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L6_wlan1 - EEC173B/ECS152C Spring 2010 Wireless LANs Design...

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Page 1 EEC173B/ECS152C, Spring 2010 Wireless LANs Evolution of Technology & Standards IEEE 802.11 Design Choices Architecture & Protocols PHY layer MAC layer design 802.11 Frame format 802.11 MAC management Synchronization, Handoffs, Power 2 Wireless LANs: Design Requirements Global, seamless operation No special permissions or licenses needed to use the LAN Ad hoc networks, no planning, no wiring Simple MAC to support multiple PHY layers Mechanism to support multiple overlapping network Provisions to handle interference Mechanisms to handle hidden terminals Robust transmission technology Easy to use for everyone, simple management Low power for battery use 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 3 Design Choices Q1: Which frequency range to use? Q2: PHY layers: IR or RF? Q3: MAC: CSMA (random access) or TDMA? Q4: Radio Technology: Direct sequence of frequency hopping? Q5: Peer to peer architecture of Base station approach? 4 Evolution Early experiences (1970 72): IBM, HP, Motorola Abandoned due to limited performance and unavailability of frequency bands Early challenges: Complexity and cost Bandwidth Coverage Interference Frequency administration Emergence of unlicensed bands Release of Industrial, Scientific and Medical (ISM) bands in 1985 Applications: military, home and enterprise networks, mobile networks, teethe less access 5 IEEE 802.11 Standardization group formed in 1990, first standards completed in 1997 IEEE 802.11 is the first WLAN standard; only one to secure a market IEEE 802.11b Also known as wireless Ethernet and Wi Fi Operates in an unlicensed radio spectrum at 2.4 GHz Wireless Ethernet access at 11 Mbps Other standards: 802.11a, 802.11g, 802.11e, … Supports both infrastructure as well as ad hoc modes 6 Comparison: infrastructure vs. ad hoc networks infrastructure network ad-hoc network AP AP AP wired network AP: Access Point
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