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Copyright 2006 Huawei Technologies Co., Ltd. All rights reserved.
WCDMA Access
Procedure
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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. Access Procedure in UMTS
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. Access Procedure in UMTS
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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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. Access Procedure in UMTS
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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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
Measurement tr igger condition
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Cell Reselection
Inter-RAT measurement
Squal Ssearchrat
Qqualmeas Qqualmin Ssearchrat
Qqualmeas Qqualmin + Ssearchrat
Measurement tr igger condition
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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. Access Procedure in UMTS
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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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 Procedure
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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Random Access Procedure
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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Random Access Procedure
The following figure shows the RACH procedure
Nodetect
Nodetect
Nodetect ACK
message
p-p
p-m
p-p p-m
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Random Access Procedure
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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Random Access Procedure
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
1. Access Procedure in UMTS
2. Access Procedure Messages
3. Access Procedure Performance Analysis
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Contents
2. Access Procedure Messages
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. Access Procedure Messages
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 Message
RRC CONNECTION
REQUEST
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RRC Connection Message
RRC CONNECTION
SETUP
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RRC Connection Message
RRC
CONNECTION
SETUP
COMPLETE
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RRC Connection Message
RRC CONNECTION RELEASE
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RRC Connection Message
RRC CONNECTION REJECT
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RRC Connection Message
DCCH is mapped on common channel (RACH/FACH)
DCCH is mapped on dedicated channel (DCH)
Mapping of DCCH
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Contents
1. Access Procedure in UMTS
2. Access Procedure Messages
3. Access Procedure Performance Analysis
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Contents
3. Access Procedure Performance Analysis
3.1 Performance Indicators
3.2 The Influence Factors for Performance
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Contents
3. Access Procedure Performance Analysis
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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The Influence Factors for Performance
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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The Influence Factors for Performance
Complex radio environment will cause slow fading,
which will influence the access procedure
Radio environment
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The Influence Factors for Performance
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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