Exact calculation of the effect of ISI and AWGN on the performance of QAM and SQAM systems

The authors apply the Gauss quadrature rule to the calculation of the probability-of-error performance of QAM (quadrature amplitude modulation) and SQAM (staggered QAM) systems. This method allows the exact calculation of error probability performance including the effects of the intersymbol interference (ISI) of additive white Gaussian noise (AWGN). The sensitivity of QAM and SQAM systems to timing jitter and phase jitter is analyzed. It is shown that the superiority of SQAM over WAM depends strongly on the filter roll-off factor. SQAM provides better performance compared to QAM only the roll-off factor is larger than about 0.5. It is also shown that the mean-square-error analysis for estimating the probability-of-error performance can lead to erroneous performance prediction, particularly in regard to the superiority of SQAM systems