HF Communication Research Articles

Correlation betweenfoEsand zonal winds over Rome, Okinawa and Townsville using Horizontal Wind Model (HWM14) during solar cycle 22

• The ionosonde foEs is highly correlated with the disturbed zonal wind. • The study may be used for predicitng foEs to support modern HF communication. • A comprehensive future work may be carried out to increase spatio-temporal coverage. The relation between ionosonde critical frequency of ionospheric sporadic E-layer ( f o E s ) and disturbed zonal wind is studied over Okinawa (26.68°N, 128.15°E), Rome (41.98°N, 12.49°E) and Townsville (19.63°S, 146.8°E) during different solar activity years, 1987 (moderate), 1996 (low) & 2001 (high) (Okinawa and Townsville) and 1987 (moderate), 1995 (low) & 2000 (high) (Rome). The variation of monthly hourly medians of f o E s shows annual trend with maximum values in local summer. However, it does not show dependence on solar activity. The correlation is studied between median f o E s values and the zonal winds obtained from climatological Horizontal Wind Model (HWM14). The strong correlation coefficients obtained between the parameters suggest that HWM14 may be used as a proxy to predict the climatology of the sporadic layers. A more comprehensive study based upon the same procedure is planned in future.

Space Weather Services for Civil Aviation—Challenges and Solutions

This paper presents a review on the PECASUS service, which provides advisories on enhanced space weather activity for civil aviation. The advisories are tailored according to the Standards and Recommended Practices of the International Civil Aviation Organization (ICAO). Advisories are disseminated in three impact areas: radiation levels at flight altitudes, GNSS-based navigation and positioning, and HF communication. The review, which is based on the experiences of the authors from two years of running pilot ICAO services, describes empirical models behind PECASUS products and lists ground- and space-based sensors, providing inputs for the models and 24/7 manual monitoring activities. As a concrete example of PECASUS performance, its products for a post-storm ionospheric F2-layer depression event are analyzed in more detail. As PECASUS models are particularly tailored to describe F2-layer thinning, they reproduce observations more accurately than the International Reference Ionosphere model (IRI(STORM)), but, on the other hand, it is recognized that the service performance is much affected by the coverage of its input data. Therefore, more efforts will be directed toward systematic measuring of the availability, timeliness and quality of the data provision in the next steps of the service development.

CALCULATION OF POLARIZATION LOSSES FOR HF COMMUNICATION CHANNEL (Part 1)

The article describes an algorithm for calculating polarization losses, which are one of the energy characteristics of a HF communication channel when planning radio link of various paths and arbitrary relative positions of the receiving and transmitting points. Using the proposed method, numerical modeling of this type of loss for a given set of input parameters of communication link in the decameter range has been carried out. Based on the calculation results, conclusions were drawn regarding the behavior of polarization losses under various conditions.

Markov Model for HF Joint Spectrum Occupancy at Two Distant Locations

Abstract Even with the present-day development of mobile communications in UHF and SHF spectral bands and recent trends to move to mmWave, HF radio communications still offer advantages that make them exclusive in some application areas. Cognitive Radio principles can be applied to HF communications, to make use of the spectrum more efficiently. A significant improvement of Cognitive Radio technique can be achieved by spectrum occupancy prediction, which enables proactive efficient spectrum utilization. Hidden Markov Models (HMM) can be a useful tool for statistical spectrum occupancy prediction. In some of our previous works, we investigated a simple HMM in time domain, as well as a bidimensional model, that take into account both the time domain and the frequency domain. In this paper, we propose to extend the coverage of the model, by considering in addition to time and frequency the geographical position of the two points involved in the radio connection. The work is motivated by the fact that the two points of the radio link in HF can be far apart, and the channel availability at the two points could be different. Therefore, finding and exploiting correlations between the spectrum occupancy at the two points might improve the connectivity. The proposed model is validated using real spectrum occupancy data collected simultaneously at two locations situated in two cities, namely Timișoara and Sibiu, Romania. The measurements have been made using two identical USRP equipment, GPS coordinated, and identical HF broadband antennas.

