Lte Interface Protocol Structure

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LTE Radio Interface - Physical Layer

• LTE Interface Protocol Structure

LTE Radio Interface - Physical Layer • LTE Interface Protocol Structure


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Table of Contents:

1 LTE Air Interface Protocols ................................................................................ 4 2 Types of Channels and Channel Mapping ......................................................... 6 3 Exercise ............................................................................................................ 8



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1 LTE Air Interface Protocols

Up to this point, we have been examining the physical structure of the LTE interface. Now it is time to look at the LTE interface from a wider perspective and understand the role of the different protocol layers in the protocol structure.

The main function of the Medium Access Control (MAC) protocol is the management of uplink and downlink transport resources for the terminals connected to the eNodeB.

The Radio Link Control (RLC) protocol performs segmentation and reassembly of PDCP packets into smaller blocks that can be handled by the MAC layer. The RLC layer also offers ARQ retransmission - if this is required - in addition to the lower-layer HARQ retransmission.

One of the main tasks of the Packet Data Convergence Protocol (PDCP) is to compress and decompress IP packet headers using the Robust Header Compression (RoHC) protocol defined in RFC 4995.

In the user plane, the IP user traffic is carried over PDCP. In the control plane, the Radio Resource Control (RRC) and Non Access Stratum (NAS) protocols handle the signalling traffic between the terminal and the network.

Move your mouse pointer over the protocols in the figure to see a short description of each protocol.



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2 Types of Channels and Channel Mapping

In addition to the physical channels previously presented in this course, there are so-called transport channels - located at the horizontal interface between the physical layer and MAC layer - and logical channels - located at the horizontal interface between the MAC layer and RLC layer.

Note that, when compared to previous technologies such as WCDMA / HSPA, the number of transport channels has been reduced. Instead of several dedicated channels, there is a single shared channel in downlink and a single shared channel in uplink.

As far as the channel mapping is concerned, dedicated traffic channels carrying the user data (DTCH) and dedicated control channels (DCCH) are mapped into the downlink shared channel (DL-SCH) or uplink shared channel (UL-SCH) which in turn is mapped into the PDSCH or PUSCH, respectively.

Logical common control channels (CCCH) are also mapped into transport shared channels.

Other mapping branches are related to the paging procedure, the broadcasting of important system information in downlink, the distribution of multicast information, and the random access procedure in uplink.

Note that some of the physical channels do not carry any higher-layer information, so there is no channel mapping for these channels.

Use your mouse pointer to investigate more details in the channel mapping figure.



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3 Exercise

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Lte Interface Protocol Structure