SINGLE SCATTERER TEST USING PHASE

Abstract

A vehicle based method of determining the extent to which a target object is a single scatterer, said vehicle including a radar system including a radar transmit element, adapted to send a radar signal towards said target object, and an antenna receive element adapted to receive radars signals reflected from said target object, said method comprising: a) transmitting a radar signal from said radar transmit element to said target object; b) receiving the reflected signal of the signal transmitted in step a) from the target object at said receiver element; c) processing the received signal to provide phase data in the frequency domain; d) determining a measure of the phase change between frequencies; e) determining whether the target object is a single scatterer based on the results of step d).

Claims

1. A vehicle based method of determining the extent to which a target object is a single scatterer, said vehicle including a radar system including a radar transmit element, adapted to send a radar signal towards said target object, and an antenna receive element adapted to receive radars signals reflected from said target object, said method comprising: a) transmitting a radar signal from said radar transmit element to said target object; b) receiving the reflected signal of the signal transmitted in step a) from the target object at said receiver element; c) processing the received signal to provide phase data in the frequency domain in relation to discrete bins comprising frequency ranges; d) determining a phase difference between at least two bins; e) determining whether the target object is a single scatterer based on the results of step d), wherein the target object is considered to be a non-single scatterer if the phase change from one frequency bin to a neighboring frequency bin is above a threshold.

2. A method as claimed in claim 1, wherein in step c) signal data is converted from the base time-domain to a range-Doppler frequency domain.

3. A method as claimed in claim 1, wherein step c) includes providing a range-Doppler map in terms of range-Doppler frequency domain.

4. A method as claimed in claim 1, wherein step c) includes providing phase data in term of range-Doppler frequency bins.

5. A method as claimed in claim 1, wherein step d) comprises determining bin-to-bin phase change.

6. A method as claimed in claim 1, wherein if the absolute bin-to-bin phase change or the slope of the phase change to respective frequency exceeds a threshold, the target is considered to be a non-single scatterer.

7. A method as claimed in claim 1, wherein steps d) and e) are only performed for the bins from a main-lobe region of the received radar point spread function.

8. A method as claimed in claim 1, wherein in step c) only phase information from the 2-D measured data in a range-Doppler domain is extracted for frequencies or bins where the amplitude or power exceeds a threshold or which have a minimum signal-to-noise ratio.

9. A method as claimed in claim 1, wherein step d) comprises measuring bin-to-bin phase change across the measured 2-D point spread function evaluated in a range-Doppler domain.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0024] The present invention is now described by way of example with reference to the accompanying drawings in which:

[0025] FIG. 1 shows a flowchart of basic methodology according to one example;

[0026] FIG. 2 shows a schematic showing two PSFs corresponding to two scattering centers located in a close proximity to each other in space/in spectrum;

[0027] FIG. 3 shows the results of phase determined against frequency bin for a spectral response of a non-single-scatterer target (comprised as a superposition of two individual targets/responses).

DETAILED DESCRIPTION

[0028] Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the various described embodiments. However, it will be apparent to one of ordinary skill in the art that the various described embodiments may be practiced without these specific details. In other instances, well-known methods, procedures, components, circuits, and networks have not been described in detail so as not to unnecessarily obscure aspects of the embodiments.

[0029] One or more includes a function being performed by one element, a function being performed by more than one element, e.g., in a distributed fashion, several functions being performed by one element, several functions being performed by several elements, or any combination of the above.

[0030] It will also be understood that, although the terms first, second, etc. are, in some instances, used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first contact could be termed a second contact, and, similarly, a second contact could be termed a first contact, without departing from the scope of the various described embodiments. The first contact and the second contact are both contacts, but they are not the same contact.

[0031] The terminology used in the description of the various described embodiments herein is for describing embodiments only and is not intended to be limiting. As used in the description of the various described embodiments and the appended claims, the singular forms a, an and the are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that the term and/or as used herein refers to and encompasses all possible combinations of one or more of the associated listed items. It will be further understood that the terms includes, including, comprises, and/or comprising, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

[0032] As used herein, the term if is, optionally, construed to mean when or upon or in response to determining or in response to detecting, depending on the context. Similarly, the phrase if it is determined or if [a stated condition or event] is detected is, optionally, construed to mean upon determining or in response to determining or upon detecting [the stated condition or event] or in response to detecting [the stated condition or event], depending on the context.

[0033] The aim of the proposed method is to determine the extent to which a scatterer under test (SUT) is a single scatterer (originates from a single scattering center). For example, pulse-Doppler radar signal processing can be used to separate reflected signals into a number of peaks, which occur in the 2-D spectral domain (called range-Doppler map). This spectral data is utilized to carry out the here proposed single scatterer test.

[0034] The problem of determination if a radar backscatter return originates from a single scattering center is solved using an efficient method of a 2-D phase evaluation in the range-Doppler domain.

