Patent ID: RE38899

Claim:
A secure method of establishing the location of an object by calculating in-situ the location of the object from received radio signals wherein the radio signals are received from a beacon via a two-way communication between the beacon and a sensor on the object, comprising computing and transmitting at said sensor a signal including a challenge value and observing a clock associated with said sensor, recognizing at said beacon the transmitted sensor signal, observing at the beacon a clock associated with the beacon, constructing a response message including the sensor's received challenge value, the beacon's location, its location certificate and a time stamp, and transmitting the response message to said sensor, recognizing at said sensor said transmitted response message, observing the sensor clock, and validating the response message, computing the signal transit time and estimating the distance to the beacon, and based on the location of the beacon and the distance, calculating the location of the sensor and thereby the location of the object, and transmitting in response to a request from a requestor a message comprising the digitally signed calculated location of the object.