Radio Wave Signals Research Articles

Modeling of very low frequency (VLF) radio wave signal profile due to solar flares using the GEANT4 Monte Carlo simulation coupled with ionospheric chemistry

Abstract. X-ray photons emitted during solar flares cause ionization in the lower ionosphere (~60 to 100 km) in excess of what is expected to occur due to a quiet sun. Very low frequency (VLF) radio wave signals reflected from the D-region of the ionosphere are affected by this excess ionization. In this paper, we reproduce the deviation in VLF signal strength during solar flares by numerical modeling. We use GEANT4 Monte Carlo simulation code to compute the rate of ionization due to a M-class flare and a X-class flare. The output of the simulation is then used in a simplified ionospheric chemistry model to calculate the time variation of electron density at different altitudes in the D-region of the ionosphere. The resulting electron density variation profile is then self-consistently used in the LWPC code to obtain the time variation of the change in VLF signal. We did the modeling of the VLF signal along the NWC (Australia) to IERC/ICSP (India) propagation path and compared the results with observations. The agreement is found to be very satisfactory.

DISTINGUISHABILITY OF NEUTRINO FLAVORS THROUGH THEIR DIFFERENT SHOWER CHARACTERISTICS

We propose a new flavor identification method to distinguish mu and tau type ultra high energy cosmic neutrinos (UHECN). Energy loss of leptons in matter is an important information for the detection of neutrinos originated from high energy astrophysical sources. 50 years ago, Askaryan proposed to detect Cherenkov radiowave signals emitted from the negative charge excess of neutrino-induced particle shower. The theory of Cherenkov radiation under Fraunhofer approximation has been widely studied in the past two decades. However, at high energies or for high density materials, electromagnetic shower should be elongated due to the Landau-Pomeranchuck-Migdal (LPM) effect. As such the standard Fraunhofer approximation ceases to be valid when the distance between the shower and the detector becomes comparable with the shower length. Monte Carlo simulations have been performed recently to investigate this regime. Here we adopt the deduced relationship between the radio signal and the cascade development profile to investigate its implication to lepton signatures. Our method provides a straightforward technique to identify the neutrino flavor through the detected Cherenkov signals.

SPARSITY OF THE FIELD SIGNAL-BASED METHOD FOR IMPROVING SPATIAL RESOLUTION IN ANTENNA SENSOR ARRAY PROCESSING

The goal of array processing is to gather information from propagating radio-wave signals, as their Direction Of Arrival (DOA). The estimation of the DOA can be carried out by extracting the information of interest from the steering vector relevant to the adopted antenna sensor array. Such task can be accomplished in a number of difierent ways. However, in source estimation problems, it is essential to make use of a processing algorithm which feature not only good accuracy under ideal working conditions, but also robustness against non-idealities such as noise, limitations in the amount of collectible data, correlation between the sources, and modeling errors. In this work particular attention is devoted to spectrum estimation approaches based on sparsity. Conventional algorithms based on Beamforming fail wherein the radio sources are not within Rayleigh resolution range which is a function of the number of sensors and the dimension of the array. DOA estimation techniques such as MUSIC (Multiple Signal Classiflcations) allow having a larger spatial resolution compared to Beamforming-based procedures, but if the sources are very close and the Signal to Noise Ratio (SNR) level is low, the resolution turns to be low as well. A better resolution can be obtained by exploiting sparsity: if the number of sources is small, the power spectrum of the signal with respect to the location is sparse. In this way, sparsity can enhance the accuracy of the estimation. In this paper, an estimation procedure based on the sparsity of the radio signals and useful to improve the conventional MUSIC method is presented and analyzed. The sparsity level is set in order to focus the signal energy only along the actual direction of arrival. The obtained numerical results have shown an improvement of the spatial resolution as well as a reduced error in DOA estimation with respect to conventional techniques.

