| The multiple-input multiple output(MIMO) radar systems are equipped with multiple independent transmit/receive antennas. MIMO radar with widely separated antennas can form multiple independent transmit-to-receive pairs, while MIMO radar with collocated antennas can transmit different waveforms at different transmit antennas.Sky over-the-horizon(OTH) radar systems have become one of the most important means for early warning of airborne and sea-surface targets. For OTH radar systems, the transmit signals can be reflected by the ionosphere and overcome the effect from the curve of the earth to monitor and track the targets beyond several thousand kilometers. Capitalizing on recent advances, the advantages of MIMO radar technology have recently been applied to OTH radar systems. In this work, an OTH radar system which uses MIMO radar techniques is called a MIMO-OTH radar system.Based on the target detection and waveform design for MIMO and OTH radar systems, the main contributions of this work are as follows:(1) Research on moving target detection in non-Gaussian clutter for MIMO radar with widely separated antennasIn most research on target detection employing MIMO radar with widely separated antennas, the clutter is assumed to be Gaussian distributed. However, in actual radar environment, the statistical character of the clutter is more likely to be non-Gaussian. In this work, several moving target detectors designed for Gaussian clutter model are considered, and the non-Gaussian clutter model with the Log-Normal(LN) distribution is formulated. The receiver operating characteristic(ROC) curves for MIMO radar and phased array radar systems in both Gaussian and non-Gaussian clutter are given in the simulations. Further, in the case of non-Gaussian clutter, the detection performances of different radar systems for different target velocities are compared. Finally, conclusions with practical value are drawn based on the simulation results.(2) Compressed sensing(CS) moving target detection for MIMO radar with widely spaced antennasThe moving target detection based on CS MIMO radar with widely separated antennas is studied. The traditional centralized MIMO radar requires an exhaustive search on every possible two dimensional target velocity, resulting in huge computational complexity. In this work, the CS technique is adopted to drastically reduce the computational burden and evaluate the reduction of the required complexity. The moving target detector for the CS MIMO radar is derived. The performance of the proposed detector is analyzed.(3) Transmit beampattern and waveform design for MIMO radarThe transmit beampattern and waveform design are studied in MIMO radar systems with collocated antennas. The waveform transmitted at each antenna is defined as a weighted sum of discrete prolate spheroidal(DPS) sequences, which have orthogonal property. Assume that different transmit antennas use the same set of DPS sequences while the weighting factors are variable, so that the correlation between different waveforms can be varied with the weighting factors. Optimum waveforms are designed to achieve a desired transmit beampattern under the constraint of the total transmit energy. Unlike a traditional process, in which the waveform covariance matrix is designed in the first step and then the optimal waveforms are synthesised in the second step based on the designed waveform covariance matrix, in this work a new method, which needs only one step to design both of the transmit beampattern and the waveforms, is proposed based on the principle of producing the DPS squences. The effectiveness of the proposed method is shown by numerical simulations.(4) LFM-based waveform design for cognitive MIMO radar with constrained bandwidthWaveform design is studied for a cognitive MIMO radar system faced with a combination of additive Gaussian noise and signal dependent clutter. The linear frequency modulation(LFM) signals are employed as transmitted waveforms. Based on the sensed statistics of the target and clutter-plus-noise, assuming the LFM waveforms transmitted at different transmitters can have different starting frequencies and bandwidths, these waveform parameters are designed to maximize the signal-to-clutter-plus-noise ratio(SCNR) at the receiver of the cognitive MIMO radar system. The constraints of the allowable range of operating frequency and total transmit energy are considered. The tested examples show that the designed waveforms are nonorthogonal which leads to superior performance compared with that of the frequency spread(FS) LFM waveforms commonly used in the traditional MIMO radar systems.(5) Waveform design for MIMO-OTH radar with widely separated transmit antennas and collocated receive antennasThe waveform design problem is studied for a MIMO-OTH radar system faced with a combination of additive Gaussian noise and signal dependent clutter. Considering the operational frequency of the MIMO-OTH radar is generally limited to a certain frequency band due to propagation and implementation issues, the waveform transmitted at each antenna is constructed as a weighted sum of DPS sequences which have good orthogonal and band-limited properties. Optimum waveforms(possibly nonorthogonal) are designed to maximize the target detection performance of the MIMO-OTH radar system with the constraint of fixed total transmitted energy. The performance of the proposed waveforms is analyzed.(6) Waveform design for MIMO-OTH radar with widely separated antennas.Waveform design is studied for MIMO-OTH radar with widely spaced antennas. The multi-quasi-parabolic(MQP) model is adopted to describe the characteristics of the ionosphere. The time delay and target Doppler frequency corresponding to each ray path associated with each transmit-to-receive pair are computed using the MQP model. Considering a more practical scenario by assuming a moving target, optimum waveforms are designed to maximize the target detection performance of the MIMO-OTH radar system when the other parameters are fixed. The performance of the proposed waveforms in a more general case and the energy allocation of the optimized waveforms are analyzed.
|
PDF Full Text Request