Performance analysis of Propagation Models of Wi-MAX in Urban, Suburban Area

Transcription

1 Performance analysis of Propagation Models of Wi-MAX in Urban, Suburban Area 1 K. Shiva Rani, 2 J. Mrudula 1 PG Student (M. Tech), Dept. of ECE, Geethanjali College of Engineering and Technology, Hyderabad. 2 Associate Professor, Dept. of ECE, Geethanjali College of Engineering and Technology, Hyderabad kshivarani41@gmail.com Abstract: Wi-Max (Worldwide Interoperability for Microwave Access) is a standards-based technology enabling the delivery of last mile wireless broadband access as an alternative to cable and DSL. The technology is specified by the Institute of Electrical and Electronics Engineers Inc., as the IEEE 2.16 standard. Calculation of Path losses and Received Signal Strength Indicator (RSSI) very useful for initial deployment of Wi-MAX networks. In this paper I compare and discuss the path loss models and RSSI for different propagation models at 2.4, 3.5 and 5.8GHz. Key words: NLOS, WI-MAX, WI-FI, RSSI, Propagation Models I. INTRODUCTION Worldwide Interoperability for Microwave Access (Wi- MAX) is currently one of the hottest technologies in wireless. The Institute of Electrical and Electronics Engineers (IEEE) 2 committee, which sets networking standards such as Ethernet (2.3) and Wi-Fi (2.11), has published a set of standards that define Wi-MAX. IEEE (also known as Revision D) was published in 2004 for fixed applications; 2.16 Revision E. The Wi-MAX Forum is an industry body formed to promote the IEEE 2.16 standard and perform interoperability testing. The Wi-MAX Forum has adopted certain profiles based on the 2.16 standards for interoperability testing and Wi-MAX certification. These operate in the 2.5GHz, 3.5GHz and 5.8GHz frequency bands, which typically are Licensed by various government authorities. Wi-MAX, is based on an RF technology called Orthogonal Frequency Division Multiplexing (OFDM), which is a very effective means of transferring data when carriers of width of 5MHz or greater can be used. Below 5MHz carrier width, current CDMA based 3G systems are comparable to OFDM in terms of performance. Wi-MAX is a standard-based wireless technology that provides high throughput broadband connections over long distance. Wi-MAX can be used for a number of applications, including last mile broadband connections, hotspots and high-speed connectivity for business customers. It provides wireless metropolitan area network (MAN) connectivity at speeds up to 70 Mbps and the Wi-MAX base station on the average can cover between 5 to 10 km. The Wi-MAX air interface is designed to operate over a range of frequencies from 2.5 to 2.69 GHz, from 3.4 to 3.6 GHz and from to GHz. The channel bandwidth can be an integer multiple of 1.25 MHz, 1.5MHz and 1.75 MHz with a maximum of 20 MHz, The licensed frequency 2.5 GHz is used in America and 3.5 GHz is used in Europe, Asia, and Africa. A) Wi-MAX vs. WLAN Unlike WLAN, Wi-MAX provides a media access control (MAC) layer that uses a grant-request mechanism to authorize the exchange of data. This feature allows better exploitation of the radio resources, in particular with smart antennas, and independent management of the traffic of every user. This simplifies the support of real-time and voice applications. One of the inhibitors to widespread deployment of WLAN was the poor security feature of the first releases. Wi-MAX proposes the full range of security features to ensure secured data exchange: - Terminal authentication by exchanging certificates to prevent rogue devices, - User authentication using the Extensible Authentication Protocol (EAP), - Data encryption using the Data Encryption Standard (DES) or Advanced Encryption Standard (AES), both much more robust than the Wireless Equivalent Privacy (WEP) initially used by WLAN. Furthermore, each service is encrypted with its own security association and private keys. B) Wi-MAX vs. Wi-Fi Wi-MAX operates on the same general principles as Wi- Fi -- it sends data from one computer to another via radio signals. A computer (either a desktop or a laptop) 25

