Table of Contents:

Definition and Overview

1. Characteristics and Evolution of Data Communications for a Mobile Environment

2. Overview of the Wireless Environment

3. Overview of Traditional Mobile Wireless Systems

4. OFDM for Mobile Communications

5. Leading-Edge Mobile OFDM Technologies

6. Conclusion

Self-Test

Glossary

PDF of this tutorial

Definition of OFDM
Orthogonal frequency division multiplexing (OFDM) is a communications technique that divides a communications channel into a number of equally spaced frequency bands. A subcarrier carrying a portion of the user information is transmitted in each band. Each subcarrier is orthogonal (independent of each other) with every other subcarrier, differentiating OFDM from the commonly used frequency division multiplexing (FDM).

Overview
This tutorial describes OFDM and its application to mobile communications. OFDM is a modulation and multiple-access technique that has been explored for more than 20 years. Only recently has it been finding its way into commercial communications systems, as Moore's Law has driven down the cost of the signal processing that is needed to implement OFDM–based systems.

OFDM, or multitone modulation as it is sometimes called, is presently used in a number of commercial wired and wireless applications. On the wired side, it is used for a variant of digital subscriber line (DSL). For wireless, OFDM is the basis for several television and radio broadcast applications, including the European digital broadcast television standard, as well as digital radio in North America. OFDM is also used in several fixed wireless systems and wireless local-area network (LAN) products. A system based on OFDM has been developed to deliver mobile broadband data service at data rates comparable to those of wired services, such as DSL and cable modems.

It is important that the overall system design be well matched to the service profiles to maximize the performance of the system and balance the ultimate user experience it provides relative to the cost to the operator. OFDM enables the creation of a very flexible system architecture that can be used efficiently for a wide range of services, including voice and data. For any mobile system to create a rich user experience, it must provide ubiquitous, fast, and user-friendly connectivity. OFDM has several unique properties that make it especially well suited to handle the challenging environmental conditions experienced by mobile wireless data applications.