Trellis-coded modulation on digital microwave radio systems-simulations for multipath fading channels

Extensive simulations have been made to examine the performance of digital microwave radio systems based on TCM (trellis-coded modulation). Two coded systems have been simulated: the coded 1024-QAM (quadrature amplitude modulation) system uses separate TCM schemes for the I and Q channels, while the coded 512-CR system treats I and Q channels together. Theoretically predicted lower bounds on error performance were approached by both systems for additive white Gaussian noise channels. With residual ISI (intersymbol interference) the coded system achieved larger coding gains than with additive white Gaussian noise alone, due to the ability of the Viterbi decoder to correct short burst errors. The coded 512-CR system performed better than the coded 1024-QAM system in all circumstances. This is attributed to the use of combined I and Q channel coding and the more complex convolutional encoder used in the coded 512-CR system. It is concluded that TMC used in conjunction with adaptive equalization can achieve significant improvements in error performance on digital microwave radio systems