Channel Structure and Function

ZTE University

Objectives

At the end of this course, you will be able to

master:

Classification of channels

Structure and Function of channels

Content

Classification of channels

Structure and Function of channels

Physical layer procedure

RNS RNS

CN

RNCRNC

Iu Iu

Iur

Iub IubIub Iub

Architecture of UMTS

UE

NodeBNodeBNodeBNodeB

Channel Type

Physical channel

Transport channel

Logical channelNode B

RNC

Physical channel

Transport channel

Logical channel

UE

Concept of channel

PHY layer

MAC layer

RLC layer

Transport channel

Physical channel

Logical channel

L1

L2

Channel Type

Logical channels:

Describe what is transported (i.e., the information to be

transmitted)

Transport channels:

Describe how the logical channels are to be transmitted.

Physical channels:

Represent the transmission media providing the platform through which the information is actually

transferred.

Protocol stack of the Uu interface

L3

cont

rol

cont

rol

cont

rol

cont

rol

Logical

Channels

Transport

Channels

C-plane signalling U-plane information

PHY

L2/MAC

L1

RLC

DCNtGC

L2/RLC

MAC

RLC

RLCRLC

RLC

RLCRLC

RLC

Duplication avoidance

UuS boundary

BMCL2/BMC

control

PDCPPDCP L2/PDCP

DCNtGC

Radio

Bearers

RRC

Logical Channels

Control Channel (CCH) Broadcast Control Channel (BCCH)

Paging Control Channel (PCCH)

Dedicated Control Channel (DCCH)

Common Control Channel (CCCH)

Traffic Channel (TCH) Dedicated Traffic Channel (DTCH)

Common Traffic Channel (CTCH)

Transport Channel

Random Access Channel (RACH)

Broadcast Channel (BCH)

Paging Channel (PCH)

Forward Access Channel (FACH)

Common Packet Channel (CPCH)

Common Transport Channels

Dedicated Transport Channels

Downlink Shared Channel (DSCH)

Dedicated Channel (DCH)

Physical Channel

Dedicated Physical Channel (DPCH)

Physical Random Access Channel (PRACH)

Physical Common Packet Channel (PCPCH)

Uplink Physical Channels

Secondary Common Control Physical Channel (S-CCPCH)

Common Pilot Channel (CPICH)

Primary Common Control Physical Channel (P-CCPCH)

Synchronization Channel (SCH)

Physical Downlink Shared Channel (PDSCH)

Downlink Physical Channels

Acquisition Indication Channel (AICH)

Page Indication Channel (PICH)

Dedicated Physical Channel (DPCH)

LogicChannel

TransportChannel

CCCHDCCH

DTCH

RACH CPCH DCH

Uplink Downlink

PCCH BCCHDCCH

DTCHCCCH CTCH

PCH BCH FACH DSCH DCH

Mapping relationship

TransportChannel

CCCHDCCH

DTCH

RACH CPCH DCH

Uplink Downlink

PCCH BCCHDCCH

DTCHCCCH CTCH

PCH BCH FACH DSCH DCH

Mapping relationship

Transport Channels

DCH

RACH

CPCH

BCH

FACH

PCH

DSCH

Physical Channels

Dedicated Physical Data Channel (DPDCH)

Dedicated Physical Control Channel (DPCCH)

Physical Random Access Channel (PRACH)

Physical Common Packet Channel (PCPCH)

Common Pilot Channel (CPICH)

Primary Common Control Physical Channel (P-CCPCH)

Secondary Common Control Physical Channel (S-CCPCH)

Synchronization Channel (SCH)

Physical Downlink Shared Channel (PDSCH)

Acquisition Indication Channel (AICH)

Page Indication Channel (PICH)

Content

Classification of channels

Structure and Function of channels

Physical layer procedure

WCDMA frame structure

Physical Channels(1)

The physical channel is in a 3-layer structure by

the time:

Superframe

One superframe lasts 720ms, and consists of 72 radio frames.

radio frame

One radio frame has a period of 10ms, and comprises 15

timeslots with the same length. Corresponding to 38400 chips,

it is a basic unit of the physical layer.

