Communications: directive radio wave systems and devices (e.g. – Directive – Position indicating
Reexamination Certificate
2000-07-27
2002-04-02
Hellner, Mark (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Position indicating
C342S451000
Reexamination Certificate
active
06366242
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates in general to object location and tracking systems, and is particularly directed to a reader geometry visualization software tool, that may be readily executed on a geo-location system installer's personal computer. The tool is operative to enable the installer to prospectively configure and measure the performance of the geometry layout of a plurality of tag transmission readers of a tagged object radio geo-location system to be deployed in an asset management environment. The tagged object radio geo-location system may be of the type described in the above-referenced applications.
BACKGROUND OF THE INVENTION
The above-referenced '710 application describes a radio tag-based object location system, that is operative to provide continuous accurate identification and geographical location of a plurality of objects in an asset management environment, such as a warehouse, manufacturing plant, electronic system engineering and testing facility, and the like. For this purpose, as illustrated diagrammatically in
FIG. 1
, a plurality of tag transmission readers
10
may be installed at relatively unobtrusive locations within and/or around the perimeter of the environment, such as doorway jams, ceiling support structures, etc. The tag emission readers
10
are an asset management environment
12
, that contains objects/assets
14
, whose location is reported to an asset management data base
20
. The data base
20
may be accessible by way of a standard computer workstation or personal computer
26
.
In order to geo-locate an object, each of the readers
10
monitors the environment
12
for transmissions from one or more randomly transmitting tags
16
, each of which is affixed to an object to be tracked. The radio transmitter of a respective tag
16
is configured to randomly and repeatedly transmit or ‘blink’ a short duration, wideband (spread spectrum) pulse of RF energy, which is encoded with information, such as that representative of the identification of the object, and other object-associated information stored in tag memory. By repeatedly transmitting in this manner, the plurality of tags be considered to be akin to a field of random ‘blinking’ fireflies.
Each tag transmission 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, in order to determine which spread spectrum signals received by the reader is a first-to-arrive spread spectrum signal burst transmitted from the tag. First-to-arrive signals extracted by the reader output processor from the signals supplied from a plurality of readers
10
are coupled to an object location processor, within the RF processor system
24
. The object location processor is operative to execute time-of-arrival differentiation of the detected first-to-arrive transmissions, and thereby locate the tagged object.
One of the key performance drivers in configuring and installing such a radio tagged object geo-location system is the proper placement of the tag transmission readers. Even where a system layout technician is provided with guidelines of where to distribute the readers, it would be preferable to have a priori knowledge of the likelihood of success and cost of the layout design.
SUMMARY OF THE INVENTION
In accordance with the present invention, this objective is successfully addressed by a software-based visualization tool, that may be readily executed on a technician's personal computer. As will be described, this tool is operative to display a map of the asset management environment. The map contains, or is modified by the geo-location system installer to contain, obstacles or environmental clutter that may impair RF transmissions from tags to a plurality of tag transmission readers that are selectively distributed throughout the map by the installer. The locations of the readers and obstacles are then used to define the parameters of a mathematical model of a tag-based geo-location system, such as that described in the '710 application, for monitoring tagged objects in the monitored environment.
In order to provide the designer with a ‘picture’ of the line of sight coverages relative to respective readers of a given reader placement geometry, a ‘show reader visibility’ subroutine may be invoked prior to computing and displaying the performance of the map-parameterized geo-location system. This subroutine performs a 360° line-of-sight ray tracing operation from each proposed reader toward the outer boundaries of the environment. Any ray emanating from a reader and encountering an obstacle is truncated at its intersection with the obstacle. The truncated rays are displayed as colored lines, to create a differentially colored map overlay.
This differentially colored map overlay contains colored regions emanating from the readers toward the perimeter of the map, and uncolored areas extending from the truncated rays and indicating those portions of the environment that cannot be seen by any reader. If part of the intended coverage area includes any uncolored portion of the map overlay, the designer knows that a change in reader geometry is required. The performance of the mathematical model of the reader geometry-parameterized geo-location system is then computed and displayed on the map. For this purpose, a performance analysis subroutine estimates the accuracy to which a tag located anywhere within the coverage area of the proposed reader layout can be geo-located by the system.
In accordance with a non-limiting but preferred embodiment, the performance estimate is computed as a geometric dilution of precision (gdop) value for the intended coverage area. The gdop operates on the principle of assessing the first derivative of location with respect to differential time-of-arrival associated with various reader combinations. The absolute value of this derivative may is classified with respect to thresholds associated with respectively different degrees of performance, as will be described. The resulting performance estimate of the proposed reader geometry layout is visually characterized on the displayed map, as by way of added hatching, different colors, shades of grey, and the like, to indicate the how accurately the proposed reader layout will enable the system to locate tagged objects anywhere in the intended coverage area.
Once presented with a (colorized map) visualization of the estimate of performance of the system model for a proposed reader geometry layout on the displayed map, the user may selectively modify the reader geometry parameters. If the map's performance coloring indicates a less than acceptable accuracy, the user may reconfigure the reader geometry layout for further performance analysis. This interactive sequence is repeated until the designer is satisfied with the predicted performance of the system for the proposed reader geometry as displayed on the (color-coded) map. A site file is then saved for subsequent resource allocation evaluation.
REFERENCES:
patent: 5045860 (1991-09-01), Hodson
patent: 5119104 (1992-06-01), Heller
patent: 5216429 (1993-06-01), Nakagawa et al.
patent: 5583517 (1996-12-01), Yokev et al.
patent: 5661492 (1997-08-01), Shoap et al.
Belcher Donald K.
Boyd Robert W.
Stryker David J.
Hellner Mark
Wherenet Corporation
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