1. doc.: IEEE 802.15-04/451r2 Submission November, 2004 Celestino A. Corral et al., FreescaleSlide 1 Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [Multi-Band OFDM Interference on In-Band QPSK Receivers Revisited] Date Submitted: [14 November, 2004] Source: [Celestino A. Corral, Shahriar Emami, Gregg Rasor] Company [Freescale] Address [3301 Quantum Blvd., Boynton Beach, Florida, USA 33426] Voice:[561-739-3280], FAX: [ ] Re: [] Abstract:[This document provides simulation and theoretical results that demonstrate MB-OFDM is an extremely harmful type of interference to wideband in-band QPSK systems such as C-band TVRO receivers.] Purpose:[For discussion by IEEE 802.15 TG3a.] 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.

2. doc.: IEEE 802.15-04/451r2 Submission November, 2004 Celestino A. Corral et al., FreescaleSlide 2 Multi-band OFDM Interference on In-Band QPSK Receivers Revisited Celestino A. Corral, Shahriar Emami and Gregg Rasor Freescale Semiconductor 3301 Quantum Blvd. Boynton Beach, Florida November 14, 2004

3. doc.: IEEE 802.15-04/451r2 Submission November, 2004 Celestino A. Corral et al., FreescaleSlide 3 Motivation  Goal: To provide additional simulation results for the source of interference in MB-OFDM modulation. Focus is on interference to in-band high data rate wireless systems, particularly TVRO satellite receivers using QPSK modulation.  Note: Multi-band UWB, including MB-OFDM, concentrates its energy in a narrower bandwidth than a comparable DS- UWB system under equal effective isotropic radiated power (EIRP). The filter captured energy is higher.  Approach: Analyze the source of interference from a time and spectrum perspective.  Additionally: Clarify initial results of Portland meeting.

4. doc.: IEEE 802.15-04/451r2 Submission November, 2004 Celestino A. Corral et al., FreescaleSlide 4 Multi-band UWB Power  FCC states power spectral density for UWB devices must be -41.3 dBm/MHz in band between 3.1 and 10.6 GHz.  Since multi-band signals hop over a selected band of frequencies, the power spectrum is scaled by the hop and averaged over the band.  The resulting power spectral density is made equal to a system over any arbitrary band. PSD level Multi-band spectrum Integrate the spectrum over band and average by band To implement equal PSD over hop bandwidth, we need requiring a power scaling. f1f1 f2f2 fxfx

5. doc.: IEEE 802.15-04/451r2 Submission November, 2004 Celestino A. Corral et al., FreescaleSlide 5 Multi-band UWB Power Equate power Both systems have equal range and total equal power. Assuming DS-UWB bandwith is 2 GHz and MB-OFDM bandwidth is 528 MHz. Actual MB-OFDM PSD over its transmission bandwidth.

6. doc.: IEEE 802.15-04/451r2 Submission November, 2004 Celestino A. Corral et al., FreescaleSlide 6 OFDM and AWGN  Subcarriers are orthogonally spaced in frequency.  Data modulation on subcarriers randomizes amplitude and phase.  Peak-to-average approaches that of AWGN as the number of subcarriers increases, but is bound to 10 log (N). Peak-to-Average Power Plots f1f1 f2f2 f3f3 f4f4 … Some similarities are evident number of subcarriers

7. doc.: IEEE 802.15-04/451r2 Submission November, 2004 Celestino A. Corral et al., FreescaleSlide 7 OFDM and AWGN AWGN OFDM Temporal SnapshotPDF Both signals have the same average power and identical PDF… But they’re not the same!

8. doc.: IEEE 802.15-04/451r2 Submission November, 2004 Celestino A. Corral et al., FreescaleSlide 8 OFDM and AWGN  Energy in time equals energy in spectrum  Spectral densities are inversely proportional to the bandwidth of the signal.  OFDM concentrates more of its energy over a narrower spectrum than DS-UWB, hence higher spectral density.  This is evident at the output of the matched filter with optimum sampling. DS-UWB spectrum MB-OFDM spectrum Spectral densities f (GHz) 3.15.1 0.528 Amplitude In-band filter bandwidth OFDM AWGN

9. doc.: IEEE 802.15-04/451r2 Submission November, 2004 Celestino A. Corral et al., FreescaleSlide 9 OFDM and AWGN If the power spectral densities are equal, OFDM will have less energy than DS-UWB. AWGNOFDM Matched Spectral Densities Another viewpoint: At a given spectral density for OFDM, DS-UWB can transmit more energy!

