F a C T S_CS Fail Resolution11

Presentation Confidential between MTN and audience

PCFAIL & PSFAIL RESOLUTION

BTS Field & Radio HLS, MTN Nigeria



Content

• Introduction• Signaling Access• Signaling Connection Setup• Possible Causes of High PCFAIL• PCFAIL Resolution Steps• Possible Causes of High PSFAIL• PSFAIL Resolution Steps• PC&SFAIL Long Term Resolution Steps• MTN Nigeria Case Study• Recommendations • Conclusion


Introduction

PCFAIL and PSFAIL are statistical counters that assist in the determination of the integrity of RF access system; which include Antenna system & Transceiver units.

High count suggests an abnormality in RF quality of the affected cell. This ultimately causes drop in CSSR-(call setup success rate), and hence degraded Quality of Service, QoS.Measure of QoS is directly related to Customer Experience.

If QoS is degraded, revenue loss becomes inevitable as Customers are deprived quality access to utilize the services of the network.


CCALLSincremented at every attempt to allocate an SDCCH in a cell regardless of whether the allocation succeeded or failed. The attempts are made at signalling connection set up, at handover and at assignment.

CMSESTABincremented once the signalling link between the MS and MSC is established, this is defined by an SCCP CONNECTION CONFIRMED message received from the MSC or a HANDOVER COMPLETE or a HANDOVER PERFORMED message sent to the MSC.

CCONGSA signaling congestion counter which is incremented when an allocation attempt fails due to no idle SDCCH channels.

CFAILCCALLS-CESMSTAB-CCONGS

CESTIMMASSNumber of SDCCH establishment failure due to time-out after sending Immediate Assignment, timer T3101 expired.

CESTIMASS is incremented after the expiration of T3101 timer. The timer start counting once the IMMEDIATE ASSIGNMENT COMMAND is sent to the MS from the BSC. And stop once the BSC received ESTABLISH INDICATION form the BTS.

Signaling Access


Signaling Connection Setup

MS MSCBTS BSC

RR(RACH)Channel Request

Channel Required

Channel Activation

Channel Activation ACK

Immediate AssignmentRR(AGCH)

(L2 - UI)

A interfaceUm interface

CM SERV REQ (L2-SABM)

EST IND<CM SERV REQ>

<CM SERV REQ>

CR(COMPL - L3 - INFO)L2 - UA

(CKSN,MS ID,SER type,CLmk)

CC

RR(SDCCH)

RR(SDCCH)

Immediate Assign Command

(SDCCH ID)

T3120 +

T3120 -

T3101 +

T3101 -

T303 +

Abis interface

CCALLS, CCONGS

AN

Y

OT

HE

R

FA

ILU

RE

W

ITH

IN T

HIS

R

AN

GE

IS

C

FA

IL

CMSESTAB

T3101 expires


Possible Causes of High PCFAIL PCFAIL: Represents a failure on the control channel.Major Contributors: Inconsistent cell RF configuration – Timing advance and

coverage footprint overshooting Inconsistent cell neighbor relation definition High downlink and uplink interference MAIO alarm Antenna system fault affecting the BCCH carrier TX path e.g.

Feeder line fault giving rise to high VSWR and lost RX path; faulty antenna

Antenna Feeder swap Direct external or co-channel interference on the BCCH

channel Signaling instability on the core or from Transport medium

(Abis path intermittent failure or LAPD congestion). Faulty Transceiver Unit, with or without visible fault

indication. Wrong port termination on diplexer unit.


Every sector has two Antenna system connection represented as jumpers originating from the output of the transceiver units; DRU,DTRU,QTRU,GRFU,MRFU etc and are expected to be properly terminated on the antenna with minimal reflection-Voltage standing wave ratio).

The broadcast channel- BCCH of each cell occupy the first Transceiver, hence the first TX path on the sector by default, while the second Tx path is available for traffic.PCFAIL also occurs when the TX path (Transceiver & antenna system) housing the BCCH carrier and other system information does not have proper termination on the external antenna largely due toreflection on the antenna system or bad transmitter on the transceiver unit. Direct external/co-channel interference on the BCCH channel also affect the PCFAIL count, this however depend on the degree of severity of interference coming from a direct neighbor cell

Possible Causes of High PCFAIL ---contd


PCFAIL Resolution Steps: -Short Term Resolution Steps

Short Term Resolution StepsCells with high PCFAIL to be pulled by NQA or RF Optimization from FACTSRF Optimization team to carry out the basic test of forcing the BCCH to an alternate TX path and monitoring the effect on performanceRF Optimization/Switch /RHLS team to confirm consistency of cell data including Timing Advance and neighbor relation definition, Escalation sent out to Field Operations to carry out necessary on-site test and correctionsPhysical Antenna System optimization including antenna down tilt and azimuth/elevation correction to be carried out by RF Optimization


On site ChecksEnsure Jumper cable termination on Diplexer unit conform with the port arrangement on diplexer unit- note Diplexer unit is frequency dependent Carry out an Antenna system sweep to confirm integrity of the antenna path and carry out DTF to locate fault point along a faulty antenna pathReplace faulty component (s) along a faulty antenna pathReplace faulty DRU/transceiver on the affected TX path

PCFAIL Resolution Steps: – On Site Checks


Coverage Control with Timing Advance TuningAlthough, physical tuning (antenna down tilt and antenna height control) is the best way to control coverage, to reduce the impact of overstretched cell coverage (distant Mobiles trying to access the network) and over shooting cells, the following Coverage and MS access Control Parameters can be investigated and tuned appropriately in cells with high PCFAIL.

