Chapter 4_DT ANALYSIS&OPTIMIZATION.pdf

Content Drive-test logs Processing and Analysis           

Drive test Data Analysis Flow chart Introduction to TEMS Drive Test Tool Analysis of Cell Dominance ( Pilot Pollution ) Analysis of DL CPICH Coverage ( RSCP ) Analysis of UL Coverage and Interference ( UE TX PWR ) Analysis of Missing or Deletion of Neighbors Soft-Handover analysis and Impact Analysis of Inter Radio Access Technology Handover ( IRAT HO ) Analysis of Multi RAB Analysis of Drop Calls Analysis of Poor R99 and HSPA Throughput

Copyright © All rights reserved

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Drive test Data Analysis Flow chart Introduction to TEMS Drive test tool Analysis of Cell Dominance ( Pilot Pollution ) Analysis of DL CPICH Coverage ( RSCP ) Analysis of UL Coverage and Interference ( UE TX PWR ) Analysis of Missing or Deletion of Neighbors Soft-Handover analysis and Impact Analysis of Inter Radio Access Technology Handover ( IRAT HO ) Analysis of Multi RAB Analysis of Drop Calls Analysis of Poor R99 and HSPA Throughput


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Drive test Data Analysis Flow chart Scanner and UE drive logs

A 1. 2. 3. 4. 5.

Compare scanner measurements with planned quality and coverage thresholds

Coverage target agreed with customer

No

CPICH RSCP => planned threshold e.g. -90 dBm

Low CPICH Ec A Ec/No target agreed with customer & depends service mix

Yes

CPICH Ec/No => planned threshold e.g. -12 dBm

Currently X = Max AS size = 3 No

amount of Scrambling Codes > X

Yes No

Possible Actions/Solutions Antenna Tilting Change Antenna Type Change Antenna Height Change CPICH Tx Pwr (Add sites)

No

Yes Pilot Pollution

A

Dominance Area OK Bad Ec/No?

Multi-path Problem

Yes A

Yes No

A

A


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How to Start? Where to start? TECHCOM Identify theConsulting most common RF issues like…

Cell overshoot Lack of dominant server Frequent change of best server Pilot pollution Weak active set Missing neighbors


Identify most common service quality issues like… Service availability Drops and blocks Voice call quality Latency and throughput for data

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Analysis TECHCOM Consulting Metrics needs to consider by RF Engineer for analysis in general

Uplink BLER – To identify the areas of poor uplink quality

Coverage plot in terms of RSCP – To identify the areas of poor coverage

Active Set Size Plot – To identify the areas of high secondary traffic and too many servers.

Best Server Plot (1st Best SC based on Ec/No) – To verify the sector wise coverage, SC inconsistencies, Sector Swaps, etc. Ec/No Plot of the 1st Best Server – To identify areas of poor Ec/No Downlink BLER plot – To identify the areas of poor down link quality UE Transmit Power Plot – To identify the areas of poor uplink coverage and path imbalance


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Analysis TECHCOM Consulting Metrics needs to consider by Cluster RF Engineer to identify issues and reach optimization solutions.

Analysis of Pilot Pollution / Interference / Pilot Overshoot – To identify the possible cause of poor Ec/No, poor DL BLER, High SHO overhead, etc.

Swap Sector Analysis / SC inconsistency Check – To identify the sector swaps and/or improper data fill of Scrambling codes

Drop Calls / Access Failure Analysis – To identify the reason for Drop calls and Access Failures and provide to solutions to resolve.

Azimuth Verification – To identify the difference between the azimuth deployed and azimuth designed.

Metrics needs to consider by RNC Engineer may need to do on a RNC Level for all the sites.

Missing Neighbor Analysis – To identify the reported missing neighbors and recommend the required neighbor list changes.

Neighbor List Inconsistency Check – To identify issues like one way neighbors, neighbor data fill issues, IRAT Neighbor issues, etc. SC Inconsistency Check – To identify any SC collisions based on Neighbor List


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RF Optimization - Tools Consulting ForTECHCOM RF Optimization and neighbour verification both Scanner (3G & 2G) and UE measurements are required simultaneously.

Post-Processing tool is required for data analysis Individual call failures or drops can be analyzed with Drive test tools (e.g. TEMS) but to get bigger picture, a proper analysis tool is required Actix can be used for

NetActPlanner can be used to verify the proposed coverage optimization solution e.g. Antenna tilting or Panning

On going contents will be based on analysis of TEMS.


