KPI ANALYSIS

REASONS AND SOLUTIONS

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 SD Drop TCH Blocking TCH Assignment TCH Drop HOSR

Get Service

Get SDCCH

Establish SD Channel

Est. TCHConn. 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? 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.2. Check LAC boundary, If location update is more then change

the LAC of that site and set C2 and HYS.3. Use of Dynamic SDCCH (It is a BSC parameter and will be

applied on whole BTS).4. Hardware check / shift SD to new time slot5. Some times BMA and HYS parameters are useful to remove SD

Blocking.

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(10s) 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 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.

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,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..

Check for parameter: Check the Timer T 3101

Check the Timer T 200(20ms)

T11 Expired(10 s)

MAIO check.

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.

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(TRx) 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 TRXs Check BOIA card.

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 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.

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..

Parameter Check:1. Retune Rx level Acc min Neighbour.It can change bw -

90,-95,-105.2. Check HSN.3. Check SYN.4. Retune LDR, LUR, IDR, IUR.5. Retune LMRG, QMRG, PMRG.

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.

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)