π/4-FQPSK: an efficiency improved, standardized π/4-DQPSK compatible modulation/nonlinearly amplified RF wireless solution

A new modulation solution suitable for digital wireless communications and broadcasting applications, named Feher´s π/4-FQPSK, is presented. This solution is an implementation of quadrature crosscorrelated Feher et. al. (1986, 1987) inventions. It has the combined advantages in spectral efficiency and power efficiency, as well as compatibility with IS-54 and IS-136 standardized π/4-DQPSK. Many researchers demonstrated that conventional π/4-QPSK has a significant spectral spreading in nonlinearly amplified systems. To reduce spreading, we introduce an in-phase (I) and quadrature (Q) or I/Q cross correlated baseband processor into the conventional π/4-DQPSK architecture, which reduces the envelope fluctuation significantly. While conventional π/4-DQPSK requires linearized, relatively expensive and low power efficient RF stage, Feher´s π/4-FQPSK can be operated in nonlinearly amplified, e.g. “C-class” power efficient systems. That is desirable for applications requiring high transmit efficiency, such as cellular/wireless/personal communications and broadcasting systems. The architecture of the π/4-FQPSK modem is described and its performance for different applications is evaluated through computer simulations and compared with some other modulation schemes including quadrature crosscorrelated GMSK. The compatibility of the π/4-FQPSK with the US digital cellular standard (IS-54 and IS-136) is also studied. The results demonstrate that π/4-FQPSK is both power and spectrally efficient for many applications