High-Resolution Broadband Millimeter-Wave Astrophysical Spectrometer with Triple Product Acousto-Optical Processor

An advanced conceptual design of a high-bit-rate triple product acousto-optical processor is presented that can be applied in a number of astrophysical problems. We briefly describe the Large Millimeter Telescope as one of the potential observational infrastructures where the acousto-optical spectrometer can be successfully used. A summary on the study of molecular gas in relatively old (age > 10 Myr) disks around main sequence stars is provided. We have identified this as one of the science cases in which the proposed processor can have a big impact. Then we put forward triple product acousto-optical processor is able to realize algorithm of the space-and-time integrating, which is desirable for a wideband spectrum analysis of radio-wave signals with an improved resolution providing the resolution power of about 105 - 106. It includes 1D-acousto-optic cells as the input devices for a 2D-optical data processing. The importance of this algorithm is based on exploiting the chirp Z-transform technique providing a 2D-Fourier transform of the input signals. The system produces the folded spectrum, accumulating advantages of both space and time integrating. Its frequency bandwidth is practically equal to the bandwidth of transducers inherent in acousto-optical cells. Then, similar processor is able to provide really high frequency resolution, which is practically equal to the reciprocal of the CCD-matrix photo-detector integration time. Here, the current state of developing the triple product acousto-optical processor in frames of the astrophysical instrumentation is shortly discussed.

Total electron content of the ionosphere at two stations in East Africa during the 24–25 October 2011 geomagnetic storm

The equatorial ionosphere has been known to become highly disturbed and thus rendering space-based navigation unreliable during space weather events, such as geomagnetic storms. Modern navigation systems, such as the Global Positioning System (GPS) use radio-wave signals that reflect from or propagate through the ionosphere as a means of determining range or distance. Such systems are vulnerable to effects caused by geomagnetic storms, and their performance can be severely degraded. This paper analyses total electron content (TEC) and the corresponding GPS scintillations using two GPS SCINDA receivers located at Makerere University, Uganda (Lat: 0.3o N; Lon: 32.5o E) and at the University of Nairobi, Kenya (Lat: 1.3o S; Lon: 36.8o E), both in East Africa. The analysis shows that the scintillations actually correspond to plasma bubbles. The occurrence of plasma bubbles at one station was correlated with those at the other station by using observations from the same satellite. It was noted that some bubbles develop at one station and presumably “die off” before reaching the other station. The paper also discusses the effects of the geomagnetic storm of the 24–25 October 2011 on the ionospheric TEC at the two East African stations. Reductions in the diurnal TEC at the two stations during the period of the storm were observed and the TEC depletions observed during that period showed much deeper depletions than on the non-storm days. The effects during the storm have been attributed to the uplift of the ionospheric plasma, which was then transported away from this region by diffusion along magnetic field lines.

Combined THEMIS and ground‐based observations of a pair of substorm‐associated electron precipitation events

Using ground‐based subionospheric radio wave propagation data from two very low frequency (VLF) receiver sites, riometer absorption data, and THEMIS satellite observations, we examine in detail energetic electron precipitation (EEP) characteristics associated with two substorm precipitation events that occurred on 28 May 2010. In an advance on the analysis undertaken by Clilverd et al. (2008), we use phase observations of VLF radio wave signals to describe substorm‐driven EEP characteristics more accurately than before. Using a >30 keV electron precipitation flux of 5.6 × 107 el. cm−2 sr−1 s−1 and a spectral gradient consistent with that observed by THEMIS, it was possible to accurately reproduce the peak observed riometer absorption at Macquarie Island (L = 5.4) and the associated NWC radio wave phase change observed at Casey, Antarctica, during the second, larger substorm. The flux levels were near to 80% of the peak fluxes observed in a similar substorm as studied by Clilverd et al. (2008). During the initial stages of the second substorm, a latitude region of 5 < L < 9 was affected by electron precipitation. Both substorms showed expansion of the precipitation region to 4 < L< 12 more than 30 min after the injection. While both substorms occurred at similar local times, with electron precipitation injections into approximately the same geographical region, the second expanded in an eastward longitude more slowly, suggesting the involvement of lower‐energy electron precipitation. Each substorm region expanded westward at a rate slower than that exhibited eastward. This study shows that it is possible to successfully combine these multi‐instrument observations to investigate the characteristics of substorms.

