1. May 2005
Project: IEEE P Working Group for Wireless Personal Area Networks (WPANs)
Submission Title: [MB-OFDM Proposal Update]
Date Submitted: [ 11 May, 2005]
Source: [C. Razzell] Company [Philips]
Address [1151 McKay Drive, San Jose, CA 95131]
Voice:[ ], FAX: [ ],
Re: [TG3a Down selection Process]
Abstract: [Contains technical details of Merged Proposal #1]
Purpose: [Provides motivation and justification for the MB-OFDM proposal under consideration]
Notice: This document has been prepared to assist the IEEE P It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein.
Release: The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P
C. Razzell et al

2. MB-OFDM Proposal Summary
May 2005
MB-OFDM Proposal Summary
C. Razzell
C. Razzell et al

3. Contents: Spectrum mask requirements Why OFDM is preferred
May 2005
Contents:
Spectrum mask requirements
Why OFDM is preferred
Time-frequency codes for additional spreading
MB-OFDM PHY details and performance
Summary of benefits compared with direct sequence approach
Conclusions
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4. Spectrum Mask Requirements (USA)
May 2005
Spectrum Mask Requirements (USA)
Max. Total Tx power = log( ) + 30 = – 2.5dBm
For 10m 4GHz need approx. –10dBm
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5. Ultra wideband signals using OFDM
May 2005
Ultra wideband signals using OFDM
Orthogonal Frequency Division Multiplexing
Can efficiently multiplex many sub-carriers to occupy ~500MHz of spectrum
OFDM intrinsically deals with multipath issues by keeping the symbol rate low (e.g., 3.2MHz)
Technology similar to a
But only supports QPSK, not 16-QAM nor 64-QAM
Uses less ADC precision and lower arithmetic precision than a/g signal processing
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6. Why OFDM is preferred(1)
May 2005
Why OFDM is preferred(1)
OFDM is spectrally efficient:
IFFT/FFT operation ensures that sub-carriers do not interfere with one other.
Since the sub-carriers do not interfere, the sub-carrier can be brought closer together  High spectral efficiency.
OFDM has an inherent robustness against narrowband interference:
Narrowband interference will affect at most a couple of tones.
Do not have to drop the entire band because of narrowband interference.
Erase information from the affected tones, since they are known to be unreliable. Use FEC to recover the lost information.
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7. Why OFDM is preferred(2)
May 2005
Why OFDM is preferred(2)
OFDM has excellent robustness in multi-path environments.
Zero prefix preserves orthogonality between sub-carriers --- linear convolution with the c.i.r. is made to look like circular convolution
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8. Why OFDM is preferred(3)
May 2005
Why OFDM is preferred(3)
OFDM has excellent robustness in multi-path environments:
Allows receiver to capture multi-path energy more efficiently.
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9. Why OFDM is preferred(4)
May 2005
Why OFDM is preferred(4)
Ability to comply with worldwide regulations:
Channels and tones can be turned on/off dynamically to comply with changing regulations.
Can arbitrarily shape spectrum in software with a resolution of ~4 MHz.
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10. Time-frequency codes for additional spreading
May 2005
Time-frequency codes for additional spreading
The FCC requires that UWB systems transmit with a bandwidth of >500MHz at all times
Direct generation of OFDM signals of ~500MHz bandwidth is feasible with current CMOS technology
However, 500MHz bandwidth alone is not optimum
Tx power is limited to –14.3dBm under FCC rules
Limited frequency diversity
Desire a method to multiply the occupied bandwidth without impacting signal processing requirement…
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11. Example OFDM UWB Tx chain
May 2005
Example OFDM UWB Tx chain
128 pt IFFT in 312.5ns
528 MHz
507.35MHz
128 pt IFFT, 100 QPSK data tones, 12 pilots
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12. MB-OFDM uses sequenced multiband approach to enhance OFDM
May 2005
MB-OFDM uses sequenced multiband approach to enhance OFDM
Total wideband power is
log10(3) +
10log10(122) +
10log10(4.125) =
-9.5dBm
Occupied bandwidth (and power) multiplied by a factor 3 with almost no signal processing overhead!
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13. Time Frequency Codes for Multiple Access
May 2005
Time Frequency Codes for Multiple Access
Typical methods for achieving multiple access: Spreading (CDMA), Coding
In MB-OFDM, an additional method is used: Time-Frequency (TF) Codes:
Time-Frequency Codes:
Spread information over all three bands in a given period of time.
Designed such that (on average) only 1/3 of the symbols would collide (FEC code can compensate for the collisions).
Performance is governed by SIR = (Psig/Pint) (W/R).
In realistic multi-path conditions: “BW expansion = (W/R) is all that matters”.
Systems with same BW expansion have similar multiple piconet capability.
Channel Number
Preamble Pattern
Mode 1 DEV: 3-band Length 6 TFC 1 2 3 4
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14. Overview of Multi-band OFDM
<month year>
doc.: IEEE <doc#>
May 2005
Overview of Multi-band OFDM
Key Idea #1:
Divide the spectrum into bands that are 528 MHz wide.
Advantages:
Transmitter and receiver process smaller bandwidth signals (528 MHz).
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<author>, <company>

