channel structure and function.ppt

8/14/2019 Channel Structure and Function.ppt

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Channel Structure and Function

ZTE University

TD&W&PCS BSS Course Team


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Objectives

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

Classification of channels

Structure and Function of channels


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Physical layer procedure

Content


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Channel Type

Physical channel

Transport channel

Logical channel

Node BRNC

Physical channel

Transport channel

Logical channel

UE



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Concept of channel

PHY layer

MAC layer

RLC layer

Transport channel

Physical channel

Logical channel

L1

L2



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Channel Type

Logical channels:

Describe what is transported (i.e., the types of

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



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Protocol stack of the Uu interface

L3

control

control

control

control

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



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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)



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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 ChannelsDownlink Shared Channel (DSCH)Dedicated Channel (DCH)



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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)



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Mapping relationship

Transport ChannelsDCH

RACHCPCHBCHFACHPCH

DSCH

Physical ChannelsDedicated 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)



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Content


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WCDMA frame structure



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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.


S f


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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



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Uplink physical channel

2 UL Dedicated physical channelDPDCH and DPCCH

2 UL Common physical channelPRACH and PCPCH


UL Common physical

channel

UL Dedicated physical

channel

Dedicated physical

Control channel DPCCH

Dedicated physical

data channelDPDCH

Physical randomAccess channel

PRACH

Physical common

Packet channel

PCPCH

St t d F ti f h l


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Uplink Dedicated physical channel

St t d F ti f h l


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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


St t d F ti f h l


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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


PRACH

St t d F ti f h l


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Downlink physical channel

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


DPCH

SCH

CPICH

PICH

AICH

CCPCH

PDSCH

DL common physical

channel



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Downlink dedicated physical channel



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CPICH



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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.




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P-CCPCH



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SCH (1)

The Synchronization Channel (SCH) is a downlink signal used for cellsearch.

The SCH consists of two sub channels, the Primary and SecondarySCH.

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




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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.




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S-CCPCH



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PICH

PICH carries PIPage IndicationSF=256radio frame=10ms

consists 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



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Content



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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'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.




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Step2: Frame synchronization and code-group identification

During the second step of the cell search procedure, the UE uses the

SCH'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.




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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 found

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 and the system- and cell

specific BCH information can be read.

ys ca aye p ocedu e



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Cell search procedure

y y p



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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

y y p


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Exercise

pls write down the 3 type of channel. and describe theircategory.

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.


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channel structure and function.ppt

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