[0035] The 2-D frequency-domain data (the range-Doppler map) is analyzed. Typically the data is arranged in terms of a set of frequency ranges or bins. As it is a matter of interference between signals reflected from scattering centers located in relative close proximity to each other (in terms of range/Doppler frequencies), relative phase difference between signals can be directly evaluated in the frequency domain local to the superposed signal frequency bin.

[0036] In the proposed method, phase information from the (2-D) measured complex data (in the range-Doppler domain) is extracted at the position of the peak (considering only those bins where the amplitude exceeds some threshold or having a minimum SNR, respectively). Then, the bin-to-bin phase change across the (whole) measured 2-D PSF (corresponding to a detected target) is evaluated in the range-Doppler domain. The amount of the neighboring bins is not limited. Even having only two neighboring bins (offering the needed SNR), the test can be executed.

[0037] The method is preferably executed on the bins from the main-lobe 2-D region of the PSF (also called peak).

[0038] In a preferred example, the method may be reduced (for a better runtime performance) to the phase analysis of only the vectors in the two orthogonal dimensions (range and Doppler) going through the estimated amplitude peak position (as a function of range/Doppler frequency). This provides a sub-set of bins compared to the analysis of all bins of a 2-D PSF.

[0039] In the specifics of the methodology, if the absolute bin-to-bin phase change (slope) exceeds some known threshold (which may be different for the different bins of a PSF), then the target is considered to be a non-single scatterer.

[0040] For example, the phase of all bins belonging to the main lobe of an ideal single scatterer PSF would be namely equal/flat when the windowing function is symmetrical, the number of samples (processed by e.g. a Fourier transform) is odd, and (if zero padding is needed) the so-called zero-phase zero padding approach is applied.

[0041] This methodology is applicable to a system which includes a single receiver channel (receiver element), but also on M range-Doppler responses (maps) from N receiver (RX) channels.

[0042] FIG. 1 shows a flow chart of the general methodology according to one aspect.

[0043] A (vehicle-based) radar system comprising an antenna transmit element and a receive element (or array) having at least one receive element sends out a radar signal and so the received reflected signal from a target object is received by the receiver element(s) and processed. The subsequent processing of the received radar signal, i.e. analysis is described with reference to flowchart of FIG. 1.

[0044] In the proposed method, 2-D frequency-domain data (a range-Doppler map) is analyzed. In step S1 the phase of the signal is extracted from the 2-D frequency domain data at the position of the amplitude peak. Typically, the data is arranged in terms of a set of frequency rangesso called Doppler bins. As it is a matter of interference between signals reflected from scattering centers located in relative close proximity to each other in space (and/or having similar Doppler frequency), amplitude spectral information from the (2-D) measured complex data (in the range-Doppler domain) are evaluated at the position of the resulting peak to determine if the measured response originates from a single scattering center or not.

[0045] In step S2 the frequency (bin) to frequency (bin) phase is determined.

[0046] In step S3 the phase change from one frequency (bin) to a neighboring one frequency (bin) is compared with a threshold. If this phase difference (after phase unwrapping) exceeds the threshold in step S4, the target is identified as a non-single scatterer.

[0047] Consider a situation where two scattering centers (referred to as Target 1 and 2) are located in a close proximity to each other in space (having the same Doppler frequency). Then, at the receiver antenna, a superposition of those two scattered signals occurs. In the range-Doppler map, the PSFs from two targets e.g. of a non-single scatterer (named PSF1 and PSF2) referenced as PSF 1,A and PSF 2,A may be close to each other and would overlapsee FIG. 2. Thus, the amplitudes and the phases of the complex-valued PSFs have a strong influence on the resulting PSF due to complex superposition of the individual PSFs (see FIG. 2). The peak amplitude is shown at frequency fR1,A and fR2,A respectively for the PSF1,A and PSF 2,A.

[0048] Exemplarily, a 1-D case was simulated where two PSFs with a frequency distance of 1.0 frequency bin were put in a close proximity to each other. The first PSF (PSF1) has amplitude of 1.0 and phase of 0 degrees, and the second one (PSF2) has amplitude of 0.9 and phase of 30 degrees.

[0049] FIG. 3 shows the results of phase determined against frequency bin for the first PSF only (reference numeral 1) the second PSF only (reference numeral 2) and for the actual superposed signal (which is the signal that would be received in reality): reference numeral 3.

[0050] So FIG. 3, shows the simulated phase spectrum (e.g. phase vs. frequency bins shown as a 1-D cut through a 2-D frequency map). As one can see, the phase of the superposed resulting peak is not flat. Thus, the peak under tests is determined to originate from a non-single scatterer.

[0051] In contrast to the method disclosed on European Patent Application

[0052] EP 16188715, no symmetry needs to be considered. Thus, the here proposed method could be executed even having only two neighboring bins (offering the needed SNR), instead of three, which would be needed in EP 16188715.

[0053] The method is very sensitive, can be executed on a single range-Doppler map (originating from a single RX channel), and has a low computational cost.