2 equipped with Wi-MAX would receive data from the Wi-MAX transmitting station, probably using encrypted data keys to prevent unauthorized users from stealing access. The fastest Wi-Fi connection can transmit up to 54 megabits per second under optimal conditions. Wi-MAX should be able to handle up to 70 megabits per second. Even once that 70 megabits is split up between several dozen businesses or a few hundred home users, it will provide at least the equivalent of cable-modem transfer rates to each user. The biggest difference isn't speed; it's distance. Wi- MAX outdistances Wi-Fi by miles. Wi-Fi s range is about feet (30 m). Wi-MAX will blanket a radius of 30 miles (50 km) with wireless access. The increased range is due to the frequencies used and the power of the transmitter. Of course, at that distance, terrain, weather and large buildings will act to reduce the maximum range in some circumstances, but the potential is there to cover huge tracts of land. Wi-MAX is not designed to clash with Wi-Fi, but to coexist with it. Wi-MAX coverage is measured in square kilometers, while that of Wi-Fi is measured in square meters. The original Wi-MAX standard (IEEE 2.16) proposes the usage of GHz frequency spectrum for the Wi-MAX transmission, which is well above the Wi-Fi range (up to 5GHz maximum). But 2.16a added support for 2-11 GHz frequency also. One Wi-MAX base station can be accessed by more than 60 users. Wi- MAX can also provide broadcasting services also. Wi-MAX specifications also provides much better facilities than Wi-Fi, providing higher bandwidth and high data security by the use of enhanced encryption schemes. Wi-MAX can also provide service in both Line Of Sight (LOS) and Non-Line of Sight (NLOS) locations, but the range will vary accordingly. Wi-MAX will allow the interpenetration for broadband service provision of VoIP, video, and internet access simultaneously. Wi-MAX can also work with existing mobile networks. Wi-MAX antennas can "share" a cell tower without compromising the function of cellular arrays already in place. II. PERFORMANCE PARAMETERS Prior to the deployment of wireless communication, its network performance has to be evaluated to ensure efficiency and reliability. There is very little research done in the area of wireless network performance for communication in smart grids. Network performance parameter such as path loss indirectly affects the quality of signal of the wireless network. Path Loss: Path loss arises when an electromagnetic wave propagates through space from transmitter to receiver. The power of signal is reduced due to path distance, reflection, diffraction, scattering, free-space loss and absorption by the objects of environment. It is also influenced by the different environment (i.e. urban, suburban and rural). Variations of transmitter and receiver antenna heights also produce losses. In our thesis we mainly focus on path loss issue. In general it is expressed as: PL = Power Transmitted Power Received in db Received Signal Strength Indicator (RSSI) In telecommunications, received signal strength indicator (RSSI) is a measurement of the power present in a received radio signal. RSSI is a generic radio receiver technology metric, which is usually invisible to the user of the device containing the receiver, but is directly known to users of wireless networking of IEEE 2.11 protocol family. RSSI is an indication of the power level being received by the antenna. Therefore, the higher the RSSI number, the stronger the signal. RSSI can be used internally in a wireless networking card to determine when the amount of radio energy in the channel is below a certain threshold at which point the network card is clear to send (CTS). Once the card is clear to send, a packet of information can be sent. The Received Signal Strength Indicator (RSSI) or Signal Strength is a measure of how strong the most recent signal was when it reached its destination. The RSSI value ranges from 0 to 255. Higher RSSI values indicate a stronger signal. Reliable communication can best be achieved with RSSI values greater than 70. If the RSSI is too low the wireless communications may become intermittent or fail entirely. The received signal strength for Okumura model, Hat model and COST-231 model can be calculated as P r = P t + G t + G r PL A Pr is received signal strength in dbm. Pt is transmitted power in dbm. Gt is transmitted antenna gain in dbm. Gr is received antenna gain in dbm. PL is total path loss in dbm. A is connector and cable loss in dbm. In this work, connector and cable loss are not taken into consideration III. PATH LOSS MODELS In our paper, we analyze five different models which have been proposed by the researchers at the operating frequency of 2.5., 3.5 and 5.8 GHz. We consider free space path loss model which is most commonly used idealistic model. We take it as our reference model; so that it can be realized how much path loss occurred by the others proposed models. 26

