Performance evaluation of pragmatic TCM codes through band-limited nonlinear satellite channel: a computer simulation approach

In band-limited nonlinear satellite applications, various papers have shown that respectable coding gains can be achieved by Ungerboeck (1987) TCM (trellis code modulation) codes, making them popular in this application owing to the advantage of performance improvement without bandwidth increase or transmitter power increase, and with the codes displaying their robustness to the nonlinearity and band-limiting that prevail in satellite channels. A recent paper by Viterbi (1989) proposed pragmatic codes which had a single coder and decoder for various bandwidth efficiencies and achieve a performance comparable to that of Ungerboeck codes on a linear Gaussian channel. These codes are punctured versions of the basic ¹/ ₂ rate convolutional code mapped into MPSK signal phase constellation. The performance on band-limited nonlinear satellite channel of pragmatic 8 PSK codes is studied with respect to equivalent Ungerboeck 8 PSK codes. Computer simulation is used to estimate the coding gains achieved on these various codes, and lower bounds for bit error probability are estimated through formulas approximated by Forney (1973). Signal space diagrams are also plotted to show the band-limiting effect, giving a better picture of the signal point dispersion phenomenon caused by severe band-limitation of the satellite channel.<>