On the performance of trellis-coded modulation in digital microwave radio

Trellis-coded modulation (TCM) techniques are considered for use in a digital microwave radio (DMR) system employing high-level M-QAM modulation. Emphasis is placed on whether the coding gain offered at high signal-to-noise ratio is also in effect during deep selective fades. A specific Ungerboeck code, used in a 512-cross modulation scheme was found to have a lower probability of outage (for a bit-error-rate (BER) threshold of 10^-3), than an uncoded 256-QAM system having the same symbol rate. The same linear adaptive finite-tap transversal equalizer was used in both the uncoded and the coded systems. Further work was done to see what effect various code parameters had on the fade performance. The result was that the TCM system always outperformed the uncoded system (up to a BER of 10^-3 ) under deep selective fades