Orthogonal phase modulation for detection and communication in radar

Abstract

A method of orthogonal modulation of radar waves of a phase-modulated continuous wave radar system. The method includes selecting an equidistant bi-phased or multi-phased phase-modulation sequence, phase-modulating the continuous radar wave, and transmitting the orthogonal phase-modulated continuous radar wave towards a scene. The method includes generating a detection sequence (s) by applying an outer coding (H) to the phase-modulation sequence, selecting a communication range (C) in the complex number plane, based on the selected phase-modulation, generating a communication sequence (c) having a plurality of sequence members, mapping the communication sequence (c) into the communication range (C) by applying an injective mapping function () to the sequence members, and calculating a numerical product of members of the detection sequence (s) with members of an image of the mapped communication sequence (c). Phase-modulating the continuous wave of the radar system is carried out according to the calculated numerical products.

Claims

1. A method of orthogonal modulation of radar waves of a phase-modulated continuous wave radar system by a sequence of numerical communication symbols, the method comprising steps of: selecting an equidistant bi-phased or multi-phased phase-modulation sequence, wherein members of the sequence are given by complex roots of unity, phase-modulating the continuous radar wave of the radar system, and transmitting the orthogonal phase-modulated continuous radar wave towards a scene, and the method being characterized by the following steps of: generating a detection sequence (s) by applying an outer coding (H) to the bi-phased or multi-phased phase-modulation sequence, selecting a communication range (C) in the complex number plane, based on the selected equidistant bi-phased or multi-phased phase-modulation, generating a communication sequence (c) comprising a plurality of sequence members, wherein the members are natural numbers, mapping the communication sequence (c) into the communication range (C) by applying an injective mapping function () to the members of the communication sequence (c), calculating a numerical product of members of the detection sequence (s) with members of an image of the mapped communication sequence (c), wherein the step of phase-modulating the continuous radar wave of the radar system is carried out according to the calculated numerical products.

2. The method as claimed in claim 1, wherein the selected equidistant bi-phased or multi-phased phase-modulation sequence is selected from a group comprising m-sequence, Zadoff-Chu sequence, Legendre sequence or Almost Perfect Autocorrelation Sequence.

3. The method as claimed in claim 1, wherein the phase-modulated continuous wave radar system is configured to work in a multiple-input and multiple-output configuration, and the step of generating a detection sequence (s) includes applying a Hadamard matrix (H).

4. The method as claimed claim 1, wherein the injective mapping function () can be expressed as: $\left(c\right)=\exp \left(i\frac{\left(2c-\left(T+1\right)\right)}{n\left(T+1\right)}\right)$ wherein c denotes the value of a member of the communication sequence (c), n denotes the maximum possible number of different roots of unity for the members of the equidistant bi-phased or multi-phased phase-modulation, and T denotes the maximum value of the members of the communication sequence (c).

5. A method of demodulating phase-modulated continuous radar waves that are orthogonally modulated by a sequence of numerical communication symbols by the method as claimed in claim 1, wherein the phase-modulated continuous radar waves are directly received, the method comprising steps of: applying a communication backprojection function to the received phase-modulated continuous radar waves for mapping the numerical communication symbols to the communication range (C), wherein the communication backprojection function can be expressed as: $\left(\tilde{c}\right)=\underset{k=0}{\overset{n-1}{.Math.}}{c}_k\left(\tilde{c}\right)e^{-2i\frac{k}{n}}\tilde{c},$ wherein n denotes the maximum possible number of different roots of unity for the members of the equidistant bi-phased or multi-phased phase-modulation, {tilde over (c)} is an image of a member of the communication sequence (c) in the communication range (C), and .sub.C.sub.k({tilde over (c)}) is the characteristic function with a value of 1 if the argument lies within the subset C.sub.k of the complex unit circle and a value of 0 else, and extracting the numerical communication symbols by applying the inverse function of the injective mapping function () to images of the mapped numerical communication symbols in the communication range (C).

6. A method of demodulating phase-modulated continuous radar waves that are orthogonally modulated by a sequence of numerical communication symbols by the method as claimed in claim 1, wherein the phase-modulated continuous radar waves are received after having been reflected by a target, the method comprising steps of: applying a detection sequence backprojection function to the received phase-modulated continuous radar waves for projecting all phases lying in a specific subset of the complex unit circle onto a specific complex root of unity that lies within the specific subset, wherein the detection sequence backprojection function can be expressed as: $\left(\tilde{c}\right)=\underset{k=0}{\overset{n-1}{.Math.}}{c}_k\left(\tilde{c}\right)e^{2i\frac{k}{n}}$ wherein n denotes the maximum possible number of different roots of unity for the members of the equidistant bi-phased or multi-phased phase-modulation, {tilde over (c)} is an image of a member of the communication sequence (c) in the communication range (C), and .sub.C.sub.k({tilde over (c)}) is the characteristic function with a value of 1 if the argument lies within the subset C.sub.k of the complex unit circle and a value of 0 else, and applying a phase-modulated continuous wave radar signal processing method to the projected phases.

