Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)

January 2004

K. Siwiak / TimeDerivative, Inc.Slide 1

doc.: IEEE 802.15-04/0036r1

Submission

Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)

Submission Title: [Designer’s Guide to TG3a UWB Link Margins]Date Submitted: [13 January 2004; r1 on 18 January 2004]Source: [Kazimierz “Kai” Siwiak]Company [TimeDerivative, Inc.]Address [PO Box 772088, Coral Springs, FL 33071]Voice [+1-954-937-3288]E-Mail: [ [email protected] ]Re: [Link Margins for UWB from the system designer’s point of view]Abstract: [This contribution describes UWB system link margins from a “customer’s” point of view, and contrasts those margins with the SG3a / TG3a selection criteria. ]Purpose: [UWB Link margins in the selection process were determined for the purpose of comparing the relative merits of various UWB approaches. While suitable for that purpose, the results are optimistic for practical system designs. This contribution documents areas of additional practical link losses, and is a first step in practical link design. The additional losses are different for different UWB PHYs.]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.

January 2004


doc.: IEEE 802.15-04/0036r1

Submission

System Designers’ Guide to UWB Link Margins

Kai Siwiak

IEEE Submission

Vancouver IEEE January 2004

January 2004


doc.: IEEE 802.15-04/0036r1

Submission

Introduction

• The data rate and range capabilities of TG3a UWB PHYs derived from Selection Criteria 03/031r5 are excessively optimistic

• The Selection Criteria are designed for PHY selection and are NOT useful for system designs

• Several factors detracting from the link margin are presented here need to be considered

• Different results are seen for different UWB PHYs

January 2004


doc.: IEEE 802.15-04/0036r1

Submission

Selection Criteria is Not a Design Tool

The Selection Criteria Link Calculation is:

• Optimistic in “free space” by 5 to 11 dB depending on the variety of UWB used

• Optimistic by 11 to 17 dB in multipath

The actual link is margin-starved!

• System Designers’ dilemma: “How good is the link, really?”

January 2004


doc.: IEEE 802.15-04/0036r1

Submission

The Selection Criteria

• Selection criterion is a convenience– Was a suitable basis for 15.3a PAR– Calculation is almost “equal for all,” but artificial– Result is contrived, but generally adequate for PHY selection

• Link margin for design must be found more accurately– Noise BW error is corrected– EIRP is corrected based on FCC OATS measurement method– Multipath propagation model included– Effects of multipath must be included

January 2004


doc.: IEEE 802.15-04/0036r1

Submission

Channel Noise BW Error• Rb term in 03/031r5 is throughput, not channel BW

• True channel noise BW is Rb/(FEC Rate)

• Effect is: link SNR overestimated by the amount of the FEC rate

Rb FEC Rate

Channel rate

Link Margin Effect

DS-UWB 110 Mb/s 0.44 250 Mb/s -3.6dB

MBOFDM 110 Mb/s 11/32 320 Mb/s -4.6dB

January 2004


doc.: IEEE 802.15-04/0036r1

Submission

Effect of FEC in the Free Space [Selection Criteria Scenario]

• In AWGN FEC can be a net loss at low Eb/N0

• In multipath...– Need Monte Carlo

simulations– FEC drives BER

curve to the AWGN value

BE

R

Eb/N0

with FEC

BPSK orQPSK

Eb/N0 pre-FEC operatingpoint

January 2004


doc.: IEEE 802.15-04/0036r1

Submission

EIRP: The FCC WaySelection criterion uses -41.3 dBm/MHz

– FCC says:• Derate full anechoic chamber results by 4.7dB [see FCC R&O 02-48]• Or, measure in semi-anechoic chamber or certified OATS

– 4.7dB accounts for a constructive coherently adding ground reflection (in FCC semi-anechoic chamber)

– The net effect similar for both systems because receiver is 1 MHz BW

Wavelet Length

Direct + reflected Link margin effect

DS-UWB 0.22 m

(0.73 ns)

Add coherently thru 1 MHz FCC receiver filter, 20 log(1+0.718)

-4.7dB

MBOFDM 80 m

(242 ns)

Add coherently

20 log (1+0.718)

-4.7 dB

January 2004


doc.: IEEE 802.15-04/0036r1

Submission

PSD Measurements on FCC OATS

ED = “1”

