We are studying an advanced satellite broadcasting system, which uses the 21GHz broadband high-power satellite transponders, using the Communication and Broadcasting Engineering Test Satellite (COMETS). In the COMETS satellite broadcasting experiments, highly frequency-effective Trellis-Coded 8-PSK (TC8PSK) modems were developed. This paper studies the degradation of bit error performance of TC8PSK caused by nonlinear amplification (AM/AM and AM/PM conversion), group delay, and amplitude-frequency characteristics of the satellite transponder. We found that the nonlinearity and amplitude-frequency characteristics are dominant factors for degradation, using computer simulation and COMETS experiments.
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