npi training - accessibility

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50 pt

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NPI TrainingAccessibility

Top right corner for field-mark, customer or partner logotypes. See Best practice for example.

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Text 24 pt

Bullets level 2-520 pt

Limited Internal NPI Training - Accessibility 2005-09-202

Agenda

Objective Accessibility Time Plan Key Performance Indicators – KPIs Benchmark concept – NETQB Accessibility Definition Accessibility KPIs


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Objective

On completion of this section the attendants should be able to:

Understand the Accessibility Concept Have a good knowledge of the Accessibility KPIs Understand the impact of parameter settings and the radio

network configuration on Accessibility performance Be able to do an Accessibility Network Performance Audit

and provide high level recommendations Be able to identify and correct Accessibility performance

problems


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Accessibility – Time plan

Accessibility – 10 days

Day 1:– Objective– Key Performance Indicators – KPIs– Benchmark concept – NETQB– Accessibility Definition– Accessibility KPIs– Paging– Location Area Update


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Accessibility – Time plan

Day 2&3:– Random Access Failures– SDCCH Congestion– SDCCH Drop

Day 4&5:– TCH Assignment Failures– Start of Accessibility practical exercise

Day 6 to 10:– Accessibility practical exercise– Review of exercise accessibility reports


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Key Performance Indicators - KPIs

Key Performance Indicators (KPIs) are used to categorize the Network elements such as MSCs and BSCs.

The KPI values allow the operator to visually compare

their network with other networks, and also highlight areas that may require focusing for improvements.


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Key Performance Indicators - KPIs

KPI TOP 25% TOP 50% Below TOP 50%Paging Succes Rate (1st

+2nd

page) > 95.10 >= 93.24 < 93.24Location Update Success Rate > 98.23 >= 97.12 < 97.12

Random Access Failure > 0.27 >= 0.81 < 0.81SDCCH Time Congestion < 0.0026 <= 0.0114 > 0.0114

SDCCH Drop Rate < 0.66 <= 0.87 > 0.87TCH Assigment Failure > 0.22 >= 0.38 < 0.38

TCH Drop Rate < 0.84 <= 1.19 > 1.19Call Minutes Between Drop > 155.52 >= 106.34 < 106.34

Handover Success Rate > 98.66 >= 97.51 < 97.51SQI UL Bad < 0.75 <= 1.49 > 1.49

Accessibility

Retainability

Voice Quality


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Benchmark Concept - NETQB

In the Quality Benchmark report performance from an operator’s radio network individual nodes (BSCs and MSCs) are compared and rated in relation to world references from Ericsson Global Benchmarking database.

Ericsson Benchmarking database is periodically updated with data from its installed basis, i.e. Ericsson MSCs and BSCs installed in mobile telephony networks around the world.

The KPI references are calculated on all BSCs in Ericsson global database carrying more than 600 Erlangs. The total number of BSCs in Ericsson benchmarking database in July 2005 was 1166. From those, 927 BSCs were selected with traffic above 600 Erl.


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Benchmark Concept - NETQB

Top 25%: Performance level of 25th percentile of all nodes in the world above 600 Erl. Nodes color-coded in green have world-best-in-class performance in the related indicator.

Top 50%: Performance level of 50th percentile of all nodes in the world above 600 Erl. Nodes color-coded in yellow have world-average performance in the related indicator. These nodes could be addressed when time and resources are available

Below Top 50%: Performance level below the 50h percentile of all nodes in the world above 600 Erl. Nodes color-coded in red have poor performance compared to the world references. Prioritization of improvement actions and Network Performance Improvement (NPI) services to these nodes are recommended.

KPI TOP 25% TOP 50% Below TOP 50%Paging Succes Rate (1st+2nd page) > 95.10 >= 93.24 < 93.24Location Update Success Rate > 98.23 >= 97.12 < 97.12Random Access Failure > 0.27 >= 0.81 < 0.81SDCCH Time Congestion < 0.0026 <= 0.0114 > 0.0114SDCCH Drop Rate < 0.66 <= 0.87 > 0.87TCH Assigment Failure > 0.22 >= 0.38 < 0.38TCH Drop Rate < 0.84 <= 1.19 > 1.19Call Minutes Between Drop > 155.52 >= 106.34 < 106.34Handover Success Rate > 98.66 >= 97.51 < 97.51SQI UL Bad < 0.75 <= 1.49 > 1.49


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Accessibility Definition

Service Accessibility is defined by ITU-T E.800 as:

“The ability of a service to be obtained, within specified tolerances and other given conditions, when requested by the user.”

Total number of successful calls set up/Total call accesses to the network


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Accessibility DefinitionCall to an MS

9805024

BSC

MSC/VLR

TRC

BTS

BTS

1

2

4

5

2

2

2

3

1

4

35

6

1. MSC/VLR sends paging command to all BSCs belonging to the location area (LA) where MS is located

2. BSC forwards the paging command to all BTSs in that LA, and the BTSs in their turn page the MS on the PCH

3. The MS responds to the BTS on the RACH and the BTS forwards the response to the BSC (forward to MSC)

4. The BSCs checks with the BTS if it has an SDCCH available and the BTS grants the MS an SDCCH by using the AGCH

5. The MS and the BTS signal on the SDCCH, measurement reports sent on SACCH are forwarded from the BTS to the BSC and once the signalling is done the BSC decides which TCH to use

6. TCH connection established between MS and BTS

Accessib ili ty


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Accessibility KPIs



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Paging



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Paging – Overview

All BSC in the MSC

BSC wt cells using

specified LAC

MSC

local

global

Paging message Cells with specified LAC

Paging command

Paging command

Paging Request

Paging Request


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Paging – Overview

MS can be paged by IMSI or TMSI Up to 4 Paging Requests per Paging block

MS only listens for paging at particular PCH sub-channel corresponding to its Paging Group

IMSI IMSI T T TTor

Note: T = TMSI

TTIMSIor


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Paging - Overview

9702690

Listeningto PCH

Listeningto PCH

1 53 4207 2 3 4 57 0 16

Sleep mode

7 0 1

Sleep modeMeasuring on

neighbors

Listeningto PCH Measuring on

neighbors

TDMAframes

BSF S CFC FC S

Paging group

F (FCCH): Frequency Correction ChannelS (SCH):Synchronization ChannelB (BCCH):Broadcast Control ChannelC (CCCH):Common Control Channel;Paging Channel (PCH) or Access Grant Channel (AGCH)

BCCH + CCCH(downlink)


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Paging - Overview

2nd page according to PAGREPGLOB

2nd page according to PAGREP1LA

Local Paging?

Paging in one LA. Wait for response:

PAGTIMEFRST1LA

Paging in MSC area. Wait for response:

PAGTIMEFRSTGLOB

yes no

VLR has an LAI (normal case) LAI is missing

Answer? Successful

Answer?Answer?

Paging in one LA. Wait for response: PAGTIMEREP1LA


PAGTIMEREPGLOB


PAGTIMEREPGLOB

No repeated paging

Successful

unsuccessful

Either TMSI/IMSI

1 2 3 0

IMSI used

Answer?

10

yes

yes yes

yes

no no

nono


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Paging – Overview

Upon receipt of a paging request message and if access to the network is allowed, the addressed MS shall initiate within 0.5 s the immediate assignment procedure. The establishment of the main signaling link is then initiated by use of an SABM with information field containing the PAGING RESPONSE message

Upon receipt of the PAGING RESPONSE message the network stops timer PAGTIMERFRST1LA (PAGTIMEFRSTGLOB).

If timer PAGTIMERFRST1LA (PAGTIMEFRSTGLOB) expires and a PAGING RESPONSE message has not been received, the network may repeat the paging request message and start timer PAGREP1LA (PAGREPGLOB).


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Paging - Overview

1

2

PAGING

PAGING COMMAND

PAGING REQUEST

MSC BSC BTS MS

A-interface

Processor Load too high?

YN

Paging queue full?

NY

Step NPAG1GLTOT or NPAG1LOTOT


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Paging - Overview

MSMSC BSC BTS

Channel RequestChannel Required

Establish Indication (Paging Resp.)SCCP Conn. Req (Paging Resp.)SCCP Conn. Conf.

SABM, Page Response

Channel Activation

Channel Activation Ack.

