MOBILE RADIO PROPAGATION ALONG MIXED PATHS IN FOREST ENVIRONMENT

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1 Journal of Microwaes and Optoelectronics, Vol., No. 4, September MOBIL ADIO POPAGATION ALONG MIXD PATHS IN FOST NVIONMNT Gerásio P. S. Caalcante; Mário A.. Sanches and ômulo A. N. Olieira * Abstract This work proposes a simple model of trajectory of rays, based on knifeedge diffraction, to calculate the intensity field receied by a mobile station inside a forest enironment with relief discontinuity. To alidate the model, a radio propagation measurement campaign was carried out, in the county of Benfica, near the city of Belém, State of Pará. The measurement system consisted of a fixed laboratory transmitting a carrier at 9 MHz and a mobile laboratory specially mounted to measure and store the instantaneous alues of power of the receied signal. The results were compared to the simulations made with the proposed model, which presented the best performance comparing to other models utilized in this work. Index Terms radio propagation problem factors, mobile system in forest enironment, point-to-point models. I. INTODUCTION The propagation of radio waes oer irregular surfaces is of great importance to design of fixed and mobile radio systems. The behaior of propagating electromagnetic waes through forests and thick woods has been extensiely studied in the last decade []-[3]. Usual assessments of radio propagation in egetation focus either on communication paths for which both transmitter and receier are located in the egetation, or for which the transmitter is within the egetation while the receier is in the air aboe the egetation. Howeer, all this studies do not include propagation on a mobile enironment where systems operate in the 8/9 MHz frequency band. The aim of the present paper is to propose a simple model using ray trace techniques for mixed paths in forest enironment. The model makes use of diffraction and/or reflections on abrupt discontinuities caused by the presence of a road inside the forest enironment [4]. In this work is utilized a small number of rays paths contributing to the receied electromagnetic field. An important feature of this work is to show that these analytical results can be described in terms of ray paths, which permit the calculation of mobile radio loss in a large class of forest enironment. As an example, the ray representation is discussed in the context of a propagation path that traerses through two wooded regions, which are separated by a paed road. A campaign of propagation measurements was carried out in order to alidate the proposed model. * Gerásio P. S. Caalcante and Mário A. Sanches. Departamento de ngenharia létrica do Centro Tecnológico da Uniersidade Federal do Pará-UFPA CP:869, CP: Belém-PA Brazil, Tel/Fax: gerasio@guama.cpgee.ufpa.br; ômulo A. N. Olieira Centro Federal de ducação Tecnológica do Pará-CFT- CP: 866 This work was supported in part by FINP/CNPq/POPSP-UFPA under grant.

2 Journal of Microwaes and Optoelectronics, Vol., No. 4, September II. FOMULATION OF TH POBLM The idealized model for mixed-path considerations in a forest enironment is shown in Fig.. A paed road crosses a forest layer haing an effectie tree height h. The complete propagation path then takes the form of a succession of ray trajectories. As each of the trajectories is simple and is identified with a well-defined loss, the total radio loss oer the actie composite propagation path can be systematically determined. Fig. (a) shows the "road-angle" α that indicates the relatie position of the ray path and the o o road direction. This angle can assume alues in the interal α < 9. Fig.(b) shows the geometry of the propagation enironment studied where two knife-edges are considered. The first is located in point A and the second in point B associated with the first and second discontinuity of the forest, respectiely. Also, it is showed the situation where only two rays are considered as the most important components of the receied field. Due the first discontinuity the field is considered by diffraction in a knife-edge and a reflection on the road. In the second discontinuity the road cuts the forest gien origin to a field component ( ) that reaches the receier by a single diffraction on the edge of the egetation. A second component ( ) reaches the receier after diffraction on the edge of the egetation and a reflection at the forest on the other side of the road. To establish the field in the mobile receier it is conenient to considerate before the resultant field at point produced by diffraction at point A (corresponding to component) and reflection on the road (corresponding to component). This can be accompanied through Fig.(b). T FOST a OAD FOST OAD MOBIL FOST w d d (a) (b) Fig.. Geometry of the model: (a) superior iew of forest; (b) lateral iew of the forest

