Methods and apparatus for accurately determining signal time of arrival
View Patent ↗A technique for determining the time of arrival of a signal involves correlating a received signal with a correlation function to produce a stream of correlation samples including a peak sample, pre-peak samples, and post-peak samples. A curve matching table includes sets of values, where each set of values represents discrete points of a correlation function having a peak at a respective different time shift relative to the timing of the peak sample. The sets of values include first sets of values that are matched with a first set of samples having no post-peak samples from the correlation samples, and second sets of values that are matched with a second set of samples having at least one post-peak sample. The time of arrival of the signal is determined from the timing of the peak of the correlation function represented by the set of values that produces the best match.
1. A method for determining the time of arrival of a signal at a mobile communication device, comprising:
(a) correlating a received signal in a receiver in accordance with a correlation function to produce a stream of correlation samples including a peak sample, a plurality of pre-peak samples, and a plurality of post-peak samples, wherein the time of arrival of the signal corresponds to a timing of a peak of the correlation function, which lies in a vicinity of the peak sample;
(b) storing a curve matching table comprising a plurality of sets of values, each of the sets of values representing discrete points of a correlation function having a peak at a respective different time shift relative to the timing of the peak sample, wherein the plurality of sets of values includes first sets of values to be matched with a first set of samples from the stream of correlation samples and second sets of values to be matched with a second set of samples from the stream of correlation samples;
(c) matching each of the first sets of values to the first set of samples, the first set of samples including no post-peak samples;
(d) matching each of the second sets of values to the second set of samples, the second set of samples including at least one post-peak sample, wherein one set of values among the first and second sets of values produces a best match; and
(e) determining the time of arrival of the signal based on timing of the peak of the correlation function represented by the one set of values that produced the best match.
2. The method of claim 1 , wherein the first sets of values are not matched to the second set of samples and the second sets of values are not matched to the first set of samples.
3. The method of claim 1 , wherein (b) includes storing the curve matching table in a look-up table.
4. The method of claim 1 , wherein:
(c) includes, for each first set of values, pairing each sample in the first set of samples with a corresponding value in the first set of values and performing a least-squares computation on differences of each pair; and
(d) includes, for each second set of values, pairing each sample in the second set of samples with a corresponding value in the second set of values and performing a least-squares computation on differences of each pair.
5. The method of claim 1 , wherein the first sets of values represent time-shifted correlation functions having a peak after the peak sample, and the second sets of values represent time-shifted correlation functions having a peak before the peak sample.
6. The method of claim 1 , further comprising:
(f) determining range to a source of the signal from the time of arrival of the signal.
7. The method of claim 6 , further comprising:
(g) transmitting information about the range to another device.
8. The method of claim 1 , further comprising:
(f) determining a position of the mobile communication device from the range to a plurality of sources of signals.
9. The method of claim 1 , further comprising:
(f) controlling a display device of the mobile communication device to display information about the mobile communication device's position determined from the time of arrival of the signal.
10. A mobile communication device, comprising:
a receiver configured to receive a signal in accordance with a correlation function to produce a stream of correlation samples including a peak sample, a plurality of pre-peak samples, and a plurality of post-peak samples, wherein the time of arrival of the signal corresponds to a timing of a peak of the correlation function, which lies in a vicinity of the peak sample;
a storage device configured to store a curve matching table comprising a plurality of sets of values, each of the sets of values representing discrete points of a correlation function having a peak at a respective different time shift relative to the timing of the peak sample, wherein the plurality of sets of values includes first sets of values to be matched with a first set of samples from the stream of correlation samples and second sets of values to be matched with a second set of samples from the stream of correlation samples;
a processor configured to: match each of the first sets of values to the first set of samples, the first set of samples including no post-peak samples; match each of the second sets of values to the second set of samples, the second set of samples including at least one post-peak sample, wherein one set of values among the first and second sets of values produces a best match; and determine the time of arrival of the signal based on a timing of the peak of the correlation function represented by the one set of values that produced the best match.
11. The mobile communication device of claim 10 , wherein the processor does not match the first sets of values to the second set of samples and the processor does not match the second sets of values to the first set of samples.
12. The mobile communication device of claim 10 , wherein the storage device is configured to store the curve matching table in a look-up table.
13. The mobile communication device of claim 10 , wherein:
the processor matches each of the first sets of values to the first set of samples by pairing each sample in the first set of samples with a corresponding value in the first set of values and performing a least-squares computation on differences of each pair; and
the processor matches each of the second sets of values to the second set of samples by pairing each sample in the second set of samples with a corresponding value in the second set of values and performing a least-squares computation on differences of each pair.
14. The mobile communication device of claim 10 , wherein the first sets of values represent time-shifted correlation functions having a peak after the peak sample, and the second sets of values represent time-shifted correlation functions having a peak before the peak sample.
15. The mobile communication device of claim 10 , wherein the processor is further configured to determine a range to a source of the signal from the time of arrival of the signal.
16. The mobile communication device of claim 15 , further comprising:
a transmitter configured to transmit information about the range to another device.
17. The mobile communication device of claim 15 , wherein the processor is further configured to determine a position of the mobile communication device from the range to a plurality of sources of signals.
18. The mobile communication device of claim 10 , further comprising:
a display device configured to display information about the mobile communication device's position determined from the time of arrival of the signal.
19. The mobile communication device of claim 10 , wherein the mobile communication device is a mobile telephone and information determined from time of arrival of the signal is transmitted by the mobile telephone to support an emergency response system.
20. A computer readable medium storing instructions, that when executed by a computer, cause the computer to perform functions of:
receiving a stream of correlation samples resulting from correlating a received signal in accordance with a correlation function, the correlation samples including a peak sample, a plurality of pre-peak samples, and a plurality of post-peak samples, wherein the time of arrival of a signal corresponds to a timing of a peak of the correlation function, which lies in a vicinity of the peak sample;
retrieving data from a curve matching table comprising a plurality of sets of values, each of the sets of values representing discrete points of a correlation function having a peak at a respective different time shift relative to the timing of the peak sample, wherein the plurality of sets of values includes first sets of values to be matched with a first set of samples from the stream of correlation samples and second sets of values to be matched with a second set of samples from the stream of correlation samples;
matching each of the first sets of values to the first set of samples, the first set of samples including no post-peak samples;
matching each of the second sets of values to the second set of samples, the second set of samples including at least one post-peak sample, wherein one set of values among the first and second sets of values produces a best match; and
determining the time of arrival of the signal based on timing of the peak of the correlation function represented by the one set of values that produced the best match.