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M. Junaid Mughal 2006 Wireless Communications Principles and Practice 2 nd Edition T.S. Rappaport Chapter 4: Mobile Radio Propagation: Large-Scale Path.

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Presentation on theme: "M. Junaid Mughal 2006 Wireless Communications Principles and Practice 2 nd Edition T.S. Rappaport Chapter 4: Mobile Radio Propagation: Large-Scale Path."— Presentation transcript:

1 M. Junaid Mughal 2006 Wireless Communications Principles and Practice 2 nd Edition T.S. Rappaport Chapter 4: Mobile Radio Propagation: Large-Scale Path Loss UMAIR HASHMI Spring 2011

2 M. Junaid Mughal 2006 Reflection from Conductors A perfect conductor reflects back all the incident wave back. Ei = Er Өi = Өr ( E in plane of incidence) Ei = - Er Өi = Өr ( E normal to plane of incidence) UMAIR HASHMI Spring 2011

3 M. Junaid Mughal 2006 Ground Reflection (Two-Ray) Model UMAIR HASHMI Spring 2011 Propagation Model that considers both the direct (LOS) path and a ground reflected path between transmitter and the receiver. Reasonably accurate model for predicting large scale signal strength over distance of several kilometres. The E-field due to Line-Of-Sight is given by E LOS The E-field for the ground reflected wave is given by E g The Total E-field is a sum of LOS and Reflected components,

4 M. Junaid Mughal 2006 Ground Reflection (Two-Ray) Model UMAIR HASHMI Spring 2011

5 M. Junaid Mughal 2006 Ground Reflection (Two-Ray) Model UMAIR HASHMI Spring 2011

6 M. Junaid Mughal 2006 Ground Reflection (Two-Ray) Model UMAIR HASHMI Spring 2011

7 M. Junaid Mughal 2006 Ground Reflection (Two-Ray) Model UMAIR HASHMI Spring 2011 The path difference between the LOS path and the ground reflected path is represented by lambda

8 M. Junaid Mughal 2006 Ground Reflection (Two-Ray) Model UMAIR HASHMI Spring 2011 The phase difference and the time arrival delay between the two E-components is given by: When d becomes large, difference between d and d becomes negligible and E LOS and E g could be considered equal in magnitude

9 M. Junaid Mughal 2006 Ground Reflection (Two-Ray) Model UMAIR HASHMI Spring 2011

10 M. Junaid Mughal 2006 Ground Reflection (Two-Ray) Model UMAIR HASHMI Spring 2011 Now sin(Ө) is approximately equal to Ө when Ө < 0.3 radians.

11 M. Junaid Mughal 2006 Ground Reflection (Two-Ray) Model UMAIR HASHMI Spring 2011 The received power Pr and Path Loss PL will be given by:

12 M. Junaid Mughal 2006 Ground Reflection (Two-Ray) Model UMAIR HASHMI Spring 2011

13 M. Junaid Mughal 2006 Ground Reflection (Two-Ray) Model UMAIR HASHMI Spring 2011 Example A mobile is located 5 km away from a BS and uses vertical lambda/4 monopole antenna with gain of 2.55 dB to receive cellular signals. The E-field at 1 km from the transmitter is measured to be V/m. The carrier frequency is 900 MHz. a)Find length and gain of receiving antenna b) Find receiver power at the mobile using 2-ray ground reflection model assuming height of transmitting antenna is 50m and receiving antenna is 1.5 m.

14 M. Junaid Mughal 2006 Diffraction UMAIR HASHMI Spring 2011 Diffraction is a process that allows radio signals to propagate around curved surfaces and objects and to propagate behind obstructions. Visible Region Shadow Region Obstruction

15 M. Junaid Mughal 2006 Diffraction geometry UMAIR HASHMI Spring 2011

16 M. Junaid Mughal 2006 Diffraction geometry UMAIR HASHMI Spring 2011 Visible Region Shadow Region Obstruction

17 M. Junaid Mughal 2006 Contribution of Huygens Secondary Sources at the Receiver UMAIR HASHMI Spring 2011 Obstruction Tx Rx

18 M. Junaid Mughal 2006 Fresnel Zone Geometry UMAIR HASHMI Spring 2011 A transmitter and receiver separated in free space. An obstructing screen of height h is placed at a distance d 1 from the transmitter and d 2 from the receiver. The difference between the direct path and the diffracted path is called the excess path length Δ. Assuming h >λ

19 M. Junaid Mughal 2006 Fresnel Zone Geometry UMAIR HASHMI Spring 2011

20 M. Junaid Mughal 2006 Fresnel Zone Geometry UMAIR HASHMI Spring 2011 Now tan x is approximately equal to x for x < 0.5 radians Fresnel – Kirchoff Diffraction Parameter v is given by

21 M. Junaid Mughal 2006 Fresnel Zone Geometry UMAIR HASHMI Spring 2011 The phase difference between LOS and diffracted path is a function of i)Height and Position of the obstruction ii)Transmitter and Receiver Location FRESNEL ZONES Fresnel Zones represent successive regions where secondary waves have a path length from the transmitter to the receiver which are nλ/2 greater than the total path length of a LOS path The successive concentric circles on the plane have path length increment by λ/2. The successive circles are called Fresnel Zones and successive Fresnel Zones have the effect of producing constructive and destructive interference.

