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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: [ Multi-Band OFDM Interference on In-Band QPSK Receivers ] Date Submitted: [ 13 July, 2004 ] Source: [ Celestino A. Corral, Shahriar Emami, Gregg Rasor ] Company [ Motorola ]

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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: [Multi-Band OFDM Interference on In-Band QPSK Receivers] Date Submitted: [13 July, 2004] Source: [Celestino A. Corral, Shahriar Emami, Gregg Rasor] Company [Motorola] Address [8000 W. Sunrise Blvd., Plantation, Florida, USA 33322] Voice:[954-723-3864], FAX: [954-723-3883] 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 TVRO receivers. A MB-OFDM interference model is derived based on simulation and analytical results.] 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. Celestino A. Corral et al., Motorola

  2. Multi-band OFDM Interference on In-Band QPSK Receivers Celestino A. Corral, Shahriar Emami and Gregg Rasor Motorola 8000 W. Sunrise Blvd. Plantation, Florida July 13, 2004 Celestino A. Corral et al., Motorola

  3. Motivation • Goal: To characterize the impact of Multi-band OFDM UWB interference on in-band broadband wireless system like C-band satellite receivers. • Note: Multi-band OFDM (MB-OFDM) and Multi-band UWB (MB-UWB) requires power scaling of the waveform to compare competing technologies based on interpretation of FCC rules. • Model of MB-OFDM interference derived. This model is bounded by periodically gated AWGN and impulsive MB-OFDM interference. • Reconcile observed test results of MB-OFDM interference on satellite receivers as presented in ABQ meeting. Celestino A. Corral et al., Motorola

  4. Multi-band UWB Power • FCC states power spectral density for UWB devices must be -41.2 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. Multi-band spectrum PSD level f1 f2 fx Integrate the spectrum over band and average by band To implement equal PSD over hop bandwidth, we need requiring a power scaling. Celestino A. Corral et al., Motorola

  5. Multi-band UWB Power Equate power Both systems transmit with equal power at a given range. Actual MB-OFDM PSD over its transmission bandwidth. Assuming DS-UWB bandwith is 2 GHz and MB-OFDM bandwidth is 528 MHz. Celestino A. Corral et al., Motorola

  6. In-band Receiver Filters BW < 40 MHz High-Q band-pass filter can be approximated by [1]: Band-pass Filter Frequency Response Q > 50 typical complex frequency of band-pass filter complex frequency of low-pass prototype filter fc > 3 GHz Step response of band-pass filter has low-pass impulse response envelope: Temporal characteristics of high-Q band-pass filter determined by low-pass prototype. This includes rise time, which obeys the following relation [2]: Not a function of filter approximation or order Rise time of band-pass filter determined by 3dB bandwidth of low-pass prototype. [1] A. Papoulis, The Fourier Integral and its Application, Chap. 7, New York: McGraw-Hill, 1962. [2] G. E. Valley, Jr., and H. Wallman, Vacuum Tube Amplifiers, New York: McGraw-Hill, 1948. Celestino A. Corral et al., Motorola

  7. In-band Receiver Filters Band-pass filter rise time for 40 MHz bandwidth. Filter responds quite fast and observes virtually full power of filtered MB-OFDM signal. Filter with slower response. Portion due to filter bandwidth Portion due to temporal response Received power: in dB Celestino A. Corral et al., Motorola

  8. Coherent Detection QPSK Simulation Noise Source Block Diagram of Simulator Matched Filter Window Detector • QPSK system at 27.05 Msym/sec, similar to Dubai EDTV at 4020 MHz. • 0 < Eb/No < 30 dB. • 1000 symbols, 500 packets per Eb/No set. • Sample rate: 120 samples/QPSK symbol. • Multi-band OFDM and all gated noise is 896 samples long. • Assume perfect synchronization • Assume perfect phase estimation • Input filter bandwidth wide enough so rise time not a factor • Interference bandwidth is very large relative to filter bandwidth and approaches thermal noise as in [3]. [3] J. Brandao, “Interference effect on the performance of PSK and QAM systems,” IEE Proceedings I, vol. 138, pp. 331—337, Aug. 1991. Celestino A. Corral et al., Motorola

  9. Simulation Results: Gated Noise 3 dB Celestino A. Corral et al., Motorola

  10. Simplified Theoretical Reason Probability of symbol error for QPSK [4] Q-function for communication Gated noise duty cycle: Np is time interference is present, Ns is time interference is silent. Probability of error is due only to when the noise is present Pep; for the case it is silent Pes = 0: Actual error must be scaled by duty cycle as this is time interference is present equivalent “quasi-fading” of bit energy relative to fixed noise power No Q is very sensitive to r under high signal-to-noise (SNR), meaning small changes in duty cycle will impact probability of error when minor changes in bit energy is most significant. [4] J. G. Proakis, Digital Communications, 4th Ed., Boston, MA: McGraw-Hill, 2001. Celestino A. Corral et al., Motorola

