DESIGN AND ANALYSIS OF TRELLIS CODES FOR ORTHOGONAL SIGNAL SETS

This paper studies trellis codes to be used with orthogonal signal con stellations. The intended application is in direct-sequence code-divis ion multiple-access communication systems. The problem of designing go od codes is addressed showing how to construct trellis codes from bloc k codes with good burst-error detecting capabilities. Several examples are given resulting in codes equivalent to those found previously by computer search in [8]. The procedure presented can be done by hand an d is applicable for designing codes with long constraint lengths and l arge signal sets where a computer search becomes prohibitive. Performa nce of such coded systems can be determined through transfer functions of the specific codes used. A general transfer function is given whic h provides a reasonable approximation to the actual transfer function of good codes. Thus, a first-order approximation to the performance of a given system can be determined without actually going through the p rocess of designing and analyzing a specific code.