Kpi 2g Troubleshooting

2G TROUBLESHOOTING Accessibility/Retainability

DCR (Retainability)

There are two types of call drops given below:

>Call drop over SDCCH: Indicating the call drop occurs in the

course during which BSC assigns a SDCCH to an MS but a TCH

has not been successfully assigned yet .

>Call drop over TCH: Indicating the call drop occurs after BSC

assigns a TCH to MS successfully.

The Channel currently occupied is of TCH type when BSC

sends a clear Request message to MSC.

The cause values for sending clear Request are as follows:

> Radio Interface Message Failure

>O&M Intervention

> Equipment Failure

>Protocol Error Between BSS and MSC

>Preemption

Causes of Drop Call:

>Coverage

>HO

>UPLINK /DOWNLINK CAUSED BY ANTENNA & FEEDER

SYSTEM

>Interference

>Transmission Failure

Coverage:

Discontinuous coverage (Blind area):

>Call drop is caused by isolated BTS. As the signal is of weak

strength and poor quality at the edge of an isolated BTS,

handover to other cells cannot be implemented, and thus call

drop occurs.

>If BTS lies in the place where the landform is intricate and

radio propagation environment is complicated (e.g., a

mountainous area), it may cause call drop owing to

discontinuous coverage.

Poor Indoor Coverage :

>In the place where many buildings are located, call drop

easily occurs due to high transmission attenuation, low

indoor level and great penetrate loss.

Beyond Coverage :

>Owing to some reasons, the coverage of a serving cell is

beyond the defined coverage. For example, the power in cell

A is so high that a MS still occupies the signals of cell A after it

moves out of the coverage of the adjacent cell B that has

been defined by cell A and reaches cell C.

>However, cell A has not defined cell C as an adjacent cell

yet, so at this time the MS cannot find a proper cell when it

tries to perform a handover according to the adjacent cell B

provided by cell A, thus call drop occurs.

Shortage of coverage :

It may be caused by some equipment failure in a cell. For

example, the antenna is obstructed or the carrier taking

BCCH (power amplifier) gets faulty.

Handover:

Unreasonable Parameters :

>For example, if the level of the handover candidate cell is

set to be too low and the handover threshold is set to be too

little, some MSs will be handed over to the adjacent cell

when the level of the adjacent is a little stronger than that of

the serving cell for a time.

>But after a while, if the signal of the adjacent cell faint, and

it happens no proper cell is available for handover, call drop

could occur. See example 6 for call drop resulting from

improper settings of handover parameters.

Adjacent cell undefined:

>If an adjacent cell has not been defined yet, MS will keep

communicating in the serving cell until it goes out of its

coverage. At this time, call drop shall occur since MS cannot

be handed over to a cell with stronger signals.

>Existence od adjacent cells with same BSIC and BCCH

Frequency .

Traffic Congestion :

>Unbalance of traffic may cause handover failure due to lack

of handover channel available for the destination BTS. When

reestablishment of handover channel fails too, call drop

occurs.

>BTS Clock out of synchronization and frequency offset

beyond limits ,which can cause handover failure and call drop

.

Interference

>There are co-channel interference, adjacent-channel

interference and inter-modulation interference. When MS

receives signals in the serving cell with strong co-channel or

adjacent-channel interference, it may aggravate BER and

make MS cannot accurately demodulate BSIC of the adjacent

cell or BTS cannot correctly receive measurement reports of

MS.

>The interference threshold is set as co-channel carrier-to-

interference ratio C/Iƒ9dB and adjacent-channel carrier-to-

interference ratio C/Aƒ9dB. When the interference index is

so bad that it exceeds the threshold, conversations in

network shall be interfered, thus conversation of poor quality

and call drop might occur.

Causes UL /DL caused by Antenna & Feeder System

>Improper installation of antenna and/or feeder. For

example, the Tx antenna between two cells is installed just

reversedly, which shall make the uplink signal level is much

poorer than the downlink one, thus cause call drop, single

pass or difficult connection occurring far from the BTS.

>If single polarization antenna is adopted, a cell has two sets

of such antennas. If their azimuths are different, call drop

might occur.

• A directional cell has a main antenna and a diversity

antenna, so it is possible that BCCH and SDCCH of this

cell come from the two different antennas. Different

azimuths will cause different coverage, consequently,

although the user can receive BCCH signal, it cannot

occupy SDCCH sent by another antenna when

originating a call, thus call drop occurs.

