This paper presents some trellis codes that provide high coding gain over the frequency non-selective slowly Rayleigh distributed fading channel. It is shown that the use of two encoders in parallel - used to specify the in-phase and qudrature components of the transmitted signal - results in great minimum time diversity than the conventional design in which a single encoder is used. Using this approach - which we label ﲉ-Q TCM - codes with bandwidth efficiencies of 1,2 and 3 bits/sec/Hz are described for various constraint lengths. The performance of these codes is bounded analytically and approximated via simulation; the results show a large improvement in the BER when compared with conventional TCM schemes. Indeed, when this approach is applied to channels with independent Rayleigh fading, the resulting coding gain is close to that implies by the cutoff rate limit, even for only moderately complex systems.

The proposed codes are also simulated over channels with correlated fading; it is concluded that an interleaver span of 4v yields performance close to what is achieved with ideal interleaving.