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Copyright © 2007 Huawei Technologies Co., Ltd. All rights reserved.
WCDMA Radio Frequency Optimization
Page2Copyright © 2007 Huawei Technologies Co., Ltd. All rights reserved.
Foreword
RF (Radio Frequency) optimization is the most
important step to ensure the quality of the network.
RF optimization will solve network problems related
to neighbor cell list, coverage and interference.
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Objectives
Upon completion of this course, you will be able to:
Know the steps of RF optimization
Know how to solve the RF problems caused by
neighbor cell list, poor coverage and interference
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Contents
RF Optimization Workflow
Typical Problems Analysis in RF optimization
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RF Optimization WorkflowStart
Preparation: Set the optimization target Divide the optimization cluster Draw out the test route line Prepare the DT tools
Data Collection: DT test Indoor DT test RNC configuration data
The DT result is satisfied with optimization target?
RF optimization finished
Y
Problem Analysis neighbor cell list poor coverage pilot pollution handover interference
N
Adjustment: Engineering parameters adjust Neighbor cell list adjust
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RF Optimization Workflow
Target ItemReference
ValueRemark
Coverage Probability ≥95%CPICH Ec/Io ≥ -12dB & RSCP ≥ -95dBm
CPICH Ec/Io ≥ -12dB ≥95% Scanner result
CPICH RSCP ≥ -95dBm
≥95% Scanner result
SHO Percentage 30%-40%
Pilot pollution Percentage
≤5%
Set RF optimization target, for example:
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RF Optimization Workflow RF optimization clusters division
Cluster is the area for one time drive test One cluster should contains 15 to 25 sites Cluster division should consider the following factor,
such as: Terrain Traffic Route line
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RF Optimization Workflow Preparation for DT (drive test)
Hardware Test phone Scanner GPS
Software Drive test software, for example, GENEX Probe Drive test post process software, for example, GENEX
Assistant
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Contents
Preparation of RF Optimization
Typical Problems Analysis in RF
optimization
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Contents
Typical Problems Analysis in RF optimization
RF case related to neighbor cell list
RF case related to bad coverage
RF case related to interference
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Case 1 Description
In DT, call drop happened
Check the signaling trace at UE side
Call Drop After call drop, begin
to read system information
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Data analysis
Check cell information from UE active set and cell information from scanner at
call drop points.
From Scanner From UE
No SC 170 cell!!
Why?
Case 1
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Data analysis
Checking monitor set
Missing neighbor cell
Delayed handover
Check monitor set for the scramble measured
by scanner
SC 170 is not in monitor set
Case 1
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Data analysis
Check the latest measurement controlmeasurement control
Search for the latest intra-frequency measurement control
Call drop point
Case 1
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Measurement ID is 1. It is Intra-frequency measurement control
Check the list of intra-frequency neighbor cell in measurement
control and no SC 170
The primary scramble of the cell is 6
Case 1
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Solution
Add neighbor cells in neighbor cell list
Summary
In the beginning stage of network, it is very common that missing neighbor cell cased cause call drop.
Analysis with signaling procedure is the common way to find and solve the problem
Some problems can be avoided if the Combined Neighbor Cell Algorithm is switched on.
Case 1
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Phenomenon description
In DT, call drop
happened at cell A
Case 2
Cell B (PSC277)
Cell A (PSC58)
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Phenomenon description In Cell A, UE keeps reporting PSC 277 1A event.
RNC received this event and send Active Set Update to UE according to the signaling trace record
UE send Active Set Update complete to RNC
Then, RNC send Active Set Update to delete PSC 277 from active set
Finally call drop happened due to RL failure
Case 2
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Problem Analysis From the signaling trace of DT, it looks like the handover is complete successfully.
But, according to the signaling trace from CDT, the handover failed actually.
Case 2
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Problem Analysis Signaling trace from CDT shows:
Case 2
UE NodeB RNC
Measurement control (1A Event for PSC 227)
Radio Link Setup
Radio Link Setup Response
Active set update
Active set update complete
Radio Link Failure
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Cell B (PSC277)
Cell A (PSC58)
Cell C (PSC277)
Problem Analysis After checking the neighbor cell list, the following problem
is found
Cell C has the same PSC as Cell B
Case 2
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Cell ID PSC
A 58
B 277
C 277
Cell ID NCell ID
A C
C A
Cell B (PSC277)
Missing configuring NCell
Mistake for configuring N
Cell
Case 2 Problem Analysis
The neighbor cell list shows
Cell C (PSC277)
Cell A (PSC58)
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Problem Analysis Based on the analysis above, the new NodeB is not the one of cell B, but the one of cell C
Even the cell C prepared resource for UE according to the RNC command of “Radio Link Setup”, it can not find the UE uplink signal.
