Baseband pulse shaping for π/4 FQPSK in nonlinearly amplified mobile channels

We apply baseband pulse shaping techniques for π/4 QPSK in order to reduce the spectral regeneration of the bandlimited carrier after nonlinear amplification. These Feher´s patented techniques, namely, π/4 FQPSK (superposed QPSK) and π/4 CTPSK (controlled transition PSK), may also be noncoherently demodulated. Application of these techniques is in fast fading, power efficient channels, typical of the mobile radio environment. Computer simulation and experimental studies demonstrate that with these baseband waveshaping techniques, carrier envelope fluctuations are significantly reduced, and the out-of-band power after nonlinear amplification is suppressed by up to 20 dB compared to π/4 QPSK. In frequency noninterleaved land or satellite mobile radio systems operating in a nonlinear, fading and ACI (adjacent channel interference) environment, these techniques may achieve 20%-50% higher spectral efficiency compared to π/4 QPSK. In mobile cellular systems using π/4 QPSK, such as the new North American and the Japanese digital cellular systems, the application of these baseband pulse shapes may allow more convenient and less costly amplifier linearization