22 M. Junaid Mughal 2006 Fresnel Zone Geometry UMAIR HASHMI Spring 2011 The radius of the nth Fresnel Zone is given by

23 M. Junaid Mughal 2006 Knife-Edge Diffraction Model UMAIR HASHMI Spring 2011

24 M. Junaid Mughal 2006 Knife-Edge Diffraction Model UMAIR HASHMI Spring 2011 The receiver is at point R which is located in the shadowed region (called Diffraction Zone). The field strength at R is a vector sum of the fields due to all of the secondary Huygen;s sources in the plane. The Electric Field of a knife edge diffracted wave is The Diffraction Gain due to the presence of a knife edge is given by

25 M. Junaid Mughal 2006 Knife-Edge Diffraction Model UMAIR HASHMI Spring 2011

26 M. Junaid Mughal 2006 Fresnel Zone Geometry UMAIR HASHMI Spring 2011 The Diffraction Gain for different values of v is:

27 M. Junaid Mughal 2006 Knife-edge diffraction loss (Summing Secondary Sources) UMAIR HASHMI Spring 2011

28 M. Junaid Mughal 2006 Fresnel Zone Geometry UMAIR HASHMI Spring 2011 EXAMPLE Compute the diffraction loss for the three cases in fig. when λ=1/3m, d 1 =1km, d 2 =1km and (a) h=25m, (b) h=0 (c) h= -25m. Compare the answers with the values obtained from the graph.

29 M. Junaid Mughal 2006 Fresnel Zone Geometry UMAIR HASHMI Spring 2011 EXAMPLE Determine (a) Loss due to knife-edge diffraction and (b) the height of the obstacle required to induce 6 dB diffraction loss. Assume f = 900MHz

30 M. Junaid Mughal 2006 Scattering UMAIR HASHMI Spring 2011 When a wave impinges on a rough surface, the reflected wave is spread out (diffused) in all directions due to scattering. The dimensions of the objects inducing Scattering are comparable to λ To judge if a surface is smooth or rough (if we will have reflection or scattering) when a wave impinges upon that surface, the Critical Height h c is given by hc = λ / ( 8 sin Өi ) If maximum protuberance hmax < hc : Smooth Surface hmax > hc : Rough Surface The reflected E-Fields for h > hc is given by :

31 M. Junaid Mughal 2006 Radar Cross Section Model (RCS Model) UMAIR HASHMI Spring 2011 The Radar Cross Section (RCS) of a scattering object is defined as the ratio of the power density of the signal scattered in the direction of the receiver to the power density of the radio wave incident upon the scattering object. The bistatic radar equation is used to compute the propagation of a wave travelling in free space that impinges on a distant scattering object and then reradiated in the direction of the receiver. The objects are assumed to be in the Far-Field region (Fraunhofer region) P R (dBm) = P T (dBm) + G T (dBi) + 20 log λ + RCS [dB m 2 ] – 30 log (4 pi) – 20 log d T – 20 log d R

32 M. Junaid Mughal 2006 Radar Cross Section Model (RCS Model) UMAIR HASHMI Spring 2011

33 M. Junaid Mughal 2006 SUMMARY UMAIR HASHMI Spring 2011 What is Large Scale Path Loss? Free space Propagation Model Friis Free space propagation model Relating power to Electric field The three Basic Propagation mechanisms Reflection Reflection coefficients Polarization rotation Brewster angle Reflection from perfect conductors Ground Reflection (Two Ray Model)

34 M. Junaid Mughal 2006 SUMMARY UMAIR HASHMI Spring 2011 Diffraction Fresnel Zone Geometry Knife Edge Diffraction Multiple Knife edge Diffraction Scattering Rough Surface Scattering Radar Cross section Now we know all the propagation mechanisms and can use them to predict path loss in any environment

35 M. Junaid Mughal 2006 Log-Distance Path Loss Model UMAIR HASHMI Spring 2011 Radio Propagation Models Log-distance Path Loss Model Received Power decreases logarithmically with distance, whether in outdoor or indoor radio channels Reference distance should be in the far field region of the antenna

36 M. Junaid Mughal 2006 Log-Distance Path Loss Model UMAIR HASHMI Spring 2011

37 M. Junaid Mughal 2006 Log-Normal Shadowing UMAIR HASHMI Spring 2011 Surrounding environment clutter not considered in previous model. Received power can vary at quite a significant value at 2 points having same T-R separation distances. Path Loss (PL) is random and distributed log-normally about the mean distance-dependent value.

