Performance Analysis of Decode-and-Forward Relay Network Under Adaptive M-QAM

In this paper, the performance of a cooperative Decode-and-Forward (DF) relay network with adaptive M-ary Quadrature Amplitude Modulation (M-QAM) is analyzed. A five mode adaptive M-QAM scheme is employed, and the system performance is investigated for both fixed switching levels and for optimized switching levels with a target bit error rate (BER) constraint. Expressions for average BER, spectral efficiency, and outage probability are derived to investigate the performance of the cooperative system under independently and identically distributed (i.i.d.) Nakagami-m fading wireless environments. Adaptive M-QAM with optimized switching levels maintains the target BER constraint while fixed switching levels achieves a conservative BER, which is lower than the target.