Granted Patent B2

US 8,130,146 · App. 12/181,727 · Granted Mar 6, 2012

Abstract

Claims (24)

1. A method for measuring the time of arrival of one or more signals comprising:

receiving, at a receiving node, at least one signal including a first pseudorandom code and a second pseudorandom code from a transmitting node;

identifying, at the receiving node, an approximated frequency difference between the receiving node and the transmitting node using a phase difference between each of a maximum value of a cross-correlation provided by the first pseudorandom code and the second pseudorandom code;

applying, at the receiving node, the approximated frequency difference to the reception of the received signal; and

calculating, at the receiving node, the approximated time of arrival of the received signal comprising a time, measured with a local clock, when the cross-correlation has achieved the maximum value.

2. The method of claim 1 , wherein the transmitting node sends the at least one signal as one or more RANGE messages each including a pseudorandom code repeatedly for a plurality of times.

3. The method of claim 1 , further comprising prior to receiving the signal:

broadcasting, by the receiving node, a LOCATION message including a “Request for Coordinates” flag set to TRUE to notify the transmitting node that the receiving node requires references for computing its own position.

4. The method of claim 3 , further comprising:

receiving, by the receiving node, data associated with reception of RANGE messages from one or more neighbor nodes.

5. The method of claim 4 , wherein the received data comprises, for each neighbor: a neighbor identification, a time of arrival of a last RANGE message received from that neighbor node, an apparent difference of frequencies between the receiving node and the neighbor node, and a one bit COORDINATE DATA flag.

6. The method of claim 5 , wherein the COORDINATE DATA flag value is selected from a group of values comprising: no coordinates, Geocentric, Geographic, Local, and Relative.

7. The method of claim 2 , wherein the received RANGE signals comprise a sequence of received quadrature (I, Q) samples, the method further comprising operating the receiving node to:

de-rotate each received sample thereby resulting in a vector of components;

compute a phase shift correction from at least one de-rotation angle of the de-rotated samples;

correlate the de-rotated samples with a pseudorandom code sequence;

structure the result of correlation as a matrix comprising a plurality of matrix elements arranged with a plurality of rows and a plurality of columns;

average at least some of the matrix elements on each of the columns into a vector of elements;

process the averaged vector of elements for identifying a best correction of time of arrival of a direct path in relation with the approximated time of arrival measured by the node;

compute the frequency difference from the phase shift correction and the approximated frequency difference; and

compute the Doppler frequency shift between at least two neighboring nodes.

8. The method of claim 7 , wherein a shift considers a second half of the vector first, and further wherein a first half of the vector is considered during the processing the shifted average vector step.

9. The method of claim 7 , further comprising operating the receiving node to:

compute a relative speed between the at least two neighboring nodes from the Doppler frequency shift.

Assignments (12)