Mobile Ppropagation Channel - Large-scale Path Loss (2 Slides)

8/2/2019 Mobile Ppropagation Channel - Large-scale Path Loss (2 Slides)

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3/7/20

1

MOBILE PROPAGATION CHANNEL:

LARGE-SCALE PATH LOSS

2

Introduction

Mobile radio channel is an important controllingfactor in wireless communication systems

Transmission path between transmitter and receivercan vary in complexity LOS (Line-Of-Sight) - simplex

Wired channels are stationary and predictable, radiochannels are extremely random and have complex

models Modeling of radio channels is done in statistical

fashion based on measurements for each individualcommunication system or frequency spectrum



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Propagation Models To predict the average received signal

strength at a given distance from thetransmitter - large scale propagationmodels, hundreds or thousands of meters

To predict the variability of the signalstrength, at close spatial proximity to aparticular location -Small scale or fading

models

4

Free Space Propagation Model

The free space propagation model is used topredict received signal strength when thetransmitter and receiver have a clear,unobstructed line-of-sight path between them

The free space model predicts that receivedpower decays as function of the transmitter-receiver (T-R) separation distance raised tosome power



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6


Free space power received by a receiver antennawhich is separated from a radiating transmittingantenna by a distance d (Friis free space equation):

P t is the transmitted power

P r (d) is the received powerG t , G R is the transmitter and receiver antenna giand is the T-R separation distance in metersL is the system loss factor not related to propagation (L ≥1)λ is the wavelength in meters

2

2 2

. . .( )

( 4 ) . .

t t r r

P G G P d

d L



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Free Space Propagation Model The gain of an antenna is related to its

effective aperture, A e

A e is related to the physical size of theantenna

λ is related to the carrier frequency

2

4 e AG

8


The effective isotropic radiated power (EIRP )represents the maximum radiated power availablefrom a transmitter in the direction of maximumantenna gain, compared to an isotropic radiator

In practice, effective radiated power (ERP ) is used

instead of EIRP to demonstrate the maximumradiated power as compared to a half-wave dipoleantenna

t t IRP PG



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Free Space Propagation Model The path loss for the free space model when

antenna gain are included is given by

When antenna gains are excluded, theantennas are assumed to have unity gain andpath loss is given by

2

2 210 log 10 log

4

t t r

r

P GG PL dB

P d

2

2 210 log 10 log

4

t

r

P PL dB

P d

10


The Friis free space model is a only validpredictor for P r for values of which are in thefar-field of the transmitting antenna

The far-field, or Fraunhofer region, of atransmitting antenna is defined as the regionbeyond the far-field distance d

f , related to

the largest linear dimension of the transmitterantenna aperture and the carrier wavelength



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Free Space Propagation Model The Fraunhofer distance is given by

D is the largest physical linear dimension of the antenna

d f must satisfy , and

22

f

Dd

f d Df d

12


Large-scale propagation models use a close-in distance,d 0 , as a known received power reference point

The received power, P r (d) , at any distance d > d 0 , maybe related to P r at P 0

The reference distance must be chosen such that it lies inthe far-field region, that is, d 0 ≥ d f , and d 0 is chosen to besmaller than any practical distance used in the mobilecommunication system

The received power in free space at a distance greaterthan d 0 is given by

2

00 0,r r f

d P d P d d d d

d



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Free Space Propagation Model Large dynamic range of received power

levels, often dBm or dBW units are usedto express received power levels

P r (d) is in dBm

P r (d 0 ) is in watts

( ) 10 log 20 log

0,001,r o o

r o f

P d d P d d d d

W d

14

Example

Given a transmitter produces 50 W of power. If this

power is applied to a unity gain antenna with 900MHz carrier frequency, find the received power at afree space distance of 100 m from the antenna. Whatis P r (10 km). Assume unity gain for the receiverantenna



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Example The received power at 100m

The received power at 10Km

W Ld

GG P md P r t t

r

6

22

2

22

2

10.5,31.100.)4(

)3/1.(1.1.50

)4(100

63,5.10

100 10 log 24, 50,001

r d m dBm

100( 10 ) 24,5 20 log 64,5

10000r P d km dBm

16

Propagation Mechanisms

Receiving power is generally the mostimportant parameter predicted by large-scale propagation model based on thephysics of reflection, scattering, anddiffraction



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Propagation Mechanisms Reflection occurs when a propagating

electromagnetic wave impinges upon an object whichhas very large dimensions when compared to thewavelength of the propagating wave.

