The Study of Rain Specific Attenuation for the Prediction of Satellite Propagation in Malaysia

Specific attenuation is the fundamental quantity in the calculation of rain attenuation for terrestrial path and slant paths representing as rain attenuation per unit distance (dB/km). Specific attenuation is an important element in developing the predicted rain attenuation model. This paper deals with the empirical determination of the power law coefficients which allow calculating the specific attenuation in dB/km from the knowledge of the rain rate in mm/h. The main purpose of the paper is to obtain the coefficients of k and α of power law relationship between specific attenuation. Three years (from 1st January 2006 until 31st December 2008) rain gauge and beacon data taken from USM, Nibong Tebal have been used to do the empirical procedure analysis of rain specific attenuation. The data presented are semi-empirical in nature. A year-to-year variation of the coefficients has been indicated and the empirical measured data was compared with ITU-R provided regression coefficient. The result indicated that the USM empirical measured data was significantly vary from ITU-R predicted value. Hence, ITU-R recommendation for regression coefficients of rain specific attenuation is not suitable for predicting rain attenuation at Malaysia.     

长春和新乡雨衰时间序列的马尔科夫链模拟

基于马尔科夫理论建立的N阶马尔科夫链模型,模拟了长春和新乡地区的降雨衰减时间序列,比较了长春和新乡地区单个模拟和实测雨衰时间序列的概率分布;分别统计了长春和新乡地区50组模拟雨衰时间序列的百分概率分布,并与国际电信联盟无线电通信研究组(ITU-R)提供的卫星轨道位置为92°E、频率为12.5GHz在线极化情况下长春和新乡雨区不同降雨衰减值下的时间百分概率进行了比较,一致性很好,从而验证了N阶马尔可夫链模型在中国部分地区的可用性。模拟结果对我国在Ku及以上频段通信卫星的抗衰落技术的发展具有重要的应用价值。     

5G毫米波短距离链路雨衰减特性分析

雨衰减严重影响第5代(the 5th Generation,5G)移动通信系统性能.在路径长度小于1 km的短距离链路情况下,现有雨衰减预测模型调整因子大于1,导致预测雨衰减随路径变短而增大,无法支撑毫米波短距离链路系统设计.通过分析国际电信联盟无线电通信部(Radiocommunication Sector of International Telecommunication Union,ITU-R)短距离链路雨衰减试验数据,发现湿天线衰减与路径雨衰减相当,得到毫米波短距离链路必须考虑湿天线衰减的结论.建立了湿天线衰减与降雨率的关系模型,分频段对模型参数进行了拟合,拟合结果与实测数据吻合得较好.提出了考虑湿天线衰减的短距离雨衰减建模新思路,可解决短距离雨衰减预测问题.研究结果有助于提高5G毫米波系统余量设计的可靠性.     

Ku-band slant-path radiometric measurements at three locations in Brazil

This paper presents results of the 12 GHz propagation experiment that is being conducted in Brazil. The data obtained are useful to investigate the impairment due to rain attenuation in satellite links operating in tropical and equatorial climates. Radiometric sky noise temperature and rainfall rate are being measured at three locations. At one location, site diversity measurements are also being conducted. Cumulative distributions of sky-noise temperature, equivalent attenuation and rainfall rate at each site are presented together with worst-month statistics. Also, the joint-probability distribution of equivalent attenuation at the diversity sites is shown. Finally, the measured probability distributions of attenuation are compared to those obtained from the measured rainfall rate distributions, using prediction models.     

Performance characteristics of a 300-GHz radiometer and some atmospheric attenuation measurements

A 300-GHz Dicke-type superheterodyne radiometer receiver was used for measurements of atmospheric attenuation of electromagnetic waves over an open path at frequencies near 300 GHz. The average measured values of horizontal attenuation at 304 GHz and 316 GHz, presumably due to atmospheric water vapor absorption, were, respectively, 3.35 dB/km and 5.55 dB/km per g/m³of water vapor density. Absorption variations at 304 GHz with respect to water vapor density were shown in the measured results. The variation of the effective zenith sky temperature with respect to atmospheric water vapor density was also determined. The minimum detectable temperature difference(Delta T)_{min}, was obtained by measuring the rms value of noise in the receiver output. The best value achieved was3.16degK. Based on this result, the receiver noise figure and the mixer conversion loss were determined indirectly. The results were 31.4 dB and 22.9 dB, respectively. A blackbody radiation source served to calibrate the radiometer.     