>As there are Abis interface and A interface link, poor quality

transmission and unstable transmission link also may cause

call drop.

• Observe transmission and board alarms (e.g., FTC

failure alarm, A interface PCM out of sync alarm, LAPD

link break alarm, power amplifier alarm, HPA alarm,

TRX alarm, CUI/FPU alarm). Based on alarm data,

analyze whether transmission is intermittent or

whether there are faulty boards (e.g., the carrier board

is faulty or in poor contact).

• Check transmission paths, test BER and check whether

E1 connector or grounding of equipment is reasonable,

thus decrease call drops by ensuring stable

transmission quality.

• Observe whether there are too many call drops caused

by transmission problem via traffic measurement.

a) in TCH performance measurement of traffic

measurement observe whether there are too many A

interface failures when TCH is occupied.

b) In TCH performance measurement observe whether

the TCH availability rate is abnormal.

c) In TCH performance measurement observe

whether there are too many call drops caused by

interruption of terrestrial link.


Drop Call Rate está relacionado con los sigs KPIs:

>TCH Drop Rate

>HO Success Rate

TCH Drop Call (Retainability):

The formula for measuring TCH Drop Rate (Optimi, Movistar,

Ericsson <Ericsson uses more parameters in case of

denominator who make reference to HO>) is:

��_�_ �= �� + �� + �� + ��

�� + �� + �� + �� 100

TFNDROP � The total number of dropped full-rate TCH in UL

subcell.

TFNDROPSUB� The total number of dropped full-rate TCH in

OL subcell.

THNDROP � The total number of dropped half-rate TCH in

UL subcell.

TCHNDROPSUB � The total number of dropped half-rate in

OL subcell.

THCASSALL � Number of assignement complete messages

for all MS power classes in UL subcell, half-rate.

THCASSALLSUB � Number of assignement complete

messages for all MS power classes in OL subcell, half-rate.

TFCASSALL � Number of assignement complete messages

for all MS power classes in UL subcell, full-rate.

TFCASSALLSUB � Number of assignement complete

messages for all MS power classes in OL subcell, full-rate.

The TCH Drop Call reasons has the following priority order:

>Excessive TA

– TA > TALIM cell parameter

>Low signal strength in downlink and/or uplink

– SSUL < LOWSSUL (BSC parameter)

– SSDL < LOWSSDL

>Bad quality in downlink and/or uplink

– RxQualUL> BADQUL (BSC parameter)

– RxQualDL> BADQDL

>Sudden loss of connection

– None of the above

>Other

– Non radio-related

TCH Drop Call Optimization

Analyze the following issues that could be possible reasons

for poor TCH Drop performance:

– Low Signal strength on Uplink/Downlink

– Interference on Uplink/Downlink

– Excessive TA

– Incorrect/Not optimum Parameter settings for example

power regulation

– Missing Ncells or Congestion in Ncells

– MS or MS Battery problems

– Subscriber Behavior

– Antenna/Hardware or Transmission faults

– Incorrect Installations

Dropped Calls on TCH

Check radio network features

Power regulationused properly?

DTXused?

Check output power

Check locating parameters

Bad parametersetting?

Powerbalance?

Adjust output power

IntroduceDTX

Correct parametersetting

Frequencyhopping

used?

Activate frequencyhopping

NO

Correct power regulationparameters

YES

NO

YES

YES

NO

NO

YES

NO

Missingneighbours? YES Run NCS

YES

Check dropped callreason

Badquality?

Low signalstrength

Perform interferenceanalysis

Perform low signalstrength analysisA

NO

NO

YES

YESNO

Most dropped Call during

HO?

Check losthandovers

Perform handoveranalysis

Swap & repairHW

Check siteposition

Dragoonsite?

Check MS fleet

Best serverexists?

Check antennainstallation

Perform site survey

Check BTS Error Log

HWfault?

Transmissionfault?

Check link quality andSynchronization

Remove site or change

frequency

Perform linkinvestigation

Add site

Perform MTR/CTRrecordings

Perform drive tests

High timingadvance

END

A

Check site location & TALIM

YES

NO

YES

NO

NO

YES

NO

YES

YES

NO

NO

YES

Check Dropped Calls per TS basis


DCR (RETAINABILITY)

Causas:

>Low SS UL

>Low SS DL

>Sudden

>RxQual UL

>RxQual DL

>Others

RxQual UL:

Causas:

Una celda A radia e interfiere el área de cobertura de una

celda B. Los MS conectados a la celda B están interfiriendo a

los MS conectados en la celda A.

