Searching for good time-variant TCM codes as an optimization problem

The authors propose a new method for searching for good trellis modulation (TCM) codes using a gradient based optimization technique. The search is based on the criterion of maximizing the free distance to average energy ratio subject to a given discrimination rate. It is found that the new approach is very suitable for finding good time-variant TCM codes. Most of the previously proposed codes fall into the subsets of its searching space. Practical problems in software implementation and experimental results are described