Firstly

a mathematical model of cooperative system in asymmetric channel considering the link diversity gain between the source and destination was presented. An analytical expression of the average outage probability which was proved accurate by simulation was derived by using the method of characteristic function. Theory and simulation indicate that the outage probability of the cooperative system has a close relationship with the relays’ number

location and the power allocation ratio of the cooperative system and it makes higher performance gain to consider the direct link between the source and the destination. And then the effect of the relay nodes location for the optimal power allocation ratio was studied based on the mathematical model. The results show that the optimal power allocation ratio is limited by the re- lays’ locations.