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

Abstract

Techniques for improving service continuity for multicast broadcast service (MBS) communications during handover are described. Techniques are included that support hitless handover and data transfer during handover for peer-to-multiple (PTM) MBS transmissions. Hitless handover can be achieved in part by a user equipment (UE) providing a target base station with an indication of the next packet of an MBS session to be received following an RRC reconfiguration message and an indication of an MBS packet that was provided by the source base station but not properly received by the UE prior to the RRC reconfiguration message. If an MBS session is not established on the target base station before handover, data transfer from the source base station to the target base station can be performed. If an MBS session is established on the target base station before handover, data transfer can be omitted.

Description

[Technical field]

[0001] This application relates to wireless communications, and more particularly to systems, apparatus, and methods for improving service continuity for Multicast and Broadcast Services (MBS) communications. [Background technology]

[0002] The use of wireless communication systems is growing rapidly. In recent years, wireless devices such as smartphones and tablet computers have become increasingly sophisticated. Many mobile devices (i.e., user equipment devices, or UEs) now not only support telephony, but also provide access to the Internet, e-mail, text messaging, and navigation using the Global Positioning System (GPS), and are capable of running sophisticated applications that utilize these features. In addition, there are many different wireless communication technologies and 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™, and the like.

[0003] One aspect of cellular communication systems involves Multicast Broadcast Service (MBS) communication, and thus improvements in this area are desirable. Summary of the Invention

[0004] Presented herein are embodiments of an apparatus, system, and method that improve Multicast Broadcast Service (MBS) communications with service continuity during handover.

[0005] A method for performing communication of a Multicast Broadcast Service (MBS) session is disclosed, in which 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 a 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 to the UE a peer-to-peer (PTP) message including a next PDU of the MBS session, the next PDU of the MBS session having been previously transmitted by the source base station via a peer-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 for the MBS session from the UE, where the dropped PDU was sent by the source base station but not properly received by the UE, and the target base station may send a peer-to-peer message to the UE that includes the dropped PDU.

[0007] In some scenarios, the next PDU indication and the dropped PDU indication 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 for the MBS session via peer-to-peer messages or peer-to-multiple messages based at least in part on the number of UEs served by the target base station that subscribe to the MBS session.

[0010] In some scenarios, the target base station may establish the MBS session with a core network element of the wireless communication network in response to receiving the request to initiate handover. The target base station may receive 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 a next PDU of the MBS session. After receiving the next PDU, the target base station may subsequently receive a subsequent PDU 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 MBS handover reconfiguration at the UE is complete. In response to receiving the indication that MBS handover reconfiguration at the UE is complete, the target base station may provide instructions to the source base station to stop forwarding PDUs for the MBS session subsequent to establishing the MBS session with the core network element.

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

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

[0014] In some scenarios, the target base station may receive an indication from a core network element of the wireless communication network of a sequence number to be assigned to a designated PDU of the MBS session, and the target base station may assign sequential sequence numbers to PDUs following the designated PDU.

[0015] In some scenarios, the target base station may receive 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 the target base station may transmit the packet including the MBS payload data to the UE, the packet sequence number of the MBS packet being used as a 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 the method, a wireless communication device may receive a multicast transmission from a first base station of a wireless network, the multicast transmission including at least one data packet of the multicast session. 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 the transmission 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 a next successive data packet of the multicast session following a last data packet of the multicast session received from the first base station, where the next successive data packet was previously included in the multicast transmission from the first base station after the wireless communication device stopped receiving the transmission from the first base station.

[0017] In some scenarios, the wireless communications 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 the second base station that includes dropped data packets of a multicast session, the dropped data packets being included in the multicast transmission from the first base station prior to the command to perform the handover but not properly received by the UE.

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

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

[0021] In some scenarios, the instructions 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 the method, a first base station of a wireless communication network may transmit a multicast transmission to a user equipment (UE) including at least one data packet of the multicast session. 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. Subsequent to transmitting the instruction, the first base station may transmit to the second base station an indication of a next packet of the MBS session to be transmitted to the UE. Subsequent to transmitting the instruction, the first base station may start 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. In response to receiving an indication from the second base station that the handover is completed, the first base station may stop forwarding packets of the MBS session.

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

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

[0025] Devices, apparatus and systems for carrying out any of the aforementioned methods are also disclosed.

[0026] It should be noted that the techniques described herein may be implemented in and / or used in conjunction with many different types of devices, including, but not limited to, base stations, access points, cellular telephones, portable media players, tablet computers, wearable devices, unmanned aerial vehicles, unmanned aerial controllers, automobiles and / or motor vehicles, and various other computing devices.

[0027] This Summary is intended to provide a brief overview of some of the subject matter described in this document. It should therefore 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 herein. Other features, aspects, and advantages of the subject matter described herein will become apparent from the following detailed description, drawings, and claims. [Brief description of the drawings]

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

[0029] [Figure 1] FIG. 1 illustrates an exemplary (and simplified) wireless communication system according to some embodiments.

