Abstract

An improved method and apparatus for automatically monitoring objects, such as vehicles, for example, wherein signpost units are positioned at predetermined locations and each signpost unit transmits a binary signpost code for reception via units installed in the objects being monitored and the objects being monitored receive the signpost codes and store object location information. In one aspect, the present invention contemplates a method and an apparatus which has a multi-mode operation capability wherein the location of the monitored objects is reported when the monitored object enters a different coverage region in an automatic reporting mode, wherein only those monitored objects within a predetermined region or on a predetermined route report to the base station in a region or route reporting mode, and wherein only the locations of predetermined monitored objects are reported to the base station in a polling mode. In another aspect, the present invention contemplates an improved method and an apparatus for locating and operating the signpost units to reduce the total number of signpost units required to cover a given number of locations wherein each signpost unit establishes a uniquely identifiable near-field region and a uniquely identifiable far-field region, the signpost units being located to establish uniquely identifiable overlap regions wherein a portion of the far-field region of at least one of the signpost units overlaps a portion of the far-field region on another signpost unit. The method and apparatus of the present invention also provides a non-polling location technique eliminating the necessity of interrogating the monitored objects at regular intervals and reducing the radio channel time required for reporting object location.