ACTS propagation experiment: attenuation distribution observationsand prediction model comparisons

Empirical cumulative distribution functions for satellite-to-ground path attenuation relative to clear-sky values were compiled for 22 path years of data collected by the ACTS propagation experiment. These statistics are for two frequencies, 20.2 and 27.5 GHz, with elevation angles ranging 8-52°, latitudes ranging 28-65°, and five different rain-rate climate regions. The attenuation estimation accuracy was better than 0.3 dB. The availability of the equipment for making measurements was higher than 90% for 18 of 22 path years of observation. The empirical distribution functions were compared with predicted cumulative distribution functions generated by four different attenuation-prediction models: the model recommended by the radiocommunications sector of the International Telecommunications Union (ITU-R); the Dissanayake, Allnutt, and Haidara (DAH) rain-attenuation model; and the Crane-Global and Crane-Two Component models when combined with three different rain-rate distribution prediction models: the ITU-R model the Crane-Global model and the Rice-Holmberg model. On the basis of the expected differences between model predictions and experimental measurements, the only attenuation model that provided acceptable predictions was the DAH model when combined with either the Crane-Global rain-zone model or the Rice-Holmberg rain-race model. A major problem in interpreting the results of the model-versus-measurement comparison is the unmodeled contribution of water on the surface of the ACTS propagation terminal antenna reflector     

Slant path rain attenuation predictions for Ku and Ka band frequencies from rain cell size distribution over a tropical region in southern India

Rain cell size distribution that provides an insight into the modelling of effective slant path length and also imperative for site diversity studies are carried out for a tropical inland location, Tirupati (13.6°N, 76.3°E), India. Rain cell size distribution obtained from 5 years (2013–2015 and 2017–2018) of Parsivel disdrometer measurements is observed to follow the power law. Reduction factor that accounts for the inhomogeneity of the rain along the propagation path for the region of study is modified in terms of the rain cell size distribution of the area. Slant path rain attenuation, a major propagation impediment at Ku and Ka-band links, is then studied using the results from the regional rain characteristics by modifying the CCIR 564-4 report. The attenuation results are compared with Garcia-Lopez, Excell, Bryant, and Ramachandran models while considering the ITU-R P. 618-13 as the standard model.     

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.     

11·6 GHz rain attenuation measurements in Peru

This paper presents the results of a K_u-band propagation experiment conducted in a high-rainfall-rate region in Peru. Sky noise measurements were made with an 11·6 GHz radiometer over a period of 18 months. Simultaneous rainfall was also recorded with a tipping bucket rain-gauge. The paper describes the experimental equipment, the characteristics of the measurement site, and the results obtained from the experiment in the form of long-term distributions of rain rate and path attenuation. Duration statistics of attenuation are also presented. In the absence of an absolute calibration of the radiometer in terms of the path attenuation, selection of the best medium temperature to be used poses a problem. For comparison, sky noise to path attenuation conversion was done with two medium temperatures, 280 and 290 K. When compared with model predictions, 290 K seems to be more appropriate for the climate concerned. Both the attenuation and fade duration statistics are found to follow a lognormal distribution fairly closely.     

Rainfall propagation impairments for medium elevation angle satellite‐to‐earth 12 GHz in the tropics

Rain attenuation is the dominant propagation impairment for satellite communication systems operating at frequencies above about 10 GHz. The rainfall path attenuation at 12.255 GHz measured at Universiti Sains Malaysia (USM) for 4 years (2 January to 5 December) is presented. This paper presents an empirical analysis of rain rate and rain attenuation cumulative distribution functions obtained using 1‐min integrated rainfall data and comparison of the measured data with data obtained from well‐established rain model attenuation predictions. Copyright © 2008 John Wiley & Sons, Ltd.     

Scattering of radiowaves by a melting layer of precipitation inbackward and forward directions

A melting layer of precipitation is composed of melting snowflakes (snow particles); the assumption of spherical particles along with mass conservation is used. The melting layer is studied by deriving the size distribution of the melting snow particles, the thickness of a melting layer, the density of a dry snow particle, and the average dielectric constant of a melting snow particle. Vertical profiles of radar reflectivity and specific attenuation are computed at 1-100 GHz by using the Mie theory for five raindrop size distributions at rain rates below 12.5 mm/h. The radar bright band is explained with computed radar reflectivities at 3-10 GHz. It is shown that the radar bright band can be absent in the melting layer at frequencies above 20 GHz. This agrees with radar observations at 35 and 94 GHz. The specific attenuation, as well as the average specific attenuation of the melting layer, is divided into absorption part and scattering part. The latter is increasingly significant with the increase of frequency. The total zenith attenuation due to stratiform rain is divided into the rain zenith attenuation and the additional zenith attenuation, which is the difference between zenith attenuation, due to the melting layer, and attenuation, due to the same path length of the resulting rain. The additional zenith attenuation increases with the increase of rain rate even at frequencies above 20 GHz. This should be taken into account in radar remote sensing and satellite-Earth communications     

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.     

