wireless_lans.slides - Wireless LANs Characteristics IEEE...

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Slides courtesy of Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/ 1 Wireless LANs Characteristics IEEE 802.11 PHY MAC Roaming .11a, b, g, h, i … Textbooks: Jochen Schiller, Mobile Communications / Mobilkommunikation, published by Pearson, available in English and German http://www.inf.fu-berlin.de/inst/ag-tech/resources/mobile_communications.htm
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Characteristics of wireless LANs Slides courtesy of Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/ 2 Advantages very flexible within the reception area Ad-hoc networks without previous planning possible (almost) no wiring difficulties (e.g. historic buildings, firewalls) more robust against disasters like, e.g., earthquakes, fire - or users pulling a plug... Disadvantages typically very low bandwidth compared to wired networks (1-10 Mbit/s) many proprietary solutions, especially for higher bit-rates, standards take their time (e.g. IEEE 802.11) products have to follow many national restrictions if working wireless, it takes a very long time to establish global solutions like, e.g., IMT-2000
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Design goals for wireless LANs Slides courtesy of Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/ 3 global, seamless operation low power for battery use no special permissions or licenses needed to use the LAN robust transmission technology simplified spontaneous cooperation at meetings easy to use for everyone, simple management protection of investment in wired networks security (no one should be able to read my data), privacy (no one should be able to collect user profiles), safety (low radiation) transparency concerning applications and higher layer protocols, but also location awareness if necessary
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Comparison: infrared vs. radio transmission Slides courtesy of Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/ 4 Infrared uses IR diodes, diffuse light, multiple reflections (walls, furniture etc.) Advantages simple, cheap, available in many mobile devices no licenses needed simple shielding possible Disadvantages interference by sunlight, heat sources etc. many things shield or absorb IR light low bandwidth Example IrDA (Infrared Data Association) interface available everywhere Radio typically using the license free ISM band at 2.4 GHz Advantages experience from wireless WAN and mobile phones can be used coverage of larger areas possible (radio can penetrate walls, furniture etc.) Disadvantages very limited license free frequency bands shielding more difficult, interference with other electrical devices Example WaveLAN, HIPERLAN, Bluetooth
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Slides courtesy of Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/ 5 Comparison: infrastructure vs. ad-hoc networks infrastructure network ad-hoc network AP AP AP wired network AP: Access Point
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802.11 - Architecture of an infrastructure network Slides courtesy of Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/ 6 Station (STA) terminal with access mechanisms to the wireless medium and radio contact to the access point Basic Service Set (BSS) group of stations using the same radio frequency Access Point
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