Magnetospheric radio tomographic imaging with IMAGE and Wind

[1] Recent theoretical studies have shown the feasibility and potential scientific value of radio tomographic imaging of Earth's magnetosphere by measuring Faraday rotation and phase difference (or group delay) of coherent radio wave signals. On 15 August 2000, a 6 W linearly polarized 828 kHz signal transmitted by the Radio Plasma Imager (RPI) on the IMAGE spacecraft was clearly detected by WAVES X and Z antennas on Wind spacecraft. Following our previous analysis of the path-integrated product change of the magnetic field and plasma density based on the spin rate measurement, we report here Faraday rotation measured from absolute antenna orientation using the phase difference between the spin-phase modeled RPI signal and the WAVES X- and Z-antenna received RPI signals. The new approach gives Faraday rotation without the mod (π) ambiguity. The average electron density extracted along a typical signal propagation path over a 1 hour measurement window agrees well with empirical models of the northern polar region derived from years of measurements. Finally, we demonstrate preliminary 2-D radio tomographic imaging of magnetospheric plasma density using the Faraday rotation measurement.

Single Step Generation of Micro and Radio Wave Signals in a Short Cavity Fiber Laser

Generation of stable micro or radio waves by frequency down-conversion has always been a challenging but rewarding task in radio over fiber systems. In this letter, a novel method for such a generation using a short-cavity fiber laser is demonstrated. For this purpose, an all-fiber laser is designed to have two stable longitudinal laser modes, each of them having two orthogonal polarization modes. Hence, four microwave signals, two in 1.2 GHz range and the other two in 14 GHz range, and one radio wave signal were generated by beating these lasing modes on a square law detector. Various measurements show high level of stability in generated micro/radio waves because they originate from the single laser cavity. According to the authors' knowledge, this is the first demonstration of the dual longitudinal mode operation of a short-cavity fiber laser for down-conversion from optical frequency directly to radio frequency.

BioRadioTransmitter: A Self-Powered Wireless Glucose-Sensing System

Although an enzyme fuel cell can be utilized as a glucose sensor, the output power generated is too low to power a device such as a currently available transmitter and operating system, and an external power source is required for operating an enzyme-fuel-cell-based biosensing system. We proposed a novel biosensor that we named BioCapacitor, in which a capacitor serves as a transducer. In this study, we constructed a new BioCapacitor-based system with an added radio-transmitter circuit and a miniaturized enzyme fuel cell. A miniaturized direct-electron-transfer-type compartmentless enzyme fuel cell was constructed with flavin adenine dinucleotide-dependent glucose dehydrogenase complex-based anode and a bilirubin-oxidase-based cathode. For construction of a BioRadioTransmitter wireless sensing system, a capacitor, an ultra-low-voltage charge-pump-integrated circuit, and Hartley oscillator circuit were connected to the miniaturized enzyme fuel cell. A radio-receiver circuit, comprising two field-effect transistors and a coil as an antenna, was used to amplify the signal generated from the biofuel cells. Radio wave signals generated by the BioRadioTransmitter were received, amplified, and converted from alternate to direct current by the radio receiver. When the capacitor discharges in the presence of glucose, the BioRadioTransmitter generates a radio wave, which is monitored by a radio receiver connected wirelessly to the sensing device. Magnitude of the radio wave transmission frequency change observed at the radio receiver was correlated to glucose concentration in the fuel cells. We constructed a stand-alone, self-powered, wireless glucose-sensing system called a BioRadioTransmitter by using a radio transmitter in which the radio wave transmission frequency changes with the glucose concentration in the fuel cell. The BioRadioTransmitter is a significant advance toward construction of an implantable continuous glucose monitor.