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Drive test Data Analysis Flow chart Introduction to TEMS Drive test tool Analysis of Cell Dominance ( Pilot Pollution ) Analysis of DL CPICH Coverage ( RSCP ) Analysis of UL Coverage and Interference ( UE TX PWR ) Analysis of Missing or Deletion of Neighbors Soft-Handover analysis and Impact Analysis of Inter Radio Access Technology Handover ( IRAT HO ) Analysis of Multi RAB Analysis of Drop Calls Analysis of Poor R99 and HSPA Throughput


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Introduction to TEMS Drive test tool TECHCOM Consulting Workspace

Worksheet

After installing TEMS and opening the Data collection window we need to create a workspace so, that we can save the windows for 3G drive test, saving us from tedious work of opening it every time we want to collect drive data.

Once we have opened a new worksheet, we will start with a map which shows us our current location and also guides us the area and the roads we need to cover with the help of GPS. It also displays all our Node B’s if cell file is loaded.

We need to open a new worksheet for the same and the procedure has been shown in the following slide.


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MAP WINDOW

Select presentation on the information bar. Go to positioning and select map.


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Cell File Load To TECHCOM see the Consulting NodeBs installed in the operator’s network we need to add the cell file to our Map.

Following are the steps for same – Go to configuration on the tools bar. Select General. Select Cell file Load. Go to ADD and select the required cell file.

Select General

Cellfile Load


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Vectors TECHCOM Consulting and put them on the map to Select the vectors show the roads highways, railways etc.

We can also remove and add things by going to “Layer control” option on top of the map toolbar.


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Serving/Active Set + Neighbors


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Serving/Active Set + Neighbors TECHCOM Consulting This window contains a lot of aspects of 3G and has a lot to be explained –

Cell ID – This is the identity or name given to a particular Node B and its cell by the operator. UARFCN – It is the frequency band allotted to the operator. One spectrum bandwidth is of 5MHz in WCDMA or 3G.This window shows us the centre frequency of the bandwidth allotted to the operator. Cell Name – It is the name given to particular Node B’s by the operator generally along the lines of the name of the area the Node B is located in. Scrambling Code – Scrambling code is a code assigned to a particular cell. There are 512 such codes for the network to differentiate among


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different Node B’s and these codes can be repetitive. They are of two types primary and secondary. AS – This stands for Active Set. Active Set is the set of Scrambling Code which the U.E is currently latched on and there can be a maximum of 3 Scrambling codes in Active Set. MN – MN Stands for monitored neighbor i.e the neighbor cell that is detected by the U.E as a neighbor and is also defined as a neighbor in the network. U.E will initiate a Handover onto the monitored neighbor in case the monitored neighbor has a stronger Rx level than the AS. DN - DN stands for Detected Neighbor and as the name suggests it is the neighbor detected by the UE but, is not defined in our network . It can be because of Overshooting of a site, incomplete neighbor list or in case of a new site. It is very important to optimize and have no DN’s as they are one of the major reasons of Call drops in 3G.

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Layer 3 Messages

Layer 3 Messages are the messages on the Uu interface i.e between Mobile station and the Node B.


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Radio Parameters


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Radio Parameters TECHCOM Consulting are the parameters of a Radio parameters Mobile equipment

CPICH Ec/No – Common Pilot channel Ec/No is the ratio of energy of the chip and the combined power of all the signals including the pilot itself received by the UE at that particular point. It is a very important factor for call quality. CPICH RSCP – Received Signal Code Power is the level of the signal received by the U.E from a particular pilot. UE Tx Power – As the name suggests it is the transmitting power of a Mobile Station. Its value can vary from -50 to 50. The minimum the Tx power of the Mobile station the better it is for call quality.


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UTRA Carrier RSSI - It is the Received Signal Strength Indicator of the Mobile Station or the U.E. It tells us the total Power Received by the Mobile Station from all the Pilots including itself at that particular location. SIR – It is the signal to interference Ratio is the ratio of Energy in the DPCC(Dedicated Physical Control Channel) to that of the interference and noise received by the U.E. Target SIR – It is the target Signal to Interference ratio that Mobile Equipment is supposed to achieve by increasing or decreasing its power. It is set by the use of Power Control procedure. SQI - It is the speech Quality Index which is a parameter to rate the voice Quality on that particular call. It ranges from 0 – 30 with 30 being the best quality. RRC State – It tells the current state and channel as in Idle or dedicated. Mode – It is the mode that we are using GSM or WCDMA.

