Comparative analysis of timing error detectors for symbol synchronization of the coherent system of digital communication with QPSK modulation

DOI: 10.31673/2412-9070.2019.061218

Abstract

The article discusses the principles of building a coherent digital communication system with QPSK modulation, explores the constellations of signals at the output of the phase synchronization circuit. To achieve the goal set in the article, a comparative analysis of the synthesis methods of synchronization systems in telecommunication devises was carried out; the main trends and available means of constructing synchronization and filtering devices in the presence of a real interference complex are established; mathematical models and methods for estimating the error of clock synchronization systems have been developed. The receiver must take into account the effects of a static frequency shift, a variable time delay of the symbol delay, and Gaussian noise. Symbol synchronization is based on a change in the sign of the data to obtain the correct synchronization error signal. The interpolator creates consistent filter output signals that are aligned with symbol boundaries and optimal sampling times. The functions that the symbol synchronization circuit performs, the features of constructing a synchronization error detector (SED) are analyzed. The improved receiver circuit phase shift keying signals by using circuit solutions to improving conditions for synchronization by using direct digital synthesizers synthesis are proposed. SED of Gardner, Early-Late, Mueller & Muller, their error and S-curve equations are investigated. The dependence of the relative synchronization error on the signal-to-noise ratio is obtained. It was concluded that the Early-Late SED has a large S-curve slope, the most uniform dependence of the relative synchronization error on the signal-to-noise ratio, which decreases from 4% to 1% with an increase in the signal-to-noise ratio from 2 dB to 35 dB. It is said that the introduction of a symbolic synchronization circuit in the receiver system allows to improve the power of telecommunications devices with phase shift keying. Symbol synchronization allows you to stabilize the digital communication mode when using interpolation and decimation in forming filters.

Keywords: coherent communication; synchronization error; symbol synchronization; timing error detector.

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