Outdoor path loss models for ieee 802.16

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outdoor path loss models for IEEE 802.16

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Outdoor path loss models for ieee 802.16

  1. 1. Outdoor Path loss models for IEEE 802.16 in suburban and campus-like environments Damiano De Luca(b), Fabio Fiano(d), Franco Mazzenga(a), Cristiano Monti(b), Stefano Ridolfi(e), Francesco Vallone(c) (a) Dipartimento di Ingegneria Elettronica, University of Rome Tor Vergata, Via del Politecnico 1, 00133, Roma, Italy (b) Consorzio Universit`a Industria Laboratori di Radiocomunicazioni, RadioLabs (c) Ericsson Telecomunicazioni (d) University of Rome Tor Vergata (e) British Telecom Italia Contact author: F. Mazzenga, email: mazzenga@ing.uniroma2.it Abstract— Wireless metropolitan area networks (WMANs) based on IEEE 802.16 standard are widely deployed to provide users with wireless network connectivity, anytime, anyplace. In particular IEEE 802.16 standard has been developed to provide fixed and mobile broadband applications at lower costs for installation as compared with traditional wired infrastructures. In this paper we present the main results of a measurement campaign on propagation at 3.5 GHz conducted by BT Italy and Ericsson with the University of Rome Tor Vergata. Path loss channel model obtained from experimental data are also presented. I. INTRODUCTION The evolution of broadband Internet access anywhere, at any time, can became a reality thanks to the novel broadband technologies such as WiMAX. WiMAX promises to open new, economically viable market opportunities for operators, wire- less Internet service providers and equipment manufacturers. The flexibility of wireless technology, combined with high troughput, scalability and long-range features of the IEEE 802.16 standard helps to fill the broadband coverage gaps and reach millions of new residential and business customers worldwide. IEEE 802.16 [2],[3] is a specification for fixed broadband wireless metropolitan access networks (MANs) that can use a point-to-multipoint architecture. The Worldwide Microwave Interoperability Forum is a non-profit consortium dedicated to promoting the adoption of this technology and ensuring that different vendors’ products will interoperate. In the typical operation mode the WiMAX system consists of two parts: a WiMAX base station and a WiMAX receiver, also referred as customer premise equipment (CPE) that can be fixed on mobile. The 802.16 devices operating in the 3.5 − 3.8 GHz band, are designed for easy, fast and low cost installation. However accurate planning for outdoor cellular- like WMAN is required in order to obtain maximum system capacity and an estimate of the number of BSs required to cover a service area for a specified quality of service. Current practice of network planning is based on the path loss models that are specific of the propagation environment around the BSs. Up to now only few results on propagation models in the 3.5 − 3.8 GHz band have been presented in the literature [4]. In this paper we present the main results of a measurement campaign on propagation at 3.5 GHz conducted by BT-Italia and Ericsson with the University of Rome Tor Vergata. The considered tests area are depicted in fig.1 and Fig.2. Fig. 1. Measurement test area - BT Italy In both cases up to 200 measurements (mainly acquired in NLOS conditions) of the received power have been collected during the measurement campaign but about 170/180 only have been used to evaluate the parameters of path loss models. The paper is organized as a follows: section II and section III the measurement setup and data process are respectively described; section IV shows the outdoor path loss channel model while in section V the results are described. As an example of application the section VI shows the link budget. II. MEASUREMENT SETUP The area in Fig.1 includes the BT Italy employee’s building in Rome and it is representative of a typical suburban propaga- tion environment. The buildings are not higher than 43 m and the width of the streets can vary from 4 up to 10 m. The Base Station antenna was positioned on the most visible building 1-4244-0353-7/07/$25.00 ©2007 IEEE This full text paper was peer reviewed at the direction of IEEE Communications Society subject matter experts for publication in the ICC 2007 proceedings. 4902