Assessment of the capabilities and applicability of ionospheric perturbation indices provided in Europe

Perturbations in the ionosphere are of great interest not only for scientific research, but also for applications using transionospheric radiosignals (e.g. GNSS applications and HF communication), because the transmission of radiosignals is sensitive to the electron density in the ionosphere. However, ionospheric perturbations have manifold character. Their spatial range can vary between global and very local effects (a few hundreds of km range) and their temporal range varies between seconds and days. All these perturbations have different physical background and different impact on applications. Many ionosphere perturbation indices that characterize the state of ionospheric perturbations have been introduced in the past (e.g. ROTI, S4, σPhi, AATR, Reff, W-index, SISTED, SOLERA, DIXSG, IBI, Dfu/Dfl, etc.). This manuscript is an assessment of a subset of diverse ionospheric indices developed and/or applied in Europe. It describes the objectives of the indices, demonstrates their character in a case study for September 2017, indicates their applicability for different use cases in science and industry and guides users to find the appropriate index for their purposes.

An Improved Data Rate Change Algorithm based on Adaptive Frame Length

In order to solve the high bit error rate (BER) caused by rate oscillation in traditional Data Rate Change (DRC) algorithm, an improved DRC algorithm based on Adaptive Frame Length (AFL) was proposed. Firstly, the frame length and transmission rate of the initial transmission were determined by the parameters of the current channel and the information of previous empirical values. Then, if two frames with the same length were successively sent in the transmission process, the frame length would be accordingly increased. If the retransmission failed twice in a row, the frame length would be halved in the next transmission. Finally, the frame error rate was calculated based on the current frame length. The data rate would be updated If the value was less than the present threshold. Compared with RapidM DRC, the average bit error rate of the link decreased by 4.8 percentage points, and the link availability increased by 10 percentage points. The experimental results show that the proposed algorithm can eliminate the rate oscillation and improve the communication capability of the HF communication system.

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.

A Study of SuperDARN Response to Co‐occurring Space Weather Phenomena

AbstractThe Sun was remarkably active during the first week of September 2017 producing numerous solar flares, solar radiation storms, and coronal mass ejections. This activity caused disruption to terrestrial high‐frequency (HF, 3–30 MHz) radio communication channels including observations with the Super Dual Auroral Radar Network (SuperDARN) HF radars. In this paper, we analyze the response of SuperDARN groundscatter observations and decreases in background sky noise level in response to multiple solar flares occurring in quick succession and co‐occurring with solar energetic protons and auroral activity. We estimate the attenuation in HF signal strength using an approach similar to riometry and find that the radars exhibit a nonlinear response to compound solar flare events. Additionally, we find that the three different space weather drivers have varying degrees of influence on the HF signal properties at different latitudes. Our study demonstrates that in addition to monitoring high‐latitude convection, SuperDARN observations can be used to study the spatiotemporal evolution of disruption to HF communication during extreme space weather conditions.

Features of the HF Signal Propagation on Oblique Sounding Paths During Solar and Magnetic Activity in September 2017

We present the results of studying the influence of solar and magnetic activity in September 2017 on the HF signal characteristics on subauroral and midlatitude paths. A connection between the ionospheric effects caused by the magnetic storm and the magnetic disturbance intensity is established. It is shown that the formation of a strong sporadic Es layer in the auroral ionosphere during a magnetic storm makes it possible to use the propagation mode with reflection from Es in the interests of HF communication to neutralize the effects of the negative phase of the storm and absorption growth when unfavorable conditions for the F-mode propagation with reflection from the upper ionosphere occur.

HF Noise Measurement in the Western Part of Romania

Abstract Despite the extraordinary development of mobile communications, HF radio links have several advantages that make them unique in some application areas. Knowledge of HF noise is critical for the setup of a point to point HF communication. The paper presents HF noise measurements performed using a broadband antenna and Software Defined Radio equipment for signal acquisition, followed by offline signal processing. The recording has been split into several sub-bands of small bandwidth and for each sub-band the mean power has been computed, to find the sub-band with the lowest power. It might be assumed that the frequency band having the lowest power contains only noise. An analysis of the influence of sub-band size on the noise level hasalso been made. Measurements cover a large part of HF band and a large time interval to observe the noise behaviour.The paper analyses the noise level over short and long time periods, and over a large frequency band, and reports also simultaneous noise measurements in two locations in the western part of Romania, a dense urban one and a small town one, to highlight the differences caused by man-made noise of industrial type.

