Performance of Cooperative Transmissions in Flat Fading Environment with Asynchronous Transmitters

Channel dispersion is inevitable in asynchronous cooperative transmissions even in flat fading environment, which may greatly degrade the gain of cooperative diversity and cast doubts on their application in wireless sensor networks for energy efficiency or reliability. This paper studies the interference caused by such channel dispersion, and shows that the average SIR can be decreased to 10 dB even in noiseless transmissions. We propose two methods to mitigate the dispersion: a simple sampling time optimization method, and an over-sampling combining method. Simulations show that they can achieve average SIR near 30 dB and near 60 dB, respectively, with two cooperative transmitters