Cramer-Rao bound of low angle estimation for VHF monostatic MIMO radar

The Cramer-Rao Bound of different multipath model conditions for VHF monostatic MIMO radar systems in low angle area is derived in this paper. The RMSE of simulation results of ML estimator verifies the CRB. It is shown that the type of multipath model has a large effect on performance of CRB. The results indicate that the phase difference of multipath signal and SNR loss of received signals are the main reason of CRB fluctuate in the low angle area. In addition, the CRB of Multipath Model-I has the singular point of angle estimation when the phase difference of multipath signal is in phase or revised, while the CRB of Multipath Model-II has the singular point only when the phase difference of multipath signal is reversed. Meanwhile, the Multipath Model-III that utilizes both the geometry of multipath model and reflection coefficient has the lowest CRB than other multipath conditions. The CRB of horizontal polarization is more stable than CRB of vertical polarization for different ground scenarios under Multipath Model-I. Besides, with the increasing of height of MIMO radar, it brings about more singular point for CRB in low angle area for Multipath Model-I condition.