HF Communication Quality Level Increase when Using the Pre-session Diagnostics of a Multidimensional Ionospheric Radio Channel

HF Communication Quality Level Increase when Using the Pre-session Diagnostics of a Multidimensional Ionospheric Radio Channel

Diagnostics of HF radio channel: based on data from backscatter ionospheric sounding by continuous chirp signal

Backscatter ionospheric sounding (BIS) is a powerful tool for monitoring and predicting conditions of operation of HF communication systems. The BIS method is adopted to determine coverage areas of radio waves and maximum usable radio frequencies, distance along the ground to a scatterer, as well as to gain information about ionospheric structure and conditions. To solve these problems, we propose a method for direct diagnostics of HF radio channel at the leading edge of BIS signals on ionograms. The method relies on real-time automatic processing and interpretation of BIS ionograms. We present algorithms for determining the maximum usable frequencies and characteristics of oblique sounding signals from current BIS data, without correcting ionospheric parameters. We realize the algorithm for recovering ionospheric parameters at the path midpoint.

Диагностика КВ-радиоканала по данным возвратно-наклонного зондирования ионосферы непрерывным ЛЧМ-сигналом

Backscatter ionospheric sounding (BIS) is a powerful tool for monitoring and predicting conditions of operation of HF communication systems. The BIS method is adopted to determine coverage areas of radio waves and maximum usable radio frequencies, distance along the ground to a scatterer, as well as to gain information about ionospheric structure and conditions. To solve these problems, we propose a method for direct diagnostics of HF radio channel at the front edge of BIS signals on ionograms. The method relies on real-time automatic processing and interpretation of BIS ionograms. We present algorithms for determining the maximum usable frequencies and characteristics of oblique sounding signals from current BIS data, without correcting ionospheric parameters. We realize the algorithm for recovering ionospheric parameters at the path midpoint.

Model based Computerized Ionospheric Tomography in space and time

Reconstruction of the ionospheric electron density distribution in space and time not only provide basis for better understanding the physical nature of the ionosphere, but also provide improvements in various applications including HF communication. Recently developed IONOLAB-CIT technique provides physically admissible 3D model of the ionosphere by using both Slant Total Electron Content (STEC) measurements obtained from a GPS satellite - receiver network and IRI-Plas model. IONOLAB-CIT technique optimizes IRI-Plas model parameters in the region of interest such that the synthetic STEC computations obtained from the IRI-Plas model are in accordance with the actual STEC measurements. In this work, the IONOLAB-CIT technique is extended to provide reconstructions both in space and time. This extension exploits the temporal continuity of the ionosphere to provide more reliable reconstructions with a reduced computational load. The proposed 4D-IONOLAB-CIT technique is validated on real measurement data obtained from TNPGN-Active GPS receiver network in Turkey.

Radio Propagation Prediction for HF Communications

The refraction and apparent reflection of HF radio waves by the ionosphere enables long range HF radio communications. The ionosphere is a distinctly irregular medium that is mostly driven by solar activity. Ionospheric models are useful in the prediction of ionospheric behaviour and in the provision of data required for the analysis and forecasting of ionospheric propagation. This paper provides a compact review of HF radio propagation prediction techniques and approaches for HF communications. The paper also highlights the numerous approaches have been used to date in an attempt to estimate F2 usable frequencies. The review presented in this paper is inspired by the most recent advances in the field of ionospheric prediction and modelling.