Immediate Assignment Command

Immediate Assignment

Paging Paging CommandPaging Request

UA

PCH

RACH

AGCH

SDCCH

SDCCH

Random Access

Step NPAGE1RESUCC or NPAGE2RESUCC


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Paging - Overview

BTS

BSC

MSC

LA 1

Paging

Paging

Paging

Removed due to overflow

Removed due to overflow

Removed due to time-out

Removed due to time-out

Monitor and detect congestion on paging channel


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Paging – Strategy

Recommended paging strategy is:– First page as local page the MS by TMSI– Second page as global page the MS by IMSI

Other strategies and constraints:– No second page: Less paging load, but risk more unsuccessful

paging– Second local page: Less paging load, risk more unsuccessful

paging– Second page by TMSI: Utilize less paging capacity, but some

pages maybe unsuccessful if TMSI of MS is wrong in VLR


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Paging – BSC Capacity

It is difficult to estimate BSC Paging Capacity Rule of thumb: BSC can accommodate 8500 Paging

Commands/sec To further optimize the BSC paging capacity, paging

queue overflow can be monitored with the following formula:

Where TOTCONPAG - step for every discarded paging message when paging queue is full

TOTPAG - paging messages received from MSC

%100TOTPAG

TOTCONPAGFAIL_PAG


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Paging – BTS Capacity

CCCH consists of 2 sub-channels for DL: PCH & AGCH AGCH used to allocate resource to MS during call setup PCH used to send paging request to MS Two types of Channel Configuration:

– Combined BCCH/SDCCH 3 CCCH blocks

– Non combined BCCH/SDCCH 9 CCCH blocks

AGCH can have dedicated blocks or work by stealing mode


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Paging – BTS Capacity

Incoming paging command are buffered in a queue One queue for each paging group When paging blocks are available, BTS will send these

paging commands as paging requests over the air interface

If queue is full, further incoming pages are discarded If queue at BTS for too long time, the page may be lost

since MSC do not receive any page response after timer expired


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Paging – Reducing Paging

IMSI attach/detach– If ATT = ON, MS will send attach/detach information to

MSC/VLR when it is powered on/off. – Decrease unnecessary paging to MS not connected to network– Constraint is higher SDCCH utilization

Periodic Registration– Avoid paging MS which lost coverage and not able to inform the

system that it is inactive– Timer T3212 specifies the period for periodic registration– Shorter T3212 leads to less paging, but higher utilization of

SDCCH


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Paging Capacity Impacting parameters

BCCHTYPE: NCOMB or COMB– Non-combined BCCH will give higher paging capacity than

combined BCCH

AGBLK: 0 – 1– AGBLK=0 gives higher paging capacity than AGBLK=1

MFRMS: 2 – 9– The lower value for MFRMS, the higher paging capacity due to

trunking efficiency– MFRMS setting is a trade off between battery consumption and

call set up time


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Paging – Optimization

Analyze the following issues that could be possible reasons for poor Paging Performance:

– Insufficient coverage– High interference– Non-optimum Paging Strategy– Non-optimum Paging parameter settings– Paging Congestion in MSc, BSC or BTS– De-activated or incorrect use of Paging features


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Paging – Optimization

The following actions can improve Paging Congestion:

MSC Paging Congestion– Increase SAE

BSC/BTS Paging Congestion– Check Paging Strategy– Increase number of Location Areas (This will increase SDCCH

load)– Set BCCHTYPE to NCOMB– Use TMSI paging requests– Ensure IMSI attach/detach is activated (ATT = yes)– Decrease T3212/BTDM (This will increase SDCCH load)


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Paging – OptimizationLow Paging Success

N o TM S I A ttach / D etach?

A ctiva te

W rong period ic loca tionupdating se tting?

C orrect T3212 in B S C ,B TD M & G T D M in M S C

S D C C HC ongestion?

Increase S D C C H channe l A daptive configura tion fea ture

P agingcongestion?

P lan m ore LA U se TM S I paging

TM S I pagingnot use?

A ctiva te

afte r no t period icregistra tion not use? A ctiva te

E N D

Yes

No

Yes

Yes

Yes

Yes

Yes

No

No

No

No

No

Im p lic it de tach


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Paging - KPI

Paging Success Rate is measured on MSc level and calculated with the following formula:

Paging Success Rate (1st+2nd page)

– Successful First and Second Pages of Total Number of First Pages

This is the End-User perceived Paging Success Rate, which is used as the Paging KPI.

[%]100*

1

NPAG1LOTOTNPAG1GLTOT

CNPAG2RESUCCNPAG1RESUC1

TOTALCELLS

TOTALCELLS


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Paging – Additional indicators

The following Paging indicator is useful when studying paging performance (MSc level):

Paging Success Rate (1st page)

Successful First of Total Number of First Pages

This is the formula showing the system behavior

[%]100*

1

NPAG1LOTOTNPAG1GLTOT

CNPAG1RESUC1

TOTALCELLS

TOTALCELLS


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Paging – STS Counter Summary

Paging Success STS counters– NPAG1GLTOT: The number of first global page attempts over A-Interface– NPAG1LOTOT: The number of first page attempts to a location area over

A-Interface– NPAG1RESUCC: The number of page responses to first page attempt on

A-interface– NPAGE2RESUCC: The number of page responses to repeated page over

A-interface

Paging Congestion STS counters– TOTPAG: Number of paging messages received from the MSC – TOTCONGPAG: Number of Paging messages discarded due to congestion– PAGPCHCONG: Number of discarded paging messages due to full paging

Queue. – PAGETOOOLD: Number of discarded paging messages due to old paging

messages.


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Paging – Parameter SummaryParameter Range Recommended Description

MFRMS 2-9 CCCHMultiframe

4 MF period betweentransmission ofpaging message tosame paging group

AGBLK 0-7 0 Reserved CCCHblocks for AGCH

BCCHTYPE COMB,COMBC,NCOMB

- Channel configuration

T3212 0-255 40 Time between periodregistration

ATT YES, NO YES IMSI Attach/ detachallowed

CRH 0-14 (steps of2) dB

4 Hysteresis used whenMS in idle crosses aLA area

GPRSNWMODE 0-3 2 (No Gs-Interface & noMPDCH used)

Whether or not Gs-interface & MPDCHused


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Paging – Parameter SummaryParameter Recommended Description

BTDM T3212 * 6 Implicit detach supervisionGTDM 6 min

Range: 0-255Extra guard time beforesubscriber set to detached

TDD OFF (default) Time inactive IMSI in VLRbefore it is removed

PAGTIMEFRST1LA 4sec (default)Range: 2-10sec

Time supervision for pageresponse for first page

PAGTIMEFRSTGLOB 4sec (default)Range: 2-10sec

Time supervision for pageresponse for first global page

PAGREP1LA 2 (recommend)Range: 0-3

How second page is sent

PAGEREPGLOB 0Range: 0-1

How global page is repeated

PAGTIMEREP1LA 7sec (default)Range: 2-10sec

Time supervision for pageresponse for second page

PAGTIMEREPGLOB 7sec (default)Range: 2-10sec

Time supervision for pageresponse for second globalpage


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Paging – Parameter Summary

Parameter Recommended DescriptionTMSIPAR 1 or 2 TMSI should be used or notTMSILAIMSC 0 (default)

Range: 0-1New TMSI to be allocated atchange or LAI withinMSC/VLR

SECPAGEPATH 1 (recommend)Range: 0-2

Define which interface 2nd

paging is sentTIMPAGINGM 9 sec

Range:2-20secTime supervision for 1st CSpaging sent over Gs interface

SGSN Parameter Parameter Recommended Description

T3133 5 secFixed

Time supervision for PSPaging


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Location Update

KPI TOP 25% TOP 50% Below TOP 50%

Location Update Success Rate > 98.23 >= 97.12 < 97.12Random Access Failure > 0.27 >= 0.81 < 0.81SDCCH Time Congestion < 0.0026 <= 0.0114 > 0.0114SDCCH Drop Rate < 0.66 <= 0.87 > 0.87TCH Assigment Failure > 0.22 >= 0.38 < 0.38TCH Drop Rate < 0.84 <= 1.19 > 1.19Call Minutes Between Drop > 155.52 >= 106.34 < 106.34Handover Success Rate > 98.66 >= 97.51 < 97.51SQI UL Bad < 0.75 <= 1.49 > 1.49




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Location Update – Overview

In Idle Mode the MS is powered on but not allocated a dedicated channel

The purpose of Idle Mode is for the MS to be able to access the system and be reached by the system any time and anywhere

Idle Mode behavior is managed by the MS Idle Mode is controlled by the parameters which the MS

receives on BCCH. Location Updates enable the to register its current location

to the network so that the network knows where to route incoming calls.


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9702628

Good enoughdownlink

To ensure good enough uplink

C1=(received_signal_level-ACCMIN)-max(CCHPWR-P,0)

ACCMIN - minimum received signal in MS to allow access

CCHPWR - maximum MS power at access

P - maximum power output of MS according to its class

C1>0

Cell selection process


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9702629

C21 = C1+CRO-TO* q(PT-T); PT=31

C21 = C1-CRO PT=31

CRO - Cell reselection offset

TO - Temporary negativ offset

PT - Time for application of a temporary offset

T - Timer1 C2 is only supported by phase 2 mobiles

Cell reselection process

q(x) = 0, x <01, x 0


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9702630

• The serving cell becomes barred

• Repeated unsuccessfull access attempts(MAXRET)

• Downlink signalling failure

• C1<0 for serving cell more than 5s

• C2neighbour>C2serving(+CRH) more than 5s

Cell reselection process


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Cell Reselection Hysteresis (CRH) Receiving signal strength (RXLEV) hysteresis for required cell re-

selection over a location area border. Each change of location area requires a location update to be

performed, which increases signaling load. CRH is used in order to prevent ping-pong effects for cell selection

across location area borders If the CRH value is set too low, the fluctuations in signal strength may

lead to a ping-pong effect for location updating.This will cause an undesired increase in the signaling load on the SDCCH

If the parameter is set too high, the mobile may camp on the wrong cell (not the strongest one) for too long when entering a new location area.


