LTE Communication Channels

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The information flows between the different protocols are known as channels and signals. LTE uses several different types of logical, transport and physical channel, which are distinguished by the kind of information they carry and by the way in which the information is processed.

  • Logical Channels: : Define whattype of information is transmitted over the air, e.g. traffic channels, control channels, system broadcast, etc. Data and signalling messages are carried on logical channels between the RLC and MAC protocols.

  • Transport Channels: Define howis something transmitted over the air, e.g. what are encoding, interleaving options used to transmit data. Data and signalling messages are carried on transport channels between the MAC and the physical layer.

  • Physical Channels: Define whereis something transmitted over the air, e.g. first N symbols in the DL frame. Data and signalling messages are carried on physical channels between the different levels of the physical layer.

Logical Channels

Logical channels define what type of data is transferred. These channels define the data-transfer services offered by the MAC layer. Data and signalling messages are carried on logical channels between the RLC and MAC protocols.

Logical channels can be divided into control channels and traffic channels. Control Channel can be either common channel or dedicated channel. A common channel means 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 distinguished by the information they carry and can be classified in two ways. Firstly, logical traffic channels carry data in the user plane, while logical control channels carry signalling messages in the control plane. Following table lists the logical channels that are used by LTE:

Channel NameAcronymControl channelTraffic channel
Broadcast Control ChannelBCCHX 
Paging Control ChannelPCCHX 
Common Control ChannelCCCHX 
Dedicated Control ChannelDCCHX 
Multicast Control ChannelMCCHX 
Dedicated Traffic ChannelDTCH X
Multicast Traffic Channel MTCH X

Transport Channels

Transport channels define how and with what type of characteristics the data is transferred by the physical layer. Data and signalling messages are carried on transport channels between the MAC and the physical layer.

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

Channel NameAcronymDownlinkUplink
Broadcast ChannelBCHX 
Downlink Shared Channel DL-SCHX 
Paging Channel PCHX 
Multicast Channel MCHX 
Uplink Shared Channel UL-SCH X
Random Access Channel RACH X

Physical Channels

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

  • Physical Data Channels

  • Physical Control Channels

Physical data channels

Physical data channels are distinguished by the ways in which the physical channel processor manipulates them, and by the ways in which they are mapped onto the symbols and sub-carriers used by Orthogonal frequency-division multiplexing (OFDMA). Following table lists the physical data channels that are used by LTE:

Channel NameAcronymDownlinkUplink
Physical downlink shared channelPDSCHX 
Physical broadcast channel PBCHX 
Physical multicast channelPMCHX 
Physical uplink shared channel PUSCH X
Physical random access channel PRACH X

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

Field NameAcronymDownlinkUplink
Downlink control informationDCIX 
Control format indicator CFIX 
Hybrid ARQ indicatorHIX 
Uplink control information UCI X

Physical Control Channels

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

The information travels as far as the transport channel processor in the receiver, but is completely invisible to higher layers. Similarly, the physical channel processor creates physical signals, which support the lowest-level aspects of the system.

Physical Control Channels are listed in the below table:

Channel NameAcronymDownlinkUplink
Physical control format indicator channelPCFICHX 
Physical hybrid ARQ indicator channel PHICHX 
Physical downlink control channelPDCCHX 
Relay physical downlink control channelR-PDCCHX 
Physical uplink control channelPUCCH 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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