That does why the “Radio Link Failure” is sent by NodeB
Case 2
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Solution Change the wrong neighbor cell list
Case 2
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Summary
Phenomenon for wrong neighbor cell list
From DT, radio link branch is added into active set, then deleted from active set repeatedly.
SHO success rate is low
Radio link failure is low in the wrong neighbor cell, for example, cell C in case 2
Call drop is high in the cell with wrong neighbor cell, for example, cell A in case 2
Case 2
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Summary
About SHO event, UE will only report PSC to RNC in Measurement Report
RNC will find the right cell according to the neighbor cell list between cell ID and PSC
This problem is mainly happened in dense urban when is PSC is reused a lot
Case 2
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Description
Case 3
14603 (Frequency A)
14602 (Frequency B) 14031 (Frequency B)
Inter-RAT handover based on coverage
14605 (Frequency C)
Inter-frequency handover based on capacity
Call drop rate high
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Description UE is in Cell 14602 with frequency B
When 14602 is in high load level, UE will be handed over to 14603 with another frequency A
When 14603 is in high load level, UE will be handed over to 14605 with frequency C
Because frequency A and C are not used continuously at this area, UE has to be handed over to Cell 14031 with frequency B
14603 and 14605 can share the load level, but the call drop rate in 14603 is very high.
Case 3
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Analysis Because it’s difficult to do drive test for collecting signaling trace, the IOS (Information of Subscriber) trace is used. Based on the analysis for the call dropped UE, there is one thing is common:
Before call drop in 24603, all UEs initiated compress mode, and send Measurement Report to RNC periodically, but handover is not triggered.
Case 3
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Analysis
Case 3
2D Event
Compress mode
Inter-frequency measurement
control
Inter-frequency Measurement
report
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Analysis Open “Inter-frequency Measurement Control”, the Cell 14605 with frequency C is put in the first place
And in the following measurement report, UE only report Cell 14605
But the cell 14605 cell signal level is lower than -90dBm, which can not trigger handover, till call drop.
Case 3
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Analysis Measurement Control
Case 3
Cell 14605 with Frequency C
Cell 14031 with Frequency B
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Analysis Measurement Report
Case 3
Cell 14605 with Frequency C
Cell 14605 CPICH & Ec/Io
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Question Why the handover can not be triggered?
Since the network give UE the information of cell 14605 and cell 14031, Why UE only report cell 14605?
Did UE measure cell 14301, just not report it?
Or, UE never measure cell 14301, just 14605?
Case 3
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Analysis UE report cell 14605 CPICH RSCP is 19, which is -96dBm.
After checking the RNC configuration file, this CPICH RSCP level can not trigger inter-frequency handover
Actually, because cell 14605 and 14603 are in one sector, their signal level should be same.
Case 3
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Analysis If UE can report cell 14031, the handover may be triggered
After analyze the compress mode principle, it is found that UE can only monitor 1 WCDMA frequency in the gap of compress mode.
Case 3
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Analysis Because UE can not measure cell 14301 with frequency B, only monitor cell 14605 with frequency C, and meanwhile cell 14605 and 14603 signal level are
same, the call dropped due to the poor signal of 14605 and 14603
How to make UE monitor cell 14301 with frequency B instead of 14605 with frequency C?
Case 3
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Solution Delete the neighbor relation from 14603 with frequency A to 14605 with frequency C
Add the neighbor relation from 14602 with frequency B to 14605 with frequency C
Case 3
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Solution
Case 3
14603 (Frequency A)
14602 (Frequency B) 14031 (Frequency B)
14605 (Frequency C)
Inter-RAT handover based on coverage
Inter-frequency handover based on capacity
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Summary Do not configure two different frequency neighbor cells in WCDMA system
Case 3
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Contents
Typical Problems Analysis in RF optimization
RF case related to neighbor cell list
RF case related to bad coverage
RF case related to interference
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Description In drive test for RF optimization, call drop happened in the circle area
Case 1
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Analysis After analyze the signal level of this area, the call drop is caused by discontinuous coverage of the cell with PSC 442
Case 1
Problem Zone
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Analysis After checking the RF transmission environment,
the signal is blocked by the glass wall
Case 1
The Wall
Call drop
Antenna
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Solution Solution 1: Decrease the downtilt to increase the signal level
Maybe the problem area will become better, but due to the wall, this problem may still exist nearby.
