Design and Modeling of Propagation Models for WiMAX Communication System at 3.7GHz & 4.2GHz

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1 Design and Modeling of Propagation Models for WiMAX Communication System at 3.7GHz & 4.2GHz B.Chandran Mahesh 1, Dr. B. Prahakara Rao 2 1 Malineni Perumallu College of Engineering, Affiliated to JNTUK, Kakinada cmahesh86@gmail.com 2 Professor in Dept.of ECE, JNTUK, Kakinada drpr@rediffmail.com ABSTRACT WiMAX technology is ased upon the IEEE standard enaling the delivery of wireless roadand services anytime, anywhere. WiMAX products can accommodate fixed and moile usage models across a range of applications. The IEEE standard was developed to deliver non-line-of-sight (NLoS) connectivity etween a ase station and suscrier station. The Worldwide Interoperaility of Microwave Access (WiMAX) technology ecomes popular and receives growing acceptance as a Broadand Wireless Access (BWA) system. Estimation of path loss is very important in initial deployment of wireless network and cell planning. Numerous path loss (PL) models (e.g. Okumura Model, Hata Model) are availale to predict the propagation loss. In this paper we compare and analyze five path loss models ( COST 231 Hata model, ECC-33 model, SUI model, Ericsson model and COST 231 Walfish-Ikegami model) in uran, suuran and rural environments in NLOS condition. Our main concentration in this paper is to find out a suitale model for different environments to provide guidelines for cell planning of WiMAX at operating frequencies 3.7 GHz and 4.2 GHz. There are several empirical propagation models which can precisely calculate up to 2 GHz. But eyond 2 GHz, there are few reliale models which can e referred for the WiMAX context. There are few proposed models [1]-[4], which focus on frequency range at 3.7 to 4.2GHz out of which we ase our analysis. In this paper, we compare and analyze path loss ehavior of some proposed models at GHz frequency and. Thus, a network engineer may consume his/her time y using our referred model for deploying the initial planning. Keywords: Path loss, Time dispersive, Frequency correction factor, Multi-screen diffraction loss. 1. INTRODUCTION In wireless communication systems, transfer of information etween the transmitting antenna and the receiving antenna is achieved y means of electromagnetic waves. The interaction etween the electromagnetic waves and the environment reduces the signal strength send from transmitter to receiver, that causes path loss. Different models are used to calculate the path loss. Frequency and has a major consequence on the dimension and planning of the wireless network. The operator has to consider etween the availale frequency and and deploying area. The following representation shows the real idea aout using the frequency and all over the world. We choose 3.7GHz-4.2 GHz and in our studies ecause it is widely used and all over the world. Moreover, this and is licensed, so that interfere is under control and allows using higher transmission power. Furthermore, it supports the NLOS condition and etter range and coverage than 2.5 GHz and 5.8 GHz. In an ideal condition, WiMAX recommends up to 75 Mps of it rate and range within 50 km in the line of sight etween transmitter and receiver [2]. But in the real field, measurements show far differences from ideal condition i.e. it rate up to 75 Mps and coverage area etween 5 and 8 km. To reach the optimal goal, we identified the following impairments of the transmission etween transmitter to receiver. 1. Path loss 2. Co-channel and adjacent-channel interference 3. Fading 4. Doppler spread Path loss (PL): Path loss arises when an electromagnetic wave propagates through space from transmitter to receiver. Volume 2, Issue 1, January 2014 Page 1

