OME200301 GSM BTS Trouble Shooting docx

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OME200301 GSM BTS
Trouble Shooting
ISSUE 3.0
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References

M900/M1800 Base Station Subsystem
Troubleshooting Manual

M900/M1800 Base Station Controller
Technical Manual
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Upon completion of this course, you will be
able to:

Know how to find the fault in BTS

Know the common fault types

Grasp BTS fault disposal method

Know how to prevent the fault
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Chapter 1 General Introduction
Chapter 1 General Introduction
Chapter 2 Typical Cases
Chapter 2 Typical Cases
Chapter 3 BTS Fault Prevention
Chapter 3 BTS Fault Prevention
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Chapter 1 General Introduction
Chapter 1 General Introduction
Section 1 The Way To Locate Fault
Section 1 The Way To Locate Fault
Section 2 Basic Disposal Method
Section 2 Basic Disposal Method
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The ways to locate faults

Alarm

Alarm console

Alarm box

OMC Shell

Traffic statistics


Drive test

Routine inspection

Customer complain
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Locating fault equipment

If BSC has fault, usually it will affect some Sites or all of Sites

If BTS has fault, usually it just affect itself and the handover
success rate of adjacent cells

During implementation or expansion, we can “Interchange ”
BTS and judge whether the fault is because of BSC or BTS

During maintenance, BSC faults don’t just affect one BTS
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Common fault types

BTS fault

Antenna & Feeder

Transmission


Hardware connection fault

Hardware fault
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Chapter 1 General Introduction
Chapter 1 General Introduction
Section 1 The Way To Locate Fault
Section 1 The Way To Locate Fault
Section 2 Basic Disposal Method
Section 2 Basic Disposal Method
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Basic disposal method

Analyzing the Alarm Information

Alarm information come from the BSS alarm system, indicated
usually through sound, light, LED, and screen output, etc

It includes the detailed description of the abnormality, possible
causes and restoration suggestions, involves the hardware, link,
trunk and CPU loading ratio, etc It is a gist for the fault analysis and
location

Analyzing the Indicator Status


Indicators can indicate the work status of circuit, link, optical path,
node and active/standby mode besides that of the corresponding
boards, usually used along with the alarm information generally

Analyzing Traffic Statistics Result

It is the most useful method for locating RNO fault.
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Basic disposal method

Analyzing Apparatus & Meter Test Result

It reflects the fault nature with the visual and quantified data

Some common Apparatus & Meter
−
Signaling Analyzer, Test phone, Sitemaster, etc.

Tracing the Interface

It is applied in locating the failure causes of subscriber call connection
and inter-office signaling cooperation, etc.

The trace result can help to find the cause of call failure directly and
locate the problem or to get the index for the subsequent analysis

Calling Test


It is a simple and quick method to judge whether the call processing
function and relative modules of the BSS are normal or not
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Basic disposal method

Comparison/Interchange

Comparison: compare the faulted components or phenomenon with the
normal ones, and find the differences so as to find the problem
−
It is usually used in the situation with simple fault range

Interchange: if the fault can not be located even after the standby
components are replaced, you can interchange the normal components
(such as board, optical fiber, etc.) with the potential faulted components,
and to compare the work status so as to specify the fault range or part
−
It is usually used in the situation with complicated fault range

Switching/Resetting

It can not locate the fault cause accurately, and due to the randomness
of software running, the fault may be not able to recur, thus it is difficult
to know the real fault and solve the problem

This method is just an emergency method, applicable only in the
emergent situation
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Chapter 1 General Introduction
Chapter 1 General Introduction
Chapter 2 Typical Cases
Chapter 2 Typical Cases
Chapter 3 BTS Fault Prevention
Chapter 3 BTS Fault Prevention
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Chapter 2 Typical Cases
Chapter 2 Typical Cases
Section 1 Antenna & Feeder Fault
Section 1 Antenna & Feeder Fault
Section 2 Transmission Fault
Section 2 Transmission Fault
Section 3 Hardware connection fault
Section 3 Hardware connection fault
Section 4 Hardware fault
Section 4 Hardware fault
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BTS feeder system structure
TX
RX
RXD
T
R

X
CDU
TTA
Feede
r
TTA
Feede
r
arreste
r
optional
Antenn
a
arreste
r
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Common faults
Type Fault phenomena
On downlink signal
No downlink signal
MS fails to access the network, calls
cannot be established, call drop, TRX idle
for a long time
Downlink signal
weakened
Poor conversion quality, BTS coverage
shrink
On uplink signal

