An Overview on LTE

Contents Introduction Network Structure Protocol stack Evolution of Cellular technology LTE air interface capabilities LTE standards Network Structure Basic components and their functions EPC and various interfaces Protocol stack User plane Control plane EPS NAS protocols Overview about channels Some operations and procedures

Introduction

Evolution of Cellular technology Rel99 WCDMA Rel5 HSDPA Rel6 HSUPA Rel7 Rel8 Rel9 HSPA+ Rel8 Rel9 Rel10 LTE

LTE air interface capabilities Scalable channel bandwidths 1.4Mhz to 20Mhz TDD and FDD Waveforms OFDMA in DL SC-FDMA in UL Modulation for data channels QPSk,16-QAM,64-QAM MIMO support Inter-cell interference management

LTE air interface capabilities (continued) DL and UL performance is better than HSPA rel6. Coverage Mobility Interworking with existing 3G and non-3G networks.

Radio Frame structures in LTE Two possible radio frame structures FDD TDD

Evolved Network architecture EPC /P-GW /P-GW

Architecture of EPC

Architectural differences between 3G and LTE Centralized radio resource management High latency Usage of both circuit switched and packet networks. Internetworking with 3GPP technologies only. Distributed Radio resource management Low latency All IP packet core network. Internetworking with both 3GPP and non- 3GPP technologies.

Protocol stack (user plane) UE eNB S-GW P-GW IP-NW

Protocol stack (control plane)

EPS – NAS protocols Two protocols for NAS Evolved Mobility Management Evolved Session Management

EPS idle and active states EMM registration\deregistration ESM active\inactive EMM connected\idle RRC connected\idle

EPS attach procedure UE eNB MME/S-GW P-GW HSS authentication Attach request+ PDN connectivity request S1 signal connection setup authentication Subscriber info Default EPS bearer setup Attach accept EPS bearer setup accept Attach conform

Access stratum channel terminology Logical channels Transport channels Physical channels

Initial acquisition Needs two synchronization signals PSS SSS Additional sys information over PBCH and PDSCH Procedure: Switch on the mobile Receive the PSS signal Receive the SSS signal Read the PBCH for SIB and PDSCH for MIB Register to the network

Handover and Cell Switching Single communication link between eNB and UE No more soft handover Two types of handovers in LTE Network based handover Traditional handover process UE based – Radio Link Failure handover Triggered by RLF so need to be done by UE.

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