As the coprime array develops, the coprime multiple-input multiple-output (MIMO) radar has been proposed to achieve a large array aperture. However, holes also exist in the sum-difference coarray of the coprime MIMO radar, thus making the lags out of continuous range unavailable for the subspace based direction of arrival (DOA) estimation algorithm. In this paper, a coarray interpolation algorithm is proposed for the coprime MIMO radar to improve the estimation performance. The interpolation is completed by solving a nuclear norm based optimization problem, where the Toeplitz structure of the interpolated covariance matrix is exploited to reduce the computational complexity. The lags that are not continuous are utilized by using the proposed algorithm. Thus, the number of degrees of freedom (DOFs) and the estimation accuracy are improved. Numerical simulations are designed to examine the corresponding estimation performance.

DOA estimation; MIMO radar; Nuclear norm