The interference immunity of decameter circuit with spatial interference compensation

В статье представлена оценка помехоустойчивости декаметрового канала связи, использующего пространственный метод компенсации естественных помех. Метод компенсации базируется на результаты экспериментальных исследований пространственно-корреляционных свойств сигналов и естественных помех декаметрового диапазона. Для реализации метода используется цифровая антенная решетка с пространственно-корреляционным методом обработки сигналов. Также в канале использована гауссовая амплитудная модуляция, формирующая шумоподобный сигнал с расширенной базой. Оценка помехоустойчивости построена на модели ионосферного канала с релеевскими замираниями с учетом пространственно-корреляционных свойств сигналов и естественных помех. Анализ проведенных исследований показал возможность компенсации помех за счет роста антенных элементов в антенной решетке, которая, как следствие, позволит повысить помехоустойчивость ионосферного декаметрового канала связи при низких отношениях уровней сигнал/шум на входе приемного тракта. Возможность обеспечения высокой помехоустойчивости в ионосферных декаметровых каналах позволит использовать новые виды связи для обмена данными в судами и кораблями ВМФ в пределах акваторий Мирового океана. The interference immunity assessment of the decameter circuit using a spatial method of natural interference compensation is presented. The compensation method is based on experimental studies results of spatial and correlation properties of decameter range signals and natural interference. For the method realization the digital array with a spatially-correlation signals processing method is used. Also in the channel the Gaussian amplitude modulation forming a noise-shaped signal with extended base is used. The interference immunity assessment is based on the ionospheric channel model with the Rayleigh fadings taking into account signals and natural interference spatially-correlation properties. The simulation findings showed the interference compensation possibility due to increase in antenna array elements which, as a result, will allow to increase the interference immunity of ionospheric decameter circuit at the low levels of signal/noise ratio in the reception path entrance. The possibility of ensuring high interference immunity in ionospheric decameter circuits will allow to use new communication types for data exchange with NAVY battleships and vessels within the World Ocean water areas.

DISPERSION DISTORTION TRACKING COMPENSATOR BASED ON THE SIGMA-POINT KALMAN

The article proposes an algorithm for nonlinear optimal filtering of the dispersion characteristic slope of the ionospheric channel (DC slope) based on the Kalman sigma-point filter when sounding the channel with broadband signals. The relevance of the applied algorithm can be explained by the fact that at present in the modern world the relevance of the transmission of broadband information signals in the decameter range has increased. The reception of such signals is complicated by the effects caused by the influence of the frequency dispersion of the ionospheric channel on the signal. The above influence leads to significant distortions of the useful signal and a decrease in the quality of information reception in general. The above influence leads to significant distortions of the useful signal and a decrease in the quality of information reception in general. Therefore, the effect of frequency dispersion cannot be neglected and must be taken into account when developing algorithms for optimal reception. Thus, estimation of the parameters of the frequency dispersion of the ionospheric channel becomes an urgent task. The article provides recurrent formulas for calculating the optimal filtration of the DC slope. Moreover, an algorithm for joint estimation of dispersion distortions and their compensation is presented, which allows improving the quality of estimation. The results of simulation modeling of the algorithms are given: the obtained estimate and the true value of the frequency dispersion parameters for two cases – a Markov damped process and a process with random increments. The absolute error in estimating the DC slope is also considered. The computational efficiency of the algorithm for estimating the DC slope using the Kalman sigma-point filter with and without compensation is calculated. In addition, functional diagrams of optimal filtering of the DC slope with compensation and without compensation are given. The ways of implementing the proposed algorithm on an ARM processor are considered.

DIAGNOSTICS OF THE STOCHASTIC IONOSPHERIC CHANNEL IN THE DECAMETER BAND OF RADIO WAVES

We propose a method for direct diagnostics of a stochastic ionospheric radio channel. This method can recalculate probe signal characteristics into transmitted signal characteristics. We derive analytical equations of second-order statistical moments for trajectory characteristics of the main and probe signals propagating in a three-dimensional randomly inhomogeneous ionosphere. We take into account boundary conditions at signal transmission and reception points. As a model of random irregularities of permittivity of the ionosphere, we utilize the concept of a changing space-time correlation ellipsoid, which is self-consistent with spatial changes in the average ionosphere. Time fluctuations of random irregularities are taken into account by the hypothesis of frozen transfer. We use analytical relationships to calculate the expected statistical characteristics of decameter signals along oblique probing paths of the ionosphere. An operational numerical algorithmization of the formulas derived is proposed. We report results of numerical experiments to determine the expected phase variances, group delay, and Doppler frequency shift of the main signal on a given single-hop path, based on measurements of these characteristics of a probe signal on a secondary path. We demonstrate the efficiency of the proposed method for diagnosing statistical trajectory characteristics of a decameter signal along single-hop paths under conditions when ground points of transmission and reception of the main and probe signals are outside the vicinity of focusing points of the wave field.