Diffraction occurs when the radio path between thetransmitter and receiver is obstructed by a surfacethat has sharp irregularities

Scattering occurs when the medium through whichthe wave travels consists of objects with dimensionsthat are small compared to the wavelength and

where the number of obstacles per unit volume islarge

18

Reflection

Reflection occur from the surface of theearth and from buildings and walls

When a radio wave propagating in onemedium impinges upon anothermedium having different electrical

properties, the wave is partiallyreflected an partially transmitted



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Reflection The electric field intensity of the reflected and

transmitted waves may be related to theincident wave the medium of origin throughthe Fresnel reflection coefficient (Γ)

The reflection coefficient is a function of thematerial properties, and generally depends onthe wave polarization, angle of incidence, and

the frequency of the propagation wave

20

Law Of Reflection At TheBoundary Between 2 Dielectrics

Reflection coefficient

Transmission coefficient

r

i

E

E

1t

i

E T

E



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Ground Reflection (2-ray)

Model In mobile radio channel, the 2-ray ground

reflection model is a useful propagationmodel that is based on geometrics optics, andconsiders both direct path and a groundreflected propagation path betweentransmitter and receiver

This model has been found to be reasonablyaccurate for predicting the large-scale signal

strength over distance of several kilometersfor mobile radio systems

22

Ground Reflection (2-ray)Model



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Model In mobile communication systems, the

maximum T-R separation distance is atmost only a few tens of kilometers, andthe earth may be assumed to be flat

The total received E-field, E TOT , is thena result of the direct line-of-sight

component, E LOS , and the groundreflected component, E g

24


If E 0 is the free space E-field (V/m) at thereference distance d0 from the transmitter,then for d > d 0 , the free space propagatingE-field is given by

where represents the envelope of

the E-field at d distance from the transmitter

0 0, cos c

E d d E d t t

d c

0 0( , )d t E d d



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Model Two propagating waves arrives at the receiver: the

direct wave that travel a distance d ’ ; and thereflected wave that travel a distance d ”

The direct LOS component at the receiver can beexpressed

The E-field for the ground reflected wave can beexpressed

0 0'

( ', ) cos'

LOS c

E d d E d t t

d c

0 0 ''( '', ) cos

'' g c

E d d E d t t

d c

26


According to laws of reflection in dielectrics:

Where Γ is the reflection coefficient for ground

For small values of θ i , the reflected wave isequal in magnitude and 1800 out of phasewith the incident wave

i o

g i E E (1 )t i E E



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Model The resultant E-field, assuming perfect

ground reflection (i.e. Γ = 1 and E t = 0) is thevector sum of ELOS and Eg

TOT LOS g E E E

0 0 0 0' ''( , ) cos[ ( 1) cos

' ''TOT c c

E d E d d d E d t t t

d c d c

28




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Model The path difference between line-of-sight and the

ground reflected paths can be expressed

The phase difference θ Δ between the two E-fieldcomponent and the time delay τ d between the

arrivals of the components

2 2 2 2" ' ( ) ( )t r t r d d h h d h h d

2" ' t r h h

d d d

2 c

c

2d

cc f

30


As d becomes large, the difference between the distanced ’ and d ” becomes very small, and the amplitudes of E LOS

and E g is virtually identical and differ only in phase

The E-field at the receiver at the distance d from the

transmitter can be written as

0 0 0 0 0 0

' "