[0030] [Diagram 2] FIG. 1 illustrates an exemplary base station in communication with an exemplary wireless user equipment (UE) device, in accordance with some embodiments.

[0031] [Diagram 3] 1 is an example block diagram of a UE in accordance with some embodiments.

[0032] [Figure 4] 1 is an exemplary block diagram of a base station according to some embodiments.

[0033] [Diagram 5]1 is a block diagram of an MBS architecture and distribution method according to some embodiments.

[0034] [Figure 6] 1 is a signal flow diagram of a conventional handover procedure according to some embodiments.

[0035] [Figure 7] 1 is a signal flow diagram of a conventional MBS handover procedure according to some embodiments.

[0036] [Figure 8] 1 is a signal flow diagram for hitless handover of MBS transmission according to some embodiments.

[0037] [Figure 9] 1 is 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 previously enabled on both base stations, according to some embodiments.

[0038] [Figure 10] 1 is 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 not previously activated on the target base station, according to some embodiments.

[0039] While the features described herein are susceptible to various modifications and alternative forms, specific embodiments thereof have been 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 are not intended to limit the invention to the particular forms disclosed, but rather to cover all modifications, equivalents, and alternatives within the spirit and scope of the present subject matter as defined by the appended claims. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0040] acronym Various acronyms are used throughout this disclosure. Definitions of the most prominently used acronyms that may appear throughout this disclosure are provided below: ●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 / Receive ● TX: Send / Transmit ●UE: User Equipment ●UL: Uplink ●UMTS: Universal Mobile Telecommunications System ●UPF: User Plane Function term Below is a description of terms that may appear in this disclosure.

[0041] Memory medium - any of various types of non-transitory memory or storage devices. The term "memory medium" is intended to include, for example, installation media such as CD-ROM, floppy disk, or tape devices; computer system memory or random access memory such as DRAM, DDR RAM, SRAM, EDO RAM, Rambus RAM; non-volatile memory such as flash, magnetic media such as hard drives, or optical storage, registers, or other similar types of memory elements, and the like. Storage media may include other types of non-transitory memory, or combinations thereof. In addition, the memory medium may be located in a first computer system where the program is executed, or in a second, different computer system that connects to the first computer system via a network such as the Internet. In the latter case, the second computer system can provide the first computer system with program instructions to execute. 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 (e.g., embodied as a computer program) that can be executed by one or more processors.

[0042] Carrier Medium - memory media as described above, as well as physical transmission media such as a bus, network, and / or other physical transmission medium that carries signals, such as electrical, electromagnetic, or digital signals.

[0043] 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 device, an Internet appliance, a personal digital assistant (PDA), a television system, a grid computing system, or any other device or combination of devices. In general, the term "computer system" may be broadly defined to encompass 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 communications. Examples of UE devices include mobile phones or smartphones (e.g., iPhone™, Android™ based phones), tablet computers (e.g., iPad™, Samsung Galaxy™), portable gaming devices (e.g., Nintendo DS™, PlayStation Portable™, Gameboy Advance™, iPhone™), wearable devices (e.g., smart watches, 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), unmanned aerial controllers (UACs), and the like. In general, the term "UE" or "UE device" may be broadly defined to encompass any electronic, computing, and / or telecommunications device (or combination of devices) that is easily carried by a user and capable of wireless communications.

[0045] Wireless Device - any of various types of computer systems or devices that perform wireless communications. A wireless device can be portable (or mobile) or may be stationary or fixed to a location. A UE is an example of a wireless device.

[0046] Communications Device - Any of various types of computer systems or devices that perform communications, which may be wired or wireless. A communications device may be portable (or mobile) or may be stationary or fixed to a particular location. A wireless device is one example of a communications device. A UE is another example of a communications device.

[0047] Base Station (BS) - The term "base station" has all of its ordinary meanings and includes at least a wireless communication station that is installed at a fixed location and used for communication as part of a wireless telephone 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. A processing element may include, for example, a processor and associated memory, a portion or circuitry 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 the various combinations of the above.

[0049] Wi-Fi - The term "Wi-Fi" has the full scope of its 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. 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.

[0050] Automatically - refers to an action or operation being performed by a computer system (e.g., software executed by a computer system) or device (e.g., circuit mechanisms, programmable hardware elements, ASICs, etc.) without user input directly specifying or executing the action or operation. Thus, the term "automatically" is in contrast to an operation that is manually performed or specified by a user, where the user provides input to directly perform the operation. An automatic procedure may be initiated by input provided by a user, but the subsequent actions that are performed "automatically" are not specified by the user; that is, they are not performed "manually" with the user specifying 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, selecting radio selections, etc.) is considered to be manually filling out the form, even though the computer system must update the form in response to the user actions. A form may be filled out automatically by a computer system, where the computer system (e.g., software executed by the computer system) analyzes the fields of the form and fills out the form without user input specifying answers to the fields. As noted above, a user can invoke automatic filling of a form, but is not involved in the actual filling of the form (e.g., the user does not manually specify answers in fields, but rather the answers are automatically completed). This specification provides various examples of operations that are automatically performed in response to actions taken by a user.

