18th International Conference on Electronics, Communications and Computers
Automatic Generation of Rain-Attenuation Maps According to the Rain-Rate Provided by Instant Data of Meteorological Stations in Mexico. Velasco-Casillas, C. ToledoFlores, F. Cuevas-Ruíz, J. L. Departamento de Ingeniería Eléctrica y Electrónica. ITESM_CEM. e-mail:
[email protected];
[email protected];
[email protected]
Aragón-Zavala, A.
Delgado-Penin, J. A.
Departamento de Mecatrónica. Instituto Tecnológico y de Estudios Superiores de Monterrey Campus Querétaro. (ITESM_CQRO).
Signal Theory and Communications Department (TSC). Universidad Politécnica de Cataluña. e-mail:
[email protected]
calculated for several frequencies. The chosen frequencies in which the maps are designed are the most susceptible to rain-attenuation. In those frequencies the satellite television and the HAP (28 GHz and 48 GHz in Europe) operates.
Abstract In frequencies over 10 GHz the rain is the most important factor to take in count to evaluate the attenuation level. For several kinds of applications is very useful to known this attenuation in the link every moment while the link is in operation to implement some strategy to mitigate it. According to the ITU-R, there is a procedure to calculate the rain attenuation, however this methodology gives only an average and constant attenuation value. In this work, an automatic procedure to obtain the instant attenuation level for several frequencies using the data provided by MNS (Meteorological National System) in Mexico is explained and their publication in a WEB server is showed. Using these values, an attenuation maps are elaborated and published in that WEB server too.
The databases are provided by the MNS and consist of a data base with seven meteorological variables which are: direction and speed of the wind, the average of temperature, average of rain (amount of rain) pressure, relative humidity and irrandiancy that help us to calculate the rain-rate (amount of rain per unit time); also consider the latitude and longitude of the stations to know their location. In Matlab the altitude, longitude and attenuation are fit in a matrix for an interpolation of the data and get the graphical attenuation. These maps are shown in the preliminary web site prepared for submission. There is a set ITU-R recommendations to calculate the specific attenuation from the rain rate which are briefly mention in section II. In section III is exposed the procedure to obtain the attenuation level from the data base mentioned previously. In section IV we explain the way to generate the rain-attenuation maps and the specific level of attenuation for several places are presented. Some results and conclusions are explained in section V and VI-
Key Words- Generation of Rain-Attenuation Maps, Meteorological Stations.
I. Introduction In Mexico there are a few attenuation zones established by the ITU-R due to the distribution of rain-rate. The generation of rain-attenuation maps resulting by the theorical ITU-R recommendations are obtained depending by the latitude, elevation and rain-rate. Actually there are plenty of communication companies interested in maintaining an optimal link to offer their service or know the current conditions and the information given by the attenuation maps provided for this methodology cold be very usefull.
II. Calculation of Rain-Attenuation The structure of the rain precipitation could be analyzed from two components: horizontal and vertical. The vertical component is used to calculate the rain attenuation with a certain pitch. The structure is built using two layers of effective precipitation arriving at different depths. Both layers with a latitude provided by the ITU-R. The attenuation depends on the length of the area and intensity of the precipitation. The attenuation can be expressed as:
The methology exposed in this paper provide an real rain-rate value obtained from the Automatic Meteorological Stations (AMS). These ones are located along the different climatic zones of Mexico and provide instant rain-rate each 10 minutes and we use these data to calculate the attenuation level and to generate a attenuation maps. These attenuation levels can be
x
kr = k ∫ R(r ) a dr 0
0-7695-3120-2/08 $25.00 © 2008 IEEE DOI 10.1109/CONIELECOMP.2008.33
65
(1)
cannot be obtained from local data sources, an estimate can be obtained.
Where k and a depends on the frequency of the link, temperature and type of rain.
Step 2: Determine the 0° C isotherm height, then calculate the rain height from:
The recommendation of the ITU-R 838 establishes the procedure of the specific attenuation from the rain intensity. At the equation (2 ) is shown the exponential law used to calculate the rain attenuation .
σ = kR α
h0 + 0.36 → R0.01 < 10mm / h hr = R0.01 h0 + 0.36 + log 10 → R0.01 ≥ 10mm / h
(2) Where hr is the rain height and h0 is the ITU-R recommendation.
Where k and α depends on the frequency and polarization of the electromagnetic wave. The constants appears in Recommendation Tables of ITU-R 838; also can be obtained by interpolation considering a logarithmic scale for k and linear for α. These constants are considered on horizontal journeys and linear polarizations; if there is any inclination or angle of elevation they are no longer valid and formulas are needed to be correct by a factor, which in an urban environment is needed. To calculate the parameter of radio attenuation constant k and α according to the recommendation of the ITU 838-3; it should be considered round raindrops and fall without any inclination. K = 2kv + 2kh
Step 3: For θ>5°compute the slant-path length from: h − hs Ls = R senθ
(6)
Where Ls is our slant – path length in km, hr the rain height we got from (5) , hs is the height above mean sea level of the earth station and θ is elevation angle (degrees). For θθ, LR =
cosθ ( h − Else, LR = R hs ) senθ
Applying the theory of sections II and III we can adapt real data to those equations and aproximate rainattenuation maps. The data comes from The AMS along the mexican territory and they are shown in Figure 1.
