channel structure and function

Channel Structure and Function

ZTE University

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Objectives

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

Ø Classification of channels

Ø Structure and Function of channels



Classification of channels

Structure and Function of channels

Physical layer procedure

Content



RNS RNS

CN

RNCRNC

Iu Iu

Iur

Iub IubIub Iub

Architecture of UMTS


UE

NodeBNodeBNodeBNodeB



Channel Type

n Physical channel

n Transport channel

n Logical channel

Node 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

n Logical channels:

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

transmitted)

n Transport channels:

Ñ Describe how the logical channels are to be transmitted.

n Physical channels:

Ñ Represent the “transmission media” providing the platform

through which the information is actually transferred.




Protocol stack of the Uu interface

L 3

cont

rol

cont

rol

cont

rol

cont

rol

L o g ic a lC h a n n e ls

T ra n s p o r tC h a n n e ls

C -p la n e s ig n a ll in g U -p la n e in fo rm a t io n

P H Y

L 2 /M A C

L 1

R L C

D CN tG C

L 2 /R L C

M A C

R L CR L C

R L CR L C

R L CR L C

R L C

D u p li c a tio n a v o id a n c e

U u S b o u n d a ry

B M C L 2 /B M C

c o n tro l

P D C PP D C P L 2 /P D C P

D CN tG C

R a d ioB e a re r s

R R C




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

CCCHDCCHDTCH

RACH CPCH DCH

Uplink Downlink

PCCH BCCH DCCHDTCHCCCH CTCH

PCH BCH FACH DSCH DCH

Mapping relationship


TransportChannel

CCCHDCCHDTCH

RACH CPCH DCH

Uplink Downlink

PCCH BCCH DCCHDTCHCCCH 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)

n The physical channel is in a 3-layer structure by the time:

Ñ Superframe

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

Ñ radio frame

ü 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.

Ñ Timeslot

ü 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)

n 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

n 2 UL Dedicated physical channel (DPDCH and DPCCH)

n 2 UL Common physical channel (PRACH and PCPCH)


UL Common physical channel

UL Dedicated physical channel

Dedicated physical Control channel DPCCH

Dedicated physicaldata channel

DPDCH

Physical randomAccess channel

PRACH

Physical common Packet channel

PCPCH




Uplink Dedicated physical channel



PRACH

n Physical Random Access Channel

Ñ PRACH consists preamble part and message part

Ñ 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




n Physical Random Access Channel Ñ 10ms message part is split into 15 timeslots, each timeslot consists of

2560chips.

Ñ Each timeslot includes data part and control part. They are transmitted in parallel .

Ñ 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

Control TFCINTFCI bits


PRACH



Downlink physical channel

n DL physical channel include Dedicated physical channel、1 Shared

physical channel and five Common control channels.


DPCH

SCH

CPICH

PICH

AICH

CCPCH

PDSCH

DL common physicalchannel




Downlink dedicated physical channel




CPICH



CPICH

n There is 2 types of CPICH:P-CPICH and S-PICHn P-CPICH:

Ñ P-CPICH of different cell uses the same Cch,256,0 OVSF code to spread ,the bit rate of P-CPICH is also fixed.

Ñ The P-CPICH is scrambled by the primary scrambling code.Ñ There is one and only P-CPICH per cell.Ñ 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.

n S-CPICH:Ñ A arbitrary channelization code of SF=256 is used for the S-CPICH.Ñ A S-CPICH is scrambled by either the primary or a secondary scrambling code.Ñ There may be 0,1 or several S-CPICH per cell.Ñ 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)

n The Synchronization Channel (SCH) is a downlink signal used for cell search.

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

n 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)

n P-SCHÑ The Primary SCH consists of a modulated code of length 256

chips. The modulated code need not spreading and scrambling.Ñ The primary synchronization code (PSC) is transmitted once every

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

n S-SCHÑ The Secondary SCH consists of repeatedly transmitting a length

15 sequence of modulated codes of length 256 chips.Ñ the Secondary Synchronization Codes (SSC), transmitted in

parallel with the Primary SCH. Ñ Each SSC is chosen from a set of 16 different codes of length 256. Ñ This sequence on the Secondary SCH indicates which of the code

groups the cell's downlink scrambling code belongs to.





S-CCPCH



PICH

n PICH carries PI（Page Indication），SF=256，radio frame=10ms，

consists 300bits，288 bits for paging indication，12 bits Tx Off。

n 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

n UE has to get the system information before it registers with

the network and access to services.

n The system information is beared in the BCH channel, and

its data is mapped into the Primary CCPCH.

n So the cell search procedure is mainly to decode the data of

P-CCPCH.




Cell search procedure (1)

n The cell search is typically carried out in three steps:

n Step1: Slot synchronization

Ñ 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.

Ñ 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





n Step2: Frame synchronization and code-group identification

Ñ 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.

Ñ 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

8176：PSC

8177：SSC

…

8191：SSC

8176

8177

8191

No. 511 Scrambling Code Group

8160：主扰码

8161：辅扰码

…

8175：辅扰码

8160

8161

8175


8064：主扰码

8065：辅扰码

…

8079：辅扰码

8064

8065

8079

No. 504 Scrambling Code Group…

8176：PSC

8177：辅扰码

…

8191：辅扰码

112

113

127


16：PSC

17：SSC

…

31：SSC

16

17

31


0：PSC

1：SSC

…

15：SSC

0

1

15


No.63 Primary Scrambling Code Group… …

No.0 Primary Scrambling Code Group



Mapping of the Secondary Synchronization Code





n Step3: Scrambling-code identification

Ñ During the third and last step of the cell search procedure, the UE

determines the exact primary scrambling code used by the cell.

Ñ 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.

n 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

To find the primary scrambling code from common

pilot CH

Scrambling code (one of 8) Common

Pilot CH

Fixed 30 kbps channel spreading factor 256 Synchronization,

BCCH info

PCCPCH

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

Frame Synchronization,

Code Group

(one of 64)

Secondary

SCH

Synchronization 256 chips

The same in all cells

Chip, Slot, Symbol

Synchronization

Primary SCH

NoteSynchronization

acquiredChannel




RACH procedure

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

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

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

n UE transmits 1 ms long preamble with the selected signature

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

n UE decodes AICH message to see whether the NodeB has detected the preambleÑ If AICH is not detected, the preamble is resend with 1 dB higher transmit power

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




RACH procedure




channel structure and function

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