Agilent Measurement Journal - Issue 5 - 2008 - (Page 17)

L Long-Term Evolution (LTE) is a project name of the Third Generation Partnership Project (3GPP) which aims to deﬁne a new air interface for mobile communications. LTE is an evolution of 3GPP’s Universal Mobile Telecommunication System (UMTS) towards an all-IP network. It will provide a framework for increasing data rates and overall system capacity; reducing latency; and improving spectral efﬁciency and cell-edge performance (Figure 1).1 Unlike UMTS, which is based on wideband code division multiple access (W-CDMA) technology, LTE is based on orthogonal frequency-division multiple access (OFDMA). In this regard, LTE is similar in concept to Mobile WiMAX™, another emerging technology for wireless broadband access, although the systems operate with different frame structures, subcarrier spacing and channel bandwidths. In Issue Four of Agilent Measurement Journal we covered the LTE uplink in the article “3GPP LTE: Introducing Single-Carrier FDMA.” This article will focus on the OFDMA LTE downlink, brieﬂy describing the physical layer characteristics as deﬁned in the 3GPP Release 8 speciﬁcations. Overview of OFDM To better understand the LTE downlink, let’s look ﬁrst at how the downlink resources are accessed by the users. The LTE downlink uses OFDMA, which is a variant of orthogonal frequency-division multiplexing (OFDM). For an overview of OFDM technology, please see “Understanding the Use of OFDM in IEEE 802.16 (WiMAX™)” in Issue Two of Agilent Measurement Journal. Although the article explains the basics of OFDM with reference to WiMAX, the general principles apply to LTE as well. LTE at a glance November 2004 LTE/SAE High-level requirements • Reduced cost per bit • More lower-cost services with better user experience • Flexible use of new and existing frequency bands • Reduced terminal complexity and reasonable power consumption Flexible channel bandwidths Bandwidth MHz 1.4 3 5 10 15 20 Access mode FDD and TDD FDD and TDD FDD and TDD FDD and TDD FDD and TDD FDD and TDD Speed Downlink peak data rates (64QAM) Antenna conﬁguration SISO 2x2 MIMO Peak data rate (Mbps) 100 172.8 Uplink peak data rates (single antenna) Modulation depth QPSK 16QAM Peak data rate (Mbps) 50 57.6 4x4 MIMO 326.4 64QAM 86.4 The 1.6 MHz and 3.2 MHz TDD bandwidths have recently been deleted, and the six remaining bandwidths apply to both FDD and TDD. Mobility Optimized: 0 to 15 km/h High performance: 15 to 120 km/h Functional: 120 to 350 km/h Under consideration: 350 to 500 km/h Services Packet-switched voice and data. No circuit-switched services supported. Figure 1. A look at some of the key characteristics of LTE Spectral efﬁciency 3-4x Rel-6 HSDPA (downlink) 2-3x Rel-6 HSUPA (uplink) Latency Idle to active < 100 ms Small packets < 5 ms Agilent Measurement Journal 17

Table of Contents Feed for the Digital Edition of Agilent Measurement Journal - Issue 5 - 2008

Agilent Measurement Journal Issue 5 Finding a New Path when Assumptions Break Down Contents Testing MIPI D-PHY Protocols Oscilloscope Firmware Update DNA Replication Joining the LTE/SAE Trial Initiative Testing Proteins Praise for DC Power Analyzer Scripting Features for AMDS Testing Hybrid PCBA Systems Improving the Gene Expression System Workflow Turning a “Good Enough” Test Strategy into One That’s Reliable, Repeatable and Traceable Understanding the Effects of Limited-Bandwidth Channels on Digital Data Signals Introducing the 3GPP LTE Downlink Validating the 26 Validating the Physical and Protocol Layers in DDR Memory Interfaces Understanding Total Jitter Measurements of Low Probabilities Using Behavioral-Model Simulation to Accurately Predict First-Order PLL Performance Creating Synchronous High-Frequency Sampling across Multiple Digitizers Overcoming the Challenges of Testing FlexRay Networks Understanding Operating Life and Repeatability of Electromechanical Switches and their Effect on Total Cost of Ownership Implementing Micro and Nano LC/MS Techniques for High Sensitivity Lipidomics Analysis

Agilent Measurement Journal - Issue 5 - 2008

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