HF Channel Research Articles

Increasing the probability of transfer GMDSS broadcast messages when transmitted over HF channel in case fading

Improving the quality of communication in the Global Maritime Distress and Safety System of navigation is one of the components of the development of the Arctic zone of the Russian Federation in terms of information support. At the same time, the most difficult is to ensure communication in the A3 and A4 areas, where a communication HF channel plays a not small role. The transfer of messages over HF channel in the broadcasting mode of SITOR-B is considered. To improve probabilistic characteristics in the work, a statistical analysis of the decisions of the demodulator is carried out. It is shown that the probability density functions are “noisy”, which is associated with the non-zero probability of a bit error. Models of Rayleigh, Rice and Nakagami distributions were used for statistical analysis. It is shown that in the case of low values of the signal-to-noise ratio, which is characteristic of high latitude tracks, a Nakagami model is preferable. The symbol error rate and message error rate in a fading communication channel, as well as the probability of receiving an erroneous message are shown. The results presented in this work can significantly improve the probabilistic characteristics of the HF radiolines when transmitting messages in SITOR-B mode.

Superacidic Properties of Protonated PtFn (n = 1–6) and Their Ability to Form Supersalts: DFT Study

AbstractIn the present communication, this study has modeled protonated PtFn (n = 1–6), a new series of superacids. The calculated vertical de‐attachment energy (VDE) of PtFn (n = 1–6) reestablishes the superhalogenic behavior. The vibrational frequency, dissociation energy through the HF channel, and optimized geometries are utilized to discuss the stability of HPtFn (n = 1–6). The deprotonation energy of HPtFn is used to calculate the acidic strength of HPtFn (n = 1–6). The acidity of protonated PtFn (n = 1–6) is directly related to its counterpart superhalogen anions. The computed correlation factor (R2 = 0.9754) shows that VDE is directly associated with acidity. The mechanism of acidity of HPtFn (n = 1–6) is described by using natural bond orbital analysis charges on atoms. The electronic properties of HPtFn (n = 1–6) are calculated using the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy. The nature of chemical reactivity is also determined by the HOMO–LUMO plot of HPtFn (n = 1–6). It has formed the supersalts using superacids HPtFn (n = 1–6) and superbase (OLi3OH), and the nature of supersalts is compared with traditional salt LiF. The most stable conformers of supersalts PtFnOLi3 (n = 2–6) are analyzed for optoelectronic properties. It has computed the dissociation of supersalts through neutral and anions through superhalogns and superalkalis. The computed results show that PtF4OLi3 favors dissociation through anions as in traditional salts. The nonlinear optical parameters are calculated using dipole moment, mean polarizability, anisotropic polarizability, molar reflectivity (MR), order parameters, and hyperpolarizability of PtFnOLi3 (n = 2–4). The estimated nonlinear optical properties parameters are compared with corresponding parameters of traditional salt LiF by the same level theory.

Active and passive sensors for diagnostics quasi-zenith ionospheric HF communication channels

Background. There is a growing need for active sensory diagnostics of partial HF channels to provide frequency support to quasi-zenith HF radio links in varying signal propagation conditions. Enhancing the efficiency of active sensor algorithms, particularly by reducing emission time, is topical. To address this, a transition from sequential to parallel (simultaneous) diagnostics is proposed. Another significant challenge in HF communication is narrowband interference, and overcoming this issue involves the method of passive sensory diagnostics. This method assesses the availability of partial channels by analyzing the spectral density of interference power within them.
 Aim. The goal of this study is to develop algorithms and software tools that implement spectral monitoring and parallel sensing of partial channels for sensory diagnostics of ionospheric channels in quasi-zenith HF communication.
 Methods. The proposed approach involves integrating dynamic diagnostic methods into the development of intelligent sensors for ionospheric HF radio links, along with the creation of data analysis methods. Specialized computer software is employed to address the defined tasks. Experimental studies are conducted using the developed devices, which include intelligent active and passive radio sensors for HF radio links, to assess the load on HF communication channels.
 Results. A sensor for orthogonal quasi-zenith ionospheric radio channels has been created, incorporating algorithms for synthesizing a group pulse with orthogonal subcarriers while minimizing the peak factor. Additionally, algorithms for separating subcarriers and calculating the correlation function at the reception have been developed. The sensor employs the OFDM-BPSK signal modulation method, enabling operation in simultaneous-sequential sounding mode across the potential frequency range for communication. This led to an 8-fold reduction in the total signal emission time.
 Conclusion. The scientific results obtained have broad practical applications, particularly in enhancing the efficiency of wideband HF communication systems using spread spectrum signals.

