consists UPTU wireless comm. Unit-1 P-1

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UNIT-1
Mobile Radio Propagation
Large-Scale Path Loss

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•Electromagnetic wave propagation
•reflection
•diffraction
•scattering
•Urban areas
•No direct line-of-sight
•high-rise buildings causes severe diffraction loss
•multipath fading due to different paths of varying lengths
•Large-scale propagation models predict the mean signal strength for an arbitrary
T-R separation distance.
•Small-scale (fading) models characterize the rapid fluctuations of the received
signal strength over very short travel distance or short time duration.
Introduction to RadioWave Propagation

3. 3
transmitted
signal
received
signal
Ts
max
LOS
LOS
Reflection
Diffraction
Scattering

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• Small-scale fading: rapidly fluctuation
– sum of many contributions from different directions with
different phases
– random phases cause the sum varying widely. (ex: Rayleigh
fading distribution)
• Local average received power is predicted by large-scale model
(measurement track of 5 to 40 )

5. • Free Space Propagation Model
• The free space propagation model is used to predict received
signal strength when the transmitter and receiver have a clear
line-of-sight path between them.
– satellite communication
– microwave line-of-sight radio link
• Friis free space equation
: transmitted power :T-R separation distance (m)
: received power : system loss
: transmitter antenna gain : wave length in meters
: receiver antenna gain
Ld
GGP
dP rtt
r 22
2
)4(
)(
t
P
)(dPr
t
G
r
G
d
L

6. • The gain of the antenna
: effective aperture is related to the physical size of the antenna
• The wave length is related to the carrier frequency by
: carrier frequency in Hertz
: carrier frequency in radians
: speed of light (meters/s)
• The losses are usually due to transmission line
attenuation, filter losses, and antenna losses in the communication
system.A value of L=1 indicates no loss in the system hardware.
2
4 e
A
G
e
A
c
c
f
c 2
f
c
c
L )1( L

7. • Isotropic radiator is an ideal antenna which radiates power with unit
gain.
• Effective isotropic radiated power (EIRP) is defined as
and represents the maximum radiated power available from transmitter
in the direction of maximum antenna gain as compared to an isotropic
radiator.
• Path loss for the free space model with antenna gains
• When antenna gains are excluded
• The Friis free space model is only a valid predictor for for values of
d which is in the far-field (Fraunhofer region) of the transmission
antenna.
tt
GPEIRP
22
2
)4(
log10log10)(
d
GG
P
P
dBPL rt
r
t
22
2
)4(
log10log10)(
dP
P
dBPL
r
t
r
P

8. • The far-field region of a transmitting antenna is defined as the region
beyond the far-field distance
where D is the largest physical linear dimension of the antenna.
• To be in the far-filed region the following equations must be satisfied
and
• Furthermore the following equation does not hold for d=0.
• Use close-in distance and a known received power at that
point
or
2
2 D
d f
Dd f f
d
Ld
GGP
dP rtt
r 22
2
)4(
)(
0
d )( 0
dPr
2
0
0
)()(
d
d
dPdP rr
f
ddd 0
d
ddP
dP r
r
00
log20
W001.0
)(
log10dBm)( f
ddd 0

9. TheThree Basic Propagation Mechanisms
• Basic propagation mechanisms
– reflection
– diffraction
– scattering
• Reflection occurs when a propagating electromagnetic wave
impinges upon an object which has very large dimensions when
compared to the wavelength, e.g., buildings, walls.
• Diffraction occurs when the radio path between the transmitter
and receiver is obstructed by a surface that has sharp edges.
• Scattering occurs when the medium through which the wave
travels consists of objects with dimensions that are small
compared to the wavelength.

