LTE Technology ; An Evolution

By;Usman Qureshi

RF Optimization EngineerChina Mobile Pakistan.

Outline• Motivation of LTE• LTE Technology Basics

Key ParametersOFDMA and Downlink Frame StructureSC-FDMA and Uplink Frame StructureNetwork & Protocol ArchitectureLTE UE categories

• Radio ProceduresCell SearchSystem Information BroadcastEPS Bearer SetupDownlink & Uplink Data TransmissionMobilityMIMO

LTE Market Situation – Based on HSPA Success Story

•HSPA growth is based on the Uptake Of Mobile Data services world wide.More than 250 networks world wide have already commercially launched HSPA.

•Mobile Data Traffic is growing Exponentially, caused by Mobileinternet offerings and improved user experience with new device types.

•LTE is accepted worldwide as the long term evolution perspective for today’s Today’s 2G and 3G networks based on WCDMA/HSPA, GSM/EDGE, TD-SCDMA, etc

Evolution of LTE (FDD & TDD)

LTE Vs HSPA

LTE – Basic Drivers

• Reduced Latency Radio Access Network Latency (User Plane UE-RNC-UE) below 10ms.

Significantly reduced control panel Latency.

• Higher User Data Rates 100 Mbps (Downlink) & 50 Mbps (Uplink)

• Improved System Capacity & Coverage Support for Scalable Bandwidth:1.4, 3 , 5, 10, 15, 20 Mhz

Support for Internetworking with Legacy networks

• Cost Reduction Reduced CAPEX & OPEX including Backhaul.

Cost Affective Migration from Legacy networks.

• Improved Spectrum Efficiency 2-4 times better than 3GPP Release 6

Support for Paired & unpaired spectrum (FDD & TDD mode)

LTE/SAE Network Architecture

Protocol Stack – User Plane

Protocol Stack – Control Plane

LTE Key Parameters

What is OFDM ?

OFDM Signal Generation Chain

OFDM Signal generation is based on Inverse Fourier Transform (IFFT) operation On transmitter side.

On Receiver side, an FFT operation will be used.

OFDMA & OFDMOFDM allocates users in time domain only

OFDMA allocates users in time & Frequency domain

LTE Downlink Frame Structure

•LTE Provides QPSK, 16QAM, 64QAM as downlink modulation schemes.•Cyclic prefix is used as guard interval, with different configurations;

Normal Cyclic Prefix Extended Cyclic Prefix

•15 Khz subcarrier spacing•Scalable Bandwidth.

OFDMA Time- Frequency Multiplexing

LTE Spectrum FlexibilityLTE Physical layer supports any bandwidth from 1.4 MHz to 20 MHz in steps of 180 KHz (resource block)Current LTE specification supports a subset of 6 different system bandwidthsAll UEs must support the maximum bandwidth of 20 MHz.

Mapping between Logical & Transport

LTE Radio Procedures

Lte Initial Access Procedure is shown below, before going into the details ofThese procudres

Downlink Physical Channels & Signals

Cell Search in LTE

Cell Search in LTE, Reference Signals

Random Access Procedure

Hybrid ARQ in the downlink

Uplink Physical Channels & Signals