10. doc.: IEEE 802.15-04/451r2 Submission November, 2004 Celestino A. Corral et al., FreescaleSlide 10 Ungated OFDM BER Results OFDM DS-UWB Ungated OFDM with equal EIRP is more harmful interference than DS-UWB DS-UWB spreads its energy over greater bandwidth, so it produces less interference

11. doc.: IEEE 802.15-04/451r2 Submission November, 2004 Celestino A. Corral et al., FreescaleSlide 11 OFDM Modeled as Gated AWGN 9 dB 3 hops AWGN In doc. 315r0 the MB-OFDM results were with two phenomena captured: PSD growth due to equal EIRP Additional interference due to averaging of EIRP over the hop depth. We need to equate the PSD so that the averaging of the EIRP produces the actual PSD growth (i.e., we need to make the PSD’s of each interference the same).

12. doc.: IEEE 802.15-04/451r2 Submission November, 2004 Celestino A. Corral et al., FreescaleSlide 12 Gated AWGN Revisited Symbol Error Rate (QPSK): Bit Error Rate: Interference is Gated: New Bit Error Rate: = 0 interference present interference not present interference present interference silent

13. doc.: IEEE 802.15-04/451r2 Submission November, 2004 Celestino A. Corral et al., FreescaleSlide 13 Consider Interference-to-Noise Probability of Bit Error: where Interference-to-Noise Ratio Asymptotic Behavior (N s = 0): Probability of bit error as time of interference presence increases (gating approaches continuous operation) Asymptotic Loss of Gated Noise Model Relative to Continuous Noise:

14. doc.: IEEE 802.15-04/451r2 Submission November, 2004 Celestino A. Corral et al., FreescaleSlide 14 BER versus INR for 3 Hops Lower INR results in less interference, but not zero. In evaluating INR we cannot assume users are cognizant of regulatory rules. DS-UWB causes lower interference relative to MB-OFDM when latter is modeled as gated noise.

15. doc.: IEEE 802.15-04/451r2 Submission November, 2004 Celestino A. Corral et al., FreescaleSlide 15 Plot of Theoretical Loss for Gated Noise Source Evaluating: Lower INR results in less loss (back-off), but not zero. Loss is higher for longer hops DS-UWB is always lower interference relative to an MB-OFDM system.

16. doc.: IEEE 802.15-04/451r2 Submission November, 2004 Celestino A. Corral et al., FreescaleSlide 16 Filtered MB-OFDM Revisited  For filtered MB-OFDM, it is assumed that the filter rise time is still sufficient to capture the full interference levels.  Filtering consists of the ideal rejection of subcarriers outside the desired bandwidth.  Energy is made equal over the bandwidth of the filter by scaling the interference using 10 log(M/N) where M is the number of subcarriers captured and N is total number of subcarriers. Variance:

17. doc.: IEEE 802.15-04/451r2 Submission November, 2004 Celestino A. Corral et al., FreescaleSlide 17 Filtered MB-OFDM Results Ideal filtering implemented: 40 MHz bandwidth corresponds to 8 subcarriers passed, all others infinitely rejected. Power scaled so that PSD of MB-OFDM and AWGN are the same. As Eb/No increases, trend seems to be that SER improves.

18. doc.: IEEE 802.15-04/451r2 Submission November, 2004 Celestino A. Corral et al., FreescaleSlide 18 Cipped MB-OFDM Results Clipping level set at 9 dB per the MB-OFDM proposal. Clipping has no impact on BER results. Impulsive characteristic is suppressed, but main contributor is still the bursty nature of the MB- OFDM interference. Since clipping is employed, the model presented in Portland with AWGN and impulsive noise is no longer applicable.

19. doc.: IEEE 802.15-04/451r2 Submission November, 2004 Celestino A. Corral et al., FreescaleSlide 19 Gated Noise Interference with FEC Convolutional code, constraint length K = 7 with hard decision, yields about 5 dB coding gain for all cases. No interleaving performed. FEC improves BER performance of all interference. MB-OFDM as gated noise is still worse interferer.

20. doc.: IEEE 802.15-04/451r2 Submission November, 2004 Celestino A. Corral et al., FreescaleSlide 20 Impulse Radio Comparisons PRF = 22.2 MHz PRF = 2.22 MHz Impulse radio modeled as gated AWGN process similar to MB-OFDM. Pulse width is 2 nsec, corresponding to 500 MHz bandwidth. EIRP averaged over the hop depth of the gated noise model for MB- OFDM. Practical PRF range considered.

21. doc.: IEEE 802.15-04/451r2 Submission November, 2004 Celestino A. Corral et al., FreescaleSlide 21 Impulse Radio Comparisons For very high PRF, impulse radio approaches AWGN. For lower PRF, SER for impulse radio rises moderately. Under constraint of identical 500 MHz bandwidth, impulse radio interference is lower than MB-OFDM modeled by same gated noise process.

22. doc.: IEEE 802.15-04/451r2 Submission November, 2004 Celestino A. Corral et al., FreescaleSlide 22 Conclusions  Ungated OFDM is a more harmful interferer than DS-UWB under equal EIRP constraint because the energy is concentrated over a narrower bandwidth.  Gated noise model was used to evaluate MB-OFDM interference under equal PSD constraint. Results show higher interference from gated noise than continuous noise.  Gated noise model was extended to handle interference-to- noise ratios and theoretical loss difference between systems established for lowest hop depth N = 3.

