The problem of maximizing the minimum free squared Euclidean distance of a trellis code is developed from a geometric point of view. This approach provides a new way of constructing constellations for trellis coding. A decomposition of the trellis topology leads to a systematic construction of signal sets and generators for geometrically uniform trellis codes. An algorithm is proposed to construct geometrically uniform trellis codes, and examples show how to obtain large free distance trellis codes. This approach unifies the construction of convolutional codes over the binary field and trellis codes over the real field.

A Markovian technique is described to calculate the exact performance of the Viterbi algorithm used as either a channel decoder or a source encoder for a convolutional code. The probability of information bit error and the expected Hamming distortion are computed for codes of various rates and constraint lengths. The concept of tie-breaking rules is introduced and its influence on decoder performance is examined. Computer simulation is used to verify the accuracy of the results. Finally, we discuss the issue of when a coded system outperforms an uncoded system in light of the new results.>