# US 2026/0276802 A1 · Resolving a multipath ambiguity in a tdm-mimo radar

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- Number: US 2026/0276802 A1
- Document ID: US20260276802A1
- Status: Published application
- Kind: A1
- Application number: 19/564,706
- Filed: 2026-03-12
- Published: 2026-09-17
- Earliest claimed: 2025-03-17
- Assignees: Axis AB
- Applicants: Axis AB
- Inventors: Anders MANNESSON; Santhosh NADIG
- Web page: https://patentgrep.com/patent/US20260276802A1

## CPC

- G01S 13/34: using transmission of continuous, frequency-modulated waves while heterodyning the received signal, or a signal derived therefrom, with a locally-generated signal related to the contemporaneously transmitted signal
- G01S 13/42: Simultaneous measurement of distance and other co-ordinates (indirect measurement G01S13/46)
- G01S 7/03: Details of HF subsystems specially adapted therefor, e.g. common to transmitter and receiver
- G01S 7/354: {Extracting wanted echo-signals (Doppler systems G01S13/50)}
- G01S 7/356: {involving particularities of FFT processing}
- G01S 13/343: {using sawtooth modulation}
- G01S 13/584: {adapted for simultaneous range and velocity measurements}
- H04B 7/024: Co-operative use of antennas of several sites, e.g. in co-ordinated multipoint or co-operative multiple-input multiple-output [MIMO] systems
- H04B 7/0413: MIMO systems
- G01S: RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- H04B: TRANSMISSION

## Abstract

A TDM MIMO FMCW radar comprises at least one row of physical receivers with a first spacing in a first direction, and further comprises a plurality of physical transmitters arranged with a second spacing in said first direction. To determine whether a peak in an angle spectrum corresponds to a direct reflection or a first-order multipath artefact, a full-array angle spectrum based on all elements of a virtual array signal, and a single-subarray angle spectrum based on one subarray are computed. If a peak in the full-array angle spectrum and a corresponding baseline peak in the single-subarray angle spectrum are co-located, it is concluded that the peak represents a direct reflection in the scene. Otherwise, if the peak and the baseline peak are not co-located, it is concluded that the peak represents a first-order multipath artefact.

## Claims

### Claim 1

A method of resolving a first-order multipath ambiguity for a virtual array of a time-division multiplexing, TDM, multiple-input multiple-output, MIMO, frequency-modulated continuous-wave, FMCW, radar, wherein:
the TDM MIMO FMCW radar comprises at least one row of physical receivers with a first spacing in a first direction, and further comprises a plurality of physical transmitters arranged with a second spacing in said first direction, and
the virtual array comprises a plurality of subarrays, each subarray generated by a combination of the row of physical receivers and one of the physical transmitters,
the method comprising:
obtaining a virtual array signal of a range-Doppler bin relating to a scene, each element of the virtual array signal corresponding to one virtual antenna element of the virtual array;
computing a full-array angle spectrum based on all elements of the virtual array signal;
computing at least one single-subarray angle spectrum based on the virtual array signal restricted to one of the subarrays;
assessing whether a peak in the full-array angle spectrum is co-located with a corresponding baseline peak in a computed single-subarray angle spectrum;
if the peak and the baseline peak are co-located, concluding that the peak in the full-array angle spectrum represents a direct reflection in the scene; and,
if the peak and the baseline peak are not co-located, concluding that the peak in the full-array angle spectrum represents a first-order multipath artefact.

### Claim 2 (depends on 1)

The method of claim 1, wherein assessing whether the peak and the baseline peak are co-located comprises:
deducing an expected location of the peak in the full-array angle spectrum from the baseline peak's location in the single-subarray angle spectrum, or deducing the baseline peak's expected location from the location of the peak in the full-array angle spectrum; and
detecting non-noise signal content at the expected location.

### Claim 3 (depends on 2)

The method of claim 2, wherein detecting non-noise signal content includes a comparison with a threshold.

### Claim 4 (depends on 3)

The method of claim 3, wherein the threshold is a preconfigured constant.

### Claim 5 (depends on 3)

The method of claim 3, wherein the threshold corresponds to a noise floor of the virtual array signal.

### Claim 6 (depends on 3)

The method of claim 3, wherein:
computing at least one single-subarray angle spectrum includes identifying an angle of the baseline peak; and
the non-noise signal content is detected by estimating a similarity of the full-array angle spectrum and the virtual array's steering vector for the identified angle.

### Claim 7 (depends on 6)

The method of claim 6, wherein said similarity is estimated using an adaptive coherence estimator, ACE, of the virtual array's steering vector for the identified angle.

