Distributed adaptive power allocation in cooperative wireless communication systems

The performance of the cooperative transmission system can be improved significantly by allocating powers optimally among cooperative nodes when the system has a total power constraint. For a two-hop cooperative transmission system with only one relay node, the closed-form expression of the optimal power allocation factor was derived and a relay activation condition was acquired. If and only if the fading characteristics of the channels satisfy this condition, the relay transmits signals to the destination; otherwise, it will stay in the idle state. For a system with more than one relay node, the closed-form power allocation factors are difficult to derive directly based on the output signal-to-noise ratio (SNR) of the system. So, an SNR upper bound was derived and a novel power allocation scheme was proposed. The whole power allocation was divided into two stages and the optimal power allocation was implemented by using an iterative algorithm. Simulation results show that for a system with only one relay node, the proposed power allocation scheme can yield about 1~2 dB performance gains compared to the equal power allocation, as the number of relays increase, the performance of the system improved greatly when using the iterative power allocation method.