Centimeter wave propagation experiments using the beacon signals of CS and BSE satellites

The wave propagation experiments using Japanese geostationary satellites CS (20/30 GHz) and BSE (12/14 GHz) satellites have been performed at the Kashima earth station of the Radio Research Laboratories (RRL). Cumulative rain attenuation and cross-polarization discrimination (XPD) statistics are given for the period of three years at 11.7 GHz (vertical polarization) and for the period of four years at 19.5 GHz (circular polarization). It is shown that the yearly rainfall rate and attenuation distributions are well approximated by log-normal distributions, and the XPD distribution is well approximated by a normal distribution. Monthly and time-of-day variation of the attenuation and XPD distributions are presented. Duration statistics of attenuation and XPD are presented and characterized. Other characteristics in the wave propagation, such as effective path length, frequency dependence of attenuation, and joint statistics of attenuation and XPD are derived and discussed. Rainfall events are classified into three rainfall types, "stratus," "cumulus," and "others" using measurements of the radar reflectivity factor along the satellite-to-earth path, and the dependence of XPD characteristics on the rainfall type is also presented and discussed. Some prediction methods of calculating attenuation and XPD statistics are applied to the data obtained in these experiments and the predicted results are compared with the measured ones. It is found that some corrections are needed when the XPD statistics are predicted from the attenuation statistics using the theoretical relation between XPD and attenuation.     

Effect of rain- and ice-induced depolarisation on dual-polarised 21GHz-band digital satellite broadcasting system

The effects of attenuation and depolarisation along the Earth-space path on a dual-polarised 21 GHz-band digital broadcasting satellite service are studied by using both theoretical and measured attenuation and depolarisation relations. It is concluded that the effects of rain- and ice-depolarisation are not significant for digital modulation     

Microwave depolarization versus rain attenuation on earth space in Malaysia

The wave propagation experiments using Japanese geostationary satellite Superbird‐C have been performed at the Universiti Sains Malaysia earth station. A relationship between rain depolarization and attenuation, valid for earth‐space path at microwave wavelengths, is presented. Cumulative rain attenuation and cross‐polarization discrimination (XPD) statistics are given for the period of 4 years (2002–2005) at 12.255 GHz. XPD varied from 44 dB at 1% to 16 dB at 0.001% of time the abscissa is exceeded. Comparisons were made with available data sets and with five simple XPD models and the results indicate a good performance by the simple isolation model and the CHU model compared with the others. These results serve as checks on the theoretical models needed for predicting communication system performance in geographical regions especially for equatorial climate where measurements are not available. Copyright © 2008 John Wiley & Sons, Ltd.     

Theoretical relationship between rain depolarisation and attenuation

An approximate theoretical relationship between rain depolarisation and attenuation, valid for Earth-space paths at microwave and millimetre wavelengths, is presented. The relationship is sufficiently general that it allows the prediction of rain-depolarisation statistics from attenuation statistics available for other frequencies, polarisations and elevation angles.     

广州地区33．5GHz和93GHz降雨传播特性测量

本文给出了１９９２年７—９月份广州地区Ｏ．４ｋｍ地面电路３３．５ＧＨｚ和９３ＧＨｚ雨衰减测量结果及雨衰减和降雨率短期统计结果之间的关系，并利用这一结果和长期降雨率统计对雨衰减预报作了初步探讨。同时分析了３３．５ＧＨＺ和９３ＧＨＺ雨衰减频率换算关系。文中还导出了雨致交叉极化鉴别度（ＸＰＤ）与实测差分衰减和差分相移之间的理论关系。在８ｍｍ波段可忽略差分相移的情况下，给出了利用３３．５ＧＨｚ部分实测差分衰减计算的ＸＰＤ结果，并与理论模式预测值作了比较。     

Analysis of the interference due to differential rain attenuationinduced by an adjacent path on a triple-site diversity Earth-spacesystem

The reliable design of satellite communication systems requires the consideration of interference effects. Interference caused by differential rain attenuation from an adjacent Earth-space system is taken under consideration. In particular, a method to predict rain differential attenuation statistics used for single/double site Earth-space systems is extended to include triple-site diversity ones. The modified method is again based on a model of convective rain cells as well as on the lognormal assumption for the point rainfall rate distribution at the location under consideration. In an analogous fashion with the (C/N) ratio, a “(C/I) diversity gain” is also adopted here and some very useful remarks concerning the effectiveness of the triple-site diversity protection as a countermeasure technique are deduced. As a general conclusion, it can be stated that the triple-site scheme not only reduce the potential large attenuation margins significantly, but also leads to the establishment of the minimum separation between satellites operating under permitted interference levels     

Worst month statistics of attenuation and XPD on Earth-space path

Using the attenuation and cross-polarization discrimination (XPD) statistics measured in the CS (20/30 GHz) and BSE (12/14 GHz) centimeter wave propagation experiments performed for over four and three years, the worst month statistics of attenuation and those of XPD on earth-space path at 11.7 and 19.5 GHz are derived. The probability relation between the annual and worst month statistics is approximated by a power-law relation, and the constants for the relation are derived by a least squares procedure. It is found that the relation is independent of both frequency and polarization. The cumulative probability ratios of the worst month to annual statistics at the same attenuation or XPD values are derived as a function of annual cumulative probability. The ratios are well described by the Brussaard model of the worst month statistics. Attenuation ratio and XPD difference among the annual and worst month statistics are also derived and compared with the predicted results.     

