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Analyzing Peak Power Margin for UWB Waveforms Under FCC Rules

This study investigates peak-to-average margin for UWB waveforms, essential for FCC compliance and enhancing performance.

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Analyzing Peak Power Margin for UWB Waveforms Under FCC Rules

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  1. Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [Peak Power Margin for UWB waveforms] Date Submitted: [ 11 May, 2005] Source: [C. Razzell] Company [Philips] Address [1151 McKay Drive, San Jose, CA 95131] Voice:[+1 408 474 7243], FAX: [+1 408 474 8131], E-Mail:[charles.razzell@philips.com] + [R. Aiello] Company [Staccato Communications] Address [5893 Oberlin Drive, Suite 108, San Diego, California 92121] Voice:[+1 408 474 7243], FAX: +1 858 812 1000], E-Mail:[roberto.aiello@staccatocommunications.com] + [D. Leeper] Company [Intel Corporation] Address [CH6-460, 5000 W Chandler Blvd., Chandler, AZ, 85226] Voice:[ +1 480 552 4574], FAX: [], E-Mail:[david.g.leeper@intel.com] Re: [Previous 802.15.3a panel session discussion of FCC Waiver implications] Abstract: [Analysis and measurement of peak power headroom under FCC rules.] Purpose: [Consider carefully when evaluating claims of performance enhancements under FCC waiver] 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. C. Razzell, R. Aiello, D. Leeper

  2. Outline • Under the recent FCC waiver, gating may be applied to UWB waveforms to allow higher signal level in bursts shorter than 1ms • The only power limit, in addition to the average -41.2dBm/MHz, is peak power limit of 0dBm in a 50MHz bandwidth • However the standard measurement procedure is at 3MHz • DS-UWB authors have stated that waiver provides 4x advantage over MB-OFDM, in terms of increase in throughput, increase in transmit power, decrease in power consumption (*). This implies that: • DS-UWB signals have at least 6dB peak to average margin advantage with respect to MB-OFDM • Higher signal level, lower duty cycles signals have advantage in terms of increase in throughput, increase in transmit power, decrease in power consumption • This work seeks to determine the peak to average margin, that limits the “headroom” available for increasing the signal level power in bursts shorter than 1ms • Simulation for MB-OFDM, AWGN and DS-UWB • Conducted (not radiated) measurements for MB-OFDM and AWGN (*) Source: FCC Waiver Ruling, March 10, 2005, Technical Overview Martin Rofheart, Director of Ultra-Wideband Operations, Freescale Semiconductor C. Razzell, R. Aiello, D. Leeper

  3. Simulation Results C. Razzell, R. Aiello, D. Leeper

  4. FFT Simulation Methodology(Mimics Modern Digital Spectrum Analyzer) • Baseband simulation with a sampling rate of 2640MHz • A single MB-OFDM sub-band is simulated with 5x oversampling • A 1 in 3 duty cycle is applied to simulate frequency sequencing • A DS-UWB impulse waveform with a 220MHz PRF and a chip rate of 1320Mcps is simulated with 2x oversampling • 1ms of time domain data was generated for FFT analysis. • The number of points in the FFT is given by NFFT=Fs/RBW, where Fs is the sampling frequency and RBW is the desired resolution bandwidth. • N non-overlapping FFTs were taken, where N=TS*RBW, where TS is the simulation time. • The mean and the max of the N values in each FFT bin were taken as the estimated spectra C. Razzell, R. Aiello, D. Leeper

  5. 3MHz bandwidth, DS-UWB case C. Razzell, R. Aiello, D. Leeper

  6. 3MHz bandwidth, MB-OFDM case C. Razzell, R. Aiello, D. Leeper

  7. 3MHz bandwidth, AWGN case C. Razzell, R. Aiello, D. Leeper

  8. Power (dBm) 1 3 10 30 50 Resolution Bandwidth (MHz) Summary of FFT Simulation Results C. Razzell, R. Aiello, D. Leeper

