UMTS KPI-Optimisation & Tools

UMTS KPI-Optimisation and Tools

Sanjay Kumar/Hemal Doshi

All Rights Reserved © Alcatel-Lucent 2008

Before we start:

We will first look at the general optimisation process, RF aspects, call flow alongwith the KPIs. After that we will see the Optimisation techniques by means of Drill down analysis and all the UMTS Tools used for the optimisation for TNZ network.


General Optimisation Process:

Pre-Optimization is an optional phase and might be required especially for new network deployment or network extensions. This phase might incorporate tasks such as hardware functionality checks (proper integration), coverage verification, adjustments for initial antenna tilts, creation of initial neighbour lists, and RF parameter declaration. Other optional tasks in this phase may include initial scanner drive test for coverage and neighbour list verifications.The objectives of the Service Measurement Based Optimization and the Drive Test Based Optimization are to assess and improve network performance and quality. Both optimization phases are independent of each other


Primary RF Optimisation objectives:

Minimize Call Setup Failures

Minimize Drop Calls

Maximize Voice Quality

Maximize Data Throughput

Ensure defined system service coverage

Maximize reliability of IRAT handover


Overview of RF Optimisation process:

Service Measurement based optimisation to be carried out based on report analysis.Pre-optimisation is mainly covered during the planning phase of the network.


Importance of Scanner Measurement in Drive Test:

Scanner Measurement Tools measure the UMTS physical layer. The system performs

absolute and relative channel power measurements of the Primary Synchronization

Channel (PSCH), Secondary Synchronization Channel (SSCH) and the Primary Common

Pilot Channel (P-CPICH). These three channel measurements can be performed

simultaneously for multiple scrambling codes. Scanners are able to perform power

measurements on the GSM DCS or PCS bands at the same time. The UMTS and/or GSM

channel power measurements are executed without using a UMTS/GSM test terminal.

Required key measurement capabilities are:

• Scrambling Code Power Ec and Ec/Io (CPICH)

• Scrambling Code Group and Scrambling Code Number

• RSSI (Io)

• Power measurements on GSM, DCS or PCS channels

Scanner measurement tools are used for pilot coverage surveys to analyze pilot

coverage, best server and pilot pollution, and to identify missing neighbors and non-

UMTS interference.


Service Measurement Based Optimization:

Service measurement tools must be utilized during the Service Measurement Based

Optimization. These tools are used primarily after network launch when live traffic

exists. Network performance data are collected at the OMC level.

Specific quality and performance criteria, within a UMTS network, are assessed by

certain measures and events. These specific measures and events are performance

metrics that are composed of a series of quality indicators. Since there is a large

amount of quality indicators used for functional and performance tests, a subset of

Key Performance Indicators (KPI’s) is chosen that best represent the quality and

performance of a UMTS network.

The network performance is in general verified by the following factors:Call Availability (i.e. successful Set-up of the Call or Accessibility)Call Reliability (i.e. Successful Maintenance of the Call as opposed to Dropped Call)Call QualityCall Mobility

A Call refers to both Circuit Switched Call and Packet Switched Call (Session).


Each of the classes listed above can be measured by specific KPIs as following:

Call Availability: Successful Radio Resource Control (RRC) Connections

Establishment Rate, Dropped RRC Connections Rate and Total Radio Access

Bearer (RAB) Establishment Success Rate.

Call Reliability: Total RAB Dropping Rate.

Call Quality: Uplink and Downlink Block Error Rate (BLER).

Call Mobility: Intra and Inter RNC Soft Handover Success Rate, Relocation

Preparation (for UMTS to GSM HO) and UMTS to GSM Handover Success Rate,

Location Area (LA) Update Success Rate, and Routing Area (RA) Update

Success Rate.

Now we will see the basic RF UMTS optimisation/problem aspects, WCDMA call

flow to understand the performance counters in more detail.


RF Optimisation Aspects:

The most common challenges of RF Optimization are Coverage, Pilot

Pollution/Interference, Around-the-Corner-Problem and Missing Neighbours.