Performance study of HF communication using NOMA over narrowband HF channel

AbstractHigh frequency systems (HF) are still used in many communication applications. Data can be sent for hundreds of kilometers at a low power cost with only one drawback, low bitrate. To increase the bitrate, several methods were reported using the single‐Tone modulation with 24 kHz bandwidth, but still not practical in real‐time applications because, the 24 kHz is unavailable due to the instability of the ionosphere layer. In this work, we propose a structured method built on the Non‐Orthogonal Multiple Access technique (NOMA) to increase the bit rate per HF narrowband channel. To increase the data rate, two parts of the data are divided and sent to one user over two different power levels. We use the NOMA technique on the receiver's side to recognize the two parts of data. The results show a significant improvement (up to 45%) using NOMA in narrowband 3 kHz channels. The bit rate at the receiver has increased up to 200 Kb/s concerning, while the maximum bit rate recorded by conventional methods used in previous studies is 138 Kb/s. The system is built on the SDR platform and tested in multiple channels, weather, and power conditions in real‐time experiments to validate its reliability.

Creation of a HF and VHF Radio Communication Channel Through an Artificial Ionospheric Repeater

Creation of a HF and VHF Radio Communication Channel Through an Artificial Ionospheric Repeater

Examining the Performance of MIL-STD-188-110D Waveform 0 Against FBMC-SS Over Skywave HF Channels

This paper provides a comprehensive performance comparison between a current robust military waveform; namely, MIL-STD-188-110D, Waveform 0, and a filter bank multicarrier spread-spectrum (FBMC-SS) waveform proposed for communications through ionospheric/skywave HF channels. Waveform 0 is effectively a direct sequence spread spectrum waveform that uses Walsh multi-codes to enhance the information transmission rate. It may thus be referred to as Walsh-DSSS. FBMC-SS, on the other hand, makes use of filter banks to provide excellent performance when the received signal is subject to partial band interference. Successful application of FBMC-SS for communications across skywave HF channels has been previously demonstrated, both theoretically and through experimental work. However, very little has been done to contrast FBMC-SS against Walsh-DSSS. The goal of this paper is to first add new features to FBMC-SS to bring it on par with Walsh-DSSS. These features include: (i), introduction of multi-codes that achieve a comparable (or better) data rate to Walsh-DSSS; and (ii), addition of a scrambling step applied to the multi-codes to make the receiver detection robust against widely spread multipaths. With this established, in the second part of the paper, we examine the performance of the developed FBMC-SS against Walsh-DSSS when both are applied for communications across skywave HF channels. The two waveforms are compared both through a theoretical study and through experimental works across several skywave channels ranging from hundreds to thousands of kilometers.

