Near Ground/Floor RF Path Gain Measurements in Indoor Corridors at 2400 MHz for Wireless Sensor Communications

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1 Available online at Procedia Engineering 30 (2012) International Conference on Communication Technology and System Design 2011 Near Ground/Floor RF Path Gain Measurements in Indoor Corridors at 2400 MHz for Wireless Sensor Communications Abstract T. Rama Rao b, D. Balachander a, D. Murugesan c, S. Ramesh d and M.V.S.N. Prasad e, a* RADMIC, Dept. of Telecommunications Engineering, SRM University, Kattankulathur , Chennai, India National Physical Laboratory, Dr.K.S.krishnan Road, Pusa, New Delhi , India Radio frequency (RF) propagation path gain (PG) measurements were made in typical narrow straight and wide straight indoor corridors at 2400 MHz in a modern multi-storied building utilizing RF equipment and Matlab simulations of Ray-tracing technique, free space model, ITU-R model and full-3d Ray-tracing model of Wireless Insite. Measured PG values showed similar patterns with simulated values in most of the scenarios. The research work presented in this paper is predominately geared towards characterizing radio link for Wireless Sensor Communications/Networks in typical indoor corridor environments Published by Elsevier Ltd. Selection and/or peer-review under responsibility of ICCTSD 2011 Open access under CC BY-NC-ND license. Keywords: Indoor Propagation;Path gain;field strength measurements;ray-tracing technique;wireless Sensor Communications.; 1. Introduction In today s world, wireless is the new electricity. With the propelling developments in design & fabrication technologies and brisk demands for ubiquitous wireless connectivity for various applications/services, the wireless communications landscape is changing rapidly. Recent advances [1, 2, 3, 4] have resulted in the ability to integrate sensors, wireless communications and digital electronics into a single integrated circuit package. This capability is enabling networks comprised of very low cost sensors that are able to communicate with each other. Measuring, monitoring and controlling nearly any process is becoming feasible with the current generation of wireless sensors. Wireless Sensor Networks (WSN) are emerging as a significant technology and have the potential to revolutionize the harnessing of data from the physical world, enabling applications that previously were not practical and are attracting *D. Balachander. Tel.: address: dpchander@gmail.com Published by Elsevier Ltd. doi: /j.proeng Open access under CC BY-NC-ND license.

2 T. Rama Rao et al. / Procedia Engineering 30 (2012) increased interest for applications [3, 4, 5, 6] in a variety of fields. such as the large-scale monitoring of the earth s environment, civil structures [7], animal habitats, industrial sensing and diagnostics [11], critical infrastructure protection, gathering sensing information in inhospitable locations including biochemical hazard detection & tracking, health monitoring, consumer & military uses [8, 9, 10]. All the sensor measurements & control commands are transmitted over wireless links connecting the nodes and the information/data moves hop by hop along a route.wireless sensor transceiver systems typically have their antenna elements located at or near ground/floor (0 to 30 cm height), which are considerably lower than hand-held devices. As the wireless sensor antennas operate so near to the ground, the distance at which line-of-sightblockage occurs is comparatively short. And, at low antenna heights the path ismore likely to be blocked by trees, bushes, grass, walls or other natural man-made structures. Further, antenna impedance and field pattern fluctuate with varying height above the ground plane [12, 13] regardless of the antenna orientation. Non-uniform ground dielectric properties can also affect the path loss and finite conductivity of the ground cannot be ignored in the near-ground radiation problem [14, 15]. The lossy ground directly generates effects antenna mismatch and a complex reflection coefficient, that together account for the loss mechanisms. These and other effects lead to a significant decrease in the signal strength when the antennas are touching or near to the ground/floor. Due to this, the terrain and environments where the sensor node is deployed has significant influence on the attenuation factors along the RF propagation path. Successful WSN ssystem design and deployment necessitates a sound knowledge of the RF channel characteristics. This knowledge will lead to the selection of an appropriate modulation scheme and radiated power that will ensure adequate reception while preserving battery life. Energy efficient wireless communications is an essential requirement for WSN s in many environmental monitoring applications. Radio propagation measurements have been performed and models developed for cellular frequencies [16, 17, 18, 19].However, those measurements are not directly applicable to WSN s scenario because the sensor node antennas are likely to lie on or near the ground/flooras opposed to a person holding a mobile phone and the environments in which wireless sensor nodes deployed are typically different from the cellular network scenarios. Around 11 db decrease in signal strength [20]was observed when a cellular phone user lowers from a standing position to a lying position. Channel measurements at MHz were performed with ground-lying antennas by Sohrabi, Manriquez and Pottie [21]. The range of pathloss exponent and shadowing variance for indoor & outdoor environments were determined. Foran, Welch and Walker [22] analyzed the effects associated with placing a man-portable radio transceiver very near the ground. Signal strength of 16.8 db was observed at 915 MHz when a soldier drops from the crouched position to the prone position. Channel measurements at 300 & 1900MHz were presented for near-ground propagation, characterizing the effect of antenna heights, radiation patterns and foliage by Joshi et al.[23]. Molina et al.[24] performed channel measurement campaigns in open quasi-ideal areas at 868 MHz for WSN s. And, ShurjeelWyne et al. [25] proposed a statistical model for indoor office wireless sensor channels utilizing sensor node locations.petrova M et al [26] analyzed the properties & performance through measurement of the RSSI(Received Signal Strength Indicator) using transceiver boards. Browne, David Wet al. [27] demonstrated a radio test-bed at 2.4 & 5.8 GHz.ChangsuSuh et al. [28] have done performance evaluation areas of WSN s and IEEE standard, designed a wireless propagation model and RF physical stack based on the 2-Ray ground path loss model and transceiver board.an empirical investigation to the attainable accuracy of RF positioning system based on RSSI using sensor node test bed & simulations done by C. Ladha, B.S Sharif, and C.C Tsimenidis [29]. G. Ferrari et al. [30] analyzed the performance of realistic WSN s in various indoor scenarios. Some experiments conducted for the practical transmission distances between wireless sensors and their BS s under different environmental conditions and with different antennas by R.A. Abd-Alhameed et al [31] using wireless sensor nodes at 900 & 2400 MHz A Practical RF Propagation Model for WSNs [32] proposed by TsenkaStoyanova et al, considering the most important WSN s constraints & RF signal propagation path loss factors and verified with 2.4GHz radio modules. Victor P. Gil J and Ana G Armada

