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Distributed Adaptive Power Allocation for Wireless Relay Networks

In this paper, we consider a 2-hop wireless relay network. We explore transmit power allocation among the source and relays to maximize the received SNR at the destination. We consider two relaying protocols, "amplify and forward" (AAF) and "decode and forward" (DAF) and calculate the respective power allocations for both uncoded and coded system. For a 2- hop relay system with one relay node, we derive a closed-form power allocation solution and based on it we propose a relay active condition. If and only if the fading channel coefficients satisfy this condition, the relay transmits the signals to the destination; otherwise, the relay will stay in an idle state. For a system with more than one relay nodes, general closed-form power allocation solutions based on the extact SNR expression are not tractable, so we calculate a SNR upper bound and derive a sub-optimum power allocation solution based on this bound. The simulation results show that for a 2-hop relay channel, the proposed adaptive power allocation (APA) scheme can bring the system a considerable SNR gains compared to the equal power allocation scheme. This gain will be further monotonically increased as the number of relays increases.