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9702631

• PLMN not allowed

• No SIM card inserted

• Illegal MS

• IMSI unknown in HLR

• .....

• Emergency calls only

• Cell reselection as normal,but CRH is ignored

• No updating

Limited service state

Cell selection process


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Text 24 pt




9702632

• Normal - at change of Location area

• Periodic - according to T3212

• IMSI attach/detach, ATT

Location updating process


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Location Update – Strategy

Location Area Code (LAC) is part of Cell Global Identity Circuit Switched (CS) paging done based on LAC

Larger LA – Higher paging load– Less LAC update, lower SDCCH utilization

Smaller LA– Lower paging load– More LAC update, higher SDCCH utilization


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Location Area – Strategy

Location Area (LA) dimensioning strategies: Size of a LA must not exceed the maximum paging capacity for the BTS /

BSC In a rural area, it is easy to find LA border cells. But there’s no reason to

have a smaller LA than required General rule of thumb : 1 LAC per BSC If a BSC covers a large area with high traffic, consider splitting the LA. This

will reduce the paging load in BTS and BSC In larger cities, SDCCH load will be higher for LA border cells. If difficult is

experienced to find LA border cells and the BSC coverage area is small, several BSCs can share one LA

Define LA border at cells with low subscriber density

Good information is available in the Location Area Dimensioning Guideline


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Location Update – Optimization

Analyze the following issues that could be possible reasons for poor Location Update success rate:

– Insufficient coverage– High interference– Location Area borders not optimum– Low CRH Hysteresis– Short time for periodic registration (T3212)– Insufficient SAEs– SDCCH congestion


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Location Update – OptimizationLow Location Updating

Success

borderce ll?

R eallocate to another LA or M SC Increase C R H

Low C R HH ysteris is? Increase C R H

Bad LAD em ension ing?

R e-d im ension ing LA

Short perod icregistra tion?

C heck T3212 in BSC &BTD M in M SC

Interference? C heck frequency p lan Activa te rad io feature

Software F ileC ongestion?

C orrect se ttings for S AE 500 B lockM LU AP, M LC A P,M LV AP,M M M LR

SD C C HC ongestion?

Increase SD C C H channel Adaptive configura tion feature

Autom aticderegistra tion?

Activa te autom aticde-registra tion

EN D

Yes

No

Yes

Yes

Yes

Yes

Yes

Yes

Yes

No

No

No

No

No

No


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Text 24 pt



Location Area Update - KPI

Location Area Update Success Rate is calculated using the following formula:

Location Update Success Rate

– Successful Location Updates of Total Number of Location Updates

[%]100*1

NLOCNRGTOT NLOCOLDTOT

CNLOCNRGSUC CNLOCOLDSUC

1

TOTALCELLS

TOTALCELLS


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LA – STS Counter Summary

OBJECT TYPE: LOCAREAST Events are counted per Location Area

– NLAPAG1LOTOT = # of first page attempt to a LA– NLAPAG2LOTOT = # of repeated page attempt to a LA– NLAPAG1RESUCC = # of page response to first page to a

LA– NLAPAG2RESUCC = # of page response to repeated

page to a LA– NLAPAGERR = # of unsuccessful page response to

a LA


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Random Access






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Text 24 pt



Random Access – Overview

The measurements are done per cell for random access channels. For every cell there are counters registering the number of random

access attempts received in the BSC.

Random Accesses can be distributed into the following types: MS Originated RA Call Re-establishment Emergency Calls Answer to Paging All Other Cases

– IMSI Attach/Detach– Location Updates– Period Registration


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The failed random access counter (RAACCFA) is incremented when an access attempt is failed.

There is also a counter for all accepted random accesses (CNROCNT) that means all except failed random access.

A failed random access burst does not necessarily lead to a call setup failure, as the MS sends many RA bursts each time it tries to connect to the network. This counter always incremented in an accepted random access.


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MSMSC BSC BTSChannel Request

Channel Required

1

2

3

Immediate Assignment RejectY

4 Channel Activation

5n6


Channel ActivationChannel Activation Ack.

6n

Chan. Neg. Ack.

Chan. Neg. Ack.Immediate Assignment

Establish IndicationSCCP Conn. ReqSCCP Conn. Conf.

SABM, UA

5

N

Too high TA ?Wrong Cause Code? SW file congestion?

Step CNROCNT or RAACCFA

Y

NToo high processor load ?

Step related RA counter

Free ch. Available?

YNActivation of channel successful?

Y

N

Random Access


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Text 24 pt



RA – Important parameters

ACCMIN– ACCMIN controls the access threshold to the system– Often the setting of ACCMIN is decided by non-technical reasons– A low setting of ACCMIN can cause RA failures, TCH drops and bad

quality– A high setting of ACCMIN can stop users accessing the system

resulting in lost revenue

MAXRET– MAXRET controls the number of Random Access retries allowed when

the MS accesses the system– A lower setting of MAXRET can improve RA performance but also

result in MSs not being able to access the system


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RA – Important parameters

CRH– Cell reselection hysteresis between different location areas– CRH can be adjusted for cells on LA borders to reduce the amount of

RA attempts

T3212– T3212 determines the time between periodic updates

ATT– ATT indicates if IMSI attach/detach is active

CB– CB indicates if a certain cell is barred for access


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Text 24 pt



Random Access – Optimization

Analyze the following issues that could be possible reasons for high Random Access failure rate:

– High interference– Lack of Coverage– High Timing Advance– Handover access burst mistaken as random access burst– Non-optimized parameter settings– Software Congestion (SAE)– Unbalanced link budget


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Text 24 pt



Random Access – OptimizationNot Approved Random Accesses

C heck B S IC a lloca tion

C heck frequency p lan

A ccess burst fromanother co-channel

ce ll

C heck ce ll param eter se tting

M A XTA toolow?

C heck S A E (C O FLP ,D B TS P :T A P =S A A C TIO N ;)

S oftware filecongestion?

C heck in te rfe rence

H igh no isefloor?

END

R educe in te rfe rence

Increase S A E

IncreaseM A XTA

C hange B S IC or

frequency p lan

C heck if unknown access code

YES

NO

NO

YES

NO

YES

NO

YES

C heck s ite loca tion

H igh loca tedsite?

C onsider tilting orlowering s ite

NO

YES


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Text 24 pt



Random Access – Optimization

f1

BSIC xxf1

BSIC xx

f2

BSIC yy

Random Access

Handover Access

Random Access

5 33-4 bits established cause4-5 bits random number 8

8 6

Info Parity

8 6

6

X 8 6

14 4

Tail Coded2 x 18

Final Burst Tail Synch Info

BSIC

Handover Access

Base Station Identity Code

Handover access burst mistaken as random access burst


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Text 24 pt



Random Access Failure - KPI

The Random Access Failure rate is calculated using the following formula:

Random Access Failure Rate

– Failed Random Accesses of Total Number of Random Access Attempts

[%]100*)(

1

1

PDRACRAACCFACNROCNT

RAACCFA

TOTALCELLS

TOTALCELLS


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Text 24 pt



Random Access Failure - KPI

RAACCFA

CNROCNT +PDRAC+ RAACCFA100 [%]

Number of accepted random

accesses (CS)

Packet Data Random Access per cell

)

Number of Failed random accesses

PS+CS

Number of Failed random accesses

PS+CS

TA>MAXTA -> RAACCFA incr

The Random Access Failure rate is calculated using the following formula:


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Text 24 pt



RA – Additional indicators The following Random Access indicators are useful when studying

RA performance:

– RA_LOA_REJ: Rejected Random Accesses due to load regulation of Total Number of Accepted Random Accesses

– RA_ANSWPAG: Random Accesses with Cause “Answer to Paging” of Total Number of Accepted Random Accesses

100

CNROCNT

RATRHFAREG

ERRATRHFAOTHALRATRHFAEMC

100

21

21

2

1

RACALRRACALRRACALRE

RAEMCALRAOTHERRAORDAT

RAORSPERAOSREQRAAPOPS

RAAPAGRAAPAGRAANPAG

RAAPOPSRAAPAG

RAAPAGRAANPAG


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RA – Additional indicators The following Random Access indicators are useful when studying RA

performance:

– RA_SERVICE: Mobile Originated RA (i.e. Random accesses caused by the MS user) of Total Number of Accepted RA

