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Interference Testing of MB-OFDM vs. DS & Noise: Results and Implications

Detailed findings from interference testing of MB-OFDM and DS waveforms, revealing significant differences in interference levels impacting range performance and regulatory acceptance. Results challenge existing simulation data, highlighting real-world implications for decision-makers in wireless technology.

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Interference Testing of MB-OFDM vs. DS & Noise: Results and Implications

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  1. Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [Results of Interference Testing of MB-OFDM, DS, and Gated and Non-Gated Noise ] Date Submitted: [11 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. McCorkle, XtremeSpectrum Inc.

  2. 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 McCorkle, XtremeSpectrum Inc.

  3. 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, plus real MB-OFDM, noise and DS-UWB. McCorkle, XtremeSpectrum Inc.

  4. 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) McCorkle, XtremeSpectrum Inc.

  5. 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 McCorkle, XtremeSpectrum Inc.

  6. OFDM And DS Noise Spectrum In 10 MHz RBW McCorkle, XtremeSpectrum Inc.

  7. 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 McCorkle, XtremeSpectrum Inc.

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  10. Test Results • 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 Results & Trends Matched “Theory” • Noise, non-hopped continuous-OFDM, and DS were all ~ equal • Effect was less than “duty-cycle” for short bursts (e.g. 1,2,3 sequence) • Effect moved upward toward“duty-cycle” with longer bursts(e.g. 1,1,2,2,3,3) • Results are consistent with earlier measurements using Video Cipher (analog) receiver McCorkle, XtremeSpectrum Inc.

  11. 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 McCorkle, XtremeSpectrum Inc.

  12. 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 McCorkle, XtremeSpectrum Inc.

  13. 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 McCorkle, XtremeSpectrum Inc.

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