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Satellite communication systems operating at Ku (12/14 GHz) and Ka band (20/30 GHz) frequencies are used for broadband multimedia and internet based services. At these frequencies, the signal will be affected by various propagation impairments such as rain attenuation, cloud attenuation, tropospheric scintillation, ionospheric scintillation, water vapour attenuation, and rain and ice depolarization. Among all the propagation impairments, rain attenuation is the most important and critical parameter. In this paper, rain attenuation is calculated at KL University, Guntur using ITU-R rain attenuation model. The preliminary results of the work will be used to calculate the attenuation experimentally and comparison can be made, which helps to develop a new rain attenuation model at Ku and Ka bands.
ACEEE Int. J. on Communications, Vol. 03, No. 03, Nov 2012 Estimation of Rain Attenuation based on ITU-R Model in Guntur (A.P), India M. Sridhar1,K. Padma Raju2, and Ch. Srinivasa Rao3 1 Department of ECE, KL University, Guntur, India Email: sridhar.m@kluniversity.in 2 Department of ECE, JNTU Kakinada, Kakinada, India Email: padmaraju_k@yahoo.com 3 Department of ECE, Sri SaiAditya Institute of Science & Technology, Surampalem, India Email: ch_rao@rediffmail.com Abstract — Satellite communication systems operating at Ku maximum attenuation and therefore, is the limiting factor in (12/14 GHz) and Ka band (20/30 GHz) frequencies are used Ku and Ka band satellite link design [3]. for broadband multimedia and internet based services. At these The rain drops absorb most of the electromagnetic energy at frequencies, the signal will be affected by various propagation these frequency ranges and some of the energy gets scattered impairments such as rain attenuation, cloud attenuation, by Rayleigh and Mie scattering mechanisms [4]. The rain tropospheric scintillation, ionospheric scintillation, water drop size distribution is exponential when expressed vapour attenuation, and rain and ice depolarization. Among all the propagation impairments, rain attenuation is the most mathematically as, ( D ) important and critical parameter. In this paper, rain N ( D ) N 0 e Dm mm-1m-3 (1) attenuation is calculated at KL University, Guntur using where Dm is the median drop diameter and N(D)dD is the ITU-R rain attenuation model. The preliminary results of the number of drops per cubic meter with diameters between D work will be used to calculate the attenuation experimentally and D + dD mm [5]. The rainfall rate R is related to N (D) and and comparison can be made, which helps to develop a new also to the terminal velocity of V (D) the falling drops in rain attenuation model at Ku and Ka bands. meters per second with diameter D by Index Terms — satellite communication, propagation R 0.6 10 3 D 3V ( D ) N ( D ) dD mm/hr (2) impairments, rain attenuation, ITU-R model, rain fall rate A. Rain Attenuation Prediction Models The amount of fading due to rain is a function of the I. INTRODUCTION frequency and is highly correlated with rain rate. By using Communications system design requires the development rain statistics for a given region, it is possible to determine of a link budget between the transmitter and the receiver that the probability that a given fade depth will be exceeded. The provides an adequate signal level at the receiver ’s rain availabilityof a communication link is the complement of demodulator to achieve the required level of performance the probability of the link fade margin being exceeded [6]. and availability [1]. The performance and availability of the Rain fade mitigation techniques like power control, signal link can be specified or measured using Bit Error Rate (BER) processing and site diversity methods are used to improve and Carrier-to-Noise ratio (C/N). It is the link designer’s task the performance of link design and this requires proper to ensure that loss of signal occurs for no longer than the prediction of attenuation due to rain [7]. There are two time permitted