Identifiability issues for rotationally invariant arrays

The ESPRIT algorithm provides a computationally efficient approach for direction of arrival (DOA) estimation in situations where the sensor array is composed of two identical translated subarrays. The subarrays need not be calibrated in order to obtain the DOA estimates. The problem of DOA estimation using sensor arrays composed of two identical, uncalibrated, and rotated subarrays is considered. It is shown that, unlike ESPRIT, such rotationally invariant arrays do not provide an identifiable parameterization of the problem. Unique DOA estimates are not possible without additional calibration information when more than one signal is presented