LFMCW based MIMO imaging processing with keystone transform

In this paper, a new signal processing technique for Multiple-Input Multiple-Output (MIMO) image processing of a Linear Frequency-Modulated Continuous Wave (LFMCW) automotive radar was developed. The image is the range-speed-direction data cube. The technique comprises two improvements to the standard MIMO image processing: 1) A fast unambiguous Doppler target detection. 2) An improved direction finding with estimated virtual antenna elements besides the synthesized virtual antenna elements. High speed automotive targets go through several range cells in the observation period making it difficult to obtain coherent accumulated power. Another problem with high speed targets in combination with a low Sweep Repetition Frequency (SRF) is ambiguous Doppler speed measurement. In order to remove range migration and obtain coherent accumulated power the keystone transform is applied. The direction finding resolution depends on the number of transmitter- and the receiver elements of the MIMO configuration. A combination of the transmitter and receiver elements give synthesized virtual elements with corresponding antenna width. In order to improve the direction finding, the antenna width with extrapolated virtual antenna elements was extended. The Band Width Extrapolation (BWE) method is applied for estimating these extrapolated virtual antenna elements. The proposed method is verified by simulation and real radar measurements.