Citation
Abstract
The balanced modulator, which is comprised of two matched amplitudemodulation modules, is widely used in phase-modulated communication systems. In practice, the perfect balance between these amplitude-modulation modules is di–cult to maintain, and the amplitude and phase imbalance can cause signal distortion and also introduce an undesired interfering tone signal component when such an unbalanced modulator is used to modulate the data directly onto the RF carrier. The rendered imperfection inevitably degrades the receiver performance and, particularly in a quadrature-phase-shift-keyed (QPSK) system, causes cross-talk between channels. This article describes the error performance of binary-phase-shift-keyed (BPSK) and QPSK signals generated from unbalanced modulators and tracked by the conventional Costas loop and a generalized Costas loop, respectively, with the effect of modulator unbalance on the steady-state lock points of these carrier tracking loops being taken into consideration. Also, a more generalized model that includes the possible phase deviation from the ideal 90-deg separation between the in-phase and quadrature channels of QPSK is considered in this article.
Details
- Volume
- 42-130
- Published
- August 15, 1997
- Pages
- 1–13
- File Size
- 325.3 KB