Communications: directive radio wave systems and devices (e.g. – Directive – Including a satellite
Reexamination Certificate
2002-12-20
2004-07-27
Tarcza, Thomas H. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a satellite
C342S357490, C342S357490, C342S455000, C342S457000, C701S214000, C701S301000
Reexamination Certificate
active
06768447
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for securely determining the location and/or the positioning of an object moving along a course which is known by the location device.
The term “course” is intended to mean a subset of the space delimited by a tubular surface of arbitrary and variable cross section, in which the vehicle is strictly constrained to move. In the event that the cross section of this tube can be neglected, this gives two equations linking longitude, latitude and altitude of the moving object.
The present invention relates more precisely to a method for determining the location of a train moving on a railway track whose exact path is known.
The same principle can be applied to the case in which a single equation is known (movement of the moving object on a known surface).
The present invention relates to a method for determining the location and/or the positioning of a vehicle, this securely in terms of railway transport, that is to say it involves being able to determine the location, or more precisely the zones of non-presence of said vehicle on a section, this quasi-instantaneously, for a vehicle moving on a known course, and doing so with a given probability.
This location is based on the use of navigation satellites or equivalent terrestrial navigation beacons, generically referred to below as “satellites”.
DESCRIPTION OF THE RELATED TECHNOLOGY
In railway signaling, a train is not permitted to enter a specific section of track until it is certain that the train in front has departed therefrom, that is to say that the track section in question is free. To that end, it is necessary to ascertain with a margin of error which is predetermined, and of course extremely small, and to do so securely in terms of railway transport; for example with a maximum error level of the order of 10
−9
and preferably of the order of 10
−12
, the zones in which non-presence of a train can be relied upon, and to do so at each iteration of the calculation.
It is known to determine the precise location of an object, and a fortiori of a train, with the aid of calculation of the position with respect to three satellites, the receivers that can receive the information from said satellites being capable of calculating the coordinates of said moving object with a relatively high precision.
However, it is necessary to add a precise measurement of the universal time, which may prove to be complex and sometimes costly to implement at the level of a receiver, for example one arranged in the train. Furthermore, it should be noted that it is necessary for the various satellites to belong to the same constellation and for them to use the same reference time.
For this reason, a fourth satellite is generally used, which permits precise location of the object in question by solving a system of four equations with four unknowns, so as to obtain the three coordinates of the point in question and the value of the time.
In reality, on the basis of knowledge of the coordinates of these satellites, an estimate is made by calculating the distance separating said satellites from the receiver object whose location is intended to be estimated.
Numerous strategies for increasing the quality and/or the quantity of information being used, in both the civilian and military fields, have made it possible to improve the precision of these measurements.
To that end, the following may be mentioned, inter alia:
increase of the number of satellites involved in the measurement (including on the ground),
correlation between successive measurements in order to reduce the weight of certain causes of errors,
radio broadcasting (via satellite or otherwise) of local correction information (DGPS, WAAS, for example),
increase of the precision of the timing measurement by synchronisation with the carriers of the satellites,
use of maintenance and control information broadcast by the ground monitoring network or networks of the constellations of satellites.
These various items of information are compiled in order to refine as much as possible the most probable value of the position of the object of interest and to increase its precision.
Furthermore, coding and autocorrelation techniques have also been suggested in order to assure protection against electromagnetic interference or malicious acts liable to occur when measurements are being taken.
Lastly, for certain applications, the satellite location system may be supplemented with complementary sensors, which can further improve the quantity or the quality of the available information, for example atmospheric pressure sensors in aeronautics, train-axle rotation sensors coupled with a Doppler radar, partial or complete inertial stations, etc.
SUMMARY OF CERTAIN INVENTIVE ASPECTS
It is therefore an aim of the present invention to describe a method and a device which permit secure location and/or positioning of an object, and thus a fortiori of a vehicle such as a train, moving on a known course.
The term secure location is intended to mean the location, or more exactly the non-presence of a train outside a zone which is redefined at each calculation, with a error level of less than 10
−9
and preferably capable of reaching 10
−12
.
The present invention relates to a method for determining the location and/or the positioning of an object, in particular a vehicle such as a train, moving along a known course, and this securely in terms of railway transport, characterised in that said location and/or said positioning of said object is determined by a valid calculation at a given time based on the one hand, on an elementary measurement involving at least one satellite and, on the other hand, on a secure mapping of said known course.
Preferably, said secure mapping makes it possible to obtain two relationships with three unknowns representing the coordinates of said object whose location and/or positioning is intended to be ascertained, while at least one other relationship between the same three unknowns is obtained with the aid of the information transmitted by at least one satellite whose position is known.
More precisely, the present invention relates to a method in which each elementary measurement consists in determining an individual domain along said course between two mileage points, said domain depending on the standard deviation of the timing measurement errors of said elementary measurement, the speed of light, a coefficient linked with the coordinates of said satellite in question and the course of the track, and a weighting factor defining the geometry of the error distribution for any measurement recording, so that the probability of non-presence of the train in said individual domain is predefined.
Advantageously, each measurement recording is redundant, which makes it possible to determine a plurality of individual domains by a plurality of elementary measurement recordings carried out simultaneously at the same given time, which are based on different satellites or on pairs of satellites.
According to a first embodiment, an elementary measurement will be carried out with the aid of a pair of satellites using the same reference time. Preferably, the pair of satellites will belong to the same constellation.
According to another preferred embodiment, an elementary measurement will be carried out with the aid of at least one satellite belonging to a constellation and a receiver linked with the object moving along the known course, said receiver having a clock synchronised with the reference time of said constellation to which the satellite belongs.
This means that it is sufficient to increase the number of satellites in order to take a plurality of elementary measurements simultaneously.
Preferably, the existence of a common domain is determined, which is defined as the intersection of the, and preferably of all the, various individual domains. Particularly advantageously, the individual domains which have no point in common with the common domain are rejected.
Hence, if there is a non-null common domain, the domain of
Alstom Belgium S.A.
Knobbe Martens Olson & Bear LLP
Mull F H
Tarcza Thomas H.
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