Analysis of electromagnetic propagation of 5 scenarios in Mexico City

Transcription

1 7th Latin Amerian Workshop On Communiations Analysis of eletromagneti propagation of 5 senarios in Mexio City Jorge Sosa Pedroza 1, Fabiola Martínez Zúñiga 2, Ma. Elena Aevedo Mosqueda 3 Instituto Politénio Naional, ESIME Zaateno Seión de Estudios de Posgrado e Investigaión Edifiio Z-4, 3 er piso, Col. Lindavista, C.P.07738, Méxio, D.F. jsosa@ipn.mx 1, fmartinezzu@ipn.mx 2, eaevedo@ipn.mx 3 Abstrat. We present a study of eletromagneti attenuation over different environments of Mexio City, for an empirial modifiation of Free Spae Attenuation (FSA). Our work uses results of in-site measurements in different plaes in the ity. We intend to measure attenuation in different plaes to ompare and validate modifiation of FSA. Even we are working in different ommuniations standards, we present results for WiMAX at 3.5 GHz. Resumen. Presentamos en este trabajo un estudio de atenuaión en propagaión eletromagnétia en diferentes esenarios en la iudad de Méxio, para una modifiaión empíria de la Atenuaión del Espaio Libre (AEL). Nuestro trabajo usa resultados de mediión en diferentes lugares de la iudad. La intenión es omparar on las mediiones de atenuaión para omparar y validar la modifiaión de AEL. Aunque hemos heho el experimento para diferentes estándares de omuniaiones, presentamos en este trabajo los resultados para WiMAX en 3.5 GHz. Keywords: Modifiation of Free Spae Attenuation, Measurement of urban attenuation, WiMAX. Palabras lave: Atenuaión del espaio libre, Mediiones de atenuaión en zonas urbanas, WIMAX. I. INTRODUCTION Wireless ommuniation systems are evolving rapidly, EM attenuation in urban areas is now a most for the system design. Altough models as Okumura [1], Hata [1], Cost 231 (a modifiation of that of Hata), Ereg [3], Shittu [4] and others, are used all around the world to predit propagation losses, for eah site should be tested to prove at least, the deviation between predition and measurement. We have done measurements all over Mexio City in different frequenies, omparing them with predition of most popular models, for different ommuniations standards as WiMAX (Worldwide Interoperability Mirowave Aess), whih is a metropolitan area servie used with one or more base stations at different frequenies: 2.3 GHz, 2.5 GHz, 3.3 GHz, 3.5 GHz and 5.8 GHz [5,6]. Our analysis onsiders omparison of two models: COST 231 and Ereg, for similar environment as the senario 2 (shown below); for COST we use the big ity model, applying all ommuniations system parameters to equation (1) P COST = log f log A T a(a R ) +( log A T ) log d + C (1) Where: f = 3.5 GHz. A T = 30 m (Transmission height antenna) d = m C = 3 (orretion fator) Reeiver height antenna orretion: a(h R ) = 3.2 [log (11.75 A R )] , with A R = 1.5 m EIRP=19.5 db For Ereg Model we use the A zone, meaning hills and a medium density of trees. Then we use equation 2: P Ereg = P FSA γ log ( d d 0 ) + s; d d 0 (2) Where: P FSA. = Free spae loss d 0 = Referene distane (100 m). γ = (a b h b + h b ) + x σ γ ; 10 m h b 80m s = yσ Using Ereg parameters, we define: σ = μ σ + z σ σ a = 4.6 b = = μ σ = 10.6 σ σ = 2.3 σ γ = 0.57 Results of our omparison between measurements made in Mexio City and atual models, show important differenes, as seen in figure 1. Figure 1 shows that Mexio City environment is different to those where, the models are defined. This paper, analyze our own senarios and adjust the Free Spae Model (FSM) trying to find the best relationship between measurements and model modifiations. Considering those differenes of figure 1, we Copyright 2015 for the individual papers by the papers authors. Copying permitted for private and aademi purposes. This volume is published and opyrighted by its editors. Latin Amerian Workshop On Communiations' 2015 Arequipa, Peru Published on CEUR-WS:

