256-QAM Modem Performance in Distorted Channels

Performance degradations of 256-QAM modems in distorted channels are studied in this correspondence. Illustrative linear, parabolic, and sinusoidal amplitude and group delay channel distortions, caused by filter imperfections and/or by selective radio fades, are investigated. To enable an easy comparison with 64-QAM systems, we present the degradations of these systems in the same figures as those of 256-QAM modems. It is shown that linear (slope) group delay and sinusoidal (ripple) amplitude distortions cause the most significant performance degradations.