[0051] Configured to - Various components may be described as "configured to" perform a task. In such contexts, "configured to" is a broad description that generally means "having a structure" to perform a 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 that generally means "having circuitry" to perform a task or tasks during operation. Thus, a component may be configured to perform a task even when the component is not currently on. In general, the circuitry that forms the structure corresponding to "configured to" may include hardware circuitry.

[0052] In the description herein, for convenience, various components may be described as performing a task or tasks. Such descriptions should be construed to include the phrase "configured to." It is expressly intended that the description of a component as being configured to perform one or more tasks does not apply to the interpretation of that component under 35 U.S.C. § 112, sixth paragraph. FIG. 1 and FIG. 2—An exemplary communication system

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

[0054] As shown, the 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. through 106N over a transmission medium. Each of the user devices may be referred to herein as a "user equipment" (UE) or a UE device. Accordingly, the user devices 106 are referred to as UEs or UE devices.

[0055] The base station 102 may be a base transceiver station (BTS) or cell site and may include hardware and / or software to enable wireless communication with the UEs 106A-106N. If the base station 102 is implemented in the context of LTE, it may alternatively be referred to as an "eNodeB" or "eNB". If the base station 102 is implemented in the context of 5G NR, it may alternatively be referred to as a "gNodeB" or "gNB". The base station 102 may also be equipped to communicate with the 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 other possibilities). Thus, the base station 102 may facilitate communication between user devices and / or between the user devices and the network 100. A communication area (or coverage area) of a base station may be referred to as a "cell". Also, as used herein, from the perspective of a UE, the base station may be considered to represent a network as far as the UE's uplink and downlink communications 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 stations 102 and user devices 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 telecommunications 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] Thus, base station 102 and other similar base stations operating according to the same or different cellular communication standards may be provided as one or more networks of cells that may provide continuous or near-continuous overlapping service to UE 106 and similar devices over a geographic area via one or more cellular communication standards.

[0058] It should be noted that the UE 106 may be 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 or 3GPP2 cellular communication standards. In some embodiments, the UE 106 may be configured to perform techniques to support service continuity during MBS handover, such as in accordance with various methods described herein. The UE 106 may also or alternatively be configured to communicate using WLAN, BLUETOOTH™, 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] FIG. 2 illustrates an exemplary user equipment 106 (e.g., one of devices 106A-106N) in communication with a base station 102, according to some embodiments. The UE 106 may 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 aircraft controller (UAC), or virtually any type of wireless device. The UE 106 may include a processor (processing element) configured to execute program instructions stored in a memory. The UE 106 may perform any of the method embodiments described herein by executing such stored instructions. Alternatively or in addition, the UE 106 may include a programmable hardware element, such as a Field Programmable Gate Array (FPGA), an integrated circuit, and / or any of a variety of other possible hardware components configured to perform any of the method embodiments described herein, or any portion of any of the method embodiments described herein (e.g., individually or in combination). The UE 106 may be configured to communicate using any of a number of wireless communication protocols. For example, the 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] The 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, the UE 106 may share one or more portions of a receive chain and / or a transmit chain between multiple wireless communication standards. A shared radio may include a single antenna or multiple antennas (e.g., for MIMO) for performing wireless communication. In general, a radio may include any combination of a baseband processor, analog RF signal processing circuitry (e.g., including filters, mixers, oscillators, amplifiers, etc.), or digital processing circuitry (e.g., for digital modulation and other digital processing). Similarly, a radio may perform one or more receive and transmit chains using the hardware described above.

[0061] In some embodiments, the UE 106 may include a separate transmit and / or receive chain (e.g., including separate antennas and other radio components) for each wireless communication protocol over which the UE 106 is configured to communicate. As a further possibility, the UE 106 may include one or more radios shared among multiple wireless communication protocols and one or more radios used exclusively by a single wireless communication protocol. For example, the UE 106 may include a shared radio for communicating using either LTE or CDMA2000 1xRTT (or LTE or NR or LTE or GSM) and a separate radio for communicating using each of Wi-Fi and BLUETOOTH™. Other configurations are possible. Figure 3 - Block diagram of an exemplary UE device