E d E d E d

d d d

2sin2cos22

0000

d

d E

d

d E E

TOT



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Model

32


If θ Δ < 0.3 radian

E-field can be approximately as

K is constant related to E 0 , the antenna height and thewavelength

2sin 0, 3

2 2

t r h hrad

d

20 20

3

t r t r h h h hd

0

2

2 2( / )o t r

TOT

E d h h k E V m

d d d



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Model The received power at the distance d from the

transmitter can be expressed as

Path loss 2-ray model (with antenna gains) can beexpressed in dB as

When θ Δ = Π , then d = (4h t h r )/λ is where the ground appears inthe first Fresnel zone between the transmitter and receiver

2 2

4( ) t r

r t t r

h h P d P G G

d

( ) 40log 10log 10log 20log 20logt r t r PL dB d G G h

34

Example

A mobile is located 5 km away from a base station.and uses a vertical /4 monopole antenna with a gainof 2.55 dB to receive cellular radio signals. The Efield at 1 km from the transmitter is measured to be10-3 V/m. The carrier frequency used is 900 MHz.

(a) Find the length and gain of the receiving antenna

(b) Find the received power at the mobile using the

2-way ground model assuming the height of thetransmitting antenna is 50 m and receiving antenna

is 1.5 m above the ground.



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Example Wavelength:

Length of the antenna:

Gain of antenna:

Since

Received power

m f

c33,0

10.900

10.36

8

4 8.33 L cm

2.55 1.8G dB

r t hhd

mV

mV d

k

d

hh

d

d E d E r t

R

/10.1,113)10.5.(33,0

5,1.50.2

10.5

10.1.10.2

)/(22

)(

633

33

2

00

dBmdBW

W kmd P r

68,9268,122

10.4,54

33,08,1

377

10.1,113)5( 13

226

36

Diffraction

Diffraction allows radio signals to propagatearound the curved surface of the earth,beyond horizon, and to propagate behindobstructions

The received field strength decreases rapidlyas a receiver moves deeper into obstructed(shadow) region.

The diffraction field still exists and often hassufficient strength to produce a useful signal



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Diffraction – Fresnel Zone

Geometry Consider a transmitter and receiver separated

in free space as shown in below figure

Let an obstructing screen of effective height h with infinite width be placed between them ata distance d 1 from the transmitter and d 2

from the receiver

The wave propagating from the transmitter to

the receiver via the top of the screen travelsa longer distance than if a direct line-of-sightpath existed.

38

Diffraction – Fresnel ZoneGeometry



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Geometry Assuming h << d 1 , d 2 and h >> λ

The difference between the direct path andthe diffracted path, called the excess pathlength ( Δ ) can be obtained as

The corresponding phase difference is given

2

1 2

1 2

( )

2

h d d

d d

2

1 2

1 2

( )2 2

2

h d d

d d

40




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Geometry

42


When

Fresnel Kirchoff diffraction parameter v is given by

Where has units of radians, the corresponding phasedifference can be expressed as

tgx x

21

21

d d

d d h

1 2 1 2

1 2 1 2

2 2d d d d v h

d d d d

2

2v



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Geometry In practical diffraction problems, it is advantageous to reduce all

heights by a constant, so that the geometry is simplified withoutchanging the values of the angles

The concept of diffraction loss as a function of the pathdifference around an obstruction is explained by Fresnel zones.

The Fresnel zones represent successive regions wheresecondary waves have a path length from the transmitter toreceiver which are nλ/2 greater than the total path length of aline-of-sight path

The successive Fresnel zone have the effect of alternatelyproviding constructive and destructive interference to the totalreceived signal

The radius of the nth Fresnel zone circle is denoted by r n and beexpressed in terms of n , λ, d 1 , and d 2

1 21 2

1 2

,n n

n d d r d d r

d d

44




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Geometry In mobile communication systems, diffraction loss

occurs from the blockage of secondary waves suchthat only a portion of the energy is diffracted aroundan obstacle

That is, an obstruction causes a blockage of energyfrom some of the Fresnel zones, thus allowing onlysome of the transmitted energy to reach the receiver.

