MIMO radar networks with incoherent sensor nodes

Abstract

Multiple-Input Multiple-Output (MIMO) radars constitute a proven approach to realize cost-efficient high-precision environment sensing solutions. Its vari- ant with widely distributed antennas benefits from spatial diversity, offering a large field of view and avoiding ghost targets. Until recently, operation of such a MIMO radar required the distribution of a common high-frequency car- rier signal or other elaborate synchronization solutions. This work introduces a system concept and prototypical realization of an incoherent MIMO radar network based on integrated radar sensors without wired high-frequency links. The network simultaneously performs monostatic and bistatic measurements between all pairs of sensor nodes, using independently generated Frequency- Modulated Continuous-Wave (FMCW)-modulated transmit signals with fixed frequency offsets. In addition to optimum parametrization of the network, the complete signal processing chain for the operation of this network is presented. First, co- herency is established by estimating the unknown time, frequency, and phase offsets, yielding high-precision range and speed measurements. Subsequently, these estimates are used to distinguish the contour of targets or estimate their position using multilateration algorithms. The latter include bistatic measure- ments of both range and speed, which is shown to improve the precision of target position estimates by a factor of 10 with the used system parameters. The performance limits of this approach considering random and systematic nonidealities are determined by deducing them from fundamental stochastic processes. They are verified with a newly introduced computationally efficient simulation which regards the correlation in the stochastic processes. This re- veals strict requirements for the purity of the independently synthesized signals to allow bistatic measurements. The prototypical realization of the network with three sensor nodes using integrated radar transceivers operating at 122GHz proves the feasibility of the approach. With chirp sequences of 30 ramps of 1ms length and 1GHz bandwidth, unambiguous range precisions of < 1mm are achieved using a small metal panel at 1m distance. The reconstructed phases exhibit a precision of < 0.1rad, allowing ambiguous range precisions of < 10µm and speed precisions of < 1mm/s. The attainable high precision and comparatively low realization effort make the proposed network approach a favorable design for a wide range of applications.