Performance of the 16QAM modem in the satellite communication environment

This paper presents computer simulation results of the 16QAM modem in the satellite communication environment. An end-to-end communications system including a 16QAM modulator, klystron, satellite transponder, 16QAM demodulator, timing recovery loop, phase recovery loop, and channel filters are modeled by using SPW. Satellite transponder components modeled in SPW include up/down converters, channelizer and TWTA. Laboratory measured data are used to model the transmitter klystron and transponder TWTA. Simulation results show that the bit error rate (BER) performance is severely degraded by nonlinear amplifiers. Techniques to minimize the BER performance degradation using "high power amplifier back-off" and "predistortion of the transmitter symbols" are discussed.