Patent Document ID: 20090286548
Application ID: 12121916
Patent Status: 0

Claim One:
1. An apparatus for estimating location of an object by monitoring radio packets, said packets being periodically transmitted by a plurality of radio beacons deployed at known positions over a location estimation area, said packets comprising (i) an identifier unique to a given one of the beacons and (ii) a unique sequence number, said apparatus comprising: a plurality of antennas, each of said antennas having an output; a memory; and at least one processor, coupled to said memory and said antenna outputs, said processor being operative to carry out the following steps for k=1 to K: monitor for incoming ones of the packets; upon receipt of a packet from a k th one of the beacons: measure received signal strength, RSSI, at each of said antenna outputs; decode the packet to obtain the unique identifier and the unique sequence number; and spatially average the received signal strength at each of said antenna outputs; repeat said measuring, decoding, and spatial averaging steps for a plurality of additional packets from the k th one of the beacons during a pre-defined time window T, to obtain a plurality of spatially averaged received signal strengths; temporally average the plurality of spatially averaged received signal strengths over the pre-defined time window T, to obtain a spatially and temporally averaged value of received signal strength; and approximate a distance d k from said apparatus to the k th one of the beacons based on the spatially and temporally averaged value of received signal strength, the approximate distance d k being designated as {circumflex over (d)} k ; said processor being further operative to estimate the location as an approximate intersection of spheres with radii {circumflex over (d)} k , each centered at the known position of the k th one of the beacons; wherein K is at least two in a case where said object is constrained to move in a single spatial dimension, K is at least three in a case where said object is constrained to move in two spatial dimensions, and K is at least four in a case where said object is free to move in three spatial dimensions, and wherein K comprises a number of said beacons that have successfully transmitted one or more of said radio packets to the object during the time window T.