for that service. The development of an approaches to predict the rain attenuation namely, a physical accurate link budget, which includes losses due to the method in which rain is described all the way along the path, passage of the signal through the atmosphere, is critical. and an empirical method which uses the effective path length There are many phenomena that lead to signal loss on and rainfall rate using the information from various data bases transmission through the earth’s atmosphere. These include: [8]. Various rain attenuation prediction models are available cloud attenuation, tropospheric scintillation, ionospheric based on the geographical and climatic conditions. The Scintillation, Water vapour attenuation, rain and ice important models are Crane global model [9], Two-component depolarization, and rain attenuation [2].Among all the model [10], Simple Attenuation model (SAM), Excell model, propagation impairments, rain attenuation is the most MismeWaldteufel model, Garcia model [1], International important for frequencies above 10 GHz, as it causes Telecommunication Union Radio Communication sector M. Sridhar is with KL University, Guntur, Andhra Pradesh, India (ITU-R) model [2], Bryant model, Dissanayake, Allnutt and (email: sridhar.m@kluniversity.in). Haidara (DAH) model [11], and Moupfouma model [12]. Dr. K. Padma Raju is presently working as Principal, University Among these models, ITU-R model provides the most College of Engineering, JNTU Kakinada, Kakinada, Andhra Pradesh, accurate statistical estimate of attenuation on slant paths [2]. India (email: padmaraju_k@yahoo.com). Dr. Ch. Srinivasa Rao is working as Principal, Sri Sai Aditya Insti- B. ITU-R P. 618 - 9 Rain Attenuation Model tute of Science & Techology, Surampalem, Andhra Pradesh, India The ITU Radio communication Sector (ITU-R) is one (email:ch_rao@rediffmail.com). © 2012 ACEEE 6 DOI: 01.IJCOM.3.3. 4 ACEEE Int. J. on Communications, Vol. 03, No. 03, Nov 2012 among the three divisions of the International manner [15]: Telecommunication Union (ITU) which is responsible Step 1. Calculate the rain height h R(Km)from the for radio communication. It manages the international radio- recommendation ITU-R P.839 as frequency spectrum and satellite orbit resources and also enhances standards for radio communication systems with hR h0 0.36 Km (3) the objective of ensuring the effective use of the spectrum. where h 0is the 0° C isotherm height above mean sea level at The ITU-R provides global rain statistics by dividing the the desired location [16]. earth into rain regions and assigning a rain rate to each region along with the probability of that rain rate being exceeded [6]. This model uses the rain rate at 0.01% probability level for the estimation of attenuation and then applies an adjustment factor to the predicted rain fade depth for other probabilities. It can be used for the frequencies from 4 - 55 GHz and 0.001 - 5% percentage probability range. It is based on log-normal distribution and both rain intensity and path attenuation distribution conform to the same log-normal distribution. Inhomogeneity in rain in both horizontal and vertical directions is considered in the prediction [13]. Figure 1. Schematic presentation of an earth-space path II. METHOD FOR E STIMATION OF RAIN ATTENUATION A: Frozen precipitation The proposed experimental setup is at KL University, B: Rain Height Guntur which is located 29.08 m above sea level. The latitude C: Liquid precipitation D: Earth-Space path and longitude of the location are 16.46' N and 80.54' E respectively. Two DTH receivers operating in Ku band is Step 2. Determine the slant-path length L s , below the rain installed in the location which receives the signal from NSS6 height from satellite ( 95 E). A disdrometer can be used to measure and ( h hs ) Ls R Km if 5 (4) record the rainfall intensity (mm/hr) with 1-min integration sin where is Elevation angle in degrees,h s is the height of the time which also specifies rain drop size. The satellite signal location above sea level in Km, and