Short-wave Signals Research Articles

Research on automatic modulation recognition of shortwave signals in few‐shot scenarios based on knowledge distillation

AbstractAutomatic modulation recognition plays an important role in wireless communication and radio regulation. Existing deep learning‐based automatic modulation recognition techniques perform well with large datasets and high computational power but require significant resources for labelled data and complex pre‐processing. This paper proposes a multi‐information fusion method for few‐shot modulation recognition, which involves converting I/Q signals into A/P signals and training with a combination of VGG and LSTM network models. An ensemble knowledge distillation (EKD) approach is employed to streamline the network model, meeting the demands for deploying neural network models on compact devices. Experimental results demonstrate that using only 1% of the shortwave modulation signal dataset as the training set, the proposed model achieves an average classification accuracy of 71.08% under all signal‐to‐noise ratios, surpassing the currently popular deep learning models. Moreover, two small‐scale networks, MobileNetV3 and convolutional neural network are trained, through EKD. Compared to the teacher network, the floating‐point operations of the distilled models are reduced by 99.8% and 99.7%, respectively, and the average prediction accuracy only decreases by 16.05% and 8.09%. The lightweight, few‐shot networks designed in this study for shortwave modulation signals aim to achieve fast and accurate modulation recognition on compact devices.

A DPD Algorithm of Maximum Likelihood Based on DOAs and Doppler

Direct position determination (DPD) is a single step method that estimates the position of target by received signals. Localization in 3D scene is a complicated problem, because the signal propagation channel is complex, and it has many kinds of interference and noise. This paper establishes the Over-the-horizon (OTH) shortwave signals and line-of-sight propagation of ultra short wave model, and proposes a joint localization algorithm. We compare the Cramér-Rao Bound(CRB) and the root mean square error (RMSE) between the proposed algorithm and DPD used single information like DOA and Doppler. The simulation results verify the superiority of the proposed algorithm, and prove it has higher accuracy.

Automated Estimation of Sub-Canopy Topography Combined with Single-Baseline Single-Polarization TanDEM-X InSAR and ICESat-2 Data

TanDEM-X bistatic interferometric system successfully generated a high-precision, high-resolution global digital elevation model (DEM). However, in forested areas, two core problems make it difficult to obtain sub-canopy topography: (1) the penetrability of short-wave signals is limited, and the DEM obtained in dense forest areas contains a significant forest signal, that is, the scattering phase center (SPC) height; and (2) the single-baseline and single-polarization TanDEM-X interferometric synthetic aperture radar (InSAR) data cannot provide sufficient observations to make the existing physical model reversible for estimating the real surface phase, whereas the introduction of optical data makes it difficult to ensure data synchronization and availability of cloud-free data. To overcome these problems in accurately estimating sub-canopy topography from TanDEM-X InSAR data, this study proposes a practical method of sub-canopy topography estimation based on the following innovations: (1) An orthogonal polynomial model was established using TanDEM-X interferometric coherence and slope to estimate the SPC height. Interferometric coherence records forest height and dielectric property information from an InSAR perspective and has spatiotemporal consistency with the InSAR-derived DEM. (2) Introduce Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2) data to provide more observational information and automatically screen ICESat-2 control points with similar forest and slope conditions in the local area to suppress forest spatial heterogeneity. (3) A weighted least squares criterion was used to solve this model to estimate the SPC height. The results were validated at four test sites using high-precision airborne light detection and ranging (LiDAR) data as a reference. Compared to the InSAR-derived DEM, the accuracy of the sub-canopy topography was improved by nearly 60%, on average. Furthermore, we investigated the necessity of local modeling, confirming the potential of the proposed method for estimating sub-canopy topography by relying only on TanDEM-X and ICESat-2 data.

Short-Wave Sensitive ("Blue") Cone Activation Is an Aggravating Factor for Visual Snow Symptoms.

