10. kpi & optimisation

10. KPI & Optimisation


Netwing 2008 – NWT

Summary

• GSM Network Planning Process

• GSM Overview

• Radio Propagation & Interference

• Network Dimensioning

• Network Characteristics

• KPI & Optimisation




Parameter Planning

• Parameter Plan (1)

• Handovers (2)

• Location Areas (3)

• Frequency Plan (4)

•BCC Plan (5)




Parameter Plan

• Parameter planning means creating a default set of BSS parameters

• It is performed right before the network launch

• Relevant BSS parameter for NW planning

• frequency• transmit power• definition of neighbouring cells• definition of location areas• handover parameters• power control parameters• cell selection parameters




HandoversHandover Criteria & Priority

1. Interference (UL or DL)

2. UL quality

3. DL quality

4. UL level

5. DL level

6. MS-BS distance (max or min)

7. Turn-around-corner MS

8. Rapid field drop

9. Fast/Slow-moving MS

10.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

Imperative HO




Location AreasLocation Area Design 1/2

• Location updating affects all mobiles in network

•LocUp in idle mode•LocUp after call completion

• Location updating causes signaling and processing load within the network

• Avoid oscillating LocUpdate

• Trade-off between Paging loadand Location Update signaling

Location area 1

Location area 2

major road




Location AreasLocation Area Design 2/2

• Different MSC cannot use the same LAC.

• Location areas are important input for transmission planners

• should be planned as early as possible

• Never define location area borders along major roads!

• Dual band or microcellular networks require more attention on LAC planning

• co-located DCS and GSM cells are defined to the same LAC

• same MSC to avoid too much location updates which would cause very high SDCCH blockings




• Tighter re-use of own frequencies more capacity more

interferences

• Target• to minimise

interferences at an acceptable capacity level

• First when a complete area has been finalised

• Automatic frequency planning tools

R

D

Frequency PlanBasics




• Do not use• hexagon cell

patterns• regular grids• systematic

frequency allocation

• Use• interference

matrix calculation

• calibrated propagation models

• minimise total interference in network

R

D

f2

f3

f4f5

f6

f7

f3

f4f5

f6

f2

f3

f4f5

f6f2

f3

f4f5

f6

f7

f2

f3

f4f5

f7

f2

f3

f4f5f2

f3

f4f5

f6

f7

Frequency PlanBest Method




Frequency PlanMultiple Re-Use-Factor

• Capacity increase with multiple RuFs

• e.g. network with 300 cells• bandwidth : 8 MHz (40 radio channels)

• Single RuF =12• NW capacity = 40/12 * 300 = 1000

TRX

• Multiple RuF• BCCH layer: re-use =14,

(14 frq.)• normal TCH: re-use =10,

(20 frq.)• tight TCH layer: re-use = 6, (6 frq.)• NW cap. = (1 +2 +1)* 300 = 1200

TRX




NCC = Network Colour CodeBCC = Base station Colour CodeBSIC = Base station Identity Code =

NCC + BCC

• For each mobile, BSIC and ARCFN identify unambiguously a cell in the whole network

• BCC is made by 3 binary digits 8 possible values

• The BCC plan can be done manually

BCC PlanBasics




Network Optimization

• Network Optimization (1)

• Performance Evaluation (2)

• Optimization Process (3)




Network Optimization

• Improving network quality from a subscribers point of view

• Improving network quality from an operators point of view




Performance EvaluationBasics

• Network is under permanent change detect problems and symptoms early!

OMC

field tests

customer complaints

It´s far too latewhen customers

complain!




Performance EvaluationKey Performance Indicators

• KPIs are figures used to evaluate Network performance

• post processing of NMS data or • drive test measurements data

• Usually one short term target and one long term target

• check the network evolution and which targets are achieved

• KPIs calculated with NMS data• network performance on the operator

side.

• KPIs from drive test • performance on the subscribers side

• Usually turn key projects are evaluated according to some predefined KPIs figures like drop call rate




Performance EvaluationWith NMS

• The most reliable KPIs to evaluate the network performance with NMS are:

• SDCCH and TCH Block• Blocking percentage [%]• Drop call rate [%]• Handover failure and/or success rate• Call setup success rate • Average quality DL and UL

• The targets are always defined by the customer but the following figures can be considered as satisfactory results:

Item Target Lowest acceptable

Dropped calls <2 % 4 %

Handover success >98 % 96 %

Good Qual samples (0..5) >98 %95 %




Performance EvaluationWith Drive Tests

• Evaluate network performance from the subscriber 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 a possible interference source in the area

• compare the performance of different networks (benchmarking)

• display the signal level on the digital maps to individuate areas with lack of coverage eventually improve the propagation model

• verify the neighbour list parameter plan




Optimization Process

• There are not strict processes for optimization because the activity is driven by the network evolution




