Performance of dual-hop DF relaying systems with QAM schemes over mixed η-μ and κ-μ fading channels

Performance of a dual-hop decode-and-forward relaying system that uses quadrature amplitude modulation (QAM) scheme is analyzed over mixed eta-mu and kappa-mu fading channels. Closed-form expressions are derived for the average symbol error rate (ASER) for rectangular QAM and cross QAM schemes using moment-generating function-based approach. The obtained ASER expressions accommodate other mixed fading channels addressed in the literature, as special cases. Further, a simple expression for the asymptotic ASER has been obtained, useful to determine the system performance at high signal-to-noise-ratio values. The obtained asymptotic ASER results reveal that the diversity order is determined by the most severely faded link while the coding gain is affected by the total power of the system. Additionally, we analyze the optimal power allocation method, which provides a practical design rule to optimally distribute the total transmission power between the source and the relay to minimize the ASER. Extensive numerical and computer simulation results are presented that confirm the accuracy of presented mathematical analysis.