DIAGNOSTICS OF THE STOCHASTIC IONOSPHERIC CHANNEL IN THE DECAMETER BAND OF RADIO WAVES

We propose a method for direct diagnostics of a stochastic ionospheric radio channel. This method can recalculate probe signal characteristics into transmitted signal characteristics. We derive analytical equations of second-order statistical moments for trajectory characteristics of the main and probe signals propagating in a three-dimensional randomly inhomogeneous ionosphere. We take into account boundary conditions at signal transmission and reception points. As a model of random irregularities of permittivity of the ionosphere, we utilize the concept of a changing space-time correlation ellipsoid, which is self-consistent with spatial changes in the average ionosphere. Time fluctuations of random irregularities are taken into account by the hypothesis of frozen transfer. We use analytical relationships to calculate the expected statistical characteristics of decameter signals along oblique probing paths of the ionosphere. An operational numerical algorithmization of the formulas derived is proposed. We report results of numerical experiments to determine the expected phase variances, group delay, and Doppler frequency shift of the main signal on a given single-hop path, based on measurements of these characteristics of a probe signal on a secondary path. We demonstrate the efficiency of the proposed method for diagnosing statistical trajectory characteristics of a decameter signal along single-hop paths under conditions when ground points of transmission and reception of the main and probe signals are outside the vicinity of focusing points of the wave field.

Variation of Ionospheric Narrowband and Wideband Performance for a 12,760 km Transequatorial Link and Its Dependence on Solar and Ionospheric Activity

The ionosphere provides a channel that is able to propagate electromagnetic waves for long-haul communications, allowing Non-Line-Of-Sight (NLOS) radio communications in the high-frequency band (HF). Nonetheless, its performance as a communications channel mainly depends on solar activity, as Earth’s diurnal and seasonal cycles modify the ionospheric ionization by the sun and consequently the channel performance. La Salle and the Observatori de l’Ebre have conducted oblique soundings of a 12,760 km ionospheric channel from Livingston Island (South Shetland Archipelago—Antarctica −62.7∘S, 299.6∘E) to Cambrils (Spain −41.0∘N, 1.0∘E) to evaluate this evidence and analyze the characteristics of this particular channel. The final goal of the project is to establish a stable communications link to be used as a backup for low throughput data transmission from the various geomagnetic and meteorological sensors located in the Spanish Antarctic Station. The aim of this paper is to confirm the relationship between the channel availability of narrowband and wideband communications and the resulting channel parameters with the solar and ionospheric activity for four consecutive sounding campaigns.

Результаты исследования пространственно-корреляционных характеристик однолучевого ионосферного декаметрового канала связи

В статье представлены результаты экспериментальных исследований пространственно-частотных характеристик ионосферного декаметрового канала связи, проведенных на базе новейшего ионозонда-радиопеленгатора размещенного в г. Ростов-на-Дону. При исследовании оценивалось временное рассеяние принимаемого сигнала на частотах не превышающих максимально применимую частоту радиотрассы при приме интерференционного поля всех дискретных лучей и для случая приема отдельных дискретных лучей с диффузной многоученостью, выделенных узконаправленной антенной ионозонда-радиопеленгатора. На основе обработки результатов экспериментов получены пространственно-частотные характеристики ионосферного канала декаметровой связи, характеризующие зависимость временного рассеяния принятого сигнала от частоты и угла прихода отраженного ионосферного луча, позволяющие производить выбор оптимального угла позиционирования антенны в вертикальной плоскости и оптимальной рабочей частоты по критерию минимума временного рассеивания сигнала. С учетом технологических возможностей приема сигналов с временным рассеиванием, приведен результат вычисления достигаемых скоростей работы модемов в ДКМ каналах связи для различных вертикальных углов позиционирования приемной направленной антенны.The article presents the results of experimental studies of the spatial-frequency characteristics of the ionospheric decameter communication channel, based on the latest ionosonde radio direction finder located in Rostov-on-Don. In the study, the temporal scattering of the received signal was evaluated at frequencies not exceeding the maximum applicable radio path frequency when the interference field of all discrete beams is applied and for the case of receiving individual discrete beams with diffuse multi-learning distinguished by a narrowly directed antenna of the ion-probe-direction-finder. Based on the processing of the experimental results, the spatial and frequency characteristics of the decameter communication ionospheric channel are obtained, which characterize the dependence of the temporal scattering of the received signal on the frequency and angle of arrival of the reflected ionospheric beam, allowing the choice of the optimal antenna positioning angle in the vertical plane and the optimal operating frequency according to the criterion of the minimum time signal scattering . Taking into account the technological capabilities of receiving signals with temporary dispersion, the result of calculating the achieved speeds of modems in DCM communication channels for various vertical positioning angles of a receiving directional antenna is presented.