Locating the source of a wireless signal

1. A method of determining a location of a wireless source, the method comprising:

sending a synchronization signal to wireless sensor devices distributed at distinct locations over a geographic region, the wireless sensor devices configured to passively monitor wireless signals in the geographic region;

receiving wireless source signals collected by the wireless sensor devices after receiving the synchronization signal, each wireless source signal comprising a radio-frequency (RF) transmission from a wireless source in the geographic region, each wireless source signal detected by a respective wireless sensor device at a time indicated by the synchronization signal; and

identifying, at a data analysis system, a location of a wireless source in the geographic region based on cross-correlating the wireless source signals collected by three or more distinct wireless sensor devices,

wherein identifying the location of the wireless source in the geographic region is based on solving a system of equations, the system of equations comprising n equations:

cδτ ij =[|{right arrow over ( r b )}−{right arrow over ( r l )}|+|{right arrow over ( r s )}−{right arrow over ( r l )}|]−[|{right arrow over ( r b )}−{right arrow over ( r j )}|+|{right arrow over ( r s )}−{right arrow over ( r j )}|]

where {right arrow over (r s )}=(x s , y s , z s )represents the location of the wireless source, {right arrow over (r b )}=(x b , y b , z b ) represents a location of a base station, {right arrow over (r l )}=(x i , y i , z i ) represents a location of the i-th wireless sensor device, {right arrow over (r j )}=(x j , y j , z j ) represents a location of the j-th wireless sensor device, c represents the speed of light, and δτ ij represents a peak identified in a cross-correlation output.

2. The method of claim 1 , wherein the synchronization signal indicates a synchronized start time when the wireless sensor devices begin recording the wireless source signals.

3. The method of claim 1 , comprising identifying the location of the wireless source in the geographic region by:

cross-correlating respective pairs of the wireless source signals;

identifying one or more peaks in each of the cross-correlation outputs;

identifying arrival-time information based on the one or more peaks; and

identifying the location based on the arrival-time information.

4. The method of claim 2 , wherein the synchronization signal indicates a synchronized end time when the wireless sensor devices finish recording the wireless source signals.

5. The method of claim 3 , wherein cross-correlating respective pairs of the wireless source signals comprises applying a correlation function between S i (t) and S j (t), where S n (t) represents the wireless source signal waveform received from an n-th wireless sensor device, i and j are indices of the respective wireless sensor device, and i≠j.

6. The method of claim 1 , wherein each wireless sensor device is a wireless spectrum-inspection device.

7. The method of claim 1 , wherein the wireless sensor devices are configured to passively monitor cellular network signals formatted according to any of multiple distinct cellular network standards.

8. The method of claim 1 , wherein passively monitoring wireless signals in the geographic region comprises monitoring wireless signals exchanged in a wireless communication network without requesting services from the wireless communication network.

9. The method of claim 1 , wherein each wireless sensor device comprises:

an RF interface configured to detect RF signals in a local wireless environment about the wireless sensor device;

a signal analysis subsystem configured to process the RF signals; and

a communication interface configured to transmit data to a remote system.

10. A wireless-signal source locator system comprising:

wireless sensor devices distributed at distinct locations over a geographic region and configured to passively monitor wireless communication network signals in the geographic region, each wireless sensor device configured to:

receive a synchronization signal;

detect, at a time indicated by the synchronization signal, a wireless source signal comprising a radio-frequency (RF) transmission from a wireless source in the geographic region; and

transmit the wireless source signal; and

a data analysis system comprising one or more processors configured to identify a location of the wireless source based on cross-correlating the wireless source signals transmitted by three or more distinct wireless sensor devices,

wherein identifying the location of the wireless source in the geographic region is based on solving a system of equations, the system of equations comprising n equations:

cδτ ij =[|{right arrow over ( r b )}−{right arrow over ( r l )}|+|{right arrow over ( r s )}−{right arrow over ( r l )}|]−[|{right arrow over ( r b )}−{right arrow over ( r j )}|+|{right arrow over ( r s )}−{right arrow over ( r j )}|]

where {right arrow over (r s )}=(x s , y s , z s ) represents the location of the wireless source, {right arrow over (r b )}=(x b , y b , z b ) represents a location of a base station, {right arrow over (r l )}=(x i , y i , z i ) represents a location of the i-th wireless sensor device, {right arrow over (r j )}=(x j , y j , z j ) represents a location of the j-th wireless sensor device, c represents the speed of light, and δτ ij represents a peak identified in a cross-correlation output.

11. The system of claim 10 , wherein the synchronization signal indicates a synchronized start time when the wireless sensor devices begin recording the wireless source signals.

12. The system of claim 11 , wherein the synchronization signal indicates a synchronized end time when the wireless sensor devices finish recording the wireless source signals.

13. The system of claim 10 , wherein the data analysis system is configured to identify the location of the wireless source in the geographic region by:

cross-correlating respective pairs of the wireless source signals;

identifying one or more peaks in each of the cross-correlation outputs;

identifying arrival-time information based on the one or more peaks; and

identifying the location based on the arrival-time information.

14. The system of claim 13 , wherein cross-correlating respective pairs of the wireless source signals comprises applying a correlation function between S i (t) and S j (t), where S n (t) represents the wireless source signal waveform received from an n-th wireless sensor device, i and j are indices of the respective wireless sensor device, and i≠j.

15. The system of claim 10 , wherein each wireless sensor device is a wireless spectrum-inspection device.

16. The system of claim 10 , wherein the wireless sensor devices are configured to passively monitor cellular network signals formatted according to any of multiple distinct cellular network standards.

17. The system of claim 10 , wherein passively monitoring wireless signals in the geographic region comprises monitoring wireless signals exchanged in a wireless communication network without requesting services from the wireless communication network.

18. The system of claim 10 , wherein each wireless sensor device comprises:

an RF interface configured to detect RF signals in a local wireless environment about the wireless sensor device;

a signal analysis subsystem configured to process the RF signals; and

a communication interface configured to transmit data to a remote system.