KPI ANALYSIS : KPI ANALYSIS REASONS AND SOLUTIONS

Some Relations-1- : Some Relations-1- One BSC=6 BCSU (Base control signaling unit). One BCSU = support 110 TRX. 1 TRX= 8 time slots. Total no. of TRX = 110 *6=660 TRX in single BSC One BSC = One LAC One BSC= 660* 8 = time slots but if dual rate is implemented that it consider as two slots. One BSC= two Lac also but for city one LAC b/c it effects SD blocking and LAC updation on that channel.

Some Relations-2- : Some Relations-2- One BSC= 1 to 248 BCF. One BSC= 1 to 248 BTS One BTS means = one sector of any configuration One BCF means= one site of three or four sector BCF= Base control function. BTS= Base transceiver system. NSEI= is hardware and software device which supports the GPRS in n/w

Some Relations-3- : Some Relations-3- One NSEI= supports 64 BTS and 128 TRX if any one of them is full then we can assign second NSEI port in same BSC 1TRX=117 subscriber 1 subscriber=25 m erlangs (TCH) 1 subscriber=.004 m erlangs(SD) 1 TRX=2.94 erlang(2% GOS ) 2 TRX=8.2 erlang(2% GOS ) 3 TRX=14.6 erlang(2% GOS ) 4 TRX=21.2 erlang(2% GOS ) If BSC 3VI, OSS is 4 and System is S11 then max capacity of BSC is 660 TRXs. If OSS 4.2 and system S12 is using then max capacity of BSC will be 2000TRXs

KPI’s to be monitored : KPI’s to be monitored SD Blocking SD Drop TCH Blocking TCH Assignment TCH Drop HOSR

Slide 6: KPI’s to be monitored

Slide 7: Get Service Get SDCCH Establish SD Channel Est. TCH Conn. Call Phone Ref. Phone SD Blking SDCCH Seizer TCH Blking CSSR or TCH Assignment Call Establishment Call completion Rate (TCH Drop call)

What is Dropped Call? : What is Dropped Call? All cell resources are available but calls are failing, then we have a call drop scenario. This could be caused by software errors, congestion, C7 link failures,HW problems or many other reasons. If a call is abnormally disconnected, a Clear Request is sent to the MSC .If the Call is disconnected in a normal Fashion then Clear Message with cause code Call Control is sent. It is important to establish what types of calls are failing, and over what percentage of the network it is occurring.

SDCCH CHANNEL : : SDCCH CHANNEL : SDCCH is a dedicated channel which is using for LAC updation, Call setup, SMS in idle mode. It works in UL & DL.

SD Blocking: : SD Blocking: SD blocking means that you are not getting SD resource for the call origination. When MS connects with NW then RACH and AGCH are provided. After AGCH,SDCCH is provided but if SDCCH is not provided at this time due some problems or due to unavailable of SD by BSC ,it’s called as SD Blocking. There are no of reasons for that.If such a case arises the customer will not be able to originate any call.

Difference Between Blocking and Congestion: : Difference Between Blocking and Congestion: It is very important to know difference between blocking and congestion. Some people think that both are same, but they differ from each other. If all the SD resources are full and not available for SD assign then its come into congestion. If at a particular time call is attempted and it fails then it known as Blocking.

Reasons for SD Blocking: : Reasons for SD Blocking: Some of them are- LAC boundary. HW Prob.

Solutions for removal of SD Blocking: : Solutions for removal of SD Blocking: Here are some steps by which we can reduce SD Blocking- Check the No. of SDCCH channel Available, if less then increase SD channel taking care that there is no TCH Blocking. Check LAC boundary, If location update is more then change the LAC of that site and set C2 and HYS. Use of Dynamic SDCCH (It is a BSC parameter and will be applied on whole BTS). Hardware check / shift SD to new time slot Some times BMA and HYS parameters are useful to remove SD Blocking.

Usefull Reports For SD Blocking: : Usefull Reports For SD Blocking: Use 182 to analyses SD Blocking reasons. 130 for SD congestion.