  9. Simulation Results at 50 MHz & 3 MHzObserved Peak Power “Headroom” • 50 MHz limit • DS-UWB: 17dB • AWGN: 13 dB • MB-OFDM: 8 dB • 3 MHz measurement • DS-UWB: 0 dB margin • AWGN: 1 dB margin • MB-OFDM: 1 dB margin Power (dBm) C. Razzell, R. Aiello, D. Leeper

  10. Measurements C. Razzell, R. Aiello, D. Leeper

  11. Measurement Setup • Equipment Used • Staccato Communications’ Ultrawideband full-rate transmitter: Model number SC1010DB2 • Spectrum Analyzer: Rohde and Schwarz R&S FSP (9KHz – 13.6GHz) • Noise Source: NoiseCom (NC346 Series) 50MHz – 24GHz) • Calibration: • RMS power levels (MB-OFDM and Thermal Noise) observed by activating the RMS detector on SA. Corresponding power offsets (simple delta) introduced to achieve the -41dBm/MHz FCC mandate • Remainder of setup notes in backup foils C. Razzell, R. Aiello, D. Leeper

  12. C. Razzell, R. Aiello, D. Leeper

  13. Summary measurement results • 10 MHz measurement • AWGN: 7 dB • MB-OFDM TFC 1: 9 dB • MB-OFDM TFC 6: 16dB • 3 MHz measurement • AWGN: .7 dB margin • MB-OFDM TFC 1: 3.7 dB • MB-OFDM TFC 6: 10dB C. Razzell, R. Aiello, D. Leeper

  14. Discussion and Conclusions C. Razzell, R. Aiello, D. Leeper

  15. Discussion • Measurement of peak power based on a 50MHz measurement bandwidth cannot be performed with normal commercial EMC test equipment • 3 MHz RBW adopted by FCC for their own labs • Allowance is made for wider bandwidths, but the measurement technique will be scrutinized closely • Using a 3MHz bandwidth, there is virtually no headroom for gating • DS-UWB and AWGN have 0-1dB margin at 3MHz (simulation and measurement are in agreement for AWGN) • MB-OFDM has 1-3.7dB margin at 3MHz (simulation and measurement agree within 2dB) • At 50MHz bandwidth there are measurement challenges, but if overcome and accepted by the FCC: • > 8dB headroom for MB-OFDM (simulation and measurement) • 15dB for DS-UWB (simulation) C. Razzell, R. Aiello, D. Leeper

  16. Conclusions - recommendations • Estimates of peak power headroom are dependent on the measurement or simulation methods chosen • Simulation shows similar margins at 3MHz, larger margin for DS-UWB at 50MHz • Measurement shows larger margin for MB-OFDM at 3 and 10MHz • MB-OFDM transmitters could take advantage of the waiver’s gating rule to increase the signal level by a factor of 6 • Additional peak-to-mean ratio introduced by pulse gating will increase concern for interference potential to narrowband receivers by a similar amount. • We know that all receivers with bandwidths greater than a few kilohertz will experience proportionally increased peak interference powers • With slow gating, less chance for channel filtering to perform averaging and for FEC interleavers to perform randomization • UWB transmitters need to co-exist peacefully with other services in the same frequency of operation • Slow gating waveforms with an additional 15dB of peak power have not been subject to extensive coexistence studies • We prefer to take a more cautious approach until more data is available C. Razzell, R. Aiello, D. Leeper

  17. Backup C. Razzell, R. Aiello, D. Leeper

  18. Measurement set-up (contd..) • MB-OFDM measurements (TFC mode 1 and 6) • Center Frequency: 3096 MHz (center frequency of BAND_ID 2 of Band Group 1). • Frequency span: 500MHz • Trace detector: Max Peak Detector with MAX hold ON • Resolution BW: 1, 3, 10MHz; Video BW: 10MHz (constant) • Sweeptime: 500ms • Thermal Noise measurements • Center Frequency: 4092 MHz • Frequency span: 1600MHZ • Trace detector: Max Peak Detector with MAX hold ON • Resolution BW: 1, 3, 10MHz; Video BW: 10MHz (constant) • Sweeptime: 500ms C. Razzell, R. Aiello, D. Leeper

