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10. KPI & Optimisation

Summary

GSM Network Planning Process

GSM Overview

Radio Propagation & Interference

Network Dimensioning

Network Characteristics KPI & Optimisation

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Parameter Planning

Parameter Plan (1) Handovers (2)

Location Areas (3)

Frequency Plan (4)

BCC Plan (5)

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Parameter Plan

Parameter planning means creating adefault set of BSS parameters

It is performed right before the networklaunch

Relevant BSS parameter for NWplanning

frequency transmit power definition of neighbouring cells definition of location areas

handover parameters power control parameters cell selection parameters

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10. KPI & Optimisation Handovers

Handover Criteria & Priority

1. Interference (UL or DL)

2. UL quality3. DL quality4. UL level5. DL level6. MS-BS distance (max or min)

7. Turn-around-corner MS8. Rapid field drop9. Fast/Slow-moving MS10. Better cell (Power budget or Umbrella)11. PC due to Lower quality thresholds (UL and DL)12. PC due to Lower level thresholds (UL and DL)13. PC due to Upper quality thresholds (UL and DL)14. PC due to Upper level thresholds (UL and DL)

Radio Resource HO

Imperativ

e HO

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10. KPI & Optimisation Location Areas

Location Area Design 1/2

Location updating

affects all mobiles innetwork

LocUp in idle modeLocUp after callcompletion

Location updatingcauses signalingand processing loadwithin the network

Avoid oscillatingLocUpdate

Trade-off betweenPaging loadand Location Updatesignaling

Location area 1

Location area 2

major road

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10. KPI & Optimisation Location Areas

Location Area Design 2/2

Different MSC cannot use the sameLAC.

Location areas are important input for transmission planners

should be planned as early as possible

Never define location area bordersalong major roads!

Dual band or microcellular networksrequire more attention on LAC planning

co-located DCS and GSM cells are definedto the same LAC

same MSC to avoid too much locationupdates which would cause very highSDCCH blockings

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Tighter re-use of

own frequenciesmore capacitymoreinterferences

Target to minimise

interferences at anacceptablecapacity level

First when acomplete area hasbeen finalised

Automaticfrequency planningtools

R

D

Frequency PlanBasics

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Do not use hexagon cell

patterns regular grids systematic

frequencyallocation

Use interference matrix

calculation calibrated

propagationmodels minimise total

interference innetwork

R

D

f2

f3

f4f5

f6

f7

f3

f4f5

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f2

f3

f4f5

f6f2

f3f4f5

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f7

f2

f3

f4f5

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f3

f4f5 f2

f3

f4f5

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Frequency PlanBest Method

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NCC = Network Colour Code

BCC = Base station Colour CodeBSIC = Base station Identity Code = NCC +BCC

For each mobile, BSIC and ARCFNidentify unambiguously a cell in thewhole network

BCC is made by 3 binary digits 8possible values

The BCC plan can be done manually

BCC PlanBasics

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Network Optimization

Network Optimization (1)

Performance Evaluation (2)

Optimization Process (3)

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Network Optimization

Improving network quality from asubscribers point of view

Improving network quality from anoperators point of view

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10. KPI & Optimisation Performance Evaluation

Basics

Network is under permanent changedetect problems and symptoms early!

OMC

field tests

customer complaints

Its far too latewhen customers

complain!

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10. KPI & Optimisation Performance Evaluation

With Drive Tests

Evaluate network performance from thesubscriber point of view

KPIs information DL quality, call success rate, handover

success rate, DL signal level not statistically as reliable as NMS

information

Added value of drive test measurement find out the geographical position of

problems like bad DL quality to look for apossible interference source in the area

compare the performance of different

networks (benchmarking) display the signal level on the digital mapsto individuate areas with lack of coverageeventually improve the propagation model

verify the neighbour list parameter plan

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Optimization Process

There are not strict processes for optimization because the activity isdriven by the network evolution

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10. KPI & Optimisation Optimization Process

