SYSTEM AND METHOD FOR DETECTING AND LOCATING A SIGNAL SOURCE

Abstract

Systems and methods for detecting and locating a signal source. The system contains an antenna array with antennas, a control unit that is connected to the antenna array, and an evaluation unit to receive data from the control unit. The antennas are designed to acquire a signal emitted by the signal source. The control unit is designed to ascertain a cross-correlation or covariance matrix of a signal received from the antenna array, and to transmit the cross-correlation or covariance matrix to the evaluation unit. The evaluation unit is designed to ascertain a position of the signal source on the basis of the cross-correlation or covariance matrix received from the control unit.

Claims

1. A system for detecting and locating a signal source, the system comprising: an antenna array with a plurality of antennas; a control unit connected to the antenna array; an evaluation unit configured to receive data from the control unit; wherein the antennas are configured to acquire a signal emitted by the signal source, wherein the control unit is configured to ascertain a cross-correlation or covariance matrix of a signal received from the antenna array, wherein the control unit is configured to transmit the cross-correlation or covariance matrix to the evaluation unit, and wherein the evaluation unit is configured to ascertain a position of the signal source based on the cross-correlation or covariance matrix received from the control unit.

2. The system of claim 1, wherein the control unit is configured also to transmit information as follows about the antenna array to the evaluation unit, in addition to the cross-correlation or covariance matrix: a position of the antenna array at a time point at which the signal emitted by the signal source was acquired; an alignment of the antenna array; a size and or geometry of the antenna array; and a noise power level.

3. The system of claim 1, wherein the system comprises a plurality of antenna arrays and a plurality of control units, wherein a respective control unit is assigned to an antenna array, wherein each antenna array of the plurality of antenna arrays is spatially distanced from other antenna arrays of the plurality of antenna arrays and configured to acquire the signal emitted by the signal source from a respective separate direction, wherein each control unit is configured to ascertain the cross-correlation or covariance matrix of the antenna array that is assigned to it, and to transmit the ascertained cross-correlation or covariance matrix to the evaluation unit, and wherein the evaluation unit is configured to ascertain the position of the signal source based on at least some of the cross-correlation or covariance matrices received from the plurality of control units.

4. The system of claim 1, wherein the evaluation unit is spatially separate from all the antenna arrays and control units.

5. The system of claim 1, wherein the evaluation unit is together with the antenna array and the control unit in a mobile unit.

6. The system of claim 1, wherein the control unit is configured to transmit the cross-correlation or covariance matrix of the antenna array from a plurality of temporally sequential signal acquisition processes to the evaluation unit.

7. A method for detecting and locating a signal source, comprising: acquiring a signal emitted by the signal source by an antenna array; ascertaining a cross-correlation or covariance matrix of the acquired signal; transmitting the cross-correlation or covariance matrix to an evaluation unit; and ascertaining a position of the signal source in the evaluation unit based on the cross-correlation or covariance matrix.

8. The method of claim 7, wherein the signal emitted by the signal source is acquired by a plurality of antenna arrays that are at different geographical positions, wherein a cross-correlation or covariance matrix is ascertained for each acquisition of the signal emitted by the signal source by each antenna array, and wherein the position of the signal source is ascertained based on at least some of the ascertained cross-correlation or covariance matrices.

9. The method of claim 7, wherein the signal emitted by the signal source is acquired with a single antenna array at different time points at different positions, wherein a cross-correlation or covariance matrix is ascertained for each acquisition of the signal emitted by the signal source by the individual antenna array, and wherein the position of the signal source is ascertained based on at least some of the ascertained cross-correlation or covariance matrices.

10. The method of one of claim 7, wherein, in addition to the cross-correlation or covariance matrix, information about the antenna array is also transmitted to the evaluation unit as follows: a position of the antenna array at a time point at which the signal emitted by the signal source was acquired; an alignment of the antenna array; a size and or geometry of the antenna array; and a noise power level.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Example embodiments are considered in more detail below with reference to the appended drawings. The illustrations are schematic and not true to scale. The same reference signs refer to identical or similar elements. In the figures:

[0042] FIG. 1 shows a schematic illustration of parts of a system according to one example embodiment.

[0043] FIG. 2 shows a schematic illustration of a system according to a further example embodiment.

[0044] FIG. 3 shows a schematic illustration of a system according to a further example embodiment.

[0045] FIG. 4 shows a schematic illustration of the signal processing in an antenna of an antenna array.

[0046] FIG. 5 shows a schematic illustration of an antenna aperture model for the signal processing.

[0047] FIG. 6 shows a schematic illustration of a system according to one example embodiment.

