09 WCDMA RNO Access Failure Problem Analysis

WCDMA Access Problems Analysis

ReviewReview

Access is associated with the call setup

success rate of the network. This KPI can be

optimized by means of “Call setup test” and the

consequent trouble-shooting based on access

failure analysis.

ObjectivesObjectives

� Be familiar with the access

procedure in UMTS

� Do analysis on access problems

independently

When finished this course,you will be able to:

Course ContentsCourse Contents

Definition of access failure

Access problem analysis process

Common reasons for access problems

Case study

Definition of access failureDefinition of access failure

General originating call setup signaling flow:


General terminating call setup signaling flow:


Call setup succeeds when the call setup

phase is completed (when CC Connect is

received). If the call fails to reach the CC

Connect stage, it should be pegged as an

access failure .





Case study

Access problem analysis processAccess problem analysis process

�� Preparation before AnalysisPreparation before Analysis

� Access problem analysis

methods

Preparation before analysis Preparation before analysis

Be familiar with the planning information which can be obtained from planning

reports;

Be familiar with history records of optimization;

Get the latest reliable summary sheet of the engineering parameters;

Get the latest configuration of radio parameters;

Obtain the network traffic statistics and the subscriber complaint information of

access.

Access problem analysis processAccess problem analysis process

� Preparation before Analysis

�� Access problem analysis Access problem analysis

methodsmethods

Access problem analysis methodsAccess problem analysis methods

General methods of access problem analysis:

Traffic statistics data analysisCustom complaint collection

Call setup test in specific area

Coverage analysis

Signaling analysis

Access problem analysis methodsAccess problem analysis methods

Traffic statistics data and custom complaint collection reveal problems exactly, further trouble-shooting can be carried out by call setup test. While for a pre-commercial or trial network, call setup test is the effective way.





Case study

Common reasons for access problemsCommon reasons for access problems

�� RF reasonsRF reasons

� Radio Parameter Settings

� Other reasons

RF reasonsRF reasons

Poor coverage

Strong Uplink or downlink Interference


� RF reasons

�� Radio Parameter SettingsRadio Parameter Settings

� Other reasons

Radio parameter settings Radio parameter settings

Improper threshold of Qqualmin and Qrxlevmin

Improper settings of access threshold

Inappropriate settings of preamble power ramp step and retransmission times

Inappropriate setting of adjacent cells

Inappropriate setting of synchronization parameters

Unsuitable power allocation rate for common channel

Unsuitable initial power of uplink and downlink dedicated channel

Unsuitable setting of uplink Initial SIR target value of dedicated channel


� RF reasons

� Radio Parameter Settings

�� Other reasonsOther reasons

Other reasonsOther reasons

Data configuration problems

Access problems caused by cell load





Case study

Case studyCase study

�� Access failure due to synchroniAccess failure due to synchroni--zaza

tion failuretion failure

� Access failure during RB setup

� Access failure during handover pr

ocess

� Access failure due to terminating

UE

Access failure due to synchronization failureAccess failure due to synchronization failure

Access failure location:


UE Txpower reaches maximum value 21 dBm during VP call setup. So this call

setup failure may be caused by Uplink synchronization failure:


UE does not send RRC Connection Setup Complete to RNC after receiving RRC

Connection Setup message from RNC :


� Access failure due to synchroni-za

tion failure

�� Access failure during RB setupAccess failure during RB setup


ocess


UE

Access failure during RB setupAccess failure during RB setup

Access failure location:


UE Tx power is very low and downlink pilot Ec is high before access failure,butEc/Io is not very good :


The cause of call setup failure is Requested circuit/channel not available:


RNC didn’t receive RB

Setup Complete message

after it has sent RB Setup

message to UE. Timeout of

RNC is reached after 1.5s:



tion failure


�� Access failure during handover prAccess failure during handover pr

ocess ocess


UE

Access failure during handover processAccess failure during handover process

Access failure location (Scanner Rscp ):


ScannerEc/I0 :


Scanner BestServer :


During access process, UE Txpower is rising rapidly :


And the downlink Bler reaches 100%:


UE report the measurement of cell Sc508 which request the active set update:


The report was

received properly and

“RRC_ACTIVE_UPDATE”

was sent as response

while UE didn’t received it

which results in the

access failure:


Let’s turn to the performance of the terminating UE. During the access process, the measurements from the terminating UE were not satisfactory either:


While the radio links

hold on till successful

handover is completed:


Then the originating UE loses connection to the network and access released

where the cause is “destination out of order” from the signal traced by the terminating UE:



tion failure



ocess

�� Access failure due to terminating Access failure due to terminating

UEUE

Access failure due to terminating UEAccess failure due to terminating UE

Access failure location (UE Ec/I0 ):


The coverage is not bad where the UE originates the VP access:


CN send “disconnect” message with the cause “bearer capability not authorized”

before access failure:


setup signaling procedure for RRC and RAB have already finished. The cause of disconnect is the same:


The reason is: we use two mobile to test video phone, for the originating call mobile camped in 3G network, but the terminating call mobile camped in 2G network that moment, so video call setup failed, the missing signaling of terminating UE can also explain it:

SummarySummary

Access process is complicated since different devices are

involved and scenario varies. Careful study from signal

distribution to signaling procedure makes things easy.

Examples above are derived from tests carried out before,

which give general idea of trouble shooting, advanced

researches will be supplemented. .

09 WCDMA RNO Access Failure Problem Analysis

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