WO1999013352A2

WO1999013352A2 - Range positioning system

Info

Publication number: WO1999013352A2
Application number: PCT/US1998/016530
Authority: WO
Inventors: Randolph G. Hartman
Original assignee: Honeywell Inc.
Priority date: 1997-08-07
Filing date: 1998-08-07
Publication date: 1999-03-18
Also published as: AU1448999A; WO1999013352A3

Abstract

A system for determining the three dimensional position of an object by use of at least four RF transmitters whose positions are accurately known with each transmitter sensing a common time based signal containing its position information to a remote receiver on or proximate the object, the receiver using the information in the data signals to determine the position of the object.

Description

RANGE POSITIONING SYSTEM BACKGROUND OF INVENTION L. FIELD OF THE INVENTION

The present invention relates to range positioning systems and more particularly to range positioning systems utilizing a plurality of RF transmitters which broadcast their known position to a remote receiver which can utilize the transmitted data to calculate the position of the receiver.

2. DESCRIPTION OF THE PRIOR ART Global Positioning Systems (GPS) are well known in the art. These systems utilize a plurality of earth orbiting satellites whose position is known with great accuracy and which broadcast position data and time data to receivers, usually on or close to earth, for use in calculating the receivers position e.g. its longitude, latitude and altitude. Usually, the receiver includes a processor to identify which of several satellites the data is being received from and, knowing where that receiver is located at the time of transmission and knowing the delay between transmission and receipt, the processor can calculate its own position with considerable accuracy.

Because of various factors such as the clocks in the satellites being slightly mistimed or because of atmospheric aberrations, the satellite signals being received may contain some errors and accordingly, to achieve even greater accuracy, ground based receivers whose position is accurately known may be also utilized to detect any errors that exist in the satellite signals and to broadcast error signals to the receiver for use in correcting the satellite signal errors. These systems are sometimes called Differential Global Positioning Systems (DGPS). Although GPS and DGPS have great utility for determining the position of a receiver that can receive signals from at least four of the satellites at one time (for GPS) or can receive signals from at least four of the satellites and at least one ground error calculating receiver (for DGPS), there are situations where this is not possible. In certain areas where surrounding tall objects may exist, being able to receive signals from at least four satellites is often impossible and since there are very few ground based error calculating receivers at the present time, being able to receive signals from one of them is highly unlikely. A need exists for a positioning system that can be assured of being able to receive signals from four RF transmitters of accurately known position so as to be able to determine the x, y and z coordinates or three dimensional position of a remote receiver. It is particularly desirable to provide a position determining system for use in remote or confined areas such as low lying farms for automatic farm machinery control or in mountainous regions for tracking purposes or inside of buildings for security assistance. It is also desirable to provide such systems with a minimum of complexity and cost.

BRIEF DESCRIPTION OF THE INVENTION The present invention fulfills the need for a simple, low cost positioning system for use in a predetermined location such as remote or confined areas and that will always be able to receive transmissions from at least four transmitters simultaneously. This is achieved by mounting the plurality of receivers around the predetermined location at selected positions and encoding them with their exact location and supplying them with a common clock. The selected positions are chosen so that regardless of the receiver's position within the predetermined area, it will always be able receive signals from at least four of the transmitters. For example, on a farm, the transmitters may be positioned at or near the four corners and, perhaps, placed in high positions so when the farmer with a receiver moves about the farm, he will always have a line of sight to four transmitters and thereby be able to determine his exact location.

In a building or other structure, the transmitters may be most anywhere so long as their transmissions are not blocked by large metal structures.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a conceptualized area in which a receiver is surrounded by four transmitters.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In Figure 1, four RF transmitters, E, , E₂, E₃ and E₄ are shown identified by reference numerals 10, 12, 14 and 16 respectively each having a transmitting antenna identified by reference numerals 20, 22, 24 and 26 respectively. While five or more transmitters may be used to assure reception, only four have been shown for simplicity. A receiver 30, which may be mounted on or proximate an object, such as a tractor, whose position is desired to be known or controlled, is shown in an area, such as a farm, where the transmitters are mounted. The receiver includes a receiving antenna 32 and a position monitor box 34 which will contain the necessary computer programmed to determine position from the received signals.

