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

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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 above...

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