  2. 2. Fig. 2. Measurement test area - Ericsson campus Fig. 3. Measured path loss for each point (BT Italy) (see Fig.1) and the measurement equipment was installed on a car that moved in the area. The receiver antenna gain was 3 dB and the equipment operates at 3.5 GHz. Received power was measured parking the car in the areas evidenced in Fig.1. The car is also equipped with a GPS receiver used to determine its position for each measure. The area in Fig.2 includes the Ericsson research laboratories in Rome and it is representative of a typical campus-like propagation environment. The buildings are not higher than 16 m and the width of the streets can vary from 2 up to 8 m. The transmitting antenna was positioned on the highest building (see the red arrow in Fig.2) and the measurement equipment was installed on a van that moved in the area. The receiver antenna gain was 3 dB and the equipment operates at 3.5 GHz with a signal bandwith of 3.5 MHz. The measurement equipment consisted of: one IEEE 801.16- 2004 Base Station model Airspan Macromax equipped with at 60-degree antenna and a portable PC with an IEEE 802.16- 2004 Self Install CPE designed to sit next to a computer on a desktop. CPE antenna containing four 90-degree with high-gain directional antennas providing 360 degree coverage (CPE selects antenna with best RF reception). The values of the received power were extracted from the CPE using a software provided by BT Italy. The test consisted on hold the position of the Base Station and CPE too and measuring the power received with an EIRP of 23dBm (200mW). Outdoor measurements are collected by driving around map shown in Fig.1 and Fig.2 for about 1 Km maximum from the Base Station. Every point over the map represents a fixed position of the CPE where we collected about 30 samples of the received power for a total measurement time interval of 100s. Graphics in fig.3 and in fig.4 show the path loss values for each point where samples were collected for both scenarios. Fig. 4. Measured path loss for each point (Ericsson campus) III. DATA PROCESS For each set of measured values and for both scenarios we have preliminarily removed some sample that were considered too far from the majority of values (outlier) as shown in the next figures representing the model fitting. We also have excluded the samples with too large standard deviation. This remedy tries to remove the environment variability measure- ment noise caused by the presence of cars, bus, etc. during the measure. IV. OUTDOOR PATH LOSS CHANNEL MODEL The path loss model considered in this paper are summa- rized in this Section. Most models aim to predict the median This full text paper was peer reviewed at the direction of IEEE Communications Society subject matter experts for publication in the ICC 2007 proceedings. 4903
  3. 3. path loss, i.e. the loss not exceeded at fixed percent of locations and/or for fixed percent of the time. This fixed value is tied to the service to provide. Knowledge of the signal statistics then allows the estimation of the variability of the signal so to determine the percentage of the specified area that has an adequate signal strength. The One Slope (OS) model assumes a linear dependence between the path loss (dB) and the logarithm of distance. In the formulation for (OS) model 1, d is distance between the transmitter and the receiver i.e. and usually expressed in meters L(d) = l0 + 10γ log(d), (dB) (1) and l0 is the path loss at 1 meter distance, γ is the power decay index or the path loss exponent dual (γ=2 is free space) with l0 = −27.5 + 20 log(f), (dB) (2) V. RESULTS The parameters of the model (1) have been obtained through best square fitting with collected data. The statistics of data points in the scenarios are represented as follows (Table I, Table II). Parameters were obtained considering only the data showing the RSSI standard deviation. γ RSSI Standard Deviation (σ) l0 Free space 2 1.348 129.01 OS 3.032 1.348 41.10 TABLE I PATH LOSS EXPONENT, RSSI STANDARD DEVIATION AND l0 (BT ITALY) γ RSSI Standard Deviation (σ) l0 Free space 2 0.6525 103.28 OS 3.533 0.6525 9.711 TABLE II PATH LOSS EXPONENT, RSSI STANDARD DEVIATION AND l0 (ERICSSON) Subsequently, starting from the fitting obtained from the path loss models in (1), we show the typical parameters of the models considered at 3.5 GHz with experimental data. To evaluate the goodness of the model with respect to data, we considered the R-Square and RMSE. The first parameter called R-Square measures how successful the fit is in explaining the variation of the data e.g R-square is the square of the correlation between the response values and the predicted response values. It is also called the square of the multiple correlation coefficient and the coefficient of multiple determi- nation. R-square is defined as the ratio of the sum of squares of the regression (SSR) and the total sum of squares (SST), where SST = SSR + SSE. Given these definitions, R-square is expressed as R − SQUARE = 1 - SSE/SST. R-square can take on any value between 0 and 1, with a value closer to 1 indicating a better fit. The second parameter is called Root Mean Squared Error and is also known as the fit standard error and the standard error of the regression. A RMSE value closer to 0 indicates a better fit. To evaluate the goodness of the model with respect to data we also considered the fitting of the experimental data with a free space alike model considering the constant l0 as an unknown and γ=2. Results have been reported in table III and IV. A. First Area : BT ITALY This test refers at BT ITALY area shown in Fig.1. In this case the 1 becomes L(d) = l0 + 10γ log(d) (dB) (3) with l0 representing a constant that provides the lower error in the fitting calculation. The l0 value is shown in table I. The cumulative