A simulation of multipath effects on the cross-polarization discrimination in microwave line-of-sight links

A ray-tracing computer model, combining the effects of the curvature of the Earth, of the radiation patterns of the antennas, as well as those of the reflection at the Earth’s surface, has been developed in order to simulate multipath effects on the relationship between cross-polarization discrimination (xpd)and co-polar attenuation (cpa)values occurring in frequency-reuse line-of-sight microwave links. Measured refractive-index vertical profiles have been used as input data to this model, in order to study the dependence of the parameters of the law relating xpd and cpa on the characteristics of the link. Based on the observed dependence, experimental values for the parameters of this law, available in the literature, have then been analyzed.     

Ice crystals and raindrop canting angle effects applied to satellite interference prediction with respect to heavy rain climatic zones

For frequencies above 10GHz the performance of the operating satellite systems is mainly aggravated because of the potential existing severe rain attenuation. As a result of the above fading mechanism, the dominant interference sources encountered in this frequency band are the following: differential rain attenuation induced by an adjacent satellite system operating in the same frequency, and cross talk between orthogonally polarized signals. The latter source concerns of course satellite systems employing the dual polarization mode. In the present paper, an already existing method to predict interference statistics, due to above reasons, is properly modified to include ice crystals and raindrop canting angle effects. The assumption that the point rainfall rate statistics follows a gamma form, valid for heavy rain climatic regions such as J, M, N, P, Q zones, is also adopted. The sensitivity of various parameters affecting the interference performance, after introducing the novel assumptions, is finally investigated.     

Letter to the editor: Differential rain attenuation statistics on two converging point-to-point terrestrial links located in a tropical climatic region

An analytical procedure for the prediction of differential rain attenuation statistics on two converging point-to-point terrestrial links located in a tropical climatic region is presented. It is based on an appropriate convective raincell model and the fundamental assumption that the point rainfall rate statistics follows a gamma form. A tropical raindrop size distribution is also adopted. Numerical results are compared with a set of available experimental data over pairs of converging terrestrial links in Brazil.     

Time series prediction of rain attenuation from rain rate measurement using synthetic storm technique for a tropical location

A comparison of measured attenuation series with the attenuation series obtained from rain rate measurement by using synthetic storm technique is made for Ku band signal at a tropical location. Validity of the model is tested for the long-term statistics in terms of the cumulative distribution of attenuation occurrence and fade duration. Applicability of the model is also shown to be valid event-wise. It has been demonstrated that the long term statistics of predicted rain attenuation are insensitive to storm translation speed. No significant differences are found when cumulative distributions of predicted attenuation values are compared for different data sampling intervals. It has been observed that there exists a good correlation between the predicted and measured values of attenuation for at least 80% of the events.     

基于雨胞分布的视距链路雨衰减预报模型

基于指数雨胞分布,推导得到路径调整因子,提出了一种新的视距链路雨衰减预报模型.利用ITU-R视距链路雨衰减数据库数据回归得到了预报模型中的参数.通过和ITU-R模型以及近几年发展的几种雨衰减模型比较表明,这一模型较其他模型具有更好的预测精度.     

Potential use of optimal polarisations in sensing the canting angle distribution of raindrops

The optimal polarisation of rain backscatter is investigated to determine the Gaussian canting angle distribution of the raindrops. It is found that the COPOL MAX is sensitive to the canting angle distribution. The means and variance of the canting angle distribution can be obtained from the average COPOL MAX and its spread.<>     

Investigation of wind and rain effects in a foliated tropical region for fixed wireless access

This paper investigates the effects of trees on fixed wireless access operating at 5.8 GHz frequency of the Unlicensed National Information Infrastructure (UNII) band. Measurements are focused on the temporal scale of the received signal strength for a three different links (one line of sight (LOS) link and two non-line of sight (NLOS) link). The statistical characterisation of the combined effects of typical weather phenomena often experienced in a tropical region is presented. As expected, the LOS link is not affected even during heavy rain condition. However, the presence of trees in the vicinity of the transmission path can cause relevant signal deterioration in the case of NLOS link, where the fading of the received signal varies from 2 to 16 dB as the strength of wind and rain increases. Rician distribution can be used to characterise the temporal variation of these weather effects. The work reported in this paper enables the effects of wind, rain and humidity to be properly taken into consideration in the deployment of fixed wireless links in a foliated channel, allowing an optimisation of planning for the end users.     

