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HUAWEI TECHNOLOGIES CO., LTD.
TROUBLE SHOOTING & CASE STUDY---- GSM RNP & RNO 2008-02
All Rights Reserved © 2008, Huawei Technologies CO., LTD. Page 2
CONTENT
Foundational Trouble Shooting Method & Skill
Enhanced Case Study of GSM RNO
All Rights Reserved © 2008, Huawei Technologies CO., LTD. Page 3
Trouble Shooting Method Overview
Signaling AnalysisRemote Trace and AnalysisA, Abis, Um interface…
Drive TestCheck on siteTest a point or a line in detail
OMC Traffic StatisticsRemote monitor and AnalysisNetwork, BSC, Cell level…
NetworkTrouble
All Rights Reserved © 2008, Huawei Technologies CO., LTD. Page 4
Trouble Shooting Procedure
User complaint specified (when, where, how) It happen in cell level or BSC level, in some place or all It happen in some hour or whole day It happen for some kind mobile phone, or some kind operator, or all
What’s the trouble?
Check and fix hardware alarm or connection problem Parameter check and optimization Find interference source and get rid of it Expand network capacity or upgrade for the software version
How to resolve it?
Traffic statistics analysis, the problem caused by radio part or BSS part. If caused by BSS part any alarm, check if any operation done at the time point which problem occur Signal tracing and analysis, find the detail reason Drive Test and Call Quality Test
Why get the trouble?
Summarize the experience
All Rights Reserved © 2008, Huawei Technologies CO., LTD. Page 5
Hard for Call Setup
Call Setup include SDCCH Assignment( also called immediately assignment) and TCH Assignment
Immediately assignment low
► Interference? Repeater? Same BCCH and Same BSIC?
TCH assignment low
► All BSC low, especially in BH -> A-interface congestion?
► Only one cell low, check if it’s congested?
► If no congestion, check if any TRX fault, check UL\DL balance, check if TCH got interference, check if BCCH coverage different with some TCH TRX coverage( cross feeder, two set antenna for one cell & different coverage)
► If coverage really poor in some place, try to improve the coverage by adjust antenna down-tilt and azimuth.
All Rights Reserved © 2008, Huawei Technologies CO., LTD. Page 6
Coverage Reduce
This kind case often happen in swap project
► Check if the coverage will be changed by the new antenna
type, antenna direction or down-tilt, new configuration, new
combiner, BTS power
► For Co-BCCH cell, check if the parameter setting wrong,
make most user stay in OL( 1800band), so that cause
subscriber feel coverage reduce
► Check if any problem with handover, can’t handover to the
nearest site, so that make it seem to be Rx-Lev reduced.
► Check if the propagation environment changed( new
building appear)
All Rights Reserved © 2008, Huawei Technologies CO., LTD. Page 7
Call Drop
Call Drop may caused by hardware of wireless
► For hardware part, transmission problem may cause call
drop, it often happen with the whole BSC, or three sectors
of one site.
► For wireless part, also can divide into radio call drop and
handover call drop.
► If too much radio call drop, check the frequency plan,
interference, UL\DL balance, check the coverage, check the
parameter Radio Link Timeout.
► If too much handover call drop, check the neighbor cell
configuration, check parameter setting of T7, T3103.
All Rights Reserved © 2008, Huawei Technologies CO., LTD. Page 8
TCH or SDCCH congestion
TCH congestion
► If HR was disabled? Check the Traffic Busy Threshold set properly or not.
► Check the channel status monitor, if any TRX fault? if Co-BCCH cell OL can’t
use( ECSC wrong, TRX haven’t been active).
► Check the handover and cell reselection parameter, check the cell
layer, share the traffic load with neighbor cell.
► Open direct retry, open traffic handover.
SDCCH congestion
► Too much location update? Increase CRH, T3212 to reduce location update
► GPRS abnormal make SDCCH overflowed? Check the related GPRS
parameter
► Too few SDCCH channel? Config more SDCCH channel
► Check the parameter setting of dynamic transfer between SDCCH and TCH
LAC
All Rights Reserved © 2008, Huawei Technologies CO., LTD. Page 9
Handover Failure
Outgoing or Incoming
► If outgoing handover failure, check with which target cell it often failed,
if target cell congested or CSSR low.