Additional aspects such as Cell Breathing, Inter/Intra System Handover, Near Far

Problem and HSxPA should also be checked for overall improvement.

1) Radio Coverage: Radio coverage is defined as an area where the Link Budget

condition, in particular the limited traffic channel path loss (UL or DL) for a

service type is met.

Poor RF coverage is typically characterized as:

Coverage Hole or Outer Coverage Area – Area with insufficient pilot RSCP signal

strength

No Dominant Pilot Area – Area with sufficient pilot RSCP signal strength but no

dominant Ec/Io pilot. Usually the case when many equal strength pilots are

measured that lower the overall signal-to-interference.


2) Pilot Pollution: Multiple pilot receptions in the same area increase the

overall level of interference. Pilots not used by the terminals cause

interference to the ongoing communication, which in the worst case may

cause a call failure. Typically the term pilot pollution describes the existence

of too many pilots in an area, which aren’t required to sustain the call. Pilot

pollution occurs when the following conditions take place:

Number of present pilots are larger than the Active Set Size

Present pilots have similar signal strengths

Present pilots have poor Ec/Io ratios

Polluted area shows usually good RSSI values


3) Near-Far problem: The Near-Far problem occurs when an UE transmits on

high power near the cell site, thus creating excessive interference for another

UE located far away from the cell site. The goal of the cell site is to receive all

UE’s at equal signal strengths. Therefore fast closed loop power control is

needed to direct mobiles to power up/down very quickly.

The optimization goal is to ensure that all power control algorithms are

working properly. Power control parameters are tuned only when there are

obvious power control failures.


4) Cell Breathing: A spread spectrum system like UMTS has the characteristic

of cell breathing, which is dependent on the network loading. An increase of

the network load is associated with an increase of the network interference,

which means more power is transmitted by the network cells and users. High

interference lowers the quality of service at the initial cell coverage border

and thus shrinks the effective coverage area. Inversely, low load leads to low

network interference, which increases the effective cell coverage


5) Missing Neighbors: Missing Neighbours are pilots that are not defined in the neighbour list.

These pilots are measured with an adequate receive level but cause interference because

they cannot be added to the active set.

It is important that all received UMTS sectors are either eliminated if not required to sustain

the communication or declared in the neighbour list. An un-optimized neighbour list has a

big impact to the quality and performance of connection. The practise shows that mostly

missing neighbour relations are encountered around RNC borders.

Neighbour list are pre-optimized during the radio network design stage. Scanner data can be

used to automatically compute a neighbour list for an initial network rollout. Furthermore,

root cause analysis of drive test failures will also provide information on missing neighbour

relations. In all cases extensive drive test are required. Another possibility to optimise

neighbour lists is to use the performance management counters (handover matrix) once

commercial traffic is present.


6) Intra System Handover: Unnecessary delays in intra system handovers

(soft/softer handovers) may cause uplink/downlink interference. Quick intra

system handovers are required for rapid changes in path loss between the UE

and the sector due to fading. Also, unnecessary handovers due to non-

contiguous UMTS coverage or pilot pollution require additional signalling

resources, and increase downlink interference.


7) Inter RAT Handover: The Inter Radio Access Technologies handover (Inter RAT or

IRAT) covers the transfer of a connection from a UTRAN system to another system

technology. The transition from UMTS to another technology should usually occur at

the UMTS coverage border. The optimization tasks cover:

Definition of sharp transition borders to avoid unnecessary handoversUnderlying system should provide continuous stable coverageIdle mode parameters should also be considered and harmonized to avoid ping-pong

effects

The optimization of the IRAT handover may require the modification of the UMTS

coverage to achieve sharp boarder and reliable radio conditions. This can be

realized through antenna configuration changes (tilt, azimuth) and/or parameter

settings. The performance of the IRAT handover depends mainly on the design of

the IRAT neighbours. The practice shows that reliable IRAT handover is achieved

through the RSCP threshold criteria for border cells, while core sites may find Ec/Io

criteria in better defining the handover regions.


