- 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 types of data,we refer to different channels.
- The channels carried are categorized into: Logical, Transport, and Physical Channels.
- The logical channels define the way in which the data will be transferred, 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 governs physical characteristics of the signal.
Control Channels in W-CDMA are:
- 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.
- 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 signalling during an active connection.
- Common Control Channel (CCCH): Point to multipoint, UL/DL
This bi-directional channel is used to transfer control information.
Traffic Channels in W-CDMA are:
- 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.
Transport Channels in W-CDMA are:
- Transport Channels are divided into common channels and dedicated channels.
Dedicated Transport Channel:
- Dedicated Channel (DCH): This is used to transfer data to a particular UE. Each UE has its own DCH in each direction.
Common Transport Channel:
- Broadcast Channel (BCH): This channel broadcasts information to the UEs in the cell to enable them to identify the network and the cell.
- Forward Access Channel (FACH): Downlink; transports small amount of data from BCCH/CCCH/DCCH/CTCH to either a specific UE or over the entire cell.
- Paging Channel (PCH): 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.
- Random Access Channel (RACH): This channel carries requests for service from UEs trying to access the system.
- Common Packet Channel (CPCH): This channel provides additional capability beyond that of the RACH and for fast power control.