Checar:

TA - Time in advance

RxQual DL:

Causas:

Una BTS A radia e interfiere el área de cobertura de una celda

B y la BTS A interfiere a los MS conectados a la BTS B.

Checar:

Cobertura de BTS A y B

TA – Timing Advance

Asignación de frecuencias

HCN

Asinación de MAIO

HW – Posible radio dañado

Low SS UL:

Checar:

TA relacionado con problema en TMA. Observar gráfica de

SS_DL y SS_UL si se mueve un valor de 12dB por lo tanto si es

TMA.

Low SS DL:

Checar:

HW - Antena dañada

HW - VSWR con valor alto

HW - TRX dañado

Sudden:

Checar: Problema relacionado directamente con HW

Others:

Checar:

Corrimientos en enlace

Transcoders de la BSC

HOFR (RETAINABILITY)

The formula for measuring HOFR (Optimi, Movistar) is:

�� = �� − �� 100

ATT= HOVERCNT � sum of HO attempts

SUCC=HOVERSUC � sum of HO Successful

Handover in Ericsson BSS system is controlled by what is

called as the locating algorithm in the BSC. Locating algorithm

operates on the basis of Measurement Reports (MR)i sent in

by the MS on SACCH.

The inputs that the BSC uses for making a handover decision,

from the received MRs from the MS is the DL signal strength,

DL quality, and the signal strength of the six best reported

neighbours. From the serving BTS, for the same MS the BSC

will use UL signal strength, UL quality and TA.

Possible reasons for poor HO Performance:

>Neighbor Cells impact the following radio network areas:

- Coverage

- Interference

- Incorrect parameter settings

- Unnecessary or Missing NCELL relations

- Hardware or Link/Transmission Faults

- Missing Frequencies in the Measurement list

- Poor Inter MSC/BSC handover performance

- TCH Congestion

- Frecuency plan, specifically for BCCH carriers

- The values of the hysteresis

- The filter lengths

- The BSIC planning

- The length of the active mode BA list

- The defined nieghbours

- The settings of parameters controlling TA and BQ

urgency HO

- The setting of parameters controlling Assignment to

other cell

- The values of the layer change thresholds when more

than one Hierarchical layer si used

>Handovers for Downlink Quality

-The HO is performed because DL conditions on the serving

cell are becoming too poor, there the BSC selects the best

neighboring cell as the target for the HO

Investigation

-Too strict configuration of the Handover parameters

-Hardware problems : Especially if the rates are high (around

100%) it can be due to the radio parts of the BTS on the

downlink (TRX, transmission antenna, feeders ...)

-GSM interference : co-channel or adjacent channel

-Radio Coverage : HO for UL Quality as well as HO for Level

reasons (UL and/or DL) shall be observed on the cell.

>Handovers for Uplink Quality- The HO is performed

because UL conditions on the serving cell are becoming too

poor, there the BSC selects the best neighboring cell as the

target for the HO

>Investigation

-Bad parameters settings

-If rates are high, probably hardware problem on the radio

uplink transmission part (TRX, antenna, diversity, feeders)

-Coverage problems(if also associated to HO for uplink level)

-Jamming on the uplink (if confirmed by bad RACH efficiency)

-GSM interference : if there’s an equivalent rate of handovers

for downlink quality

>Handovers for Downlink Level

-The HO is performed because DL conditions on the serving



>Investigation

-In normal cases, this should be very rare so if the rates are

high it is probably: Bad parameters settings or Hardware

problems on the downlink

>Handovers for Uplink Level

-The HO is performed because UL conditions on the serving



>Investigation

-Insufficient coverage (if associated also with an equivalent

rate of uplink quality)

-Bad handover parameters settings for the cell

-Hardware problems (high rates) if the downlink and the

uplink are not balanced

-Could come from ping pong handover between two cells

(one leaves one of the cells for quality, then comes back for

level and so on, for example)


ACCESSIBILITY

Ability for mobiles to set up calls.