SD Drop: : SD Drop: As per diagram shows when we assigned SD for call origination and at that time due to some problem or any mismatch comes by which SD loss occurs, it is called as SD Drop. It occurs between allocation of SD and before TCH allocation. Sometimes SD drop occurs because queuing is not activated in the system. If SD drop is high plz look on parameters like- overshooting , shift the SD time slot , may be hardware issue, interference, change the values of RXP, PMAX, may be issue of uplink or downlink issue in that cells for UL put a TMA in that cell and for DL provide tilt ,re orient that antenna

If SD Drop is high: : If SD Drop is high: If SD drop is high plz look on parameters like- Overshooting Shift the SD time slot Hardware issue Interference Change the values of RXP PMAX It may be uplink or downlink issue in which cells for UL put a TMA in that cell and for DL provide tilt Re orient that antenna

Reasons of SD Drop: : Reasons of SD Drop: Hardware Fault. Interference. MAIO mismatch. Bad Coverage. High TR Fail. Outage. Overshooting. Abis Drop. High Path Loss. Wrong Parameter Planning. Due to ICM Band(CDMA) High LAPD Utilization Heavy blocking and DR feature being used extensively

Solutions for removal of SD Drop: : Solutions for removal of SD Drop: Interference: Check the BCCH Plan (C/I or C/A). Co-BSIC & Co BCCH. Use latest ND 111 and MapInfo to find out proper frequency to reduce interference. Arrange Drive Test: The best way to find the real issues for Interference makes DT. Check interference by Interference scanning. Check clean BCCH by frequency scanning.

Overshooting: : Overshooting: LAC Planning. If a cell is picking call from long distance, Check the sample log according to TA. Cell orientation need to be defined according to clutter. Mount position Effective Tilt.

Cont… : Cont… High TR Fail: Check and clear TR fail from OSS end. Bad Coverage: If the drop call is due to low signal strength uplink, check the receive path of this particular TRX. Check receiver sensitivity, VSWR, feeder connection and etc. Drops due to Low Signal Strength. If the drop call reason is due to low signal strength downlink, then, check the transmit path. Check cards, feeder and etc. Use MapInfo or Google Earth to find location of sites.

Cont.. : Cont.. High LAPD Utilization: Check LAPD util report from OSS, and define 32 kbps signaling instead of 16kbps Hardware Fault: Check Alarms. TRX condition. Check Path Imbalance. VSWR of the Cell. Connector Connection. Some times you will find issues on BCCH TRX.In this case BCCH shift from one to other TRX will reduce SD drop.

Cont… : Cont… Due to ICM Band(CDMA): Some time SD drops takes place due to near sites of CDMA. Check the ICM band value of that site. Use BPF (Band pass filter). Use the spectrum analyzer.

Cont.. : Cont.. Check for parameter: Check the Timer T 3101 Check the Timer T 200(20ms) T11 Expired(10 s) MAIO check.

Useful Reports for SD Drop: : Useful Reports for SD Drop: Use report ZEOL to find the alarms. Use 208 for Path loss analysis. Use 196 for UL-DL Interference. Use 163 report for SD drop. Use report 216 for detail SD Drop. 232 report for TA report. 62 for Adj cell having same or adj freq. ND 111 for freq plan. 204 for BTS and cell report.

TCH Blocking: : TCH Blocking: When TCH is not allocated to the user after SD allocation ,it is TCH Blocking. It is the failed call attempts which the MS user can notice. It takes place due to lack of TCH Resource.

Reasons for TCH Blocking: : Reasons for TCH Blocking: Some of them are- High Utilization of TCH Time slot faulty. Lock TRXs. HW Problem.

Solutions for removal of TCH Blocking: : Solutions for removal of TCH Blocking: Implement half rate or Dual rate. Check FRL & FRU. Add another TRX. If TRX addition not possible, try to share the traffic of that cell with the neighboring cell by changing tilt or orientation.