一种改进气象雷达测雨性能的新方法

常规气象雷达无法分离雷达反射率和雨衰减率，因此用它测雨具有一些原理上的误差。本文提出一种雷达和卫星系统反演沿地空路径降雨率分布的新方法。推导出反演沿路径雨衰减率的递推方程组。给出了实现该方法的雷达和卫星联合测雨系统，以及应用该系统测量得到沿地空路径降雨率分布的典型结果。     

Results of 11.6 GHz radiometric experiment in Kenya: second year

Three experiments were set up within a joint African radiometric propagation measurement program to provide data at frequencies above 10 GHz for predictive modelling. The authors report the results of the second year of measurements in Nairobi, Kenya, along with mean results for the two years. Significant differences are evident between the measured results and the ITU-R (formerly CCIR) rain zone and path attenuation predictions     

Measurement of Rain Induced Attenuation over a Line of Sight Link Operating at 28.75 GHz at Amritsar (INDIA)

The need of higher bandwidth systems has led the system designer to shift into higher frequency region. But working at these high frequency regions is not that easy. The paper presents results of the measurements of rain induced attenuation of a LOS link operating at 28.75 GHz at Amritsar (31°36′ N 74° 52′ E) for a single event that occurred on the 15th Nov., 2004. The results have been compared with those of ITU-R Model. It is observed that there is a significant difference between the attenuation levels measured and those predicted by using ITU-R model.     

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.     

Attenuation caused by rain at frequencies above 10 GHz

Measurements of the attenuation caused by rain have been performed on a 20 km test path at frequencies of 12, 15, 19, 29 and 39 GHz. Simultaneously the rain intensity has been measured with ten rain gauges installed along the path so that the average spacing of the rain gauges is about 2 km. For a oneyear period the results of the rain gauge network were used to determine the statistical distribution of the pointrain intensity, and the path averaged and timeaveraged rain intensities. Comparisons were made between the experimental rain attenuation and the attenuation calculated from the measured rain intensities using Miescatter theory. In nearly all cases good agreement was obtained. Using the pointrain rate distribution, the prediction method of S. H. Lin for rain attenuation statistics was tested.     

Rain attenuation statistics over terrestrial microwave link at 19.4 GHz at Amritsar

Rain induced attenuation at 19.4 GHz over a terrestrial path link of 2.29 km was measured for the period of one year (i.e. from January to December 2001) at Amritsar (31/spl deg/36' N 74/spl deg/ 52' E). An empirical model for predicting rain-induced attenuation on terrestrial line of sight microwave link has been proposed in this paper. Experimentally measured results have been compared with those obtained using international radio communication union (ITU-R). It has been observed that our results differ from those predicted using ITU-R model.     

Predicting Antenna Noise Temperature Due to Rain Clouds at Microwave and Millimeter-Wave Frequencies

Model-oriented methods to predict antenna noise temperature due to rainfall along slant paths are developed and illustrated for communication systems at Ka-band and above. The adopted Sky Noise Eddington Model (SNEM) relies on an accurate analytical solution of the radiative transfer equation and on stratiform and convective rainfall stratified structures, synthetically generated from cloud-resolving model statistics. The approach to predict antenna noise temperature is based on the multiple regression analysis, trained by SNEM-derived cloud radiative data sets, and can handle either slant-path attenuation or columnar liquid water or rain rate as input predictors. Statistical scaling with respect to frequency and zenith angle is also analyzed and modeled in the microwave and millimeter-wave range. In order to test the proposed prediction technique, measurements of the ITALSAT satellite ground-station at Pomezia (Rome, Italy) are taken into consideration for two case studies. Combined data from the ITALSAT three-beacon receiver at 18.7, 39.6, and 49.5 GHz and from a three-channel microwave radiometer at 13.0, 23.8, and 31.6 GHz are processed. Results are shown and discussed in terms of antenna noise temperature estimation by using the satellite-beacon path attenuation as predicting variable.     

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。