| Waveform design is the key point of the multiple-input multiple-output(MIMO) radar research area, since the performance of the MIMO radar depends on the specific signal design. The stand or fall of waveform design directly affects the performance of the MIMO radar. According to the different task MIMO radar undertakes, radar performance can be improved through the targeted MIMO waveform design.Therefore, research on MIMO radar waveform design related theory and the algorithm is of great significance and application value. At the same time, as a new hotspot in the research field of radar and its unique ‘receiver-transmitter’ closed loop structure, the cognitive radar has the greater potential to improve the performance of radar. Waveform design is an essential part of cognitive radar system to highlight the ‘cognitive’ feature. Currently, how to design waveform to improve the ability of rejecting the interferences of cognitive radar has drawn more and more attention.For MIMO radar orthogonal phase codes set design problem, genetic algorithm(GA) and simulated annealing(SA) algorithm are commonly optimization design method to improve the autocorrelation sidelobe and cross-correlation properties. But for different application background of waveform design, some specific requirements are raised. Based on the guarantee of obtaining low autocorrelation sidelobe peak and low cross-correlation peak, the waveform design with the constraint of having strict orthogonality and with the constraint of having zero correlation zone(ZCZ) was researched, respectively.At present, research results of cognitive radar waveform design are mainly concentrated in arbitrary waveform. Because these arbitrary waveforms are not constant envelope signals, however, they can’t take full advantage of the transmission power. To address this problem, the cognitive radar constant envelope waveform design method was studied to improve the radar performance(eg. the target detection probability).The key technologies of both the orthogonal phase codes set design for MIMO radar and the constant envelope waveform design for cognitive radar are researched in this thesis. There are some results have been acquired till now. The main contributions of this thesis are summarized as follows:1. An optimization binary orthogonal code design method based on Hadamard matrix was proposed. The proposed method used the orthogonality of Hadamard matrix. The orthogonal binary codes obtained by the proposed method have low autocorrelation sidelobe peak and low cross-correlation peak and can maintain the orthogonality of each code, which can improve the target measurement precision and clutter cancellation effect. The method only needs less computer storage space to optimize the longer phase codes set. Therefore, it can be used in the design of radar long phase codes.2. Based on sequential quadratic programming(SQP) algorithm, an optimization design method of orthogonal phase codes set with ZCZ was studied. To address the problem of the target detection performance is directly determined by the sidelobe of the pulse compression output after transmit and receiver beamforming, the sum of transmit orthogonal signals(hereinafter referred to as ‘the sum signal’) and its ambiguity function sidelobe characteristics were introduced into the objective function. The orthogonal phase codes obtained by the proposed method have low autocorrelation sidelobe peak and low cross-correlation peak in ZCZ, and the ambiguity function of the sum signal have high mainlobe to peak sidelobe ratio(MPSR) and good Doppler tolerance.3. The characteristics of airborne MIMO radar clutter were investigated. The influences of autocorrelation sidelobe and cross-correlation of orthogonal waveforms on airborne MIMO radar clutter echo was modeled. The effect of the range sidelobe on airborne MIMO radar clutter rank was studied through theoretical analysis and formula derivation. The analysis shows that the range sidelobe can increase the clutter rank for the application of airborne MIMO radar.4. For cognitive radar waveform design problem, we researched the constant envelope waveform design methods in the presence of colored noise and in the presence of clutter, respectively. Under maximum output signal-to-noise ratio(SNR) and signal-to-clutter-and-noise ratio(SCNR)) criterion, it is a optimum design method based on SQP algorithm and by minimizing mean squared error(MMSE) between the energy spectrum density(ESD) of the designed waveform and the optimal ESD. This method can improve output SNR(or SCNR) compared with the conventional waveform such as linear frequency modulation(LFM) signal. Particularly, for the waveform design problem in the presence of colored noise, a constant-envelope MIMO cognitive waveform design method was proposed. The method makes full use of the characteristics of more transmit degrees of freedom(DOF) of MIMO radar, and further improves the output SNR. The designed waveforms have the constant envelope characteristic.5. Under the effect of element position errors, a cognitive transmit pattern design method was proposed. When the mechanical distortions occur, the cognitive transmit pattern still can place pattern nulls in the directions of interferences while preserving the main beam response of the target of interest, which can reject the interferences. Based on that, cognitive space-time transmit pattern design method is studied. This method can effectively reduce clutter energy, reduce the requirement of receiver dynamic range and simplify the structure of the signal processing at the receiver.
|
PDF Full Text Request