Patent ID: 7616965

Claim:
A method for determining a location floor of a device within a building, the method comprising: determining a likelihood of the device being located on each of a plurality of floors of the building using a likelihood calculation; and identifying the location floor of the plurality of floors as a floor having an associated highest likelihood calculation, wherein the likelihood calculation for a floor includes calculating a distance from the device to each of a plurality of reference routers including one or more virtual coplanar reference routers, wherein each of the one or more virtual coplanar reference routers comprise a projection of a location of a non-coplanar reference router located on another floor to a virtual reference point within the floor, and wherein calculating the distance to each of the one or more virtual coplanar reference routers comprises calculating a virtual time of arrival between the device and the virtual coplanar reference router by: calculating a time of arrival between the device and the non-coplanar reference router determining a distance between the other floor and the floor, and using the time of arrival and the distance, and calculating the virtual time of arrival using the time of arrival and the distance, wherein the projection of the non-coplanar reference router comprises projecting a three dimensional measurement onto a two dimensional plane.