GLOBAL POSITIONING SYSTEM USING BROADBAND NOISE REDUCTION

• US 20080211715A1
• Filed: 08/16/2007
• Published: 09/04/2008
• Est. Priority Date: 08/17/2006
• Status: Abandoned Application

• Current Assignee: Cornerturn LLC, Technology Focus LLC
• Original Assignee: Cornerturn LLC, Technology Focus LLC
• Inventors: SLATER, Joshua G., SAGLEMBENI, Anthony, FEINTUCH, Paul L., BORRELL, Ronald A.
• Application Number:
  US11/839,616
• Publication Number:
  US 20080211715A1
• Time in Patent Office: Days
• US Class Current: 342/357.12
• CPC Class Codes: G01S 19/24 Acquisition or tracking or demodulation of signals transmitted by the system synchronisation aspects of direct sequence spread spectrum modulation H04B1/7073
• CPC Class Codes: G01S 19/29 carrier including Doppler, related G01S19/246 takes precedence

Abstract

The present invention is directed to a global positioning system (GPS) having improved signal-to-noise ratio for reducing the required signal level for which GPS may be implemented in electronic devices or cell phones. The acquisition function of the GPS receiver is improved by inserting new signal processing for broadband noise reduction that allows subsequent improved estimation of critical time shift and frequency shift parameters needed for GPS acquisition at lower received signal levels. The decoding of the navigation bits from the satellite transmissions is improved to provide ephemeris data needed for computing navigation solutions at lower received signal levels, by examining the output of the same new signal processing for broadband noise reduction for spikes in the power of the output time series that correspond to navigation bit flips.

Claims

1. A method for GPS signal processing comprising:

sensing GPS signals from a plurality of satellites through an antenna and preamplifier;

receiving the GPS signals from the antenna and preamplifier in an RF stage;

down converting the GPS signals from RF to IF frequencies in a down converter;

converting the IF GPS signals to digital GPS signals in an analog-to-digital converter (A/D);

inputting the digital GPS signals to a digital signal processor;

buffering the digital GPS signals in the digital signal processor to obtain a block of time sampled digital GPS signals;

multiplying the block of time sampled digital GPS signals by a coarse acquisition (C/A) code in the digital signal processor to obtain a decoded GPS signal, the C/A code being concatenated over a time interval that matches the buffered block of time sampled digital GPS signals;

filtering and decimating the decoded GPS signal in the digital signal processor to reduce the sample rate to produce a reduced sample rate signal;

reducing a broadband noise component of the reduced sample rate signal by;

applying the reduced sample rate signal to a bulk delay to provide a delayed version of the reduced sample rate signal,

adaptively filtering the delayed version of the reduced sample rate signal in an adaptive filter to generate an adaptive filter output signal,

subtracting the adaptive filter output signal from the reduced sample rate signal to generate an error signal,

feeding back the error signal to the adaptive filter, and

iteratively adjusting a plurality of filter weighting parameters in the adaptive filter in response to the error signal to modify the adaptive filter output signal having a reduced level of the broadband noise component;

performing spectral analysis of the adaptive filter output signal to detect a shifted carrier frequency by performing spectral bin-to-bin comparisons on a plurality of discrete frequency bins;

selecting a peak spectral bin based on a greatest power value for all time shifts associated with the C/A codes, and comparing the greatest power value in the peak spectral bin to a threshold value;

associating the time shift of the C/A code and the frequency bin with greatest power value that exceeds the threshold, to be the time shift estimate and frequency shift estimate;

passing the time shift estimate and frequency shift estimate to a signal tracking function to produce a refined time shift estimate and a refined frequency shift estimate; and

passing the refined time shift estimate and the refined frequency shift estimate from the signal tracking function to a navigation processor that combines the refined time shift estimate and the refined frequency shift estimate with ephemeris data to calculate a GPS location.

2. The method of claim 1, wherein the step of adaptively filtering includes providing an adaptive filter that uses a Least Mean Square (LMS) algorithm to iteratively adjusting a plurality of filter weighting parameters in the adaptive filter.

