LTE Architecture Overview

In this tutorial, we will discuss on the LTE Architecture Overview.

What is LTE?

  • LTE stands for Long Term Evolution
  • Next Generation mobile broadband technology-By 3GPP
  • Promises data transfer rates of 100Mbps
  • Based on UMTS 3G technology
  • Optimized for All-IP traffic

Motivation for LTE ?

  • LTE can be used to get the higher data rate and and spectral efficiency.
  • Need for Packet Switched optimized system
  • Need for high quality of services
  • Need for ALL IP low cost infrastructure (Simple architecture/reduce number of NEs)
3GPP Standard Evolution

LTE characteristics


  • LTE uses 100 Mbps (DL) with OFDMA and 50 Mbps (UL) with SC-FDMA.
  • C-plane Latency < 100ms and U-plane < 5ms
  • Higher Bandwidth


  • Uses MIMO multiple antenna technology
  • SC-FDMA: Reduces Inter cell Interference
  • 200 users per cell in active state


  • Can be in parallel with existing RAT
  • Support of VoIP


  • New and existing bands
  • Scalable channel bandwidths of 1,4, 3, 5, 10, 15 and 20
  • Simpler E-UTRAN architecture. RNC and CS domain are not used
  • Duplex Flexibility – FDD and TDD

LTE Architecture

LTE Architecture
  • The E-UTRAN consists of eNBs, providing the E-UTRA U-plane (PDCP/RLC/MAC/PHY) and C-plane (RRC) protocol terminations towards the UE.
  • Each eNBs are interconnected with each other through X2 interface.
  • Each eNBs are connected with EPC core network through S1 interface.
    S1-MME with MME
    S1-U with SGW


EnodeB : (E-UTRAN Node B)

  • Scheduling and dynamic allocation of resources to UE in both uplink and downlink direction.
  • Controlling mobility of UE in connected mode
  • Triggers state transition from IDLE to connected mode and vice versa
  • Admission control and congestion control
  • Buffering of the data during handover

MME: (Mobility Management Entity)

  • Handles mobility management in idle mode.
  • Maintains UE context during RRC idle state.
  • Responsible for NAS signalling and NAS signalling security
  • Does bearer management for the UE.
  • Tracking Area list management

SGW: (Serving Gateway)

  • Acts as mobility anchor for the data bearers.
  • Buffers the downlink data when UE is in IDLE mode
  • Packet routing and forwarding.
  • Synonymous to SGSN of pre release 8 networks

PGW: (PDN Gateway)

  • Allocation of IP address to the mobile
  • Filters downlink user IP packets into different QoS based bearers.
  • Contacts PCRF to determine the QoS for bearers
  • Packet filtering, charging and Policy Enforcement features.

PCRF (Policy and Charging Rules Function)

  • Takes charging enforcement decisions.

Now we have understood the LTE Architecture Overview. Let’s discuss LTE EPC Overview in next tutorial.

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