Depending on the geometry of the obstruction, thereceived energy will be a vector sum of the energy

contributions from all unobstructed Fresnel zones.

46


If an obstruction does not block the volumecontained within the first Fresnel zone, thediffraction loss will be minimal, and diffractioneffects may be neglected

In fact, a rule of thumb used for design of line-of-sight microwave links is that as longas 55% of the first Fresnel zone is kept clear,then further Fresnel zone clearance does notsignificantly alter the diffraction loss



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Geometry

48




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Geometry

50

Knife-edge Diffraction Model

It is impossible to make very precise estimates of thediffraction losses

In practice, prediction is a process of theoreticalapproximation modified by necessary empiricalcorrections

The limiting case of propagation over a knife-edgevies good insight into the order of magnitude of diffraction loss

When shadowing is caused by a single object such asa hill or mountain, the attenuation caused bydiffraction can be estimated by treating theobstruction as a diffracting knife-edge



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52


Consider a receiver at point R , located in theshadowed region

The field strength at point R is a vector sumof the fields due to all of the secondaryHuygen’s source in the plane above the knife-edge



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Knife-edge Diffraction Model The E-field strength, E d , of a knife-edge

diffracted wave is given by

E 0 is the free space field strength in the absenceof both the ground and the knife-edge

F(v) is the complex Fresnel integral and is a function of theFresnel-Kirchoff diffraction paremeter v

2

2

0

(1 )( )

2

j t

d

v

E jv e dt

E

54


The diffraction gain due to the presence of a knife-edge, as compared to the free space E-field, is givenby

The approximate solution is given

( ) 20 log ( )d

G dB F v

0.95

2

( ) 0 1

( ) 20 log(0, 5 0, 62 ) 1 0

( ) 20 log 0.5 0 1

( ) 20 log 0.4 0,1184 (0, 38 0,1 ) 1 2, 4

0,225( ) 20 log 2, 4

d

d

v

d

d

d

G dB v

G dB v v

G dB e v

G dB v v

G dB vv



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ExampleCompute the diffraction loss between the

transmitter and receiver assuming, = 1/3m, d 1 = 1 km, d 2 = 1 km and h = 25m

56




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Example Given

= 1/3 m,

d 1 = 1 Km,

d 2 = 1 Km

h = 25 m

Fresnel diffraction parameter

Diffraction loss is 21.71 dB

1 2

1 2

2 2 1 0 0 0 1 0 0 02 5 2 .7 4

1 / 3 1 0 0 0 * 1 0 0 0

d d v h

d d

( ) 20log 0.225 2.74 21.71v dB

58

Multiple Knife-edge Diffraction

In many practical situations, especially in hill terrain,the propagation path may consist of more than oneobstruction, in which case the total diffraction lossdue to all of the obstacles must be computed

Bullington suggested that the series of obstacles bereplaced by a single equivalent obstacle so that thepath loss can be obtained using single knife-edge

diffraction model This method oversimplifies the calculations and often

provides very optimistic estimates of received signalstrength



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60


Millington gave a wave-theory solution for thefield behind two knife edges in series

This solutions is very useful and can beapplied easily for predicting diffraction lossdue to two knife edges.

However, extending this to more than twoknife edges becomes a formidable

mathematical problem Many models that are mathematically less

complicated have developed to estimate thediffraction losses due to multiple obstruction



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Scattering A radio wave impinges on a rough

surface, the reflected energy is spreadout (diffused) in all directions due toscattering

The actual received signal is oftenstronger than what is predicted by

reflection and diffraction models alone

62

Practical Link Budget Design

Most radio propagation models are derived using acombination of analytical and empirical models

Empirical approach is based on fitting curves oranalytical expressions that recreate a set of measured data Advantages: Takes into account all propagation factors, both

known and unknown

Disadvantages: New models need to be measured fordifferent environment or frequency

Over many years, some classical propagation modelshave been developed, which are used to predictlarge-scale coverage for mobile communicationsystem design