Call attempts

Start from: Successful random accesses

To: successful immediate SDCCH assignements

Finally: Successful assignement on TCH

Probable causes related to accessibility:

- Congestion due to amount of traffic

- Interference (Quality of network)

- Hardware or Transmission issues

- Software file congestion

- Coverage (no coverage)

Accessibility includes de following KPIs:

- Paging Success Rate

- Location Update Success Rate

- Random Access Failure

- SDCCH Time Congestion

- TCH Assignment Failure

Paging Success Rate (ACCESSIBILITY)

The formula for measuring Paging Success Rate (Optimi,

Movistar) is:

__�= �� − ��

�� + �� + �� + �� 100

PAGPCHCONG � Number of paging messages discarded due

to full cell paging queue

PAGETOOOLD � Number of paging messages discarded due

to being too long in the paging queue. At the point when a

page is taken from the paging queue, its age is calculated and

compared to the BTS parameter AGE-OF-PAGING (the

parameter is set to 5seg in Ericsson BSS). If it is too old, it is

discarded and PAGETOOLD is incremented.

THCASSALL � Number of assignement complete messages

for all MS power classes in UL subcell, half-rate.

THCASSALLSUB � Number of assignement complete

messages for all MS power classes in OL subcell, half-rate.

TFCASSALL � Number of assignement complete messages

for all MS power classes in UL subcell, full-rate.

TFCASSALLSUB � Number of assignement complete

messages for all MS power classes in OL subcell, full-rate.

Paging process:

> Step-1

In response to an incoming call, the MSC initiates the paging

process by broadcasting a “paging request” message on the

paging sub channel (IMSI or TMSI of the MS and its Paging

Group) and starts timer T3113. A “paging message” consists

of the mobile identity (IMSI or TMSI) of the MS being paged

and its “paging group number”.

>Step-2

The BSC receives this page and processes the paging request

and schedules it for transmission on the PCH at appropriate

time.

>Step-3

The MS on its part will analyse the paging messages sent on

the paging sub channel corresponding to its paging group.

>Step-4

Upon receipt of a page at the MS, the MS responds by

transmitting a channel request on the RACH.

>Step-5

BSS in response to the received “channel request”, will

process it and immediately assign the MS a SDCCH

(immediate assignment / assignment reject; done over

AGCH).

>Step-6

Check use of radiofeatures

C

NO

Are all radiofeatures used?

YES

Check coverage

NO

Low SS on cellborder?

Perform drive test

YES Improve coverage

Check interference

YES

Badquality?

Reduce interference forpotential candidate

YES

Delayed handover

decision?

Check handoverparameters

YES

Introduce unusedfeatures

· Timer Expiry AfterMS is Lost

NO

D

NO

Unsuccessful Handovers

Check congestionperformance

TCHcongestion?

Check SAE setting

NO

SWcongestion?

Check Locating parameters

Check Neighbouring cell definitions

Wrong cellsdefined?

Missingneighbours?

Too manyneighbours?

Too manymeasurement

channels?

Strange or corruptparameter setting?

NO

NO

NO

NO

NO

Add TCHcapacity

YES

Increase SAEYES

Remove incorrectdefinitions

YES

Add missingrelation

YES

Remove unnecessaryrelations

YES

Review and correct thedefined MBCCHNO

YES

C

NO

Correct parametersYES

D

Check BTS Error Log

HWfault?

Check link quality

Transmissionfault?

Swap & repair HWYES

NO

Improvetransmission

YES

Perform site visit

NO

Check antennainstallation

Antenna connected towrong feeder?

Incorrectdowntilt?

Hidedantenna?

Bad antennainstallation?

NO

NO

NO

Change feederYES

Correct tiltingYES

Change antennaposition

YES

Correct installationYES

END

NO

Is the cell at inter-MSCborder?

YES

Check inter-MSC HO

performance

NO


MS Paging response- After receiving the immediate

assignment command, MS switches to the assigned “SDCCH”

and transmits a “Paging Response”.

>Step-7

The establishment of the main signalling link is then initiated

(E1) with information field containing the “PAGING

RESPONSE” message and the “paging response” is sent to the

MSC.

>Step-8

Upon receipt of the “Paging Response” MSC stops the timer

T3113. If the timer T3113 expires and a “Paging Response”

message has not been received, the MSC may repeat the

“Paging Request” message and start T3113 all over again. The

number of successive paging attempt is a network dependent

choice

>Paging Capacity for BTS:

MFRMS*(CCCH blocks - AGBLK) * X (X=4 when TMSI based

paging is used & X=2 when IMSI based paging is used)

When the rate of “paging load” at the RBS becomes higher

than what the RBS is able to handle (paging capacity of RBS),

RBS will start discarding pages (check for high “page discard”

stats at the cell level).

Paging Queue Length = 14 – (Number of Paging Groups/10)

Which means higher the number of paging groups in a cell

(that is higher the MFRMS settings), lower will be the Paging

Queue length, this will compensate for lower number of

Paging Queue available at lower MFRMS. One “Paging

Queue” per “Paging Group” is available at the cell level (that

means when we decrease the number of paging groups for

the cell by reducing MFRMS to lower numbers, we actually

reduce the number of available paging queue).

