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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.

Objectives. The aim of this paper is to study the noise immunity of digital information transmission in systems with orthogonal frequency division multiplexing (OFDM) and quadrature amplitude modulation (QAM) of subcarriers in the presence of narrowband interference. As a way of managing this interference, the paper studies the use of a demodulator with soft outputs and subsequent decoding of the convolutional code and low-density paritycheck (LDPC) code used in the system.Methods. The results presented in the article were obtained using statistical radio engineering, mathematical statistics, encoding theory, and computer modeling.Results. The paper presents a simple method for calculating soft bit estimates in the M-point signal QAM demodulator, where M is an even power of two. A considerable amount of numerical results were obtained which show the dependence of the transmitted information bit error rate on M, as well as on the signal-to-noise ratio, signal-to-narrowband interference, and code rates.Conclusions. It can be concluded from the above results that the use of encoding with soft demodulator decisions significantly improves the noise immunity of OFDM signal reception, and enables narrowband interference to be managed efficiently. LDPC encoding is superior to convolutional encoding in increasing the noise immunity of OFDM signal reception both in the absence and in the presence of narrowband interference. Along with the use in QAM-OFDM systems, the proposed simple method for demodulating QAM signals with soft decisions can be used in any wireless communication system using M-position QAM signals, where M is 2 to an even power.

Objectives. Orthogonal frequency division multiplexing (OFDM) has become the standard for various high-speed wireless communication systems due to its several advantages, one of which is the efficient use of bandwidth. The main disadvantage of OFDM is the high peak-power-to-average-power ratio (PAPR), which is indicated by an increase in the bit error rate due to the nonlinearity of the power amplifier. The paper sets out to evaluate the possibility of reducing the PAPR value using a limitation method developed by the authors involving an additional compensation signal in a channel with white Gaussian noise, as well as to analyze its main parameters.Methods. Statistical radio engineering and computer modeling methods are used according to optimal signal reception theory.Results. The effect of the OFDM signal limitation level and the number of additional signals when using the limitation method with an additional compensation signal on the quality (reduction of transmission losses) of the OFDM signal is analyzed. The results show a decrease in the OFDM signal PAPR value, along with the dependencies of the bit error rate on the signal-to-noise ratio at fixed limitation values and a determined number of additional signals in the channel with white Gaussian noise.Conclusions. The proposed limitation method with an additional signal when transmitting an OFDM signal in a channel with white Gaussian noise provides compensation for information losses due to signal level limitations in the transmission channel. Increasing the limitation level is shown to increase the PAPR value, while varying the number of additional signals changes PAPR insignificantly. In order to ensure the effective implementation of the limitation method with an additional compensation signal, the parameters of the threshold limitation level and number of additional signals should be selected depending on the predicted signal-to-noise ratio in the system.

Objectives. Signals with multiple phase shift keying (M-PSK) exhibiting good spectral and energy characteristics are successfully used in many information transmission systems. These include satellite communication systems, GPS, GLONASS, DVB/DVB-S2, and a set of IEEE 802.11 wireless communication standards. In radio communication channels, the useful signal is affected by various interferences in addition to noise. One of these is harmonic interference. As a result, high intensity harmonic interference practically destroys the reception of M-PSK signals. One of the important requirements for the quality of data transmission is the system error tolerance. There are different ways of improving the quality of information transmission. One of these is the use of corrective encoding technology. The aim of the paper is to assess the noise immunity of a coherent demodulator of M-PSK signals using Hamming codes (7,4) and (15,11), and convolutional encoding with Viterbi decoding algorithm (7,5) when receiving M-PSK signals under noise and harmonic interference in the communication channel.Methods. The methods of statistical radio engineering, optimal signal reception theory and computer simulation modeling were used.Results. Experimental dependencies of the bit error rate on the signal-to-noise ratio and on the intensity of harmonic interference of coherent reception of M-PSK signals in a channel with noise and harmonic interference were obtained using computer simulation modeling. This was done without using correction codes and with Hamming code (7.4) and (15.11) and convolutional encoding with Viterbi decoding algorithm (7,5).Conclusions. It is shown that the application of the correction codes effectively corrects errors in the presence of noise and harmonic interference with lower intensity. The correction is ineffective in the presence of high intensity interference. These results can provide important guidance in designing the reliable and energy efficient system.

