N. V. Ryabova

Propagation of broadband HF signals in a medium with nonlinear dispersion

Effect of nonlinear dispersion on distortions of broadband signals due to propagation in ionospheric channel is considered with allowance for matched processing in detector. Distortions of the shape of pulse response are studied versus nonlinearity parameter, and the effect of geophysical factors on the parameter is analyzed. The pulse response is used to estimate the group delay. It is demonstrated that the problem of propagation of broadband signals is reduced to the analysis of distortions of an equivalent signal with uniform in-phase spectrum in the ionospheric channel similar to the distortions of the pulse response of the channel. For the polynomial dispersion characteristic of the channel, the effect of nonlinearity on the pulse characteristics is described using incomplete Airy functions and the shape of the envelope of such a characteristic becomes asymmetric. Owing to uncertainty, the parameter of the group delay in the channel with the nonlinear dispersion cannot be accurately determined using the data on the pulse characteristic as distinct from the dispersion-free or linear-dispersion channel.

Software-defined radio technology in the problem concerning with the successive sounding of HF ionospheric communication channels

The problem concerning new software-defined radio technology is investigated as applied to the successive sounding of HF ionospheric communication radio channels. The algorithm for quadrature processing of chirp signals subjected to elementwise compression in the frequency domain is developed. It is established that a channel scattering function and a delay power profile are related to a compressed-signal spectrum and their basic parameters. Data on the key characteristic of HF communications modems are presented. The efficiencies of different modems are estimated using the experimental data on channel parameters. It is demonstrated that the aforementioned technology can be used to estimate not only HF communication channel parameters from the pass band of a radio line but also select the optimal one and, furthermore, makes it possible to combine communications and radio sounding systems in the single device.

Developing methods and software for research the effects of phase dispersion depending of the state of ionospher based on LabVIEW

Methods and software are developed for research the effects of phase dispersion, depending of the ionospher, based on LabVIEW. It is found that the leading edge increased with increasing of the third order parameter of impulse response, which leads to the case without the frequency dispersion, while trailing edge moving away from the peak, which leads to the case of linear frequency dispersion. Ionospheric radio channel with a bandwidth of 1 MHz is destroyed with the nonlinearity parameter equal to 267,4 ms/MHz2. Developed filtering methods ionograms oblique sounding ionosphere.

Studying the parameters of frequency dispersion for radio links of different length using SDR based sounding system

Methods and software were developed for studying parameters of frequency dispersion for radio links of different length. We used SDR based sounding system for studying a HF radio channel and determining parameters of frequency dispersion. The software component was implemented using licensed software Lab VIEW. The hardware component was implemented using a programmable transceiver USRP N210. We studied the parameters of broadband radio channels (up to 1 MHz) for near-vertical incidence skywave (NVIS) radio path (up to 500 km), as well as the parameters of the regular component of the third order phase dispersion for long-distance radio path (1000–3500 km). We studied parameters of frequency dispersion depending on the time of day, path length as well as the central channel frequency.

The impact of solar flares analysis on the intensity variations of the total electron content of the middle latitudes ionospherein the European Region

It is carried out the analysis of number of solar flares changein the work and their impact on the intensity changes of TEC variations for Yoshkar-Ola city according to the 2012 and 2015 years.

The comparative analysis of the intensity of the total electron content of the ionosphere variations above Yoshkar-Ola and Irkutsk cities

In the study there was carried out the analysis of the daily dynamics of the TEC, the intensity of variations changes and seasonally analysis of TEC variations for Yoshkar-Ola and Irkutsk, according to 2012.

Processing signals of passive chirp ionosonde in the problem of estimation the HF channel availability

The problem of increasing the efficiency of data transmission through a HF radio channel in the case of using passive sounding was studied. The paper presents the main characteristics of the stochastic radio channel with scattering (delay spread, Doppler spread and the signal-to-noise ratio) and communication modem, which have an impact on the efficiency of a communication system. Algorithm for estimating the channel characteristics using passive sounding was developed. Besides, the algorithms aimed at estimating the gain in emitted power and data transfer rate when adapting the communication system to the channel conditions were developed. It was experimentally found that for the mid-latitude radio paths, the power gain is 4.5 … 12 dB, and the gain in data transfer rate increases up to twice.

FMICW signal shaping for single antenna vertical sounding ionosonde using USRP platform

The problem of forming an FMICW signal for vertical-incidence single-antenna ionosonde based on the USRP platform using SDR technology was solved. We carried out studies aimed at getting a constant level of a received signal, unambiguous determining virtual reflection height in the required range as well as reducing interference and correlation noise during transmission and compression. The developed algorithms were implemented in software and experimentally tested.

Modeling and studying ionograms of oblique sounding of HF radio channels for radio links of various length using a digital ionosonde with USRP platform

The paper analyses the outcomes of numerical studies into the effect of phase dispersion on broadband elements of a FMCW signal with varying central spectrum frequencies corresponding to the central frequencies of radio channels. We used the International Reference Ionosphere (IRI) model as the background ionosphere, which takes into account the spatiotemporal variability of the radio channel. The data corresponding to the extreme values in the annual distribution of solar activity were selected for modeling ionograms. The effect of the second-order phase dispersion on power delay profile distortions was analyzed.

Estimation of the effective recombination coefficient by variations in the maximum usable frequencies of one-hop high-frequency radio lines during the solar eclipses of March 29, 2006, and August 1, 2008

This paper presents the results of experimental investigations of variations in maximal usable frequencies (MUFs) during solar eclipses with the use of the method of panoramic tilt sounding by chirps in Eastern Europe and Western Siberia. The characteristics of perturbations of MUFs have been obtained experimentally. It has been established that the effective recombination coefficient increases by 24% in the ionospheric F region with an increase in the maximum eclipse phase from 0.49 to 1.0.