Background and Purpose: Visual Snow (VS) is a disorder characterised by the subjective perception of black-and-white visual static. The aetiology of this condition is not known. In our previous work we suggested that there is a link between short-wave (S or “blue” cone) signals and severity of visual snow symptoms. Therefore we aimed to further characterise this potential link.Methods: Patients (n = 22) with classic VS based on the diagnostic criteria and healthy controls (n = 12), underwent Intuitive Colorimetry (IC) testing (Cerium Visual Technologies). Twelve hue directions (expressed as angle in CIE 1976 LUV space relative to D65) were rated on a five-point scale from preferred (relieving, positive score) to non-preferred (exacerbating, negative score), and overall preferred and non-preferred angles were chosen.Results: A non-preferred violet region near the tritanopic confusion line / S-cone axis (267 deg.) was strongly associated with exacerbation of VS symptoms (range 250–310 deg, mean 276 ± 16, n = 20, Rayleigh p < 0.001). Two subjects with non-preferred region > 90 deg from mean were considered as outliers. Median rank at hue angle 270 deg was significantly lower than at angle 90 (−1.5 vs. 0.0, p < 0.001, Wilcoxon non-parametric rank-sum test). Patients showed preference for one of two spectral regions which relieved VS symptoms: orange-yellow (range 50–110 deg., mean 79 ± 24, n = 14) and turquoise-blue (range (210–250 deg., mean 234 ± 27, n = 8).Conclusion: Our results show that visual snow symptoms are exacerbated by colour modulation that selectively increased levels of S-cone excitation. Because S-cone signals travel on primordial brain pathways that regulate cortical rhythms (koniocellular pathways) we hypothesis that these pathways contribute to the pathogenesis of this disorder.

Analysis of Three Channel SW Interference Adaptive Cancellation System

Aiming at the adjacent channel interference problem of short-wave, a model of three-way short-wave interference signals has been established. The interference cancellation of the short-wave interference signal of three adjacent channels is analyzed, and the time-domain characteristics of the adaptive interference cancellation system are simulated. The theoretical and simulation analysis of the adaptive system show that the offset of the bypass signal will be affected when the intermediate signal frequency is biased to one side because of the existence of the intermediate channel bandwidth.

Extended Analysis of Real‐Time foF2 Mapping in Mideastern China Based On Shortwave Signals

AbstractA method for the real‐time mapping of the critical frequency of the F2 layer (foF2) is established using shortwave radio signals as the radiation sources, thereby eliminating the need for ionosonde stations, and tested in mideastern China. The ionospheric foF2 in the reflection area between the receiving station and the radio stations is obtained using a probabilistic inversion method. Subsequently, Kriging is used for the real‐time foF2 mapping. To heighten the performance of the reconstruction, the International Reference Ionosphere 2012 (IRI‐2012) Model was used as a background for ionospheric interpolation to calculate regional variant. The mapping accuracy is estimated using ionosonde data derived from seven stations in mideastern China: Xinxiang (35.2°S, 113.9°E), Wuhan (30.6°S, 114.6°E), Qingdao (36.1°S, 12.4°E), Suzhou (30.3°S, 120.6°E), Xian (34.3°S, 108.9°E), Chongqing (29.6°S, 106.5°E), and Guangzhou (23.1°S, 113.3°E). The data were recorded approximately every 15 min during two recording intervals between 04:00 UTC LT on 31 October 2012, and 03:30 UTC on 1 November 2012. The estimates of foF2 obtained from the reconstruction method and the foF2 values predicted using IRI are compared with the measurements from the vertical ionosondes at the above seven stations. The root‐mean‐square error and percent deviation are calculated to evaluate the performance of the inversion model. The results indicate that the new method for real‐time foF2 mapping based on shortwave signals is a promising candidate technique for obtaining ionospheric parameters and studying the ionosphere.

Ground-based observations and simulation of ionospheric VLF source in experiments on modification of the polar ionosphere

The phase velocities of TE and TEM waves at frequencies of 1017 and 3017 Hz, as well as the effect of precipitations during auroras on the velocities, are estimated in the Earth–ionosphere waveguide on the basis of observations of electromagnetic fields of an ionospheric source in experiments on modification of the lower ionosphere by a modulated high-power short-wave signals performed by the Arctic and Antarctic Research Institute (AARI) at the EISCAT/Heating test bench in October 2016. Probable electron density profiles in the plane-stratified ionosphere are retrieved from the numerical solution of a wave equation, which are used for the calculation of the phase velocities close to measured ones.

