KPI Optimisation Tools

7/28/2019 KPI Optimisation Tools

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UMTS KPI-Optimisationand Tools

Sanjay Kumar/Hemal Doshi


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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 Optimisationtechniques by means of Drill down analysis and all the UMTS Tools used

for the optimisation for TNZ network.


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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


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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.


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7/41All Rights Reserved Alcatel-Lucent 2008

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 ofKey

Performance Indicators (KPIs) 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 Quality

Call Mobility

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


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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.


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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.


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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 arent

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


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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 UEs 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.


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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


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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.


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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.


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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 handovers

Underlying system should provide continuous stable coverage

Idle 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.


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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 andCore Network.


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

traffic type (VoIP, Streaming, HTTP), user classes (different subscription levels), andavailable 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 overlap

Create clear dominant pilot coverage through antenna configuration tuning (tilt,azimuth) to avoid unnecessary handovers

Remove existing over shooters which create interference and possible instable radio

conditions

Minimize pilot pollution areas


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Call Flow WCDMA


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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


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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.


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Performance analysis - Call flow - RB allocation Counters

8 -> VS.RadioBearerSetupSuccess -

#1650

VS.RadioBearerSetupUnsuccess -

#602

Sub-Counter #0: timeout

Sub-Counter #1:

RADIO_BEARER_SETUP_FAILUR

E

Sub-Counter #2: Any other failure

causing a RB setup procedure to be

unsuccessful. See

details under 'Triggering Event'.

RAB.FailEstab.CS - #2629 2631 PSRAB.FailEstab.CS.ULLoad

RAB.FailEstab.CS.DLPwr

1 -> VS.RadioBearerSetupRequest - #16522/3 -> VS.RadioBearerEstablishmentUnsuccess - #1629

4 -> VS.RadioLinkReconfPrepReq - #56

5 -> 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.RadioBearerSetu

pRequest - #1652

7 -> VS.RadioLinkReconfigurationCommit - #51

VS.RadioLinkReconfigurationCancel - #26


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Performance analysis Blocking phases, Bottlenecks

Blocking phases Call admission

Call reconfiguration

MobilityBottlenecks:

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


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Performance analysis - RB allocation bottle neck Counters

1 -> VS.RadioBearerSetupRequest - #1652

2/3 -> VS.RadioBearerEstablishmentUnsuccess - #1629

4 -> VS.RadioLinkReconfPrepReq - #56

5 -> 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 - #26

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 PS

RAB.FailEstab.CS.ULLoad

RAB.FailEstab.CS.DLPwrRAB.FailEstab.CS.CodeStarvRAB.FailEstab.CS.RLFailOtherRAB.FailEstab.CS.RLFailNodeBErrRAB.FailEstab.CS.RLFailNodeBResourceRAB.FailEstab.CS.RLReconfigExpRAB.FailEstab.CS.RBSetupFailRAB.FailEstab.CS.RBSetupExp


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Metric Classification

1. Performance metrics

Accessibility / Retainability

2. Mobility Metrics

Avg no of RL per user / Soft handoff success rate / Inter freq / Inter RNC

3. Traffic metrics

Erlangs / Traffic in Mbytes

4. Quality metrics

Throughput per sub / BLER


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Drill down Analysis - Accessibility

Accessibility

< target

Identify Top Ncells

Identify Worstperiod

RFConditions

RRCCongestion

AlarmCorrelation

High nbunspecified

Ctg

Qual-Air-Uplink RSSI (dBm)Qual-Air-Ec/No Distribution

Qual-Air-RSCP distribution

Cap-RRC-Congestion-DlCode rateCap-RRC-Cogestion-DlPower rate

Cap-RRC-Congestion-RSSI rateCap-RRC-Congestion-Quality rateCap-RRC-Congestion-Overload rate

Cap-RRC-Congestion-TimeoutCap-RRC-Congestion-ALCAPfail

Cap-RRC-Congestion-ManOvldCap-RRC-Congestion-NodeBPrb

Cap-RRC-Congestion DCHCap-RRC-Congestion CRNTICap-RL-SF128 Code Channel Usage

RRC RAB SCCP

Perf-CN-Iu SCCP Connection success rate CN

SCCP RNCanalysis

Perf-RAB-RAB establishment success ratePer-fRRC-RRC establishment success rate (UEperspective)

RNC-AlarmsNode B alarms

CN Alarms


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Drill down Analysis - Traffic

Traffic

Metrics

Identify Top N

cells

Identify Worst

period

RF

Conditions

Alarm

Correlation

RL Analysis HW

OAM

Reasons

RNC-Alarms

Node B alarms

CN Alarms

CORE

CORE

Network

issues

Outages

Overload

Forced releases

Throughput

Total Calls

Idle activityCall holding times

Call duration

RNC

RNC/RAB

resources


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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


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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


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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:


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


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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 tooptimize 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.


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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.


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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 UTRANperformance management portfolio(eg. NPO, RFO) for performance monitoring,

optimization and troubleshooting.


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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 tracesnapshots. 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.


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