RLC Layer HARQ Retransmission Control for Delay-Sensitive Satellite Links
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Solution Overview
Problem
In satellite communication systems and LTE networks, the use of Hybrid Automatic Repeat Request (HARQ) for delay-sensitive flows leads to long end-to-end delays and poor voice quality due to high retransmission Round Trip Time (RTT), resulting in unnecessary packet retransmissions and increased latency.
Innovation Solution
The method involves disabling the t-reordering feature by setting its timer to zero in the Radio Link Control (RLC) Unacknowledged Mode, allowing subsequent RLC blocks to be processed immediately, and enabling the user terminal to override retransmission requests, sending new data instead, thereby avoiding unnecessary retransmissions and reducing latency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If HARQ retransmission is enabled for packet loss recovery, then packet loss rate is reduced, but end-to-end delay increases significantly
Solution Approach 1:
The system performs preliminary action by proactively detecting packet loss at the RLC layer before HARQ retransmission can occur. By identifying lost packets early and notifying the transmitter, the system enables immediate retransmission without waiting for the standard HARQ round trip, thus reducing end-to-end delay while maintaining packet loss recovery capability
Solution Approach 2:
The invention implements enhanced feedback mechanism where the RLC layer monitors packet reception and sends explicit loss notifications to the transmitter. This feedback loop allows the transmitter to identify and retransmit lost packets immediately, bypassing the delay inherent in traditional HARQ processes while maintaining reliable packet delivery
2Reliability
If HARQ retransmission is performed over satellite links, then link reliability is improved, but round trip time increases due to long propagation delay
Solution Approach 1:
The system performs preliminary detection of packet loss at the RLC layer before the standard HARQ round trip completes. By identifying lost packets early in the transmission process and initiating retransmission immediately, the system reduces the effective round trip time for satellite links while maintaining link reliability through proactive packet loss recovery
Solution Approach 2:
The invention segments the packet loss recovery function into two independent layers: RLC layer handles loss detection and notification, while physical layer handles actual retransmission. This segmentation allows the RLC layer to operate independently of satellite propagation delay, enabling immediate loss detection and notification without waiting for the full HARQ round trip to complete
3Reliability
If the RLC waits for HARQ packet recovery before processing subsequent packets, then packet loss is recovered, but processing delay increases for delay-sensitive flows
Solution Approach 1:
The invention extracts the packet loss detection and notification function from the HARQ process and places it in the RLC layer. This allows the RLC to independently identify lost packets and notify the transmitter without waiting for HARQ recovery, enabling subsequent packets to be processed immediately while packet loss recovery continues in parallel
Solution Approach 2:
The system maintains continuity of useful action by allowing the RLC layer to continuously monitor and detect packet loss independently of the HARQ process. By notifying the transmitter immediately upon detecting loss, the system ensures continuous packet flow processing without interruption or waiting for HARQ recovery, maintaining uninterrupted data flow for delay-sensitive applications
Data Source
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AI summary
A method for reducing retransmission of packets by a sender is disclosed. The method includes: providing a network comprising a physical layer, a medium access control (MAC) layer and an Radio Link Control (RLC) layer; providing a retransmission packet in the physical layer, wherein the retransmission packet comprises a flow having a reordering feature in the RLC layer; enabling Hybrid Automatic Repeat reQuest (HARQ) in the physical layer and the MAC layer; receiving a HARQ request for a retransmission; and transmitting a new packet with the physical layer in response to the HARQ request, when the reordering feature for the flow in the retransmission packet is disabled.