Control of car-like (wheeled) multi robots for following and hunting a moving target

The main purpose of this paper is to design a decentralized controller for some car-like (wheeled) multi robots to follow and hunt a moving target. Considering geometric dimensions, mass and moment of inertia, robots are very similar to actual cars in which the outputs of the controller are steering and driving wheel torques. All robots are equipped with range and bearing sensors along with antenna, to communicate radio wave signals. A Kalman filter is implemented to estimate relative position, state variables of the target and state variables of other robots. The controller is designed to carry out the group maneuver of the system, based on the system dynamics analysis of inertial agents, as well as minimizing the norm of the error between desired and actual acceleration. A simulation study considering the group maneuver of four robots has been carried out, and the achieved results in positions, velocities and other relevant state variables of agents are depicted in the paper. The control torques of the steering system and driving wheels are derived and depicted appropriately. These results guarantee the performance of the addressed controller coupled with the Kalman filter, despite the existence of nonholonomics in dynamics, inertial behaviors, etc.

Potentials of acousto-optical spectrum analysis on a basis of a novel algorithm of the collinear wave heterodyning in a large-aperture KRS–5 crystalline cell

The technique under proposal for a precise spectrum analysis within an algorithm of the collinear wave heterodyning implies a two-stage integrated processing, namely, the wave heterodyning of a signal in a square-law nonlinear medium and then the optical processing in the same solid state cell. The technical advantage of this approach lies in providing a direct multichannel parallel processing of ultra-high-frequency radio-wave signals with essentially improved frequency resolution. This technique imposes specific requirements on the cell's material. We focus our attention on the solid solutions of thallium chalcogenides and take the TlBr-TlI (thallium bromine-thallium iodine) solution, which forms KRS-5 cubic-symmetry crystals with the mass-ratio 58% of TlBr to 42% of TlI. Analysis shows that the acousto-optical cell made of a KRS-5 crystal oriented along the [111]-axis and the corresponding longitudinal elastic mode for producing the dynamic diffractive grating can be exploited. With the acoustic velocity of about 1.92 × 105 cm/s and attenuation of ∼10 dB/(cm GHz2), a similar cell is capable of providing an optical aperture of ∼5.0 cm and one of the highest figures of acousto-optical merit in solid states in the visible range. Such a cell is rather desirable for the application to direct 5000-channel parallel spectrum analysis with an improved up to 10−5 relative frequency resolution.

Permutation Method for ICA Separated Source Signal Blocks in Time Domain

A new permutation method for ICA (independent component analysis)- based blind separation is presented. The objective here is to concatenate ICA separated signals in adjacent time blocks. The proposed method utilizes the associativity in column vectors of an estimated mixing matrix and a tracking filter. It has advantages of no required array calibration, efficient computation, and real time updatability. These superiorities are highly beneficial for radar or communication system type applications. Furthermore it is shown, by an experiment using radio wave signals, that the proposed permutation algorithm successfully permutes the separated signal blocks.

Direct multi-channel optical spectrum analysis of radio-wave signals using collinear waveheterodyning in the single acousto-optical cell

An attempt is made to improve the accuracy of a multi-channel parallel acousto-opticalspectrum analysis through involving an additional nonlinear conversion into dataprocessing. For this purpose we investigate the potential of exploiting a co-directionalcollinear wave heterodyning within an analysis of ultra-high-frequency radio-wave signals.The wave heterodyning under the proposal is performed via mixing the longitudinal elasticwaves of finite amplitudes. It leads to a two-cascade processing in the single-crystallinecell and makes it possible to improve the relative frequency resolution of theacousto-optical spectrum analysis by an order of magnitude at the same frequency range.Both the theoretical findings and the corresponding estimations were used inproof-of-principle experiments directed at creating a new type of acousto-optical cell. Thegeneral concept of the proposed method and the basic conclusions are confirmed byexperiments with the developed acousto-optic cell made of a lead molybdate crystal.

