Simulated Signal Acquisition with Multiple Pulsed Pseudolite Signals

1. Charles Tytler Simulated Signal Acquisition with Multiple Pulsed Pseudolite Signals

2. Pseudolites • Pseudo-satellites: • Ground-based transmitters of GPS signals • Augment GPS • Applications: • Indoor GPS • Mining, Caves • Underground/Underwater Surveying • Differential GPS

3. The Near-Far Problem • The largest difficulty in pseudolite installation • A common problem for CDMA systems Illustration of distance from pseudolite and its effect on signal tracking

4. Pulsing Pseudolite Signals • Pseudolites use PRN codes 33-37 • Pulsing Scheme in simulation defined by RTCM SC-104 • Pulse Duration = 1/11 C/A Code Period • 90.91µs (93 Chips) • Every 10th period transmits 2 pulses • Pulse Duty Cycle = 10% • Entire PRN code received in 10 periods PURPOSE: • Allows pseudolite to transmit at high power without blocking out signals from satellites

5. Simulating Received Signal • White Noise: -141dBW • Satellite signals: -160dBW

6. Signal Acquisition • Pseudolite signal tracking with all four transmitting • Takes up approximately 40% of the signal • Cross-correlation plots • Correlation vs. Time delay • Each peak represents a PRN code match for a code period • Peaks should occur every 1ms Simulated for 20ms and sampled at 12MHz

7. SATELLITES 1 Pseudolite 2 Pseudolites 3 Pseudolites 4 Pseudolites

8. Pseudolite Blanking • Since satellite signals are overpowered by pseudolite pulses • Better to have zero input than interfering pulses • Receiver “blanks” all input when it detects saturation • Would need modification to GPS receivers

9. Satellite Signal Acquisitionwith and without blanking Pseudolite Blanking Applied

10. Future Recommendations • Use of multiple pseudolites in isolated areas such as open pit mining is very practical • Pseudolite configurations should be investigated • Allow use of multiple pseudolites by local users • Limit interference to other nearby receivers • Cost effective techniques for both hardware and software implementation of pseudolite blanking

11. References Cobb, H. S., “GPS Pseudolites: Theory, Design, and Applications,” Ph.D. Thesis, Stanford University, September 1997. Abt, T. L., Soualle, F., Martin, S., “Optimal Pulsing Schemes for Galileo Pseudolite Signals,” Journal of Global Positioning Systems, 2007, Vol. 6, No. 2: p166-141. Anyaegbu, E., et al, “An Integrated Pulsed Interference Mitigation for GNSS Receivers,” The Journal of Navigation, 2008, Vol. 61, No. 2: p239-255. Braasch, M., Van Dierendonck, A. J., “GPS Receiver Architectures and Measurements,” Proceedings of the IEEE, January 1999, Vol. 87, No. 1. Jovancevic, A., et al, “Piercing the Veil,” GPS World, March 2007, Vol. 18 Issue 3, p30-37. < http://www.gpsworld.com/defense/navigation/piercing-veil-3155?page_id=1> Zhang, Lei, “Simulation on C/A Codes and Analysis of GPS/Pseudolite Signals Acquisition,” Science in China Series E: Technological Sciences, Science in China Press, May 2009, Vol. 52, No. 5: p.1459-1462. Borre, K., et al, A Software-Defined GPS and Galileo Receiver: A Single-Frequency Approach. Birkhauser, Boston, MA, 2007. Misra, P., Enge, P., Global Positioning System: Signals, Measurements, and Performance. Ganga-Jamuna Press, Lincoln, MA, 2006, 2nd Edition.