► If incoming handover failure, check if the current cell congested or
CSSR low.
Intra-cell, Internal, or External
► Intra-cell handover can be triggered by channel resource adjustment
handover, OL\UL handover, normal intra-cell handover. If OL\UL
handover problem, check the related parameter.
► Internal handover check the handover cause, which kind handover
occupy the highest percentage.
► External handover case should refer to the detail signaling procedure, it
may caused by cell parameter wrong setting in BSC or MSC, even
caused by some interface problem between different equipment vendor
All Rights Reserved © 2008, Huawei Technologies CO., LTD. Page 10
Handover Failure
MS BTSserving BSCserving MSCBTStarget
Meas Report Meas Result
Channel Activation
Channel Act Ack.
HO CommandHO Command
HO AccessHO Detection
SABMEstablish Ind
UA
Handover Complete Handover Complete HO Complete
RF Channel Release
RF Ch. Rel. Ack.
BSCtarget
HO RequiredHO Request
HO Request Ack.HO Command
Phys Information
( SCCP Con Required )
( SCCP Con Conf ) .
Clear Command
Clear Complete
SCCP Released
SCCP Rel. Cmp.
All Rights Reserved © 2008, Huawei Technologies CO., LTD. Page 11
Handover from HW MSC to E MSC
E-MSC need define HW cells’ CGI information
HW-MSC need define the LAC data of target cell
E-BSC no need define HW cell data
HW-BSC need define the external cell data: CGI, BCCH and BSIC
All Rights Reserved © 2008, Huawei Technologies CO., LTD. Page 12
Single Way Call, Cross Call, Echo, Noise
Large amount of call test.
► From PLMN call to PSTN, from one operator call to another
operator, call test within one operator, call the people who stay
in the same BSC and other BSC, use different mobile phone for
test
Something wrong with EC( Echo Canceller) or
TC( Transcoder)
Loop back Test to check if the transmission got any
problem
Check the hardware quality, hardware alarm and
connection
Pay attention to the operation which had been done
by the time point that the problem occur
All Rights Reserved © 2008, Huawei Technologies CO., LTD. Page 13
CONTENT
Foundational Trouble Shooting Method & Skill
Enhanced Case Study of GSM RNO
All Rights Reserved © 2008, Huawei Technologies CO., LTD. Page 14
Case 1: In VINH LINH site hard making call
Description:
► Subscriber complain that it is difficult to make call at QTVLH (Vinh
Linh).
Procedure test:
► Drive test
► Check on the hardware alarm, and hardware condition.
► Check on antenna orientation, and antenna tilting.
► Check on the RF parameter, found some parameter does not suitable.
Solution:
► Change of T3212 from 40 to 20. To standardize with MSC setting.
Follow up:
► drive test and follow up with the mobile phone dealer. No more
complaint received on the following days.
All Rights Reserved © 2008, Huawei Technologies CO., LTD. Page 15
Case 2: Coverage Issue in HA_TINH site
Case Description► Customer complained
the signal was weak
near the HA TINH site
Analysis► According to drive test
result, in Hopping
channels, we can see
► The signal of 87, 89
frequency is 15dB better
than the other two
► In HA_TINH_A sector we
can’t handover to this
cell
► We suspect HA_TINH site
has swap feeder
All Rights Reserved © 2008, Huawei Technologies CO., LTD. Page 16
Traffic statistics► Use the UL\DL
balance to check
the swap feeder
problem
Summary for
swap feeder case► Swap between TCH
TRX (TCH
assignment failure)
► Swap between TCH
and BCCH TRX (one
sector area no main
BCCH signal, also
TCH assignment
failure)
HA_TINH A and B Swap feeder before and after (above is before)
Swap between TCH TRX Swap between TCH and BCCH TRX
Case 2: Coverage Issue in HA_TINH site
All Rights Reserved © 2008, Huawei Technologies CO., LTD. Page 17
Case 3: Weak signal in one street of THANH HOA
GA_THANH_HOA
► TTA alarm cause the site coverage reduce
Before the alarm had been fixedBefore the alarm had been fixed
After the alarm had been fixedAfter the alarm had been fixed
All Rights Reserved © 2008, Huawei Technologies CO., LTD. Page 18
Case 4: Coverage issue in HA_TINH market
Subscribers in HA_TINH market complained
signal is weak inside the market.
