dsss - 2.4 GHz ± Use the same channels as 802.11b ± OFDM...

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bxyics 1 bxyics 1 Direct Sequence Spread Spectrum (DSSS) ± Each bit is represented by multiple bits in the transmitted signal, using a spreading code ± Chip code/spreading code ± Wider bandwidth ± Lower signal power ± High process gain bxyics 2 Barker Code ± A Barker code is a string of digits a i = ± 1 of length l 2 such that ± for all 1 k . ± DSSS uses 11-chip Barker code 1 1 = + k l i k i i a a bxyics 3 CCK: Complimentary Code Keying
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bxyics 2 bxyics 4 802.11b channels bxyics 5 802.11b bxyics 6 FHSS and DSSS ± FHSS has a greater resistance to narrow band interference ± DSSS equipments are widely available and cheaper than FHSS ± DSSS has much higher data rate and throughput
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bxyics 3 bxyics 7 Orthogonal Frequency-Division Multiplexing (OFDM) ± A signal is split into several narrowband channels at different frequencies bxyics 8 802.11g ± Ratified in 2003 ±
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Unformatted text preview: 2.4 GHz ± Use the same channels as 802.11b ± OFDM above 20Mbps ± DSSS below 20Mbps bxyics 9 802.11a ± Ratified in 1999 ± OFDM ± 16 Channels in USA ± 20 MHz each channel ± Data rate: 6, 9, 12, 18, 24, 36, 48, 54 mbps bxyics 4 bxyics 10 802.11a bxyics 11 802.11a bxyics 12 Join a wireless network ± Three steps ± Probing (scanning) ± Two types ± Authentication ± Association bxyics 5 bxyics 13 Authentication methods ± Open system authentication ± Shared key authentication bxyics 14 Association ± AP and stations swap information ± Transmit rates, etc ± Stations added to AP forwarding database ± Data transmission begins after associated bxyics 15 802.11 Frames ± Management frames ± Control frames ± Data frames...
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dsss - 2.4 GHz ± Use the same channels as 802.11b ± OFDM...

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