Single and multiple relay selection schemes with optimum relay factors in wireless sensor networks

Cooperative diversity has been recently proposed as a technique to form virtual antenna arrays in systems with single-antenna nodes. The Amplify-and-Forward (AF) relaying strategy is one of the most popular cooperative diversity schemes due to its low complexity. Selection AF (SAF) relaying, single or multiple relay selection, has recently been proven to achieve the same diversity order as and lower power consumption than All-Participate (AP) networks. Most SAF methods assume constant power for best relay(s), regardless of channel conditions. In these methods relay(s) with weak channels amplify received signal with considerable gain that cause reduction of performance. In this paper, we propose single and multiple relay selection strategies for two-hop relay networks. In the first part of paper, we specify factor of each relay based on MMSE criterion and relay with highest SNR is chosen for cooperation. Our simulation results show that performance of this method is better than previous works. Second part of this paper proposes selection of two, three or any number of relays and uses them. As we see in the simulation results double relay selection has better performance than single relay selection, triple than double and so on and diversity order of all is complete.