8) HSDPA: High Speed Downlink Packet Access (HSDPA) is a major feature of the

3GPP Release 5 providing enhancements to the downlink transmission capacity

(higher end-user data throughput). New physical channels such as HS-PDSCH

(downlink), HS-SCCH (downlink), and HS-DPCCH (uplink) are required to be traced

and analyzed.

The End-to-End optimization strategy for HSDPA applies following considerations:Plan drive/indoor/walk-testing activities to cover HSDPA cells and collect HSDPA

relevant data.Define all Key Performance Indicators (KPIs) according to a precise methodology,

which makes KPIs comparable throughout the measurement campaigns.Definition of a methodology to correlate test results with relevant network

performance counters.Monitoring capabilities on the interfaces to collect the relevant traces on UTRAN

and Core Network.


The HSDPA performance depends, in general, on radio channel coverage condition,

traffic type (VoIP, Streaming, HTTP…), user classes (different subscription levels), and

available downlink resources. HSDPA related metrics are round trip time (RTT),

throughput per user, HS-DSCH cell change success rate, and HS-DSCH data

interruption time during cell change.

The cell change procedure does not support soft/softer handover for the downlink HS-

DSCH.

The “hard” handover constrains on the HS-DSCH require the following radio

optimization aspects to be considered to maximize HSDPA performances (throughput)

and avoid degradation, including eventual drops:Optimize soft/softer handover boundaries to avoid excessive sector coverage overlapCreate clear dominant pilot coverage through antenna configuration tuning (tilt,

azimuth) to avoid unnecessary handoversRemove existing “over shooters” which create interference and possible instable radio

conditionsMinimize pilot pollution areas


Cell change should be performed not too late, when the UE has already moved

into the area of the new best cell to avoid radio link quality as well as

throughput degradation. On the other hand cell change should not be

performed too early to avoid ping-pong effects by switching back to the

previous best cell if the radio conditions vary.Local optimization is initially done through the tuning of the parameters

hysteresis and time-to-trigger (e.g. in dense urban environment).

9) HSUPA: High Speed Uplink Packet Access (HSUPA) is aimed to improve

throughput, reduce delay and enhance the capacity of a release 6 compliant

3GPP UTRAN. Unlike HSDPA, mobility is supported through soft handovers.


Call Flow – WCDMA


Metrics

1. Accessibility Voice =

2. Accessibility HSPA =

3. Retainability Voice =

4. Retainability HSPA = 1-((AbnormalReleaseRequest_HSDPA) /

(IuAbnormalReleaseRequest_HSDPA + RadioBearerReleaseSuccess HSDPA +

HSDPAToDCHTransitionSuccess+

IF((AODownsizingStep1Success_AO012_C_HSDPA -

AOUpsizingSuccess_AO014_C_HSDPA > 0),

AODownsizingStep1Success_AO012_C_HSDPA -

AOUpsizingSuccess_AO014_C_HSDPA, 0.0))

_HSPARABAttTrch

rch_HSPARABSucEstT*

_HSPAFRRCConreq

st_HSPARRCSucConE

ceRABAtt_Voi

VoiceRABSucEst_

_VoiceFRRCConReq

st_VoiceRRCSucConE

ice_CellRelComp_Vo

oice_CellAbRelReq_V1


Performance Analysis - Approach

Adopt Top down analysis approach

Filter out HW alarms before in depth analysis

Monitor one/two week of busy hour data (busy hr defined on traffic).

Identify sub metrics for drill down.

Identify the counters impacting the performance metric.

If parameter changes required implement in cluster, monitor the performance & backup with drive data, for any degradations before implementing global change.


Performance analysis - Monitoring Methodology

All Metrics Taken in Busy hourAverage at busy hour over two weeks is compared with 1, ie the blocking exists if there is on average one blocking event per day


Performance analysis - Call flow - RB allocation – Counters

8 -> VS.RadioBearerSetupSuccess - #1650 VS.RadioBearerSetupUnsuccess - #602

• Sub-Counter #0: timeout• Sub-Counter #1: RADIO_BEARER_SETUP_FAILURE• Sub-Counter #2: Any other failure causing a RB setup procedure to be unsuccessful. Seedetails under 'Triggering Event'.