3 3.1 Free Space Path loss Model: Free Space Path Loss Model (FSPL) Path loss in free space PLFSPL defines how much strength of the signal is lost during propagation from transmitter to receiver. FSPL is diverse on frequency and distance. The calculation is done by using the following equation. P LFSPL = log10 (d) + 20log10 (f) Where, f: Frequency [MHz] d: Distance between transmitter and receiver [m] Power is usually expressed in decibels (dbm). 3.2 Stanford University Interim (SUI) Model IEEE 2.16 Broadband Wireless Access working group proposed the standards for the frequency band below 11 GHz containing the channel model developed by Stanford University, namely the SUI models. The SUI model describes three types of terrain; they are terrain A, terrain B and terrain C. Terrain A can be used for hilly areas with moderate or very dense vegetation. This terrain presents the highest path loss. In our paper, we consider terrain A as a dense populated urban area. Terrain B is characterized for the hilly terrains with rare vegetation. This is the intermediate path loss scheme. We consider this model for suburban environment. Terrain C is suitable for flat terrains or rural with light vegetation, here path loss is minimum. The basic path loss expression of The SUI model with correction factors is presented as PL = A + 10* log 10 (d/d o ) + X f +X h + s for d> d0 Where the parameters are d: Distance between BS and receiving antenna [m], d 0: [m] Xf: Correction for frequency above 2 GHz X h : Correction for receiving antenna height[m]s: Correction for shadowing: Path loss exponent The parameter A is defined as A= 20 log 10 (4πd o /λ) And the path loss exponent γ is given by γ = a bh b + (c/h b ) Where, the parameter hb is the base station antenna height in meters. This is between 10 m and m. The constants a, b, and c depend upon the types of terrain. Parameter Terrain A (Urban area) Terrain B (Suburban area) Terrain C (Rural area) a b [1/m] C [m] Table I: Parameters for Different Type of Terrains for SUI Model 3.3 Hata-Okumura extended model or ECC-33 Model One of the most extensively used empirical propagation models is the Hata-Okumura model, which is based on the Okumura model. This model is a well-established model for the Ultra High Frequency (UHF) band. Recently, through the ITU-R Recommendation P.529, the International Telecommunication Union (ITU) encouraged this model for further extension up to 3.5 GHz. PL = A fs + A bm -G b -G r A fs : Free space attenuation [db] A BM : Basic median path loss [db] G B : Transmitter antenna height gain factor G r : Receiver antenna height gain factor These factors can be separately described and given by as A fs = log 10 (d) + 20 log 10 (f) A bm = log 10 (d) log 10 (f) [log 10 (f)] 2 G b = log 10 (h b /200) { [log 10 (d)] 2 } When dealing with gain for medium cities, the Gr will be expressed in G r = [ log 10 (f)][log 10 (h r ) 0.585] For large city G r = 0.759h r Where d: Distance between transmitter and receiver antenna [km] f: Frequency [GHz] hb: Transmitter antenna height [m] hr: Receiver antenna height [m] 3.4 COST 231 Walfish-Ikegami (W-I) Model This model is a combination of J. Walfish and F. Ikegami model. The COST 231 project further developed this model. Now it is known as a COST 231 Walfish-Ikegami (W-I) model. This model is most suitable for flat suburban and urban areas that have uniform building height.among other models like the Hata model, COST 231 W-I model gives a more precise path loss. This is as a result of the additional parameters introduced which characterized the different environments. It distinguishes different terrain with different proposed parameters. The equation of the proposed model is expressed in For LOS condition PL LOS = log (d) + 20 log (f) And for NLOS condition PL NLOS 27

4 Where = L FSL + L rts + L msd (for urban ) = L FS if L rts + L msd > 0 (for sub urban) LFSL= Free space loss L rts = Roof top to street diffraction L msd = Multi-screen diffraction loss IV. Calculation Parameters Values of parameters are given below Parameters Distance from transmitter to receiver Transmitter height Receiver antenna height Operating Frequency Average building height Building to building distance Street width Values 5km 50m Urban area 30m Suburban area 20m Rural area 2m to 10m 2.4,3.5 and 5.8GHz 15m 50m 25m Table II: Calculation Parameters IV. CALCULATION RESULTS A. Results from calculations for suburban area Figure 1, 2 and 3; show the results from calculations for suburban area: Figure 3: Comparison of path loss models for suburban area at 2.4GHz. B. Results from calculations for urban area Figure 4, 5 and 6; show the results from calculations for urban area: 170 Figure 4: Comparison of path loss models for urban area at 3.5GHz m receiver antenna height in suburban environment ks-ecc 33 b+- freespace 6m receiver antenna height in urban environment ks-freespace b+- ECC 33 6m receiver antenna height in urban environment ks-freespace b+- ECC m receiver antenna height in suburban environment ks-ecc 33 b+- freespace 70 Figure 1: Comparison of path loss models for suburban area at 3.5GHz. Figure 5: Comparison of path loss models for urban area at 5.8GHz. 6m receiver antenna height in urban environment ks-freespace b+- ECC m receiver antenna height in suburban environment ks-ecc 33 b+- freespace Figure 6: Comparison of path loss models for urban area at 2.4GHz. Figure 2: Comparison of path loss models for suburban area at 5.8GHz. 28

