On design of TCM in channels with different fading

When trellis coded modulation (TCM) is used on fading channels with interleaving/deinterleaving, the design of the codes for optimum performance is guided by the length of the shortest error event path and the product of the branch distance along that path. It is shown for a Rician fading channel, with a large value of the fading factor, that these two criteria are unsuitable for optimum code design. Simulation is used to compare the error performance of three differently designed, 4-state rate, 2/3 trellis codes in channels with different fading. The results show that when the fading factor is larger than ten, the primary design criterion of TCM in a Rician fading channel is the free Euclidean distance, and that the length of the shortest error event path plays a lesser role