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WCDMA Access Procedure
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Review
Access is associated with the call setup success
rate of the network. Mastering the access
procedure can increase this KPI with the access
parameters optimization.
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Objectives
Know the detailed access
procedure in UMTS
Know how to optimize the
access procedure
Upon completion of this course,you will be able to:
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Course Contents
Random access procedure
RRC setup procedure
RAB setup procedure
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Random access procedure
Physical channel about access
Random access procedure
Parameters optimization
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PRACH access slot
#0 #1 #2 #3 #4 #5 #6 #7 #8 #9 #10 #11 #12 #13 #14
5120 chips
radio frame: 10 ms radio frame: 10 ms
Access slot
Random Access Transmission
Random Access Transmission
Random Access Transmission
Random Access Transmission
UE can start the random-access transmission at the beginning of aaccess slot
There are 15 access slots per two frames
what access slots are available is given by higher layers
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Structure of the random-access transmission
Each random-access transmission consists of one or several
preamblesof length 4096 chips and a messageof length 10
ms or 20 ms.
Each preamble is of length 4096 chips and consists of 256
repetitions of a signature of length 16 chips.
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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Structure of the random-access transmission
The preamble-to-preamble distance p-p shall be larger than or
equal to the minimum preamble-to-preamble distance
p-p,min .
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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Structure of the random-access transmission
when AICH_Transmission_Timing is set to 0
p-p,min = 15360 chips (3 access slots)
p-a = 7680 chips
p-m = 15360 chips (3 access slots)
when AICH_Transmission_Timing is set to 1, then
p-p,min = 20480 chips (4 access slots)
p-a = 12800 chips
p-m = 20480 chips (4 access slots)
The parameter AICH_Transmission_Timing is
signalled by higher layers.
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Random access procedure
Physical channel about access
Random access procedure
Parameters optimization
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Concepts in random access procedure
Preamble Signature
AC (Access Class)
ASC (Access Service Class)
RACH sub channels
Access slot set
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Preamble Signature
Value of nPreamble
signature 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
P0(n) 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
P1(n) 1 -1 1 -1 1 -1 1 -1 1 -1 1 -1 1 -1 1 -1
P2(n) 1 1 -1 -1 1 1 -1 -1 1 1 -1 -1 1 1 -1 -1
P3(n) 1 -1 -1 1 1 -1 -1 1 1 -1 -1 1 1 -1 -1 1
P4(n) 1 1 1 1 -1 -1 -1 -1 1 1 1 1 -1 -1 -1 -1
P5(n) 1 -1 1 -1 -1 1 -1 1 1 -1 1 -1 -1 1 -1 1
P6(n) 1 1 -1 -1 -1 -1 1 1 1 1 -1 -1 -1 -1 1 1
P7(n) 1 -1 -1 1 -1 1 1 -1 1 -1 -1 1 -1 1 1 -1
P8(n) 1 1 1 1 1 1 1 1 -1 -1 -1 -1 -1 -1 -1 -1
P9(n) 1 -1 1 -1 1 -1 1 -1 -1 1 -1 1 -1 1 -1 1
P10(n) 1 1 -1 -1 1 1 -1 -1 -1 -1 1 1 -1 -1 1 1
P11(n) 1 -1 -1 1 1 -1 -1 1 -1 1 1 -1 -1 1 1 -1
P12(n) 1 1 1 1 -1 -1 -1 -1 -1 -1 -1 -1 1 1 1 1
P13(n) 1 -1 1 -1 -1 1 -1 1 -1 1 -1 1 1 -1 1 -1
P14(n) 1 1 -1 -1 -1 -1 1 1 -1 -1 1 1 1 1 -1 -1
P15(n) 1 -1 -1 1 -1 1 1 -1 -1 1 1 -1 1 -1 -1 1
The preamble signature corresponding to a signatures consists of 256 repetitions of a length
16 signature Ps(n) shown as the following table. UE gets signature from system info type5.
