G.V. Kulikov – Dr.Sc.(Eng.), Professor, 

RTU MIREA (Moscow)

E-mail: kulikov@mirea.ru

R.R. Usmanov – Post-graduate Student, 

RTU MIREA (Moscow)

E-mail: renat-usmanov@yandex.ru

D.S. Trofimov – General Director, 

JSC «Torii» (Moscow)

Amplitude and phase-shift keying (APSK) signals have long and successfully used in different high-capacity digital data systems, especially modern satellite systems. This type of signals is utilized in DVB-family satellite broadcasting standards (DVB-S2 и DVB-S2X). For the certain range of tasks the noise immunity of such signals in presence of harmonic interference is necessary to be calculated.

This type of interference represents a model of disturbing narrowband signal from an adjacent radio station.

In the article calculated bit error ratios vs. signal-to-noise ratios relationships for optimal reception of amplitude and phase-shift keying in channels with additive white Gaussian noise (AWGN) are given for the case of 16APSK and 32APSK signals in presence of harmonic interference.

Calculations were carried out by using of statistical radio engineering methods. Conditional for the random initial phase of harmonic interference statistical characteristics of random processes at the outputs of the correlators in APSK signals receivers were calculated. These random processes for considered conditions of signal receiving in AWGN channel have normal distributions. By means of averaging over the random initial phase of the harmonic interference the bit error ratios vs. signal-to-noise ratios relationships are obtained. Additionally relationships between bit error ratios and harmonic interference intensities (for fixed signal-to-noise ratios) and relationships between bit error ratios and harmonic interference frequency offset (for fixed signal-to-noise ratios and interference intensities) are obtained.

Computational results demonstrate the significant impact of harmonic interference on the AWGN immunity of considered signals. The influence of considered interference depends on its frequency offset from carrier. Most harmful effect of harmonic interference is achieving when its frequency hits the main lobe of the signal spectrum. Thereby the spectrum area sensitive to considered interference expands with rising of the data (symbol) rate. Computational results show, that the higher order of APSK signals is, the greater harmful effect of harmonic interference is.

In order to achieve empirical corroboration for calculated results an experiment was carried out. The experimental results qualitatively correspond to computational results. Achieving of strict numerical correspondence between calculated and experimental results is hindered by impossibility of strict correspondence between parameters of theoretical signals and signals in the experiment. Moreover, available for experiment receivers differs from correlational receivers of theoretical model.

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