The aim of this thesis is to find an optimal power allocation strategy for the transmitting nodes in a network scenario which comprises two sources, a single relay and a single destination. The main problem which is present in such network configurations is the self-interference phenomenon created by the relay, which attempts to transmit and receive at the same time on the same frequency band. Finding the correct power level (both at sources and relay) which allows the overall rate maximization is a theme of great interest, since many wireless applications present this problem and the use of relays is expected to increase in the near future.