An improved π/4-DQPSK compatible Feher´s “π/4-FQPSK” nonlinearly amplified modulation

In this paper, a new modulation scheme suitable for digital satellite and land mobile communications, named π/4-FQPSK, is presented. It has the combined advantages of π/4-QPSK and FQPSK techniques by using Feher´s patented techniques. Many researchers have shown that conventional π/4-DQPSK has significant spectral spreading in nonlinearly amplified channels. To reduce spreading we introduce an I/Q cross correlation baseband processor, which reduces the envelope fluctuation significantly. This makes the new modulation technique more suitable for nonlinear amplification, which is desirable for applications requiring high transmit efficiency such as digital satellite and land mobile communications. Unlike other power and spectrally efficient modulation systems, such as FQPSK-1, the π/4-FQPSK modulated signal can be detected noncoherently, due to the fact that there is no offset between the I and Q channel signals. The results of computer simulations demonstrate that π/4-FQPSK modulation technique is both power and spectrally efficient