Distributed orthogonal space-time coding with relay selection

In this paper we employ relay selection in two-hop distributed orthogonal space time coding system. The proposed system has a single source, a single destination, and N relays. In the second hop, before transmitting signal to destination the best two relays out of N relays are selected based on the instantaneous channel conditions between the source and relays. This simple technique of relay selection can improve the end to end bit error performance of system without any increase in the total transmission power of the network and without any added complexity to the decoding process at the receiver side. The bit error performance (BER) of the proposed system is examined using computer simulation. The results show that a gain of about 3 dB at BER=10^-2 is achieved by selecting the best two relays out of three. Further improvement in the BER performance can be achieved by increasing the number of relays N. However, no significant improvement in BER performance can be observed by increasing the number of relays N beyond 8.