Communications: directive radio wave systems and devices (e.g. – Directive – Position indicating
Reexamination Certificate
2000-08-29
2002-04-30
Hellner, Mark (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Position indicating
C342S451000, C342S465000
Reexamination Certificate
active
06380894
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates in general to object location and tracking systems that identify identification of locations of radio-tagged objects, and is particularly directed to the use of a periodically exercised, reference tag-based mechanism for removing timing errors associated with cable plant and other components of signal transport paths between a plurality of geographically distributed readers and an object location processor. The object location processor executes time-of-arrival differentiation of first-to-arrive transmissions from tags as detected by the readers. Removal of timing errors ensures that the object location processor will precisely geolocate a tagged object in the field of view of the readers.
BACKGROUND OF THE INVENTION
As described in the introductory portion of the above-referenced '710 application, the U.S. Patent to Heller, U.S. Pat. No. 5,119,104, entitled: “Location System Adapted for Use in Multipath Environments” describes a motion-based system for tracking objects ‘tagged’ with micro-miniaturized radio transmitters, that are normally in a quiescent mode, until triggered by associated motion sensors. When the object is moved, a motion sensor causes its tag transmitter to emit an RF signal encoded with the identification of the tag; as long as the object is moving, its tag will transmit. Using multi-lateration receivers distributed in the monitored area of interest, and referenced to a time base for time-of-arrival processing, the location of a radio tag and thereby its object can be tracked, while the object is being moved, up to the point where it is at rest. The tag radio then reverts to quiescent mode, with transmission disabled until the object is again moved.
A principal shortcoming of such a motion-dependent object tracking system is the fact that, in addition to being dependent up the object being moved, and contrary to what the patent alleges, the patented system does not effectively solve the problem of multipath inputs to its tracking receiver subsystem. This latter shortcoming is due to the fact that it employs relatively simple amplitude detection receivers that operate on the assumption that the strongest signal will be the first-to-arrive signal. This means that the Heller approach will erroneously use a later arriving, large amplitude, multipath signal, rather than a relatively weak, but first-to-arrive signal, that has traveled to the receiver in a direct path through an attenuating medium.
A further deficiency of the system proposed in the Heller patent is the fact that it is not concerned with the more fundamental problem of asset management. Asset management not only addresses the need to locate and track processed components in the course of their travel through a manufacturing and assembly sequence, but is also concerned with the more general problem of component and equipment inventory control, where continuous knowledge of the whereabouts of any and all assets of a business, factory, educational, military or recreational facility, and the like, is desired and/or required. An asset management system may also benefit from status information that can be provided to the tag, by means of an auxiliary sensor associated with the tag—something not addressed by the Heller scheme.
Advantageously, the deficiencies of conventional object location systems, such as that proposed in the Heller patent, are successfully remedied by tagged object geolocation systems of the type described in the U.S. Patents to Belcher et al, U.S. Pat. Nos. 5,920,287, and 5,995,046, assigned to the assignee of the present application and the disclosures of which are incorporated herein.
The overall architecture of these significantly improved tagged object geolocation systems is shown diagrammatically in
FIG. 1
as comprising a plurality of tag emission readers
10
geographically distributed within and/or around an asset management environment
12
. The environment contains a plurality of objects/assets
14
, whose locations are to be monitored on a continuous basis and reported to an asset management data base
20
, which is accessible by way of a computer workstation or personal computer, as shown at
26
. Each of the tag emission readers
10
monitors the asset management environment for emissions from one or more tags
16
affixed to the objects
14
. Each tag
16
repeatedly transmits or ‘blinks’ a very short duration, wideband (spread spectrum) pulse of RF energy, that is encoded with the identification of its associated object and other information stored in tag memory.
For this purpose, the tag emission readers
10
are installed at fixed (precisely geographically known), relatively unobtrusive locations within and/or around the perimeter of the environment, such as doorway jams, ceiling support structures, and the like. Each tag reader
10
is coupled to an associated reader output processor of an RF processing system
24
, which is operative to correlate the spread spectrum signals received from a tag with a set of spread spectrum reference signal patterns, and thereby determine which spread spectrum signals received by the reader is a first-to-arrive spread spectrum signal burst transmitted from the tag.
The first-to-arrive signals extracted by reader output processors from the signals supplied from the tag emission readers
10
are coupled to an object location processor within the processing system
24
. The object location processor performs time-of-arrival differentiation of the detected first-to-arrive transmissions, and thereby locates (within a prescribed spatial resolution (e.g., on the order of ten feet) the tagged object of interest.
In order to mitigate against the potential for fades and nulls resulting from multipath signals destructively combining at one or more readers, the geolocation system of
FIG. 1
may be augmented to employ a spatial diversity-based receiver-processing path architecture. In accordance, with this architecture, rather than employ a single RF signal processing path for each reader location, a plurality of readers (e.g., two readers) are installed at each monitoring location, and associated signal processing paths are coupled therefrom to the geometry (triangulation) processor.
FIG. 2
diagrammatically shows a non-limiting example of this augmented geolocation system in which a plurality (e.g., two) of tag emission readers are located at geographically distributed monitoring locations, three of which are shown at
10
1
,
10
2
,
10
3
. Monitoring location
10
1
has first and second tag readers
10
1
-
1
and
10
1
-
2
, whose respective output signal processing paths include first arrival detector units
11
1
-
1
and
11
1
-
2
. Coupled with the RF signal processing circuits of the front ends of the tag readers
10
1
-
1
and
10
1
-
2
are antennas
210
1
-
1
and
210
1
-
2
. To provide spatial diversity-based mitigation of multipath signals, the antennas
210
1
-
1
and
210
2
-
1
are spaced apart by a distance sufficient to effectively statistically minimize destructive multipath interference at both antennas simultaneously.
For the other two monitoring locations of
FIG. 2
, monitoring location
10
2
has first and second spatially diverse antennas
210
2
-
1
and
210
2
-
2
, which feed tag readers
10
2
-
1
and
10
2
-
2
, whose outputs are coupled by way of first arrival detector units
11
2
-
1
and
11
2
-
2
to triangulation geometry processor
400
. Similarly, monitoring location
10
3
has first and second spatially diverse antennas
210
3
-
1
and
210
3
-
2
, which feed tag readers
10
3
-
1
and
10
3
-
2
, coupled to tag readers
10
3
-
1
and
10
3
-
2
, the outputs of which are coupled by way of first arrival detector units
11
3
-
1
and
11
3
-
2
to the triangulation geometry processor
400
.
The triangulation geometry processor
400
employs a standard multi-lateration algorithm that relies upon time-of-arrival inputs from at least three detectors (in the example of
FIG. 2
, three detector unit pairs
11
1
-
1
/
11
1
-
2
;
11
2
-
1
/
11
2
-
2
; and
Belcher Donald K.
Boyd Robert W.
Wohl Michael A.
Allen Dyer Doppelt Milbrath & Gilchrist, P.A.
Hellner Mark
Wherenet Corporation
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