3 Journal of Microwaes and Optoelectronics, Vol., No. 4, September A. The Field eceied at Point. The expression for the receied field in point is gien by: = [ f ( ) + OAD f ( ) ] () where, is the free space field, OAD is the Fresnel reflection coefficient at road and f ( ) C( ) j S( ) = = or C(ν * ) and S(ν * ) are the Fresnel integrals with the parameter ν * gien by H =. F Here H * represents the path obstruction or liberation and F * is the first Fresnel zone ray. From Fig. we obtain the following Fresnel parameters ν * alues: = () ( d + W )cos α = h λ[( d + W )cosα W ] W (3) For ν = and ν > more simple expression may be used instead and it is proen that these approximation lead to errors smaller than db [5]: = (4) OAD =.5 (5)

4 Journal of Microwaes and Optoelectronics, Vol., No. 4, September = + (6) Then OAD (7) B. Field eceied in the Mobile Knowing that field at point M is due the field arriing from point, we can use the analytical continuation arguments to found the field at point considering that the transmitter being at point M. From reciprocity theorem we found that field at point M, mobile receier as follows: = (8). 5 BM OAD =.5 (9) Then d + w mobile = () d BM + + FOST Inserting (7) into () we obtain =.5 3P G ( d + w) 5 + T T OAD BM mobile ( ) () d d + W FOST + BM + FOST

5 Journal of Microwaes and Optoelectronics, Vol., No. 4, September where P T G T is the effectie radiated power by base station, FOST is the Fresnel reflection coefficient at forest and BM = ( h h r ) d cos α λ( d cosα w) w () = ( h h ) r λ( d cosα d cos α W + w)(w w) (3) BM = ( h h r ) ( d + w) cos α λ[( d + w)cosα w] w (4) = ( h h ) r λ[( d + ( d + w) cos α w)cosα W + w](w w) (5) From () we can obtain the receied aerage power: P = (6) mobile III. MASUMNT CAMPAIGN The arrangement of the measurement systems is showed in Fig.. The measurements were taken in a coered by radio signal transmitted by fixed station in the surroundings of Belém, state of Pará in a town called Benfica. The transmitted signal was a CW wae at 9 MHz, using a collinear antenna in a twele-height tower (Fig. a). The transmitter was installed on a building of the DMC (Delegacia do Ministério das Comunicações). The mobile receier has traeled along a 5.6-km road inside a forest at a speed of approximately km/h in one direction and at 4 km/h on the other (Fig. b). The measurement results were recorded on a tape recorder for off line processing. The map of measurement enironment (Fig. c) indicates the transmitter position, and the path of mobile receier unit in road. Fig. d shows a iew of the road crossing forest.

6 Journal of Microwaes and Optoelectronics, Vol., No. 4, September Fig a- Transmitter antenna Fig b- Mobile eceier Unity Fig.c- Map of Benfica road inside forest Fig d- Benfica road Fig. - Measurement enironment

7 Journal of Microwaes and Optoelectronics, Vol., No. 4, September IV. SULTS The recorded data obtained of set up measurement were A/D conerted and processed for comparison with the theoretical simulations. Comparatie analysis was performed using all the experimental data and the point-to-point models of Multirays [4], Lee [6], Blomquist-Ladell [7], and the proposed here. For the models applications, the following set of parameters were considered and showed in the Table I: TABL I PAAMTS USD IN TH MODLS Parameters Symbols Values Frequency f 9 MHz Aerage height forest h m Transmitter height h t m Mobile receier height h r 3 m Transmitter antenna gain G T.4 db eceier antenna gain G.4 db Transmitted power P T 3 dbm oad paed, width W m Vehicle position w 7.75 m Forest relatie permittiity ε F. Forest conductiity σ F. ms/m oad relatie permittiity ε.7 oad conductiity σ 4 ms/m Transmitter distance range d 5 to 56 m oad-angle range α 67 to 84 degrees To illustrate the effect of the two knife-edges in the model, Fig.-3 shows the ariation of the receied aerage power as a function of distance d in the representatie case. This result is compared with the model proposed by Olieira et al. [4], called Multirays where they consider only one knife-edge. In the figure we can obsere a best fit to the experimental data by proposed model in this work.