Young Network Case

In a young network the primary targetis normally the coverage

In this phase usually there is a massiveuse of drive test measurement

check the signal and the performance of the competitors

GPS

NMSX

MMAC

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10. KPI & Optimisation Optimization Process

Mature Network Case

In a mature network the primary targets are quality

indicators drop call rate, average quality, handover failures

Important use the information from NMS a general view of the network performance

Drive test measurements are still used but not in a massive way in areas where new sites are on air where interference and similar problems are

pointed out by NMS data analysis

Drop Call Rate (%)

0

0.5

1

1.5

2

2.5

3

3.5

Mon Tue Wed Thu Fri Sat Sun Mon Tue Wed

Call Bids / 10000

Average

Busy Hour

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KPI

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KPI Definitions

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Indicators Coverage

Signal Strength -outdoors In building, In-Car penetration signal levels Uplink Voice Quality Downlink Voice Quality Call Drops Cell Power control

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10. KPI & Optimisation Indicators Capacity

Erlangs per Cell TCH success TCH assignment failures TCH Drop calls TCH Blocking Cell congestion Congestion Relief Usage BHCA against rated MSC limit mErl/subs. against rated MSC limit SMS/subs. Against MSC limit MM values(HO,LU,Paging) against limits Overload : Voice/Signalling/Processor

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10. KPI & Optimisation Indicators Quality

RxLev Handovers Call Drops Call Success Rate Call set up success rate Call completion rate Call set up time Voice quality(MOS) RxQual Echo

TCH success TCH assignment failures TCH Drop calls SDCCH traffic blocking SDCCH drop calls SDCCH Success rates

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Analysis - Typical SetupFailure Causes - Distribution

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Analysis - Typical DroppedCall Causes Distribution

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KPINetwork Health Statistics

We have considered a typical network with BSCs toanalyse the network performance. To undertake thisactivity stastics of atleast 2 weeks should be analysed.The key parameters to be considered are;

Call Success RateCall Setup Success Rate

Handover Success RateDropped Call RateSDCCH Blocking RateTCH Blocking Rate

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Customer sets a bench mark for these parameters as a measure of qualityof the network and expects the performance to be equal or better than

this. The typical value of the bench marks for each of the abovementioned parameters are as follows,

Call Success Rate - 98 %Call Setup Success rate - 98 %

Handover Success Rate - 98 %Dropped Call Rate - 1%

SDCCH Blocking Rate - 0.5 %TCH Blocking Rate - 2 %

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.& Optimisation

LETS START OPTIMIZATION

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& Optimisation Blocked Calls

Blocked Calls can occur due to : Access FailuresSDCCH CongestionSDCCH DropTCH Congestion

Trouble shooting cause :Use Layer 3 messages to analyze the causeDecode System Information Type 3 messages.

Note the parameter , max_retransmission ;

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& Optimisation

Blocked Call Analysis -

1 3

Channel Request Channel RequestRACH .

: Imm AssignmentRACHmax_retrans Service Request

NO RESPONSE FROM N/WACCESS FAILURE ! Signalling:

Signalling2

NO TCH ASSIGNMENTChannel Request Mobile Returns To Idle

RACH TCH BLOCKED !Imm Assign Reject

SDCCH BLOCKED !

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10. KPI

A F il

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& Optimisation Access Failure -Troubleshooting

Access Failure - Uplink Problem

Causes:

1. AGCH Overload at Base Station2. RACH Collisions3. MS out of Range4. Poor Uplink quality5. BTS Receiver Problem

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& Optimisation Blocked Call Analysis

SDCCH Congestion CauseLocation Updates

to be analysed with OMC statistics first.If high, determine the source to target cell ratioDrive around the suspected area in the Idle ModeConfigure Delta LAC < > Constant 0 alarms Optimize Location Updates

Interference Analyze OMC statistics on Idle Channel Interference Carry out Uplink Interference Measurements using Viper

Heavy TrafficVerify from OMC statistics SDCCH CongestionCarry Call Setup Time measurementsOptimize set up time if high, else modify channel configuration

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& Optimisation

Blocked Call

Solutions To Blocked Calls Optimize coverage

Optimize Cell loadingInterference managementChannel configurationsOptimize neighbors

TCH Blocked - Causes

Interference-- Verify Idle Channel Interference reports from OMC-- If suspected, carry out uplink interference measurements

Heavy Traffic-- Verify the TCH Holding time and no of attempts statistics from OMC-- During low traffic hours, Activate Cell barring in the cell-- Carry out Time slot testing , by setting Ignore Cell Barring.