[0062] FIG. 3 illustrates a block diagram of an exemplary UE 106, according to some embodiments. As illustrated, the UE 106 may include a system on chip (SOC) 300, which may include portions for a variety of purposes. For example, as illustrated, the SOC 300 may include a processor(s) 302, which may execute program instructions for the UE 106, and a display circuit 304, which may perform graphic processing and provide display signals to a display 360. The SOC 300 may also include a sensor circuit 370, which may include components for sensing or measuring any of a variety of possible characteristics or parameters of the UE 106. For example, the sensor circuit 370 may include a motion sensing circuit configured to detect movement of the UE 106, for example, using a gyroscope, an accelerometer, and / or any of a variety of other motion sensing components. As another possibility, the sensor circuit 370 may include one or more temperature sensing components, for example, for measuring the temperature of one or more antenna panels and / or each of the other components of the UE 106. Any of a variety of other possible types of sensor circuitry may additionally or alternatively be included in the UE 106, as desired. The processor(s) 302 may be coupled to a memory management unit (MMU) 340, which may be configured to receive addresses from the processor(s) 302, translate those addresses to locations in 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 circuitry 304, radio circuitry 330, connector interface (I / F) 320, and / or display 360. The MMU 340 may be configured to perform memory protection and page table translation or setup. In some embodiments, the MMU 340 may be included as part of the processor(s) 302.

[0063] 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 (including, for example, NAND flash 310), a connector interface 320 (for example, for coupling to a computer system, a dock, a charging station, etc.), a display 360, and radio circuitry 330 (for example, for LTE, LTE-A, NR, CDMA2000, BLUETOOTH™, Wi-Fi, GPS, etc.). The UE device 106 may include at least one antenna (e.g., 335a) and possibly multiple antennas (e.g., exemplified by antennas 335a and 335b) for performing wireless communication 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, the one or more antennas are collectively referred to as antennas 335. For example, the UE device 106 may use the antenna 335 and perform wireless communications using the radio circuitry 330. As mentioned above, in some embodiments, the UE may be configured to communicate wirelessly using multiple wireless communication standards.

[0064] The UE 106 may include hardware and software components for implementing methods by which the UE 106 performs techniques for supporting service continuity during a multicast broadcast service (MBS) handover, such as described further below in this specification. The processor(s) 302 of the UE device 106 may be configured to perform 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). Additionally, the processor(s) 302 may be coupled to or interoperate with other components to perform techniques for supporting service continuity during a multicast broadcast service (MBS) handover in accordance with 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 controllers dedicated to 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., LTE-A and / or NR controller) 354, and a BLUETOOTH™ controller 356, where in at least some embodiments, one or more or all of these controllers may be implemented as respective integrated circuits (ICs or chips for short) 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 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 have fewer or more similar controllers for the various different RATs that 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 procedures disclosed herein, or portions thereof. FIG. 4 - Block diagram of an exemplary base station

[0066] 4 illustrates a block diagram of an exemplary base station 102, according to some embodiments. It should be noted that the base station of FIG. 4 is only one example of a possible base station. As shown, the base station 102 includes a processor(s) 404 that may 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 in memory (e.g., memory 460 and read-only memory (ROM) 450) or 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 a plurality of devices, such as the UE device 106, with access to the telephone network as described above in FIGS. 1 and 2. The network port 470 (or additional network ports) may also or alternatively be configured to couple to a cellular network, such as, for example, 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 instances, 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 serviced by the cellular service provider).

[0068] The base station 102 may include at least one antenna 434, and possibly multiple antennas. The antenna(s) 434 may be configured to operate as a wireless transceiver and may be further configured to communicate with the UE device 106 via a 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 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 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, 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 a local area network(s), and may include, for example, 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 more and more popular as a solution to improve resource efficiency when a base station has information to convey to multiple UEs. In some scenarios, a UE subscribing to an MBS session may be served by multiple different base stations and may also move between cells. In legacy systems such as LTE, handover of MBS communication between cells may result in dropped and / or missed MBS packets. However, with the prevalence of MBS, there is a desire to improve the reliability of MBS communication, which may be achieved in part by providing service continuity during handover.

[0070] Unicast communication represents an example of peer-to-peer (PTP) communication from a base station, e.g., base station 102, to a single UE, e.g., UE 106. In contrast, MBS communication represents an example of peer-to-multiple (PTM) communication with a base station, e.g., base station 102, in communication with multiple UEs, e.g., 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 defined group of UEs, e.g., the group of UEs subscribed to a corresponding MBS session.

[0071] FIG. 5 illustrates a block diagram of an MBS architecture and distribution method, such as used in NR, according to some embodiments. As illustrated, a core network (CN) 502 of a wireless communication network (e.g., a cellular provider network) may receive MBS traffic, such as from a content source. The CN 502 may replicate the MBS traffic for distribution to appropriate UEs, such as UEs that subscribe to an MBS session involving the MBS traffic. As illustrated, 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, such as conventional 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 MBS traffic to be distributed to multiple UEs to the RAN 504 (e.g., to a base station of the RAN 504) via a shared transport 506C. When the base station receives the MBS traffic over the shared transport, the base station may determine whether to deliver the MBS traffic over multiple PTP communications to each UE or to deliver the MBS traffic to multiple UEs over an MBS message. The base station may make this determination based on, for example, the number of UEs that should receive the MBS traffic, the reception quality, and / or various other factors.