7. A communication sequence demodulating device for demodulating phase-modulated continuous radar waves that are orthogonally modulated by a sequence of numerical communication symbols by the method as claimed in claim 1, wherein the phase-modulated continuous waves are directly received, the device comprising: a radar wave receiving unit that is configured for receiving phase-modulated continuous radar waves, and a radar signal processing unit that is configured for carrying out a method that comprises the steps of: applying a communication backproiection function to the received phase-modulated continuous radar waves for mapping the numerical communication symbols to the communication range (C), wherein the communication backproiection function can be expressed as: $\left(\tilde{c}\right)=\underset{k=0}{\overset{n-1}{.Math.}}{c}_k\left(\tilde{c}\right)e^{-2i\frac{k}{n}}\tilde{c},$ wherein n denotes the maximum possible number of different roots of unity for the members of the equidistant bi-phased or multi-phased phase-modulation, {tilde over (c)} is an image of a member of the communication sequence (c) in the communication range (C), and .sub.C.sub.k({tilde over (c)}) is the characteristic function with a value of 1 if the argument lies within the subset C.sub.k of the complex unit circle and a value of 0 else, and extracting the numerical communication symbols by applying the inverse function of the injective mapping function () to images of the mapped numerical communication symbols in the communication range (C).

8. A detection sequence backprojection demodulating device for demodulating phase-modulated continuous radar waves that are orthogonally modulated by a sequence of numerical communication symbols by the method as claimed in claim 1, wherein the phase-modulated continuous waves are received after having been reflected by a target, the device comprising: a radar wave receiving unit for receiving phase-modulated continuous radar waves, and a radar signal processing unit that is configured for carrying out a method that comprises the steps of: applying a detection sequence backproiection function to the received phase-modulated continuous radar waves for projecting all phases lying in a specific subset of the complex unit circle onto a specific complex root of unity that lies within the specific subset, wherein the detection sequence backproiection function can be expressed as: $\left(\tilde{c}\right)=\underset{k=0}{\overset{n-1}{.Math.}}{c}_k\left(\tilde{c}\right)e^{2i\frac{k}{n}}$ wherein n denotes the maximum possible number of different roots of unity for the members of the equidistant bi-phased or multi-phased phase-modulation, {tilde over (c)} is an image of a member of the communication sequence (c) in the communication range (C), and .sub.C.sub.k({tilde over (c)}) is the characteristic function with a value of 1 if the argument lies within the subset C.sub.k of the complex unit circle and a value of 0 else, and applying a phase-modulated continuous wave radar signal processing method to the projected phases.

9. An automotive phase-modulated continuous wave radar system, comprising a radar wave transmitting unit that is configured to orthogonally modulate phase-modulated continuous radar waves by a sequence of numerical communication symbols by conducting a method as claimed in claim 1, and to transmit the orthogonal modulated radar waves towards a scene with potential objects to be detected, a communication sequence demodulating device for demodulating the orthogonal modulated radar waves, wherein the orthogonal modulated radar waves are directly received, the communication sequence demodulating device comprising: a radar wave receiving unit that is configured for receiving phase-modulated continuous radar waves, and a radar signal processing unit that is configured for carrying out a method that comprises the steps of: applying a communication backproiection function to the received phase-modulated continuous radar waves for mapping the numerical communication symbols to the communication range (C), wherein the communication backproiection function can be expressed as: $\left(\tilde{c}\right)=\underset{k=0}{\overset{n-1}{.Math.}}{c}_k\left(\tilde{c}\right)e^{-2i\frac{k}{n}}\tilde{c},$ wherein n denotes the maximum possible number of different roots of unity for the members of the equidistant bi-phased or multi-phased phase-modulation, {tilde over (c)} is an image of a member of the communication sequence (c) in the communication range (C), and .sub.C.sub.k({tilde over (c)}) is the characteristic function with a value of 1 if the argument lies within the subset C.sub.k of the complex unit circle and a value of 0 else, and extracting the numerical communication symbols by applying the inverse function of the injective mapping function () to images of the mapped numerical communication symbols in the communication range (C), and a detection sequence backprojection demodulating device for demodulating the orthogonal modulated radar waves, wherein the orthogonal modulated radar waves are received after having been reflected by a target, the device comprising: a radar wave receiving unit for receiving phase-modulated continuous radar waves, and a radar signal processing unit that is configured for carrying out a method that comprises the steps of: applying a detection sequence backproiection function to the received phase-modulated continuous radar waves for projecting all phases lying in a specific subset of the complex unit circle onto a specific complex root of unity that lies within the specific subset, wherein the detection sequence backproiection function can be expressed as: $\left(\tilde{c}\right)=\underset{k=0}{\overset{n-1}{.Math.}}{c}_k\left(\tilde{c}\right)e^{2i\frac{k}{n}}$ wherein n denotes the maximum possible number of different roots of unity for the members of the equidistant bi-phased or multi-phased phase-modulation, {tilde over (c)} is an image of a member of the communication sequence (c) in the communication range (C), and .sub.C.sub.k({tilde over (c)}) is the characteristic function with a value of 1 if the argument lies within the subset C.sub.k of the complex unit circle and a value of 0 else, and applying a phase-modulated continuous wave radar signal processing method to the projected phases.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further details and advantages of the present invention will be apparent from the following detailed description of not limiting embodiments with reference to the attached drawing, wherein:

