Relay Selection in One-Way and Two-Way Cooperative Diversity Network

The cooperative diversity network has been proposed as an efficient technique to provide the system performance as that of a multiple antenna system by forming a virtual antenna array. The virtual antenna array can effectively combat the multi-path fading effect and improves the diversity gain of the system. The node cooperation can be done by phased array technique or distributed space time coding but the phased array technique requires tracking and control of multiple carrier phase differences so these techniques are less practical and increases the complexity and cost of the transceiver system, hence to reduce the hardware complexity and the cost, the distributed relay selection is one of the most suitable way in order to have all the features of the cooperative communication. This can be done in several ways like best relay selection, Nth best relay selection or incremental best relay selection. The work presented here includes the relay selection in amplify and forward (AF) one-way and two-way relaying system.In the best relay selection the best relay only forwards the source signal to the destination, but in case of the unavailability of the best relay we need to switch to the second best or third best or in general Nth best relay. The analysis of the outage probability and the average channel capacity for Nth best relay selection has been done. The incremental best relay selection is proposed to overcome the loss in spectral efficiency which generally arises in the conventional relay selection schemes in the cooperative diversity network because in the regular cooperative diversity network the selected relay(s) are used every time to transmit the source message regardless of the channel conditions even if some time they are not needed when the direct path has significantly high SNR to transmit the source message. The incremental best relaying network uses the limited feedback from the destination terminal to provide some control signals via feedback path, if the destination sends the negative acknowledgment then the relay retransmit the source message in order to exploit the spatial diversity and increases the spectral efficiency. The asymptotic mathematical analysis of the outage probability and the average channel capacity for incremental best relaying has been done. The symbol error rate analysis using different relay selection protocol like optimal and suboptimal relay selection along with the comparison of the performances for two cases i.e. when relay selection is applied and when all relays participate in the transmission have been included