Evolution Trends and Paradigms of Low Noise Frequency Synthesis and Signal Conversion Using Silicon Technologies

Silicon technologies for HF applications have been proven for more than two decades, and technologies have greatly evolved. Whether CMOS or BiCMOS technologies, the unique combination of radio frequency, baseband, and digital functions allow a very high level of integration. While it is possible to achieve fully integrated transceivers, the major advantages of these silicon technologies lie mainly in their unparalleled performance in the field of frequency synthesis and frequency conversion. We propose in this paper a review of the major results obtained on these RF components since the beginning of the 2000s, also considering the impact of the technology node. The back-end of line (BEOL) process on which depends the quality of microwave monolithic integrated circuits (MMICs) is briefly presented in the introductory part. If circuit performances are tightly bound to the active devices (i.e., the heterojunction bipolar transistor SiGe HBT or CMOS transistor), passive elements (i.e., quality factor of inductors and varactors, losses of transmission, or interconnection lines) as well as the definition of the substrate also play a major role. The core of the article is oriented toward the noise of synthesized signals and frequency conversion. Frequency synthesis is presented through the analog design of a voltage-controlled oscillator (VCO) or through the direct digital frequency synthesis (DDFS), for which respective figures of merit are presented and discussed in a second section. The spectral purity of the oscillators being decisive in the definition of the throughput of a link is approached through the comparison of different figures of merit (FoM) for a set of circuits achievements over the selected period. If the realization of free oscillators is closely bound to the phase-locked loop (PLL)-type control loop for VCOs, the DDFS solution provides more direct and more flexible alternative at first sight. Therefore, these two solutions are analyzed collectively. Finally, the oscillator integrated in the transmitter or receiver supplies the needed LO (local oscillator) power to the frequency mixer in the frequency conversion module: henceforth, the third part of this study focuses on high-frequency mixer realizations. We thus consider this LO power in some advanced figure of merit mentioned in the second section. The design trade-off of the mixer is presented in an approach combining LO (conversion gain, channel isolation, and phase noise) and RF (HF noise figure and channel isolation) constraints. The final section provides a summary of the results and trends mentioned in the paper.

ANALYTICAL MODEL OF PACKET TRANSMISSION OF SPEECH AND DATA IN HF RADIO CHANNELS IN A COMPLEX SIGNAL-INTERFERENCE ENVIRONMENT

The author has carried out an analytical simulation of the process of signal formation and processing in the HF channel during packet transmission of speech and data in a complex signal-interference environment. The totality of the result obtained can be the basis for the development of complex mathematical models of HF channels.

On the performance of OFDM and single carrier communication over wideband HF channel: theory and practice

Using wideband High Frequency (WBHF) communication has not been a luxury now due to the urgent need for the transfer of large files over long distances without the need for sophisticated infrastructure. The channel model helps in evaluating the performance of communications systems without the need for a real transmission. The existing HF ITU-R(International Telecommunication Union Radio) channel models are valid only for narrowband channels of bandwidth 3KHz and are valid up to 12KHz. Another channel model for WBHF with bandwidth up to 1MHz was given by Vogler yet, the model was mathematically intractable and allow no further analysis to take place. Noting that, WBHF demands channel bandwidth greater than 12KHz (e.g:24KHz). In this paper, we present a WBHF channel model that is both accurate and mathematically tractable laying the foundation for an informative comparison between different communication systems. The accuracy of the proposed model is first to cross verified against Vogler’s wideband model in terms of the channel impulse response, frequency response and channel scattering characteristics. This comparison leaves our model qualified to evaluate a newly developed standard of HF wideband Waveforms presented to support high data rates and link reliability requirements. Further, we establish a detailed comparison between OFDM and single carrier signaling schemes over the considered WBHF proposed ionospheric channel, under many parameters that affect the performance of both systems. We investigate the justification of using both systems under different channel conditions, we also derive the necessary rate formulas for each signaling scheme and provide simulation environment of both systems on selected samples of the ITU-R channel models for the HF ionospheric channel representing most of the channel conditions. It is coming up that in quiet channel conditions the OFDM outperforms SCCP, while in disturbed conditions SCCP shows more robustness against channel conditions than OFDM. Simulation results are shown that support our analytical results. In addition, we present a Software Defined Radio Hardware implementation of an OFDM wideband HF Transceiver. The developed implementation has been evaluated using an equivalent baseband channel model based on the ITU-R HF channel model.

