Rain-induced attenuation for Ku-band satellite communications in the west coast of Peninsular Malaysia, Penang

Accurate rainfall rate is important for predicting rain attenuation over a satellite link. Raindrops are able to take in, spread out, and change the polarization of satellite signals that pass through the atmosphere of the earth, especially in equatorial regions like Malaysia where heavy rainfall normally occurs. Satellite communications system network operating at Ku-Band will experience rain fade due to absorption and scattering of signal. This paper aims to discuss the range of effects of rain on the transmission of electromagnetic signal and to determine the significance of rainfall rate in the prediction of rain attenuation based on measurements carried out in the northern region of Peninsular Malaysia (Penang). At 0.01% of time, 140?mm/h and 22?dB of rain rate and attenuation were observed, respectively.     

Microwave Signal Attenuation Over Terrestrial Link at 26?GHz in Malaysia

The effect of rain on the microwave systems is more critical especially for countries located in tropical and equatorial region that experience high rainfall rate throughout the year. In order to predict a reliable and an accurate rain prediction model, it is required to determine the one-minute integration time of rainfall rate together with direct measurement of rain attenuation. In order to counter the current trend of employing higher frequencies especially in tropical and equatorial regions, there is an urgent need to carry out studies related to the effect of rain in order to get a better rain attenuation prediction model. Therefore, the purpose of this study is to investigate the effect of rain on terrestrial microwave system operating at 26?GHz in Malaysia. The rain intensity with one minute integration time is measured at Universiti Teknologi Malaysia-Skudai (UTM-Skudai) and 99 rain gauges located throughout the Peninsular Malaysia. This study explains the detailed experimental set up and analyses of both rain rate and rain attenuation measurements. The analysis on large-scale study area includes the comparisons between the measured rainfall data and the Drainage and Irrigation Department (DID) rainfall data and also with the Malaysia Meteorological Services (MMS) rainfall data. This study has successfully proposed a new rain rate and rain attenuation prediction model and the obtained results show satisfactory performance and good agreement.     

Rain attenuation model for south east asia countries

A model for predicting rain attenuation on Earth-to-space is developed by using the measured data obtained from tropical and equatorial regions that was revised from the ITU model. The proposed rain attenuation model uses the complete rainfall rate cumulative distribution as input data. It is shown that significant improvements in terms of prediction error over existing attenuation models are obtained     

A New Prediction Model of Rain Attenuation That Separately Accounts for Stratiform and Convective Rain

An improved version of the exponential cell (EXCELL) rain attenuation model is presented here. Analogously to the original one, it predicts attenuation through a cellular representation of precipitation, but, in addition, is able to discriminate between stratiform and convective rain by means of an embedded algorithm. Accordingly, two separate physical rain heights, derived from the ERA-15 database, are used to calculate stratiform and convective rain attenuation and, when considering stratiform precipitation, the melting layer contribution to attenuation is added. Eventually, the predicted cumulative distribution function (CDF) of excess attenuation is the combination of the contributions due to stratiform and convective precipitation types. Some input parameters of the prediction model, such as those defining the melting layer process or the rain plateau embedding rain cells, can be modified in order to account for the local meteorological characteristics.      

Diurnal variations in rain attenuation on Ku band earth–space paths

This paper presents analytical results of the diurnal variations in Ku band rain attenuation along earth–space paths at four locations in Southeast Asia and proposes a new model that can predict rain fade in a short period of every 2 h daily. Data from four radiometers and four rain gauges over a 3 year period were analysed to obtain the characteristics of diurnal variations in rain attenuation and rainfall as well as cumulative attenuation distributions in every 2 h interval. The results of this analysis are applied to develop an intensive prediction model using the knowledge of rainfall and attenuation statistics. This model is tested with the measured data and is found to be useful for the design of a more efficient Ku band satellite system especially between 99 per cent and 99·9 per cent link availability in an area of heavy rainfall. © 1998 John Wiley & Sons, Ltd.     

Unavailability due to rain of VSAT networks operating in Ka and Ku bands in Brazil

The unavailability due to rain of VSAT star networks operating on Ku and Ka bands in Brazil is analysed in this paper. A large number of simulations performed over the Earth–space links resulting from combinations of four (real and hypothetical) satellites with six Brazilian Earth stations provide a good characterization of the rain unavailability in tropical and equatorial regions subject to heavy rainfall and thunderstorms. The simulations also compare the influence on the estimated unavailability of the use of two different ITU‐R rain attenuation models and two values (calculated and measured) for the rainfall rate exceeded during 10^?2% of the time, the climatic parameter in the models, in addition to the link polarization employed. The results obtained point to VSAT star networks as a practical solution to provide telecommunications services to remote communities. Copyright © 2006 John Wiley & Sons, Ltd.     

Modelling attenuation by rain in tropical regions

The data in the CCIR data banks were employed for a statistical study of the relative performance of several rain attenuation prediction procedures in temperate and tropical regions. The results show that the models worked well, in general, when used for prediction at latitudes more than 30° from the equator, but, in the equatorial region, significant prediction errors were observed for all the models. Three sources of error were discovered. The most important is the use of too few rain climate zones to span the wide range of rain conditions present in the equatorial region. The second is an inadequate procedure for taking the naturally occurring vertical variations of specific attenuation into account. Finally, for the CCIR attenuation prediction model, the use of a universal shape for the cumulative distribution of path attenuation must be called into question.     

