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

Abstract

A new modulation solution suitable for digital wireless communications and broadcasting applications, named Feher's /spl pi//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 /spl pi//4-DQPSK. Many researchers demonstrated that conventional /spl pi//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 /spl pi//4-DQPSK architecture, which reduces the envelope fluctuation significantly. While conventional /spl pi//4-DQPSK requires linearized, relatively expensive and low power efficient RF stage, Feher's /spl pi//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 /spl pi//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 /spl pi//4-FQPSK with the US digital cellular standard (IS-54 and IS-136) is also studied. The results demonstrate that /spl pi//4-FQPSK is both power and spectrally efficient for many applications.