ENVELOPE FLUCTUATION STATISTICS OF FILTERED PSK AND OTHER DIGITAL MODULATIONS

Radio signals derived using constant-envelope digital modulations (e.g., PSK, FSK and variations thereon) are impervious to the nonlinear characteristics of high-power RF amplifiers such asTWT's. However, constant-envelope modulations that must be heavily filtered to meet spectrum emission requirements, or intrinsically spectrum-efficient modulations such as Quadrature Partial Response Signaling (QPRS), exhibit envelope fluctuations that render them vulnerable to amplifier nonlinearities. This paper describes a study, based on the use of Monte Carlo computer simulations, of the RF envelope variations associated with different digital modulations. Simulations and statistical analyses of these variations have been conducted for both filtered PSK and QPRS. The PSK category includes such special cases as Staggered Quaternary PSK (SQPSK); Minimum Shift Keying (MSK);L-ary PSK with cosine rolloff shaping (divided equally between transmitter and receiver); and linear phase modulation using shaped (nonrectangular) baseband pulses. Copyright © 1979 by The Institute of Electrical and Electronics Engineers, Inc.