Relationship between Lightning Discharges and Rapid Changes in Cross Polarization Discrimination of the Ka-band Satellite Radio Signal

Rapid changes in cross-polarization discrimination (XPD) of the satellite radio wave signal (19.45GHz) are observed at 1sec interval in the thunderstorm events. About one third of the rapid changes are found to coincide with the cloud-to-ground lightning strokes which occurred on the south side of our earth station at the distance up to 20km. The distribution of the lightning location indicates that the center of thunder clouds primarily exists to the westward of the radio wave propagation path. At the moment of the rapid changes, more than half the observed data indicate the decrease in XPD. Also, more than two thirds of them show the changing direction of cross-polar phases toward i90deg, which means the decrease in canting angles of ice crystals possibly causing the depolarization changes. These features seem to be enhanced in the middle stage of each lightning event The decrease in XPD may be related to cancellation efiects of depolarization due to the difierence in canting angles between the ice crystals near the lightning and those in other places far from the lightning. Thus, the measurements of XPD and cross-polar phase are shown to be important to reveal the electriflcation process of thunder clouds and to predict lightning discharges. In satellite communication links, degradation of cross-polarization discrimination (XPD) of the radio wave is caused by raindrops and ice crystals along the propagation paths. In thunderstorm events, moreover, rapid changes of XPD and cross-polar phase relative to co-polar phase are fre- quently observed at time intervals of less than 1sec (1,2). These peculiar phenomena are considered to be related to the change of electric fleld due to lightning discharges as well as the aerodynamic forces of convective air ∞ows (3). Up to now, however, detailed mechanisms of the rapid changes of XPD and cross-polar phase are not understood very well. In this study, statistical distributions of the changes of XPD and cross-polar phase are examined using the Ka-band beacon signal observations of Japan's domestic communication satellites (4) which have been conducted for the past 17 years at 1sec (partly 0.1sec) interval in Osaka Electro- Communication University. The thunderstorm events are observed more than 70 times from 1990 to 2006, and more than 2500 examples of rapid XPD changes are obtained during these years in our university. The occurrence time and the amplitude of these changes are then compared with the lightning location and time provided by the Kansai Electric Power Company in Osaka area. Also, the decrease and increase in XPD and cross-polar phase are discussed in relation to the alignment of ice crystals due to electrostatic force and convective air ∞ow in thunder clouds.

Temperature Effects on Anomalous Radio Duct Propagation in Korean Coastal Area

Atmospheric radio ducts can trap VHF/UHF radio waves and propagate them over long distances. 284.4625MHz Japanese radio wave signal measurements show that the radio waves are propagated to Korea coastal regions when ground temperatures exceed 10°C. This paper discusses the reasons for the existence of this critical temperature threshold.

Joint Statistics of Rain Attenuation at 20 GHz in Madrid and Aveiro

Rain attenuation is the most severe propagation impairment affecting radiowave signals in the Ka-band. The use of these frequencies for satellite communication systems is facilitated by the implementation of fade mitigation techniques (FMTs). Spatial correlation of rain rate and rain attenuation for distances of several hundred kilometers has been rarely characterized in experiments, however it is relevant for site diversity studies, with distances in this range, and for the design and operation of multibeam satellite systems with shared on-board radio resources. In this letter, experimental results regarding joint statistics of rain and rain attenuation are presented for Madrid, Spain, and Aveiro, Portugal, located 420 km apart. These results have been achieved from two years of simultaneous measurements of the Eutelsat HB-6 Ka-band beacon at 19.7 GHz. It is shown that high-attenuation events are independent, whereas there is some correlation for low-attenuation levels.

Acousto-optical spectrum analysis of ultra-high-frequency radio-wave analogue signals with an improved resolution exploiting the collinear acoustic wave heterodyning

This article is devoted to the problem of improving the frequency resolution inherent in a parallel acousto-optical spectrum analysis via involving an additional nonlinear phenomenon into the data processing. In so doing, we examine possible application of the wave heterodyning to the real-time scale acousto-optical analysis of the frequency spectrum belonging to ultra-high-frequency radio-wave signals peculiar, for example, for radio-astronomy. The nonlinear process of wave heterodyning is realized through providing a co-directional collinear interaction of the longitudinal acoustic waves of finite amplitudes. This process, which is beforehand studied theoretically and investigated experimentally via the acousto-optical technique as well, allows us either to improve the frequency resolution of spectrum analysis at a given frequency range or to increase by a few times the current frequencies of radio-wave signals under processing. The first step along this way is connected with the experimental modeling of the acoustic wave heterodyning in solids via exploitation of the specific acousto-optical cell based on a liquid, which allows the simplest realization of a cell with the needed properties. Then, these theoretical and practical findings are used in our experimental studies aimed at creating a new type of acousto-optical cells, which are able to improve the resolution inherent in acousto-optical spectrum analyzer operating over ultra-high-frequency radio-wave signals. In particular, the possibility of upgrading the frequency resolution through the acoustic wave heterodyning is experimentally demonstrated using the cell made of lead molybdate crystal. The obtained results demonstrate practical efficiency of the novel approach presented.