Cross polarization on line-of-sight links in a tropical location:effects of the variation in canting angle and rain dropsizedistributions

The effects of the variation in canting angle of falling raindrops and the distribution of raindrop sizes in different types of rain on cross polarization discrimination (XPD) on line-of-sight propagation paths in a tropical location in the frequency range 1-50 GHz are investigated. The dropsize distribution (DSD) model of Adimula and Ajayi (see Ann. Telecomm., vol.51, no.1/2, p.87-93, 1996) has been used. Although, some previous studies of XPD assumed equi-orientation of the raindrops along the propagation paths, the present study employs the more realistic distribution of canting angles along the path. The results obtained show that the XPD improves by about 4-7 dB over those based on the equi-orientation model. It is also shown that for the same copolar fade and for frequencies greater than about 10 GHz, the variation of the XPD with copolar attenuation (CPA) is relatively insensitive to the assumed DSD in rain and that the deterioration in signal quality or outage will be influenced more by the signal attenuation rather than by the cross-polarization interference     

Rain induced depolarization from 1 GHz to 300 GHz in a tropical environment

The rain induced depolarization in a tropical environment has been studied using a tropical raindrop size distribution developed by Ajayi and Olsen (A-O). The differential attenuation, differential phase shift and cross polarization discrimination, XPD, were computed over a frequency range of 1GHz to 300GHz for spheroidal drops and up to 33GHz for Pruppacher-Pitter drops. The variations of XPD with frequency, rainfall rate and copolar attenuation, CPA, were investigated. A mathematical relationship was established between the XPD and the CPA, canting angle and frequency of propagation from 5GHz to 300 GHz for spheroidal drops and up to 33 GHz for Pruppacher-Pitter drops. The results obtained using the A-O drop size distribution have been compared with those assuming the Laws and Parsons (L-P) distribution. The Pruppacher-Pitter drop shape has been found to give rise to higher XPD, especially at low CPA and high frequencies.     

Wave attenuation characteristics of the 11.5 GHz Earth-space path in Warsaw region

In Poland wave attenuation measurements in the Earth-space path, operating at 11.5 GHz, have been carried on simultaneously with the rain rate measurements, accomplished under the propagation path in five spaced out sites. Moreover the accuracy of prediction models, used for prediction of attenuation due to rain, was evaluated. The obtained results are presented in the paper.     

Rain Attenuation Ratios on Short Microwave and Millimeter Wave Bands Earth-Space Paths

The knowledge of the ratio of rain attenuation at one frequency to that at another on slant paths is useful for the design of satellite-to-Earth communication links and up-link power control systems. It is well known that the rain attenuation is influenced by parameters of precipitation along the slant path such as DSD (raindrop size distribution), raindrop temperature, rainfall rate, and so on. In this paper, based on several DSDs applied to various climate zones, at short microwave and long millimeter wave bands, the attenuation ratios are estimated on Earth-space paths. A comparison of the prediction results with the experiment data in Boston and Kashima areas is carried out. It is shown that the M-P and Weibull DSD applied to rain attenuation ratios estimation are better DSD at higher latitude regions. The Guangzhou DSD applied to rain attenuation ratios prediction is better in tropical and subtropical areas in China. The lognormal DSD may be a appropriate DSD applied to predict rain attenuation ratios in tropical areas at A_down>1dB or R>15mm/h. However, the attenuation ratios predicted by the Guangzhou DSD disagree with by the lognormal DSD, it requires that the DSD applied to predict rain attenuation ratios are further studied in tropical areas.     

Multigigabit transmission through rain in a dual polarizationfrequency reuse system: an experimental study

An experimental terrestrial link was set up for the purpose of evaluating very-high-data-rate communications in dual-polarization frequency reuse systems. Possible applications are in the field of satellite communications. Two 3.2-Gb/s signals using staggered quadriphase shift keying (SQPSK) were transmitted on opposite senses of circular polarization over a 7-km path located in Crane rain region D3. Performance degradation of the demodulator as a function of cross-polarization discrimination (XPD) was evaluated and found to closely match simulation predictions. However, the relationship between XPD and rain attenuation was found to be more complex than thought previously, displaying a relatively slowly varying hysteresis effect as well as significant interactions with characteristics of the receive antenna. The latter effect suggests that careful control of antenna characteristics may be required if such high-data-rate techniques are to be employed in space-ground links     

The relationship of rain-induced cross-polarization discrimination to attenuation for 10 to 30 GHz earth-space radio links

Rain depolarization is quantified through the cross-polarization discrimination (XPD) versus attenuation relationship. Such a relationship is derived by curve fitting to a rigorous theoretical model (the multiple scattering model) to determine the variation of the parameters involved. This simple isolation model (SIM) is compared to data from several earth-space link experiments and to three other models.     

