User's Manual

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Chapter 1 Samsung LTE System Overview

LTE eNB System Description v2.0 2

Figure 1. Functional Distinctions of E-UTRAN and EPC

eNB

The eNB is a logical network component of Evolved UTRAN (E-UTRAN), which

is located on access side in LTE system.

The eNBs can be interconnected with each other by X2 interface. The eNBs are

connected by S1 interface to Evolved Packet Core (EPC).

The wireless protocol layer of eNB is divided into layer 2 and layer 3. The layer 2

is subdivided into Media Access Control (MAC) layer, Radio Link Control (RLC)

layer, and PDCP layer, each of which performs independent functions. Also,

layer3 has Radio Resource Control (RRC) layer.

The MAC layer distributes air resources to each bearer according to its priority.

Also, it performs multiplexing function and HARQ function for the data, which is

received from the multiple upper logical channels.

The RLC layer performs the following functions:

 Segments and reassembles the data, which is received from PDCP layer under

the size specified by MAC layer

 Requests retransmission to recover if data transmission fails in the lower layer

(ARQ)

 Reorders the data recovered by performing HARQ in MAC layer (re-ordering)

The PDCP layer performs the following functions:

 Header compression and decompression

 Encrypts/decrypts user plane and control plane data