DETAILED DESCRIPTION

[0048] FIG. 1 shows a system generally designated 10 for detecting and locating a signal source 60 on the basis of signals that are emitted by the signal source 60. The system 10 comprises a carrier platform 20, for example a mobile platform in the form of an aircraft. The carrier platform 20 carries an antenna array 30 with a plurality of antennas 32 as well as a control unit 40 connected to the antenna array 30.

[0049] The antenna array 30 receives a signal emitted by the signal source 60. The control unit 40 ascertains a cross-correlation or covariance matrix for the signal received from the antenna array. The cross-correlation or covariance matrix is transmitted by the control unit 40 to the evaluation unit 50, for example over a wireless radio transmission channel that is established between the carrier platform 20 and the evaluation unit 50.

[0050] FIG. 2 shows a further example of a system 10 with multiple carrier platforms 20. In this example, all the carrier platforms 20 are mobile units. It is also, however, conceivable that some of the carrier platforms 20 are stationary.

[0051] The evaluation unit 50 is spatially separated from all the carrier platforms 20; for example, the evaluation unit 50 is part of a stationary ground unit, or it is arranged in a vehicle. In any event, the evaluation unit 50 performs the function of a central data reception site for data (in particular the cross-correlation or covariance matrix) from the carrier platforms 20.

[0052] A data transmission channel 25 is established between each of the carrier platforms 20 and the evaluation unit 50. The data transmission channel enables a transmission of data from the carrier platforms 20 to the evaluation unit 50. The data transmission channel can, however, also be configured as a bidirectional data transmission channel, to enable the transmission of data from the evaluation unit 50 to the carrier platforms 20.

[0053] The data transmission channel 25 is, in particular, designed as a wireless transmission channel. The carrier platforms 20 and the evaluation unit 50 comprise transmit/receive units suitable for these purposes, but these are not shown separately. Any suitable transmission protocol and transmission technology can be used for the purposes of the data transmission between the carrier platforms 20 and the evaluation unit 50. Tactical military data links can, in particular, be used.

[0054] FIG. 3 shows a design of the system of FIG. 2 in which the evaluation unit 50 is not arranged as a separate device, but is linked in terms of location and structure to a carrier platform 20. This does not, however, change anything about the function. The evaluation unit 50 receives the cross-correlation or covariance matrix from all the carrier platforms 20, including the carrier platform 20 to which the evaluation unit 50 is assigned, in this embodiment also. The evaluation unit 50 receives the cross-correlation or covariance matrix from the antenna array 30 that is located on the same carrier platform 20 as the evaluation unit 50, for example via a wired transmission channel. It is, however, also possible in this case to establish a wireless connection between the antenna array 30 and the evaluation unit 50, even when they are arranged on the same carrier platform 20.

[0055] Even though only one signal source 60 is shown in FIGS. 1, 2, 3, it is to be noted that the system 20 is also suitable for detecting and locating multiple signal sources 60.

[0056] FIG. 4 shows a general view of the construction of a receiving unit 35 with antenna 32, along with downstream signal processing in a demodulator 70 or mixer and an analog/digital converter 90. The structure shown in FIG. 4 can be considered a typical, analog RF channel. The antenna 32 receives the signal 62 emitted from a signal source, along with external noise 64. Further noise can also arise or be impressed on the signal in the illustrated arrangement, for example through the electronic components. The signals are transmitted from the antenna 32 to filter units 68. Internal noise 66 may act on the processed signals in the filter units 68 as well as the associated wiring. The signals output by the receiving unit 35 are passed to a demodulator 70 in which the signals are processed using an oscillator 72 and low-pass filters 74. The signals are subsequently passed from the demodulator 70 to an analog/digital converter 90 with two converter units 92. The demodulator 70 and the analog/digital converter 90 each comprise two branches to enable the processing of complex signals with a real component and an imaginary component.

[0057] FIG. 5 shows a model for a linear antenna array. It may be the case that the distance d between the individual antennas varies, in order to cover different frequencies or frequency ranges. The antenna array 30 in FIG. 5 comprises m antennas 32.

[0058] The digitized received signals on the carrier platform p can be represented using the following equations that describe the ascertainment of a direction using an antenna array:

{right arrow over (y)}={right arrow over (a)}.Math.{right arrow over (s)}+{right arrow over (n)}  (1)

[0059] wherein {right arrow over (y)}=[{right arrow over (y)}.sub.1, . . . , {right arrow over (y)}.sub.M].sup.T represents the received signals for all the antennas of the antenna array, the complex amplitudes {right arrow over (a)}.sub.d=([a.sub.1(θ), . . . , a.sub.M(θ)]).sup.T and {right arrow over (a)}=diag {{right arrow over (a)}.sub.d} for all the antennas depend on the angle of incidence θ.sub.m, m=1, . . . , M, the signal is represented as {right arrow over (s)}=[{right arrow over (s)}.sub.1, . . . , {right arrow over (s)}.sub.M].sup.T and the noise as {right arrow over (n)}=[{right arrow over (n)}.sub.1, . . . , {right arrow over (n)}.sub.M].sup.T.

