Achieving full-diversity and fast maximum likelihood decoding in asynchronous analog network coding

This study designs space-time codes in analog network coding for asynchronous two-way relay networks, where asynchronous transmissions can cause diversity loss. We propose a novel code, called zero-padded interleave reversal Alamouti code (ZP-IR AC) to achieve full diversity with fast maximum likelihood decoding. Specifically, to combat symbol misalignment caused by asynchronous transmissions, the two terminals insert zero padding when transmitting to relays. Thereafter, the second relay performs an interleave reversal procedure to retain full diversity at each terminal. A salient feature of ZP-IR AC is that it can be decoupled into several independent parts that facilitate fast maximum likelihood decoding. Simulations of ZP-IR AC show full diversity gain. The bit error rate performance of ZP-IR AC is comparable to that of the synchronized Alamouti code and outperforms those of some recent schemes.