7_Wireless Propagation Theory and Propagation Model(V0_1)

8/13/2019 7_Wireless Propagation Theory and Propagation Model(V0_1)

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CDMAWireless Propagation Theory and

Propagation Model



Contents

Ø Characters of Wireless Propagation

Ø Classification of Propagation ModelsØ Free Space Propagation Model

Ø The Application of Propagation

Models in Cellular Design



Radio Propagation on the Open Land

The received signals are the sum of the direct

wave and reflected wave.



Radio Propagation in the Dense Urban

Mobile telephone is hard to receive direct wave. In general,

the received signals are the sum of reflected, diffracted and

scattered waves.



Reflection Reflection occurs when the propagation electromagneticwave encounters an object which has very largedimensions compared to the wavelength of the

propagation wave. Reflection normally occurs on the surfaces of the earth buildings and walls.



Reflection

t coefficien on Transmissi 1 ! E

E

t coefficien Reflection E

E

i

t

i

r

+==

=



Diffraction

Diffraction occurs when the radio path between the

transmitter and receiver is obstructed by the edges of

the objects.

Diffraction allows radio signals to propagate around the

curved surface of the earth beyond the horizon, and to

propagate behind obstructions.



Diffraction Loss

The obstructions position and height

decide the diffraction loss .



Diffraction Arithmetic

Step one!calculate the diffraction factor

( )

21

212

d d

d d

hv λ

+

=

( ) ( )

( )dx x j

jv F

v

∫

∞

−

+

=2/exp

2

1 2π

( ) ( )v F Log E

E Log dBG d 2020

0

==

Step two!calculate the diffraction loss



Approximation of the Diffraction Loss

( )

=

v Log dBG

225.020

( ) ( )

−−−= 2

1.038.01184.04.020 v Log dBG

( ) ( )( )v Log dBG 95.0exp5.020 −=

( ) ( )v Log dBG 6.05.020 −=

( ) 0=dBG v"#1

-1"v"0

0"v"1

1"v"2.4

2. 4"v



Multiple obstructions

The Epstein-Peterson technique is based on the assumptionthat the total loss can be evaluated as the sum of the

attenuation due to each respective significant obstruction.

Epstein Peterson method



ScatteringScattering occurs when the medium through which the wave travels

consists of objects with dimensions that are small compared to the

wavelength, and where the number of obstacles per unit volume is

large.

Scattering waves are produced by rough surfaces, small objects, or byother irregularities. In practice, foliage, street signs, and lamp posts can

cause scattering in the mobile communication system.



Characters of Wireless PropagationRadio propagation is related to terrain and clutter around

the base station. Increasing the antennas height can

enlarge the propagation distance of the transmitter.

Radio transmission is very complex which is impacted by

reflection, diffraction and scattering. Sometimes they will

cause serious fading.

Radio propagation is also related to the frequency. The

higher the frequency is used, the shorter the propagation

distance is.





Wireless Propagation in Dense Urban

Mobile telephone is hard to receive direct wave. In general, the

received signals are the sum of reflected, diffracted and scattered

waves



Wireless Propagation in Dense Urban

"#$%&'()*LOS+,



!"#$%&

-./012345678"#*+,9:0;<0

#=>



Contents


Ø

Classification of Propagation ModelsØ Free Space Propagation Model





Classification of the Propagation Models(1)Empirical Models

Empirical models are equations derived from the statistic and analysis

based on a great deal of measured data.

Okumura # Hata

Model,

COST231-Hata Model,

Lee Model, etc.



Classification of the Propagation Models (2)

Deterministic models

Methods that directly use electromagnetic theory to calculate the field in the

surroundings. The description of surroundings can be gotten from the terrain

and clutter database. The accuracy of the description determines the models

resolution.

Ray Tracing ModelGeometrical theory of

diffraction$GTD%, physicaloptics$PO%method and finite

difference time domain

method(FDTD),etc.



Classification of the Propagation Models (3)Semi-empirical or Semi-deterministic Models

The semi-empirical or semi-deterministic models are some equations

derived from the deterministic models used in urban or indoor

surroundings. Often we correct them based on test data to make them

more accurate.

Ikegami Model,

COST

Walfish-IkeganiModel,

ZTE models,

etc.



Application of different type of Models

Empirical Models and Semi-empirical Models are suitable for

predicting the area where the environment is uniform and the

coverage radius is large.

