Abstract: There is therefore provided a method of estimating the location of a mobile device, the mobile device being configured for use in a cellular mobile communications network comprising a plurality of base stations, the method comprising generating a database of locations visited by the mobile device by obtaining measurements of the position of the mobile device over time using a satellite-based positioning system; obtaining the identity of the base station serving the mobile device at the time of each measurement of the position of the mobile device; and analyzing the measurements to identify locations visited by the mobile device, each location being associated with a particular base station, such that the mobile device is attached to said base station when at said location; and during subsequent use of the mobile device, in the event that it is not possible to use the satellite-based positioning system to measure the position of the mobile device, estimating the location of the mobile device as one or more ide

Abstract: A system for transporting inventory items includes an inventory holder capable of storing inventory items and a mobile drive unit. The mobile drive unit is capable of moving to a first point with the inventory holder at least one of coupled to and supported by the mobile drive unit. The mobile drive unit is additionally capable of determining a location of the inventory holder and calculating a difference between the location of the inventory holder and the first point. The mobile drive unit is then capable of determining whether the difference is greater than a predetermined tolerance. In response to determining that the difference is greater than the predetermined tolerance, the mobile drive unit is also capable of moving to a second point based on the location of the inventory holder, docking with the inventory holder, and moving the mobile drive unit and the inventory holder to the first point.