3. The method of claim 1, wherein the bulk delay predetermined amount of time is greater than the correlation time of the broadband noise component of the delayed version of the reduced sample rate signal, and less than a correlation time of the GPS signal component of the reduced sample rate signal, such that the delayed signal broadband noise component is decorrelated, and the delayed version of the GPS signal portion of the reduced sample rate signal is correlated with respect to the reduced sample rate signal.

4. The method of claim 1, wherein the step of iteratively adjusting a plurality of filter weighting parameters in the adaptive filter further includes developing a transfer function that passes the GPS signal portion of the reduced sample rate signal while lowering the broadband noise component of the reduced sample rate signal.

5. The method of claim 1, wherein the time shift is used to estimate the value of the propagation travel time from the satellite to the GPS receiver.

6. The method of claim 1, wherein the signal tracking function includes the step of using Delay Lock Loops (FLL) and Phase Lock Loops (PLL) for refining and tracking changes in the time shift estimate and the frequency shift estimate.

7. The method of claim 1, wherein the step of performing spectral analysis of the adaptive filter output signal is achieved by using a Fast Fourier Transform (FFT) algorithm.

8. The method of claim 1, further including replicating, for each of the plurality of time shifts of the C/A code, all of the digital signal processing steps in claim 1 up to and including spectrum analysis.

9. The method of claim 8, wherein the step of replicating is performed in one-half C/A code bit chip time steps, until the C/A code repeats.

10. The method of claim 9, wherein the step of multiplying by the C/A code time-shifted replicas reduces the bandwidth of the digital GPS signals and removes the spectral spreading induced by the C/A code modulation.

11. The method of claim 9, wherein the C/A code repeats every 1024 bit chips, and use ½

bit chip shifts to generate 2048 versions of the C/A code being concatenated over a time interval that matches the buffered block of time sampled digital GPS signals

12. A method for GPS signal processing comprising:

sensing GPS signals from a plurality of satellites through an antenna and preamplifier;

receiving the GPS signals from the antenna and preamplifier in an RF stage;

down converting the GPS signals from RF to IF frequencies in a down converter;

converting the IF GPS signals to digital GPS signals in an analog-to-digital converter (A/D);

inputting the digital GPS signals to a digital signal processor;

buffering the digital GPS signals in the digital signal processor to obtain a block of time sampled digital GPS signals;

multiplying the block of time sampled digital GPS signals by a coarse acquisition (C/A) code in the digital signal processor to obtain a decoded GPS signal, the C/A code being concatenated over a time interval that matches the buffered block of time sampled digital GPS signals;

filtering and decimating the decoded GPS signal in the digital signal processor to reduce the sample rate to produce a reduced sample rate signal;

reducing a broadband noise component of the reduced sample rate signal by;

applying the reduced sample rate signal to a bulk delay to provide a delayed version of the reduced sample rate signal,

adaptively filtering the delayed version of the reduced sample rate signal in an adaptive filter to generate an adaptive filter output signal,

subtracting the adaptive filter output signal from the reduced sample rate signal to generate an error signal,

feeding back the error signal to the adaptive filter, and

iteratively adjusting a plurality of filter weighting parameters in the adaptive filter in response to the error signal to modify the adaptive filter output signal having a reduced level of the broadband noise component;

detecting flips in the NAV bits and decoding the NAV bits by detecting a plurality of negative spikes in a short time power estimate of the time waveform of the adaptive filter output signal, and associating the occurrence of the detected spikes with a change of the NAVbits from a zero to a one or from a one to zero, and by associating a corresponding time of the spike with a boundary in time of the NAV bit shift; and

passing the NAVbits to a navigation processor where the NAV bits are decoded into a set of ephemeris data, the ephemeris data being used in navigational calculations to obtain a GPS location.

13. The method of claim 12, wherein the step of adaptively filtering includes providing an adaptive filter that uses a Least Mean Square (LMS) algorithm to iteratively adjusting a plurality of filter weighting parameters in the adaptive filter.