TALIMTiming Advance Limit for handover. Urgency detection parameter. TALIM determines the maximum timing advance that the MS is recommended to use in the cell.If the measured and averaged timing advance value is equal to or greater than TALIM, the cell must be abandoned urgently if there exists a neighboring cell that can take over the connection. If no such cell exists no action is taken.

MAXTAMaximum Timing Advance before an MS is considered lost. If the measured timing advance value for an access burst is equal to or greater than MAXTA, then the connection set-up signaling is terminated by the system.If the measured and averaged timing advance value for an ongoing call is equal or greater than MAXTA, the call is released.

PCFAIL Resolution Steps:-Coverage Control with Timing Advance Tuning and Other RF Parameters Tuning


Other RF Parameters TuningOther RF parameters changes that can be carried out to improve PCFAIL KPI include the following:

Neighbour relations audit and additions where necessary BCCHNO changes on close neighbor cells with co-channel interference Standardization of hopping frequency set on 900 UL cells MAIO and HSN changes on 900 UL and 1800 OL where inconsistencies are discovered SDCCH re-dimensioning, including movement of majority of SDCCH per cell from CHGR1 to CHGR0 to increase chances of call setup success LAYER adjustments IRC feature should be implemented for improvement in uplink quality Correction of discrepancies including outer cell MSC definitions if there is any ACCMIN with values of100 or more can be changed to 96 for cells in dense urban, with CRO=2 for better cell reselection. Other cells in rural areas shooting into the city can have their ACCMIN changed to 98, with CRO=1 or 2, depending on the CFAIL count of the cell

PCFAIL Resolution Steps:-Coverage Control with Timing Advance Tuning, Other RF Parameters Tuning

PSFAIL FORMULA - TCH SEIZURE ATTEMPTS & SUCCESS

1. TASSALL Incremented at first attempt to change a connection

from a signalling channel to traffic channel for speech or data, If the assignment attempt is unsuccessful, independent of reason, the counter is incremented for the cell where the mobile station was tuned to an SDCCH or TCH used for signalling. The counter is initiated by reception of an ASSIGNMENT REQUEST or HANDOVER REQUEST (cause = directed retry).

2. TCASSAL Incremented for the same conditions as the TASSAL

counter if the attempt was successful. The ‘TCASSAL' counter is incremented for the target cell. The counter is incremented at the ASSIGNMENT COMPLETE (to the MSC) HANDOVER COMPLETE (to the MSC)


PCFAIL Resolution Steps

Identify affected cell/cells

START

Yes

NoConfirm from RF Optimization , NQA or FACTS

:

.

PCFAIL SHORT TERM RESOLUTION QUICK GUIDE

Escalate to RHLS

Yes

Performance improvement?No

END

No

RF Optimization force the BCCH to the alternate TX path

RF Optimization to confirm cell RF parameters including TA, cell baring and neighbor relation definitions and fine tune appropriately; Physical optimization and down tilt to also be considered

Field Operations to confirm right site configuration/reload IDB

Performance improvement?


Field Operations to verify the integrity of the TransceiverDiplexer Physical cable connections/terminationsAntenna path with Antenna System Sweep

Replace any faulty componentClear all BTS internal alarms

Yes

Yes

No

PSFAIL FORMULA - TCH SEIZURE ATTEMPTS & SUCCESS

SFAIL Failure to change connection from a signalling

channel to a traffic channel

SFAIL = TASSALL – TCASSAL

PSFAIL= 100*SFAIL/TASSALL


Possible Causes of High PSFAIL Issues that can cause T3101 to expiresPSFAIL: Represents TCH assignment failure rate.Major Contributors: Overload of AGCH (Access grant channel) False Access :- When a Channel Request message is received by

the system, an SDCCH is allocated by sending an Immediate Assignment message. If it happens that the channel request was caused by radio disturbances, no more messages are received from the non-existing MS and the system waits a certain time before performing a disconnection.

Uplink and Downlink interference. Direct external or co-channel interference on the TCH channel Unusable Transmission path for traffic channel (LAPD

congestion, intermittent A-bis failure). Swap sector on the Over Lay, OL, for Multi Band Cells. High RF Reflection on the antenna system (VSWR). Faulty Transceiver unit, without visible fault indication. Inconsistencies on IDB/Antenna system combination

configuration BTS internal alarms Faulty Antenna


PSFAIL Resolution Steps:-Short Term Resolution Steps

In PSFAIL, unlike PCFAIL, traffic is visible on the affected cell, however it will result in Traffic channel congestion as insufficient TX carrier is detected which will eventually affect CSSR negatively.

