Analysis on the structure of distributed space-time code for TWRNs with relay having multiple antennas

The lower bound of pairwise error probability (PEP) is derived for two-way relaying networks (TWRNs), in which the relay node has M antennas. PEP analysis shows that the error performance can decay with lnSNR/SNR^M by linearly combining signals from M antennas at the same relay. Compared with the ln^MSNR/SNR^M reported by Jing et. al., the optimum diversity gain can be greatly improved. In addition, we also present one possible design for the case of M=4, simulations illustrate that the selected design has a preferable diversity gain function.