Timeslot

A timeslot is a unit composed of a bit domain, corresponding to

2560 chips. The bit number and structure of a timeslot depends

on the specific type of the physical channel.

Physical Channels(2)

The frame structure of the physical channels is shown:

Tslot #1 Tslot #2 Tslot #I Tslot #15

Ttimeslot= 2560 chip

Frame #0 Frame #1 Frame #I Frame #71

Tframe=10 ms

Tsuperframe=720 ms

Uplink physical channel

2 UL Dedicated physical channel (DPDCH and

DPCCH)

2 UL Common physical channel (PRACH and

PCPCH)

UL Common physical channel

UL Dedicated physical channel

Dedicated physical

Control channel DPCCH

Dedicated physical

data channelDPDCH

Physical random

Access channelPRACH

Physical common

Packet channel

PCPCH

Uplink Dedicated physical channel

PRACH

Physical Random Access Channel

PRACH consists preamble part and message part

Random access transmit 1or more 4096 chips length

preambles and 10ms or 20ms length message part.

Message partPreamble

4096 chips 10 ms (one radio frame)

Preamble Preamble

Message partPreamble

4096 chips 20 ms (two radio frames)

Preamble Preamble

PRACH transmitted structure

PRACH

Physical Random Access Channel

10ms message part is split into 15 timeslots, each timeslot consists

of 2560chips.

Each timeslot includes data part and control part. They are

transmitted in parallel .

Data part :SF=32~256 , control part: SF=256.

PilotNpilot bits

DataNdata bits

Slot #0 Slot #1 Slot #i Slot #14

Tslot = 2560 chips, 10*2k

bits (k=0..3)

Message part radio frame TRACH = 10 ms

Data

ControlTFCI

NTFCI bits

Downlink physical channel

DL physical channel include Dedicated physical channel1 Shared physical channel and five Common control channels.

DPCH

SCH

CPICH

PICH

AICH

CCPCH

PDSCH

DL common physicalchannel

Downlink dedicated physical channel

CPICH

CPICH

There is 2 types of CPICH:P-CPICH and S-PICH

P-CPICH: P-CPICH of different cell uses the same Cch,256,0 OVSF code to

spread ,the bit rate of P-CPICH is also fixed.

The P-CPICH is scrambled by the primary scrambling code.

There is one and only P-CPICH per cell.

The P-CPICH is broadcast over the entire cell. it is used to search cell primary

scrambling code during cell selection procedure. And it is also used for measurement and estimation during handover, cell selection and cell re-selection.

S-CPICH: A arbitrary channelization code of SF=256 is used for the S-CPICH.

A S-CPICH is scrambled by either the primary or a secondary scrambling code.

There may be 0,1 or several S-CPICH per cell.

A S-CPICH may be transmitted over the entire cell or part of the cell. It is may be a phase reference for a dl DPCH, but it is decided by high layer signalling.

P-CCPCH

SCH (1)

The Synchronization Channel (SCH) is a downlink signal

used for cell search.

The SCH consists of two sub channels, the Primary and

Secondary SCH.

The 10 ms radio frames of the Primary and Secondary

SCH are divided into 15 slots, each of length 2560 chips.

Structure of synchronization channel

SCH (2)

P-SCH The Primary SCH consists of a modulated code of length

256 chips. The modulated code need not spreading and scrambling.

The primary synchronization code (PSC) is transmitted once every slot

The PSC is the same for every cell in the system.

S-SCH The Secondary SCH consists of repeatedly transmitting a

length 15 sequence of modulated codes of length 256 chips.

the Secondary Synchronization Codes (SSC), transmitted in parallel with the Primary SCH.

Each SSC is chosen from a set of 16 different codes of length 256.

This sequence on the Secondary SCH indicates which of the code groups the cell's downlink scrambling code belongs to.