– RA_OTHER: RA with Cause “All Other Cases”, e.g. Location Updating, Detach, Attach, etc. of Total Number of Accepted RA

100

21

21

RACALRRACALRRACALRE



RAAPAGRAAPAGRAANPAG

RAORDATRAORSPERAOSREQ

100

21

21

RACALRRACALRRACALRE



RAAPAGRAAPAGRAANPAG

RAOTHER


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Text 24 pt



RA – Additional indicators The following Random Access indicators are useful when studying RA

performance:

– RA_EMERG: RA with Cause “Emergency Calls” of Total Number of Accepted Random Accesses

– RA_CALLREE: RA with Cause “Call Reestablishments”of Total Number of Accepted Random Accesses

–

100

21

21

RACALRRACALRRACALRE



RAAPAGRAAPAGRAANPAG

RAEMCAL

100

21

21

21

RACALRRACALRRACALRE



RAAPAGRAAPAGRAANPAG

RACALRRACALRRACALRE


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Text 24 pt



RA – Examples in ESPA

Random Access examples in ESPA


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Text 24 pt



SDCCH Congestion






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Text 24 pt



SDCCH Congestion – Overview

SDCCH Activities:

Mobility Management– Normal Location update– Periodic Registration– IMSI Attach / Detach

Connection Management– Call setup– SMS Point to Point– Fax Setup– Supplementary Services


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Channel Configuration:

Channel Configuration can be done as follow

– Combined BCCH/SDCCH on 1 TS (SDCCH/4)– Non-Combined BCCH and SDCCH on 2 TS (SDCCH/8)

Cell Broadcast Channel (CBCH)– The Cell Broadcast service provides the transmission of an SMS from

a message-handling centre to all MSs in the serving area of the BTS. – If the Cell Broadcast service is active in a cell, one signaling sub-

channel is replaced by one CBCH resulting in a SDCCH/7


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SDCCH Channel Allocation Profile (CHAP)

Channel Allocation is the feature that selects and allocates suitable channels when one or more channels are required

Channel Allocation Profile (CHAP) is the parameter that provides different channel allocation strategies

For SDCCH assignments, CHAP 8 prioritize new assignments as follows:

1. OL/SDCCH2. UL/SDCCH (if OL/SDCCH is congested)


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Text 24 pt




OL (CHGR 0)

UL (CHGR 1)TT T T T T T T

ST T T T T T T

TT T T T T T T

SB T T T T P P

A new assignment will use the SDCCH in OL first

OL (CHGR 0)

UL (CHGR 1)TT T T T T T T

ST T T T T T T

TT T T T T T T

SB T T T T P P

If the OL is congested, the SDCCH in UL will be used

NoteSDCCH congestion in the OL will increment, but this is not customer perceived since the SDCCH in UL will then be utilized

B

S

T

P

BCCH timeslot

SDCCH timeslot

TCH timeslot

PDCH timeslot


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Text 24 pt



SDCCH Capacity Features

Adaptive Configuration of Logical Channels (ACLC):

Dynamic dimensioning of Logical Channel (SDCCH) on demand

Adaptive configuration of logical channels will dynamically dimension the cell with more (or less) SDCCH/8s on demand.

Reduced SDCCH congestion Increase in Network Capacity SDCCH dimensioning becomes less critical


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Adaptive Configuration of Logical Channels (ACLC):

Number of intra-cell handovers might increase slightly The reason is that when a timeslot is to be reconfigured,

any ongoing traffic on that timeslot is handed over to other idle channels.

With OL/UL subcell structure in the site with normal and extended range cells, ACLC will place all additional SDCCH/8 in the UL.

In the OL/UL subcell structure UL need to have one SDCCH configured


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Text 24 pt




ACLC:

SDCCH Increase


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Text 24 pt




ACLC:

SDCCH Decrease


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Text 24 pt




Increased SDCCH Capacity (MAXNOSDCCHTRX):

Double number of SDCCH/8 per cell– 2 x no of TRX per cell– maximum 32 SDCCH/8 per cell

Increased signaling capacity

B S S

S S

S S

S S

TRX 1TRX 2

TRX 3TRX 4


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Flexible SDCCH Allocation:

Allocate SDCCH where most suitable in a cell

Up to 4 SDCCH/8 per TRX (impacts TRH dimensioning)

TRX HW mapping

Carrier (Air-Interface) mappingB

S S S S S S S S

B

S S S S

S S S S


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LAPD Concentration/Multiplexing Concentrates up to four LAPD signaling links upon one 64

kbit/s A-bis time slot The concentration ratio is the number of TRXs sharing the

same 64 kbit/s A-bis time slots for LAPD signaling. Max no of SDCCH/ TRX is limited by the use of LAPD

Concentration/Multiplexing



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LAPD Concentration



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Text 24 pt



Immediate Assignment on TCH Feature

When a connection is to be established, normally the immediate assignment procedure allocates a Stand alone Dedicated Control CHannel(SDCCH) for the call set-up signaling. This feature allows signaling to be done on a Traffic CHannel (TCH).

For speech/data connections, the operator can choose between three general strategies:

– Immediate assignment on TCH is not allowed. – Immediate assignment on TCH as last preference.– Immediate assignment on TCH as a first preference.



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SDCCH Dimensioning Strategy

GOS Approach: SDCCH should be dimensioned for better GOS compare to TCH.

Typical range is 0.5% - 1%. Immediate Assignment of TCH with “TCH as last option strategy” is

recommended. It is recommended to add SDCCH when 0.5 Erlang of signaling traffic

is carried by TCH. Half Rate penetration, usage of Extended Range cell and HSCSD

should be taken into consideration.

STS Approach: Accurate dimensioning is achieved by using STS cell statistics


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SDCCH Congestion Optimization

Analyze the following issues that could be possible reasons for SDCCH Congestion:

SDCCH Dimensioning Incorrect use of SDCCH capacity features such as

Adaptive Configuration of Logical channels TCH Congestion Location Areas not optimized SMS usage and Cell Broadcast channel SDCCH Availability


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The following recommendations will have a positive impact on SDCCH congestion

Try not to use combined BCCH/SDCCH (SDCCH/4) Use the optional SDCCH capacity features such as the Adaptive

Configuration of Logical Channel feature when available. Use Immediate Assignment on TCH, SDCCH first. For manual dimensioning, use STS cell statistics Configure one SDCCH on the BCCH carrier and the others on the

hopping layer (Non-BCCH) Use the Ericsson SDCCH Dimensioning guideline.


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The following issues are worth taking into account when analyzing SDCCH Congestion:

Use LAPD STS statistics to evaluate LAPD congestion and optimize the LAPD Concentration factor

Analyze border cells with a large amount of random access attempts resulting in SDCCH congestion.

– Use Random Access optimization to solve the SDCCH congestion

Take into account Timeslot priority when deciding where to configure SDCCH/8


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SDCCH Congestion OptimizationSDCCH Congestion

C heck s ite position

Location area

border?C hange Location

A rea Border

C heck and increaseC R H

C heck TC H tra ffic

TC HC ongestion?

C heck S M S activity

M any SM Sm essages?

E

C heck period icregistra tion

Too frequentregistra tion?

C heck H W ava ilab ilty

Lowava ilab ility?

See TC H & SD C C H

Availab ility

Add TC Hcapacity

R edim ension SD C C H

C hange registra tionin terva l tim ers

NO

YES

NO

NO

NO

YES

YES

YES

NO

YES

YES


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Text 24 pt



SDCCH Congestion OptimizationC heck channel configura tion

C om binedSD C C H ?

C heck tra ffic trend

Short te rmtra ffic growth?

C heck S D C C H d im ension ing

E

U nderd im ensionedSD C C H ?

C heck S D C C H m ean ho ld ing tim e

Long m ean ho ld ingtim e?

Is ce ll b roadcastused?

Avoid ce ll b roadcast ifpossib le

M ake channelnon-com bined

N o activity

C heck H W and num berof Fa lse Accesses

R edim ensionSD C C H

END

NO

NO

YES

YES

YES

YES

YES

NO

NO

NO

C heck A daptive configuration o flogica l channel and param eters

AC STATE off? Sw itch onYES


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SDCCH Congestion - KPI

The SDCCH Time Congestion is calculated using the following formula:

SDCCH Time Congestion

– SDCCH Time Congestion of Total Measurement Interval

[%]100*_

60*1

CELLSNBPERIOD

CTCONSUBCTCONGSTOTALCELLS


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SDCCH Congestion – STS Counter Summary

OBJECT TYPES: – CLSDCCH, CELLCONF

– CCALLS: Allocation attempt counters (incremented at signaling connection setup, at handover and at assignment).

– CCONGS: incremented when an allocation attempt fails due to no idle channels.

– CTCONGS: When the last available channel is allocated, the counter is incremented each second until a channel becomes idle.

