09- Owj200105 Wcdma Access Procedure Issue1.0

8/12/2019 09- Owj200105 Wcdma Access Procedure Issue1.0

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Copyright 2006 Huawei Technologies Co., Ltd. All rights reserved.

WCDMA Access

Procedure


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Copyright 2006 Huawei Technologies Co., Ltd. All rights reserved. Page2

Objectives

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

The main access procedures

The messages of access procedure

The performance indicators of access procedure


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Contents

1. Access Procedure in UMTS

2. Access Procedure Messages

3. Access Procedure Performance Analysis


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Contents


1.1 Definition of Access Procedure

1.2 Cell Search

1.3 Cell Selection and Reselection

1.4 Random Access Procedure


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Definition of Access Procedure

Two operating mode of UE

Idle mode

After turning on, UE will stay in idle mode, which is identified by

the NAS identification, such as IMSI, TMSI or P-TMSI etc

Connected mode

UE will switch to connected mode which could be CELL_FACH

state or CELL_DCH state from the idle mode

After releasing RRC connection, UE will switch to the idle mode

from the connected mode


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Definition of Access Procedure

Definition about access procedure

From the view of access stratum, access is the procedure UE

shift from idle mode to connected mode.

UE can do the registration, service application,authentication and non-access stratum actions


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Contents



1.2 Cell Search




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Cell Search

UE doesnt have UTRAN carrier information

In order to find a suitable cell to stay, UE will scan all the

frequencies in UTRAN. In each carrier, UE just need to find a

cell with best signal

UE has UTRAN carrier information

UE will try whether the original cell is suitable to stay. If not, UE

still need to scan all the frequencies about UTRAN in order to

find a suitable cell in PLMN


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Synchronization ProcedureCell Search

Slot synchronization

Frame synchronization and

code-group identification

Scrambling-code

identification

UE uses PSC to acquire slot

synchronization to a cell

UE uses SSC to find framesynchronization and identify the

code group of the cell found in the

first step

UE determines the primary scrambling code

through correlation over the CPICH with all

codes within the identified group, and then

detects the P-CCPCH and reads BCH

information


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Synchronization ProcedureCell Search

Slot synchronization

Frame synchronization and

code-group identification

Scrambling-code

identification

UE uses PSC to acquire slot

synchronization to a cell

UE uses SSC to find framesynchronization and identify the

code group of the cell found in the

first step

UE determines the primary scrambling code

through correlation over the CPICH with all

codes within the identified group, and then

detects the P-CCPCH and reads BCH

information


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Contents



1.2 Cell Search




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Cell Selection After cell search, UE will judge whether current PLMN is a

right one. If so, the UE will measure the signal of the cell

and use S criteria to judge whether the cell is suitable to

camp on. This process is cell selection

If the cell signal does not satisfy the S criteria, UE will start

the cell selection and PLMN selection again


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Cell Selection PLMN selection

UE can get the system information from PCCPCH

In system information, the PLMN information is transmitted in

MIB

After getting the MIB, UE can judge weather the current PLMN

is the right one. If so, UE will get the SIB scheduling

information from the MIB; if not, UE will search another carrier,

do this procedure again


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Cell Selection Decision criteria

UE can get Cell selection and re-selection info from SIB3,

which contains Qqualmin, Qrxlevmin/Maximum, allowed UL TX

powerUE_TXPWR_MAX_RACH

S criteria: Srxlev > 0 & Squal > 0, where:

Squal = QqualmeasQqualmin

Srxlev = QrxlevmeasQrxlevminPcompensation


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Cell Selection

S criteria parameters

explanationParameters ExplanationSqual Cell Selection quality value (dB)

Srxlev Cell Selection RX level value (dBm)

Qqualmeas Measured cell quality value. The quality of the received signalexpressed in CPICH Ec/N0 (dB) for current cell

Qrxlevmeas Measured cell RX level value. This is received signal, CPICH RSCP

for current cells (dBm)

Qqualmin Minimum required quality level in the cell (dB)

Qrxlevmin Minimum required RX level in the cell (dBm)

Pcompensation maxUE_TXPWR_MAX_RACHP_MAX0, dBm

UE_TXPWR_MA

X_RACH

Maximum TX power level an UE may use when accessing the cell

on RACH (read in system information) (dBm)

P_MAX Maximum RF output power of the UE (dBm)


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Cell Reselection

In idle mode, UE should monitor the quality of current cell

and adjacent cell in order to camp on the best cell to initiate

service. This process is cell reselection

Trigger conditions

Event trigger in idle mode

In idle mode, if the cell can not satisfy S criteria during Nserv

DRXs continuously.