[0072] For MBS communication, the handover procedure can also leverage existing procedures for PTP communication, such as traditional PDU sessions, although these existing procedures are insufficient by themselves and need to be improved to accommodate MBS communication.

[0073] 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 TS38.300 version 16.3.0, section 9.2.3.2, which is incorporated herein by reference in its entirety as if fully set forth herein. A summary is provided below.

[0074] FIG. 6 illustrates signaling flows between a UE (such as UE 106), source and target base stations (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 a source base station and may exchange user data with the source base station, which 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] At 608-612, the source base station and the target base station may perform handover preparation. Specifically, as shown, at 608, the source base station may send a handover request to the target base station, for example over the Xn interface. In response, the target base station may perform admission control at 610 and may send a handover request acknowledgement message to the source base station at 612. The handover request acknowledgement message may include new RRC settings.

[0080] At 614, the source base station and the UE may exchange one or more messages to initiate 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. Upon completion of these steps, at 628, the UE may provide an indication to the target base station that the RAN handover is complete. For example, the UE synchronizes to the target base station and sends an RRC reconfiguration complete message.

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

[0082] The source base station may receive user data for the UE from the UPF(s) and may forward the user data to the target base station while the handover is in progress, at 624. The target base station may buffer the user data received from the source base station until the handover is complete, at 626.

[0083] After the target base station receives an indication that the RAN handover is complete at 628, the target base station may send a handover success message to the source base station at 630. 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 DL PDCP SN sender state.

[0084] The source base station may continue to receive user data for the UE from the UPF(s) and may forward the user data to the target base station at 634. Since handover reconfiguration is now complete at the UE, the target base station may forward the user data to the UE and receive user data from the UE at 636. The target base station may hand over the user data from the UE to the UPF(s) at 638.

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

[0086] In response, 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 towards the source base station for each PDU session / tunnel and may then release U-plane / TNL resources towards the source gNB, if any. The source base station may forward the end marker packets to the target base station.

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

[0088] At 648, the AMF may acknowledge the path switch request message of 640 with a path switch request acknowledgement message. Upon receiving the path switch request acknowledgement message from the AMF, at 650, the target base station may send a UE context release message to inform the source base station about the success of the handover. The source base station may then release the radio and C-plane related resources associated with the UE context. Any ongoing data transfer may continue.

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

[0090] Second, as described above, upon receiving the handover, the target base station may initiate a path switch at 640. Before the path switch is completed, the CN forwards UE specific data to the source base station, which forwards the packets to the target base station via the Xn interface. Once the path switch is completed, the CN may send an end marker to the source base station and forward the 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 forwarded from the source base station.

[0091] For DRBs not configured with DAPS, the source base station may send an SN state transfer message 622 to the target base station to convey the uplink PDCP SN receiver state and downlink PDCP SN sender 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 state of out-of-sequence UL PDCP SDUs that the UE needs to retransmit in the target cell. The downlink PDCP SN sender state 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. 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 SN STATUS TRANSFER (622) as defined by 3GPP TS 38.423 version 16.3.0, section 9.1.1.4. TIFF0007656699000001.tif70166

[0093] Table 2 defines the fields of the information element (IE) “List of DRBs to be transferred” shown in Table 1. TIFF0007656699000002.tif251170

[0094] Figure 7 illustrates a signal flow diagram of a conventional MBS handover procedure according to some embodiments. Figure 7 illustrates signal flow between a UE (such as UE 106), source and target base stations (such as base station 102), an AMF of a core network, and one or more UPF(s) of the core network.

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

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

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

[0098] At 712, the source base station may forward an RRC reconfiguration message including the 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 in response to the RRC reconfiguration message at 712 and may provide an indication to the target base station that the RAN handover is complete at 716. For example, the UE synchronizes to the target base station and sends an RRC reconfiguration complete message.

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

[0101] After the target base station receives an indication that the RAN handover is complete at 716, the target base station may negotiate a path switching procedure with the AMF at 722, e.g., to trigger the core network to switch the DL data path towards the target base station and 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] Once the path switching procedure is complete, the target base station may send a UE context release message to inform the source base station about the success of the handover, at 724. The source base station may then release resources associated with the UE context.

[0103] In some scenarios, the source base station may continue to transmit an MBS communication for the UE, e.g., at 716 or 724, until the handover is complete. However, similar to the scenario shown in Figure 6, upon receiving the RRC reconfiguration message at 712, the UE may stop receiving the MBS communication from the source base station.

[0104] At 726, the UE may transmit a PDCP status report to the target base station, e.g., indicating the PDU(s) lost during the PTP / PTM transmission of 718. In response, at 728, the target base station may retransmit the lost PDU(s) via a unicast (PTP) message to the UE. However, the procedure of Figure 7 does not provide for identifying or retransmitting via the target base station the PDU(s) lost prior to 712. The procedure of Figure 7 also does not provide for identifying or retransmitting via the target base station the PDU(s) missed during handover. Figure 8 - Hitless handover for MBS transmission

[0105] FIG. 8 illustrates a signal flow diagram for hitless handover for MBS transmission according to some embodiments. Specifically, in the example scenario of FIG. 8, the NW performs retransmission of the missed MBS packet in the target cell via PTP communication. New data transmission for the same MBS session / MBS DRB in the target cell may be transmitted via either PTM or PTP communication. PDU information for retransmission may be based on UE PDCU status report after the UE accesses the target cell. FIG. 8 illustrates a specific scenario of an MBS handover procedure similar to the procedure illustrated in FIG. 7.

