OMF000401 Case Analsyis-Handover ISSUE1.4

Course ContentsMeasurement points of handover Searching process of handover data Analysis of handover problem Handover cases... Handover Access New FACCHHandover Complete New FACCH Atte

OMF000401 Case Study

Course Contents

Measurement points of handover

Searching process of handover data Analysis of handover problem

Handover cases

 Intra BSC handover

 Inter BSC handover

Measurement Points of Handover

Handover Access (New FACCH)

Handover Complete (New FACCH)

Attempted outgoing internal inter cell handovers

Attempted incoming internal inter cell handovers

Successful incoming internal inter cell handovers Successful outgoing internal inter cell handovers

Measurement Points of Intra BSC Handover

Handover formula definition

 Inter cell radio handover success rate

=(Successful incoming internal inter cell handovers + Successful outgoing internal inter cell handovers) / (Incoming internal inter cell handovers + Outgoing internal inter cell handovers )

 Internal inter cell handover success rate

=(Successful incoming internal inter cell handovers + Successful outgoing internal inter cell handovers) / (Attempted incoming internal inter cell handovers + Attempted outgoing internal inter cell handovers)

Inter cell radio handover success rate >= Internal inter cell handover success rate

Measurement Points of Intra BSC Handover

Possible causes of intra BSC handover failure

 No channel available in the target cell

 Channel activation negative acknowledgement － CHAN ACK NACK

 Transmitting channel activation message failure

 Channel activation timeout

 MS access failure (It may be caused by radio interface.)

 Max resend time of physical information * radio link connected with the timer < time interval of EST IND ~ HO DETECT (120~180ms)

 Waiting until timeout after establish indication (MS has not receiv

ed UA frame or has not sent handover complete message)

Measurement Points of Intra BSC Handover

 Intra BSC handover

 Inter BSC handover

Measurement Points of Handover

Measurement Points of Inter-BSC Handover

Handover Command

Handover Access

Handover Detect Handover Complete

Handover Complete

Clear Command (HO Successful)

RF Channel Release

Clear Complete

Attempted outgoing interBSC inter cell handovers

Attempted incoming interBSC inter cell handovers

Successful incoming inter BSC handovers Successful outgoing interBSC inter cell handovers

Signaling intra MSC

Signaling flow between MSC

t MAP_Send_HO_Report_AC

K

MS

HO-REQUEST HO-REQUEST-ACK

HO-Command

MS

HO-Access MAP_Process_Access_Signalling

HO-Complete MAP_Send_End_Signal

Clear-Command Clear-Complete

MAP_Send_End_Signal_ACK

Some intermediate steps are omitted

IAI ACM

Measurement Points of Inter-BSC Handover

Signaling flow between MSC

t MAP_Send_HO_Report_AC

K

MS

HO-REQUEST HO-REQUEST-ACK

HO-Command

MS

HO-Access MAP_Process_Access_Signalling

HO-Complete MAP_Send_End_Signal

Clear-Command Clear-Complete

MAP_Send_End_Signal_ACK

Some intermediate steps are omitted

IAI ACM

Measurement Points of Inter-BSC Handover

Measurement Points of Inter-BSC Handover

 Inter BSC handover

 Success rate

=(Successful incoming inter BSC inter cell handovers + Successful outgoing inter BSC inter cell handovers) / (Attempted incoming inter BSC inter cell handovers + Attempted outgoing inter BSC inter cell handovers )

Course Contents

Measurement points of handover

Searching process of handover data

Analysis of handover problem Handover cases

Searching Process of Handover Data (1)

MS on system message 5.

BSIC and signal level of the adjacent cells and serving cells

the module ID, cell ID and CGI of all adjacent cells through BCCH frequency and BSIC in Adjacent Cell Relation Table and Cell Description Table (or External Cell Description Table).

ranking (on LAPD board) Once a proper target cell is found, the handover request message which includes the target cell CGI will

be sent to MPU of BSC host, and then MPU will confirm the module ID of the cell in Cell Module Information Table based on the CGI.

Searching Process of Handover Data (2)

makes statistics of "outgoing inter cell handover request".

of the target cell and service cell is sent to MSC on the handover required.

in “LAI And GCI Table ” Once the cell is found, MSC will confirm which BSC is belong to, and send the handover request message to this BSC.

MSC will go to “Adjacent MSC Table" and find the target MSC, then send the handover request message to that MSC.

