Parameter Estimation for Coherent Passive MIMO Radar with Unknown Signals under Direct Path Influence

Abstract

When the radar antennas are properly placed so that each antenna falls within the same target beamwidth, the coherent processing can be employed. This paper studies the problem of joint target position and velocity estimation for a coherent passive radar system. The received observation model with direct path influence is developed in frequency domain. Due to the nature of passive processing, the samples of transmitted signals from the illuminators of opportunity are assumed deterministic unknown. The maximum likelihood estimator is presented and the Cramer-Rao bound (CRB) is derived. We show that the direct path signals can help improve the estimation performance. Then, we extend the discussion to the case where the transmitted signals are known to have constant modulus. Again, we show that incorporating the direct path signals in the received observations can have a positive influence on estimating target parameters. Compared with the case of not knowing the constant modulus constraint, the knowledge of constant modulus constraint brings extra performance gain.Index Terms-Coherent passive MIMO radar, joint estimation, constant modulus, Cramer-Rao bound (CRB).