1 UMTS RF Optimization

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UMTS RF Optimization

ZTE University


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Content

UMTS Radio Transmission Theory

RF Optimization Policy RF Adjustment and Network Simulation


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Mobile Communication Environments

Low antenna of UE

z Transmission paths are always influenced by terrains and man-madeenvironments; various terrains and complex buildings, forests and so on

make signals received as overlap of scattering signals and reflectedsignals.

Mobility of UE

z UE is always moves, or the peripheral environments change. This makes a

transmission path between a base station and an UE change all the time.In addition, the difference of direction and speed of an UE relative to thebase station also causes changes of signal levels.

Signal levels change at random

z

Signal levels change with time and position; it can be described only withprobability distribution of random process.


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Waveguide effect exists in urban environment

Powerful signals canobserved in streets in the

direction from the north tothe south

No influence of the channeleffect is imposed in this

area

Radiating

direction N

Powerful signals canobserved in streets in the

direction from the east tothe west

Transmitter Platitude direction

Effects of Street Waveguide


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Serious man-made noises

z Man-made noises include noises in starting motor vehicles, power

line noises and industrial noises. Serious Interference

z Generally, there are co-frequency interference, adjacent-channelinterference, intermodulation interference, local to remote ratio

interference. co-frequency interference and adjacent-channelinterference are the main factors.


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Types of Radio Wave Transmission

Types of radio wave transmission: Direct wave, reflected

wave, diffracted wave and scattering wave


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B

A

d

D

LOS NLOS

RFD

Penetration through buildings/vehicles

Multi-path transmission

Types of Radio Wave Transmission

Sight distance and non-sight distance transmission, multi-pathenvironments of complex forms

Loss through buildings/vehicles


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)()()( 0 trtmtr = )()()( 0 drdmdr =

Radio Signal Presentation Methods

A signal is a random value, so it must be characterized jointly by amedian and a transient value. An actually received signal is a medianoverlapped with a transient value. The median is called slow fading

and the transient value is called quick fading.

m(x) is slow fading, or local average, or long-term fading.

r0(x) is quick fading, or Rayleigh fading, or short-term fading.

The two methods for presenting signal field strength are used indifferent occasions: The signal presented in a time function is used forstudying signal fading; while a signal presented in a distance functionis used for studying transmission loss curve. Variation of the medianlevel of a received signal with time is far less than that with location.


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)2

)(exp(

2

1)(

2

2

myyP

=

=


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)exp(2

)(2

2

2

r

r

r

rrP = )exp(1)exp(

2)(

2

2

0 2

2

2

r

Rdr

r

r

r

rRrP

R

==


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Other Features of Signal Transmission

Time delay extended width

Related bandwidth

Inter-code Interference


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Transmission Theory

Definition of Transmission Theory

For a radio link, the loss (or fading) value of power level of a signal

from the output end of a transmitting antenna through certaintransmission paths to the input end of the antenna. Usually, it isexpressed in dB .

Common Relations between Transmission Theory and

Distance In mobile communication, the greater the transmission distance is,

the greater the transmission loss will be. Within 1~20 km, roughly40dB/dec. dec is 10 times the distance; in case of greater distance,

it will be increased to 50~60dB/dec.


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Common Types of Transmission Theory

Free Space Transmission Theory

Diffraction Loss

Reflection Loss Building Penetration Loss

Human Body Loss

In-vehicle Loss Vegetation Loss


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f(n)=ST+RT=SR+n*/2

S

R

T Gap (0.577 time of the 1st Fresnel

radius)

Fresnel Region and Transmission clearance

Fresnel Region

An area between curves satisfying f(n) and f(n-1) is called the nthFresnel region. When N=1, it is called the 1st Fresnel region, anellipsoid; the 1st Fresnel region contains 1/2 of the transmitting energy.

In addition, tests and theories demonstrate that, if the gap is greaterthan 0.577 time of the radius of the 1st Fresnel region, the loss will beequal to the loss of the free space.

Transmission Gap

0.577 time of the 1st Fresnel radius.


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Content


RF Optimization Policy RF Adjustment and Network Simulation


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Single station

check

Base station group

optimizationWhole network

optimization

Satisfy

the

indexes

orno

t?

Find out base station

group that do not

satisfy requirements

No

Common RF Optimization Process


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Single Station Check

Confirm site information

z Longitude and latitude, configuration, height above sea level, peripheralenvironments and so on.

Confirm antenna feeder information

z Antenna type, azimuth, down-tile angle and height.

Check antenna feeder link

z Standing wave ratio, primary set and diversity RSSI check, primary set and

diversity lock balance.

Confirm system parameters

z List of adjacent areas, overhead channel transmitting power, PNconfiguration, switching parameters.

