Relay selection with optimal amplification factors in imperfect cooperative networks

In conventional amplify-and-forward relay networks, relays retransmit signals with predetermined transmit power and amplification factors assuming perfect channel knowledge. This paper proposes a relay selection scheme with amplification factor optimization according to the minimum mean square error criterion when the channel state information is imperfect due to the channel estimation error. Relays can adaptively adjust their amplification factor and transmit power according to the quality of the channels. The relay selection includes both single and multiple relay selection schemes. Finally, numerical results prove the advantage of our proposed scheme compared with the relay selection on the basis of the normalized amplification factor. The impact of channel estimation error is analyzed. We also investigate how the number of selected relays has an impact on the system performance.