HF Communication Research Articles

Sporadic E critical frequency detection using three EIA region ionosonde stations over Southeast Asia

This paper presents the occurrence of the sporadic E layer critical frequency (foEs) measured from three ionosonde stations in the Southeast Asia equatorial ionization anomaly (EIA) regions. These three ionosonde stations include two in Thailand: Chiang Mai (18.76°N, 98.93°E, Dip 12.7°) and Chumphon (10.72°N, 99.37°E, Dip 3.0°), and one in Indonesia: Kototabang (0.2°S, 100.32°E, Dip -10.1°). The daily hourly foEs values observed during 2010 and 2015 were statistically analyzed for foEs occurrence during low and high solar activity periods. Additionally, the number of foEs occurrences was analyzed in terms of the percentage of occurrence (%foEs). The results show that the occurrences of foEs from all three stations were similar, with the monthly hourly occurrence of foEs peaking in the June solstice season (May, June, July, August). Meanwhile, foEs appeared relatively low during the September equinox (September, October) and the December solstice (November, December, January, February) seasons. Furthermore, the frequency of foEs occurrence peaks around 16-20 LT, except in 2015 at Chiang Mai and Chumphon, where peaks were observed at 10 LT and 15 LT, respectively. Additionally, comparing the three stations reveals that in 2010, the maximum number of foEs occurrences was at Chiang Mai (≈21%), followed by Kototabang (≈19%) and Chumphon (≈16%). In 2015, the highest number was observed at Kototabang (≈17%), followed by Chumphon (≈14%) and Chiang Mai (≈8%). Furthermore, the maximum frequency of foEs was highest at Chiang Mai (20-25 MHz), followed by Chumphon (15-20 MHz) and Kototabang (10-15 MHz). Additionally, foEs occurrences during low solar activity (2010) were higher than those during high solar activity (2015). It was assumed that the occurrence of foEs in the Southeast Asian sector was anti-correlated with the solar cycle and asymmetric characteristics. We hope that this analytical information will be useful for future HF and VHF communications design in the Southeast Asia region.

A Frequency Selecting Method for High-Frequency Communication Based on Ionospheric Oblique Backscatter Sounding

Ionospheric oblique backscatter sounding is an effective means of monitoring the ionosphere which can be used as a frequency selection system to serve HF communication and ensure its quality and stability. But how to obtain effective information from the oblique backscatter ionogram is still a hot issue. Due to this situation, a frequency selecting method for HF communication based on ionospheric oblique backscatter sounding is proposed in this study. After obtaining the ionograms, pattern recognition is used to separate the vertical echoes and the oblique backscatter echoes. Next, the leading edge of the oblique backscatter echoes are extracted, and then a two-dimensional electron density profile can be reconstructed. Then, with the help of ray tracing, the usable frequency range can be estimated. Finally, according to the signal-to-noise ratio reflected by the ionograms, several optimal communication frequencies can be selected. In order to verify this method, oblique ionograms are obtained through oblique sounding experiments to evaluate its accuracy. The result indicates that the usable frequency range and the selected frequencies are in accordance with the echo of the oblique ionogram, so the practicability and accuracy of the method are validated. Eventually, the maximum usable frequencies (MUFs) obtained from oblique backscatter sounding are compared with the MUFs from the oblique sounding ionogram; its Mean Absolute Percentage Error (MAPE) is 7.8% and its root mean squared error (RMSE) is 1.34 MHz.

HF-NVIS Data Communication: OFDM Transmission Testing and Optimization Strategies

Abstract Orthogonal frequency division multiplexing (OFDM), a technique that uses frequency division multiplexing to allow parallel transmission of data over multiple subchannels, is widely used in various wireless systems. Its effectiveness even extends to HF links, where it has demonstrated superior performance compared to single-carrier schemes. In addition, OFDM’s robustness to multipath fading and its ability to efficiently utilize the available bandwidth make it a preferred choice for modern communication systems, but also for scenarios with complex communication links, such as HF range communications. The objective of this experimental research is to analyze and improve the performance of the OFDM technique adapted to HF communication channels. This study is motivated by the lack of a protocol to regulate HF communications using OFDM. The analysis and optimization method starts by considering the fundamental bandwidths of HF channels (ranging from 3 to 24 kHz). For this purpose, OFDM-specific modifications have been analyzed, including changes in the FFT size (representing the number of subcarriers), adjustment of the number and amplitude of pilots, analysis of the impact of packet length modification (pre-OFDM), and evaluation of guard intervals. In essence, our goal is to implement an OFDM technique commonly used in modern data communications in the context of traditional HF communications systems.

