Perpustakaan Digital ITB

Most early communication satellite systems are power-limited; as improvements are made on launch vehicles and satellites become larger, the tendency has shifted from powerlimited to bandwidth-limited systems. In bandlimited nonlinear satellite applications, various papers have shown that respectable coding gains can be achieved by Ungerboeck 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 proposed pragmatic codes which have 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 f rate convolutional code mapped into MPSK signal phase constellation. In this paper, the performance on band-limited nonlinear satellite channel of pragmatic 8PSK codes is studied with respect to equivalent Ungerboeck 8PSK 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. 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.