7 UMTS RF Optimization-36

UMTS RF Optimization

ZTE University

Content

UMTS Radio Transmission Theory

RF Optimization Policy

RF Adjustment and Network Simulation

Mobile Communication Environments

Low antenna of UE

Transmission paths are always influenced by terrains and man-made

environments; various terrains and complex buildings, forests and so on

make signals received as overlap of scattering signals and reflected

signals.

Mobility of UE

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 the

base station also causes changes of signal levels.

Signal levels change at random

Signal levels change with time and position; it can be described only with

probability distribution of random process.


Waveguide effect exists in urban environment

Powerful signals can

observed in streets in the direction from the north to

the south No influence of the channel

effect is imposed in this area

Radiating direction N

Powerful signals can

observed in streets in the direction from the east to

the west

Transmitter Platitude direction

Effects of Street Waveguide


Serious man-made noises

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

line noises and industrial noises.

Serious Interference

Generally, there are co-frequency interference, adjacent-channel

interference, intermodulation interference, local to remote ratio

interference. co-frequency interference and adjacent-channel

interference are the main factors.

Types of Radio Wave Transmission

Types of radio wave transmission: Direct wave, reflected

wave, diffracted wave and scattering wave

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-path

environments of complex forms

Loss through buildings/vehicles

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

Radio Signal Presentation Methods

A signal is a random value, so it must be characterized jointly by a

median and a transient value. An actually received signal is a median

overlapped 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 in

different occasions: The signal presented in a time function is used for

studying signal fading; while a signal presented in a distance function

is used for studying transmission loss curve. Variation of the median

level of a received signal with time is far less than that with location.

)2

)(exp(

2

1)(

2

2

myyP

L

dymy

LyP )2

)(exp(

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Statistical Features of Slow Fading

Definition of slow fading

It is the average of attenuated signals received, that is, average (or

field strength value or loss value) of signal levels attained in a

specified length L. The value of L is 40 wavelengths, with 36~50

signals for test.

Cause of slow fading

Slow fading is caused by changes of terrains and man-made

environments on transmission paths.

Probability density function and accumulation probability

distribution function of slow fading

)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

Statistical Features of Quick Fading

Definition of quick fading

It is the transient value of fading signals received.

Cause of quick fading

When transmission is reflected due to obstruction by scattering

objects (mainly buildings) or natural obstacles (mainly forests) in

the vicinity (within 50~100 wavelengths) of an UE, there will be

multi-path wave interference on the ground, leading to a standing

wave field. When the MS passes the standing wave field, the

received signals presents quick fading, and the field strength

fluctuates.

Probability density function and accumulation probability

distribution function of quick fading

Other Features of Signal Transmission

Time delay extended width

Related bandwidth

Inter-code Interference

……

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 certain

transmission paths to the input end of the antenna. Usually, it is

expressed 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, roughly

40dB/dec. dec is 10 times the distance; in case of greater distance,

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

Common Types of Transmission Theory

Free Space Transmission Theory

Diffraction Loss

Reflection Loss

Building Penetration Loss

Human Body Loss

In-vehicle Loss

Vegetation Loss

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 nth

Fresnel region. When N=1, it is called the 1st Fresnel region, an

ellipsoid; the 1st Fresnel region contains 1/2 of the transmitting energy.

In addition, tests and theories demonstrate that, if the gap is greater

than 0.577 time of the radius of the 1st Fresnel region, the loss will be

equal to the loss of the free space.

Transmission Gap

0.577 time of the 1st Fresnel radius.

Content




Single station

check

Base station group

optimization Whole network

optimization

Satisfy

the

ind

exes o

r no

t?

Find out base station

group that do not

satisfy requirements

No

Common RF Optimization Process

Single Station Check

Confirm site information

Longitude and latitude, configuration, height above sea level, peripheral

environments and so on.

Confirm antenna feeder information

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

Check antenna feeder link

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

diversity lock balance.

Confirm system parameters

List of adjacent areas, overhead channel transmitting power, PN

configuration, switching parameters.