No uplink signal Calls cannot be established
BTS sensitivity
weakened
Poor conversation quality, BTS coverage
shrink
Feeder system faults
Standing wave alarm Standing wave alarm occurs at CDU
LNA alarm LNA alarm occurs at CDU
TTA alarm TTA alarm occurs at CDU
TTA feeding fails
No DC feeding voltage at CDU antenna
port after TTA configuration
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Common faults on downlink

Description

No downlink signal

Downlink signal weakened

Analysis

No downlink signal
−
Step1: View the history alarms and real-time alarm at OMC
or local maintenance console
−

Step2: If there is emergent standing wave alarm at CDU, it is
the most possible cause for which TMU turns off the
transmitter power amplifier resulting in no downlink signal
▪
check the standing wave ratio at jumper side of CDU
antenna port
▪
If the standing wave ratio is beyond limits, locate the
faulty point segment by segment
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Common faults on downlink

Analysis

No downlink signal
−
Step3: Since there is no downlink signal, there must be a
broken point in the RF signal path. If this point is located at
the part from CDU antenna port to tower top, then CDU
should be able to detect the emergent standing wave alarm.
Otherwise, it can be concluded that the broken point is
located between TRX output to CDU antenna point
▪
Check whether the cable connection between CDU TX-
COM and TX-DUP is correct
−
Step4: If the operations above fail to locate the failure,
change the CDU

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Common faults on downlink

Analysis

Downlink signal weakened: The symptom of this failure is that
the coverage of BTS or carrier shrinks. Follow the steps below to
handle this problem:
−
Step1: Check whether the output power of TRX is normal.
−
Step2: Check whether the standing wave ratio at jumper side
of CDU antenna port is normal.
−
Step3: Check insertion loss of CDU transmitting path.
−
Step4: Check whether the connectors involved in the RF
signal path are tightened
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Common faults on uplink

Description

No uplink signal

BTS sensitivity weakened


Analysis

No uplink signal
−
Step1: Try another antenna feeder (CDU excluded) which has proven
to be normal to substitute the one without uplink signal
▪
If the uplink signal at the new feeder recovered while the one at
the original feeder fails, then the original antenna feeder has
problems
▪
If the phenomenon remains, then CDU has problems. Check
whether the cable connection between RXD OUT and HL_IN or
between HL_OUT and HL_IN is correct
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Common faults on uplink

Analysis

No uplink signal
−
Step2: If the failure cannot be located yet, change the CDU, and
make the related record ;
▪
Notes: Restore the antenna feeder connection to it original
status
−

When changing the antenna feeder, make sure that:
▪
The two corresponding antenna feeders should be in the same
cell/sector
▪
The antenna connection should be restored to the original status
after locating the failure. Otherwise, the coverage of the cell may
be affected. This is the basic principle to obey when using this
method to locate the problem
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Common faults on uplink

Analysis

BTS sensitivity weakened
−
If TTA is configured, first check whether there is any TTA alarm
▪
If so, the TTA is working abnormally
▪
Otherwise, check the CDU antenna port feeding
»
If no feeding is detected, then the CDU is faulty and needs to be
changed
»
If DC voltage is normal, then it is considered that the TTA is
normal
−

After confirming that TTA is normal, check the standing wave ratio of
antenna feeder
▪
If it is too large, then the connection of antenna feeder RF path is
poor or something else
▪
If the standing wave is normal, check the performance of CDU
receiving channel, such as gain and noise factor
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Common faults on uplink

Analysis

BTS sensitivity weakened
−
The common faults can be located by adopting the
methods above. But it is inevitable that there are some
problems which can not be located by this method since
it is not a comprehensive test. For example, if the gain
decrease and noise factor increase of TTA is not
reflected in the working current, the problem cannot be
detected
−
On such occasions, make clear records of the
operations which have been done so far for further
analysis
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Common faults on feeder system

Description

CDU alarm (SWR, TTA)

Analysis

Standing wave alarm
−
Check the SWR of antenna feeder (CDU excluded). If it is lower
than 1.5, while CDU SWR alarm has been generated, this alarm
should be regarded as a mis-alarm, and the CDU needs to be
changed
−
If the SWR is higher than 1.5, it is necessary to adjust the
connection of antenna feeder until it is lower than 1.5
−
The installation specification requires the SWR be lower than1.3
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Common faults on feeder system

Analysis

TTA alarm
−
CDU measures the TTA feeding current through the antenna port. If

the current is not in the normal TTA working current range
(45~170mA), CDU generates TTA alarm
−
If the feeding current is normal while there is TTA alarm, then it can be
considered as a TTA mis-alarm. Use another CDU to substitute the
faulty CDU. Keep the faulty CDU for further analysis.
−
If the feeding current is beyond limits, TTA is faulty and needs to be
changed
−
For the migration site, it is also necessary to confirm the type of
lightning arrester when using TTA