2 The power of signal is reduced due to path distance, reflection, diffraction, scattering, free-space loss and asorption y the ojects of environment. It is also influenced y the different environment (i.e. uran, suuran and rural). Variations of transmitter and receiver antenna heights also produce losses. In our paper we mainly focus on path loss issue. In general it is expressed as: PL=POWER TRANSMITTED/POWER RECEIVED in db. Co-channel and adjacent-channel interference: Co-channel interference or crosstalk occurs when same frequency is used y two different transmitters. Adjacent-channel interference (ACI) arises when a signal gained redundant power in an adjacent channel. It is caused y many reasons like improper tuning, incomplete or inadequate filtering or low frequency. Fading: Fading is a random process; a signal may experience deviation of attenuation due to multipath propagation or shadowing in any ostacles in certain roadcast media. Doppler spread: A moile user causes a shift in the transmitted signal path y its velocity. This is known as Doppler shift. When signals travelled in different paths, thus may experience different Doppler shifts with different phase changes. Contriuting a single fading channel with different Doppler shift is known as the Doppler spread. The paper is organized in the following order: In Chapter 2, we discussed types of WiMAX technology propagation models. In Chapter 3, Math models for path loss are introduced. In Chapter 4, simulation output of less path loss models in different areas is presented. In Chapter 5, the conclusions of the paper are presented. 2. TYPES OF PROPAGATION MODELS It is necessary to estimate propagation characteristics of a system through a medium so that the signal parameters can e more accurate in moile system. Propagation analysis is very important in evaluating the signal characteristics. For wireless communication system, the system should have the aility to predict the accurateness of the radio propagation ehavior. Thus it has ecome pivotal for such system design. The site measurements are expensive and costly. Propagation models have een developed as low cost, convenient alternative and suitale way. Channel modeling is essential for characterized the impulse response and to predict the path loss of a propagating channel. Path loss models are important to design ase stations, that can e estimated us to radiate the transmitter for service of the certain region. Channel characterization deals with the fidelity of the received signal. The main thing of designing a receiver is to receive the transmitted signal that has een distorted due to the multipath and dispersion effects of the channel, and that will receive the transmitted signals. It is very important to have the knowledge aout the electromagnetic environment where the system is operated, and the location of the transmitter and receiver. Models for path loss can e categorized into three types a. Empirical Models. Deterministic Models c. Stochastic Models 2.1 Empirical Models: Sometimes it is impossile to explain a situation y a mathematical model. In that case, we use some data to predict the ehavior approximately. By definition, an empirical model is ased on data used to predict, not explain a system and are ased on oservations and measurements alone [17]. It can e split into two sucategories, time dispersive and nontime dispersive [1]. The time dispersive model provides us with information aout time dispersive characteristics of the channel like delay spread of the channel during multipath. The Stanford University Interim (SUI) model [1] is the perfect example of this type. COST 231 Hata model, Hata and ITU-R [1] model are example of non-time dispersive empirical model. 2.2 Deterministic: This makes use of the laws governing electromagnetic wave propagation in order to determine the received signal power in a particular location. Nowadays, the visualization capailities of computer increases quickly. The modern systems of predicting radio signal coverage are Site Specific (SISP) propagation model and Graphical Information System (GIS) dataase. SISP model can e associated with indoor or outdoor propagation environment as a deterministic type. Wireless system designers are ale to design actual presentation of uildings and terrain features y using the uilding dataases. 2.3 Stochastic: Volume 2, Issue 1, January 2014 Page 2

3 This is used to model the environment as a series of random variales. Least information is required to draw this model ut it accuracy is questionale. Prediction of propagation at 3.7GHz-4.2GHz frequency and is mostly done y the use of oth empirical and stochastic approaches. 3. MATH MODELS FOR PATH LOSS In our paper, we analyze five different models which have een proposed y the researchers at the operating frequency of 3.7 GHz -4.2GHz[1-4]. We also choose our parameters for est fitted to the Asian environments. In this chapter 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 e realized how much path loss occurred y the others proposed models. 3.1 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 y using the following equation [4]: PL FSPL log ( d ) 20log( f ). (1) f: Frequency in MHz, d: Distance etween transmitter and receiver in mts. Power is usually expressed in deciels (dbm). 3.2 Stanford University Interim (SUI) Model IEEE Broadand Wireless Access working group proposed the standards for the frequency and elow 11 GHz containing the channel model developed y Stanford University, namely the SUI models [1], [2]. The SUI model descries three types of terrain; they are terrain A, terrain B and terrain C. Terrain A can e 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 uran area. Terrain B is characterized for the hilly terrains with rare vegetation. This is the intermediate path loss scheme. We consider this model for suuran environment. Terrain C is suitale for flat terrains or rural with light vegetation, here path loss is minimum. The asic path loss expression of The SUI model with correction factors is presented as [1]: d PL A log X f X s d 0 for d > d0.. (2) Where the parameters are d: Distance etween BS and receiving antenna [m], d 0: 0 [m] X f : Correction for frequency aove 2 GHz X h : Correction for receiving antenna height[m] s : Correction for shadowing, : Path loss exponent The random variales are taken through a statistical procedure as the path loss exponent γ and the weak fading standard deviation s is defined. The log normally distriuted factor s, for shadow fading ecause of trees and other clutter on a propagations path and its value is etween 8.2 db and.6 db [1]. The parameter A is defined as [1], [2]: 4 d A 20 log 0 and the path loss exponent γ is given y [1]:.(3) a h c h.(4) where, the parameter h is the ase station antenna height in meters. This is etween m and 80 m. The constants a,, and c depend upon the types of terrain, that are given in Tale 3.1. The value of parameter γ = 2 for free space propagation in an uran area, 3 < γ < 5 for uran NLOS environment, and γ > 5 for indoor propagation [2]. For the aove correction factors this model is extensively used for the path loss prediction of all three types of terrain in rural, uran and suuran environments. Tale 3.1: The parameter values of different terrain for SUI model. Model Parameter Terrain A Terrain B Terrain C Volume 2, Issue 1, January 2014 Page 3

