Radio Propagation Theory and Models ISSUE1.0

8/11/2019 Radio Propagation Theory and Models ISSUE1.0

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Radio Propagation Theory and Models

ISSUE1.0

Wireless Curriculum

Development Section


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Course objectives

Master the basic knowledge about radio propagation

theory.

Master the functions of the propagation models and

memorize the names and application ranges of several

common models.

Understand the basic principles of site address

selectionand antenna model selection.

After studying this course, you should be able to:


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Course contents

Chapter 1 Radio Propagation Theory

Chapter 2 Propagation Models

Chapter 3 Site Selection and Antenna Model Selection


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300-3000GHz

EHFExtremely High

Frequency

30-300GHz

SHFSuper High Frequency3-30GHz

UHFUltra High Frequency300-3000MHz

VHFVery High Frequency30-300MHz

HFHigh Frequency3-30MHzMFMedium Frequency300-3000KHz

LFLow Frequency30-300KHz

VLFVery-low Frequency3-30KHz

VFVoice Frequency300-3000Hz

ELFExtremely Low

Frequency

30-300Hz

3-30HzDesignationClassificationFrequency

Basic Principles of Radio Propagation

----Spectrum Division

The frequencies in different frequency bands have different propagation

characteristics.


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Direct wave and ground-reflected wave

(Most common propagation form)

Tropospheric wave

(A highly random propagation form)

Mountain-diffracted wave

(Source of signals in shadow area)

Ionospheric wave

(Beyond-the-horizon communication path)

Propagation Path


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(1) Building-reflected wave

(2) Diffracted wave

(3) Direct wave

(4) Ground-reflected wave

Propagation Path


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Distance (m)

Receiver Power (dBm)

10 20 30

-20

-40

-60

Slow Fading

Fast Fading

Radio Propagation Environment

Two Kinds of Fading


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Resistance to signal fast fading

Time diversitySymbol interleaving, error detection and error

correction encoding

Space diversityAdoption of main and diversity antenna for

reception

Frequency diversity450M broadband communication: frequency

diversity

RAKE receptionAdoption the RAKE receiver for receiving

multiple unrelated multi-paths signals

Measures against fast fading ---- diversity


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The radio propagation is influenced by the terrain and artificial

environments. The radio propagation environment directly determines

what propagation mode is to be selected.

Major factors influencing the environment

Morphology form (high mountain, hilly ground, flat land and water

area);

Quantity, distribution and material characteristics of the artificial

buildings;

Characteristics of vegetation in the region;

Climate;

Natural and artificial electromagnetic noises.

Artificial environment

Dense Urban ,Urban area, suburb and rural area ,high way


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Propagation losses in free space

Ploss=32.4+20lgfMHz+20lgdkm

When the frequency is fixed, it can be expressed as:

Ploss=L0+10

lgd

=2 path loss slope

Propagation losses in flat area

Ploss= 10lgd -20lghb- 20lghm

=4 path loss slope

hb: Height of the BS antenna

hm: Height of the MS antenna

Losses in Propagation


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Losses in PropagationDiffraction loss

The electromagnetic wave is diffused all around at the diffraction

point;The diffracted wave covers all directions except for the

obstruction;

The diffusion loss is the most serious;

The calculation formula is rather complex, which varies with

different diffraction constants.


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Penetration loss

The indoor signal depends on the penetration loss of the building;

There is evident differences between signals at the window of the room

and signals in the middle of the room;

The materials of the building have great influence on the penetration loss;

The arrival angle of the electromagnetic wave has great influence on the

penetration loss too.

XdBmWdBm

Penetration loss=X-W=B dB

0 0 0 0

Dw1 w2

E1

E2

Reflection and refraction of the electromagnetic wave when it penetrates

the wall.


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0 0 0 0

Dw1 w2

E1

E2

XdBmWdBm


Penetration loss

The indoor signal depends on the penetration loss of the building.

Signal beside the indoor window differs greatly from that in the central part

of the room.

