Performance of trellis coded 16-QAM in a two-link satellite channel

The performance of trellis coded 16-ary QAM (quadrature amplitude modulation) signaling transmitted through a two-link, nonlinear satellite channel is studied. A 3/4-rate coding and a 4-state, simple convolutional encoder is considered. The bandlimited signal is distorted by a nonlinear amplifier on board the satellite which introduces AM-AM and AM-PM conversions. Additive white Gaussian noise is assumed to be added to the signal on both up and down links. Bit error rates are computed for uncoded 8-ary coherent phase-shift keying (CPSK) and trellis coded 16-ary QAM transmissions as a function of up and down link carrier-to-noise ratios. A raised cosine filter with a roll-off factor of α=0.4 equally split between the transmitter and the receiver, giving a spectral efficiency of 2.14 b/s/Hz, is assumed. It is shown that as output backoff is increased, coding gain is also increased and can reach a value of over 3 dB. However, when the best performances of the two signalings are compared, the coding gain is about 1 dB