Check and test basic functions

Basic call process, soft switching, softer switching.

Check station coverage

Base Station Group Optimization

Spectrum scanning

Load-free test

Load test

Whole Network Optimization

Test on various radio indexes of the system

Analysis on test results

Confirm whole network adjustment scheme

Performance Test Indexes

Voice quality--FER

Call connection rate (call completion rate and paging

response rate)

Resource utilization—CPU utilization-

Switching completion rate

Call drop rate

Network coverage rate

Forward coverage

Pilot coverage

Service coverage

Backward coverage

Common RF Problems

Call Drop

Discontinuity

Access Failure

Call Drop Analysis

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

Improve the coverage of the points.

List of adjacent areas is not complete

Configuration of list of adjacent areas is not complete.

Interference

There is in-band interference source.

Pilot pollution is serious

Faults with base stations

Incorrect connection of antenna feeders, GPS fault causes

asynchrony between the time and the system, interruption of

transmission.

Hard switching takes place

Access Failure

Interference

Coverage over weak areas, blind zones or pilot pollution

areas makes it impossible for signaling interaction between

the base station and the mobile phone to be completed

during the access.

Mobile phone performance


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


Antenna directional angle

During optimization, attention

should be paid to antenna

directional angle, as shown in

the figure on the right.

If the antenna coverage area is

a vast space of residence, and

the buildings are of the similar

structure, the antenna direction

shall be alongside the direction

of the buildings (as the red

arrow on the left); if the antenna

direction is the same as the

arrow on the right, the quality of

signals in the coverage area

may not be good.


RF Optimization Policy for Pilot Pollution

Adjust the antenna down-tilt angle, so as to reduce the coverage

area, and further reduce the number of pilots in the pilot pollution

area.

Appropriately reduce the transmitting power of the cell, so as to

reduce the signal strength to narrow the coverage area, and also

further reduce the number of pilots in the pilot pollution area.

If the two measures are of no use, we can increase base stations in

the pollution areas, so that there will be a master pilot signal, to

solve the pollution. But be careful in taking this measure, as it may

impose great influence on the entire network.

Content




Before Adjustment

The diagram on the right

shows part of the base

stations of the Guangzhou

MTNet Pilot Network.

Where, the directional

angle of the antenna in the

DiTuChuBanShe is 30°,

the mechanica down-tilt

angle is 6° and the

electronic down-tilt is 2 °.

Before Adjustment

This is a pilot

intensity simulation

diagram: We can

see that the pilot

intensity is quite

satisfactory as a

whole.

This is a pilot Ec/Io

simulation diagram:

We can see that the

pilot Ec/Io in the

middle (the yellow

part) of the diagram

is not so satisfactory.

Before Adjustment

This is a pilot pollution

simulation diagram: We

can see pilot pollution in

the lower middle (the

brown part) of the

diagram. Taking the pilot

Ec/Io simulation effect in

the previous diagram

into consideration, we

should perform RF

optimization here.

Before Adjustment

After Adjustment

Analysis shows that adjustment

of RF parameters in the

DiTuChuBanShe may improve

the current situation.

Adjust the mechanical down-tilt

of the antenna in the

DiTuChuBanShe as 0°, and

leave the electronic down-tilt

angle unchanged as 2 °.

Through this adjustment, the

pilot intensity of the

DiTuChuBanShe, where there

is pilot pollution, is improved,

and becomes the maste pilot,

so that pilot pollution is

improved and the pilot Ec/Io

here is enhanced.

This is the effect of

pilot intensity

simulation after

adjustment. We can

see that the pilot

intensity after

adjustment is much

improved than that

before adjustment.

After Adjustment

The effect of pilot

Ec/Io simulation

after adjustment.

We can also see

that the pilot Ec/Io

after adjustment is

much improved

than that before

adjustment.

After Adjustment

This is the effect of

pilot pollution

simulation after

adjustment. We can

see that big brown

part (with pilot

pollution) has been

greatly reduced.

This proves that the

RF adjustment has

fulfilled the

optimization aims.

After Adjustment

7 UMTS RF Optimization-36

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