3 838 T. Rama Rao et al. / Procedia Engineering 30 (2012) [33] made field measurements and guidelines for the application of WSN s to the environment and security utilizing RSSI of sensor boards. While wide-ranging work using RF measurements [20, 21, 22, 23, 24] and RSSI measurements using commercial wireless sensor boards [26, 27, 28, 29, 30, 31, 32, 33] have been performed to characterize the WSN radio link in other parts of the globeby various researchers especially in indoor environments, no such results have been reported for WSN scenarios in India.The differences in building materials and construction practices in India when compared to the other countries in which WSN radio-link studies have been performed suggests that indoor propagation might be different. Given the sensitive dependence of WSN performance on the radio link, any differences that exist should be understood before deploying WSN s. The objective of this paper is to provide information relevant to measuring and modeling the radio link for WSN geometries, frequencies and typical configurations. The work presented in this paper is part of a larger effort to model the WSN radio link in a range of settings within the indoor environmental circumstances of Indian sub-continent. The next section provides experimental details followed by comparison of measured and modeled results. That comparison provides insights into the mechanisms affecting the WSN propagation paths. 2. Experiment Details 2.1. Measurement Details Near ground/floor RF propagation measurements were made in indoor corridor environments (narrow straight & wide straight corridors) at 2400 MHz utilizing RF equipment, Vector Signal Generator (Agilent N5182A) and Vector Signal Analyzer (Agilent N9010A) at transmitted power of 10 dbm (0.01 watt with BPSK modulated signal). Transmitting and receiving antenna heights are 2 cm and 10 cm from the floor/ground respectively and Omni-directional transmitting (Tx), receiving (Rx) antenna gains of 2, 5, 8 & 14 dbi with vertical polarization Environment Description Narrow Straight Corridor: We carried out RF propagation measurements in a narrow straight corridor of 14.0 m length, 1.83 m wide and 2.52 m height in a modern multi-floored building, which is made-up with concrete and steel. The left and right walls of the narrow straight corridor are made of concrete (relative permittivity ε r = 7.0 [16, 34, 35, 36]) with glass windows (ε r = 4.0). The floor of the corridor is covered with Porcelain tiles (ε r = 6.0) and Concrete Ceiling is covered with Gypsum board (ε r = 3.0). Wide Straight Corridor: We also carried out measurements in a wide straight corridor of 10.0 m length, 2.82 m wide and 3.1 m height. The left and right walls of the narrow straight corridor are made of concrete (ε r = 7.0) with iron grilled glass windows. The Concrete Ceiling of the straight corridor floor is filled with Green Granite (ε r = 7.75) Simulation Details Matlab simulations were executed utilizing a deterministic approach of a simple 2-D Ray-tracing technique based on classical geometrical optics and image method [16, 19] to account for the direct ray & reflected rays from wall, floor and ceiling, respectively. Further, for comparison & evaluation purpose, we have executed Matlab simulations of ITU-R site-general model [37] and full 3D Ray-tracing model of commercial software Wireless Insite [38].(The Mathematical equations anddetailed treatment of these models could be found in respective references).