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Access Class
The SIMs/USIMs of all the UEs are allocated with one of Access Class 0~9. In addition,
one or more special access classes (Access Class 11~15) might be allocated to the
SIM/USIM storage information of the UEs with high priority, as shown below:
Access Class 15 --- PLMN Staff;
Access Class 14 --- Emergency Services;
Access Class 13 --- Public Utilities;
Access Class 12 --- Security Services;
Access Class 11 --- For PLMN Use.
Different from Access Class 0~9 and 11~15, the control information of
Access Class 10 is sent to UEs by means of air interface signalling,
indicating whether the UEs belonging to Access Class 0~9 or without IMSIcan be accessed to the network in case of emergency calls. For the UEs
with Access Class 11~15, they cannot initiate the emergency calls when
Access Class 10 and Access Class 11~15 are all barred.
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Access Service Class
The PRACH resources (access timeslots and preamble signatures in FDD
mode) can be classified into several ASCs. One ASC defines a partition of
certain PRACH resources.
The ASCs are numbered within the range 0
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Access Slot Set
Access slot set 1contains PRACH slots 0 7 and starts p-a
chips before
the downlink P-CCPCH frame for which SFN mod 2 = 0. Access slot set 2
contains PRACH slots 8 - 14 and starts (p-a 2560) chips before the
downlink P-CCPCH frame for which SFN mod 2 = 1.
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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RACH sub channels
SFN modulo 8 of
corresponding P-
CCPCH frame
Sub-channel number
0 1 2 3 4 5 6 7 8 9 10 11
0 0 1 2 3 4 5 6 7
1 12 13 14 8 9 10 11
2 0 1 2 3 4 5 6 7
3 9 10 11 12 13 14 8
4 6 7 0 1 2 3 4 5
5 8 9 10 11 12 13 14
6 3 4 5 6 7 0 1 2
7 8 9 10 11 12 13 14
A RACH sub-channeldefines a sub-set of the total set of uplink access
slots. There are a total of 12 RACH sub-channels.
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Random access procedure
START
Choose a RACH sub channel fromavailable ones
Get available signatures
Set Preamble Retrans Max
Set Preamble_Initial_Power
Send a preamble
Check the corresponding AI
Increase message part power by Pp-mbased on preamble power
Set physical status to be RACH message
transmitted
Set physical status to be Nack on AICH
received
Choose a access slot again
Counter >0 && Preamble power -
maximum allowed power < 6dB
Choose a signature and increase preamble
transmit power
Set physical status to be Nack on AICH
received
Get negative AI
No AI
Report the physical status to MAC
END
Get positive AI
The counter of preamble retransmit
subtract 1; Commanded preamble powerincreased by Power Ramp Step
N
Y
Send the corresponding message part
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Random access procedure
Before random-access procedure, Layer 1 shall receive the
following information from the RRC layers:
The preamble scrambling code.
The message length in time, either 10 or 20 ms.
The AICH_Transmission_Timing parameter [0 or 1].
The set of available signatures and the set of available RACH sub-channels
for each ASC.
The power-ramping factor Power Ramp Step.
The parameter Preamble Retrans Max.
Preamble_Initial_Power.
The Power offset P p-m = Pmessage-control Ppreamble.
The set of Transport Format parameters, This includes the power offset
between the data part and the control part of the random-access message for
each Transport Format.
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Random access procedure
Layer 1 shall also receive the following information from the
MAC layers :
The Transport Format to be used for the PRACH message
part. The ASC of the PRACH transmission.
The data to be transmitted .
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Random access steps
1. Derive the available uplink access slots in the next fullaccess slot set and Randomly select one access slot .
2. Randomly select a signature from the set of available
signatures within the given ASC .
3. Set the Preamble Retransmission Counter to Preamble
Retrans Max.
4. Set the parameter Commanded Preamble Power to
Preamble_Initial_Power.
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Random access steps
5. Transmit a preamble using the selected uplink access slot,
signature, and preamble transmission power.
6. Check the corresponding AI, if received positive AI, send the
message part and set L1 status RACH message transmitted.
If received negative AI, set L1 status Nackon AICH received.
