Drop call presentation for Optimization / Cara mengatasi Drop Call untuk Optim

Overview 

 Dropped calls – abnormal disconnections during call setup/conversation Subscriber perception TCH drop interrupt conversation when SDCCH drop, user redial again 

Analysis focus on TCH drop 

Overview cont 

- TCH Drop
- Excessive Timing Advance
- Low Signal Strength
- Bad Quality
- Sudden Loss
- Other reason

 TxNDROP (x=F for full rate, x=H for half rate) total number of dropped TCH connections incremented when there’s abnormally terminated connections 

 Dropped Call - Excessive Timing Advance 

 Drop call due to excessive TA occurs when TA>TALIM . Counter TxDISTA is incremented.

Prolem reason
Location : high site, site close to water - able to capture far away traffic Parameters :
1) TALIM – low TALIM gives the perception that more dropped calls are due to excessive TA
2) MAXTA – call release is TA>=MAXTA

Excessive TA – troubleshooting 

Check MAXTA & TALIM. Setting MAXTA & TALIM to a higher value ( MAXTA=63, TALIM=62) could help If cell coverage is very large, can consider to reducing coverage by down tilting, reducing antenna height, lowering output power If site is in rural area and need to cover large area – Extended Range feature might be useful

Dropped Call - Low Signal Strength 

Dropped calls due to low signal strength can occur in downlink (DL), uplink (UL) or bothlink (BL)

Related counters:

TxDISSUL= dropped connections on low SS on UL
TxDISSDL= dropped connections on low SS on DL
TxDISSBL= dropped connections on low SS on BL

 Low SS - Probable Reasons 

Isolated site Antenna/Feeders – too much downtilt, incorrect orientation, hidden antenna, faulty antenna/feeders Output power – incorrect power settings BSC Exchange property – improper LOWSSUL/DL settings Unforseen subscriber behaviour – use MS in lifts, car park Missing NREL Obstacles – building, hills, tunnel etc.

 Low SS – troubleshooting 

Check power settings (BSPWRB, BSPWRT),
power balance Check neighbour relations use site position on map and manually determine neighbour use NCS/NOX to find suitable neighbour consistency check to find missing relations BTS error log – check for any hardware faults indicating high VSWR Check power settings (BSPWRB, BSPWRT), power balance
Check neighbour relations
use site position on map and manually determine neighbour use NCS/NOX to find suitable neighbour consistency check to find missing relations
BTS error log – check for any hardware faults indicating high VSWR

Low SS – troubleshooting cont

Run MRR Check TA & RxLev distribution. If subs. are on low TA and low SS drops, then might lack indoor/street coverage. If subs are on high TA, that could indicate coverage gaps or missing neighbour relation Can also compare results with TCP coverage plots. This gives indication of obstacles covering the antenna, faulty antenna/feeder which might cause low SS Perform drivetest Check for missing neighbours, swapped feeders, probable obstacles

Dropped Call – Bad Quality 

Dropped calls due to bad quality can occur in downlink (DL), uplink (UL) or bothlink (BL)
Related counters:
TFDISQAUL= dropped connections at bad quality on UL
TFDISQADL= dropped connections at bad quality on DL
TFDISQABL= dropped connections at bad quality on BL

 * Setting of BADQUL and BADQDL influences the bad quality counters 

Bad Quality – Probable Reasons 

Frequency plan – adjacent and co-channel interference
No dominant server – low SS
Missing NREL – MS is not able to connect to strongest server
Hardware problems – antennas, feeders, connectors
Environment – near open water
External – other networks, microwave links, illegal transmitters

Bad Quality – troubleshooting 

Display C/I & C/A plots in TCP – check if cell is located in an interference area.
Consistency check/MCOM – to determine adjacent and co- channel interference
Check ICM – determine any uplink interference
Check handover statistics and observe neighbour relation with high number of BQ handover.This might give location of BQ area
Run MRR – check average RxQual in the cell
Run FAS – displays interference level for selected freq.

Bad Quality – troubleshooting cont. 

Perform drivetest
can locate interferer by halting the effected cell & performing freq. scanning to locate the interfering cell. can also use spectrum analyser
check for missing NREL
QLIMUL & QLIMDL – ensure correct settings. Recommended QLIMUL/DL = 55 for hopping and QLIMUL/DL = 45 for non-hopping
Reduce interference – if can’t change freq, then consider downtilt/power down interferer
Use features – IHO,DTX, Frequency hopping, MS/BTS Power Control

Dropped Call – Sudden Loss 

Valid when none of the first 3 types of droppped calls (i.e. excessive TA, low SS, BQ) are indicated and locating procedure indicates missing measurement results from MS Related counter
TFSUDLOS = dropped connections due to suddenly loss connections

Sudden Loss – Probable Reason 

Environment – sudden drop in SS, such as when subscribers enter into building, lift, tunnel etc. Battery – MS battery finishes during conversation, or battery being pulled out
BTS/MS hardware fault
Transmission fault – synchronization/ABIS link fault
Interference – very sudden and severe occurrence of interference or bad quality

Sudden Loss – troubleshooting 

RLINKT & RLINKUP – check is correct settings. Consider increasing for certain scenarios Check synchronization and link faults
Check BTS error log
Check if its related to human behaviour

Other reasons – Probable reasons 

No specific counters – reasons for it occuring are subjective
Hardware faults – BTS or MS
Transmission/link problems
Maintainence work – affecting network service
Interference – severe interference

problems Other reasons - troubleshooting 

Check BTS error log – any HW faults
Check with O&M – transmission problems, maintainence work during the effected time period
Check if ICM/MRR - indicating uplink interference in cell
Check object type MOTS – help find faulty devices

Summary 

Dropped calls : Excessive TA, Low SS, Bad Quality, Sudden Loss, Others Counters and formulas Probable reasons for dropped calls and trouble shotting Tools : Statics/SPOS & Turtle MCOM RNO (MRR,FAS,NCS,FOX,NOX) TCP Consistency Check