In wireless communications, medium-scale fading is usually modelled as a multiplicative and slowly time varying random process. The received signal r(t) can be expressed as [1] where ( is the average transmitted signal energy, s(t) is the transmitted signal, h(t) is the random process that characterizes the medium-scale fading, and n(t) is an additive white gaussian noise process with a double-sided variance of N o /2. The medium-scale fading is considered as log-normally distributed for any t value. In a slow-varying environment,