09 WCDMA RNO Access Procedure Analysis

WCDMA Access Procedure

ReviewReview

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.

ObjectivesObjectives

� Know the detailed access

procedure in UMTS

� Know how to optimize the

access procedure

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

Course ContentsCourse Contents

Random access procedure

RRC setup procedure

RAB setup procedure

Random access procedure Random access procedure

�� Physical channel about accessPhysical channel about access

� Random access procedure

� Parameters optimization

PRACH access slotPRACH 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




UE can start the random-access transmission at the beginning of a access slot

There are 15 access slots per two frames

what access slots are available is given by higher layers

Structure of the random-access transmissionStructure of the random-access transmission

� Each random-access transmission consists of one or several

preambles of length 4096 chips and a message of 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.

M essa g e p a r tP rea m ble

4 0 9 6 ch ip s1 0 m s (on e ra d io fr a m e)

P rea m ble P rea m ble

M essa g e p a r tP rea m ble

4 0 9 6 ch ip s 2 0 m s (tw o ra d io fr a m es)

P rea m ble P rea m ble


The preamble-to-preamble distance τp-p shall be larger than or

equal to the minimum preamble-to-preamble distance

τp-p,min .

One access slot

τp-a

τp-mτp-p

Pre-amble

Pre-amble Message part

Acq.Ind.

AICH accessslots RX at UE

PRACH accessslots TX at UE


when AICH_Transmission_Timing is set to 0

τp-p,min = 15360 chips (3 access slots)

τp-a = 7680 chips

τp-m = 15360 chips (3 access slots)

when AICH_Transmission_Timing is set to 1, then

τp-p,min = 20480 chips (4 access slots)

τp-a = 12800 chips

τp-m = 20480 chips (4 access slots)

The parameter AICH_Transmission_Timing is

signalled by higher layers.





Concepts in random access procedureConcepts in random access procedure

� Preamble Signature

� AC (Access Class)

� ASC (Access Service Class)

� RACH sub channels

� Access slot set

Preamble SignaturePreamble Signature

Value of n Preamble

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.

Access ClassAccess 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 IMSI

can 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.

Access Service ClassAccess 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<= i <=7, and the maximum

number of ASCs is 8. "0" indicates the highest priority and "7" indicates the

lowest priority.

� AC to ASC mapping. In case the UE is member of several ACs it shall

select the ASC for the highest AC number.

AC 0 – 9 10 11 12 13 14 15

ASC 1st IE 2nd IE 3rd IE 4th IE 5th IE 6th IE 7th IE

Access Slot SetAccess Slot Set

Access slot set 1 contains PRACH slots 0 – 7 and starts τp-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 (τp-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#4τp-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

RACH sub channelsRACH sub channels

1413121110987

210765436

1413121110985

543210764

8141312111093

765432102

1110981413121

765432100

11109876543210

Sub-channel numberSFN modulo 8 of corresponding P-

CCPCH frame

A RACH sub-channel defines a sub-set of the total set of uplink access

slots. There are a total of 12 RACH sub-channels.

Random access procedureRandom 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.


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 .

Random access stepsRandom access steps

1. Derive the available uplink access slots in the next full

access 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.

Random access stepsRandom 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 “Nack on 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 “No ack on AICH” .





ConstantValueConstantValue

� 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 set

too 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.

PRACH Power Ramp Step 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 of

wasting 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.

Maximum Preamble Retransmit Times 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 access

process will be lengthened, but some power will be saved. It is

a value to be weighed.

Maximum Preamble Cycle TimesMaximum 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.



RRC setup procedure

RAB setup procedure

RRC Setup ProcedureRRC Setup Procedure

Parameters optimizationParameters 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

T300 and N300T300 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 be

that a UE repeats the access attempt and the connection setup request

transmission, and consequently other users will be influenced seriously.

PCPreamblePCPreamble

� 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 data

delay. 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.

NInSyncIndNInSyncInd

� 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 of

the 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.

NOutSyncIndNOutSyncInd

� 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 maintenance

process, this parameter is adopted together with the successive

synchronization indication counter.

TRLFailureTRLFailure

� This value defines the timer TRlFailure duration. 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.

N312 and T312N312 and T312

� When the UE starts to set up the dedicated channel, it starts the T312 timer,

and after the UE detects N312 synchronization 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.

N313, N315, T313N313, 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.



RRC setup procedure

RAB setup procedure

RAB Setup ProcedureRAB Setup Procedure

Appendix: MOC signaling processAppendix: MOC signaling process

D o w nlink S y nch ro nisa t io n

U E N o d e BS e rving R N S

S e rvingR N C

D C H -FPD C H -FP

R R CR R C C C C H : R R C C o nne c t io n R e q ues t

N B A P R a d io L ink S e tup R esp o nse

N B A P

N B A P R a d io L ink S e tup R e q ue st

C C C H : R R C C o nne c t io n S e tup

S ta rt R X

S ta rt T X

R R C

R L C

R R CD C C H : R R C C o nne c t io n S e tup C o m p le te

D C H -FPD C H -FPU p link S y nch ro nisa t io n

N B A P

Q .A A L 2Q .A A L 2

Q .A A L 2 E sta blish R e q ue st

E sta blish C o nf irm

Inita l D irec t T ra nsfe r

C N

D C C H :R R C

R L C

R R C

R R C

R R C

Q .A A L 2

D C C H : R R C C o nnec t io n S e tup C o m p le te a c k

In ita l D irec t T ra nsfe r


Inital Direct Transfer

RRC

RANAPRANAP

UE Node BServing RNS

ServingRNC CN

Initial UE Message

RANAPRANAP

DCCH

Direct Transfer

RANAPRANAP Direct Transfer

:

Direct Transfer DCCH ::

Direct Transfer DCCH ::

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


(Call Proceeding)

Inital Direct Transfer


UE Node BServing RNS

ServingRNC CN

DCCH :

DCCH :Downlink

Uplink

Direct Transfer

Direct Transfer

RRCRRC

RRC

RRC

RRC

RAB Assignment RequestRANAPRANAP

Establishment( )

Q.AAL2Q.AAL2

Q.AAL2 Establish Request

Establish Confirm

Q.AAL2

NBAPPrepare

NBAPRadio Link Reconfiguration

NBAPRadio Link ReconfigurationNBAPReady


UENode B

Serving RNS ServingRNC

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 RANAPEstablishment( )

Commit

DCCH : Radio Bearer Setup Complete ackRLCRLC


UENode B


CN

RRC


RRC


(Alerting)

(Connect)

RRC

RRC


(Connect Acknowledge)

RRC


(Rlease Complete)


(Release)

RANAPRANAP Direct Transfer (Disconnect)

RRC

DCCH ::

DCCH ::

Downlink

Uplink

Direct Transfer

Direct Transfer

RRC

RRC

DCCH :: Downlink

DCCH :: Downlink

Direct Transfer RRC

DCCH :: UplinkRRC Direct Transfer

Direct Transfer RRC

DCCH :: Uplink Direct Transfer RRC


UENode B


CN

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

NBAP Radio Link Deletion

NBAP Radio Link Deletion

NBAP

NBAPComplete

SummarySummary

� 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 call

procedure.

09 WCDMA RNO Access Procedure Analysis

Documents

random access procedure

access procedure

parameters optimization

access class 11 15

access class 10

access class 0 9

3 access slots

4 access slots