how to analyze call drop by dt

HUAWEI TECHNOLOGIES CO., LTD.

www.huawei.com

Huawei Confidential

Security Level:2008-7-18

Call Drop Analysis

Trainning Document

HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential

Content

What is call drop?

The types of call drop

Basic call drop reasons

Call drop issues during DT

Call drop cases


What is Call Drop?

The abnormal channel released during call due to the reasons

such as:

1. Blind/poor coverage area;

2. Bad quality;

3. Irrationality parameters configuration;

.

.

.

n. Hardware problems.


I can not allocate channel for you!!!

Hello……?

Hello……?

Hello……?

Why call drop again?

What is Call Drop?


The types of call drop

TCH call drop

The abnormal TCH channel released after TCH channel has

been allocated to MS

SDCCH call drop

The abnormal SDCCH channel released after SDCCH channel

has been allocated to MS


Basic call drop reasons

Radio Link Time out

T3103 Time out

System problems (hardware)


Radio Link Time out

MSMS BTSBTS MSCMSCBSCBSC

Measurement report

Measurement result

Connection failure

Clear REQ (radio interface failure)

(1)

(2)

(3)

(1) Dedicated Channel Mode Set Up

(2) Abis Monitor Activation

(3) Can not Decode SACCH, and Then Radio Link Time out.


T3103 Time out

MSMS BTS1BTS1 MSCMSCBTS2BTS2 BSCBSC

Handover commandHandover

Physical info(TA)SABM

UA

Handover Complete

Access

Handover command

HO_DETECT

EST Indication

HO_Complete

Reset T3103

Set T3103Ch_Ack

Ch_Act

IndicationHandover


System problems (hardware)

DDRU board is not on working;

High VSWR(>1.2);

The feeder connector is loose;


Call drop issues during DT

Coverage;

Interference;

Handover;

Antenna & feeder system;

Others;


Coverage issues & reason

Discontinuous coverage area;

Reason: very lower RexLev, especially due to single site

Overshooting;

Reason: call drop after handover delay

Uplink & downlink is imbalance;

Reason: MS can not transmit & receipt signal, the call drop

will happen when BTS can not allocated channel


Coverage issues DT


Coverage issues


DT analysis suggestions

� Enhance TOP or increase antenna height or decrease down

tilt, otherwise add new sites for discontinuous coverage area;

� Check the neighbour cells and their antenna parameters or

TOP for overshooting area;

� Make the Balance of uplink and downlink (need OMC data);


Interference issues

� Co-channel & adjacent channel interference;

Reason: frequency planning problems

� Repeater interference;

Reason: another type of co-channel & adjacent channel

interference that due to the repeater nearby;

� Exterior interference;

Reason: there are exist some ARFCNs that used by other

operators or other communication devices


Interference issues DT


Interference issues

123

116

113

114

112

110

116

124

102

118

102

110

Broad band Repeater

Interference

Interference

Interference



� Check the frequency planning of neighbour around service

cell, modify it if any Co-channel & adjacent channel;

� Otherwise, find any broad band repeater near by;

� Check the interference come from other communication

devices (should inform operator if any);


Handover

� Abnormal handover parameters configuration;

Reason: lower rexlev set for handover & irrationality margin

for handover

� Missing neighbour;

Reason: MS can not find the proper neighbour cell for

handover

� Co-BCCH & Co-BISC (50% HOSR);

� Congestion (Deficiency Channel for allocating);

� BTS clock asynchronization (MS can not decode signal);



� Optimization handover parameters;

� Add missing neighbour;

� Change the BSIC;

� Increase AMR ratio if possible or expansion capacity;

� Calibrate BTS clock (BSS hardware problem).


Antenna & feeder system

� Antenna issue

Reason: Cross cable connection for Co-site neighbour cells;

� Antenna Tilt issue;

Reason: Antenna Tilt issue is not identical (monopole)

� Antenna azimuth issues;

Reason: Antenna azimuth issues is not identical (monopole)

� Installation issues for Antenna & feeder system

Reason: loose connector for feeder & jumper or higher VSWR



� Solve cross cable connection issues;

� Adjust identical tilt for monopoles for same cell;

� Adjust identical azimuth for monopoles for same cell;

� Fasten the feeder & jumper connectors and decreasing the

VSWR by using proper activities.


Others

� The software version issue

Reason: The software version issue of BTS is not updated;

� BTS hardware issues;

Reason: some BTS hardware alarms (BSS)



� Updated the BTS software version;

� Inform BSS engineers to check the hardware issues and

solve them.

Thank youwww.huawei.com

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