Error analysis of M-QAM with equal-gain diversity over generalised fading channels

M-ary quadrature amplitude modulation (M-QAM) is a spectrally efficient modulation scheme, used for video transmission applications in third and forthcoming generations of wireless networks. In the paper, the authors present a unified framework for the error performance of M-QAM, employing L-branch equal-gain combining over generalised fading channels, such as Nakagami-m, Rice, Hoyt or Weibull. For each channel model an exact closed-form expression is derived for the moments of the EGC output signal-to-noise ratio (SNR). Using these expressions, the symbol error performance of M-QAM is studied, with the aid of the moment-generating function approach and the Pade approximants theory. The proposed mathematical analysis is illustrated by selected numerical results, pointing out the effect of the input SNRs unbalancing, as well as the fading severity on the system's performance. Simulations are also performed to check the validity and the accuracy of the proposed analysis.