System for determining position and velocity of targets from signals scattered by the targets

• US 20040130480A1
• Filed: 11/10/2003
• Published: 07/08/2004
• Est. Priority Date: 05/11/2001
• Status: Active Grant

• Current Assignee: Totalforsvarets Forskningsinstitut (FOI)
• Original Assignee: Totalforsvarets Forskningsinstitut (FOI)
• Inventors: Hellsten, Hans
• Granted Patent: US 6,850,186 B2
• Time in Patent Office: Days
• US Class Current: 342/59
• CPC Class Codes: G01S 13/003 Bistatic radar systems; Multistatic radar systems
• CPC Class Codes: G01S 13/878 Combination of several spaced transmitters or receivers of known location for determining the position of a transponder or a reflector G01S13/874 takes precedence
• CPC Class Codes: G01S 7/003 Transmission of data between radar, sonar or lidar systems and remote stations
• CPC Class Codes: G01S 7/2813 Means providing a modification of the radiation pattern for cancelling noise, clutter or interfering signals, e.g. side lobe suppression, side lobe blanking, null-steering arrays specially adapted to secondary radar systems G01S13/762; aerials or aerials systems H01Q21/29, H01Q25/00

Abstract

The present invention relates to a system for using signals scattered by targets to determine position and velocity for each of the targets and comprises a set of transmitters and receivers of electromagnetic or acoustic signals, said transmitters and receivers dispersed to known points. Each pair of transmitter and receiver, mono-static or bi-static, is named a measuring facility. The ranges of the transmitters are chosen so that a target at an arbitrary point within the position space can be measured via scattering in the target by at least four, but preferably many more, measuring facilities.

For each measuring facility, target detection occurs with constant false alarm rate in the form of probabilities over resolution cells with regards to range and Doppler velocity and conceivable targets are placed in a 2-dimensional linear space of ranges and Doppler velocities, said 2-dimensional linear space belonging to the measuring facility. 3-dimensional positions and 3-dimensional Doppler velocities are represented as a 6-dimensional linear position and velocity space subdivided into resolution cells with the same resolution of range and Doppler velocity that is found at the measuring facilities.

For each intersection representing detections at at least 4 measuring facilities the probability is calculated that the intersection is a false alarm emanating from intersections between sub-sets from different targets and when the probability falls below a predefined value, it is given that the intersection contains at least one target. The target positions and target velocities are extracted through this.

Claims

1. A system for using signals scattered by targets to determine position and velocity for each of the targets in a position space, comprising a set of transmitters and receivers of electromagnetic or acoustic signals, said transmitters and receivers dispersed to known points in the position space, where each pair of transmitter and receiver, mono-static or bi-static, is named a measuring facility, further comprising analysis equipment for storage and analysis of received signals, which includes determination of instants for transmission and reception according to established principles for radar and parameterising of received signals as a function of path between point of transmission and point of reception, however without the usual requirement in radar on directional information, characterised in

that the range of the transmitters is chosen so that one target at an arbitrary point within the position space can be measured via scattering in the target by at least four measuring facilities,

that for each measuring facility a target detection takes place with constant false alarm rate—

CFAR—

where the noise intensity is given a threshold value and the cells where the signal intensity surpasses the threshold value are given to be target candidates,

that the analysis equipment utilises a target positioning algorithm that implies that each measuring facility φ

places n_φ

target candidates in n_φ

of N resolution cells in a 2-dimensional linear space of range and Doppler velocities S²_φ

associated to the measurement facility and that 3-dimensional positions and 3-dimensional Doppler velocities are represented as a 6-dimensional linear position and velocity space S⁶ partitioned into N³ resolution cells X ⊂

S⁶ with the same resolution of range and Doppler velocity as found in the measurement facilities and

that the analysis equipment, based on the assumption that there is equal probability that a target is found in each and every of the cells X ⊂

Y_jφ

, where Y_jφ

⊂

S⁶ is a sub-set representing a single target candidate j=1,2, . . . ,n_φ

at some single measuring facility φ

, and also based on the expected number of targets

$M=\underset{\forall <br><br>\mathrm{\varphi <br><br>}}{\max }<br><br>\text{\hspace{1em}<br><br>}<br><br>n_{\mathrm{\varphi <br><br>}}.$

calculates, for each cell X ⊂

Y_jφ

∩

Y<sub>j′

φ

′</sub>

∩

. . . ∩

Y<sub>j(n)φ

(n)</sub> which represents detections at at least n≧

4 measuring facilities, the probability p^FA(n,M,N) that the cell contains a false alarm emanating from intersections between sub-sets Y_jφ

which originate from different targets and

gives, when the probability falls below a predefined value, that the intersection contains at least one target and extracts through this target positions and target velocities.