4 T. Rama Rao et al. / Procedia Engineering 30 (2012) Observations/Results The following Figures and Tables provide measured and simulated Path Gain (PG) values obtained in our RF propagation measurements/simulations in indoor corridors at 2.4 GHz with antennas placed near to the ground/floor.fig.1shows PG values of measured using RF equipment, modeled using Ray-tracing, free space and 3-D based Wireless Insite (WI) model are showing similar trends except from the beginning of the path distance. The ITU-R model differed with other except in middle of path distance. However, 2-Ray model PG values differed largely with the measured and simulated values. Table 1 summarizes PG values at 2.4 GHz obtained in a narrow straight corridor with Porcelain tile flooring with Tx& Rx antennas height at 2 cm. Remarkably here, measured PG mean values are in close agreement with the WI model. Fig.2 shows PG values of measured using RF equipment, modeled using Ray-tracing, free space model, 2-Ray model, simulated ITU-R model and WI model are showing similar trends up to 4 m and after that except 2-Ray model, all other simulated PG values are continued similar patterns. Table 2 summarizes PG values at 2.4 GHz obtained in a narrow straight corridor with Porcelain tile flooring with Tx& Rx antenna height at 10 cm. Here too, measured PG mean values are in close agreement with the simulated values of WI. Fig.1 Case A-Measured & Simulated PG in a narrow straight Fig.2 Case B-Measured & Simulated PG in a narrow straight corridor with porcelain tile flooring at 2cm antennas height corridor with porcelain tile flooring at 10cm antennasheight Fig.3 Case C-Measured & Simulated PG in a wide straight Fig.4 Case D-Measured & Simulated PG in a wide straight corridor with green granite flooring at 2cm antennas height corridor with green granite flooring at 10cm antennas height

5 840 T. Rama Rao et al. / Procedia Engineering 30 (2012) Table 1.Summary of PG values in a narrow straight corridor with porcelain tile flooring and antennas height at 2cm All Values in db Maximum Minimum Mean Standard Deviation Free Space Loss Ray-Tracing Model Ray Model Measured 2dBi Antenna Measured 5 dbi Antenna ITU-R Model Wireless Insite 2 dbi Wireless Insite 5 dbi Table 2.Summary of PG values in a narrow straight corridor with porcelain tile flooring and antennas height at 10cm All Values in db Maximum Minimum Mean Standard Deviation Free Space Loss Ray-Tracing Model Ray Model Measured 8dBi Antenna Measured 14 dbi Antenna ITU-R Model Wireless Insite 8 dbi Wireless Insite 14 dbi Table 3. Summary of PG values in a wide straight corridor with green granite flooring and antennas height at 2cm All Values in db Maximum Minimum Mean Standard Deviation Free Space Loss Ray-Tracing Model Ray Model Measured 2dBi Antenna Measured 5 dbi Antenna ITU-R Model Wireless Insite 2 dbi Wireless Insite 5 dbi Fig.3 shows PG values of measured using RF equipment, modeled using Ray-tracing, free space model, simulated ITU-R model and WI model are showing similar patterns from 2 m of the path distance. The 2- Ray model deviated largely with others from the path distance of 2m. Table 3 summarizes PG values at

6 T. Rama Rao et al. / Procedia Engineering 30 (2012) GHz obtained in a wide straight corridor with green granite flooring with Tx& Rx antenna height at 2 cm. Fig.4 shows PG values of measured using RF equipment, modeled using Ray-tracing, 2-Ray model, free space model, simulated ITU-R model and WI model are showing similar trends up to 9 m of the path distance. Table 4 summarizes PG values at 2.4 GHz obtained in a wide straight corridor with green granite flooring with Tx& Rx antenna height at 10 cm. Here as well, measured PG mean values are in close agreement with the modelled values of WI model.table 5 shows predicted models standard deviation of errors (error = predicted value measured value) deduced from the above four cases, which provides suitability of the simulated &modeled methods with measured PG values in our study. Table 4.Summary of PG values in a wide straight corridor with green granite flooring and antennas height at 10cm All Values in db Maximum Minimum Mean Standard Deviation Free Space Loss Ray-Tracing Model Ray Model Measured 8dBi Antenna Measured 14 dbi Antenna ITU-R Model Wireless Insite 8 dbi Wireless Insite 14 dbi Table 5. Standard deviation of model errors in narrow straight/ wide corridors Models Narrow Straight Corridor Wide Straight Corridor Case A Case B Case C Case D Free Space Loss Ray-Tracing Model Ray Model ITU-R Model Wireless Insite Model Conclusions In view of the recent developments in Wireless Sensor Communications/Networks, comparisons of near ground/floor RF propagation measurements/simulations were made at 2400 MHz in a typical indoor narrow straight and wide straight corridor environments in a modern multi-storied building. In our field strength measurement study we observed that, measured PG values using RF equipment and modeled using 3D Ray-tracing model of Wireless Insite are in close agreement in all cases. Modeled using Raytracing, free space and ITU-R model are showing similar patterns in all cases. And, in all scenarios, PG values of 2-Ray model are deviating largely and ITU-R model also showing differences with others.