RAB.FailEstab.CS - #2629 2631 PSRAB.FailEstab.CS.ULLoadRAB.FailEstab.CS.DLPwrRAB.FailEstab.CS.CodeStarvRAB.FailEstab.CS.RLFailOtherRAB.FailEstab.CS.RLFailNodeBErrRAB.FailEstab.CS.RLFailNodeBResourceRAB.FailEstab.CS.RLReconfigExpRAB.FailEstab.CS.RBSetupFailRAB.FailEstab.CS.RBSetupExp

1 -> VS.RadioBearerSetupRequest - #1652

2/3 -> VS.RadioBearerEstablishmentUnsuccess - #1629

4 -> VS.RadioLinkReconfPrepReq - #565 -> VS.RadioLinkReconfigurationPrepareSuccess - #50 VS.RadioLinkReconfigurationPrepareUnsuccess - #40

• Sub-Counter #0: RADIO_LINK_RECONFIGURATION_FAILURE• Sub-Counter #1: Timeout nbap• Sub-Counter #2: Rrm refusal• Sub-Counter #3: Iub Layer Congestion• Sub-Counter #4: NodeB (CEM) lack of L1 resources• Sub-Counter #5: Lack of Transport Identifier (CID or UDP Port) on the Iub• Sub-Counter #6: Lack of bandwidth on the Iub• Sub-Counter #7: INode refusal• Sub-Counter #8: NodeB out of order (No answer)

6 -> VS.RadioBearerSetupRequest - #1652

7 -> VS.RadioLinkReconfigurationCommit - #51 VS.RadioLinkReconfigurationCancel - #26


Performance analysis – Blocking phases, Bottlenecks

Blocking – phases Call admission Call reconfiguration Mobility

Bottlenecks: Air interface – power, codes, load Node B resources – CEM, CCM, Licensing Backhaul – Iub BW RNC – CPU

Blocking Cause:VS.RadioBearerEstablishmentUnsuccess - #1629

• Sub-Counter #0: invalid RAB parameters value• Sub-Counter #1: unavailable dl code resources• Sub-Counter #2: unavailable dl power resources• Sub-Counter #3: Unspecified• Sub-Counter #4: RL failure or RLC error• Sub-Counter #6: CAC RNC Processing resources• Sub-Counter #7: NodeB (CEM) lack of L1 resources• Sub-Counter #8: Lack of transport identifier on the Iu• Sub-Counter #9: Lack of bandwidth on the Iu• Sub-Counter #10: Lack of transport identifier on the Iur• Sub-Counter #11: Lack of bandwidth on the Iur• Sub-Counter #12: Lack of transport identifier on the Iub• Sub-Counter #13: Lack of bandwidth on the Iub


Performance analysis - RB allocation bottle neck Counters

1 -> VS.RadioBearerSetupRequest - #16522/3 -> VS.RadioBearerEstablishmentUnsuccess - #16294 -> VS.RadioLinkReconfPrepReq - #565 -> VS.RadioLinkReconfigurationPrepareSuccess - #50 VS.RadioLinkReconfigurationPrepareUnsuccess - #40

• Sub-Counter #0: RADIO_LINK_RECONFIGURATION_FAILURE• Sub-Counter #1: Timeout nbap• Sub-Counter #2: Rrm refusal• Sub-Counter #3: Iub Layer Congestion• Sub-Counter #4: NodeB (CEM) lack of L1 resources• Sub-Counter #5: Lack of Transport Identifier (CID or UDP Port) on the Iub• Sub-Counter #6: Lack of bandwidth on the Iub• Sub-Counter #7: INode refusal• Sub-Counter #8: NodeB out of order (No answer)

6 -> VS.RadioBearerSetupRequest - #16527 -> VS.RadioLinkReconfigurationCommit - #51 VS.RadioLinkReconfigurationCancel - #268 -> VS.RadioBearerSetupSuccess - #1650 VS.RadioBearerSetupUnsuccess - #602

• Sub-Counter #0: timeout• Sub-Counter #1: RADIO_BEARER_SETUP_FAILURE• Sub-Counter #2: Any other failure causing a RB setup procedure to be unsuccessful. Seedetails under 'Triggering Event'.

