Evgeniy M. Lobov

This article presents the results of developing an algorithm for coherent processing of wideband non-binary orthogonal signal-code structures for voice transmission in a decameter radio channel. The structure of a radiogram, including preamble and data symbols, is presented, taking into account message length limitations for real-time voice transmission. An ensemble of orthogonal wideband phase-shift keyed signals is used as signals. The noise-correcting code used is a non-binary low-density parity-check code whose Galois field dimension is matched to the number of signals in the ensemble. Decoding is performed using a belief propagation algorithm, which involves calculating aposteriori probabilities for each possible transmitted symbol, taking into account observations. The article presents analytical expressions for calculating these probabilities, taking into account multipath signal propagation, assuming separation of the paths without their mutual interference, and also taking into account different a priori uncertainties regarding the complex channel transmission coefficients for each path. Three types of a priori information are assumed: fully known complex channel gains, an unknown phase shift of the channel gains, or an unknown phase shift and level of the channel gains. A fourth, widely used, quadratic ray summation option is also considered. In coherent processing, complex channel gains are assumed to be known or measured in some way. This article considers several options for measuring complex channel gains: using a separate measurement channel using the maximum likelihood method and using a Kalman filter. In one version, the Kalman filter operates on data from a separate measurement channel, while in another version, it operates on preamble symbols and on radiogram data symbols with feedback on decisions regarding the data symbols. Using the Waterson model of the ionospheric channel, this article substantiates the autoregressive order of the Kalman filter from the perspective of algorithm complexity and achievable noise immunity. Noise immunity curves are presented for the coherent processing algorithm using the Kalman filter and non-coherent processing algorithms. The corresponding energy gain is estimated.

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.

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.

We consider two of the most relevant problems that arise when modeling the properties of a tunnel radio communication channel through a plasma layer. First, we studied the case of the oblique incidence of electromagnetic waves on a layer of ionized gas for two wave polarizations. The resonator parameters that provide signal reception at a wide solid angle were found. We also took into account the unavoidable presence of a protective layer between the plasma and the resonator, as well as the conducting elements of the antenna system in the dielectric itself. This provides the first complete simulation for a tunnel communication channel. Noise immunity and communication range studies were conducted for a prospective spacecraft radio line.

A new numerical method for finding the probability of adjacent errors in a channel with Rayleigh fades is proposed. Within the framework of the Markov model of normal independent random processes forming a complex random process that simulates signal fading, it is shown that the joint probability density of the module of the complex envelope (CO) of the signal at adjacent time points can be represented as the product of the probability density of the module of the CO signal at the initial time and the conditional probability densities of the module of the CO signal at adjacent time points. The probability of occurrence of two or more consecutive erroneous symbols (adjacent errors) in a channel with fading is defined as the averaging of the corresponding probability in a channel with white Gaussian noise over the joint probability density of the CO signal module at adjacent time points. By approximating a multidimensional integral with finite integral sums and dividing the joint probability density into multipliers, we can find the desired probability of adjacent errors in the form of a multiple product of several typical matrices. These matrices can be calculated in advance using conditional probability densities of the signal modulus at adjacent time points. The proposed algorithm has no restrictions on the type of modulation. The results of the calculation and numerical experiment to determine the probabilities of the occurrence of adjacent errors are presented.

In this paper, the properties of a filterbank multicarrier modem operating in a broadband high-frequency channel are considered. The quality of work of algorithms for estimation and equalization of the channel impulse response is investigated. Methods for improving the quality of a filterbank multicarrier modem operation in an ultra-wideband ionospheric channel are considered.

In this article authors demonstrates the possibility of using filter bank multicarrier signals with existing code sequences and algorithms for processing channel symbols of the 5G standard, which allows to get a gain in the spectral efficiency of the baseband signal and increase the transmission rate by eliminating the cyclic prefix. Quality indicators are the probability of detecting and skipping the synchro-preamble, the probability of decoding a block of the public channel, as well as the amplitude of the error vector. It is shown that the considered indicators do not deteriorate when passing to a new form of the group signal in conditions of white Gaussian noise.

The use of digital receivers for processing broadband recordings involves processing and storing large amounts of data. The use of compression of the dynamic range of this data with loss of information and compression of data without loss of information will significantly reduce the amount of information storage, or increase the storage period of information before it is rewritten with a fixed volume of the storage device, and will also allow using lower-speed communication channels to transfer processed information to storage devices or post-processing. When using the dynamic range compression algorithm, a digital filter bank plays an important role, which allows you to divide the spectrum of a wideband signal into subchannels with a corresponding decrease in the rate of each subchannel. The article discusses the effect of bit width truncation on error-rate performance of processed records, and also includes the results of computer simulation.

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.

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.