8 Journal of Microwaes and Optoelectronics, Vol., No. 4, September eceied Aerage Power (dbm) xperimental Data Multirays [4] This Model q.(6) Distance (Km) Fig. 3- Variation of the receied aerage power with distance of the theoretical (Multirays, Proposed Model) and experimental results. In Fig.4 experimental results and the theoretical simulations with the models can be obsered. eceied Aerage Power (dbm) -4 xperimental Data Lee -5 Blomquist-Ladell Multirays [4] -6 This Model q.(6) Distance (Km) Fig. 4- Variation of the receied aerage power with distance of the theoretical (Blomquist-Ladell, Lee, Multirays, Proposed Model) and experimental results.

9 Journal of Microwaes and Optoelectronics, Vol., No. 4, September A simple way to make a quantitatie comparison is calculating the statistics of the error between the measured alues with the model results and with the linear regression. Table II presents this comparatie analysis. The absolute error,, between measurements and prediction is calculated for arious distances from transmitter, by: = MF K (7) j j j where j is the range of distances, MF j is the aerage measured alue inside the range j and K j is the alue of that range predicted by the model. Table II presents the absolute aerage error, standard deiation and the MS error. The absolute aerage error is calculated from (7) by the following expression: _ = F F j= j (8) where F is the number of distance ranges considered and j is the range itself. The standard deiation, σ, is calculated from the absolute error (7) and the absolute aerage error (8) by: F _ σ = j F ( ) (9) F j= The MS error is an association of the two preious parameters. Hence, by the use of (8) and (9) it can be written by: _ = ( ) + σ MS ()

10 Journal of Microwaes and Optoelectronics, Vol., No. 4, September Models TABL II OS COMPAISON BTWN MODLS Absolute Aerage rror (db) Standard Deiation(dB) MS rror (db) Linear egression This model Multirays [4] Lee Blomquist-Ladell V. CONCLUSION This work has presented a theoretical study to calculate the intensity field receied by a mobile station inside a forest enironment. The results inole relatiely simple formulas, which can be interpreted in terms of ray paths that represent diffracted and reflected waes. To alidate the model, a radio propagation measurement campaign was carried out. The measured experimental results, obtained with the mobile laboratory specifically mounted for this experiment, demonstrate that this model can be used to describe the receied field of cellular mobile systems in roads and highways crossing forested areas. The results demonstrated that the proposed model presented the best performance comparing to Multirays, Lee and Blomquist-Ladell point-to-point models simulated in this work. ACKNOWLDGMNT The authors are pleased to acknowledge the substantie support and encouragement of this work by Mr. Siqueira, L. G. of the CTUC/PUC/io, as well as by engineers of DMC/PA (Delegacia do Ministério das Comunicações-Pará). FNCS. T. Tamir, adio Wae Propagation Along Mixed Paths in Forest nironments, I Trans. on Antennas and Propagation, AP-5 (4), pp47-477, July G. P. S. Caalcante, and A. J. Giarola, Optimization of adio-communication in Three Layered Media, I Transactions on Antennas and Propagation, ol.3, n o, G. P. S. Caalcante, ogers D. A. and A. J. Giarola. "adio Loss in Forest Using a Model With Four Layered Media, adio Science, ol. 8, n o 5, A. N. Olieira, G. P. S. Caalcante, and G. L. Siqueira, ay Tracing Model for Mobile Systems in a Forested nironments, ITS98 International Telecommunication Symposium, São Paulo, Basil, pp.6-3, Aug. 998.

11 Journal of Microwaes and Optoelectronics, Vol., No. 4, September F. Ikegami, S. Yoshida, T. Takeuchi and M. Umehira, "Propagation Factors Controlling Mean Field Strength on Urban Streets", I Trans. on Antennas and Propagation, AP-3 (8), pp. 8-89, Aug W. C. Lee, Mobile Communications Design Fundamentals, John Wiley & Sons, Inc J. D. Parsons, The Mobile adio Propagation Channel, John Wiley & Sons, Inc. 99.

RECOMMENDATION ITU-R P Attenuation in vegetation

RECOMMENDATION ITU-R P Attenuation in vegetation Rec. ITU-R P.833-3 RECOMMENDATION ITU-R P.833-3 Attenuation in egetation (Question ITU-R 0/3) (99-994-999-00) The ITU Radiocommunication Assembly considering a) that attenuation in egetation can be important