wave-propagation

2. What is propagation?
How radio waves travel between two
points?
They generally do this in four ways:
• Directly from one point to another
• Follow the curvature of the earth
• Become trapped in the atmosphere and traveling
longer distances
• Refracting off the ionosphere back to earth.

3. Propagation Modes
• Ground-wave propagation
• Sky-wave propagation
• Space wave propagation

4. 4
Transmitter Receiver
Earth
Sky wave
Space wave
Ground wave
Troposphere
(0 - 12 km)
Stratosphere
(12 - 50 km)
Mesosphere
(50 - 80 km)
Ionosphere
(80 - 720 km)

5. Radio Frequency Bands
Classification Band Initials Frequency Range Characteristics
Extremely low ELF < 300 Hz
Infra low ILF 300 Hz - 3 kHz
Very low VLF 3 kHz - 30 kHz
Low LF 30 kHz - 300 kHz Surface/groun
d waveMedium MF 300 kHz - 3 MHz
High HF 3 MHz - 30 MHz Sky wave
Very high VHF 30 MHz - 300 MHz Space wave
Ultra high UHF 300 MHz - 3 GHz
Super high SHF 3 GHz - 30 GHz
Extremely high EHF 30 GHz - 300 GHz Satellite wave
Tremendously high THF 300 GHz - 3000 GHz
5

6. Ground Wave Propagation

7. Ground Wave Propagation
• Follows contour of the earth
• Can Propagate considerable distances
• Frequencies up to 3 MHz
• Example
– AM radio

8. Ground-Wave Propagation
• At frequencies up to about 3 MHz, the most
important method of propagation is by ground waves
which are vertically polarized. They follow the
curvature of the earth to propagate far beyond the
horizon. Relatively high power is required.
Direction of wave travel
Increasing
Tilt
Earth

9. Ground-Wave
• Radio waves follow the Earth’s surface
• AM broadcasts during the day
• Works best at lower frequencies (40, 80, and
160 meters)
• Relatively short-range communications

10. Sky Wave Propagation
• Signal reflected from ionized layer of atmosphere
back down to earth
• Signal can travel a number of hops, back and forth
between ionosphere and earth’s surface
• Reflection effect caused by refraction
• Examples
– Amateur radio
– CB radio

11. Line-of-Sight Propagation

12. Line-of-Sight
• Signals travel in a straight line from
transmitting to receiving antenna
• Useful in VHF and UHF ranges
• Television, AM/FM broadcast
• Signals are easily reflected, causing problems
with mobile operation

13. Line-of-Sight Propagation
• Transmitting and receiving antennas must be within
line of sight
• Refraction – bending of microwaves by the
atmosphere
– Velocity of electromagnetic wave is a function of the
density of the medium
– When wave changes medium, speed changes
– Wave bends at the boundary between mediums

14. MOBILE RADIO
PROPAGATION

15. MOBILE RADIO PROPAGATION
• Mobile radio channel is an
important controlling factor in wireless
communication systems.
• Transmission path between transmitter and
receiver can vary in complexity.
• LOS (Line Of Sight)  Simplest

16. WHY SHOULD WE HAVE
PROPAGATION MODELS
With propagation models, we can
•Provide installation guidelines
•Mitigate interference
•Design better wireless system

17. •Wired channels are stationary and
predictable; radio channels are extremely
random and have complex models.
•Modeling of radio channels is done in
statistical fashion based on measurements for
each individual communication system or
frequency spectrum.
MOBILE RADIO PROPAGATION

18. Propagation Models
Aim:
• To predict the average received
signal strength at a given distance
from the transmitter -
Large scale propagation models,
hundreds or thousands of meters.
• To predict the variability of the
signal strength, at close spatial
proximity to a particular location -
Small scale or fading models.

19. Free-space and received fields

20. Reflections from Ground and
Buildings
Electric Properties of Material Bodies
Permittivity ε F/m  Farads/m
Permeability µ H/m  Henries/m
Conductivity σ S/m  Siemens/m
ε = ε0 εr
ε0 = Permittivity of free space =
8.85 • 10-12
F/m
εr = Relative permittivity
µ0 = Permeability of free space =4Π x 10 -7

21. Typical electromagnetic properties

22. Superposition for polarization

23. Laws of Reflection at the
Boundary Between Two Dielectrics
Er = Γ  Reflection
coefficient
Et = T = 1 + Γ 
Transmission
coefficient
EE
ii
EE
ii
EE
ii EE
rr
EE
tt
θθ
ii θθ
rr
θθ
ii == θθ
rr

