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.

Mobile Communication Environments

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

Mobile Communication Environments

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.

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2

myyP

LdymyLyP )

2)(exp(

21)( 2

2

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 rr

r

rrP )exp(1)exp(2)( 2

2

0 2

2

2 rRdr

rr

r

rRrPR

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

UMTS Radio Transmission Theory RF Optimization Policy RF Adjustment and Network Simulation

Single station check

Base station group optimization

Whole network optimization

Satisfy the indexes or not?

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

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

RF Optimization Policy

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

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

UMTS Radio Transmission Theory RF Optimization Policy RF Adjustment and Network Simulation

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

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.

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.

After Adjustment

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.

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

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.