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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
Mark Webster, IntersilSlide 2 of 22
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
Mark Webster, IntersilSlide 3 of 22
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
Mark Webster, IntersilSlide 4 of 22
doc.: IEEE 802.11-00/202r1
Submission
+1
-1
Barker Code Viewed in Discrete Domain
11 Chip BARKER Code
DFT SPECTRUM
July 2000
Mark Webster, IntersilSlide 5 of 22
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
Mark Webster, IntersilSlide 6 of 22
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
Mark Webster, IntersilSlide 7 of 22
doc.: IEEE 802.11-00/202r1
Submission
Pulse ShapeEnvelop
Constituent Stacked Carriers
Spread Spectrum: Stacked Carriers Composite
July 2000
Mark Webster, IntersilSlide 8 of 22
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
Mark Webster, IntersilSlide 9 of 22
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
Mark Webster, IntersilSlide 10 of 22
doc.: IEEE 802.11-00/202r1
Submission
2 Mbps Subcarrier Constellations
All Subcarrierscarry QPSK at their respective
phase tilt.
July 2000
Mark Webster, IntersilSlide 11 of 22
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
Mark Webster, IntersilSlide 12 of 22
doc.: IEEE 802.11-00/202r1
Submission
5.5 Mbps Codeword Subcarrier Spectrums
July 2000
Mark Webster, IntersilSlide 13 of 22
doc.: IEEE 802.11-00/202r1
Submission
8 pt.IFFT
ComputeAmp/Phzof eachSubcarrier
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
Mark Webster, IntersilSlide 14 of 22
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
Mark Webster, IntersilSlide 15 of 22
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
Mark Webster, IntersilSlide 16 of 22
doc.: IEEE 802.11-00/202r1
Submission
8 pt.IFFT
ComputeAmp/Phzof eachSubcarrier
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
Mark Webster, IntersilSlide 17 of 22
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
Mark Webster, IntersilSlide 18 of 22
doc.: IEEE 802.11-00/202r1
Submission
8 pt.IFFT
ComputeAmp/Phzof eachSubcarrier
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
Mark Webster, IntersilSlide 19 of 22
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
Mark Webster, IntersilSlide 20 of 22
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
Mark Webster, IntersilSlide 21 of 22
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
Mark Webster, IntersilSlide 22 of 22
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.