Terrestrial HARQ Controller for Satellite Link Latency
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Solution Overview
Problem
Current communication systems face challenges in maintaining reliable and efficient error correction in non-terrestrial communications, particularly due to the complexity of the hybrid automatic repeat request (HARQ) process and the latency introduced by satellite-based retransmissions.
Innovation Solution
The proposed solution involves relocating the HARQ controller from the donor base station to the terrestrial base station, which integrates a buffer to manage redundancy versions and facilitates direct retransmissions to user equipment, optimizing error handling by reducing latency through terrestrial connections for acknowledgments and retransmissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If HARQ controller is located at donor base station for non-terrestrial communications, then error correction capability is improved, but transmission latency increases due to satellite-based retransmissions
Solution Approach 1:
The system segments the HARQ process into two parts: initial transmission via satellite (non-terrestrial) and retransmission via terrestrial base station. This segmentation allows the reliability function to remain with the satellite while the time-critical retransmission function is handled by the lower-latency terrestrial infrastructure, thus resolving the contradiction between error correction capability and transmission latency.
Solution Approach 2:
The terrestrial base station acts as an intermediary for HARQ retransmissions. Instead of the satellite directly handling all retransmissions (which causes high latency), the terrestrial base station mediates the retransmission process by receiving NACKs and sending retransmissions directly to the UE, thereby reducing overall transmission latency while maintaining error correction capability.
2Reliability
If satellite handles all retransmissions for HARQ process, then communication reliability is improved, but system complexity increases
Solution Approach 1:
The system segments the HARQ functionality between satellite and terrestrial base station. The satellite handles initial transmission and forwarding, while the terrestrial base station handles retransmissions. This segmentation distributes system complexity across two nodes rather than concentrating all HARQ complexity in the satellite, making the overall system more manageable while maintaining communication reliability.
Solution Approach 2:
The terrestrial base station is given multiple functions: it serves as both a regular cellular base station and as the HARQ retransmission point for non-terrestrial communications. This multi-functionality allows the system to maintain reliability through satellite communication while using the versatile terrestrial base station to handle time-critical HARQ operations, thereby managing system complexity more effectively.
3Reliability
If redundancy versions are transmitted via satellite for retransmission, then error correction is improved, but transmission speed decreases
Solution Approach 1:
Instead of the conventional approach where the same path (satellite) is used for both initial transmission and retransmission, the system inverts the retransmission path to use terrestrial infrastructure. This inversion allows retransmissions to occur via the faster terrestrial channel while the satellite continues to provide the initial error-corrected transmission, thus improving transmission speed without sacrificing error correction capability.
Solution Approach 2:
The system applies different transmission qualities to different parts of the communication process: satellite transmission is used for the initial transmission where error correction is paramount, while terrestrial transmission is used for retransmissions where speed is critical. This local optimization of transmission quality based on the specific phase of communication resolves the contradiction between error correction and transmission speed.
Data Source
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AI summary
A system comprising the system comprising a gateway (30), a non-terrestrial node (10), a terrestrial node (40) and at least a user equipment (22) as well as a HARQ controller, wherein the gateway (30) is configured to forward a data packet, said data packet to be transmitted to the user equipment (22), to the non-terrestrial node (10), wherein the non-terrestrial node (10) is configured to forward the received data packet to the user equipment (22) using a signal, wherein the user equipment (22) is configured to analyze the received data packet with regard to a transmission error and/or to analyze the signal from the non-terrestrial node (10) with regard to a signal quality and to generate a negative acknowledgment command or an acknowledgement command dependent on the transmission error or to generate another signal indicating the reception signal quality dependent on the reception signal quality, wherein the user equipment (22) is configured to transmit the acknowledgement command and the non-acknowledgement command or the other signal to the terrestrial node (40) which communicates with the non-terrestrial node (10).