Coherent Measurements With MIMO Radar Networks of Incoherent FMCW Sensor Nodes

This work introduces a method for coherent multiin multiout (MIMO) processing over a network of frequency-modulated continuous wave (FMCW) radar sensor nodes with independent signal synthesis. The coherency between the bistatic channels is established algorithmically based on the frequency and phase-offset estimation from pairs of sensor nodes and subsequent least-squares estimation on the overdetermined equation system. For the chirp-sequence radar, the proposed processing allows range and speed measurements, as offsets are estimated and corrected for each individual ramp. The applicability of the method is demonstrated in a prototypical setup of a radar network with three sensor nodes comprising integrated 122-GHz transceivers. The obtained bistatic phase precisions of < 0.1 rad approximately match those of the monostatic measurements of the same radar nodes. For a sequence of 30 ramps of 1-ms duration, this translates to ambiguous range precisions $ < 10~\mu \text{m}$ and speed precision < 1 mm/s. The absence of wired high-frequency links between the nodes makes the approach well suited for short-range radar networks in cost-sensitive applications.