireless communication circuit, the processor circuit being configured to cause the wireless communication device to perform the steps described in any one of Examples 15 to 20.

[0208] 22. In some embodiments, an apparatus comprises: a processor configured to cause a wireless communication device to perform the steps of any one of embodiments 15 to 20.

[0209] 23. In some embodiments, an apparatus comprises: means for performing the steps of any one of embodiments 15 to 20.

[0210] 24. In some embodiments, a method for performing communication of a multicast and 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); in response to determining to initiate a switching process to switch the UE to a second base station of the wireless communication network, transmitting an instruction for performing the switching to the UE; after transmitting the instruction, providing an indication of a next packet of the MBS session to be transmitted to the UE to the second base station; after transmitting the instruction, starting to forward packets of the MBS session to be transmitted to the UE to the second base station, the forwarded packets of the MBS session including the next packet; and in response to receiving an indication of completion of the switching from the second base station, stopping forwarding the packets of the MBS session.

[0211] 25. In some implementations of embodiment 24, the method further comprises providing a handover request including information about the MBS session to the second base station.

[0212] 26. In some implementations according to Example 25, the method further includes: receiving a handover request confirmation message indicating MBS session configuration information of the second base station from the second base station; and including the MBS session configuration information of the second base station in the instruction for performing the handover.

[0213] 27. In some embodiments, a first base station operating in a wireless communication network includes: a wireless communication circuit; and a processor circuit, the processor circuit being communicatively connected to the wireless communication circuit, the processor circuit being configured to cause the first base station to perform the steps described in any one of Examples 24 to 26.

[0214] 28. In some embodiments, an apparatus comprises: a processor configured to cause a first base station to perform the steps of any one of embodiments 24 to 26.

[0215] 29. In some embodiments, an apparatus comprises: means for performing the steps of any one of embodiments 24 to 26.

[0216] It is understood that the use of personally identifiable information should be subject to privacy policies and practices that are generally recognized to meet or exceed industry or government requirements for maintaining user privacy. Specifically, personally identifiable information data should be managed and processed to minimize the risk of unintentional or unauthorized access or use, and the nature of authorized use should be clearly stated to users.

[0217] By interpreting each message / signal X received by a user equipment (UE) in the downlink as a message / signal X transmitted by the base station, and interpreting each message / signal Y transmitted by the UE in the uplink as a message / signal Y received by the base station, any of the methods for operating a UE described herein may become the basis for the corresponding method for operating a base station.

[0218] The 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-implemented 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 ASICs. In other embodiments, the subject matter may be implemented using one or more programmable hardware elements such as FPGAs.

[0219] In some embodiments, a non-transitory computer-readable storage medium (e.g., a non-transitory memory element) may be configured such that it stores program instructions and / or data, wherein the program instructions, if 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 any method embodiments described herein, or any combination of such subsets.

[0220] In some embodiments, a device (e.g., a UE) may be configured to include a processor (or a group of processors) and a memory medium (or a memory element), wherein the memory medium stores program instructions, wherein the processor is configured to read and execute the program instructions from the memory medium, wherein the program instructions are executable to implement any of the various method implementations described herein (or any combination of the method implementations described herein, or any subset of any method implementations described herein, or any combination of such subsets). The device may be implemented in any of various forms.

[0221] Although the above embodiments have been described in considerable detail, numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. It is intended that the following claims be interpreted to encompass all such variations and modifications.

Claims

1. A method of performing communication for a Multicast and Broadcast Service (MBS) session, the method comprising: By the target base station of the wireless communication network: receiving, from a source base station of the wireless communication network, a request to initiate 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; receiving an indication of discarded PDUs for the MBS session from the UE, wherein the discarded PDUs were transmitted by the source base station but were not correctly received by the UE; as well as One or more peer-to-peer (PTP) messages including the next PDU of the MBS session and the discarded PDU are transmitted to the UE, wherein the next PDU of the MBS session was previously transmitted by the source base station via a point-to-multipoint (PTM) message after the request to initiate the handover. 2 . The method of claim 1 , wherein the indication of the next PDU and the indication of the discarded PDU are received from the UE in a Packet Data Convergence Protocol (PDCP) status report. The method of claim 1 , wherein the indication of the next PDU is received from the source base station.

4. The method according to claim 1, further comprising: Whether to transmit subsequent PDUs of the MBS session via peer-to-peer messaging or via point-to-multipoint messaging is determined based at least in part on a number of UEs subscribed to the MBS session served by the target base station.

5. The method according to claim 1, further comprising: 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 forwarded to the UE, the at least one PDU including the next PDU of the MBS session; as well as After receiving the next PDU, subsequent PDUs for the MBS session are received from the core network element.

6. The method according to claim 5, further comprising: receiving, from the UE, an indication that the MBS handover reconfiguration at the UE is complete; as well as In response to receiving an indication of MBS handover reconfiguration completion at the UE, and after establishing the MBS session with the core network element, providing an instruction to the source base station to stop forwarding PDUs of the MBS session.

7. The method according to claim 6, further comprising: Prior to receiving an indication of MBS handover reconfiguration completion at the UE, each PDU of the at least one PDU of the MBS session received from the source base station is forwarded to the UE via at least one PTP message.

8. The method according to claim 1, further comprising: The MBS session is established with a core network element of the wireless communication network, wherein the MBS session is established before receiving the request to initiate the handover.

9. The method according to claim 1, further comprising: receiving, from a core network element of the wireless communication network, an indication of a sequence number of a designated PDU to be allocated to the MBS session; as well as Sequential sequence numbers are assigned to PDUs following the designated PDU.

10. The method according to claim 1, further comprising: receiving, from a core network element of the wireless communication network, an MBS packet including MBS payload data for the MBS session, the MBS packet having a packet sequence number; as well as A packet including the MBS payload data is transmitted 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.

11. An apparatus for wireless communication, the apparatus comprising: A processor configured to cause a wireless communication device to: receiving a multicast transmission comprising at least one data packet of a multicast session from a first base station of the wireless network; receiving an instruction from the first base station to perform a handover to a second base station of the wireless network; in response to receiving the instruction, cease receiving transmissions from the first base station and establish a connection with the second base station; transmitting an identifier of a discarded data packet to the second base station, wherein the discarded data packet was included in a multicast transmission from the first base station prior to the instruction to perform the handover but was not properly received by the wireless communication device; as well as receiving at least one unicast transmission from the second base station, the at least one unicast transmission including a next sequential data packet for the multicast session following a last data packet for the multicast session received from the first base station and the discarded data packet, wherein the next sequential data packet was previously included in a multicast transmission from the first base station after the wireless communication device ceased receiving transmissions from the first base station.

12. The apparatus of claim 11 , wherein the processor is further configured to cause the wireless communication device to: An identifier of the next sequential packet is transmitted to the second base station prior to receiving the unicast transmission.

13. The apparatus of claim 11 , wherein the processor is further configured to cause the wireless communication device to: A multicast transmission including at least one data packet for the multicast session is received from the second base station.

14. The apparatus of claim 11, wherein the instructions for performing the handover to the second base station include configuration information for establishing a connection with the second base station for multicast transmission.

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