Power allocation of distributed space-frequency coding for OFDM-based hybrid relay selection

Cooperative communications in conjunction with orthogonal frequency division multiplexing (OFDM) has recently emerged as a promising technique to mitigate multi-path fading and provides high spectral efficiency in broadband wireless communications systems. In this paper, we investigate resource allocation of an OFDM modulation scheme combined with distributed space-frequency codes (DSFC) based upon a hybrid relay selection protocol. The optimum problem is divided into two suboptimal problems. The first one is to optimize the power allocation between the source and relay nodes under a sum power constraint. Then the relay power is optimized for the selected relay nodes according to the channel power gain of the second time slot. Simulation results show that a substantial improvement in terms of bit error rate (BER) and capacity performance can be achieved in comparison with conventional relaying protocols.