03 channel structure and function 44

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WR_BT03_E1_1

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



Classification of channels

Structure and Function of channels

Physical layer procedure

Content



RNS RNS

CN

RNC RNC

Iu Iu

Iur

Iub Iub Iub Iub

Architecture of UMTS

UE

NodeB NodeB NodeB NodeB



Channel Type

Physical channel Transport channel

Logical channel

Node BRNC

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 betransmitted.

Physical channels:

Represent the “transmission media” providing the

platform through which the information is actually

transferred.



Protocol stack of the Uu interface

L3

c o n t r o l

c o n t r o l

c o n t r o l

c o n t r o l

Logical

Channels

Transport

Channels

C-plane signalling U-plane information

PHY

L2/MAC

L1

RLC

DCtGC

L2/RLC

MAC

RLCRLC

RLCRLC

RLC

RLCRLC

Duplication avoidance

UuS boundary

BMCL2/BMC

control

PDCPPDCP L2/PDCP

DCtGC

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)



Logic

Channel

Transport

Channel

CCCH DCCH DTCH

RACH CPCH DCH

Uplink Downlink

PCCH BCCH DCCH DTCH CCCH CTCH

PCH BCH FACH DSCH DCH

Mapping relationship

Transport

Channel

CCCH DCCH DTCH

RACH CPCH DCH

Uplink Downlink

PCCH BCCH DCCH DTCH CCCH 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



WCDMA frame structure



Physical Channels(1)

The physical channel is in a 3-layer structure by thetime:

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 andDPCCH)

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 channel

PRACH

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*2

k

bits (k=0..3)

Message part radio frame TRACH = 10 ms

Data

ControlTFCI

NTFCI bits



Downlink physical channel

DL physical channel include Dedicated physicalchannel、1 Shared physical channel and five

Common control channels.

DPCH

SCH

CPICH

PICH

AICH

CCPCH

PDSCH

DL common physical

channel



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, cellselection 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 secondaryscrambling 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 thecell. It is may be a phase reference for a dl DPCH, but it isdecided 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 length256 chips. The modulated code need not spreading andscrambling.

The primary synchronization code (PSC) is transmittedonce every slot

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

S-SCH

The Secondary SCH consists of repeatedly transmitting alength 15 sequence of modulated codes of length 256 chips.

the Secondary Synchronization Codes (SSC), transmittedin 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 codebelongs to.



S-CCPCH



PICH

PICH carries PI（

Page Indication），

SF=256，

radio frame=10ms，consists 300bits，288 bits for

paging indication，12 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



Cell Search

UE has to get the system information before itregisters 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




Step2: Frame synchronization and code-groupidentification

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 thefirst 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

8176：PSC

8177：SSC

…

8191：SSC


81608161

8175

8160：主扰码 8161：辅扰码

…

8175：辅扰码


8064

8065

8079

8064：主扰码

8065：辅扰码

…

8079：辅扰码

…


112

113

127

8176：PSC

8177：辅扰码

…

8191：辅扰码


16

17

31

16：PSC

17：SSC

…

31：SSC


0

1

15

0：PSC

1：SSC

…

15：SSC

No.63 Primary Scrambling Code Group

… …

No.0 Primary Scrambling Code Group



Mapping of the Secondary Synchronization Code




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 CPICHwith 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 sothat the cell specific BCH information can be read.



Cell search procedure



Summary of the process

Channel Synchronizationacquired

Note

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 synchronizationcodes. 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.

03 channel structure and function 44

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