S-CCPCH

PICH

PICH carries PIPage IndicationSF=256radio frame=10msconsists 300bits288 bits for paging indication12 bits Tx Off

PICH relates to S-CCPCH which mapping to PCH

b1b0

288 bits for paging indication12 bits (transmission

off)

One radio frame (10 ms)

b287 b288 b299

PICH frame structure

Content

Classification of channels

Structure and Function of channels

Physical layer procedure

Cell Search

UE has to get the system information before it

registers with the network and access to services.

The system information is beared in the BCH

channel, and its data is mapped into the Primary

CCPCH.

So the cell search procedure is mainly to decode

the data of P-CCPCH.

Cell search procedure (1)

The cell search is typically carried out in three

steps:

Step1: Slot synchronization

During the first step of the cell search procedure the UE

uses the SCH channel's primary synchronization code

to acquire slot synchronization to a cell.

This is typically done with a single matched filter (or any

similar device) matched to the primary synchronization

code which is common to all cells. The slot timing of the

cell can be obtained by detecting peaks in the matched

filter output.

Sketch of Slot Synchronization

Cell search procedure (2)

Step2: Frame synchronization and code-group

identification

During the second step of the cell search procedure, the

UE uses the SCH channel's secondary synchronization

code to find frame synchronization and identify the code

group of the cell found in the first step.

This is done by correlating the received signal with all

possible secondary synchronization code sequences,

and identifying the maximum correlation value. Since

the cyclic shifts of the sequences are unique the code

group as well as the frame synchronization is

determined.

Downlink Scrambling Code Grouping

No. 511 Scrambling Code

Group

8176

8177

8191

8176PSC8177SSC8191SSC

No. 510 Scrambling Code Group

8160

8161

8175

816081618175

No. 504 Scrambling Code

Group

8064

8065

8079

806480658079

No. 7 Scrambling Code

Group

112

113

127

8176PSC81778191

No. 1 Scrambling Code

Group

16

17

31

16PSC17SSC31SSC

No. 0 Scrambling Code

Group

0

1

15

0PSC1SSC15SSC

No.63 Primary Scrambling Code Group

No.0 Primary Scrambling Code Group

Mapping of the Secondary Synchronization Code

Cell search procedure (3)

Step3: Scrambling-code identification

During the third and last step of the cell search

procedure, the UE determines the exact primary

scrambling code used by the cell.

The primary scrambling code is typically identified

through symbol-by-symbol correlation over the CPICH

with all codes within the code group identified in the

second step.

After the primary scrambling code has been

identified, the Primary CCPCH can be detected so

that the cell specific BCH information can be read.

Cell search procedure

Summary of the process

ChannelSynchronization

acquiredNote

Primary

SCH

Chip, Slot, Symbol

Synchronization

Synchronization 256 chips

The same in all cells

Secondary

SCH

Frame Synchronization,

Code Group

(one of 64)

15-code sequence of secondary

synchronization codes. There are 16

secondary synchronization codes. There

are 64 S-SCH sequences corresponding to

the 64 scrambling code groups 256 chips,

different for different cells and slot intervals

Common

Pilot CH

Scrambling code (one

of 8)

To find the primary scrambling code from

common pilot CH

PCCPCH Synchronization,

BCCH info

Fixed 30 kbps channel spreading factor 256

RACH procedure

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

It selects randomly one of the available sub-channels and signatures

The downlink power is measured and the initial RACH power level is set with a proper margin due to open loop inaccuracy

UE transmits 1 ms long preamble with the selected signature

Node B replies by repeating the preamble using Acquisition Indication Channel (AICH)

UE decodes AICH message to see whether the NodeB has detected the preamble

If AICH is not detected, the preamble is resend with 1 dB higher transmit power

If AICH is detected, a 10 or 20 ms long message part is transmitted with the same power as the last preamble

RACH procedure

Exercise

pls write down the 3 types of channel and describe

their mapping relations.

One radio frame has a period of ( )ms, and

comprises( ) timeslots with the same length.

Corresponding to ( ) chips, it is a basic unit of

the physical layer.

pls describe the main function of each physical

channel.

pls describe the cell search procedure.

pls describe RACH procedure.