1. Submission Title: [Harmonizing-TG3a-PHY-Proposals-for-CSM]
March 2004
Project: IEEE P Working Group for Wireless Personal Area Networks (WPANs)
Submission Title: [Harmonizing-TG3a-PHY-Proposals-for-CSM]
Date Submitted: [18 March 2004]
Source: [Matt Welborn] Company [Motorola]
Address [8133 Leesburg Pike Vienna, VA USA]
Voice:[ ],
Re: []
Abstract: [A proposal for a common frequency plan for DS-UWB and MB-OFDM to enable a common signaling mode]
Purpose: [Provide technical information to the TG3a voters regarding a possible common signaling mode compromise]
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
Welborn Motorola

2. Outline Goals of harmonizing Specific proposal Enable interoperability
March 2004
Outline
Goals of harmonizing
Enable interoperability
Maximize performance
Minimize complexity
Specific proposal
Frequency plan
FEC
Welborn Motorola

3. Multiple Modes in a Single PHY
March 2004
Multiple Modes in a Single PHY
A single PHY with multiple modes to provides a more complete solution for TG3a
A base mode that is required in all devices, used for control signaling & data traffic (CSM)
Beacons and control signaling
9.2 Mbps data rate, higher rates possible
Higher rate modes also required to support 110 & 200+ Mbps:
Compliant device can implement either DS-UWB or MB-OFDM for higher rate modes
Provides a wider range of technical options for UWB applications
Welborn Motorola

4. Frequency Plan for Data Modes
March 2004
Frequency Plan for Data Modes
Common frequency plan for all modes
Based on common, cheap 26 MHz cell phone crystal
Minimal impact to existing MB-OFDM & DS-UWB proposals
MB-OFDM: use 572 MHz band spacing
572 MHz = 22 x 26 MHz
Three bands between 3.1 & 4.8 GHz
12 bands total (4 band groupings)
DS-UWB: use 4 different chip rates offset by 13 MHz each
CSM center frequency is 3978 MHz
Same as band #2 center for both MB-OFDM and DS-UWB
CSM chip rate is 3978 / 9 = 442 MHz
Welborn Motorola

5. What Does CSM Look Like? One of the MB-OFDM bands!
March 2004
What Does CSM Look Like? One of the MB-OFDM bands!
Proposed Common Signaling Mode Band
(500+ MHz bandwidth)
9-cycles per BPSK “chip”
DS-UWB Low Band
Pulse Shape (RRC)
3-cycles per BPSK “chip”
3978
Frequency (MHz)
3100
4900
MB-OFDM (3-band)
Theoretical Spectrum
Welborn Motorola

6. Processing Rates for Data Modes
March 2004
Processing Rates for Data Modes
DS-UWB uses 1326 MHz chip rate = 1/3 of 3978 MHz
MB-OFDM uses 572 MHz band center spacing
Increase of ~8% over original 528 MHz centers
ADC, DAC, FFT 8% faster clock speed
Removes need to transmit guard tones, still > 500 MHz BW
Increases transmit power by 0.34 dB
12 bands total (4 groupings of 3 bands)
Center frequencies: (n+1) MHz, n=1:12
Three bands between 3.1 & 4.9 GHz
One grouping still overlaps UNII
Places center of band #2 at 3978 MHz (will be used for CSM)
Welborn Motorola

7. Analysis of Two FEC Options
March 2004
Analysis of Two FEC Options
CSM & both PHY modes need a common code
k=7 or k=6 convolutional code?
k=6 decoder is half the complexity of k=7 decoder
Viterbi decoder is a significant portion of the baseband complexity
What is the performance difference?
Gain is important at low rate and when punctured to high rates
Gain is important in AWGN, but more so in fading channel
K=7 code has more gain in AWGN – how much?
Multipath performance depends on code & diversity
MB-OFDM combines FEC with tone diversity at 110 Mbps
Which is better: 1/3 FEC with 2x diversity or ½ FEC with 3x diversity?
Welborn Motorola

8. Code Performance in AWGN
March 2004
Code Performance in AWGN 2 3 4 5 6 7 8 9 10 -9 -8 -7 -6 -5 -4 -3 -2 -1
BER Performance of k=7 & k=6 codes
BPSK
R=11/32
R=5/8
R=3/4
K6,R=1/2
Eb/No (dB)
BER
K=7 code is 0.6 dB better than k=6 code in AWGN
K=7 code punctured to rate ¾ gives 4.3 dB gain
Welborn Motorola

9. Diversity Improves Code Performance
March 2004
Diversity Improves Code Performance
Comparison of K=7 code with 2x diversity and k=6 code with 3x diversity 10 -3
2X+K7
3X+K6
AWGN+K7 10 -4
2x diversity using /32 k=7 code in faded channel
0.7 dB 10 -5
BER 10 -6
K=7 rate 11/32 code in AWGN 10 -7
3x diversity using rate ½ k=6 code in faded channel 10 -8 4
4.5 5
5.5 6
6.5
Eb/No (dB)
K=6 code with 3x diversity gives 0.7 dB better code performance in fading environment than k=7 with 2x
Welborn Motorola

10. Conclusion of FEC Analysis
March 2004
Conclusion of FEC Analysis
For 110 Mbps mode in multipath, it is better to use more diversity and less FEC
Rate ½ k=6 code with 3x diversity improves performance by 0.7 dB in multipath
Rate ½ k=6 decoder is half the complexity
Over 1 dB better performance at 110 Mbps
Includes 0.34 dB increased transmit power
Lower complexity & power consumption
Reduction in Viterbi complexity more than compensates for increased bandwidth
Benefits both DS-UWB and MB-OFDM modes
Welborn Motorola

11. March 2004
Increased Symbol Rate
If we increase the bandwidth, the MB-OFDM symbol length is shorter: ~224 ns
Increase symbol rate to 3.3 MHz
3.3 MHz * 200 bits/symbol = 660 Mbps raw bit rate
110 Mbps mode: 3x tone diversity with rate ½ FEC
205 Mbps mode: 2x tone diversity with r=5/8 code
495 Mbps mode: 1x tone diversity with r=¾ code
Other optional modes still available
Increased symbol rate and shorter symbol still result in longer cyclic prefix
70 ns cyclic prefix plus 10 ns guard time
Welborn Motorola

12. Overview of CSM Signal Uses 3978 MHz center frequency
March 2004
Overview of CSM Signal
Uses 3978 MHz center frequency
Same as band 2 for both MB-OFDM and DS-UWB
Uses 442 MHz “chip rate” for spread BPSK modulation
Uses length 24 ternary spreading code
Unique codes for each piconet channel
Symbol interval is 55 ns – ISI will be negligible
Uses rate ½ k=6 convolutional code
Code is common to CSM, DS-UWB and MB-OFDM
Data rate is 9.2 Mbps
442 MHz / 24 * (1/2 code) = 9.2 MHz
Higher rate possible with a shorter spreading code (e.g. L=12)
Welborn Motorola

13. March 2004
Link Budget for CSM
Welborn Motorola

14. Conclusions A plan to harmonize the two existing PHY proposals
March 2004
Conclusions
A plan to harmonize the two existing PHY proposals
Common frequency plan – Band #2 for CSM
Common FEC mode – also shared with CSM
Reduced complexity for DS-UWB and MB-OFDM implementations
Lower complexity than baseline MB-OFDM receiver
Increased performance in multipath
Enables a shared band for common signaling
A single PHY with multiple modes
CSM, DS-UWB and MB-OFDM
Welborn Motorola