Useful Report for TCH Blocking: : Useful Report for TCH Blocking: 135 TCH Congestion

TCH Assignment: : TCH Assignment: It’s a process of by which TCH is assigned to the MS. After the SD request MS gets TCH successfully and the call transfers to TCH it means TCH assignment is successful. For the best KPI TCH assignment should tend to 100%. It degrades due to HW problems.

Reasons for TCH Assignment failure: : Reasons for TCH Assignment failure: Hardware Fault(TRXs,Combiner,Duplexer,Cables) VSWR

High Path Loss. Faulty TMA. High TCH Blocking. Loose connections. DR being used extensively

Solutions for removal of TCH Assignment: : Solutions for removal of TCH Assignment: Clear VSWR IF TRXs are faulty lock them and try to replace them soon to avoid blocking Path Imbalance clear. Connection from BTS to Antenna Connector connection Check TMA. Check Duplexer,Combiner,TRXs connections,Multicuppler etc. Check BOIA card. Check BB2F Card.

Reports for TCH Assignment: : Reports for TCH Assignment: ZEOL to check alarms 208 for path imbalance 196 for UL-DL interference ZAHP for Flick report

TCH Drop: : TCH Drop: Drop during conversation is known as TCH drop. It takes place after connect ACK msg on TCH.TCH drop occurring. For TCH drop first cross check the BCCH of that cell, hardware issue may be, change RXP and RLT value. Find out there is any interference ,neighbor defined.

Reasons for TCH Drop: : Reasons for TCH Drop: Wrong Parameter Planning. BAD HOSR. Hardware Fault. High TR Fail. Overshoot. Outage. Due to Low Coverage. Due to ICM Band(CDMA)

Solutions for removal of TCH Drop: : Solutions for removal of TCH Drop: Check Parameter: Check the BCCH Plan (C/I or C/A). Co-BSIC & Co BCCH. Check the Timer T 100(should be 20 ms) Check Overshooting: If a cell is picking call from long distance, Check the sample log according to TA.. Site Orientation. Effective tilt should be check. Mount position should be check

Cont.. : Cont.. Improve HOSR: Check the Hopping plan. Check the Neighbor Plan High TR Fail: Check and clear TR fail from oss end.

Cont.. : Cont.. Bad Coverage: If the drop call is due to low signal strength uplink, check the receive path of this particular TRX. Check receiver sensitivity, VSWR, feeder connection and etc. Drops due to Low Signal Strength. If the drop call reason is due to low signal strength downlink, then, check the transmit path. Check cards, feeder and etc. Use MapInfo or Google Earth to find location of sites. Effective tilt should be check. Mount position should be check.

Cont.. : Cont.. Check HW: Check Alarms on site. Check TRXs. Check Slips. Check the Hopping plan. Check BB2F card. Check VSWR, Path imbalance. Connector Connection. Check TMA

Cont.. : Cont.. Drop Reason because of HW Issues: if drops are only on one site, then go for a check for that particular even attach with that site. If drops are on all sites connected to a single link, then check the slip or interference on that Abis interface. If Drops are distributed on all site of the BSC, then check the slips on A-ter. Down Time of the cell. TRX condition. BTS should not getting the temperature alarm continuously.

Reports for TCH Drop: : Reports for TCH Drop: 166 for TCH Drop ZEOL for alarms. ZAHP for Flicks. 232 for TA report.

208 Path Imbalance report. 204 for BTS report. 216 for all parameter. 196 for UL-DL Qul. 62 for Adj cell having same or adj freq.

HOSR: : HOSR: Hand over success rate: If HOSR will be good TCH drop will also be good. If Handover success rate degrades call drop rate will take place.

Reasons for HOSR: : Reasons for HOSR: Improper Neighbor planning. CO-BCCH-BSIC issues in Neigh. Parameter Check. HSN clash. SL value. LAC boundary. DAC value mismatch. Syn mismatch. Overshoot. HW Issues. Low Coverage

Solutions for removal of HOSR: : Solutions for removal of HOSR: Arrange Drive Test: The best way to find the real issues for HO fail make DT and check layer 3 msg gor HO fail.By DT it is very easy to find the fail between cells. Neighbor Tuning: Try to retune neighbors Avoid CO-BCCH-BSIC neighbors. Avoid extra neighs. Delete long distance neighs. Check neighs are defined form both ends. If there are high fail delete and recreate neighs.