24. EE
tt
Vertical Propagation
(Or Parallel Polarization)
E-field in the plane of incidence
EE
ii EE
rr
θθii θθrr
HH
ii HH
rrεε11,, µµ11,, σσ11
εε22,, µµ22,, σσ22
θθ tt

25. Vertical Propagation
(Or Parallel Polarization)
Γ|| = -εr sinθi + (εr - cos2
θi)1/2
εr sinθi + (εr - cos2
θi)1/2
= η2sinθt - η1sinθi
η2 sinθt + η1sinθi

26. Horizontal Propagation
(Or Perpendicular Polarization)
E-field normal to the plane of incidence
EE
ii EE
rr
EE
tt
θθii θθrr
HH
ii HH
rr
εε11,, µµ11,, σσ11
εε22,, µµ22,, σσ22
θθ tt

27. Horizontal Propagation
(Or Perpendicular Polarization)
Γ|| = -εr sinθi + (εr - cos2
θi)1/2
εr sinθi + (εr - cos2
θi)1/2
= η2sinθt - η1sinθi
η2 sinθt + η1sinθi

28. Brewster Angle:
No Reflected Wave
Γ|| = 0
ðεr sinθB = (εr - cos2
θB)1/2
εr
2
sin2
θB = εr- cos2
θB
= εr – 1 + sin2
θB

29. 2 Cases
sinθB = [(εr-1)/(εr
2
-1)]1/2
[First medium is air ε1 = ε0, ε2 = ε0εr]
sinθB = [(εr
2
- εr)/(εr
2
-1)]1/2
[Second medium is air ε2 = ε0, ε1 = ε0εr]

30. Reflection from Perfect Conductor
Parallel/ Perpendicular/
vert. polarization horiz. polarization
θi= θr θi= θr
Ei = Er Ei = - Er
EE
ii EE
rr
EE
tt
θθ
ii θθ
rr

31. Mobile Radio Propagation
Propagation basics
Properties of Radio waves
Antenna Basics
Introduction to Radio Propagation
mechanisms

32. Introduction
• The mobile radio channel places fundamental
limitations on the performance of wireless
communication systems
• Path may be
 LOS
 NLOS Obstructed by buildings, hills, foliage, cars on
streets etc.
• Radio Channels are random and time varying
• Modelling radio channels have been one of the
difficult parts of the mobile radio design.

33. Propagation Basics
• When electrons move, they create EM waves that can
propagate through space.
• By attaching an antenna of the appropriate size to an
electrical circuit EM waves can be broadcast efficiently and
received by a receiver at some distance away.
• The radio, microwave, infrared and visible light portions of
EM spectrum can be used to disseminate information.
Information can be sent by modulating amplitude, frequency or
phase of the waves

34. Properties of Radio Waves
• Easy to be generated
• Travel long distances (Without Loss)
• Penetrate buildings.
• May be used for both indoor and outdoor
communication
• Omni directional- can travel in all directions
• Can be narrowly focused at high frequencies (greater
than 100Mhz) using parabolic antennas.

35. ANTENNA BASICS
• THE FREE SPACE RECEIVED POWER IS GIVEN
BY FRIIS FREE SPACE EQUATION
• d- Distance at which signal is received
• L- System loss factor (nothing to do with
propagation)
• Received power is dependent on all the above factors.
Ld
GGp
dP rtt
r 22
2
)4(
)(
π
λ
=

36. Frequency Dependence
• Behave like light at higher frequencies
• Difficulty in passing Obstacles.
• Rectilinear Property: More direct paths (Straight line
paths)
• Absorbed by rain, fog particles.
• Behave more like radio at lower frequencies
• Can pass obstacles at lower frequencies
• Power falls off sharply with distance from source.
• Subject to interference from other radio wave
sources.

37. RADIO PROPAGATION
MECHANISMS
• REFLECTION
metallic
non-metallic(wood etc.)
• SCATTERING-THROUGH THIS NLOS IS
POSSIBLE
• DIFFRACTION
• RADIO PROPAGATION MECHANISM
DIFFERENT FOR DIFFERENT
FREQUENCY.

38. Basics of Mobile Radio Propogation
• VLF,LF,MLF bands radio waves follow ground.
AM radio broadcasting uses MF band.
• Surface of earth acts as a guide (curvature taken
into consideration).
• AT HF ground waves tend to be absorbed by
earth.So we go for ionospheric propagation

39. BASICS OF MOBILE COMMUNICATION
• Modeling the radio channel is typically done
in statistical manner
• The statistical modeling is done based on
measurement data made specific for
The intended communication system .
The intended spectrum.

