Trellis coded communication systems-colored noise and the swapping technique

An analytical approach for investigating the effect of noise correlation on the performance of trellis-coded communication systems is described. Several trellis codes are investigated in the presence of colored noise, and computer simulation and real-time experimental results are given to confirm the analysis. In some practical cases, the actual coding gain could be as small as a fraction of 1 dB as opposed to the nominal 4-5 dB of coding gain that can be obtained on additive white Gaussian noise (AWGN) channels. A filter swapping technique which eliminates the performance degradation due to the effect of noise correlation is proposed. It is shown that if the equalizer is moved from the receiver to the transmitter and is scaled to satisfy an average power constraint, then the noise at the Viterbi decoder input is white and the signal-to-noise ratio remains the same. Doing this allows the nominal coding gain to be achieved.<
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