Rayleigh fade compensation QPRS coherent mobile radio modems operated at a practical 2 b/s/Hz efficiency

For fast-fading digital mobile systems, a spectrally efficient technique that can achieve more than 2 bit/s/Hz with a built-in fade canceler is proposed. Recent studies show that fading in digital mobile communications can be canceled by adding redundant bits to the customer data or with pilot-based techniques. The objective is to extend this concept to a more spectrally efficient class IV quadrature partial-response signaling (QPRS) system. However, in such schemes, if the pilot is corrupted by the phase noise caused by the pilot-data interference, the fade cancellation will not effectively remove the error floor. The class IV system has an inherent advantage in that it has a spectral null at DC and a low energy content at the ends of the band. Such systems also have a higher speed tolerant. It is shown that a small bandwidth around DC can be vacated to insert the pilot. Preliminary results indicate that the residual error floor can be reduced from 10^-2 to 10^-5 in fast-fading channels. The improvement in bit error ratio performance of the band-vacated QPRS is compared to the unfiltered QPRS