A Method for Weakening Residual Errors in Multi - beam Swath Joins based on Terrain Spectrum Analysis

Some factors lead to spurious signals in the multi-beam sounding process, including complex changes of the sea, the vessel motion attitede, the unreasonable setting of equipment parameters and so on. Although these factors were filtered strictly and the system errors were compensated in the post processing, residual errors still exist in multi-beam swath joins. Such errors produce uplift and abnormal phenomena in the measured terrain between swaths. Therefore, a new method of terrain spectrum analysis was established to improve the efficiency of massive data processing and to accurately reflect the submarine topography. This method was based on the blend of extraction technology of short-wave signals and fitting model of long-wave signals, among which wavelet analysis was used to extract the terrain highfrequency signals (short-wave) and multi-surface function was applied to fit the long-wave signals. Then, the two types of signals were fused to reconstruct the actual seabed topography. Finally, the indexes of depth discrepancy were used to estimate the effect of residual errors. Experimental results show that the proposed method could effectively eliminate the uplift phenomenon of the seabed Digital Elevation Model (DEM), and correctly reflect the detailed topographical variation. This work could further improve the sounding accuracy and the efficiency of swath joins, and beneficial to the fusion of multi-beam digital signals and the image information of side scan sonar.

A chromatic channel in which short-wave and long-wave cone signals are opposed to middle-wave cone signals?

A chromatic channel in which short-wave and long-wave cone signals are opposed to middle-wave cone signals?

The Filipino Broadcasters on Overseas Propaganda Radio in World War II

The use of radio broadcasting for propaganda in the Second World War is well known. In the Philippines, the pre-war KZRH was taken over by the invading Japanese forces, who changed its call letters to PIAM and used it to try to win the hearts and minds of Filipinos. Counter-propaganda was heard on the short-lived resistance stations Voice of Freedom and Voice of Juan dela Cruz as well as shortwave signals emanating from the US and other countries. Also recorded in historical accounts is the work of some Filipinos who broadcast on PIAM, Voice of Freedom and Voice of Juan dela Cruz. Little is known, however, about the work of Filipinos in overseas propaganda radio stations, such as that of Carmen Ligaya on KGEI in San Francisco, California, who was the US’s answer to Tokyo Rose; of at least seventeen others who also broadcast on KGEI; and of Norman Reyes on the Zero Hour on Radio Tokyo. Their experiences, previously under-examined, indicate the extent by which radio broadcasting has since been a tool for shaping public consciousness, particularly in wartime.

Radio Wave Generation Using Dark and Bright Soliton

In this study we propose a new system for radio wave using a soliton pulse within a micro waveguide and nano-waveguide. The system consists of two micro ring resonators and a nano ring resonator that can be integrated into a single system. The input soliton power, coupling coefficients, and ring radii, are used to control the short-wave and millimeter-wave output signals being generated and filtered in a single system. The large bandwidth signal is generated using a soliton pulse within a Kerr-type nonlinear medium. The signals with broad bandwidth or wavelength can then be generated. Results obtained have shown the potential of using this system for a broad light spectra generation.

Analytical Treatment of Parametric Effects in a Ring Resonator

We propose two systems of a nano-waveguide to study the effects of ring resonator radii and coupling coefficient. The first proposed system is introduced as a single ring resonator. The change of the center wavelength from the output signal is monitored and analyzed. It shifts towards higher wavelength of the spectrum. The multistage ring resonator system consists of two micro and a nano ring resonators that can be integrated into a single system. The soliton pulse propagating within a Kerr type nonlinear medium is used to generate the large bandwidth signals. By using the suitable parameters, for instance, the input power of soliton, coupling coefficients, and ring radii, the short-wave and millimetre-wave output signals can simultaneously be generated in a multi-stage ring resonator (MMRR). We found that by using the MMRR, a desired response can be achieved over a broader portion of the spectrum compared to the single-stage ring resonator (SMRR) in which it is more preferable in applications.

