LTE Communication Channels - LTE

What is LTE Communication Channels?

We know that data will be carried out as information, which flows between the various protocols. These protocols are distinguished as channels and signals. LTE uses different types of logical, transport and physical channel, which are well known by the kind of information they carry and by the way in which the information is being processed.

  • Logical Channels : The RLC and MAC protocols. carry the information of any type which is transmitted through the air,e.g control channels, traffic channels,Data signalling messages and system broadcasting.
  • Transport Channels : It define the way of how the data is being transmitted over the air, e.g. what are encoding, interleaving options used to transmit data.In between the MAC and the physical layer, data and signalling of messages are carried on transport channels.
  • Physical Channels : This define whereis something(data) transmitted over the air, e.g. first Y symbols in the DL frame.Between the different levels of the physical layer, data and signalling of messages are carried on physical channels.

Logical Channels

Logical channels define what type of data is transferred. These channels define the data-transfer services offered by the MAC layer.Between the RLC and MAC protocols, the data and signalling messages are carried out in Logical layer.
  • Logical channels can be divided into control channels and traffic channels. Control Channel can be either common channel or dedicated channel. A common channel is common to all users in a cell (Point to multipoint) while dedicated channels means channels can be used only by one user (Point to Point).
  • Logical channels are well known by the data they are carrying and can be classified in two categories. First, the logical traffic channels will carry data in the user plane, while logical control channels carry signalling messages in the control plane. Below table lists the logical channels that are used by LTE:

Channel Name

Acronym

Control channel

Traffic channel

Broadcast Control Channel

BCCH

X

Paging Control Channel

PCCH

X

Common Control Channel

CCCH

X

Dedicated Control Channel

DCCH

X

Multicast Control Channel

MCCH

X

Dedicated Traffic Channel

DTCH

X

Multicast Traffic Channel

MTCH

X

Transport Channels:

Transport Channels define the way of how the data is being transmitted over the air, e.g. what are encoding, interleaving options used to transmit data.In between the MAC and the physical layer, data and signalling messages are carried on transport channels.

They are distinguished by the ways in which the transport channel processor manipulates them. Below table lists the transport channels that are used by LTE:

Channel Name

Acronym

Downlink

Uplink

Broadcast Channel

BCH

X

Downlink Shared Channel

DL-SCH

X

Paging Channel

PCH

X

Multicast Channel

MCH

X

Uplink Shared Channel

UL-SCH

X

Random Access Channel

RACH

X

Physical Channels

Physical channels define whereis something(data) transmitted over the air, e.g. first Y symbols in the DL frame.

Data and signalling messages are carried on physical channels between the different levels of the physical layer and accordingly they are divided into two components

  • Physical Data Channels
  • Physical Control Channels

Physical data channels

Physical data channels are well known by the ways by which the physical channel processor would manipulate them. By the ways, with which they are mapped onto the sub-carriers and symbols that are being used by Orthogonal frequency-division multiplexing (OFDMA). Below table lists the physical data channels used by LTE:

Channel Name

Acronym

Downlink

Uplink

Physical downlink shared channel

PDSCH

X

Physical broadcast channel

PBCH

X

Physical multicast channel

PMCH

X

Physical uplink shared channel

PUSCH

X

Physical random access channel

PRACH

X

The transport channel processor composes different types of control information, to assist the low-level operation of the physical layer. These are listed in the table below:

Field Name

Acronym

Downlink

Uplink

Downlink control information

DCI

X

Control format indicator

CFI

X

Hybrid ARQ indicator

HI

X

Uplink control information

UCI

X

Physical Control Channels

The transport channel processor creates the control information which assistss the low-level operation of the physical layer and also sends this particular data to the physical channel processor in the form of physical control channels.

The data travels as long as the transport channel processor in the receiver travels, but is fully invisible to the higher layers. As well, the physical channel processor will create the physical signals that assist the lowest-level aspects of the system.

Physical Control Channels are listed in the table below:

Channel Name

Acronym

Downlink

Uplink

Physical control format indicator channel

PCFICH

X

Physical hybrid ARQ indicator channel

PHICH

X

Physical downlink control channel

PDCCH

X

Relay physical downlink control channel

R-PDCCH

X

Physical uplink control channel

PUCCH

X

The base station also transmits two other physical signals, which help the mobile acquire the base station after it first switches on. These are known as the primary synchronization signal (PSS) and the secondary synchronization signal (SSS).

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