Call Drop Analysis Guideline

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Call Drop Analysis Guideline


B.1 Air Interface Problem. The Call Drop Reason can be classified into several reason with Raw statistic relation.

– Coverage, Neighbor and Interference Problem.• VS.RAB.Loss.CS.RF

• VS.RAB.Loss.CS.RF.RLCRst

• VS.RAB.Loss.CS.RF.ULSync

• VS.RAB.Loss.CS.RF.UuNoReply

• VS.RAB.Loss.CS.RF.Oth

A. Call Drop Reason

B.2 Non Air Interface Problem. The Call Drop Reason can be classified into several reason with Raw statistic relation.

– Abnormal Problem• VS.RAB.Loss.CS.Abnorm

– Cell congestion problem• VS.RAB.Loss.CS.Congstion.CELL

– Signalling problem• VS.RAB.Loss.CS.SRBReset

– RNC problem• VS.RAB.RelReqCS.OM, VS.RAB.RelReqCS.RABPreempt,

VS.RAB.RelReqCS.UTRANgen – IU Interface problem

• VS.RAB.Loss.CS.Aal2Loss


.

B. Call Drop Analysis Flow


The methodology to analyze Call Drop problem containing several step below:

1. Data Preparation.

2. Coverage Analysis.

3. Neighbor Analysis.

4. Interference Analysis.

5. Equipment Analysis.

6. Signalling Analysis.

C. Methodology


• The Threshold of CPICH RSCP <=-95 dBm consider as Poor Coverage.

• If the uplink transmit power reaches the maximum before call drop, the call drop is probably due to poor uplink coverage.

• If the downlink transmit power reaches the maximum before call drop and the downlink BLER is weak, the call drop is probably due to poor downlink coverage.

• Poor Coverage could be due to cross feeder, missing neighbor, inconsistency neighbor parameter, neighboring sites down, and node b power amplifier failure.

C.2 Coverage Analysis

• Hourly/Daily Statistic KPI(RAB release triggered by UTRAN per cell, Cell TX and RX Power, etc).

• The latest Site Map, Neighbor relation, and cell configuration/parameter data.

• Single subscriber tracing recorded by RNC.

• CHR recorded by RNC.

• Active and History Alarm.

• Data files collected by DT.

C.1 Data Preparation


• The DL interference or Pilot Pollution classified If ECNO <=-12 dB and RSCP >=-80 dBm.

• The DL Power in connected mode will reaching maximum level to compensate DL interference or Pilot Pollution problem.

• The UL interference increases the UE downlink transmit power in connection mode, very high BLER causes call drop due to synchronization failure.

• UL interference might be internal or external. Most of scenario uplink interference are external.

• Pilot Polluter definition is if Cpich EcNo4th > Cpich EcNo1st - 5 dB in Scanning test.

C.4 Interference Analysis

• The neighbor definition 3G-3G should be created both way.

• Neighbor relation checking to avoid any missing neighbor of 3G-3G, 3G-2G, and 2G-3G relation.

• Neighbor, reselection and handover parameter checking needed to avoid improper setting

like Qqualmin and Qrxlevmin, even1A,1B,1C,2D,2F threshold and timer.

C.3 Neighbor Analysis


C.5 Equipment Analysis • The History and Active Alarm can help to give quick reference for analyzing the network

problem.

• The Alarm information of RNC, Node b, MSS, MGW, and Interface(Transmission) can we gather as early diagnosis to reduce time if we found Call Drop problem.

• Alarms that affect Call Drop mainly include transmission alarms of the carrier signaling (E1/T1, SAAL,NCP/CCP, MTP3B, internal IPC and AAL2PATH) and equipment alarms (Power Amplifier, VSWR, clock, CPU, DSP, etc.). If such alarms occurred, find out the causes and eliminate these alarms immediately.


• Radio network signaling includes signaling of four standard interfaces of UU, IU IUB and IUR. When an abnormality occurs in the signaling flow, we can check which part of signaling flow is missing.

• The missing of signaling flow should be correlated to UU,IUB,IU, and IUR interface problem.