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.     

Rainfall Dynamics Over Two Indian Tropical Stations for Radio Communication

The influence of rainfall on radio wave propagation at frequencies above 10 GHz is crucial over ground to space radio links, especially in tropical regions because of the high intensity rainfall. This often makes direct-to-home; very small aperture terminal systems operating at these frequencies to be subjected to many fade occurrences due to heavy rain. In addition to annual and worst month’s cumulative statistics, dynamic characteristics of seasonal and diurnal variations, together with average event length and separation over the day are needed to give the detailed insights for system design. This paper presents the characteristics of rain distribution based on 5-year rainfall data over two locations in India. Rain intensities for the average year and the average worst months, and monthly and diurnal dynamic characteristics of rain events were obtained. The resulting rain intensities are also compared with the relevant ITU-R recommendations. These results are useful to estimate signal outages in a year over the region and for proper planning of radio-communication in the location.     

Rain attenuation at 15 and 35 GHz

In order to satisfy future earth-to-space communications needs, new regions of the electromagnetic spectrum must be exploited. A program to determine the feasibility of using millimeter waves for this application has been conducted at Air Force Cambridge Research Laboratories (AFCRL) for approximately 6 years and it has been shown that at frequencies of 15 GHz (lambda = 2.0cm) and 35 GHz (lambda = 8.6mm) atmospheric attenuation is relatively low except for conditions of heavy clouds and precipitation. A portable radiometric system designed to measure attenuation at 15 and 35 GHz under conditions of precipitation was constructed and located in Hilo, Hawaii, a region where it rains frequently thus making it possible to conduct many attenuation measurements for varying rainfall rates. Attenuation was determined from both extinction and emission measurements as a function of zenith angle and rain rate. On the basis of the results that were obtained, it is concluded that for orographic rain up to rates of 50 mm/h in Hawaii: 1) attenuations up to approximately 10 dB can be calculated quite accurately from an emission measurement; 2) zenith attenuations are well correlated with rain rate and can be estimated from the regression lines which have been obtained; 3) attenuations at angles off zenith are not as well correlated with rain rate and thus the values obtained from the regression lines are only approximate; 4) attenuations at 15 and 35 GHz are well correlated.     

降雨粒子电磁特性分析及雨区目标成像

从理论仿真的角度,描述了传输矩阵方法的基本原理,并以Ku、Ka波段为例,对降雨粒子模型的双波段散射衰减特性进行了仿真比较。从宏观角度对不同雨强、不同频率下的雨衰进行了定量分析。提出了一种针对雨区三维复杂目标进行成像仿真的技术,仿真结果表明:在Ku波段下,当雨强超过10mm/h(中雨)时,雨衰对SAR图像的影响就必须被考虑;当雨强达到50mm/h(大雨)时,SAR图像将出现十分严重的图像质量恶化。在Ka波段下,即便小雨的影响都可在SAR图像中显现;而中等以上降雨将导致SAR图像几乎或完全湮没。     

A Stochastic Dynamic Model of Rain Attenuation

A dynamic mathematical model of rain attenuation has been developed and is presented in this paper. This model permits the expression of analytic relationships between parameters commonly used to describe the properties of interest for communication. The dynamic model is based on the lognormal distribution of rain attenuation and utilizes a memoryless nonlinear device to transform attenuation and rain intensity into a one-dimensional Gaussian stationary Markov process. Hence, only one parameter is required to introduce the dynamic properties of rain attenuation into the model. Experimental results and the known properties of rain have been used to derive and to verify the model; comparative results are presented and demonstrate good correspondence. The application of the model to the statistical analysis of the performance of communications systems is illustrated in the paper. The use of a dynamic rain attenuation model is necessary in order to analyze radio communication systems with transmit power control to offset the effects of rain attenuation, and where the finite response time of the control system affects the performance. An advantage of the model is the simplicity with which it allows simulation of communication link performance under the influence of rain attenuation. Such simulations are of great interest for complex models of adaptive networks where several deteriorating effects, including finite response times, are present.     

不同类型降水对毫米波传播特性的影响研究

为了提高复杂降水条件下毫米波传播衰减的评估精度,通过分析多个地区的降水谱特征,得出具有代表性的层状云降雨、积层混合云降雨、积雨云降雨以及干雪、湿雪的谱分布参数,然后结合降水粒子的形状、相态、介电模型,计算降水体目标在毫米波波段的散射特性.结果表明,降水强度不是唯一影响毫米波传播衰减的因素; 降水粒子相态、谱分布、入射波频率和温度等对毫米波传播特性均有不同程度的影响,其中谱分布和数密度是影响降雨对毫米波衰减的主要因素; 冰水构成比例是影响降雪对毫米波衰减的主要因素; 不同相态的降水,尤其是干雪、湿雪和雨对毫米波传播影响的差异较大; 而温度的影响较小.并建立了考虑谱分布和温度的降水衰减模型.     