New Building HA_TINH
Market
Suggestion for this issue is adding new
site or add indoor coverage system for
market.
All Rights Reserved © 2008, Huawei Technologies CO., LTD. Page 19
Case 5: Bad Voice Quality issue in HA TINH BSC
Case Description
► Voice quality turned bad since March 19th in the city area of
HA_TINH
Analysis
► Check the hardware equipment, no abnormal
► Later receive the same kind of complaint from other area of HA
TINH BSC, so we suspect the E1 fault
► Co-operated with VMS1 MSC engineer, we tested the transmission
between TC and MSC one by one and found 3 E1 fault
Solution
► Locked the fault E1 and changed to other transmission, and then
voice quality became ok.
All Rights Reserved © 2008, Huawei Technologies CO., LTD. Page 20
Case 6: Call Drop increased in THANH HOA city
Case Description
► In THANH HOA city,
some cell suddenly
got the call drop
times increased
Analysis
► According to the
traffic statistics
analysis, UL
interference is
strong in
THANGH_HOA_C cell,
and a little strong in
GA_THANH_HOA_B
Chart 1: THANH_HOA_C turns bad at 7:00 am. Jan 5th
Chart 2: GA_THANH_HOA_B turns bad at 7:00 am. Jan 5th
All Rights Reserved © 2008, Huawei Technologies CO., LTD. Page 21
Case 6: Call Drop increased in THANH HOA city
Where is the interference?
All Rights Reserved © 2008, Huawei Technologies CO., LTD. Page 22
Case 6: Call Drop increased in THANH HOA city
Objects Date Time
Frequency84 ( main set/sub set)
Frequency85 ( main set/sub set)
Frequency86 ( main set/sub set)
Frequency87 ( main set/sub set)
THA_THA2_THANH-HOA-C 20070112
6:30:00
-89/-99 -88/-102 -89/-99 -90/-95
THA_THA2_THANH-HOA-C 20070112
6:45:00
-89/-98 -88/-102 -89/-99 -90/-95
THA_THA2_THANH-HOA-C 20070112
7:00:00
-89/-98 -88/-101 -89/-98 -90/-95
THA_THA2_THANH-HOA-C 20070112
7:15:00
-89/-98 -88/-101 -89/-100 -90/-96
THA_THA2_THANH-HOA-C 20070112
7:30:00
-103/-108 -105/-109 -104/-108 -102/-108
THA_THA2_THANH-HOA-C 20070112
7:45:00
-106/-106 -109/-109 -108/-107 -108/-108
THA_THA2_THANH-HOA-C 20070112
8:00:00
-103/-104 -109/-108 -109/-109 -108/-108
THA_THA2_THANH-HOA-C 20070112
8:15:00
-106/-104 -109/-109 -107/-108 -106/-107
THA_THA2_THANH-HOA-C 20070112
8:30:00
-102/-104 -107/-108 -105/-106 -105/-108
THANH_HOA_C interference disappeared at about
7:30am in Jan 12th
THANH_HOA_C interference disappeared at about
7:30am in Jan 12th
All Rights Reserved © 2008, Huawei Technologies CO., LTD. Page 23
Case 6: Call Drop increased in THANH HOA city
After the
interference
disappear, this
area cells’ TCH
call drop
decreased GATHANH_HOA_B interference disappeared at about 7:30am in Jan 12th
THANH_HOA_3C interference disappeared at about 7:30am in Jan 12th
All Rights Reserved © 2008, Huawei Technologies CO., LTD. Page 24
Case 7: KY_LOI Call Drop Case
Sampling Time Objects TCH call dropTCH seizure
failures (internal clear)
2006-12-25 12:00
M:2, No: 4, Name: KY_LOI-2 2 2
2006-12-25 13:00
M:2, No: 4, Name: KY_LOI-2 11 10
2006-12-25 14:00
M:2, No: 4, Name: KY_LOI-2 9 9
2006-12-25 15:00
M:2, No: 4, Name: KY_LOI-2 14 13
2006-12-25 16:00
M:2, No: 4, Name: KY_LOI-2 7 6
Case Description► KY_LOI site is high in call drop, and the call drop type is not RF call drop
Analysis► The mainly reason of Call Drops in KY_LOI site is “internal clear”. This
reason means that, there is some problem with the BSC hardware
equipment, or the transmission hardware equipment.
