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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.
Propagation Modes
• Ground-wave propagation
• Sky-wave propagation
• Space wave propagation
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)
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
Ground Wave Propagation
Ground Wave Propagation
• Follows contour of the earth
• Can Propagate considerable distances
• Frequencies up to 3 MHz
• Example
– AM radio
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
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
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
Line-of-Sight Propagation
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
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
MOBILE RADIO
PROPAGATION
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
WHY SHOULD WE HAVE
PROPAGATION MODELS
With propagation models, we can
•Provide installation guidelines
•Mitigate interference
•Design better wireless system
•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
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.
Free-space and received fields
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
Typical electromagnetic properties
Superposition for polarization
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
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
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
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
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
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
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]
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
Mobile Radio Propagation
Propagation basics
Properties of Radio waves
Antenna Basics
Introduction to Radio Propagation
mechanisms
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.
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
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.
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
=
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.
RADIO PROPAGATION
MECHANISMS
• REFLECTION
metallic
non-metallic(wood etc.)
• SCATTERING-THROUGH THIS NLOS IS
POSSIBLE
• DIFFRACTION
• RADIO PROPAGATION MECHANISM
DIFFERENT FOR DIFFERENT
FREQUENCY.
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
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.
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.
THE GAIN OF AN ANTENNA
• THE GAIN OF AN ANTENNA G IS
RELATED TO EFFECTIVE APERTURE Ae
BY
2
4
λ
π eA
G =
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
BASICS ANTENNA
• HIGHER THE FREQUENCY HIGHER THE
GAIN FOR THE SAME SIZE ANTENNA.
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
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 )
BASICS -ANTENNA
• the path loss represents signal attenuation as a
positive quantity(measured in db )
))4/(log(10/log10 222
)( dGtGrppP rtdBL πλ−==
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
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
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
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.
• 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
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
==
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( −===
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( −=−==
• 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.
Propagation mechanisms
• Scattering occurs when the medium has
objects that are smaller or comparable to the
wavelength.(small objects, water droplets dust
particles etc.
Reflection from smooth surface
SUMMARY OF MODELS
Higher the freq higher the
path loss
wave-propagation
wave-propagation
wave-propagation
wave-propagation
wave-propagation
wave-propagation
wave-propagation
wave-propagation
wave-propagation
wave-propagation
wave-propagation
wave-propagation

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wave-propagation

  • 1.
  • 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
  • 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
  • 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
  • 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.
  • 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
  • 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.
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  • 94. Higher the freq higher the path loss

Editor's Notes

  1. Transmitting and receiving antennas must be within line of sight Satellite communication – signal above 30 MHz not reflected by ionosphere Ground communication – antennas within effective line of site due to refraction
  2. A brief discussion about refraction is warranted. Such as light or radio wave travels at approximately . Vacuum If moving from a less dense to a more dense medium, the wave will bend toward the more dense medium. Shorter and bent Continuous, gradual bending
  3. Higher the freq higher the path loss