7. If no AI received, select the next access slot, signature and
decrease the preamble retransmission counter by one,
increase the preamble power by power ramp step. Check if the
counter more than 0 and the preamble power less than the
maximum allowed. If true, send a preamble again. Otherwise,
set L1 status Noack on AICH.
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Random access procedure
Physical channel about access
Random access procedure
Parameters optimization
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ConstantValue
Preamble_Initial_Power = DL_Path_Loss + UL_interference +
Constant_Value. This parameter is used for the UE to estimate
the initial PRACH transmission power according to the open
loop power.
Influence on the network performance: If this parameter is settoo big, the initial transmission power will be too big, but the
access process will become shorter; if it is set too small, the
access power will satisfy the requirements, but the preamble
requires multiple ramps, which will lengthen the access
process.
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PRACH Power Ramp Step
PRACH PowerRampStep is the ramp step of the preamble
power by the UE before it receives the NodeB capture
indication.
Influence on the network performance: If this value is set too
big, the access process will be shortened, but the probability ofwasting power will be bigger; if it is set too small, the access
process will be lengthened, but some power will be saved. It is
a value to be weighed.
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Maximum Preamble Retransmit Times
PreambleRetransMax is the maximum preamble
retransmission times of the UE within a preamble ramp cycle.
Influence on the network performance: If this value is set too
big, the access process will be shortened, but the probability of
wasting power will be bigger; if it is set too small, the accessprocess will be lengthened, but some power will be saved. It is
a value to be weighed.
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Maximum Preamble Cycle Times
Mmax defines the maximum times of the random access
preamble cycle. When the UE transmits a preamble and has
reached the maximum retransmit times
(PreambleRetransMax), if the UE has not received the capture
indication yet, it will repeat the access attempt after the
specified waiting time; but the maximum cycle times cannot
exceed Mmax.
Influence on the network performance: If this parameter is set
too small, the UE access success rate will be influenced; if it is
set too big, the UE will probably try access attempt repeatedly
within a long time, which will increase the uplink interference.
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Course Contents
Random access procedure
RRC setup procedure
RAB setup procedure
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RRC Setup Procedure
UE SRNC
RRC RRC
RRC
RRC
RRC
RRCRRC Connection Setup Complete
NODEB
NBAP NBAP
NBAP NBAP
Radio Link Setup Requset
Radio Link Setup Response
RRC Connection Request
RRC Connection Setup
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Parameters optimization
T300 and N300
DPDCH Power Control Preamble Length (PCPreamble)
Successive Synchronization Indication Times (NInSyncInd)
Successive Out-of-sync Indication Times (NOutSyncInd)
Radio Link Failure Timer Duration (TRLFailure)
N312 and T312
N313, N315, T313
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T300 and N300
After the UE transmits RRC CONNECTION REQUEST message, the T300
timer will be started, and the timer will be stopped after the UE receives RRC
CONNECTION SETUP message. Once the timer times out, if RRC
CONNECTION REQUEST message is retransmitted less than the number of
times specified by the constant N300, the UE repeats RRC CONNECTION
REQUEST; otherwise it will be in the idle mode.
Influence on the network performance: The T300 setting should be
considered together with the UE, UTRAN processing delay and the
propagation delay. The bigger T300 is, the longer time the UE T300 will wait
for. The bigger N300 is, the higher success probability of the RRC connection
setup will be, and the longer RRC setup time will probably be. It will likely bethat a UE repeats the access attempt and the connection setup request
transmission, and consequently other users will be influenced seriously.
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PCPreamble
PCPreamble defines the lasting time of DPCCH transmission by the UE
before the UE transmits DPDCH.
Influence on the network performance: At first, this parameter has been
originally used in the uplink and downlink power control convergence to
prevent the uncontrollable power of the UE at the beginning. Later, it was
considered in some proposals that NodeB needs some time to find the uplink
signal after the UE starts DPCCH transmission. This delay depends on the
searching process and the propagation delay. It makes no sense to start the
uplink DPDCH transmission process before the end of this process, because
the data cannot be received normally at this time, and data loss will occur; or,
if it is the confirmation mode, the retransmission may cause more serious datadelay. If this parameter is set improperly, it will lead to data loss and
retransmission delay, which will consequently influence the service rate and
the transmission delay.