Cont.. : Cont.. Parameter Check: Retune SL.It can change bw -90,-95,-105. Check HSN. Check SYN. Retune LDR, LUR, IDR, IUR. Retune LMRG, QMRG, PMRG. DAC value Check: Check DAC value. If DAC value is high or low tune it at the TH value. It should be 2050.

Cont.. : Cont.. Overshoot: When neighs are far away then chances of HO fail increases. In this case ping-pong HI takes place by which fail takes place. So it the inter distance is high its batter to del that kind of neigh. LAC Boundary- Check LAC boundry. High fail takes place there will be Inter BSC cells. High fail takes place there will be Inter MSC cells. Define proper LAC in neigh cells.

Cont.. : Cont.. HW Issues: Clear HW issues. Check TRXs. Check outages. Check BOIA Card. Because if it is faulty incoming and outgoing HO will be fail. Clear Reports: Clear ZEAT. Clear 60. Clear 67. Clear 61.

Reports for HOSR : : Reports for HOSR : 153 reports for HO fail bw two cells. 154 HO analyses. 60 for discrepancy. 67 for Sync report. 61 for one way neigh. ZEAT for CO-BCCH-BSIC neighs 74 for HO definition report. ZELO for inter MSC HO report. 150 for high HO fail. 157 for high HO attempt and call ratio. 158 for intra BSS HO observation. 62 for Adj cell having same or adj freq.

High RACH Failures: : High RACH Failures: Other reasons look for Random access statistics, if there is a lot of random access failures try to check hardware too. It includes thorough hardware audit including CF Reloading, IDB Setting and reloading, Software synchronization, filter check etc)

Some Important Alarms: : Some Important Alarms: BTS Operation Degraded (7604) - It shows VSWR on cell. TRX Operation Degraded (7607)-It shows critical alarm on TRXs. Channel Fail Rate (7745)-It shows faulty TS on TRXs. BCF Operation degradation ()-It shows DAC value alarm. Ex-TCH Interference (7744)-TRXs faulty or back plan problem. Mean Holding Time(7743)-to detect faulty channels. Working SD Ratio Below TH level (7712)- .Its for the ratio of SDs. LAPD Fail-

TX link fail. Antenna Connection Faulty (7606)-Shows faulty in cable connections. High Temp Alarm-TRXs begins fluctuating.

THANK YOU :

Dropped Call(TCH Drop-SDCCH Drop)-TCH Drop Analysis

Step to check TCH Drop Analysis.

1. Radio Link Time-Out

Every time a SACCH message can not be decoded the radio link time-out counter is

decreased by 1. If the message can be decoded the counter is incremented by 2. However,

the value can not exceed the initial value. The initial value is set by the parameter RLINKT

for radio link time-out in the mobile station and by RLINKUP for timeout in the BSC. If the

mobile moves out of coverage and no measurement reports are received in the BSC, there

will be a radio link time-out and the message Channel Release (cause: abnormal release,

unspecified) is sent to the mobile station and the SACCH is deactivated in the BTS. A Clear

Request message is sent to the MSC. To be sure that the mobile has stopped transmitting,

the BSC now waits RLINKT SACCH periods before the timeslot is released and a new call

can be established on the channel.

2. Layer 2 Time-Out

If the BTS never get an acknowledge on a Layer 2 message after the time T200XN200, the

BTS will send Error Indication (cause: T200 expired) to the BSC, which will send Channel

Release (cause: abnormal release, timer expired) to the mobile station and a Clear Request

to the MSC. The SACCH is deactivated and the BSC waits RLINKT SACCH periods before

the timeslot is released and a new call can use the channel. This is only valid if the call is in

steady state, i.e. not during handover or assignment. 

