March 2004

Welborn MotorolaSlide 1

doc.: IEEE 802.15-04/163r0

Submission

Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)Project: IEEE P802.15 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:[703-269-3000], E-Mail:[mwelborn@xtremespectrum.com]

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 P802.15. 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 P802.15.

March 2004

Welborn MotorolaSlide 2

doc.: IEEE 802.15-04/163r0

Submission

Outline

• Goals of harmonizing– Enable interoperability– Maximize performance– Minimize complexity

• Specific proposal– Frequency plan– FEC

March 2004

Welborn MotorolaSlide 3

doc.: IEEE 802.15-04/163r0

Submission

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

March 2004

Welborn MotorolaSlide 4

doc.: IEEE 802.15-04/163r0

Submission

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

March 2004

Welborn MotorolaSlide 5

doc.: IEEE 802.15-04/163r0

Submission

What Does CSM Look Like?One of the MB-OFDM bands!

MB-OFDM (3-band)Theoretical Spectrum

3978

3100 4900

Proposed Common Signaling Mode Band (500+ MHz bandwidth)9-cycles per BPSK “chip”

Frequency (MHz)

DS-UWB Low BandPulse Shape (RRC)3-cycles per BPSK “chip”

March 2004

Welborn MotorolaSlide 6

doc.: IEEE 802.15-04/163r0

Submission

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: 3406+572(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)

March 2004

Welborn MotorolaSlide 7

doc.: IEEE 802.15-04/163r0

Submission

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?

March 2004

Welborn MotorolaSlide 8

doc.: IEEE 802.15-04/163r0

Submission

Code Performance in AWGN

• 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

2 3 4 5 6 7 8 9 1010

10

10

10

10

10

10

10

10

-9

-8

-7

-6

-5

-4

-3

-2

-1BER 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

March 2004

Welborn MotorolaSlide 9

doc.: IEEE 802.15-04/163r0

Submission

Diversity Improves Code Performance

• K=6 code with 3x diversity gives 0.7 dB better code performance in fading environment than k=7 with 2x

4 4.5 5 5.5 6 6.510 -8

10 -7

10 -6

10 -5

10 -4

10 -3

Comparison of K=7 code with 2x diversity and k=6 code with 3x diversity

2X+K73X+K6AWGN+K7

K=7 rate 11/32 code in AWGN

2x diversity using 11/32 k=7 code in faded channel

3x diversity using rate ½ k=6 code in faded channel

0.7 dB

Eb/No (dB)

BER

March 2004

Welborn MotorolaSlide 10

doc.: IEEE 802.15-04/163r0

Submission

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

March 2004

Welborn MotorolaSlide 11

doc.: IEEE 802.15-04/163r0

Submission

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

March 2004

Welborn MotorolaSlide 12

doc.: IEEE 802.15-04/163r0

Submission

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)

March 2004

Welborn MotorolaSlide 13

doc.: IEEE 802.15-04/163r0

Submission

Link Budget for CSMCSM with rate-1/2 k=6 code

CSM with rate-1/2 k=6 code

FEC Rate 0.5 0.5Spreading Code Length 24.0 12.0Data Rate (Mbps) 9.2 18.3Theoretical Tx Power -14.8 -14.8Transmit Power (dBm) -16.7 -16.0Total Path Loss (dB) 64.4 64.4Received Power -81.1 -80.4Noise Power per Bit -104.4 -101.4Noise Figure 6.6 6.6Total Noise Power -97.8 -94.8Code Gain 4.8 4.8Required Eb/No 4.8 4.8Implementation Loss 2.5 2.5Link Margin at 10 m 9.4 7.1Sensitivity -90.5 -87.5

March 2004

Welborn MotorolaSlide 14

doc.: IEEE 802.15-04/163r0

Submission

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