2 propose to use a modifiation of FSA equation, omparing it with regression urves of measurement. Figure 1. Comparison of measurement with COST and Ereg The idea is to measure field attenuation in an area with defined harateristis, make modifiation of FSA equation and after that, take measurement in other different plae in the ity, with similar harateristis and ompare the new measurement regression urves with former modifiation of FSA. For the experiment we hoose to different plaes, 30 Km apart, one in the north and the other in the south of Mexio City. Experiment starts with hoosing similar senarios in both sites, we find 4 areas with similar harateristis, those from 1 to 4. The fifth senario was in downtown, whih is a unique plae in the ity and do not have a similar site to be ompared with, but we presented beause it was part of the measurements. We propose to use Free Spae Attenuation, modifying the equation exponent. As is known, FSA supposes a free obstale region between transmitter and reeiver; it is given by [3]: where PL FS = ( 4πdf 2 ) (3) d: distane between transmitter and reeiver f: operating frequeny : speed of light Equation (3) is often expressed in db as: repeat the proedure. On the other hand we want to emphasize that we are omparing only attenuation due the environment, this means that we take a measurement power at some distane of base station and relate it to the measurement at other distane. We are still working in the proedure, and we are now measuring in similar areas in other plaes in the ity, to ompare the original results. II. MEASUREMENT METHODOLOGY Measurements were performed using base stations loated in National University (UNAM) with base station in the Humanities Building at the south of the ity, in Instituto Politénio Naional (IPN) with station loated in the Direión de Cómputo y Comuniaiones (DCyC) at the ity s north and the Instituto de Cienia y Tenología (ICYT) in downtown. Three senarios were hosen due their similarities but also by their differenes. Table I shows harateristis of ommuniations system, transmitter antenna height is almost the same for all senarios. TABLE I COMMUNICATION SYSTEM FEATURES Operating frequeny Bandwidth Transmitter power Transmitter antenna height Reeiver antenna height Transmitter antenna gain Reeiverer antenna gain 3,4785 GHz 3,5 MHz -7 dbw m 2 m 14,8 dbi 3,6 dbi Measurements were made using an analyzer Anritsu Master Spetrum MS2721B, whih inludes a GPS antenna for referened positioning. Figure 2 shows the measurement sheme; the equipment was mounted on top of a vehile, saving the reeived power level and geographi loation (latitude and longitude oordinates) at eah measurement point. LP EL = 20 log 4π + 20 log d + 20 log f (4) The new proposed equation is: PL FS = ( 4πdf ) X ± Y (5) Adjustment is made hanging the exponent value (X) for the slope and (Y) for losses magnitude, in equation (5). Next step was to adjust FSM finding a math for slope and attenuation as best as possible with measurement regression urves. After that we ompare modified urves with similar senario in other plae, and if there is onordane, we an suppose that modifiation of equation (5) is good enough. We understand that this analysis is valid only for the used frequeny, for a different one we have to Fig 2. Measurement sheme 2-2 Measurements were taken every 20 seonds, at that time analyzer updates GPS position. A data base with extension wxme is onstruted, extrating measurements from spetrum analyzer, beoming in omputer txt files ontaining latitude,

3 longitude, distane and input power. Database is used to onstrut linear regression urves, to be ompared with adjustments of FSA. III. IDENTIFICATION OF SCENARIOS We identified 5 senarios aordingly of existing features of different areas in Mexio City, whih are desribed in following paragraphs: A. Senario 1: low buildings with low tree density This senario onsiders an area with a low tree density, and low high buildings, as shown in Figure 3. Figure 5. Senario 3 Figure 3. Senario 1 B. Senario 2: low buildings with medium tree density The senario onsiders an area with medium tree density and a low height of the buildings as the one shown in figure 4. Figure 6. Senario 4 Figure 7. Senario 5 Figure 4. Senario 2 C. Senario 3: area with a high tree density Figure 5 shows a senario with a high tree density. D. Senario 4: tall buildings with medium tree density The senario onsiders an area with medium tree density and high height buildings. E. Senario 5: olonial ity Senario 5 is a unique environment of Mexio City (and many Latin Amerian ities), it is loated at histori downtown; it has some very unique onstrution features suh as: large width walls, tall buildings, and narrow streets. Figures 8 and 9 show UNAM (south of the ity) with yellow mark, showing position of base station at Humanidades II building and the one at IPN (north of the ity) with mark in DCyC building (Direión de Cómputo y Comuniaiones). Measurements were taken in both zones for senarios 1 through 4, eah one bounded for different olors. The blue frame define senario 1, while senario 2 is red, green is the senario 3 and senario 4 orange.