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Log-Distance Path Loss Model The average large-scale path loss for an arbitrary T-R

separation is expressed as a function of distance byusing a path loss exponent, n

n is the path loss exponent

d 0 is the close-in distance which is determined frommeasurements close to the transmitter

d is the T-R separation distance

0

( )

n

d PL d

d

0

0

( )[ ] ( ) 10 logd

PL d dB PL d nd

64

Log-Distance Path Loss Model



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Log-normal Shadowing Log-distance path loss model does not

consider the fact that the surroundingenvironmental clutter may be vastly differentat two different location having the same T-R separation

This leads to measured signals which arevastly have shown that at any value d, thepath loss at a particular location is random

and distributed log-normal (normal in dB)about the mean distance dependent value

66

Log-normal Shadowing

That is

And (antenna gains included in PL(d) )

X б is a zero-mean Gaussian distributed random variable (indB) with standard deviation б (also in dB)

0

0

( )[ ] ( ) ( ) 10 logd

PL d dB PL d X PL d n X d

( )[ ] ( )[ ] ( )[ ]r t P d dBm P d dBm P L d dB



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Log-normal Shadowing Since PL(d) is a random variable with a normal

distribution in dB about the distance dependentmean, so is P r (d) , and Q -function or error function(erf ) amy be used to determine the probability thatthe received signal level will exceed a particular level

The Q -function2

21 1

( ) 1

2 2 2

x

z

z Q z e d x e r f

( ) 1 ( )Q z Q z

68

Log-normal Shadowing

The probability that the received signal level willexceed a certain value γ can be calculated from thecumulative density function

Similarly, the probability that the received signal levelwill be belowγ is given by

( )

Pr ( ) r r

P d P d Q

( )

Pr ( ) r r

P d P d Q



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Determination of Percentage

of Coverage Area For a circular coverage area having radius R

from a base station, let there be somedesired received signal threshold γ

We are interested in computing U(γ) , thepercentage of useful service area, i.e. thepercentage of area with a received signal thatis equal or greater than γ

70

Determination of Percentageof Coverage Area

Let d = r represent the radial distance from thetransmitter

It can be shown that Pr[P r (r) > γ] is the probabilitythat the random received signal at d = r exceeds thethreshold γ within an incremental area dA



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of Coverage Area U(γ) can be found by

2

2 2

0 0

1 1P r ( ) P r ( )

R

r r U P r d A P r r d r d

R R

0

0

( ) ( )1 1Pr ( )

2 2 2

[ ( ( ) 10 lg )]1 1

2 2 2

r r r

t

P r P r P r Q erf

r P PL d n

d er f

72


In order to determine the path loss as referenced tothe cell boundary (r = R ), it is clear that

0

0

( ) 10 log 10 log ( ) R r

PL r n n PL d d R

0

0( ) 10 log 10 log

1 1P r ( )

2 2 2

t

r

R r P PL d n nd R

P d erf



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of Coverage Area If we let

Then

0

0

( ) 10 log

2

t

R P PL d n

d a

1 0 lo g

2

n eb

2

0

1 1ln

2

R r U r erf a b dr

R R

74


By substituting

By choosing the signal level such that

(i.e. a = 0)

log( )t a b r R

2

1 21 1

1 ( ) 12

ab

bab

U erf a e erf b

( )r P R

2

11 1

1 12

bU e erf b



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of Coverage Area

76

Example

Four received power measurements were taken at the distances

of 100m, 200m, 1 km and 3 km from a transmitter. Thesemeasured values are given in the following table.

The path loss equation model for other measurements followslog normal shadowing model where d0 = 100 m.



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Example(a) Find the minimum mean square error

(MMSE) estimate for the path lossexponent n.

(b) Calculate the standard deviation aboutthe mean value

(c) Estimate the received power at d = 2 kmusing the resulting model

(d) Predict the likelihood that the receivedsignal at 2 km will be greater than -60dBm.

