BLOCK VERSUS TRELLIS - AN INTRODUCTION TO CODED MODULATION

Coded modulation has had a very significant impact on the communications scene in the decade or so since its introduction, finding practical applications from voice-band modems for telephone lines to deep-space communications. The paper introduces the principles of coded modulation and describes the two main schemes: block coded modulation (BCM) and trellis coded modulation (TCM). In particular it considers the argument between the proponents of BCM and TCM, and points out some pitfalls in the use of performance measures such as asymptotic coding gain for these schemes. It concludes that in terms of performance versus decoder complexity the schemes seem to be quite close, and the choice of the system designer may be determined by other factors.