3. Release Indication

When the BTS received a layer 2 DISC frame from the mobile it replies with a Layer 2 UA

frame to the mobile station and a Release Indication to the BSC. The system does only

react on Release Indication if it is received during a normal disconnection situation. If such

a message is received unexpectedly this will usually cause radio link time-out or timer T200

expiration as the mobile station stops the transmitting of measurement reports. It is also

possible that the release will be normal depending on when the Release Indication is

received.

4. MSC Time-Out

Normal Release:

If the MSC never received a response on a message (e.g. Identity Request) and there is no

radio link time-out or layer 2 time-out, the MSC will send a Clear Command to the BSC.

The time-out is depending on the message. When receiving Clear Command, the BSC will

send a Channel Release (cause: normal release) and then deactivates the SACCH.

Reject (only SDCCH):

If the MSC never receives a response on the first message after Establish Indication, the

MSC will send a reject message. If the connection was a Location Update it will be a

Location Update Reject (cause: network failure) and if the connection was a mobile

originating call (CM Service Request) a CM Service Reject (cause: network failure) will be

sent. The MSC will then send a Clear Command to the BSC and the call is cleared by

Channel Release (cause: normal release).

5. Assignment to TCH

Before sending an Assignment Command from the BSC at TCH assignment, the following

two criterion have to be fulfilled:

a. There must be a TCH channel available, i.e. no congestion

b. The locating algorithm must have received at least one valid measurement report.

If either of the criterion is not fulfilled, Assignment Command will not be sent and a

Channel Release (cause: abnormal release, unspecified) will be sent to the mobile station

and a Clear Request to the MSC. 

TCH Drop reason (1)

The classification of TCH Drop Reasons are arranged in the order of priority:

1.Excessive Timing Advance

2.Low Signal Strength

3.Bad Quality

4.Sudden Loss of Connection

5.Other Reasons

Excessive Timing Advance

The TCH Drop counters due to Excessive Timing Advance will pegged when the during the

time of disconnection, the last Timing Advance value recorded was higher than the TALIM

Parameter. This drop reason is commonly apparent to isolated or island sites with a wide

coverage area.

Action:

Check if the cell parameter TALIM is < "63"

Solution:

Set TALIM to a value close to 63.

Tilt antenna/reduce antenna height/output power, etc. for co-channel cells.

TCH Drop Reasons (2)

Low Signal Strength on Down or Uplink or Both Links

The drops counters due to Low Signal Strength will be pegged when the Signal Strength

during the last Measurement Report before the call dropped is below the LOWSSDL and/or

LOWSSUL Thresholds. LOWSSDL and LOWSSUL are BSC Exchange Property parameters

which is used only for statistics purposes and does not affect the behavior of calls. If both

UL and DL Signal Strength are below the thresholds, only Drop due to Low SS BL will

pegged. Normally a call is dropped at the border of large rural cell with insufficient

coverage. Bad tunnel coverage cause many dropped calls as well as so called coverage

holes. Bad indoor coverage will result in dropped calls. Building shadowing could be

another reason.

Action:

Check coverage plots.

Check output power.

Check power balance and link budget.

Check if Omni site.

Check antenna configuration & type.

Check antenna installation.

Perform drive tests & site survey.

Check TRX/TS with high CONERRCNT.

Solution:

Add a repeater to increase coverage in for example a tunnel.

Change to a better antenna (with higher gain) for the base station.

Add a new base station if there are large coverage holes.

Block/Deblock TRX

TCH Drop Reasons (3)

Poor Quality on Down or Uplink or Both Links

The drops counters due to Bad Quality will be pegged when the Signal Strength during the

last Measurement Report before the call dropped is above the BADQDL and/or BADQUL

Thresholds. BADQDL and BADQUL (expressed in DTQU) are BSC Exchange Property

parameters which is used only for statistics purposes and does not affect the behavior of

calls. If both UL and DL Quality are above the thresholds, only Drop due to BAD Quality BL

will pegged.

