microsoft powerpoint - oeo000010 lte eran6.0 handover fault diagnosis issue 1

8/13/2019 Microsoft PowerPoint - OEO000010 LTE eRAN6.0 Handover Fault Diagnosis ISSUE 1

1/24

Course Name

Confidential Information of Huawei. No

Spreading Without Permission

www.huawei.com

Copyright 2013 Huawei Technologies Co., Ltd. All rights reserved.

LTE eRAN6.0 HandoverFault Diagnosis


Objectives

Upon completion of this course, you will be able to:

Deep understand the handover procedure

Solve the typical handover fault

Page1


2/24

Course Name




Contents

1. Handover Procedure Review

2. Handover KPI Introduction

3. Handover Fault Analysis

4. Case Study

Page2


Typical X2 Handover Flow

See note page

Page3


3/24

Course Name




Key Message MeasurementConfiguration

Page4


Key Message Measurement Report

Both include serving cell

and neighbor cell

PCI should be included as

an indicator of neighbor cell.

Multiple neighbor cells

measurement results could

be combined inside

Page5


4/24

Course Name




Key Message Handover Request

Page6


Key Message HandoverAcknowledgment

After target eNodeB

admitted handover in

service, it sends handover

acknowledgment

message to source cell,

including:

ERAB admitted list

Transparent RRC

handover command

Page7

Transparent RRChandover command


5/24

Course Name




Key Message RRC HandoverCommand

Source eNodeB send RRC

handover command to UE,

including:

Target cell PCI

Radio resource

configuration

RACH configuration

Handover security

configuration

Page8


Contents




4. Case Study

Page9


6/24

Course Name




Handover Success Rate Evaluation

Page10

Handover preparationattempts

A

B

Handover executionattempts

CHandover executionSuccess


Relevant Counters Intra eNB HO

Page11


7/24

Course Name




Relevant Counters Inter eNB HO

Page12


Handover Preparation Failure Conter

Page13

Measurement Counter Description

L.HHO.Prep.FailOut.MM

E

Number of outgoing handover preparation failures

due to faults in the EPC

L.HHO.Prep.FailOut.NoR

eply

Number of outgoing handover preparation failures

due to no responses from the target cell

L.HHO.Prep.FailOut.PrepFailure

Number of outgoing handover preparation failuresdue to handover preparation failures at the target

cell

L.HHO.Prep.FailOut.HOCancel Number of outgoing handover failures due tohandover cancellation messages sent by the

source cell


8/24

Course Name




Contents




4. Case Study

Page14


Contents


3.1 Typical Handover Fault Scenarios

3.2 Generic Procedure

3.2 Problem Diagnosis & Analysis

Page15


9/24

Course Name




Early Handover

Page16


Delayed Handover

Page17


10/24

Course Name




Delayed Handover (Cont.)

Page18


Contents


3.1 Typical Handover Fault Scenarios

3.2 Generic Procedure


Page19


11/24

Course Name




Procedure for Fault Analysis

Step 1: Located fault point

From the tracing message, we can located the handover fault

point, therere 3 key fault points during handover procedure

No measurement report

No handover command

No handover complete message

Step 2: Analyze the root cause

Channel quality issue

Configuration issue

Transmission quality issue

Page20


Generic Analysis Method Channel quality problem

Observe RSRP,RSRQ, SINR IBLER, DL/UL grant from driver test tools

Observer performance monitoring from M2000 including scheduling statistic,

CQI report, MCS, SINR eg.

Configuration problem

Check the neighbor/ANR configuration

Check the X2 configuration

Check EPC authentication & security configuration

Transmission problem

Check relevant alarm

Check the latency using some packet analysis tools

Page21


12/24

Course Name




Contents


3.3.1 No measurement report

3.3.2 No handover command

3.3.3 No handover complete message

Page22


Problem Analysis No MeasurementControl Message

Page23

Scenario : eNodeB doesnt send measurement control

message

Solution: Check related handover switch


13/24

Course Name




Problem Analysis Black ListConfiguration Scenario : UE receives measurement control message, but UE

doesnt send any measurement report

Possible cause:

