Channel Structure And Function: Zte University Td&w&pcs Bss Course Team

Channel Structure and Function

ZTE University TD&W&PCS BSS Course Team

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

Classification of channels

Channel Type UE 

Physical channel



Transport channel



Logical channel

Node B

Logical channel Transport channel Physical channel

RNC

Classification of channels

Concept of channel

RLC layer Logical channel

L2 MAC layer

Transport channel PHY layer Physical channel

L1

Classification of channels

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

Classification of channels

Protocol stack of the Uu interface GC

Nt

DC

Duplication avoidance GC

Nt

DC UuS boundary U-plane information

C-plane signalling

L3

control

control

control

control

control

RRC

Radio Bearers PDCP

PDCP

L2/PDCP BMC

RLC

RLC

RLC

RLC RLC

RLC

RLC

RLC

L2/BMC

L2/RLC

Logical Channels MAC

L2/MAC Transport Channels

PHY

L1

Classification of channels

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)

Classification of channels

Transport Channel Common Transport Channels

Broadcast Channel (BCH) Paging Channel (PCH) Random Access Channel (RACH) Forward Access Channel (FACH) Common Packet Channel (CPCH) Downlink Shared Channel (DSCH)

Dedicated Transport Channels

Dedicated Channel (DCH)

Classification of channels

Physical Channel Uplink Physical Channels

Physical Random Access Channel (PRACH) Physical Common Packet Channel (PCPCH) Dedicated Physical Channel (DPCH)

Downlink Physical Channels

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) Dedicated Physical Channel (DPCH)

Classification of channels

Mapping relationship Uplink Logic Channel

Transport Channel

CCCH

DCCH DTCH

RACH CPCH DCH

Downlink PCCH BCCH CCCH CTCH

PCH

BCH

FACH

DSCH

DCCH DTCH

DCH

Classification of channels

Mapping relationship Transport Channels DCH

Physical Channels Dedicated Physical Data Channel (DPDCH) Dedicated Physical Control Channel (DPCCH)

RACH

Physical Random Access Channel (PRACH)

CPCH

Physical Common Packet Channel (PCPCH) Common Pilot Channel (CPICH)

BCH

Primary Common Control Physical Channel (P-CCPCH)

FACH

Secondary Common Control Physical Channel (S-CCPCH)

PCH Synchronization Channel (SCH) DSCH

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

Structure and Function of channels

WCDMA frame structure

Structure and Function of channels

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.

Structure and Function of channels

Physical Channels(2) 

The frame structure of the physical channels is shown:

Ttimeslot= 2560 chip

Ts lot # 1Ts lot # 2

Tsl ot #I

Tslo t #1 5

Tframe=10 ms

Fr ame # 0 Fra me #1

Fr ame # I

Tsuperframe=720 ms

Fr ame #7 1

Structure and Function of channels

Uplink physical channel 

2 UL Dedicated physical channel （ DPDCH and DPCCH ）



2 UL Common physical channel （ PRACH and PCPCH ）

Dedicated physical Control channel DPCCH Dedicated physical DPDCH data channel Physical random PRACH Access channel Physical common Packet channel

PCPCH

UL Dedicated physical channel

UL Common physical channel

Structure and Function of channels

Uplink Dedicated physical channel

Structure and Function of channels

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.

Preamble

Preamble

Preamble

4096 chips Preamble

Message part

10 ms (one radio frame) Preamble

Preamble

4096 chips

Message part

20 ms (two radio frames)

PRACH transmitted structure

Structure and Function of channels

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. Data Ndata bits

Data Pilot Npilot bits

Control

TFCI NTFCI bits

Tslot = 2560 chips, 10*2k bits (k=0..3)

Slot #0

Slot #1

Slot #i Message part radio frameRACH T = 10 ms

Slot #14

Structure and Function of channels

Downlink physical channel 

DL physical channel include Dedicated physical channel 、 1 Shared physical channel and five Common control channels. SCH CPICH PICH DL common physical channel

AICH CCPCH PDSCH

DPCH

Structure and Function of channels

Downlink dedicated physical channel

Structure and Function of channels

CPICH

Structure and Function of channels

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.

Structure and Function of channels

P-CCPCH

Structure and Function of channels

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

Structure and Function of channels

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.

Structure and Function of channels

S-CCPCH

Structure and Function of channels

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 。

288 bits for paging indication b0 b1

12 bits (transmission off) b287 b288

One radio frame (10 ms)

PICH frame structure

b299

Content

Classification of channels Structure and Function of channels Physical layer procedure

Physical layer procedure

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.

Physical layer procedure

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'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.

Physical layer procedure

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 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.

Physical layer procedure

Cell search procedure

Physical layer procedure

Summary of the process

Channel Primary SCH

Synchronization

Note

acquired Chip, Slot, Symbol

Synchronization 256 chips

Synchronization

The same in all cells 15-code sequence of secondary synchronization

Secondary SCH

Frame Synchronization, Code Group (one of 64)

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

Scrambling code (one of 8)

Pilot CH PCCPCH

To find the primary scrambling code from common pilot CH

Synchronization, BCCH info

Fixed 30 kbps channel spreading factor 256

Exercise 

pls write down the 3 type of channel. and describe their category.



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.