Prediction of rain effects on earth-space communication links operating in the 10 to 35 GHZ frequency range

This paper reviews the effects of precipitation on earth-space communication links operating the 10 to 35 GHz frequency range. Emphasis is on the quantitative prediction of rain attenuation and depolarization. Discussions centre on the models developed at Virginia Tech. Comments on other models are included as well as literature references to key works. Also included is the system level modelling for dual polarized communication systems with techniques for calculating antenna and propagation medium effects. Simple models for the calculation of average annual attenuation and cross-polarization discrimination (XPD) are presented. Calculation of worst month statistics are also presented.     

Some probabilistic properties of the line-of-sight angle error to a remote object (Corresp.)

Closed-form expressions are derived for the distribution and the expectation of the error of the line-of-sight angle to a remote object when the rectangular position coordinates are independent identically distributed normal variates. Generalized results also are provided both for the cumulative distribution function for a hyperspace ofNdimensions and for a spherically symmetric probability density function in three-dimensional space.     

Time series predictor of Ku band rain attenuation over an Earth–space path at a tropical location

A channel model is proposed to predict the time series of Ku band rain attenuation during a rain event at a tropical location. The model is based on considering the Gaussian distribution of the conditional occurrence of rain attenuation with a particular value of the attenuation occurring before. The mean (μ) and standard deviation (σ) for the distribution are modeled with the experimental data. The measured attenuation at a particular time instant is used to obtain μ and σ and to predict the attenuation after certain interval. The channel model has tested well giving the predicted attenuation that agrees with the measured value with a mean error within 15% higher than 1 dB. Validity of the model is also tested with the first‐order and second‐order statistics of attenuation occurrence, on a long‐term basis. The method can also be applied even if attenuation measurements are missing for certain period of time with increased error. Copyright © 2011 John Wiley & Sons, Ltd.     

Measurements and prediction of differential rain attenuation in convergent links

Measurements of differential rain attenuation in line-of-sight microwave and millimetre-wave convergent links were performed at two sites in Brazil. Cumulative distributions of differential rain attenuation for 36 pairs of links were obtained and an empirical prediction model has been derived.     

Sunrise and sunset effects as observed on microwave propagation over a line-of-sight path

Microwave signal propagation provides an effective measure of studying the variable nature of the atmosphere. Sunrise and sunset periods are characterized by the dissolution and formation of nighttime temperature inversions. Signal amplitude recordings at 6.7 GHz over DumDum-Andul line-of-sight (LOS) communication link during post-sunrise period are characterized by the appearance of an enhancement in signal strength (as high as 20 dB). The sunset effect or the evening transition is observed as an enhancement in signal amplitude of about 10- 12 dB over the link. The signal characteristics observed during transition periods over the 6.7 GHz DumDum-Andul link are studied herein.     

Space communications with variable elevation angle faded by rain: Radio links to the Sun–Earth first Lagrangian point L1

How rain attenuation affects space links with variable elevation angles is not yet fully researched. The aim of this paper is to investigate this topic by simulating rain attenuation at K_a Band, in slant paths with variable elevation angles, with the Synthetic Storm Technique (SST), in links connected with spacecrafts at the Sun–Earth first Lagrangian point L₁, viewed from Spino d'Adda (Italy), Tampa (Florida), White Sands (New Mexico). The input to the SST is a large database of time series of 1‐min rain rate recorded on site, 10 years in Spino d'Adda, 4 years at Tampa and White Sands. After recalling known results on the elevation angle of the Sun (i.e. L₁), θ_s (°), seen from latitude λ (°), I report what seems to be a new result: the mode of the probability density function of θ_s in a year, in the range 0 ≤ λ ≤ 90° ? ε (Earth axis tilt angle ε = 23.44°), coincides with the peak angle found at the day of the Winter solstice at the site, a result valid also for other planets, once their tilt angle is used. Compared to the complementary probability distribution function (pdf) of rain attenuation calculated for a geostationary (GEO) link (fixed elevation angle), the pdf to L₁ depends on the rain‐rate pdf during the contact time with L₁, according to the local climate. I show that, to obtain a good and easier estimate of the rain attenuation pdf in L₁ links, we can consider a GEO link with elevation angle equal to the mean angle and rain rate pdf, both during the contact time, and that the mode angle gives an upper bound to the rain attenuation pdf in the sites considered. Copyright © 2015 John Wiley & Sons, Ltd.     

