ACEEE Int. J. on Communications, Vol. 03, No. 02, 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 (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.
maximum attenuation and therefore, is the limiting factor in Ku and Ka band satellite link design [3]. The rain drops absorb most of the electromagnetic energy at these frequency ranges and some of the energy gets scattered by Rayleigh and Mie scattering mechanisms [4]. The rain drop size distribution is exponential when expressed mathematically as, ( D ) N ( D ) N 0 e Dm mm-1m-3 (1) where Dm is the median drop diameter and N(D)dD is the number of drops per cubic meter with diameters between D and D + dD mm [5]. The rainfall rate R is related to N (D) and also to the terminal velocity of V (D) the falling drops in meters per second with diameter D by (2) R 0.6 10 3 D 3V ( D ) N ( D ) dD mm/hr
Index Terms — satellite communication, propagation 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 frequency and is highly correlated with rain rate. By using rain statistics for a given region, it is possible to determine the probability that a given fade depth will be exceeded. The rain availabilityof a communication link is the complement of the probability of the link fade margin being exceeded [6]. Rain fade mitigation techniques like power control, signal processing and site diversity methods are used to improve the performance of link design and this requires proper prediction of attenuation due to rain [7]. There are two approaches to predict the rain attenuation namely, a physical method in which rain is described all the way along the path, and an empirical method which uses the effective path length and rainfall rate using the information from various data bases [8]. Various rain attenuation prediction models are available based on the geographical and climatic conditions. The important models are Crane global model [9], Two-component model [10], Simple Attenuation model (SAM), Excell model, MismeWaldteufel model, Garcia model [1], International Telecommunication Union Radio Communication sector (ITU-R) model [2], Bryant model, Dissanayake, Allnutt and Haidara (DAH) model [11], and Moupfouma model [12]. Among these models, ITU-R model provides the most accurate statistical estimate of attenuation on slant paths [2].
I. INTRODUCTION Communications system design requires the development of a link budget between the transmitter and the receiver that provides an adequate signal level at the receiver ’s demodulator to achieve the required level of performance and availability [1]. The performance and availability of the link can be specified or measured using Bit Error Rate (BER) and Carrier-to-Noise ratio (C/N). It is the link designer’s task to ensure that loss of signal occurs for no longer than the time permitted for that service. The development of an accurate link budget, which includes losses due to the passage of the signal through the atmosphere, is critical. There are many phenomena that lead to signal loss on transmission through the earth’s atmosphere. These include: cloud attenuation, tropospheric scintillation, ionospheric Scintillation, Water vapour attenuation, rain and ice depolarization, and rain attenuation [2].Among all the propagation impairments, rain attenuation is the most important for frequencies above 10 GHz, as it causes M. Sridhar is with KL University, Guntur, Andhra Pradesh, India (email: sridhar.m@kluniversity.in). Dr. K. Padma Raju is presently working as Principal, University College of Engineering, JNTU Kakinada, Kakinada, Andhra Pradesh, India (email: padmaraju_k@yahoo.com). Dr. Ch. Srinivasa Rao is working as Principal, Sri Sai Aditya Institute of Science & Techology, Surampalem, Andhra Pradesh, India (email:ch_rao@rediffmail.com).
© 2012 ACEEE DOI: 01.IJCOM.3.2. 4
B. ITU-R P. 618 - 9 Rain Attenuation Model The ITU Radio communication Sector (ITU-R) is one 6
ACEEE Int. J. on Communications, Vol. 03, No. 02, Nov 2012 among the three divisions of the International Telecommunication Union (ITU) which is responsible for radio communication. It manages the international radiofrequency spectrum and satellite orbit resources and also enhances standards for radio communication systems with the objective of ensuring the effective use of the spectrum. The ITU-R provides global rain statistics by dividing the 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].
