Performance of pi /4 SQAM in a hard-limited channel in the presence of AWGN

A strategy that reduces the spectral spreading when an ideal hard-limiter is used as a first approximation to a fully saturated power amplifier is presented. This strategy combines superposed quadrature amplitude modulation (SQAM) filtering with the pi /4-shift quadrature phase-shift keying (QPSK) digital transmission format adopted for the first generation of US digital cellular systems. Simulation results showed that this pi /4 SQAM filtering strategy increased capacity by 35% in comparison to hard-limited pi /4 QPSK. Using computer-aided design, a receive filter that would limit the degradation of E/sub b//N/sub 0/ to less than 1.4 dB at a bit error rate of P/sub e/=10/sup -4/ was selected.<
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