78

Example

The MMSE estimate may be found using the followingmethod: Let p i be the received power at a distance d i and let be the estimate for pi using the (d/d 0 )

n

path loss model. The sum of squared errors betweenthe measured and estimated is given by

The value of n which minimizes the mean squareerror can be obtained by equating the derivative of

J (n ) to zero, and then solving by n

i p̂

k

i

ii p pn J

1

2ˆ)(



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Example We find

Since P (d 0 ) = 0 dBm, the following estimates for in dBm

The sum of squared errors is then by

Setting

0ˆ ( ) 10 log

100

ii i

d p p d n

i p̂

1ˆ 0 p 2

ˆ 3 p n 3ˆ 10 p n 4

ˆ 14.77 p n

2 2 2 2

2

( ) (0 0) (20 ( 3 )) ( 35 ( 10 )) ( 70 (14.77 ))

65.25 2887.8 327.153

J n n n n

n n

( )654.306 2887.8 0 4.4

dJ nn n

dn

80

Example

The variance at n = 4.4 can be obtained2 ( )

4

J n

2 2 2 2( ) (0 0) (20 13.2) ( 35 44) ( 70 64.988) 152.36 J n

2 152.36 4 38.09

6.17dB



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Example The estimate of the received power at d = 2Km is

given by

The probability that the received signal level will begreater than -60dBm is given by

2000ˆ 0 10.4, 4 log 57, 24

100 p dBm

%4,6717,6

)24,57(60

)(60)(Pr

Q

d P QdBmd P r r

82

Outdoor Propagation Model

Longley-Rice Model

Okumura Model

Hata Model



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Longley-Rice Model Applicable to point-to-point communication systems

in frequency range from 40MHz to 100GHz, overdifferent kind of terrain

Longley-Rice propagation prediction model is alsoreferred to as the ITS irregular terrain model

Longley-Rice model is also available as a computerprogram calculate large-scale median transmissionloss relative to free space loss over irregular terrainfor frequencies between 20MHz to 10GHz

There have been many modifications and corrections

to the Longley-Rice model to deal with radiopropagation in urban area – this is particularlyrelevant to mobile radio

84

Okumura Model

It is one of the most widely used models forsignal prediction in urban area.

This model is applicable for frequencies inrange 10MHz to 1920MHz (although it istypically extrapolated up to 3000MHz) anddistance of 1Km to 100Km

It can be used for base station antennaheight ranging from 30m to 1000m



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Okumura Model Okumura developed a set of curves giving the

median attenuation relative to free space ( A m u) , inan urban area over a quasi-smooth terrain with abase station effective antenna height (h te ) of 200mand a mobile antenna height (h r e) of 3 m

To determine path loss using Okumura’s model, thefree space loss between the points of interest is firstdetermined, and then the value of A mu(f,d) (as readfrom the curves) is added to it along with correction

factors to account for the type of terrain.

86

Okumura Model

The model can be expressed as

Where L 50 is the 50th percentile (i.e. median) value of propagation path loss

L F is the free space path loss

A mu is the median attenuation relative to free space

G (h re ) is the base station antenna height gain factor

G (h re ) is the mobile antenna height gain factor

G area is the gain due to the type of environment

50( ) ( , ) ( ) ( )

F mu te re area L dB L A f d G h G h G



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Okumura Model

88

Okumura Model



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Okumura Model Okumura found that G (h te ) varies at a rate of

20dB/decade and G (h re ) varies at a rate of 10dB/decade for height less than 3m

( ) 20 lg 1000 30200

( ) 10 lg 33

( ) 20 lg 10 33

tete te

re

re re

rere re

hG h m h m

hG h h m

hG h m h m

90

Okumura Model

Other corrections may also be applied to Okumura’smodel

Okumura’s model is wholly based on measured dataand does not provide any analytical explanation

Okumura’s model is considered to be among thesimplest and best in terms of accuracy in path lossprediction for mature cellular and land mobile radio

systems in cluttered environment It is very practical and has become a standard for

system planning in modern land mobile radio systemin Japan



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Okumura Model The major disadvantage with the model

is its slow response to rapid changes interrain, therefore the model is fairlygood in urban and suburban area, butnot good as in rural area

