Lossless Handover for Active Multicast Broadcast Sessions
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Solution Overview
Problem
Existing mobile communication systems face challenges in achieving lossless handover during active multicast broadcast sessions, particularly in ensuring continuous data reception and maintaining in-order delivery of packets across cell transitions.
Innovation Solution
The proposed solution involves a wireless transmit/receive unit (WTRU) that sends a packet data convergence protocol (PDCP) status report after handover, temporarily suspends in-order delivery of multicast radio bearer (MRB) PDCP, and forwards out-of-order packets to higher layers, while maintaining connections with both source and target cells until packet reception is synchronized.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the WTRU immediately detaches from the source cell after handover, then the handover speed is improved, but packet loss occurs and service continuity is compromised
Solution Approach 1:
The WTRU performs preliminary actions by maintaining the source cell connection active after handover completion and before full detachment. This allows the WTRU to continue receiving packets from the source cell that may have been transmitted during the handover transition, ensuring no packets are lost while still achieving fast handover.
Solution Approach 2:
The source cell connection is maintained in an active state for a predetermined time period after handover, allowing continuous reception of packets from both source and target cells. This continuity ensures that packets transmitted during the transition period are not lost, while the connection is subsequently released to complete the handover process.
2Reliability
If the WTRU maintains connection with both source and target cells after handover, then packet loss is minimized, but device complexity and resource consumption increase
Solution Approach 1:
The connection state is made dynamic rather than static. The source cell connection is temporarily maintained in an active state for a predetermined time period after handover, then automatically released. This dynamic approach allows the system to adapt to the specific needs of the handover process without permanent complexity.
Solution Approach 2:
The WTRU maintains the source cell connection for a predetermined time period, which may be longer than the minimum necessary time. This excessive action ensures that even if packets are transmitted slightly after the handover completion, they will still be received, providing a margin of safety without requiring complex coordination mechanisms.
3Manufacturing precision
If the WTRU sends PDCP status report after handover, then in-order delivery is improved, but transmission time and processing overhead increase
Solution Approach 1:
The PDCP status report is sent as a preliminary action immediately after handover completion, before the source cell connection is released. This ensures that any out-of-order packets are quickly identified and can be retransmitted or handled appropriately, maintaining in-order delivery at the application layer without delaying the handover process.
Data Source
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AI summary
A wireless transmit-receive unit (WTRU) may be configured to perform one or more actions. The WTRU may be configured to receive a handover command. The WTRU may be configured to connect to a target cell and receive one or more packets from the target cell. The WTRU may be configured to receive one or more packets from a source cell. The WTRU may be configured to determine, based on at least one of the received one or more packets from the source cell or the received one or more packets from the target cell, that there are no missing packets. The WTRU may be configured to release, based on the determination that there are no missing packets, a resource associated with the source cell.