KPI ANALYSIS
REASONS AND SOLUTIONS
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
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
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
SD Blocking COMPLETE SD Drop TCH Blocking TCH Assignment TCH Drop HOSR
KPI’ s to be monitored Parameter
Showcase Threshold
Non-Showcase Threshold
SD Blocking
0.25
0.5
SD Drop
1.2
1.7
TCH Blocking
0.5
0.5
TCH Assignment
98.5
98
TCH Drop
1.5
3
HOSR
95
92
Call Establishment
Get Service
Get SDCCH
Establish SD Channel
SD Blocking
Est. TCH Conn.
Call Phone
Ref. Phone
TCH Blocking SDCCH Seizer
CSSR or TCH Assignment
Call completion Rate (TCH Drop 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 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 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:
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: Some of them are
LAC boundary. HW Prob.
Solutions for removal of SD Blocking:
Here are some steps by which we can reduce SD Blocking-
1.
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.
2.
3.
4. 5.
Usefull Reports For SD Blocking:
Use 182 to analyses SD Blocking reasons. 130 for SD congestion.
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 likeovershooting , 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 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:
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: 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:
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… 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.. 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… 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.. 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:
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:
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.
Useful Report for TCH Blocking:
135 TCH Congestion YAHA TAK PADTEIN HAIN AAJ
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.
Reports for TCH Assignment:
ZEOL to check alarms 208 for path imbalance 196 for UL-DL interference ZAHP for Flick report
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. High TR Fail. 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
Cont.. Improve HOSR:
Check the Hopping plan.
Check the Neighbor Plan
High TR Fail:
Check and clear TR fail from oss end.
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.. 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.. 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:
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: 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. Delete long distance neighs. Check neighs are defined form both ends. If there are high fail delete and recreate neighs .
Cont.. 1. 2. 3. 4. 5.
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:
1.
Check DAC value. If DAC value is high or low tune it at the TH value. It should be 2050.
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.. 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 :
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:
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:
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(7609)-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
- Manish Kumar Singh A3132
