Resolving a multipath ambiguity in a TDM-MIMO radar

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 d_r in a first direction, and further comprises a plurality of physical transmitters arranged with a second spacing d_t in said first direction, the 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 the TDM MIMO FMCW radar by performing operations comprising:
• obtaining, from the TDM MIMO FMCW radar, a virtual array signal z 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 an angle spectrum for the range-Doppler bin;
• providing an intermediate signal v by:
• selecting a first leading peak in the angle spectrum of the virtual array signal,
• applying to the virtual array signal an inverse phase-shift vector a_t{circumflex over ( )}*(φ{circumflex over ( )}_1)⊗a_r{circumflex over ( )}*(φ{circumflex over ( )}_1) corresponding to an estimated phase φ{circumflex over ( )}_1 of the first leading peak, and
• subtracting a constant signal with an amplitude corresponding to the first leading peak;
• providing a test signal w by:
• applying to the intermediate signal an inverse phase-shift vector a_t{circumflex over ( )}*(Δφ{circumflex over ( )})⊗a_r{circumflex over ( )}*(Δφ{circumflex over ( )}) corresponding to an estimated offset phase Δφ{circumflex over ( )}, which relates the first and a second leading peak in the angle spectrum of the virtual array signal, wherein the first and second leading peaks are the two largest peaks in the angle spectrum, and
• subtracting a constant signal;
• detecting non-noise content of the test signal;
• if the test signal has non-noise content, concluding that the virtual array signal contains a first-order multipath artefact and, in response, excluding the first leading peak from subsequent radar processing for the range-Doppler bin;
• and,
• if the test signal has noise content only, concluding that the first leading peak corresponds to a direct reflection in the scene and, in response, including the first leading peak in the subsequent radar processing for the range-Doppler bin.

A non-transitory computer-readable medium storing instructions which, when executed by a signal processing device having a processor and a memory, cause the signal processing device 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 d_r in a first direction, and further comprises a plurality of physical transmitters arranged with a second spacing d_t in said first direction, the method comprising:

• obtaining, from the TDM MIMO FMCW radar, a virtual array signal z 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 an angle spectrum for the range-Doppler bin;
• providing an intermediate signal v by:
• selecting a first leading peak in the angle spectrum of the virtual array signal,
• applying to the virtual array signal an inverse phase-shift vector a_t{circumflex over ( )}*(φ{circumflex over ( )}_1)⊗a_r{circumflex over ( )}*(φ{circumflex over ( )}_1) corresponding to an estimated phase Δφ{circumflex over ( )}_1 of the first leading peak, and
• subtracting a constant signal with an amplitude corresponding to the first leading peak;
• providing a test signal w by:
• applying to the intermediate signal an inverse phase-shift vector a_t{circumflex over ( )}*(Δφ{circumflex over ( )})⊗a_r{circumflex over ( )}*(Δφ{circumflex over ( )}) corresponding to an estimated offset phase Δφ{circumflex over ( )}, which relates the first and a second leading peak in the angle spectrum of the virtual array signal, wherein the first and second leading peaks are the two largest peaks in the angle spectrum, and
• subtracting a constant signal;
• detecting non-noise content of the test signal;
• if the test signal has non-noise content, concluding that the virtual array signal contains a first-order multipath artefact and, in response, excluding the first leading peak from subsequent radar processing for the range-Doppler bin;
• and,
• if the test signal has noise content only, concluding that the first leading peak corresponds to a direct reflection in the scene and, in response, including the first leading peak in the subsequent radar processing for the range-Doppler bin.