Propagation impairment on Ka-band satcom links in tropical and equatorial regions

Due to pressures in the commercial sphere for increased information transfer rates or from the military to further miniaturize equipment to improve its portability, there has been a steady move toward higher carrier frequencies. For more than a decade now, increasing numbers of satellite communications systems have been in operation at millimeter wavelengths. Even where there is a clear view of the satellite from the ground station, a range of meteorological phenomena still combine to make propagation impairment a serious problem. Because of their complexity, difficulties in modeling them, and deficiencies in basic physical understanding, progress in engineering such systems has involved a large dose of empiricism. Ideally, this means a solid database of propagation measurements, made as nearly as possible in the intended geographical area of operations. Because of the time and cost of their accumulation, attempts have been made to use classification into climate zones on a worldwide basis to extend existing data to a wider range of situations. However, most of the measurements in the databases have been made in northern hemisphere temperate zones. Much evidence suggests that in tropical and equatorial zones, the factors that make important contributions to propagation impairment are different, putting a strong question mark over the use of existing design methods. This review looks at those deficiencies and their likely impact on system performance. At this time, rather than providing definitive answers - which must wait on further work - the best that can be done is to highlight difficulties and encourage realistic expectations. In a final section, the review examines the question of whether costly, application-specific measurement programs might now be avoided by mining increasingly sophisticated national meteorological records.     

Absorption and scintillation effects at 3 mm wavelength on a short line-of-sight radio link

Measurements on a path 150m long, with narrow-beam transmitting and receiving antennas 2m above the ground at one end of the path, and a reflecting plate at the other end, at the same height, have shown attenuation in rain to be about 17dB/km and 8dB/km for rainfall rates of 48mm/h and 7mm/h, respectively. Amplitude variations of up to ±0.4dB can occur in a time interval of the order of 1s during sunny, humid conditions in summer.     

An analysis of the effects of ground reflection in line-of-sight phase systems

The presence of a reflected component in a line-of-sight radio system influences the phase variability resulting from atmospheric changes along and near the path. An analysis is made of a simple case showing the general nature of this effect and the parameters upon which it depends. A method is presented for calculating the phase behavior of the resultant signal, in terms of that expected from a single direct component, and the relevant system parameters.     

E&C跟踪对极化角的影响及解决方法

针对船载卫通站使用线极化卫星通信过程中出现的反极化信号干扰问题,根据不同状态下信号电平变化,发现干扰信号强度与天线跟踪角度有关.结合天线采用的三轴稳定体制结构特点,建立天线转动几何模型,通过不同跟踪模式下天线角度的比较,对其相互关系进行了分析,推导出了该体制下极化角计算公式,据此进行极化补偿,有效解决了EC模式下跟踪线...     

卫星接收后馈天线极化角调整装置的技术改造

简要阐述了对卫星接收后馈天线极化角调整装置进行技术改造的必要性,并给出了具体的改造方法。进行技术改造后,彻底改善了卫星广播电视的收看效果,在天线上安装双极化、双波段馈源,1副天线相当于4副,节约了经费,提高了天线的利用率。     

Survival probability of precipitations and rain attenuation in tropical and equatorial regions

This contribution presents a stochastic model useful for the generation of a long-term tropospheric rain attenuation time series for Earth space or a terrestrial radio link in tropical and equatorial heavy rain regions based on the well-known Cox–Ingersoll–Ross model previously employed in research in the fields of finance and economics. This model assumes typical gamma distribution for rain attenuation in heavy rain climatic regions and utilises the temporal dynamic of precipitation collected in equatorial Johor, Malaysia. Different formations of survival probability are also discussed. Furthermore, the correlation between these probabilities and the Markov process is determined, and information on the variance and autocorrelation function of rain events with respect to the particular characteristics of precipitation in this area is presented. The proposed technique proved to preserve the peculiarities of precipitation for an equatorial region and reproduce fairly good statistics of the rain attenuation correlation function that could help to improve the prediction of dynamic characteristics of rain fade events.