4 a (m-1) c (m) ECC-33 Model (Electronic Communication Committee) One of the most extensively used empirical propagation models is the Hata-Okumura model [8], which is ased on the Okumura model. This model is a well-estalished model for the Ultra High Frequency (UHF) and. Recently, through the ITU-R Recommendation P.529, the International Telecommunication Union (ITU) encouraged this model for further extension up to 3.5 GHz [14]. The original Okumura model does not provide any data greater than 3 GHz. Based on prior knowledge of Okumura model, an extrapolated method is applied to predict the model for higher frequency greater than 3 GHz. The tentatively proposed propagation model of Hata-Okumura model with report [14] is referred to as ECC-33 model. In this model path loss is given y [1]: PL A fs A m G G r. (5) A fs : Free space attenuation [db] A m : Basic median path loss [db] G : Transmitter antenna height gain factor G r : Receiver antenna height gain factor These factors can e separately descried and given y as [1]: A fs log log A m G d 20 f d log f log f log log h d log When dealing with gain for medium cities, the Gr will e expressed in [1]: 2 (6)... (7).... (8) G r log f log hr (9) for large city G r 0.759hr () Where, d: Distance etween transmitter and receiver antenna [km] f: Frequency [GHz] h : Transmitter antenna height [m] h r : Receiver antenna height [m] This model is the hierarchy of Okumura-Hata model. So the uran area is also sudivided into large city and medium sized city. 3.4 COST 231 Walfish-Ikegami (W-I) Model (Co-operative for Scientific and Technical research) This model is a comination of J. Walfish and F. Ikegami model. The COST 231(Co-operative for Scientific and Technical research) project further developed this model. Now it is known as a COST 231 Walfish-Ikegami (W-I) model. This model is most suitale for flat suuran and uran areas that have uniform uilding 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. For LOS condition PL Los logd 20log f... (11) and for NLOS condition Volume 2, Issue 1, January 2014 Page 4

5 LFSL Lrts Lmsd PL Nlos for uran and suuran (12) L fs Where, 3.5 Ericsson Model L FSL = Free space loss L rts = Roof top to street diffraction L msd = Multi-screen diffraction loss To predict the path loss, the network planning engineers are used a software provided y Ericsson company is called Ericsson model [2]. This model also stands on the modified Okumura-Hata model to allow room for changing in parameters according to the propagation environment. Path loss according to this model is given y [2]: Where, g(f) is defined y [2]: 2 g f d a log h a log h.log 3.2 log 11. h PL a0 a1 log g f log f 4.78 f 2 log The default values of these parameters (a0, a1, a2 and a3) for different terrain are given in Tale 3.2 Tale 3.2: Values of parameters for Ericsson model. r. (13).. (14) Environment a0 a1 a2 a3 Uran Suuran 43.20* 68.93* Rural 45.95* 0.6* *The value of parameter a0 and a1 in suuran and rural area are ased on the Least Square (LS) method in [18]. 3. METRICS OF THE PROPAGATION MODELS In our computation the distance etween transmitter antenna and receiver antenna is Km, transmitter antenna height is 30m and receiver antenna height is m. The path loss is oserved at two operating frequencies that are 3.7 GHz and 4.2 GHz for five propagation models in uran, suuran and rural environments. We exploited free space model as a reference model and NLOS condition in our comparisons. The following tale 4.1 presents the parameters we applied in simulation. Tale 4.1: Simulation parameters Parameters Values Base station transmitter power Moile transmitter power Transmitter antenna height Receiver antenna height Operating frequency Distance etween Tx-Rx Building to uilding distance Average uilding height 43 dbm 30 dbm 30 m 3 m, 6 m and m 3.7&4.2 GHz km 50 m 15 m Volume 2, Issue 1, January 2014 Page 5