Semi-empirical Models are also suitable for the uniform

environment but the coverage radius is relative small.

Deterministic Models are suitable for the atactic environmentand indoor situation. The coverage radius is very small.

Meanwhile, it asks for high resolution of the digital map.



Contents


Ø

Classification of Propagation Models

Ø Free Space Propagation Model





The free space propagation model is used to predict

the received signal strength when there is a clear and

unobstructed line-of-sight path between thetransmitter and receiver. It is a standard used to

evaluate the propagation performance of other

environment.

Satellite communication systems and microwave

line-of-sight radio links typically undergo the free

space propagation.

Free Space Propagation Model



The path loss for the free space model

included the antenna gains is given by

−==

22

2

)4(log10log10)(

d

GG

P

P dB PL r t

r

t

π

λ

Path Loss of the Free Space Model




MHz mi

MHz km

f d dB

f d dB

log20log2058.36

log20log2045.32

++=++=

−==

22

2

)4(log10log10)(

d P

P dB PL

r

t

π

λ

When antenna gains are excluded, the antennas areassumed to have unity gain, and path loss is given

by






Contents


Ø

Classification of Propagation ModelsØ Free Space Propagation Model





Okumura-Hata Model

Okumura-Hata is an empirical formulation

of the graphical path loss data provided by

Okumura.

This Model presents the urban area

propagation loss as a standard formula and

supplied correction equations for applicationto other situations.



Okumura-Hata Model is restricted to the following

conditions:

Frequency f150&1500 MHz

Effective height of the Base station antenna!30&200 m

Height of the Mobile antenna!1&10 m

Communication distance!1&35km

Okumura-Hata Model



The standard formula for mean path loss in urban

areas is given by

Okumura-Hata Model

d hhah f L

b

mbb

lg)lg55.69.44( )(lg82.13lg16.2655.69

⋅−+−−+=

d!Distance from the base station(km)

f!Frequency(MHz)

L b!Mean path loss in urban areas (dB)

hb!h

m!Base station and mobile antenna effective height.



The mobile antenna height correction factor

=

<<−<<−

−−−

=

mh

MHz f h

MHz f h

f h f

ha

m

m

m

m

m

5.10

cityLarge150040097.4)75.11(lg2.3

2001501.1)54.1(lg29.8

citymediumandSmall)8.0lg56.1()7.0lg1.1(

)(2

2



Okumura-Hata'(

Base station height 150m

mobile antenna 1.5m

Frequency 900MHz



COST231-Hata Model

COST231-Hata Model is also based on Okumuras test data.

Its an empirical formulation via Okumuras high frequency

graphical path loss data.

This Model is restricted to the following conditions:

Frequency f : 1500&2000 MHz

Effective height of the Base station antenna :30&200 m

Height of the Mobile antenna : 1&10 m

Communication distance: 1&35km



COST231-Hata Model

γ

))(lglg55.69.44(

)(lg82.13lg9.333.46

d h

hah f L

b

mbb

−+

−−+=

d :Distance from base station(km)

f :Frequency(MHz)

L b :Mean path loss in urban areas (dB)

hb!hm:Base station and mobile antenna effective

height.



General Model

The model is given by

K1K2K3K4K5K6 are correction

factors' is a series of clutter correction factors.

These correction factors can be corrected based on

the practical test data.

Clutter

K



ZTE Models for Extended Coverage



The Application of the Propagation Model in

Cellular Design

In order to predict the base stations coverage radius and

received power we can use this function:

bf r t r t t r L L LGG P P +−−++=

received power, transmitting power

receive antenna gain , transmitting antenna gain

forward and reverse link feed line loss

path loss

)(dBm P r )(dBm P t

)(dBGr )(dBGt

)(dB Lr )(dB Lt

)(dB Lbf



Propagation Model Correction

The propagation decay rate in different

environment is different, such as in urban,suburban

and rural. We can choose different model and

correction factors. The prediction software provides

a model that we can correct its parameters using the

test data. The corrected model can improve the

simulation precision greatly.



A citys digital map



Propagation Model Applications



Simulation results of the coverage

forward received power by mobile telephone reverse transmitting power by mobile telephone



Simulation Results of the Extended Coverage



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7_Wireless Propagation Theory and Propagation Model(V0_1)