38 M. Junaid Mughal 2006 Log-Normal Shadowing UMAIR HASHMI Spring 2011 Log-Normal distribution describes the random shadowing effects which occur over a large number of measurement locations which have the same T-R separation distance. This phenomenon is called the log-normal shadowing. Implies that measured signal levels at specific T-R separation have a Gaussian (normal) distribution about the distance-dependent mean.

39 M. Junaid Mughal 2006 Log-Normal Shadowing UMAIR HASHMI Spring 2011

40 M. Junaid Mughal 2006 Log-Normal Shadowing UMAIR HASHMI Spring 2011

41 M. Junaid Mughal 2006 Determination of Percentage of Coverage Area UMAIR HASHMI Spring 2011 The percentage of useful service area i.e. the percentage of area with a received signal level that is greater or equal to a threshold value.

42 M. Junaid Mughal 2006 Determination of Percentage of Coverage Area UMAIR HASHMI Spring 2011

43 M. Junaid Mughal 2006 Determination of Percentage of Coverage Area UMAIR HASHMI Spring 2011

44 M. Junaid Mughal 2006 Determination of Percentage of Coverage Area UMAIR HASHMI Spring 2011

45 M. Junaid Mughal 2006 Determination of Percentage of Coverage Area UMAIR HASHMI Spring 2011

46 M. Junaid Mughal 2006 Determination of Percentage of Coverage Area UMAIR HASHMI Spring 2011

47 M. Junaid Mughal 2006 Determination of Percentage of Coverage Area UMAIR HASHMI Spring 2011

48 M. Junaid Mughal 2006 Outdoor Propagation Models Longley Rice Model UMAIR HASHMI Spring 2011 Point to point communication 40 MHz to100 GHz Different kinds of terrain Median Tx loss predicted by path geometry of terrain profile & Refractivity of troposphere Diffraction losses predicted by? Geometric losses by?

49 M. Junaid Mughal 2006 Outdoor Propagation Models Longley Rice Model UMAIR HASHMI Spring 2011 Operates in 2 modes Point-to-point mode Area mode prediction Modification Clutter near receiver Doesnt determine corrections due to environmental factors

50 M. Junaid Mughal 2006 Outdoor Propagation Models Durkins Model UMAIR HASHMI Spring 2011 Computer simulator described for field strength contours of irregular terrain Split into 2 parts, first reconstructs radial path profile & second calculates path loss Rx can move iteratively to establish contour Topographical database can be thought of as 2- dimensional array Each array element corresponds to a point on map & elevation Radial path may not correspond to discrete data points thus interpolation

51 M. Junaid Mughal D Propagation Raster Model UMAIR HASHMI Spring 2011

52 M. Junaid Mughal 2006 Representing Propagation UMAIR HASHMI Spring 2011

53 M. Junaid Mughal 2006 UMAIR HASHMI Spring 2011 Height reconstructed by diagonal, vertical & horizontal interpolation methods Reduced to 1 D Now determine whether LOS – difference btw heights and line joining Tx & Rx Positive height difference

54 M. Junaid Mughal 2006 Algorithm for LOS UMAIR HASHMI Spring 2011

55 M. Junaid Mughal 2006 UMAIR HASHMI Spring 2011 Then checks first Fresnel Zone clearance If terrain profile fails first Fresnel Zone Clearance a) non LOS b) LOS but inadequate Fresnel Zone Clearance

56 M. Junaid Mughal 2006 Non-LOS Cases UMAIR HASHMI Spring 2011 a) Single Diffraction Edge b) Two Diffraction Edges a) Three Diffraction Edges a) More than three Diffraction Edges Method sequentially tests for each Angles btw pine joining Tx & Rx and each point on reconstructed profile. Max angle (d i,h i ) Angles between line joining Tx & Rx and Tx Antenna to every point on reconstructed profile For single diffraction d i =d j

57 M. Junaid Mughal 2006 Multiple Diffraction Computation UMAIR HASHMI Spring 2011

58 M. Junaid Mughal 2006 Okumuras and Hatas Model UMAIR HASHMI Spring 2011

59 M. Junaid Mughal 2006 Hatas Model UMAIR HASHMI Spring 2011 Empirical formulation of graphical path loss data Valid from 150 MHz to 1500 MHz. Urban Area Propagation loss as a standard and supplied correction equations for application to other situations hte=30 m to 200m, hre=1m to 10m Compares very closely with Okumura model as long as d doesnt exceed 1km Well suited for large cell communications but not PCS

60 M. Junaid Mughal 2006 PCS Extension to Hata Model UMAIR HASHMI Spring 2011 Hatas model to 2GHz

61 M. Junaid Mughal 2006 ASSIGNMENT UMAIR HASHMI Spring 2011 Review the Outdoor Propagation Models presented in the slides showing their salient features and how they differentiate from each other.


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