Problem on Bad Quality is usually associated with Co-channel Interference on BCCH or

TCH. Faulty MAIO assignment can cause frequency collisions on co-sited cells especially on

1x1 Reuse. External interference is also one possible cause of problem on quality.

Action:

Check C/I and C/A plots.

Check Frequency Plan (Co-BCCH or Co-BSIC Problem).

Check MAIO, HOP, HSN parameters.

Check FHOP if correctly configured (BB or SY).

Check for External Interference.

Perform drive tests.

Solution:

Change BCCH frequency.

Change BSIC.

Change MAIO, HOP, HSN.

Change FHOP.

Record RIR or on-site Frequency Scanning to identify source of interference.

Use available radio features.

TCH Drop Reasons (4)

Sudden Loss of Connection

Drops due to Sudden Loss are drops that have not been registered as low signal strength,

excessive timing advance, bad quality or hardware (other) reasons, and the locating

procedure indicates missing measurement results from the MS.

There are some common scenarios that could lead to Sudden Loss of connections such as

very sudden and severe drops in signal strength, such as when subscribers enter into

buildings, elevators, parking garages, etc., very sudden and severe occurrence of

interference, MS runs out of battery during conversation, Handover Lost, BTS HW faults,

Synchronization or A-bis link fault (transmission faults), and

MS Faults.

Action:

Check BTS Error Logs, Alarms and Fault Codes.

Check CONERRCNT per TRX and TS.

Check Transmission Link (A-bis).

Check for DIP Slips.

Check LAPD Congestion.

Correlate Handover Lost to Drops due to Sudden Loss

Solution:

Fix Hardware Faults and Alarms.

Reset TRX with high CONERRCNT.

Ensure that Synchronization and A-bis Link are stable.

Change RBLT with high DIP Slips.

Change CONFACT or increase Transmission Capacity

Investigate HO Lost Problem

TCH Drop Reasons (5)

TCH Drops due to Other Reasons

TCH drops due to Other Reasons are computed by subtracting the sum of drops due to

Excessive TA, Low SS, Bad Quality and Sudden Loss from the Total TCH Drop Counts.

Drops due to Other Reasons are generally associated with hardware problems,

transmission link problems on A-bis, Ater or Ainterfaces, and sometimes Handover Lost.

Action:

Check BTS Error Logs.

Check Alarms and Fault Codes.

Check CONERRCNT per TRX and TS.

Check Transmission Link (A-bis).

Check for DIP Slips.

Correlate Handover Lost to Drops due to Other Reasons

Solution:

Fix Hardware Faults and Alarms.

Reset TRX with high CONERRCNT.

Ensure that Synchronization and A-bis Link are stable.

Change RBLT with high DIP Slips.

Investigate HO Lost Problem

Problem reason of drop in SDCCH

Low Signal Strength on Down or Uplink

The reason for poor coverage could be too few sites, wrong output power, shadowing, no

indoor coverage or network equipment failure.

Action: Check coverage plots.Check output power. Perform drive tests. Check BTS error

log

Solution: Add new sites. Increase output power. Repair faulty equipment.

Poor Quality on Down or Uplink

Action: Check C/I and C/A plots. Check frequency plan. Perform drive tests.

Solution: Change frequency. Use available radio features.

Too High Timing Advance

Action: Check if the cell parameter TALIM is < style="font-weight: bold;">Solution: Set

TALIM to a value close to 63. Tilt antenna/reduce antenna height/output power, etc. for

cochannel cells.

Mobile Error

Some old mobiles may cause dropped calls if certain radio network features are used.

Another reason is that the MS is damaged and not working properly.

Action: Check MS fleet.

Solution: Inform operator.

Subscriber Behavior

Poorly educated subscribers could use their handsets incorrectly by not raising antennas,

choosing illadvised locations to attempt calls, etc.

Action: Check customer complaints and their MS.

Battery Flaw

When a subscriber runs out of battery during a conversation, the call will be registered as

dropped call due to low signal strength or others.

