gps beamforming with low-cost rtl-sdrs - gnu radio · 2020-05-13 · 3 streamed 60 seconds of data...
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GPS Beamforming with Low-cost RTL-SDRs
Wil Myrick, Ph.D.
September 13, 2017
GNU Radio Conference 2017
2
Recap from GRCon 2016
Timelineof Signal Processing Experience
MWF Invented by Dr. Scott Goldstein and Dr. Irving Reed (1996)
GNU Radio Initial Release (2001)
Completed MWF based GPS STAP Ph.D. Thesis with Dr. Michael Zoltowski (2000)
Revisited GPS Work and GNU Radio (2013)
Asynchronous Distributed Sensor Processing with FM
SoOPs (2014)
Embedded GPS Research
(2015)
+
GNSS-SDR GPS Processing
Adjust the frequencies and phases based on tracking
information from the RTL-SDRs
3
Streamed 60 seconds of data from each RTL-SDR
(2016)
Demodulated navigation data for each detected
channel (2016)
Tracked delay, frequency, and phase from each
RTL-SDR (2016)
Time, frequency, and phase alignment based on
RTL-SDRs sharing no common external references
RTL-SDR based GPS beamformer with GNSS-SDR
GPS position estimates from beamformed RTL-
SDRs
GNSS-SDR on Raspberry Pi 3
From GRCon16 to GRCon17
http://gnss-sdr.org/documentation/how-gnss-sdr-works
GNU Radio
Receiver based
on GNSS-SDR
Framework
(CTTC)
• Built on GNU Radio blocks
• Supports real-time positioning based on RTL-SDRs
• Supports custom algorithm integration
4
Robust Positioning, Navigation, and Timing (PNT)
Robust PNT
# GPS Receivers + # Other RF Sensors
Anti-Spoofing
Anti-JamMultipath Ro
bu
st P
NT
Spatial Beamforming enables a variety of solutions that provide Robust PNT on single platforms
IoT Devices
IoT devices with low SWAP-C could share PNT information potentially providing Robust PNT solutions for a group of IoTDevices
Explore Distributed GPS Beamforming with a Variety of SDRs
Standard Beamforming Solutions
Fusion of SDR Measurements
ENSCOTCR-D
Low Swap-CRTL-SDR
5
GPS Beamforming with RTL-SDRs
Asynchronous SDR Receivers
GNSS Signals
Low-Cost RTL-SDRs Lack External Clock Inputs
6
Yacht Spoofing
UAV Spoofing
Typical Approaches to Synchronizing RTL-SDRs
Multi-RTL Approach
Other References: http://superkuh.com/rtlsdr.html#clocks.align.multirtl
Images from https://github.com/ptrkrysik/multi-rtl
“Multi-RTL is GNU Radio block that transforms cheap multiple RTL-SDR receivers into multi-channel receiver” Reference: https://github.com/ptrkrysik/multi-rtl
Typical approaches
to leveraging
multiple RTL-SDRs
involve hardware
modifications so a
single clock source
is shared between
the RTL-SDRs
7
Overall RTL-SDR “Software” Synchronization Approach
Coarse Bit Synchronization based on PRN
Fine Chip Code Synchronization based on PRN
IF I&Q Samples
A/D Asynchronous Snapshot Files
GPS Beamforming based on Carrier Phase Extraction
IF I&Q Samples
A/D
IF I&Q Samples
A/D
RTL-SDR Software Synchronization
GPS Extraction
GNU Radio GNSS-SDR Receiver
W. Myrick, M. Picciolo, J. Scott Goldstein,“A COTS based Asynchronous Distributed Array Processor utilizing Reduced-Rank STAP,” IEEE Radar Conference, May 2013
Asynchronous Snapshots
Bit and Code Synchronization
Carrier Phase and Code Frequency Extraction
8
RTL-SDR “Software” Synchronization Approach
9
Asynchronous Snapshots with RTL-SDRs
Coarse Bit Synchronization based on PRN
Fine Chip Code Synchronization based on PRN
Asynchronous Snapshot Files
GPS Beamforming based on Carrier Phase Extraction
RTL-SDR Software Synchronization
GPS Extraction
GNU Radio GNSS-SDR Receiver
RTL-SDR1_file_asyncRTL-SDR2_file_asyncRTL-SDR3_file_asyncRTL-SDR4_file_async
Script to capture 60 seconds of GPS data from RTL-SDRs
RTL-SDR1_file_syncRTL-SDR2_file_syncRTL-SDR3_file_sync
RTL-SDR4_file_async
RTL-SDR data files are synchronized relative to RTL-SDR4 afterRTL-SDR software synchronization
Synchronization of RTL-SDRs relative
to RTL-SDR4
10
GPS Acquisition across RTL-SDRs
Coarse Bit Synchronization based on PRN
Fine Chip Code Synchronization based on PRN
Asynchronous Snapshot Files
GPS Beamforming based on Carrier Phase Extraction
RTL-SDR Software Synchronization
GPS Extraction
GNU Radio GNSS-SDR Receiver
RTL-SDRs provide varying GPS acquisition results
RTL-SDR 1 RTL-SDR 2 RTL-SDR 3 RTL-SDR 4
13 13 13 13
15 15 15 15
29* 29* 29* 29*
2 - 2 2
5 5 5 5
20 20 - 20
* PRN 29 was used as reference transmitter for RTL-SDR synchronization
11
Coarse (Data) and Fine (Code) Synchronization
Coarse Bit Synchronization based on PRN
Fine Chip Code Synchronization based on PRN
Asynchronous Snapshot Files
GPS Beamforming based on Carrier Phase Extraction
