802 11 b Modulation Scheme Presented By Nishant

802. 11 b Modulation Scheme Presented By: Nishant Divecha 1

Evolution of the 802. 11 b Major Problems at the Physical Layer caused by nature of the chosen media that had to be addressed in 802. 11 b • Bandwidth allocation; • External interference; • Reflection. 2

The physical layer of the original 802. 11 standardized three wireless data exchange techniques: • Infrared (IR); • Frequency hopping spread spectrum (FHSS); • Direct sequence spread spectrum (DSSS). 3

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Complementary Code Keying 5

DSSS Frequency Channel Plan 6

802. 11 DSSS Radio Interface • 1 Mbps 1 Msymbol/s BPSK spread by 11 chip Barker code, (-4 d. B Bandwidth = 11 MHz, main lobe = 22 MHz), IEEE 802. 11 • 2 Mbps 1 Msymbol/s QPSK spread by 11 chip Barker code (-4 d. B Bandwidth = 11 MHz, main lobe = 22 MHz), IEEE 802. 11 • 5. 5 Mbps 2 Msymbol/s QPSK like symbols spread by 8 chip Complementary Code Keying (CCK). IEEE 802. 11 b • 11 Mbps 4 Msymbol/s QPSK like symbols spread by 8 chip Complementary Code Keying (CCK). IEEE 802. 11 b • 54 Mbps OFDM with max. 52 sub-carriers, IEEE 802. 11 a / IEEE 802. 11 g 7

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1 Mbps (802. 11), 1 bit/symbol ; 2 symbol values DBPSK, 11 analog chips 2 Mbps (802. 11), 2 bit/symbol 4 symbol values DQPSK ; 11 analog chips 9

5. 5 Mbps (802. 11 b) 4 bit/symbol ; 16 symbol values DQPSK ; 8 analog chips 11 Mbps (802. 11 b) 8 bit/symbol ; 256 symbol values DQPSK ; 8 analog chips 10

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Typical Receiver can operate at 0 d. B SNR 12