## Pilot tone-based fading correction

#### A number of mobile radio systems use either pilot tone(s) or pilot symbols for correction of narrowband multipath fading. When correctly applied, the information provided by the reference tone concerning the instantaneous Doppler shift and amplitude/phase fluctuations of the received signal due to multipath can be used to fully correct for distortion in the wanted data signal.
Because the fading pattern can change several hundred times per second for some mobile data applications, the pilot-based correction processing must operate in real time. This requires feedforward correction techniques, of which a commonly used method is feedforward signal regeneration (FFSR). A circuit diagram for a quadrature implementation of an FFSR circuit ideally suited for M-QAM modulation is given here. Further information can be found in Bateman and McGeehan (1983).

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