LTE Radio Channels

Jakir Hossain

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LTE - Protocol Stack Layers:

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LTE - Protocol Stack Layers:

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Physical Layer (Layer 1):Its Takes care of the link adaptation (AMC), power

control, cell search (for initial synchronization and handover purposes) and other

measurements (inside the LTE system and between systems) for the RRC layer.

Medium Access Layer (MAC):MAC layer is responsible for Mapping between logical

channels and transport channels,.

Radio Link Control (RLC):RLC Layer is responsible for transfer of upper layer

PDUs, error correction through ARQ (Only for AM data transfer), Concatenation,

segmentation and reassembly of RLC SDUs.

Radio Resource Control (RRC):Broadcast of System Information related to the

access stratum (AS), Paging, establishment, maintenance and release of an RRC

connection between the UE and E-UTRAN.

Packet Data Convergence Control (PDCP):PDCP Layer is responsible for Header

compression and decompression of IP data.

Non Access Stratum (NAS) Protocols: NAS protocols support the mobility of the

UE and the session management procedures to establish and maintain IP

connectivity between the UE and a PDN GW.

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LTE logical channels:

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Logical Channels are divided into two part-

Control channels: these LTE control channels carry the control plane

information:

o Broadcast Control Channel (BCCH) : This control channel provides

system information to all mobile terminals connected to the eNodeB.

o Paging Control Channel (PCCH) : This control channel is used for

paging information when searching a unit on a network.

o Common Control Channel (CCCH) : This channel is used for random

access information, e.g. for actions including setting up a connection.

o Dedicated Control Channel (DCCH) : This control channel is used for

carrying user-specific control information, e.g. for controlling actions

including power control, handover, etc.

Traffic channels: These LTE traffic channels carry the user-plane data:

o Dedicated Traffic Channel (DTCH) : This traffic channel is used for

the transmission of user data.

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LTE DL Channels Mapping:

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LTE Downlink Physical channels:

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o Physical Broadcast Channel (PBCH): This physical channel carries system

information for UEs requiring to access the network. A PBCH message is repeated

every 40 ms, i.e. one TTI of PBCH includes four radio frames.

o Physical Control Format Indicator Channel (PCFICH) : As the name implies

the PCFICH informs the UE about the format of the signal being received. It

indicates the number of OFDM symbols used for the PDCCHs, whether 1, 2, or 3.

o Physical Downlink Control Channel (PDCCH) : The main purpose of this

physical channel is to carry mainly scheduling information of different types:

Downlink resource scheduling

Uplink power control instructions

Uplink resource grant

Indication for paging or system information

o Physical Hybrid ARQ Indicator Channel (PHICH) : As the name implies, this

channel is used to report the Hybrid ARQ status. It carries the HARQ ACK/NACK

signal indicating whether a transport block has been correctly received. The

HARQ indicator is 1 bit long - "0" indicates ACK, and "1" indicates NACK.

.

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LTE UL Channels Mapping:

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LTE Uplink Physical channels:

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o Physical Uplink Control Channel (PUCCH) : The Physical Uplink Control

Channel, PUCCH provides the various control signalling requirements.

o Physical Uplink Shared Channel (PUSCH) : This physical channel found on the

LTE uplink is the Uplink counterpart of PDSCH

o Physical Random Access Channel (PRACH) : This uplink physical channel is

used for random access functions.