A method of determining a location of a mobile device, the method comprising: receiving, at a data analysis system, data generated by wireless sensor devices (110, 1310) distributed at distinct locations over a geographic region, the wireless sensor devices configured to passively monitor wireless communication network signals in the geographic region, the data comprising arrival-time information generated by each respective wireless sensor device based on: a device signal transmitted by the mobile device in the geographic region and received by the wireless sensor device (110, 1310), the device signal formatted by the mobile device for transmission to a base station (120, 1302) according to a wireless communication network protocol; and a reference signal received by the wireless sensor device (110, 1310) to synchronize the wireless sensor device; and identifying, by operation of the data analysis system, a location of the mobile device based on analyzing the arrival-time information generated by three or more of the wireless sensor devices (110, 1310), wherein the wireless communication network protocol comprises a cellular network standard, the reference signal comprises a base station signal transmitted by the base station, the base station signal formatted by the base station for transmission to one or more mobile devices according to the cellular network standard, and wherein the location of the mobile device is identified by solving a system of equations based on arrival-time information generated by n wireless sensor devices, the system of equations comprising n equations: cδτ i = r s → − r b → + r s → − r ι → − r ι → − r b →, where r s = ( x s,y s,z s) represents the location of the mobile device, r b = ( x b,y b,z b) represents a location of the base station, r ι ̅ = x i y i z i represents a location of the i- th wireless sensor device, c represents the speed of light, and δτ i represents the time-difference measured between the reception of the reference signal and the device signal by the i-th wireless sensor device. receiving, at a data analysis system, data generated by wireless sensor devices (110, 1310) distributed at distinct locations over a geographic region, the wireless sensor devices configured to passively monitor wireless communication network signals in the geographic region, the data comprising arrival-time information generated by each respective wireless sensor device based on: a device signal transmitted by the mobile device in the geographic region and received by the wireless sensor device (110, 1310), the device signal formatted by the mobile device for transmission to a base station (120, 1302) according to a wireless communication network protocol; and a reference signal received by the wireless sensor device (110, 1310) to synchronize the wireless sensor device; and a device signal transmitted by the mobile device in the geographic region and received by the wireless sensor device (110, 1310), the device signal formatted by the mobile device for transmission to a base station (120, 1302) according to a wireless communication network protocol; and a reference signal received by the wireless sensor device (110, 1310) to synchronize the wireless sensor device; and identifying, by operation of the data analysis system, a location of the mobile device based on analyzing the arrival-time information generated by three or more of the wireless sensor devices (110, 1310), wherein the wireless communication network protocol comprises a cellular network standard, the reference signal comprises a base station signal transmitted by the base station, the base station signal formatted by the base station for transmission to one or more mobile devices according to the cellular network standard, and wherein the location of the mobile device is identified by solving a system of equations based on arrival-time information generated by n wireless sensor devices, the system of equations comprising n equations: cδτ i = r s → − r b → + r s → − r ι → − r ι → − r b →, where r s = ( x s,y s,z s) represents the location of the mobile device, r b = ( x b,y b,z b) represents a location of the base station, r ι ̅ = x i y i z i represents a location of the i- th wireless sensor device, c represents the speed of light, and δτ i represents the time-difference measured between the reception of the reference signal and the device signal by the i-th wireless sensor device.