[0060] It is assumed that the narrowband signal is the same for all the antennas, and as a rule only varies in the complex amplitude a(θ.sub.m), where {right arrow over (s)}.sub.m={right arrow over (s)}.sub.m*, m, m*=1, . . . , M applies.

[0061] Referring to FIG. 5, the vector a for the antenna array is described as

a.sub.m(θ)=e.sup.−jω.sup.m  (2)

[0062] where ω.sub.m=2πf.sub.cc.sub.0.sup.−1(m−1)d sin(θ)

[0063] The classic beam forming technique uses the following function, which is examined for maxima:

{circumflex over (θ)}=arg max 1.sub.θ{right arrow over (a)}.sub.d.sup.H{right arrow over (R)}{right arrow over (a)}.sub.d  (3)

[0064] wherein the covariance matrix R of the antenna array represents the received signal

{right arrow over (R)}=E[{right arrow over (y)}.sup.H{right arrow over (y)}]  (4)

[0065] Once the angle of incidence {circumflex over (θ)} has been ascertained, it can be used for locating the signal source and transmitted for the triangulation with the aid of further angles of incidence that have been ascertained by other antenna arrays.

[0066] By way of example, FIG. 6 shows the approach described herein for detecting and locating a signal source 60. Three carrier platforms 20 with an antenna array (not shown) and a control unit (not shown) acquire a signal 62 emitted from the signal source 60. A cross-correlation or covariance matrix of the received signal is formed for each carrier platform. The cross-correlation or covariance matrix is transmitted to the evaluation unit 50. The evaluation unit 50 uses the cross-correlation or covariance matrix from a plurality or from all the carrier platforms 20 in order to locate the signal source 60. The covariance matrix R from equation (4) is transmitted to the evaluation unit 50. The covariance matrix R describes the properties of the signal received from the individual antenna arrays. Numerical optimization methods can be used to locate the signal sources.

[0067] A probability function can be formulated as follows on the basis of equation (1):

[00001]$\begin{array}{cc}p\left(\stackrel{.fwdarw.}{y}|\theta \right)\propto \exp \left\{-\frac{1}{2{\sigma }^2}{\left(\stackrel{.fwdarw.}{y}-\stackrel{.fwdarw.}{a}\stackrel{.fwdarw.}{s}\right)}^H\left(\stackrel{.fwdarw.}{y}-\stackrel{.fwdarw.}{a}\stackrel{.fwdarw.}{s}\right)\right\}& \left(5\right)\end{array}$

[0068] The signal s can be replaced by its least-square estimate:

{right arrow over (s)}=({right arrow over (a)}.sup.H{right arrow over (a)}).sup.−1{right arrow over (a)}.sup.H{right arrow over (y)}  (6)

[0069] Substituting equation (6) into equation (5) and using equation (4), we obtain:

[00002]$$\begin{gathered} \begin{array}{cc}p\left(\stackrel{.fwdarw.}{y}|\theta \right)\propto \exp \left\{-\frac{1}{2{\sigma }^2}{.Math.\left(\stackrel{.fwdarw.}{I}-{\stackrel{.fwdarw.}{a}\left({\stackrel{.fwdarw.}{a}}^H\stackrel{.fwdarw.}{a}\right)}^{-1}{\stackrel{.fwdarw.}{a}}^H\right)\stackrel{.fwdarw.}{y}.Math.}^2\right\} \\ \propto \exp \left\{-\frac{1}{2{\sigma }^2}\mathrm{tr}\left[\left(\stackrel{.fwdarw.}{I}-{\stackrel{.fwdarw.}{a}\left({\stackrel{.fwdarw.}{a}}^H\stackrel{.fwdarw.}{a}\right)}^{-1}{\stackrel{.fwdarw.}{a}}^H\right)\stackrel{.fwdarw.}{R}\right]\right\}& \left(7\right)\end{array} \end{gathered}$$

[0070] The carrier platform p can be described with reference to its position coordinates x, i.e. p({right arrow over (y)}|{right arrow over (x)}}. The angle of incidence of a signal onto an antenna array of a carrier platform p is given as

θ.sub.p=arctan 2(x.sub.p.sup.E,x.sub.p.sup.N)  (8)

[0071] with the relative position of the target position with reference to the carrier platform p:

x.sub.Δ=x−x.sub.p  (9)

[0072] where x.sub.p is the position of a carrier platform.