Fade rates at 13 GHz on Earth-space paths

Fade rate distributions for 13 GHz signals on Earth-space paths have been compiled from the equivalent of 15 station-years of radiometer data that were recorded in Canada. Fade rates of up to 0.42 dB per second were found with the high fade rates tending to occur when the attenuation was also high. As with attenuation statistics, fade rate statistics for Earth-space paths are determined mainly by the climate that is local to the ground station.     

Rain fades on low elevation angle Earth-satellite paths:comparative assessment of the Austin, Texas, 11.2 GHz experiment

Only a few years of rain attenuation data for Earth-space paths are available for low elevation angle paths, and these show a consistent tendency by the CCIR fade prediction model to underpredict rain fades. The authors contribute to the database four years of 11.2 GHz measurements, taken on a 5.8° elevation path in Austin, Texas, USA and assess higher than predicted fade results with respect to earlier measurements and the CCIR model. At the fiducial 0.01 percent of time, the rain fall rate was 73 mm/h and the attenuation exceeded the 25 dB measurement fade margin. It is found that the monthly variability of rain fall rates and decibel fades follows a normal distribution. Durations of rainfall and fades are classified into events, episodes, interevent gaps (longer than 4.2 h), and interepisode gaps (shorter than 4.2 h). Rainfall interevent gaps and event durations, as well as fade event, episode, and gap durations are log-normally distributed     

Measurements of rainfall attenuation at 8 and 15 GHz

Measurements of attenuation at frequencies of 8 and 15 GHz, and their correlation with rainfall rate, along a 15.78 km path near Ottawa, are described. Empirical expressions which relate the observed attenuation to the measured rainfall rate are derived and compared with similar expressions obtained on the basis of earlier theoretical studies of the problem. It is concluded that while the theoretical predictions of attenuation in rain are reasonably satisfactory, at least for rains observed at Ottawa, there is a definite tendency for observed attenuations at low rainfall rates to be somewhat higher than the expected values. The cumulative distribution of rainfall attenuation over a six-month period is compared with the attenuation predicted on the basis of average rainfall data obtained during the last five years. Although the agreement between observation and prediction, using the theoretical relation between rainfall rate and attenuation, is good for path attenuations greater than 2 dB, it can be greatly improved if the empirical expression relating rainfall rate to attenuation is used.     

Rain induced cross polarization at millimeter waves in a Xi'an environment

The rainfall intensity accumulative distribution, raindrop size and canting angle distributions in Xi'an(108.9 E, 34.3 N) have been obtained from data measured over a long period of time. Rain induced crose polarization in this environment has been studied. The crose polarization discrimination, XPD, was compu ted over a frequency range of 19.3 to 300 GHz for non spherical drops. The variations of XPD with frequency, rainfall rate and copolar attenuation, CPA, were investigated. The computational resulte are in good agreement with experimental data. A mathematical relationship was established between the XPD and CPA, raindrop canting angle, which result is in good agreement with experimental data. The cumulative distribution of rain induced cross polarization for eleven years and in month have been ob tained with the cumulative distribution of the rain rate from the data measured from 1975 to 1985. The role of multiple scattering also has been discussed, it is shown that the multiple scattering play an important part in short millimeter wave.     

Site diversity for satellite earth terminals and measurements at 28GHz

This work reviews site diversity concepts and models and presents the results of a site diversity experiment, in which radiometers were used to measure attenuation on Earth-space paths, performed at Columbus, Ohio, for a period of one year. Attenuation statistics are presented first in the form of the joint probability density function of attenuation at the two sites. From these are derived the cumulative two-dimensional distribution of attenuation at both sites, the cumulative distribution of attenuation at each site, the effective cumulative distribution of attenuation for a diversity system that always switches to the better of two signals, and the effective cumulative distribution of attenuation for a system with maximal-ratio signal combining. The switched-system diversity gain is compared with D.B. Hodge's (1982) predictive model, and the diversity improvement is compared with L. Boithias' (Radiowave Propagation, McGraw-Hill, 1987) model. Fade-duration and interfade-interval statistics are presented for each site and for systems that use switching and maximal-ratio combining. Rain-rate and interrainfall interval statistics are included     

神经网络方法在降雨去极化效应预报中的应用

利用神经网络中的ＢＰ算法，通过在已知的传播路径上降雨同极化衰减ＣＰＡ来预算降雨去极化分辨率ＸＰＤ，且将计算结果与其他算法进行了对比。本文的工作是神经网络方法在建立电波大气传输效应预报模型应用中的有益尝试。     

沙尘暴对地空路径上Ka频段电波传播的影响

通过分析陆地上毫米波在沙尘暴中传播时的衰减和交叉极化分辨率，给出了一定高度毫米波传播的衰减和交叉极化分辨率的计算公式，并提出了一种计算地空路径沙尘暴衰减和交叉极化分辨率的等效模型。在不同的地球站点、不同的能见度、不同的沙尘粒子含水量、不同的粒径分布下进行了数值计算，并对结果进行了分析。