Rain Attenuation Statistics Research Articles

Experimental rain attenuation statistics estimated from radar measurements useful to design satellite communication systems for mobile terminals

Based on experimental data, we have reported a reliable method to scale the cumulative time T/sub F,T/(A) that rain attenuation A (dB) is exceeded in a fixed satellite system to the time T/sub M,T/(A) that it is exceeded in a satellite system for mobile terminals. Zigzag routes and ring-roads simulated city patterns; straight routes simulated freeways. In all cases, T/sub M,T/(A) can be expressed as T/sub M,T/(A)=/spl xi/T/sub F,T/ (A) with a probability scaling factor /spl xi/ independent of A. The simulations have been made at 19.77 GHz with satellite elevation angle /spl theta/ of 30.6/spl deg/, 45/spl deg/, 60/spl deg/, 80/spl deg/, and 90/spl deg/. For the horizontal structure of rain, we have used a very large number of rain-rate maps of rain storms randomly observed in 1989-1992 by a meteorological radar placed at Spine d'Adda (northern Italy). The vehicle speed was modeled as a log-normal random variable. We found: (a) in zigzag routes, T/sub M,T/(A)<T/sub F,T/(A), i.e., /spl xi/<1, with results depending on vehicle speed modeling and starting conditions; (b) in a ring-road, there is no difference between fixed and mobile systems (/spl xi/=1); and (c) in straight freeways, T/sub M,T/(A)/spl Lt/T/sub F,T/(A)(/spl xi//spl Lt/1); T/sub M,T/(A) can change significantly in different straight lines and in opposite directions (anisotropy and asymmetry) for medium-large attenuation. When compared to zigzag routes or ring-roads, the performance in straight freeways is the most optimistic. For /spl theta/>30.6/spl deg/ and for the same pattern, /spl xi/ is fairly independent of /spl theta/. Since the radar rain maps are a reliable estimate of the horizontal structure of rain, the findings, which can be considered frequency-independent, stand as a very good prediction of the results obtainable by experiments.

Differential Rain Attenuation Statistics Including an Accurate Estimation of the Effective Slant Path Lengths - Abstract

The differential rain attenuation is considered to be one of the main propagation factors causing interference between adjacent Earth-Space paths. In the present paper, an existing method to predict the differential rain attenuation statistics is properly modified to include a more complicated but accurate estimation of the slant path lengths affected by the rain medium. The modified method is oriented to be generally applicable, particularly in the case of satellite paths operating under low elevation angles in the Ku-band, where the accurate estimation of the effective slant path lengths is very critical. The present results are compared with a set of available simulated data for the differential attenuation over pairs of paths located in Montreal. The influence of various other parameters such as the geographic latitude and climatic zone is also examined.

A Global Method for the Prediction of the Slant Path Rain Attenuation Statistics

A method for the prediction of the slant path rain attenuation statistics is proposed, based on the Weibull distribution for the representation of the point rainfall rate statistics. The inhomogeneity of the rainfall medium is described by means of the spatial autocorrelation function. Numerical results derived by using the proposed model have been compared with available experimental data taken from the most recent ITU-R database. Comparison is also made with another prediction method recommended by the International Radio Consultative Committee and some useful conclusions are deduced. More particularly, the present method has been found to give improved results for the higher percentages of time. On the other hand, the CCIR method is superior for the lowest levels (0.003% and 0.001%) .

Analysis of the interference due to differential rain attenuation induced by an adjacent path on a double‐site diversity system using frequency reuse

One of the main propagation effects on interference between adjacent Earth‐space paths is considered to be the differential rain attenuation. In the present paper a method to predict differential rain attenuation statistics, valid for single‐site communication systems, is extended to include double‐site interfered systems operating under the dual‐polarization mode. The extended procedure is again based on a model of convective rain cells as well on the lognormal model for point rainfall rate statistics. Numerical results are presented referring to realistic diversity systems operating under the hypothesis of using both single and dual polarization and suffering from differential rain attenuation. Some very useful conclusions are deduced on the reliable and economic design of future communication systems where orbital and frequency congestion are quite expectable.

Availability and performance of satellite links suffering from interference by an adjacent satellite and rain fades

An analysis is presented relating rain attenuation statistics to BEP performance of Earth-space links subjected to interference by an adjacent satellite operating in the same frequency band. A systematic design method is proposed that takes into account the BER objectives specified by the ITU for the design of satellite links. Numerical results based on the proposed method have been obtained to investigate the combined effect of rain and interference for the Ku and Ka bands and for various data rates and climatic zones.

