MODELING OF CELLULAR MOBILE RADIO COMMUNICATION IN URBAN AREAS

BHAROTI SINHA Department of Electronics & Computer engineering Indian Institute Of Roorkee, Roorkee – 247 667(INDIA)

Abstract: A numerical modeling of the propagation path loss using Uniform Theory of Diffraction (UTD) has been presented here. Computed results at 835 MHZ have been presented for various parameters of interest. The results at 2.154GHz have been obtained and compared with that of Walfish and Bertoni [1]. These are found to be in excellent agreement thereby establishing the validity of the code. Method is simple, efficient and reliable. Both shadow zone and line of sight zone have been considered.

Key Words:Propagation Model, Mobile communication ,urban area, shadow zone

Introduction 3.The contributions of ray 3 and ray 4 can be neglected For satisfactory working of the cellular mobile radio due to their in significant amplitude. systems, an accurate predict ion of the path losses is 4.Backward diffracted field is neglected. necessary. Most of thecellular mobile users are located 5.The buildings are replaced by opaque absor -bing in the urban areas, also the urban environment is screens. more complicated. Hence the predication of urban path With these assumptions, model appears to be as in Fig. loss needs more attention. There are number of models (2). available but none of these predict the total losses Where, completely.In this paper a theoretical model for predicting narrow band path loss for mobile 2 2 D1 = d  (h  h ) communication in urban areas have been presented. t t b 2 2 The method is based on Uniform Theory of D2 = dr  (hb  hr ) (1)

Diffraction [2] and is applicable to the shadow zone 2 2 of the buildings as well in the illu -minated zone when r2 = (2d  dr)  (hb  hr ) the mobile antenna is in a moving vehicle. D1, D2, r2 are the path lengths between the base station Modeling [2] antenna and the local screen, between local screen and In urban environment, the buildingare aligned in a mobile antenna and the reflected ray due to the wall of row. Various possible paths in the presence of the buil the building next to the mobile respectively. The angle -dings are shown in Fig.(1). Ray 1 to ray 4 represent the ,  and  are indicated in Fig. 2. diffracted ray path due to building next to the  hb  hr  mobile to the base station, reflected wave due to  = tan-1 2d  dr  building on other side of mobile, incoming signal   arriving over the top of the building to the mobile h  h   = tan-1 t b ------(2) and ground reflected energy, respectively.    dt  The simplifying assumptions can be made in the h  h  model for urban areas which are satisfied in actual -1 b t  = tan   cases to the great extent.These can be summarized as  dr  [2]- Path Loss Prediction: 1.The earth surface is plane. The total path loss Lt in db is defined as – 2.The buildings are assumed to be of uniform height. Lt = L0 + L1 + Lmd + Lr ------(3) D X  2k 2 sin(( ) / 2)2 1 1 D / D Where, L0, L1 and Lmd are the losses due to free 2 1 space propagation, local screen (building) in the D 2 X  2k 2 cos(( ) / 2) vicinity of the mobile, and multiple diffractions 2 1 D / D caused by the buildings respectively. L is the loss 2 1 r ------(11) caused by the reflection of the diffracted electric fields from the walls of the building next to mobile. D II These losses are given as – s,h is the same as (10) except X3 and X2 are (a) Free space propagation loss- replaced by X3 and X4 and  by . L0 = 92.4 + 20 log10 f(GHz) + 20 log10 D(Km) ------(4) r X 2k 2 Where, 3  1 r2 / D1 D = (h  h ) 2  (h  h )2 t r t r r2 X 4  2k ------(5) 1 r2 / D1 ------(12) (b) The loss due to local screen- 1 L1 = -20log10 |D sh|+ 10 log10D2(m)+

 D1 (D1  D2 ) X 10 log10  2  ------(6) jX  j1/ 2  D  F(X )  X exp( j / 4  X )  2 j X e  e d (c) The loss due to multiple diffractions caus -ed by 6 ------(13) buildings between base station and mobile - En+1/E0 is the normalized electric field amplitude at the E n1 screen position n+1 and Ndt/d Lmd = -20 log10 E0 The model is applicable for the mobile located in the ------(7) shadow zone characterized by- (d) The loss caused by multiple reflections-    D (D  D ) D II h  h L  20log 1 R 2 1 2 s,h exp( jk(r  D )) t b r 10 H ,V I 2 2 or dt  (2d  d r ) r2 (D1  r2 ) D s,h (db  d r ) ------(8) ------(14) In this,RH,V is the reflection coefficient.‘H’‘V’ stand for For hb = 10m, ht = 50m, hr = 1.6m, dr = 5m, equation the horizontally and vertically polarized electric field (15) tells us that Dt > 547.6m  2 And for dt = 1000m, ht < 83.04m cos  H ,V  r  sin  RH ,V   2 cos  H ,V  r  sin  Line of sight (LOS) propagation model [4]: when the mobile is located in the vehicle over the flat terrain LOS propagation using 2-ray model is given in  H  1andV  1/  r fig. (3). r represents path length of the direct ray and ------(9) 1 r2 is the path length due to ground reflected ray. The received power can be expressed as- r for concrete walls in the range 300MHZ TO 2 P    1 1 3ghZ IS 5. r  exp( jkr )  R exp( jkr ) 2 1   1 2 Diffraction coefficient Ds,h is defined as as – Pt 4  r1 r2 ------(15) Pt and Pr denote the base station power and power I  exp( j / 4)  F(X 1 )   F(X 2 )  Ds,h    ∓  received by the mobile antenna. 2 2K  sin( ) / 2  cos( ) / 2 2 2 ht d where ------(10) r1  d  (ht  hr ) , X  ht  hr and ‘R’ the reflection coefficient may be expressed as- Conclusion: cos    sin 2  Propagation models have been proposed for mobile R  H ,V r communication in shadow zone as well as 2 cos  H ,V  r  sin  line of sight zone.Computed results are ------(16) reliable and are modified compared to previously available models.some Results conclusions have been drawn,but the For the validity of the code, Weizhang’s [4] results illuminated zone have not been considered. have been compared (fig 3). The computed results are in good agreement, thereby establishing the validity of simulation.Various losses and their depen- References dence on various parameters are given in Figs (3- (1)J. Walfish and H.L. Berton, “A Theorretical Model 4.1-4.6(a,b,c)The losses are less at 900 MHz compared of UHF Propagation in Urban Envi -ronments”, IEEE. to that at 2.154 GHz which can be attributed as there is Transaction on Antennas and Propagation, Vol. 36, pp. decrease in propagation loss at low frequencies. Total 1788-1796, Dec. 1988 loss increases with distance dt, decreases with increase (2)R.G. Kouyumjian and P.H. Pathak, “A Uniform in base station height but shows an erratic Geometrical Theory of Diffraction for an Edge in a behaviour when the mobile is moved away from the Perfectly Conducting Surface”, Proceedings IEEE, Vol. local screen, which is mainly due to multiple 62, pp. 1448-1461, Nov. 1974. reflections and diffraction taking place. (3)Wei-Zhang, “A Wide Band propagation Model Off course the pattern of local screen loss remains Based on UTD for Cellular Mobile Radio constant with changes in ht, dt, dr but the respective Communication;, IEEE Transactionon A &P, Vol. 45, magnitudes change. Same is the case with free space pp. 1669-1678, Nov. 1997. propagation .Fig.4.1 shows the path loss as a function (4)D. Har, H.H. Xia and H.L. Bertoni, “Path Loss of distance for a two ray model of LOS propagation. Predication Models for Microcells”, Vol. 48, pp. 1453- 1462, Sept. 1999.