The building materials have a great impact on the penetration loss.

The incident angle of the electromagnetic wave has a great impact on thepenetration loss.

Penetration loss=X-W=B dBThe reflection and refraction of the electromagnetic wave during the

penetration of the wall


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14 ~ 206 ~ 102 ~ 40 ~ 1Reflection loss (dB)

0.1 ~ 0.20.3 ~ 0.50.6 ~ 0.80.9~1Equivalent ground reflection factor

Cities, mountain areas and forestsFieldsPaddy fieldsWater surfacesGround property


Reflection loss


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What distribution is fast fading subject to?

What distribution is slow fading subject to

Rayleigh distribution

Logarithmic normal distribution

QUESTION


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Propagation Models

The propagation model is used in prediction of influence on

path loss in the radio wave propagation by the terrain and

artificial environments;

The propagation model is the foundation of the coverage

planning. A good model can ensure the precision of the

planning;The radio propagation model is influenced by the working

frequency of the system. Different propagation models have

different working frequency ranges. Moreover, there are

differences between indoor propagation model and outdoorpropagation model;

When using the propagation model, please pay attention to

the unit of each parameter.


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The typical models are set up by scientists gradually based on the CW test data.

Several Common Propagation Models

Model Application range

Okumura-Hata Applicable to the 150-1500 MHz macrocell prediction

Cost231-Hata Applicable to the 1500-2000 MHz macrocell prediction

Walfish-Ikegami Applicable to prediction in the 800-2000MHz urban area ordense urban area environments

Keenan-Motley Applicable to the 800-2000MHz indoor environment prediction

K arameter Models Applicable to the 800-2000MHz macrocell prediction

Propagation Models


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Okumura-Hata Model

Propagation Models

mhbbp AdhhfL log)log55.69.44(log82.13log16.2655.69

Lp f

bh

mh

d

mhA

Path loss (dB)

BS antenna height (m)

MS antenna height (m)

Carrier frequency (MHz)

Distance between the BS and MS

(Km)

MS antenna correction factor (dB)

)8.0log56.1()7.0log1.1( fhfA mhm

97.4)75.11(log2.3 2 mh hA m

Middle or small-size cities:

Big cities:

The frequency range is 150MHz to 1500MHz.


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Okumura-Hata Model

Propagation Models

In urban areas, the standard model can be modified as:

In rural areas (open country), the model can be modified as:

In rural areas (quasi open country), the model can be modified as:


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Cost231-Hata Model

Propagation Models

mhbbp CAdhhfL m log)log55.69.44(log82.13log9.333.46

mC

mC0dB Large-size cities or central areas of the suburbs

3dB Big cities

The frequency range is 1500MHz to 2000MHz.

P ti M d l


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Propagation Models

The general planning software model expressions are as follows:

Lp=K1 + K2lgd + K3(hm) + K4lg(hm) + K5lg(Heff) + K6lg(Heff)lgd

+K7diffn+ Kclutter

K1-Constant related with the frequency (MHz); K2-Constant related to the distance (km);

K3, K4-MS antenna height (m) correction factor; K5, K6-BS antenna height (m) correction factor;

K7-Diffraction correction factor; Kclutter-Ground fading correction factor;

d-Distance between the BS and MS (km); hm, Heff-Valid heights of the MS antenna and BS

antenna (m)

The initial K parameter is converted from the classical model.


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Propagation Models

In the following table, some K values and fading values in the wave

propagation analysis in a medium-size city are given.

