核环境中HF无线电波传播的计算机模拟

低空核爆炸时会产生附加电离区,对高频无线电波的传播有很大的影响。文章在讨论通信核效应的基础上,介绍针对核爆的电离效应、核辐射产生的电子密度的时空分布等通信核效应问题,设计开发了高频通信核效应计算机模拟系统,并利用该系统针对实际通信电路进行了模拟计算。结果表明,该系统不仅可直接应用于理论研究,同时亦具有很强的实用价值。     

Recovery effect in radiowave propagation

The recovery effect in homogeneous propagation, often referred to as sea gain, is analysed by means of the Compensation Theorem. The resulting solution takes the form of an integral equation, but in the particular case when the second medium is a perfect conductor a solution in simple integral form is possible. Numerical results applied to sea water, considered as a perfect conductor in the low MHz range, agree well with those obtained by experiment.<>     

Investigation of radiowave propagation in the solar system

The radiowaves transmitted by space probes and received on the Earth gave information on the media interacting with them. The results of the investigations of the Mars and Venus atmospheres, the Moon and Venus' surfaces, and the plasma near the sun obtained by modern experimental methods of radiowave propagation, are described.     

Comparison of a diffraction based radiowave propagation model with measurements

A comparison between a theoretical diffraction based radio propagation model and measured path loss data for flat terrain in New Zealand in terms of variation in path length, frequency and environment is described. Results of measured town planning data for the model are also given.<>     

The intelsat slant-path radiowave propagation experiments in tropical regions

The requirement for INTELSAT to operate world-wide in a diverse range of climates has motivated a number of experiments within the INTELSAT R&D programme to identify and model propagation impairments. The effects of some propagation phenomena, such as depolarization, were anticipated. Others (e.g. ionospheric scintillation at gigahertz frequencies) were unexpected or exhibited unusual features (rain attenuation in tropical climates). This paper presents the background of the INTELSAT R&D propagation measurements, with special emphasis on those in tropical regions, and provides the principal results. Several ongoing experiments are also discussed.     

Urban radiowave propagation: a 3-D path-integral wave analysis

A discussion concerning the need for three-dimensional (3-D) urban radiowave propagation models is presented and followed by a review of previously published work on this topic using the asymptotic path-integral technique. The limitations and advantages of this technique are explained and it is applied to study diffraction by a small number of canonical geometries. The validity of this technique is verified by comparison with controlled laboratory measurements taken at millimetric wave frequencies. Finally, its ability to classify field components according to their distribution in space is employed in order to analyze the observed field strength distributions in the model environments     

Empirical prediction of radiowave propagation by neural network simulator

A first step towards a planning tool for mobile radio communication based on adaptive learning from measurement data is presented.<>     

Millimetric wavelengths radiowave propagation for line-of-sightindoor microcellular mobile communications

Discusses millimeter waves for indoor microcellular communications. The results of propagation experiments conducted at 60.4 GHz (the oxygen absorption band) and 38.25 GHz to determine multipath characteristics in a number of indoor microcell channels employing omnidirectional antennas are presented. Cumulative distribution functions for received signal envelope, as well as corresponding power spectra are given. In addition, a comparison between the fading statistics measured at 60.4 GHz and 38.25 GHz under similar conditions is made. The change in multipath characteristics due to the presence of different building materials is also illustrated. A ray model is developed to represent indoor microcell propagation by considering a direct ray plus rays which have undergone single and double reflections from the walls. Specular floor-reflected and ceiling-reflected rays are included when the antennas radiation pattern does not preclude them. Using this simple model, the signal variations and the amplitude of reflected rays with respect to the line of sight (LOS) ray as functions of mobile receiver position are predicted and used to assist in interpreting experimental results. Theoretical results are found to be in good agreement with measured ones, with the model also being used to predict structure-induced root mean square (rms) delay spread along receiver routes in an indoor microcell environment. This parameter is a measure of multipath conditions in a mobile radio channel and is inversely proportional to the maximum usable data signalling rate of a channel     

Neurofuzzy classification and rule generation of modes of radiowave propagation

This paper describes, in a neurofuzzy framework, a method for the classification of different modes of radiowave propagation, followed by generation of linguistic rules justifying a decision. Weight decay during neural learning helps in imposing a structure on the network, resulting in the extraction of logical rules. Use of linguistic terms at the input enables better human interpretation of the inferred rules. The effectiveness of the system is demonstrated on radiosonde data of four different seasons in India.     

Measurements and modelling of wind influence on radiowave propagation through vegetation

Movement of vegetation structures introduces an adverse environment for high frequency radiowave propagation. This paper examines a series of vegetation scattering measurement campaigns during various wind conditions. The measurements were divided into controlled and outdoor environments. The controlled environment measurements were conducted in an anechoic chamber at 0.9, 2, 12 and 17 GHz. The outdoor measurements were carried out at 1.8 GHz and involved in recording of a transmitted signal originating from an existing digital cellular system (DCS-1800) base station. The obtained results are discussed and presented in terms of their first- and second-order statistics. Analysis demonstrates that the received signal behaviour is highly wind dependent, especially when the environment is changing from calm to a windy condition. The signal fast-fading is found to be Rician distributed and an empirical model of the k-factor variation over wind speed is also presented.     