h Ris the rain height in Km. strength will be measured using a spectrum analyzer and the Step 3. Obtain the horizontal projection, LG , of the slant path information can be recorded with a data logger. The rainfall length from rate exceeding 0.01% of an average year in mm/hr for the location is calculated using Recommendation ITU-R P. 837-5 LG Ls cos Km (5) which requires the coordinates of the location. The input Step 4. Determine the rainfall rate, R0.01 ,exceeded for 0.01% parameters requiredto this model are: point rainfall rate for of an average year, with 1-min integration time. It can be 0.01% of an average year (mm/hr) with 1-min integration time, calculated with the help of statistical data available in various height of the location above mean sea level (Km), elevation meteorological databases or from the maps provided by angle of the receiver (degrees), latitude of the location ITU-R P.837. (degrees), frequency (GHz), polarization angle (degrees), and Step 5. Calculate the specific attenuation, R , by using the effective radius of the Earth (Km) [14]. Table I gives the frequency dependent regression coefficients provided in geographical and experimental parameters for the experimental ITU-R P.838 Recommendation and R0.01 using [17], site. TABLE I. GEOGRAPHICAL/EXPERIMENTAL PARAMETERS FOR THE LOCATION R k ( R0.01 ) dB/Km (6) Latitude 160.46’N where k and depend on frequency, polarization, raindrop size distribution and temperature and obtained using, Longitude 80 0.54’E k H kV ( k H kV ) cos 2 cos(2 t ) Height Above Sea Level 0.029 Km k (7) 2 Elevation Angle 64.5 0 k H H kV V ( k H H kV V ) cos 2 cos(2t ) (8) Polarization Angle 40.4 0 2k A. Calculation of Attenuation based on ITU-R Model where t is the polarization tilt angle relative to horizontal. Fig. 1 shows the schematic representation of earth –space Step 6. Determine the horizontal path adjustment factor, r0.01 path link and the details of the parameters used in the model. for 0.01% of the time using Based on the geographical conditions and measured rainfall r0 .0 1 1 using the disdrometer, the rain attenuation can be calculated LG R (9) 1 0 .7 8 0 .3 8 1 e 2 L G using ITU-R P. 618 - 9 model in the following f © 2012 ACEEE 7 DOI: 01.IJCOM.3.3. 4 ACEEE Int. J. on Communications, Vol. 03, No. 03, Nov 2012 where f is the frequency in GHz. TABLE II.VARIATION OF RAINFALL RATE AND ATTENUATION WITH RESPECT TO % Step 7. Calculate the adjusted rainy path length, L R (Km), TIME EXCEEDED % Time Rainfall Rate Attenuation through rain using exceeded (mm/hr) (dB) L r (10) L R G 0 .0 1 fo r co s 0.001% 115.89 25.28 ( hR hS ) (11) 0.01% 62.83 12.47 LS for where sin 0.1% 17.32 2.03 1 hR hS tan (12) 1% 1.96 0.11 LG r0.01 Step 8. Obtain the vertical reduction factor v0.01 , 5% 0 0 for 0.01% of the time by using integration time. The obtained rainfall rate with different % 1 (13) v 0.01 time exceedence of average year will be compared and studied LR R 1 sin 31(1 e /1 ) 0.45 with practical rainfall rates measured with disdrometer f2 arrangement as a next step in the research work. where 36 , for 36 (14) 0, for 36 (15) Step 9. Determine the effective path length through rain, L E (Km), given by LE LR v0.01 (16) Step 10. Calculate the predicted attenuation exceeded for 0.01% of an average year by using A0.01 R LE dB (17) Step 11. The estimated attenuation to be exceeded for the other percentages of an average year, in the range 0.001% to 10% may then be estimated using A0.01 as p 0.65 5 0 .03 ln ( p ) 0.04 5 ln ( A0.01 ) sin (1 p ) A p A0.01 ( ) 0.01 (18) where p is the percentage probability of interest and is given by Figure. 