Joint Adaptive Network–Channel Coding for Energy-Efficient Multiple-Access Relaying

An energy-efficient orthogonal multiple-access relay channel (MARC) system is developed, where accumulator and differential detection (DD) are used at the source and relay nodes, respectively. However, the weak decoding capability of DD degrades the frame error rate (FER) performance of the orthogonal MARC system if the conventional decode-and-forward relaying strategy is applied. In this paper, a novel joint adaptive network-channel coding (JANCC) technique is proposed to support DD by making efficient use of the erroneous estimates output from DD. In the JANCC technique, the destination constructs a vector identifying the indexes of the source nodes whose information parts contain errors and sends it to the relay to request a retransmission. The relay performs network coding by taking the exclusive-or (xor)-operation only over the stored estimates specified by the identifier vector, which aims to avoid unnecessary erroneous estimates being coded. In addition, a bit-flipping probability p_nc is obtained between the two sequences; one is the network-coded sequence sent from the relay, and the other is their corresponding xor-ed information sequence. The decoding algorithm of JANCC exploits probability p_nc at the destination to update the log-likelihood ratio during the iterative decoding process. Hence, the information sequences received at the destination are able to be recovered, although the redundancy forwarded from the relay is generated from the erroneous estimates. Compared with the system where iterative decoding is performed at the relay, the utilization of DD significantly reduces the computational complexity, which leads to meaningful power savings with only a small loss in FER performance.