Radio Wave Signals Research Articles

Major advances in epilepsy in the last century: A personal perspective

Major advances in epilepsy in the last century: A personal perspective

Error Compensation for Cricket Indoor Location System

Event Abstract Back to Event Error Compensation for Cricket Indoor Location System Shuqiao Zhou1*, Haoran Feng1 and Ruixi Yuan1 1 Tsinghua University, Center for Intelligent and Networked Systems (CFINS), China Cricket is a fine-grained indoor location system utilizing beacons transmitting both ultrasound and radio wave signals. However, the system accuracy is greatly impacted by the relative angle and distance between the beacon and listener. This paper proposes a low cost method to improve the system precision by means of incremental error compensation. The ultrasonic detecting error, which directly affects the accuracy of time-difference-of-arrival (TDOA), is first analyzed and verified via experiments. Then an error compensation method is designed based on total least squares (TLS) to further improve the Cricket’s localization performance. Experimental results show that the average error of localization is reduced to 5.60cm with compensation, compared with 9.06cm of the original Cricket method. The standard deviation of the errors is reduced from 7.80cm to 3.99cm. This method lays a foundation for further improving the existing ultrasound-related distance measurement method. Conference: 2nd International Workshop on Sensor Networks and Ambient Intelligence In conjunction with PDCAT'09, Hiroshima, Japan, 8 Dec - 11 Dec, 2009. Presentation Type: Oral Presentation Topic: Oral presentations Citation: Zhou S, Feng H and Yuan R (2009). Error Compensation for Cricket Indoor Location System. Front. Neuroinform. Conference Abstract: 2nd International Workshop on Sensor Networks and Ambient Intelligence In conjunction with PDCAT'09. doi: 10.3389/conf.neuro.01.2009.16.109 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 23 Nov 2009; Published Online: 23 Nov 2009. * Correspondence: Shuqiao Zhou, Tsinghua University, Center for Intelligent and Networked Systems (CFINS), Beijing, China, zhousq05@mails.tsinghua.edu.cn Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Shuqiao Zhou Haoran Feng Ruixi Yuan Google Shuqiao Zhou Haoran Feng Ruixi Yuan Google Scholar Shuqiao Zhou Haoran Feng Ruixi Yuan PubMed Shuqiao Zhou Haoran Feng Ruixi Yuan Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Study of Ionospheric Irregularities in the Vicinity of SED Region During a Super Geomagnetic Storm

基于IGS提供的TEC数据, 研究了2003年10月大磁暴期间的暴时密度增强(Storm Enhanced Density, SED)现象; 利用GPS观测数据, 计算出ROTI (Standard deviations of ROT)指数, 分析了SED边界附近电离层小尺度不均匀体结构的时间和空间演变. 研究表明, 在磁暴主相期间SED边界附近不均匀体随着磁暴的发展逐渐增多; 在主相的中后期不均匀体的分布密集度达到最大; 在恢复相期间, 不均匀体分布很少; 随着磁暴的发展, 不均匀体开始主要集中在40~45ºN范围内, 随后向高纬漂移, 主要集中在45~55ºN范围内.

Space Weather and the Global Positioning System

Space Weather and the Global Positioning System

A Study on Site Diversity Techniques Related to Rain Area Motion Using Ku-Band Satellite Signals

Directions and speeds of the motion of rain areas are estimated for each type of rain fronts, using time differences detected in the rain attenuation of the Ku-band satellite radio wave signals that have been measured at Osaka Electro-Communication University (OECU) in Neyagawa, Osaka, Research Institute of Sustainable Humanosphere (RISH) in Uji, Kyoto, and MU Observatory (MU) of Kyoto University in Shigaraki, Shiga, for the past five years since September 2002. These directions and speeds are shown to agree well with those directly obtained from the motion of rain fronts in the weather charts published by Japan Meteorological Agency. The rain area motion is found to have characteristic directions according to each rain type, such as cold and warm fronts or typhoon. A numerical estimate of the effects of site diversity techniques indicates that between two sites among the three locations (OECU, RISH, MU) separated by 20-50km, the joint cumulative time percentages of rain attenuation become lower as the two sites are aligned along the directions of rain area motion. In such a case, compared with the ITU-R recommendations, the distance required between the two sites may be, on an average, reduced down to about 60-70% of the conventional predictions.

