Detection of time of arrival of CDMA signals in a wireless location system
First Claim
1. In a wireless location system for use in locating a mobile transmitter, a method for improving a time difference of arrival (TDOA) estimate produced by cross-correlating a local signal with a reference signal, using either a time-domain or frequency-domain cross-correlation process, wherein the local signal is a copy of a signal transmitted by the mobile transmitter as received at a first antenna and the reference signal is a copy of the signal transmitted by the mobile transmitter as received at a second antenna, the method comprising:
- receiving the local signal at a first location measurement unit (LMU);
processing the local and reference signals to produce a correlation function comprising a correlation-time-frequency map;
searching the correlation function for a global maximum above a detection assurance threshold, and identifying a valid global maximum correlation peak;
reducing the correlation-time-frequency map to a two-dimensional time-correlation timeslice centered on a frequency of the valid global maximum correlation peak;
searching the two-dimensional time-correlation timeslice for a local maximum above the detection assurance threshold occurring earlier in time than the global maximum correlation peak; and
performing a leading edge discovery procedure to find an earlier leading edge concealed within a correlation envelope of the two-dimensional time-correlation timeslice.
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Abstract
In a Wireless Location System (WLS) deployed in connection with a CDMA-based wireless communications system, Location Measurement Units are used to collect multi-path corrupted radio signaling for use in time difference of arrival (TDOA) and hybrid positioning methods. Signal processing techniques are used to enhance the WLS'"'"'s ability to determine the minimally time-delayed multi-path component and thus increase the accuracy of the TDOA location in CDMA-based wireless communications systems. The signal processing includes a filtering technique for reducing the leading sidelobes of the cross-correlation function as well as a leading edge discovery procedure.
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Citations
46 Claims
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1. In a wireless location system for use in locating a mobile transmitter, a method for improving a time difference of arrival (TDOA) estimate produced by cross-correlating a local signal with a reference signal, using either a time-domain or frequency-domain cross-correlation process, wherein the local signal is a copy of a signal transmitted by the mobile transmitter as received at a first antenna and the reference signal is a copy of the signal transmitted by the mobile transmitter as received at a second antenna, the method comprising:
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receiving the local signal at a first location measurement unit (LMU); processing the local and reference signals to produce a correlation function comprising a correlation-time-frequency map; searching the correlation function for a global maximum above a detection assurance threshold, and identifying a valid global maximum correlation peak; reducing the correlation-time-frequency map to a two-dimensional time-correlation timeslice centered on a frequency of the valid global maximum correlation peak; searching the two-dimensional time-correlation timeslice for a local maximum above the detection assurance threshold occurring earlier in time than the global maximum correlation peak; and performing a leading edge discovery procedure to find an earlier leading edge concealed within a correlation envelope of the two-dimensional time-correlation timeslice. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23)
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24. A wireless location system (WLS) for use in locating a mobile transmitter, comprising:
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a network of location measurement units (LMUs) including at least a first LMU and a second LMU;
wherein said first LMU includes a processor and a computer readable storage medium coupled to said processor, said computer readable storage medium comprising instructions for configuring said processor to compute a time difference of arrival (TDOA) estimate in accordance with a prescribed method, including by cross-correlating a local signal with a reference signal, using either a time-domain or frequency-domain cross-correlation process, wherein the local signal is a copy of a signal transmitted by the mobile transmitter as received at a first antenna associated with the first LMU and the reference signal is a copy of the signal transmitted by the mobile transmitter as received at a second antenna associated with the second LMU, said prescribed method comprising;receiving the local signal at said first location measurement unit (LMU); processing the local and reference signals to produce a correlation function comprising a correlation-time-frequency map; searching the correlation function for a global maximum above a detection assurance threshold, and identifying a valid global maximum correlation peak; reducing the correlation-time-frequency map to a two-dimensional time-correlation timeslice centered on a frequency of the valid global maximum correlation peak; searching the two-dimensional time-correlation timeslice for a local maximum above the detection assurance threshold occurring earlier in time than the global maximum correlation peak; and performing a leading edge discovery procedure to find an earlier leading edge concealed within a correlation envelope of the two-dimensional time-correlation timeslice. - View Dependent Claims (25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46)
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Specification