Convolutional codes for multi-level modems

The letter is concerned with predicting the performance of forward error correcting systems using binary convolutional codes for multilevel modulation schemes. The code comparison is based on the first few terms of the truncated generator function of the codes, where the distance between the code words is expressed in terms of the geometric Euclidean distance of the signal constellation. A table showing the results of a systematic search for the best codes is presented, and some performance simulation curves are also given. It is shown that optimum code selection depends not only on dfree, but also on additional weight and structure properties, which are very conveniently determined by the truncated generator function.