Determining Watterson model time delays using adaptive filters

Short radio waves have the property of being reflected from the ionosphere, which is why data transmission via HF communication channels can be carried out over many kilometers without additional transmitting devices. The use of broadband communication channels increases the data transmission speed, but at the same time leads to severe distortion of the received signal. Using the Watterson model, the HF communication channel was simulated in Matlab in the Simulink environment. For various possible values of the model parameters, least mean squares (LMS) equalizer algorithms were used to determine these coefficients.

Assessment of IRI2020 model accuracy in predicting ionospheric parameters: Insights from multiple ionosonde stations

This research assesses the performance of the IRI2020 model in forecasting the ionospheric critical frequency of the F2 layer (foF2) and Maximum Usable Frequency (MUF) of the ionosphere from 2020 to 2023 across multiple ionosonde stations. The primary objective is to analyse the characteristics of foF2 and MUF across various longitudinal sectors during the solar minimum to ascending phase of solar cycle 25 and to evaluate the IRI2020 model’s performance in replicating observed data. Additionally, the study explores the influence of various space weather parameters on the variability of these ionospheric parameters. The findings reveal that the IRI2020 model overestimates the daily mean values of both foF2 and MUF(3000)F2 across the stations over the three years. While exhibiting good performance in capturing the pattern of hourly predictions, the model tends to overestimate foF2 more than MUF(3000)F2, with better predictions observed for MUF(3000)F2. However, hourly estimations display a mix of underestimation and overestimation, predominantly overestimating values. Correlations ranged from 0.58 to 0.92 for foF2 and 0.72 to 0.91 for MUF(3000)F2, showing variability across stations. As solar activity increases, seasonal variations become more evident, especially in stations located in the northern hemisphere.In contrast, stations in the southern hemisphere exhibit less pronounced seasonal variations, suggesting a notable hemispheric asymmetry. Although the IRI2020 better captured the general trend of foF2 and MUF(3000)F2 in our investigation, the percentage deviation for MUF(3000)F2 ranges from 1 % to 15.1 %, which can result in a significant range reduction for practical applications like HF communications. Stations closer to the geomagnetic equatorial line exhibit stronger seasonal asymmetry and higher deviations. Some key space weather parameters, including sunspot number R, F10.7 and R/F10.7 ratio, were found to significantly influence ionospheric variability, with sunspot number R and R/F10.7 showing a stronger correlation with foF2 and MUF(3000)F2. These suggest that the variability of the solar active region parameters primarily controls ionospheric foF2 and MUF(3000)F2.

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.

IM-Based Pilot-Assisted Channel Estimation for FTN Signaling HF Communications

IM-Based Pilot-Assisted Channel Estimation for FTN Signaling HF Communications

Short-Term Fine-Grained Regional MUF Prediction for HF Communication Based on Time-Series Decomposition

Short-Term Fine-Grained Regional MUF Prediction for HF Communication Based on Time-Series Decomposition

SISTEM PENANGKAL PETIR DI GEDUNG TELEKOMUNIKASI DAN GEDUNG PAI MATSC

On Friday, 11 November 2022, there was damage to the radio link equipment in the HF and MSSR radio transmitter communication systems due to a lightning strike operating at the Makassar Air Traffic Service Center (MATSC) office. This lightning strike is a phenomenon that poses a threat to the operation of flight navigation services carried out by the MATSC branch of Perum LPPNPI. The purpose of this study is to evaluate the external lightning protection system that has been installed and also to determine the effectiveness of the conventional lightning protection system on the antenna tower next to the MATSC radio PAI building. This study uses quantitative research methods. Retrieval of data using the method of observation and measurement. The calculation results found that the PAI Building was included in category IV, meaning that the lightning strike hazard level is 80%. While the antenna tower has a protection level category III, which means it has a danger level of 90%. However, from the observations, only the tower antenna is provided with a conventional type of lightning rod, while the PAI Building does not have a lightning rod system. The calculation results show that the existing conventional lightning rod protection angle is around 35o with a protection radius of 16.58 m. So that with this radius, the PAI building does not fully get protection from the dangers of lightning strikes.
 
 Keywords: Lightning Protection System, Antenna Tower, PAI MATSC Building

An investigation into how space weather operational centre products meet end-user needs

