Optimized Power Allocation in Selective Decode-and-Forward Cooperative Communication

Cooperative relay transmission is an emerging concept in wireless communication, in which single-antenna devices are allowed to take benefit of spatial diversity to improve reliability and error performance. In this work, Selective Decode-and-Forward (SDF) cooperative relaying scheme is analyzed, in which decoding and subsequent retransmission are undertaken by the relay node only when the received signal meets certain threshold constraints at that node. This paper describes power optimization in relay nodes for a dual-hop half-duplex SDF-based cooperative relay communication system, with all nodes using single antenna. For the system, average end-to-end probability of error is derived, leading to evaluation of asymptotically tight upper bound under high signal-to-noise ratio (SNR). Optimal power allocation to minimize the bit error rate (BER) is formulated and a closed-form solution for this convex optimization problem is derived and verified through simulation. The BER performance is compared with that of direct source to destination link which indicated performance enhancement, owing to virtual MIMO effect. A variety of numerical results reveal that cooperate scheme with optimal power allocation has an improved performance, compared to its direct link counterpart.