Power adaptation in space-time block code

Transmission power adaptations are considered in a space-time block code (STBC) system utilizing feedback channel gain information. We investigate the optimal power adaptation scheme that minimizes the average BER subject a fixed average transmission power constraint. We present the power gain provided by the optimal adaptation scheme over the conventional STBC without power adaptation. The power gain provided is found to be 13.8 dB at BER of 10^-5 in a Rayleigh fading channel. Also, we analyze the performance of STBC system with optimal truncated power adaptation which compensates for fading above a certain fade depth: below the cutoff level data transmission is suspended (ie, outage condition is declared). Finally, we propose a simple adaptation scheme for STBC systems based on two-bits feedback information that provides a power gain of 4.3 dB at BER of 10^-5