Rain attenuation measurements over terrestrial microwave links operating at 15 GHz in Malaysia

This paper presents the experimental results of rain rate and rain attenuation measurements on six terrestrial microwave links in tropical Malaysia. The rain attenuation data were collected from six DIGI MINI‐LINKs (DiGi Telecommunications Sdn. Bhd., Malaysia, Shah Alam, Selangor Darul Ehsan, Malaysia) operating at 15 GHz with 99.95 % availability. The experimental results were compared with the International Telecommunication Union Radiocommunication Sector (ITU‐R) method and other existing rain attenuation prediction models. The main focus is on the ITU‐R prediction method, which underestimates the measured rain attenuation, more especially at extremely higher rain rates. The relationship between ITU‐R prediction errors and rainfall rates was studied, and it is shown that the two quantities are related by a quadratic function. The study will provide useful information on the design and planning of terrestrial radio links in Malaysia and similar tropical environments. Copyright © 2011 John Wiley & Sons, Ltd.     

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.     

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.     

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.     

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.     

Modified rain attenuation model for tropical regions for Ku‐Band signals

Attenuation measurement on Ku‐ band satellite signal in a tropical site, Fiji is presented. Rain‐attenuation prediction by ITU‐R and the Crane Global models showed noticeable deviation to the measured values. Unlike the monotonic decrease predicted by these models, exceedance of rain‐rate and attenuation in Fiji and other tropical regions showed the presence of breakpoints. For Suva, the breakpoint in rain‐rate and attenuation were at 58 mm/h and 9.4 dB with exceedances of 0.009 and 0.018%, respectively. Modifications to the ITU‐R model are proposed in this paper, for adopting it in the tropics. These modifications are based on the properties that in the tropics (i) the accumulation time factor at the breakpoints is an invariant (ii) for elevation angles <60° and at high rain rates multiple rain cells intersect the slant path. The attenuation exceedance is predicted by two expressions similar to the ITU‐R model, one for rain‐rates lower than the breakpoint rain‐rate and the other above it. The modified prediction model show remarkable agreement with the measured Ku‐band attenuation in seven tropical sites. Copyright © 2006 John Wiley & Sons, Ltd.     

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.     

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.     

视距链路的雨衰减预报模式研究

基于ITU-R的视距链路雨衰减数据库中的数据,本文提出了一种新的视距链路雨衰减的预报模式,给出了一种新的路径调整因子与不同时间概率雨衰减转换公式.与其他几种预报模式的比较表明,新模式与实验结果有更好的一致性.     

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.     

Effect of Atmospheric Parameters on Satellite Link

The rainfall path attenuation measured at Universiti Sains Malaysia (USM) for 4 years (January 02 to January 06) is presented. The data obtained are useful to investigate the impairment due to rainfall attenuation in satellite links operating in tropical and equatorial climates. It shows that the logarithmic function with ground rain rate deviates at very high rain rate. A rainfall rate of 130 mm/h causes the rainfall attenuation threshold (> 20 dB) to be exceeded. Maximum exceedences for rain rate and attenuation were observed during the wet months. The cumulative distributions of attenuation derived from the measured data are presented and compared with those obtained with existing prediction methods.     

Diversity improvement estimation from rain Radar databases using maximum likelihood estimation

This research examines route diversity as a fade mitigation technique in the presence of rain, for terrestrial microwave links. The improvement in availability due to diversity depends upon the complex spatio-temporal properties of rainfall. To produce a general model to predict the advantage due to route diversity it is necessary to be able to predict the correlation of rain attenuation on arbitrary pairs of microwave links. This is achieved by examination of a database of radar derived rain rate fields. Given a representative sample of rain field images, the joint rain attenuation statistics of arbitrary configurations of terrestrial links can be estimated. Existing rain field databases often yield very small numbers of high joint attenuation events. Consequently, estimates of the probability of joint high attenuation events derived from ratios of the number of occurrences can be highly inaccurate. This paper assumes that pairs of terrestrial microwave links have joint rain attenuation distributions that are bi-lognormally distributed. Four of the five distribution parameters can be estimated from ITU-R models. A maximum likelihood estimation (MLE) method is used to estimate the fifth parameter, i.e., the covariance or correlation. The predicted diversity statistics vary smoothly and yield plausible extrapolations into low probability situations.     

Electromagnetic Waves Attenuation due to Rain: A Prediction Model for Terrestrial or L.O.S SHF and EHF Radio Communication Links

Because of the interest raised for SHF and EHF radio communications, the attenuation of electromagnetic waves by rain will always constitute a major concern for telecommunication engineers and scientists. The rain attenuation prediction models exposed in literature calculate the attenuation related to a given rain rate or else to a given percentage of time. The new model proposed in this paper, predicts with a good accuracy the percentage of time for which any given rain attenuation will be exceeded on terrestrial SHF, EHF radiowaves links, provided the rain rate R₀₀₁ (mm/h) that represents rain rate value exceeded for 0.01% of time in the locality of interest is available. R₀₀₁ (mm/h) data being available for most of the localities across the world in ITU-R data base, we may conclude that this new model proposed here, can be broadly and successfully used.     

