Interference Analysis of MB-OFDM, DS, and Gated/Non-Gated Noise

1. Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [Results of Interference Analysis & Testing of MB-OFDM, DS, and Gated / Non-Gated Noise ] Date Submitted: [13 November 2003] Source: [John McCorkle] Company [XtremeSpectrum] Address [8133 Leesburg Pike Vienna VA 22182] Voice:[1-703-269-3000] FAX: [1-703-749-0249], E-Mail: [john@XtremeSpectrum.com ] Abstract: [Tests were very carefully done with multiple observers to find out, for equal levels of interference, what the relative power was between DS and MB-OFDM waveforms. Data shows MB-OFDM is substantially more interfering-- 5 to 9 dB, not 1 dB. Regulators are very unlikely to accept "full power" MB-OFDM in the light of these results and industry pressure. Range performance numbers presented by MBOA must be cut by ~1/2 (5.2 dB) for baseline 3-hop mode and by ~1/3 (9.4 dB) for 7-hop mode. Range is cut by an additional 1/2 at 480 Mbps due to Rayleigh fading (i.e. by ~1/4 (11 dB) for baseline 3 hop and by ~1/6 (15 dB) for 7 hop). This difference is huge and makes the DS far more forgiving in terms of implementation losses, or gives DS much higher performance capability. Most critical, it that DS is far less interfering and will be found far more acceptable world-wide by both regulators and the RF industry.] Purpose: [Provide technical information critical in choosing between competing proposals] 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. John McCorkle, XtremeSpectrum

2. UWB Interference and Regulatory Compliance • After the initial proposal of MB-OFDM, some TG members expressed concern about its compliance with FCC rules • Frequency hoppers were not tested or analyzed in the FCC rulemaking process • Rules seem to imply that FCC compliance testing will require stopping any FH – thus a 5-10 dB reduction in transmitted power • No clarification has been provided by the FCC either directly or through the MBOA John McCorkle, XtremeSpectrum

3. Analysis Requested by FCC • Primary concern is that the FCC would determine that FH-UWB results in higher interference levels than those anticipated by R&O • If so, it would be difficult for the FCC to change rules to accommodate MB-OFDM – even if it wanted to • Significant opposition to initial UWB by other users • Any move to loosen rules would be opposed • Therefore, the FCC encouraged the IEEE to evaluate interference potential of any proposed standard • Initial analysis indicated that MB-OFDM interference is worse than AWGN or DS-CDMA at same power John McCorkle, XtremeSpectrum

4. MB-OFDM Interference is Identical to that of Prohibited GatedUWB Signals • Further analysis now indicates that FH-UWB leads to interference levels that exceed those anticipated by FCC in R&O • Followed analysis approach used by NTIA • MB-OFDM has interference characteristics identical to gated UWB signals – specifically prohibited by the rules unless their transmit power is reduced • Clear indication that these interference levels exceed those considered acceptable in the R&O • Gated UWB signals with the same interference characteristics as MB-OFDM would require 5-10+ dB power reduction to comply with existing rules John McCorkle, XtremeSpectrum

5. Gated UWB Interference Restricted by UWB Rules • NTIA and FCC wrote the UWB rules to differentiate between gated and non-gated UWB signals • Gated signals are required to reduce transmit power to protect potential victims from excessive pulsed interference • Part 15.521 (d): “If pulse gating is employed where the transmitter is quiescent for intervals that are long compared to the nominal pulse repetition interval, measurements shall be made with the pulse train gated on.” • MB-OFDM is a hybrid waveform that appears as a non-gated signal in its full FH-spread bandwidth, but appears as a gated signal to any victim receivers • Escapes classification as a gated UWB signal under rules • Still results in the same interference potential as a gated signal that has not applied the required power reduction John McCorkle, XtremeSpectrum

6. MB-OFDM Signal Appears as a Gated Signal to Potential Victim Receivers John McCorkle, XtremeSpectrum

7. NTIA Interference Analysis • Extensive analysis performed by the NTIA & FCC • Actual testing of UWB transmitters with specific receivers • Analytical analysis for general & specific waveforms/systems • Interference characterization through simulated and measured Amplitude Probability Distribution (APD) analysis • APDs form a critical part of the NTIA analysis for victim receivers, particularly when the interference has non-Gaussian characteristics (like MB-OFDM): "The APD gives insight to the potential interference from UWB signals in a wide variety of receiver bandwidths and UWB characteristics, especially when the combination of interferer and victim produces non-Gaussian interference in the victim receiver. If the interference is Gaussian, victim receiver performance degradation is correlated to the interfering signal average power alone and there is no need for further analysis using the APD. If the interference is non-Gaussian or sinusoidal, information in the APD may be critical to quantifying its effect on victim receiver performance degradation.” -- NTIA Special Publication 01-383, January 2001, [emphasis added] John McCorkle, XtremeSpectrum

