DAPS Handover Uplink Interruption Reduction
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Solution Overview
Problem
During dual active protocol stack (DAPS) handovers in 5G wireless systems, uplink data interruptions occur due to delayed forwarding of buffered uplink packets from the target cell to the user plane function (UPF) or serving gateway, especially when there are no pending uplink medium access control (MAC) or radio link control (RLC) transmissions to the source cell upon UL switch, leading to unnecessary delays in industrial Internet of Things (IIoT) services with small packet sizes.
Innovation Solution
The user equipment (UE) transmits an indication to the source or target cell that there are no more pending uplink MAC and RLC transmissions after the UL switch, allowing the target cell to forward received UL packets to the UPF or serving gateway without waiting for a handover success message or sequence number status transfer, thereby reducing uplink data interruption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the target cell waits for handover success message or sequence number status transfer before forwarding buffered uplink packets, then packet forwarding accuracy is improved, but uplink data interruption time increases
Solution Approach 1:
The target cell performs preliminary forwarding of buffered uplink packets to the UPF before receiving the handover success message or sequence number status transfer. By anticipating the need to forward packets and doing so in advance, the system reduces uplink interruption time while maintaining forwarding accuracy through subsequent sequence number alignment.
Solution Approach 2:
The system uses sequence number status transfer as feedback to verify and correct the forwarding of uplink packets. After preliminary forwarding, the target cell receives sequence number status information that confirms whether packets were correctly received and forwarded, allowing for any necessary corrections.
2Loss of time
If the target cell forwards buffered uplink packets immediately after UL switch, then uplink data interruption time is reduced, but packet forwarding accuracy may deteriorate
Solution Approach 1:
The target cell performs preliminary forwarding of buffered uplink packets immediately after UL switch without waiting for handover completion confirmation. This preliminary action reduces uplink interruption time while maintaining reliability through subsequent verification using sequence number status information.
3Reliability
If the system waits for sequence number status transfer before forwarding packets, then forwarding accuracy is improved, but device complexity increases
Solution Approach 1:
The target cell performs preliminary forwarding of packets before receiving sequence number status transfer, eliminating the need to wait for complex handover coordination. This approach maintains forwarding accuracy by using sequence number information when available while reducing the complexity of handover coordination procedures.
Data Source
AI summary
Systems, methods, apparatuses, and computer program products for reducing uplink interruption in dual active protocol stack (DAPS) handover. For example, the user equipment may transmit an indication either to a source cell or to a target cell that there is no more pending uplink medium access control and radio link control (re)-transmissions to be transmitted to the source cell, after the uplink switch to the target cell occurs during a DAPS handover. Based on the received indication, the network (e.g., the source cell or target cell) may perform one or more actions to enable forwarding of the uplink packets received from the user equipment by the target cell to a user plane function and/or serving gateway.