1. Introduction What is communication ?
Significance of guided and unguided communication
Wireless / Mobile Communication
Radio Propagation Effects

2. Propagation Scenario 2

3. Mobile Radio Propagation
Large Scale Propagation Effects
Distance dependent loss
Reflection
Diffraction
Scattering
Useful in estimating radio coverage
Small Scale Propagation Effects
Rapid fluctuations of received signal strength over short durations or short distances
Multipath propagation – time dispersive
Mobility – frequency dispersive

4. Large-scale /small-scale propagation

5. Propagation phenomena5

6. 1 – 2 Km
50-100 6

7. Free space propagation model - LOS
Pr(d) = Pt Gt Gr 2 / (4d)2 L  Pr(d0)(d0/d)2
Assumes far-field (Fraunhofer region)
Far field distance df >> D and df >>  , where
D is the largest linear dimension of antenna
 is the carrier wavelength
df = 2D2/ 
do > df Fraunhofer region/far field (1m -1 km)
No interference, no obstructions
Effective isotropic radiated power – EIRP = Pt Gt
Effective radiated power – ERP
Antenna gains  dBi, dBd
Path loss PL(dB) = 10log (Pt/Pr)

8. Radio Propagation Mechanisms
Reflection
Propagating EM wave impinges on an object which is large as compared to its wavelength
- e.g., the surface of the Earth, buildings, walls, etc.
Conductors & Dielectric materials (refraction)
Diffraction
Radio path between transmitter and receiver is obstructed by a surface with sharp irregular edges
Waves bend around the obstacle, even when LOS (line of sight) does not exist
Fresnel zones
Scattering
Objects smaller than the wavelength of the propagating wave
- e.g. foliage, street signs, lamp posts
“Clutter” is small relative to wavelength

9. Reflection q qr qt Perfect conductors reflect with no attenuation
Light on the mirror
Dielectrics reflect a fraction of incident energy
“Grazing angles” reflect max*
Steep angles transmit max*
Light on the water
Reflection induces 180 phase shift
Why? See yourself in the mirror
Reflected field intensity
Fresnel reflection coefficient 
Brewster angle   = 0 ? q qr qt

10. Classical 2-ray Ground reflection model

11. 2-Ray Model For d > do, the free space propagating field 
E(d,t) = (Eodo/d) cos { c(t – d/c)}
ELOS(d’,t) = (Eodo/d’) cos { c(t – d’/c)}
Eg(d’’,t) =  (Eodo/d’’) cos { c(t – d’’/c)}
i = o  Eg =  Ei ; Et = (1+) Ei

12. 2-Ray Model
For small grazing angles, assuming perfect horizontal E-field polarization and ground reflection , | =-1, Et = 0
|ETOT| = |ELOS + Eg |
ETOT(d,t) = (Eodo/d’) cos { c(t – d’/c)}
+(-1)(Eodo/d’’) cos { c(t – d’’/c)}

13. Method of images

14. 2-Ray model Using method of images, Path difference
 = d’’ – d’ = {(ht+hr)2+d2} 1/2 –{(ht-hr)2+d2} 1/2
If d >> (ht+hr) ; using Taylor series expansion,
 = d’’ – d’  2hthr /d
 = 2 /  =  c / c and d = / c = /2 fc

15. 2-Ray model At time t = d’’/c ; |ETOT(d) |
ETOT(d, t) = (Eodo/d’) cos { c((d’’ – d’)/c)} - (Eodo/d’’) cos0
= (Eodo/d’)   - (Eodo/d’’)  (Eodo/d) [   - 1]
|ETOT(d) |
= { (Eodo/d)2 cos ( - 1)2 + (Eodo/d)2 sin ( )2 } ½

16. 2-Ray model
|ETOT(d) |= { (Eodo/d)2 cos ( - 1)2 + (Eodo/d)2 sin ( )2 } ½
|ETOT(d) |= (Eodo/d) (2-2cos  ) ½ = (2Eodo/d) sin(  /2)
sin(  /2)  (  /2) < 0.3 rad  d > 20 ht hr / 
ETOT(d)  (2Eodo/d) (2  ht hr / d)  k / d 2 V/m
Pr= Pt Gt Gr (ht hr )2/ d 4
PL(dB) = 40 log d – ( 10logGt + 10logGr + 20loght + 20loghr )

17. 2-Ray model Summary For small T-R separation 
ETOT(d,t) = (Eodo/d’) cos { c(t – d’/c)}
+(-1)(Eodo/d’’) cos { c(t – d’’/c)}
For large T-R separation 
ETOT(d)  (2Eodo/d) (2  ht hr / d)