Solution 2:Increase the antenna height After checking the installation condition, it’s very hard to increase the height Even increased the height, the problem may still exist due to the wall.
Case 1
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Solution Solution 3:
Move the antenna position if possible, and the main direction antenna is parallel with the side of the wall
Case 1
Original Position
New Position
Wall
Move the antenna position to right about 15 meters
considering the installation condition
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Solution Solution 3:
About the antenna downtilt, two strategies are designed. First, 10 degrees
Case 1
10 Degree
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Solution Solution 3:
Second, 5 degrees
Case 1
5 Degree
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Summary Before RF adjustment, site survey should be done.
Find the problem and the reason, design several strategies for the adjustment
One time adjustment, and check the performance at the same time. Adjustment and performance checking should be done at the same to improve the work efficiency.
Case 1
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Description In drive test for RF optimization, the area Ec/Io is bad
Case 2
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Analysis Checking the cell distribution at this area
Case 2
PSC185
PSC184PSC186
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Analysis One site with 3 cells, PSC184, 185 and 186 cover this area
Two cells, PSC 184 and 185, are separated to two sectors to cover different direction
Case 2
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Analysis The area is covered by different cell – PSC 184 and 185
No dominant cell – PSC 184 and 185 is the best cell crossly in this area
Case 2
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Solution Change the sector PSC, or combine some sector
Previously, 3 cells
PSC 184: sector 1 & sector 3
PSC 185: sector 2 & sector 4
PSC 186: sector 5
After adjustment, 2 cells:
PSC184: sector1 & sector3
PSC185: sector4 & sector5
Delete sector 2
Case 2
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After adjustment, the drive test for PSC 184 and 185
Case 2
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The comparison result for scanner Ec/Io
Case 2
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The comparison result for UE Ec/Io
Case 2
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Summary In order to get better coverage performance at the place with complicated transmission environment, splitter is used to separate one cell into different sectors
to cover different area.
In this case, the sector should be designed reasonably to control the interference
Case 2
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Description In drive test for RF optimization, bad Ec/Io is found on the bridge
Case 3
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Analysis Check the RSCP value of scanner, the result shows the RSCP value is good.
Case 3
Based on this, pilot pollution need be considered in this area. Check the top N pilot RSCP and Ec/Io in scanner result
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Analysis From the DT result, it shows the RSCP value is strong, but the Ec/Io is bad. And the signal level of different cell are very similar. Find the cells which cover this area
Case 3
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Analysis
Case 3
Site 1 Cell A
Site 5 Cell C
Site 2 Cell C Site 3 Cell C
Site 4 Cell C
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Analysis On the bridge, the signal from different cell can cover this area due to reflection of the river and no building.
From DT, following cell cover this area:
Site 1 cell A
Site 2 cell C
Site 3 cell C
Site 4 cell C
Site 5 cell C
Case 3
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Analysis Need to find the best cell
Check the map, the site 6 is very near to the
bridge.
Case 3
Site 1 Cell A
Site 5 Cell C
Site 2 Cell C Site 3 Cell C
Site 4 Cell C
Site 6
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Analysis After checking site 6 RF environment, it is difficult to increase the antenna
height or move site 6 position to avoid the blocking caused by the building
Case 3
The residence buildings are much higher than antenna, which block
the signal of site 6
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Analysis Then, site 1 cell A can be the best
cell to cover this area
Case 3
Site 1 Cell A
Site 5 Cell C
Site 2 Cell C Site 3 Cell C
Site 4 Cell C
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Analysis Then, try to increase the signal of site 1 cell A, and
decrease other cells
To confirm this, DT for site 1 cell A needs to be done
Case 3
Site 1 Cell A
Site 5 Cell C
Site 2 Cell C Site 3 Cell C
Site 4 Cell C
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Solution Increase the signal of site 1 cell A
Change the antenna downtilt from 10 to 7 Increase CPICH Tx power 1.5 dB higher
Decrease other cell signal – change the antenna downtilt From 7 to 10 for site 2 cell C From 5 to 8 for Site 3 cell C From 9 to 11 for site 4 cell C From 9 to 11 for site 5 cell C
Case 3
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Confirmation After the modification, the DT shows the pilot pollution area as below
Case 3
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Confirmation The Ec/Io comparison
Case 3
After
Before
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Summary To solve the pilot pollution, the following issues has be considered
Find the reason caused pilot pollution
– Due to no strong signal
– Due to too much strong signal
After the adjustment, the DT has to be done at this cluster to confirm that no new problem appeared
Case 3
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Description
In DT, video call quality is decreased at the problem area. Also, the PS call drop happened several times
Case 4
Problem Area
3G Antenna
2G Antenna
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Analysis RSCP distribution in DT
Case 4
Problem area
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Analysis Ec/Io distribution in DT
Case 4
Problem area
Problem area
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Analysis Checking the RF environment, the antenna is installed on 10-meter platform
2G and 3G antenna are installed at one platform, but 3G antenna is a little bit inner than 2G antenna.
