wcdma channel concept.ppt

8/10/2019 wcdma channel concept.ppt

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WCDMA CHANNELS

By

Manish Srivastava


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WCDMA OSI MODEL

Physical channels

(Code,frequency,etc)

Logical channels

(What is transmitted)

Transport channels

(How it is transmitted)

Radio Resource Control (RRC)

Physical Layer

Medium Access Control (MAC)

RLC RLC RLC


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OSI reference model

WCDMA protocol stack is based on OSI (open system

interconnection) reference model

OSI reference model ,developed by ISO, is a set of seven layers.

Each of this layer performs certain tasks on the data to make it travel

from one device to another over a network. These tasks at each

layer, prepare it for the next layer.

Layer : Application- This is the layer that actually interacts with

the user. For example if the user chooses to transfer files or read

messages , application layer interfaces with the operating system.

Layer 6: Presentation- Layer 6 takes the data provided by the

Application layer and converts it into a standard format that the

other layers can understand.

Layer 5: Session- Layer 5 establishes, maintains and ends

communication with the receiving device.
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Layer 4: Transport- This layer maintains flow controlof data ,means that if data is coming from more than one application ,

transport layer integrates it into a single stream for the physical

network. It also provides error checking and recovery of data

between the devices.

Layer 3: NetworkThis layer determines the way that the data will

be sent to the recipient. Logicalprotocols, routingand addressingare

handled here.

Layer 2: Data link-This layer transforms the physical layer from a

raw transmission facility to a reliable link..

Layer 1: Physical- This is the level of the actual hardware. It defines

the physical characteristics such as connections, voltage levels andtiming.
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For WCDMA the lower 3 layers are most important:

Layer 1: Physical layer- This layer is responsible for transporting data

across the available physical path (radio link). Main jobs of physical layer

are :

1. Forward error correction(FEC)

2. Interleaving

3. Transport channel multiplexing

4. Channel quality measurements

5. Synchronization6. Spreading , scrambling, modulation


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Layer 2 : Data link layerIt is the upper neighbor of the physical

layer. 3GPP divides it into the radio link control (RLC) and themedium access control(MAC) layer. It delivers data block by block to

layer 1 via transport channels (or fetches the data when receiving).

In the other direction, layer 2 communicates with the adjoining

network layer via Logical channels.

The RLC and MAC layers have the following essential functions:

1. Mapping of logical channels on transport channels

2. Selection of the transport format based on current needs

3. Data encryption

4. Error protection as a function of the desired QOS

5. Acknowledgement of data blocks and requests for retransmission in case of

errors


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Layer 3 : Network Layer(RRC Layer): RRC layer is directly above thelayer 2 and is responsible for radio resource control. The main RRC

tasks include :

1. Broadcasting of system information

2. Establishment and clear down a RRC connection

3. Management of radio connections

4. Cell selection in IDLE mode

5. Querying and evaluation of physical layer measurements


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Channels are simply a tool for specifying and describing the various

communication and data related services. Various type of data isexchanged between UE and base station over the radio channel. To

characterize this different type of data , we refer to different channels.

The channels carried are categorized into three: logical, transport

and physical channels. The logical channels define the way in which

the data will be transferred, the transport channel along with thelogical channel again defines the way in which the data is

transferred, the physical channel carries the payload data and

govern the physical characteristics of the signal.

There are 3 different types of channels in WCDMA

WCDMA CHANNELS :


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1. Logical channels : Used for communication between Layer 3

(RRC) & Layer 2 (RLC/MAC). Depending on the information

content ,logical channels are characterized into traffic & Control

channels.

Control Channel (Signaling)

Broadcast Control Channel (BCCH)

Paging Control Channel (PCCH)

Dedicated Control Channel (DCCH)

Common Control Channel (CCCH)

Traffic Channel

(User Data)

Dedicated Traffic

channels (DTCH)

Common Traffic

Channel (CTCH)


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Broadcast control channel ( BCCH) : Point to multipoint ,DL

It is a broadcasting channel that supplies all the UEs with basic celland network parameters(eg. Frequency lists , code lists etc).

Paging control channel(PCCH) : Point to multipoint ,DL

It transports paging information.