RAB.FailEstab.CS - #2629 2631 PSRAB.FailEstab.CS.ULLoadRAB.FailEstab.CS.DLPwrRAB.FailEstab.CS.CodeStarvRAB.FailEstab.CS.RLFailOtherRAB.FailEstab.CS.RLFailNodeBErrRAB.FailEstab.CS.RLFailNodeBResourceRAB.FailEstab.CS.RLReconfigExpRAB.FailEstab.CS.RBSetupFailRAB.FailEstab.CS.RBSetupExp


Metric Classification

1. Performance metricsAccessibility / Retainability

2. Mobility MetricsAvg no of RL per user / Soft handoff success rate / Inter freq / Inter RNC

3. Traffic metricsErlangs / Traffic in Mbytes

4. Quality metricsThroughput per sub / BLER


Drill down Analysis - Accessibility

Accessibility

< target

Identify Top N cells

Identify Worst period

RF Conditions

RRC Congestion

Alarm Correlation

High nb unspecified

Ctg

Qual-Air-Uplink RSSI (dBm)Qual-Air-Ec/No DistributionQual-Air-RSCP distribution

Cap-RRC-Congestion-DlCode rateCap-RRC-Cogestion-DlPower rateCap-RRC-Congestion-RSSI rateCap-RRC-Congestion-Quality rateCap-RRC-Congestion-Overload rateCap-RRC-Congestion-TimeoutCap-RRC-Congestion-ALCAPfailCap-RRC-Congestion-ManOvldCap-RRC-Congestion-NodeBPrbCap-RRC-Congestion – DCHCap-RRC-Congestion – CRNTICap-RL-SF128 Code Channel Usage

RRC RAB SCCP

Perf-CN-Iu SCCP Connection success rate CN

SCCP RNC analysis

Perf-RAB-RAB establishment success ratePer-fRRC-RRC establishment success rate (UE perspective)

RNC-AlarmsNode B alarmsCN Alarms


Drill down Analysis - Retainability

Retainability

< target



RF Conditions

Alarm Correlation

Mobility

Qual-Air-Uplink RSSI (dBm)Qual-Air-Ec/No DistributionQual-Air-RSCP distributionQual-Air-BLER-AMRQual-RL-SIRQual-Nb-Thermal noise

RL Analysis OAM

OAM Reasons


UE Prob

Qua-lRL-call drop RL

Mobility Success rates

RFO Traces

CORE

CORE Network issues

OutagesOverloadForced releases


Drill down Analysis - Traffic

Traffic

Metrics



RF Conditions

Alarm Correlation

RL Analysis HW

OAM Reasons


CORE

CORE Network issues


ThroughputTotal CallsIdle activityCall holding timesCall duration

RNC

RNC/RAB resources


Drill down Analysis - Quality

Quality

Metrics



RF Conditions

Alarm Correlation

RL Analysis HW

OAM Reasons


UE Prob

RFO Traces

CORE

CORE Network issues


UplinkDownlinkBLERNoise risePower usedEcNo distribution


UMTS RF Parameters:

RF Optimization may require the adjustment of various RF parameters. Some

of those have complex interactions with one another affecting the system in

terms of coverage, capacity and call quality. Therefore, it is important to

prioritize the parameters depending on their ability to improve performance

with minimal complexity and trade-offs.

Regarding their tuning occurrence the RF parameters can be classified into

three classes: Primary, Secondary and Fixed parameters.

Primary Parameters

These parameters may require frequent adjustments, often from one cell site

to another. These include:

Neighbour Lists

Antenna Parameter (antenna tilt, azimuth, height and type)

Pilot Channel Power


Secondary Parameters

The secondary parameters can be used for further fine-tuning, especially in

specific problem areas and include:

Handover parameters (inter + intra RAT)

Access parameters

Cell Selection / Re-selection parameters

HSDPA parameters

HSUPA parameters


Fixed Parameters

The fixed parameters are not typically adjusted during the RF Optimization.

