This paper evaluates the effect of spatial interleaving in the Viterbi algorithm with combined intersymbol interference (ISI) equalization, trellis-coded modulation (TCM) decoding and multi-signal detection. Through computer simulations, it is confirmed that spatial interleaving provides substantial diversity gains in both frequency-flat and frequency-selective Rayleigh fading channels. In Nakagami-Rice fading channels, performance improvement is significant at low Rician factor because of overcoming the burst errors incurred by signal fading. Spatial interleaving does not require additional computational complexity, memory buffer and decoding delay, differently from time interleaving. Moreover, the optimum combined TCM and ISI maximum likelihood sequence estimation (MLSE) can employ interleaving with almost no extra complexity, and iteration between equalization and decoding is not needed through the use of spatial interleaving.