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& Optimisation

Dropped CallTroubleshooting

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& Optimisation Drop Calls Analysis1 2

Channel Request Channel Request

Imm Assignment Imm Assignment

Service Request Service Request

Signalling SDCCH Signalling: :

Signalling SpeechTCH

RLT = 0 ; DROPS RLT = 0 ; DROPSSDCCH DROP ! TCH DROP !

3 SDCCH / TCH

Handover Command

Hand Access

Handover Failure

HANDOVER FAILURE DROP !

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& Optimisation Dropped Call Analysis

SDCCH Drops - CausesCoverageInterference & MultipathBTS performance

TCH Drops - CausesCoverageInterference & MultipathBTS performancePre-emption

Handover Failure - CausesThreshold parameters

Missing neighbors

Solutions to DroppedCalls

Optimize CoverageInterferenceManagementOptimize neighborsOptimize handover

parametersEffective FrequencyHoppingUse of DTX & Power control

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& Optimisation

SDCCH Drop - CoverageSDCCH Drop - Co- Channel InterferenceSDCCH Drop - Adjacent Channel InterferenceSDCCH Drop - Uplink Problem

TCH Drop - CoverageTCH Drop - Co-Channel InterferenceTCH Drop - Adjacent Channel InterferenceTCH Drop - Uplink ProblemHandover Failure

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10. KPI & O ti i ti

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& Optimisation

Speech Quality Parameters

RxQUAL : Measured on the midamble.Indicates poor speech quality due to radio interface impairments

FER : Measured on the basis of BFI ( Ping -Pong effect on speech )Preferred under Frequency Hopping situation

Audio holes : Blank period of speech, due to malfunctioning of Transcoder boards or PCM circuits.

Mean Opinion Score (MOS) : ITU standard for estimating speech quality.


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& Optimisation

Speech Quality Parameters

Mean Opinion Score

Criteria for Voice Quality : A set value x at which y percent of customers rate the voice quality at Circuit Merits(CM) 4 - 5.

MOS Quality Scale

5 Excellent ( speech perfectly understandable)

4 Good ( speech easily understandable, some noise)

3 Fair ( speech understandable with a slight effort ,occasional repetitions needed)

2 Poor ( speech understandable only withconsiderable effort , frequent repetitions needed)

1 Unsatisfactory ( speech not understandable)

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10. KPI & Optimisation Troubleshooting No

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& Optimisation Troubleshooting - NoHandover

Create a Handover PLAN

Total Attempted CallsTotal Dropped CallsTotal Blocked CallsRxQual FullRxLeve FullRLT Current ValueARFCNNeighbor Cell MeasurementsRR MessagePhone State

Weak Neighbors - Reported by Phone


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& Optimisation

CH 40 CH 35

CH 27

CH 88

CH 29

CH 35

CH 98

CH 72 BSIC23

BSIC 16

BSIC22

BSIC 75

BSIC 15

BSIC 21

BSIC57

BSIC 53

CH 25 BSIC17 PHONE REPORTS

CH RxQual RxLev27 1 -8035 -8540 -8325 -95

Frequency Re-use

'A' NET

'A' NET

'A' NET

'B' NET

'B' NET'B' NET

'B' NET

'B' NET

'B' NET

Channel 29 is not in the neighbour list !

