Implementation of Relay HARQ Transmission and Reception Procedures

This document presents a method for implementing relay Hybrid Automatic Repeat Request (HARQ) transmission and reception procedures, along with a comparative analysis of delay performance for three different combining schemes. Specifically, the relay HARQ implementation involves adding a relay node between the source and destination nodes, where the relay node receives data and then forwards it to the destination node. During this process, HARQ mechanisms are employed to enhance data transmission reliability. In code implementation, this typically involves creating separate transmission handlers for source, relay, and destination nodes with HARQ protocol state machines managing ACK/NACK feedback and retransmission logic. To evaluate different combining approaches, we conducted delay performance comparisons of three distinct combining schemes: Maximum Ratio Combining (MRC), Maximum Ratio Selection Combining (MRSC), and Minimum Ratio Combining (MinRC). From an algorithmic perspective, MRC optimally combines all received signals by weighting them according to their signal-to-noise ratios, while MRSC selects the best signal path and MinRC employs a conservative combining strategy. These implementations typically require SNR estimation modules and combining weight calculation functions in the receiver processing chain. Through these comparisons, we can identify the advantages and disadvantages of different combining schemes, thereby providing valuable recommendations and improvement directions for optimizing relay HARQ transmission and reception procedures. The performance evaluation framework can be implemented using simulation scripts that model transmission delays, packet error rates, and combining efficiency metrics across various channel conditions.