All Rights Reserved © 2008, Huawei Technologies CO., LTD. Page 25
Case 7: KY_LOI Call Drop Case
There are many
LAPD_OML alarms
in KY_LOI site
Suggestion is to
check and fix the
LAPD alarm of this
site
All Rights Reserved © 2008, Huawei Technologies CO., LTD. Page 26
Case 8: Immediate Assignment failure in THANH HOA
Abnormal signaling procedure is showed below,
after Assignment can’t receive SABM frame. It will
send DEACTIVATE_SACCH when the Timer T3101
expired.
In THANH HOA province, some cells got many times Immediate Assignment Failure. Below is the normal signaling procedure for Immediate Assignment.
All Rights Reserved © 2008, Huawei Technologies CO., LTD. Page 27
Case 8: Immediate Assignment failure in THANH HOA
Solution► Modify the
parameter
MAX_TA from 62
to 40, in order to
forbid too far
access
Reason► Only in THANH
HOA BSC has
this issue, we
suspect repeater
make the ghost
access.
All Rights Reserved © 2008, Huawei Technologies CO., LTD. Page 28
Case 9: No half rate for whole BSC
Case Description► After swapping 1 Alcatel BSC to Huawei BSC, BSC has no half rate traffic.
Analysis► Network topology: Before swap it’s Alcatel MSC-Alcatel BSC, After swap it’s
Alcatel MSC-Huawei BSC.
► Signaling analysis: We traced the A interface signaling and found the
“Assignment Request” from MSC only permit this BSC “FR speech version 1”. So
we judged this problem was caused by wrong data configuration of BSC or MSC.
► Check BSC data configuration: Check cell data configuration in BSC, it’s
correct. Check circuit pool number, it was set to 7, which means this BSC can
support “FR speech version 1,FR speech version 2,HR speech version 1”.
► Check MSC data configuration: We check the Alcatel MSC data configuration,
The half rate parameter was set to “DR (dual rate)” nor “DRMSV (dual rate and
multiple speech version)”, which means only permitted “FR speech version 1”.
All Rights Reserved © 2008, Huawei Technologies CO., LTD. Page 29
Case 9: No half rate for whole BSC
Solution► Change MSC half rate parameter from “DR (dual rate)” to “DRMSV (dual
rate and multiple speech version)”, problem was solved.
All Rights Reserved © 2008, Huawei Technologies CO., LTD. Page 30
Case 10: Handover Frequently in Cao-Lanh
Issue Description:► During Drive Test in Cao-Lanh site in Dec 12th, two places show handover
frequently.
A: Weak coverage area, frequently ping-pong between Tran-Quoc-Toan2_DTP and Cao-Lanh1_DTP
B: Triangle handover: UL of cell A -> OL of cell A -> UL of Neighbor cell B -> UL of cell A -> …
Drive Test by VNP
All Rights Reserved © 2008, Huawei Technologies CO., LTD. Page 31
Case 10: Cao-Lanh Drive Test after Optimization
Result► After doing optimization, Frequently Handover issue had been resolved, as showed below:
Action1: Change Cao-Lanh1_DTP azimuth from 340->320 to improve Place A coverage, it’s the main road direction.
