Implementation of Relay HARQ Transmission and Reception Procedures

Relay HARQ (Hybrid Automatic Repeat reQuest) is a reliability-enhancing technique designed for wireless relay networks. Its core concept involves using relay nodes to facilitate data transmission between source and destination nodes, combined with automatic retransmission mechanisms to improve transmission efficiency. In code implementation, this typically requires designing state machines for different nodes and implementing feedback handling logic.

Transmission Procedure: The source node first transmits data packets to both the relay node and destination node. When decoding fails, the receiving end (relay or destination node) sends a NACK feedback signal. Upon receiving NACK, the source node retransmits the data packet while the relay node may simultaneously forward previously stored data copies to assist decoding. This process iterates multiple times until successful decoding or maximum retransmission attempts are reached. Code implementation requires maintaining transmission counters and implementing timeout mechanisms using timer functions.

Reception Procedure: The destination node attempts decoding after receiving initial transmission data. If decoding fails, it stores the received signal and awaits retransmitted data from either source or relay nodes. After multiple transmissions, the destination node employs combining techniques to process multiple signal copies, enhancing decoding success probability. Implementation requires buffer management algorithms to store and align received signal samples.

Comparison of Three Combining Techniques and Delay Performance: Selection Combining (SC): Selects the signal with highest SNR for decoding. Simple implementation but limited performance; lower latency but potentially higher retransmission count. Code implementation involves SNR threshold comparisons using conditional statements. Maximum Ratio Combining (MRC): Weighted combination of multiple received signals with weights proportional to SNR. Optimal performance but high computational complexity, potentially increasing processing delay. Implementation requires matrix operations for optimal weight calculation. Equal Gain Combining (EGC): Equal-weight combination of received signals. Lower complexity than MRC but slightly inferior performance. Latency intermediate between SC and MRC. Implementation uses phase alignment and simple averaging algorithms.

In practical applications, while MRC delivers optimal BER performance, it may increase processing delay; SC suits low-complexity scenarios; EGC provides a compromise between performance and latency. Selection requires trade-offs based on system requirements, often implemented through configurable parameters in communication protocols.