[0106] It should be appreciated that some of the signal flows have been simplified in Figure 8 to clearly focus attention on the details pertaining to this example, although in some implementations the broad arrows shown in Figure 8 may represent multiple communications similar to those shown in similar locations in Figure 7, for example.

[0107] FIG. 8 illustrates the signal flow between a UE (such as UE 106) and a source base station and a target base station (such as base station 102).

[0108] As shown in Figure 8, at 802, a UE may establish an RRC connection with a source base station. At 806, the source base station may send one or more MBS PTM communications for the MBS session to the UE (and to other UEs subscribing to the MBS session). Specifically, in the example of Figure 8, the MBS PTM communication may include four PDUs having sequence numbers 1 through 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] The source base station and the target base station may perform MBS handover preparation at 812. In some scenarios, this may include steps similar to 706-710 in FIG.

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

[0111] The UE may move the RRC connection to the target base station in response to the RRC reconfiguration message at 816 and may send an indication to the target base station that the RAN handover is complete at 824. For example, the UE synchronizes to the target base station and sends an RRC reconfiguration complete message. As 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] The 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 a PDU(s) of the MBS session that was dropped or missed, such as PDU 3 in the scenario of Figure 8. As another example, the PDCP status report may include the SN or other indication of the next PDU of the MBS session that should be received by the UE, such as PDU 5 in the scenario of Figure 8. For example, the PDCP status report may include the SN immediately following the SN of the last PDU of the MBS session (e.g., PDU 4) that was received by the UE prior to 816.

[0113] Once the RRC reconfiguration is complete at the UE, the target base station may begin transmitting communications for the MBS session to the UE. Figure 8 illustrates two possible scenarios, one indicated by 828 and the other indicated by 830-832.

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

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

[0116] In some implementations, the target base station may dynamically determine whether to transmit 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 FIG. 8 is the only UE (or one of a small number of UEs) receiving the MBS session in the target cell, the target base station may determine to transmit the MBS PDU via PTP communication. However, if some UEs in the target cell are receiving the MBS session, the target base station may determine to transmit the MBS PDU to those some UEs via PTM communication. However, in either case, the PDUs dropped by the UE shown in FIG. 8, along with the PDUs that the UE missed during handover, should be retransmitted only to that UE, not to all UEs in the target cell receiving the MBS session. Therefore, these PDUs may be transmitted via PTP transmission in both the scenarios of 828 and 830. Figure 9 - Data transfer from source gNB with MBS session set up to target gNB

[0117] Figure 9 illustrates 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 previously activated on both base stations, according to some embodiments. Figure 9 illustrates 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 a core network. Specifically, the procedure of Figure 9 illustrates an example where the same MBS session is set up and activated on both the source base station and the target base station, according to some embodiments.

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

[0119] At 906, the source base station may send to the UE (and to other UEs subscribed to the MBS session) one or more MBS PTM communications that include at least a portion of the data for the MBS session received at 904. Specifically, in the example of Figure 9, the MBS PTM communication may include four PDUs having sequence numbers 1 through 4. In this example, PDUs 1, 2, and 4 are successfully received, but PDU 3 is dropped.

[0120] In the scenario of Figure 9, the MBS session is also set up and enabled at the target base station. Thus, 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, although 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 subscribed UEs 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 in Figure 7. Note, however, that since the MBS session is already configured and enabled at the target base station, MBS session establishment (as shown at 708) is not necessary and may be omitted (not performed).

[0122] At 916, the source base station may send an RRC reconfiguration message to the UE along with the 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 or equivalent to the RRC reconfiguration message at 816.

[0123] At 918, the source base station may send an SN state transfer message to the target base station. For example, the SN state transfer message may include the SN or other indication of the next PDU of the MBS session to be received by the UE, such as PDU 5 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., PDU 4) of the MBS session that was received by the UE prior to 916.

[0124] The UE may move the RRC connection to the target base station in response to the RRC reconfiguration message at 916 and may send an indication to the target base station that the RAN handover is complete at 924. For example, the UE may synchronize to the target base station and send an RRC reconfiguration complete message. As 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.

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

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

[0127] Once the RRC reconfiguration is complete at the UE, the target base station may begin transmitting communications for the MBS session to the UE. Figure 9 shows two possible scenarios, the same as Figure 8, one indicated at 928 and equivalent to 828, and the other indicated at 930-932 and equivalent to 830-832.