>Paging capacity in BSC:

Paging Bottleneck at the BSC usually is the number of RP

signals that can be sent from the CP to the RPDs in the TRHs.

Calculations for number of pages per second:

(1)

(2)

RPSIG � Maximum number of RP signals per second

TRXpTRH � Average number of TRXs per TRH

NO_LA � Number of Location Areas

NO_TRH � Number of TRHs belonging to the BSC

NO_TRX � Number of TRXs belonging to the BSC

NO_CELLS � Number of cells

RPp � Probability that an RP signal is sent to an TRH

NO_PAGE � Number of pages per second

With “more” TRHs the paging capacity for the BSC decreases.

With “more” LACs within a BSC the paging capacity for the

BSC increases.


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

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)

Location Update (ACCESSIBILITY)

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

RPpTRHNO

RPSIGPAGENO

⋅=

__

⋅−−=

LANOTRXNO

CELLSNORPp

TRXpTRH

__

_11

Low Paging Success

No TMSI Attach / Detach?

Activate

Wrong periodic locationupdating setting?

Correct T3212 in BSC,BTDM & GTDM in MSC

SDCCHCongestion?

� Increase SDCCH channel� Adaptive configuration feature

Pagingcongestion?

� Plan more LA� Use TMSI paging

TMSI pagingnot use?

Activate

after not periodicregistration not use? Activate

END

Yes

No

Yes

Yes

Yes

Yes

Yes

No

No

No

No

No

Implicit detach

Low Location UpdatingSuccess

bordercell?

� Reallocate to another LA or MSC� Increase CRH

Low CRHHysterisis? Increase CRH

Bad LADemensioning? Re-dimensioning LA

Short perodicregistration?

Check T3212 in BSC &BTDM in MSC

Interference?� Check frequency plan� Activate radio feature

Software FileCongestion?

Correct settings for SAE 500 BlockMLUAP, MLCAP,MLVAP,MMMLR

SDCCHCongestion?

� Increase SDCCH channel� Adaptive configuration feature

Automaticderegistration? Activate automatic

de-registration

END

Yes

No

Yes

Yes

Yes

Yes

Yes

Yes

Yes

No

No

No

No

No

No


SDCCH Congestion(Accessibility)

SDCCH Activities:

>Mobility Management

– Normal Location update

– Periodic Registration

– IMSI Attach / Detach

– Connection Management

– Call setup

– SMS Point to Point

– Fax Setup

SDCCH Channel Allocation:

>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

SDCCH Channel Allocation Profile (CHAP)

>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/SDCCH

2) UL/SDCCH (if OL/SDCCH is congested)

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

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

>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.

>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 SDC

SDCCH Congestion

Check site position

Location areaborder?

Change LocationArea Border

Check and increaseCRH

Check TCH traffic

TCHCongestion?

Check SMS activity

Many SMSmessages?

E

Check periodicregistration

Too frequentregistration?

Check HW availabilty

Lowavailability?

See TCH & SDCCH

Availability

Add TCHcapacity

Redimension SDCCH

Change registrationinterval timers

NO

YES

NO

NO

NO

YES

YES

YES

NO

YES

YES

Check channel configuration

CombinedSDCCH?

Check traffic trend

Short termtraffic growth?

Check SDCCH dimensioning

E

UnderdimensionedSDCCH?

Check SDCCH mean holding time

Long mean holdingtime?

Is cell broadcastused?

Avoid cell broadcast ifpossible

Make channelnon-combined

No activity

Check HW and numberof False Accesses

RedimensionSDCCH

END

NO

NO

YES

YES

YES

YES

YES

NO

NO

NO

Check Adaptive configuration oflogical channel and parameters

ACSTATE off? Switch onYES


SDCCH Drops(Accessibility):

The formula for measuring SDCCH Drop Rate(Ericsson,

Optimi) is:

�_�_� = �� − �� − �� 100

CNDROP � The total number of dropped SDCCH channels in

a cell

CNRELCONG � Total number dropped (released connections

on SDCCH due to TCH or Transcoder congestion in UL subcell.

CNRELCONGSUB � The subset d for OL subcell

CMSESTAB � Total number of successful MS channel

establishment on SDCCH.