16High Building

5Dense urban

0Urban

-2.50Suburban

-2.50Parallel_Low_Buildings

-2.90Village

5.00Industrial & Comm ercial Areas

13.00Forest

-1.00Rangeland

-2.00Open Areas

-3.00Wetland

-3.00Inland Water

Clutter attenuation value

-0.8K7

-6.55K6

-13.82K5

0.00K4

-2.49/800MHz Urban,-2.93/2000MHz Urban

0/800MHz Lar e cit -2.93/2000MHz Lar e cit

K3

44.90K2

149/800MHz Urban ,162.5/2000MHz Urban

145/800MHz Lar e cit 165.5/2000MHz Lar e cit

K1

Parameter v alueK parameter name


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Model Correction - CW Test

To obtain the radio propagation model in compliance with the actual environment and increase the

correctness of the coverage prediction so as to lay a good foundation for the network planning, it is

necessary to correct the propagation model for some typical environments.

Select the site and establish an simulated BS;

Select the path and perform drive test to the collected data;

Correct the model using the model correction tool software and obtainK1, K2, , KCLUTER.


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Model Correction

Select representative propagation environments, such as dense urban

area, general urban area and suburb

and find some test points. As many as land object types should be

covered.

For each artificial environment, three or more test stations are

preferred so as to remove the influence of the location factors.Obtain test data at different directions and distances. There should be

multiple test data for the same distance.

The sampling should be in compliance with the Li law: Wavelength: 40;

50 sampling points

Upper limit for the car speed: Vmax=0.8/Tsample


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QUESTION

What is the application range of the Okumura-Hata

model?

What is the difference between Okumura-Hata and

Cost231-Hata?

What parameters are the K5 and K6 in the software-

planning model about?

What is the significance of the CW test?


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SUMMARY

This chapter introduces the significance of the

propagation model.

It also introduces the parameters and their

experience values of several common propagation

models. It deals with the significance and method of the

CW test.


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Basic principles for site selection

The importance of site selection (>80%)

The orderfor urban site selection (dense,

general, suburban)

The heightof site selection (dense, general,

suburban)

Attention for the barriers ahead (avoiding it

by using the Fresnel zone)


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Cell layout and site selection

The concrete principles for site selection:

The site should be put in an ideal place in the regular mesh as much aspossible. Its deviation should be less than one fourth of the base station

radius.

On the condition that the base station layout will not be affected, the

existing devices should be utilized as much as possible, so as to reduce the

cost and shorten the cycle of construction.

Generally, peaks of a high altitude above the sea level (100~300 m higher

than the altitude of the urban area) in the outskirt of a city or in the suburbs

should not be selected. On one hand, this is intended to facilitate the control

of the coverage area; on the other, it reduces the level of difficulty in the

project construction and facilitates maintenance.


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Cell layout and site selection

The newly built base station should be located in a place where it can enjoy convenienttransportation, use the mains and occupy little fertile land with a safe environment;

The location should away from the large-power radio transmitter, radar station or other

interference sources;

The location should be far from the forest so that the absorption loss of plant can be

avoided

Attention should be paid to the influence of the signal reflection and time dispersion when

the site is located in the mountainous area, the dense lake area or lake area with steep bank,

a hilly city, or an environment with high metal buildings;

When the base station is located among the buildings in the urban area, the height of the

buildings can be flexibly utilized to fulfill the division of the network hierarchical structure;

When there are relatively few base stations in the early period of network construction,

the sites selected should ensure the good coverage of the key areas;

The physical radiation of the main beam of the antenna along streets, rivers, etc. should

be avoided, so as to avoid the pilot frequency pollution or insular effect resulting from the

wave-guide effect;

The concrete principles for site selection (continued):


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Antenna feeder system----feeder

Feeder selection

Feeder loss

450M7/82.7dB/100m5/41.9dB/100m

800M7/84.03dB/100m5/42.98dB/100m

1900M7/86.46dB/100m5/44.77dB/100m

Principles for feeder selection

450MHzbasically only 7/8feeder should be selected.

800MHzwhen the feeder length is greater than 80m, 5/4feeder

should be adopted.1900MHzwhen the feeder length is greater than 50m, 5/4feeder

should be adopted.

The curvature of the feeder should not be too great, and the external

conductor should be well grounded.


