Peak to sigma ratio measurement with active geo-location for wireless local area network devices
A method and wireless devices (WDs) for geo-location of wireless devices are disclosed. According to one aspect, a method in a first WD includes: transmitting a sequence of ranging signals and receiving a plurality of ranging response signals from a second WD, the ranging response signals being responsive to the ranging signals. For each of the plurality of ranging response signals, a received sequence of bits is determined. A correlation between the received sequence of bits and an expected sequence of bits is determined. The method also includes determining a subset of the plurality of received sequences of bits deemed not to arise from noise, and determining the subset being based at least in part on the correlations. The method also includes determining a distance between the first WD and the second WD based at least in part on a plurality of received sequences in the subset.
1. A method in a first wireless device (WD) to discriminate between valid round trip time (RTT) measurements arising from reception of a signal from a second WD and false RTT measurements arising from noise, the method comprising:
transmitting a plurality of ranging signals to the second WD;
receiving from the second WD a plurality of ranging response signals responsive to the plurality of ranging signals; and
for each ranging response signal of the plurality of ranging response signals:
determining a sum of correlations, each correlation being between an expected bit sequence and a received bit sequence in the ranging response signal;
determining a standard deviation of the sum of correlations;
determining a first ratio of a peak value of the sum of correlations to the standard deviation to obtain a peak to standard deviation ratio (PSR); and
rejecting an RTT measurement corresponding to the peak value of the sum correlations when the PSR is less than a threshold.
2. The method of claim 1 , the method further comprising:
for N previous ranging signals, recording PSRs for each ranging signal of the plurality of ranging signals;
grouping and summing the PSRs for the N ranging signals in specific ranges;
determining a second ratio of the sum of the PSRs in a first range to a sum of PSRs in a second range, the second range having lower values than the first range; and
rejecting an RTT measurement for a ranging response signal of the plurality of ranging response signals when a corresponding PSR is less than a threshold and the ratio is also less than a threshold.
3. The method of claim 2 , further comprising, when a PSR is above a threshold, using a time of occurrence of the PSR to determine a distance between the first WD and the second WD.
4. The method of claim 3 , wherein the threshold R is 0.4.
5. The method of claim 2 , further comprising, when a PSR is above a threshold and the second ratio is within a specified range, then using a time of occurrence of the PSR to determine a distance between the first WD and the second WD.
6. The method of claim 2 , further comprising, when the second ratio is less than the threshold and a PSR is within a specified range, then not using a time of occurrence of the peak value to determine a distance between the first WD and the second WD.
7. The method of claim 2 , further comprising accepting an RTT measurement for a ranging response signal of the plurality of ranging response signals when at least one of the following occurs:
a PSR for the RTT measurement is equal or greater than a first threshold T 1 ;
the PSR for the RTT measurement is greater than a second threshold T 2 and less than the first threshold T 1 and the first ratio is greater than a threshold R; and
the PSR for the RTT measurement is greater than a third threshold T 3 and less than the second threshold T 2 and the first ratio is greater than a threshold R.
8. The method of claim 7 , wherein:
the first PSR threshold T 1 is 5;
the second PSR threshold T 2 is 4.5; and
the third PSR threshold T 3 is 3.5.
9. The method of claim 2 where the first range of the sum of PSRs is 4 to 4.5, and the second range of the sum of PSRs is 3.5 to 4.
10. The method of claim 2 , further comprising, based at least in part on the second ratio, performing one of:
indicating that a valid RTT measurement has been received;
using a time of occurrence of a peak value corresponding to the valid RTT measurement to determine a distance between the first WD and the second WD; and
discarding a time of occurrence of the peak value.
11. A first wireless device (WD) configured to discriminate between valid round trip time (RTT) measurements arising from reception of a signal from a second WD and false RTT measurements arising from noise, the first WD comprising:
a radio interface configured to:
transmit a plurality of ranging signals to the second WD; and
receive from the second WD a plurality of ranging response signals responsive to the plurality of ranging signals; and
processing circuitry in communication with the radio interface, the processing circuitry configured to: for each ranging response signal of the plurality of ranging response signals:
determine a sum of correlations, each correlation being between an expected bit sequence and a received bit sequence in the ranging response signal of the plurality of ranging response signals;
determine a standard deviation of the sum of correlations;
determine a first ratio of a peak value of a sum of the correlations to the standard deviation to obtain a peak to standard deviation ratio (PSR); and
reject an RTT corresponding to the peak value when the PSR is less than a threshold.
12. The first WD of claim 11 , wherein the processing circuitry is further configured to:
for N previous ranging signals, record PSRs for each ranging signal of the plurality of ranging signals;
group and sum the PSRs for the N previous ranging signals in specific ranges; and
determine a second ratio of the sum of the PSRs in a first range to a sum of PSRs in a second range, the second range having lower values than the first range; and
reject an RTT measurement for a ranging response signal of the plurality of the ranging response signals when a corresponding PSR is less than a threshold and the ratio is also less than a threshold.
13. The first WD of claim 12 , wherein, when a PSR is above a threshold, the processing circuitry is further configured to use a time of occurrence of the PSR to determine a distance between the first WD and the second WD.
14. The first WD of claim 13 , wherein the threshold R is 0.4.
15. The first WD of claim 12 , wherein, when a PSR is above a threshold and the second ratio is within a specified range, the processing circuitry is further configured to use a time of occurrence of the PSR to determine a distance between the first WD and the second WD.
16. The first WD of claim 12 , wherein, when the second ratio is less than the threshold and a PSR is within a specified range, the processing circuitry is further configured to refrain from using a time of occurrence of the peak value to determine a distance between the first WD and the second WD.
17. The first WD of claim 12 , wherein the processing circuitry is further configured to accept an RTT measurement for a ranging response signal of the plurality of ranging response signals when at least one of the following occurs:
a PSR for the RTT measurement is equal or greater than a first threshold T 1 ;
the PSR for the RTT measurement is greater than a second threshold T 2 and less than the first threshold T 1 and the first ratio is greater than a threshold R; and
the PSR for the RTT measurement is greater than a third threshold T 3 and less than the second threshold T 2 and the first ratio is greater than a threshold R.
18. The first WD of claim 17 , wherein:
the first PSR threshold T 1 is 5;
the second PSR threshold T 2 is 4.5; and
the third PSR threshold T 3 is 3.5.
19. The first WD of claim 12 , where the first range of the sum of PSRs is 4 to 4.5, and the second range of the sum of PSRs is 3.5 to 4.
20. The first WD of claim 12 , wherein the processing circuitry is further configured to, based at least in part on the second ratio, perform one of:
indicating that a valid RTT measurement has been received;
using a time of occurrence of a peak value corresponding to the valid RTT measurement to determine a distance between the first WD and the second WD; and
discarding a time of occurrence of the peak value.