The article investigates the quality of algorithms for esimate the main parameters of wideband signals in the problem of over-the-horizon radar under conditions of dispersion distortions in the Earth’s ionosphere. The boundary values of the variances of the estimates of propagation delay, frequency shift and phase, wideband phase-shift keyed signals are investigated. It is shown that dispersion distortions of the radar signal lead to a correlation between the estimates of the delay and frequency shift. The curves of the dependence of the frequency-time ratio depending on the length of the used pseudo-random sequence and the degree of dispersion distortions are obtained. Analytical curves of the Cramer-Rao lower bounds are constructed for the variances of estimates and the values of the correlation coefficients of the estimated parameters in the presence of dispersion distortions, which are confirmed by the results of simulation.

Increasing the data transfer rate is an urgent task in cellular, high-frequency (HF) and special communication systems. The most common way to increase the data rate is to expand the bandwidth of the transmitted signal, which is often achieved through the use of multitone systems. One such system is the filter bank multicarrier (FBMC). In addition, speed improvements are achieved using multi-input–multi-output (MIMO) systems. In this study, we developed an algorithm for equalizing FBMC signals with offset-QAM modulation (OQAM) with self-interference compensation due to its correlation properties in a MIMO channel with memory. An analytical derivation of the proposed algorithm and an analysis of the computational complexity are given. According to the results of simulation modeling and a comparative analysis of performance in terms of the bit error rate and error vector magnitude with solutions with similar computational complexity, a similar level of performance was shown compared to a more complex parallel multistage algorithm, and a better performance was demonstrated compared to a one-tap algorithm.

In recent years, thanks to the rapid progress of the technology for creating invisible ultraviolet LEDs and the technology for detecting ultraviolet rays, ultraviolet communication has gradually become an urgent object of research due to its inherent advantages: low solar background noise, the possibility of organizing communication in the absence of direct visibility (NLOS) and good stealthiness. The strong scattering characteristics of the ultraviolet signal in atmospheric render ultraviolet waveband the ideal choice for achieving NLOS optical communication. This article reviews the research history and status of ultraviolet communication both in Russia and abroad, and especially introduces three main issues of ultraviolet communication: channel model, system analysis and design, light sources and detectors. For each aspect, current open issues and prospective research directions are analyzed.

Currently, there is a tendency to increase the speed of information transmission by increasing used frequency band. However, when switching to broadband signals and operating under conditions of a high level of noise, a wide dynamic range is required when digitizing the received signal. To increase the dynamic range, it is proposed to use a hybrid filter bank, which allows processing the broadband signal with low-speed precision analog-to-digital converters. In this paper, was calculated and simulated a hybrid analysis-synthesis filter bank for the 26.25 MHz-86.25 MHz frequency range. Using matched filters, we estimated the distortion of a linearly frequency-modulated signal during the passage of filter banks without intermediate processing, after upsampling and downsampling intermediate signals from the outputs of analog filters. To reduce phase shifts and time delays arising during signal processing by synthesis filters, compensation delays and phase shifts were introduced, adjusted to distortions carried by the processing system. It was shown that phase correction allows reducing signal distortions. It was also shown that in the case of receiving a mixture of signal and noise, the distortion introduced by the processing system does not significantly affect the signal-to-noise ratio of the output signal.

This article describes a method to compensate distortions carried by analog analysis filters of a hybrid filter bank. Were obtained expressions describing hybrid filter bank based ADC with addition of compensator. Described processing system was modeled and quantitative measurements of signal distortions were calculated for system with and without compensator. Were shown that insertion of a compensator can significantly improve the characteristics of the system. Methods to increase the computational efficiency of the compensator were described. Dependencies were obtained between the accuracy of compensation and the computational complexity of the compensator.

The detector is an integral part of the device for receiving and processing radio signals. Signals that have passed through the ionospheric channel acquire an unknown Doppler shift and are subject to dispersion distortions. It is necessary to carry out joint detection and parameter estimation to improve reception quality and detection accuracy. Modern hardware base developing makes it possible to implement a device for joint detection and evaluation of signals based on standard processors (CPU) and graphic processors (GPU). The article discusses the implementation of a signal detector that allows for real-time operation. A comparison of implementations of algorithms for estimating the Doppler frequency shift through multiplication by a complex exponent and the fast Fourier transform (FFT) is performed. A comparison of computational costs and execution speed on the CPU and GPU is considered.