Monday, 23 December 2013

Wireless Data Networks

Current wireless networks use standards developed by the IEEE:
LAN/MAN Standards Committee (aka IEEE 802).
802.11: Wireless Local-Area Networks (Wi-Fi)
802.11b: 11Mbps (6.5Mbps typ) @ 2.4GHz, 100m
802.11a: 54Mbps (25Mbps typ) @ 5GHz, 50m
802.11g: 54Mbps (11Mbps typ) @ 2.4GHz, 100m
802.11n: 540Mbps (200Mbps typ) @ 2.4GHz or 5GHz, 250m
802.15: Wireless Personal-Area Networks
802.15.1: (Bluetooth) 1-3Mbps @ 2.4GHz, 1:10:100m
802.15.3: (UWB) 100-500Mbps @ 3.1-10.6GHz, 1-3m
802.15.4: (ZigBee) 40kbps
@ 915MHz, 250kbps @2.4GHz, 10-75m
802.16: Broadband Wireless Access (WiMAX)
up to 70Mbps and up to 100km
(but not at the same time!)
@ 1-10GHz, or @ 10-66GHz
12 channels in 5GHz band
20MHz bandwidth (16.6MHz occupied)
Orthogonal Frequency Divi
sion Multiplexing (OFDM)
52 subcarriers (48 data, 4 pilot) 
802.11a Transmitter:
802.11a Receiver:

802.11a Packet Structure:
802.11a Virtual CSMA/CA :
Full Collision Detect would require full duplex radio ($$$)
Transmitter sends Request-To-Send packet specifying
source, destination and duration (cts+pkt+ack)
Receiver sends Clear-To-Send packet with duration (pkt+ack)
Everyone receiving RTS or CTS will mark channel as busy for
given duration
Transmitter sends Data packet, receiver checks CRC and
replies with ACK packet.

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