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.