[0073] If uncorrelated white Gaussian noise is assumed, and with the reference to the signals received from a carrier platform p as {right arrow over (y)}.sup.p, the individual probability function for each carrier platform results, and can be combined as follows:

p({right arrow over (Y)}|{right arrow over (x)}}=Π.sub.p=1.sup.Pp({right arrow over (y)}.sup.p|{right arrow over (x)}}  (10)

[0074] where {right arrow over (Y)}=[{right arrow over (y)}.sup.1, . . . , {right arrow over (y)}.sup.P]

[0075] The target state vector can be given, on the basis of Bayes theorem, as:

[00003]$\begin{array}{cc}p(\stackrel{.fwdarw.}{x}|\stackrel{.fwdarw.}{Y}\}=\frac{p\left(\stackrel{.fwdarw.}{Y}|\stackrel{.fwdarw.}{x}\right)p\left(\stackrel{.fwdarw.}{x}\right)}{p\left(\stackrel{.fwdarw.}{Y}\right)}& \left(11\right)\end{array}$

[0076] Known filter techniques can be applied to this to perform an estimation, so that the parameters that maximize the probability are ascertained.

[0077] As already described further above, the covariance matrix R of a signal acquired by the antenna array must be transmitted to the evaluation unit 50. Taken together, the position of the carrier platform 20 or of the antenna array {right arrow over (x)}.sub.p, the orientation {right arrow over (C)}.sub.p of the antenna array 30, the size and/or geometry {right arrow over (d)}.sub.p of the antenna array and the respective noise power levels σ.sub.p.sup.2 are transmitted in addition to the covariance matrix {right arrow over (R)}.sup.p.

[0078] The evaluation of the probability functions can take place in parallel for all necessary data points. In addition to conventional single- and multi-core processors (CPUs, central processing units), as well as DSPs (digital signal processors) including, for example, FPGAs (field programmable gate arrays) or GPGPUs (general purpose graphics processing units) can be used for this purpose. The information of an individual carrier platform transmitted between the carrier platforms 20 or from the carrier platforms 20 to the evaluation unit 50 does not in itself have to be restricted to the data that unambiguously locates a signal source. Rather is the data from multiple carrier platforms combined in the evaluation unit, and the location of the signal source does not take place until reaching the evaluation unit 50, as shown in FIG. 6.

[0079] The carrier platforms 20 work together and merge the signals they have acquired in the evaluation unit 50. The carrier platforms 20 thus do not have to be able to locate the signal source 60 on the basis of their own data. The location of the signal source 60 rather takes place in the evaluation unit 50 which utilizes the cross-correlation or covariance matrices of the signals 62 acquired by the individual carrier platforms 20.

[0080] The subject matter disclosed herein can be implemented in or with software in combination with hardware and/or firmware. For example, the subject matter described herein can be implemented in or with software executed by a processor or processing unit. In one example implementation, the subject matter described herein can be implemented using a computer readable medium having stored thereon computer executable instructions that when executed by a processor of a computer control the computer to perform steps. Example computer readable mediums suitable for implementing the subject matter described herein include non-transitory devices, such as disk memory devices, chip memory devices, programmable logic devices, and application specific integrated circuits. In addition, a computer readable medium that implements the subject matter described herein can be located on a single device or computing platform or can be distributed across multiple devices or computing platforms.

[0081] While at least one example embodiment of the present invention(s) is disclosed herein, it should be understood that modifications, substitutions and alternatives may be apparent to one of ordinary skill in the art and can be made without departing from the scope of this disclosure. This disclosure is intended to cover any adaptations or variations of the example embodiment(s). In addition, in this disclosure, the terms “comprise” or “comprising” do not exclude other elements or steps, the terms “a”, “an” or “one” do not exclude a plural number, and the term “or” means either or both. Furthermore, characteristics or steps which have been described may also be used in combination with other characteristics or steps and in any order unless the disclosure or context suggests otherwise. This disclosure hereby incorporates by reference the complete disclosure of any patent or application from which it claims benefit or priority.

LIST OF REFERENCE SIGNS

[0082] 10 System [0083] 20 Carrier platform [0084] 25 Data transmission channel [0085] 30 Antenna array [0086] 32 Antenna [0087] 35 Receiving unit [0088] 40 Control unit [0089] 50 Evaluation unit [0090] 60 Signal source [0091] 62 Emitted signal [0092] 64 External noise [0093] 66 Internal noise [0094] 68 Filter unit [0095] 70 Demodulator [0096] 72 Oscillator [0097] 74 Low-pass filter [0098] 90 Analog/digital converter [0099] 92 Converter unit