18. 2-Ray model Summary For large T-R separation,
ETOT(d)  k / d 2 V/m
The free space power is related to square of the electric field and hence,
Pr= Pt Gt Gr (ht hr )2/ d 4
Path Loss in dB 
PL(dB) = 40 log d – ( 10logGt + 10logGr + 20loght + 20loghr )

19. Diffraction Diffraction occurs when waves hit the edge of an obstacle
“Secondary” waves propagate into the shadowed region
Water wave example
Diffraction is caused by the propagation of secondary wavelets into a shadowed region.
Excess path length results in a phase shift
The field strength of a diffracted wave in the shadowed region is the vector sum of the electric field components of all the secondary wavelets in the space around the obstacle.
Huygen’s principle: all points on a wavefront can be considered as point sources for the production of secondary wavelets, and that these wavelets combine to produce a new wavefront in the direction of propagation. 19

20. Diffraction geometry 20

21. Fresnel Screens
Path difference between successive zones = /2 21

22. Fresnel Zones

23. Fresnel Zone Clearance

24. Fresnel Zone Clearance

25. Fresnel Zone Clearance
A rule of thumb used for
line-of-sight microwave links 
55% of the first Fresnel zone
to be cleared.

26. Fresnel Zone Clearance
A rule of thumb used for
line-of-sight microwave links 
55% of the first Fresnel zone
to be cleared.

27. Diffraction geometry 27

28. Diffraction geometry 28

29. Diffraction Parameter
Assuming h << d1, d2 & h >>,
Excess path length   h2 (d1+ d2 )/(2 d1d2)
Phase difference  = 2/ =  2 / 2 ?
 =+ and considering tan   ,
  h (d1+ d2 )/(d1d2)
Fresnel-Kirchoff diffraction parameter 
 = h {2(d1+ d2 )/(d1d2)}1/2
=  {2 d1d2 /((d1+ d2 ))}1/2

30. Fresnel diffraction geometry30

31. Diffraction Gain Electric Field Strength Ed
Ed = Eo F()
F()  complex Fresnel integral evaluated using tables / graphs
Diffraction gain Gd(dB) = 20 log |F()|

32. Approximate solution for Gd(dB)
Gd(dB) = 20log(  ) -1  0
Gd(dB) = 20log{0.5exp(-0.95  )} 0  1
Gd(dB) = 20log{0.4-[ ( 2 )]1/2}   2.4
Gd(dB) = 20log{0.225/  }  > 2.4

33. Knife-edge diffraction loss33

34. Multiple knife-edge diffraction34

35. Scattering Rough surfaces
Lamp posts and trees, scatter energy in all directions
Critical height for roughness  hc = /(8 sini)
Smooth if its minimum to maximum protuberance h < hc
For rough surfaces, Scattering loss factor S to be multiplied with surface reflection coefficient, rough = S ; S is a function of , h, i
Nearby metal objects (street signs, etc.)
Usually modeled statistically
Large distant objects
Analytical model: Radar Cross Section (RCS)
Bistatic radar equation 35

36. Measured results 36

37. Measured results 37

38. Propagation Models
Large scale models predict behavior averaged over distances >> 
Function of distance & significant environmental features, roughly frequency independent
Breaks down as distance decreases
Useful for modeling the range of a radio system and rough capacity planning,
Path loss models, Outdoor models, Indoor models
Small scale (fading) models describe signal variability on a scale of 
Multipath effects (phase cancellation) dominate, path attenuation considered constant
Frequency and bandwidth dependent
Focus is on modeling “Fading”: rapid change in signal over a short distance or length of time. 38

39. Free Space Path Loss
Path Loss is a measure of attenuation based only on the distance to the transmitter
Free space model only valid in far-field;
Path loss models typically define a “close-in” point d0 and reference other points from there: 39

40. Log-distance Path Loss
Log-distance generalizes path loss to account for other
environmental factors 
Choose a d0 in the far field.
Measure PL(d0) or calculate Free Space Path Loss.
Take measurements and derive n empirically. n 40

41. Typical large-scale path loss41

42. Log-Normal Shadowing Model
Shadowing occurs when objects block LOS between transmitter and receiver
A simple statistical model can account for unpredictable “shadowing”
PL(d)(dB)=PL(d)+X
Where X is a zero-mean Gaussian RV (in dB) (distributed log normally), with standard deviation of  (in dB)
 is usually from 3 to 12 dB 42