電離層シンチレーションの影響下におけるGPS受信機の性能評価

Ionospheric scintillation induces a rapid change in the amplitude and phase of radio wave signals. This is due to irregularities of electron density in the F-region of the ionosphere. It reduces the accuracy of both pseudorange and carrier phase measurements in GPS/Satellite Based Augmentation System (SBAS) receivers and can cause loss of lock on the satellite signal. Scintillation is not strong at mid-latitude regions, but severe effects occur mainly in a band approximately 15-degree latitude on either side of the magnetic equator and sometimes in the polar and auroral regions. Most scintillation occurs for a few hours after sunset during the peak years of the solar cycle. In Japan, several ionospheric scintillations were observed by Electronic Navigation Research Institute (ENRI). This work intended to investigate the scintillation characteristics in Japan and statistically evaluate constant bandwidth phase locked loop (PLL) and a Fast Adaptive Bandwidth (FAB) PLL performance under the ionospheric scintillation condition. The results show that the characteristics are consistent with the models proposed in early studies and the FAB PLL has the flexibility against the scintillation effects compared with the constant PLL.

Simulation and Design of a Very Small Magnetic Core Loop Antenna for an LF Receiver

SUMMARY In this paper, we evaluated the characteristics of the magnetic core loop antenna that is used to receive long wave radio signals for time standards. To evaluate the receiving sensitivity of the antenna, we calculated the antenna factor of the magnetic core loop antenna by combining a magnetic field simulation and a circuit simulation. The simulation results are in good agreement with the results obtained from the experiments. We then investigated the optimization of the antenna shape, and showed the re

Effects of Tropical Rainfall to the Ku-Band Satellite Communications Links at the Equatorial Atmosphere Radar Observatory

This study investigates the effects of tropical rainfall on the Ku-band satellite communications links that connect Research Institute for Sustainable Humanosphere (RISH), Kyoto University in Japan to Equatorial Atmosphere Radar Observatory (EAR; 0.2 � S, 100.3 � E) in Indonesia, using the satellite Superbird C (144 � E in orbit). Rain attenuation of the up- and down-link radio wave signals is, for the first time, obtained at the same time in the tropics, monitoring each signal level that has been received at both stations in Japan and Indonesia for the past three years from 2003 to 2005. The up-link attenuation at each station can be estimated from the down-link signal level measured at its opposite station, because SCPC (Single Channel Per Carrier) signals used in this experiment are linearly amplified without saturation of the satellite transponders. At EAR in Indonesia, a slightly larger attenuation ratio between up and down links is statistically presented for the attenuation range of higher that 10 dB, suggesting the effects of smaller raindrop size distributions (DSD) than observed at RISH in Japan. This tendency is more conspicuous in the rainfall events when the observed attenuation shows only one peak in its time series, indicating the effects of simple convective precipitating clouds with one single cell. At RISH in Japan, a larger difference between worst month and yearly average statistics is found, due to a larger variation of the ground temperature that affects the slant-path length during the seasons, although the yearly average time percentages as such are larger at EAR than RISH up to the up-link attenuation of 15 dB. Using time percentages of their local rainfall rates, fairly good agreement is found between the observations and the ITU-R (International Telecommunication Union—Radiocommunication Sector) predictions for both locations. At EAR in Indonesia, however, the time percentages of the attenuation of more than 10 dB become significantly smaller than those predicted by the ITU-R methods for both up and down links. This indicates the remarkable reduction of equivalent path lengths down to about 2 km, caused by a fairly localized structure of convective precipitating clouds. Simultaneous X band radar observations have revealed that intense echo cores of typical rain cells causing severe attenuation

Using tweek atmospherics to measure the response of the low-middle latitude D-region ionosphere to a magnetic storm

Tweek atmospherics are pulse signals from ELF/VLF electromagnetic waves caused by lightning discharges; these signals have characteristic cut-off frequencies due to long-distance propagation by the Earth–ionosphere waveguide mode. We developed a method of estimating tweek reflection heights (equivalent electron densities) in the low-middle latitude D-region ionosphere by accurate measurement of their first-order mode cut-off frequency (∼1.8 kHz). This research is the first to show reflection-height measurements of the D-region ionosphere's response to the great geomagnetic storm in October 2000 using tweek atmospherics observations. We found transient lowering/rising in the small bay D st-variation and rising near the maximum depression of the major bay D st-variation. Comparing this response in tweek reflection heights with the intensities of 40 kHz radio-wave signals, electron density profiles from the IRI-2001 model and measured by MF radars, and the ionospheric F-region parameter ( h′ F) from ionosonde data, we determined two cases where the lowering/rising of the D-region was coupled with vertical motion of the F-region and one where it was not. Based on simultaneous total electron content (TEC) perturbation data, we suggest the following possible mechanisms for these two results: E × B vertical plasma drift due to ionospheric electric fields, and the propagation of large-scale traveling ionospheric disturbances (LSTIDs) from the auroral to low-latitude ionosphere, respectively.