2. System according to claim 1, characterised in that transmitter and receiver are placed as grid points in an essentially equidistant grid on a surface, which bounds the surveyed position space, e.g. an earth surface, with the distance between the corner points essentially the same, d, and where the range of the signals when having an essentially planar surface is at least 2d, implying at least 6 independent bi-static configurations per grid point and that the range, in the case where the surface is not essentially planar, is adapted to give just as many bi-static configurations as in the planar case.

3. System according to claim 2, characterised in that a pair consisting of a transmitter and a receiver are placed as said grid points in the essentially equidistant network.

4. System according to claim 2 or 3, characterised in that the system also utilises the combined transmitters/receivers for mono-static measurements.

5. System according to claim 2, characterised in that when the range of the signals is kd;

k=2,3, . . . and wherethus the signals from 7,19, . . . ,3k(k+1)+1, . . . grid points must be distinguishable by each receiver, the total bandwidth B for the signal is partitioned into 3k(k+1)+1 adjacent sub-bands, where each sub-band transmits within a hexagon of 3k(k+1)+1 grid points and is received by the middle station in the hexagon, after which, when the signals scattered by targets have been registered, a new distribution of sub-bands among grid points within the hexagon is sent etc. until each grid point within the hexagon has sent each sub-band within the total bandwidth, and that this transmission pattern is copied through translations in the grid to congruent hexagons of 3k(k+1)+1 grid points covering an arbitrarily large surface, whereby it is achieved that each receiving station never obtains the same sub-band from more than one grid point within the assumed range and each sub-band can be uniquely traced to the grid point of its transmission.

6. System according to anyone of the claims 1-5, characterised in that the analysis equipment determines for each resolution cell X ⊂

S⁶ a first integer value n(X) which is the number of measuring facilities that have a range allowing them to detect targets lying in the resolution cell, and a second integer value n′

(X) which is the number of measuring facilities which actually detect targets at that range and with the Doppler velocity which means that a target can lie in the resolution cell and that the analysis equipment for each resolution cell forms the quotient α

(X)=n′

(X)/n(X) and states that the resolution cell X contains a target if the quotient α

(X) exceeds a predefined value which is chosen depending on the certainty of detecting targets in a given resolution cell and which is therefore larger than zero and less than or equal to one.

7. System according to claim 6, characterised in that the resolution cells are first chosen essentially larger than the range- and Doppler resolution, that the resolution cells X ⊂

S⁶ which the analysis equipment indicates to contain targets are partitioned in such a way into two or more resolution sub-cells that the number of resolution sub-cells after partitioning is essentially as large as the initial number of resolution cells, that the analysis equipment then carries out a corresponding second analysis of the new set of resolution sub-cells and those resolution sub-cells are chosen and given to contain targets which fulfil the chosen requirement, after which the cells which have been given to contain a target are partitioned again and a new analysis is done etc. until the final resolution sub-cell size converges with the resolution of range- and Doppler velocity.

8. System according to claim 7 characterised in that at least two cell subdivisions are utilised starting from a predefined subdivision level, and which has cells congruent but different from each other for each subdivision level a translation a fraction of the cell length in the spatial domain, that the analysis equipment carries out its analysis on all cell subdivisions, whereby the target position can be established to fractions of the spatial cell length in that the target is detected in certain overlapping cells at a certain subdivision level and therefore is completely contained in the intersection of these cells.

9. System according to claim 8, characterised in that a (X)≈

1 for resolution cells with a spatial extension down to the maximal size of an expected target and that α

(X)=4/n(X) for smaller resolution cells.

10. System according to anyone of the previous claims, characterised in that the transmitters and receivers comprise

an antenna arrangement consisting of

a number on a mast, along a vertical axis, located antenna elements which via a feeding network together give a 3-dimensional radiation diagram with a main part of the energy uniformly distributed within a cone with regard to the vertical axis and where the cone angle can be controlled by imposing varying phase shifts on the different antenna elements during feeding of the elements and

a number of antenna elements arranged along a horizontal circle that is concentric with the vertical axis, with essentially even distribution of the antenna elements along the circle and a feeding network for antenna elements, such that one or more beams directed horizontally can be obtained by imposing varying phase shifts on the different antenna elements during feeding of the elements and

a unit which by linear combination combines signals from the horizontally and vertically oriented elements, so that the signal from the horizontal ring is subtracted from signals from the vertically arranged antenna elements, which results in a radiation diagram that is insensitive in directions where the horizontal ring has directed beams.