14. The method of claim 12, wherein the bulk delay predetermined amount of time is greater than the correlation time of the broadband noise component of the reduced sample rate signal, and less than a correlation time of the GPS signal component of the reduced sample rate signal, such that the delayed signal broadband noise component is decorrelated, and the GPS signal portion of the delayed version of the reduced sample rate signal is correlated with respect to GPS signal portion of the reduced sample rate signal.

15. The method of claim 12, wherein the step of iteratively adjusting a plurality of filter weighting parameters in the adaptive filter further includes developing a transfer function that passes the GPS signal portion of the reduced sample rate signal while lowering the broadband noise component of the reduced sample rate signal.

16. A method for GPS signal processing comprising:

sensing GPS signals from a plurality of satellites through an antenna and preamplifier;

receiving the GPS signals from the antenna and preamplifier in an RF stage;

down converting the GPS signals from RF to IF frequencies in a down converter;

converting the IF GPS signals to digital GPS signals in an analog-to-digital converter (A/D);

inputting the digital GPS signals to a digital signal processor;

buffering the digital GPS signals in the digital signal processor to obtain a block of time sampled digital GPS signals;

multiplying the block of time sampled digital GPS signals by a coarse acquisition (C/A) code in the digital signal processor to obtain a decoded GPS signal, the C/A code being concatenated over a time interval that matches the buffered block of time sampled digital GPS signals;

filtering and decimating the decoded GPS signal in the digital signal processor to reduce the sample rate to produce a reduced sample rate signal;

reducing a broadband noise component of the reduced sample rate signal by;

applying the reduced sample rate signal to a bulk delay to provide a delayed version of the reduced sample rate signal,

adaptively filtering the delayed version of the reduced sample rate signal in an adaptive filter to generate an adaptive filter output signal,

subtracting the adaptive filter output signal from the reduced sample rate signal to generate an error signal,

feeding back the error signal to the adaptive filter, and

iteratively adjusting a plurality of filter weighting parameters in the adaptive filter in response to the error signal to modify the adaptive filter output signal having a reduced level of the broadband noise component;

performing spectral analysis of the adaptive filter output signal to detect a shifted carrier frequency by performing spectral bin-to-bin comparisons on a plurality of discrete frequency bins;

selecting a peak spectral bin based on a greatest power value for all time shifts associated with the C/A codes, and comparing the greatest power value in the peak spectral bin to a threshold value;

associating the time shift of the C/A code and the frequency bin with greatest power value that exceeds the threshold, to be the time shift estimate and frequency shift estimate;

passing the time shift estimate and frequency shift estimate to a signal tracking function to produce a refined time shift estimate and a refined frequency shift estimate; and

passing the refined time shift estimate and the refined frequency shift estimate from the signal tracking function to a navigation processor that combines the refined time shift estimate and the refined frequency shift estimate with ephemeris data to calculate a GPS location.

detecting flips in the NAV bits and decoding the NAV bits by detecting a plurality of negative spikes in a short time power estimate of the time waveform of the adaptive filter output signal, and associating the occurrence of the detected spikes with a change of the NAVbits from a zero to a one or from a one to zero, and by associating a corresponding time of the spike with a boundary in time of the NAV bit shift; and

passing the NAVbits to a navigation processor where the NAV bits are decoded into a set of ephemeris data, the ephemeris data being used in navigational calculations to obtain a GPS location.

17. A method for GPS signal processing comprising:

sensing GPS signals from a plurality of satellites through an antenna and preamplifier;

receiving the GPS signals from the antenna and preamplifier in an RF stage;

down converting the GPS signals from RF to IF frequencies;

buffering the GPS signals to obtain a block of time-sampled GPS signals

multiplying the block of time-sampled GPS signals by a concatenated coarse acquisition code to obtain a decoded GPS signals;

modifying the decoded GPS signal to produce a reduced sample rate signal having a reduced sample rate relative to the decoded GPS signal;

reducing the spectral level of the broadband noise component of the reduced sample rate GPS signal by broadband noise reduction filtering the reduced sample rate GPS signal to produce an broadband noise reduced filtered signal;

spectrally analyzing the broadband noise reduced filtered signal;

obtaining a time-shift estimate and a frequency shift estimate from the spectrally analyzed broadband noise reduced filtered signal;

refining the time shift estimate and the frequency shift estimate; and

passing the refined time shift estimate and the refined frequency shift estimate to a navigation processor that utilizes the refined time shift estimate and the refined frequency shift estimate to calculate a GPS location.

