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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: [Effect of Pulse Repetition Frequency on UWB System Design] Date Submitted: [May 15, 2002] Revised: [May 16, 2002]

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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: [Effect of Pulse Repetition Frequency on UWB System Design] Date Submitted: [May 15, 2002] Revised: [May 16, 2002] Source: [Roberto Aiello, Naiel Askar, Jason Ellis, David Furuno, Larry Taylor] Company [General Atomics Inc.] Address [General Atomics- Photonics Division, 10240 Flanders Ct, San Diego, CA 92121-2901] Voice [(858) 457-8700], Fax [(858) 457-8740], E-mail [jason.ellis@ga.com] Re: [Ultra-Wideband System Design Considerations] Abstract: [UWB technology is characterized by parameters different from CW systems. Some of these parameters, such as Pulse Repetition Frequency (or symbol/chip rate), have a significant effect on system design. This tutorial analyzes some of these parameters and describes how they influence performance metrics important to the standard.] Purpose: [IEEE 802.15.3SGa Tutorial May 16, 2002] 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 or organization. The material in this document is subject to change in form and content after further study. The contributor reserves 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. General Atomics Advanced Wireless GroupRoberto Aiello, Ph.D. (Aiello@IEEE.org)Naiel Askar, Ph.D. (Naiel.Askar@GA.com) Jason Ellis (Jason.Ellis@GA.com)David Furuno, Ph.D.(David.Furuno@GA.com) Larry Taylor (Larry.Taylor@ACM.org)www.ga.com/uwb Effect of Pulse Repetition Frequencyon UWB System Design General Atomics- Advanced Wireless Group

  3. Tutorial’s Objectives • Provide useful information to PHY proposers and voting members • Introduce parameters specific to UWB that influence a system’s design: Pulse Repetition Frequency, Modulation, use of spectrum, etc. • Focus on general concepts, not specific designs or implementations as in previous tutorials in 802.15.3 • Discuss tradeoffs relevant to 802.15.3 standard General Atomics- Advanced Wireless Group

  4. Effects of Pulse Repetition Frequency (PRF) on System Design • We define “pulse” as a single electro-magnetic emission • One pulse can carry 1 bit, less than1 bit, or more than 1 bit of information • PRF is the frequency at which UWB pulses are transmitted • PRF may vary from pulse to pulse; however, systems that utilize high average PRF approach design issues differently than those using low average PRF • PRF affects many key system parameters • Mutual interference of UWB systems • Interference between UWB and CW systems • Synchronization • Power consumption General Atomics- Advanced Wireless Group

  5. Examples of Low and High PRF UWB 1/PRF From: 00083r0P802-15_WG-UWB-Tutorial-1-Time-Domain 1/PRF From: 00195r4P802-15_TG3-XtremeSPectrum-Multimedia-WPAN-PHY General Atomics- Advanced Wireless Group

  6. UWB definitions* • 7,500MHz available spectrum for unlicensed use • US operating frequency: 3,100 – 10,600 MHz • Emission limit: -41.3dBm/MHz EIRP • Indoor and handheld systems • Other restrictions and measurement procedures in Report & Order • UWB device defined as • Fractional bandwidth greater than 0.20 • Occupies more than 500 MHz • UWB device NOT defined as • Modulation or pulsed modulation • Carrierless • Impulse radio *Source: FCC 02-48, UWB Report & Order, released 22 April 02 General Atomics- Advanced Wireless Group

  7. Ton (Ton + Toff) Other Definitions • PRF • The rate at which pulses are transmitted, i.e. # pulses/second • PRF represents the average rate if pulses are transmitted aperiodically • Implies a specific Power/Pulse • FCC limits impose power/pulse as a function of PRF • Drops 3dB with each doubling of PRF • Duty Cycle • Ton is dominated by Delay Spread • Ton + Toff = 1/PRF • Duty Cycle  Delay Spread * PRF Amplitude Toff Ton 1/PRF Time General Atomics- Advanced Wireless Group

  8. Mutual Interference of UWB Systems Impact of High PRF on: Impact of Low PRF on: HighPRF Variable Impact (function of coding) Tricky! LowPRF Low Impact (function of duty cycle) Low Impact (noise like) General Atomics- Advanced Wireless Group

  9. Analogy with Spread Spectrum NB Signal NB Interference r e Narrowband (NB)/Spread spectrum (SS) w o P Spread Spectrum Signal Frequency Pulsed Interference Low PRF Signal Low PRF/High PRF r e w o P High PRF Signal Time General Atomics- Advanced Wireless Group

  10. Interference Between UWB & CW Systems • Effect of UWB on CW systems is independent of PRF • PRF >> CW receiver’s BW • UWB behaves like white noise* • PRF << CW receiver’s BW • UWB behaves like a pulse* • SG3a requirements will most likely cause PRF > CW receiver’s BW • Effect of CW on UWB systems is independent of PRF • Limited by SIR defined as • High PRF compensates lower power/pulse with processing gain Power / Pulse CW Power * See for example NTIA Special Publication 01-43, “Assessment Of Compatibility Between Ultrawideband Devices and Selected Federal Systems” General Atomics- Advanced Wireless Group

  11. Impact of PRF on Initial Synchronization • Initial synchronization accumulates enough signal energy to exceed a threshold N is number of pulses required to meet threshold Ethreshold is set higher than the noise level of combined pulses Ethreshold = N * Epulse • Low PRF • Noise between pulses doesn’t contribute • Small number of pulses is required • High PRF • Multipath, if ignored, reduces the available Epulse • Large number of pulses is required • High PRF systems must deal with more noise than low PRF • Low PRF systems may get away with non-coherent combining General Atomics- Advanced Wireless Group

  12. P = C . V2 . f . N . n% P is Power Consumption C is process gate capacitance V is voltage swing f is clock frequency N is number of gates n% is percentage of gates that switch each clock Key Considerations Voltage swing for pulse generation Higher swing for low PRF systems (output stage only) Processes that must run at maximum clock rate Correlator for high PRF receive chains Synchronization circuitry Power Consumption Considerations High PRF Low PRF << x >> optimal • Low PRF Advantages • Low clock rate • Easy synchronization • Low ISI • High PRF Advantages • Low modulation order • Low power/pulse General Atomics- Advanced Wireless Group

  13. Conclusions • UWB is a means of accessing 7,500 MHz of unlicensed spectrum – it is not a specific communications method • PRF needs to be understood in terms of Delay Spread, Duty Cycle and Power per Pulse • PRF impacts system design in terms of • Mutual interference (UWB - UWB) • Interference (UWB - CW) • Synchronization • Power consumption General Atomics- Advanced Wireless Group

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