Yu.A. Bryukhanov1, S.S. Poeluev2, V.S. Nadin3

1-3 P.G. Demidova Yaroslavl State University (Yaroslavl, Russia)

The effect of harmonic interference on the probability of erroneous reception of a radio signal with quadrature amplitude shift keying is considered. The purpose of this work is to analyze the errors of receiving signals with quadrature amplitude shift keying (QAM) under the influence of harmonic interference with random parameters. It is assumed that the useful signal, additive white Gaussian noise and interference are simultaneously fed to the input of the demodulator in the receiver. The demodulation of the signal is carried out according to the quadrature coherent scheme. The dependence of the demodulated symbol energy on the relative frequency detuning, the initial phase, and the noise level is established. The demodulator of QAM signals is presented in the form of two independent quadrature channels for demodulating signals with amplitude keying. Expressions are obtained for calculating the probability of error in receiving radio signals under the influence of harmonic interference. It is shown that the reception error depends significantly on the initial phase of the interference. In this regard, statistical averaging of the error probability over the initial phase of the noise was performed. To identify regularities, calculations were made of the average error probability of receiving radio signals with quadrature amplitude shift keying for a number of values of interference parameters, as well as the ratio of the bit energy to the noise power spectral density in the absence of interference for two values of the useful signal symbol alphabet size. Dependences of reception errors and power losses on the level and frequency detuning of harmonic interference are established. It is shown how many times the average probability of a reception error increases under the influence of interference compared to the probability of errors in the absence of interference. The calculated dependences of the reception error and energy losses on the amplitude and frequency detuning of the harmonic interference are presented. It is shown that the energy losses are determined by the size of the alphabet, the amplitude, frequency, and initial phase of the noise and, for constant size of the alphabet and noise parameters, do not depend on the magnitude of the error in the absence of noise.

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