– CTRALACC: Traffic level accumulator. – CNSCAN: Scanning counter. Incremented one by one at each time

CTRALACC is updated.– CNDROP: Number of abnormally terminated SDCCH connections.– CNUCHCNT: Number of SDCCH channels defined (adaptive

configuration of logical channels is not considered).


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SDCCH Congestion – STS Counter Summary

OBJECT TYPES: – CLSDCCH, CELLCONF

– CAVAACC: Every tenth second the number of available channels is scanned and the value is added to CAVAACC.

– CAVASSCAN: Scanning counter. Counts the number of times CAVAACC is updated.

– CMSESTAB: successful connection establishments on the SDCCH (incremented at signaling connection setup, at handover and at assignment).

– CNRELCONG: Incremented when a connection on SDCCH is released due to radio resource congestion, that is when there is congestion on TCH or congestion on transcoder resources (CNDROP is incremented at the same time).

– CONFATTC: Number of reconfiguration attempts from SDCCH to TCH.

– CONFATTT: Number of reconfiguration attempts from TCH to SDCCH.


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SDCCH Congestion – Examples in ESPA

SDCCH Congestion examples in ESPA


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Text 24 pt



SDCCH Drops






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Text 24 pt



SDCCH Drops – Overview

SDCCH Drops are classified into one of the following categories:

SDCCH Drops because of Timing Advance SDCCH Drops because of Low Signal Strength SDCCH Drops because of Bad Quality SDCCH Drops due to Other Reasons


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SDCCH Drops – Overview

MSMSC BSC BTSChannel Request

Channel Required

1

2

3

Immediate Assignment RejectY

4 Channel Activation

5n6


Channel ActivationChannel Activation Ack.

6n

Chan. Neg. Ack.

Chan. Neg. Ack.Immediate Assignment

Establish IndicationSCCP Conn. ReqSCCP Conn. Conf.

SABM, UA

Signaling Connection Set-up

5

N

Too high TA ?Wrong Cause Code?

Y

NToo high processor load ?

Step related RA counter

Free ch. Available?

YNActivation of channel successful?

Y

N

Random Access

Step CMSESTAB counter


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SDCCH Drops – OverviewAssignment: Assignment to Serving Cell

MSC BSC BTS MS

Assignment Request

N

Y

SABMUAEstablish Indication

Assignment Command

Assignment Complete

Assignment Compl.

Channel Activation

XChannel Act. Ack.

Channel Act. Neg. Ack.

RF Channel Release, old channel

RF Channel Release Ack.

Possible to assign channel?

If TCH Congestion CNRELCONG is stepped (time out).


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SDCCH Drops – OverviewConnection Release, Normal Disconnection

MSC BSC BTS MS

Clear Command

Channel ReleaseClear Complete

Deactivate SACCH

DISC

UARelease Indication

RF Channel Release

RF Channel Release Ack

SCCP Rel.

SCCP Rel. Ack.

1

Check Cause codes, if not HO successful or Call Control, step drop call counter, CNDROP


Slide title 40 pt


Text 24 pt



SDCCH Drops – OverviewConnection Release, Abnormal Disconnection

MSC BSC BTS

Clear Command

Channel Release

Clear CompleteDeactivate SACCH

DISC

UARelease Indication

RF Channel Release

RF Channel Release Ack

SCCP Rel.

SCCP Rel. Ack.

Clear Request Step drop call counter, CNDROP


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SDCCH Features

SDCCH Power Regulation

BTS and MS power regulation for the SDCCH can be activated on the system with the parameter SDCCHREG.

Power regulation will decrease the interference in tight re-use networks

SDCCH power regulation should not be used in coverage limited networks

Remember that DL power regulation is never performed on the BCCH carrier

For SDCCH power regulation the “Full” measurement set is always used


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Text 24 pt



SDCCH Features

Handover on the SDCCH:

SCHO switches on and off the possibility of performing handovers on the SDCCH. It is defined per cell. If SCHO is set to OFF, handover to as well as from that cell is inhibited on the SDCCH.

IBHOSICH switches on and off the possibility of making inter-BSC handover on SDCCH. It is defined per BSC.

IHOSICH switches intra-cell handover on SDCCH on/off. It is defined in the BSC.

SDCCH Handovers should not be used in coverage limited networks


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Text 24 pt



SDCCH Drop Optimization

Analyze the following issues that could be possible reasons for SDCCH Drops:

Low signal strength Interference Pathloss Imbalance between UL/DL High Timing Advance MS error or Subscriber behavior TCH Congestion Transmission Congestion (LAPD Concentration) Hardware or Transmission failures


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Text 24 pt



SDCCH Drop Optimization

The following issues are worth taking into account when analyzing SDCCH Drops:

SDCCH Drops and TCH Drops often drop because of the same RF reasons, such as for example insufficient coverage

Only use SDCCH power regulation and SDCCH HO when the network has good coverage

BSC and transmission problems can impact SDCCH drops so investigate Transcoders, A-interface and LAPD

SDCCH Drops on the hopping layer are normally showing worse values than SDCCH on the BCCH


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Text 24 pt



SDCCH Drop OptimizationC h e c k S D C C H D r o p p e d P e r C e ll

C h eck d ro preaso n

B adq u a lity ?

C h eck IC M C h eck freq u en cy P lan

F req u en cy scanR u n M R R & F A S

L o wS S ?

R efe r to L o w S San a ly s is f lo w ch a rt.

H ig hT A ?

C h eck s ite lo ca tio n& T A L IM

T C HC o n g es tio n ?

C h eck S _ D R -S _ N T C In c rease T C H o r u s in g

C h eck B T S e rro rlo g

H Wfau lt?

S w ap &R ep a ir H W

B

N O

Y E S

Y E S

Y E S

Y E S

Y E S

N O

N O

N O

N O

R ad io F ea tu res , C L S , H C S


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Text 24 pt



SDCCH Drop OptimizationB

T ra n sm iss io n fa u lt?

P e rfo rm lin kin v e s tig a tio n

C h e c k L in k Q u a lity

C h e c k M S fle e t

P e r fo rm D r iv e T e s t

P e r fo rm M T R /C T R /M R R

P e rfo rm s ite su rv e y

C h e c k a n te n n a in s ta lla tio n

E N D

Y E S

N O


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Text 24 pt



SDCCH Drop Rate - KPI

The SDCCH Drop Rate is calculated using the following formula:

SDCCH Drop Rate

– Dropped SDCCH Connections of Total Number of SDCCH Connections

[%]100*

1

1

TOTALCELLS

TOTALCELLS

CMSESTAB

CNRELCONGCNDROP


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Text 24 pt



SDCCH Drop Rate - KPI

The SDCCH Drop Rate is calculated using the following formula:

CNDROP - CNRELCONG

CMSESTAB100 [%]

Successful MS channel establishment on SDCCH (SDCCH HOs counts twice)

Dropped SDCCH connections and TCH & TRA

congestion releases

Number of SDCCHs released due to TCH or TRA congestion (OL & UL)


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SDCCH Drop – Additional indicators The following SDCCH Drop indicators are useful when studying

the SDCCH Drop performance:

– S_DR_SS_OU: Dropped SDCCH Connections due to Low Signal Strength of Total Number of Dropped SDCCH Connections in OL/UL subcell

– S_DR_BQ_OU: Dropped SDCCH Connections due to Bad Quality of Total Number of Dropped SDCCH Connections in OL/UL subcell

100

CNDROP

CDISSSSUBCDISSS

100

CNDROP

CDISQASUBCDISQA


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Text 24 pt



SDCCH Drop – Additional indicators The following SDCCH Drop indicators are useful when studying

the SDCCH Drop performance:

– S_DR_TA_OU: Dropped SDCCH Connections due to Excessive Timing Advance of Total Number of Dropped SDCCH Connections in OL/UL subcell

– S_DR_OTHOU: Dropped SDCCH Connections due to Other Reasons of Total Number of Dropped SDCCH Connections in OL/UL subcell

100CNDROP

CDISTA

100

CNDROP

CDISTACDISQASUBCDISQACDISSSUBCDISSSCNDROP


Slide title 40 pt


Text 24 pt



SDCCH Drops – STS Counter Summary

OBJECT TYPES: CELLCCHDR, CLSDCCH, CELLCCHHO

– CMSESTAB: Successful MS channel establishment on SDCCH– CNDROP: Dropped SDCCH connections – CNRELCONG: Number of SDCCHs released due to radio

resource congestion– CDISSS: Number of Dropped SDCCH connections due to Low

Signal Strength– CDISQA: Number of Dropped SDCCH connections due to Bad

Quality– CDISTA: Number of Dropped SDCCH connections due to

excessive Timing Advance


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Text 24 pt



SDCCH Drops – Examples in ESPA

SDCCH Drop examples in ESPA


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Text 24 pt



TCH Assignment Failure






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Text 24 pt



TCH Assignment Failure – Overview

The TCH assignment success rate measures how often a call set-up, ordered by the MSC, has been successful