When UE detected itself in non-service area


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Cell Reselection

Intra-frequency measurement

Squal Sintrasearch

Qqualmeas Qqualmin Sintrasearch

Qqualmeas Qqualmin + Sintrasearch

Measurement tr igger condition


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Cell Reselection

Inter-frequency measurement

Squal Sintersearch

Qqualmeas Qqualmin Sintersearch

Qqualmeas Qqualmin + Sintersearch



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Cell Reselection

Inter-RAT measurement

Squal Ssearchrat

Qqualmeas Qqualmin Ssearchrat

Qqualmeas Qqualmin + Ssearchrat



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Cell Reselection

Rs = Qmeas,s + Qhysts

Rn = Qmeas,n- Qoffsets,n- TOn* (1 Ln)

TOn= TEMP_OFFSETn* W(PENALTY_TIMEn Tn)

Ln= 0 if HCS_PRIOn= HCS_PRIOsLn= 1 if HCS_PRIOn HCS_PRIOs

W(x) = 0 for x < 0

W(x) = 1 for x >= 0

R criteria for cell-ranking:

where

Decision cr iter ia


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Cell Reselection

Parameters Explanation

Rs The R value of current serving cell

Qmeas,s The quality value of current serving cell

QHyst,s The hysteresis for the current serving cell

Rn The R value of adjacent cells

Qmeas,n The quality value of adjacent cells

Qoffset s,n The load level offset for cell reselection

Parameters explanation


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Cell Reselection Hysteresis Time

TimeTreselection

Quality

Rn

Rs

Qmeas,n

Qmeas,s

Qhyst,s

Qoffsets,n


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Contents



1.2 Cell Search




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Random Access Procedure

Definition

Random access procedure is initiated by UE in order to get

service from the system. Meanwhile, the access channels are

allocated to the UE by system.

This process may happen in the following scenario:

Attach and detach

LA update and RA update

Signaling connection for services


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Random access channel

AICH accessslots

10 ms

#0 #1 #2 #3 #14#13#12#11#10#9#8#7#6#5#4p-a

#0 #1 #2 #3 #14#13#12#11#10#9#8#7#6#5#4

PRACHaccess slots

SFN mod 2 = 0 SFN mod 2 = 1

10 ms

Access slot set 1 Access slot set 2


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Random Access Procedure The access slots of different RACH sub-channels

are illustrated by the following table

SFN mod 8 Random access sub-channels number

0 1 2 3 4 5 6 7 8 9 10 11

0 1 2 3 4 5 6 71 12 13 14 8 9 1 112 1 2 3 4 5 6 73 9 1 11 12 13 14 84 6 7 1 2 3 4 55 8 9 1 11 12 13 146 3 4 5 6 7 1 27 8 9 1 11 12 13 14


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Message partPreamble

4096 chips10 ms (one radio frame)

Preamble Preamble

Message partPreamble

4096 chips 20 ms two radio frames

Preamble Preamble


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The following figure shows the RACH procedure

Nodetect

Nodetect

Nodetect ACK

message

p-p

p-m

p-p p-m


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One access slot

p-a

p-mp-p

Pre-amble

Pre-amble Message part

Acq.Ind.

AICH accessslots RX at UE

PRACH accessslots TX at UE


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The interval between two preambles should be longer than

the minimum value

p-p p-p,min

Parameters about the procedure


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Random Access ProcedureSTART

Choose a RACH sub channel from

available ones

Get available signatures

Set Preamble Retrans Max

Set Preamble _Initial _ Power

Send a preamble

Check the corresponding AI

Increase message part power by p

-m based on preamble power

Set physical status to be RACH

message transmitted Set physical status to be Nackon AICH received

Choose a access slot again

Counter> 0 & Preamble power-

maximum allowed power


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Contents





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Contents


2.1 System Information Broadcast

2.2 RRC Connection Messages


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System Information Broadcast System information structure

Information elements are broadcasted in SIB, and the same category

information can be put into one SIB

The structure of system information is like a tree, which showed in the

following figure: the MIB contains the scheduling information about SIB; the

upper class SIB contains the same information of lower class one


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Contents


2.1 System Information Broadcast

2.2 RRC Connection Messages


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RRC Connection Message

Typical RRC connection messages

RRC_CONNECTION_REQUEST

RRC_CONNECTION_SETUP RRC_CONNECTION_SETUP_COMPLETE

RRC_CONNECTION_REJECT

RRC_CONNECTION_RELEASE


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RRC Connection Setup on

RACH/FACH


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RRC Connection Setup on DCH


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RRC CONNECTION

REQUEST


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RRC CONNECTION

SETUP


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RRC

CONNECTION

SETUP

COMPLETE


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RRC CONNECTION RELEASE


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RRC CONNECTION REJECT


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DCCH is mapped on common channel (RACH/FACH)

DCCH is mapped on dedicated channel (DCH)

Mapping of DCCH


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Contents





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Contents


3.1 Performance Indicators

3.2 The Influence Factors for Performance


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Contents


3.1 Performance Indicators

3.2 The Influence Factors for Performance


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The Influence Factors for Performance

Incorrect Tcell setting influenced the Cell Search

Speed

Tcell is used to define the relative time delay between

the starting transmission time of SCH, CPICH and

BFN

Tcell


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In RRC CONNECTION REQUEST message, UE

has to report the measurement result about current

cell and neighbor cells

If there are too many neighbor cells, UE needs

longer time to do the measurement. Then, the user

access time will be longer

Neighbor list


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Complex radio environment will cause slow fading,

which will influence the access procedure

Radio environment


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The path loss can be different on different clutters, which

will influence the preamble transmission power calculation

in the open loop power control procedure

By the formula, the compensation for the difference path

loss of uplink and downlink is Constant Value.

Preamble_Initial_Power = Primary CPICH TX powerCPICH_RSCP + UL interference + Constant Value

Clutter dif ference


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References

3GPP 25.211 Physical channels and mapping of transportchannels onto physical channels (FDD)

3GPP 25.213 Spreading and modulation (FDD)

3GPP 25.214 Physical layer procedures (FDD)

3GPP 25.331 Radio Resource Control Protocol

Specification


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09- Owj200105 Wcdma Access Procedure Issue1.0

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