sion model in which develop- ers rushed to create products. And while this resulted in rapid introduc- tion of Wi-Fi products and services, it created a variety of problems- including the release of dysfunctional standards. The technology waddled around through varying degrees of commer- cial success for the intervening 5 years until June 1997, when the IEEE released the initial 802.11 standard for high-speed transmission using infrared and two forms of radio transmission within the unlicensed 2.4 GHz frequency band. The first of these was frequency hopping spread spectrum (FHSS), the second was direct sequence spread spectrum (DSSS). It is useful to understand the difference between these two tech- niques; they are described in the following sections. We begin with an explanation of spread spectrum. Spread Spectrum The idea behind spread-spectrum transmission is a simple concept: dis- guise a narrowband transmission within a broadband transmission by "spreading" or "smearing" the narrowband component within the broad- band carrier. This is done using either of two basic techniques: frequency hopping, in which a control signal directs the two communicating devices to "hop" randomly from frequency to frequency to avoid eavesdropping; or direct sequence, in which the signal is combined with a random "noise" signal to disguise its contents under the command of a control signal that knows how to separate the signal "wheat" from the noise "chaff." Frequency Hopping Spread Spectrum (FHSS) The development of FHSS is one of those stories that is worth knowing about-simply because it is SO much fun to tell and so remarkable in the telling. During World War II there was considerable angst among Allied forces over the Axis Powers' ability to thwart radio-controlled torpedoes launched from submarines by jamming the radio signals that guided Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Te