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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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Mobile Communication Environments
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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Mobile Communication Environments
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
UMTS Radio Transmission Theory
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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RF Optimization Policy
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
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
UMTS Radio Transmission Theory
RF Optimization Policy
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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