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WCDMA HSPA/GSM Data Line Chart

This window gives us the data throughput ( in kbps ) for both 3G and 2G modes depending on which mode the mobile equipment is. RLC DL Throughput – This is the total throughput on the downlink at that particular point.


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GSM Neighbors

This window is very helpful in case of 2G – 3G Handovers as we can see all the 2G neighbors of that particular 3G cell in the compressed mode state. Copyright © All rights reserved

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Drive test Data Analysis Flow chart Introduction to TEMS Drive test tool Analysis of Cell Dominance (Pilot Pollution) Analysis of DL CPICH Coverage ( RSCP ) Analysis of UL Coverage and Interference ( UE TX PWR ) Analysis of Missing or Deletion of Neighbors Soft-Handover analysis and Impact Analysis of Inter Radio Access Technology Handover ( IRAT HO ) Analysis of Multi RAB Analysis of Drop Calls Analysis of Poor R99 and HSPA Throughput


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Analysis of Cell Dominance (Pilot Pollution) TECHCOM Consulting Pilot pollution is the condition of a low ratio of usable signal energy to unusable signal energy.

Another definition is the number of pilots within the UE Reporting Range > max active set.


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What is Pilot Pollution? Consulting CellTECHCOM pilot signals received at a test point have no difference in signal strength (either strong or weak), but no dominant pilot is received.

The symptom is that the received pilot power is good but Ec/Io of each cell is weak. At present, most WCDMA equipments supports up to three active sets. If the number of similar Ec/Io values of different cells is more than three, it can be regarded as a kind interference towards three radio links in the active sets.

Cell coverage and capacity is reduced by high DL noise levels. BLER is high, and throughput is thus lowered.

Dropped calls are more likely; signaling may fail. After minimizing pilot pollution, effect of the same is Optimal Dominance means Good Ec/No and Hence Good Voice quality, Good Video Quality and Good Throughput.

UE’s may change serving cell frequently in idle or cell- FACH states. UE’s in cell-DCH state may change active set members frequently.


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Pilot Pollution Corrective Actions Cause

Method

Lack of any strong pilot

Strengthen the best pilot

Too many strong pilots

Weaken unwanted pilots

Point of Change

Action

DL Power

Raise or lower the CPICH power

Antenna changes

Adjust down tilt, azimuth, or height.

Location

•Use building shadowing to weaken a pilot • Increase cell-to-cell distance.


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Scrambling Code Dominance Plot


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Pilot Pollution on TEMS

No any Strong Dominance of Signal rather receive all signals with Poor EcNo


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Pilot Pollution on ACTIX


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RSCP Plot for individual SC

SC 130


SC 138

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SC 146

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RSCP Good and Ec/No Poor Condition Overlapping area & Good RSCP


Overlapping area & Poor EcNo

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Pilot Pollution It is a direct relationship between RSCP and Ec/No…. Ec/No = RSCP/RSSI Pilot Pollution = High BLER + Frequent active set changes RSCP

EcNo


= Pilot Pollution

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Drive test Data Analysis Flow chart Introduction to TEMS Drive test tool Analysis of Cell Dominance (Pilot Pollution) Analysis of DL CPICH Coverage (RSCP) Analysis of UL Coverage and Interference ( UE TX PWR ) Analysis of Missing or Deletion of Neighbors Soft-Handover analysis and Impact Analysis of Inter Radio Access Technology Handover ( IRAT HO ) Analysis of Multi RAB Analysis of Drop Calls Analysis of Poor R99 and HSPA Throughput


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Analysis of DL CPICH Coverage ( RSCP ) Consulting TheTECHCOM Objective of Coverage Analysis is to make sure that the coverage of a site or the cluster from the drive test meets the coverage objective of the RF Design.

To get an accurate view of Coverage and Quality on the ground then Field Measurements with Scanner and UE are required.

Poor coverage = Weak Pilot + No Dominant Pilot + Poor Active Set Pilot Quality + Dropped Call Good Coverage = Strong Pilot + Dominant Pilot + Good Active set Pilot Quality + No Dropped Call The objective of RSCP analysis is to meet the required RF Design KPI in terms of RSCP. This KPI would differ from market to markets.


