Orthogonal STBC in General Nakagami-m Fading Channels: BER Analysis and Optimal Power Allocation

We analyze the performance of multiple-input multiple-output (MIMO) systems employing orthogonal space-time block codes (STBC) in general Nakagami-m fading channels with channel coefficients having not necessarily identical fading parameters and average power gains. First, we derive an exact analytical closed-form expression for the average bit error rate (BER) of M-ary quadrature amplitude modulation. Then, we determine asymptotically tight high and low SNR approximations of the exact BER expression and we quantify the coding gain and diversity order of our system as a function of the channel parameters. Finally, we derive the optimal power allocation strategies for the high and the low SNR regime, assuming that statistical channel knowledge is available at the transmitter-side, and we determine the performance improvement that can be achieved this way compared to uniform power allocation.