Lossless Downlink Handover via Last Packet Notification
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Solution Overview
Problem
Existing cellular mobile communication systems face challenges in achieving seamless and lossless downlink handovers due to difficulties in determining a suitable time-offset for packet transmission, leading to potential packet loss or transmission discontinuity during handovers in WCDMA networks.
Innovation Solution
The solution involves determining the last packet to be transmitted from the first radio base station and informing the user equipment (UE) of this information, allowing the UE to request the second radio base station to commence transmission once the last packet is received, ensuring continuous and lossless handovers by coordinating the timing of the cell change with user-plane data transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a time-offset is assigned for handover preparation, then the handover can be coordinated, but it is difficult to determine a suitable time-offset that ensures all packets are transmitted without loss or duplication
Solution Approach 1:
The system performs preliminary actions by notifying the UE in advance about the last packet that will be transmitted from the source base station before handover. This allows the UE to prepare for the handover timing and ensures that no packets are lost or duplicated during the transition, as the UE knows exactly when to expect the final packet from the old base station.
Solution Approach 2:
The system implements feedback by providing the UE with information about the last packet to be transmitted. This feedback mechanism enables the UE to adjust its reception timing and buffer management accordingly, ensuring seamless packet reception during handover without requiring complex centralized coordination.
2Speed
If the handover is executed quickly, then transmission continuity is improved, but packet loss may occur if the time-offset is insufficient for completing data transmission
Solution Approach 1:
The source base station determines and notifies the UE about the last packet to be transmitted before handover execution. This preliminary information allows the handover to be executed quickly while ensuring that the UE can accurately receive all packets up to the last one, preventing packet loss even with minimal time-offset.
Solution Approach 2:
The UE uses the notified information about the last packet to autonomously manage its reception timing and buffer. This self-service approach allows the UE to handle the handover transition without requiring extended coordination time, enabling fast handover execution while maintaining complete packet delivery.
3Reliability
If the handover is delayed to ensure all packets are transmitted, then packet loss is prevented, but transmission discontinuity occurs
Solution Approach 1:
By notifying the UE in advance about the last packet to be transmitted, the system enables the UE to prepare for the exact handover timing. This eliminates the need to delay handover for extended periods, as the UE can seamlessly continue reception immediately after the last packet, preventing transmission discontinuity while ensuring complete packet delivery.
4Reliability
If buffering is performed in the radio base station with HARQ retransmission, then transmission errors are combated efficiently, but seamless and lossless handovers become more challenging
Solution Approach 1:
The system extracts the handover coordination function from complex centralized control by providing simple notification information (the last packet identifier) to the UE. This allows HARQ buffering to remain in the base station for reliable error handling, while the simplified notification mechanism enables seamless handover without increasing overall system complexity.
Data Source
AI summary
The present invention relates to a UE, base station network node and methods thereof in a cellular mobile communication system. One method concerns handover from a first radio base station to a second radio base station wherein, it comprises the steps receiving a notification from the first radio base station that currently serves said UE, said notification indicating the last packet to be transmitted to this user equipment from said first radio base station on a first connection; and informing the second radio base station by a request to commence transmission from this second radio base station when the notified last packet is received at the UE.