Optimization ProcessYoung Network Case

• In a young network the primary target is normally the coverage

• In this phase usually there is a massive use of drive test measurement

• check the signal and • the performance of the competitors

GPS

NMS X

MMAC




Optimization ProcessMature 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




KPI




KPI Definitions




Indicators – Coverage

• Signal Strength -outdoors

• In building, In-Car penetration signal levels

• Uplink Voice Quality

• Downlink Voice Quality

• Call Drops

• Cell Power control




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




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




Analysis - Typical Setup Failure Causes - Distribution




Analysis - Typical Dropped Call Causes Distribution




KPINetwork Health Statistics

We have considered a typical network with BSC’s to analyse the network performance. To undertake this activity stastics of atleast 2 weeks should be analysed. The key parameters to be considered are;

Call Success Rate Call Setup Success Rate Handover Success Rate

Dropped Call Rate SDCCH Blocking Rate

TCH Blocking Rate




Customer sets a bench mark for these parameters as a measure of quality of the network and expects the

performance to be equal or better than this. The typical value of the bench marks for each of the above mentioned

parameters are as follows,

Call Success Rate - 98 %Call Setup Success rate - 98 %Handover Success Rate - 98 %Dropped Call Rate - 0.5%

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




LET’S START OPTIMIZATIONLET’S START OPTIMIZATION




Blocked Calls

Blocked Calls can occur due to :•Access Failures•SDCCH Congestion•SDCCH Drop•TCH Congestion

Trouble shooting cause :•Use Layer 3 messages to analyze the cause•Decode System Information Type 3 messages.•Note the parameter , “max_retransmission” ; “CCCH CONF” and “BS_AG_BLKS_RES”




Blocked Call Analysis - L3 messages

1 3

Channel Request Channel RequestRACH .

: Imm AssignmentRACHmax_retrans Service Request

NO RESPONSE FROM N/WACCESS FAILURE ! Signalling

:Signalling

2NO TCH ASSIGNMENT

Channel Request Mobile Returns To IdleRACH TCH BLOCKED !

Imm Assign Reject

SDCCH BLOCKED !




Blocked Call - Cause troubleshooting

Access Failures- CCCH Overload at the Base Station

- Uplink Interference at the Base Station

- Low Rxlev at the Base Station

- Downlink Low Rxlev ( Coverage Hole )

- Downlink Interference

- Excess Cell Range




Access Failure - Troubleshooting

Access Failure - Uplink Problem

Causes:Causes:

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




Blocked Call Analysis

SDCCH Congestion Cause Location 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” alarmsOptimize Location Updates

InterferenceAnalyze OMC statistics on “ Idle Channel Interference”Carry out Uplink Interference Measurements using Viper

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




Blocked Call

Solutions To Blocked CallsOptimize coverageOptimize 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.




Dropped Call Troubleshooting




Drop Calls Analysis

1 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 !




Dropped Call Analysis

• SDCCH Drops - Causes•Coverage•Interference & Multipath•BTS performance

• TCH Drops - Causes•Coverage•Interference & Multipath•BTS performance•Pre-emption

• Handover Failure - Causes•Threshold parameters•Missing neighbors

• Solutions to Dropped Calls

•Optimize Coverage•Interference Management•Optimize neighbors•Optimize handover parameters•Effective Frequency Hopping•Use of DTX & Power control




•SDCCH Drop - Coverage•SDCCH Drop - Co- Channel Interference•SDCCH Drop - Adjacent Channel Interference•SDCCH Drop - Uplink Problem•TCH Drop - Coverage•TCH Drop - Co-Channel Interference•TCH Drop - Adjacent Channel Interference•TCH Drop - Uplink Problem•Handover Failure




Poor Quality

•Poor Speech Quality could be due to •Patchy Coverage ( holes)•No Target cell for Handover•Echo , Audio holes, Voice Clipping•Interference ---:

•Co-channel•Adjacent channel•External•Multipath•Noise




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.




Speech Quality Parameters

Mean Opinion Score

Criteria for Voice Quality : A set value “x” at which “y” percent of customersrate 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)




Troubleshooting Handover Problems




Troubleshooting - No Handover

Create a Handover PLAN

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

Weak Neighbors - Reported by Phone




Analyzing - No Handover

No Neighbor( very weak)




CH 40

CH 35

CH 27

CH 88

CH 29

CH 35

CH 98

CH 72BSIC 23

BSIC 16

BSIC 22

BSIC 75

BSIC 15

BSIC 21

BSIC 57

BSIC 53

CH 25BSIC 17PHONE 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 Neighbors

Real Time




Troubleshooting - Handover Parameter Settings

•Decide the Target Cell for handover in the Trouble Spot•Filter the Handover.txt file on Handover Attempts ( before AND after numbers)•Filter again on Neighbor ARFCN = Target Cell ARFCN•Create another column as HO_Margin , with Delta for Neighbor_Level to RxLev•Plot this on the MAP and see wether Handover Margin can be reduced to improve quality OR increased to avoid Ping-Pong effects•If handover margin settings are proper, and still handover is not occurring then it could be a problem with Handover decision and processing parameters at the BSC.




