1. SE40 Meeting on Pseudolites JRC test results
04-05 July 2011

2. Conclusion and Future Work
Outline
Previous Results
Saturation Loss Model
Experimental Setup
Results
Conclusion and Future Work

3. Previous Results Experiments on Commercial Receivers - conducted mode
- pulsed and continuous pseudolite signals
- measurements and position domain analysis
(results published in “Impact of Pseudolite Signals on Non-Participating GPS Receivers”, JRC Scientific and Technical Report)
Scoping Study on Pseudolites
Investigation of pseudolite technology and applications (published as JRC Scientific and Technical Report)

4. Impact on Non-participating Receivers
4/14
Assess the pseudolite impact on non-participating receivers:
+ theoretical analysis:
development of a model able to predict the loss caused by pseudolite signals
+ experimental analysis:
Hardware and software simulations Experiments using RF signals in conducted and radiated mode
Software based and hardware commercial receivers
GPS and GALILEO
+ use of commercial pseudolites
- Space System Finland (SSF)

5. Theoretical Analysis: Model Assumptions
5/14
Theoretical model capable of predicting the impact of pulsed pseudolite signals on non-participating receivers.
Signal Conditioning
ADC
ADC working in saturation mode
Ideal and very slow AGCs: the AGC gain is constant
Down-conversion
Filtering
AGC
Loss computed at the correlator output (impact of the despreading process)
Complex Correlator Output
Local
Carrier
Local
Code

6. Theoretical Analysis: Receiver Losses
6/14
Account for:
Quantization effects: ADC and AGC
Pulse duration
Spectral separation between pseudolite and GNSS signals
Simulation results supporting the theoretical analysis
Pulse duty cycle
Quantization loss
ADC: number of bits
AGC gain

7. Receiver Losses: Results
7/14
Theoretical results supported by “field tests” (simulation of RF pseudolite signals)
Experiments using commercial hardware receivers
Good agreement with theoretical results
Residual differences due to lack of information on the commercial Rx (black box):
number of bits, AGC type, ...

8. Experimental Setup (I/II)
8/14
Experiments in Anechoic Chamber
Up to three GPS PLs
Space Systems Finland
GPS + Galileo Constellation simulator
Spirent Communications
Two commercial receivers
GPS + Galileo: Simulated
Experiments:
Single PL: continuous
Single PL: pulsed
3 PLs: pulsed
Anechoic
Chamber
GPS
Pseudolites
SSF
Receivers:
Javad: Survey GPS+Galileo
u-Blox: High Sensitivity GPS

9. Experimental Setup (II/II)
9/14
Fixed PL – Rx geometry maintained throughout tests
~ 5 m between PL and Rx antennas
Tx power and/or pulse duty cycle was varied
Baseline performance  simulator run with all PLs switched off
Performance metric  C/N0 loss for satellite signals relative to baseline
PL Antennas
Rx Antenna

10. Impact of Pulsed PL (I/II)
10/14
Single PL – Pulse Duty Cycle (PDC) ~ 9.35 %
Constant geometry – Transmit power increased by 3 dB every 5 minutes
C/N0 loss in non-participating receivers averaged over all satellites
Notes:
Galileo less affected  impact of spectral separation coefficients
Javad receiver shows greater loss than u-Blox  impact of receiver bandwidth and, potentially, bit-depth

11. Impact of Pulsed PL (II/II)
11/14
“Ideal” loss model: (loss incurred with no quantization effects)
SSC – Spectral separation coefficient
P/N0 – Effective PL power to noise density ratio
“ideal” model  loss gets worse with increasing P/N0
In practice  Saturation limits loss
N.B.  The “better” the receiver (larger BW, more bits) the worse the effect of the pulsed PL

12. Continuous vs. Pulsed
12/14
Continuous case: Receivers had difficulty tracking as PL C/N0 increased
Continuous case: additional losses due to compression by AGC
Advantages of pulsing apparent from the results
Lines  Continuous PL
Markers  Pulsed PL
Note:
u-Blox shows greater losses for continuous PL  due to ability to track weaker signals
Javad fails to track most GPS signals when P/N0 > 54 dB-Hz

13. Multiple Pulsed Pseudolites
13/14
For this test  PLs configured to operate in pulsed mode
Power levels high  receivers operate in saturation
Pulse duty cycle varied in range 2 to 9 %
Aggregate duty cycle up to 3 times these values
Note:
At PDC ~ 4%  loss is similar to single PL with PDC of 9%
u-Blox experiences marked increase in losses for larger PDC
Effect of AGC?

14. Conclusion and Future Work
14/14
Conclusions
Developed a loss model to account for quantization effects
For the same effective P/N0, continuous mode PLs induce greater losses than pulsed mode PLs
Due to capture of the AGC
Radiated-mode test-bed confirms conducted-mode results
Future Work
Further analysis of these results – particularly multiple PL case
Improve model to account for non-ideal AGC (i.e. consider the impact of the pulsed PL on the AGC)
Further testing
Acknowledgement
JRC thanks Space Systems Finland for the generous loan of the pseudolites used in these tests.