KPI ANALYSIS
REASONS AND SOLUTIONS
Some Relations-1
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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.
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One BSC= 1 to 248 BTS
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One BTS means = one sector of any configuration
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One BCF means= one site of three or four sector
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BCF= Base control function.
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BTS= Base transceiver system.
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NSEI= is hardware and software device which
supports the GPRS in n/w
Some Relations-3
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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
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SD Blocking
SD Drop
TCH Blocking
TCH Assignment
TCH Drop
HOSR
KPI’s to be monitored
Parameter
Showcase
Threshold
0.25
Non-Showcase
Threshold
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
SD Blocking
Call Establishment
Get
Service
Get
SDCCH
Establish
SD Channel
SD Blking
Est. TCH
Conn.
Call Phone
Ref. Phone
TCH Blking
SDCCH Seizer
CSSR or TCH
Assignment
Call completion
Rate (TCH Drop
call)
What is Dropped Call?
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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.
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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 :
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SDCCH is a dedicated channel which is
using for LAC updation, Call setup, SMS in
idle mode. It works in UL & DL.
SD Blocking:
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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:
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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
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LAC boundary.
HW Prob.
Solutions for removal of SD Blocking:
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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:
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Use 182 to analyses SD Blocking reasons.
130 for SD congestion.
SD Drop:
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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
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Shift the SD time slot
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Hardware issue
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Interference
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Change the values of RXP PMAX
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It may be uplink or downlink issue in which cells for UL
put a TMA in that cell and for DL provide tilt
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Re orient that antenna
Reasons of SD Drop:
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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:
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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:
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The best way to find the real issues for Interference
makes DT.
Check interference by Interference scanning.
Check clean BCCH by frequency scanning.
Overshooting:
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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:
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Check and clear TR fail from OSS end.
Bad Coverage:
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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.
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If the drop call reason is due to low signal strength downlink,
then, check the transmit path. Check cards, feeder and etc.
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Use MapInfo or Google Earth to find location of sites.
Cont..
High LAPD Utilization:
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Check LAPD util report from OSS, and define 32 kbps signaling
instead of 16kbps
Hardware Fault:
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Check Alarms.
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TRX condition.
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Check Path Imbalance.
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VSWR of the Cell.
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Connector Connection.
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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):
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Some time SD drops takes place due to near sites of
CDMA.
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Check the ICM band value of that site.
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Use BPF (Band pass filter).
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Use the spectrum analyzer.
Cont..
Check for parameter:
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Check the Timer T 3101
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Check the Timer T 200(20ms)
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T11 Expired(10 s)
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MAIO check.
Useful Reports for SD Drop:
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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:
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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
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Time slot faulty.
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Lock TRXs.
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HW Problem.
Solutions for removal of TCH Blocking:
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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:
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135 TCH Congestion
TCH Assignment:
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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:
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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:
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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:
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ZEOL to check alarms
208 for path imbalance
196 for UL-DL interference
ZAHP for Flick report
TCH Drop:
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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:
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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:
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Check the BCCH Plan (C/I or C/A).
Co-BSIC & Co BCCH.
Check the Timer T 100(should be 20 ms)
Check Overshooting:
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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:
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Check the Hopping plan.
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Check the Neighbor Plan
High TR Fail:
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Check and clear TR fail from oss end.
Cont..
Bad Coverage:
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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.
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If the drop call reason is due to low signal strength downlink, then,
check the transmit path. Check cards, feeder and etc.
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Use MapInfo or Google Earth to find location of sites.
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Effective tilt should be check.
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Mount position should be check.
Cont..
Check HW:
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Check Alarms on site.
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Check TRXs.
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Check Slips.
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Check the Hopping plan.
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Check BB2F card.
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Check VSWR,
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Path imbalance.
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Connector Connection.
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Check TMA
Cont..
Drop Reason because of HW Issues:
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if drops are only on one site, then go for a check for that particular
even attach with that site.
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If drops are on all sites connected to a single link, then check the
slip or interference on that Abis interface.
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If Drops are distributed on all site of the BSC, then check the slips
on A-ter.
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Down Time of the cell.
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TRX condition.
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BTS should not getting the temperature alarm continuously.
Reports for TCH Drop:
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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:
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If HOSR will be good TCH drop will also be
good.
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If Handover success rate degrades call drop
rate will take place.
Reasons for HOSR:
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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:
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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:
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Try to retune neighbors
Avoid CO-BCCH-BSIC neighbors.
Avoid extra neighs.
Delete long distance neighs.
Check neighs are defined form both ends.
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If there are high fail delete and recreate neighs.
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Cont..
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Parameter Check:
5.
Retune SL.It can change bw -90,-95,-105.
Check HSN.
Check SYN.
Retune LDR, LUR, IDR, IUR.
Retune LMRG, QMRG, PMRG.
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DAC value Check:
1.
Check DAC value. If DAC value is high or low tune it at
the TH value. It should be 2050.
1.
2.
3.
4.
Cont..
Overshoot:
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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
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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:
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Clear HW issues.
Check TRXs.
Check outages.
Check BOIA Card. Because if it is faulty incoming and outgoing
HO will be fail.
Clear Reports:
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Clear ZEAT.
Clear 60.
Clear 67.
Clear 61.
Reports for HOSR :
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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:
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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:
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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 (7601)-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