1-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:
Some of them are
-High Utilization of TCH
-Time slot faulty.
-Lock TRXs.
-HW Problem.
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.
2-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:
-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:
-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.
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3-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:
-Wrong Parameter Planning.
-BAD HOSR.
-Hardware Fault.
-Overshoot.
-Outage.
-Due to Low Coverage.
-Due to ICM Band(CDMA)
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
Improve HOSR:
-Check the Hopping plan.
-Check the Neighbor Plan
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.
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
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.
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4-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:
-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:
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.
-Deletelong distance neighs.
-Check neighs are defined form both ends.
-If there are high fail delete and recreate neighs.
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.
HW Issues:
-Clear HW issues.
-Check TRXs.
-Check outages.
-Check BOIA Card. Because if it is faulty incoming and outgoing HO will be fail.