Communications: directive radio wave systems and devices (e.g. – Determining distance – Combined with determining direction
Reexamination Certificate
2001-12-19
2003-06-17
Lobo, Ian J. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Determining distance
Combined with determining direction
C342S118000, C342S133000, C342S417000
Reexamination Certificate
active
06580387
ABSTRACT:
TECHNICAL FIELD
The invention relates to a method for determining the range to a moving object by means of a sensor capable of measuring the bearing or angle to the object. The invention affords greater accuracy in such calculations than has hitherto been possible.
BACKGROUND ART
Determining the range of an object by means of an instrument or a sensor that is only capable of providing information on the bearing or angle to the object is a longstanding problem, an example of the application of which is the so-called triangulation of radio transmitters. If the range is to be determined using only a single measuring instrument or sensor, the sensor must have a movement in relation to the target over a number of successive measurements. In order to obtain particularly reliable measurement data, it may be advantageous if, between the measurements, the sensor platform is made to move along a path that optimizes the measurements.
Conventional methods of determining the range to a moving object by means of a single angle-only sensor have often assumed that the target moves without acceleration between the measurements, the term acceleration being used in the sense of “variation of the speed vector”, in other words it has been assumed that the target does not alter either its course or its speed between the measurements. These methods work well if the assumption regarding the absence of acceleration on the part of the object is correct, but unfortunately this is often not the case. Such a method is described in [1].
One known method of achieving good accuracy in determining the range to a moving, accelerating target is to use so-called Interacting Multiple Models (IMM), which are described in and elsewhere. According to this method, two models for the target are assumed, on the one hand a so-called straight trajectory model, which means that the target is assumed not to accelerate, and on the other a model according to which the target is assumed to accelerate only between the measurements, a so-called maneuvering model. In calculations according to IMM, the maneuvering model is allowed to influence the straight trajectory model, and conversely the straight trajectory model is allowed to influence the maneuvering model in a predefined manner in accordance with the probabilities for each model. In applying the IMM method of determining the range of maneuvering targets on the basis of measurements by a single directional sensor, a conflict arises between the range finding and any tracking of a maneuvering target. This conflict means that the existence of maneuvering models leads to poor accuracy of the range calculations when the target is not maneuvering.
DISCLOSURE OF INVENTION
There is consequently a need for a method which, by means of an angle-only sensor, is capable of providing more reliable range calculations to a moving target than methods hitherto known.
The present invention achieves this through a method for calculating the range of an object by means of a sensor capable of determining the angle to the object, where the sensor and the object have a movement relative to one another, comprising the following after a measurement:
on the assumption that the target maintains a constant velocity, a number of possible target ranges are calculated. For each such possible range an area of uncertainty is calculated, within which the target may be located, a so-called “straight trajectory model”,
on the assumption that the target accelerates, a number of possible target ranges are calculated. For each such possible range an area of uncertainty is also calculated, within which the target may be located, a so-called “manoeuvring model”, and a number of the straight trajectory models have a manoeuvring model assigned to them.
In calculating the target range in the straight trajectory models that have associated manoeuvring models, data from the respective manoeuvring model is incorporated to a predetermined extent if the probability that the target manoeuvres exceeds a predetermined limit, which can also be applied when calculating other data for the target.
The range of the target from the sensor is calculated as a weighted average of a number of ranges of the straight trajectory models, where the weighting being based on the probability of each straight trajectory model, which is a procedure that can also be used when calculating other data for the target. In calculating the possibility of the target maneuvering, use may also be made of prior knowledge of the type of target, geography etc.
REFERENCES:
patent: 5479360 (1995-12-01), Seif et al.
patent: 5504489 (1996-04-01), Kronhamn
patent: 5739789 (1998-04-01), Kronhamn
patent: 5877722 (1999-03-01), Shams
patent: 6064942 (2000-05-01), Johnson et al.
“Bearings-Only Target Motion Analysis Based on a Multihypothesis Kalman Filter and Adaptive Ownship Motion Control”, Kronhamn, IEE Proc.-Radar, Sonar Navig., vol. 145, No. 4, Aug. 1998, pp. 247-252.
“The Interacting Multiple Model Algorithms for Systems with Markovian Switching Coefficients”, IEEE Transactions On Automatic Control, vol. 33, No. 8, Aug. 1988, pp. 780-783.
Lobo Ian J.
Nixon & Vanderhye P.C.
Telefonaktiebolaget LM Ericsson (publ)
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