Two Years Characterization of Concurrent Ku-band Rain Attenuation and Tropospheric Scintillation in Bandung, Indonesia using JCSAT3

Transcription

1 Two Years Characterization of Concurrent Ku-band Rain Attenuation and Tropospheric Scintillation in Bandung, Indonesia using JCSAT3 F2A.5 Joko Suryana Utoro S Department of Electrical Engineering, Institute of ITB Indonesia joko@ltrgm.ee.itb.ac.id, utoro@ltrgm.ee.itb.ac.id Kenji Tanaka Kiyoshi Igarashi National Institute of Information and Communications Technology Japan ken@nict.go.jp, igarashi@nict.go.jp Mitsuyoshi Iida Association of Radio Industries and Businesses ( ARIB ) Japan m-iida@arib.or.jp Abstract -In this paper, we present two years statistics on concurrent rain attenuation and tropospheric scintillation in Bandung ( 6.9 S, E ), Indonesia using GHz horizontally polarized CW beacon signals of JCSAT3 ( Pos = 128 E, Az = 73,2,El = 64,7 ) satellite. From the experiment results, we have found out that on a rainfall rate R mm/h, the rain attenuation A 0.01 measured was around 17 db. Concerning to the tropospheric scintillation, we have noted that in a tropical region such as Indonesia, the magnitude of the Ku-band scintillation is seasonal dependence, reaching variance 0.4 db (maximum) in rainy season and 0.2 db (minimum) in dry season. Keywords : Ku-band, Rain Attenuation, Rainfall Rate, Troposheric Scintillation I. INTRODUCTION Most of Asia - Pacific region currently has insufficient transport and telecommunications networks to reach its people dispersed over a vast area, including many remote and rural districts. Regarding this background, satellite communications is considered as the most effective and important method in the region for constructing an AII (Asia-Pacific Information Infrastructure). In Ku-band satellite communication links, signal-level fluctuations caused by signal-level attenuation by rain, together with tropospheric scintillation, are among the major problems in radio-wave transmission. The attenuation of the signal due rain is the most remarkable propagation effect of the signal in the Ku-band frequency. This kind of lost occur due to the previous thing, can be greater than 15 db in a short amount of time. On the other hand, scintillation generated on propagation paths at low elevation angles may produce considerable signal fading in excess of 10 db. Therefore, accurate estimates of signal degradation due to these effects must be included in the design of low margin satellite communication systems. The expected results and outputs of our Ku-band propagation experiments are [1]: Collecting the multi years Ku-band Propagation Data Development of Prediction Models of Rainfall Rate, Rain Attenuation and Scintillation Performing Multiple Site Analysis. Development of Mitigation schemes for Propagation Anomalies Measurement Recording and Analyzing the Ionospheric and Troposheric Scintillation Contribute to Regulatory Organization This paper is intended firstly for presenting the completed two years statistics ( January 1999 January 2001 ) on the rainfall rate and rain attenuation in Bandung ( 6.9 S, E), Indonesia using GHz horizontally polarized CW beacon signals of JCSAT3 ( Pos=128 E, Az=73,2, El=64,7 ) satellite. Secondly, is for identifying the Rainfall and Rain Attenuation Characteristic in the regular rainy (October April) and regular nonrainy ( April-October) seasons. Third, this paper is also intended for making the comparison between Tropospheric scintillation measurement processed by using Savitzy Golay Filter with ITU-R Model calculation for Bandung and also present the statistics of scintillation profile during rainy and dry seasons in Indonesia /05/$ IEEE 1575 ICICS 2005

