Recent studies have shown that trellis-coded modulation can achieve coding gains in the residual intersymbol interference environment that exists after adaptive equalization on terrestrial digital microwave radio (DMR) systems. Simulated system signatures for 140 Mb/s DMR systems incorporating trellis-coded 512-QAM modulation are presented and the results compared to the system signatures of equivalent uncoded 256-QAM systems. At a threshold bit-error rate (BER) of 10/sup -3/, the signature of the uncoded system can be degraded by the addition of coding. However, at a threshold BER of 10/sup -4/, it is found that trellis coding improves the system signature. Conditional probabilities of outage and the percentage of error-free seconds are also calculated for the coded and uncoded systems.
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