4 Eah senario was visually distinguished from both base stations photos. As an example, area for senario 1 is mostly filled by buildings with few green zones. Others an be distinguished in photographs from tree density. Figure 10. Base Station of senario 5. Figure 8. Radio base loated in the UNAM IV. RESULTS One the senarios were identified in maps, measurement tables were onstruted and obtained linear regression urves we were ready to modify FSA using UNAM measurement and then ompare them for those at IPN. To do so we adjust FSA finding a math for slope and attenuation as best as possible. Adjustment is made hanging the exponent value (X) for the slope and (Y) for losses magnitude, in equation 5 onsidering a differene no higher than 3 db: L FSA = ( 4πdf ) X ± Y (5) Following urves show results of our analysis. Figure 11 shows adjustments for senario 1; we found that X=3 and Y=29 then: L S1 = ( 4πdf 3 ) + 29 Figure 9. Base station in IPN Figure 10 shows the unique senario 5. Although is not lear from the photo the differenes with other senarios, is possible to distinguish them from Figure 10, speially the narrow bakground street between the olonial buildings. After eah bounded polygon was defined by its geographial position, we reated tables with eah point measurements and then onstruted regression urves showing attenuation behavoir. To validate senarios 1-4 we take measurements in UNAM to define FSA new parameters and then ompare them with those taken in IPN to validate X and Y parameters. Figure 11. Adjustment of FSM for senario 1.

5 100 m and 1200 m. Differenes are greater for larger distanes, meaning senario 4 needs further analysis. Figure 12. Comparison and adjust of FSA for senario 2. Figure 12 depits measurements omparison for senario 2. giving: L S2 = ( 4πdf 2 ) 28 We selet a FSM adjust urve between both base station regression urves, giving a differene between FSM and measurement no higher than 1.5 db. As seen the exponent value do not hange (X=2); magnitude of attennuation fator is seleted as Y = -28 for senario 2. In the same way we ompare urves for senario 3, as shown in Figure 13; again the slope of regression urves are similar, with a differene of power no greater than 5 db. After adjustment, we selet a urve for FSA between both regression urves; lost equation is expressed as: L S3 = ( 4πdf 2 ) 31 Figure 14. Comparison and adjust of FSA for senario 4. Although two power slopes are different, a good FSA adjustment was found as: L S4 = ( 4πdf 3 ) + 21 As senario 5 is unique, is not possible to ompare with any other urve. Figure 15 shows FSA adjustment of regression urve. As an be seen from Figure 15, there is a sharp slope fall, similar to that of senario 3, meaning a zone of high attenuation, due the tall buildings with very dense walls and narrow streets. Adjustment for FSA is: L S5 = ( 4πdf 2 ) 36 Figure 13. Comparison and adjust of FSA for senario 3. Following same proedure, we ompare results for senario 4. Regression urves are shown in Figure 14. As seen slopes of both urves are different, although no more than 1.5 db between Fig. 15. Adjust of FSM for senario 5. Table II shows a summary of adjustments for all senarios.

6 TABLE II SUMMARY OF FSM ADJUSTMENT Exponent Loss (db) Senario Senario Senario Senario Senario As seen in Table II, senarios 1 and 4 have similar slopes, with an exponent of 3. Furthermore the loss adjustment for FSM is inreased with 29 and 21 db respetively. For senarios 2 and 3, the slope has the same exponent of 2, and loss requires an adjustment of -28 and 31 db respetively, only a 3 db differene. V. CONCLUSION After identifiation of some ommon senarios in Mexio City as: low buildings-low tree density; low buildings-medium tree density; high tree density zone; tall buildings-medium tree density; Colonial City, we ompare measurements over ity streets with FSA, to find a relationship between them. Considering similarities for two base stations, we validate senarios seletion, at least for 4 of them, leaving senario 5 as unique. Comparing measurements for eah senario with adjusts of exponent and amplitude of FSA losses, we onlude that model an predit path loss for WiMAX or similar ommuniation standard. We think that 5 db differenes is a good margin, to predit propagation of mobile ommuniation systems over an environment as Mexio City. Probably we have to define an aepted margin, but aordingly with our experiene a 10 db ould be a good number. REFERENCES [1] Y. Okumura et al. Field strength and variability in VHF and UHF land-mobile radio servie Rev. Ele. Commun. Lab., vol. 16, [2] Masaharu Hata Empirial Formula for Propagation Loss in Land Mobile Radio Servies IEEE Transations on Vehiular Tehnology, Vol. VT-29, No. 3, August [3] Vinko Ereg et al. An Empirial Based Path Loss Model for Wireless Channels in Suburban Environments, IEEE, Journal on Seleted Areas in Communiations, Vol. 17, No. 7 July [4] W.A Shittu, Predition of Reeived Signal Power and Propagation Path Loss in Open/Rural Environments using modified Free-Spae Loss and Hata Models, [5] S. Y. Tang, WiMAX Seurity and Quality of Servie, 1 st ed, Ed. Wiley, [6] D. Pareek, WiMAX Taking Wireless to the MAX, 1 st ed, Ed. Taylor & Franis Group, 2006.