UMTS channels | logical, transport, physical

This tutorial on UMTS covers UMTS logical channels, transport channels and physical channels.

As shown in the figure, there are three types of UMTS channels viz. logical channels(RLC layer), transport channels(MAC layer) and physical channels(PHY layer). As they tranverse between layers they map to other layer frames. For example logical channels are mapped to transport channels and transport channels are mapped tp physical channels.

UMTS channels

UMTS logical channels

As shown in the figure, UMTS/WCDMA logical channels are divided into control channels and traffic channels(DTCH,CTCH). As the name suggests traffic channels carry information(voice) annd control channels carry signalling information useful to establish and maintain connection between UE and network(NodeB).Following are the functions of each of these logical channels. Pls. note that DL stands for Downlink from network to UE and UL stands for Uplink from UE to Network.
DTCH(DL and UL, point to point)- Dedicated Traffic channel,carry user information.
CTCH(unidirectional point to multi-point)-Common traffic channel.
BCCH(DL broadcast)- Broadcast Control Channel, carry SYSTEM INFORMATION
CCCH(Bidirectional)- Common Control Channel
DCCH(Dedicated Control Channel, point to point bidirectional)
PCCH(Paging Control Channel,DL)-carry paging information
SHCCH(Shared Channel Control Channel,Bidirectional)

UMTS logical channels

UMTS/WCDMA Logical Channel Function Direction Duplex Mode
Dedicated traffic channel(DTCH) carry user plane data (speech/packet data) Uplink(UL)/Downlink(DL) FDD/TDD
Dedicated control channel(DCCH) carry signalling messages used for control operations Uplink/Downlink FDD/TDD
Shared control channel(SHCCH) carry control messages Uplink/Downlink TDD
Common control channel(CCCH) It is used to carry control messages Uplink/Downlink FDD/TDD
Common traffic channel(CTCH) It is used to carry user traffic(e.g.cell broadcast SMS) Downlink FDD/TDD
Paging control channel(PCCH) It is used to carry paging messages directed towards UE Downlink FDD/TDD
Broadcast control channel(BCCH) It is used to carry broadcast messages towards UE Downlink FDD/TDD

UMTS Transport channels

UMTS transport channels

Following are the transport type of UMTS channels.
BCH(DL broadcast) - SYSTEM/Cell related INFORMATION
FACH(DL/Forward Access Channel)- carry control information from network to UE
PCH (DL)- Paging Channel
DCH (UL or DL) - Dedicated Channel
DSCH(DL) - Downlink Shared Channel
USCH(UL)- Uplink Shared Channel
RACH(UL)- Random Access Channel

UMTS/WCDMA Transport Channel Function Direction Duplex Mode
Random access channel(RACH) It is used for initial access of the network by UE Uplink FDD/TDD
Common packet channel(CPCH) It is used as contention channel for bursty data Uplink FDD/
Forward access channel(FACH) It is used to transfer user data/control signalling messages Downlink FDD/TDD
Downlink shared channel(DSCH) It is used as shared channel carrying dedicated user data/control messages in the downlink Downlink FDD/TDD
Uplink shared channel(USCH) It is used as shared channel carrying dedicated user data/control messages in the uplink Uplink TDD
Broadcast channel(BCH) Broadcast channel to all UEs in a cell Downlink FDD/TDD
Paging channel(PCH) Broadcast of paging & notification messages,also allows UE to make use of sleep Mode Downlink FDD/TDD
Dedicated Channel(DCH) It is used as dedicated channel to transfer traffic/control messages in both the direction Uplink/Downlink FDD/TDD

UMTS Physical channels

UMTS physical channels

Following are physical type of UMTS channels for 3.84Mcps case.
P-CCPCH- Primary Common Control Physical Channel
SCH- Synchronization Channel
S-CCPCH- Secondary Common Control Physical Channel
PICH- Paging Indicator Channel
DPCH(DL)- Dedicated Physical Channel in the downlink
PDSCH-Physical Downlink Shared Channel
DPCH(UL)-Dedicated Physical Channel in the uplink
PUSCH- Physical Uplink Shared Channel
PRACH- Physical Random Access Channel
PNBSCH- Physical Node B Synchronization Channel

Mapping between channels

WCDMA logical channels transport channels physical channels mapping

UMTS Channels

Following are links to various UMTS channels which cover SCH, SCCPCH, PRACH, PICH, PDSCH, PCPCH, PCCPCH, DPDCH, DPCH, DPCCH, CSICH, CPICH, CD CAICH, AICH channels.

WCDMA SCH channel
WCDMA PICH channel
WCDMA DPCH channel
WCDMA AICH channel

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