Active geo-location range for wlan devices
AssigneeSR Technologies, Inc.
InventorGraham K. SMITH
Life of this patent
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Abstract
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 predetermined ranging packet and correlating the raw received bit stream of the response packet with the predetermined bit stream. In one embodiment, the disclosed method applies to the reception of IEEE 802.11 direct sequence spread spectrum DSSS ACK and DSSS CTS packets in response to DSSS data null and DSSS RTS packets respectively, in the 2.4 GHz band.
Claims21
A method in a first wireless device (WD), the method comprising:
- transmitting a ranging signal and recording a time of transmitting the ranging signal;
- receiving a direct sequence spread spectrum, DSSS, signal transmitted from a second WD in response to the ranging signal;
- demodulating and de-spreading the received DSSS response signal to produce a received sequence;
- determining an expected sequence;
- correlating raw bits of the received sequence with raw bits of the expected sequence to determine a correlation value, the correlation value being indicative of an extent to which the received sequence matches the expected sequence;
- comparing the correlation value to a predetermined threshold, T;
- and
- when the correlation value exceeds the threshold, T, then:
- recording a time of reception of the received DSSS response signal;
- and
- determining a geo-location of the second WD based at least in part on the time of transmission of the ranging signal and the time of reception of the DSSS response signal.
A first wireless device (WD), comprising:
- a transceiver configured to transmit a ranging signal and receive a direct sequence spread spectrum, DSSS, signal from a second WD in response to the ranging signal;
- processing circuitry in communication with the receiver, the processing circuitry configured to:
- de-spread the received DSSS signal to produce a received sequence;
- and
- determine an expected sequence;
- and
- a correlator in communication with the processing circuitry, the correlator configured to:
- correlate raw bits of the received sequence with raw bits of the expected sequence to determine a correlation value, the correlation value being indicative of an extent to which the received sequence matches the expected sequence;
- the processing circuitry being further configured to:
- compare the correlation value to a predetermined threshold, T;
- and
- when the correlation value exceeds the threshold, T, then:
- record a time of reception of the received DSSS response signal;
- and
- determine a geo-location of the second WD based at least in part on a time of transmission of the ranging signal and the time of reception of the DSSS response signal.
An airborne station, comprising:
- a transceiver configured to:
- transmit a ranging signal, the ranging signal being one of a return-to-send, RTS, signal and a data null signal;
- and
- receive a direct sequence spread spectrum, DSSS, signal from a ground station, the signal being spread by an 11 bit barker code;
- processing circuitry configured to:
- de-spread the received DSSS signal to produce a received sequence, the received sequence having one of a Clear To Send (CTS) signal and an acknowledgement (ACK) signal;
- obtain an expected sequence;
- correlate the received sequence with the expected sequence to determine a correlation value, the correlation value being indicative of an extent to which the received sequence matches the expected sequence;
- compare the correlation value to a threshold, T, the threshold, T, being based on a bit error probability, which in turn is based on a signal to noise ratio (SNR);
- and
- when the correlation value exceeds the threshold, T:
- determine a time associated with the received sequence;
- and
- determine a range of the WD based on the time associated with the received sequence.
Dependencies are inferred from the claim text.