A Simultaneous Short-Wave and Millimeter-Wave Generation Using a Soliton Pulse Within a Nano-Waveguide

A novel system of a simultaneous short-wave and millimeter-wave generation using a soliton pulse within a nano-waveguide is proposed, whereas the broad spectrum of optical output can be generated. By using the suitable parameters, for instance, input soliton power, coupling coefficients, and ring radii, the short-wave and millimeter-wave output signals can be simultaneously generated and filtered in a single system. Such a system consists of two microring resonators and a nanoring resonator that can be integrated to be a single system. Initially, the large bandwidth signal is generated by using a soliton pulse within a Kerr-type nonlinear medium, whereas the signals with broad bandwidth or wavelength can be generated. Results obtained have shown the potential of using the technique for a broad light spectra generation, where the required filtering signals are allowed to form the simultaneous up-link and down-link conversion using two different frequency (wavelength) carriers within a single system.

Sounding of an artificially perturbed ionosphere by means of an ionosonde/position finder with chirp modulation of the signal

We describe the operation of an ionosonde/position finder with chirp modulation of the signal. The first results of measuring the characteristics of short-wave radio signals scattered by artificial small-scale inhomogeneities, which were obtained by means of an ionosonde/position finder on the IZMIRAN—“SURA”—Rostov-on-Don path are presented. It was found that under certain ionospheric conditions, the angular and frequency selection of the scattered signals take place, in which case the signals are observed simultaneously in several frequency intervals (mainly, in three, namely, 6–9.5 MHz, 10–12 MHz, and 15–18 MHz) with different angles of incidence of radio waves in the vertical plane. In this case, the incidence angles were 20◦–35◦, 18◦–32◦, and 10◦–20◦ from the horizon for the first, second, and third frequency interval, respectively. Ionograms of oblique sounding were modeled allowing for the scattering of radio waves by artificial small-scale inhomogeneities. It is shown that at frequencies from 10 to 12 MHz, aspect conditions are fulfilled for the signals ducting along the high-angle beam (Pedersen mode). At frequencies 15–18 MHz (higher than the maximum observable frequency of the forward signal on the path IZMIRAN—Rostov-on-Don), aspect scattering conditions are fulfilled for the signals incident on a scattering area in the ascending part of the trajectory. At low frequencies 6–9.5 MHz (below the maximum observed frequency of the forward signal on the IZMIRAN—Rostov-on-Don path), the observable additional signals are caused by the scattering of radio waves by artificial inhomogeneities with subsequent relfection of the scattered signal from the Earth on the “SURA”—Rostov-on-Don path.

Relative latencies of cone signals measured by a moving vernier task

When a bipartite blue and red bar is swept across a bright yellow field, the blue half of the bar appears to lag behind the red and to exhibit a longer persistence (J. D. Mollon & P. G. Polden, 1976). This effect has been taken to reveal the longer time constants of the short-wave channels of the visual system. In Experiment 1, we quantified the effect by a nulling technique: The average latency of the short-wave bar relative to the long-wave was 17.9 ms, and the average value for the relative persistence, i.e. the apparent temporal separation of the trailing edges of the bars, was 48.3 ms. However, the conditions of the original demonstration and those of Experiment 1 place the short-wave and long-wave channels in very different states: The yellow field produces little light adaptation in the short-wave cones, but polarizes opponent channels that carry short-wave signals. In Experiment 2 we selected an adapting field that equally raised the short- and long-wave mechanisms above their absolute thresholds but did not so strongly polarize post-receptoral channels. We adjusted the two stimuli to be equally above threshold on this field. When light adaptation and stimulus conditions were equated in these ways, there was very little difference either in the perceived latency or in the perceived duration of the short-wave and long-wave stimuli. We discuss possible reasons why different estimates of sensory latencies may be obtained from reaction times and from perceptual judgments.

