Relay selection in wireless cooperative networks using decode-and-forward transmission

The problem of selecting a set of relay nodes is considered in a two-hop wireless cooperative networks using decode-and-forward (DF) protocol. To minimize the system outage probability and the energy consumption, we propose a method with 2 thresholds to select the optimal relays. The first threshold is to control the system target rate R. During the transmission the instantaneous signal-to-noise-ratio (SNR) of the relays are compared to the threshold 2. Those relays whose instantaneous SNR is larger than the threshold 2 are allowed to transmission. The advantage of our method is that whether one relay is active or silence is completely independent from another and no mutual communication is required. Besides the threshold 2 can be decided before the transmission, with no need for in-time updating. Hence our method greatly simplifies the relay selection difficulty, and improves the tractability. Two methods of designing the threshold 2 are proposed, which are focused on minimizing outage and power consumption, respectively. And the system outage probability expression is thereafter derived. Simulation results verify the theoretical expression. And the relations between outage probability and energy consumption affected by different threshold are given simultaneously.