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Drive Test RSCP Vs RF Design Predicted RSCP

NOTE


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DL Coverage ( RSCP ) Optimization Consulting TheTECHCOM intention of DL Coverage Optimization is to improve the RSCP to a level as optimum as possible. It is always recommended to identify the 1st Best Server in terms of Ec/No, in the area you are optimizing.

Incorrect CPICH Power Incorrect NodeB parameters like, ulAttenuation, dlAttenuation, TMA insertion loss, etc. Node B Hardware Issues, Alarms, etc.

Following could be the causes of poor coverage from a sector. Obstructions – Buildings, Hoardings, etc. Either very high or very low Electrical / Mechanical Tilts Improper Antenna Azimuth Improper Antenna High Feeder Cable Loss due to higher feeder cable length Feeder Cable / Connecter issues


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DL Coverage ( EcNo ) Optimization Consulting DL TECHCOM coverage in UMTS is not just the RSCP but the combination of RSCP and Ec/No.

Poor Coverage (RSCP) – At the cell edges when the RSCP is bad, obviously Ec/No will be bad. But this area is categorized as a Poor Coverage Area.

Following could be the causes for EcNo. Pilot Pollution – Having too many pilots at a good RSCP in a location Pilot Spillover (Boomer Cells) – Spillovers causes increase in Io in the far field causing poor Ec/No Missing 3G Neighbors – Without the proper neighbor definitions, a strong undefined neighbor becomes an interference, which could reduce Ec/No. Improper IRAT Trigger – If the IRAT Handover to 2G is not done at the right time, it could lead to poor Ec/No.


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Improper Cell Selection / Reselection – A UE camped on a wrong cell could initiate a call in a poor Ec/No environment. High Traffic on the Cell – High Traffic increases Io and causing reduction in Ec/No Improper Soft Handover Parameters.

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Coverage Analysis


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Coverage Analysis


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Drive Test For Coverage TECHCOM Consulting SCANNER Vs PHONE

Scanners are better than phones, no neighbor list dependency Use roof mounted antennas with identical gains or known gains. Adjust for phone vs. scanner gains in postprocessing. Limit cluster size of 10-15 sites so drive test <4 hours. Check RF Operations for alarms, solve if necessary. Drive as many streets as possible, involving ALL sectors.


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Pre Drive Vs Post Drive TECHCOM Consulting

•If lack of coverage is indicated then coverage enhancement is required. •Has excessive tilting been used? Is up-tilting or an Panning the antenna an option for some cells.

•After optimization start post drive •Same route has to be covered which earlier was done. •Same routes gives us the better idea to focus on optimization if needed.

•Re site audit if required in terms of antenna tilt, azimuth and height. •For initial roll out stages (low traffic) increasing the P-CPICH power is an option the feasibility will depend upon the margins in the link budget but many operators are not allowed.

•Clear the site related alarms if any •After completion of all start the post drive.


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RSCP Pre Drive Plot This cluster has been done before Optimization

Cluster - 20 sites On Air Site – 14 sites

Poor Coverage Area

Legends 0 to -74dBm -74 to -80dBm -80 to -87 dBm -87 to -97dBm -97 to -127dBm


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RSCP Post Drive Plot This cluster has been done after Optimization

Cluster - 20 sites On Air Site – 18 sites

Improved Coverage Area

Legends 0 to -74dBm -74 to -80dBm -80 to -87 dBm -87 to -97dBm -97 to -127dBm


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Conditions for Radio Environment

• • • •

RSCP RSCP RSCP RSCP


EcNo EcNo EcNo EcNo

= Coverage Limited = Poor Radio Condition = Good Coverage = Pilot Pollution

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RSCP Poor & Ec/No Good (Coverage Limited)


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RSCP Poor & Ec/No Poor ( Poor Radio Condition )


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RSCP Good & Ec/No Good ( Good Coverage )


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RSCP Good & Ec/No Poor (Pilot Pollution)


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Drive test Data Analysis Flow chart Introduction to TEMS Drive test tool Analysis of Cell Dominance (Pilot Pollution) Analysis of DL CPICH Coverage (RSCP) Analysis of UL Coverage and Interference (UE TX PWR) Analysis of Missing or Deletion of Neighbors Sot-Handover analysis and Impact Analysis of Inter Radio Access Technology Handover ( IRAT HO ) Analysis of Multi RAB Analysis of Drop Calls Analysis of Poor R99 and HSPA Throughput


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UE TX Power TECHCOM Consulting

User Equipment Transmit Power ‐ It indicate how much Mobile is transmitting power, Lower transmit power is better for network. UE can transmit between ‐40 to + 21 dBm and Data card ‐40 to +23 dBm. If Up Link has interference then UE has to transmit more power to reach Node B. Desire value <10 +dBm

It is recommended to use the Long Call Handset, for the fact that, the UE transmits the right power when it is on call. During idle mode UE does not transmit continuously.