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

SDCCH Drop Optimization


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

>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

RANDOM ACCESS SUCCESS RATE (Accessibility):

The formula for measuring SDCCH Drop Rate(Ericsson) is:

�� = 1 − �� + �� + �� 100

RAACCFA � Number of Failed Random Accesses. This

counter is incremented for a Random access received with

too high TA, values that are not used or in case of "software

file congestion" (i.e. when the internal storage area in the

BSC is full which is a very rare case only occurring at very high

loads

CNROCNT � Number of Failed Random Accesses. This

counter is incremented for a Random access received with

too high TA, values that are not used or in case of "software

file congestion" (i.e. when the internal storage area in the

BSC is full which is a very rare case only occurring at very high

loads.

PDRAC � The counter value is incremented when a 44.058

CHANNEL REQUIRED containing 44.018 CHANNEL REQUEST

with establishment cause "One Phase Packet Access" or

"Single Block Packet Access" is received on RACH.

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


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)

Check SDCCH Dropped Per Cell

Check dropreason

Badquality?

• Check ICM• Check frequency Plan•

Frequency scan•Run MRR & FAS

LowSS?

• Refer to Low SSanalysis flowchart.

HighTA?

• Check site location& TALIM

TCHCongestion ?

• Check S_DR-S_NTC• Increase TCH or using

Check BTS errorlog

HWfault?

• Swap &Repair HW

B

NO

YES

YES

YES

YES

YES

NO

NO

NO

NO

Radio Features, CLS, HCS

B

Transmission fault?

• Perform linkinvestigation

Check Link Quality

Check MS fleet

Perform Drive Test

Perform MTR/CTR/MRR

Perform site survey

Check antenna installation

END

YES

NO


TCH Assignment Failure (Accessibility):

The formula for measuring TCH Assignment Failure (Ericsson)

is: ��= �� + �� !"�� + �#$ − %&'"�� + �#$$

�� + �� "�� + �#$ − %&'"�� + �#$$ ( �100

outg(AB+AW)=SUMEOABSUCC+SUMEOAWSUCC+SUMOABSU

CC+SUMOAWSUCC

inc(AB+AW)=SUMEIABSUCC+SUMIAWSUCC+SUMIABSUCC+S

UMIAWSUCC

SUMEOABSUCC � Sum of Successful External Assignment

Handovers to Better Cell (Outgoing Handover)

SUMEOAWSUCC � Sum of Successful External Assignment

Handovers to Worse Cell (Outgoing Handover)

SUMOABSUCC � Sum of Successful Internal Assignment

Handovers to Better Cell (Outgoing Handover)

SUMOAWSUCC � Sum of Successful Internal Assignment

Handovers to Worse

Cell (Outgoing Handover)

SUMEIABSUCC � Sum of Successful External Assignment

Handovers to Better Cell (Incoming Handover)

SUMEIAWSUCC � Sum of Successful External Assignment

Handovers to Worse Cell (Incoming Handover)

SUMIABSUCC � Sum of Successful Internal Assignment

Handovers to Better Cell (Incoming Handover)

SUMIAWSUCC � Sum of Successful Internal Assignment

Handovers to Worse Cell (Incoming Handover)

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

-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

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

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

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)


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

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.

Not Approved Random Accesses

Check BSIC allocation

Check frequency plan

Access burst fromanother co-channel

cell

Check cell parameter setting

MAXTA toolow?

Check SAE (COFLP,DBTSP:TAP=SAACTION;)

Software filecongestion?

Check interference

High noisefloor?

END

Reduce interference

Increase SAE

IncreaseMAXTA

Change BSIC or

frequency plan

Check if unknown access code

YES

NO

NO

YES

NO

YES

NO

YES

Check site location

High locatedsite?

Consider tilting orlowering site

NO

YES

Check TCH congestion

Low TCH Assignment Success Rate

Congestion on TCH?

Check output power

Low outputpower?

Check output powerparameters

Corrupt parametersetting?

Check Signal Strength ofBCCH and TCH

Low SS for callaccess?

Check BTS Error Log

HWfault?

NO

YES

END

Correct parameters

Swap & repairHW

Check coverage plots

Perform drive tests

Dominantserver exists?

YES

NO

YES

AddBTS

NO

Add tranceivers or BTSYES

NO

YES

YES

NO

Adjust TCH outputpower

NO

Check Interference

Disturbanceon SDCCH ortarget TCH?

Improve & adjustfrequency plan

NO

YES

Kpi 2g Troubleshooting

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Transcript of Kpi 2g Troubleshooting