Ome200301 Gsm Bts Trouble Shooting Issue3.0

HUAWEI TECHNOLOGIES CO., LTD. All rights reserved

www.huawei.com

Internal

OME200301 GSM BTS Trouble Shooting

ISSUE 3.0

HUAWEI TECHNOLOGIES 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 su

ccess rate of adjacent cells

During implementation or expansion, we can “Interchange ” BT

S 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

RXD

T

R

X

CDU

TTAFeeder

TTAFeeder

arrester

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 failsNo DC feeding voltage at CDU antenna

port after TTA configuration


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



Analysis

No downlink signal

− Step3: Since there is no downlink signal, there must be a bro

ken point in the RF signal path. If this point is located at the p

art 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-C

OM and TX-DUP is correct

− Step4: If the operations above fail to locate the failure, chang

e 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 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



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



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



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


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 th

an 1.5, while CDU SWR alarm has been generated, this alarm sho

uld 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 connecti

on 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 th

e 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 b

e considered as a TTA mis-alarm. Use another CDU to substitute the f

aulty CDU. Keep the faulty CDU for further analysis.

− If the feeding current is beyond limits, TTA is faulty and needs to be c

hanged

− For the migration site, it is also necessary to confirm the type of lightni

ng 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

Handling process

Generally the reason maybe that the E1 grounding is not go

od, it cause interference, or transmission device is faulty

− Check the TMU in the BTS to check E1 grounding settin

gs

− Test the resistance of the E1 connector and that of the r

ack to measure the insulation situation

− Check whether the E1 connector in the DDF (when confi

gured) is grounded

− Check whether the E1 enclosure of the transmission dev

ice is grounded


Transmission Fault 2: OML alarm frequently

Handling process

− 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



Handling process

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)



Handling process

Step7: change the TMU DIP switch that corresponded to the grou

nding of the E1 cable to OFF (ungrounded), the trouble still existe

d

Step8: remove the E1 connector from the DDF and change the T

MU DIP switch that corresponded to the grounding of the E1 cabl

e to OFF (ungrounded). The trouble disappeared

Step9: for confirming the reason, replace the TMU (with the E1 ca

ble 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 connec

tor 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

− On the site, the maintenance engineer found the following

▪ 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

Handling process 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

− On the site, the maintenance engineer found the following

▪ 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

Handling process

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 preventionBTS 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 acc

ording to the alarm description and suggestion. if you cannot re

move 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

www.huawei.com

Thank You

Ome200301 Gsm Bts Trouble Shooting Issue3.0

Documents

fault analysis

fault cause

fault nature

fault equipment

real fault

rno fault

rights reserved page

bts huawei technologies