Check and test basic functionsz Basic call process, soft switching, softer switching.

Check station coverage


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Base Station Group Optimization

Spectrum scanning

Load-free test

Load test


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Whole Network Optimization

Test on various radio indexes of the system

Analysis on test results

Confirm whole network adjustment scheme


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Performance Test Indexes

Voice quality--FER

Call connection rate (call completion rate and paging

response rate) Resource utilizationCPU utilization-

Switching completion rate

Call drop rate Network coverage rate

z Forward coverage

Pilot coverage

Service coverage

z Backward coverage


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Common RF Problems

Call Drop

Discontinuity

Access Failure


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Call Drop Analysis

Forward coverage is not satisfactory (Ec/Io and Ec)

z Improve the coverage of the points.

List of adjacent areas is not completez Configuration of list of adjacent areas is not complete.

Interference

z There is in-band interference source.

Pilot pollution is serious

Faults with base stations

z Incorrect connection of antenna feeders, GPS fault causes

asynchrony between the time and the system, interruption oftransmission.

Hard switching takes place


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Discontinuity Analysis

Forward coverage is not satisfactory (Ec/Io and Ec)

z Improve the coverage of the points.

List of adjacent areas is not completez Configuration of list of adjacent areas is not complete.

Interference

z There is in-band interference source.

Pilot pollution is serious


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Access Failure

Interference

Coverage over weak areas, blind zones or pilot pollution

areas makes it impossible for signaling interaction betweenthe base station and the mobile phone to be completedduring the access.

Mobile phone performance


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RF Optimization Policy

Adjust the antenna down-tilt angle

Adjust the antenna directional angle

Adjust the antenna height Change the antenna type

Appropriately adjust the base station transmitting power

Adjust the base station location Increase the base stations


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Antenna directional angle

z During optimization, attentionshould be paid to antenna

directional angle, as shown inthe figure on the right.

z If the antenna coverage area isa vast space of residence, andthe buildings are of the similar

structure, the antenna directionshall be alongside the directionof the buildings (as the redarrow on the left); if the antennadirection is the same as the

arrow on the right, the quality ofsignals in the coverage areamay not be good.


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RF Optimization Policy for Pilot Pollution

z Adjust the antenna down-tilt angle, so as to reduce the coveragearea, and further reduce the number of pilots in the pilot pollutionarea.

z Appropriately reduce the transmitting power of the cell, so as toreduce the signal strength to narrow the coverage area, and alsofurther reduce the number of pilots in the pilot pollution area.

z If the two measures are of no use, we can increase base stations inthe pollution areas, so that there will be a master pilot signal, tosolve the pollution. But be careful in taking this measure, as it mayimpose great influence on the entire network.


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Content



RF Adjustment and Network Simulation


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Before Adjustment

The diagram on the rightshows part of the base

stations of the GuangzhouMTNet Pilot Network.

Where, the directionalangle of the antenna in the

DiTuChuBanShe is 30,the mechanica down-tiltangle is 6 and theelectronic down-tilt is 2.


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Before Adjustment

This is a pilotintensity simulation

diagram: We cansee that the pilotintensity is quitesatisfactory as a

whole.


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This is a pilot Ec/Iosimulation diagram:We can see that thepilot Ec/Io in themiddle (the yellowpart) of the diagram

is not so satisfactory.

Before Adjustment


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This is a pilot pollutionsimulation diagram: Wecan see pilot pollution in

the lower middle (thebrown part) of thediagram. Taking the pilotEc/Io simulation effect in

the previous diagraminto consideration, weshould perform RFoptimization here.

Before Adjustment


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After Adjustment

Analysis shows that adjustmentof RF parameters in theDiTuChuBanShe may improve

the current situation.z Adjust the mechanical down-tilt

of the antenna in theDiTuChuBanShe as 0, andleave the electronic down-tilt

angle unchanged as 2.

z Through this adjustment, thepilot intensity of theDiTuChuBanShe, where there

is pilot pollution, is improved,and becomes the maste pilot,so that pilot pollution isimproved and the pilot Ec/Iohere is enhanced.


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This is the effect ofpilot intensitysimulation afteradjustment. We cansee that the pilotintensity after

adjustment is muchimproved than thatbefore adjustment.

After Adjustment


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The effect of pilotEc/Io simulationafter adjustment.We can also seethat the pilot Ec/Ioafter adjustment is

much improvedthan that beforeadjustment.

After Adjustment


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This is the effect ofpilot pollutionsimulation afteradjustment. We cansee that big brownpart (with pilot

pollution) has beengreatly reduced.

This proves that theRF adjustment has

fulfilled theoptimization aims.

After Adjustment


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