GPS Beamforming with Low-cost RTL-SDRs Wil Myrick, Ph.D.

Transcription

1 with Low-cost RTL-SDRs Wil Myrick, Ph.D. September 13, 2017 Conference 2017

2 Recap from GRCon 2016 MWF Invented by Dr. Scott Goldstein and Dr. Irving Reed (1996) Initial Release (2001) Revisited GPS Work Distributed Sensor and (2013) Processing with FM SoOPs (2014) Embedded GPS Research (2015) GNSS-SDR GPS Processing Timeline of Signal Processing Experience Completed MWF based GPS STAP Ph.D. Thesis with Dr. Michael Zoltowski (2000) + Adjust the frequencies and phases based on tracking information from the RTL-SDRs 2

3 From GRCon16 to GRCon17 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 Receiver based on GNSS-SDR Framework (CTTC) Built on GNU Radio blocks Supports realtime positioning based on RTL- SDRs Supports custom algorithm integration 3

4 Robust PNT Robust Positioning, Navigation, and Timing (PNT) Standard Beamforming Solutions IoT Devices Explore Distributed with a Variety of SDRs Anti-Spoofing Fusion of SDR Measurements Multipath Robust PNT Anti-Jam # GPS Receivers + # Other RF Sensors Spatial Beamforming enables a variety of solutions that provide Robust PNT on single platforms IoT devices with low SWAP-C could share PNT information potentially providing Robust PNT solutions for a group of IoT Devices Low Swap-C RTL-SDR ENSCO TCR-D 4

5 with RTL-SDRs GNSS Signals Low-Cost RTL-SDRs Lack External Clock Inputs SDR Receivers 5

6 Typical Approaches to Synchronizing RTL-SDRs Multi-RTL Approach Yacht Spoofing UAV Spoofing Typical approaches to leveraging multiple RTL-SDRs involve hardware modifications so a single clock source is shared between the RTL-SDRs Images from Multi-RTL is block that transforms cheap multiple RTL-SDR receivers into multi-channel receiver Reference: Other References: 6

7 Overall RTL-SDR Software Approach RTL-SDR Software Snapshots IF I&Q Samples A/D IF I&Q Samples A/D Bit and Code IF I&Q Samples A/D W. Myrick, M. Picciolo, J. Scott Goldstein, A COTS based Distributed Array Processor utilizing Reduced-Rank STAP, IEEE Radar Conference, May 2013 Carrier Phase and Code Frequency Extraction 7

8 RTL-SDR Software Approach 8

9 Snapshots with RTL-SDRs RTL-SDR Software Script to capture 60 seconds of GPS data from RTL-SDRs RTL-SDR1_file_async RTL-SDR2_file_async RTL-SDR3_file_async RTL-SDR4_file_async of RTL-SDRs relative to RTL-SDR4 RTL-SDR1_file_sync RTL-SDR2_file_sync RTL-SDR3_file_sync RTL-SDR4_file_async RTL-SDR data files are synchronized relative to RTL-SDR4 after RTL-SDR software synchronization 9

10 GPS Acquisition across RTL-SDRs RTL-SDR Software RTL-SDRs provide varying GPS acquisition results RTL-SDR 1 RTL-SDR 2 RTL-SDR 3 RTL-SDR * 29* 29* 29* * PRN 29 was used as reference transmitter for RTL-SDR synchronization 10

11 Coarse (Data) and Fine (Code) RTL-SDR Software Leverage RTL-SDR 4 as the reference 19 ms 24 ms 62 ms 11

12 Coarse (Data) and Fine (Code) RTL-SDR Software Leverage RTL-SDR 4 as the reference 12

13 Carrier on RTL-SDRs RTL-SDR Software Differential phase of PRN 29 relative to RTL-SDR 4 Clock Drift 13

14 Carrier on RTL-SDRs (PRN 29) RTL-SDR Software Differential carrier phase with clock drift compensation 14

15 Carrier on RTL-SDRs (PRN 15) RTL-SDR Software Differential carrier phase with clock drift compensation 15

16 Carrier on RTL-SDRs (PRN 13) RTL-SDR Software Differential carrier phase with clock drift compensation 16

17 Carrier on RTL-SDRs (PRN 2) RTL-SDR Software Differential carrier phase with clock drift compensation 17

18 Carrier on RTL-SDRs (PRN 20) RTL-SDR Software Differential carrier phase with clock drift compensation 2 18

19 Carrier on RTL-SDRs (PRN 5) RTL-SDR Software Differential carrier phase with clock drift compensation 19

20 RTL-SDR Performance RTL-SDR Software RTL-SDR Beamforming Performance per PRN RTL-SDR 4 Beamformer Gain 5.06 db 5.39 db 4.56 db 2.89 db 4.47 db 4.14 db Ideal Gain: ~6dB 20

21 GPS Acquisition across RTL-SDRs RTL-SDR Software GNSS-SDR operating on Raspberry Pi 3 PROMPT SCREEN 21

22 RTL-SDR Beamformer Comparison (SDR 2) RTL-SDR 2 Only Best RTL-SDR Beamformer 22

23 RTL-SDR Beamformer Comparison (SDR 3) RTL-SDR 3 Only Best RTL-SDR Beamformer 23

24 RTL-SDR Beamformer Comparison (SDR 4) RTL-SDR 4 Only Best RTL-SDR Beamformer 24

25 Robust PNT Summary and Next Steps Initial results show feasibility of GPS beamforming utilizing RTL-SDRs without hardware modification Software 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 Low Swap-C RTL-SDR Explore Distributed with a Variety of SDRs Fusion of SDR Measurements # GPS Receivers + # Other RF Sensors ENSCO TCR-D 25

26 Questions? Wilbur L. Myrick, Ph.D. (703) Ideas to Reality