АЛГОРИТМЫ ОЦЕНКИ И КОМПЕНСАЦИИ ДИСПЕРСИОННЫХ ИСКАЖЕНИЙ ШИРОКОПОЛОСНЫХ СИГНАЛОВ ИОНОСФЕРНЫХ РАДИОЛИНИЙ СВЯЗИ

Introduction: radio communication in the decameter range is actively used for communication in remote and hard-to-reach regions of the world. Decameter communication is also a relevant type of radio communication for regions that have suffered serious damage due to natural disasters. The relevance of using decameter radio communication in the above cases is due to the fact that this technology can offer reliable and cheap solutions. The second area of application of decameter radio communications is communications in the Arctic and Antarctic. Practical significance: when receiving signals with a spread spectrum, it becomes necessary to take into account the effect of the frequency dispersion of the ionospheric channel, since it leads to significant distortions of the useful signal and a decrease in the quality of communication in general. An urgent task is to estimate the parameters of the frequency dispersion of the ionospheric channel and to develop algorithms and devices for compensating dispersion distortions of broadband signals. Discussion: this article presents algorithms for estimating and compensating the dispersion distortions of wideband signals in the HF channel. The subbanding estimation method and maximum likelihood estimation (MLE) of the slope of the dispersion characteristic (the slope of DC) are studied. In addition, this article examines the joint MLE of the slope of DC and other parameters of the wideband signal and offers three methods of dispersion distortion compensation. The first method of compensation is a matched filter compensation. The second one is compensation based on the filter bank. Finally, the third method uses a tracking compensator to solve the problem. The experimental results demonstrated in the article were carried out on a one jump track with a length of about 2900 km.

First observations of the McMurdo–South Pole oblique ionospheric HF channel

Abstract. We present the first observations from a new low-cost oblique ionosonde located in Antarctica. The transmitter is located at McMurdo Station, Ross Island, and the receiver at Amundsen–Scott Station, South Pole. The system was demonstrated successfully in March 2019, with the experiment yielding over 30 000 ionospheric echoes over a 2-week period. These data indicate the presence of a stable E layer and a sporadic and variable F layer with dramatic spread F of sometimes more than 500 km (in units of virtual height). The most important ionospheric parameter, NmF2, validates well against the Jang Bogo Vertical Incidence Pulsed Ionospheric (VIPIR) ionosonde (observing more than 1000 km away). GPS-derived TEC data from the Multi-Instrument Data Analysis Software (MIDAS) algorithm can be considered necessary but insufficient to predict 7.2 MHz propagation between McMurdo and the South Pole, yielding a true positive in 40 % of cases and a true negative in 73 % of cases. The success of this pilot experiment at a total grant cost of USD 116 000 and an equipment cost of ∼ USD 15 000 indicates that a large multi-static network could be built to provide unprecedented observational coverage of the Antarctic ionosphere.

Direct observation of reactive rainbow in F + CH3D → CH3(00) + DF(v = 4)

Rainbow structure in the scattering angular distribution plays an important role in deepening our understanding about atoms/molecules collisions. It is a quantum interference phenomenon and has been extensively studied for decades in the elastic and rotationally inelastic processes. In a recent study of the chemical reaction of F + CH3D, an intriguing bulge feature was discovered in the pair-correlated angular distribution of the CH2D(00) + HF(v = 3) channel, which was interpreted as the rainbow effect in chemical reaction. Further conjectures were put forward, suggesting that reactive rainbow could be a general phenomenon provided that three conditions were met. One of the conditions is that the reactive event behaves elastic-like. To test the hypotheses, this work turns to the alternative isotopic product channel, CH3 + DF, and examines the dynamical attributes over a wide range of collision energy (E c) from about 2.1–19.5 kJ mol−1. We found that similar bulge features indeed appear in another isoergic channel of CH3(00) + DF(v = 4). Moreover, an inverse-linear E c-dependency of the bulge angle was clearly established, reminiscent of the key relationship in characterising the l-type rainbow of elastic collisions. A l-type rainbow is manifested as the angular bulge in the isoergic product channels of a chemical reaction.

