Noise immunity of signal reception with multiple frequency-shift keying against retransmitted interference

Objectives. Radio engineering information transmission systems are widely used in robotic systems employed in various military and civilian services. If such systems are used in a harsh environment, where a large amount of retransmitted interference occurs, for example, if a complex is buried under rubble or is located in reinforced concrete pipes or other utility facilities, communication with the command post may be lost. Thus, the task of maintaining reliable communications under difficult conditions of radio wave propagation is very urgent. In the field of telecommunications, multiposition types of modulation are widely used, which, despite their good spectral characteristics, provide low noise immunity under conditions of nonfluctuating interference, especially in cases of retransmitted interference. Therefore, it is relevant to explore the possibility of using multiple frequency-shift keying (M-FSK) signals in radio systems with complex interference environments. The paper sets out to analyze the noise immunity of coherent reception of M-FSK signals against the background of retransmitted interference.Methods. Statistical radio engineering and mathematical modeling methods are used according to the theory of optimal signal reception.Results. A model of the M-FSK signal and retransmitted interference is provided. The statistical parameters of the distributions of random processes occurring in a multichannel coherent receiver of M-FSK signals against retransmitted interference are obtained; based on this, the bit error rate is calculated when receiving M-FSK signals of different positionality M against retransmitted interference with different intensities.Conclusions. The impact of retransmitted interference is shown to result in a decrease in the noise immunity of M-FSK signal reception, which is greater the higher its intensity. With increasing positionality of M-FSK signals at low intensity of retransmitted interference, the noise immunity of reception is significantly improved; however, high-intensity interference significantly increases the bit error rate. The presence of interference with a relative intensity of 0.5 causes energy losses from 4 to 6 dB depending on the positionality. When M > 4, M-FSK signals gain significantly in terms of noise immunity over signals with multiple phase-shift keying, quadrature amplitude modulation, and amplitude and phase-shift keying.