(11) (12) (13)
The expressions in (11) should be in degrees and (12) , (13) in km. Step 8: The effective path length is
LE = LR v 0.01
(14) Figure 1. Location of the AMS. Source NMI (Mexico).
Where LR is the one from (12).
To obtain the rain-rate parameter for the rainattenuation is necessary to divide the monthly average of precipitations between the hours equivalent to one month and multiplied by the days of the month.
Step 9: The predicted attenuation exceeded for 0.01% of an average year is obtained from:
A0.01 = γ R L E
(15)
Figure 2. A block diagram of the process AGAM
67
In Figure 2 is shown a diagram that explained the steps that we considered to develop the maps and the website that can be consulted for rain-attenuation maps.
The rain-attenuation maps at 11GHz, 28GHz and 48GHz frequencies were analyzed due that in these frequencies are working present and future technologies such as wireless broadband networks examples. Within the 11GHz, satellites of SKY are operating. Also the radio broadcasters and television receiver.
V. Results Through the rain-attenuation maps with data from the AMS is possible to have a better approximation to real situation this map is shown in Figure 3. The principal advantage to use the measurements given by the MNS is that the attenuation level obtained from this methodology is changing according to the real rain rate; in the traditional process postulated by the ITU-R for Mexico there are only two different attenuation levels. Taken the rain attenuation values from the AMS, we can obtain a real value each 10 minutes.
The graph in Figure 4 allows us to compare the results of our maps and the procedure of the ITU-R verifying that the process is more reliable and efficient securities. We can see the remarkable difference in attenuation at the AMS marked with the number 11 located in Ciudad del Carmen, Campeche. The difference between the ITU Rain-Attenuation and AMS Rain-Attenuation is about 12.6039 dB. Is possible to see the Rain-Attenuation result of the ITU and AMS number 25 in Nochixtlán, Oaxaca. The difference is about the 2.1698776 dB. Thus we can see that when handling data from the AMS rain-attenuation at different points is always superior to the values of rain-attenuation of the ITU proceedings.
VI. Conclusions According to our investigations based on the current models of attenuation in the Ka-Band we achieve improve the methodology of those models by using databases from meteorological center: In this way the use of database from EMAs instead of the ITU-R’s data we got more accurate information; the obtained data is more real.
Figure 3. Rain-Attenuation Map for Mexico (AMS).
Figure 4. Comparison of Rain-Attenuation.
68
The frequencies analyzed were the more used in our country, as for satellite television or for virtual university in our campus; However, the methodology can be applied to another bands. It is clear that the improvement of the methodology is by using real data from the AMS and at the same time we can display interesting results. The purpose to collocated these maps in a webpage is that everybody can access the information in order of helping the providers of satellite services or any kind of services working in this bands..
VII. Acknowledgments We would like to thank to Emmanuel Álvarez, manager of the historical records of the AMS, José L. Razo Quevedo, in charge of the network of projects surface of The National Commission of Water (Mexico) and The Chair of Communication ITESM-CEM
7. References [1] Bobadilla-Del-Villar, C.E. and Cuevas-Ruíz, J. L. “Compute rain attenuation. An approach supported in ITU-R recommendations for the Ku Band”. Proc. IEEE International Conference on Electronics, 16th Communications and Computers (CONIELECOMP). Mexico, 2006 [2] Loo, C and Butterworth, J. “Land mobile satellite channel measurements and modeling”, Proc. IEEE, vol 86, Nº 7, July 1998. [3] Wenzhen, L. “Ka-Band Land Mobile Satellite Channel Model Incorporating Weather Effects”. IEEE Trans. Commun. 2001. [4] Zhao, Z. C. “A predictin model of rain attenuation along Earth-Space path”. IEEE. 2003 [5] Matricciani, E. “Experimental rain attenuation statistics estimated from radar measurements useful to design satellite communications systems for mobile terminals”. IEEE transactions on vehicular technology, vol 49, Nº 5, September 2000. [6] Emiliani, L. D. Agudelo, J. Gutierrez, E. Restrepo, J and Fradique-Mendez, C. “Development of RainAttenuation and Rain-Rate Maps for Satellite System Design in the Ku and Ka Bands in Colombia”. Informatics and Telecommunications Research Group. Universidad Pontificia Bolivariana. Medellín, Colombia. IEEE Antennas and Propagation Magazine, vol. 46, Nº 6. December 2004.
69
