Location system adapted for use in multipath environments

Abstract

A radiolocation system for multipath environments, such as for tracking objects in a semiconductor fabrication facility (FIGS. 1a-1b), includes an array of receivers (20) distributed within the tracking area, coupled to a system processor (40) over a LAN. A TAG transmitter (30) located with each object transmits, at selected intervals, spread spectrum TAG transmissions including at least a unique TAG ID. In a high resolution embodiment, object location is accomplished by time-of-arrival (TOA) differentiation, with each receiver (FIG. 2b) including a TOA trigger circuit (64) for triggering on arrival of a TAG transmission, and a time base latching circuit (65) for latching the TOA count from an 800 MHz time base counter. In a low resolution embodiment, each receiver of the array is assigned a specific location-area, and receives TAG transmissions almost exclusively from TAGs located in that area, thereby eliminating the need for any time-of-arrival circuitry.

Description

TECHNICAL FIELD OF THE INVENTIONThe invention relates generally to position location systems, and more particularly relates to a radiolocation system adapted for use in an environment subject to multipath effects. In even greater particularity, the invention relates to such a system that accomplishes position location using either (a) time-of-arrival differentiation for radiolocation transmissions received at multiple receivers (high resolution), or (b) area-detection using receivers that receive radiolocation transmissions from assigned areas (low resolution).RELATED PATENTThis patent incorporates by reference the subject matter of U.S. Pat. No. 4,864,588, titled Remote Control System, Components and Methods, which is assigned to Hillier Technologies Limited Partnership.BACKGROUND OF THE INVENTIONPosition or object location systems are finding increasing application in manufacturing and materials handling environments. For example, such systems have utility for factory automation, ...

AI Technical Summary

Benefits of technology

The technical advantages of the invention include the following. The location system is adaptable to use in a multipath environment, such as found in manufacturing and other business facilities, where the reception of direct-path transmissions is affected by the presence of multipath noise. Object location can be accomplished by either a high resolution approach using time-of-arrival differentiation, or a low resolution (low cost) approach using area detection by receivers configured to detect TAG transmissions from an assigned area. Using unlicensed, commercially available spread spectrum equipment facilitates discrimination between the direct-path transmissions of interest and multipath noise.

For the high resolution embodiment, TOA-DETECTION triggering and time base TOA COUNT latching can be separated from the spread spectrum communications function to permit the use of commercially available spread spectrum equipment. A high-speed TOA triggering circuit provides TOA-DETECTION triggering within the early cycles of the arrival of a TAG transmission. A time base latching circuit using a synchronized time base counter operating in the range of 800 MHz provides resolution on the order of 10 feet. Noise filtering optimizes time-of-arrival detection for TAG transmissions, providing adjustable signal-level and signal-duration thresholds to minimize the effects of random pulsed noise.

Problems solved by technology

However, a problem with radio communications in the typical business environment--which includes walls, silvered windows and other fixed structures--is that, for the frequencies of interest (i.e., above 100 MHz), random reflections introduce multipath distortions in tag transmissions arriving at a given receiver.

Moreover, in such an environment, the unpredictable attenuation of transmissions passing through walls and other structures makes signal strength only marginally useful for communicating distance / location information.

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