(2) FIG. 1 shows a schematic top view on an automotive traffic scenery including two mutually approaching vehicles, each vehicle being furnished with an automotive PMCW radar system in accordance with an embodiment of the invention,

(3) FIG. 2 is an illustration of positions of a detection sequence for a bi-phased phase-modulation, positions of a communication sequence and a communication range in the complex plane,

(4) FIG. 3 is an illustration of positions of a detection sequence for a multi-phased phase-modulation with n=4, and a position of a communication range in the complex plane,

(5) FIG. 4 shows an exemplary scheme of an orthogonal modulation by a communication sequence out the coding in addition to an outer coding given by Hadamard coding,

(6) FIG. 5 is an illustration of the effect of a communication backprojection function for a multi-phased phase-modulation with n=5,

(7) FIG. 6 is an illustration of the effect of a detection sequence backprojection function for a multi-phased phase-modulation with n=5,

(8) FIG. 7 shows a block diagram of one of the automotive PMCW radar systems pursuant to FIG. 1 in accordance with the invention,

(9) FIG. 8 is an illustration of the detection sequence and the communication sequence,

(10) FIG. 9 illustrates the resulting phase-modulations at different states,

(11) FIG. 10 shows real (upper half) and imaginary (lower half) parts of the received phase-modulated continuous radar waves before and after applying the communication backprojection function,

(12) FIG. 11 shows the resulting sequence after applying the communication backprojection function and applying the inverse function of the injective mapping function to the images of the mapped numerical communication symbols in the communication range, and

(13) FIG. 12 shows the reconstructed detection sequence per chip after applying the detection sequence backprojection function, multiplying with the outer coding and applying a PMCW radar signal processing method.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

(14) FIG. 7 shows a block diagram of one of the identically designed automotive PMCW radar systems 10 pursuant to FIG. 1 in accordance with an embodiment of the invention. The PMCW radar system 10 includes a radar wave transmitting unit 12, a communication sequence demodulating device 14 and a detection sequence backprojection demodulating device 16.

(15) The radar wave transmitting unit 12 is configured to orthogonal modulate phase-modulated continuous radar waves by a sequence of numerical communication symbols, and to transmit the orthogonal modulated radar waves towards the scene in front of the vehicle 18 shown in FIG. 1 with potential objects such as the obstacle 24 to be detected. The radar wave transmitting unit 12 comprises a plurality of four transceiver antenna units (not shown), which are arranged at a front region 22 of the respective vehicle 18, 20 and that are configured to work in a MIMO configuration. It will be appreciated that the number of four transceiver antenna units is only chosen as an example but that any other number of transmitters is possible.

(16) In a first step 32 of the method (FIG. 7) of orthogonal modulation of radar waves of the PMCW radar system 10, an equidistant multi-phased phase-modulation is selected, which in this specific embodiment is a bi-phased phase-modulation, wherein members of the phase-modulation are given by complex roots of unity, in this case 1 and +1, i.e. n=2.

(17) In another step 34 of the method, a bi-phased phase-modulation sequence is selected to be (1111111111111111).

