Project: IEEE P 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, Flanders Ct, San Diego, CA ] Voice [(858) ], Fax [(858) ], 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 SGa Tutorial May 16, 2002] Notice: This document has been prepared to assist the IEEE P 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 P

doc.: IEEE /211r2 Submission May 2002 General Atomics- Advanced Wireless GroupSlide 2 General Atomics Advanced Wireless Group Roberto Aiello, Ph.D. Naiel Askar, Ph.D. Jason Ellis David Furuno, Ph.D. Larry Taylor Effect of Pulse Repetition Frequency on UWB System Design

doc.: IEEE /211r2 Submission May 2002 General Atomics- Advanced Wireless GroupSlide 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 Discuss tradeoffs relevant to standard

doc.: IEEE /211r2 Submission May 2002 General Atomics- Advanced Wireless GroupSlide 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 than 1 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

doc.: IEEE /211r2 Submission May 2002 General Atomics- Advanced Wireless GroupSlide 5 Examples of Low and High PRF UWB From: 00195r4P802-15_TG3-XtremeSPectrum-Multimedia-WPAN-PHY 1/PRF From: 00083r0P802-15_WG-UWB-Tutorial-1-Time-Domain

doc.: IEEE /211r2 Submission May 2002 General Atomics- Advanced Wireless GroupSlide 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

doc.: IEEE /211r2 Submission May 2002 General Atomics- Advanced Wireless GroupSlide 7 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 T on is dominated by Delay Spread –T on + T off = 1/PRF –Duty Cycle  Delay Spread * PRF Other Definitions T on (T on + T off ) T on T off 1/PRF Time Amplitude

doc.: IEEE /211r2 Submission May 2002 General Atomics- Advanced Wireless GroupSlide 8 Mutual Interference of UWB Systems High PRF Impact of High PRF on: Low PRF Impact of Low PRF on: Low Impact (function of duty cycle) Low Impact (noise like) Tricky! Variable Impact (function of coding)

doc.: IEEE /211r2 Submission May 2002 General Atomics- Advanced Wireless GroupSlide 9 r Time Low PRF Signal Pulsed Interference Analogy with Spread Spectrum P o w e r Frequency NB InterferenceNB Signal Spread Spectrum Signal Narrowband (NB)/ Spread spectrum (SS) Low PRF/ High PRF NB in band interferer/ Low PRF signal NB out of band interferer/ High PRF signal NB / Low PRF signalLarge effectSmall effect SS / High PRF signalMedium effect P o w e High PRF Signal

doc.: IEEE /211r2 Submission May 2002 General Atomics- Advanced Wireless GroupSlide 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 *See for example NTIA Special Publication 01-43, “Assessment Of Compatibility Between Ultrawideband Devices and Selected Federal Systems” CW Power Power / Pulse

doc.: IEEE /211r2 Submission May 2002 General Atomics- Advanced Wireless GroupSlide 11 Impact of PRF on Initial Synchronization Low PRF –Noise between pulses doesn’t contribute –Small number of pulses is required High PRF –Multipath, if ignored, reduces the available E pulse –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 Initial synchronization accumulates enough signal energy to exceed a threshold N is number of pulses required to meet threshold E threshold is set higher than the noise level of combined pulses E threshold = N * E pulse

doc.: IEEE /211r2 Submission May 2002 General Atomics- Advanced Wireless GroupSlide 12 Power Consumption Considerations Low PRF Low PRF Advantages Low clock rate Easy synchronization Low ISI High PRF High PRF Advantages Low modulation order Low power/pulse > optimal P = C. V 2. 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

doc.: IEEE /211r2 Submission May 2002 General Atomics- Advanced Wireless GroupSlide 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