Abstract
By transmitting multiple independent waveforms at the transmit side and processing echoes of spatial targets at the receive side, Multiple Input Multiple Output (MIMO) radar enjoys virtual array aperture expansion and more degree of freedom (DOF), both of which favors the application of direction finding or estimation of direction of arrival (DOA). The expanded virtual aperture provides higher angular resolution which also promotes the precision of DOA estimation, and the extra DOF brought by waveform diversity can be leveraged to focus energy in certain spatial region for better direction-finding capacity. However, beamspace methods which match certain beampatterns suffer from deteriorated performance and complexity in implementation, and the advantage of virtual array aperture is limited by its virtual element redundancy. As an important performance indicator of DOA estimation, Cramer–Rao Bound (CRB) is closely connected to the array configuration of the system. To reduce the complexity of the system and improve CRB performance at the same time, in this paper, the virtual array of MIMO radar is designed directly by selecting outputs from matched filters at the receive side. For the sake of fair comparison, both scenarios with and without priori directions are considered to obtain optimized virtual array configuration, respectively. The original combinatorial problems are approximated by sequential convex approximations methods which produce solutions with efficiency. Numerical results demonstrate that the proposed method can provide thinned virtual arrays with excellent CRB performance.
Highlights
In various applications of radar system, such as beamforming and interference suppression, the Direction of Arrival (DOA) is often needed as a priori information [1]
The performance of DOA estimation can be improved by proper beamforming and interference suppression [2]. erefore, DOA estimation is a prerequisite for various applications as well as the purpose after other processing procedures, which is of great importance to the array of the radar system [3]
In Multiple Input Multiple Output (MIMO) radar, each element of transmit array sends one of multiple independent waveforms, the echoes of which are received by the receive array and processed through matched filters. e data after matched filtering operation is equivalent to the one received by an array with larger array aperture, which is often referred to as virtual array. e aperture of virtual array is usually larger than that of both transmit and receive array, which is helpful for DOA estimation since larger aperture is productive for angle resolution [4]
Summary
In various applications of radar system, such as beamforming and interference suppression, the Direction of Arrival (DOA) is often needed as a priori information [1]. Such expansion of virtual array aperture is limited by the redundancy of virtual array elements rendered by the adoption of uniform array configuration at both transmit and receive side Even though both transmit array and receive array are uniformly distributed without spatial tapering in most cases of MIMO radar, the virtual array configuration obtained by the spatial convolution of transmit array and receive array is characterized by the fact that one element in the virtual array may correspond to several pairs consisting of elements from both transmit array and receive array, producing redundancies of virtual array elements [5]. Such redundancy leads to the waste of element
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