Asymptotic SEP Analysis of Two-Way Relaying Networks With Distributed Alamouti Codes

Asymptotic symbol error probability (SEP) performance with an optimal maximum likelihood (ML) receiver and square quadrature amplitude modulation (QAM) constellations is investigated for two-way amplify-and-forward (AF) half-duplex relaying networks employing distributed Alamouti space-time block codes (DASTCs) recently proposed by Duong By developing a novel strategy to particularly deal with some specific Gaussian integrals, two asymptotic SEP formulas are derived for both fixed- and variable-gain AF protocols. These analytic results reveal that, when the signal-to-noise ratio (SNR) is large, the diversity gain for the variable-gain AF is 2, whereas the diversity gain function for the fixed-gain AF is proportional to SNR^-2 ln SNR.