Action: Check if MS power regulation is used. Check if DTX uplink is used.

Congestion on TCH

The SDCCH is dropped when congestion on TCH.

Action: Check TCH congestion

Solution: Increase capacity on TCH or using features like Assignment to another cell, Cell

Load Sharing, HCS, Dynamic Half-Rate Allocation and FR-HR Mode Adaptation etc

TYPICAL RADIO PROBLEMSSeveral sources of information for optimization: QoS indicators, Coverage predictions, Customer complaints, Drive tests, Abis/A traces, Other teams information (NSS statistics).

I. Coverage ProblemBad coverage :A network facing coverage problems has bad RxLev. RxQual can be bad at the same time. Sometimes the RxLev can look OK on the street (i.e. from drivetest) but coverage inside the buildings can be poor due to building losses. Building losses can range from 10 to 30 dB or more.

Indications :• Customers complain about dropped calls and/or “No Network”

• OMC QoS indicators

– TCH failure rate

– Call drop rate

– Low proportion of better cell HO

– High rate of DL & UL Level HO (possibly also DL/UL quality HO)

• A interface indicators

– High rate of Clear Request message, cause radio interface failure

• Drive Test

– Poor RxLev ( < -95 dBm)

Investigation and Optimization :

• If actual coverage OK compared to predicted ones

– Improve coverage by adding Macro site, Microcell site (Border or Shadow areas), or IBC site (In-building coverage).

– Use parameter setting ex. Bi-layer Handover.

• If actual coverage is not the one predicted by planning tool

– Check antenna system (azimuth, crossed sector?)

– Check prediction in the tool (EIRP, Clutter Type, Obstructing building?). Most of the time the prediction will be incorrect, as it is only a computer simulation

– Increase or decrease antenna down-tilt

– Check BTS output power set in the OMC-R (BS_TXPWR_MAX: should always be set at 0)

From Drive test or Abis Interface

– RxLev < -95 dBm and

– RxQual > 4

II. Interference ProblemInterference:

A network facing interferences problems presents good RxLev and bad RxQual in the same time on some areas.

Indications:• Customers complain about bad speech quality (noisy calls) and/or call drops

• OMC QoS indicators

– SDCCH/TCH Drop

– Low proportion of better cell HO

– High rate of DL/UL quality HO and interference HO

– Low HO success rate

• A interface indicators

– High rate of Clear Request message, cause radio interface failure

• Drive Test

– RxQual > 4 with RxLev > -85 dBm

Typical causes:

• GSM interferences: Co-channel, adjacent.

• Non GSM Interference: Other Mobile Network, Other RF sources.

Co-channel interference:

• C/I = Carrier-to-interference ratio

• +12 dB is taken into account for Alcatel ( +9 dB according to GSM standard) (i.e. interference can be 9 12 dB weaker than serving cell to cause poor RxQual).

• Indications: Downlink and/or Uplink Interference, High rate of quality handover, call drop, and call setup failure.

• Investigation: Drive test analysis, Lumpini: Co-channel checking, Check prediction to verify which cell could be causing the interference, Frequency plan C/I < 12 dB.

• Optimization: Antenna optimization, Change frequency, Reduce BTS power (not an option in TA Orange network), Concentric cell.

Adjacent channel interference:• C/A = Carrier-to-adjacent ratio

• -6 dB is taken into account for Alcatel ( -9 dB according to GSM standard).

• Indications : Downlink and/or Uplink Interference, High rate of quality handover, call drop, and call failure

• Investigation: Adjacent HO statistics (if they are defined as neighbors). If they often handover, then adjacent channel interference could be a problem. Drive test analysis ; Lumpini: Adjacent channel checking ; Cell coverage prediction; Frequency plan C/I < -6 dB.

