HUAWEI TECHNOLOGIES CO., LTD.
www.huawei.com
Huawei Confidential
Security Level:2008-7-18
Call Drop Analysis
Trainning Document
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Content
What is call drop?
The types of call drop
Basic call drop reasons
Call drop issues during DT
Call drop cases
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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.
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I can not allocate channel for you!!!
Hello……?
Hello……?
Hello……?
Why call drop again?
What is Call Drop?
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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
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Basic call drop reasons
Radio Link Time out
T3103 Time out
System problems (hardware)
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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.
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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
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System problems (hardware)
DDRU board is not on working;
High VSWR(>1.2);
The feeder connector is loose;
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Call drop issues during DT
Coverage;
Interference;
Handover;
Antenna & feeder system;
Others;
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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
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Coverage issues DT
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Coverage issues DT
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Coverage issues
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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);
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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
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Interference issues DT
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Interference issues
123
116
113
114
112
110
116
124
102
118
102
110
Broad band Repeater
Interference
Interference
Interference
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DT analysis suggestions
� 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);
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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);
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DT analysis suggestions
� Optimization handover parameters;
� Add missing neighbour;
� Change the BSIC;
� Increase AMR ratio if possible or expansion capacity;
� Calibrate BTS clock (BSS hardware problem).
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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
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DT analysis suggestions
� 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.
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Others
� The software version issue
Reason: The software version issue of BTS is not updated;
� BTS hardware issues;
Reason: some BTS hardware alarms (BSS)
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DT analysis suggestions
� Updated the BTS software version;
� Inform BSS engineers to check the hardware issues and
solve them.
Thank youwww.huawei.com
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