A Novel Efficient Signal Processing Approach for ...

A Novel Efficient Signal Processing Approach for Combined Acquisition of GPS L1 and L2 Civilian Signals Craig R. Benson Sana U. Qaisar Michael J. Ryan University of New South Wales, Canberra AUSTRALIA November 8, 2016

Military Communications and Information Systems Conference, Canberra Australia Nov 8-10, 2016

Contents • • • • • • • • • •

Introduction to GNSS GPS Modernization Basic GPS Receiver Operation GPS Signl Acquisition Synchronized L1 and L2C Signals Combined GPS L1/L2C Acquisition Existing Approaches Proposed Approach Results Conclusions

GNSS Spectrum Each one of the following is a Global Navigation Satellite System (GNSS)

Multiple GNSS Constellations Each constellation has multiple transmission frequencies (carriers) Each carrier transmits multiple signals

System of (Global Navigation Satellite ) Systems

GNSS Radio Spectrum

[ESA– navipedia]

4

Global Positioning System (GPS) First fully operational GNSS

MEO: 20,200km World-wide coverage 15 degrees mask 60 degrees apart Period = Half sidereal day 30-operational

[USAF]

5

GPS Modernization Program Introduction of New Capabilities New Civil and Military Signals

Boeing

Lockheed Martin

Boeing

Lockheed Martin

http://www.navcen.uscg.gov/?Do=constellationstatus

6

GPS L-Band Multiple Civilian Signals

1 GHz

L5 L1C L2C

2 GHz

L1 C/A

Synchronized Transmission of L1 and L2C signals Challenges & Opportunities

How GPS receivers process signals?

PNT

Synchronizing with the satellite signal? Finding and Keeping the signals

Acquisition

Tracking

GPS Signal Acquisition 2 dimensional search space

GPS Signal Acquisition Circuit Carrier Doppler and Code Phase Search on I and Q Branches

Collect adequate signal energy to declare detection

Combined GPS L1/L2C Signal Acquisition

Increases SNR at the receiver Prevents coherent processing for extended duration on individual channels High Doppler search resolution: (2/3T)Hz

Existing Approaches for Combined L1/L2C Signal Acquisition Non-Coherent Combining L1 Channel

Coherent integration period limited to 1ms to reduce the Doppler search space

T=1ms (·)2

(·)2

Post Correlation Processing: Non-coherent (squared) combining of I and Q samples on each channel to address residual Doppler effects

+ (·)2

(·)2

L2 Channel

T=1ms

Existing Approaches for Combined L1/L2C Signal Acquisition Differentially-Coherent Combining

Coherent integration period limited to 1ms to reduce the Doppler search space

L1 Channel

T=1ms Z-1 (·)2

+

(·)2

Post Correlation Processing: Relative delay introduced for processing I and Q samples prior to squaring, on each channel

Z-1

+ Z-1

Exploits temporal decorrelation of noise to improve the SNR when compared to noncoherent combining

(·)2

+

(·)2

Z-1

L2 Channel

T=1ms

Existing Approaches for Combined L1/L2C Signal Acquisition Generalzed Differentially-Coherent Combining

Coherent integration period still limited to 1ms to reduce the Doppler search space

L1 Channel

T=1ms Z-k

Post Correlation Processing A number of relative delay introduced for processing I and Q samples prior to squaring, on each channel

k=1,2,3, ...

(·)2

+

(·)2

Z-k

+ Z-k

Attempts to fully exploit temporal decorrelation of noise to improve the SNR when compared to standard differentially-coherent combining

(·)2

+

(·)2

Z-k

L2 Channel

T=1ms

Proposed Approach for Combined L1/L2C Signal Acquisition

Two stage signal processing Nyquist-rate and audio-rate

L1 Channel

Doppler (±5kHz) search accomplished at audio stage with low processing cost (10ksps) Makes Doppler search computationally feasible over T=20ms coherent integration period L2 Channel

Acquisition Results of Real Signal From IIR-M GPS Satellites Relative processing gains for 20ms coherent integration Audio sampling interval

Proposed approach attains full coherent processing gain L2C remains 5.3dB weaker than L1

Processing/Computational Cost Comparison

20ms

Traditional Approaches Cost O(fs/Tk)

Conclusions Synchronized Transmission

Proposed Acquisition Appraoch

Acquisition Results