Forecasting the occurrence of ionospheric scintillation activity in the equatorial ionosphere on a day-to-day basis

In the low-latitude ionospheric F region, ambient conditions after sunset are often conducive to the generation of small-scale plasma density structures by the Rayleigh–Taylor instability mechanism. Radio wave signals passing through these electron density irregularities experience amplitude fluctuations that lead to radio wave “scintillation”. The scintillation index, S4, is a measure of the severity of these amplitude fluctuations. It is well known that the occurrence frequency of scintillation activity depends on solar cycle, season, longitude and local time, with a large day-to-day variability. In this paper, we present the results of a continuing study that utilizes a ground-based digital sounder at the magnetic equator to provide a “forecast” of the subsequent occurrence of scintillation activity and a network of UHF and L-band receivers that measure the S4 index, on a night-to-night basis. To establish the “forecasting” relationship, observations were carried out in 1998 and 1999 in the Peruvian/Chilean longitude sector. The relationship between the magnitude of the vertical E × B drift velocity enhancement just after sunset as determined by the Jicamarca Digisonde and the magnitude of the S4 index subsequently observed an hour or two later by the scintillation receivers at Ancon, Peru and Antofagasta, Chile was established. In most cases at both UHF and L-band frequencies, this relationship is not linear, but there appears to be a “threshold” in E × B drift of ∼ 20 m / s . On nights when E × B drift was less than 20 m/s, the UHF S4 index generally was less than 0.5, while on nights when E × B drift exceeded 20 m/s, the S4 index was greater than 0.5. The day-to-day variability of this relationship will be presented and discussed. Since October 1, 2001, the Jicamarca Digisonde has been used to “forecast” the occurrence of UHF S 4 > 0.5 or S 4 < 0.5 on a night-to-night basis. The validity of the “forecast” is subsequently confirmed by UHF S4 observations at Ancon, Peru and Antofagasta, Chile. The resulting statistics for these nightly S4 forecasts from November 1, 2001 to April 30, 2002 will be presented and discussed.

3‐D refractivity field from GPS double difference tomography

GPS meteorology can be successfully used to model the tropospheric refraction effect on radiowave signals. We describe an approach to estimate and model the spatial distribution of the tropospheric water vapor. We refine the tomographic software package AWATOS which is based on the assimilation of GPS double difference observations. The observations are allocated to a voxel model, which is defined according to the distribution of the GPS stations. Performing a least‐squares adjustment, the refractivity of each voxel is determined. Tests of the software are performed, based on simulated and real data. The latter were obtained during a dedicated field campaign on the Big Island of Hawaii. The tomographic profiles are compared with radiosonde data. The results obtained for continuous atmospheric conditions fit well, whereas larger differences occur in discontinuous atmospheric weather conditions. Overall, an accuracy of 5–20 ppm (refractivity units) has been achieved.

A New EMI Test Method for Electronic Medical Devices Exposed to Mobile Radio Wave

AbstractA new testing method that can evaluate with high reliability the electromagnetic interference of cellular phones with electronic medical devices is proposed. In this test method, a standard dipole antenna or an actual cellular phone is used. Radio wave signals similar to those used in real communications are applied continuously or intermittently to electronic medical devices. In this way, the influence of both the far field and the near field can be evaluated in the worst case. The fundamental configuration, the test procedure, and the electromagnetic interference experienced by actual electronic medical devices are described. Evaluation tests of typical electronic medical devices including the implantable cardiac pacemakers are presented. In comparison with the existing test method of the IEC, highly reliable and accurate results are obtained. The present test method has been used for electromagnetic interference tests of various electronic medical devices, including pacemakers. The results provide a basis for the guidelines regarding the electromagnetic effects of cellular phones on electronic medical devices developed by the Electromagnetic Compatibility Conference (EMCC) Japan. © 2001 Scripta Technica, Electron Comm Jpn Pt 1, 85(4): 1–9, 2002

Determining the polarization ellipse parameters of a multimode radiowave signal

A spectral-polarization method is proposed to determine the polarization-ellipse parameters of a radiowave signal in the wave front plane by analysis of three mutually orthogonal projections of the field vector. First, we calculate the complex Doppler spectra for the temporal variations of those projections. Then, these data are used to determine the polarization parameters of the electromagnetic wave for each spectral component. Formulas illustrating the proposed technique are presented, and the results of numerical simulation showing the possibility of practical implementation of the idea are given.