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Major electrical indices of the antenna


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Major mechanical indices of the antenna

Antenna input interface

Antenna size

Antenna weight

Wind load

Operating temperature

Humidity requirements

Lightning protection

Three kinds of protection

capabilities


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Antenna feeder design----antenna selection

Selection of urban base station antenna

Generally directional antennas with 60~65horizontal half-power angle should be selected;

Generally 15dBi medium gain antennas should be selected;

It is recommended to select the antenna with a electronic tilt angle (3~6);

Dual polarization antennas are recommended;

Selection of suburban base station antenna

Direction antennas with a 65or 90horizontal half-power angle can be selected according

to the actual situation;Generally 15~18dBi medium and high gain antennas should be selected;

The adoption of the preset tilt angle should be determined according to the specific

situation;

Both dual polarization antennas and vertical polarization antennas can be selected;


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Antenna feeder design----antenna selection

Selection of rural base station antenna

90or 120directional antennas or omni-directional antennas can be selected according to

the specific situation and requirements.

Generally the gain of the directional antennas selected shall be relatively high (16~18dBi).

The preset tilt antennas generally should not be selected; for the high-altitude site, the zero

filler antennas are preferred.

Vertical polarization antennas are suggested.

Selection of road base station antenna

Generally directional antennas of narrow beam and high gain are selected. Depending the

concrete situation, 8-shaped antennas, omni-directional or deformed omni-directionalantennas can also be selected.

As the road base station requires a long coverage distance, generally the preset tilt

antennas should not be selected.

Vertical polarization antennas are recommended.

The front-to-back ratio of the selected directional antenna should not be too high.


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Antenna design-antenna height

Principles for antenna height design

Antennas in different cells of the same base station may be of different heights.

This may be limited by the installation space in a specific direction, or due to the

requirements of the cell planning.

For urban areas that are relatively even, generally the valid height of the antenna is

about 25m.

The height of the antennas in the suburban base station can be increased

appropriately. Generally it is about 40 m.

If the antennas are too high, the coverage power level around the antennas will be

lowered (nicknamed black under the tower), especially for the omni-directional

antennas.

Moreover, if the antennas are too high, problems such as serious unexpected

coverage and pilot solution will occur, which will affect the network quality.


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Antenna design- Azimuth

Principles for antenna azimuth design

The azimuths of the three sectors of the urban base stations should be kept as consistent

as possible, and fine adjustment should be made locally. As for the junction between the

urban and suburban parts, arterial road, suburban isolated sites, etc., the antenna azimuth

can be adjusted according to the key coverage objects.

The main beam of the antenna should be directed to the area of high traffic density, so as

to increase the signal strength in that area and improve the conversation quality.

The antenna cross-coverage depth between adjacent urban sectors should not exceed 10%.

The cross-coverage depth between adjacent cells in suburban and rural areas should not

be too big, and the included angle between the antenna directions of two adjacent sectors inthe same base station should be no less than 90.

To prevent the unexpected coverage, the main beam of the antenna should avoid being

directed to a straight street in dense urban areas.


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Antenna design - tilt

The employment of the antenna tilt technique can effectively control the

coverage area and reduce the system internal interference.

The antenna tilt angle should be determined according to the concrete

situations, so that the interference between intra-frequency cells can bereduced while the coverage requirements can be met.

In the design of the tilt angle, comprehensive consideration should be given to

such factors as the transmitting power of the base station, the antenna height,

the cell coverage and the radio propagation environment.

Principles for antenna tilt design


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The electrical or mechanical mode can be adopted for the antenna beam tilt. The angle of theelectric tilt is related to the antenna type selected and generally is fixed. The angle of the mechanical

tilt can be adjusted; but generally it will not exceed 15due to the restriction of the installation fittings

and the propagation characteristics of radio signals.

The electric tilt and mechanical tilt produce different surface radiations. When the tilt angles are

small, there is only minor difference; with the increase of the tilt angle, the difference also becomes

more evident.

Antenna design - tilt


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Radio Propagation Theory and Models ISSUE1.0

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