Potential beneficiaries of the COSPAR Space Weather Roadmap can be classified in two groups – 1) operational space weather service providers, which can be viewed as direct users of the science developed through the COSPAR roadmap process; 2) end-users such as the electricity and satellites sectors whose requirements should define the metrics and parameters delivered through the products of space weather service providers, which therefore are intimately linked to the focus and evolution of the COSPAR roadmap.With regard to Group (1), interaction with COSPAR that feeds Group 2 requirements into the roadmap process may be enhanced via specific activities such as:•Participation in COSPAR bodies such as the Panel on Space Weather and ISWAT.•Participation in ISES and WMO space weather teams that are increasingly engaging with COSPAR to better coordinate research and operational space weather activities.•Promoting actions to ensure the R2O-O2R circle is complete - this may include adopting specific R2O-O2R actions or best-practice identified through WMO, ISES, or COSPAR activities that may also be effectively used to focus future iterations of COSPAR space weather roadmaps.Group 2 members often exist at one step further removed from the research community (i.e., they typically speak to operational service providers (Group (1) and these service providers interact with the research community), so there is a risk that their requirements are not fully addressed by the operational service providers and of a disconnect with the research community. To strengthen the research/operational centre/end-user chain, we first need to know how the operational centres and end-users interact, via a survey. Following this, we can better target research to support operational centres and understand how the research to end-user connections may be improved.In this paper, we describe such a survey and present the results. The survey focuses on the level of engagement between operational centres and end-users, end-user views of the quality of existing services, and their views on how further research can be exploited to better meet their requirements. We focus on the six key end-user sectors of Power, Aviation, Satellites, HF communications, GNSS, and Aurora Watchers. Via these examples, the connection from end-user impacts through to operations through to research requirements can be clarified. We further summarise the survey findings in terms of the end-user impact pathways defined in Schrijver et al. (2015).

A Prediction Method of Ionospheric hmF2 Based on Machine Learning

The ionospheric F2 layer is the essential layer in the propagation of high-frequency radio waves, and the peak electron density height of the ionospheric F2 layer (hmF2) is one of the important parameters. To improve the predicted accuracy of hmF2 for further improving the ability of HF skywave propagation prediction and communication frequency selection, we present an interpretable long-term prediction model of hmF2 using the statistical machine learning (SML) method. Taking Moscow station as an example, this method has been tested using the ionospheric observation data from August 2011 to October 2016. Only by inputting sunspot number, month, and universal time into the proposed model can the predicted value of hmF2 be obtained for the corresponding time. Finally, we compare the predicted results of the proposed model with those of the International Reference Ionospheric (IRI) model to verify its stability and reliability. The result shows that, compared with the IRI model, the predicted average statistical RMSE decreased by 5.20 km, and RRMSE decreased by 1.78%. This method is expected to provide ionospheric parameter prediction accuracy on a global scale.

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.

Expanding undistorted transmission bandwidth for HF communications by leveraging the physical effect of intramode dispersion type transition

Expanding undistorted transmission bandwidth for HF communications by leveraging the physical effect of intramode dispersion type transition

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

Complex Complementary Sequence Real Orthogonal Spreading OFDM Scheme for HF Communication Link

Complex Complementary Sequence Real Orthogonal Spreading OFDM Scheme for HF Communication Link

CAPACITY ESTIMATION METHOD WITH LINEAR COMPUTATIONAL COMPLEXITY OF NARROW-BAND IONOSPHERIC DECAMETER CHANNELS WITH PSK-N-SIGNALS

The paper presents a new algorithm with linear time complexity, depending on the effective channel memory, for estimating the resolution time and capacity of a frequency-selective communication channel using a linear receiver and a multi-position phase-shift keying signal. The main limitation of the method is the possibility of its application for frequency-selective communication channel with symmetrical amplitude-frequency response relative to the central frequency of the channel, which is equal to the frequency of the received signal. From a practical point of view, this method can be used in the construction of radio engineering systems with serial data transmission in narrow-band ionospheric decameter communication channels (3-12 kHz). The key features of this method are: 1) constant number of equations equal to 1; 2) linear dependence of the number of terms in the equation on effective memory; 3) a new, more accurate procedure for estimating the effective memory of the channel, which allows you to simultaneously determine the resolution time and capacity. These features provide an increase in frequency efficiency by reducing overhead costs for setting the parameters of a serial phase radio engineering data transmission system for HF communication channels with a bandwidth of 3-12 kHz.

The Matrix Model of Discrete Matching Elements for HF Computational Automatic Tuning Units

The article is devoted to a new and relevant direction in the HF communication technology - the construction of high-speed computational antenna tuning units (ATU). The implementation of automatic ATU requires the designing of power circuits models adequate, as practice shows, the construction of models to physical reality in order to ensure their controllability. Practically powerful device elements are not in fact concentrated, the distributed nature of their parameters is noticeably manifested in the HF range. Matching ATU on the base of antenna input impedance measuring involves forming of accurate control commands for the elements, especially in conditions where the settings are narrow-band. A new approach to the description of a power circuit discrete elements transforming properties using the theory of linear passive four-pole and matrices, which has the ultimate accuracy, is proposed. A method to form a matrix description of on-off discrete elements of a power circuit based on the results of characteristic field measurements of the mounted device is presented. This approach made it possible to significantly reduce the amount of tabulated data describing the functional dependences of the complex coefficients of wave transmission matrices and to “smooth out” the experimental error. Complex cases are considered, which are of the greatest interest for practice - options for a four-pole cascade and parallel connection of reactive elements in the branches of the power circuit. The current state of computer technology makes it possible to sharply increase the complexity of the mathematical models used. The matrix model takes into account a significant variety of operating factors and does not require them to be “customized” to existing analytical methods. The adequacy, in this simulation, is determined by practical needs that arise in the design of power circuits of matching antenna devices and their tuning algorithms. In fact, the model is considered adequate if the errors in the calculation of the response function according to the model do not exceed the errors in its experimental determination. The proposed matrix approach made it possible to significantly improve the accuracy of modeling, while the error does not exceed 1 %. Also, this approach allows to find several options for setting a given quality and choose the best one for any parameter, while reducing the duration of the process up to 25 times. At the additional metrological advantages appeared in such devices serial production.