7 842 T. Rama Rao et al. / Procedia Engineering 30 (2012) Further, it is observed that 2-Ray model & ITU-R models are predicting higher standard deviation of error values than the simulated Ray-tracing, free space and Wireless Insite models. Further, this work noticed that, along with the physical and material properties of the reflecting surfaces in the vicinity of the transmitter & receiver antennas, conductivity of the ground/floor and the geometry of the measurement environment are playing major roles for the significant decrease in the signal strength when the antennas are touching or near to the floor. As noted above, what is reported here is only part of the overall effort to understand the possible unique nature of Indian WSN radio-link propagation scenarios. What is covered is preliminary work to measure & model radio-link behavior for a number of realistic WSN situations. The value of this work is that it demonstrates the variation between several measurement approaches, and it highlights the differences between commonly used modeling techniques. Acknowledgements Authors are very much appreciative to the Department of Science & Technology, Government of India for providing financial backing in executing this research work. References [1] Akyildiz I, Su W, Yogesh S and Cayirci E. A Survey on Sensor Network. IEEE Communications Magazines, August, [2] Lewis, F.L., Wireless Sensor Networks, Smart Environments: Technologies, Protocols, and Applications, ed. D.J. Cook and S.K. Das, John Wiley, New York, [3] Edgar H Callaway Jr. Wireless Sensor Networks: Architectures & Protocols. Auerbach Publications, [4] Savo G. Glisic. Advanced Wireless Networks: 4G Technologies. John Wily, 2006 [5] Chong C.Y and Kumar S.P. Sensor Networks: Evolution, Opportunities and Challenges. Proc. of the IEEE, Vol.91, No.8, August 2003, Pp [6] Culler D, Estrin D and Srivastava M. Overview of Sensor Networks. IEEE Computer Society, August [7] N. Xu, S. Rangwala, K. Chintalapudi, D. Ganesa, R. Govindan, and D. Estrin. A wireless sensor network for structureal monitoring, In Proc. of the ACM Conf. on Embedded Networked Sensor Systems. Nov [8] A. Cerpa, J. Elson, D. Estrin, L. Girod, M. Hamilton and J. Zhao. Habitat monitoring: Application driver for wireless communications technology. Proc. the Workshop on Data Communications in Latin America and the Caribbean, April2001. [9] A. Mainwaring, J. Polastre, R. Szewczyk, D. Culler and J. Anderson. Wireless sensor networks for habitat monitoring. ACM Int. Workshop on WSNs and Applications, USA, September [10] R. Szewczyk, A. Mainwaring, J. Polastre and D. Culler. An analysis of a large scale habitat monitoring application. In Proc. 2nd ACM Conf. on Embedded Networked Sensor Systems (SenSys). November [11] Rajeev.S, Ananda.A, Choon Chan.M and Tsang Ooi."Mobile, Wireless, and Sensor Networks: Technology,Applications and Future Directions", W, John Wiley, [12] W.C. Jakes (editor), Microwave Mobile Communication, IEEE Press, New Jersey, [13] R.E. Collins and F.J. Zucker (editors). Antenna Theory - part 2. McGraw-Hill, [14] John S. Seybold. Introduction to RF propagation. John Wiley & Sons, [15] William H. Tranter etal., Wireless Personal Communications Channel Modeling and Systems Engineering ; Chapter 1; Kluwer Academic Publishers, [16] Rappaport T.S. Wireless Communications: Principles and Practice. Prentice Hall, [17] Lee W.C.Y. Wireless & Cellular Telecommunications. McGraw Hill [18] Parsons J.D. Mobile radio propagation channel. John Wiley, [19] Betroni H.L. Radio Propagation for Modern Wireless Systems. Prentice Hall, [20] Welch T.B, Wood J.R, McParlin R.W, Schulze L.K, Flaherty T.P, Carlone Hanson S.G, Cahill R.J and Foran R.A. Very near ground RF propagation measurements for wireless systems. Vol.3, Pp.: , VTC [21] Sohrabi K, Manriquez B and Pottie G.J. Near ground wideband channel measurements in MHz. IEEE 49th Vehicular Technology Conf., Vol. 1, July 1999, pp

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