Fade compensation in QPRS mobile radio modems

It is shown that a spectral efficiency of about 2 b/s/Hz, compared to 1.6 b/s/Hz of the new cellular standard π/4-QPSK (quadrature phase shift keying), could be achieved with a 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 pseudorandom pilot sequence which is used for coherent detection. The MLSE (maximum likelihood sequence estimation)-type receiver improves the performance in multipath fading channels. This scheme is evaluated in terms of spectral and power efficiency and its ability to eliminate 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 a slow-fading mobile channel, the digital fade compensated scheme is within 2 dB of the ideal coherent QPRS