An application of trellis coded modulation to digital microwave radio and its performance

The authors describe a modified symbol-rate-increased TCM (trellis coded modulation) for digital microwave radio systems. The symbol-rate-increased TCM accomplishes coding redundancy through bandwidth expansion instead of through signal point expansion, in order to obtain a greater coding gain than the Ungerboeck-type TCM. However, this scheme requires the bandwidth to be expanded by a fixed factor m/(m-1) for a 2^mQAM (quadrature amplitude modulation) system. The proposed scheme allows the bandwidth expansion ratio to be varied to an arbitrary value smaller than m/(m-1). Simulation results have clarified that the proposed scheme achieves a significant improvement over an uncoded scheme