Waveform and system design for colocated MIMO radar
Date of Issue2014
School of Electrical and Electronic Engineering
Centre for Signal Processing
This thesis analyzes and develops waveforms and signal processing techniques that are used to improve the performances of range, velocity, and direction-of-arrival (DOA) estimation for multiple-input-multiple-output (MIMO) radar systems with colocated transmit and receive antennas. The main contributions of this work consist of four parts, which are summarized as follows. The starting point of this work is MIMO radar waveform design. The freedom to transmit non-coherent waveforms, i.e., the waveform diversity, enables many new features for MIMO radar to improve target detection and parameter estimation. However, it also introduces new challenges for the waveform design, e.g., minimiz-ing the cross-ambiguity functions (CAF’s). To tackle this problem, we consider the extension of two frequency-hopping waveforms from single-input-single-output (SISO) radar to MIMO radar, the Costas array coded (CAC) waveforms and the quadratic congruence coded (QCC) waveforms. Exhaustive search is carried out for suboptimal solutions to .nding a set of codes that mutually exhibit least cross-ambiguity properties. The general problem of the code selection for global optimum is formulated as an open question. The suboptimal Costas and quadratic congru-ence codes are used throughout this thesis when other designs are considered. The second contribution of this thesis is on receiver instrumental variable .lter (IVF) design for joint range and Doppler sidelobe suppression. The commonly used matched .lter (MF) maximizes the signal-to-noise ratio (SNR) of its output. However, it is ine.cient in improving the signal-to-clutter ratio (SCR). Alterna-tively, an IVF enables a trade-o. between the SNR and SCR at the receiver. We .rst analyze the performances of existing range domain only IVF designs using integrated sidelobe level (ISL) constraint and zero sidelobe (ZS) constraint, respec-tively. The results indicate the possibility of using phased-array radar for improved performance. Then a rectangular area centered at the origin on the range-Doppler plane is considered for joint clutter sidelobe suppression, where both MIMO and phased-array radar are considered. Closed-form solutions and simulation results are provided. The conclusion is then drawn in a trade-o. manner. Compromis-ing the waveform diversity, the phased-array radar design turned out to be more e.cient in terms of sidelobe suppression, SNR loss, and computational complexity. Another advantage introduced by MIMO radar waveform diversity is the .exible design of transmit beampatterns, which is the topic of the third part of this thesis. Existing works have provided many solutions. However, little attention has been paid to several aspects of the performance such as the ripple within the energy focusing section, the sidelobe attenuation, and the transition bandwidth. Hence, we propose a feasibility problem (FP) formulation based on the nonlinear mapping from MIMO radar transmit beampattern design to multiple-input-single-output (MISO) .nite impulse response (FIR) .lter design. One of the advantages of the proposed method is that it takes quantitative controls of the above parameters in the design. Moreover, the minimum number of transmit antenna to achieve a given transmit beampattern is obtained. Via simulations, the transmit beampattern formula, which has a similar form as Kaiser’s formula, is obtained for antenna selection given a set of design speci.cations. In addition, a robust design method is proposed. The robust design establishes a trade-o. between the radio-frequency ampli.er (RFA) requirements and the number of transmit antennas. It also leads to signi.cant relaxation of waveform correlation requirements. As a result, the robust design uses a set of easily generated and wildly used linear frequency modulated (LFM) waveforms to achieve the transmit beampattern identical to that designed under ideal orthogonality assumption. The last contribution of this thesis is presenting a fairer comparison between MIMO and phased-array radar. Throughout this thesis, the performance of phased-array radar is considered in comparison with MIMO radar in various aspects. The most signi.cant di.erence between the two systems is that phased-array radar transmits coherent waveforms whereas MIMO radar transmits non-coherent wave-forms. Implicitly, it is the coherent gain versus the diversity gain. The two systems establish a trade-o. for researchers and engineers to choose under di.erent objec-tives, design environments, and given conditions. Via the comparisons on the basic system models, receiver identi.ability, receiver IVF design, and transmit beampat-tern design, we conclude that MIMO radar outperforms phased-array radar when multiple targets exist whereas the latter outperforms the former when one is dealing with only a single target.
DRNTU::Engineering::Electrical and electronic engineering::Antennas, wave guides, microwaves, radar, radio