Case Study Of Radio Network Optimization.ppt

HUAWEI TECHNOLOGIES CO., LTD.

TROUBLE SHOOTING & CASE STUDY---- GSM RNP & RNO 2008-02

All Rights Reserved © 2008, Huawei Technologies CO., LTD.

CONTENT

Foundational Trouble Shooting Method & Skill

Enhanced Case Study of GSM RNO


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


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


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.


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)


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.


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


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


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.


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


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


CONTENT

Foundational Trouble Shooting Method & Skill

Enhanced Case Study of GSM RNO


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.


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


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


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


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.


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.


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



Where is the interference?



Objects Date Time

Frequency84 ( main set/sub set)




THA_THA2_THANH-HOA-C 20070112

6:30:00

-89/-99 -88/-102 -89/-99 -90/-95


6:45:00

-89/-98 -88/-102 -89/-99 -90/-95


7:00:00

-89/-98 -88/-101 -89/-98 -90/-95


7:15:00

-89/-98 -88/-101 -89/-100 -90/-96


7:30:00

-103/-108 -105/-109 -104/-108 -102/-108


7:45:00

-106/-106 -109/-109 -108/-107 -108/-108


8:00:00

-103/-104 -109/-108 -109/-109 -108/-108


8:15:00

-106/-104 -109/-109 -107/-108 -106/-107


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



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


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


2006-12-25 15:00

M:2, No: 4, Name: KY_LOI-2 14 13

2006-12-25 16:00


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.


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


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.


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.


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”.


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.


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


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.


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


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.


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.



HO back to UL(900 band) of Cao-Lanh3_DTP



HO back to OL(1800 band) of Cao-Lanh3_DTP


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


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


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



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


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.



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.



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


Thank You

Case Study Of Radio Network Optimization.ppt

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