(18) In the next step 36 of the method, a detection sequence s is generated by applying an outer coding to the bi-phased phase-modulation sequence, which in this specific embodiment is given by the fourth row of the 44 Hadamard matrix H=[1111].

(19) Then, in another step 38 of the method, a communication range C in the complex number plane is selected, based on the selected equidistant bi-phased phase-modulation, to be the section of the complex unit circle between angles of

(20) $-\frac{}{2}$
and

(21) $+\frac{}{2}.$

(22) A communication sequence c is generated in another step 40, comprising a plurality of 18 sequence members, which are natural numbers: c=(414141332233414141)

(23) The communication sequence c is filled up with zeros to match an integral multiple of the fourth row of the 44 Hadamard matrix H. The detection sequence s (mixed with H) and the communication sequence c are illustrated in FIG. 8.

(24) In the next step 42 of the method (FIG. 7), the communication sequence c is mapped into the communication range C by applying the injective mapping function (c) to the members of the communication sequence c.

(25) Further, a numerical product of members of the detection sequence s (mixed with H) with members of the image of the mapped communication sequence c is calculated in another step 44. Then, the continuous wave of the radar system 10 is phase-modulated according to the calculated numerical products in another step 46. In the next step 48, the phase-modulated continuous radar wave is transmitted towards the scene.

(26) The resulting transmitted phase-modulations after mixing the detection sequence s (mixed with H) with the mapped communication sequence c is illustrated in FIG. 9. Herein, the original communication sequence c is located in the positive real half plane (straight crosses). After mixing with the detection sequence s (mixed with H), the resulting phase shifts are located over the whole complex plane (diamonds). In FIG. 9, the various data series are downscaled for the purpose of clarity. In reality, all phases lie within the complex unit circle

(27) Referring again to FIG. 7, in the communication sequence demodulating device 14 of the communication partner PMCW radar system 10, which is identical to the one of the ego radar system, the transmitted phase-modulated continuous radar waves are received. In a step 50 of a demodulation method, which is carried out by the radar signal processing unit of the communication sequence demodulating device 14, the communication backprojection function is applied to the received phase-modulated continuous radar waves. As shown in FIG. 9 by open squares, the communication backprojection function maps the numerical communication symbols back to the positive real half plane, i.e. to the communication range C. A waveform of the received phase-modulated continuous radar waves (dotted lines) before and after applying the communication backprojection function (solid line) is illustrated in FIG. 10 (upper half: real part, lower half: imaginary part).

(28) The resulting sequence after applying the communication backprojection function and applying the inverse function of the injective mapping function to the images of the mapped numerical communication symbols in the communication range C in another step 52 (FIG. 7) is illustrated in FIG. 11.

(29) The orthogonal modulation of the phase-modulated continuous radar waves by the communication sequence c is of no relevance to the ego radar system 10. Rather, the ego radar system 10 serves to resolve the detection sequences (mixed with H).

(30) In the detection sequence backprojection demodulating device 16 of the Ego radar system 10 (FIG. 7), phase-modulated continuous radar waves that have been reflected by a target are received by a radar wave receiving unit. In a step 54 of a demodulation method, which is carried out by the radar signal processing unit of the detection sequence backprojection demodulating device 16, the detection sequence backprojection function is applied to the received phase-modulated continuous radar waves for projecting all phases lying in a specific subset of the complex unit circle U onto a specific complex root of unity that lies within the specific subset, in this case all phases lying in the positive real half plane to +1, and all phases lying in the negative real half plane to 1, see FIG. 9 (slanted crosses).

(31) After a step 56 (FIG. 7) of multiplying with the outer coding given by the Hadamard matrix H, another step 58 of applying a PMCW radar signal processing method to the projected phases is performed by the radar signal processing unit of the detection sequence backprojection demodulating device 16, in which the sequence is exactly reconstructed, as is shown in FIG. 12 (transmitted detection sequence: solid line, detection sequence from processing received phase-modulated continuous radar waves: dots).

(32) Although in this specific embodiment the ego radar system 10 installed in vehicle 18 and the radar system 10 installed in vehicle 20 are identically designed, it will be readily acknowledged by those skilled in the art that the desired communication, even if only one-way, can also take place if vehicle 20 is equipped only with a communication sequence demodulating device as disclosed herein, and is not furnished with a radar wave transmitting unit or a detection sequence backprojection demodulating device.

(33) While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments.

(34) Other variations to be disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word comprising does not exclude other elements or steps, and the indefinite article a or an does not exclude a plurality, which is meant to express a quantity of at least two. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting scope.