• Optimization : Antenna optimization, Change frequency, Reduce BTS power (not an option in TA Orange network), use Concentric cell

Non GSM interference :• Other mobile network : Inter-modulation with GSM BTS/MS receiver

• Other RF interferers

– Radar

– Shop anti-theft mechanism

– Medical devices

– Other man-made radio transmission

– Illegal usage of GSM frequencies (e.g. illegal imported devices, illegal usage of other organization, …)

III. Unbalance power budget Problem– A cell facing unbalanced power budget problems presents a too high path-loss difference between UL and DL (often DL>UL)

– Lower Rx diversity gain of cross polarized antenna in rural area compared to dense area

– Crossed feeders

– Traffic not directly in boresight of antenna, where cross-polar discrimination is lower

– Loose connectors

– Faulty antenna, feeder, TMA

– Rule : try to have delta as small as possible to avoid access network possible only in 1 direction (usually BTS->MS : OK and MS->BTS : NOK), i.e. uplink limited

Indicators:• OMC QoS indicators

– High ratio of Uplink level Handover cause

– Low incoming HO success rate

– DL level looks OK for HO, but UL is too weak when HO is attempted

– Degradation of TCH failures and OC call drop indicators

• A interface indicators

– High rate of Clear Request message, cause radio interface failure

• O&M Alarms

– Voltage Standing Wave Ratio (VSWR)

– TMA

Investigation :

– Abis monitoring: ABS(delta Path loss) > 10Check if problem is occurring for 1 TRX or all.

– ABS(delta path loss) = ABS(UL Path loss – DL Path loss)

– UL Path loss = MS transmitted power – measured received UL level

– DL Path loss = BTS transmitted power – combiner loss – measured received DL level

– Large difference between uplink and downlink level triggered HO.

– Use PM observation counter (in OMC-R)

– RT11

Optimization : This equipment should be checked– TRX types (MP, HP)

– Antennas or common RF components, TMA (common to all TRX of the BTS)

– TRX RF cables, LNA

IV. TCH congestion ProblemTCH Congestion :• TCH Congestion rate (TCH Assignment Phase) is too high (more than 2%)

• Rule : try to meet the offered traffic (asked by users) by providing the right number of resources (TRX extension)

Indications:– Customers complain about “Network busy”

– OMC QoS indicators: High “TCH Congestion rate”, “RTCH Assignment fail-Congestion”, Low “incoming Intra/Inter BSC HO success rate” (no TCH available), High “Directed Retry rate or Congestion Relief (Motorola)” if activated, A interface indicators: “BSS Congestion failure in OC”(High rate of Assignment Failure message, No radio resource available)

– Drive Test : Handover to better cell is slow, or never occurs

Optimization:– Special events :

Foreseeable:  (footballs match, important meeting, Exhibition, etc): Add some extra TRXs, Add special mobile BTSs (Cell on Wheel), Activate HR (may not always be possible due to BSC capacity limitations)

Not foreseeable: car crash on the highway

– Daily periodic problems : At busy hour:

Hardware solution: Add TRX(s), concentric cell, new site, Optimize cell boundaries (i.e. antenna optimization) to share traffic with surrounding cells.

Software solution: Directed Retry, Traffic Handover, Half Rate (Alcatel), Congestion Relief (Motorola) Flow control (Motorola).

Problems and responsible parties

• Coverage problem :

If the measured RxLev does not match the prediction:

– Check the prediction, check panoramic pictures for obstructions

– Field Operation team to check physical configuration (tilt, azimuth, antenna height…). Also check for faults in the antenna system (VSWR, sweep antennas, DTF test, etc.)

– If Field Operation find no problem, antenna optimization may be required (if necessary)

If the field realities match the prediction:

RF team to add new sites (tri-sector, micro cellular, indoor cells) to improve poor/no coverage area (Optimizer requests for some new sites to RF team regarding to the drive test result).

• Interference problem :

Optimization team to identify the interference source and request Spectrum Management team to correct it in case of internal source (new frequency planning…)

• Unbalanced power budget problem :

Field Operation team to check the impacted BTS (Antenna, TMA, RF cables, LNA, diversity system…) according to request from Optimizer.

• TCH Congestion problem :

Regional RF to request TRX expansion.