Time-reversal space-time codes in asynchronous two-way double-antenna relay networks

We consider an asynchronous two-way relay network, in which two double-antenna relays assist in the communication between two single-antenna terminals through analog network coding. The asynchronous transmission between relays and terminals causes symbol misalignments and results in diversity loss in space-time block code (STBC). We propose a zero-padded time-reversal quasi-orthogonal STBC that can achieve full diversity with low-complexity maximum likelihood (ML) decoding, given a bounded delay. With ML decoding, the proposed code is decomposed into several independent parts, which leads to single complex symbol decoding. Proof of full diversity is established, and the decoding complexity order is analyzed for the proposed design. Simulations confirm the full diversity gain. The bit error rate performance in asynchronous scenarios is almost the same as that in synchronous scenarios.