WCDMA uses an OSI model with 7 layers. The lower 3 layers - physical, data link, and network layers - are most important for WCDMA. The physical layer uses different physical channels to transmit data over the air interface. Logical channels define how data is transferred, transport channels define how data is transmitted, and physical channels carry payload data and define signal characteristics. There are three types of channels - logical, transport, and physical - that work together to transmit various types of control and traffic data between the UE and base station.

1. WCDMA CHANNELS
By –
Manish Srivastava

2. WCDMA OSI MODEL
Radio Resource Control (RRC)
Logical channels
RLC RLC RLC (What is transmitted)
Medium Access Control (MAC)
Transport channels
(How it is transmitted)
Physical Layer
Physical channels
(Code,frequency,etc)

3. 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 7: 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.

4. Layer 4: Transport - This layer maintains flow control of 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: Network – This layer determines the way that the data will
be sent to the recipient. Logical protocols, routing and addressing are
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 and
timing.

5. 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. Synchronization
6. Spreading , scrambling, modulation

6.  Layer 2 : Data link layer – It is the upper neighbor of the physical
layer. 3GPP divides it into the radio link control (RLC) and the
medium 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

7.  Layer 3 : Network Layer(RRC Layer): RRC layer is directly above the
layer 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

8. WCDMA CHANNELS :
 Channels are simply a tool for specifying and describing the various
communication and data related services. Various type of data is
exchanged 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 the
logical 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 –

9. 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) Traffic Channel
(User Data)
Broadcast Control Channel (BCCH)
Dedicated Traffic
channels (DTCH)
Paging Control Channel (PCCH)
Dedicated Control Channel (DCCH) Common Traffic
Channel (CTCH)
Common Control Channel (CCCH)

10. Control channels:
 Broadcast control channel ( BCCH) : Point to multipoint ,DL
It is a broadcasting channel that supplies all the UE’s with basic cell
and network parameters(eg. Frequency lists , code lists etc).
 Paging control channel(PCCH) : Point to multipoint ,DL
It transports paging information.
All the UE’s 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.

11. TRAFFIC CHANNELS:
 Dedicated traffic channel (DTCH): Point to point ,UL/DL
DTCH is used to transport user data from Node B to a specific UE
and 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
UE’s

12. Transport Channels:
 Characterizes “HOW” data is transported over the air interface . Each
transport channel is accompanied by the Transport format
indicator(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 layers
for suitable transportation.
 Unpack incoming data and sort for delivery to upper layers
 Offers flexible data speeds and channel encoding  Efficient usage
of radio resources. They are all unidirectional.
 Transport channels are divided into common channels and dedicated
channels.

13. Dedicated Transport Channel
DCH (Dedicated Channel) This is used to transfer data to a particular UE. Each UE
has its own DCH in each direction
Common Transport Channel
BCH (Broadcast Channel) This channel broadcasts information to the UEs in the cell
to enable them to identify the network and the cell.
FACH (Forward Access Channel) Downlink; Transports small amount of data from
BCCH/CCCH/DCCH/CTCH to either a specific UE or over
the entire cell
PCH (Paging Channel) Downlink; Transports data from PCCH to UE over entire
cell. This channel carries messages that alert the UE to
incoming calls, SMS messages, data sessions or required
maintenance such as re-registration.
RACH (Random Access Channel) This channel carries requests for service from UEs trying to
access the system
CPCH (Common Packet Channel) This channel provides additional capability beyond that of
the RACH and for fast power control.

14. Mapping Logical To Transport Channels
In The UE
BCCH PCCH DCCH CCCH CTCH DTCH
BCH PCH CPCH RACH FACH DSCH DCH
In The Node B
BCCH PCCH DCCH CCCH CTCH DTCH
BCH PCH CPCH RACH FACH DSCH DCH

15. Physical Channels Overview
Chan Name Uplink/ Description
nel Downlin
k
CPIC Common CPICH Downlin Reference channel for estimation of received
H Channel k signal strength & quality; Fixed bit pattern
which is stored in Physical layer; Determines
coverage of a cell
P- Primary Common Downlin This channel continuously broadcasts
CCPC Control Physical k system identification and access control
H Channel information.
S- Secondary Downlin This channel carries the Forward
CCPC Common Control k Access Channel (FACH) providing
H Physical Channel control information, and the Paging
Channel (PACH) with messages for
UEs that are registered on the
network.
PRAC Physical Random Uplink Used by the UE for call setup; UE sends a
H Access Channel preamble to Node B and on receipt, Node B
sends an immediate ACK or NACK on

16. PCPC Physical Common Uplink Used by UE for packet data transfer involving
H Packet Channel small quantities
DPDC Dedicated Uplink / Used for dedicated mode transfer of user data
H Physical Data Downlink (from DCH) & associated control data (from
Channel DCCH) to & from UE
DPCC Dedicated Uplink / Used for dedicated signaling to and from UE; To
H Physical Control Downlink ensure coherent detection it contains both
Channel necessary pilot symbols & commands for fast
power control
P/S - Primary / Downlink Used for WCDMA cell search and timing
SCH Secondary synchronization; Never spread or scrambled
Synchronization
Channel
PDSC Physical Downlink Downlink This channel shares control information to
H Shared Channel UEs within the coverage area of the node
B.

17. PICH Paging Indication Downlin Paging messages are indicated to the
Channel k intended UE by use of bit masks; On
positive identification, UE starts reading
S-CCPCH to find page
AICH Acquisition Downlin Determines whether system can be
Indication k accessed or not; Uses simple bit
Channel sequences for operation
AP-AICH Access Preamble Downlin UTRAN uses this to confirm reception of
- AICH k acquisition preamble sent by the UE on
the PCPCH
CSICH CPICH Status Downlin Channel informs UE about current
Indicator Channel k availability of CPCH uplink transport
channel for packet data use
CD/CA - ICH Collision Downlin UTRAN uses this channel to inform UEs
Detection / k about any packet collisions on the uplink
Channel & also about the current assignment of
Assignment the packet data channel.
Indicator Channel

18. Mapping Transport To Physical Channels
BCH PCH CPCH RACH FACH DSCH DCH
PHYSICAL
P- S- PICH PCPCH PRACH PDSCH DPDCH
CCPCH CCPCH AP-AICH AICH P/S - DPCCH
CSICH SCH
CD/CA-ICH

19. Thank
you!