Connected to the four transmitters 10, 12, 14 and 16 by lines 40, 42. 44 and 46 respectively is a single signal generator 50 which receives a common time based data signal from a data generator 52 connected to a single common clock 54. While the connections from the signal generator to the transmitters has been shown as hard wired, the signals may be broadcast. Several unobvious advantages accrue by the use of a single clock and signal generator. The only time differences between the various emitters is the transmission delay from the signal generator 50 to the transmitters and, since the positions of the transmitters are fixed with respect to the signal generator, these may be easily calibrated out by moving the receiver 30 to several known locations and calculating the time delays associated with each transmitter. Furthermore, using a single common clock removes any errors that might otherwise occur due to clock performance since such errors are common to all transmitters and the error is thus removed from the solution.

Each transmitter receives the common time based signal from signal generator 50 and operates to create a spread spectrum signal similar in characteristics to the prior art GPS satellite signals. Each transmitter has a unique code to identify it and transmits its signals at a low level so as not to interfere with other RF signals in the area.

The program for computing the position of receiver 30 can be the same as the prior art GPS programs but may be simplified with minor modifications since there is no need to try to adjust to a common time base or compensate for clock errors nor is there normally any need to try to compensate for atmospheric aberrations.

After setting the system up, the receiver 30 will track the transmitted signals and determine a three dimensional solution to its own position relative to the transmitters. The system is easily calibrated by feeding back the position information when the receiver 30 is at, say, four known locations relative to the transmitters. For example, by moving the receiver to the four transmitter locations and taking a reading at each, any errors between the calculated position and the actual position will be known and the receiver may be calibrated to correct for them. The calibration also determines the signal delay between the signal generator and the emitters and validates the location data on the signal. Once calibrated, the position information should be accurate to within very close tolerances, e.g. a decimeter. It may be desirable for the position sensor receiver to be not sensitive to the

"near far problem" i.e. the overloading from a near transmitter compared to the signal from a remote transmitter. This problem is usually considered in the design of the GPS receivers which interface to pseudolites. A discussion of the "near/far" situation may be found , for example, in an paper entitled "Precision Landing Tests With Improved Integrity Beacon Pseudolites" by Stewart Cobb et al, given at the 8th International

Technical Meeting of The Satellite Division of the Institute of Navigation, September 12-15, 1995 printed in the proceedings of Ion GPS-95 Part 1 of 2, on page 827-833. Specifically on pages 829-830.

It is therefore seen that I have provided a simple, accurate and cost effective system for determining three dimensional position in a remote or confined area. Many modifications will occur to those skilled in the art. For example, more than four transmitters may be used in areas where a receiver cannot always receive signals from the same four transmitters. Also, when multipath problems are encountered as, for example, by reflections from nearby objects, techniques for minimizing such problems may be employed. Several methods to reduce or eliminate multipath problems are known in the art. I, therefore, do not intend to be limited to the specific structures used in connection with the description of the preferred embodiments herein.

Claims

CLAIMSThe embodiments of the invention in which an exclusive property or right is claimed are defined as follows:

1. A positioning system comprising: a plurality of transmitters each located at a known positions and each connected to a single signal generator which provides each transmitter with its position information so that each transmitter broadcasts a signal containing its position information; and a receiver located to receive the transmissions from the plurality of transmitters and operable to calculate the receiver's position from the position information in the transmissions.

2. The system of claim 1 wherein the transmitters further broadcast a common clock signal.

3. The system of claim 2 wherein the plurality of transmitters are at least four in number.

4. The system of claim 3 wherein the signal generator receives information as to the location of the transmitters from a data generator and the common clock signal from a single clock.

5. The system of claim 4 wherein the position information is three dimensional.

6. A positioning determining system comprising: a signal generator including a single common clock; a plurality of transmitters, each connected to the signal generator to receive therefrom information regarding each transmitter's three dimensional position and a common clock signal and operable to broadcast its position information and the common clock signal; and a movable receiver located to receive the transmitted information from at least four of said plurality of transmitters, said receiver including a processor operable to determine the receiver's three dimensional position therefrom.

7. The method of determining the location of a movable member within a predetermined area comprising the steps of:

A. positioning a plurality of transmitters at known locations so that at least four transmitters are in a line of sight to all locations within the predetermined area; B. connecting each transmitter to a source of position information so that each transmitter broadcasts information concerning its own position;

C. positioning a receiver proximate the member to receive the transmissions from the transmitters; and

D. programming the receiver to calculate the position of the receiver, and thus the member, from the information transmitted by the transmitters.

8. The method of claim 7 further including the steps of calibrating the receiver by positioning the receiver at predetermined known locations, checking the determined position against the known locations to establish any error signals and modifying the programming of the receiver to compensate for any such errors.