Power Allocation Strategies for Distributed Space-Time Codes in Amplify-and-Forward Mode

The idea of space-time coding, devised for multiple-antenna systems, can be applied to communication over a wireless relay network. In this paper, we derive an approximate formula for the bit error rate (BER) of distributed space-time codes in amplify-and-forward (AF) mode, in which each relay transmits a scaled version of the linear combination of its received symbols. Assuming M-PSK or M-QAM modulated, full-rate, and full-diversity space-time codes, we derive two power allocation strategies minimizing the approximate BER expressions, for constrained transmit power. Our analytical results have been verified by simulation results.