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
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wireless_lans.slides - Wireless LANs Characteristics IEEE...

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