manner [15]: Step 1. Calculate the rain height h R(Km)from the recommendation ITU-R P.839 as
II. METHOD FOR E STIMATION OF RAIN ATTENUATION
Figure 1. Schematic presentation of an earth-space path
The proposed experimental setup is at KL University, Guntur which is located 29.08 m above sea level. The latitude and longitude of the location are 16.46' N and 80.54' E respectively. Two DTH receivers operating in Ku band is installed in the location which receives the signal from NSS6 satellite ( 95 E). A disdrometer can be used to measure and record the rainfall intensity (mm/hr) with 1-min integration time which also specifies rain drop size. The satellite signal strength will be measured using a spectrum analyzer and the information can be recorded with a data logger. The rainfall rate exceeding 0.01% of an average year in mm/hr for the location is calculated using Recommendation ITU-R P. 837-5 which requires the coordinates of the location. The input parameters requiredto this model are: point rainfall rate for 0.01% of an average year (mm/hr) with 1-min integration time, height of the location above mean sea level (Km), elevation angle of the receiver (degrees), latitude of the location (degrees), frequency (GHz), polarization angle (degrees), and effective radius of the Earth (Km) [14]. Table I gives the geographical and experimental parameters for the experimental site. TABLE I. GEOGRAPHICAL/EXPERIMENTAL PARAMETERS
FOR THE
hR h0 0.36 Km
where h 0is the 0° C isotherm height above mean sea level at the desired location [16].
A: B: C: D:
160.46’N
Longitude
80 0.54’E
Height Above Sea Level
0.029 Km
Elevation Angle
64.5 0
LG Ls cos Km
Polarization Angle
40.4
(5)
Step 4. Determine the rainfall rate, R0.01 ,exceeded for 0.01% of an average year, with 1-min integration time. It can be calculated with the help of statistical data available in various meteorological databases or from the maps provided by ITU-R P.837. Step 5. Calculate the specific attenuation, R , by using the frequency dependent regression coefficients provided in ITU-R P.838 Recommendation and R0.01 using [17],
R k ( R0.01 ) dB/Km
(6)
where k and depend on frequency, polarization, raindrop size distribution and temperature and obtained using,
0
Frozen precipitation Rain Height Liquid precipitation Earth-Space path
Step 2. Determine the slant-path length L s , below the rain height from ( h hs ) Ls R Km if 5 (4) sin where is Elevation angle in degrees,h s is the height of the location above sea level in Km, and h Ris the rain height in Km. Step 3. Obtain the horizontal projection, LG , of the slant path length from
LOCATION
Latitude
(3)
k H kV ( k H kV ) cos 2 cos(2 t ) k 2 k H H kV V ( k H H kV V ) cos 2 cos(2t )
(7) (8)
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 1 Based on the geographical conditions and measured rainfall r0 .0 1 LG R using the disdrometer, the rain attenuation can be calculated (9) 1 0 .7 8 0 .3 8 1 e 2 L f using ITU-R P. 618 - 9 model in the following 7 © 2012 ACEEE DOI: 01.IJCOM.3.2. 4 G
ACEEE Int. J. on Communications, Vol. 03, No. 02, Nov 2012 where f is the frequency in GHz. Step 7. Calculate the adjusted rainy path length, L R (Km), through rain using L r (10) L R G 0 .0 1 fo r co s where
LS
( hR hS ) for sin
tan
1
hR hS LG r0.01
(12)
1 1
sin 31(1 e /1 )
0.001%
(11)
Step 8. Obtain the vertical reduction factor for 0.01% of the time by v 0.01
TABLE II.VARIATION OF RAINFALL RATE AND ATTENUATION WITH RESPECT TO % TIME EXCEEDED % Time Rainfall Rate Attenuation exceeded (mm/hr) (dB)
v0.01 , using (13)
115.89
25.28
0.01%
62.83
12.47
0.1%
17.32
2.03
1%
1.96
0.11
5%
0
0
integration time. The obtained rainfall rate with different % time exceedence of average year will be compared and studied with practical rainfall rates measured with disdrometer arrangement as a next step in the research work.