  19. Peak envelope value of bandpass filtered Gaussian Noise C. Razzell, R. Aiello, D. Leeper

  20. Peak envelope value of bandpass filtered Gaussian Noise C. Razzell, R. Aiello, D. Leeper

  21. Peak Power Measurement per FCC R&O We believe that there is a simpler method of measuring peak emission levels in a manner that also takes into account the interference potential of the equipment. In order to perform a peak measurement on a spectrum analyzer, the VBW must be at least as large as the RBW. The largest VBW on a spectrum analyzer is about 7 MHz. Thus, the widest RBW that could be employed is 3 MHz. However, there are several receivers used by the authorized radio services that employ greater bandwidths. Thus, the concern is how to ensure that peak measurements performed with a 3 MHz RBW will protect receivers that employ a wider bandwidth from harmful interference. The peak EIRP limit is 20 log (RBW/50) dBm when measured with a resolution bandwidth between 1 MHz and 50 MHz. RBW is the resolution bandwidth in megahertz actually employed. This bandwidth must be centered on the frequency at which the highest radiated emission occurs. We intend to employ at our laboratory a measurement procedure using a 3 MHz resolution bandwidth. However, we will permit responsible parties to test their UWB products using different resolution bandwidths ranging from 1 MHz to as high as 50 MHz. The use of a higher resolution bandwidth may be particularly helpful for measuring a system operating at a higher PRF. If a resolution bandwidth greater than 3 MHz is employed, the application for certification filed with the Commission must contain a detailed description of the test procedure, calibration of the test setup, and the instrumentation employed in the testing. C. Razzell, R. Aiello, D. Leeper

  22. 1MHz bandwidth, DS-UWB case C. Razzell, R. Aiello, D. Leeper

  23. 1MHz bandwidth, MB-OFDM case C. Razzell, R. Aiello, D. Leeper

  24. 1MHz bandwidth, AWGN case C. Razzell, R. Aiello, D. Leeper

  25. Caveats on AWGN Peak Power • The peak power of a Gaussian signal source is not bounded, and does not stabilize over time • As observation time increases, measured peak values continue to increase without limit • The maximum value is given by a single sample, which was the worst case over the entire simulation run • Over several trials of the same experiment, different results can be obtained C. Razzell, R. Aiello, D. Leeper

  26. Peak/Mean envelope value vs. Sample Size for a Complex Gaussian Source C. Razzell, R. Aiello, D. Leeper

  27. C. Razzell, R. Aiello, D. Leeper

  28. Waveforms MB-OFDM Tx DS-UWB Tx LPF AWGN Additional Peak Power Simulation SetupSimulating Traditional Analog (Envelope-Detector) Spectrum Analyzer Scaled to -41.3 dBm/MHz avg PSD for all waveforms True RMS Volts True Peak Voltage BPF 6-Pole Butterworth BW = 1, 3, 10, 50 MHz Fixed Center Freq = 4.092 GHz 1 ms observation times • Notes • MB-OFDM clipped at 9 dB PAR • DS-UWB BPSK Low-Band • Code Length 6, Code Set 1 • AWGN BW ~ 1600 MHz C. Razzell, R. Aiello, D. Leeper

  29. Peak & Avg Power vs Resolution BandwidthMB-OFDM, DS-UWB, and AWGNSimulated Analog (Envelope Detector) Spectrum Analyzer • Fixed RBW filter ctr freq = 4092 MHz • 1 ms simulation • Avg PSD = -41.3 dBm/MHz for all waveforms Peaks Power (dBm) Averages C. Razzell, R. Aiello, D. Leeper

  30. Headroom (dB) Resolution Bandwidth (MHz) Headroom Against FCC Peak Power LimitsMB-OFDM, DS-UWB, and AWGNSimulated Analog (Envelope Detector) Spectrum Analyzer C. Razzell, R. Aiello, D. Leeper

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