Rain attenuation prediction during rain events in different climatic regions

https://doi.org/10.1016/j.jastp.2015.03.003Get rights and content

Highlights

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    Development of channel model to predict time series of rain attenuation.

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    Validity of time series prediction method for different locations over the world.

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    Model parameters for one tropical location can be used for other tropical locations.

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    Separate model parameters are derived for temperate regions for better prediction.

Abstract

A rain attenuation prediction method has been applied to different climatic regions to test the validity of the model. The significant difference in rain rate and attenuation statistics for the tropical and temperate region needs to be considered in developing channel model to predict time series of rain attenuation for earth space communication links. Model parameters obtained for a tropical location has been successfully applied to predict time series of rain attenuation at other tropical locations. Separate model parameters are derived from the experimental data obtained at a temperate location and these are used to predict rain attenuation during rain events for other temperate locations showing the effectiveness of the technique.

Introduction

Due to the congestion at the lower frequency bands, the satellite communication systems are now operating at the higher frequency Ku or Ka bands (Ku or Ka). However in these bands, mainly above 10 GHz, rain events cause severe attenuation to the propagating signal along earth space communication link. If time series prediction of rain attenuation during rain events is possible, fade countermeasure techniques such as adaptive control of signal power, coding and data rate can be effectively implemented to mitigate this attenuation effect. Channel models in the form of time series generators of rain rate and attenuation have been developed previously (Alassur et al., 2004, Fontan et al., 2007, Heder and Bito, 2008, Carrie et al., 2009, Lemorton et al., 2007). So far, they have not been used to predict rain attenuation or rain rate during rain events at different points of time. There exist various short term rain attenuation prediction methods (Castanet, 2001, Gremont, 1997, Van de Kamp, 2002, Montera et al., 2008, Bolea-Alamanac et al., 2003), all of which predict a single attenuation value a short time before the actual occurrence, but not the time series of attenuation values for the entire rain event. The above mentioned models are validated on long term basis and not on event by event basis. In the present study, a channel model has been developed to predict time series of rain attenuation during the entire rain event.

This model is not only tested on long term basis but also event wise. In our earlier paper (Das and Maitra, 2012, Das and Maitra, 2012), the same method has been discussed for rain attenuation and rain rate prediction for experimental data obtained at Kolkata, a tropical location. However, the effectiveness of the methodology needs to be tested for any locations in the globe. In this paper, rain rate and attenuation statistics obtained at tropical and temperate regions are compared. From the measured data set, model parameters are developed separately for tropical and temperate regions which are being used to predict the time series of rain attenuation for both the regions.

Section snippets

Comparision between tropical and temperate region

Data sets from different sites in tropical region as well as in temperate region are taken to check the validity of our model. The details of the measurement links are given in (Maitra et al., 2007, Chakravarty and Mitra, 2010, Adhikari et al., 2011, Riva, 2004, Propagation data and prediction methods required for the design of Earth-space telecommunication systems, 2009, Sánchez-Lago et al., 2007) and also in Table 1 in a short form. To get proper comparison of attenuation statistics, for

Rain attenuation predictor

The measured attenuation values are divided into three segments namely, constant (C), down (D) and up (U) segment according to the following criteriaΔkTs=Cconstantif|akTs–ak−1Ts|≤1dBDdownifakTs–ak−1Ts<−1dBUupifakTs–a(k−1)Ts>1dB

where a(kTs) is the attenuation sample measured at the instant kTs, k=1,2,3, …., Ts is the time interval between two consecutive samples.

The distributions of conditional occurrence that if at an instant the attenuation is x dB then the attenuation will be y dB after Ts

Conclusion

The comparison of measured rain rate and attenuation statistics obtained from tropical and temperate regions indicates the difference in rain characteristics of the two regions. The method to predict the rain attenuation values during rain events has been applied to different regions. Models of μ and σ of conditional distributions of rain attenuation developed for a tropical location, Kolkata is successfully applied to predict rain attenuation series for other tropical locations. However these

Acknowledgements

This work has been supported by the grants from the Indian Space Research Organization ISRO under the project “Integrated studies of water vapor, liquid water content and rain of the tropical atmosphere and their effects on radio environment”. We wish to acknowledge Carlo Riva for supplying data of Spino d’ Adda and also for giving the opportunity to access ITU-R data bank. We also thank F.P. Fontan for giving attenuation data of Oberpfaffenhofen.

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