2.Variations of rainfall rate (mm/hr) with respect for p 1%, 0 (19) to % time exceeded if 36 (20) for p 1%, 0 The attenuation of the signal is obtained at 11 GHz frequency, using ITU-R P. 838 - 1 Recommendation for different rainfall 0.005( 36) for 25 and 36 (21) rates. It is evident from Fig. 3 that the attenuation increases 0.005( 36) 1.8 4.25 sin , (22) with rainfall rate. The theoretical results will be used to study for 25 and 36 and compare the amount of attenuation introduced practically in the extended future research work. III. RESULTS AND DISCUSSION The theoretical values for rain attenuation are calculated for different rainfall rates using ITU-R model at KL University. The DTH receiver installed in the site operates in Ku band whose elevation angle is 64.50 . The rainfall rates are calculated based on the geographical latitude and longitude, and will be used to measure attenuation at different frequencies [15]. Table II gives the variation of rainfall rate and attenuation with respect to % time exceeded of an average year at 11 GHz. The rainfall rate is calculated using the ITU-R P. 837 - 5 Recommendation and the variation of the rainfall rate (mm/hr) is as shown in Fig. 2, for different exceedence percentages. At 11 GHz operating frequency, it can be observed that the maximum rainfall rate is 115.89 mm/hr at 0.001% time of an average year. The rainfall rate is 62.83 mm/ Figure. 3. Variation of attenuation with respect to rainfall rate hr exceeded for 0.01% of an average year, with 1-min The attenuation is calculated for frequencies from 1 GHz to © 2012 ACEEE 8 DOI: 01.IJCOM.3.3. 4 ACEEE Int. J. on Communications, Vol. 03, No. 03, Nov 2012 15 GHz with a rainfall rate 0.01 62.83 mm/hr using ITU- R rain attenuation is the predominant. In this paper, ITU-R model R model. With an increase in frequency, there is a significant is used to predict the rainfall rate and attenuation due to rain, increase in the attenuation as shown in Fig. 4. The attenuation at KL University, Guntur. The attenuation is calculated, for is 0.00814 dB at 1 GHz frequency and 21.39 dB at 15 GHz. different rainfall rates and exceedence percentages of an average year. The preliminary results indicate that the attenuation increases with frequency and rainfall rate. These predicted values can be compared with the measured experimental data after installation of the setup in the location. ACKNOWLEDGMENTS The authors wish to thank Dr. K. Sarat Kumar, Associate Dean, Sponsored Research and Dr. D. Venkata Ratnam, KL University for their valuable suggestions. This work was supported in part by a grant from Department of Science and Technology, New Delhi, India. REFERENCES [1] Pratt, T., C. W. Bostian, and J. E. Alnutt, “Satellite Figure.4. Rain Attenuation Variation with Frequency at Rainfall Communication”, John Wiley and Sons, 2003,536 pp. Rate R0.01 62.83 mm/hr [2] Cost Action 255 Final Report, “Radiowave Propagation The rain attenuation is calculated for 0.001% to 5% Modelling for SatCom Services at Ku-Band and Above”, ESA exceedence percentages of an average year as shown in Publications Division, Noordwijk, The Netherlands, 2002. Fig. 5. The attenuation is 25.28 dB with 0.001% and 0 dB [3] K. P. Liolis, A. D. Panagopoulos, and S. Scalise, “On the with 5% exceeded time of an average year. The rainfall rate combination of tropospheric and local environment (mm/hr) for the location is obtained from India Meteorological propagation effects for mobile satellite systems above 10 Department and studied for five consecutive years from GHz”, IEEE Trans. Veh. Technol., vol. 59, no. 3, pp. 1109– 2007 – 2011. The statistical analysis is done by calculating 1120, Mar. 2010. [4] Timothy, K. I.; Ong, J. T. &Choo, E. B. L. (2002), “Raindrop cumulative distribution function for every month using Size Distribution Using Method of Moments for Terrestrial MATLAB and it has been observed that the rainfall rate is and Satellite Communication Applications in Singapore”, IEEE maximum and for more duration during July and Augustas Transactions on Antennas and Propagation, Vol. 15, No. 10, shown in Fig. 6. and hence the rain attenuation will be October 2002, 1420- 1424, ISSN: 0018-926X. predominant during the above period. 