lec13_wifi0 - Lecture 13: Wi-Fi Systems Why Wi-Fi as...

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Lecture 13: Wi-Fi Systems Why Wi-Fi as opposed to cell networks? Wireless data doesn't always mean cellular data. The IEEE 802.11 standard has emerged as a surprising new alternative (or complement to cellular), upstaging even cellular’s 3G. Once hailed as a pervasive wireless data solution (at least on the drawing board), 3G technology has been delayed to a point that stretches its credibility. Testing the patience of wireless operators and consumers alike, the 3G promise has also betrayed investors world wide. The GNP-sized investments in 3G spectrum licenses and required infrastructure is enough to seal shut even the deepest pockets in the business. The beauty of the 802.11 wireless LAN (WLAN a.k.a. Wi-Fi) solution is that it doesn't even touch the cellular network. It simply channels the data from the unlicensed 802.11 spectrum at the Hot Spot access location into a gateway and on to the wired Internet. And it is inherently scaleable and easy to deploy. The technology is based on the concept of "Hot Spots," micro-network coverage areas between 20 and 100 meters in radius around a low-powered, high frequency (2.4 GHz - 5 GHz) access point. The access point, in turn, is connected to a gateway to the wired Internet. Users with the proper modem card and software can enjoy high-speed wireless Internet access while inside the Hot Spot coverage area. Today's 802.11 technology delivers data between 11 and 54 Mbps. The higher the speed, the shorter the range. Competitive opportunities suddenly surface for ISPs, software companies (MSN, etc.) and others well positioned for mass deployment because almost anyone can enter this market. 20 million public wireless LAN subscribers now account for some 60,000 Hot Spots in the world.
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Lecture 13: Wi-Fi Systems (cont.) So far, 4 existing IEEE protocol standards exist for 802.11 networks: a/b/g/n: Standard Frequency Bandwidth Comment a 5 GHz 54 Mbps first in use b 2.4 11 most popular g 2.4 11 + more secure w/more channels n 2.4,5 100 + MAC w/efficient physical layer s/w Within the 2.4-GHz frequency band, the 802.11 standard defines 14 "center frequency channels." Figure 4 shows a channel arrangement using channel 1 (2.412 GHz), channel 6 (2.437 GHz), and Channel 11 (2.462 GHz). Channels 1, 6, and 11 are commonly used
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lec13_wifi0 - Lecture 13: Wi-Fi Systems Why Wi-Fi as...

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