Abstract
In this paper, we propose a variable-rate based relay selection scheme for decode-and-forward cooperative networks. Adaptive modulation is used as a practical implementation of the variable-rate transmission. In specific, we exploit the variable rate transmission to choose the maximum rate, and select the best relay that has the best end-to-end path between the source and destination nodes. We derive a closed-form expression for the cumulative distribution function of the output signal-to-noise ratio, and a closed-form expressions for the average spectral efficiency and average bit error rate. Simulation results are given to verify the analytical ones, and demonstrate that the scheme can improve the average spectral efficiency in the low average SNR region, and achieve better average BER compared with the conventional direct transmission.