Overview

From APPLIED MICROWAVE & WIRELESS, VOL. 10, NO. 2, March 1998

Communication systems engineers working in digital data transmission have long been aware of the need for a trade between the prime power efficiency of RF amplifiers and the spectral containment of the data signal produced at the output of those amplifiers. Maximum output power implies maximum prime power efficiency, but not necessarily the best spectral containment. Although the power spectral density of a digital data signal may be well contained by basic bit pulse shaping or by signal pre-filtering at the input of a power amplifier, it remains an axiom of experience that the nonlinear saturating effect of the power amplifier generally tends to cause the spectral sidelobes of the data signal to regrow.

One class of signals that enjoys immunity from the regrowth effect [1] is the constant carrier envelope signal, for example, minimum shift keying (MSK) or other forms [2] of digital frequency shift keying (FSK). Classical MSK, unfortunately, lacks the inherent spectral containment [1] required in the regulatory environment of modern wireless communications, and the spectrally contained forms of FSK, such as [3] Gaussian minimum shift keying (GMSK), require rather complex detection schemes to deliver maximum communications efficiency.

Of considerable interest for its simplicity of implementation [4] is the offset quadrature phase shift keyed (OQPSK) modulation format, which includes both classical MSK and...