A New Modification on Relay Selection by Considering the Effect of Relay Occupancy

Aims: Considering the effect of relay occupancy at relay selection schemes and also proposing a new approach which helps the selection schemes to find the best free relay.
Study Design: Comparative study by simulation in MATLAB software.
Place and Duration of Study: Digital Communications Signal Processing (DCSP) Lab. of Shahid Rajaee Teacher Training University (SRTTU), Since 1st June 2012 up to 1st August 2014.
Methodology: In the existing research works, relay-based system is modeled by a pair of transmitter-receiver nodes and a number of relays. Also, it is assumed that the selected relays are always free. In this investigation, the effect of relay occupancy due to other pairs is considered. For this purpose, a uniform distribution is applied for all relays to show the effect of free or busy relay nodes. Then, the performance of the relay selection methods is obtained by using two well-known performance metrics, bit error rate (BER) and outage probability. As the main goal of this research, a new approach is proposed which first finds the free relays and then applies one of the selection methods, Max-Min SNR Selection (MMS), Max-Sum rate Selection (MSS) and Hybrid Selection (HS), to find the best relay which satisfies the optimization problem.
Results: For both Amplify and Forward (AF) and Decode and Forward (DF) relays, the new approach will reduce outage probability of HS scheme. For AF relays, BER of MMS and HS schemes will be decreased but it has neglected effect on the outage probability of MSS scheme. For DF relays, BER of MMS, MSS and HS schemes will be decreased.
Conclusion: According to optimization problem for each relay selection scheme, the proposed approach can significantly reduce the outage probability and BER in realistic conditions which the effect of other nodes is considered.