2 II. KU-BAND PROPAGATION ISSUES There are several of main problems of propagation using Ku-band satellite links : Rain attenuation - The attenuation of the signal due rain is the most remarkable propagation effect of the signal in the Ku-band frequency. This kind of lost occur due to the previous thing, can be greater than 15 db for a small amount of time. Gaseous absorption - The lost of approximately 1dB happens due to the steam absorption of oxygen and water. Cloud attenuation - The clouds that are in the propagation trajectory can attenuate the signal at the frequency of the Ku-band. The amount of attenuation that happens is of approximately of 1 db or more. Scintillation - This term is indicative of fast fluctuations in the amplitude of the signal. This is caused by the changes that happen by the variation of the tim in the refractive index of the atmosphere. It can also be caused by rainstorms. Depolarization - The transference of energy from a state of polarization in its orthogonal state can be caused by the atmosphere, mainly in clouds and the rain. Atmospheric noise - The atmosphere has a temperature equivalent of a black body. In the frequency of Ku-band, this temperature varies from about 10K to close to the temperature of the ambient. Wet antenna - The condensation in the antennas causes additional lost of the signal In this paper, we just concern about the concurrent Kuband rain attenuation and tropospheric scintillation issues. III. KU-BAND PROPAGATION MEASUREMENT SYSTEM AT ITB BANDUNG The Ku-band propagation measurement system uses a small antenna and a front end shared by the beacon receiver and the Earth Station IDU as shown in figure 1 below [1]. The meteorological data recorded from the sensors (Raingauges, Temperature, Wind speed and direction, Humidity, Barometer and Solar sensors ) is GPSsynchronized with beacon level measurement. The PC-based data acquisition system consists of eight channels for measuring the seven meteorological parameters of six sensors and one propagation parameter, i.e beacon level. The PC hardware and software for data collection receives all data transmitted from data acquisition board, logs the data to disk, and displays the collected data for user viewing which iplemented with LabView. Figure 2.shows us the Data Acqusition System for Ku-band Propagation Measurement installed at ITB Bandung. Figure 2. Data Acqusition System for Ku-band Propagation Measurement installed at ITB Bandung. IV. RAINFALL RATE AND RAIN ATTENUATION STATISTICS AT BANDUNG, INDONESIA Figure 1. Shared Ku-band antenna for Beacon Receiver and Earth Station IDU at ITB, Bandung From the experiment results [1], we have found out that on rainfall rate R mm/h, the rain attenuation A 0.01 measured is around 17 db, therefore the P region with R 0.01 = 145 mm/h of ITU-R recommendation was found to over estimate for Bandung and we suggest that Q-region of ITU-R model [2] with R 0.01 = 115 mm/h is more suitable for Bandung. Figure 3 below shows us the two years rainfall rate profile and the Ku-band rain attenuation for Bandung. We see that application of Ku-band Satellite links in Indonesia is reliable enough regarded to the rain attenuation. 1576

3 This measurement results is a proof for satellite operators in Indonesia to make them more optimistic for using Ku-band transponders as one of promising and prospective business. The corresponding maximum rain attenuation recorded ( db ) per month is shown as in figure 5. We see that on october, there is a high rain attenuation (33 db). Fortunately, this event occurred in very short time (less than 1 minute ). Figure 5. Maximum rain attenuation per month [1] V. ITU-R MODEL FOR KU-BAND TROPOSPHERIC SCINTILLATION AT BANDUNG Figure 3. Two years rainfall rate profile and the Ku-band rain attenuation for Bandung [1][6] Relating to the Rainfall and Rain Attenuation Characteristic in the regular rainy (October April) and regular nonrainy ( April-October) seasons, we also noted that the higher rain intensity occurred at may, June, October and November as figure 4. Tropospheric scintillation is a rapid fluctuation of signal amplitude and phase due to turbulent irregularities in temperature, humidity and pressure, which translate into small-scale variations in refractive index. Scintillation becomes important for low margin systems operating at high frequency and low elevation angles. When receiving a Kuband (or above) signal at low elevation angles (<15 degrees). For calculating the tropospheric scintillation using ITU-R model, the required Input Parameter are [3]: Antenna diameter D ( meter ) Operating Frequency f ( GHz ) Elevation Angle θ ( degree) Step 1 : Determine L, the slant path distance to the horizontal thin turbulent layer, from : L = 2 [ sin θ 8.5sinθ ] x 10 6 Step 2 : Determine the Z from Z = D L f.(1).(2) Figure 4. Maximum rainfall rate per month [1] 1577

