Digital communications over satellite channels

The problem of digital data transmission over bandlimited nonlinear channels in the presence of intersymbol interference, white Gaussian noise in the uplink and downlink paths, is considered. The satellite transponder is assumed to be either of the hard-limiter or soft-limiter type. A maximum likelihood receiver is developed to detect B phase shift keying signals transmitted over a satellite channel. It is shown that for wideband channels, the receiver structure corresponds to the one-sample test for both hardlimiting and softlimiting transponders. As part of the derivation of optimum receivers, a square law structure is obtained for the softlimiter case with intersymbol interference. The analysis is then repeated for the Q phase shift keying system with similar results. Also, the problem of in-bank carrier interference in the presence of uplink and downlink noise is considered by deriving the likelihood receiver for this case. It is shown that the optimum receiver is of the one-sample type for the wide band channel and of the square law type for the band limited case.