Doc.: IEEE 802.11-00/202r1 Submission July 2000 Mark Webster, IntersilSlide 1 of 22 Frequency Domain...

July 2000

Mark Webster, IntersilSlide 1 of 22

doc.: IEEE 802.11-00/202r1

Submission

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.

July 2000


doc.: IEEE 802.11-00/202r1

Submission

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.

July 2000


doc.: IEEE 802.11-00/202r1

Submission

1 and 2 Mbps BARKER Mode:Time Domain Modulator

1 Mbps: BPSK2 Mbps: QPSK

time

time

Time DomainMultiply

NarrowSinc Spectrum

WideSinc Spectrum

July 2000


doc.: IEEE 802.11-00/202r1

Submission

+1

-1

Barker Code Viewed in Discrete Domain

11 Chip BARKER Code

DFT SPECTRUM

July 2000


doc.: IEEE 802.11-00/202r1

Submission

+1

-1

Chip Pulse

time

PeriodicallyExtendedBarker Samples

PeriodicallyExtendedBarker Chips

convolution

Barker Code Spreading Detail

Pulse ShapeEnvelop

July 2000


doc.: IEEE 802.11-00/202r1

Submission

Barker Mode Signaling Revisited

1 Mbps: BPSK2 Mbps: QPSK

time

Time Domain Multiply EqualsFrequency Domain Convolution

time Composite

July 2000


doc.: IEEE 802.11-00/202r1

Submission

Pulse ShapeEnvelop

Constituent Stacked Carriers

Spread Spectrum: Stacked Carriers Composite

July 2000


doc.: IEEE 802.11-00/202r1

Submission

phzFreqRespDeg 40.4941 -24.9605 -90.4150 57.6877 138.6759 0 -138.6759 -57.6877 90.4150 24.9605 -40.4941

ampFreqResp 1.0000 1.0000 1.0000 1.0000 1.0000 0.2887 1.0000 1.0000 1.0000 1.0000 1.0000

freqMHz -5 -4 -3 -2 -1 0 1 2 3 4 5

Sub-CarrierAmplitude/Phase

July 2000


doc.: IEEE 802.11-00/202r1

Submission

11 pt.IFFT

ComputeAmp/Phzof eachSubcarrier

P/S

BarkerSpectrum

BPSK/QPSKRotation

InfoBit(s)

1 and 2 Mbps BARKER Mode:Frequency Domain Modulator

ConstellationMapper

-5 -4 -3 -2 -1 0 1 2 3 4 5Freq (MHz)

A1ej1

A2ej2

A3ej3 A5e

j5

A4ej4

A6ej6

A11ej11A7e

j7

A8ej8 A10e

j10

A9ej9

11

111

July 2000


doc.: IEEE 802.11-00/202r1

Submission

2 Mbps Subcarrier Constellations

All Subcarrierscarry QPSK at their respective

phase tilt.

July 2000


doc.: IEEE 802.11-00/202r1

Submission

5.5 Mbps CCK Mode:Time Domain Modulator

QPSK

time

time

Time DomainMultiply

time

time

time

4 SpreadingCodes

July 2000


doc.: IEEE 802.11-00/202r1

Submission

5.5 Mbps Codeword Subcarrier Spectrums

July 2000


doc.: IEEE 802.11-00/202r1

Submission

8 pt.IFFT


P/S

4 CodewordSpectrums

QPSKRotation

2 InfoBits

5.5 Mbps CCK Mode:Frequency Domain Modulator

ConstellationMapper 8

81

2 InfoBits

A1ej1

A2ej2

A3ej3 A5e

j5

A4ej4 A6e

j6

A7ej7

A8ej8

1 2 3 4 5 6 7 8

July 2000


doc.: IEEE 802.11-00/202r1

Submission

5.5 Mbps Subcarrier Constellations

3 unique QAMconstellations

to within aphase tilt.

QPSK 8 QAM

QPSK

5 QAM

5 QAM

8 QAM

8 QAM8 QAM

July 2000


doc.: IEEE 802.11-00/202r1

Submission

11 Mbps CCK Mode:Time Domain Modulator

QPSK

time

time

Time DomainMultiply

time

time

time

64 SpreadingCodes

July 2000


doc.: IEEE 802.11-00/202r1

Submission

8 pt.IFFT


P/S

64 CodewordSpectrums

QPSKRotation

2 InfoBits

11 Mbps CCK Mode:Frequency Domain Modulator

ConstellationMapper 8

81

6 InfoBits

A1ej1

A2ej2

A3ej3 A5e

j5

A4ej4 A6e

j6

A7ej7

A8ej8

1 2 3 4 5 6 7 8

July 2000


doc.: IEEE 802.11-00/202r1

Submission

11 Mbps Subcarrier Constellations

Sub-Carriers1, 3, 5, 7

Sub-Carriers2, 4, 6, 8

QAMConstellations

9 QAM 24 QAM

July 2000


doc.: IEEE 802.11-00/202r1

Submission

8 pt.IFFT


P/S8 InfoBits

11 Mbps PBCC Mode:Frequency Domain Modulator

Constellation Mapper Exists, but is Complicated

8

A1ej1

A2ej2

A3ej3 A5e

j5

A4ej4 A6e

j6

A7ej7

A8ej8

1 2 3 4 5 6 7 8

July 2000


doc.: IEEE 802.11-00/202r1

Submission

Scrambler ViterbiEncoder

Interleaver ConstellationMapper

IFFTAdd

CyclicExtension

802.11A OFDM MODULATOR BLOCK DIAGRAM

Data Sub-CarrierConstellations

BPSK: 6, 9 MbpsQPSK: 12, 18 Mbps16 QAM: 24, 36 Mbps64 QAM: 48, 54 Mbps

OFDM DIRECTLY EMBRACESFREQUENCY DOMAIN SIGNALING

Used to Eliminate the Needfor IBI Equalizer

BPSKPilot

Subcarriers

CyclicallyExtends

Sub-Carriers

July 2000


doc.: IEEE 802.11-00/202r1

Submission

16Samples

64Samples

IFFT/FFT SPANCyclicExtend

4 usecs OFDM Symbol

312.5 KHz Tone Spacing

52Subcarriers . . .

frequency

time

802.11a OFDM Symbol

20 MHz x 4 usecs = 80 samples

~16.25 MHz

Equivalent to64 Chip Codewords

July 2000


doc.: IEEE 802.11-00/202r1

Submission

Cyclic Extensions Can BeUsed on Any Codeword

OriginalCodeword

Cyclically-ExtendedCodeword

1 2 3 4 5 6 7 8 9 10 11

10 11 1 2 3 4 5 6 7 8 9 10 11

Smoothly ExtendsSub-Carriers in Time

July 2000


doc.: IEEE 802.11-00/202r1

Submission

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.

Doc.: IEEE 802.11-00/202r1 Submission July 2000 Mark Webster, IntersilSlide 1 of 22 Frequency Domain...

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