The major issues impacting TCH assignment failures are:– TCH congestion– Radio reasons such as coverage and interference– Hardware or transmission problems


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Capacity and Grade of Service

When designing a network one of the important decisions to make is what Grade of Service (GOS) to dimension the network for

The GOS will determine the amount of sites needed and the capacity installed in each site

Grade of Service (GOS) is defined as:– The probability of a lost call due to the reliability of the system and the

availability of circuits and other equipment– Most networks are dimensioned for a GOS = 2%

Capacity are planned to ensure low congestion by using the Erlang B model


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Erlang

An Erlang is a unit of telecommunications traffic measurement. Strictly speaking, an Erlang represents the continuous use of one voice path. In practice, it is used to describe the total traffic volume of one hour

One Erlang represents a circuit occupied for one hour. – 1 Erlang = 1 call Hour/ Hour

Several traffic models exist which share their name with the Erlang unit of traffic. They are formulae, which can be used to estimate the number of channels required in a network


Slide title 40 pt


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Erlang B

The most commonly used traffic model in radio networks is Erlang B The Erlang B traffic model is used to work out how many channels are

required if the traffic figure (in Erlangs) during the busiest hour is known. The model assumes that all blocked calls are immediately cleared

The three variables involved are Busy Hour Traffic (BHT), Congestion (Blocking) and Channels:

– Busy Hour Traffic (in Erlangs) is the number of hours of call traffic there are during the busiest hour of operation of a telephone system.

– Blocking is the failure of calls due to an insufficient number of channels being available.

– Channels are the available capacity.


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Hardware Capacity and Configuration

SB T T T E E T BCCH (CHGR 0)

TT T T T T T T Hopping (CHGR 1)

SB

T

TRXBCCH timeslotSDCCH timeslotTCH timeslotEDGE timeslot

Legend

E


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Text 24 pt



TCH Assignment Failure – OverviewHourly Traffic


Slide title 40 pt


Text 24 pt




Congestion

Congestion can be defined as follow:– The probability that a call attempt cannot be handled

successfully, because of not enough free circuits and other switching equipments

– The Congestion (Blocking) Probability represented by B (n, A) is determined by Offered traffic A and the number of available circuits n

STS are used to calculate congestion but different formulas exist each showing a different view of congestion


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Text 24 pt




Congestion – Subscriber congestion

Good to show impact on customer but may hide capacity shortage

STS Formula: Compares failed TCH assignment attempts due to congestion with total number of TCH assignment attempts

100

TASSALL

TxNRELCONGCNRELCONG


Slide title 40 pt


Text 24 pt




Congestion – TCH Time congestion

When the last idle channel used for speech with a specific speech version is allocated and a new allocation attempt is done irrespective if pre-emption is successful or not, the 'TCH congestion time counters' are started incrementing each second until a channel becomes idle.

The counters TFTCONGS, TFTCONSUB, THTCONGS and THTCONSUB are not started if the allocation attempt is done for intra cell handover due to channel rate change or half rate packing.

Good for optimization but values are worse than what customer perceive

STS Formula: TCH Time Congestion in Underlaid Subcell of Total Measurement Interval

10060

PERLEN

TxTCONGS


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Text 24 pt




Congestion – Attempt congestion

The 'TCH congestion at assignment' counters are incremented when an allocation attempt of a channel for assignment or immediate assignment fails due to no idle channels available

STS Formula:

100

TxCALLS

TxCONGSHOTxCONGSAS


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Congestion – TCH Hard Time congestion Hard Time congestion counters are only valid for FR The hard time congestion counter is incremented each

second when all radio resources are occupied and when it is not possible to free any resources with help of pre-emption of any kind

STS Formula: TCH Hard Time Congestion in Underlaid Subcell of Total Measurement Interval

10060

PERLEN

GSTFTHARDCON


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Text 24 pt




Congestion – Congestion at Handover

The 'TCH congestion at handover' counters are incremented when an allocation attempt of a channel for handover fails due to no idle channels available in target cell.

STS Formula: Congestion At Handover of Total Number of Handover Decisions in OL/UL Subcell

100

SUMIHODEC

UBTxCONGSHOSTxCONGSHO


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• Time congestion (GoS for a cell)

• Subscriber perceived congestion (Subscriber Percieved GoS)

Transcoder resource congestion during imm ass on TCH (4 counters FR/HR/SUB). TFNDROP also steps.

Number of SDCCHs released due to TCH or TRA congestion (OL & UL)

TASSALL steps in target cell at successful assignment and in originating cell if assignment fails.

TFTCONGS

PERLEN * 60100 [%]100 [%]

TCH FR congestion time (sec) Starts when congestion and one more allocation attempt is done.

Measurement Time in Minutes AFR UL: TFV3TCONGS

TCASSALL

TASSALL100 [%]100 [%](1- )Failed first TCH assignments:

Alternative:

CNRELCONG + TxNRELCONG

TASSALL - Inc(AB+AW) + Outg(AB+AW)100 [%]100 [%]

Not needed on BSC level

TFTHARDCONGS

TFTCONGS:

TFTHARDCONGS:

B/S T T T T P P P Allocation is still possible.

B/S T T T T P P P When allocation fails.

Also for OL but not for HR


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Congestion – Formula comparison

0

10

20

30

40

50

60

70

80

90

100

1 2 3 4 5 6 7 8 9

Cell

Co

ng

es

tio

n

Attempt congestion

Time Congestion

GOS

Subs. Perceived cong.


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Congestion Improvement

Congestion can be improved by short, medium and long term actions

Medium and Long term:– Expansions: Add capacity to existing cells– Sectorize omni cells– Indoor and capacity microcells– Additional macro sites

Short term:– Optimization of access parameters– Activation and optimization of capacity features


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Congestion Improvement - Expansions Expansions need to be planned in advance – Before

capacity is needed Important for operators to have an expansion procedure in

place Expansions can be limited by a variety of issues, for

example available spectrum The following presentation take a more detailed look at

traffic and capacity management


Slide title 40 pt


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Congestion Improvement – Short Term

The following features can be used to ensure efficient use of installed capacity and to reduce congestion:

– Overlaid/Underlaid subcells– Cell Load Sharing (CLS)– AMR Half-rate (AHR)– Assignment to Worse Cell– Hierarchical Cell Structures (HCS)


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TCH Assignment Failure – Features

Overlaid/Underlaid Subcells

Cells are split into OL/UL subcell pairs OL and UL share the same BCCH The fundamental idea is that traffic close to the site is

moved to the Overlaid subcell while traffic closer to the edge of the cell is carried on the Underlaid


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Parameter settings available on a subcell level:– Intra Cell Handover– Power Control– Output power– Urgency conditions– Training Sequence Code

Additional statistics and recordings on a subcell level Ability to differentiate and prioritize between hopping and

non-hopping (BCCH) layers


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OLUL

OLUL

Only mobiles near the site are allowed on the OL to maximize quality on OL

Allows tighter reuse of channels in the OL



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Overlaid/Underlaid Subcells – Frequency Re-use A tighter frequency re-use is possible on the OL subcell

since the OL channels cause and receive less interference

Fu

Fu

Fu

Fo

Fo

Fo

Fo

Fo

Fo

Fo


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Overlaid/Underlaid Subcells - Configuration BCCH in UL, TCH in OL

Chgr 1

Chgr 2 Normally used with high FL

Higher Re-use of TCH channels

OL Subcell

BUL Subcell Chgr 0

BCCH TRX

With Subcell Load Distribution, both CHGR1 and 2 will take traffic close to the site

Lower power on CHGR1 and 2 possible

If CHGR 1 has more freq than CHGR 2, assignments will be made to CHGR 1 first (see channel admin)


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Overlaid/Underlaid Subcells - Configuration BCCH in OL, TCH in UL

Chgr 1

Chgr 2

Normal configuration

Tight BCCH re-use

UL Subcell

BOL Subcell Chgr 0

BCCH TRX

The hopping channels in the UL subcell are used during low and normal traffic

At high traffic load, SCLD will move the mobiles with the lowest path loss to the OL subcell


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Overlaid/Underlaid Subcells – BCCH in OL Configuration BCCH has many disadvantages relative to TCH’s

– Non-frequency hopping (no frequency diversity)– No power control

BCCH OL is still covering same area as the UL

OL

UL

BCCH

TCH


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TCH Assignment Failure – FeaturesOverlaid/Underlaid Subcells – Subcell change UL to OL

9702676

• A subcell change will be requested when:downlink path loss is equal or below LOL - LOLHYSTANDtiming advance is lower than TAOL - TAOLHYST.


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TCH Assignment Failure – FeaturesOverlaid/Underlaid Subcells – Subcell change OL to UL

9702677

• A subcell change will be requested when:Downlink path loss exceeds LOL + LOLHYST ORtiming advance is equal to or increases above TAOL +TAOLHYST.