8. APD Analysis for DS-CDMA and MB-OFDMM Amplitude Probability Distribution in 50 MHz BW, 250 us Observation 20 AWGN DS - Root-Raised Cosine OFDM3 15 OFDM7 OFDM13 10 dB 5 Note: The OFDM Signals have non-Gaussian APDs that indicate large amplitudes with higher probability than for DS-UWB or AWGN 0 -5 -10 .001 0.01 0.05 0.1 0.2 0.37 Probability of exceeding ordinate John McCorkle, XtremeSpectrum

9. APD Analysis for MB-OFDM & Gated DS-CDMAM Amplitude Probability Distribution in 50 MHz BW, 250 us Observation 20 11% Gated DS OFDM7 11% Gated AWGN AWGN 15 Note: The 11% Gated DS would be specifically prohibited by the UWB rules unless power is reduced by 9.6 dB 10 dB 5 0 Note: The OFDM-7 Signal has the same APD and interference properties as the prohibited gated DS UWB signal -5 -10 .001 0.01 0.05 0.1 0.2 Probability of exceeding ordinate John McCorkle, XtremeSpectrum

10. APD Analysis Conclusions • In the initial rulemaking, the FCC only studied signals that continuously occupied a single frequency band • Restrictions on gated signals only effective for such signals • MB-OFDM does not meet this criterion • APD analysis shows that MB-OFMD has identical interference properties as gated UWB signals that are specifically prohibited by the existing rules • An FCC rule change or interpretation to accommodate MB-OFDM or other FH-UWB waveforms would potentially undermine the effectiveness of the rules in preventing harmful interference • Would require an FNPRM & public proceedings to effect any rule change which might permit MB-OFDM in even a limited form • Changes would certainly be opposed by UWB opponents • ETSI submission already noting increased interference from FH (Draft TR 101 994-1 (2003-10), Comments by Vodaphone) John McCorkle, XtremeSpectrum

11. Testing Introduction • Last week Motorola and XtremeSpectrum and others Tested Digi-Cipher II C-band • Tests were at Motorola BCS C-Band “antenna farm” in San Diego • Joint participation included completing setup, all calibration, all equipment checks, and all measurements • Gated-Noise measurements were done on the first day • Channel at 3.88 GHz had 25 Mbps and used 3/4 rate FEC • Satellite disappeared partway thru the next day • OFDM measurements made at end of second day and were more robust • More stable satellite (0.11 dB peak-to-peak over measurement time) • Channel at 3.82 GHz had 19.9 Mbps and used 3/4 rate FEC • More carefully done • Double checks against continuous OFDM noise between every two measurements • Two observers had two days of practice • Results were similar to previous tests with Video-Cipher Analog C-Band • Claims had been made that digital systems would be less effected • Results showed significant difference between MB-OFDM and DS-UWB John McCorkle, XtremeSpectrum

12. Comparison To Simulation Results Presented Previously • Simulation results presented previously appear to have had two flaws • Simplifications did not account for everything - multiple FEC, interleaver, characteristics of MPEG break down, etc. • Background noise level was so high that the TV was already broken before interference was added • Wrong part of FEC curve • Masking any difference between different types of interference. • In these tests, everything was real -- real SNR, real receiver, real interleaver, real FEC, real MPEG, real everything, plus real MB-OFDM, noise and DS-UWB. John McCorkle, XtremeSpectrum

13. Test Setup at San Diego BCS Indoor(near antenna) Pwr-Supply Port-Select Variable Duty Cycle Pulse Gen RF Switch RF Switch -10dB coupler Var Atten -10dB coupler Noise Gen AMIQ 10 MHz RBW R&S Spec Analyzer 6 GHz BW Realtime TEK SCOPE LPF LPF OFDM XSI UWB SMIQ Antenna Media Lab 3.7- 4.2 GHZ LNB 8 MHz RBW Agilent Spec Analyzer Splitter Video Display Digi-Cipher II C-Band RCVR Outdoor (antenna farm) John McCorkle, XtremeSpectrum

