Ome200301 gsm bts trouble shooting issue3.0

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OME200301 GSM BTS
Trouble Shooting
ISSUE 3.0

HUAWEITECHNOLOGIES CO., LTD.
Page 2All rights reserved
References
 M900/M1800 Base Station Subsystem
Troubleshooting Manual
 M900/M1800 Base Station Controller
Technical Manual

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

Chapter 1 General IntroductionChapter 1 General Introduction
Chapter 2 Typical CasesChapter 2 Typical Cases
Chapter 3 BTS Fault PreventionChapter 3 BTS Fault Prevention

Section 1 The Way To Locate FaultSection 1 The Way To Locate Fault
Section 2 Basic Disposal MethodSection 2 Basic Disposal Method

The ways to locate faults
 Alarm
 Alarm console
 Alarm box
 OMC Shell
 Traffic statistics
 Drive test
 Routine inspection
 Customer complain

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

Common fault types
 BTS fault
 Antenna & Feeder
 Transmission
 Hardware connection fault
 Hardware fault

Section 1 The Way To Locate FaultSection 1 The Way To Locate Fault
Section 2 Basic Disposal MethodSection 2 Basic Disposal Method

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.

 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

 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

Section 1 Antenna & Feeder FaultSection 1 Antenna & Feeder Fault
Section 2 Transmission FaultSection 2 Transmission Fault
Section 3 Hardware connection faultSection 3 Hardware connection fault
Section 4 Hardware faultSection 4 Hardware fault

BTS feeder system structure
TX
RX
RX
D
T
R
X
CDU
TTAFeeder
TTAFeederarrester
optional
Antenna
arrester

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

Common faults on downlink
 Description
 No downlink signal
 Downlink signal weakened
 Analysis
− 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

 Analysis
− 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

 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

Common faults on uplink
 Description
 No uplink signal
 BTS sensitivity weakened
 Analysis
− 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

 Analysis
− 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

 Analysis
− 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

 Analysis
− 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

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

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

Transmission Fault
 Description
 Alarm console
− “BIE board PCM loss of sync.”, “LAPD_OML alarm”
 Traffic Statistic console
− The handover successful rate, call drop rate of the cell is
abnormal
 Consumer complaint
− Cannot take a call, bad quality, call drop

Transmission Fault
 Possible causes
 Transmission device, board or E1 is faulty
− More transmission device, more fault
 Transmission code is different (use CRC4 or not)
 E1 connection quality is bad
− It will cause bad quality, even transmission broken
 High BER (bit error rate)
− Microwave, HDSL transmission, especially in rainy
weather
 The grounding system is faulty

Transmission Fault 1: E1 broken
 Handling process
 Probably the reason may be that the E1, transmission device or board is
faulty
− Step1: perform self-loop test over BTS and check whether the LIU
indicator of the TMU board is OFF. If no, it can be considered that
the problem lies in TMU board. Please replace TMU board
− Step2: perform self-loop test over BSC and check whether the E1
indicator of BIE board is OFF. If not, it can be considered that the
problem lies in the transmission device
− Step3: check the transmission NM and check whether a transmission
related alarm is given. Based on the alarm (if any), you may judge
whether the problem lies in the transmission device
− Step 4: if neither of them is faulty, it can be considered that the
problem lies in the cooperation between the transmission device and
BSC (or BTS)

Transmission Fault 2: OML alarm frequently
 Generally the reason maybe that the E1 grounding is not
good, it cause interference, or transmission device is faulty
− Check the TMU in the BTS to check E1 grounding
settings
− Test the resistance of the E1 connector and that of the
rack to measure the insulation situation
− Check whether the E1 connector in the DDF (when
configured) is grounded
− Check whether the E1 enclosure of the transmission
device is grounded

Transmission Fault 2: OML alarm frequently
− Check whether the system is in the single-point-grounded state. If
not, modify the system to the single-point-grounded state, then
check whether the trouble is removed
− If the trouble is still not removed after the above measures, it may
be considered that the problem lies in the transmission device, E1 or
E1 interface board. Check the connection and perform loop test
segment by segment to locate the fault
− Check the transmission NM and check whether a transmission
related alarm is given. If yes, please handle it as the related alarm
details