Short‐scale diversity in a dynamic rain fade environment

This article is concerned with using time‐varying uniformly spaced rainfall data to investigate the concept and values of instantaneous diversity gain. This has been obtained on a minute‐by‐minute basis in order to illustrate the behaviour of a VSAT communication system which switches to the most reliable link every minute. The simulations have been carried out using a whole year of rain data obtained from the recordings of a dense rain gauge network located in Barcelona. After illustrating the concept of instantaneous diversity gain, this paper shows the results obtained for various site separations and 20 GHz. These results have been plotted together with the values given by some long‐term‐based models. The comparison shows that such models are not appropriate for dynamic site diversity. This was found to increase the reliability of a VSAT system, especially under severe rain conditions in which the rainfall rates are spatially arranged in rain cells and the attenuation experienced by the two sites is strongly decorrelated. The correlation coefficient between the attenuation series calculated for several separation distances has also been obtained to illustrate this concept. Finally, the paper gives the attenuation distributions calculated for a VSAT system with and without site diversity and for several site separations. Copyright © 2005 John Wiley & Sons, Ltd.     

A novel method for the statistical prediction of rain attenuation in site diversity systems: theory and comparative testing against experimental data

Site diversity is a promising technique to overcome severe attenuation on earth–space communication links. This technique is based on the experimental evidence that intense rain cells are limited in extent, so that the replacement of one station with two or more stations separated by a few kilometres may substantially reduce the outage probability of the communication system. In this paper the physical EXCELL rain cell model, developed at our laboratory for the prediction of single-site rain attenuation statistics, has been extended to the case of diversity configuration systems. For comparison purposes, two among the best-performing models found in the literature, proposed by Hodge and Matricciani, have been considered. The values predicted by the three models have been compared against data of 41 experiments with a maximum separation distance between ground stations of 15 km, collected both from the ITU-R databank and from the open literature. This site separation range is the most interesting one, because attenuations in diversity paths tend to be uncorrelated above 20–30 km and hence the benefit obtained by a diversity scheme becomes marginal. The measured and predicted ‘relative diversity gains’ at various time percentages have been compared: the RMS values of relative gain error show that EXCELL is the best-performing model. © 1998 John Wiley & Sons, Ltd.     

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.     

A Formula for the Conversion of 5-Minute Average, 10 Minute Average Rain Rate into 1-Minute Average Rain Rate for Prediction of Rain Induced Attenuation

The attenuation of microwave signal due to rain is a well established fact now. Localized models based on the rain rate and attenuation statistics is the basic necessity for a RF communication system designer. For development of any such model, we need long term statistics. These days most of the metrological data that is available is in the form of either 5-min or 10-min average rain rate and if we want to utilize this data, we need to convert this into 1-min equivalent average rain fall. In this paper, a formula has been purposed for the conversion of 5 min and 10 min average rain rate into 1 min equivalent average rain rate.     

Probability distributions of rain attenuation obtainable with linear combining techniques in space‐to‐Earth links using time diversity

The purpose of this paper is to show how the complementary probability distribution of rain attenuation is drastically changed in the lower rain attenuation range by applying linear combining techniques, namely, equal‐gain combining and the maximal‐ratio combining, discussed in the historical paper by Brennan in 1959. These combing techniques can also be applied to the Automatic Repeat Request techniques. Defined the instantaneous processing gain and the equivalent attenuation in the 3 cases, we show examples of time series of the various parameters, based on the experimental rain attenuation time series recorded with the ITALSAT 18.7 GHz beacon, in a 37.8° slant path in Spino d'Adda (Italy). Then, we report long‐term complementary probability distribution functions of the instantaneous gain and equivalent attenuation, by simulating rain attenuation time series at 19.7 and 39.4 GHz, path elevation angle 35.5°, with the Synthetic Storm Technique, using on‐site measured rain rate time series of 10 years, by simulating the ALPHASAT link at Spino d'Adda. Similar results are also found at different frequencies and elevation angles in Tampa (Advanced Communications Technology Satellite, ACTS result test), the Isle of Guam, and Prague. The main conclusions are as follows: (1) As expected, the instantaneous time diversity gain can be large when the delay time is large and rain attenuation is large; (2) scintillation affects time diversity links as the direct links; (3) equal‐gain and maximal‐ratio combining can add up to 3 dB to the selection diversity gain when the time diversity gain is very small; and (4) equal‐gain and maximal‐ratio combining reduce the fraction of time of rain attenuation in an average year to a value less than the probability of exceeding 3 dB in the link without diversity.