ises it. The otherwise narrow- band signal, shown in Figure 6-17, is spread across a much wider chan- nel-typically on the order of 1.25 MHz. The bits in the data stream are combined with "noise bits" to create a much broader signal, and as before, only the base station and the communicating devices know the code that must be used to extract the original signal from the noise. The code is sometimes called a chipping code, and the technique is referred to as producing a "chipped signal." One way to think about this technique is as follows. Imagine that you have just been appointed Ambassador to South Africa (Congratulations!). As part of your predeparture indoctrination you have learned that the country has 11 official languages: Afrikaans, IsiNdebele, IsiXhosa, IsiZulu, Northern Sotho, Sesotho, Setswana, SiSwati, Tshivenda, Xitsonga, and English. Upon arriving in the country, you attend a recep- tion in your honor, and in attendance are dignitaries from the many regions of South Africa, all speaking their local language over glasses of mampoer and South African wine. The room is filled with people and the cacophony of eleven distinct languages is simply noise to your ears. Sud- denly, however, from across the room, emerging from the general din, you hear someone calling to you. From across the ballroom your newly appointed aide de camp is talking to you in English at a normal level, yet you understand her perfectly. Figure 6-17 Spread spectrum Original signal component graph "Spread" signal component 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 Terms of Use as given at the website. Access Technologies Chapter 6 If you understand this description, then you understand noise modu- lated spread spectrum. These two techniques, FHSS and DSSS, formed the functional basis of the original wireless LAN standards that ulti- mately coalesced into the phenomenon known as Wi-Fi. Wi-Fi Toda