Tuesday, 13 October 2015

LTE Architecture

Evolved Packet System (EPS) Architecture - Subsystems

 

The EPS architecture goal is to optimize the system for packet data transfer.
There are no circuit switched components. The EPS architecture is made up of:
EPC: Evolved Packet Core, also referred as SAE
eUTRAN: Radio Access Network, also referred as LTE
 
 
 
EPC provides access to external packet IP networks and performs a number of CN related functions (e.g. QoS, security, mobility and terminal context management) for idle and active terminals
eUTRAN performs all radio interface related functions 
 
 LTE/SAE Network Elements
 
 
 
 
  
Only network element defined as part of eUTRAN.
Replaces the old Node B / RNC combination from 3G.
Terminates the complete radio interface including physical layer.
Provides all radio management functions
To enable efficient inter-cell radio management for cells not attached to the same eNB, there is a inter-eNB interface X2 specified. It will allow to coordinate inter-eNB handovers without direct involvement of EPC during this process. 
 
LTE Radio Interface & the X2 Interface
 
 
LTE-Uu interface
Air interface of LTE
Based on OFDMA in DL & SC-FDMA in UL
FDD & TDD duplex methods
Scalable bandwidth: 1.4MHz - 20 MHz
X2 interface
Inter eNB interface
X2AP: special signaling protocol (Application Part)
Functionalities:
In inter- eNB HO to facilitate Handover and provide data forwarding.
In RRM to provide e.g. load information to neighbouring eNBs to facilitate interference management.
Logical interface: doesn’t need direct site-to-site connection, i.e. can be routed via CN as well
 
 S1-MME & S1-U Interfaces
 
 
 
S1 interface is divided into two parts:
S1-MME interface
Control Plane interface between eNB & MME
S1AP:S1 Application Protocol
MME & UE will exchange NAS signaling via eNB through this interface ( i.e. authentication, tracking area updates)
S1 Flex: an eNB is allowed to connect to a maximum of 16 MME. (LTE2, RL20)
S1-U interface
User plane interface between eNB & Serving Gateway.
Pure user data interface (U=User plane)
 
 

Budi Prasetyo

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