LR R 0.45 f2
where 36 , for 36 (14) (15) 0, for 36 Step 9. Determine the effective path length through rain, L E (Km), given by (16) LE LR v0.01 Step 10. Calculate the predicted attenuation exceeded for 0.01% of an average year by using (17) A0.01 R LE dB 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 ( ) (18) 0.01 where p is the percentage probability of interest and is given by (19) for p 1%, 0 (20) if 36
Figure. 2.Variations of rainfall rate (mm/hr) with respect to % time exceeded
for p 1%, 0 0.005( 36) for 25 and 36 (21) 0.005( 36) 1.8 4.25 sin , for 25 and 36
The attenuation of the signal is obtained at 11 GHz frequency, using ITU-R P. 838 - 1 Recommendation for different rainfall rates. It is evident from Fig. 3 that the attenuation increases with rainfall rate. The theoretical results will be used to study and compare the amount of attenuation introduced practically in the extended future research work.
(22)
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/ hr exceeded for 0.01% of an average year, with 1-min © 2012 ACEEE DOI: 01.IJCOM.3.2. 4
Figure. 3. Variation of attenuation with respect to rainfall rate
The attenuation is calculated for frequencies from 1 GHz to 8
ACEEE Int. J. on Communications, Vol. 03, No. 02, Nov 2012 15 GHz with a rainfall rateR 0.01 62.83 mm/hr using ITUR model. With an increase in frequency, there is a significant increase in the attenuation as shown in Fig. 4. The attenuation is 0.00814 dB at 1 GHz frequency and 21.39 dB at 15 GHz.
rain attenuation is the predominant. In this paper, ITU-R model is used to predict the rainfall rate and attenuation due to rain, at KL University, Guntur. The attenuation is calculated, for 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 Communication”, John Wiley and Sons, 2003,536 pp. [2] Cost Action 255 Final Report, “Radiowave Propagation Modelling for SatCom Services at Ku-Band and Above”, ESA Publications Division, Noordwijk, The Netherlands, 2002. [3] K. P. Liolis, A. D. Panagopoulos, and S. Scalise, “On the combination of tropospheric and local environment propagation effects for mobile satellite systems above 10 GHz”, IEEE Trans. Veh. Technol., vol. 59, no. 3, pp. 1109– 1120, Mar. 2010. [4] Timothy, K. I.; Ong, J. T. &Choo, E. B. L. (2002), “Raindrop Size Distribution Using Method of Moments for Terrestrial and Satellite Communication Applications in Singapore”, IEEE Transactions on Antennas and Propagation, Vol. 15, No. 10, October 2002, 1420- 1424, ISSN: 0018-926X. [5] Maitra A., “Rain Attenuation Modeling From Measurements of Rain Drop Size Distribution in The Indian Region”, IEEE Antennas and Wireless Propagation Letters. Vol. 3, P. 180– 181, 2004. [6] John S. Seybold, “Introduction to RF Propagation”, John Wiley & Sons, 2005. [7] Athanasios D. Panagopoulos, Pantelis - Daniel M. Arapoglou, and Panayotis G. Cottis, “Satellite Communications at Ku, Ka, and V Bands: Propagation Impairments and Mitigation Techniques”, IEEE Communications surveys, Volume 6, No.3, 2004. [8] Ojo, J. S., M. O. Ajewole, and S. K. Sarkar, “Rain rate and rain attenuation prediction for Satellite Communication in Ku and Ka bands over Nigeria”, Progress in Electromagnetics Research B, Vol. 5, 207-223, 2008. [9] R. K. Crane, “Prediction of attenuation by rain”, IEEE Trans. Commun., vol. 28, pp. 1717–1733, Sept. 1980. [10] R. K. Crane and H. C. Shieh, “ A two-component rain model for the prediction of site diversity improvement performance”, Radio Sci., vol. 24, no. 6, pp. 641–655, 1989. [11] A. Dissanayake, J. Allnutt, and F. Haidara, “A Prediction Model that Combines Rain Attenuation and other Propagation Impairments along Earth-Satellite Paths,” IEEE Trans. Antennas Propag., vol. 45, no. 10, 1997, pp. 1546–58 [12] Moupfouma F., Martin L. “Modelling of the rainfall rate cumulative distribution for the design of satellite and terrestrial communication systems”, International J. of Satellite Comm.,
Figure.4. Rain Attenuation Variation with Frequency at Rainfall Rate R0.01 62.83 mm/hr
The rain attenuation is calculated for 0.001% to 5% exceedence percentages of an average year as shown in Fig. 5. The attenuation is 25.28 dB with 0.001% and 0 dB with 5% exceeded time of an average year. The rainfall rate (mm/hr) for the location is obtained from India Meteorological Department and studied for five consecutive years from 2007 – 2011. The statistical analysis is done by calculating cumulative distribution function for every month using MATLAB and it has been observed that the rainfall rate is maximum and for more duration during July and Augustas shown in Fig. 6. and hence the rain attenuation will be predominant during the above period.
