Rain induced attenuation prediction model for terrestrial and satellite-Earth microwave links

At microwave frequencies, rain is the main cause of degradation of the performances of satellite and terrestrial communications systems, essentially in tropical zones. The design and implementation of such systems involve the knowledge of the propagation parameters which govern link availability and service quality. Thus it seems desirable to develop prediction methods for deriving approximate attenuation statistics for any microwave link. In this paper, a rain induced attenuation model using the concept of equivalent path length is proposed for terrestrial and satellite links. As far as slant paths are concerned, the proposed prediction model uses a parameter, the value of which depends on the geographical zone. These values are given for zones where data are available : Europe, Australia, USA, Japan. The version of the model proposed for Australia (in its tropical part) can be extended to all other tropical zones of the world.     

Improvement of a rain attenuation prediction method for terrestrial microwave links

An empirical model for predicting rain induced attenuation on terrestrial paths using effective path length is proposed. Comparison with the recently prediction method proposed by the International Radio Consultative Committee (CCIR) is made. It appears that our prediction method reveals good agreement with experimental data from different locations in the world.     

A new theoretical formulation for calculation of the specific attenuation due to precipitation particles on terrestrial and satellite radio links

The propagation of high frequency electromagnetic waves through rain is affected by absorption and scattering, which both lead to signal attenuation on satellite or terrestrial super high frequency (SHF) and extremely high frequency (EHF) links. Many factors govern rain effects on waves propagating in the atmosphere, namely raindrop size distribution, rain cumulative distribution, water temperature, refractive index and operating frequency. A high degree of accuracy in the calculation of specific attenuation caused by rain (attenuation per km) is of importance when planning high frequency radio communication systems. Until now, the kR^α expression has been widely used for such calculations. This relationship in which R (mm/h) represents the rain rate, α and k parameters determined for each frequency by interpolation, can be considered to be a compromise between the complexity and a simplified approach of the Van de Hulst relationship. In this paper, we present a new theoretical model based on physical laws and allowing the calculation of specific attenuation caused by all kinds of hydrometeor particles on high frequency electromagnetic waves. This method, which we derived from the forward scattering amplitude and the Van de Hulst relationship, is governed by wave polarization, the wave incidence angle, the radio link operating frequency, and precipitation particle size distribution in the climate of interest. Its application gives theoretical results which are in very good agreement with data gathered on terrestrial or earth–satellite links in several localities around the world. This new proposed model can be easily used and will constitute a very useful tool for evaluating satellite and terrestrial radio link performances, mainly in the future which will bring an expansion of high frequency satellite systems. © 1997 John Wiley & Sons, Ltd.     

Raindrop size distribution from microwave scattering measurements in equatorial and tropical climates

A raindrop size time averaged distribution is inferred from an indirect method by using measurements of attenuation due to rain in Congo (equatorial and tropical climates). Attenuations calculated from this distribution are compared with experimental data gathered on the Ivory Coast (tropical climate) at a different frequency.     

Rainfall rate characteristics for microwave systems in tropical and equatorial areas

The wave propagation at frequencies from about 10 GHz can suffer rain effects such as attenuation, scattering and depolarization. The magnitude of these effects depends on rain characteristics. This paper presents results of the propagation experiments undertaken in Douala (Cameroon) and in Brazzaville (Congo) under the auspices of the ITU (Geneva) with the collaboration of CNET (France Telecom). Data based on five months measurements of rain rates in Douala with a network of four rain-gauges are presented with reference also to some results of a propagation campaign in Brazzaville. The rain measurement period in Douala includes all of the rainy season. The measurement data are used to investigate the rain effect characteristics of the low latitude tropical regions of Africa and are discussed in relation to the influence of rain on microwave system performances in the region.     

Theoretical model for calculating rain-induced crosspolarisation

A mathematical model for calculating rain-induced depolarisation on microwave links is described. It is carried out by using a Gaussian distribution of canting angle and use both mean and standard deviation of each drop-size canting angle.     

Empirical model for rainfall rate distribution

An empirical but theoretically sound law derived from rainfall measurements obtained in the Congo (tropical and equatorial climates), and which provides a good fit of rainfall rate distributions observed in various hydrometeorological zones of the world, is presented. This rainfall rate distribution model is compared with the gamma and log-normal ones.     

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.