After finishing DT in 2G, signal level is very stable
Case 4
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Analysis If 3G and 2G antenna are installed at the same place, the problem may be solved.
Case 4
Problem Area
3G Antenna
2G Antenna
The short wall of this platform may block the
signal of 3G
Since 2G antenna is near to the border, the
wall influence 2G little
Wall
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Solution Solution 1
Increase the antenna height can solve this problem
Solution 2
Move the installation place near to the border
Solution 3
3G and 2G use the same place
Case 4
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Case 4
Solution Solution 3 is adopted
Road
RX
RX
TX/
RX
TX/RX
2G
BTS
3G
NodeB
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Case 4
Question Do you have other methods?
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Case 4 Summary
Sharing the same installation place for 3G and 2G is very common, and several strategies can solve the
problem
In this situation, 3G and 2G can share the feeder system, or can only share the installation platform.
Considering the factors of the installation and related resource, a easiest and simplest method should be
adopted
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Case 5
Description In DT, call drop happened a lot in the area
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Case 5 Description
Check the DT information, SC304 is in active set with the signal level – RSCP -76dBm and Ec/Io -18
Analysis Consider the pilot pollution
But only 1 cell in active set and 1 Cell in monitor set
Consider the missing neighbor cell But the cell in monitor set has very good quality – RSCP -65dBm and Ec/Io -6
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Case 5
Analysis
Check the signaling trace at UE sideBefore call drop, UE sends measurement
report to RNC with 1A event for cell 298
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Case 5
Analysis
Check the signaling trace at RNC side
RNC sent Active Set Update to UE, but no response. Then, RNC send release RRC connection –
Call Drop
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Case 5 Analysis
Based on the DT and signaling trace, this call drop can be take as
handover failure
For example
cel l 56 vs cel l 041
-30
-20
-10
0
ti me
EcNo cel l 56
cel l 041
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Case 5 Analysis
Around the corner, the original cell 304 signal level drop very quickly because of the
building shadowing, and the neighbor cell 298 increase very quickly.
After UE sent measurement report to RNC, cell 304 has become very bad when RNC
sent active set update.
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Case 5 Adjustment
Since cell 298 has better coverage at this area, handover can happen earlier Decrease the coverage performance at this area
– Increase the downtilt from 5 to 9
– Adjust the direction from 0 to 310
Increase the coverage performance at this area– Decrease the downtilt from 5 to 4
– Adjust the direction from 300 to 270
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Case 5
Adjustment
Result after adjustment
Handover area
Handover areaBefore After
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Case 5
Adjustment Comparison of Ec/Io of UE
Before After
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Case 5 Summary
Confirm the corner effect by analyzing signaling trace at UE and RNC
About corner effect, Taking the method make the handover happen earlier, such as RF optimization
Other method can also adopted
Modify 1A event
Modify CIO (Cell Individual Offset)
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Contents
Typical Problems Analysis in RF optimization
RF case related to neighbor cell list
RF case related to bad coverage
RF case related to interference
Page92Copyright © 2007 Huawei Technologies Co., Ltd. All rights reserved.
RNCId CellId CellName Time(As hour) VS.MaxRTWP VS.MeanRTWP VS.MinRTWP
16250
1KwongYu
12005-5-16 17:00
-74.5 -102.34 -105.3
16250
2KwongYu
22006-5-16 17:00
-74.3 -94.89 -105.5
16250
3KwongYu
32006-5-16 17:00
-82 -101.6 -105.4
Case 1 Description
From traffic statistic, the following RTWP problem is found
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Case 1
Analysis Connect to the problem NodeB, and monitor the RTWP Cell 62501 RTWP
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Case 1
Analysis
Cell 62502 RTWP
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Case 1
Analysis
Cell 62503 RTWP
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Case 1 Analysis
The main diversity antenna is interfered seriously
Can not find any relation between interference and time, and the interference appears randomly
Check the neighbor site, no interference
Deduction
Inter-modulation cause the interference, could be Inter-modulation caused by bad connectors
Inter-modulation by GSM
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Case 1
Analysis
Check the RF environment
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Case 1 Analysis
Check the RF environment
No blocking or any reflection due to the glass wall
The site RF condition is very good
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Case 1
Analysis
2G and 3G share the feeder system
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Case 1 Analysis
Check 2G frequency planning Sector 1 – 544 with hopping frequency 821
– 544 – 1811.6MHz & 821 – 1867MHz
Sector 2 – 538 with hopping frequency 821
– 538 – 1808.6MHz & 821 – 1867MHz
Sector 3 – 858 with hopping frequency 821
– 858 – 1874.4MHz & 821 – 1867MHz
Page101Copyright © 2007 Huawei Technologies Co., Ltd. All rights reserved.
