10-wcdma access procedure analysis.ppt

8/10/2019 10-WCDMA Access Procedure Analysis.ppt

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Huawei Confidential. All Rights Reserved

WCDMA Access Procedure Analysis

ISSUE 1.0


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Internal Use1

Access process is one of the most

important processes in WCDMA network.

It is also one the WCDMA KPI.

Understanding the access process is very

crucial for UMTS optimization

Access process steps, signaling and

performance are introduced in this slide,

which is very help for the UMTS

optimization engineers


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Object

Upon completion this course, you will be able to:

The main access procedures

The messages of access procedure

The performance indices of access

procedure


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References

3GPP 25.211 Physical channels

and mapping of transport

channels onto physical channels

(FDD)

3GPP 25.213 Spreading andmodulation (FDD)

3GPP 25.214 Physical layer

procedures (FDD)

3GPP 25.331 Radio Resource

Control Protocol Specification


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Chapter 1 The access procedure in UMTS

Chapter 2 Access procedure messages

Chapter 3 Access procedure performance analysis


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1.The defini tion about access

procedure

2.Cell search

3.Cell selection and reselection

4.Random access procedure

Chapter 1 The access procedures in UMTS


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The access procedure definition

Two operating state of UE

Idle mode

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

the non-access identification, such as IMSI, TMSI or P-TMSI

etc

Connection mode

UE will shift to connection mode which could be CELL_FACH

state or CELL_DCH state from the idle mode

After released RRC connection, UE will shift to the idle mode

from the connection mode


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The access procedure definition

Definition about access procedure From access stratum, access procedure is the process which UE

shift to connection mode from idle mode. It includes the followingfour basic processes: cell search, receiving system information,

cell selection and cell reselection, random access procedure

UE can do the registration, service application, authentication

and non-access stratum activities


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1.The definition about access

procedure

2.Cell search





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Cell search process

No UTRA carriers information for UE

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

frequencies in UTRA. In each carrier, UE just need to find acell with the most strengthen signal

UTRA carriers information for UE

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

need to scan the all frequencies about UTRA 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 slotsynchronization to a cell

UE uses SSC to find frame

synchronization and identifythe code group of the cell

found in the first step

UE determines the primary scramblingcode 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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procedure

2.Cell search





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Cell selection and reselection

After finding a cell, UE will judge whether the cell PLMN is a right

one. If it is right, the UE will measure the signal of the cell and

use S criteria to judge whether the cell is suitable to stay. Thisprocess is cell selection If the cell does not satisfied with the S criteria, UE will start the cell

selection and PLMN selection again.

The following conditions will triggerUE does cell selection: Turn on UE

Back to idle mode from connection mode

Lost cell information in connection mode

According to cell list for measurement control information, UE can

not find a suitable cell to camp


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Cell selection

PLMN selection UE can get the system information from PCCPCH

The scheduling information of MIB is already known, which are

SIB_POS=0 and SIB_REP =8. UE can get MIB at the radio frame of

SFN=0,8,16, ...

In system information, the PLMN information is transmitted in MIB

After getting the MIB, UE can judge whether the current PLMN is a

right one. If it is, UE will find the SIB scheduling information from the

MIB; if it is not, UE will search another frequency cell, do the cell

selection from scratch again (beginning)


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Cell selection

Squal = Qqualmeas Qqualmin

Srxlev = Qrxlevmeas- Qrxlevmin - Pcompensation

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

includes Qqualmin, Qrxlevmin/Maximum, allowed UL TX powerUE_TXPWR_MAX_RACH

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

If the cell is satisfied with S criteria, UE will stay in the cell and get

other system information. Then, UE will initiate a location update

registration process

If the cell is not satisfied with S criteria, UE will get Intra-

frequency/Inter-frequency adjacent cells information from SIB11.

Then, UE will judge whether these cells are satisfied with S criteria.

If the adjacent cell is suitable, UE will stay in the adjacent cell.

If no cell is satisfied with S criteria, UE will take the area as dead

zone and continue the PLMN selection and reselection process


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Cell selection

S criteria parameters explanation

Parameters Explanation

Squal Cell Selection quality value (dB)

Srxlev Cell Selection RX level value (dBm)

Qqualmeas Measured cell quality value. The quality of the received signal

expressed in CPICH Ec/N0 (dB) for current cellQrxlevmeas 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_MAX