5 Figure 7: RSSI of COST- 231 Hata model (Therotical and practical) for 2.4GHz Figure 11: RSSI of Hata- okmura model for 5.8GHz Figure 8: RSSI of COST- 231 Hata model (Therotical and practical) for 3.5GHz Figure 12: RSSI of SUI model for 2.4GHz Figure 9: RSSI of COST- 231 Hata model (Therotical and practical) for 5.8GHz Figure 13: RSSI of SUI model for 3.5 GHz Figure 13: RSSI of Hata- okmura model for 2.4GHz Figure 14: RSSI of SUI model for 5.8 GHz Figure 10: RSSI of Hata- okmura model for 3.5GHz Figure 15: RSSI of COST-231 W-I model for 2.4GHz 29

6 Figure 16: RSSI of COST-231 W-I model for 3.5 GHz Figure 17: RSSI of COST-231 W-I model for 5.8 GHz V. CONCLUSION In this paper we have analyze the performance of path losses and RSSI at 2.4, 3.5 and 5.8GHz of Wi-MAX. As expected, the results affirm that the existing and most widely used path loss models, typically COST 231 W-I, ECC-33 and SUI, do not produce an accurate result for the 5.8-GHz system as the highest operating frequency that these models can support is up to 3.5GHz only. REFERENCES [1] Doppler spread, [Online]. Available: [Accessed: April 11, 2009] [2] [Accessed: June ] [3] Well known propagation model, [Online]. Available: model [Accessed: April 11, 2009] [4] IEEE 2.16 working group, [Online]. Available: [Accessed: April 11, 2009] [5] Empirical Models, [Online] Available: [Accessed April 18, 2009] [6] Jeffrey G Andrews, Arunabha Ghosh, Rias Muhamed, Fundamentals of WiMAX: understanding Broadband Wireless Networking, Prentice Hall, [7] Josip Milanovic, Rimac-Drlje S, Bejuk K, Comparison of propagation model accuracy for WiMAX on 3.5GHz, 14th IEEE International conference on electronic circuits and systems, Morocco, pp [8] D. Pareek, The Business of WiMAX, Chapter 2 and Chapter 4, John Wiley, 2006 on IEEE 2.16, IEEE wireless communications and networking Conference, Las Vegas, NV, v2, pp , April [9] V.S. Abhayawardhana, I.J. Wassel, D. Crosby, M.P. Sellers, M.G. Brown, Comparison of empirical propagation path loss models for fixed wireless access systems, 61th IEEE Technology Conference, Stockholm, pp , [10] T.S Rappaport, Wireless Communications: Principles and Practice, 2n ed. New delhi: Prentice Hall, 2005 pp [11] Electronic Communication Committee (ECC) within the European Conference of Postal and Telecommunication Administration (CEPT), The analysis of the coexistence of FWA cells in the GHz band, tech. rep., ECC Report 33, May [12] Simic I. lgor, Stanic I., and Zrnic B., Minimax LS Algorithm for Automatic Propagation Model Tuning, Proceeding of the 9th Telecommunications Forum (TELFOR 2001), Belgrade, Nov.2001 [13] V. Erceg, K.V. S. Hari, M.S. Smith, D.S. Baum, K.P. Sheikh, C. Tappenden, J.M. Costa, C. Bushue, A. Sarajedini, R. Schwartz, D. Branlund, T. Kaitz, D. Trinkwon, "Channel Models for Fixed Wireless Applications," IEEE 2.16 Broadband Wireless Access Working Group, [14] M. Hata, Empirical formula for propagation loss in land mobile radio services, IEEE Transactions on Vehicular Technology, vol. VT- 29, pp , September [15] Y.Okumura, Field strength variability in VHF and UHF land mobile services, Rev. Elec. Comm. Lab. Vol. 16, pp , Sept-Oct [16] Rony Kowalski, The Benefits of Dynamic Adaptive Modulation for High Capacity Wireless Backhaul Solutions, Ceragon Networks, [Online]. [17] WiMAX Forum, Documentation, Technology Whitepapers, [Online]. Available at WiMAX 30