WirelessLAN

WirelessLAN - Elementsofawirelessnetwork wirelesshosts...

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Csci 232: Wireless LAN 1 Elements of a wireless network network  infrastructure wireless hosts laptop, PDA, IP phone run applications may be stationary (non-mobile)  or mobile wireless does not always  mean mobility
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Csci 232: Wireless LAN 2 Elements of a wireless network network  infrastructure  base station typically connected to wired  network relay - responsible for  sending packets between  wired network and wireless  host(s) in its “area” e.g., cell towers for  cellular networks,  802.11 access points 
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Csci 232: Wireless LAN 3 Elements of a wireless network network  infrastructure  wireless link typically used to connect  mobile(s) to base station also used as backbone link  (WiMAX) multiple access protocol  coordinates link access  various data rates,  transmission distance
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Csci 232: Wireless LAN 4 Elements of a wireless network network  infrastructure  infrastructure mode base station connects mobiles  into wired network handoff: mobile changes base  station providing connection  into wired network
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Csci 232: Wireless LAN 5 Elements of a wireless network Ad hoc mode no base stations nodes can only transmit to  other nodes within link  coverage nodes organize themselves  into a network: route among  themselves
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Csci 232: Wireless LAN 6 Wireless Link Characteristics Differences from wired link …. decreased signal strength:  radio signal attenuates as it  propagates through media (path loss) interference from other sources:  standardized wireless network  frequencies (e.g., 2.4 GHz) shared by other devices (e.g., phone);  devices (motors) interfere as well multipath propagation:  radio signal reflects off objects, ground,  arriving at destination at slightly different times …. make communication across (even a point to point) wireless link  much more “difficult” 
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Csci 232: Wireless LAN 7 Wireless network characteristics Multiple wireless senders and receivers create additional problems  (beyond multiple access): A B C Hidden terminal problem B, A hear each other B, C hear each other A, C can not hear each other means A, C unaware of their interference at  B A B C A’s signal strength space C’s signal strength Signal fading: B, A hear each other B, C hear each other A, C can not hear each other interferring  at B
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Csci 232: Wireless LAN 8 Special challenge for Wireless MAC Collision detection is difficult Transmission power is much higher than receiving power Hidden station problem A station is not able to detect a potential competitor for the medium because the  competitor is too far away Example: A is transmitting to B. C cannot hear the transmission, thus falsely concludes 
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This note was uploaded on 12/04/2009 for the course CS 183 taught by Professor Susan during the Spring '09 term at GWU.

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WirelessLAN - Elementsofawirelessnetwork wirelesshosts...

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