concept pm analysis and optimization

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Concept onGPRS Radio network Performance

Analysis and Optimization

(draft for discussion)Helmut Rau

ICM N PG NT NE A3

25.5.04



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GPRSKey Performance

Indicators

GPRSKey Performance

Indicators

GPRS radio network performance analysis + optimization

Embedding into PM concept according 3GPP TS 32.403

GPRS radio networkoptimization use casesand Key Performance

Indicators

GPRS RadioNetworkPlanning

goals

GPRS RadioNetwork Optimization

Goals

GPRS SBSperformance

Benchmarkinggoals

Problem Scenarios:Quantifiable indicatorsrelated to a goal

Measurementby

PM Counters

Measurement byNetwork internal

Tracing

Measurement byExternal testEquipment

Goals:What needs to beaccomplished

…..

Networkoperator

customer carecommunity

Measurement User Communities

Metrics:Measurements thatdetermine if a goal is beingachieved

…..

Equipment vendor developmentengineeringcommunity

Corrective actions:

Reconfigure radio network

Networkoperator traffic

engineeringcommunity



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What needs to be accomplished -> Optimization goals

GPRS radio network optimization Goals

User satisfaction goals- Service availability goals

- Data integrity goals (no loss of user data)

- Mainly important for streaming services (unconfirmed mode)

- Data throughput goals

- mainly important for ftp and HTTP services

- Goals on user data delay time

- mainly important for WAP service

Operator benefit goals

- Best utilization of available GPRS radio resources



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What needs to be accomplished -> Optimization goals

End-to-end GPRS QoS

Radio network

QoS contribution

MS

QoS contrib.Core network

QoS contribution

MS BTS BSC SGSN GGSN Internet

Abis Gb GiUm

Internet

QoS contrib.

Only when the radio network is well-configured the

required end-to-end QoS can be achieved

Due to the nature of a radio frequencies to be a scarce

and expensive resources the radio network is regard as

main bottleneck in the QoS fulfillment



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Radio network planning/optimization cyclesHigh level survey

Planningmethod

Radio network

RoutinePM data

assumptions• # subscribers• Traffic model

Radionetwork

parameters

KPIs Radio networkOptimization:• real subscriber QoS• real radio QoS• real radio resource utilization

Requirements• subscriber QoS• radio QoS

QoS Ok?

Tuning of planningmethod

Network features

updateassumptions

1

2

3

4

5

6

7

Phaseplanning

green fieldplanning

Optimizationmethod

introduction of new features

updateplanningdatabase

6

auxiliarydata



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GPRS radio network performance analysis + optimizationScope and limits of optimization

Takes place any time between two radio network planning cycles

Each network parameter configuration measure has limited impact:

- relevance on a single cell or on a cluster of cells

- No or well-known implication on the behavior and performance of other features-> example: configuration of dedicated PDCH increases the CS blocking rate

Can to a high degree be performed independently by regional authorities (regional

network operation centers)- low amount of mutual coordination might be necessary

Is performed within the frame of the pre-defined network features and serviceareas

Does not deal with significant growth of subscriber traffic compared to theassumptions from the previous planning step



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GPRS radio network performance analysis + optimizationProblem scenarios

-> typical deficiencies due to the nature of radio networks

Problem scenarios for GPRS radio network optimization

Problems

Goals

L a c k of r a d i or e s o u

r c e s

L o s s of r a d i o c ov er

a g e

L a c k of A b i s r e s o ur

c e s

L a c k of G b r e s o ur c

e s

L a c k of P P X U s

L ow

s i gn al s t r en g t h

Hi gh i n t er f er en c e

Hi gh s i gn al s t r en g t h f l u c t u a t i on

Hi gh i n t er f er en c ef l u c t u a t i on

F r e q u en t c el l r e s el e c t i on s

B uf f er ov er f l ow

P r e em p t i on b y C S c al l

L i v e- t i m e ex pi r y of p a c k e t s

Hi gh r e t r an s mi s s i onr a t e on

r a d i oi n t er f a c e

Un b al an c e d s h ar i n g of r a d i o

r e s o ur c e s b e t w e en

C S an d

( E ) GP R S t r af f i c

I n s uf f i c i en t ( E ) GP R

S l o a d

s h ar i n g b e t w e en c e

l l s

User Service availability x x x x x x

User data throughput x x x x x x x x xUser data delay time x x x x

User data integrity

(no loss of user data)

x x x x x x x x

Best operator benefit fromexisting radio resources

x x x x x x x x



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GPRS radio network performance analysis + optimizationProblem scenarios

-> typical deficiencies due to the nature of radio networks

Problem scenarios for GPRS radio network optimization Incompleteness of current problem scenario enumeration

- Currently not foreseeable, which additional problem scenarios maybecome important when the amount of GPRS traffic increases andwhen new GPRS services are offered (e.g. voice over IP, CS+PSDual Transmission Mode, normal/premium GPRS users)



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What are the adjusting-screws for optimization?