[0128] Note that since the MBS session is set up and activated before the handover begins, there is no need for the source base station to forward the MBS data to the target base station. Instead, the target base station may transmit or retransmit any of 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 a path switching procedure such as that shown at 722 in FIG. 7. Figure 10 - Data transfer from source gNB to target gNB with no MBS session established

[0129] Figure 10 illustrates 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 not previously activated on the target base station, according to some embodiments. Figure 10 illustrates 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 a core network. Specifically, the procedure of Figure 10 illustrates an example where an MBS session that the UE subscribes to in a source cell is not set up and activated in the target base station, according to some embodiments.

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

[0131] At 1006, the source base station may send to the UE (and to other UEs subscribed to the MBS session) one or more MBS PTM communications that include at least a portion of the data for the MBS session received at 1004. Specifically, in the example of Figure 10, the MBS PTM communication may include four PDUs having sequence numbers 1 through 4. In this example, PDUs 1, 2, and 4 are successfully received, but PDU 3 is dropped.

[0132] In some scenarios, the signals shown at 1002-1006 may be similar or identical to those shown at 902-906 in Figure 9. However, in the scenario of Figure 10, an MBS session has not been established or activated with 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 Figure 7. Specifically, in response to a handover request message, such as that shown at 706, an MBS session establishment (as shown at 708) may be performed, since the MBS session has not yet been set up and enabled at the target base station.

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

[0135] At 1018, the source base station may send an SN state transfer message to the target base station. For example, the SN state transfer message may include the SN or other indication of the next PDU of the MBS session to be received by the UE, such as PDU 5 in the scenario of Figure 10. For example, the PDCP status report may include the SN immediately following the SN of the last PDU (e.g., PDU 4) of the MBS session that was received by the UE prior to 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, so that these PDUs may be retransmitted to the UE following completion of the handover. However, since the MBS session establishment was performed during handover preparation, the target base station has not received MBS data from the UPF, such as PDUs 1-7, transmitted prior to that point in time. Thus, at 1020, the source base station may forward to the target base station the MBS PDUs (or corresponding MBS data) transmitted by the source base station subsequent to the RRC reconfiguration message at 1016, such as PDUs 5-7 in the example of FIG. 10.

[0137] Additionally, at 1022, the target base station may receive subsequent data for the MBS session from the UPF, such as PDUs 8-10 in the example of FIG. 10. The UPF may transmit the data at least in part in response to the MBS session establishment at 1014.

[0138] Once the RRC reconfiguration is complete at the UE, the UE may send an indication that the RAN handover is complete to the target base station at 1024. For example, the UE may synchronize to the target base station and send an RRC reconfiguration complete message.

[0139] The transmission of 1024 may also include a PDCP status report. For example, the PDCP status report may include the SN or other indication of a PDU(s) of an MBS session that was dropped or missed, such as PDU3 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 of FIG. 6. In some scenarios, the handover success message 1026 may include an instruction or direction to the source base station to stop forwarding the 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 data for the MBS session at 1022.

[0141] Once the RRC reconfiguration is complete at the UE, the target base station may begin transmitting communications for the MBS session to the UE. Figure 10 shows two possible scenarios, the same as Figure 8, one indicated by 1028 and equivalent to 828, and the other indicated by 1030-1032 and equivalent to 830-832. PDCP SN synchronization

[0142] In each of the examples of Figures 8-10, 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 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, for example.

[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 was 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 may be able to 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 the MBS session establishment or may be indicated in the header of the first MBS packet transmitted to the source base station in the MBS session (e.g., in a reserved field in 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, where the PDCP SN to be used matches 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 in the MBS session is transmitted to the source base station. As a result, the target base station assigns a UPF-specified PDCP SN that is the same as the PDCP SN that the source base station assigned to the packet based on the PDU sequential number. After the first PDU, the target base station increments the PDCP SN for each subsequent PDU. Again, the source base station may identify each packet to the target base station by referencing its own PDCP SN. Specific Examples

[0145] The following are specific examples of implementations consistent with the foregoing description: Other variations are contemplated within the full scope of the foregoing description.

[0146] 1. In some embodiments, a method for performing communications for a Multicast Broadcast Service (MBS) session includes receiving, by a target base station of a wireless communication network, a request from a remote base station of the wireless communication network 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) for the MBS session to be received by the UE, and transmitting, to the UE, a peer-to-peer (PTP) message including the next PDU for the MBS session, the next PDU having been previously transmitted by the source base station via a peer-to-multiple (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 sent by the source base station but not properly received by the UE, and sending a peer-to-peer message to the UE that includes the dropped PDU.

[0148] 3. In some embodiments according to Example 2, the next PDU indication and the dropped PDU indication 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 whether subsequent PDUs for the MBS session should be transmitted via peer-to-peer messages or peer-to-multiple messages based at least in part on a number of UEs served by the target base station that subscribe to the MBS session.

