Relay Selection and Power Allocation in CSI-Unaware Two-Hop Communication Channels

This paper studies the effect of relay selection on the average achievable rate of a two-hop block-fading channel in which some amplify-and-forward (AF) relays connect the main transmitter to the destination. It is assumed that the transmitter does not know any of the instantaneous channel state information (CSI) values regarding the first or the second hops, while a central node has the corresponding CSI of all links and decides the relay which is best to amplify its received signal, based on the Maximum-SNR criteria. The lack of CSI at the transmitter makes the transmitter employ multi-layer coding or outage approach to send its desired data to the destination. The equivalent channel gain associated with the considered communication channel is modeled, and the average achievable rate of the network is formalized. Moreover, the average achievable rate of the network is analyzed in the case of having perfect CSI at the transmitter as an upper bound. Simulation results show that increasing the number of relays can improve the average achievable rate of the network and fill the gap of not having the CSI for lower relay numbers, while the total transmit power of the network is fixed.