_RACHMaximum 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 choose the best cell to get service. This

process is cell reselection

Trigger conditions Event trigger in idle mode

In idle mode, if the cell can not satisfied with the S criteria during N

DRXs in a row, the cell reselection When UE detected in non-service area


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Cell reselection

Intra-frequency measurement

The current cell RSCP < Qrxlevmin +2*Sintrasearch

If the above inequation is not satisfied, UE will not initiate intra-

frequency measurement If the above inequation is satisfied, UE will initiate intra-frequency

measurement

If the Sintrasearch is not given in system information, UE always

measure the intra-frequency cells

Default value Sintrasearch=5

measurement tr igger condition


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Cell reselection

Inter-frequency measurementThe current cell RSCP < Qrxlevmin +2*Sintersearch

If the above inequation is not satisfied, UE will not initiate inter-

frequency measurement If the above inequation is satisfied, UE will initiate inter-frequency

measurement If the Sintersearch is not given in system information, UE always

measure the intra-frequency cells

Default value Sintersearch=4



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Cell reselection

Inter-RAT measurementThe current cell RSCP < Qrxlevmin +2*Ssearchrat

If the above inequation is not satisfied, UE will not initiate the

measurement for Msystem If the above inequation is satisfied, UE will initiate the measurement for

Msystem If the Ssearchrat is not given in system information, UE always measure

cells of Msystem

Default value Sintersearch=2


C


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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_PRIOs

Ln= 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 cri ter ia

C ll l ti


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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,s The quality value of adjacent cells

Qoffset s,n The load level offset for cell reselection

Parameters explanation

Remark: do not consider Ton for non-HCS


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procedure

2.Cell search





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Random access procedure

Definition Random access procedure is a process which is initiated by UE in order

to getting service from CN. Meanwhile, the access channels areallocated to the UE by system.

This process may happened in the following process:

Attach and detach

LA update and RA update

Signaling connection for services As for a uplink common transport channel, RACH can only carry low

rate data services, for example, the beginning access process or non-

real timing services

The transmission method on RACH is base on the ALOHA principle

PRACH is responsible for carrying RACH, which is a physical channelmapped to RACH

The AI is carried on AICH, which is used for confirming the random

access procedure

Random access proced re


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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

Random access channel

the transmission method on RACH is based on the ALOHA

principle UE can transmit the preamble at the access time slot

Each 20ms access frame is composed by two 10ms radio frames,

which is divided into 15 access time slot, and 5120 chips for each slot

The PRACH access slots and AICH access slots are showed in the

following figure


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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 7

1 12 13 14 8 9 1 11

21 2 3 4 5 6 7

3 9 1 11 12 13 14 8

4 6 7 1 2 3 4 5

5 8 9 1 11 12 13 14

6 3 4 5 6 7 1 2

7 8 9 1 11 12 13 14

R d d


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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

The message part of PRACH is divided into 15 slot, and each slot

contains 2560 chips and includes two parts

Data part, which mapped to RACH Control part, which transmit the control information of L1

Data part and control part are transmitted by multiplexed used

One 10ms message part is composed by one radio frame, and one

20ms message part is composed by two continuous radio frames.

R d d


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Nodetect

Nodetect

Nodetect ACK

message

p-p

p-m

p-p p-m

The following figure shows the RACH procedure

UE transmits the preamble on PRACH

If UTRAN received the preamble message, an AI message will betransmitted on the downlink channel as a response

If the AI is received, UE will transmit message part

If UE does not receive the AI in p-a period, the next preamble

will be transmitted after p-p period

Repeated this process like above mentioned till receiving AI


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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

The downlink AICH is taken as downlink access, and each time slot of

it contains 5120 chips

The beginning time of downlink access slot is the same as PCCPCH Uplink PRACH is divided into time slots, and each of them contains

5120 chips

The following figure shows the timing relationship between PRACH

and AICH



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The parameters about the procedure

The interval between two preambles should be longer than the

minimum value, p-p p-p,min

Parameters are defined as following

AICH_Transmission_Timing=0

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

p-a = 7680 chipsp-m = 15360 chips (3 access slots)

AICH_Transmission_Timing=1

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 given by the

command from upper layer



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The terminal decodes the BCH to find out the available RACH sub-channels and their scrambling codes and signatures

the terminal selects randomly one of the RACH sub-channels from

the group its access class allow it to use. Furthermore, the signature

is also selected randomly from among the available signatures

The downlink power level is measured and the initial RACH power

level is set with the proper margin due to the open loop inaccuracy

A RACH preamble is sent with the selected signature

The specif ic process



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A RACH preamble is sent with the selected signature

The terminal decodes AICH to see whether the base station has

detected the preamble

In case no AICH is detected, the terminal increased the preambletransmission power by a step given by the base station, as multiples

of 1dB. The preamble is retransmitted in the next available access

slot

When an AICH transmission is detected from the base station, theterminal transmits the 10ms or 10ms message part of the RACH

transmission

The specif ic process


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1. System information broadcast

2. RRC connection messages


System information broadcast


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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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System information broadcast procedure

UE, which is in the state of IDLE, CELL_PCH, URA_PCH orCELL_FACH, can get system information from BCCH

If UE gets the paging type 1 information, it will read information again

UE will not read system information in CELL_DCH. But, network canmake the UE read the updated system information under a indicator

According to protocol, system information can be broadcasted in BCCH.

