This paper presents simulation results of the improvement due to interleaver with Trellis-coded modulation scheme in a channel model of a Mobile Satellite Communications System. The transmission technique makes use of a Trellis code for 8-PSK modulation and a block interleaver with fixed interleaving span of 10 symbols and different interleaving depths assuming a delay transmission constraint of 100 ms. Performances are analyzed in terms of Bit Error Rate (BER) versus Energy to Noise Power Spectral Density ratio. An available simulation model of fading channel has been designed with a combination of Rice / Lognormal statistics. This model is suitable for all types of environments by tuning the model parameters and take into account the elevation angle and the mobile velocity.