18. A method for GPS signal processing comprising:

sensing GPS signals from a plurality of satellites through an antenna and preamplifier;

receiving the GPS signals from the antenna and preamplifier in an RF stage;

down converting the GPS signals from RF to IF frequencies;

buffering the GPS signals to obtain a block of time-sampled GPS signals

multiplying the block of time-sampled GPS signals by a concatenated coarse acquisition code to obtain a decoded GPS signals;

modifying the decoded GPS signal to produce a reduced sample rate signal having a reduced sample rate relative to the decoded GPS signal;

reducing the spectral level of the broadband noise component of the reduced sample rate GPS signal by broadband noise reduction filtering the reduced sample rate GPS signal to produce a broadband noise reduced filtered signal;

spectrally analyzing the broadband noise reduced filtered signal;

obtaining a time-shift estimate and a frequency shift estimate from the spectrally analyzed broadband noise reduced filtered signal;

refining the time shift estimate and the frequency shift estimate;

detecting flips in the NAVbits and decoding the NAVbits by analysis of spikes in a short-time power estimate of the time waveform of the broadband noise reduced filter output signal; and

passing the NAVbits and the refined time shift estimate and the refined frequency shift estimate to a navigation processor that utilizes the refined time shift estimate and the refined frequency shift estimate and the NAVbits to calculate a GPS location.

19. A system for GPS signal processing comprising:

an antenna tuned for receiving GPS signals from satellite vehicles;

a preamplifier to scale the GPS signals providing a preamplified GPS signal;

an RF filter and down converter, to convert the preamplified GPS signal from an RF GPS signal to an IF GPS signal;

an analog-to-digital converter configured to convert the IF GPS signal to a digital GPS signal; and

a digital signal processor including;

a buffer and a multiplier element configured to correlate the digitized GPS signal with a plurality of time shifted versions of the coarse acquisition (C/A) code forming a plurality of decoded GPS signals for each time shift,

a frequency shift estimation portion for processing the output of the multiplier element, the frequency shift estimation portion including;

a sample rate reducer, a broadband noise reduction (BBNR) processor followed by an FFT algorithm, and a threshold comparator portion,

the BBNR processor implementing an LMS adaptive filter consisting of a tapped delay line with weightings on each tap in the tapped delay line followed by summation of the weighted tapped delay line outputs to produce an adaptive filter output, where the weightings on each tap are updated in time using the LMS adaptive filter algorithm,

the BBNR processor configured to reduce the broadband noise level of the multiplier output by using a delayed version of the multiplier output as the input to the LMS adaptive filter and multiplier output itself as the reference in the LMS adaptive filter algorithm,

a spectral analysis processor using the FFT algorithm configured to estimate a frequency value at which a peak value occurs in the FFT output for each of the plurality time shifts of the C/A code at the multiplier input,

and the threshold comparator portion configured to select a peak value of all FFT outputs and all C/A code time shifts that exceeds a threshold value, and associating the time shift estimate and the frequency shift estimate with the combination of time shifts of the C/A code and the FFT frequency that produces the overall peak value,

a tracker portion that refines the time shift estimate and the frequency shift estimate; and

the navigation portion which computes a GPS location from the refined time shift estimate and the refined frequency shift estimate along with ephemeris data .