Objectives. Radio-technical information transmission systems are widely used in various sectors of our life, not only for telecommunications and associated domestic needs, but also for the functioning of various special services, such as emergency response units, which increasingly use robotic complexes in the course of their work. In the event of an emergency, robot devices can be used to get in under rubble, in concrete pipes or other municipal facilities, which typically result in a sharp deterioration of the necessary conditions for the propagation of radio waves. In this regard, the problem of ensuring reliable communication with the robotic complex becomes rather acute. The aim of the present work is to reduce the effect of multipath propagation of radio waves in the communication channel under complex interference conditions.Methods. The methods of statistical radio engineering and mathematical modeling are used according to optimal signal reception theory.Results. The presented model for a multi-element, spatially-distributed, in-phase receiving antenna of various configurations, featuring an electronically adjustable radiation pattern, is designed to ameliorate the multipath nature of signal propagation. A simulation of a multipath communication channel was carried out in the presence of one main and three reflected beams of radio wave propagation, as well as with harmonic interference at two angles of its arrival and different frequency detuning relative to the frequency of the useful signal. The probability of a bit error when receiving discrete information using the proposed antenna is estimated.Conclusions. The proposed signal processing algorithm on the receiving side can be used to partially compensate for the influence of the multipath effect. As a result, the noise immunity of information reception in comparison with reception on an omnidirectional antenna with one antenna element increases: for a bit error probability of 10−3, the energy gain ranges from 2 dB for two beams to 7–10 dB for three or four beams. In the presence of concentrated harmonic interference in the radio channel, its simultaneous spatial (by the antenna) and spectral (by the demodulator) filtering is also observed, the effectiveness of which depends on the direction of arrival and the frequency detuning of the interference, which also leads to a significant decrease in the error probability.

Introduction. This paper investigates a transmission system based on FBMC/OQAM multiplexing. This system is characterized by a high spectral efficiency, thereby attracting interest as an alternative transmission method in future wireless mobile communication standards. However, a disadvantage of the system is the high complexity of signal processing. There are numerous publications that study the FBMC/OQAM system from a theoretical perspective. This paper presents an experimental study of a transmission system based on FBMC/OQAM.Aim. Verification of a transmission system based on FBMC/OQAM multiplexing in a wireless channel.Materials and methods. Computer simulation modeling in Matlab and experimental research using Keysight and Rohde & Schwarz certified measuring instruments.Results. A model of synthesis and signal processing was developed, and a frame structure was proposed. The processing included synchronization, since the study was carried out in a wireless double-dispersive channel. Time synchronization was provided by the method of time-domain correlation. A preamble consisting of two symbols was used for CFO compensation. Channel estimation in FBMC/OQAM was conducted by pilot symbols spread over the time-frequency domain, a method with an auxiliary pilot to compensate for intrinsic interference, as well as Zero Forcing and a linear interpolator. As a result, dependences of the bit error rate on the Eb/N0 in various channels were obtained. An error rate of 10−4 was achieved under the Eb/N0 equal to 13.4 dB, 15.3 dB and 20.9 dB in the first, second and third channel, respectively.Conclusion. A FBMC/OQAM-based transmission system with a linear equalizer can operate without a cyclic prefix in a multipath wireless channel, providing comparable noise immunity to OFDM-CP. Long frames should be used to obtain greater spectral efficiency, due to the presence of a transition zone at the beginning and end of the FBMC/OQAM frame.

The energy and spectral advantages of signals with phase-shift keying predetermined their widespread use in modern digital navigation, communications and television systems. The use of this type of signal in a multi-position format with an increased number of possible phase states allows increasing the information capacity of the channel signal, and consequently the throughput rate of radio channels. The presence of non-fluctuation interference in such radio channels greatly reduces the noise immunity of information reception. A well-known way to deal with such interference is to use adaptive non-recursive filters in the receiver. The article evaluates the effectiveness of using such a filter with an algorithm for setting weight coefficients that controls the constant envelope of a useful signal when receiving signals with multi-position phase shift keying against the background of noise and non-fluctuation interference. Two types of such interference are considered – harmonic and relayed. Using computer simulation, the optimal filter parameters (adaptation coefficient and its length) are determined; the effect of the filter on the noise immunity of the quadrature signal receiver with multi-position phase shift keying for various combinations of interference and their intensity is estimated. It is shown that such an adaptive filter can successfully cope with the most dangerous sighting harmonic interference.

The spectrum sensing at the frequencies of white spaces is an important feature for cognitive radio networks. The characteristics of detection of licensed primary users by single secondary users will deteriorate under the influence of fading in the radio channels, both in the sensing channels and in the reporting channels of results. Reliable detection of licensed primary users is implemented on the basis of the secondary users cooperative spectrum sensing. The article considers the possibility of constructing the reporting channel based on the scheme of regenerative relaying of hard single-bit local solutions in the form of binary phase-shift keying of signals from remote secondary users to a Central Station, which forms a global decision about the result of sensing. The potential value of the gain of the scheme with relay in relation to the scheme with direct transmission and the conditions for optimal placement of the repeater in channels with Rayleigh fades are determined.