RTL-SDR Software Synchronization
GPS Extraction
Leverage RTL-SDR 4 as the reference
GNU Radio GNSS-SDR Receiver
19 ms
24 ms
62 ms
12
Coarse (Data) and Fine (Code) Synchronization
Coarse Bit Synchronization based on PRN
Fine Chip Code Synchronization based on PRN
Asynchronous Snapshot Files
GPS Beamforming based on Carrier Phase Extraction
RTL-SDR Software Synchronization
GPS Extraction
Leverage RTL-SDR 4 as the reference
GNU Radio GNSS-SDR Receiver
13
Carrier Phase Extraction on RTL-SDRs
Coarse Bit Synchronization based on PRN
Fine Chip Code Synchronization based on PRN
Asynchronous Snapshot Files
GPS Beamforming based on Carrier Phase Extraction
RTL-SDR Software Synchronization
GPS Extraction
Differential phase of PRN 29 relative to RTL-SDR 4
GNU Radio GNSS-SDR Receiver
Clock Drift
14
Carrier Phase Extraction on RTL-SDRs (PRN 29)
Coarse Bit Synchronization based on PRN
Fine Chip Code Synchronization based on PRN
Asynchronous Snapshot Files
GPS Beamforming based on Carrier Phase Extraction
RTL-SDR Software Synchronization
GPS Extraction
Differential carrier phase with clock drift compensation
GNU Radio GNSS-SDR Receiver
15
Coarse Bit Synchronization based on PRN
Fine Chip Code Synchronization based on PRN
Asynchronous Snapshot Files
GPS Beamforming based on Carrier Phase Extraction
RTL-SDR Software Synchronization
GPS Extraction
GNU Radio GNSS-SDR Receiver
Carrier Phase Extraction on RTL-SDRs (PRN 15)
Differential carrier phase with clock drift compensation
16
Coarse Bit Synchronization based on PRN
Fine Chip Code Synchronization based on PRN
Asynchronous Snapshot Files
GPS Beamforming based on Carrier Phase Extraction
RTL-SDR Software Synchronization
GPS Extraction
GNU Radio GNSS-SDR Receiver
Carrier Phase Extraction on RTL-SDRs (PRN 13)
Differential carrier phase with clock drift compensation
17
Coarse Bit Synchronization based on PRN
Fine Chip Code Synchronization based on PRN
Asynchronous Snapshot Files
GPS Beamforming based on Carrier Phase Extraction
RTL-SDR Software Synchronization
GPS Extraction
GNU Radio GNSS-SDR Receiver
Carrier Phase Extraction on RTL-SDRs (PRN 2)
Differential carrier phase with clock drift compensation
18
Coarse Bit Synchronization based on PRN
Fine Chip Code Synchronization based on PRN
Asynchronous Snapshot Files
GPS Beamforming based on Carrier Phase Extraction
RTL-SDR Software Synchronization
GPS Extraction
GNU Radio GNSS-SDR Receiver
Carrier Phase Extraction on RTL-SDRs (PRN 20)
Differential carrier phase with clock drift compensation
2
19
Coarse Bit Synchronization based on PRN
Fine Chip Code Synchronization based on PRN
Asynchronous Snapshot Files
GPS Beamforming based on Carrier Phase Extraction
RTL-SDR Software Synchronization
GPS Extraction
GNU Radio GNSS-SDR Receiver
Carrier Phase Extraction on RTL-SDRs (PRN 5)
Differential carrier phase with clock drift compensation
20
GPS Beamforming RTL-SDR Performance
Coarse Bit Synchronization based on PRN
Fine Chip Code Synchronization based on PRN
Asynchronous Snapshot Files
GPS Beamforming based on Carrier Phase Extraction
RTL-SDR Software Synchronization
GPS Extraction
GNU Radio GNSS-SDR Receiver
RTL-SDR Beamforming Performance per PRN
Beamformer Gain
RTL-SDR 4
4.14 dB4.47 dB2.89 dB
5.06 dB
Ideal Gain: ~6dB
5.39 dB 4.56 dB
21
GPS Acquisition across RTL-SDRs
Coarse Bit Synchronization based on PRN
Fine Chip Code Synchronization based on PRN
Asynchronous Snapshot Files
GPS Beamforming based on Carrier Phase Extraction
RTL-SDR Software Synchronization
GPS Extraction
GNU Radio GNSS-SDR Receiver
PROMPT SCREEN
GNSS-SDR operating on Raspberry Pi 3
22
RTL-SDR Beamformer Comparison (SDR 2)
RTL-SDR 2 Only Best RTL-SDR Beamformer
23
RTL-SDR Beamformer Comparison (SDR 3)
RTL-SDR 3 Only Best RTL-SDR Beamformer
24
RTL-SDR Beamformer Comparison (SDR 4)
RTL-SDR 4 Only Best RTL-SDR Beamformer
25
Summary and Next Steps
# GPS Receivers + # Other RF Sensors
Ro
bu
st P
NT
Explore Distributed GPS Beamforming with a Variety of SDRs
Fusion of SDR Measurements
ENSCOTCR-D
Low Swap-CRTL-SDR
Initial results show feasibility of GPS beamforming utilizing RTL-SDRs without hardware modification
“Software Synchronization” preprocessing approach of RTL-SDRs allow exploration of GPS beamforming leveraging existing GNSS-SDR processing architecture
Plan to explore distributed GPS beamforming with a mixture of SDRs in a variety of environments
Ideas to Reality™
Wilbur L. Myrick, Ph.D.
myrick.wilbur@ensco.com
(703) 321-4504
Questions?
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