20. A system for GPS signal processing comprising:

an antenna tuned for receiving GPS signals from satellite vehicles;

a preamplifier to scale the GPS signals providing a preamplified GPS signal;

an RF filter and down converter, to convert the preamplified GPS signal from an RF GPS signal to an IF GPS signal;

an analog-to-digital converter configured to convert the IF GPS signal to a digital GPS signal; and

a digital signal processor including;

a buffer and a multiplier element configured to correlate the digitized GPS signal with a plurality of time shifted versions of the coarse acquisition (C/A) code forming a plurality of decoded GPS signals for each time shift,

a frequency shift estimation portion for processing the output of the multiplier element, the frequency shift estimation portion including;

a sample rate reducer, a broadband noise reduction (BBNR) processor followed by an FFT algorithm, and a threshold comparator portion,

the BBNR processor implementing an LMS adaptive filter consisting of a tapped delay line with weightings on each tap in the tapped delay line followed by summation of the weighted tapped delay line outputs to produce an adaptive filter output, where the weightings on each tap are updated in time using the LMS adaptive filter algorithm,

the BBNR processor configured to reduce the broadband noise level of the multiplier output by using a delayed version of the multiplier output as the input to the LMS adaptive filter and multiplier output itself as the reference in the LMS adaptive filter algorithm,

a processor that estimates the bit values and the bit change times of the ephemeris data encoded in the RF signals from each satellite by implementing the following;

a processor detecting flips in the NAV bits and decoding the NAV bits by detecting a plurality of spikes in a short time power estimate of the time waveform of the adaptive filter output signal, and associating the occurrence of the detected spikes with a flips of the NAVbits from a zero to a one or from a one to zero, and by associating a corresponding time of the spike with a boundary in time of the NAV bit flip; and

a connection that passes the NAVbits to a navigation processor where the NAV bits are decoded into a set of ephemeris data, the ephemeris data being used in navigational calculations to obtain a GPS location.

21. A system for GPS signal processing comprising:

an antenna tuned for receiving GPS signals from satellite vehicles;

a preamplifier to scale the GPS signals providing a preamplified GPS signal;

an RF filter and down converter, to convert the preamplified GPS signal from an RF GPS signal to an IF GPS signal;

an analog-to-digital converter configured to convert the IF GPS signal to a digital GPS signal; and

a digital signal processor including;

a buffer and a multiplier element configured to correlate the digitized GPS signal with a plurality of time shifted versions of the coarse acquisition (C/A) code forming a plurality of decoded GPS signals for each time shift,

a frequency shift estimation portion for processing the output of the multiplier element, the frequency shift estimation portion including;

a sample rate reducer, a broadband noise reduction (BBNR) processor followed by an FFT algorithm, and a threshold comparator portion,

the BBNR processor implementing an LMS adaptive filter consisting of a tapped delay line with weightings on each tap in the tapped delay line followed by summation of the weighted tapped delay line outputs to produce an adaptive filter output, where the weightings on each tap are updated in time using the LMS adaptive filter algorithm,

the BBNR processor configured to reduce the broadband noise level of the multiplier output by using a delayed version of the multiplier output as the input to the LMS adaptive filter and multiplier output itself as the reference in the LMS adaptive filter algorithm,

a spectral analysis processor using the FFT algorithm configured to estimate a frequency value at which a peak value occurs in the FFT output for each of the plurality time shifts of the C/A code at the multiplier input,

and the threshold comparator portion configured to select a peak value of all FFT outputs and all C/A code time shifts that exceeds a threshold value, and associating the time shift estimate and the frequency shift estimate with the combination of time shifts of the C/A code and the FFT frequency that produces the overall peak value,

a tracker portion that refines the time shift estimate and the frequency shift estimate; and

the navigation portion which computes a GPS location from the refined time shift estimate and the refined frequency shift estimate along with ephemeris data.

a processor that estimates the bit values and the bit change times of the ephemeris data encoded in the RF signals from each satellite by implementing the following;

a processor detecting flips in the NAV bits and decoding the NAV bits by detecting a plurality of spikes in a short time power estimate of the time waveform of the adaptive filter output signal, and associating the occurrence of the detected spikes with a flips of the NAVbits from a zero to a one or from a one to zero, and by associating a corresponding time of the spike with a boundary in time of the NAV bit flip; and

a connection that passes the NAVbits to a navigation processor where the NAV bits are decoded into a set of ephemeris data, the ephemeris data being used in navigational calculations to obtain a GPS location.