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Text 24 pt



TCH Assignment Failure – FeaturesOverlaid/Underlaid Subcells – DTCB

Equal signal strength border

Pathloss border, LOLPathloss border, LOLPathloss border, LOLPathloss border, LOLPathloss border, LOLPathloss border, LOL

Distance to Cell Border, Distance to Cell Border, DTCB DTCB Distance to Cell Border, Distance to Cell Border, DTCB DTCB


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Overlaid/Underlaid Subcells – LOL, TAOL, DTCB

UL -> OL

If ( SSdiff DTCB + DTCBHYST )andIf ( L LOL – LOLHYST )andIf ( ta TAOL – TAOLHYST )

OL -> UL

If ( SSdiff DTCB - DTCBHYST )orIf ( L LOL + LOLHYST )orIf ( ta TAOL + TAOLHYST )

Only if NNCELLSis fulfilled

DTCB = wanted subcell border, set by command per cellSSdiff = SSs- SSstrongest neighbour

Counters for reason for subcell change


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TCH Assignment Failure – FeaturesOverlaid/Underlaid Subcells – Subcell change, LOL/TAOL/DTCB

UL subcell

OL subcell

Traffic taking area

LOL, TAOL, DTCB

SCLD=OFFSCLD=OFF

OL subcell B

UL subcell


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Overlaid/Underlaid Subcells – Subcell change with SCLD

Aims to keep traffic on the UL layer until threshold is reached

Without SCLD, mobiles that qualify (LOL, TAOL) will always be on OL even if site is not busy – this minimizes advantage of high reuse layer

With SCLD, when site is not busy, all traffic is carried on UL. When site is busy, mobiles that qualify are promoted to OL.


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Percentage ofactive TCHs

SCLDUL

SCLDLL

Subcell change OL to UL(no other condition)

No subcell change

Subcell change UL to OL(L < LOL, ta < TAOL)

When the percentage of idle full rate capable TCHs in the UL subcell equals orfalls below SCLDLL subcell changes from the UL to the OL subcell are initiated.When the same percentage exceeds SCLDUL then subcell changes from the OLto the UL are initiated. In between no subcell changes are initiated.

Percentageof idle TCHs


Overlaid/Underlaid Subcells – Subcell change with SCLD

Based upon the LOL, TAOL, and DTCB thresholds

Mobiles with highest pathloss are migrated first


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TCH Assignment Failure – FeaturesOverlaid/Underlaid Subcells – Subcell change with SCLD

B

UL subcell

OL subcellLOL, TAOL, DTCBLOL, TAOL, DTCB

SCLD=ONSCLDLL=35 % of idle TS’sSCLDUL=40 % of idle TS’s

SCLD=ONSCLDLL=35 % of idle TS’sSCLDUL=40 % of idle TS’s

OL subcell

UL subcell

Time

Traffic

Time

Traffic

UL CapacityUL Capacity

OL CapacityOL Capacity

OL traffic will be close to the site


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Overlaid/Underlaid Subcells – MRR Pathloss

PDF of downlink pathloss. 1 BSC in an urban area with BCCH in OL feature

0

0,05

0,1

0,15

0,2

0,25

Pathloss [dB]

PD

F

OL Subcell

UL Subcell


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Overlaid/Underlaid Subcells – Handovers

9702679

CS = YES

9702680

CS = NO


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Overlaid/Underlaid Subcells – Parameters

9702683

Main controlling parameters• SCTYPE identifies the subcell type, overlaid or

underlaid, within a cell.

• LOL is the path loss threshold for the serving area ofthe overlaid subcell within a cell. This parameter is setper overlaid subcell.

• TAOL is the timing advance threshold for the servingarea of the overlaid subcell within a cell. Thisparameter is set per overlaid subcell.


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9702684

• LOLHYST is the path loss hysteresis for the serving areaof the overlaid subcell within a cell. This parameter is setper overlaid subcell.

• TAOLHYST is the timing advance hysteresis for theserving area of the overlaid subcell within a cell. Thisparameter is set per overlaid subcell.

• BSTXPWR is the base station power at the reference pointfor the locating algorithm on the non-BCCH frequencieswithin a cell. This parameter is set per subcell.

• BSPWRT is the base station output power after the poweron the non BCCH frequency within a cell. This parameteris set per subcell.


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9702685

• TSC is the Training Sequence Code for the specifiedsubcell within a cell. This parameter is set per subcell, butit is not available for cells without an overlaid/underlaidsubcell structure. Note that it is recommended not tochange TSC in the underlaid subcells.

• CS indicates if a cell shares the same site as itsNeighbour. This parameter is set per neighboring cellrelation and it can take the values:

• YES, the cell is co-sited with its Neighbour.

• NO, the cell is not co-sited with its Neighbour.


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Cell Load Sharing (CLS)

9702744

• the traffic load in the cells are monitored

• if a cell has too high load, MSs close to the cellborder are made to perform a handover

• the handovers are carried out if the receiving cell haslow enough load

Note: Load share evaluations are only performed for existing TCH-connections, i.e. it is not applied during the assignment phase.


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9702745

The measure of the load is the percentage of idle TCHs

There are two levels:

• CLSLEVELif the amount of idle traffic channels is equal to ordecreases below CLSLEVEL in a cell, that cell triesto rid itself of some traffic by initiating load sharinghandover to neighboring cells

• CLSACCif the amount of idle traffic channels is above loadCLSACC in a cell, that cell is prepared to acceptincoming load sharing handovers from other cells.


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9702897

Locating conditions•CLS HO is not allowed during assignment•CLS HO is not allowed if there is an urgency condition

Conditions for neigboring cell•The cell belongs to the same BSC•The cell belongs to the same HCS-layer•Incoming CLS handovers are allowed (HOCLSACC=ON)


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9702749

RHYST:

0 % no reduction of the hysteresis50 % all hysteresis removed, the border

reduced to the nominal cell border100 % negative hysteresis

CLSRAMP: The time it takes to fully decrease the hysteresis

nominal cell border

Hysteresis area

(cell A=serving cell)(cell B=target cell)

Handover border,cell A to cell Bwithout reduction

RHYST = 75%RHYST = 50%

RHYST = 100%

RHYST = 25%

RHYST = 0%


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Normal Handover

Nominal cell border

HO border to cell A

HO border to cell B

Cell A Cell B


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Text 24 pt





HO with CLS

Nominal cell border

HO border to cell A

HO border to cell B

Cell A Cell B


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Advantage of feature: Does not degrade performance Helps avoiding congestion at pre-defined load Easy usage

Disadvantage of feature: Does not work on cells where there is no traffic on the border If neighbor cell is congested - no off-load


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Parametername

Defaultvalue

Recommen-ded value

Valuerange

Unit

CLSLEVEL 20 – 0 to 99 %

CLSACC 40 – 0 to 100 %

CLSRAMP 5 8 0 to 30 s

HOCLSACC OFF ON ON,OFF

RHYST 75 100 0 to 100 %

CLSTIMEINTERVAL 100 100 100 to 1000 ms

ERBANDSINCLUDED OFF – ON,OFF


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AMR Half-rate (AHR)

Avoid congestion by using AMR HR instead of AMR FR at high load

Possibility of doubling the AMR capacity by using AHR instead of AFR

Gain in capacity is achieved at a cost to speech quality Traffic changed between HRFR with:

– Dynamic Half Rate Allocation– Dynamic Mode Adaptation


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AMR Half-rate (AHR) – Dynamic Half Rate Allocation

DHA allocates AMR HR at call set-up and handover when few idle TCHs remain in the cell


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Text 24 pt




AMR Half-rate (AHR) – Dynamic Half Rate Allocation

Traffic threshold:New calls allocatedHR

Operator setable

EFR

AMR

EFR

AMR

EFR

AMR

EFR

AMR


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AMR Half-rate (AHR)

Dynamic HR Allocation

NO

NOYES

YES

NOYES

YESNO

Is the amount of idleFR below theDTHNAMRthreshold?

Is the amount of idleFR below theDTHAMRthreshold?

Is the mobile dualrate?

AllocateAMR HR

Allocatewanted FR

Allocate HR

Is the mobile AMRHR capable?


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AMR Half-rate (AHR) – DHA parameters

DHA - Dynamic Half Rate (HR) Allocation DTHAMR - Dynamic HR Allocation threshold for Adaptive

Multi Rate(AMR) capable mobiles DTHNAMR - Dynamic HR Allocation threshold for mobiles

not capable of AMR


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AMR Half-rate (AHR) – Dynamic Mode Adaptation Changes channel rate from FR to HR on ongoing calls

when few idle TCHs remain in the cell. From FR to HR, chooses calls with the best reported

quality (both uplink and downlink considered). Changes from HR to FR when the reported quality is below

certain threshold.