Figure. 5. Variation of Rain Attenuation with Respect to % Time Exceeded
IV. CONCLUSIONS Due to the spectral congestion of frequency bands allotted and requirement of higher bandwidths, the importance of higher frequency bands like Ku band ( 12/14 GHz) and Ka band ( 20/30 GHz) is becoming more predominant nowadays for satellite communication services. At these frequencies, various impairments will cause the signal to fade, among which © 2012 ACEEE DOI: 01.IJCOM.3.2.4
9
ACEEE Int. J. on Communications, Vol. 03, No. 02, Nov 2012 K.Padma Raju received B.Tech from Nagarjuna University, M. Tech from NIT Warangal, Ph. D from Andhra UniversityIndia and Post-Doctoral Fellowship at Hoseo University, South Korea. He has worked as Digital Signal Processing Software Engineer in Signion Systems Pvt. Ltd., Hyderabad, India, before joining Jawaharlal Nehru Technological University Kakinada, India.He has 17 years of teaching experience and is Professor of Electronics andCommunication Engineering, Jawaharlal Nehru Technological University Kakinada, India. Presently he is working as Principal, University College of Engineering, Jawaharlal Nehru Technological University Kakinada, India.He worked as Research Professor at Hoseo University, South Korea during 2006-2007. He has published 30 technical papers in National/International Journals/Conference proceedings and guiding 06 research students in the area of Antennas, EMI/ EMC and Signal Processing His fields of interest are Signal Processing Miicrowave and Radar Communications and EMI/ EMC.
1995. Vol. 13. P. 105–115. [13] Dong You Choi, Jae Young Pyun, Sun Kuh Noh, and Sang Woong Lee, “Comparison of Measured Rain Attenuation in the 12.25 GHz Band with Predictions by the ITU-R Model”, International Journal of Antennas and Propagation, Hindawi Publishers, 2012. [14] International Telecommunication Union, “Characteristics of precipitation for propagation modeling”, Recommendation ITU- R, P.837-5, Geneva 2007. [15] ITU-R P.618-9, “Propagation data and prediction methods required for the design of earth-space telecommunication systems”, International Telecommunication Union, Geneva, Switzerland, 2007. [16] “Rain height model for prediction methods”, Recommendation ITU-R P.839-3, ITU-R P Sers., Int. Telecomm. Union, Geneva, 2001. [17] “ Specific attenuation model for rain for use in predictionmethods”, Recommendation ITU-R P.838-3, ITUR P Sers., March 2005.
BIOGRAPHIES M. Sridhar received B. Tech degree from Acharya Nagarjuna University, Guntur, India in 2001 and M.Tech degree from Jawaharlal Nehru Technological University, Anantapur, India in 2009. He is a Member of The Instituition of Electronics and Telecommunications Engineers (IETE) and presently working as an Associate Professor in KL University, Guntur, India. He is pursuing Ph.D in Jawaharlal Nehru Technological University Kakinada, Kakinada, India and his research area of interest is Satellite Communications. He is having 11 years of teaching experience.
Ch. Srinivasa Rao is currently working as Professor of Electronics & Communication Engineering, Sri SaiAditya Institute of Science & Technology, Surampalem, Andhra Pradesh, India. He obtained Ph. D from University College of Engineering, Jawaharlal Nehru Technological University Kakinada, Kakinada, Andhra Pradesh, India in 2009. He received M. Tech. degree from JNTU, Hyderabad and B. Tech from Nagarjuna University. He has 12 International Journal, 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 DOI: 01.IJCOM.3.2. 4
10