Rain attenuation statistics useful for the design of mobile satellite communication systems

We have investigated how rain attenuation statistics, necessary to design fixed satellite systems working at frequencies greater than 10 GHz, are transformed to those applicable to the design of mobile satellite systems working in the same frequency bands and weather conditions in the special case of vehicles driven in zig-zag patterns to simulate city streets. The vehicles' speed has been modeled as a lognormal random variable, a mathematical model derived from measurements performed in freeways or in city traffic. We have used a large number of rain-rate time series collected in Italy (Gera Lario and Fucino) and in Canada (Montreal) to simulate rain-rate spatial fields and radio links at 19.77 GHz along a 30.6/spl deg/ slant path. The simulations have shown that a receiving or transmitting terminal moving in zig-zag patterns may experience, in the long term and for a given attenuation, a smaller outage probability, compared to the fixed terminal. For a given rain attenuation, the ratio between the outage probability of the mobile system and that of the fixed system (probability extrapolation factor /spl xi/) is estimated to be around 0.2-0.3 in the optimistic case in which the probability of encountering rain is the same for all observers (fixed or in motion)-a less optimistic estimate shows that the probability of encountering rain might be twice as large and that, as a consequence, the values of /spl xi/ mentioned must be doubled. Conservative values of /spl xi/ can be calculated by using average values of rain storm speed and vehicles and average distances covered in the rain by fixed and mobile terminals. The results are less sensitive to changes in the geometrical or other parameters of the simulations.

ITALSAT propagation experiment at 18.7, 39.6 and 49.5 GHz at Spino D'Adda: three years of CPA statistics

The ITALSAT propagation experiment, started in early 1991, allows an extensive program of measurements at 18.7, 39.6, and 49.5 GHz. This paper reports the results obtained so far from copolar signal measurements carried out at the Earth station of Spine d'Adda from 1993 to 1995. Statistics of rain and total attenuation and frequency scaling of total attenuation are presented and commented on in the light of ITU-R predictions.

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.

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.

Results of 11.6 GHz radiometric measurements inNew Zealand

The statistics of Ku-band rain attenuation and rainfall measurements for one year are presented. They were measured in Auckland, New Zealand. The rainfall statistics are accurately described by the ITU-R&apos;s ‘H’ zone rain profile. The ITU-R attenuation prediction model appears to significantly overestimate total attenuation statistics.

Some rain rate and rain attenuation statistics at millimeter wavelengths in the tropics

A study of rain rate and rain induced attenuation characteristics over two tropical stations in India has been made. The observed rain rate distributions differ significantly when compared with the CCIR report. The refractive indices have been calculated for certain frequencies at a tropical rain temperature of 20°C showing the variational pattern at different millimeter wavelengths. The present analysis also reveals that in the range 0.05 cm–0.3 cm drop diameter the variations of scattering amplitudes are systematic while in the range 0.4 cm–0.6 cm they are irregular.

Transformation of rain attenuation statistics from fixed to mobile satellite communication systems

We have proposed and discussed a method to transform rain attenuation probability distributions from fixed to mobile satellite communication systems. For a given outage probability, the power margin needed in the mobile system may be larger or smaller than that in the fixed system, depending on the speed of the vehicle relative to that of the rain storm. Simulations performed using experimental information on vehicle and rain storm speeds show that the probability distribution of the mobile system can be obtained from that of the fixed system, by multiplication of a factor which approximately varies between 0.5 and 2.0, independent of attenuation. The first is a realistic value obtained by averaging over all the possible directions of arrival of vehicles.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Worst month statistics of rain attenuation overan LOS microwave link at 11 GHz

The worst month statistics of rainfall rate and rain attenuation at 11 GHz are studied for the Assam valley, situated in the world&apos;s highest rainfall zone, using an LOS (3.2 km) microwave link of the P&amp;T Department, Government of India. The relation between the worst month and yearly probabilities of these parameters is presented. The observed relation is verified in the light of the Crane-Debrunner and Brussaard-Watson semi-empirical models. A comparative study on this aspect, with the results published from Japan, is given.

Model for the prediction of the differential rain attenuation between a terrestrial line‐of‐sight radio relay system and a low‐angle satellite path based on the two‐dimensional lognormal distribution

The main propagation effect on interference of a terrestrial line‐of‐sight radio relay system from a low‐angle satellite path is the differential rain attenuation. In the present paper, a predictive method for the differential rain attenuation statistics is proposed which is based on a modified model convective raincell structure by taking into account the conventional limits of the raincell size. The assumption that the point rainfall statistics follows a lognormal form is also adopted. The results of the predictive procedure are applied to a particular problem of terrestrial line‐of‐sight system interference from a low‐angle broadcasting satellite service in the 22.5–23 GHz band. The sensitivity of the various parameters affecting the differential attenuation is also examined. As a general remark, the conditional differential rain probability is found to be significantly dependent upon the rainfall characteristics of the climatic zone and the parameters of the spatial rainfall structure. Finally, a comparison of the present predictive procedure with a semiempirical developed model is treated and gives a quite reasonable agreement.