Adjacent satellite interference effects as applied to the outage performance of an earth- space system located in a heavy rain climatic region

Interference effects are of utmost importance to the reliable design of modern satellite communication systems operating at Ku and Ka bands. In these frequencies rain attenuation is the dominant fading mechanism particularly for Earth-space systems located in subtropical and tropical regions. On the other hand, the main propagation effect on interference between two adjacent satellite systems is considered to be the differential rain attenuation. The subject of the paper is the development of a procedure for the prediction of carrier-to-noise plus interference ratio (cnir) statistics, under the presence of rain fading conditions, applied to heavy rain climatic regions. The method is based on a model of convective raincells and the gamma distribution assumption for point rainfall rate statistics, which fits better than lognormal distribution in subtropical and tropical regions. A tropical raindrop size distribution is also adopted for the calculation of the power-law parameters of specific rain attenuation. The numerical results are concentrated on the analytical examination of various operational parameters upon the CNIR statistics and the subsequent outage performance of the system. Comparison of the proposed model with an already existing one is attempted and the necessity of the present procedure for application to locations belonging to subtropical/tropical zones becomes obvious.     

On the rain attenuation dynamics: spatial‐temporal analysis of rainfall rate and fade duration statistics

Knowledge about the dynamic characteristics of rain attenuation is of utmost importance for many applications in terrestrial and satellite communication systems operating at frequencies above 10 GHz. Long‐term rain rate statistics and rain rate duration statistics are usually available from meteorological data. In this paper, a spatial–temporal analysis is employed in order to evaluate the rain attenuation power spectrum of a terrestrial/satellite path. The predicted power spectrum is compared with experimental data. Based on the spectral analysis of rainfall rate a method for converting rain rate duration statistics to link fade duration statistics is also proposed. Fade duration statistics are presented for terrestrial and satellite links and compared with available experimental data. The agreement between the predicted results and the experimental data has been found to be quite encouraging. Finally, numerical results are presented for various climatic zones, elevation angles and frequencies. Some very useful conclusions concerning the dynamic properties of rain attenuation for a microwave path are deduced. Copyright © 2003 John Wiley & Sons, Ltd.     

The Prediction of Rain-Induced Attenuation in MM Wave Band by Rain Medium System Model

While the millimeter radio wave propagates through rainfall, it will be attenuated heavily due to assimilation and scattering of rain. It is imperative to establish a simple and effective model to predict the rain-induced attenuation. In this paper, the rainfall is taken as a random system that can attenuate the radio wave. The transfer function matrix model is selected to be the random system model. Using experiment rain attenuation data at different rain rate, the correlation entropy and residue error of the system is obtained by system identification method. On the basis of correlation entropy and residue error, we can determine the order of the predication system. At last, the predication model that can forecast heavy rain attenuation by small rain attenuation is gotten by applying the least square method. The comparison shows that the discrepancy between the predication result of the obtained model and the experiment rain attenuation data is relatively minor.     

Cell-Site Diversity Performance of LMDS Systems Operating in Heavy Rain Climatic Regions

In this paper, the potential performance advantages of ce ll-site diversity in millimeter-wave fixed cellular systems located in heavy rain climatic regions are examined. Cell-site diversity is considered an efficient technique to mitigate the aggravating effects of atmospheric propagation of radiowaves at millimeter frequency bands and, particularly, to combat rain attenuation. The paper is focused on the analytical estimation of the performance improvement of LMDS systems due to diversity reception. A physical prediction model for rain attenuation, properly modified to take into account the behaviour of the rainfall medium in tropical and subtropical areas, is the basis of the analysis. Implementations of the proposed model are presented along with an investigation of its various aspects. This work was mainly stimulated by the recent strong interest to provide technically and economically feasible solutions for broadband wireless access to the developing countries.     

11- and 18-GHz radio wave attenuation due to precipitation on a slant path

Measurements of attenuation at 11 and 18 GHz from precipitation have been made on a slant path over a three-year period in the Tokyo area using a sun tracker and a radiometer. Simultaneous rain attenuation measurements of a 2.9-km terrestrial path at 19 GHz were used to clarify the correlation characteristics between the terrestrial and the slant paths. The following results are presented: frequency, seasonal, annual, and elevation angle dependence of rain attenuation, rain rate distribution, effective distance, correlation characteristics of attenuation between slant and terrestrial paths, attenuation due to snowfall, and site diversity effect for a separation of 14.3 km at 18 GHz.     

海上云层和降水对船载高频段卫星通信的影响

介绍了海洋云层和降水的特点以及云层和降水对电波吸收的影响;描述了海洋层状雨和对流雨的降雨空间结构状态以及对高频段卫星通信雨衰的影响;分析了高频段卫星通信雨衰原因,指出了电磁波吸收、热噪声和去极化是影响高频段雨衰的重要方面,并针对海上工作环境特点提出了上行功率控制、频率分集、速率分集、自适应调制等抗雨衰方法.     

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.