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Main objective of checking the UE Transmit Power is to verify the Path Balance. Where ever there is a good RSCP, UE should transmit at a lower power. The UL & DL may not be balanced due to various factors such as like differences in Downlink and Uplink Power Control algorithms, Interference conditions, Traffic conditions, etc. To verify the path balance visually, from the UE TX Power Plot, identify the areas of high UE Transmit Power (Say > 0 dBm) and then look at the RSCP and Ec/No Plots. If you see poor RSCP, it could be a poor coverage area. In this case, an attempt should be made to improve the coverage. If you see a poor Ec/No with a good RSCP, it could be due to interference or high traffic. If it is an interference issue due to pilot pollution or overshooting pilot, an attempt should be made to improve the Pilot Ec/No.

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UE Transmit Power – UL Coverage Analysis TECHCOM Consulting

In few circumstances, UE Transmit Power could be higher with a good RSCP and Ec/No. This indicates an issue with the Uplink. This may be due to any of the following issues. TMA, Cable, Antenna, Node B Hardware issues Improper Uplink Power Control Parameters Improper IRAT Trigger Improper Cell Selection / Reselection parameters Improper Node B parameters like, ulAttenuation, dlAttenuation, TMA Insertion Loss, TMA Gain, etc. External Uplink Interference.


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UE Tx Power Explanation User is currently connected with SC 318 Node B and user is start moving towards SC 166 Node B


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Step-1

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UE Tx Power Explanation User is currently connected with SC 166 Node B and SC 318 Node B. UE is at the cell edge and has to transmit with High Power


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Step-2

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UE Tx Power Explanation User is currently connected with SC 158 Node B


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Step-3

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UE Tx Power RACH INITIAL ACCESS


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UE Tx Power Incase of Single Site In case of Single site RSCP & EcNo is good and hence Ue has to trasmitt -23 dBm


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UE Tx Power Incase of IDLE and Dedicated mode UE TX Power

In Idle Mode UE is not transmitting any power to Node B whereas in Cell_DCH / Cell_FACH mode UE is transmitting power to Node B.


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UE TX Power Pre Drive Plot

UE has to transmit more power due to non working of nearby site

Legends -30 to -3 dBm -3 to 1 dBm 1 to 5 dBm 5 to 11 dBm 11 to 30dBm


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UE TX Power Post Drive Plot

UE has to transmit less power due to working of nearby site Legends -30 to -3 dBm -3 to 1 dBm 1 to 5 dBm 5 to 11 dBm 11 to 30dBm


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UE Transmit Power – Conclusion TECHCOM Consulting

Give request to Plan site where as UE has to transmit high power to continue exiting connection with Node B. Also Node B needs to transmit with High power. Adverse effect of this situation is when traffic of near by site is increase then due to the principle of WCDMA, Node B has to drop high power users. Any time call Drop is occur when call is ongoing and any time call Block is occur when call is in initiation process.


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Drive test Data Analysis Flow chart Introduction to TEMS Drive test tool Analysis of Cell Dominance (Pilot Pollution) Analysis of DL CPICH Coverage (RSCP) Analysis of UL Coverage and Interference (UE TX PWR) Analysis of Missing or Deletion of Neighbors Soft-Handover analysis and Impact Analysis of Inter Radio Access Technology Handover ( IRAT HO ) Analysis of Multi RAB Analysis of Drop Calls Analysis of Poor R99 and HSPA Throughput


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Analysis of Missing or Deletion of Neighbors • • • •

To better understand the failure mechanisms that contribute to radio failure as measured with network statistics. Categorize the failure causes for Call Setup and drop call performance. Drop Call analysis shows that significant proportion of Interference failures is due the missing neighbour Analysis also confirms that conclusion derived from the scanner data that DL interference is major contributing factor to failure on the radio Interface KPI Route Call Drop Causes