Troubleshooting - Uplink Interference

•Uplink Interference can be due to:• Mobiles in reuse and adjacent channel cells•External 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 also time dependent if the source is not continously ON.

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




Optimization for InterferenceOptimization for Interference

After drive test - Co-Channel benchmarking, we know which cells are generating severe co-channel problemWe 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




Antenna TiltsAntenna Tilts

x6 km 1 km

A

M N

50m

Point x is having problem of C/I from Cell M Estimate the C/I improvement required at Point x. Refer to the Antenna Vertical Pattern, and calculate the tilting angle required Example : 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.




Co-Channel OptimizationCo-Channel Optimization

Static Power Control

Antenna Tilting

Trade Off with EC/No

Frequency Reallocation

Implementing Features like Dynamic Power Control, DTX and Frequency Hopping




DRT & Queuing




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 TCH HO)• 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 of the measurements of adjacent cells and gives the queuing process timeDR allowed

SDCCHTCH

congested




Directed Retry parameters

Parameters Value

drInUse Yes / No

MinTimeLimitDR 0 … 14 sec.

MaxTimeLimitDR 1 … 15 sec.drMethod 0: (Improvement not in use)

1: (Threshold evaluation method)drThreshold -47 … -110 dBm




Directed Retry

macro cell

micro cells

DR

congestion

DRcongestion




Intelligent Directed Retry

congestion

macro cell (GSM cell)

micro cells (MCN cells)

MCN subscriber

IDR

GSM subscriber

congestion

macro cell (GSM cell)

micro cells (MCN cells)

DR

NOKIA TELECOMMUNICATIONS

• Based on Directed Retry : Target Cell selection depends 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 cell basis.

Value Parameters

IdrUsed Yes/No

CellType 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 MCN Cells • No => Reject Call

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

• No TCH Available on Accessed Cell• GSM or MCN subscriber ?

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

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




Queuing of Radio Resources

• Used to avoid rejecting call set-up or HO attempt by waiting for the release of a suitable 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 requested kind 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)




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 whose requirements match with the released channel

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




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 TRX’s





• Queuing reserves SDCCH

• SDCCH occupation for call setup 7 seconds.• If maximum queuing time for calls is 10 s• => in case of queuing 50-60 % more load on SDCCH / call attempt!!

• (2 TRXs cell) with Combined BCCH / SDCCH• If maximum queue is 50 % of TRX x 8 = 8 queuing positions

If there are 4 call attempts in queue, SDCCHs are fully booked no space for short messages or for location updates on SDCCH

cell is fully overloaded!!

• Queuing reserves SDCCH

• SDCCH occupation for call setup 7 seconds.• If maximum queuing time for calls is 10 s• => in case of queuing 50-60 % more load on SDCCH / call attempt!!

• (2 TRXs cell) with Combined BCCH / SDCCH• If maximum queue is 50 % of TRX x 8 = 8 queuing positions

If there are 4 call attempts in queue, SDCCHs are fully booked no space for short messages or for location updates on SDCCH

cell is fully overloaded!!





• 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

as queuing target

• Averaging and processing for HO continues during queuing

• The timers for hoPeriodPBGT or hoPeriodUmbrella are stopped during queuing

Queuing of Radio ResourcesQueuing and Handover




• 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)




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




Dropped Call Control

radioLinkTimeout 4 ... 64 SACCH

callReestablishmentAllowed Yes/No

Parameters Values

Radio Link Timeout

• A counter is initialised at the value of the radioLinkTimeout

• When SACCH is not correctly received

•Counter decremented by 1

• When SACCH correctly received Counter incremented by 2

•When counter reaches 0 call is released

• Same behaviour UL and DL

Radio Link Timeout

• A counter is initialised at the value of the radioLinkTimeout

• When SACCH is not correctly received

•Counter decremented by 1

• When SACCH correctly received Counter 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 seconds for

serving Cell BCCHadjacent Cell BCCHs

• Strongest is consideredBCCH data decoded (cell selection param.)

If: C1 greater than 0, Cell not barred

Cell belong to selected PLMN, Call re-establishment allowed

• Call re-establishment attempted

Call re-establishment

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

• Measurements averaged over 5 seconds for

serving Cell BCCHadjacent Cell BCCHs

• Strongest is consideredBCCH data decoded (cell selection param.)

If: C1 greater than 0, Cell not barred

Cell belong to selected PLMN, Call re-establishment allowed

• Call re-establishment attempted




SDCCH ASSIGNMENT

10. kpi & optimisation

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