Changing those parameters can create complex interactions in key system

performance such as coverage, capacity, voice quality, data throughput, etc.

The impact is not easily characterized or predictable, and can vary from

network to network or within a network. These parameters should be adjusted

only after consulting the subject matter experts, e.g. system engineering

(SAE). These parameters include:

Power Control parameters

Load Control parameters

Common Channel powers (e.g. AICH, P+SSCH, BCH)

Access parameters which are not part of the secondary parameters

Handover parameters that are not part of the secondary parameters


Tools used:

1) CPV (Cell Performance Viewer): This tool is used for basic KPI monitoring &

performance reporting tool. It has a client-server architecture:

CPV CLIENT: A user-friendly GUI to report on the RAN performance & capacity

history of the Telecom NZ CDMA network.

CPV SERVER: A SQL database containing configuration and performance data

based on regular Prospect CDMA reports

Sample reports available from CPV are as below:

UMTS Performance Report

UMTS Accessibility Troubleshooting Report

UMTS Retainability Troubleshooting Report


2) RFO (RF Optimizer) is used for Call trace analysis.


3) NPO: NPO (9359) offers a full range of tools for multi-standard QoS

Monitoring and radio network optimization facilities for UMTS and GSM

networks. NPO enables you to optimize using:

QoS analysis

Configuration

Parameters tuning

Availability and alarming.

4) WiPS (Alcatel Lucent 9352 Wireless Provisioning System): This tool is for

making audit and changes in the network. This tool is similar to ALU PRC

generator in GSM.


5) SPAT3G (System Performance Analysis Tool):

SPAT3G is a performance analysis tool used to quickly troubleshoot and

improve wireless network performance. The tool supports 2G/3G1X CDMA,

1xEV-DO, and UMTS technologies. SPAT3G enables effective and efficient

performance analysis by providing the user with intuitive analysis reports in

the form of tables, trends, and geographical maps. It is used to troubleshoot

and analyze the performance of a live network using data sources including

Service Measurements, Per Call Measurement Data (PCMD), ROP,

Translations, Neighbour list data (Handoff Matrix, Undeclared Neighbour List).

6) Actix: This is the drive test Post-Processing Tool used here in TNZ.


7) WQA (Wireless Quality Analyzer): This is a web based tool and is used for

neighbour analysis. WQA (Wireless Quality Analyser-an ex Nortel product) is

part of the UTRAN performance management portfolio(eg. NPO, RFO) for

performance monitoring, optimization and troubleshooting.


Key modules of WQA

• Neighbor Tuning Module (CTn)- Tune neighbor list based on 3G-2g handover,

softhandover, HSxPA, inter-frequency, ping-pong triggers, including handoff failure

analysis based on system wide call trace. Similar to UNL+Handoff Matrix in the SPO

space with the addition in HSxPA, ping pong and advanced interfrequency analysis

• Call Failure Trace Module(CFT-based on Ctg) - call trace reporting based on call

trace ‘snapshots’. Filters, with the option of drilling down to per mobile(IMSI)

analysis(daily granularity). More than 100 causes in CFT vs. 20 at Counter level.

Covers all types of failures in LCAP, NBAP, RANAP, RNSAP, RRC, RNC Internal

Causes,etc.

• Call Trace Analysis Module(CTx=Ctb/Ctg) - This feature allows customers to optimize

UTRAN sub system, mainly the radio aspects, without requirement of drive tests.

RSCP,Ec/No behaviour(radio coverage analysis). Distance based analysis.


8) A9155: (also known as 9155) It is Alcatel-Lucent’s re-branded version of

ATOLL. The 9155 working environment provides a comprehensive and

integrated set of tools and features that allow you to create and define your

radio-planning project in a single application.


Thank You

UMTS KPI-Optimisation & Tools

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