BCH Analyzer : TOP N = 7Configure an Alarm for Missing Neighbor Subset BCH TOP N not -subset Value ARFCN

Missing NeighborsReal Time

10. KPI & Optimisation Troubleshooting Handover

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& Optimisation Troubleshooting - HandoverParameter Settings

Decide the Target Cell for handover in the Trouble SpotFilter the Handover.txt file on Handover Attempts ( before AND after numbers)Filter again on Neighbor ARFCN = Target Cell ARFCNCreate another column as HO_Margin , with Delta for Neighbor_Level to RxLevPlot this on the MAP and see whether Handover Margin can be reduced to

improve quality OR increased to avoid Ping-Pong effectsIf handover margin settings are proper, and still handover is not occurring thenit could be a problem with Handover decision and processing parameters at theBSC.


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& Optimisation Troubleshooting - Uplink Interference

Uplink Interference can be due to:

Mobiles in reuse and adjacent channel cellsExternal sources

Interference due to Mobiles will be bursty and intermittent.The behavior and its effect on quality will be time dependent.

More interference during heavy traffic hours.Interference from external sources can be continous or alsotime dependent if the source is not continously ON.

Uplink Interference measurement needs long term monitoring ,collection of data, processing the data and estimating theprobability of interference , and also estimating the source.


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& Optimisation

Optimization for Interference

After drive test - Co-Channel benchmarking, we know whichcells are generating severe co-channel problem

We also know by decoding BSIC , the interefering sourceFollowing processes could be adopted to optimize

interference---- Power Control---- Antenna Tilts---- Frequency Reallocations---- Transmitter Tests

---- Mobile dispatch inspection---- Space Diversity---- Frequency Hopping /DTX


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& Optimisation

Antenna Tilts

x

6 km 1 km

A M N

50m

Point x is having problem of C/I from Cell MEstimate the C/I improvement required at Point x.Refer to the Antenna Vertical Pattern, and calculate the tilting angle requiredExample : To get an improvement of 3 dB , a tilt of 10 degrees is required.

Tilting of Antenna in certain cases may reduce coverage also.Tilting of Antenna should be done after proper study.

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& Opt sat o

DRT & Queuing


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p

Directed Retry (DR)

DR used to avoid the loss of a call in call-setup if the accessed cell is congested When no TCH is available in serving cell, TCH can be allocated in an adjacent cell (SDCCH TCHHO) Mobile Originated (MOC) and Mobile Terminated (MTC) Calls Target cell entry based on DR Method;

Method 0 - RxLevAccessMin Method 1 - drThreshold

Imperative Handover (only equation 1) Candidates ranked based on radio properties. Steps through candidates (if congested) until MaxTimeLimitDR expires

Queuing can take place in source cell, not in target cell.

Time

AssignmentRequest

minTimeLimitDR

maxTimeLimitDR

DR not allowed : improves the reliability ofthe measurements of adjacent cells and gives thequeuing process timeDR allowed

SDCCHTCH

congested


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p

Directed Retry

macro cell

micro cells

DR

congestion

DRcongestion


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p

Intelligent Directed Retry

congestion

macro cell (GSMcell)

micro cells(MCN cells)

MCNsubscriber

IDR

GSMsubscriber

congestion

macro cell (GSM cell)

micro cells(MCN cells)

DR

NOKIA TELECOMMUNICATIONS

Based on Directed Retry : Target Cell selectiondepends on Classmark of the MS or MS Priority Adjacent Cell Type

Subscribers Classified in GSM or MCN Based on Classmark ( bitmap in BSC associates

classmarks to GSM / MCN ) Based on MS Priority ( bitmap in BSC

associates MS Priorities to GSM / MCN ) Criterion defined in the BSC

DR and IDR enabled / disabled independently on cellbasis.

ValueParametersIdrUsed Yes/NoCellType GSM / MCNAdjCellType GSM / MCN

No TCH Available on Accessed Cell GSM or MCN subscriber ?

