Active geo-location range for wireless local area network devices
A method and devices are disclosed that increase the range of active geo-location from the airborne measuring station as compared with known methods by increasing the effective receive sensitivity of the airborne measuring station. In one embodiment, this may be accomplished by transmitting a burst of predetermined ranging packets and recording the correlation values of each received bit stream of the response packets with the corresponding predetermined bit streams for each of the transmitted ranging packets within a preset reception window. A rolling maximum is then performed on the correlation values in each reception window. At the end of the burst, the rolling maximum results are summed and the time of the peak value is determined.
1. A method in a first wireless device (WD), the method comprising:
transmitting a plurality of ranging signals;
determining times of transmission for each of the plurality of ranging signals;
receiving response signals transmitted from a second WD, each response signal being in response to one of the plurality of transmitted ranging signals;
demodulating each of the received response signals to produce a received sequence of bits;
determining an expected sequence of bits for the received response signals;
correlating the received sequence of bits with the expected sequence of bits to determine a correlation value, the correlation value being indicative of an extent to which the received sequence matches the expected sequence;
determining a plurality of correlation values for a duration of a reception window for each of the plurality of ranging signals;
calculating a sum of the plurality of correlation values;
determining a peak value of the sum of the plurality of correlation values;
determining a time of the peak value referenced to an end of the plurality of ranging signal transmissions; and
determining a geo-location of the second WD based at least in part on a time of transmission of a ranging signal and the time of the peak value of the sum of the plurality of correlation values.
2. The method of claim 1 , wherein each transmitted ranging signal is one of a request-to-send, RTS, signal and a data null signal.
3. The method of claim 1 , further comprising:
determining parameters of the plurality of ranging signals by one of selecting a WD receiver address (RA) to be used as a medium access control (MAC) address of the second WD, selecting a MAC address to be used as a wireless transmitter address (TA) and selecting a duration value for the duration of the reception window.
4. The method of claim 1 , wherein the determination of the expected sequence of bits includes:
constructing medium access control (MAC) header bits based on using a transmitter address (TA) of the ranging signal as a receiver address (RA) of the response signal;
adding preamble and header bits to the MAC header bits to produce a packet; and
scrambling the packet using a predetermined seed to produce the bits of the expected sequence.
5. The method of claim 1 , the method further including:
calculating a rolling maximum value, M, of the plurality of correlation values for the duration of the reception window for each of the plurality of ranging signal transmissions, M being defined as:
For
k
=
0
to
(
W
-
s
)
,
M
k
+
s
2
=
max
{
C
}
k
k
+
s
where W=number of samples in the reception window, C are correlator values,
s=number of samples in an assumed maximum jitter of a response packet, and
max{C} k k+s is a maximum correlation value between k and k+s.
6. The method of claim 5 , wherein calculating the sum of the plurality of correlation values includes calculating a sum of the rolling maximums.
7. The method of claim 1 , further comprising applying soft bit detection of the received response signals.
8. The method of claim 1 , wherein the plurality of ranging signals are transmitted in a burst, and the method further includes:
determining that the burst has completed; and
wherein calculating the sum of the plurality of correlation values occurs after the burst is determined to have been completed.
9. The method of claim 1 , wherein correlating the received sequence of bits with the expected sequence of bits to determine a correlation value is based at least on a predefined correlation threshold.
10. A first wireless device (WD), comprising:
a transmitter configured to transmit a plurality of ranging signals;
processing circuitry in communication with the transmitter, the processing circuitry configured to:
determine times of transmission for each of the plurality of ranging signals;
receive response signals transmitted from a second WD, each response signal being in response to one of the plurality of transmitted ranging signals;
demodulate each of the received response signals to produce a received sequence of bits;
determine an expected sequence of bits for the received response signals;
a correlator in communication with the processing circuitry, the correlator configured to:
correlate the received sequence of bits with the expected sequence of bits to determine a correlation value, the correlation value being indicative of an extent to which the received sequence matches the expected sequence; and
determine a plurality of correlation values for a duration of a reception window for each of the plurality of ranging signals
the processing circuitry being further configured to:
calculate a sum of the plurality of correlation values;
determine a peak value of the sum of the plurality of correlation values;
determine a time of the peak value referenced to an end of the plurality of ranging signal transmissions; and
determine a geo-location of the second WD based at least in part on a time of transmission of a ranging signal and the time of the peak value of the sum of the plurality of correlation values.