Short Term Resolution StepsCells with high PSFAIL to be pulled by NQA or RF Optimization from FACTSRF Optimization to carry out a basic test of blocking each Trx per time on the affected cell and monitor the effect on the cell’s PSFAIL performance. Improved performance means a physical site problem. Else, RF Optimization to confirm cell RF parameters and optimize.Escalation sent out to Field service personnel to carry out necessary on-site test and corrections for cells with physical site problems


On site Checks RequiredConfirm there are no Sector/Jumper swap in the termination on the diplexer unit and the Antenna.Carry out Antenna system sweep on the Traffic TX path to isolate ReflectionSwap DRUs temporary with an unaffected sector to check if the fault will move along. Monitoring will take like 2hrs)If POINT 3 above is TRUE then Replace the DRU/transceiver on the affected TX pathEnsure RBS is cleared of all traffic affecting alarms at least. Ideal is to ensure all internal alarms are cleared

PSFAIL Resolution Steps:-On Site Checks Required


PSFAIL Resolution Steps

Identify affected cell/cells

START

Yes

NoConfirm from RF Optimization , NQA or FACTS

:

.

PSFAIL SHORT TERM RESOLUTION QUICK GUIDE

Esc

ala

te t

o R

HLS

Yes

Swapped sectors?

No

END

Yes

Check physical antenna system connection and the IDB Configuration for consistency

Recreate IDB and correct inconsistencyInconsistency discovered?


From the PSFAIL pattern Confirm if there are no Sector/Jumper swap in the termination on the diplexer unit and the Antenna.

No

Yes

No

Yes Correct sector swap

Field Support to verify the integrity of the TransceiverDiplexer Physical cable connections/terminationsAntenna path with Antenna System Sweep

Clear all BTS internal alarms Replace any faulty component

Performance improvement? No

RF Optimization block one TRX per time (2 hrs) and check effect on performance

Performance Improvement?

Yes

No

Check cell RF parameters and carry out RF optimization on affected cells


PC&SFAIL Long Term Resolution Steps

In the drive to make MTNN a network that is consistently void of high PCFAIL and PSFAIL, the following activities are recommended on a regular basis:

Constant monitoring and reporting of the values of these KPIs and other necessary ones including CSSR, PCONG, PDROP by NQA.Consistent frequency planning and tuning.RF P&O regular routine optimization work.Physical optimization and antenna down tilt where necessary.Timely and consistent site intervention where and when necessary by Field Operations.Consistent BTS routine maintenance to ensure BTS is always free of internal alarms. Field Operation personnel can refer to fault code list for the interpretation, root cause and recommended resolution steps for any alarm.


MTN Nigeria Case StudyIn 2009, a specific project to combat high PCFAIL and PSFAIL on MTN Nigeria Network was initiated and championed by BTS Field and Radio High Level Support unit.Trial was done with selected cells in March 2009, which revealed the unique contributors.After analysis, setup of In-house team to implement the project was recommended and was approved by the management.

In-house Team:1). BTS Field and Radio High Level Support Unit (3 Staff)This unit initiated and coordinated the project. They also provided the necessary second line support for the resolutions, on a site by site basis.2). 8 New Field Support Engineers, FSE, (hired and trained).These were responsible for site checks, identification of site issues and the resolution. They supervised the jobs done by the rigging service providers. 3). Few RF Planning & Optimization Engineers.They carried out cell optimization functions

External team membersIndependent rigging service provider (2 contractors).

The project ran between March and July 2009Preliminary report, covers results achieved from March 3, 2009 to July 15, 2009


MTN Nigeria Case Study:-Achievements

AchievementsPC&S FAIL Resolution Project impacted positively on the following counters and across the regions:i). Reduction in PCFAIL (percentage common channel failure)ii). Reduction in PSFAIL (percentage Call setup failure)iii). Reduction in PCONGiv). Reduction in PDROPv). Improvement in CSSR (call setup success rate)


Recommendations

RecommendationsA similar special team to resolve the present high PC and PSFAIL situation is equally recommended. This will ensure concentrated attention and guarantee a speedy short term resolution

A regular report on the status of these KPIs should be pulled and sent to all stakeholders with the Optimization team responsible for keeping these KPIs below the threshold

Field Operations should ensure a regular site routine maintenance to keep BTS free of internal alarms

Internal alarm report should be pulled and sent out regularly to all stakeholders to know the status of internal alarms on the network as this can be a great contributor to poor QoS performance on the network


Conclusion The issue of PCFAIL and PSFAIL on the network and it’s impact on CSSR has generated a lot of concerns for MTN’s Network in its drive to improve the quality of the network. To this end, time, human and financial resources need to be continuously deployed to combat this issue. With regular monitoring, optimization routine and field routine maintenance, PCFAIL and PSFAIL can be regularly maintained below the threshold and the promised quality service delivered to our subscribers.

Conclusion


Thank You!

Appreciation

F a C T S_CS Fail Resolution11

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