Radio coverage related items (1) Signal and interference level

- GPRS and EGPRS service is available in regions where CS is available

-> Coverage availability is the same for CS, GPRS and EGPRS

- The activation of the (E)GPRS coding schemes depend on signal level andinterference level

- It is recommended to assign (E)GPRS traffic only to the BCCH carrier - In case of growing data traffic an additional TCH carrier with 4/12 reuse should

be installed-> 4/12 reuse normally provides sufficient protection against interference

- 1/3 reuse with DMA (BR8) is only allowed for CS services

Radio capacity

- Lack of radio capacity impacts CS as well as packet traffic- Lack of radio capacity can be compensation by two measures:

- Expansion of existing BTSE sites by additional TRXes (frequencies)

- Installation of additional BTSE sites when no free frequency is available-> site acquisition and cabling needed-> operator might delay site installation until next planned network expansion



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Radio coverage related items (2) Antenna position, direction (beam and tilt) and maximum output power

- should be already optimized for CS independent from GPRS and EGPRS

Power control for (E)GPRS

- Until BR8 only for UL direction: reduced range for power control-> high coding schemes need high power level

- From BR8 power control for DL direction

Frequency hopping

- High (E)GPRS coding schemes better get along without frequency hopping-> (E)GPRS should be preferably assigned to dedicated TRXes (no hopping, 4/12 reuse)



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Radio resource management (RRM) related configuration parameters

Assign GPRS to the best TRXes- BCCH or TCH carrier with 4/12 reuse

Best share of radio resources between CS and PS

- configure shared and dedicated PDCHs

GPRS radio resource assignment/de-assignment:

- threshold for vertical allocation- scheduling weights of traffic types (QoS treatment)

- scheduling weight according MS priority

- parameters for queuing, preemption, …

Load balancing between cells

Adjust parameters for control of cell reselection Configure GPRS/EDGE specific adjacencies

- only possible in case of PCCCH

Configuration of enough bandwidth on Abis and Gb link

Configuration of enough PPXUs



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Which configuration parameters need not be modified- Protocol counters and timers for Abis and Gb interface

- Network feature related timers and thresholds not related to RRM

- thresholds for coding scheme selection

- thresholds for cell reselection

- thresholds for adjustment of Gb flow control

- timers for delayed TBF release (br7 only DL direction)- RLC/MAC window size

- RLC/MAC polling period,

- PFC release timer, …

- Configuration of BSC/PCU/BTS internal features

- PDCH release timer, …

Re-configuration might be appropriate in exceptional situations- to be analyzed on project level (no general concept needed)



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Use cases

Use cases for radio network analysis and optimization

A use case deals with the detection and compensation of a problem A use case is triggered by an initial problem indication

- BSC/PCU standard PM counters: thresholds exceeded

- Standard SGSN PM counters: thresholds exceeded (indicators for radio problems)

- User complaints from certain areas

- Routine test drives: bad end-to-end QoS

A use case ends with a proposal how to compensate a problem: Modification of radio network related parameters

- One or more proposals together with their implications (benefit, dependencies)

Suggestion to compensate the QoS deficiency within the next scheduled radionetwork planning activity

- QoS deficiency cannot (or only partially) be compensated within the scope of radio

network optimization, causes might be-> amount of subscriber traffic far beyond initial expectations-> severe coverage / interference problems

Suggestion that the cause of the QoS deficiency is outside the radio network

- MS, core network, internet



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“which indicators disclose radio network problems” -> KPIs

Key performance indicators (KPIs) Observable indicators which disclose the degree of QoS fulfillment

For each problem scenario a set of KPIs will be assigned

During the execution of a use case KPI evaluations can take place severaltimes:

- Increasing level of details on the network performance by subsequent KPI

evaluation

Each KPI has a “bad QoS” threshold, which can easily be checked duringnetwork analysis (or which can serve as a trigger for the invocation of network analysis)

- KPI thresholds depend on the network operators emphasis on GPRS

Different transmission layers can be observed by KPIs KPIs for the observation of the packet transmission on application layer

KPIs for the observation of the packet transmission on radio layer

KPIs for the observation of the cooperation between application and radiolayer



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Goal: No doubts about the intension of the KPI

Which transmission property is of interest

- Throughput / Delay / service availability / Which transmission layers is of interest

- RLC/MAC, LLC, BSSGP, TCP/IP, ftp, WAP, ….

Which type of object (or area) is of interest- Throughput per cell / Throughput per BSC

Which type of transmission “session” is of interest - TBF life time , PFC life time , file transfer duration , duration of a WAP session, duration

of a PTP context activation, …

Additional characterization of the transmission properties to be observed:Characterization of throughput (as example, list not complete):

- Cumulated throughput of all data transmissions of the observed cell / Throughput of a

busy PDCH of the observed cell / Throughput a subscriber experienced during a

transmission session within the observed cell

- Establishment/start phase of transmission (e.g. ftp) included in throughput calculation or

excluded (higher throughput result in latter case)

- Average throughput / Minimum throughput / Peak throughput / Constancy of throughput /

Nth percentile of throughput (each in combination with the other criteria)



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KPIs for observation of the radio transmission layer

End-to-end QoS

Radio network

-> Radio layer KPIs

MS Core network

MS BTS BSC SGSN GGSN Internet

Abis Gb GiUm

Internet

Causality between radio layer KPIs and end-to-end QoS

• Which radio layer KPIs have high significance for end-to-end QoS

fulfillment

• To which amount is the End-to-end QoS fulfillment decreased when

the radio load grows (e.g. user throughput during 50% radio load)



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KPIs for observation of the radio transmission layers

Benefits from radio layer related KPIs: KPIs can be based on the collection of performance data out of the radio network without

need for external measurement equipment

KPIs based on PM counters allow to some level of detail a continuous observation of the

whole radio network

- A KPI evaluation result may be used as trigger for network analysis

- KPIs are mainly used for localization of problem areas (regional, functional

containment) at the begin of a network analysis (root cause pre-analysis)

Radio layer performance analysis allows forecast on the end-to-end QoS

- Filtering of suspicious cells which need deeper analysis

Network operator requested radio layer KPIs Our customers frequently ask for certain (often PM counter based) KPIs without revealing

their concept of network analysis and optimization

- Vodafone: user throughput weighted by volume

- Cingular: LLC throughput per user per traffic class

An operator defined radio network KPI is useful when it allows to monitor a radio network

problem area related to end-to-end QoS for which no other KPIs exist.



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Survey on radio transmission layer related KPIs BR 7 KPIs based on PM counters

- various throughput KPIs on Abis (per cell , per CS, per subscriber)

- various throughput KPIs on Gb

- feature related KPIs (cell reselection, CS modification, TBF upgrade/downgrade)

- packet channel assignment (request, success, preemption)

- TBF drops

- … BR 8 KPIs based on PM counters

- traffic type utilization (QoS)

- cell reselection to UMTS

- Flow control



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Survey on still missing KPIs(earliest with BR9, based on counters and/or PCU internal tracing)

- Packet delay monitoring(source: KPI requested by Vodafone)

- GPRS radio level and quality monitoring

- GPRS monitoring of correlated quality and level indicators:-> e.g. CS versus C/I, CS versus RXLEV, retransmission rate versus C/I

- Besides the medium values also Nth-percentile and jitter observations are beneficial

-> Nth percentile on delay-> jitter on throughput(source: Cingular EDGE field trial, observations were based on interface traces)

- Monitoring of radio indicators not only on cell level but also on lower granularity:-> problem scenarios like cell boarder, indoor environment, high MS speed

- ….



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Radio network performance measurement chain

Standard radio networkmeasurements

KPI based on basic set of PM countersTrigger for network analysis

Extended radio network

measurements

KPI based on extended set of PM counters• Correlated Measurements• HO measurements

SCA evaluation

Cell TraceKPIs based on CTR evaluation

Test drive IMSI trace evaluationPossibly in addition end-to-end QoS tracing• Within TEMS• And/or on Abis interface• And/or on Gb interface

Optimization proposals

During the execution of the radio network performance analysis use case subsequent

measurements of increasing level of detail may be started and evaluated

?