On the delay time of the net signal from a set of quasi-monochromatic transmitters

The waveform of the net signal from a set of closely spaced acoustic or electromagnetic transmitters generating identical (up to phase and amplitude factor) quasi-monochromatic signals is considered. If the partial signals are sufficiently long, the waveform of the envelope of the net signal from the set of transmitters turns out to be close to that of the partial signal envelope up to delay. The delay does not necessarily coincide with the time it takes for an optical (or acoustic) signal to travel the distance from the transmitter to the point of observation. At different sites of the space, the delay time may be real or complex. Its real part may be positive or negative and exceed, or be shorter than, the optical (acoustic) delay time. The delay strongly depends on the position of the point of observation (i.e., on whether it is located near a dark or bright interference fringe) and, in the case of short-wave signals, may vary considerably even at a slight displacement of the point of observation.

Ionospheric distortions of high-frequency pseudorandom signals

The ionospheric propagation of shortwave signals with pseudorandom frequency shift are considered with allowance for their coherent and incoherent reception. The frequency ranges within which 1D propagation is realized over ionospheric radio links 2–8 Mm long are investigated, and the dispersion characteristics of these propagation channels are determined. The effect of the dispersion distortions on the reception of pseudorandom signals is investigated, and the maximal permissible signal parameters are estimated.

Some results of synchronous experimental study of artificial F-spread at radiophysical test sites in nizhny novgorod province

We show some results of experiments on synchronous sounding of the ionosphere by short-wave signals at the Radiophysical Research Institute’s test site in Zimenki and Vasil’sursk, Nizhniy Novgorod province, during ionospheric modification by high-power short radiowaves from transmitters of the “Sura” facility in Vasil’sursk. In the course of experiments we proved directly the decisive role of large-scale inhomogeneities of the ionospheric plasma with dimensions of from several kilometers to several dozens of kilometers in the formation of artificial F- spread. The small-scale inhomogeneities with dimensions smaller than 1 km, which are localized in a relatively thin layer near the reflection level of a high-power short radiowave, emerged only at sounding waves, propagating (reflected) in the immediate vicinity of the center of the heating region.

Frequency correlation of fluctuations of short-wave signals in the theory of refractive scattering of radiowaves in the ionosphere

We consider the problem of frequency correlation of phase fluctuations of HF signals reflecte from a turbulent ionospheric layer with an arbitrary profile of electron density in vertical and oblique sounding of the ionosphere. Expressions for evaluation of the coherence band of HF signals reflected from a randomly inhomogeneous ionosphere are obtained. Calculation results are compared with corresponding calculations of frequency correlation of fluctuations of HF radiowaves in Buker's theory of refractive scattering of radiowaves. It is shown, in particular, that the influence of splitting of rays for waves with different frequencies in an inhomogeneous ionosphere on the frequency distortions of HF signals prevails compared with the phenomenon of frequency decorrelation of fluctuating HF signals propagating in a free space beyond a turbulent ionospheric layer.

On propagation of decametric-decimentric radiowaves under conditions of middle-latitude F-spread

In this paper we analyze the influence of the large-scale inhomogeneous structure of a middlelatitude ionosphere with F-spread on the propagation of decametric-decimetric radiowaves. The phase fluctuations of short waves in the presence of middle-latitude F-spread are considered. A general integral formula for the frequency dispersion of phase fluctuations of short radiowaves during their propagation in a three-dimensional randomly-inhomogeneous ionosphere with an arbitrary electron-density distribution is obtained. For some of the simplest types of ray trajectories we find analytical solutions which allow us to obtain simple estimates of the frequency correlation of phase fluctuations of short radiowaves under conditions of middle-latitude F-spread. The amplitude fluctuations of short radiowaves under conditions of ionospheric F-spread are considered by the example of wave propagation with strong backscattering in a layered randomly inhomogeneous medium. It is shown that the presence of a strongly developed large-scale structure of electron density in a middle-latitude ionosphere with F-spread can cause reflected short-wave signals with relatively large delays and abnormally high fluctuation levels. The fluctuational and quasiregular effects accompanying the transionospheric propagation of metric-decimetric radiowaves are discussed. In particular, it is shown that under conditions of middle-latitude F-spread the inhomogeneous structure of the ionospheric plasma does not have a significant influence on the fluctuational or quasi-regular propagation characteristics of decametric-decimetric radiowaves.