Relay Terminal Buffering for Lossless Handover in LTE
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Solution Overview
Problem
In modern cellular radio communication networks, particularly in LTE and LTE-Advanced systems, there is a challenge in ensuring service continuity when remote user terminals switch from indirect to direct communication, as the source eNodeB lacks knowledge about successfully received PDCP packets by remote user terminals, leading to potential packet loss during handover or path switch procedures.
Innovation Solution
The solution involves determining whether the relay terminal or the eNodeB should buffer unacknowledged PDCP packets, with the relay terminal configured to keep packets until acknowledgment from the remote user terminal, and the eNodeB informed through flags or dedicated signaling to ensure seamless handover and path switch execution by forwarding unacknowledged packets during communication path changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the source eNodeB does not buffer unacknowledged PDCP packets during indirect communication, then the device complexity and memory usage are reduced, but packet loss occurs during handover or path switch procedures
Solution Approach 1:
The relay terminal acts as an intermediary that buffers unacknowledged PDCP packets between the source eNodeB and the remote user terminal. During handover or path switch, the relay terminal forwards these buffered packets to the target eNodeB, ensuring service continuity without requiring the source eNodeB to maintain complex buffer management.
Solution Approach 2:
The relay terminal pre-buffers unacknowledged PDCP packets during indirect communication before handover or path switch occurs. This preliminary buffering action ensures that when the communication path changes, the packets are already available for forwarding, preventing packet loss and maintaining service continuity.
2Reliability
If the relay terminal buffers unacknowledged PDCP packets, then packet loss during handover is prevented, but the memory usage and device complexity of the relay terminal increase
Solution Approach 1:
The relay terminal buffers only unacknowledged PDCP packets selectively, rather than buffering all packets. This partial buffering approach maintains packet delivery reliability for critical unacknowledged packets while avoiding excessive memory usage by not buffering packets that have already been acknowledged or are less critical.
3Measurement precision
If dedicated signaling is used to inform the eNodeB about buffered packets, then accurate packet forwarding is achieved, but the signaling overhead and communication complexity increase
Solution Approach 1:
The acknowledgment status information is extracted from the data plane and transmitted separately through dedicated signaling. This allows the source eNodeB to receive precise information about which packets are acknowledged and which are not, enabling accurate forwarding decisions without mixing control and data plane traffic.
Data Source
AI summary
Apparatuses and methods in a communication system, are provided. The method comprises controlling (500) communication between a first user terminal and the apparatus and the communication between a second user terminal and the apparatus, wherein the first user terminal acts as a relay by relaying data packets between the apparatus and the second user terminal; determining (502) whether the first user terminal or the transmitting end of data packets in the connection between the apparatus and the second user terminal will buffer data packets addressed to but not successfully received by the receiving end and transmitting (504) an indication regarding the determination to the first user terminal.