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 2002]
Revised: []
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
[[email protected]]
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.
May 2002
doc.: IEEE 802.15-02/211r0
Effect of Pulse Repetition Frequency
on UWB System Design
Advanced Wireless Group
Roberto Aiello, Ph.D. ([email protected]),
Naiel Askar, Ph.D. ([email protected])
Jason Ellis ([email protected])
David Furuno, Ph.D. ([email protected])
Larry Taylor ([email protected])
www.ga.com/uwb
Submission
Slide 2
General Atomics- Advanced Wireless Group
May 2002
doc.: IEEE 802.15-02/211r0
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
Submission
Slide 3
General Atomics- Advanced Wireless Group
May 2002
doc.: IEEE 802.15-02/211r0
General Atomics is Developing High Bit Rate
UWB Communication Systems
•
•
•
•
GA Headquarters, San Diego
Founded 1955
1,600 employees worldwide
Diversified research & development
Over one million square feet of
laboratory, engineering, test, and
manufacturing facilities covering the
range from DC to gamma… literally!
• www.GA.com
• Founded May 00 to pursue innovative
approaches to UWB communications
• Resides within the 65,000 square foot
Photonics Division
• Dedicated staff has over 30 years of
experience in UWB & full access to the
technical resources of General Atomics
• www.GA.com/uwb
Submission
Slide 4
GA Advanced Wireless Group
General Atomics- Advanced Wireless Group
May 2002
doc.: IEEE 802.15-02/211r0
General Atomics is Developing High Bit Rate
UWB Communication Systems
•
•
•
•
GA Headquarters, San Diego
Founded 1955
1,600 employees worldwide
Diversified research & development
Over one million square feet of
laboratory, engineering, test, and
manufacturing facilities covering the
range from DC to gamma… literally!
• www.GA.com
• Founded May 00 to pursue innovative
approaches to UWB communications
• Resides within the 65,000 square foot
Photonics Division
• Dedicated staff has over 30 years of
experience in UWB & full access to the
technical resources of General Atomics
• www.GA.com/uwb
Submission
Slide 5
GA Advanced Wireless Group
General Atomics- Advanced Wireless Group
May 2002
doc.: IEEE 802.15-02/211r0
General Atomics is Developing High Bit Rate
UWB Communication Systems
•
•
•
•
GA Headquarters, San Diego
Founded 1955
1,600 employees worldwide
Diversified research & development
Over one million square feet of
laboratory, engineering, test, and
manufacturing facilities covering the
range from DC to gamma… literally!
• www.GA.com
• Founded May 00 to pursue innovative
approaches to UWB communications
• Resides within the 65,000 square foot
Photonics Division
• Dedicated staff has over 30 years of
experience in UWB & full access to the
technical resources of General Atomics
• www.GA.com/uwb
Submission
Slide 6
GA Advanced Wireless Group
General Atomics- Advanced Wireless Group
May 2002
doc.: IEEE 802.15-02/211r0
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
Submission
Slide 7
General Atomics- Advanced Wireless Group
May 2002
doc.: IEEE 802.15-02/211r0
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
Submission
Slide 8
General Atomics- Advanced Wireless Group
May 2002
doc.: IEEE 802.15-02/211r0
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
Ton
(Ton + Toff)
• Ton is dominated by Delay Spread
– Ton + Toff = 1/PRF
– Duty Cycle  Delay Spread * PRF
Amplitude
• Duty Cycle
Toff
Ton
1/PRF
Time
Submission
Slide 9
General Atomics- Advanced Wireless Group
May 2002
doc.: IEEE 802.15-02/211r0
Mutual Interference of UWB Systems
Impact of High PRF on:
Power
Power
Impact of Low PRF on:
High
PRF
Pulse Period
Time
Pulse Period
Time
Variable Impact (function of coding)
Power
Power
Tricky!
Low
PRF
Time
Power
Pulse Period
Pulse Period
Pulse Period
Low Impact (function of duty cycle)
Submission
Time
Time
Slide 10
Low Impact (noise like)
General Atomics- Advanced Wireless Group
May 2002
doc.: IEEE 802.15-02/211r0
Analogy with Spread Spectrum
Narrowband (NB)/
Spread spectrum (SS)
NB Interference
Power
NB Signal
Spread Spectrum Signal
Low PRF Signal
Power
Low PRF/
High PRF
Frequency
Pulsed Interference
High PRF Signal
Time
NB in band interferer/
Low PRF signal
NB out of band interferer/
High PRF signal
NB / Low PRF signal
Large effect
Small effect
SS / High PRF signal
Medium effect
Medium effect
Submission
Slide 11
General Atomics- Advanced Wireless Group
May 2002
doc.: IEEE 802.15-02/211r0
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
Power / Pulse
CW Power
– 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”
Submission
Slide 12
General Atomics- Advanced Wireless Group
May 2002
doc.: IEEE 802.15-02/211r0
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
Input
signal Delay (sub Delay elements Delay (sub Delay elements
Delay sub
……
Input pulse
……
pulse
pulse
signal period)
Delay (sub Delay elements period)
Delay (sub Delay elements period
Delay sub
……
……
pulse Delay 1/PRF
pulse Delay N/PRF
pulse
period)
period)
period
Delay 1/PRF
Delay N/PRF
Filter Matched
Filter Matched
….
Filter Matched
to Pulse
to Pulse
to Pulse
Filter Matched
Filter Matched
….
Filter Matched
to Pulse
to Pulse
to Pulse
….
Combiner
Threshold
Energies Need to be
combined
Energies Need to be
combined
Noise to
be ignored
Noise to
be ignored
Low PRF
Low PRF
Submission
Threshold
Acquisition
Comparator
Comparator
….
Combiner
Acquisition
Energies to be combined
Energies to be combined
• 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
High PRF
Slide 13 High PRF
General Atomics- Advanced Wireless Group
May 2002
doc.: IEEE 802.15-02/211r0
Power Consumption Considerations
High PRF
<< x >>
optimal
Low PRF Advantages
High PRF Advantages
• Low clock rate
• Easy synchronization
• Low ISI
• Low modulation order
• Low power/pulse
•
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
Submission
Low PRF
Slide 14
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
General Atomics- Advanced Wireless Group
May 2002
doc.: IEEE 802.15-02/211r0
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
–
–
–
–
Submission
Mutual interference (UWB - UWB)
Interference (UWB - CW)
Synchronization
Power consumption
Slide 15
General Atomics- Advanced Wireless Group