23. doc.: IEEE 802.15-04/451r2 Submission November, 2004 Celestino A. Corral et al., FreescaleSlide 23 Conclusions  Filtered MB-OFDM seems to indicate that narrower filtering improves SER performance slightly. However, results are optimistic as they account for “ideal” filtering.  Results for clipped MB-OFDM show basically no difference when compared to unclipped MB-OFDM.  All interference sources benefit from FEC, but MB-OFDM is still worse than DS-UWB.  Impulse radio interference is less than that of MB-OFDM when both are modeled as gated AWGN processes with equal 500 MHz bandwidths and over practical PRF ranges.

24. doc.: IEEE 802.15-04/451r2 Submission November, 2004 Celestino A. Corral et al., FreescaleSlide 24 Clarification of Results Presented in Doc 412r0 – APD Analysis  APD is a methodology that captures only amplitude info:  Amplitude (A) in dB as ordinate,  1-CDF(A) plotted as abscissa.  Slide 3 clearly states “For full impact assessment, knowledge of the victim system’s modulation scheme and FEC performance is needed.”  In other words, APD is only a piece of the puzzle.  APD has value, but results must be considered under the basis of the method’s limitations.  Specifically, amplitude data alone is not sufficient, greater scrutiny is needed.  We provide examples of waveforms with similar APDs and different interference potential.

25. doc.: IEEE 802.15-04/451r2 Submission November, 2004 Celestino A. Corral et al., FreescaleSlide 25 Three Different Signals AM modulated signals: Sinusoid Quasi-Sinusoid Scrambled Sinusoid Which Waveform Interferes More?

26. doc.: IEEE 802.15-04/451r2 Submission November, 2004 Celestino A. Corral et al., FreescaleSlide 26 APD Results APD’s treat only envelope of waveforms.

27. doc.: IEEE 802.15-04/451r2 Submission November, 2004 Celestino A. Corral et al., FreescaleSlide 27 Different Spectra Sample SignalsDetail of Scrambled Sinusoid The interference potential of signals cannot be determined by APD analysis in isolation. Victim bandwidth, center frequency, modulation, etc. play a role. More information is needed! APD analysis especially breaks down when considering the impact of FEC.

28. doc.: IEEE 802.15-04/451r2 Submission November, 2004 Celestino A. Corral et al., FreescaleSlide 28 PDF of Signals PDF in Slide 25 of Doc 412 This PDF shows Gaussian noise and OFDM have the same variance (power). But this is not the case: MB- OFDM has 6 dB more power. PDF cannot be “averaged” as signal. This gives the impression OFDM is more benign than AWGN, which it is not. Actual PDF This PDF clearly shows approximately 6 dB greater power (4X variance) of OFDM. This is at output of matched filter at optimum sampling point. This PDF is present at a duty cycle of 26%; but it is not “averaged.” For the other cases, variance = 0. Even with finite values, peak signal is higher! var = 2 var = 0.5

29. doc.: IEEE 802.15-04/451r2 Submission November, 2004 Celestino A. Corral et al., FreescaleSlide 29 Interference Conditions  Slides 27—29 confirm results for simplified case of only gated noise interference present (i.e., no noise).  Considers more “realistic” case of noise always present.  Analysis then considers Eb/(No + Io) with receiver at some fixed Eb/No; increase Io after that.  By judicious selection of No, impact of Io can be suppressed; this is not representative of interference effects, only noise effects!  Analysis presented here for slides 14—16 are representative of Eb/(No + Io) effects under high SNR, which is case for TVRO systems.

30. doc.: IEEE 802.15-04/451r2 Submission November, 2004 Celestino A. Corral et al., FreescaleSlide 30 Back-Up Material: OFDM Correlation OFDM is additive noise. Compared autocorrelation of OFDM and AWGN processes. OFDM exhibits significant autocorrelation compared to AWGN.

31. doc.: IEEE 802.15-04/451r2 Submission November, 2004 Celestino A. Corral et al., FreescaleSlide 31 Back-Up Material: OFDM Correlation Compared two different OFDM systems: 128 (528 MHz) 256 (1.056 GHz) Autocorrelation improves as more subcarriers (and corresponding wider bandwidth) are employed.

32. doc.: IEEE 802.15-04/451r2 Submission November, 2004 Celestino A. Corral et al., FreescaleSlide 32 Correlation Effects  OFDM signal is highly correlated; it is not white.  Autocorrelation improves with more subcarriers and larger bandwidth.  OFDM is additive noise and approaches Gaussian with large number of subcarriers.  Receivers are typically designed for AWGN.  Receivers expect to operate on uncorrelated noise samples.  For OFDM interference, receiver performance will be inferior to AWGN.