?

?

?

Root cause(pre) analysis



Final Root causeanalysis



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KPIs for observation of the application layers (end-to-end)

Properties of application layer related KPIs:

Restrictions of BSC/PCU internal measurements methods- Application layers cannot be recorded by BSC/PCU internal tracing due to high

amount of data

- Application layers can be observed by BSC/PCU PM counters only to minor degree:-> observations related to Packet Flow Context (PFC) activation

(PFC live time may under certain conditions correspond to PDP contextactivation time)

BSC/PCU external measurement methods

- Abis / Gb protocol tester traces-> traces also allow to evaluate the cooperation between radio and application layers

- SGSN/GGSN PM counters-> SGSN PM counters are per cell and can thus be related to the BSC/PCU counters-> GGSN PM counters have no cell relation

- SGSN CDRs (Call Data Records for charging)-> evaluation on next slide

Observation of application layer behavior normally will be started only whenstandard radio network related KPIs exceed certain thresholds

- Detailed observation of certain suspicious cells

- Detailed observation of certain problem areas (e.g. indoor, cell boarder)



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Observation of the application layers by SGSN CDRs

Usage of SGSN Call Data Records Subscriber charging

Statistical evaluation for marketing purposes

Properties of SGSN Call Data Records A CDR records the data transmission volume during PDP context activation

A CDR records contains the serving cell at the time of PDP context activation

Cell reselections are not recorded

Possible benefits of CDRs for radio network performance analysis Low benefit, since continuous tracing of serving cell identity is missing

- in case of low throughput indicated by a CDR the possible problem area cannot befixed

- No correlation between CDRs and BSC/PCU PM counters or traces



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Interaction between end-to-end and segment analysis

Standard end-to-end QoSmonitoring

Standard end-to-end QoS observations• GSN PM counters (end-to-end QoS related)

• Routine test drives with TEMS-> trigger for radio + core network analysis (use case)

Cell Trace

Radio network IMSI trace

Optimization Proposals

Standard and extended radionetwork measurements

GSN segment measurements

DetailedGSN analysis

?

? Final problem localization(Route cause analysis)

Problem (pre) localization-> Radio or core or both (interaction)



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Useful documents

Cingular EDGE field trial result PCU KPIs, SGSN KPIs, interface tracing, BSC/PCU database configuration

Cingular MaxCap trial (Siemens USA) KPIs for CS, BSC configuration parameters

Radio Network performance report, UMC / Ukraine (MSP6) CS and GPRS optimization (analysis only discovered lack of radio resources)

Analysis and optimization of the (E)GPRS RLC protocol by simulations and measurements (PG R SE +ST) BSC/PCU database configuration, scope on RLC/MAC tuning

Siemens Base Station (SBS), BSC Database Parameter Description(PG SI BR7.0 – DRAFT, GPRS chapter not yet finished) SBS db configuration parameters and their interdependencies Recommendations for GPRS/EDGE

related Parameter settings in BR7.0 (PG SI)

BSC/PCU database configuration: what should stay on default value / what can be tuned

GPRS – Network Optimization Service Description L1 (MSP6) High level Product and Service description

GSM Network Optimisation, Optimisation Handbook: Radio System , Planning Manual (PMN 0) Contains only CS, Not actualized since 2000

Optimization use cases, Principle content describing an optimization use case(PG NT A3, 2003)

GPRS Performance Recommendations for optimization, of the GPRS E2E performance, Focus: BSS andrelated Interfaces(PG R ST, Version: IUS 1.2, April 07, 2003. Further releases planned)

End-to-end performance benchmarking tests, End-to-end KPIs, External test equipment




Additionally needed documents

GPRS radio network optimization use case description

(PG NT NE) Separate document for each optimization use case

Including definitions of additional radio network related KPIs (as far as needed)-> high priority due to ongoing BR9 planning

Including interactions with end-to-end and GSN performance analysis-> low priority

Upgrade of existing BR7 SBS KPI document to BR8(PG NT NE + PG R SE) based on new BR8 GPRS (and CS) PM counters

Including additional KPIs based on BR7 counters(KPIs designed after release of BR7 KPI document)

concept pm analysis and optimization

Documents