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AMR Half-rate (AHR) – Dynamic Mode Adaptation

Congestion threshold:Existing calls reallocated HR

Operator setable

EFR

AMR

EFR

AMR

EFR

AMR

EFR

AMR


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Text 24 pt



TCH Assignment Failure – FeaturesAMR Half-rate (AHR) – Dynamic Mode Adaptation, FR>HR

The total number of idle timeslots in a cell are below the DMTHAMR

and quality for a candidate is better than DMQGAMR . An attempt for FR->HR allocation is

performed.

+HOATFRHRAMR

The allocation is considered a success when the OLD CHANNEL is released. Last

message that arrived to the BSC was ASSIGNMENT COMPLETE

+HOSUCFRHRAMR

The total number of idle timeslots in a cell are below the DMTHNAMR and quality for a candidate is better than DMQGNAMR . An attempt for

FR->HR allocation is performed.

+HOATFRHRNAMR

The allocation is considered a success when the OLD CHANNEL is released.

Last message that arrived to the BSC was ASSIGNMENT COMPLETE

+HOSUCFRHRNAMR


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TCH Assignment Failure – FeaturesAMR Half-rate (AHR) – Dynamic Mode Adaptation, HR>FR

When the quality for a HR connection is considered

poor, rxqual below DMQBAMR. An attempt for

HR->FR allocation is performed.

+HOATHRFRAMR,

The allocation is considered a success when the OLD CHANNEL is released. Last message that

arrived to the BSC was ASSIGNMENT COMPLETE

+HOSUCHRFRAMR, +HOSUCHRFRNAMR.

When the quality for a HR connection is considered poor, rxqual below

DMQBNAMR. An attempt for HR->FR allocation is performed.

+HOATHRFRNAMR


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AMR Half-rate (AHR) – DYMA parameters

DMSUPP – Activates dynamic FR/HR mode adaptation, set per cell DMQB - Dynamic Half Rate (HR) to Full Rate (FR) Mode Adaptation due

to bad quality. Values on or off. DMQBAMR - Threshold triggering a switch from a HR channel to a FR if

RXQUAL (DL or UL) for AMR MS is exceeding DMQBAMR, set per cell. DMQG - Dynamic FR to HR Mode Adaptation quality evaluations.

Values on or off. DMQGAMR - Threshold triggering a switch from FR to HR channel if

RXQUAL (DL or UL) is less than DMQGAMR, set per cell DMTHAMR - Dynamic FR to HR Mode Adaptation threshold for AMR

capable mobiles.


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AMR Half-rate (AHR) – Example

DYMA load threshold = 30% => 2TS, assuming 8 TCH DHA load threshold = 15% => 1 TS, assuming 8 TCH

With quality-based channel rate change active FR -> HR quality threshold = 15 dtqu HR -> FR quality threshold = 35 dtqu


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3RxQual : 02023RxQual : 0202 -0

Traffic limit exceeded, move MS from FR to HR


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Text 24 pt





3RxQual : 0202 1 -/

Traffic limit still exceeded, move MS from FR to HRTraffic limit still exceeded, move MS from FR to HR


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Text 24 pt





RxQual : 3 202 1 0/-3 202 1 0/-


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Text 24 pt



RxQual : 3 202 1 0/43 202 1 0/4

Quality Threshold exceeded, move MS from HR to FR

Quality Threshold exceeded, move MS from HR to FR




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Text 24 pt





3RxQual : 202 1 0/-




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Text 24 pt





RxQual : 3 22 1 0/103 22 1 0/10


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Text 24 pt





RxQual : 3 22 0/10/01/00/23 22 0/10/01/00/2

Dyn. HR Allocation allocates HR directly if threshold is exceeded

0/


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Text 24 pt





RxQual : 3 22 0/10/01/00/2 0/

Pack HR calls Pack HR calls

-


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Text 24 pt




Assignment to Other/Worse Cell:

The feature operates at call setup when a TCH is to be assigned

The feature makes it possible to assign a TCH in another cell than the one currently serving in the following cases:

– Assign to another cell (preferred) if the other cell is ranked higher by locating

– Assign to worse cell if the call cannot connect to the current cell due to congestion

– Assign to worse cell if locating detects an urgency condition during call setup


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Assignment to Other/Worse Cell

Assignment to better cell advantages

– Unnecessary HOs are prevented– Less Interference since call are on best server

Assignment to worse cell advantages– Less TCH congestion – Improved possibility of successful connection– Improved utilization of capacity


Slide title 40 pt


Text 24 pt





9702700

Main controlling parameters

• ASSOC is the parameter that turns the featureAssignment to another cell ON or OFF. Theparameter is set per BSC.

• AW is set per cell and determines if an assignment toa worse cell is allowed from that cell. However, toallow assignment to a worse cell, the parameterASSOC (see above) has to be set to ON as well.

• IBHOASS determines whether assignment to anotherBSC can be performed during assignment


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9702886

• AWOFFSET is a signal strength offset parameter used to define therange around the original cell border where an assignment to a worsecell is allowed. It is set per neighbor relation.

• CAND is set per neighbor relation and specifies if the neighbor cellshall be treated as a possible candidate at assignment and athandover. The parameter can take the values:

* AWN, the cell is only a possible candidate at assignment to aworse cell. Note: The cell is not a candidate for assignmentto better cell or handover.

* NHN, the cell is a possible handover candidate in case of an assignment to a better cell and normal handover.

* BOTH, the cell is always a possible candidate, at assignment aswell as at handover.


Slide title 40 pt


Text 24 pt





9702887

• TINIT is a timer used to inhibit locating for a time interval afterImmediate assignment, Assignment or Handover in order to stabilizethe ranking values. The timer is set per BSC.

• TALLOC is used when there is an assignment failure due tocongestion or due to bad radio conditions as a result of the firstcandidate list. A new list is sent after the timer has expired. The timeris set per BSC.


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Hierarchical Cell Structures (HCS)

The priority of a cell is given by associating a layer to the cell.

Each layer is also belonging to a HCS band. The lower the layer (and HCS band), the higher is the priority.

This provides a mechanism where by the traffic may be directed towards cells belongings to the lower layer, so as the lower layer cells can serve all the traffic with sufficient signal strength


Slide title 40 pt


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Small cells have limited coverage Large cells have limited capacity Locating is primarily based on “best server” In certain situations we want to favor a “weaker cell”

– Combined microcell / macrocell network– Multiband GSM 900 / GSM 1800


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Text 24 pt





Congestion

Layer 4

Layer 2

Layer 4

Layer 4


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Text 24 pt



TCH Ass. Failure – Optimization

Analyze the following issues that could be possible reasons for TCH Assignment failures:

Low Signal strength or no dominant serving cell Interference Congestion on TCH Incorrect use of Capacity features Faulty Hardware or transmission Incorrect Output power


Slide title 40 pt


Text 24 pt



TCH Ass. Failure – Optimization

It is worth taking into account the following issues when optimizing TCH Assignment failures:

Make sure that problems with network availability are not the cause of congestion

Often congestion problems are caused by network design issues such as cells covering a large area

Try to make sure that as far as possible calls are made on the best serving cell to reduce the negative impact on Retainability and Voice Quality

Radio capacity features such as for example CLS should preferably be only used as short or medium term solutions for congestion.


Slide title 40 pt


Text 24 pt



TCH Ass. Failure – OptimizationCheck TCH congestion

Low TCH Assignment Success Rate

Congestion on TCH ?

Check output power

Low outputpower?

Check output powerparam eters

Corrupt param etersetting?

Check S igna l S trength o fBC CH and TC H

Low SS for ca llaccess?

Check BTS E rror Log

HWfault?

NO

YES

END

Correct param eters

Swap & repa irHW

Check coverage p lo ts

Perform drive tests

Dom inantserver exists?

YES

NO

YES

AddBTS

NO

Add trance ivers or BTSYES

NO

YES

YES

NO

Adjust TCH outputpower

NO

Check In terference

D isturbanceon SDC CH ortarget TCH?

Im prove & ad justfrequency p lan

NO

YES


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Text 24 pt



TCH Assignment Failure – KPI

The TCH Assignment Failure Rate is calculated using the following formula:

TCH Assignment Failure Rate

[%]100*1

1

1

TOTALCELLS

TOTALCELLS

TASSALL

BTHCASSALSUTHCASSALLUBTFCASSALLSTFCASSALL


Slide title 40 pt


Text 24 pt



TCH Ass. Failure – Examples in ESPA

TCH Assignment Failure (Service Denied) examples in ESPA


Slide title 40 pt


Text 24 pt



Accessibility - Exercise

Accessibility Exercise

Perform an Accessibility Audit on a network using ESPA Create an Accessibility document summarizing findings and

recommendations Review of Accessibility documents


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Text 24 pt



Acknowledgement

The material used in this presentation has been obtained from various sources, documents and presentations in the Ericsson world, created by a large variety of people

I would like to acknowledge all the authors/creators of the used material


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Text 24 pt



npi training - accessibility

Documents

pt t c f c p s f xt

pt day

pt agenda

pt limited internal

pt e e t e o op e t

accessibility concept

npi training accessibility

pt accessibility time