A model for the prediction of the differential rain attenuation between a satellite path and an adjacent terrestrial microwave system based on the two-dimensional gamma distribution

The main propagation effect on interference between a satellite system and an adjacent terrestrial path is considered to be the differential rain attenuation. In the present paper, a predictive method for the differential rain attenuation statistics is presented based on a convective raincell model and the assumption that the point rainfall statistics follows a gamma form. This is valid for various climatic zones of the world, such as J, M, N, P, Q zones. The results of the predictive procedure are compared with the only available set of experimental data taken from Yokosuka, Japan. The sensitivity of various parameters affecting the differential attenuation statistics is also examined.

Rain attenuation measurements: Variability and data quality assessment

Year‐to‐year variations in the cumulative distributions of rain rate or rain attenuation are evident in any of the published measurements for a single propagation path which span a period of several years of observation. These variations must be described by models for the prediction of rain attenuation statistics. Now that a large measurement data base has been assembled by the International Radio Consultative Committee (CCIR), the information needed to assess variability is available. On the basis of 317 sample cumulative distribution functions (cdf's) for the occurrence of attenuation by rain, the expected year‐to‐year variation in attenuation at a fixed probability level in the 0.001–1.0% of a year range is estimated to be 26%. The expected deviation from the predictions of any of the better attenuation models for a single year of observations is estimated to exceed 34% when a rain climate model is employed to estimate the rain rate cdf. The probability distribution for the variation in attenuation or rain rate at a fixed probability level is lognormal. The lognormal behavior of the deviations was used to compile statistics for variability, to establish hypothesis tests for identifying outliers—the observed sample cdf that deviates significantly from the expected (modeled) cdf, and to predict the attenuation level to be exceeded with a specified return period.

Prediction of rain attenuation statistics for satellite communications in the 10–45 GHz range in Canada

Presents a means of predicting rain attenuation for a 20/44 GHz SATCOM system for Canada. Rain attenuation statistics have been estimated, but not verified experimentally, for most of the Canadian territory below 69°N latitude for a geostationary SATCOM system in the 10-45 GHz range with arbitrary link parameters. The effect of site diversity on these results can be estimated. Long-term experimental rain data, the International Radio Consultative Committee (CCIR) rain attenuation prediction model and the Hodge (1982) site diversity model have been used for this purpose in the present work. The results are given in various formats to facilitate system design. This study indicates that although rain attenuation is high in this frequency range, it remains within manageable limits.

New concept used to predict slant path rain attenuation statistics

A new model for use in predicting rain attenuation from rain rate statistics has been developed based on the concept of moving rain cells with limited extension. Relevant CCIR information has been used for the necessary parameters. Results measured from 53 satellite paths were used to evaluate the prediction accuracy. The median value of the prediction error found to be +0.5 dB with a 1-sigma value of 1.0 dB for attenuation values in the range 0-10 dB. No significant variation in the prediction accuracy has been found for satellite paths in Europe, North America or East Asia, for frequencies in the range 10-20 GHz or elevation angles in the range 10-60 degrees. >

A two‐component rain model for the prediction of site diversity performance

A two‐component rain attenuation model is presented for the prediction of single‐ and joint‐(diversity) path rain attenuation statistics and for the prediction of the relative measures of diversity performance, diversity gain, and diversity improvement factor (or advantage). The model is based entirely on the use of geophysical parameters for the prediction of the effects of rain. It contains no free parameters to adjust to fit the available attenuation observations. The model is general and will handle both balanced and unbalanced diversity system design for terrestrial and satellite communication systems. Model performance was evaluated by comparison with published single‐path and site diversity observations. The model performs well when tested against the International Radio Consultative Committee (CCIR) site diversity data base, providing predictions of the single‐path attenuation values exceeded for specified percentages of a year with a root‐mean‐square difference (RMSD) from the observed values of 49% and providing predictions of the minimum attenuation value simultaneously exceeded on two links for specified percentages of a year with a RMSD of 59%.

Prediction method for the rain attenuation statistics based on a global rainfall-rate distribution model

A method for the prediction of the rain attenuation statistics is proposed, based on a global rainfall rate distribution model. This method also employs the spatial autocorrelation function to describe the inhomogeneity of the rainfall medium. A comparison with a prediction method recently proposed by the International Radio Consultative Committee and an other recent model is made, which shows that our model provides better results.