10. • Reflection from dielectrics
• Reflection from perfect conductors
– E-field in the plane of incidence
– E-field normal to the plane of incidence
riri
EEand
riri
EEand
Reflection

11. Considering orthogonal polarization
=
Where,
Now velocity (EMW) =

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Now, bondry conditions at the surface of incidence, acc to Snells law,
Using boundary conditions from maxwell eq. (by laws of reflection)
&,

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If 1st medium is free space &
The reflection coeefficients for vertical and horizontal
polarization can be reduced as:-

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Brewster Angle
The angle,at which no reflection occurs in the medium of
origin .It is given by , as:-
If 1st medium is free space and relative permittivity of 2nd is
Than,

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IV. Ground Reflection (2-Ray) Model
 Good for systems that use tall towers (over 50 m tall)
 Good for line-of-sight microcell systems in urban environments

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 ETOT is the electric field that results from a combination of a
direct line-of-sight path and a ground reflected path
 is the amplitude of the electric field at distance d
 ωc = 2πfc where fc is the carrier frequency of the signal
 Notice at different distances d the wave is at a different phase
because of the form similar to

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 For the direct path let d = d’; for the reflected path
d = d”then
 for largeT−R separation : θi goes to 0 (angle of incidence to the
ground of the reflected wave) and
Γ = −1
 Phase difference can occur depending on the phase difference
between direct and reflected E fields
 The phase difference is θ∆ due to Path difference , ∆ =
d”− d’, between

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Using method of images (fig below) , the path difference can be
expressed as:-
 From two triangles with sides d and (ht + hr) or (ht – hr)

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Using taylor series the expression can be simplyfied as:-
Now as P.D is known , Phase difference and time delay can be
evaluated as:-
If d is large than path difference become negligible and amplitude ELOS
& Eg are virtually identical and differ only in phase,.i.e
&

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If than ETOT can be expresed as:-

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Referring to the phasor diagram below:-

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or
As E-field is function of “sin” it decays in oscillatory fashion with
local maxima being 6dB greater than free space and local minima
reaching to-∞ dB.

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For d0=100meter, E0=1, fc=1 GHz, ht=50
meters, hr=1.5 meters, at t=0

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 note that the magnitude is with respect to a reference of
E0=1 at d0=100 meters, so near 100 meters the signal can be
stronger than E0=1
 the second ray adds in energy that would have been lost
otherwise
 for large distances it can be shown that

26. 26

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Q.1
Q.2 calculate the free space path loss for a signal transmitted at afrequency
Of 900MHz forT-R seperation 1Km.

28. Diffraction
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 Diffraction occurs when waves hit the edge of an obstacle
 “Secondary” waves propagated 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.

29. Illustration of diffraction II

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31. Diffraction occurs when waves hit the edge of an obstacle
“Secondary” waves propagated into the shadowed regionExcess
path length results in a phase shift
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32. consider that there's an impenetrable obstruction
of height h at a distance of d1 from the
transmitter and d2 from the receiver. ,
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α
h
d1 d2
T
R
β
γ

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The path difference between direct path and the diffracted path is
∆ =
Thus the phase difference,
∆
If,
Then,

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Thus , is It is clear that,

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Fresnel zone
 The excess total path length traversed by a ray passing
through each circle is nλ/2
,

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The radius of nth fresnel zone circle is denoted by rn
Where,

37. Fresnel diffraction geometry

38. Knife-edge diffraction
 Fresnel integral, 4.59

39. Knife edge diffraction loss
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40. Multiple knife edge diffraction
For multiple knife edges, replace them by single knife
edge, as below
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Log-distance Path Loss Models
 We wish to predict large scale coverage using analytical and
empirical (field data) methods
 It has been repeatedly measured and found that Pr @ Rx
decreases logarithmically with distance
∴ PL (d) = (d / do )n where n : path loss exponent or
PL (dB) = PL (do ) + 10 n log (d / do )

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 “bar” means the average of many PL values at a given value
of d (T-R sep.)
 n depends on the propagation environment
 “typical” values based on measured data

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 At any specific d the measured values vary drastically because
of variations in the surrounding environment (obstructed vs.
line-of-sight, scattering, reflections, etc.)
 Some models can be used to describe a situation
generally, but specific circumstances may need to be
considered with detailed analysis and measurements.

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 Log-Normal Shadowing
PL (d) = PL (do ) + 10 n log (d / do ) + Xσ
 describes how the path loss at any specific location may vary from the average
value
 has a the large-scale path loss component we have already seen plus a
random amount Xσ.

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 Xσ : zero mean Gaussian random variable, a “bell curve”
 σ is the standard deviation that provides the second parameter for
the distribution
 takes into account received signal strength variations due to
shadowing
 measurements verify this distribution
 n & σ are computed from measured data for different area types

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Assingment – determination of % coverage area.