Wide area positioning system
Systems and methods are described for determining position of a receiver. The positioning system comprises a transmitter network including transmitters that broadcast positioning signals. The positioning system comprises a remote receiver that acquires and tracks the positioning signals and/or satellite signals. The satellite signals are signals of a satellite-based positioning system. A first mode of the remote receiver uses terminal-based positioning in which the remote receiver computes a position using the positioning signals and/or the satellite signals. The positioning system comprises a server coupled to the remote receiver. A second operating mode of the remote receiver comprises network-based positioning in which the server computes a position of the remote receiver from the positioning signals and/or satellite signals, where the remote receiver receives and transfers to the server the positioning signals and/or satellite signals.
1. A positioning system comprising:
a remote receiver that acquires positioning signals from a terrestrial transmitter network;
wherein:
the remote receiver generates, for each of the positioning signals, a cross-correlation function by cross-correlating one or more signal samples extracted from that positioning signal with a reference sequence corresponding to that positioning signal;
the remote receiver determines, for each of the positioning signals, a vector of cross-correlation samples from the cross-correlation function by selecting a first set of cross-correlation samples left of a peak of the cross-correlation function and a second set of cross-correlation samples right of the peak of the cross-correlation function;
the remote receiver identifies, for each of the positioning signals, a time of arrival estimate corresponding to an earliest arriving signal path of one or more signal paths corresponding to that positioning signal using a high resolution time of arrival measurement method that uses the vector of cross-correlation samples; and
the remote receiver estimates a first position of the remote receiver based on the time of arrival estimate.
2. The positioning system of claim 1 , wherein:
the remote receiver selects uncorrelated noise samples to obtain information regarding a noise sub-space.
3. The positioning system of claim 1 , wherein:
the remote receiver identifies the time of arrival estimate for each of the positioning signals by applying the high resolution time of arrival measurement method to the vector of cross-correlation samples corresponding to that positioning signal.
4. The positioning system of claim 1 , wherein:
each vector of cross-correlation samples includes the peak of the cross-correlation function.
5. The positioning system of claim 1 , wherein:
each vector of cross-correlation samples includes the first set of cross-correlation samples left of the peak of the cross-correlation function and the second set of cross-correlation samples right of the peak of the cross-correlation function.
6. The positioning system of claim 1 , wherein:
each reference sequence is a pseudorandom sequence.
7. The positioning system of claim 1 , wherein:
the high resolution time of arrival measurement method is based on at least one of a MUSIC algorithm, an ESPRIT algorithm, or an Eigen-space decomposition method.
8. The positioning system of claim 1 , wherein the remote receiver identifies the time of arrival estimate corresponding to the earliest arriving signal path by:
generating a reference vector from a correlation function determined by a calculated function or a measurement in a channel environment that has low noise and separable or no multipath components.
9. The positioning system of claim 1 , wherein the remote receiver identifies the time of arrival estimate corresponding to the earliest arriving signal path by:
improving a signal-to-noise ratio in the vector of cross-correlation samples by coherently averaging across at least one of a plurality of pseudorandom code frames and a plurality of bits.
10. The positioning system of claim 1 , wherein the remote receiver identifies the time of arrival estimate corresponding to the earliest arriving signal path by:
calculating a Fourier Transform using the vector of cross-correlation samples.
11. The positioning system of claim 1 , wherein the remote receiver identifies the time of arrival estimate corresponding to the earliest arriving signal path by:
generating a frequency domain estimate of a channel;
generating a reduced channel estimate vector from the frequency domain estimate of the channel;
defining an estimated covariance matrix of the reduced channel estimate vector; and
performing singular value decomposition on the estimated covariance matrix.
12. The positioning system of claim 1 , wherein the remote receiver identifies the time of arrival estimate corresponding to the earliest arriving signal path by:
generating a vector of sorted singular values; and
using the vector of sorted singular values to separate signal and noise subspaces.
13. The positioning system of claim 1 , wherein the remote receiver identifies the time of arrival estimate corresponding to the earliest arriving signal path by:
generating a noise subspace matrix.
14. The positioning system of claim 1 , wherein:
the remote receiver determines the first position of the remote receiver based on a non-linear objective function and a best estimate of the first position as a set of position parameters that minimize the objective function.
15. The positioning system of claim 1 , wherein:
the remote receiver determines the first position of the remote receiver based on a solution to a set of linearized equations using a least squares method.
16. The positioning system of claim 1 , wherein:
the high resolution time of arrival measurement method is based on at least one of a signal space separation method, a noise space separation method, a singular value decomposition method, or a covariance estimation method.
17. The positioning system of claim 1 , wherein the remote receiver identifies the time of arrival estimate corresponding to the earliest arriving signal path by:
generating a reference vector from a correlation function determined by a calculated function or a measurement in a channel environment that has low noise and separable or no multipath components;
improving a signal-to-noise ratio in the vector of cross-correlation samples by coherently averaging across at least one of a plurality of pseudorandom code frames and a plurality of bits;
calculating a Fourier Transform of the vector of cross-correlation samples;
generating a frequency domain estimate of a channel using the Fourier Transform of the vector of cross-correlation samples and a Fourier Transform of the reference vector;
generating a reduced channel estimate vector from the frequency domain estimate of the channel;
defining an estimated covariance matrix of the reduced channel estimate vector;
performing singular value decomposition on the estimated covariance matrix;
generating a vector of sorted singular values;
using the vector of sorted singular values to separate signal and noise subspaces;
generating a noise subspace matrix; and
using the noise subspace matrix to identify the time of arrival estimate corresponding to the earliest arriving signal path.
18. A positioning system comprising:
a terrestrial transmitter network comprising a plurality of transmitters that broadcast positioning signals to a remote receiver; and
a server that receives, for each of the positioning signals, a cross-correlation function generated by the remote receiver by cross-correlating one or more signal samples extracted from that positioning signal with a reference sequence corresponding to that positioning signal;
wherein:
the server determines a vector of cross-correlation samples from each cross-correlation function by selecting a first set of cross-correlation samples left of a peak of the cross-correlation function and a second set of cross-correlation samples right of the peak of the cross-correlation function;
the server identifies, for each of the positioning signals, a time of arrival estimate corresponding to an earliest arriving signal path of one or more signal paths corresponding to that positioning signal using a high resolution time of arrival measurement method that uses the vector of cross-correlation samples; and
the server estimates a first position of the remote receiver based on the time of arrival estimate.