UltraWideband Radars (FM-CW) for Snow Thickness Measurements.
Assessment of Ultrawideband and Global Positioning System Compatibility
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Transcript of Assessment of Ultrawideband and Global Positioning System Compatibility
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Assessment of Ultrawideband and Global Positioning System
Compatibility
Randy Hoffman and Mike Cotton
ISART March, 2002
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Contents
• Objectives, Test Setup, and Measurement Methodologies
• Ultrawideband (UWB) Parameters and Characteristics
• Interference Results
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Project Objectives
• Primary Objective: assess the interference potential of UWB signals to GPS receivers.
• Secondary Objective: Identify GPS receiver performance metrics and establish repeatable measurement methods.
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Test Setup - Conducted
GPSSimulator
VariableAttenuator
NoiseSource
VariableAttenuator
Combiner
GPSReceiver
UWBPulser
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General Conducted Measurement Methodologies
• Metrics– Loss of lock– Satellite reacquisition time
• Associated performance criteria– Maximum UWB signal power below loss-of-lock for which
the receiver can regain satellite lock
• Monitor: pseudorange, cycle slip, position,C/N, phase lock, DOP, delta-pseudorange, accumulated Doppler cycles, Doppler
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GPS Receivers
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UWB Parameters
• Power levels – peak vs. average• Pulse shape/width• Pulse repetition frequency• Pulse spacing• Gating
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UWB Pulse Spacing
Uniform Pulse Spacing (UPS)
On-Off-Keying (OOK)
Absolute-Referenced Dithering (ARD)
Relative-Referenced Dithering (RRD)
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Gating
On time
Duty cycle = % on time
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UWB Signal Parameters
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UWB Spectral Characteristics
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Amplitude Probability
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APD Characteristics
Constant Amplitude
Gaussian Noise-likeImpulsive
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Results
• Characterization of single-source UWB signals
• GPS-performance trends due to single-source interference
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APDs of Single-Source UWB Signals
• 2 Bandwidths – 3 MHz and 20 MHz
• Composite plots– Across pulse spacing modes for specific
PRF values– Across PRF ranges for specific pulse
spacing mode
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APDs of 20-MHz PRF UWB Signals Measured in a 3-MHz Bandwidth
•Constant-amplitude
•Noise-Like
•Gating
•Peak-to-Average
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APDs of 100-kHz PRF UWB Signals Measured in a 3-MHz Bandwidth
•Low PRF Impulsive
•Resolved UWB pulses
•Gating decreases the percentage of time the signal is on
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APDs of Absolute-Reference Dithered UWB Signals Measured in a 3-MHz Bandwidth
•Higher PRF Gaussian
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UWB Categorization
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Measurement Procedure
A B C
Interference Source (dBm)
NBL
N
Nr
N+ UWB
(N + UWB)BL
Nr N+
P
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Trends
• Spectral lines are particularly invasive• Impulsive signals cause little interference• Higher PRFs have a greater impact• Dithering can produce effects that are more
Gaussian noise-like• Gating reduces the impact of interference
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Break Lock: Rx 1, Non-Gated
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Pseudorange Precision: Rx 1, 50%-ARD
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Trends
• Observational results are correlated to BL and RQT.
• RQT has been found to be the most sensitive parameter for identifying interference effects on the receiver.
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Rx 1, 5-MHz PRF, 50%-ARD, Non-Gated
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SUMMARY
• Measurement Approach
• UWB Characteristics
• Interference Trends Related to UWB Characteristics
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Contact Information:Institute for Telecommunication Sciences
•J. Randy Hoffman303/[email protected]
•Michael G. Cotton303/[email protected]
•Robert J. Achatz303/[email protected]
Mailing address:U.S. Department of Commerce325 Broadway NTIA/ITSBoulder, CO 80305
Web address for online report:http://www.its.bldrdoc.gov/
click on <Online Publications>Scroll down to NTIA Report 01-384
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Broadband Noise Power
• Broadband noise accounts for:– Sky noise– Cross-correlation noise– Other satellite signals
• Setting of broadband noise level based on ITU recommendation for minimum C/No required for GPS satellite acquisition. (set at –93 dBm/20 MHz)
• Supported by ITU simulations for worst-case GPS cross-correlation noise.
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Doppler Frequency of SV25
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1 kHz
UWB spectral line1575.570571 MHz
Satellite 25 spectral lines1575.571 MHz
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Spectral Line Alignment
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Aggregate Scenarios
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Spectral Effects of Gating
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Break Lock: Rx 1, Gated