Effect of channel distortions in the performance of digital transmission systems with QAM modulation

Analytical expressions for mean square and peak values of the intersymbol interference in QAM (quadrature amplitude modulation) digital transmission systems with some particular channel transfer functions are derived. Linear, quadratic, cubic, and sinusoidal channel amplitude responses are considered. Performance degradation curves corresponding to these distortions are obtained using a computer program for analysis and simulation of digital transmission systems. Results of performance degradation for 16-QAM and 64-QAM modulation systems are presented. For small distortion levels it is also shown that the obtained analytical results can provide a simple approximation for the performance degradation.<
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