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Frequency Domain Modulators for 802.11b

Frequency Domain Modulators for 802.11b. Mark Webster Intersil Corporation July 2000. This Microsoft Powerpoint presentation has notes attached. Please expand to “Notes Page View” mode. Overview. Examine frequency domain modulator for 802.11 1 and 2 Mbps Barker signaling.

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Frequency Domain Modulators for 802.11b

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  1. Frequency Domain Modulatorsfor 802.11b Mark Webster Intersil Corporation July 2000 This Microsoft Powerpoint presentation has notes attached. Please expand to “Notes Page View” mode. Mark Webster, Intersil

  2. Overview • Examine frequency domain modulator for 802.11 1 and 2 Mbps Barker signaling. • Examine frequency domain modulator for 5.5 and 11 Mbps CCK signaling. • Examine frequency domain modulator for 5.5 and 11 Mbps PBCC signaling. • Compare 802.11b frequency domain modulators to OFDM modulator. • Cyclic extensions for Barker or CCK transmissions (non 802.11b variant). This Microsoft Powerpoint presentation has notes attached. Please expand to “Notes Page View” mode. Mark Webster, Intersil

  3. 1 and 2 Mbps BARKER Mode: Time Domain Modulator Time Domain Multiply 1 Mbps: BPSK 2 Mbps: QPSK time Wide Sinc Spectrum time Narrow Sinc Spectrum Mark Webster, Intersil

  4. Barker Code Viewed in Discrete Domain DFT SPECTRUM 11 Chip BARKER Code +1 -1 Mark Webster, Intersil

  5. Pulse Shape Envelop Barker Code Spreading Detail Chip Pulse +1 time -1 convolution PeriodicallyExtended Barker Samples PeriodicallyExtended Barker Chips Mark Webster, Intersil

  6. Barker Mode Signaling Revisited Time Domain Multiply Equals Frequency Domain Convolution 1 Mbps: BPSK 2 Mbps: QPSK time time Composite Mark Webster, Intersil

  7. Spread Spectrum: Stacked Carriers Composite Constituent Stacked Carriers Pulse Shape Envelop Mark Webster, Intersil

  8. Sub-Carrier Amplitude/Phase freqMHz -5 -4 -3 -2 -1 0 1 2 3 4 5 ampFreqResp 1.0000 1.0000 1.0000 1.0000 1.0000 0.2887 1.0000 1.0000 1.0000 1.0000 1.0000 phzFreqRespDeg 40.4941 -24.9605 -90.4150 57.6877 138.6759 0 -138.6759 -57.6877 90.4150 24.9605 -40.4941 Mark Webster, Intersil

  9. A3ejq3 A5ejq5 A8ejq8 A10ejq10 A1ejq1 A2ejq2 A7ejq7 A4ejq4 A11ejq11 A9ejq9 A6ejq6 -5 -4 -3 -2 -1 0 1 2 3 4 5 Freq (MHz) 1 and 2 Mbps BARKER Mode: Frequency Domain Modulator 1 Compute Amp/Phz of each Subcarrier 11 Info Bit(s) BPSK/QPSK Rotation 11 pt. IFFT P/S 11 Constellation Mapper Barker Spectrum Mark Webster, Intersil

  10. 2 Mbps Subcarrier Constellations All Subcarriers carry QPSK at their respective phase tilt. Mark Webster, Intersil

  11. 5.5 Mbps CCK Mode: Time Domain Modulator Time Domain Multiply QPSK time time 4 Spreading Codes time time time Mark Webster, Intersil

  12. 5.5 Mbps Codeword Subcarrier Spectrums Mark Webster, Intersil

  13. A3ejq3 A5ejq5 A7ejq7 A1ejq1 A2ejq2 A6ejq6 A4ejq4 A8ejq8 1 2 3 4 5 6 7 8 5.5 Mbps CCK Mode: Frequency Domain Modulator 1 Compute Amp/Phz of each Subcarrier 8 2 Info Bits QPSK Rotation 8 pt. IFFT P/S Constellation Mapper 8 4 Codeword Spectrums 2 Info Bits Mark Webster, Intersil

  14. 5.5 Mbps Subcarrier Constellations QPSK 8 QAM 5 QAM 8 QAM QPSK 8 QAM 3 unique QAM constellations to within a phase tilt. 5 QAM 8 QAM Mark Webster, Intersil

  15. 11 Mbps CCK Mode: Time Domain Modulator Time Domain Multiply QPSK time time 64 Spreading Codes time time time Mark Webster, Intersil

  16. A3ejq3 A5ejq5 A7ejq7 A1ejq1 A2ejq2 A6ejq6 A4ejq4 A8ejq8 1 2 3 4 5 6 7 8 11 Mbps CCK Mode: Frequency Domain Modulator 1 Compute Amp/Phz of each Subcarrier 8 2 Info Bits QPSK Rotation 8 pt. IFFT P/S Constellation Mapper 8 64 Codeword Spectrums 6 Info Bits Mark Webster, Intersil

  17. 11 Mbps Subcarrier Constellations QAM Constellations Sub-Carriers 1, 3, 5, 7 Sub-Carriers 2, 4, 6, 8 9 QAM 24 QAM Mark Webster, Intersil

  18. A3ejq3 A5ejq5 A7ejq7 A1ejq1 A2ejq2 A6ejq6 A4ejq4 A8ejq8 1 2 3 4 5 6 7 8 11 Mbps PBCC Mode: Frequency Domain Modulator Compute Amp/Phz of each Subcarrier 8 8 Info Bits 8 pt. IFFT P/S Constellation Mapper Exists, but is Complicated Mark Webster, Intersil

  19. OFDM DIRECTLY EMBRACES FREQUENCY DOMAIN SIGNALING Used to Eliminate the Need for IBI Equalizer 802.11A OFDM MODULATOR BLOCK DIAGRAM Add Cyclic Extension Viterbi Encoder Constellation Mapper Scrambler Interleaver IFFT Data Sub-Carrier Constellations BPSK: 6, 9 Mbps QPSK: 12, 18 Mbps 16 QAM: 24, 36 Mbps 64 QAM: 48, 54 Mbps BPSK Pilot Subcarriers Cyclically Extends Sub-Carriers Mark Webster, Intersil

  20. 802.11a OFDM Symbol Equivalent to 64 Chip Codewords 20 MHz x 4 usecs = 80 samples 4 usecs OFDM Symbol Cyclic Extend IFFT/FFT SPAN 16 Samples 64 Samples time ~16.25 MHz 312.5 KHz Tone Spacing 52 Subcarriers . . . frequency Mark Webster, Intersil

  21. Cyclic Extensions Can Be Used on Any Codeword 1 2 3 4 5 6 7 8 9 10 11 Original Codeword Smoothly Extends Sub-Carriers in Time 10 11 1 2 3 4 5 6 7 8 9 10 11 Cyclically- Extended Codeword Mark Webster, Intersil

  22. Summary • 1 and 2 DSSS Barker code modulation is actually OFDM with 11 sub-carriers. Each sub-carrier uses phase-tilted QPSK. All sub-carriers are equal amplitude, but the center. • 802.11b 5.5 Mbps CCK is actually OFDM with 8 sub- carriers. Two sub-carriers carry QPSK. Two sub-carriers carry 5 QAM. Four sub-carriers carry 8 QAM. • 802.11b 11 Mbps CCK is actually OFDM with 8 sub- carriers. Four sub-carriers carry 9 QAM. Four sub-carriers carry 24 QAM. • Cyclic extensions can be added to all these signals to eliminate the need for inter-block interference (IBI) equalization. Mark Webster, Intersil

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