Common standard deviations between

predicted and measured path lossvalues are around 10dB to 14dB

92

Example

Find the median path loss using Okumura’smodel for d = 50Km, h t e = 100m, h re = 10m inan urban environment. If the base stationradiated an EIRP of 1KW at a carrierfrequency of 900MHz. Find the power at thereceiver (assume a unity gain receiving

antenna)



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Example The free space path loss L F can be calculated as:

From the Okumura curves

A mu (900MHz, 50Km) = 43 dB

G area = 9 dB

22

2 22 3 2

1 / 310 lo g 10 lo g 12 5.5

4 * 4 * (50 *1 0 ) F L d B

d

10 0( ) 20 log 20 log 6

200 20010

( ) 20 log 20 log 10.463 3

tete

rere

hG h dB

hG h dB

94

Example

The total mean path loss is

The average received power is

50( ) ( , ) ( ) ( ) 155.04

F mu te re area L dB L A f d G h G h G dB

50( ) ( ) ( ) ( )60 155.04 0 95.04

r r P d EIRP dBm L dB G dBdBm dB dB dBm



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Hata Model Hata model is an empirical formulation of the

graphical path loss data provided by Okumura

Applicable form frequencies range from150MHz to 1500MHz

Hata presented the urban area propagationloss as a standard formula and suppliedcorrection equations for application to other

solutions

96

Hata Model

The standard formula for median path loss in urbanarea is given by

f c is the frequency (in MHz) from 150MHz to 1500MHz

h te is the effective transmitter (base station) antenna height(in meters) ranging from 30m to 200m

h re is the effective receiver (mobile) antenna height (inmeters) ranging from 1m to 10m

d is the T-R separation distance (in Km)

a(hre) is correction factor for effective mobile antenna heightwhich is the function of the size of the coverage area

50 ( )( ) 69.55 26.16 log 13.82 log ( )

(44.9 6.55log )log

c te re

te

L urban dB f h a h

h d



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Hata Model For a small to medium sized city, the mobile antenna

correction factor is given by

For a large city, it is given by

( ) (1.1log 0.7) (1.56 log 0.8)re c re ca h f h f

2( ) 8.29(log1.54 ) 1.1 300re re ca h h dB f MHz

2

( ) 3.2(log11.75 ) 4.97 300re re ca h h dB f MHz

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Hata Model

The path loss in a suburban area the standard Hataformula is modified as

The path loss in open rural areas is modified as

2

50 50( ) ( ) 2 log 28 5.4c L dB L urban f

2

50 50( ) ( ) 4.78(log ) 18.33log 40.98c c L dB L urban f f



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Hata Model Although Hata’s model does not have any of

the path specific corrections which areavailable in Okumura’s model, theexpressions have significant practical value

The predictions of Hata model compare veryclose with the original Okumura model, aslong as d exceeds 1Km.

This model is well suited for large cell mobilesystems, but no personal communicationssystems (PCS) which have cells on the orderof 1Km radius

100

PCS Extension to Hata Model

European Co-operative for Scientific andTechnical research (EURO-COST) formed theCOST-231 working committee to develop anextended version of Hata model

COST-231 proposed the following formula toextend Hata model to 2GHz

The COST-231 extension of the Hata model is

restricted to the following parameters: f : 1500MHz – 2000MHz h te : 30m to 200m h re : 1m to 10m d : 1Km to 10Km



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Walfisch and Bertoni Model In dB, the path loss is given

L 0 represents free space loss

L rts represents the rooftop-to-street diffraction andscatter loss

L ms denotes multiscreen diffraction loss due to the

rows of buildings

0( )

rts msS dB L L L

104

Walfisch and Bertoni Model



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Indoor Propagation Models The indoor radio channel differs from the traditional

mobile radio channel in two aspects – the distancescovered are much smaller, and the variability of theenvironment is much greater for a much smaller of T-R separation distances.