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NInSyncInd
This parameter defines the successive synchronization indication times
required for the NodeB to trigger the radio link recovery process. The radio link
set remains in the initial state until it receives NInsyncInd successive
synchronization indications from L1, then NodeB triggers the radio link
recovery process, which indicates that the radio link set has been
synchronized. Once the radio link recovery process is triggered, the radio link
set is considered to be in the synchronized state.
Influence on the network performance: The bigger this parameter is, the
stricter the synchronization process will be, and the more difficult the sync will
be; the smaller it is, the easier the synchronization will be. However, if the link
quality is bad, a simple synchronization requirement will lead to the waste ofthe UE power and the increase of uplink interference; in the radio link
maintenance process, this parameter is used together with the successive out-
of-sync indication counter.
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NOutSyncInd
NOutSyncInd defines the successive out-of-sync indication times that are
required to receive to start the timer TRlFailure. When the radio link set is in
synchronized state, the NodeB will start the timer TRlFailure after it receives
NOutsyncInd successive out-of-sync indications. The NodeB should stop and
reset the timer TRlFailure after receiving NInsyncInd successive sync
indications. If the timer TRlFailure times out, the NodeB will trigger the radio
link failure process, and indicate the radio link set that is out-of-sync.
Influence on the network performance: If this parameter is set too small, the
link out-of-sync decision will be likely to occur; if it is set too big, out-of-sync
will not be likely to occur, but, if the link quality is bad, it will result in waste of
the UE power and increased uplink interference. In the radio link maintenanceprocess, this parameter is adopted together with the successive
synchronization indication counter.
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TRLFailure
This value defines the timer TRlFailureduration. When the radio link set is in
synchronized state, NodeB should start the timer TRlFailure after it receives
NOutsyncInd successive out-of-sync indications; and NodeB should stop and
reset the timer TRlFailure after receiving NInsyncInd successive sync
indications. If the timer TRlFailure times out, NodeB will trigger the radio link
failure process, and indicate the radio link set that is out-of-sync.
Influence on the network performance: If the timer is set too short, there will
few chances for link synchronization; if it is set too long, the radio link failure
process will probably be delayed, and the downlink interference will be
increased.
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N312 and T312
When the UE starts to set up the dedicated channel, it starts the T312 timer,
and after the UE detects N312synchronization indications from L1, it will stop
the T312 timer. Once the timer times out, it means that the physical channel
setup has failed.
Influence on the network performance: The bigger N312 is, the more
difficult the dedicated channel synchronization will be; the longer T312 is, the
bigger the synchronization probability will be, but the longer the
synchronization time will be.
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N313, N315, T313
After the UE detects N313 successive out-of-sync indications from L1, it will
start the T313 timer. And after the UE detects N315 successive sync
indications from L1, it will stop the T313 timer. Once the timer times out, the
radio link fails.
Influence on the network performance: The bigger N313 is, the more
difficult it will be to start T313, which will reduce the out-of-sync probability; the
smaller N315 is, the longer T313 will be, and the bigger the link recovery
probability will be. These three parameters should be used together.