ER = “0.718”

ground to 3 m: search for peak

3 m

1 m

= 32+22 - 3 = 0.61 m

if wavelet is shorter than about 0.61 m than the two paths add as “power,” otherwise, add as voltage: IF the test receiver BW is large enough! [It is NOT]

DUT

D

R

D= (h1-h2)2+d2

R= (h1+h2)2+d2

=R-D

metal ground plane

January 2004


doc.: IEEE 802.15-04/0036r1

Submission

MBOFDM Signal “Spectrum Analyzer Signal” on FCC OATS

0 20 40 60 80 100 120 1400

0.5

1

1.5

2

M i

i/3

0 20 40 60 80 100 120 1400

0.5

1

1.5

2

Si

i/3

128x3 carriers in full anechoic chamber

128x3 carriers on FCC semi-anechoic chamber or OATS

need to de-rate EIRP by this amount: 4.7 dB!

frequency

frequency

am

plit

ud

e

am

plit

ud

e

January 2004


doc.: IEEE 802.15-04/0036r1

Submission

Moving the Sense Antenna just moves around the Peaks

... a few cm up

a few cm down ...

0 20 40 60 80 100 120 1400

0.5

1

1.5

2

Si

i/3

0 20 40 60 80 100 120 1400

0.5

1

1.5

2

Si

i/3

need to de-rate EIRP by this amount: 4.7 dB!

11 dB peak to dip ... this is an indicator of Rayleigh fading problem

am

plit

ud

e

am

plit

ud

e

frequency

frequency

January 2004


doc.: IEEE 802.15-04/0036r1

Submission

DS-UWB Signal on FCC OATS ...

• Coherence length is the chip length, however:– Test receiver BW is 1 MHz, hence “coherence length”

is much larger than the chip length– Net result: reflection from OATS ground plane adds

coherently, even for impulses

• Signal behaves same as OFDM; same amplitude profile across the band!

• Actual effect on wide-band victim receivers much more benign for DS-UWB vs. OFDM, but EIRP is affected in the same way

January 2004


doc.: IEEE 802.15-04/0036r1

Submission

Path Loss• TG3a channel model does not consider

propagation attenuation• Median loss not taken into account

– it is NOT 1/r2 at 10m– “strongest path” breaks to 1/r3 near 3m

• One model (SBY model) of the additional loss is:– L=10 log(1-e-dt/d); where dt=3 m, d=10 m

– L=5.9 dB

Ref: K. Siwiak, H. Bertoni, and S. Yano, “Relation between multipath and wave propagation attenuation,” Electronic Letters, Vol. 39, No. 1, Jan. 9, 2003, pp. 142-143.

January 2004


doc.: IEEE 802.15-04/0036r1

Submission

Operation In Fading

• Actual average antenna gain: -1.8dB• Fading Effect on 10 m link

– DS-UWB: -1.0 dB [CDMA symbol energy is equally distributed across the 1.4 GHz signal, hence Rayleigh fading is never experienced even though selective fading could place a null at some frequencies for sinewave or long persisting signals]

– MBOFDM: -6.0 dB* [Slide 11 herein substantiates an 11 dB peak-to-dip value, or 11-4.7=6.3 dB mean-to-dip value for the “2-ray” multipath scenario on the FCC OATS site]

[ref: 15-03-0344-03-0003a]*[lesser values also claimed, however references are not available]

January 2004


doc.: IEEE 802.15-04/0036r1

Submission

Summary: Link Margin EffectShort Wavelet

(DS-UWB)

Long Wavelet (MBOFDM)

Noise BW (FEC rate) -3.6 dB -4.6 dB

EIRP (FCC) -4.7 dB -4.7 dB

Fading Loss -1.0 dB -6.0 dB*

Path loss at 10 m -5.9 dB -5.9 dB

Antenna Gain -1.8 dB -1.8 dB

Net Margin Deficit -17.0 dB -23.0 dB

After claimed +6dB -11 dB -17 dB

* lesser values also claimed

January 2004


doc.: IEEE 802.15-04/0036r1

Submission

Conclusions• UWB link is MARGIN-STARVED

– Other issues remain

• NEED to review available improvements– Modulation efficiency (need better efficiency than

BPSK/QPSK): M-BOK rather than M-QAM– FCC emission measurement method– Cost of diversity improvements need to be explored

• NEED to review the application space

Documents

Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)