Performance of cooperative relaying with adaptive modulation and selection combining

Taking advantage of the broadcast nature of wireless medium, a relay node can forward an overheard signal from the source to enhance the receiving quality. Many previous studies on cooperative relaying focus on maximal ratio combining (MRC) to exploit the spatial diversity. However, it is complex to enable different modulation levels with MRC so as to better address varying channel conditions. There has been some existing work on the performance of cooperative relaying with selection combining (SC). In this paper, we further consider adaptive modulation and coding (AMC) in a cooperative relaying scenario with selection combining. Based on the bit error rate (BER) analysis, the minimum signal-to-noise ratio (SNR) thresholds are determined to activate different modulation modes at the relay node, such that the overall BER at the destination is no greater than a target BER constraint. Simulations are conducted to verify the accuracy of the BER analysis. The numerical results demonstrate the performance gain of cooperative relaying with adaptive modulation and selection combining.