### Claim 8 (depends on 1)

The method of claim 1, wherein assessing whether the peak and the corresponding peak are co-located comprises:
localizing the peak in the full-array angle spectrum based on a correspondence criterion with respect to the corresponding baseline peak; and
comparing the location of the baseline peak and the thus localized peak.

### Claim 9 (depends on 8)

The method of claim 8, wherein the correspondence criterion includes one or more of:
having an equal relative magnitude in the angle spectrum,
being similarly situated relative to adjacent peaks in the angle spectrum,
being similarly situated relative to an overall waveform of the angle spectrum.

### Claim 10 (depends on 1)

The method of claim 1, wherein:
at least two single-subarray angle spectra are computed, each based on the virtual array signal restricted to a different one of the subarrays; and
the baseline peak is identified in a first single-subarray angle spectrum while further considering a second single-subarray angle spectrum.

### Claim 11 (depends on 1)

The method of claim 1, wherein:
it is assessed whether two peaks in the full-array angle spectrum are co-located with two corresponding baseline peaks in the computed single-subarray angle spectrum;
it is concluded that the two peaks in the full-array angle spectrum represent two direct reflections in the scene if the peaks and the baseline peaks are co-located; and
it is concluded that the two peaks in the full-array angle spectrum represent a first-order multipath artefact if the peaks and the baseline peaks are not co-located.

### Claim 12 (depends on 11)

The method of claim 11, wherein the two peaks in the full-array angle spectrum have substantially equal magnitude.

### Claim 13 (depends on 11)

The method of claim 11, wherein said two peaks are the two leading peaks in the full-array angle spectrum.

### Claim 14

A signal processing device for a time-division multiplexing, TDM, multiple-input multiple-output, MIMO, frequency-modulated continuous-wave, FMCW, radar, wherein:
the TDM MIMO FMCW radar comprises at least one row of physical receivers with a first spacing in a first direction, and further comprises a plurality of physical transmitters arranged with a second spacing in said first direction, and
the virtual array comprises a plurality of subarrays, each subarray generated by a combination of the row of physical receivers and one of the physical transmitters.

### Claim 15

A signal processing device comprising processing circuitry configured to resolve, in a virtual array signal comprising at least one range-Doppler bin, a first-order multipath ambiguity for a virtual array of time-division multiplexing, TDM, multiple-input multiple-output, MIMO, frequency-modulated continuous-wave, FMCW, radar, wherein:
the TDM MIMO FMCW radar comprises at least one row of physical receivers with a first spacing in a first direction, and further comprises a plurality of physical transmitters arranged with a second spacing in said first direction, and
the virtual array comprises a plurality of subarrays, each subarray generated by a combination of the row of physical receivers and one of the physical transmitters; whereby the signal device:
obtains a virtual array signal of a range-Doppler bin relating to a scene, each element of the virtual array signal corresponding to one virtual antenna element of the virtual array;
computes a full-array angle spectrum based on all elements of the virtual array signal;
computes at least one single-subarray angle spectrum based on the virtual array signal restricted to one of the subarrays;
assesses whether a peak in the full-array angle spectrum is co-located with a corresponding baseline peak in a computed single-subarray angle spectrum; whereby;
if the peak and the baseline peak are co-located, concluding that the peak in the full-array angle spectrum represents a direct reflection in the scene; and,
if the peak and the baseline peak are not co-located, concluding that the peak in the full-array angle spectrum represents a first-order multipath artefact.

### Claim 16

A computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out a method of resolving a first-order multipath ambiguity for a virtual array of a time-division multiplexing, TDM, multiple-input multiple-output, MIMO, frequency-modulated continuous-wave, FMCW, radar, wherein:
the TDM MIMO FMCW radar comprises at least one row of physical receivers with a first spacing in a first direction, and further comprises a plurality of physical transmitters arranged with a second spacing in said first direction, and
the virtual array comprises a plurality of subarrays, each subarray generated by a combination of the row of physical receivers and one of the physical transmitters, the method comprising:
obtaining a virtual array signal of a range-Doppler bin relating to a scene, each element of the virtual array signal corresponding to one virtual antenna element of the virtual array;
computing a full-array angle spectrum based on all elements of the virtual array signal;
computing at least one single-subarray angle spectrum based on the virtual array signal restricted to one of the subarrays;
assessing whether a peak in the full-array angle spectrum is co-located with a corresponding baseline peak in a computed single-subarray angle spectrum;
if the peak and the baseline peak are co-located, concluding that the peak in the full-array angle spectrum represents a direct reflection in the scene; and,
if the peak and the baseline peak are not co-located, concluding that the peak in the full-array angle spectrum represents a first-order multipath artefact.