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Shieh, “ A two-component rain model Exceeded for the prediction of site diversity improvement performance”, Radio Sci., vol. 24, no. 6, pp. 641–655, 1989. IV. CONCLUSIONS [11] A. Dissanayake, J. Allnutt, and F. Haidara, “A Prediction Due to the spectral congestion of frequency bands Model that Combines Rain Attenuation and other Propagation Impairments along Earth-Satellite Paths,” IEEE Trans. allotted and requirement of higher bandwidths, the importance Antennas Propag., vol. 45, no. 10, 1997, pp. 1546–58 of higher frequency bands like Ku band ( 12/14 GHz) and Ka [12] Moupfouma F., Martin L. “Modelling of the rainfall rate cu- band ( 20/30 GHz) is becoming more predominant nowadays mulative distribution for the design of satellite and terrestrial for satellite communication services. At these frequencies, communication systems”, International J. of Satellite Comm., various impairments will cause the signal to fade, among which © 2012 ACEEE 9 DOI: 01.IJCOM.3.3.4 ACEEE Int. J. on Communications, Vol. 03, No. 03, Nov 2012 1995. Vol. 13. P. 105–115. K.Padma Raju received B.Tech from [13] Dong You Choi, Jae Young Pyun, Sun Kuh Noh, and Sang Nagarjuna University, M. Tech from NIT Woong Lee, “Comparison of Measured Rain Attenuation in Warangal, Ph. D from Andhra the 12.25 GHz Band with Predictions by the ITU-R Model”, UniversityIndia and Post-Doctoral Fellow- International Journal of Antennas and Propagation, Hindawi ship at Hoseo University, South Korea. He Publishers, 2012. [14] International Telecommunication Union, “Characteristics of has worked as Digital Signal Processing precipitation for propagation modeling”, Recommendation Software Engineer in Signion Systems Pvt. ITU- R, P.837-5, Geneva 2007. Ltd., Hyderabad, India, before joining Jawaharlal Nehru [15] ITU-R P.618-9, “Propagation data and prediction methods Technological University Kakinada, India.He has 17 years of required for the design of earth-space telecommunication teaching experience and is Professor of Electronics systems”, International Telecommunication Union, Geneva, andCommunication Engineering, Jawaharlal Nehru Techno- Switzerland, 2007. logical University Kakinada, India. Presently he is working [16] “Rain height model for prediction methods”, Recommendation as Principal, University College of Engineering, Jawaharlal ITU-R P.839-3, ITU-R P Sers., Int. Telecomm. Union, Geneva, Nehru Technological University Kakinada, India.He worked 2001. as Research Professor at Hoseo University, South Korea [17] “ Specific attenuation model for rain for use in predictionmethods”, Recommendation ITU-R P.838-3, ITU- during 2006-2007. He has published 30 technical papers in R P Sers., March 2005. National/International Journals/Conference proceedings and guiding 06 research students in the area of Antennas, EMI/ BIOGRAPHIES EMC and Signal Processing His fields of interest are Signal M. Sridhar received B. Tech degree from Processing Miicrowave and Radar Communications and EMI/ Acharya Nagarjuna University, Guntur, In- EMC. dia in 2001 and M.Tech degree from Ch. Srinivasa Rao is currently working as Jawaharlal Nehru Technological University, Professor of Electronics & Communica- Anantapur, India in 2009. He is a Member tion Engineering, Sri SaiAditya Institute of of The Instituition of Electronics and Tele- Science & Technology, Surampalem, Andhra communications Engineers (IETE) and Pradesh, India. He obtained Ph. D from presently working as an Associate Professor in KL University College of Engineering, University, Guntur, India. He is pursuing Ph.D in Jawaharlal Nehru Technological University Jawaharlal Nehru Technological University Kakinada, Kakinada, Kakinada, Andhra Pradesh, India in 2009. He Kakinada, India and his research area of interest is Satellite received M. Tech. degree from JNTU, Hyderabad and B. Tech Communications. He is having 11 years of teaching from Nagarjuna University. He has 12 International Journal, experience. Conference Publications and one Monograph to his credit. He is guiding 06 research students in Digital Image/Signal Processing and Communications Engineering. Dr. Rao is a Fellow of IETE and member of IEEE & CSI. Figure. 6. Cumulative Distribution Functions of Rainfall rate during 2007 – 2011 in Guntur © 2012 ACEEE 10 DOI: 01.IJCOM.3.3. 4