• According to single subscriber tracing messages, the call drop is defined as:

1) The RNC originates RAB release (the message is RANAP_RAB_RELEASE_REQ)-TRB Reset

2) The RNC originates IU release (the message is RANAP_IU_RELEASE_REQ)- SRB Reset.

Check the call drop time and the signaling message before call drop for further analysis.

• The Imsi trace tool with all interface message and monitoring kpi(CPICH RSCP, CPICH ECNO, UL SIR, UL TX PWR, and DL TX CODE POWER) helping us distinguishing Call Drop Reason. The Call Drop related to Air Interface or not related to Air Interface problem.

C.6 Signalling Analysis


Call Drop Analysis Guide Using Signalling IMSI Trace


• It is Shows details of all calls based on output from Trace Management->Interface Trace Task->UE.

• Provide convenient, PC-based analysis

1. Call Message Event

2. The downlink CPICH RSCP and ECNO Distribution.

3. UL SIR Distribution.

4. UE Tx Power distribution.

5. DL Tx Code Pwr

IMSI Trace on LMT


Trace Viewer for Post Processing IMSI Trace Log

2 3 4 5

1. Call Message Event

2. The downlink CPICH RSCP and ECNO Distribution.

3. UL SIR Distribution.

4. UE Tx Power distribution.

5. DL TX Code Pwr.

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Call Message Event- Lac-Cell Id Identification• Filter The Message by RANAP_LOCATION_REPORT message.

• Convert The HEX value into DEC value.


• Synchronize the Time of Call Drop.

• Call Drop Message defined as:

1. The RNC send RAB Release(RANAP_RAB_RELEASE_REQ)

2. The RNC send IU Release(RANAP_IU_RELEASE_REQ).

Call Message Event- Call Drop Identification


Call Message Event- Normal Call Release(User Release)• Filter The Message by RANAP_DIRECT_TRANSFER->cm-msg->Disconnect->Cause-

Value:normal-call-clearing(16)message.


Call Message Event- Call Drop Identification(Normal Unspecified(31))

• Filter the message by RANAP_DIRECT_TRANSFER->cm-msg->Disconnect->Cause-Value:normal-unspecified(31)message.

• This Message not consider as Call Drop.

• This Message consider as problem from CN (test number timer) or MTC side.


• The Breakdown from RF Problem.• Checking CPICH and RSCP Distribution.• If RSCP <=-95 dBm Consider as Poor Coverage, Check for missing neighbor and nearby Site problem.• If ECNO <=-12 dB and RSCP >=-80 dBm consider as DL Interference/Pilot Pollution. Drive Test for

verification is needed.

Bad RSCP and ECNO Distribution

Coverage and Interference AnalysisCPICH RSCP and ECNO


• The Breakdown from RF Problem.• Checking UL TX PWR Distribution.• Max UE TX PWR is to 24 dBm.• If UE TX PWR more than 5 dBm consider as high UE TX PWR.• High UE TX PWR can be due to Excessive UL Coverage or High UL Interference, Check if any missing

neighbor or nearby Site Problem.

High UL TX PWR

Distribution

Coverage and Interference Analysis UE TX POWER


• The Breakdown from RF Problem.• Checking UL SIR Distribution.• The SIR Target for this Services is -1.5 dB.• If The SIR Measured Less than -1.5 dB can be due to Excessive UL Coverage or High UL Interference,

Check any missing neighbor or neighbor Site Problem

Bad UL SIR Distribution

Coverage and Interference Analysis UL SIR


• The Breakdown from RF Problem.• Checking DL TX Code Power Distribution.• The TX CODE POWER MAX Value for this AMR 12.2 is equal to CPICH POWER (example 33dBm) .• The TX CODE POWER MIN Value for this AMR 12.2 is equal to 18 dBm• If The TX Code Power Reaching near to CPICH POWER can be due to Poor Coverage/Fringe Cell/DL

Interference. Check any missing neighbor or neighbor Site Problem.

High DL TX CODE

POWER Distribution

Coverage and Interference Analysis DL TX CODE POWER

Call Drop Analysis Guideline

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