Models of HF Interference over Cyprus

Interference from other users, due to the long-distance propagation of HF signals, causes spectral congestion, which is considered a primary detrimental effect on HF (3–30 MHz) communication systems. More than a year of HF electric field measurements from a calibrated monopole HF antenna collected by a dedicated measurement system installed in Cyprus have been used to compare neural networks and non-linear regression for the development of single-allocation congestion models in the HF spectrum. These models can be used to advise operators on typical interference spectral congestion levels and assist in the planning and management of frequency usage by assessing the interference level to alleviate spectral congestion in the HF band over Cyprus. The performance of these alternative modeling approaches is discussed in the context of their ability to successfully capture the diurnal variability of HF interference at a certain incident field strength threshold.

Investigation of Two Prediction Models of Maximum Usable Frequency for HF Communication Based on Oblique- and Vertical-Incidence Sounding Data

As one of the key technologies of HF communication, the maximum usable frequency (MUF) prediction method has been widely discussed. To experimentally confirm the reliability of commonly used MUFs prediction models for high-frequency communication, we have compared maximum observed frequencies (MOFs) and predicted MUFs to assess the accuracy of two typical prediction models. The root-mean-square error (RMSE) and relative RMSE (RRMSE) between oblique sounding MOFs and the predicted MUFs were used to assess the model’s accuracy. The oblique sounding path was from Changchun to Jinyang, and the vertical-sounding ionosonde was located in Beijing, which was approximately the midpoint of the oblique sounding circuit. The statistical analysis results show that: (a) the trend of prediction results from the Lockwood and the Istituto Nazionale di Geofisica e Vulcanologia (INGV) model are in good agreement with the observations: the mean RMSE and RRMSE of the INGV model are less than those of the Lockwood model; (b) in the four different periods (sunrise, daytime, sunset, and nighttime) of the whole day, the maximum difference of RMSE between the Lockwood and INGV model is 0.14 MHz (the INGV performs better than the LWM), with the corresponding differences of RRMSE being 0.31% at sunrise and 0.68% at daytime; (c) in the four seasons of spring, summer, autumn, and winter, the minimum RMSE values of the Lockwood and INGV models are 1.51 MHz and 1.37 MHz, respectively, which are obtained in winter, and the corresponding RRMSEs are 11.47% and 11.79%, respectively; (d) in the high and low solar activity epochs, the mean RMSEs of the Lockwood and INGV models are 1.63 MHz, and 1.54 MHz, with corresponding mean RRMSE values of 11.47% and 11.55%. In conclusion, the INGV model is more suitable for MUF prediction over Beijing and its adjacent mid-latitude regions from the RMSE comparison of the two models.

Over-the-Horizon Channel of Radio Communication at VHF Band via Artificial Plasma Clouds

Metal cesium (Cs) vapor, released at an altitude in the upper atmosphere, generates an artificial space plasma cloud with high electron density. It can act as a scatter to realize radio communication across an over-the-horizon distance. A full-life model of radio propagation via an artificial plasma cloud is established based on its space–time evolution in this article. In addition, this model is verified by the sounding data of the rocket release experiment carried out in the United States. The multipath effect of plasma cloud scattering is studied by using ray tracing, and then, the coherent bandwidth is estimated for this spatial channel. Also, the theoretical channel model of artificial plasma cloud is established by using its space–time evolution and atmospheric wind field parameters. Considering common modulation modes and receiver noise levels, the potential communication performance is evaluated by using the proposed channel model, such as the transmission rate, the bit error rate (BER), and the available time for building up and maintaining communication links. It is shown that the maximal communication rate is up to 200 kb/s, BER overall maintains below 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−7</sup> , and the available time for a single release is about 30–60 min; for the case of this article, they are release mass of 2–10 kg, communication distances of 400–1200 km, and radio frequencies of 30–70 MHz at the VHF band. This demonstrates that the artificial channel can propagate radio waves at a much higher frequency, wider bandwidth, and higher rate than those of HF communication. Hopefully, it could be a solution to overcome the intolerable shortcoming and adverse effects on HF communication due to ionospheric disturbances especially in cases of maritime, emergency, and minimum communications