1. Frequency Domain Modulators for 802.11b
July 2000
doc.: IEEE /202
July 2000
Frequency Domain Modulators for b
Mark Webster
Intersil Corporation
July 2000
Mark Webster, Intersil
Mark Webster, Intersil

2. July 2000
doc.: IEEE /202
July 2000
Overview
Examine frequency domain modulator for and 2 Mbps Barker signaling.
Examine frequency domain modulator for and 11 Mbps CCK signaling.
Examine frequency domain modulator for and 11 Mbps PBCC signaling.
Compare b frequency domain modulators to OFDM modulator.
Cyclic extensions for Barker or CCK transmissions (non b variant).
Mark Webster, Intersil
Mark Webster, Intersil

3. 1 and 2 Mbps BARKER Mode: Time Domain Modulator
July 2000
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
July 2000
Barker Code Viewed in Discrete Domain
DFT SPECTRUM
11 Chip BARKER Code +1 -1
Mark Webster, Intersil

5. Barker Code Spreading Detail Pulse Shape Envelop Periodically Extended
July 2000
Pulse Shape
Envelop
Barker Code
Spreading Detail
Chip Pulse +1
time -1
convolution
Periodically Extended
Barker Samples
Periodically Extended
Barker Chips
Mark Webster, Intersil

6. Barker Mode Signaling Revisited
July 2000
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
July 2000
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 1 2 3 4 5
July 2000
Sub-Carrier
Amplitude/Phase
freqMHz -5 -4 -3 -2 -1 1 2 3 4 5
ampFreqResp
1.0000
0.2887
phzFreqRespDeg
Mark Webster, Intersil

9. Frequency Domain Modulator
July 2000
doc.: IEEE /202
July 2000
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 -5 -4 -3 -2 -1 1 2 3 4 5
Freq (MHz)
A1ejq1
A2ejq2
A3ejq3
A5ejq5
A4ejq4
A6ejq6
A11ejq11
A7ejq7
A8ejq8
A10ejq10
A9ejq9
Barker
Spectrum
Mark Webster, Intersil
Mark Webster, Intersil

10. 2 Mbps Subcarrier Constellations
July 2000
doc.: IEEE /202
2 Mbps Subcarrier Constellations
July 2000
Mark Webster, Intersil
Mark Webster, Intersil

11. 5.5 Mbps CCK Mode: Time Domain Modulator
July 2000
5.5 Mbps CCK Mode:
Time Domain Modulator
Time Domain
Multiply
QPSK
time
time
4 Spreading
Codes
time
time
time
Mark Webster, Intersil

12. Frequency Domain Modulator
July 2000
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
A1ejq1
A2ejq2
A3ejq3
A5ejq5
A4ejq4
A6ejq6
A7ejq7
A8ejq8
2 Info
Bits
4 Codeword
Spectrums
Mark Webster, Intersil

13. 5.5 Mbps Codeword Subcarrier Spectrums
July 2000
Mark Webster, Intersil

14. 5.5 Mbps Subcarrier Constellations
July 2000
doc.: IEEE /202
5.5 Mbps Subcarrier Constellations
July 2000
QAM
Constellations
Mark Webster, Intersil
Mark Webster, Intersil

15. 11 Mbps CCK Mode: Time Domain Modulator
July 2000
11 Mbps CCK Mode:
Time Domain Modulator
Time Domain
Multiply
QPSK
time
time
64 Spreading
Codes
time
time
time
Mark Webster, Intersil

16. Frequency Domain Modulator
July 2000
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
A1ejq1
A2ejq2
A3ejq3
A5ejq5
A4ejq4
A6ejq6
A7ejq7
A8ejq8
6 Info
Bits
64 Codeword
Spectrums
Mark Webster, Intersil

17. 11 Mbps Subcarrier Constellations
July 2000
QAM
Constellations
Sub-Carriers
1, 3, 5, 7
Sub-Carriers
2, 4, 6, 8
Mark Webster, Intersil

18. Frequency Domain Modulator
July 2000
11 Mbps PBCC Mode:
Frequency Domain Modulator
Compute
Amp/Phz
of each
Subcarrier 8
8 Info
Bits
8 pt.
IFFT
P/S
A1ejq1
A2ejq2
A3ejq3
A5ejq5
A4ejq4
A6ejq6
A7ejq7
A8ejq8
Constellation Mapper Exists,
but is Complicated
Mark Webster, Intersil

19. OFDM DIRECTLY EMBRACES FREQUENCY DOMAIN SIGNALING
July 2000
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
BPSK
Pilot
Subcarriers
Data Sub-Carrier
Constellations
BPSK: 6, 9 Mbps
QPSK: 12, 18 Mbps
16 QAM: 24, 36 Mbps
64 QAM: 48, 54 Mbps
Cyclically
Extends
Sub-Carriers
Mark Webster, Intersil

20. 802.11a OFDM Symbol . . . Equivalent to 64 Chip Codewords July 2000
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
July 2000
Cyclic Extensions Can Be
Used on Any Codeword
Original
Codeword
Smoothly Extends
Sub-Carriers in Time
Cyclically-
Extended
Codeword
Mark Webster, Intersil