Advanced System Technologies and Field Demonstration for In-Building Optical-Wireless Network With Integrated Broadband Services

This work describes a concept of a hierarchical radio-over-fiber (RoF) network architecture that provides both intra- and inter-network connectivity for end user wireline and wireless terminals with high-bandwidth, in-building access applications. An intelligent gateway router (IGR) is proposed as a unified platform to accommodate multi-gigabit, millimeter-wave services at 60-GHz band as well as being backward compatible with all current wireless access technologies such as WiFi and WiMAX. In addition, we further present an advanced multi-band optical carrier generation technique that can simultaneously deliver independent 60-GHz mm-wave, 2.4-GHz WiFi, and 5.8-GHz WiMAX signals efficiently carried over the same wavelength, and is suitable for the proposed IGR. Finally, we report, for the first time to our knowledge, a campus-wide field trial demonstration of RoF system transmitting uncompressed 270-Mbps standard definition (SD) and 1.485-Gbps high definition (HD) real-time video contents carried by 2.4-GHz radio and 60-GHz millimeter wave signals, respectively, between two on-campus research buildings distanced over 2.5-km standard single mode fiber (SMF-28) through the Georgia Institute of Technology's (GT) fiber network.

Geomagnetic storm effects on GPS based navigation

Abstract. The energetic events on the sun, solar wind and subsequent effects on the Earth's geomagnetic field and upper atmosphere (ionosphere) comprise space weather. Modern navigation systems that use radio-wave signals, reflecting from or propagating through the ionosphere as a means of determining range or distance, are vulnerable to a variety of effects that can degrade the performance of the navigational systems. In particular, the Global Positioning System (GPS) that uses a constellation of earth orbiting satellites are affected due to the space weather phenomena. Studies made during two successive geomagnetic storms that occurred during the period from 8 to 12 November 2004, have clearly revealed the adverse affects on the GPS range delay as inferred from the Total Electron Content (TEC) measurements made from a chain of seven dual frequency GPS receivers installed in the Indian sector. Significant increases in TEC at the Equatorial Ionization anomaly crest region are observed, resulting in increased range delay during the periods of the storm activity. Further, the storm time rapid changes occurring in TEC resulted in a number of phase slips in the GPS signal compared to those on quiet days. These phase slips often result in the loss of lock of the GPS receivers, similar to those that occur during strong(>10 dB) L-band scintillation events, adversely affecting the GPS based navigation.

Impairment of radio wave signal by rainfall on fixed satellite service on earth–space path at 37 stations in Nigeria

This study investigates the effect of rainfall on horizontally polarized radio waves for fixed satellite service at Ku, Ka and V bands for links to the recently launched Nigeria Communication Satellite one (NigComSat-1), for annual time availabilities of 99–99.99% in an average year for 37 stations in Nigeria. The results obtained at Ku-band downlink shows that 99.99% availability is possible in all the 37-stations in Nigeria. At Ka-band downlink the results also show that only 99.9% availability is practicable in all the 37 stations in Nigeria. At V-band downlink, 99.99% availability is also not possible in all the 37 stations in Nigeria. An availability level of 99.9% is only practicable in the North–West (NW) and North–East (NE) regions, where the attenuation is between 14 and 17.9 dB. Total fade out of signals during rainfall are probable in the South–South (SS), South–East (SE), South–West (SW) and Middle–Belt (MB) regions at 99.9% availability.