Particular DDM codes for online phase shifter calibration in automotive MIMO radar

Frequency modulated continuous wave (FMCW) multiple input multiple output (MIMO) radar systems employing Doppler division multiplexing (DDM) require calibrating the phase shifters to maintain optimal performance and minimize spurs all along the radar system's life cycle. Existing methods rely on a dedicated time slot to perform the phase shifters' calibration. Ideally, a method allowing for online estimation of the phase shifter imbalances without interrupting the radar operation would be desirable. In this work, a particular subset of the DDM coding scheme is analyzed, enabling such an online estimation. The proposed coding scheme and associated constellation imbalance estimator are detailed in this work and tested on the road, showing the robustness of the estimator.