14. Base-band Filter to 82.5MHz Base- band Samples AMIQ sample-and- Decimation (i.e., ~20 Samples @ @ 528 hold compensation (factor 1/5) subcarriers) 105.6 MHz MHz OFDM Signal Generation - Signal bandwidth reduced from 528MHz to ~82MHz for AMIQ test signal generator - Equivalent to selecting a slice of the original 528MHz spectrum for in-band interference tests John McCorkle, XtremeSpectrum

15. OFDM And DS Noise Spectrum In 10 MHz RBW John McCorkle, XtremeSpectrum

16. APD Plots For Gated-AWGN, Gated-High-PRF Pulsed UWB, and Gated-OFDM – ALL have the Same Statistics Amplitude Probability Distribution in 50 MHz BW, 250 us Observation 20 11% Gated DS OFDM7 11% Gated AWGN AWGN 15 Note: The 11% Gated DS would be specifically prohibited by the UWB rules unless power is reduced by 9.6 dB 10 dB 5 0 Note: The OFDM-7 Signal has the same APD and interference properties as the prohibited gated DS UWB signal -5 -10 .001 0.01 0.05 0.1 0.2 Probability of exceeding ordinate John McCorkle, XtremeSpectrum

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19. Test Results Results & Trends Matched “Theory” • Noise, non-hopped continuous-OFDM, and DS were all ~ equal • Affect was less than duty-cycle for short bursts (e.g. 1,2,3 sequence) • Affect moved upward towardduty-cycle with longer bursts(e.g. 1,1,2,2,3,3) • Results are consistent with earlier measurements using Video Cipher (analog) receiver • MB-OFDM is substantially more interfering than DS • 5 dB worse for baseline 3-hop with 1,1,2,2,3,3 sequence • 4 dB worse for 3-hop with 1,2,3 sequence • 9 dB worse for 7 hop John McCorkle, XtremeSpectrum

20. Implications Of These Results On Performance • MB-OFDM transmitter power must be reduced by at least 5 dB (baseline 3-hop with two piconets mode) • This power reduction equalizes DS and MB-OFDM coexistencewith existing systems (i.e. equalizes the interference potential) • This power reduction brings the interference in line with what the FCC contemplated • MB-OFDM performance is reduced by the lower power • By 5 dB in baseline mode • By 9 dB in its “upgraded” 7-hop mode John McCorkle, XtremeSpectrum

21. Add MB-OFDM Rayleigh Fading Loss • MB-OFDM has a fundamental physics shortfall relative to DS • Due to Rayleigh fading on each carrier and inability of FEC to correct • Each carrier is a narrowband radio, ~25% are faded by 6 dB or more • Shortfall grows as data rate increases -- less powerful FEC at high rates • Shortfall of MB-OFDM relative to DS is 6 dB at 480 Mbps • MB-OFDM cannot simultaneously get both performance and multi-piconet capability at higher data rates • Eliminating hopping would allow stronger FEC, combating Rayleigh fades • BUT… MB-OFDM gets it multi-piconet capability by hopping • Eliminating hopping eliminates its multi-piconet capability • Eliminating hopping has severe hardware complexity impact • 3X more instantaneous bandwidth, 3X faster ADC, 3X faster DAC, 3X faster FFT • DS gives both multi-piconet and best range at highest data rates • Uses codes for multi-user • Uses full UWB to eliminate Rayleigh fades • Uses RAKE to collect multipath energy • Uses low peak-to-average signal minimize interference potential • All scale to highest data rates John McCorkle, XtremeSpectrum

22. Summary - Conclusions • Tests were very carefully done with multiple observers • Data shows MB-OFDM is substantially more interfering • 5 to 9 dB, not 1 dB • Regulators are very unlikely to accept "full power" MB-OFDM in the light of these results and industry pressure • Range performance numbers presented by MBOA must be cut • By ~1/2 (5.2 dB) for baseline 3-hop mode • By ~1/3 (9.4 dB) for 7-hop mode • Range is cut by an additional 1/2 at 480 Mbps due to fading • ~1/4 (11 dB) for baseline 3 hop • ~1/6 (15 dB) for 7 hop • 5 to 9 dB at 110 Mbps and 11 to 15 dB at 480 Mbps is huge difference • makes the DS far more forgiving in terms of implementation losses • Gives DS much higher performance capability John McCorkle, XtremeSpectrum