802.11b Modulation Scheme

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802.11b Modulation Scheme

• Presented By
• Nishant Divecha

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Evolution of the 802.11b

• Major Problems at the Physical Layer caused by
  nature of the chosen media that had to be
  addressed in 802.11b
• Bandwidth allocation
• External interference
• Reflection.

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• 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).

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Complementary Code Keying
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DSSS Frequency Channel Plan
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802.11 DSSS Radio Interface

• 1 Mbps 1 Msymbol/s BPSK spread by 11 chip Barker
  code,
• (-4 dB Bandwidth 11 MHz, main lobe 22 MHz),
  IEEE 802.11
• 2 Mbps 1 Msymbol/s QPSK spread by 11 chip Barker
  code
• (-4 dB 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 802.11b
• 11 Mbps 4 Msymbol/s QPSK like symbols spread by 8
  chip
• Complementary Code Keying (CCK). IEEE 802.11b
• 54 Mbps OFDM with max. 52 sub-carriers, IEEE
  802.11a / IEEE 802.11g

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1 Mbps (802.11), 1 bit/symbol 2 symbol
valuesDBPSK, 11 analog chips
2 Mbps (802.11), 2 bit/symbol 4 symbol
values DQPSK 11 analog chips
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5.5 Mbps (802.11b) 4 bit/symbol 16 symbol
values DQPSK 8 analog chips
11 Mbps (802.11b) 8 bit/symbol 256 symbol
values DQPSK 8 analog chips
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Typical Receiver can operate at 0dB SNR