Wireless-Suppl - CECS 474 Computer Network Interoperability...

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CECS 474 Computer Network Interoperability Wireless (802.11) Supplement Wireless (802.11) The most popular wireless LAN technology is the IEEE 802.11 standard. Physical Properties 802.11 was designed to run over three different types of physical media : 1. Spread spectrum using frequency hopping 2. Spread spectrum using direct sequence 3. Infrared signals Spread spectrum spreads the signal over a wider frequency band than normal so that interference from other devices will not have as great an impact. 1. Frequency Hopping The signal is transmitted over an (apparently) random sequence of frequencies…first one, then a second, then a third, etc. The sequence of frequencies is computed algorithmically using a pseudorandom number generator. The sender and the receiver use the same seed value to calculate synchronized frequencies. 802.11 defines a physical layer standard that uses frequency hoping (over 79 1-Mhz-wide frequency bandwidths). It runs in the 2.4 Ghz frequency band of the elecromagnetic spectrum. Dr. Tracy Bradley Maples (Fall 2009)
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2. Direct Sequence Each bit in the frame is represented by multiple bits in the transmitted signal. The sender sends the XOR of the bit it wants to send and n random bits. This is known as an n -bit chipping code . The sender and receiver random number streams match. This spreads the signal across a frequency band that is
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This note was uploaded on 04/11/2010 for the course CECS 474 taught by Professor Maples,t during the Spring '08 term at CSU Long Beach.

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Wireless-Suppl - CECS 474 Computer Network Interoperability...

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