Communication in a fluctuating channel models and use of explicit or implicit diversity

When the transmission is fluctuating (with respect to the elementary transmission duration) diversity techniques enable to improve the performance. In a first part the Rayleigh model has been tested in long distance submarine acoustics transmission and we present some experimental results of explicit frequential diversity. In the general delay and Doppler dispersive case, we present some results of implicit diversity in order to decrease the error probability and we show the consequences of this concept on to the signal design problem. We have applied this study particularly in two cases : the multipath transmission and the fast-fading modulation case.