Signals with multiple phase-shift keying (M-PSK) have long been successfully used for highspeed information transfer in many applications – a number of adopted protocols of IEEE 802.11 wireless networks, digital satellite television DVB-S, DVB-S2/S2X systems, cellular networks CDMA and others. The most important characteristic of such systems is their noise immunity, which depends not only on the propagation conditions of radio waves in the communication channel, but also on the quality of operation of the component nodes of the information transmission systems themselves. The paper investigates the influence of the inaccuracy of estimating the frequency and phase of the carrier and the inaccuracy of the clock synchronization system on the noise immunity of coherent reception of M-PSK signals. Analytical expressions were obtained by statistical radio engineering methods. The expressions allow calculating the dependence of the probability of a bit error on the signal-to-noise ratio for various errors of the receiver auxiliary systems. In this case, the magnitudes of the errors were assumed to be either constant (static error) or dynamically changing (dynamic error). The dynamic errors were modeled using the Monte Carlo method, and the dynamic errors themselves were assumed to be Gaussian random variables. It is shown that the inaccuracy of estimating these parameters strongly influences the noise immunity of the coherent reception of the M-PSK signal, and this effect increases with increasing signal positionality. Estimates of the maximum permissible errors of the analyzed systems are given. When M-PSK signals are received, a tolerable value of the frequency of the reference oscillations can be considered as a ∆ωTs value of about 0.05. The allowable inaccuracy of the carrier phase estimation depends on the positioning of the signal and varies from π/36–π/72 for 2PSK to π/180 for 32PSK. The allowable time offset of the clock moments can be considered the value of 3–5% of the clock interval duration.

The energy and spectral advantages of signals with phase shift keying predetermined their widespread use in modern digital navigation, communications and television systems. The use of such signals is the base of communication standards of DVB-S, DVB-S2 / S2X, GLONASS, CDMA, WiFi IEEE 802.11 and others. To increase the capacity of radio channels, multiple phase shift keying (MPSK) is applied. This increases the number of possible phase states of the signal and, thus, the information capacity of the channel symbol. However, such an increase greatly affects the noise immunity of MPSK signal reception. In the article the noise immunity of receiving signals with multiple phase shift keying in the presence of noise and phase-shift interference is analyzed by the methods of statistical radio engineering. The dependencies of bit error probability on the signal-to-noise ratio, on the interference intensity, on the relative transmission speed of the interference, and on its detuning relative to the center frequency of the spectrum of the useful signal are calculated. It is shown that signals with multiple phase shift keying are very strongly influenced by phase-shift interference, and this influence increases with increasing signal positionality. The degree of reduction of the noise immunity of the reception depends on the magnitude of the relative transmission rate of the interference and its intensity. The damaging effect of the phase-shift interference is most pronounced when it hits the main lobe of the signal spectrum. As the relative transmission rate increases, the interference becomes more broadband and pseudo-noise, and it affects even with very large frequency detuning somewhat decreasing in the region of the main lobe of the signal spectrum. This decrease seems natural, since the analyzed algorithm for receiving MPSK signals is optimal for the effects of noise interference.

Signals with multi-phase shift keying (M-PSK) have long been successfully used in digital information transmission systems with high bandwidth. Their use is regulated by various communication standards. The noise immunity characteristics of their reception against the background of white Gaussian noise are well studied. The article deals with the case when, at the input of the receiver, besides noise, there is a scanning interference. The noise immunity of signal reception with multi-phase shift keying in the presence of noise and scanning interference was analyzed using statistical radio engineering methods. In this case, the interference is represented as a harmonic interference with a frequency varying according to the sawtooth law. Two cases are considered in the study. The first is when the scanning interference does not fall into the zone of the main lobe of the signal spectrum. In this case, its influence is negligible, and it practically does not change the noise immunity of the reception. The second case, when the frequency range of the scan coincides with the zone of the main lobe of the signal spectrum, is more dangerous. The dependences of the probability of a bit error on the deviation frequency of the scanning interference, its intensity and the signal-to-noise ratio are obtained. It is shown that the noise immunity of receiving signals with multi-phase shift keying deteriorates greatly in the presence of scanning interference falling in the region of the main lobe of the spectrum of the useful signal, and this effect is greatly enhanced with increasing signal positionality. When changing the frequency deviation of such interference, its effect on the noise immunity of the M-PSK demodulator changes only slightly. To increase the noise immunity of receiving signals against the background of scanning interference, it is necessary to use interference compensation algorithms, for example, tracking notch filters.

The possibilities of increasing the data rate of adaptive HF communication systems by reducing redundancy in the form of test signals used for its operation are considered. The problem is currently pressing due to increasing demands of modern adaptive data transmission systems to efficient use of allocated frequency-time resource of radio channel. For the problem solution, methods based on the analysis of the received information signal, taking into account the used signal-code construction, are proposed. Approaches for solving problems of non-test adaptive signals correction and channel state estimation in serial data communication systems using convolutional encoder are proposed. Search algorithm for segments used for channel impulse response and equalizer coefficients calculation is shown. In this case, neither a change in decoding algorithms nor calculating of equalizer impulse response is required. Expressions for estimation of the bit error rate for a convolution encoder of general form are given. The presented approaches maintain operating of adaptive HF data transmission systems in channels with intersymbol interference, ensuring the operative change of its parameters when the state of the radio channel changes significantly reducing the use of test signals, or completely abandoning them.

The construction of hydroacoustic signal for object positioning in a fast fading aquatic environment is considered. The relevant data coding options of underwater signal are proposed.

The article investigates the three different algorithms to combat intersymbol interference in a MIMO-communication systems with a 2x2 configuration (zero forcing algorithm, minimizing mean square error algorithm and the algorithm technique as a whole with elementwise decision). The mathematical modeling and the comparative characteristic of effective filtering algorithm.