Spectral Efficiency of Time-Frequency-Packed Nonlinear Satellite Systems

We consider a realistic satellite communications system for broadband and broadcasting applications in a single-carrier-per-transponder scenario. We describe how to compute the spectral efficiency of such a system when suboptimal receivers are employed and we evaluate the performance improvements that can be obtained through the adoption of the time-frequency packing technique, which removes the constraint of orthogonal signaling, and relies on both time packing of adjacent symbols and reducing the carrier spacing of the adjacent channels. Our analysis reveals that introducing controlled interference can significantly increase the spectral efficiency of this system. Moreover, if a receiver which is able to account for the interference and the nonlinear impairments is adopted, rather than a classical predistorter at the transmitter coupled with a simpler receiver, the benefits in terms of spectral efficiency can be even larger. The conclusions here reported depend, from a quantitative point of view, on the particular considered scenario and on the constraints adopted in the investigation.