Action2: Increase PBGT handover threshold between 3 sectors of Cao-Lanh site: from 4->8, and increase PBGT watch time and valid time: from (4, 3) -> (5, 4) in order to reduce PBGT handover times between different sectors of Cao-Lanh.
All Rights Reserved © 2008, Huawei Technologies CO., LTD. Page 32
1) UL of cell A -> OL of cell A► U to O HO Received Level Threshold: 35, if current signal > -75dBm, it will
trigger U->O HO, make OL get more traffic.
2) OL of cell A -> UL of Neighbor cell B► PBGT HO Threshold: 68=4dB, if Path loss A – Path loss B > 4dB, and during
PBGT watch time: 4s, last PBGT valid time: 3s.
► O to U HO Received Level Threshold: 20, it means if signal reduce to -90dBm will HO from O -> U. So it trigger PBGT HO to neighbor cell, for 1800 coverage is always weaker than 900 band.
3) UL of Neighbor cell B -> UL of cell A► But actually, this area Neighbor Cell B’s 900, is not as strong as
Cell A’s 900. So it will HO back to UL of Cell A.
If the MS stand at this area,
it may triangle handover
again and again…
Case 10: What is Triangle Handover?
ULOL
Cell A
UL
OL Cell B
3
1
2
All Rights Reserved © 2008, Huawei Technologies CO., LTD. Page 33
Case 10: Drive Test Log File Analysis 1 Now MS is using OL(1800 band) of Cao-Lanh3_DTP. Preparing HO to UL(900
band) of Cao-Lanh2_DTP by PBGT HO.
All Rights Reserved © 2008, Huawei Technologies CO., LTD. Page 34
Case 10: Drive Test Log File Analysis 2
After HO to UL(900 band) of Cao-Lanh2_DTP, it find Cao-Lanh3_DTP is stronger than Cao-Lanh2_DTP, preparing HO back to UL of Cao-Lanh3_DTP.
All Rights Reserved © 2008, Huawei Technologies CO., LTD. Page 35
Case 10: Drive Test Log File Analysis 3
HO back to UL(900 band) of Cao-Lanh3_DTP
All Rights Reserved © 2008, Huawei Technologies CO., LTD. Page 36
Case 10: Drive Test Log File Analysis 4
HO back to OL(1800 band) of Cao-Lanh3_DTP
All Rights Reserved © 2008, Huawei Technologies CO., LTD. Page 37
In order to reduce Triangle Handover, we must reduce step 2.
Why?► Step 1 is UL to OL, for Co-BCCH cells, UL is 900 for coverage, OL is 1800 for traffic load, so we prefer MS
to use OL sub cell channel if the 1800 quality is not so bad. We can’t modify parameter to avoid or
delay the HO form UL to OL, otherwise OL channel will be wasted and UL will be easy to congested.
► Step 2 is PBGT from 1800 to neighbor’s 900, PBGT is triggered only between the same layer cells. For
dual band co-site, we often set 1800 cell layer higher than 900, but for Co-BCCH cell, 900 and 1800
combined into only one cell, so OL of Cell A is the same layer with UL of Cell B, even they are using
different frequency band and 900 is much better than 1800(about 10 ~ 20dB stronger).
► In this case we must try to delay the PBGT handover from 1800 to neighbor’s 900, so we increase PBGT
handover threshold between 3 sectors of Cao-Lanh site: from 4->8, and increase PBGT watch time and
valid time: from (4, 3) -> (5, 4) to reduce PBGT handover times between different sectors of Cao-Lanh.
Case 10: How to Anti Triangle Handover
ULOL
Cell A
UL
OL Cell B3
1
2
All Rights Reserved © 2008, Huawei Technologies CO., LTD. Page 38
Case 10: PBGT Handover of Cao-Lanh After Modify PBGT Handover times
reduced after parameter optimization, this means triangle handover times also reduced accordingly.