MCN => IDR in Use in the Cell ? Yes => Directed Retry Only to MCNCells No => Reject Call

GSM => DR in Use in the Cell ?Yes => Directed Retry (any Cell) No => Reject Call


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p

Queuing of Radio Resources

Used to avoid rejecting call set-up or HO attempt by waiting for the release of asuitable TCH

Queuing Environment queuing is a BTS specific procedure (controlled by the BSC) each BTS has a queue of its own individual queue parameters and queue management for each BTS call attempts and handovers in the same queue the maximum queue length is relative to the number of traffic channels the maximum queuing time can be set individually for both queue types the queuing can be de-activated by setting queuing time or queue length to

zero different priorities according to queue type (call/HO) and/or MS priority

Entering the queue:

The queue is entered when there is no traffic channels available of requestedkind and if

queuing is allowed in the BTS queuing enabled in the assignment request from MSC queue is not full (of higher or equal priority requests)


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Prioritisation: The placement in the queue is determined by:

queue type (priority) call set-up handover attempt (non-urgent) urgent handover attempt

MS Priority level in the PIE element of Assignment Request or Handover Request time of entering the queue


Allocation of TCH When a TCH is released (in either channel release or TSL/TRX lock) the

queue is checked from top to bottom in order to find a queuer whoserequirements match with the released channel

If a suitable queued call is found the TCH is allocated to the queued call andthe queue is re-organised


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Leaving the Queue A queuer is removed from the queue when

No suitable channel is released within queuing time limit => timer expires Higher priority subscriber (queue type and/or MS priority) replaces a lower priority

queued entry when the queue is full The queuing TRX/TSL is blocked (call release) Queue size is reduced due to removing TRXs


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10. KPI & Optimisation Q i g f R di R

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Internal inter cell Handover Ranked list is produced by the Handover algorithm and passed to RR management Maximum sixteen cells as alternative target cells The best candidate with free traffic channel is selected If all BTSs in the list are congested

queuing possibility is checked in the candidates according to ranking

External inter cell Handover The BTS identified by the MSC in a HANDOVER_REQUEST message is used asqueuing target

Averaging and processing for HO continues during queuing

The timers for hoPeriodPBGT or hoPeriodUmbrella are stopped duringqueuing

Queuing of Radio ResourcesQueuing and Handover

10. KPI & Optimisation Queuing of Radio Resources

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Directed retry and queuing are parallel procedures

When the queuing and DR processes are both active for a call; If MaxTimelImitDR expires without any DR attempt, the queuing will be terminated

even if the queuing timer(s) have not elapsed If a TCH is released in the serving cell during the period when DR is not

allowed/allowed, DR process is terminated

Queuing of Radio ResourcesQueuing and Directed Retry (DR)

10. KPI & Optimisation Queuing of Radio Resources

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maxQueueLength 0 ... 100 %

timeLimitCall 0 ... 15 (s)timeLimitHandover 0 ... 10 (s)

msPriorityUsedInQueuing Yes / NoqueuePriorityUsed Yes / No

queuingPriorityCall 1 ... 14queuingPriorityHandover 1 ... 14queuingPriorityNonUrgentHO 1 14

Parameters Values

Queuing of Radio ResourcesQueuing Parameters


D d C ll C t l

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Dropped Call Control

radioLinkTimeout 4 ... 64 SACCHcallReestablishmentAllowed Yes/No

Parameters Values

Radio Link Timeout

A counter is initialised at the value of theradioLinkTimeout

When SACCH is not correctly receivedCounter decremented by 1

When SACCH correctly receivedCounter incremented by 2

When counter reaches 0 call is released

Same behaviour UL and DL

Call re-establishment

In case of a Radio Link Failure(radioLinkTimeout) within 20 seconds.

Measurements averaged over 5 secondsfor

serving Cell BCCHadjacent Cell BCCHs

Strongest is consideredBCCH data decoded (cell selectionparam.)

If: C1 greater than 0, Cell not barredCell belong to selected PLMN,Call re-establishment allowed

Call re-establishment attempted


SDCCH ASSIGNMENT

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SDCCH ASSIGNMENT

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