4 Step 3 : Determine the antenna averaging factor G(z) from : z,0 < z < 0.5 G( z) = z,0.5 < z < , z > 1.(3) Step 4 : The r.m.s amplitude scintillation, expressed as δ x, the standard deviation of the log of the received power, is then given by : 7/ / 2 δ x = f [cscθ ] [ G( z)].(4) Using the ITU-R Scintillation Model, we can calculate the rms amplitude scintillation for Bandung as Table 1 below : TABLE I. Data : Antenna diameter D = 1.8 m ITU-R SCINTILLATION MODEL FOR BANDUNG Operating frequency f = GHz Elevation Angle θ = 64,7 o. The "smoothed point" (yk)s is the average of an odd number of consecutive 2n+1 (n=1, 2, 3,..) points of the raw data yk-n, yk-n+1,, yk-1, yk, yk+1,, yk+n-1, yk+n, i.e. B. New Proposed Method : Savitzky Golay Algorithm For calculating the long term scintillation PDF, we extract the scintillation data using special LPF, namely Savitzky- Golay Filter [4] from the six months data sets. A much better procedure than simply averaging points is to perform a least squares fit of a small set of consecutive data points to a polynomial and take the calculated central point of the fitted polynomial curve as the new smoothed data point. Savitzky and Golay showed that a set of integers (A-n, A-(n-1), An- 1,An) could be derived and used as weighting coefficients to carry out the smoothing operation. The use of these weighting coefficients, known as convolution integers, turns out to be exactly equivalent to fitting the data to a polynomial, as just described and it is computationally more effective and much faster. Therefore, the smoothed data point (yk)s by the Savitzky-Golay algorithm is given by the following equation: (6) Calculation : L = 1106 m z = G(z) = δ x = db From the experiment results [7], we find out that the scintillation in tropical region is seasonal dependence, reaching variance 0.4 db (maximum) in rainy season and 0.2 db (minimum) in dry season. This results are depicted as in figure 6 : VI. KU-BAND TROPOSPHERIC SCINTILLATION DATA PROCESSING FOR BANDUNG In the pre-processing step, we were collecting clear air condition data (10 minutes/day) from two years propagation data. The collected clear air data sets consist of rainy season and dry season sets for representing the marked seasonal dependence. A. Conventional Method : Moving Average Algorithm The simpler software technique for smoothing signals consisting of equidistant points is the moving average. An array of raw data [y1, y2,, yn] can be converted to a new array of smoothed data. (5) Figure 6. Two Years Tropospheric Scintillation Graph of JCSAT3 during Rainy season Months and Dry Season Months at Bandung, Indonesia 1578

5 We also noted that the long term PDF and its spectrum shape using Savitzsky-Golay LPF is very closely with the conventional moving average LPF as illustrated in figure 7 and 8 below : Relating to the Rainfall and Rain Attenuation Characteristic in the regular rainy (October April) and regular nonrainy ( April-October) seasons, we also noted that the higher rain intensity occurred at may, June, October and November. The corresponding maximum rain attenuation recorded (db ) per month is shown as in figure 5. We see that on october, there is a short duration high rain attenuation (33 db). On the other hand, during these two years Ku-band propagation measurement, we also find out that the tropospheric scintillation in tropical region is seasonal dependence, reaching variance 0.4 db (maximum) in rainy season and 0.2 db (minimum) in dry season. ACKNOWLEDGEMENT We are grateful to the Ministry of Internal Affairs and Communications (MIC) Japan which support us to perform the Ku-band Propagation Measurements at our Laboratory of Radio Telecommunication and Microwave, Institute of Technology Bandung, Indonesia. Figure 7. Long term pdf of Tropospheric Scintillation at Bandung Indonesia [7] REFERENCES [1] Utoro Sastrokusumo et.al, Report Ku band Propagation Measurements Results in Indonesia under Post-PARTNERS Project, ITB-Interim Report, December 2000 [2] CCIR Recommendation and 837, 1992 [3] Ippolito, Louis J., Radiowave Propagation in Satellite Communications, Van Nostrand Reinhold Company, New York, [4] Mathworks, Signal Processing Toolbox, 1996 [5] Karasawa Y et.al, Tropospheric scintillation in the 14/11-GHz bands on earth-space paths with low elevation angles, IEEE Trans. Antennas Propagat., 36, [6] Joko Suryana et all, Two Years Rainfall Rate and Rain Attenuation Measurements in Indonesia under Post-PARTNERS Project Proceeding of APRASC 01, Chuo University [7] Lenni Yulianti et all, Se Seasonal Dependence of Clear Air Tropospheric Scintillation from Ku-band Propagation Using JCSAT3 in Indonesia, Proceeding of APRASC 01, Chuo University Figure 8. Corresponding Power Spectral Density of Tropospheric Scintillation at Bandung Indonesia [7] VII. SUMMARY From the experiment results, we find out that on rainfall rate R mm/h, the rain attenuation A 0.01 measured is around 17 db, therefore the P region with R 0.01 = 145 mm/h of ITU-R recommendation was found to over estimate for Bandung and we suggest that Q-region of ITU-R model with R 0.01 = 115 mm/h is more suitable for Bandung. 1579