Performance estimation and design of group demodulator for satellite FDMA/TDM transmission

The authors describe a Monte Carlo simulation of QPSK (quadrature phase shift keying) and offset QPSK group modems which take into account the effect of the nonlinearity of each ground terminal HPA. The effect of uplink fading due to rain, as encountered in satellite links operated in the Ka and Ku bands, is included. Results show that a normalized channel spacing with respect to a symbol rate of 2.5 or greater is required to reduce the effect of adjacent channel interference. At this spacing the performance of the model will still incur a E_b/N₀ (energy per bit/noise density) degradation of about 1.0 dB. In addition, design criteria for major components such as digital subfilter, rate conversion filter, carrier recovery circuits, and quantization are given