WCDMA RF optimization

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WCDMA Radio Frequency Optimization


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.


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


Contents RF Optimization Workflow Typical Problems Analysis in RF optimization


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


RF Optimization Workflow

Target Item Reference Value Remark

Coverage Probability ≥95% CPICH Ec/Io ≥ -12dB & RSCP ≥ -95dBmCPICH 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:


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


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


Contents Preparation of RF Optimization Typical Problems Analysis in RF

optimization


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


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


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


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


Data analysis Check the latest measurement controlmeasurement control

Search for the latest intra-frequency measurement control

Call drop point

Case 1


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


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


Phenomenon description In DT, call drop happened at cell A

Case 2

Cell B (PSC277)

Cell A (PSC58)


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


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


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


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


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)


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


Solution Change the wrong neighbor cell list

Case 2


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


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


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


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


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


Analysis

Case 3

2D Event

Compress mode

Inter-frequency measurement

control

Inter-frequency Measurement

report


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


Analysis Measurement Control

Case 3Cell 14605 with

Frequency C

Cell 14031 with Frequency B


Analysis Measurement Report

Case 3

Cell 14605 with Frequency C

Cell 14605 CPICH & Ec/Io


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


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


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


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


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


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


Summary Do not configure two different frequency neighbor cells in WCDMA system

Case 3


Description In drive test for RF optimization, call drop happened in the circle area

Case 1


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


Analysis After checking the RF transmission environment,

the signal is blocked by the glass wall

Case 1

The Wall

Call drop

Antenna


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


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



About the antenna downtilt, two strategies are designed. First, 10 degrees

Case 1

10 Degree



Second, 5 degrees

Case 1

5 Degree


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


Description In drive test for RF optimization, the area Ec/Io is bad

Case 2


Analysis Checking the cell distribution at this area

Case 2

PSC185

PSC184PSC186


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


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


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


After adjustment, the drive test for PSC 184 and 185

Case 2


The comparison result for scanner Ec/IoCase 2


The comparison result for UE Ec/IoCase 2


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


Description In drive test for RF optimization, bad Ec/Io is found on the bridge

Case 3


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


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


Analysis

Case 3

Site 1 Cell A

Site 5 Cell C

Site 2 Cell C Site 3 Cell C

Site 4 Cell C


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


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 4 Cell C

Site 6


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 3The residence buildings

are much higher than antenna, which block

the signal of site 6


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 4 Cell C


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 4 Cell C


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


Confirmation After the modification, the DT shows the pilot pollution area as below

Case 3


Confirmation The Ec/Io comparison

Case 3

After

Before


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


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


Analysis RSCP distribution in DT

Case 4

Problem area


Analysis Ec/Io distribution in DT

Case 4

Problem area

Problem area


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


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


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


Case 4 Solution

Solution 3 is adopted

Road

RX

RX

TX/

RX

TX/RX

2G

BTS

3G

NodeB


Case 4 Question

Do you have other methods?


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


Case 5 Description

In DT, call drop happened a lot in the area


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


Case 5 Analysis

Check the signaling trace at UE sideBefore call drop, UE sends measurement

report to RNC with 1A event for cell 298


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


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


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.


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


Case 5 Adjustment

Result after adjustment

Handover area

Handover areaBefore After


Case 5 Adjustment

Comparison of Ec/Io of UE

Before After


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)


RNCId CellId CellName Time(As hour) VS.MaxRTWP VS.MeanRTWP VS.MinRTWP1 6250

1KwongYu

12005-5-16 17:00 -74.5 -102.34 -105.3

1 62502

KwongYu2

2006-5-16 17:00 -74.3 -94.89 -105.5

1 62503

KwongYu3

2006-5-16 17:00 -82 -101.6 -105.4

Case 1 Description

From traffic statistic, the following RTWP problem is found


Case 1 Analysis

Connect to the problem NodeB, and monitor the RTWP Cell 62501 RTWP


Case 1 Analysis

Cell 62502 RTWP


Case 1 Analysis

Cell 62503 RTWP


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


Case 1 Analysis

Check the RF environment


Case 1 Analysis

Check the RF environment No blocking or any reflection due to the glass wall The site RF condition is very good


Case 1 Analysis

2G and 3G share the feeder system


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


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


Case 1 Analysis

Conclusion The third intermodulation of cell 1 and cell 2 is just in WCDMA uplink band


Case 1 Solution

Change the hopping frequency of DSC Confirmation

Check the RTWP again, the values are normal


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


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

201 11912 Aguada_C 2005-11-15

4:00 -93.94 -88.65 -105.66

201 11942 Centenario_C 2005-11-15

4:00 -95.86 -87.65 -105.66

201 11932 Centro_C 2005-11-15

17:00 -96.62 -93.65 -97.65

201 11623 Ciudad Vieja_C 2005-11-15

0:00 -96.74 -91 -105.65

201 11461 Palacio_C 2005-11-15

20:00 -97.1 -96 -104.65

201 11643 Pocitos_C 2005-11-15

2:00 -97.72 -92.65 -105.65


Case 2 Analysis

Connect to the problem NodeB, and monitor the RTWP Take one site as example


Case 2 Analysis

The main and diversity antenna have the same interference trend The different between main and diversity is less than 10dB


Case 2 Analysis

Check the location of the sites with high RTWP

High

Medium

Low


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


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


Case 2 Analysis

Maybe the interference comes from outside and the northwest direction


Case 2 Analysis

Use YBT250 to do the interference checking


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


Case 2 Analysis

Frequency analysis U Country UMTS frequency

– 1900MHz A country GSM frequency

– 1900MHz


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


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


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


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


Summary RF optimization

Neighbor cell list optimization Coverage performance optimization Interference optimization

Thank youwww.huawei.com

WCDMA RF optimization

Engineering

Transcript of WCDMA RF optimization