Optimized Power Allocation for Multiple-Antenna Multiple-Relay Cooperative Communication System

One of the main advantages of relayed communication is that it reduces the necessary transmit power and distributes transmitted power throughout the hops. This implies lower interference to the rest of the network and consequently improves performance of the system. In this paper we investigate optimized power allocation over two-hop multiple antenna fixed relays for a given power budget. Outage probability which is the probability that the link quality falls bellow the certain threshold in a Rayleigh fading channel is used as the performance criterion. It is determined that increasing the number of relays and antennas at each relay increases capacity. The outage probability of threshold maximal ratio combining (T-MRC) and threshold selection combining (T-SC) of the multiple antenna multiple fixed relays is derived. Threshold decode and forward relaying (T-DF), which is more reliable than conventional decode and forward relaying (DF) is considered. Results show that optimizing the allocation of power enhances the system performance, especially in highly unbalanced links. The system with optimized power allocation can outperform the two-hop multiple relay system using uniform power allocation and distributed beamforming at the expense of increased computational complexity.