  11. Theoretical vs. Simulated Results: Gated Noise Simulated Celestino A. Corral et al., Motorola

  12. Simulation Results: MB-OFDM 3 hops AWGN 9 dB Celestino A. Corral et al., Motorola

  13. Simulation Results: Impulsive MB-OFDM Worst-case peak-to-average power assumed for each MB-OFDM symbol Theory ?? dB Celestino A. Corral et al., Motorola

  14. Simulation Results: 3 hops Impulsive MB-OFDM upper bound MB-OFDM Gated AWGN lower bound Celestino A. Corral et al., Motorola

  15. MB-OFDM Interference Model Amplitude distribution of AWGN Amplitude distribution of MB-OFDM Amplitude distribution of Impulsive MB-OFDM MB-OFDM Model is Gaussian and Impulsive • Multi-band OFDM transmissions can be long or bursty: • Long transmissions have amplitude distribution that approaches AWGN • Bursty transmissions can be potentially impulsive • We need to combine the Gaussian and impulsive characteristics Celestino A. Corral et al., Motorola

  16. MB-OFDM Interference Model Interference has “gaps” in time; i.e., non-zero probability of time during which there is no interference in the receiver. Class A Model [5]: Interference time Receiver bandwidth Carrier-to-noise ratio Peak factor (PAP) Model Incorporates Gaussian and Impulsive Factors: for M-ary QAM impulse index Model std. dev. mean power ratio Average symbol error rate: [5] D. Middleton, “Non-Gaussian noise models in signal processing for telecommunications: New methods and results for class A and class B noise models,” IEEE Trans. Inform. Theory, vol. 45, pp. 1129—1149, May 1999. Celestino A. Corral et al., Motorola

  17. MB-OFDM Model Model Simulated Celestino A. Corral et al., Motorola

  18. Filtered MB-OFDM 40 MHz 9 subcarriers The filtered waveform is generated and then scaled to obtain same power as AWGN over the packet. The waveform is then scaled by a factor of 9/128 (in number of subcarriers) to reduce the level to a filtered amount. This is almost the same amount as 40/528 (in MHz), which corresponds to the desired power reduction relative to the full bandwidth of the 128-subcarrier symbol: 9/128 factor (40/528 factor) Assumed 0 dB Received power: Celestino A. Corral et al., Motorola

  19. Simulation Results: Filtered MB-OFDM Celestino A. Corral et al., Motorola

  20. Conclusions • Multi-band OFDM and Multi-band UWB equate power spectral density by scaling power in the hop and averaging over the entire hop bandwidth. This equates the transmitted power of a Multi-band system with DS-UWB over a fixed bandwidth. • Probability of symbol error shows gated noise is akin to quasi-fading of bit energy relative to fixed AWGN level. • The gated and scaled interference is more harmful than AWGN depending on the hop depth. Gated noise interference produces performance 3 dB from theory; MB-OFDM produces performance 8 dB from theory. • Multi-band OFDM can be impulsive. Under worst-case peak-to-average power Multi-band OFDM is a significant interferer to in-band coherent detection QPSK receivers. • MB-OFDM model was derived based on combination of Gaussian and impulsive characteristics of MB-OFDM. Celestino A. Corral et al., Motorola

  21. Narrowband Filter Response Only upper portion of response captured Wideband Filter Response Narrowband Filter Response • Fast rise time • Delay applies across entire response • Full level of interference reached within response time of the filter, and present for most of the interference time. • Total power captured • Slow rise time • Delay applies across entire response • Full level of interference not reached within response time of the filter. • Total power can be captured if rise time and interference time are about equal. Narrowband filters “favor” narrow pulsed interference; full level of interference is not captured. Celestino A. Corral et al., Motorola

  22. Backup: Gated Noise Results for Other Hops Increasing hop depth results in more degradation at high SNR. 13 3 7 Celestino A. Corral et al., Motorola

  23. Backup: MB-OFDM Results for Other Hops Increasing hop depth results in more degradation at high SNR. 13 3 7 Celestino A. Corral et al., Motorola

  24. Backup: Impulsive MB-OFDM Results for Other Hops Increasing hop depth results in more degradation at high SNR. 3 13 7 Celestino A. Corral et al., Motorola

  25. Backup: Gated Noise Theoretical Results for Other Hops 13 3 7 Celestino A. Corral et al., Motorola

  26. Backup: MB-OFDM Class A Model Results for Other Hops Celestino A. Corral et al., Motorola

  27. Decay factor: Value Properties of Q and Quasi-Fading Working with Q(x) directly is difficult. We use approximation where [4]: as then so decays more rapidly [4] P. L. Borjesson and C-E. W. Sundberg, “Simple approximations of the error function Q(x) for communication applications,” IEEE Trans. Commun., vol. COM-27, pp. 639—643, March 1979. Celestino A. Corral et al., Motorola

  28. Peak-to-Average Power “Tracking” Peak-to-average of AWGN and MB-OFDM “track” over different hop depths. Celestino A. Corral et al., Motorola

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