Case 1 Analysis
Calculate the third order intermodulation Cell 1 – 1922.4MHz Cell 2 – 1925.4MHz Cell 3 – 1859.6MHz
Check cell 2 uplink interference The interval of 2 interference is
821-544
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Case 1
Analysis Conclusion
The third intermodulation of cell 1 and cell 2 is just in WCDMA uplink band
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Case 1 Solution
Change the hopping frequency of DSC
Confirmation
Check the RTWP again, the values are normal
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Case 1 Summary
Characteristics of inner system interference The RTWP result are not same at the main and diversity antenna
The amplitude of interference is big, and the difference is more than 10 dB
High RTWP will appear in a duration, and will not change so frequently
High RTWP will not show in a certain time each day, but randomly
Page105Copyright © 2007 Huawei Technologies Co., Ltd. All rights reserved.
Case 2
Description
In a commercial network of country U, the following
RTWP problem is found from traffic statisticRNCId CellId CellName Time(As hour) RTWP_MEAN RTWP_MAX RTWP_MIN
2011191
2Aguada_C 2005-11-15
4:00-93.94 -88.65 -105.66
2011194
2Centenario_C 2005-11-15
4:00-95.86 -87.65 -105.66
2011193
2Centro_C 2005-11-15
17:00-96.62 -93.65 -97.65
2011162
3Ciudad Vieja_C 2005-11-15
0:00-96.74 -91 -105.65
2011146
1Palacio_C 2005-11-15
20:00-97.1 -96 -104.65
2011164
3Pocitos_C 2005-11-15
2:00-97.72 -92.65 -105.65
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Case 2
Analysis Connect to the problem NodeB, and monitor the RTWP Take one site as example
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Case 2 Analysis
The main and diversity antenna have the same interference trend
The different between main and diversity is less than 10dB
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Case 2
Analysis
Check the location of the sites with high RTWP
High
Medium
Low
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Case 2 Analysis
All the problem cells are in the third sector of the NodeB, and the direction is to the northwest
Many cells at this area show high interference, and the cells with low RTWP are at low place
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Case 2 Analysis
Analyze the RTWP in the nearly one month, the interference shows randomly, but if
appears, usually one whole day, or several days
The interference shows with high traffic, and also with low traffic. No evidence shows it
is related to the traffic
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Case 2
Analysis
Maybe the interference comes from outside and
the northwest direction
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Case 2
Analysis
Use YBT250 to do the interference checking
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Case 2 Analysis
All the test results show the interference comes from the same direction –
to the country A
But the distance to country A from the test place is around 50Km to 200Km
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Case 2 Analysis
Frequency analysis U Country UMTS frequency
– 1900MHz
A country GSM frequency
– 1900MHz
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Case 2 Analysis
Maybe the interference comes from A country, but looks like impossible because the
distance (50 to 200Km) is beyond the transmission
To confirm this problem, use A country cell phone at the area with high RTWP
The result shows the phone does receive the A country DSC
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Case 2 Conclusion
The interference comes from A country GSM
Even the distance is very far, the area between the border is covered by a large water
area
Due to reflection the water, the signal can be transmitted far away
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Case 2 Conclusion
After known the reason, the following character of this kind of interference is found Related to the weather
– Rain day, no interference
– Cloudy day, less interference
– Sunny day, high interference
Related to the seasons also
– Problems show at Summer more than Winter
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Case 2 Summary
Characteristics of external interference The RTWP result are same at the main and diversity antenna The amplitude of interference is small, and the difference is less than 10 dB The interference exists at large area, not just one cell, also including neighbor cells The direction of external interference is obvious The cell with high antenna is easier to be interferenced
Page119Copyright © 2007 Huawei Technologies Co., Ltd. All rights reserved.
Summary
RF optimization
Neighbor cell list optimization
Coverage performance optimization
Interference optimization
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