15. Overview of Multi-band OFDM
<month year>
doc.: IEEE <doc#>
May 2005
Overview of Multi-band OFDM
Key Idea #2:
Interleave OFDM symbols across all bands.
Advantages:
Exploits frequency diversity.
Provide robustness against multi-path / interference.
Same transmit power as if the entire band is used.
C. Razzell et al
<author>, <company>

16. Overview of Multi-band OFDM
<month year>
doc.: IEEE <doc#>
May 2005
Overview of Multi-band OFDM
Key Idea #3:
Insert a zero-padded prefix before IFFT output:
Advantages:
Prefix provides robustness against multi-path even in the worst case channel environments.
C. Razzell et al
<author>, <company>

17. Overview of Multi-band OFDM
<month year>
doc.: IEEE <doc#>
May 2005
Overview of Multi-band OFDM
Key Idea #4:
Insert a Guard Interval between OFDM Symbols:
Advantages:
Guard interval allows TX/RX sufficient time to switch between channels.
C. Razzell et al
<author>, <company>

18. System Parameters Info. Data Rate 110 Mbps 200 Mbps 480 Mbps
May 2005
System Parameters
Info. Data Rate
110 Mbps
200 Mbps
480 Mbps
Modulation/Constellation
OFDM, QPSK
OFDM, QPSK
FFT Size
128
Coding Rate (K=7)
R = 11/32
R = 5/8
R = 3/4
Frequency-domain Spreading No
Time-domain Spreading
Yes
Data Tones
100
Zero-padded Prefix
60.6 ns
Guard Interval
9.5 ns
Symbol Length
312.5 ns
Channel Bit Rate
640 Mbps
Multi-path Tolerance
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19. PLCP Frame Format PLCP frame format:
May 2005
PLCP Frame Format
PLCP frame format:
Rates : 55, 80, 110, 160, 200, 320, 400, 480 Mb/s.
Support for 55, 110, and 200 Mb/s is mandatory.
Preamble + Header = ms.
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20. Link Budget and Receiver Sensitivity
May 2005
Link Budget and Receiver Sensitivity
Assumption: BG#1, AWGN, and 0 dBi gain at TX/RX antennas.
Parameter
Value
Information Data Rate
110 Mb/s
200 Mb/s
480 Mb/s
Average TX Power
-10.3 dBm
Total Path Loss
64.2 dB 10 meters)
56.2 dB 4 meters)
50.2 dB 2 meters)
Average RX Power
-74.5 dBm
-66.5 dBm
-60.5 dBm
Noise Power Per Bit
-93.6 dBm
-91.0 dBm
-87.2 dBm
CMOS RX Noise Figure
6.6 dB
Total Noise Power
-87.0 dBm
-84.4 dBm
-80.6 dBm
Required Eb/N0
4.0 dB
4.7 dB
4.9 dB
Implementation Loss
2.5 dB
3.0 dB
Link Margin
6.0 dB
10.7 dB
12.2 dB
RX Sensitivity Level
-80.5 dBm
-77.2 dBm
-72.7 dB
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21. System Performance: Band Group #1
May 2005
System Performance: Band Group #1
The distance at which the Multi-band OFDM system can achieve a PER of 8% for a 90% link success probability is tabulated below:
Includes losses due to front-end filtering, clipping at the DAC, ADC degradation, multi-path degradation, channel estimation, carrier tracking, packet acquisition, etc.
Range*
AWGN
LOS: 0 – 4 m
NLOS: 0 – 4 m
NLOS: 4 – 10 m
RMS Delay Spread 25 ns
110 Mbps
20.5 m
11.4 m
10.7 m
11.5 m
10.9 m
200 Mbps
14.1 m
6.9 m
6.3 m
6.8 m
4.7 m
480 Mbps
8.9 m
2.9 m
2.6 m
N/A
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22. Signal Robustness/Coexistence
May 2005
Signal Robustness/Coexistence
Assumption: Received signal is 6 dB above sensitivity.
Values listed below are the required distance or power level needed to obtain a PER  8% for a 1024 byte packet at 110 Mb/s and BG #1.
Coexistence with b and Bluetooth is relatively straightforward because they are out-of-band.
Multi-band OFDM is also coexistence friendly with both GSM and WCDMA.
MB-OFDM has the ability to tightly control OOB emissions.
Interferer
Value
IEEE 2.4 GHz
dint  0.2 meter
IEEE 5.3 GHz
Modulated interferer
SIR  –9.0 dB
Tone interferer
SIR  –7.9 dB
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23. Zero IF Transceiver block diagram
May 2005
Zero IF Transceiver block diagram
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24. Brief Comparison with DS-UWB technology (1)
May 2005
Brief Comparison with DS-UWB technology (1)
Both technologies occupy similar bandwidth below 5GHz (~1.5GHz)
Tx power & link distance performance are therefore similar
MB-OFDM is a multiband technology
Allows cost-effective all-CMOS implementation
Improves feasibility of on-chip filtering for truly monolithic solutions
Reduces cost of total solution
System is robust to loss of one of the sub-bands
Due to a strong interferer
Due to application of a dynamic frequency selection algorithm
DS-UWB is a single-band technology
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25. Brief Comparison with DS-UWB technology (2)
May 2005
Brief Comparison with DS-UWB technology (2)
Multi-Band OFDM is an OFDM technology
Allows fine-grained adaptation of frequency spectrum shape for future regulatory compliance
Channel impulse response equalization comes essentially for free and is standard between implementations
Multiple levels of diversity are applied
Convolutional FEC
Time-domain spreading
Frequency domain spreading
Multiple companies have now shown silicon feasibility
All these combine to reduce impact of fading of individual sub-carriers
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26. Conclusions The industry has overwhelmingly opted to support
May 2005
Conclusions
The industry has overwhelmingly opted to support
MB-OFDM as the first major wireless PAN PHY
Inherent robustness to multi-path in all expected environments.
Excellent robustness to U-NII and other generic narrowband interference.
Ability to comply with worldwide regulations:
Channels and tones can be turned on/off dynamically to comply with changing regulations.
Can arbitrarily shape spectrum because the tones resolution is ~4 MHz.
C. Razzell et al

