For fast fading digital mobile systems, a s ec trally efficient technique that can achieve more ,Ran 2b/s/Hz with a built-in fade canceller is Recent studies show that fading in digital mo!%:g$ munications can be cancelled by adding redundant bits to the customer data or with Pilot-based techniques. The objective of this paper is to extend this concept to a more spectrally efficient class IV Quadrature Partial Response Signalin (QPRS) system. However, in such schemes if the ikt is corru ted by the phase noise caused by the plot-data interkrence, the fade cancellation will not effectively remove the error floor. The class IV system has an inherent advantage, in that it has a s ectral null at DC and a low ener y content at the en& of the band. Such systems also fave a higher speed tolerance. It is shown that a small bandwidth around DC can be vacated to insert the pilot. Our Ireliminary results indicate that the residual error oor can be reduced from lo-* to in fast fading channels. We show t h e imurovement in BER Derformance of the band-vacated QPRS compared i o -t h e unfiltered QPRS.

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Spectral efficiency of about 2b/s/Hz compared to 1.6b/s/Hz of the new cellular standard 5 4 -QPSK could be achieved with our proposed pilot symbol assisted class IV Quadrature Partial Response Signalling Scheme (QPRS) in fast fading mobile radio channels. The information bits are multiplexed with a pseudo random pilot sequence which is used for coherent detection. The MLSE type receiver improves the performance in multipath fading channels. This scheme is evaluated in terms of spectral and power efficiency, and ability in eliminating the Doppler shift caused error floor of relatively low bit rate digital mobile radio. Digital and analog channel sounding Techniques for fade compensation in class IV partial response modems are compared. In slow fading mobile channel the digital fade compensated scheme is within 2 dB of Ideal Coherent QPRS.