Unfiltered FQPSK : Another Interpretation and Further Enhancements Part 1 : Transmitter implementation and optimum reception By

Anew interpretation of unfiltered FeherPatented Quadrature Phase-Shift-Keying (FQPSK) is presented, readily identifying a means for spectral enhancement of the transmitted waveform as well as an improved method of reception. The key to these successes is the replacement of the half-symbol by half-symbol mapping, originally used to describe FQPSK by a symbol-by-symbol mapping operation combined with memory. The advantages of such an interpretation are two-fold. In particular, the original FQPSK scheme can be modified so that the potential of a waveform slope discontinuity at the boundary between half symbols is avoided without sacrificing the “constant” envelope property of the transmitted waveform. Also, a memory receiver can be employed to improve error probability performance relative to previously proposed symbol-by-symbol detection methods. The analysis presented in this paper does not include other versions of FQPSK, such as FQPSK-B, which is currently being considered for military applications. This is part one of a two-part article. Part two will be published in the March 2000 issue of Applied Microwave & Wireless magazine.