Patent ID: 8228171

Claim:
A radio frequency identification method for locating a listening tag using beacon tags comprising: transmitting a reader signal by a reader; receiving the reader signal by a plurality of beacon tags; receiving the reader signal by a listening tag; transmitting, respectively by the plurality of beacon tags, a plurality of beacon signals, wherein each of the plurality of beacon signals respectively comprises: a beacon identification, and a beacon distance to the reader; in response to the listening tag receiving the plurality of beacon signals, calculating by the listening tag neighbor distances for each of the plurality of beacon tags based on a combination of: a time at which each of the plurality of beacon signals is received by the listening tag; a time at which the listening tag receives the reader signal; and a constant processing time as a constant value for each of the plurality of beacon tags to receive and to process data of the reader signal before respectively transmitting the plurality of beacon signals; wherein, to compute the neighbor distances, the listening tag computes a delay time between the time at which the listening tag receives the reader signal and the time at which the listening tag respectively receives the plurality beacon signals, in order for the listening tag to subtract the constant processing time; wherein the neighbor distances are individual distances from the listening tag to each of the plurality of beacon tags; storing a list by the listening tag, wherein the list comprises: the beacon identification and beacon distance to the reader for each of the plurality of beacon tags; and the neighbor distances for each of the plurality of beacon tags as calculated by the listening tag; transmitting, by the listening tag, to the reader: the list; and a listening tag identification; calculating a geographical position of the listening tag based on: the beacon distance for each of the plurality of beacon tags; beacon coordinates for each of the plurality of beacon tags; and a listening tag distance which is a distance from the reader to the listening tag.