MBS Handover Lossless Service via PDU Forwarding and Sequence Reporting
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Solution Overview
Problem
Current wireless communication systems face challenges in maintaining service continuity during handovers for Multicast and Broadcast Services (MBS) communications, leading to dropped or missed packets, which affects the reliability of MBS communications as users move between cells.
Innovation Solution
The method involves a target base station receiving a request to initiate a handover for a user equipment (UE) from a source base station, transmitting peer-to-peer (PTP) messages with next or dropped protocol data units (PDUs), and determining the transmission method based on the number of UEs subscribed to the MBS session, ensuring seamless handover by establishing and managing MBS sessions with the core network.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If handover is initiated for MBS session during user mobility, then service continuity is improved, but packet loss occurs during the handover transition
Solution Approach 1:
The source base station forwards PDUs to the target base station before the handover is completed. This preliminary action ensures that the target base station has the necessary packets ready to transmit to the UE immediately after handover, preventing packet loss during the transition period.
Solution Approach 2:
The target base station acts as an intermediary by receiving forwarded PDUs from the source base station and then transmitting them to the UE. This intermediary role ensures seamless packet delivery during handover, as the target base station can buffer and forward packets without interruption to the UE.
2Reliability
If PTP messages are used to retransmit dropped PDUs, then service continuity is improved, but signaling overhead increases
Solution Approach 1:
The UE autonomously identifies dropped PDUs by detecting gaps in the PDCP sequence number sequence and reports this information to the target base station. This self-service approach eliminates the need for complex network-side mechanisms to detect and track packet loss, reducing signaling overhead while maintaining service continuity.
3Reliability
If MBS session is established with core network element during handover, then service continuity is improved, but handover latency increases
Solution Approach 1:
The MBS session is established with the core network element before the handover is executed. This preliminary establishment ensures that the target base station has active session context and can immediately begin receiving and forwarding PDUs upon handover completion, minimizing the time required for service continuity.
4Loss of information
If source base station forwards all PDUs to target base station, then packet loss is reduced, but network bandwidth consumption increases
Solution Approach 1:
The UE autonomously identifies and reports only the dropped PDUs by detecting sequence number gaps, rather than requiring the source base station to forward all PDUs. This approach significantly reduces unnecessary bandwidth consumption for retransmitting already-received packets while still achieving lossless handover for actually lost packets.
Data Source
AI summary
Techniques are described for improving service continuity for Multicast and Broadcast Services (MBS) communications during handover. Techniques are included for supporting lossless handover and data forwarding during handover for peer-to-multiple (PTM) MBS transmission. Lossless handover may be achieved in part by the user equipment (UE) providing to the target base station an indication of the next packet of the MBS session to be received following an RRC reconfiguration message, and an indication of any MBS packets provided by the source base station prior to the RRC reconfiguration message that were not properly received by the UE. Data forwarding may be performed from the source base station to the target base station if the MBS session was not configured on the target base station prior to the handover. Data forwarding may be omitted if the MBS session was configured on the target base station prior to the handover.