distribution of the model error is shown in fig.5. R SQUARE RMSE OS 0.3713 6.927 Free Space 0.3283 7.137 TABLE III SUMMARY BT ITALY Table III shows the two statistic parameters described pre- viously. Fig. 5. Cumulative distribution of the model error - OS model - Relatively to Free Space model (γ = 2) the value of parameter l0 is shows in table I and the statistic result fitting for Free Space model is shows in fig.6; R-SQUARE and RMSE are lists in table III. A qualitative comparison between the models is shown in fig. 7 B. Second Area : Ericsson Campus With respect to the Ericsson Area test shown in Fig.2, starting from the 1 This full text paper was peer reviewed at the direction of IEEE Communications Society subject matter experts for publication in the ICC 2007 proceedings. 4904
  4. 4. Fig. 6. Cumulative distribution of the model error - Free Space model - Fig. 7. Comparison between the models where l0 represents a constant that provides the lower error in the fitting calculation. The l0 value is shows in table II. The cumulative distribution of the model error is shown in fig.8. Relatively to Free Space model (γ = 2) the value of parameter l0 is shows in table II and the statistic result fitting for Free Space model is shows in fig.9; R-SQUARE and RMSE are lists in table IV. VI. LINK BUDGET In this section we show a comparison between the measured and calculated path loss with the models described above. Moreover we show an example of the coverage map calculated with parameters obtained from OS model for both environ- ments. For suburban environment as BT ITALY scenario we show the results in Table V and fig.11 obtained using a software tool provided by RadioLabs. For campus-like environments as Ericsson research labora- tories campus the Table VI and fig.12 show the results obtained R SQUARE RMSE OS 0.7083 7.280 Free Space 0.5749 8.765 TABLE IV SUMMARY ERICSSON Fig. 8. Cumulative distribution of the model error - OS model - Fig. 9. Cumulative distribution of the model error - Free Space model - from software provided by RadioLabs. Finally we show a link budget example to determine the maximum coverage ray with the receiver power sensitivity fixed at -100 dBm. The used equation is PT xGT xGRx/L(d) = Psensitivity The result of link budget is shown in Table VII. VII. CONCLUSIONS The characterization of outdoor path loss is an important step in wireless network design in order to estimate the radio This full text paper was peer reviewed at the direction of IEEE Communications Society subject matter experts for publication in the ICC 2007 proceedings. 4905
  5. 5. Fig. 10. Comparison between the models Distance(m) Pathloss(dB) OS(dB) FS(dB) 1 188.62 108.26 110.10 118.18 2 294.88 117.54 115.98 122.06 3 396.39 129.52 119.88 124.63 4 445.85 121.68 121.42 125.65 5 495.04 122.92 122.80 126.56 6 548.22 116.71 124.15 127.44 7 604.07 135.56 125.42 128.29 8 695.08 116.49 127.27 129.50 9 751.24 127.00 128.290 130.18 10 863.03 125.450 130.120 131.38 TABLE V COMPARISON PATH LOSS (BT ITALY) Fig. 11. Coverage map with OS model (BT ITALY) coverage and the costs. In this paper we used measured data to evaluate the parameters of several path loss channel models some of them proposed in the current literature. In particular, Free space and One Slop models were analyzed and results have been provided for two different categories Distance(m) Pathloss(dB) OS(dB) FS(dB) 1 23.714 69.377 58.290 74.579 2 54.337 69.759 71.012 81.781 3 80.825 66.569 77.105 85.230 4 93.981 90.687 79.418 86.540 5 137.11 92.614 85.214 89.821 6 222.56 91.265 92.646 94.028 7 240.51 97.633 93.837 94.702 8 261.15 94.897 95.099 95.417 9 346.11 95.828 99.422 97.863 10 390.98 93.500 101.29 98.922 TABLE VI COMPARISON PATH LOSS (ERICSSON) Fig. 12. Coverage map with OS model (Ericsson Campus) BTITALY ERICSSON model distance(m) distance (m) OS 996 1570 FS 927 1849 TABLE VII LINK BUDGET: MAXIMUM RAY COVERAGE of environments: sub-urban and campus-like environment. The comparison between the parameters of the models have been shown and the cumulative distribution of the considered models error are also shown. Furthermore in this work is also shown a link budget example calculated with parameters obtained from OS model for both environments. REFERENCES [1] The Business of WiMAX. Deepak Pareek. John Wiley and Soons June 2006. [2] Standard IEEE 802.16d-2004 available on site http://www.ieee802.org/16 [3] Standard IEEE 802.16e-2005 available on site http://www.ieee802.org/16 published on 28 February [4] V. Erceg, K. V. S. Hari, et al., ”Channel models for fixed wireless applications,” tech. rep., IEEE 802.16 Broadband Wireless Access Working Group, January 2001 [5] A Survey of Various Propagation Models for Mobile Communication Tapan K. Sarkar, Zhong Ji, Kyungjung Kim, Abdellatif Medouri, and Magdalena Salazar-Palma IEEE Antennas and Propagation Magazine, Vol.45, No.3,June 2003 This full text paper was peer reviewed at the direction of IEEE Communications Society subject matter experts for publication in the ICC 2007 proceedings. 4906

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