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Course Contents
Random access procedure
RRC setup procedure
RAB setup procedure
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RAB Setup Procedure
UE SRNCNodeB CN
RANAP RANAPRAB Assignment Request
RRCRRC
RRC
RB Setup
RRCRB Setup Complete
RANAP RANAPRAB Assignment Response
NBAP NBAPRL Reconfig Prepare
NBAP NBAP
NBAP NBAP
RL Reconfig Ready
RL Reconfig Commit
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Appendix: MOC signaling process
Downlink Synchronisation
UENode B
Serving RNS
Serving
RNC
DCH-FPDCH-FP
RRCRRC CCCH: RRC Connection Request
NBAP Radio Link Setup Response
NBAP
NBAPRadio Link Setup Request
CCCH: RRC Connection Setup
Start RX
Start TX
RRC
RLC
RRC
DCCH: RRC Connection Setup Complete
DCH-FPDCH-FPUplink Synchronisation
NBAP
Q.AAL2Q.AAL2
Q.AAL2 Establish Request
Establish Confirm
Inital Direct Transfer
CN
DCCH :RRC
RLC
RRC
RRC
RRC
Q.AAL2
DCCH : RRC Connection Setup Complete ack
Inital Direct Transfer
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Appendix: MOC signaling process
Inital Direct Transfer
RRC
RANAPRANAP
UENode B
Serving RNS
Serving
RNC CN
Initial UE Message
RANAPRANAP
DCCH
Direct Transfer
RANAPRANAP
Direct Transfer
:
Direct TransferDCCH ::
Direct TransferDCCH ::
RRCDownlink
RRC
RRC
Uplink
RRC
RRC
RRC
(CM Service Request)
(CM Service Accept)
(Setup)
DCCH :
DCCH : Downlink
Uplink
Direct Transfer
Direct Transfer
RRCRRC
RRC
RRC
RRC
RANAPRANAP
Direct Transfer
(Call Proceeding)
Inital Direct Transfer
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Appendix: MOC signaling process
UENode B
Serving RNS
Serving
RNC CN
DCCH :
DCCH : Downlink
Uplink
Direct Transfer
Direct Transfer
RRCRRC
RRC
RRC
RRC
RAB Assignment RequestRANAP
RANAP Establishment( )
Q.AAL2Q.AAL2
Q.AAL2 Establish Request
Establish Confirm
Q.AAL2
NBAPPrepare
NBAPRadio Link Reconfiguration
NBAPRadio Link ReconfigurationNBAPReady
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Appendix: MOC signaling process
UE
Node B
Serving RNS
Serving
RNC CN
DCCH : Radio Bearer Setup
DCCH : Radio Bearer Setup Complete
Q.AAL2Q.AAL2
Q.AAL2 Establish Request
Establish Confirm
Q.AAL2
Downlink Synchronisation
Uplink Synchronisation
Radio Link Reconfiguration
NBAP
NBAP
NBAP
NBAP
NBAP
NBAP
Apply new transport format set
RRC
RRC
RRC
RRC
RAB Assignment ResponseRANAP RANAP
Establishment( )
Commit
DCCH : Radio Bearer Setup Complete ackRLCRLC
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Appendix: MOC signaling process
UE
Node B
Serving RNSServing
RNCCN
RRC
RANAPRANAP Direct Transfer
RRC
RANAPRANAP
Direct Transfer
(Alerting)
(Connect)
RRC
RRC
RANAPRANAP Direct Transfer
(Connect Acknowledge)
RRC
RANAPRANAP Direct Transfer
(Rlease Complete)
RANAPRANAP Direct Transfer
(Release)
RANAPRANAP Direct Transfer
(Disconnect)
RRC
DCCH ::
DCCH ::
Downlink
Uplink
Direct Transfer
Direct Transfer
RRC
RRC
DCCH :: Downlink
DCCH :: Downlink
Direct TransferRRC
DCCH :: UplinkRRC Direct Transfer
Direct TransferRRC
DCCH :: Uplink Direct TransferRRC
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Appendix: MOC signaling process
UE
Node BServing RNS Serving
RNCCN
RANAPRANAP
RANAPRANAP
Iu Release Command
Iu Release Complete
Q.AAL2Q.AAL2
Q.AAL2Q.AAL2 Release Request
Release Complete
Q.AAL2Q.AAL2
Q.AAL2Q.AAL2 Release Request
Release Complete
DCCH : RRC Connection
DCCH : RRC Connection
Release
ReleaseComplete
NBAPRadio Link Deletion
NBAP
Radio LinkDeletion
NBAP
NBAP
Complete
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Summary
Random access procedure: physical channels, detailed
random access procedure, access parameters optimization.
RRC setup procedure and parameters optimization.
RAB setup procedure and the whole UE outgoing callprocedure.
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