Performance analysis of DF cooperative diversity system with OSTBC over spatially correlated Nakagami-m fading channels

In this paper, we investigate the performance of a cooperative decode-and-forward (DF) multiple-input-multiple-output (MIMO) relaying system with orthogonal space-time block code (OSTBC) transmissions over spatially correlated Nakagami-m fading channels for integer values of m. We consider both the opportunistic maximal-ratio combining (O-MRC) and λ-MRC receivers at the destination. For the former MRC, we give the closed-form expression for the cumulative distribution function (cdf) of the instantaneous end-to-end signal-to-noise ratio (SNR); relying on this, the exact analytical and asymptotic expressions are also derived for outage probability (OP) and symbol error rate (SER), whereas for the latter MRC, the closed-form expressions are derived for the exact and asymptotic bit error rate (BER) of binary phase-shift keying (BPSK) signals. The optimal value of λ that minimizes the BER is also provided by using Newton's method. It is shown that O-MRC outperforms λ-MRC since the former MRC takes the relay decoding results into account. For λ-MRC, the optimal λ decreases with the increase in the SNR and spatial correlation since increasing the SNR and spatial correlation could increase the confidence of the source-destination link and decrease the confidence of the source-relay link, respectively.