Enhanced Grayscale Image Transmission Over HF Channel

Image transmission over HF communication is suitable for long-distance coverage beyond the line of sight and across intercontinental. Unfortunately, the channel condition is degraded with low Signal to Noise Ratio (SNR) and multi-path spreading. In this paper, we aim to transmit images over HF channel and introduce some techniques to improve the received noisy images. First, a Least square estimation technique is applied to estimate the channel state information, then we propose an enhanced filter to reduce image noise effect and improve the received image appearance. This proposed enhanced filter is based on our enhanced version of the Median Filter (MF) and the Mathematical Morphology (MM). Simulation results assess the performance of the proposed filter compared with the performance of some popular filters, we conclude that the proposed enhanced filter can be used for any further detection and recognition operations, and it introduces promising results which can be used for real-time implementation with different computer vision applications.

Using the GNU Radio Software in the Ofdm Multicarrier Communications

Data transmission in HF and UHF radio channels require modern types of modulations. OFDM and Multicarrier are modulation types that have been imposed on 4G and Wi-Fi data transmission channels in 900Mhz, 1800Mhz and 2400Mhz beams. In this paper we are studying the use of these modulation types to increase the data transmission speed in HF and UHF maritime bands.

Impact of a Strong Magnetic Storm and Two X-Ray Flares on the Ionospheric HF Channel in the Summer Solstice of 2015 According to Oblique Sounding in the Eurasian Region

We present the results of observations of the impact a strong magnetic storm and two X-ray flares in the summer solstice of 2015 on the HF signal characteristics during oblique sounding of the ionosphere in the Eurasian region. It was found that the negative phase of the magnetic storm led to a strong degradation of the ionospheric channel, up to a long blackout on the paths adjacent to the subauroral latitudes. On the midlatitude paths, a decrease in the maximum observable frequency of the F layer reached 50% with respect to the average values for an undisturbed ionosphere. The propagation velocity of the negative phase of a disturbance from the subauroral to the midlatitude ionosphere is determined (it is equal to about 100 m/s). It is shown that during a magnetic storm the least observable frequency and the average signal-to-noise ratio for the propagation mode via the sporadic E s layer correlate well with the auroral AE index. Anomalous signals were detected in the main phase of the magnetic storm on the Cyprus—Rostov-on-Don path when a chirp ionosonde–radio direction finder was operated in the over-the-horizon HF radar mode. On the basis of modeling and comparison with experimental data, it is shown that the anomalous signals are due to scattering of radio waves by small-scale irregularities located in the subauroral ionospheric F region.

Impact of heliogeophysical disturbances on ionospheric HF channels

The article presents the results of the observation of a strong magnetic storm and two X-ray flares during the summer solstice in 2015, and their impact on the HF signals characteristics in ionospheric oblique sounding. It was found that the negative phase of the magnetic storm led to a strong degradation of the ionospheric channel, ultimately causing a long blackout on paths adjacent to subauroral latitudes. On mid-latitude paths, the decrease in 1FMOF reached ∼50% relative to the average values for the quiet ionosphere. It is shown that the propagation conditions via the sporadic Es layer during the magnetic storm on a subauroral path are substantially better than those for F-mode propagation via the upper ionosphere. The delay of the sharp decrease in 1FMOF during the main phase of the magnetic storm allowed us to determine the propagation velocity of the negative phase disturbances (∼100m/s) from subauroral to mid-latitude ionosphere along two paths: Lovozero – Yoshkar-Ola and Cyprus – Nizhny Novgorod. It is shown that both the LOF and the signal/noise ratio averaged over the frequency band corresponding to the propagation mode via the sporadic Es layer correlate well with the auroral AE index. Using an over-the-horizon chirp radar with a bistatic configuration on the Cyprus – Rostov-on-Don path, we located small-scale scattering irregularities responsible for abnormal signals in the region of the equatorial boundary of the auroral oval.