Before
After
All Rights Reserved © 2008, Huawei Technologies CO., LTD. Page 39
Case 11: DTP Single Way Call
V: TCH_MEAN_HOLDING_TIME (s)
15
20
25
30
35
40
45
16
12
-11
18
12
-11
20
12
-11
8 1
2-1
2
10
12
-12
12
12
-12
14
12
-12
16
12
-12
18
12
-12
20
12
-12
8 1
2-1
3
10
12
-13
12
12
-13
14
12
-13
16
12
-13
18
12
-13
20
12
-13
8 1
2-1
4
10
12
-14
12
12
-14
14
12
-14
16
12
-14
18
12
-14
20
12
-14
8 1
2-1
5
10
12
-15
12
12
-15
14
12
-15
V: TCH_MEAN_HOLDING_TIME (s)
V: TCH_MEAN_HOLDING_TIME (s)
15
20
25
30
35
40
45
50
16
12
-11
18
12
-11
20
12
-11
8 1
2-1
2
10
12
-12
12
12
-12
14
12
-12
16
12
-12
18
12
-12
20
12
-12
8 1
2-1
3
10
12
-13
12
12
-13
14
12
-13
16
12
-13
18
12
-13
20
12
-13
8 1
2-1
4
10
12
-14
12
12
-14
14
12
-14
16
12
-14
18
12
-14
20
12
-14
8 1
2-1
5
10
12
-15
12
12
-15
14
12
-15
V: TCH_MEAN_HOLDING_TIME (s)V: TCH_MEAN_HOLDING_TIME (s)
15
20
25
30
35
40
45
16
12
-11
18
12
-11
20
12
-11
8 1
2-1
2
10
12
-12
12
12
-12
14
12
-12
16
12
-12
18
12
-12
20
12
-12
8 1
2-1
3
10
12
-13
12
12
-13
14
12
-13
16
12
-13
18
12
-13
20
12
-13
8 1
2-1
4
10
12
-14
12
12
-14
14
12
-14
16
12
-14
18
12
-14
20
12
-14
8 1
2-1
5
10
12
-15
12
12
-15
14
12
-15
V: TCH_MEAN_HOLDING_TIME (s)
Sa-Dec_DTP Mean Holding Time TrendProblem Description: User complained single way call in Sa-Dec_DTP site.
Analysis: From CQT we found the percentage of single way call was nearly 90%, so we suspect it caused by equipment and transmission part. From OMC Traffic Statistics, we can see this problem began from 12-14 10pm. Because in single way bad cells, subscriber will hung up more quickly, so that MHT will be shorter, like the charts shows here.
All Rights Reserved © 2008, Huawei Technologies CO., LTD. Page 40
Case 11: DTP Single Way Call
Result: After Switch the GTNU board in 13:00 12-16, Mobile A and B can
hear each other. And then did CQT, one way call did not happen anymore.
Double checked by OMC Traffic Statistics, this problem didn’t exist.
All Rights Reserved © 2008, Huawei Technologies CO., LTD. Page 41
Case 11: DTP Single Way Call
Some days later, single way call happen again. The percentage of single way call
was about 30%
Check traffic statistics, found some abnormal in A-interface from 01-21 10:00AM.
Confirmed with customer, the subscriber complaint also start from that time point.
At last, we asked OMC engineer, they expanded some A-interface at that time, and
the A-interface quality was not good. After locked these A-interface, the single way
call disappeared.
Date Time BSC Name
AL0050:Mean Number of Uninstalled Circuits on the A Interface
AL0089:Mean Number of Circuits with Uninstalled Peer Circuits on the A Interface
21/01/2008 7:00:00 BSC_242H_DTP 78 0
21/01/2008 8:00:00 BSC_242H_DTP 78 0
21/01/2008 9:00:00 BSC_242H_DTP 78.217 0
21/01/2008 10:00:00 BSC_242H_DTP 90.089 58.744
21/01/2008 11:00:00 BSC_242H_DTP 102 109
21/01/2008 12:00:00 BSC_242H_DTP 102.283 109.303
All Rights Reserved © 2008, Huawei Technologies CO., LTD. Page 42
Thank You