43. Longley-Rice Model (ITS Irregular terrain model)
Point-to-point from 40MHz to 100GHz.
Predicts median transmission loss, Takes terrain into account, Uses path geometry, Calculates diffraction losses, forward scatter theory
Inputs:
Frequency
Path length
Polarization and antenna heights
Surface refractivity
Effective radius of earth
Ground conductivity
Ground dielectric constant
Climate
Disadvantages
Does not take into account details of terrain near the receiver
Does not consider Buildings, Foliage, Multipath
Original model modified by Okamura for urban terrain 43

44. Longley-Rice Model OPNET implementation44

45. Durkin’s Model
It is a computer simulator for predicting field strength contours over irregular terrain.
Line of sight or non-LOS
Edge diffractions using Fresnel zone
Disadvantage  cannot adequately predict propagation effects due to foliage, building, and it cannot account for multipath propagation. 45

46. 2-D Propagation Raster data
Digital elevation models (DEM) United States Geological Survey (USGS) 46

47. Algorithm for line of sight (LOS)
Line of sight (LOS) or not 47

48. Multiple diffraction computation48

49. Empirical Models Commonly used in cellular system simulations
Okumura model
Curves based on extensive measurements(site/freq specific)
Awkward (uses graphs)
Hata model
Analytical approximation to Okumura model
Cost 231 Model:
Extends Hata model to higher frequency (2 GHz)
Walfish/Bertoni:
Cost 231 extension to include diffraction from rooftops
Commonly used in cellular system simulations

50. Okumura Model
It is one of the most widely used models for signal prediction in urban areas, and it is applicable for frequencies in the range 150 MHz to 1920 MHz
Based totally on measurements (not analytical calculations)
Applicable in the range: 150MHz to ~ 2000MHz, 1km to 100km T-R separation, Antenna heights of BS upto 200m, MS upto 3m 50

51. Okumura Model
The major disadvantage with the model is its low response to rapid changes in terrain, therefore the model is fairly good in urban areas, but not as good in rural areas.
Common standard deviations between predicted and measured path loss values are around 10 to 14 dB. 51

52. Okumura –Correction factor GAREA52

53. Hata Model
Empirical formulation of the graphical data in the Okamura model. Valid 150MHz to 1500MHz, Used for cellular systems
The following classification was used by Hata:
■Urban area
■Suburban area
■Open area 53

54. Hata Model
Urban area
Suburban area
Open area
- E
- E 54

55. PCS Extension of Hata Model
COST-231 Hata Model, European standard
Higher frequencies: up to 2GHz
Smaller cell sizes
Lower antenna heights
f >1500MHz
Metropolitan centers
Medium sized city and suburban areas 55

56. Indoor Propagation Models
The distances covered are much smaller
The variability of the environment is much greater
Key variables: layout of the building, construction materials, building type, where the antenna mounted, …etc.
In general, indoor channels may be classified either as LOS or OBS with varying degree of clutter
The losses between floors of a building are determined by the external dimensions and materials of the building, as well as the type of construction used to create the floors and the external surroundings.
Floor attenuation factor (FAF) 56

57. Signal Penetration into Buildings
RF penetration has been found to be a function of frequency as well as height within the building. Signal strength received inside a building increases with height, and penetration loss decreases with increasing frequency.
Walker’s work shows that building penetration loss decrease at a rate of 1.9 dB per floor from the ground level up to the 15th floor and then began increasing above the 15th floor. The increase in penetration loss at higher floors was attributed to shadowing effects of adjacent buildings.
Some devices to conduct the signals into the buildings 57

58. Repeater Extend coverage range
Directional antenna or distributed antenna systems

59. Ray Tracing and Site Specific Modeling
Site specific propagation model and graphical information system. Ray tracing. Deterministic model.
Data base for buildings, trees, etc.
SitePlanner 59

60. Simple path loss/shadowing model:
Find Pr:
Find Noise power:

61. SINR:
Without shadowing ( = 0), BPSK works 100%, 16QAM fails all the time.
With shadowing (s= 6dB):
BPSK: QAM
75% of users can use BPSK modulation and hence get a PHY data rate of 10 MHz · 1 bit/symbol ·1/2 = 5 Mbps
Less than 1% of users can reliably use 16QAM (4 bits/symbol) for a more desirable data rate of 20 Mbps.
Interestingly for BPSK, w/o shadowing, we had 100%; and 16QAM: 0%!