Low‐complexity frequency‐domain turbo equalisation for doubly‐selective HF channel on GPP‐based SDR platform

Low‐complexity frequency‐domain turbo equalisation for doubly‐selective HF channel on GPP‐based SDR platform

Slow magnetic relaxations in a ladder-type Dy(iii) complex and its dinuclear analogue.

The complex {[Dy2(PDOA)3(H2O)6]·2H2O}n (1) (H2PDOA = 1,2-phenylenedioxydiacetic acid) was prepared from aqueous solution. Its crystal structure, built up of {-Dy-O-C-O-}n chains interlinked by PDOA ligands yielding a ladder-like arrangement, was determined at 173 K. 1 exhibits slow magnetic relaxation under a small magnetic field BDC = 0.2 T with two (LF and HF) relaxation channels. The LF relaxation time at BDC = 0.2 T and T = 1.85 K is as slow as τ(LF) = 46 ms whereas the HF channel is τ(HF) = 1.4 ms. The mole fraction of the LF species is xLF = 0.76 at 1.85 K and it escapes progressively on heating. In the dinuclear analogue [Dy2(PDOA)3(H2O)6]·3.5H2O (2) one PDOA ligand forms a bis(chelate) bridge between the two Dy(iii) atoms yielding a local structure analogous to that in 1; however its AC susceptibility data show slightly different quantitative characteristics of the single-molecule magnetic behaviour.

The investigation of ionospheric response to total eclipses on 29th March, 2006 and on 20th March, 2015 based on HF oblique sounding data

The investigation of ionosphere response to solar eclipses was carried out. Maximum observable frequencies were analyzed during two eclipses on 29th March, 2006 and on 20th March, 2015 on several oblique sounding paths which were within the range of solar flux obscuration. The model describing local changes in the ionosphere, caused by the obscuration of solar flux during eclipse, is suggested. The computer simulation of HF radiowave propagation during the eclipses was carried out on the basis of this model, while quiet ionosphere was described by IRI-2012 model. It is shown that this approach gives adequate description of HF channel during eclipses for all propagation paths under consideration while the parameters of the model were the same for all paths. As the result of computer simulation time delays of ionosperic responses during eclipses were obtained (~1800–2000s). It was found that maximum depletion of electron concentration reached 85% in D-region for both eclipses. The electron density depletions at height of F2-peak were 48% and 34% for eclipse on 29th March, 2006 and on 20th March, 2015 respectively.

Benchmark Quantum Mechanical Calculations of Vibrationally Resolved Cross Sections and Rate Constants on ab Initio Potential Energy Surfaces for the F + HD Reaction: Comparisons with Experiments.

Quantum scattering calculations within the time-independent approach in an extended interval of energies were performed for the title reaction on four ab initio potential energy surfaces. The calculated integral cross sections, vibrational branching ratios, and rate constants are compared with scattering experiments as well as with chemical kinetics rate data available for this system for both the HF and DF channels. The calculations on the CSZ (J. Chem. Phys. 2015, 142, 024303) and LWAL (J. Chem. Phys. 2007, 127, 174302) surfaces are in close agreement between them and reproduce satisfactorily the experimental measurements. The agreement with the experiments is improved with respect to calculations on the earlier SW (J. Chem. Phys. 1996, 104, 6515) and FXZ (J. Chem. Phys. 2008, 129, 011103) surfaces. The results presented here witness the remarkable progress made by quantum chemistry calculations in describing the interatomic interactions governing the dynamics and kinetics of this reaction. They also suggest that comparison with translationally and rotationally averaged experimental observables is not sufficient to assess the relative accuracy of highly accurate potential energy surfaces. The dynamics and kinetics calculations show that temperatures lower than 50 K or molecular beam energy spread below 1 meV must be reached to discriminate the accuracy of the LWAL and the CSZ surfaces.