6 Street width Street orientation angle Correction for shadowing 25 m 30 0 in uran and 40 0 in suuran 8.2 db in suuran and rural and.6 db in uran area 4.1 Path loss in uran area: In our calculation the distance varies from 500m to km, the receiver height is m and transmitter height is 30m. The numerical results for different model in uran area are shown in figure. The path loss is minimum for Ericsson model maximum for COST 231 Walfish-Ikegami model. 190 uran environment at 3.7Ghz & hr=m 190 uran environment at 4.2Ghz & hr=m Path loss (db) Path loss (db) pl-wi pl-fs pl-ecc pl-wi pl-fs pl-ecc pl-hta 0 pl-sui pl-esn Distance etween Tx and Rx (km) pl-hta 0 pl-sui pl-esn Distance etween Tx and Rx (km) 4.2 Path loss in suuran area: Fig 4.1 path loss at 3.7&4.2GHz operating frequencies in uran environment The transmitter and receiver parameters are same as used earlier. The path loss is minimum for SUI model and maximum for Ericsson model. 4.3 Path loss in rural area: The ECC 33 model is not applicale for rural area and the cost 231 W-I model has no specific parameters for rural area, we consider LOS equation for this model. The numerical results for different models are shown in tale 4.2 Tale 4.2: Path loss estimate at 6 km distance Propagation uran Suuran Rural area Uran area Suuran area Rural area Models At 3.7GHz At 3.7GHz At 3.7GHz At 4.2GHz At 4.2GHz At 4.2Ghz Free space model ECC Not applicale Not applicale COST 231 Hata Ericsson SUI COST 231 W-I CONCLUSION The metrics of the propagation models explores that the uran area path loss is higher than that of suuran and rural area path losses. There is no single model that can e suitale for all environments. We can see in uran area (data shown in tale 4.2), the Ericsson model showed the lowest path loss (153.47dB & dB at 3.7&4.2GHz respectively) as compared to other models. Alternatively, the okumura w-i model showed the heights path loss (171.60dB&176.22dB). In suuran area (data shown in tale 4.2) the SUI model showed quite less path loss ( db&137.68db) compared Volume 2, Issue 1, January 2014 Page 6

7 to other models. On the other hand, Ericsson model showed remarkale higher path loss (190.61dB&192.53dB). We can see in rural area COST-231W_I model showed the less path loss (134.19dB&135.29dB),whereas Ericsson model showed higher path loss (152 db in 3m and 142 db in 6 m). REFERENCES [1] V.S. Ahayawardhana, I.J. Wassel, D. Crosy, M.P. Sellers, M.G. Brown, Comparison of empirical propagation path loss models for fixed wireless access systems, 61th IEEE Technology Conference, Stockholm, pp , [2] Josip Milanovic, Rimac-Drlje S, Bejuk K, Comparison of propagation model accuracy for WiMAX on 3.7GHz- 4.2GHz, 14th IEEE International conference on electronic circuits and systems, Morocco, pp [3] Joseph Wout, Martens Luc, Performance evaluation of roadand fixed wireless system ased on IEEE , IEEE wireless communications and networking Conference, Las Vegas, NV, v2, pp , April [4] 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 Broadand Wireless Access Working Group, [5] [Accessed: June ] [6] M. Hata, Empirical formula for propagation loss in land moile radio services, IEEE Transactions on Vehicular Technology, vol. VT-29, pp , Septemer [7] Y.Okumura, Field strength variaility in VHF and UHF land moile services, Rev. Elec. Comm. La. Vol. 16, pp , Sept-Oct [8] T.S Rappaport, Wireless Communications: Principles and Practice, 2n ed. New delhi: Prentice Hall, 2005 pp [9] Well known propagation model, [Online]. Availale: [Accessed: April 11, 2009] [] IEEE working group, [Online]. Availale: [Accessed: April 11, 2009] [11] Jeffrey G Andrews, Arunaha Ghosh, Rias Muhamed, Fundamentals of WiMAX: understanding Broadand Wireless Networking, Prentice Hall, 2007 [12] WiMAX Forum, Documentation, Technology Whitepapers, [Online]. Availale at WiMAX Forum.org: [Accessed: April 18, 2008 [13] Doppler spread, [Online]. Availale: [Accessed: April 11, 2009] [14] 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 and, tech. rep., ECC Report 33, May [15] Rony Kowalski, The Benefits of Dynamic Adaptive Modulation for High Capacity Wireless Backhaul Solutions, Ceragon Networks, [Online]. [16] D. Pareek, The Business of WiMAX, Chapter 2 and Chapter 4, John Wiley, 2006 [17] Empirical Models, [Online] Availale: [Accessed April 18, 2009] [18] 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 AUTHOR Chandran Mahesh Bondalapati received his B.Tech., and M.Tech., degrees in Electronics and communications Engineering from Nagarjuna university and JNTU, Ananthapur in 1998 and 2007, respectively. During , he had een working as communication engineer in the field of commissioning of satellite signals through VSAT antennas. Now he is working as professor in ECE and pursuing his Ph.D. in JNTUK, Kakinada. Volume 2, Issue 1, January 2014 Page 7