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Cross Correlation Mitigation for C/A Code GPS Signals & It’s Applications

Cross Correlation Mitigation for C/A Code GPS Signals & It’s Applications. Eamonn Glennon. Cross Correlation Problem. a.k.a. Multiple Access Interference or Near/Far Problem Caused by Non-Orthogonal Spreading Codes Example of SV 1, 2 & 3 at amplitudes of 0.1, 1 and 1.

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Cross Correlation Mitigation for C/A Code GPS Signals & It’s Applications

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  1. Cross Correlation Mitigation for C/A Code GPS Signals &It’s Applications Eamonn Glennon School of Surveying & Spatial Information Systems The University of New South Wales, Australia

  2. Cross Correlation Problem • a.k.a.Multiple Access Interference or Near/Far Problem • Caused by Non-Orthogonal Spreading Codes • Example of SV 1, 2 & 3 at amplitudes of 0.1, 1 and 1 Eamonn Glennon

  3. Adaptive Orthogonalisation Using Constraints (AOUC) • Minor modify de-spreading codes to guarantee orthogonality • De-spreading codes not matched to spreading codes • “Flip-Chips” to improve problem cross correlations without degrading good/other cross correlations • Must allow for Relative Doppler Carrier (RDC) effects • Implemented using simple logic, addition & subtraction only • Estimation of strong signal amplitudes is not required • Tracking channels must be phase-locked to strong signals • Fails with 4 or 5 strong signals Eamonn Glennon

  4. Delayed Parallel Interference Cancellation (DPIC) • Variation on Successive Interference Cancellation (SIC) • Post-correlation cancellation is employed • Slave channels used to generate pure CC using pure reconstructed IF • 1 slave-channel for each cross correlation pair • Advantages include simple hardware, avoidance of multi-bit subtraction process and ability to also remove CW interference Eamonn Glennon

  5. DPIC Detailed Block Diagram Standard correlator with carrier & code outputs signals Regenerate pure IF Slave correlators for pure IF Standard correlator for weak signal Eamonn Glennon

  6. Cross Correlation Mitigation Test Methodology • Data collected using a WelNav GS700 GPS Simulator – 1,2,3 & 4 strong signal scenario’s • Captured using a SigNav MG5001 GPS board, a serial to parallel adaptor and a NI 6530 PCI digital IO card running on a standard Windows PC. • Post-processed using a derivative of the Ledvina bitwise parallel algorithm for efficient SW correlation written in C • C code called from Matlab using the MEX API Eamonn Glennon

  7. AOUC & DPIC Test Result (3 Strong Signals) AOUC 1-bitDF=208(23.2 dB) AOUC 2-bitDF=160(22.0 dB) DPICDF=279(24.5 dB) No CCM(10 dB) Eamonn Glennon

  8. Applications • Signal processing of (weak) bistatically reflected GPS signals in the presence of other strong (direct) GPS signals • Tracking of signals indoors where one or two strong (direct) GPS signals prevent detection of weaker indirect signals • Use of use pseudolites where strong pseuolites prevent acquisition of weaker GPS signals. Eamonn Glennon

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