40. BASICS OF MOBILE COMMUNICATION
• however for higher frequencies(>10Ghz)
deterministic modeling is used as statistical
modeling starts failing.
• By playing with the antenna(tilting and
changing the height coverage area can be
controlled.

41. THE GAIN OF AN ANTENNA
• THE GAIN OF AN ANTENNA G IS
RELATED TO EFFECTIVE APERTURE Ae
BY
2
4
λ
π eA
G =

42. BASICS ANTENNA
• THE EFFECTIVE APERTURE Ae IS
RELATED TO THE PHYSICAL SIZE OF
THE ANTENNA .
• IS RELATED TO THE CARRIER
FREQUENCY BY
cf
c
=λ
λ
λ

43. BASICS ANTENNA
• HIGHER THE FREQUENCY HIGHER THE
GAIN FOR THE SAME SIZE ANTENNA.

44. BASICS ANTENNA(2)
• An isotropic radiator is an ideal antenna that
radiates power with unit gain uniformly in all
directions. It is the reference antenna in wireless
systems.
• The effective isotropic radiated power(eirp) is
defined as EIRP=PTGT
• theeffectiveradiatedpower(ERP)istheradiatedpowerincomparisontothehalfwavedipole
antenna

45. BASICS ANTENNA
• Since the dipole antenna has a gain of
1.64(2.15db)
• In practice antenna gains are given in the units
of dbi
(db with respect to an isotropic source )

46. BASICS -ANTENNA
• the path loss represents signal attenuation as a
positive quantity(measured in db )
))4/(log(10/log10 222
)( dGtGrppP rtdBL πλ−==

47. BASICS -ANTENNA
• FRISS Free space model is valid in the far
field or fraunhofer region.
• Fraunhofer distance is defined as df =2d2
/λ
• we must also have df>> D and df>>n

48. Basics antanna
• THE FRISS free space equation does not hold
for d=0
• Hence we use a close-in power reference at a
distance do.
• The reference distance do is chosen such that do
>df
• thus Pr(d)=Pr(do)log(do/d)2

49. BASICS -ANTENNA
• sometimes we define the received power with
reference to 1 milliwatt as dBm
Where
is the path loss we experience from going from
d0 to d
)/log(20
001.0
)(
log10)( 0
0
dd
w
dP
dP r
r
+=
)/log(20 0
dd

50. EXAMPLE
• what will be the far field distance for a base
station antenna with.
• largest antenna dimension d=0.5m
• frequency of operation f1=900mhz(gsm)
• frequency of operation f2=1800mhz.

51. • FOR 900 MHZ
• Λ=(3x108
/900X106
) =0.33M
• df=2D2
/ Λ= 2(0.5)2
/0.33m=1.5m
• For 1800 MHz
Λ=0.17
df=2D2
/ Λ= 2(0.5)2
/0. 17m=3.0m

52. BASICS-ANTENNA
• POWER FLUX AT A DISTANCE DUE TO
AN IDEAL (POINT) ANTENNA
=
E2/120π w/m2
22
44 d
EIRP
d
Gp
P tt
d
ππ
==

53. EXAMPLE
• for a base station let pt=10w fc=900 mhz gt=2
gr=1
• the mobile station is at a distance of 5 km
• find the received power in dbm
22
2
)4(
log10
)(
d
GGp
dP rtt
r
π
λ−
=
22
2
5000.)4(
)33(.1210
log(10
π
xxx
dBmdBWmdPr 6.626.92)5000( −===

54. BASICS ANTENNA
• FOR A GSM BASE STATION LET pt=500mw,
FC=900 mhz gt=2 gr=1
• The mobile station is at a distance of 10 km
• What is the received power in dBm
• Will this GSM phone work?
• Yes because my receiver sensitivity is -100 dBm
22
2
)4(
log10
)(
d
GGp
dP rtt
r
π
λ−
=
dBmdBWmdPr
6.816.111)10000( −=−==

55. • Reflection occurs when the electromagnetic wave
impinges on an object which has very large
dimension as compared to wavelength .Eg. surface of
earth ,building etc.
• Diffraction occurs when the radio path between the
transmitter and receiver is obstructed by a surface that
has sharp irregularities.
Propagation mechanisms
Explains how radio signal can travel
urban and rural environments without a
line of sight.

56. Propagation mechanisms
• Scattering occurs when the medium has
objects that are smaller or comparable to the
wavelength.(small objects, water droplets dust
particles etc.

61. Reflection from smooth surface

85. SUMMARY OF MODELS

94. Higher the freq higher the
path loss