Cooperative diversity by censorial relays for communications over Rayleigh fading channels

It has long been recognized that diversity is one of the most effective countermeasures for fighting the occasional deep fades suffered in communications over fading channels. Recently, various schemes of adopting relays to assist a source so that together they constitute a diversity system have been widely investigated. Since cooperation between the source and the relays are involved in those schemes, they are frequently referred to as cooperative diversity systems. Our work in this paper also falls into the category of cooperative diversity. One distinctive feature of our work is that the relay is a censorial relay, which means that it evaluates the reliabilities of its own decisions regarding the received data (from source) and censors (i.e. does not send to the destination) those with low degrees of reliability. For the case that the fading is Rayleigh distributed, a closed-form BER (bit error rate) expression for the proposed system is derived and then utilized to obtain the optimal system parameters. Experimental results show two things regarding our scheme. First, simulation results match theoretical values closely. Secondly, the BER performance is significantly better as compared to uncensored and unoptimized cooperative diversity systems.