KPI Route CSF Causes

3.70% 8.33%

8.33%

29.63%

8.33%

22.22%

AS Update Failure :

RF Issue : Interference System Issue :NodeB

Cause Unknown

UE Issue

UE Issue

Unknown

11.11% 18.52%

14.81%

75.00%


RF Issue : Interference

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Missing neighbour RF Issue : Coverage

Neighbor Cells with wrong Configuration TECHCOM Consulting

A neighbor cell may has been added to an active set. It may be involved in cell re-selection or handover with other cells. When a mobile is in the idle and FACH state, the mobile reads the neighbor cell information from system messages, and measures these neighbor cells when conditions are met. If a neighbor cell fails to be set, cell re-selection cannot be complete timely which further cause call establishment failure. When the mobile is in the DCH state, RNC sends out neighbor cell information through measurement control command to ask the mobile to measure all neighbor cells where handover may occur. In this case, if a neighbor cell fails to be set, handover failures may occur and further cause call drops.


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Neighbor Cells with wrong Configuration WCDMA Pilot Set (dB) - Ec/Io -25

-20

-15

-10

-19.2

-16.07

-15.8 -5

0 Series1

-10

-8.89

-7.3

-8.2

AS

MN

MN

MN

DN

DN

DN

DN

-10

-7.3

-8.2

-15.8

-19.2

-6.2

-8.89

-16.07

-6.2

AS- Active Set MN – Monitored Neighbour DN – Detected Neighbour


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Missing or Detected Neighbour


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Detected Neighbour

Active Set- Currently serving Cell Detected Neighbor- Undefined strong detected server UARFCN DL- UMTS Absolute radio frequency channel number CPICH – Carrier Pilot Channel


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Deletion of Neighbour Need to Delete Neighbor


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Drive test Data Analysis Flow chart Introduction to TEMS Drive test tool Analysis of Cell Dominance (Pilot Pollution) Analysis of DL CPICH Coverage (RSCP) Analysis of UL Coverage and Interference (UE TX PWR) Analysis of Missing or Deletion of Neighbors Soft-Handover analysis and Impact Analysis of Inter Radio Access Technology Handover ( IRAT HO ) Analysis of Multi RAB Analysis of Drop Calls Analysis of Poor R99 and HSPA Throughput


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Soft-Handover analysis


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Soft Handover When UE has Radio Links (RLs) with same node B and other node B then type of Handover is known as Soft Handover.


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Softer Handover When UE has Radio Links (RLs) with same node B then type of Handover is known as Softer Handover


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WCDMA Handover Analysis

SC 38 is added in AS

SC 38 is added in AS


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Active Set Update TECHCOM Consulting

In 3G there can be six pilots in the active set. But, we generally set it at maximum of three(depends on the operator) to avoid Pilot pollution. In case of soft Handover all the cells which are in MN can be entered into Active set but, only till the maximum limit of three. This procedure of soft HO from monitored to Active set is called Active set update.


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Active set Update


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Active set Update

Added to Active Set

Active Set Update

Current Location


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Unreasonable Handover Area Typical handover process: measure control －> measure report－> handover decision－> handover implementation－> new measurement control. Unreasonable handover area may cause that signals jitter to fast and have not enough time to complete handover which further causes call drops. Corners and street crossroads.


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SHO Overhead Analysis TECHCOM Consulting

Soft Handover Overhead is the metric that gives the amount of radio resources being used in the Uu interface when the Active Set Size of the UE is more than 1. Two ways to measure 1. Percentage of Soft Handover Traffic to the Total Traffic 2. Average Number of Sectors used per UE during drive test


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SHO Overhead Analysis TECHCOM Consulting

1)

Percentage of Soft Handover Traffic to the Total Traffic – Handover Traffic includes soft, softer, 3-way soft, 4 way soft, etc. Total Traffic will include the Primary Traffic and the Soft Handover Traffic. This type of metric can be calculated using the respective counters to do the capacity performance analysis. As of now, since we do not have much traffic on the network, we will not be able to rely on the counter values.


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2)

Average Number of Sectors used per UE during drive test – This metric can be calculated using Active Set Size Plot from the Handset device making Long voice Call or using the Simulated Active Set Size Plot from the Scanner. This type is generally used to calculate the soft handover overhead using the drive test data.