Analysis of Handover Problem

Types of handover problems

Locating handover problem

Causes of handover problem

Types of Handover Problems

Types － Possible Results

Analysis of Handover Problem

Types of handover problems

Locating handover problem

Causes of handover problem

Locating Handover Problem

Analysis of Handover Problem

Types of handover problems

Locating handover problem

Causes of handover problem

Causes of Handover Problem

Coverage and interference at radio interface

Antenna and feeder system

Base station software or hardware

Transmission

BSC software, hardware, Data Configuration

A interface

target cell congestion

Cooperation with equipment of other manufacturers

Analysis of Handover Problem

Coverage and interference at radio interface

 Coverage:

 Poor coverage: forest, complicated topography, building direction and indoor coverage

 Isolated site: no adjacent cell

 Over shooting: island effect result in no adjacent cell

 Interference: MS can not access network or receive any signal

Adjacent Cell N3

Adjacent Cell N2

Adjacent

cell N1

Non-adjacent cell

Non-adjacent cell

Non-adjacent cell

Analysis of Handover Problem

Island effect results in handover failure

Analysis of Handover Problem

 Antenna & Feeder System

 High voltage standing wave ratio (VSWR)

 Antenna are not properly installed

 Antenna are not parallel

 The azimuth and downtilt are not correct

 Poor antenna isolation value

 RF cables, connection are loose or incorrect

Analysis of Handover Problem

Analysis of Handover Problem

 Clock board: the faulty clock board causes clock inconsistency between base stations.

Analysis of Handover Problem

 Data Configuration

 Improper setting of handover threshold (higher, lower, the edge handover threshold is higher than the power control threshold.)

 Improper setting of handover hysteresis and handover priority

 Improper setting of P, N value of statistic time

 Incomplete frequency and adjacency relation configured in BA1/BA2 table

 There are adjacent cells with the same frequency and the same BSIC

 CGI and module ID in "Cell Description Table" are different from those in "Cell Module Information Table"

 CGI, BCCH and BSIC in "External Cell Description Table" are different fro

m those in the opposite BSC

 The DPC of BSC in MSC "LAI And GCI Table" is incorrect

 A interface problem

dover, as well as abnormal communication

hen the target cell should be expanded or reduce its traffic

t are not matching to our equipment and they can not be recogniz

ed or support, which causes the handover failure, such as voice version, handover number, TUP circuit, addressing mode (CGI or LAI)

Analysis of Handover Problem

Course Contents

Measurement points of handover Searching process of handover data Analysis of handover problem

Handover cases

Case 1

the 1800 cells belong to one BSC), the incoming handover success rate of incoming BSC and intra BSC are low from the beginning of the service, while the outgoing handover success rate of intra-BSC and inter-BSC are normal

Typical Handover Cases

Case 1

Typical Handover Case

Analysis:

1 Register the traffic statistics and analyze whether the low

handover success rate is due to the failure of handover from all cells to this cell or from some few cells

2 If handover fails from some few cells to this cell, check the

handover data and see whether there is co-channel and co-BSIC problem

3 If handover fails from all other cells to this cell, check the data of this cell

4 If data cause is ruled out, check the hardware carefully Check the alarm or perform drive test to locate uplink fault or downlink fault Check step by step and find out the cause

 1 Register the incoming inter cell handover measurement function and find that the successful rate of handover from all other cells to this cell is low, although it is not always 0 percent Base on careful data checking, the data of this cell is correct

 2 Perform drive test and find that the downlink signal is normal but almost all handovers to this cell are failure Near the BTS, the handover is successful occasionally Perhaps the problem is with the uplink signal

 3 Check the uplink channel, antenna, CDU, they are no problem Change the TRX , everything is normal

Fault Description: After LAPD software upgrade of a dual-band network on 19th September, it was found that some cells in module 4 und

er 1800 network are seriously congested (40 ％～ 50 ％ ), and overall handover indices of BSC come down from 95 ％ to 90 ％ From "Inte

r -cell Hanover Measurement Function, it was found that beside modu

le 4, some cells of other modules also suffer from the problem that int

er cell handover success rate is low After 19th September, the situatio

n became worse

Case 2

Typical Handover Cases

Case 2

Analysis:

1 Check whether it is attributed to LAPD software upgrade

2 Analyze traffic statistics and the main causes of the

failure to locate the problem

Typical Handover Cases

 Solution:

 1 Check whether it is attributed to LAPD software upgrade After the upgrade, not all cells under module 4 are congested and the handover indices of some cells are not low Upgrade isn’t the cause

 2 Analyze traffic statistics:

 Congested cells are mostly at site A and site B Their traffics are lower than before the upgrade It is a pseudo congestion.

 The cells where handover success rate is low are mostly at site A,

B, C, D and E and the main cause of the failure is timer timeout.

