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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: [Designer’s Guide to TG3a UWB Link Margins] Date Submitted: [13 January 2004; r1 on 18 January 2004; r2 on 21 January 2004] Source: [Kazimierz “Kai” Siwiak] Company [TimeDerivative, Inc.]

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

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  1. 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; r2 on 21 January 2004] Source: [Kazimierz “Kai” Siwiak] Company [TimeDerivative, Inc.] Address [PO Box 772088, Coral Springs, FL 33071] Voice [+1-954-937-3288] E-Mail: [ k.siwiak@ieee.org ] 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. K. Siwiak / TimeDerivative, Inc.

  2. System Designer’s Guide to UWB Link Margins Kai Siwiak IEEE Submission Vancouver IEEE January 2004 K. Siwiak / TimeDerivative, Inc.

  3. Revisions I’ve gotten many enquiries indicated that more information is desired on this topic. These revisions add information. • rev 1: • added more detail on OATS signals • rev 2: • DS-UWB signal shape on OATS added • more detail added to the multipath losses issue • embedded antenna losses estimated • modulation efficiency added • statistical design for reliability K. Siwiak / TimeDerivative, Inc.

  4. 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 K. Siwiak / TimeDerivative, Inc.

  5. 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 for 50% reliable link • Additional factors like realistic antennas (5 dB?) and statistical link design (5 to 9 dB?) can detract further from the link The actual link is margin-starved! • System Designers’ dilemma: “How good is the link, really?” K. Siwiak / TimeDerivative, Inc.

  6. 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 K. Siwiak / TimeDerivative, Inc.

  7. 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 K. Siwiak / TimeDerivative, Inc.

  8. Effect of FEC in the Free Space [Selection Criteria Scenario] Eb/N0 pre-FEC operating point • 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 with FEC BER BPSK or QPSK Eb/N0 K. Siwiak / TimeDerivative, Inc.

  9. EIRP: The FCC Way Selection 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 (Open Air Test Site) • 4.7dB accounts for a constructive coherently adding ground reflection (in FCC semi-anechoic chamber) • The net effect similar for both systems because receiver BW is 1 MHz K. Siwiak / TimeDerivative, Inc.

  10. PSD Measurements on FCC OATS test sense antenna ground to 3 m: search for peak D= (h1-h2)2+d2 R= (h1+h2)2+d2 DUT D=R-D ED = “1” D D = 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] ER = “0.718” 1 m metal ground plane R 3 m K. Siwiak / TimeDerivative, Inc.

  11. 2 128x3 carriers in fully anechoic chamber amplitude 1.5 need to de-rate EIRP by this amount: 4.7 dB! 2 M 1 i amplitude 1.5 0.5 S 1 0 i 0 20 40 60 80 100 120 140 i/3 frequency 0.5 128x3 carriers on FCC semi-anechoic chamber or OATS 0 0 20 40 60 80 100 120 140 frequency i/3 MBOFDM Signal “Spectrum Analyzer Signal” on FCC OATS K. Siwiak / TimeDerivative, Inc.

  12. Moving the Sense Antenna just moves around the Peaks ... a few cm up 2 amplitude 1.5 need to de-rate EIRP by this amount: 4.7 dB! S 1 i 2 amplitude 0.5 1.5 0 0 20 40 60 80 100 120 140 frequency S 1 i i/3 11 dB peak to dip ... this is an indicator of Rayleigh fading problem 0.5 a few cm down ... 0 0 20 40 60 80 100 120 140 frequency i/3 K. Siwiak / TimeDerivative, Inc.

  13. DS-UWB Signal PSD on FCC OATS need to de-rate EIRP by this amount: 4.7 dB! DS-UWB signal, free space DS-UWB signal on FCC OATS 2 2 amplitude amplitude 1.5 1.5 1 1 0.5 0.5 0 0 3 3.5 4 4.5 5 5.5 3 3.5 4 4.5 5 5.5 frequency, GHz frequency, GHz K. Siwiak / TimeDerivative, Inc.

  14. 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 K. Siwiak / TimeDerivative, Inc.

  15. Path Loss • TG3a channel model does not consider propagation attenuation properly • 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 Reference: 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. K. Siwiak / TimeDerivative, Inc.

  16. Operation In Fading • Actual average antenna loss for “0 dBi” antenna: 1.8 dB • Typical embedded antenna losses are in the 5 to 8 dB range • 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] K. Siwiak / TimeDerivative, Inc.

  17. MBOFDM and DS-UWB Statistics 1 25% of the signal levels are: 6 dB below mean for MBOFDM 1 dB below mean for DS-UWB 5 dB difference 0.25 5 dB 0.1 8 dB 10% of the signal levels are: 9.5 dB below mean for MBOFDM 1.5 dB below mean for DS-UWB 8 dB difference Probability the signal energy is less than X Rayleigh faded signal need to operate somewhere below the 25% signal loss level for FEC to operate properly 1.4 GHz BW 4 MHz BW 0.01 -20 -5 -15 -10 0 5 X, signal energy relative to mean level, dB K. Siwiak / TimeDerivative, Inc.

  18. Operating in Fading • A sufficient fraction of the signal energy must be above a given level so that FEC can work [all systems] • In OFDM: • the faded components must be sufficiently interleaved so that the fading looks random rather than “burst error” • enough tones must be available for FEC to work • DS-UWB spreads all bits over all BW K. Siwiak / TimeDerivative, Inc.

  19. Signal Above the Mean Level • MBOFDM can (but doesn’t) use more bits on stronger tones (“water filling” - a very complex problem) • energy is recovered, but not utilized! • DS-UWB data is spread across entire band • all energy contains all data K. Siwiak / TimeDerivative, Inc.

  20. 1 10-1 10-2 16-PAM 8-PAM 4-PAM 10-3 Bit error probability 10-4 2-BOK/PAM 4-BOK 8-BOK 16-BOK 64-BOK 10-5 10-6 -2 0 2 4 6 8 10 12 14 16 SNR per bit, dB Modulation Efficiencies in AWGN Because the link is starved for margin, use of modulation with the highest efficiency is important ... M-BOK modulations tend to better efficiency as M increases, PAM and QAM modulations tend to become less efficient as M increases [Source: K. Siwiak, D. McKeown, Ultra-wideband Radio Technology, Wiley: UK, 2004] K. Siwiak / TimeDerivative, Inc.

  21. Modulation Efficiencies in AWGN Better Worse [Source: K. Siwiak, D. McKeown, Ultra-wideband Radio Technology, Wiley: UK, 2004] K. Siwiak / TimeDerivative, Inc.

  22. Summary: Link Margin Effect * lesser values also claimed ** various proposal report between about 5 and about 6 dB of “margin” at 10 m and 110 Mb/s K. Siwiak / TimeDerivative, Inc.

  23. More dBs needed: Statistical Link Design • “Average” stated so far; “the 50% probability that the link will be closed” • If we require more than 50% (90% typically) probability that a link be successful in some scenario then: • need to add zs dB • s is the lognormal standard deviation in dB, s=4 dB for shadowing (more for other effects) [Source: K. Siwiak, Radiowave Propagation and Antennas for personal Communications, Second Ed., Artech: MA, 1998] K. Siwiak / TimeDerivative, Inc.

  24. Conclusions • UWB link is MARGIN-STARVED • Other issues remain: real antennas (5 dB?) and statistical link design (5 to 9 dB?) • 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 K. Siwiak / TimeDerivative, Inc.

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