Electromagnetic radiations associated with major earthquakes

Measurements of subsurface electric field changes have been conducted by means of borehole antennas. Changes in the number of pulse-like signals in a VLF band (seismic radio wave signals: SRS) evolved in close accordance with the occurrence of the earthquakes. The propagation of the long distance more than 500 km indicates the occurrence of waveguide mode propagation between the ionosphere and the ground. The time evolution of the number of the pulses indicates that there are two in the SRS: one emitted directly from the epicentral area and the other, coming induced by nonlinear interaction in the ionosphere, indirectly. These results indicate that the phenomena may be used to predict the time, location and magnitude of imminent earthquakes. Moreover, prominent electromagnetic field changes are observed just at the time of the great earthquake providing clear evidence that the fault motion is accompanied by electromagnetic radiation.

Neurodiagnostic techniques.

Neurodiagnostic techniques.

Accuracy of time comparison derived from reception of LORAN‐C and Global Positioning System time signals

The accuracy of time comparison by means of the reception of common time signals, namely, LORAN‐C and Global Positioning System (GPS), is examined. Differences of UTC from the emission times of these two radio wave signals measured at four Japanese stations and one U.S. station are analyzed and compared with the clock comparison reports published by the Bureau International des Poids et Mesures. The accuracy of the time comparison via LORAN‐C signals of the northwest Pacific chain is about 3.61 μs and that via GPS is 0.14 μs. The accuracy analysis reveals the existence of systematic errors at the individual stations. In LORAN‐C, the most serious error comes from those in the delay time calibration of receiving instruments and estimation of the propagation delay over land. Calibration of the clocks by a portable clock improves the accuracy of the GPS method to the accuracy of the GPS signals.

Statistical model for UHF radio-wave signals within externally illuminated multistorey buildings

A reliable model for UHF radio-wave signal propagation into and variability within buildings is required to aid the planning of cellular mobile ratio systems serving portable transceivers. A study of this problem has been undertaken in New Zealand with the aim of developing a model suitable for New Zealand buildings and situations. Measurements were made at 851 MHz in the central business district of Auckland in eight representative buildings illuminated from two different base station sites. The measured cumulative probability density function of the received signal on a floor of a building was found to be best modelled by the Suzuki (Rayleigh plus log-normal) distribution with a free space based model used for predicting the median signal level.

Measurement of scintillation of radiowave signals through ionosphere

A theoretical formula for measuring the power—law spectrum with interferometer is presented in this paper for the study of ionosphere. The results of theoretical calculation agree well with the measurements. The radio scintillation power—law spectrum index which is caused by the irregularities in the ionosphere is determined to bep=3.5 from the results.

Lightning‐associated precipitation of MeV electrons from the inner radiation belt

Transient perturbations of subionospheric very low frequency (VLF) radiowave signals provide new evidence for lightning‐induced electron precipitation (LEP) events involving short (&lt;1 s) bursts of &gt;1 MeV electrons from the earth's inner radiation belt at L ≤1.8. The signal amplitude changes are attributed to increased absorption in the earth‐ionosphere waveguide and/or alterations of the waveguide mode structure due to localized secondary ionization enhancements produced in the nighttime lower ionosphere and the mesosphere by the precipitating electrons. The otherwise stably trapped electrons are believed to be scattered in pitch angle during cyclotron resonant interactions in the magnetosphere with the lightning‐generated whistler waves. That some precipitation bursts consist partly of MeV electrons is suggested by (i) confinement of the perturbed subionospheric signal path to low magnetic latitudes (L ≤1.8), for which corresponding electron energies for gyroresonance with typical whistler‐wave frequencies in the magnetosphere are &gt;1 MeV, and (ii) the temporal signatures of the perturbation events, which often exhibit an unusually rapid initial recovery (time constant of τ &lt;1 s) followed by further recovery at rates believed characteristic of less energetic events (τ ∼5–20 s). The latter is interpreted as a manifestation of the rapid variation with altitude of the effective loss rate for excess ionization over an exceptionally wide range of mesospheric altitudes (40–70 km) penetrated by the &gt;1 MeV electrons.

Distortion of radio wave signals by wind turbines

Power-generating wind turbines are becoming more widespread and of larger size. Evidence of distortion caused to terrestrial television broadcast services by some of these prompted the IBA into studying the problem, the results of which are given in this paper. These results should have some relevance to any form of radio wave service.Some references are given to existing literature, the theory is discussed and extended, experiments using microwaves and a model of a turbine are reported as well as measurements made round an actual turbine. Proposals are then made for a way in which the degree of damage caused to radio wave services may be predicted. Thus, the paper provides a way in which radio wave and wind turbine engineers may work together to find sites and other parameters which will allow harmonious co-existence.