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Drive test Data Analysis Flow chart Introduction to TEMS Drive test tool Analysis of Cell Dominance (Pilot Pollution) Analysis of DL CPICH Coverage (RSCP) Analysis of UL Coverage and Interference (UE TX PWR) Analysis of Missing or Deletion of Neighbors Soft-Handover analysis and Impact Analysis of Inter Radio Access Technology Handover (IRAT HO) Analysis of Multi RAB Analysis of Drop Calls Analysis of Poor R99 and HSPA Throughput


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IRAT HO – Inter Radio Access Technology Handover Hard Handover from 3G to 2G technology IRAT Process 1. 2. 3. 4.

Camp on 3G Compressed Mode Entered Compressed Mode Exited Handover from UTRAN


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IRAT HO – Step1

UE is camp on 3G

Call setup on 3G


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IRAT HO – Step2 Compressed Mode entered and For a while Data is paused and Searcher is search for available Radio Access Technology i.e. 2G and Handover is happened from UTRAN WCDMA has GSM Neighbors

Compressed Mode Entered and HO from UTRAN


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IRAT HO – Step3

After Successful of IRAT HO compressed Mode is Exited

Compressed Mode Exited


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Analysis of Multi RAB

Radio Access Bearers 1. Voice Call Session 2. Video Call Session 3. Data Call Session

Voice and Data Call has been carried out simultaneously.


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Analysis of Multi RAB

Multi RAB : Attractive Feature of 3G

CS call is running


PS Call is running

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Drop Call Analysis •

One of the major challenges in Radio network Optimization is Drop Call Analysis. A drop call occurs if the connection is terminated anytime after the UE has completed the RAB setup by sending the RAB Setup Complete on the uplink as shown.

AMR Call Flow Copyright © All rights reserved

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Drop Call Analysis Flow Chart Start Analyzing a Drop Call

Drop Call Analysis Flow Chart

UE’s best server = Scanner’s best server?

NO

Missing Neighbor / Cell YES Reselection Issue?

Neighbor List Optimization

YES DL Coverage Optimization

NO

NO

UE Best Server’s RSCP > -90 YES UE Best Server’s Ec/No > -12

NO

YES

UL Coverage / Path Balance Optimization

NO

UETXPWR < 0

NO

Optimization to create Pilot Dominance and reduce spillovers OR Optimize SC

Pilot Pollution / Boomer Cell / YES SC Collision? NO Missing Neighbor / Cell YES Reselection Issue?

Neighbor List Optimization

YES Possible Causes: 1) Poor Handover Parameters, 2) Poor Cell Reselection Parameters, 3) Inter RNC HO issues, 4) No Resource available on Target Cell during HO, 5) Hardware Issues, 6) Improper IRAT Trigger, 7) Scrambling Code Collisions.


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Drop Call Causes TECHCOM Consulting

1. Missing Neighbour 2. Handover Issues 3. DL Coverage Issues 4. UL Coverage Issues 5. Pilot Pollution 6. Over shooting Pilots / Boomer Cells 7. Cell Reselection Issues 8. SC Collisions 9. INTER RNC Handover Issues 10. Hardware Issues


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Drop Call due to Missing Intra Frequency Neighbor


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Drop Call due to Missing Intra Frequency Neighbor


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Block Call due to No Radio Bearer Setup Complete


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Block Call due to No Radio Bearer Setup Complete Normal Call Setup Procedure


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Call Setup Failure

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Drop Call Causes and Possible Solutions Behavior

Problem

Description

Possible Solution

Dropped call

SHO to wrong cell will cause drop call.

Overshooting cell come temporarily into active set and forces a suitable serving cell to be dropped out. Later RSCP suddenly drops in the “wrong cell” and causes a dropped call because there is no neighbour defined.

Pan away overshooting cell if it is too close to the serving cell, otherwise apply down tilting as well.

Dropped call

Cell suffering from UL interference = DL (CPICH) coverage much bigger than UL coverage

As the UE Tx power is not enough for target cell synchronisation, the SHO fails which will cause call drop later.

Use cell individual offset (negative value) parameter to balance the DL and UL coverage. Check traffic direction of in-car UEs to decide which cell requires offsets.