All the UEs are required to regularly read the information on the

BCCH and on the PCCH

Dedicated control channel (DCCH) : Point to point ,UL/DL

This channel is used to carry dedicated control information in both

directions.DCCH is provided in parallel to a DTCH for point to point

signaling during an active connection

Common control channel ( CCCH) : Point to multipoint ,UL/DL

This bi-directional channel is used to transfer control information.

Control channels:


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Dedicated traffic channel (DTCH): Point to point ,UL/DL

DTCH is used to transport user data from Node B to a specific UEand vice versa. This means it is dedicated to a specific subscriber.

This is a bidirectional channel used to carry user data or traffic.

Common traffic channel (CTCH) : Point to multipoint ,DL

It transfers dedicated user information for all , or a group of specified

UEs

TRAFFIC CHANNELS:


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Characterizes HOW data is transported over the air interface . Each

transport channel is accompanied by the Transport formatindicator(TFI). The physical layer combines the TFI information of

different transport channels to the Transport format combination

indicator(TFCI).

Organize & Pack data from different services from the higher layersfor suitable transportation.

Unpack incoming data and sort for delivery to upper layers

Offers flexible data speeds and channel encodingEfficient usage

of radio resources. They are all unidirectional.

Transport channels are divided into common channels and dedicated

channels.

Transport Channels:


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Mapping Logical To Transport Channels

PCCH DCCH CCCH CTCHBCCH DTCH

BCH PCH CPCH RACH FACH DCHDSCH

In The UE

In The Node B

PCCH DCCH CCCH CTCHBCCH DTCH

BCH PCH CPCH RACH FACH DCHDSCH


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Chan

nel

Name Uplink/

Downlin

k

Description

CPIC

H

Common CPICH

Channel

Downlin

k

Reference channel for estimation of received

signal strength & quality; Fixed bit pattern

which is stored in Physical layer; Determines

coverage of a cell

P-CCPC

H

Primary CommonControl Physical

Channel

Downlink

This channel continuously broadcastssystem identification and access control

information.

S-

CCPC

H

Secondary

Common Control

Physical Channel

Downlin

kThis channel carries the Forward

Access Channel (FACH) providing

control information, and the PagingChannel (PACH) with messages for

UEs that are registered on the

network.

PRAC

H

Physical Random

Access Channel

Uplink Used by the UE for call setup; UE sends a

preamble to Node B and on receipt, Node B

sends an immediate ACK or NACK on

downlink AICH or AP-AICH

Physical Channels Overview


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PCPC

H

Physical Common

Packet Channel

Uplink Used by UE for packet data transfer involving

small quantities

DPDC

H

Dedicated

Physical Data

Channel

Uplink /

Downlink

Used for dedicated mode transfer of user data

(from DCH) & associated control data (from

DCCH) to & from UE

DPCC

H

Dedicated

Physical Control

Channel

Uplink /

Downlink

Used for dedicated signaling to and from UE; To

ensure coherent detection it contains both

necessary pilot symbols & commands for fast

power control

P/S -

SCH

Primary /

Secondary

Synchronization

Channel

Downlink Used for WCDMA cell search and timing

synchronization; Never spread or scrambled

PDSC

H

Physical Downlink

Shared Channel

Downlink This channel shares control information to

UEs within the coverage area of the node

B.


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PICH Paging Indication

Channel

Downlin

k

Paging messages are indicated to the

intended UE by use of bit masks; On

positive identification, UE starts reading

S-CCPCH to find page

AICH Acquisition

Indication

Channel

Downlin

k

Determines whether system can be

accessed or not; Uses simple bit

sequences for operation

AP-AICH Access Preamble

- AICH

Downlin

k

UTRAN uses this to confirm reception of

acquisition preamble sent by the UE on

the PCPCH

CSICH CPICH Status

Indicator Channel

Downlin

k

Channel informs UE about current

availability of CPCH uplink transport

channel for packet data use

CD/CA - ICH Collision

Detection /

ChannelAssignment

Indicator Channel

Downlin

k

UTRAN uses this channel to inform UEs

about any packet collisions on the uplink

& also about the current assignment ofthe packet data channel.


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Mapping Transport To Physical Channels

PCH CPCH RACH FACH DSCH DCHBCH

PHYSICAL

P-

CCPCH

S-

CCPCH

PICH PCPCH

AP-AICH

CSICH

CD/CA-ICH

PRACH

AICH

PDSCH DPDCH

DPCCHP/S -

SCH

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