Propagation within buildings is strongly influenced byspecific features such as the layout of the building,construction materials and the building type

Indoor radio propagation is dominated by the samemechanisms as outdoor: reflection, diffraction, and

scattering In general, indoor channels may be classified either

as line-of-sight (LOS) or obstructed (OBS) withvarying degrees of clutter

106

Partition Losses (Same Floor)

Buildings have a wide variety of partitionsand obstacles which form the internal andexternal structure

Partitions that are formed as part of thebuilding structure are called hard partitions,and partitions that may be moved and whichdo not span to the ceiling are called soft

partition Partitions vary widely in their physical and

electrical characteristics, making it difficult toapply general models to specific indoorinstallation



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Partition Losses (Same Floor)

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Partition Losses (BetweenFloor)

The losses between floors of a building aredetermined by the external dimensions andmaterials of the building, as well as, the typeof construction used to create the floors andthe external surroundings

The following table illustrated values for floorattenuation factor (FAF) in three buildings

It can be seen that for all three buildings, theattenuation between one floor of the buildingis greater than the incremental attenuationcaused by each additional floor



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Partition Losses (Between

Floor)

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Log-distance Path Loss Model

Indoor path loss obeys the distance powerlaw

Where the value of n depends on thesurroundings and building type

X б represents a normal random variable in dBhaving a standard deviation of б dB

0

0

( ) ( ) 10 logd

PL dB PL d n X d



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Log-distance Path Loss Model

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Ericsson Multiple BreakpointModel

The Ericsson radio system model obtained bymeasurement in a multiple floor office building

The model has four breakpoints and considers bothan upper and lower bound on the path loss

The model also assumes that there is 30dBattenuation at d0 = 1m, which can be shown to beaccurate for f = 900MHz and unity gain antenna

Rather than assuming a log-normal shadowingcomponent, the Ericsson model provides adeterministic limit on the range of path loss at aparticular distance



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Ericsson Multiple Breakpoint

Model

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Attenuation Factor Model

An in-building propagation model thatincludes the effect of building type as well asthe variations caused by obstacles

This model provides flexibility and was shownto reduce the standard deviation betweenmeasured and predicted path loss to around4dB, as compare to 13dB when only a log-distance model was used in two differentbuildings



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Attenuation Factor Model The attenuation factor model is given

Where n SF represents the exponent value for thesame floor measurement. If a good estimate for nexists on the same floor, then the path loss on a

different floor can be predicted by adding anappropriate value of FAF

0

0

( ) ( ) 19 logSF

d PL d dB PL d dB n FAF dB

d

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FAF may be replace by an exponent whichalready considers the effects of multiple floorseparation

When n MF denotes a path loss exponent based onmeasurements through multiple floor

0

0

( ) ( ) 19 log MF

d PL d dB PL d dB n

d



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Devasirvatham, et. al. found that in-building pathloss obeys free space plus an additional loss factorwhich increase exponentially with distance as infollowing table



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Attenuation Factor Model Path loss is possible to modify as follows

Where is the attenuation constant for thechannel with units of dB per meter (dB/m)

0

0

( ) 20 logd

PL d dB PL d dB d FAF dBd

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Measured Indoor Path Loss



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Signal Penetration into

Buildings The signal strength inside of a building due to an external

transmitter is important for wireless systems that sharefrequencies with neighboring buildings or with outdoor systems

As with propagation measurements between floors, it is difficultto determine exact models for penetration as only a limitednumber of experiments have been published, and they aresometimes difficult to compare

Some generalizations can be made from the literaturemeasurements reported: signal strength received inside abuilding increase with height. At the lower floors of a building,the urban clutter induces greater attenuation and reduces thelevel of penetration. At the higher floor, a LOS path may exist,

thus causing a stronger incident signal at the exterior walls of the building

Mobile Ppropagation Channel - Large-scale Path Loss (2 Slides)

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Transcript of Mobile Ppropagation Channel - Large-scale Path Loss (2 Slides)