V.G. Dovbnya − Dr.Sc. (Eng.), Associate Professor, Professor,

Department of Space Instrumentation and Communication Systems, South-West State University (Kursk) E-mail: vit_georg@mail.ru

D.S. Koptev − 2-nd year Post-graduate Student, Lecturer,

Department of Space Instrumentation and Communication Systems, South-West State University (Kursk) E-mail: d.s.koptev@mail.ru

The presence of phase noise in the input signal of the coherent demodulator requires an increase in the bandwidth of the carrier recovery device to be able to track the phase of the allocated carrier for fluctuations in the phase of the input signal. Otherwise, a dynamic phase error appears in the coherent detection scheme of QAM signals, the signal-to-noise ratio at the output of the coherent detector decreases and, as a consequence, the reliability of information reception decreases.

The research methods are based on the theories of potential noise immunity, synchronization of demodulators, phase locked loop systems. For the carrier recovery device, the value of the noise band was chosen in the range from 0,001T to 0,02T (T is the symbol duration), since the law of distribution of the phase error can be considered Gaussian under the indicated relations. It was assumed in the work that the automatic gain control and clock synchronization devices in the radio receiving system function perfectly, and the channel frequency response corresponds to the Nyquist condition. Based on the developed analytical model, we plotted the dependences of the equivalent energy losses, respectively, on the integral relative frequency instability and the power spectral density of the phase noise of the oscillator oscillations, normalized during tuning from the carrier at 10 kHz, obtained by an iterative method in the MathCAD 11 medium. The calculation was performed for the oscillator oscillation frequency 10 GHz and a typical power spectral density distribution profile of its phase noise.

The permissible level of equivalent energy losses (from 0.2 to 0.3 dB) is provided at integral frequency instabilities of 3·10−7; 1.5·10−7; 7·10−8; 3·10−8and a spectral power density of phase noise power of not more than minus 85, 91, 97 and 103 dBW/Hz for signals with modulation types QAM-16, QAM-64, QAM-256 and QAM-1024. In the calculation, it was assumed that the integral relative frequency instability and the spectral power density of the phase noise of the received signal and the reference generator of the carrier recovery device are significantly lower than that of the local oscillation synthesizer. If we assume that the considered parameters for the master oscillator of the carrier oscillation and the oscillator of the local oscillator are comparable, then the requirements should be doubled (for the spectral power density of phase noise by 3 dB).

Thus, the analytical model developed in the article and the obtained graphical dependences make it possible to estimate the degree of influence of the integrated relative frequency instability and the power spectral density of the phase noise of oscillator oscillations on the noise immunity of receiving multi-position signals with quadrature amplitude modulation, as well as theoretically substantiate the performance requirements for the oscillator synthesizers of oscillators of radio receiving systems of digital communication lines.

Dovbnya V.G., Koptev D.S. Influence of quality of functioning of heterodines on interference of reception of signals with square amplitude modulation. Radiotekhnika. 2020. V. 84. № 9(17). P. 40−. DOI: 10.18127/j00338486202009(17)-03 (In Russian).

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