Direction-of-arrival estimation of quasi-stationary signals using two-level Khatri-Rao subspace and four-level nested array

The Khatri-Rao (KR) subspace method is a high resolution method for direction-of-arrival (DOA) estimation. Combined with 2q level nested array, the KR subspace method can detect O(N2q) sources with N sensors. However, the method cannot be applicable to Gaussian sources when q is equal to or greater than 2 since it needs to use 2q-th order cumulants. In this work, a novel approach is presented to conduct DOA estimation by constructing a fourth order difference co-array. Unlike the existing DOA estimation method based on the KR product and 2q level nested array, the proposed method only uses second order statistics, so it can be employed to Gaussian sources as well as non-Gaussian sources. By exploiting a four-level nested array with N elements, our method can also identify O(N4) sources. In order to estimate the wideband signals, the proposed method is extended to the wideband scenarios. Simulation results demonstrate that, compared to the state of the art KR subspace based methods, the new method achieves higher resolution.