Human Exposure to Electromagnetic Fields on Marine Platforms: Safety Regulations, Simulation and Measurement

A warship represents a very complicated platform with very different electronic systems operating on a variety of frequencies and working also with different output powers, some of which might reached the order of MW. The electromagnetic radiation coming from each of these systems (named as RADHAZ) may harm the personnel on board, so it turns out necessary to carry out measures in order to verify whether the intensity of the electromagnetic fields present on the ship fulfills the in force regulations (according to the maximum permitted exposure levels) or not. In this paper we will obtain the value of those electromagnetic fields for a HF communication system (the most common system in any kind of ship and also radiating high powers) by two different methods: results coming directly from measures conducted on the decks of a warship and results coming from the HEMCUVE simulation program.

Low-Profile Two-Arm Inverted-L Antenna Design for Vehicular HF Communications

Design of an electrically small, low-profile vehicular on-the-move (OTM) wideband high frequency antenna with 24 kHz instantaneous-tuned bandwidth is discussed for near vertical incidence skywave (NVIS) communications. Improvement in performance is obtained by applying multiarming and offset feed antenna modifications. These allow for attaining the desired gain >−20 dBi at 3 MHz with a lower profile compared to traditional OTM 3 kHz bandwidth antennas. Specifically, the addition of the second arm improves the bandwidth, whereas NVIS gain is enhanced by offset feeding. The electrical dimensions of the proposed two-arm design over the platform are $\lambda /13 ~(\text {L}) \times \lambda /30 ~(\text {W}) \times \lambda /400$ (H) at the lowest frequency of operation. Antenna performance and achieved benefits under the condition of mechanical breakdown are also discussed. The scaled prototype of the proposed antenna mounted on a selected vehicular platform is built using additive manufacturing. Measurement results agree well with simulations thereby verifying the design procedure and all the discussed findings.

Atmosphere-ionosphere coupling from convectively generated gravity waves

Ionospheric variability impacts operational performances of a variety of technological systems, such as HF communication, Global Positioning System (GPS) navigation, and radar surveillance. The ionosphere is not only perturbed by geomagnetic inputs but is also influenced by atmospheric tides and other wave disturbances propagating from the troposphere to high altitudes. Atmospheric Gravity Waves (AGWs) excited by meteorological sources are one of the largest sources of mesoscale variability in the ionosphere. In this paper, Total Electron Content (TEC) data from networks of GPS receivers in the United States are analyzed to investigate AGWs in the ionosphere generated by convective thunderstorms. Two case studies of convectively generated gravity waves are presented. On April 4, 2014 two distinct large convective systems in Texas and Arkansas generated two sets of concentric AGWs that were observed in the ionosphere as Traveling Ionospheric Disturbances (TIDs). The period of the observed TIDs was 20.8min, the horizontal wavelength was 182.4km, and the horizontal phase speed was 146.4m/s. The second case study shows TIDs generated from an extended squall line on December 23, 2015 stretching from the Gulf of Mexico to the Great Lakes in North America. Unlike the concentric wave features seen in the first case study, the extended squall line generated TIDs, which exhibited almost plane-parallel phase fronts. The TID period was 20.1min, its horizontal wavelength was 209.6km, and the horizontal phase speed was 180.1m/s. The AGWs generated by both of these meteorological events have large vertical wavelength (>100km), which are larger than the F2 layer thickness, thus allowing them to be discernible in the TEC dataset.

Estimation of Frequency Channel Availability for Different HF communication Modems Based on the Passive Sounding of a Multi-Dimensional Ionospheric Radio Channel

Estimation of Frequency Channel Availability for Different HF communication Modems Based on the Passive Sounding of a Multi-Dimensional Ionospheric Radio Channel

Contactless power transmission for NFC antennas in credit‐card size format

Wireless energy transmission is a key element in Contactless HF Communication Technologies, such as radio frequency identification or near field communication (NFC). This power aspect differentiates the technology from conventional wireless communication. The authors consider the circuit model as a lumped-element description with a coupled-transformer field model to formulate a representation of the problem and include the orientation of the magnetic field in planar space. The authors propose a novel computational model to reveal the dynamics of energy transfer can be represented as a set of forces projected by the oscillator at the interface of free-space. Finally, a high-frequency finite-element simulation based on the authors' model is used to solve a practical problem of two coupled elliptical spiral-loop antennas of a credit-card size, where the authors consider their contribution in the context of NFC.