The neighbor cell is in black list. In the SIB message eNdoeB

delivers all black cell list, then UE doesnt measure any of these

cells

Solution: check if all the neighbor belongs to black list

LST INTRAFREQBLKCELL

LST INTERFREQBLKCELL

Page24


Problem Analysis Poor DL Quality

Page25

Scenario : UE receives measurement control message, but

UE doesnt send any measurement report


14/24

Course Name




General Coverage Requirement forHandover

RSRP: More than -110dBm

RSRQ: More than -3dB

Page26


Problem Analysis ParametersSetting

Due to improper parameters setting, the criteria for sending

measurement report is very difficult

Related parameters:

A3 event: Mn+Ofn+Ocn-Hys > Ms+Ofs+Ocs+Off

Ocn can be adjusted to easily trigger the report sending

A4 event: Mn+Ofn+Ocn-Hys > Thresh

Ocn can be adjusted to easily trigger the report sending

Solution This case is considered as delayed handover, we

can enable MRO feature to optimize it automatically

Page27


15/24

Course Name




Contents





Page28


Problem Analysis No AvailableNeighbor Configuration

Neighbor can be configured by manual or ANR

Page29


16/24

Course Name




Handover Flow with ANR

ANR request UE support CGI report capability

Page30


Problem Analysis Target CellAdmission Failure

Due to the high load of target cell, it rejects the admission of

handover in service

Solution: Enable relevant load control algorithms on target

cell

Page31


17/24

Course Name




Problem Analysis TransmissionFailures

Page32


Problem Analysis TransmissionFailures

Page33


18/24

Course Name




Problem Analysis TransmissionFailures (Cont.)

Page34


Contents





Page35


19/24

Course Name




Problem Analysis Poor DLCoverage

Due to poor DL coverage of source cell, UE cant decode

handover command

Page36


Problem Analysis Poor ULCoverage

Due to poor uplink channel quality, eNodeB doesnt receive

random access preamble until UE sends maximum

preambles

Page37

RLF Occurs


20/24

Course Name


Spreading Without Permission 2


Contents




4. Case Study

Page38


Case 1: Inter TA Handover Due toMissing IP Path

Description: In one project, we find a lot of handover failure.

From the statistic, we observe that most of these failures

happen between inter TA cell.

Analysis

From the tracing message, we see that the failure cause is

handover preparation failure, the failure cause is GTUP

resource not available

Page39


21/24

Course Name




Analysis

In the handover request message, source eNodeB deliver

the target GTPU ID (SGW IP address) to let target eNodeB

setup uplink S1 bearer directly. We check the IP address of

SGW in the message, and find that it is not identical with

target eNodeB configuration

Page40


Solution Later we confirm this issue, this TA border is also the border of

two regions which use different SGW. And in each region ,only

one IP path is configured for current eNodeB to SGW. So the

handover will be failure when cross the different SGW.

Solution

Configure S1 IP path from the target eNodeB to source SGW,

then the problem is solved

Suggestion: This is a very typical problem, on the border cell of

inter SGW, we should remember to configure the IP path to the

SGW which belongs to the target cell as well.

Page41


22/24

Course Name




Case 2: Handover Failure Due to NoHandover Command

Description: UE sends measurement report to eNB several

times , but no feed back from eNodeB

Tracing message from eNodeB

Page42


Case 2 Analysis

From the previous message, we can see that before the

measurement report, eNB sends one RRC reconfiguration

message, but the UE doesnt feedback the complete

message.

Then we check trace on UE side, and find that UE doesnt

receive the RRC reconfiguration message

Page43


23/24

Course Name




Case 2 Conclusion

Due to poor DL coverage, UE doesnt receive the RRC

reconfiguration message, thus no complete feedback. As

the previous RRC reconfiguration procedure is not

completed, eNodeB is still waiting for reconfiguration

feedback and measurement report is not processed.

Page44


Summary

Handover flow analysis

Troubleshooting for typical handover fault

Page45

microsoft powerpoint - oeo000010 lte eran6.0 handover fault diagnosis issue 1

Documents