Dropped call

DL CPICH coverage < UL coverage

Cell with lower CPICH power than the surrounding is having “too good” UL performance, as this cells’ UL cannot be used efficiently due to SHO is decided upon DL (CPICH Ec/No).

Use cell individual offset (positive value) parameter to balance the DL and UL coverage. Note: Cell individual offsets are not taken into account when calculating the added cell TX power.


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Drop Call Causes and Possible Solutions Behavior

Problem

Description

Possible Solution

Dropped call

Round the corner effect

Dropped call/SHO failure

Too many neighbours

Use cell individual offset (positive value) parameter to balance the DL and UL coverage. Delete unnecessary neighbours. Improve dominance.

Drop Call

RAN is not working correctly during SHO.

Drop Call

Failure to decode BSIC before the call drop.

The call drops due to too rapid CPICH coverage degradation for Cell A, and therefore there is not enough time for SHO. In SHO area the number of combined neighbouring cells become more than 31. HO list is created using RNC algorithm in the final stage some of the neighbours will randomly be removed. No GSM neighbour list is sent for measurements in case there are 3 cells in Active Set. CM starts too late

Drop Call

Failure to decode BSIC before the call drop.


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BSIC verification takes too much time.

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This should be corrected in later RAN release(s).

Set higher ISHO thresholds, FMCS: CPICH EcNo, CPICH RSCP, UE TX Pwr. Set smaller measurement time for GSM cells, FMCG: Maximum measurement period, Minimum measurement interval




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PS Data Analysis TECHCOM Consulting

Low throughput can be caused by simple RF issues as well as complex end to end system issues.

Packet data is handled using common channels, dedicated channels and shared channels, each offering different capability and throughput. Which of these is assigned is dependent on UE capability, data volume, RF conditions, available resources (hardware, transmission, code etc). Throughput depends very much on the round trip time (RTT) The lower the RTT the greater the potential for higher throughput. Normally RTT is around 200ms.


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Throughput Analysis Flowchart

Start Analyzing Low Throughput

N

Escalate

Isolated to a specific area? Y

UE requires HSDPA

N

UE requires R99 DCH

Y

HSDPA Analysis


Y

R99 DCH Analysis

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N

UE requires cell FACH Y

Common / Idle Analysis

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R99 Throughput Analysis TECHCOM Consulting

R99 PS service is a best effort service. When using R99 DCH each user is allocated a dedicated channel with a radio bearer configured based on the UE requirement and available resources. The R99 DCH Bearers are fixed rate bearers, with the following rates supported in the uplink and downlink: 384kbps 128kbps 64kbps

R99 Low Throughput Causes 1. Prolonged Cell_FACH 2. Mobility – Missing Neighbour 3. Poor RF Coverage 4. High BLER 5. Rate Switching

Once the session is established the bearer rate is then adapted based on throughput requirements and to in order to control load in the cell.


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Poor PS Call ( R99 ) in Mobility


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Poor PS Call ( R99 ) in Mobility No Dominance area and Frequent change in Radio Link Addition/Removal/Replacement Cause low Throughput


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HSDPA Throughput Analysis TECHCOM Consulting

HSDPA offers users enhanced data rates and improved latency over traditional R99 bearers, with throughputs as high as 14.4Mbps achievable. With HSDPA, users make use of the DSCH (comprising several sf16 codes) rather than the DCH for data transfer in the downlink, the scheduling of user data is performed by the a new MAC entity (MAC-hs) in the NodeB rather than the RNC and fast HARQ is used to minimize RLC retransmissions caused by errors introduced over the air interface


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HSDPA Low Throughput Causes 1. Beginning of Session – TCP Slow Start 2. No HS-DSCH Assignment 3. Low CQI 4. High DTX % 5. High NACK% 6. Mobility

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Poor PS Call ( HS ) in Mobility No Dominance area and Frequent HS Serving Cell HO or Ping Pong Switching can cause low Throughput


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HSDPA TEMS Overview

Shows How many codec are used

Throughput 3.861 Mbps


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Which Modulation is used?

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HSUPA TEMS Overview

Uplink Throughput in kbps

Uplink Transmission rate ( % ) Uplink Re-transmission rate ( % )


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To Meet Network KPIs

Optimize signal coverage

Repeat until KPIs are met

Control Pilot Pollution

Optimize Neighbor Lists


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Control SHO Factor

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Thank you


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Chapter 4_DT ANALYSIS&OPTIMIZATION.pdf

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