Typical Handover Cases

Typical Handover Cases

 Solution:

 3 Check alarm:

 At 19:31 of 18 th September, the clock system alarms of site A and si

te B occurred It is found that 13M clock isn’t synchronous The cloc

k problem result in low handover success rate of the two sites Such impact is spread to the adjacent cells of these two cells and even to the whole network.

 4 Analyze handover data and traffic statistics: All cells where handover success rate is low are adjacent to A and B except A and

B themselves

Typical Handover Cases

 Solution:

 5 Reset site A and site B, the clock system is recovered, and th

e handover success rate inter/intra BSC goes up to 93 ％ The problem is solved

Conclusion:

 The problem in clock system will result in low handover success rate Pay attention to the alarm console and the excursion of the clock system

Case 3

(S vender) are connected to the same MSC After cutover, MS can no

t handover from S BSC to Huawei BSC but opposite is normal In oth

er words, “Attempted incoming interBSC inter cell handover" of Huaw

ei BSC is 0

Typical Handover Cases

Case 3

outgoing handover is normal Carefully check the outgoing cell handover signaling and handover data at S BSC

inter-Typical Handover Cases

Typical Handover Cases

Solution:

 1 Trace interface message After receiving HO-REQUEST message, Huawei BSC returns HO-FAILURE message immediately In normal conditions Huawei BSC should return HO-REQ-ACK message Carefully analyze HO-REQ message and HO-FAILURE message

Typical Handover Cases

Handover failure

Typical Handover Cases

Typical Handover Cases

t Address Indicator must be 0x43 Inform the owner of network, modify the relation parameter, and this problem is solved

Typical Handover Cases

Conclusion:

 In cooperation with equipment of other manufacturers, faults can

be located by analyzing the signaling

Fault Description: Huawei MSC cooperate with MSC of N (vender) The communication is normal The Huawei intra BSC handover and incoming BSC handover are normal, but outgoing BSC handover success rate is about 25% The handover from the N BSC to Huawei BSC is successful, but opposite is failure sometimes.

Case 4

Typical Handover Cases

Analysis: Check handover data, including the external cell description table, BA2 table, cell adjacency relation table inside Huawei BSC and N BSC and CGI at N MSC If the data are correct, check outgoing BSC handover signaling.

Case 4

Typical Handover Cases

Typical Handover Cases

 4 Trace MAP message at E interface (inter-MSC) with a signaling meter It is found that after receiving HO-Number, Huawei MSC never sends IAI (Initial Address Information)

Typical Handover Cases

Solution:

 5 Check HO-Number message from the opposite and find that the handover code format is 130********(only a number of mobile telephone, no any prefix) But this mobile company requires that roaming/handover between exchanges should be in the format: 00+country code + roaming/handover number In addition, Huawei equipment does not recognize the handover number without 00+country code Therefore the signaling is halted

 6 Discuss with N, asking them to add "00+country code" before the handover number Then outgoing BSC handover is normal

Typical Handover Cases

Conclusion:

 Problems can be located quickly and accurately if you are familiar with the signaling flow of handovers

Fault Description: In the independent MSC networking of a dual band network, Huawei 1800 network cooperate with 900 network o

f vender A After cutover, the successful rate of handover from M1

800 to M900 is low (about 60 ％ ), while the handover from M900 t

o M1800 are normal and the handover data are correct

Case 5

Typical Handover Cases

Analysis 1: Trace the signalings at A interface and E interface

Normal signaling is as follow:

t MAP_Send_HO_Report_AC

K

MS

HO-REQUEST HO-REQUEST-ACK

HO-Command

MS

HO-Access MAP_Process_Access_Signaling

HO-Complete MAP_Send_End_Signal

Clear-Command Clear-Complete

MAP_Send_End_Signal_ACK

Intermediate steps are omitted.

IAI ACM

Typical Handover Cases

Analysis 2: Abnormally signaling is as follow:

Typical Handover Cases

Solution:

 1 Analyze the Prepare-HO message sent from Huawei MSC to the opposite The voice version is full-rate version 1, 2 and half-rate version 1 It is a PHASE 2+ version However there is only full-rate version 1 in the message sent from M900 to Huawei M1800 It turns out that the opposite does not support half-rate version, so the handover fails

 2 Modify A interface circuit pool table of Huawei MSC data, only using full-rate version 1

 3 Then the outgoing BSC handover is normal

Typical Handover Cases

Case 6

two BSC, is all configured with Huawei equipment When the two BSC are cutover, the successful rate of handover from BSC1 to BSC2 is very low, but opposite is normal Intra BSC handover of BSC1 and BSC2 are normal

Typical Handover Cases