And the BCCH can map to BCH or FACH, so the size of system

information should accord with the transport block size of these two

channels



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System information update The purpose for update is to make NodeB utilize system information and

the scheduling information correctly

Utilize value tags to identify the modified SIB

If a SIB contains a valuetag, UE can identified whether the SIB is

modified by it and decides to read it

Not utilize the value tag to identify the modified SIB

If UE does not get the value tags from SIBit will initiate a timer of

value SIB_REP

When the timer is expired, UE will read the SIB again


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1. System information broadcast

2. RRC connection messages


RRC connection message


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UE UTRAN

RRC CONNECTION REQUEST

RRC CONNECTION SETUP

RRC CONNECTION SETUP COMPLETE

UE has to establish the RRC connection before getting network services,

then do the signaling exchange with CN through access stratum

Since UTRAN can decide the initial connection state (CELL_FACH orCELL_DCH), the different transport channel mapped to DCCH decide the

RRC connection establishment flows.

RRC connection messages

RRC_CONNECTION_REQUEST RRC_CONNECTION_SETUP

RRC_CONNECTION_SETUP_COMPLETE



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RRC_CONNECTION_REQUEST:

UE information elements

Initial UE identityTMSI, PTMSI, IMSI, or IMEI. UE will choose onefrom the priority of these identifications

Establishment causethe causes for RRC connection establishment,

such as Originating Conversational Call, Terminating Streaming Call,

Inter-RAT cell re-selection, Registration, etc.

Measurement information elements

Measured results on RACH report the intra-frequency cell

measurement results of intra-frequency cells which are appointed by

the SIB 11, including the PSC and Ec/Io of CPICH



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RRC CONNECTION SETUP:

UE Information Elements

After receiving the message, UE will compare the indicator to its own.

The message will be discard if they are not identical. UE will read the

connection mode in RRC StateIndication which is transmitted by

UTRAN

RB Information Elements, which includes 4 SRBSRB1: RLC UM for non-direct transfer message

SRB2: RLC AM for non-direct transfer message

SRB3:RLC UM for direct transfer message

SRB4:RLC AM for direct transfer message


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RRC CONNECTION SETUP COMPLETE

UE Information Elementsfor authentication and integrity

Other information elements including the ability of UERF

ability, the access ability for inter-system, the algorithms for

authentication and integrity, measurement capability (support the

compress mode on downlink and uplink)



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When the RRC connection is established on common transportchannel, system does not need to setup RL for the UE. But the

service will be established on the dedicate channels, so RRC will be

reconfigured on dedicate channel. And the system still needs to setup

a RL for the UE.

When the RRC connection is established on dedicate transport

channel, system need to setup RL for the UE. And the service will be

also established on the dedicate channels. But it needs a larger

bandwidth. So the RL should be reconfigured.

For both of the conditions, the RRC connection messages are same.

Comments


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1. Performance indices

2. The influenced factors for

performance


Access procedure performance indices


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Access procedure performance indices

CN: Access success rate:

The possibility which UE establish the connection correctly byinitiating calls or receiving calls

Access time delay

The time from accessing to service establishment

RAN

RRC establishment success rate, the time for cell search and

selection, the time for random access procedure

RRC Setup Success Rate = The number of RRC establishment for a serviceThe number of RRC request for a service


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1. Performance indices

2. The inf luence factors for

performance


The influence factors for performance


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Incorrect Setting of Tcell Affecting Cell Searching Speed

Unreasonable Neighboring cell List Affecting Cell Selection

Traffic Distribution in Cell Effect on Acquisition Probability

Different Clutters Affecting Open Loop Power Control



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Incorrect Tcell setting influenced the Cell Search Speed

Tcell is used to define the relative delay between the starting

transmission time of SCH, CPICH and BFN

Purpose Prevent different cells of same NodeB transmit the SCH at the

same time

If not, the second step of cell search will be influenced

Value range The unit of Tcell is 256 chip, and the value can be : 09

Tcell



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In RRC CONNECTION REQUEST message, UE has to report themeasure report about current cell and neighbor cells

If the neighbor cells are too much, UE needs longer time to do the

measurement. Then, the user access time will be longer

One of the most important optimization task is neighbor list

optimization. Under the some conditions, the numbers should be

minimized.

Neighbor l ist



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Complicated radio environment can cause the slow fading,which will influence the access procedure

Experimental conclusion Under 20km/h, UE can compensate the performance decline by

power control

Above 60km/h, UE can compensate the fading by interleaving Between 20km/h and 60km/h, the above mentioned methods can

not work out, which will need higher requirement of demodulation

threshold. That will make the access performance worse

This problems can be solved by the network planning

Radio environment



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The path loss can be different on the different clutter, which willinfluence the preamble transmission power calculation in the

open loop power control process

By the formula, the compensation for the difference path loss of

uplink and downlink is Constant Value.Preamble_Initial_Power = Primary CPICH TX power

CPICH_RSCP + UL interference + Constant Value

In real radio environment, the signal strengthen on the NodeB

side will be different from the different distance between UE and

BS or different clutter, even though the open loop power is

estimated correctly

Clutter dif ference

10-wcdma access procedure analysis.ppt

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