[0151] 6. In some embodiments according to any of Examples 1-5, the method includes, in response to receiving a request to initiate a handover, establishing the MBS session with a core network element of the wireless communication network; receiving from a source base station at least one PDU of the MBS session to be forwarded to the UE, the at least one PDU including a next PDU of the MBS session; and subsequently receiving a subsequent PDU 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 includes receiving an indication from the UE that MBS handover reconfiguration at the UE has been completed, and in response to receiving the indication that MBS handover reconfiguration at the UE has been completed and subsequently 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.

[0153] 8. In some embodiments according to Example 7, the method further includes forwarding to the UE via at least one PTP message each PDU of at least one PDU of the MBS session received from the source base station prior to receiving an indication that the MBS handover reconfiguration at the UE has been completed.

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

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

[0156] 11. In some embodiments according to any of Examples 1-9, the method includes receiving an MBS packet including MBS payload data for the MBS session from a core network element of a wireless communication network, the MBS packet having a packet sequence number, and transmitting 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 for the transmitted packet.

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

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

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

[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 the multicast session; 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 instruction, stopping receiving the transmission 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 following a last data packet of the multicast session received from the first base station, the next sequential data packet being previously included in the multicast transmission from the first base station after the wireless communication device stopped receiving the transmission from the first base station.

[0161] 16. In some embodiments according to Example 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 Examples 15-16, the method further includes receiving a unicast transmission from the second base station, the unicast transmission including dropped data packets of the multicast session that were included in the multicast transmission from the first base station prior to the command to perform the handover but were not properly received by the UE.

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

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

[0165] 20. In some embodiments according to any of Examples 15-19, the instructions to perform a handover to the second base station include 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 connected to the wireless communication circuit, the processor circuit configured to cause the wireless communication device station to perform steps according to any of Examples 15-20.

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

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

[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 sending a multicast transmission to a user equipment (UE), the multicast transmission including at least one data packet of the multicast session; in response to determining to initiate a handover procedure to hand over the UE to a second base station of the wireless communication network, sending an instruction to the UE to perform the handover; providing an indication to the second base station of a next packet of the MBS session to be transmitted to the UE following the sending of the instruction; initiating forwarding of packets of the MBS session to the second base station, the packets including the next packet, to be transmitted to the UE following the sending of the instruction; and in response to receiving an indication from the second base station that the handover is complete, stopping forwarding of packets of the MBS session.

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

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

[0172] 27. In some embodiments, a first base station operating in a wireless communication network includes wireless communication circuitry and a processor circuit communicatively connected to the wireless communication circuitry, the processor circuitry configured to cause the first base station to perform 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 includes a stage for carrying out a method according to any of Examples 24-26.

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

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

[0177] 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 an ASIC. In 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) may store program instructions and / or data that, when executed by a computer system, may be configured to cause the computer system to perform a method, such as any of the method embodiments described herein, or a combination of the method embodiments described herein, or a subset of the method embodiments described herein, or a combination of such subsets.

[0179] In some embodiments, a device (e.g., a UE) may be configured to include a processor (or set of processors) and a memory medium (or memory element), where the memory medium stores program instructions and the processor is configured to read and execute the program instructions from the memory medium, where 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 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, numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated, and it is intended that the following claims be interpreted to embrace all such variations and modifications.

Claims

1. 1. A method for performing communication of a Multicast Broadcast Service (MBS) session, comprising: By the target base station of the wireless communication network, receiving a request from a remote base station of the wireless communication network 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; sending a Peer-to-Peer (PTP) message to the UE including the next PDU of the MBS session, the next PDU of the MBS session having been previously sent by the source base station via a Peer-to-Peer Multiple (PTM) message after the request to initiate the handover; in response to receiving the request to initiate the handover, establishing the MBS session with a core network element of the wireless communication network; receiving at least one PDU of the MBS session from the source base station, the at least one PDU including the next PDU of the MBS session, to be transferred to the UE; receiving subsequent PDUs of the MBS session from the core network element subsequent to receiving the next PDU; Including, method.

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

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

5. determining whether subsequent PDUs for the MBS session should be transmitted via peer-to-peer messages or peer-to-multiple messages based at least in part on a number of UEs served by the target base station that have subscribed to the MBS session; The method of claim 1 further comprising:

6. receiving an indication from the UE that MBS handover reconfiguration at the UE is complete; providing an instruction to the source base station to stop forwarding PDUs of the MBS session in response to receiving the indication that the MBS handover reconfiguration at the UE is complete and subsequent to establishing the MBS session with the core network element; The method of claim 1 further comprising:

7. forwarding to the UE via at least one PTP message each of the at least one PDU of the MBS session received from the source base station prior to receiving the indication that MBS handover reconfiguration at the UE is complete; The method of claim 6 further comprising:

8. receiving, from a core network element of the wireless communication network, an indication of a sequence number to be assigned to a specified PDU of the MBS session; assigning sequential sequence numbers to PDUs following the designated PDU; The method of claim 1 further comprising:

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. The method of claim 1.

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