物理隔离网络环境下的病毒传播模型分析与仿真

文章为研究病毒在电网隔离网络中的传播特性与造成影响,通过建立病毒在电网信息通信物理隔离网络模型并进行仿真计算与分析,重点分析了连接率及感染节点数,对网络信息安全的影响范围分析,得出关键信息节点的严格管控和隔离结论措施。     

基于抛物方程法的部分森林覆盖山区电波传播分析

基于Fourier分步步进法的抛物方程模型求解了山区不规则地形部分森林覆盖环境的电波传播,并分析了森林对电波传播的影响.模型中为了简化边界条件,地形用分段线性函数来近似.然后预测了一个山区部分针叶林覆盖环境的电波传播,得到的结果与实测数据进行对比,二者吻合很好.最后对算法的稳定性与误差进行了分析,本文的模型能处理不规则地形、森林等复杂环境且算法效率高.     

Statistical scattering model in urban propagation environment

A statistical scattering model for mobile radio channels that has the following three features is proposed: 1) the effective scattering area (ESA) is expressed by an ellipse, the center of which is the mobile station (MS) location; 2) the major axis of the ellipse runs parallel along the street where the MS is located; and 3) the scattering power density function around the MS is expressed by a combination of two Laplacian distributions in which the standard deviations are different. To verify the proposed model and obtain realistic values for the model parameters, the spatiotemporal path data observed at a base station (BS) were measured using a 2.2-GHz band in a macrocell scenario (BS antenna height is 60 m) in a typical urban area. The scattering positions are detected from the path information such as the azimuth arrival angle and path length, assuming a single bounce. The spatial distribution of the scattering power is analyzed using principal component analysis. The results showed the ESA to be the anticipated ellipse with the major and minor axes of approximately 210 and 120 m, respectively (axis ratio: approximately 1.7). Furthermore, the power profiles that are projected for each axis of the ellipse can be approximated as Laplacian distributions. Finally, simplification of the proposed model is discussed.     

Predictions of radiowave attenuations due to a melting layer ofprecipitation

A melting layer model related to the physical constants and meteorological parameters is employed in this investigation. The specific phase shift, together with the specific attenuation, is computed at 1-100 GHz by using the Mie theory. The additional zenith attenuation, which is the difference between zenith attenuation due to the melting layer and attenuation due to the same thickness of the resulting rain, is comprehensively studied. The ratio of the difference to rain zenith attenuation may be over 1 at 1-5 GHz although the difference is much less than 1 dB. The difference can be over 1 dB at frequencies above 20 GHz. A minimum of the ratio is below 0.05 at frequencies about 40-60 GHz but the ratio can become a value of about 0.1 at 100 GHz. The additional attenuation should be taken into account in satellite-Earth communications and radar remote sensing. The power law parameters of the average specific attenuation of the melting layer and rain specific attenuation are tabulated for three raindrop size distributions at rain rates of below 25 mm/h. The power law method could be utilized in the additional attenuation calculation. It is a good approximation of the Mie theory results at 1-50 GHz and a useful estimate at 50-100 GHz     

Performance evaluation of OFDM transmission over a challenging urban propagation environment

The paper introduces a performance evaluation of orthogonal frequency division multiplexing (OFDM) transmission schemes over a challenging urban propagation environment, considering 3D scattering, providing also a comparison with 2D considerations. After an analytic calculation of the power of received signal components (faded useful signal, intercarrier interference, intersymbol interference and noise) the authors present results of system performance evaluation under different propagation conditions (e.g., various Doppler shift values) and various values of key system parameters. BER (bit error rate) calculations are provided for a 16-QAM OFDM transmission scheme over Rayleigh fading channels, with and without Reed-Solomon coding techniques. Finally, the influence of carrier offset on the system performance is examined.     

A power-spectral theory of propagation in the mobile-radio environment

The statistical properties of radio propagation between a mobile unit and a base-station terminal are derived. The power spectrum of the transmission coefficient in the multipath medium is used to determine probability distributions of amplitude and phase, correlations of fields versus time and space at mobile and base stations, level-crossing rates and durations of fades, and random frequency modulation. Duality between the power spectrum and density of time delays is shown. The correlations versus frequency and the coherence bandwidth then follow from the density of time delays. The performance of standard diversity systems is then predicted. There is a review of results previously presented by Clarke [1], however, the derivations given herein utilize expressions of the power spectrum rather than expressions of the component waves. The power-spectral approach, used throughout, allows direct application of previous statistical analyses, particularly those of Rice [2].     

Method of obtaining radiowave propagation parameters for the Earth?ionosphere duct at e.l.f.

The wave impedance of the Earth?ionosphere duct is investigated numerically and analytically in the frequency band 1 to 60 Hz. Data are presented enabling the determination of the propagation parameters of the duct by experimental measurement of the argument of the wave impedance.     

Millimeter-wave propagation at street level in an urban environment

Measurements on point-to-point transmission at street level were performed in downtown Denver, CO, with RF probes that operated at 9.6, 28.8, and 57.6 GHz. All probes were mounted on self-contained vehicles, permitting a variety of path scenarios. Information on performance of these channels for propagation in an urban environment on both line-of-sight and non-line-of-sight paths is presented. For non-line-of-sight (non-LOS) paths obstructed by buildings of several common materials, results that showed signal attenuations in excess of 100 dB. When the LOS followed a path directly through clear glass walls, the attenuation was small at all probe frequencies. However, when the glass wall had a metalized coating to reduce ultraviolet and infrared radiation, the attenuation increased by 25 to 50 dB for each metallized layer. In most cases no signals could be detected through steel reinforced concrete or brick buildings