27. doc.: IEEE 802.15-<doc#>
<month year>
doc.: IEEE <doc#>
May 2005
Conclusions
Enhanced coexistence with current and future services:
Channels and tones can be turned on/off dynamically to coexist with other devices.
Scalability:
More channels can be added as RF technology improves and as capacity requirements increase.
Multi-band OFDM is digital heavy. Digital section complexity and power scales with improvements in technology node (Moore’s Law).
MB-OFDM meets all the TG3a PAR requirements and offers the best trade-off between the various system parameters.
We would welcome your support of this proposal!
C. Razzell et al
<author>, <company>

28. May 2005
Backup
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29. Complexity (numbers supplied by TI)
May 2005
Complexity (numbers supplied by TI)
Die size for PHY core:
Active CMOS power consumption for PHY core:
Process
Complete Analog*
Complete Digital
90 nm
3.0 mm2
1.9 mm2
130 nm
3.3 mm2
3.8 mm2
* Component area.
Process
TX 55 Mb/s
TX 110, 200 Mb/s
RX 55 Mb/s
RX 110 Mb/s
RX 200 Mb/s
90 nm
85 mW
128 mW
147 mW
155 mW
169 mW
130 nm
104 mW
156 mW
192 mW
205 mW
227 mW
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30. Frequency Synthesis Circuit-level simulation of frequency synthesis:
May 2005
Frequency Synthesis
Circuit-level simulation of frequency synthesis:
Nominal switching time = ~2 ns. Need to use a slightly larger switching time to allow for process and temperature variations.
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31. May 2005
Zero-padded Prefix
In a conventional OFDM system, a cyclic prefix is added to provide multi-path protection.
Cyclic prefix introduces structure into the TX waveform  structure in the signal produces ripples in the PSD.
In an average PSD-limited system, any ripples in the TX waveform will results in back-off at the TX (reduction in range).
Ripple in the transmitted spectrum can be eliminated by using a zero-padded prefix.
A Zero-Padded Prefix provides the same multi-path robustness as a cyclic prefix (60.6 ns of protection).
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32. Proposed OFCOM (United Kingdom) Emissions Mask for UWB
May 2005
Proposed OFCOM (United Kingdom) Emissions Mask for UWB
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33. Capacity vs. distance for UWB vs. WLAN
May 2005
Capacity vs. distance for UWB vs. WLAN
This area is ripe for exploitation
(Assumes 20MHz WLAN, 1GHz UWB bandwidth)
C. Razzell et al