11. The first WD of claim 10 , wherein each transmitted ranging signal is one of a request-to-send, RTS, signal and a data null signal.
12. The first WD of claim 10 , the processing circuitry is further configured to:
determine parameters of the plurality of ranging signals by one of selecting a WD receiver address (RA) to be used as a medium access control (MAC) address of the second WD, selecting a MAC address to be used as a wireless transmitter address (TA) and selecting a duration value for the duration of the reception window.
13. The first WD of claim 10 , wherein the determination of the expected sequence of bits includes:
constructing medium access control (MAC) header bits based on using a transmitter address (TA) of the ranging signal as a receiver address (RA) of the response signal;
adding preamble and header bits to the MAC header bits to produce a packet; and
scrambling the packet using a predetermined seed to produce the bits of the expected sequence.
14. The first WD of claim 10 , the processing circuitry is further configured to:
calculate a rolling maximum value, M, of the plurality of correlation values for the duration of the reception window for each of the plurality of ranging signal transmissions, M being defined as:
For
k
=
0
to
(
W
-
s
)
,
M
k
+
s
2
=
max
{
C
}
k
k
+
s
where W=number of samples in the reception window, C are correlator values,
s=number of samples in an assumed maximum jitter of a response packet, and
max{C} k k+s is a maximum correlation value between k and k+s.
15. The first WD of claim 14 , wherein calculating the sum of the plurality of correlation values includes calculating a sum of the rolling maximums.
16. The first WD of claim 10 , wherein the processing circuitry is further configured to:
apply soft bit detection of the received response signals.
17. The first WD of claim 10 , wherein the plurality of ranging signals are transmitted in a burst and the processing circuitry is further configured to:
determine that the burst has completed; and
wherein calculating the sum of the plurality of correlation values occurs after the burst is determined to have been completed.
18. The first WD of claim 10 , wherein correlating the received sequence of bits with the expected sequence of bits to determine a correlation value is based at least on a predefined correlation threshold.
19. A method in a first wireless device (WD), the method comprising:
transmitting a plurality of ranging signals in a burst;
determining times of transmission for each of the plurality of ranging signals;
receiving response signals transmitted from a second WD, each response signal being in response to one of the plurality of transmitted ranging signals;
demodulating each of the received response signals to produce a received sequence of bits;
determining an expected sequence of bits for the received response signals;
correlating the received sequence of bits with the expected sequence of bits based at least on a predefined correlation threshold to determine a correlation value, the correlation value being indicative of an extent to which the received sequence matches the expected sequence;
determining a plurality of correlation values for a duration of a reception window for each of the plurality of ranging signals;
calculating a rolling maximum value, M, of the determined plurality of correlation values for the duration of the reception window for each of the plurality of ranging signal, the calculation of the rolling maximum value, M, being based at least on an assumed maximum jitter;
determining that the burst is complete;
calculating a sum of the plurality of correlation values based at least on the rolling maximum value;
determining a peak value of the sum of the plurality of correlation values;
determining a time of the peak value referenced to an end of the plurality of ranging signal transmissions; and
determining a geo-location of the second WD based at least in part on a time of transmission of a ranging signal and the time of the peak value of the sum of the plurality of correlation values.
20. The method of claim 19 , wherein the determination of the expected sequence of bits includes:
constructing medium access control (MAC) header bits based on using a transmitter address (TA) of the ranging signal as a receiver address (RA) of the response signal;
adding preamble and header bits to the MAC header bits to produce a packet; and
scrambling the packet using a predetermined seed to produce the bits of the expected sequence.