Typical case: OML broken for E1 grounding error
 Description
 A site’s OML was frequently interrupted and the indicator
(corresponding to the E1) at BSC flashed
− The equipment room was located at the top of a 300m-high hill. The
microwave transmission equipment room was 20m away
− On the site, the maintenance engineer found the following
▪ The E1 was grounded, as was checked from the DIP switch
▪ The E1 connector was insulated from the cabinet enclosure.
The working grounding cable of the rack was connected with
that of the equipment room
▪ The DDF, an all-metal frame, was connected to the grounding
cable of the equipment room. The E1 connector contacted the
metal of the DDF
▪ No lightning arrester was configured for the E1
▪ The E1 indicator flashed fast

 Step1: self-loop the E1 at the top of BTS cabinet and found the
indicator of the E1 cable was OFF. It means BTS is OK.
 Step2: self-loop the E1 on the DDF and found the indicator of the E1
cable was OFF. It means the E1 from BTS to DDF is OK
 Step3: self-loop the BSC on the DDF and found the E1 indicator is
OFF. It means the E1 from BSC to DDF is OK
 Step4: power the TMU off and then on, the trouble still existed
 Step5: remove the E1 from the DDF, the trouble still existed
 Step6: disconnect the E1 at the top of BTS cabinet, power off the rack
and removed the TMU. Test the resistance between the cabinet-top
E1 connector case and the grounding cable of the rack and found they
were insulated from each other (normal)

 Step7: change the TMU DIP switch that corresponded to the
grounding of the E1 cable to OFF (ungrounded), the trouble still
existed
 Step8: remove the E1 connector from the DDF and change the
TMU DIP switch that corresponded to the grounding of the E1
cable to OFF (ungrounded). The trouble disappeared
 Step9: for confirming the reason, replace the TMU (with the E1
cable ungrounded). Let the E1 connector case contact the DDF
and found the TMU E1 indicator flash fast
 Restored the TMU to the original one and removed the E1
connector from DDF, the trouble disappeared

Typical case: VSWR alarm for cable broken
 Description
 On BTS maintenance console, one TRX board in a sector was red, alarm
console showed TRX VSWR alarm.
− The site was just established
▪ The RF cable between TRX and CDU was well connected
▪ The RF jumper in the CDU was well connected and also the
connection was right
▪ The RF cable between CDU and lightening arrester was well
connected

Typical case: VSWR alarm for cable broken
 Step1: check all the connection from TRX to main feeder and
lightening arrester detailed and also re-tighten all the connections , the
problem was still there, meant the connection had no problem
 Step1: connect the CDU in current sector to the antenna in another
sector that was ok before, the TRX was still red, that meant the
antenna and feeder system had no problem , recovered the connection
 Step2: connected the TRX to a CDU in another sector that had nothing
alarm before, the TRX was still red, that meant the problem was in the
TRX side, recovered the connection
 Step3: change the faulty TRX to a new one, the TRX was still red ,
meant the TRX had no problem, recovered the connection
 Step4: change the cables between the TRX and CDU , problem
disappeared . The problem was that the cable was broken during
transport

Typical case: site failed for TRX fault
 Description
 A site had no traffic and customer complained that they could not
make a call
− It was a omni-directional site and had only one TRX
▪ All the boards was well in place and the indicators showed
that all the boards had no alarm
▪ Antenna and feeder was well connected
▪ The whole site was well grounded
▪ The power supply had no problem

Typical case: site failed for TRX fault
 Step1: checked OMC alarm console , found radio link alarm in the
site
 Step2: checked OMC BTS maintenance console, no boards was
red
 Step3: queried all the boards software, all were correct
 Step4: changed the TMU board to a new one, problem was still
there, recovered it.
 Step5: reset TRX and changed all the connections to the TRX to
new one , problem was still there, recovered it
 Step6: changed the TRX to a new one , problem disappeared,
meant the problem was in TRX

BTS fault prevention
nip the fault
in the bud

 Hardware: installation specifications is most important!
 give more attention to E1 connector
 give more attention to feeder connector
 give more attention to waterproofer of antenna and feeder system
 Confirming the grounding and lightning protection

 Checking Running status
 BTS maintenance console
− First, do “multi-site fault query”, then try to remove the fault
according to the alarm description and suggestion. if you
cannot remove the fault at provisionally, confirm the reason of
every fault at least
 Do calling test for every timeslot

Summary
In this course ,we have learned how to
 Find the fault
 Judge the fault
 Locate the fault
 Remove and prevent the fault

Ome200301 gsm bts trouble shooting issue3.0

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