XPSK: A New Cross-Correlated Phase-Shift Keying Modulation Technique

Abstract

A new modulation technique, cross-correlated phase-shift keying (XPSK), is introduced. XPSK is a band-limited offset QPSK modulation technique which has an almost constant envelope. In XPSK modulators, a controlled amount of cross correlation between the in-phase (I) and quadrature (Q) channels is introduced. I and Q cross correlation reduce the envelope fluctuation of the intersymbol-interference and jitter-free OQPSK (IJF-OQPSK) modulation scheme, introduced by Feher et al. [1], [2], from 3 dB to approximately 0 dB, thus further improving the performance of IJF– OQPSK systems in nonlinear radio systems [7], [14]. It is shown that the baseband signal of the modulator, the P e = f(E b /N o) performance, and the spectral characteristics of nonlinearly amplified (hardlimited or saturated) radio systems of XPSK and tamed frequency modems (TFM) are practically the same. The XPSK demodulator is a conventional OQPSK demodulator; the TFM demodulator requires a somewhat more complex signal processor. For this reason, the XPSK approach may lead to significant demodulator hardware cost savings, particularly in point-to-multipoint distribution systems such as broadcast systems. Copyright © 1983 by The Institute of Electrical and Electronics Engineers, Inc.