Robust Design And Processing Method For Constant Modulus Sequences

By optimizing the phase codes,design of constant modulus sequences(CMS)is mainly aiming at designing phase-code sequences that possess constant amplitudes and good ambiguity characteristics.Design of CMS can effectively overcome the influences of non-linear amplifier in transmitters,and also make full use of the transmitting power.Hence,it has been one of the most important research directions in radar and communication fields.Based on apriori information,the design of CMS can greatly improve the performance of the systems.However,when apriori information is inaccuracy,the optimized CMS based on uncertain information can deteriorate the performances of the systems.Therefore,to guarantee the stability of the system working under the uncertain information,robust design and processing method for CMS becomes the research hotspot and difficulty.This thesis mainly focuses on the detection problem of cognitive radar.Based on Signal-to-Noise Ratio(SNR)and Signal-to-Interference-plus-Noise Ratio(SINR)optimization criterions,the robust designs for CMS under different detection problems are discussed.Main contents include the following:1.For point target detection problem,the colored noise interference is firstly studied in the thesis.Based on the filter bank theory,a max-min optimization problem under uncertain target Doppler is modeled.By means of Semi-Definite programming(SDP)method,the CMS can be optimized to improve the minimum W-SNR value of the filters.As for signal-dependent clutter interference,the thesis considers the quadratic uncertainty constraints of clutter frequency covariance matrixes,based on which a max-min optimization problem is established.An iterative optimization algorithm based on Dinkelback process is also proposed to optimize the filter vector and the transmitting sequence.Compared to SDP related algorithm,the proposed algorithm enjoys an obvious promotion of performance and efficiency.2.For extended target detection problem,the colored noise interference is discussed first.Enforced on constant modulus constraint,a robust sequence design method under uncertain target impulse response(TIR)is amended.Based on the quadratic uncertainty constraint of the TIR matrix,a max-min optimization problem is modeled.The SDP method and power-method iteration algorithms are adopted to optimize the sequence.As for signal-dependent clutter interference,the thesis studies the robust transmitter-receiver design for the uncertain clutter impulse response(CIR).Based on the quadratic uncertainty constraint of CIR matrix,a max-min optimization problem is established.And an iterative algorithm based on Dinkelbach process is proposed to optimize the filter and the constant modulus sequence.3.Based on the radar space-time adaptive processing(STAP)problem of Multiple-Input-Multiple-Output(MIMO)radar under signal-dependent clutter interference,a robust design and processing method for CM sequences is analyzed,which accounts for the uncertain information of clutters.Firstly,the steering vector of clutter is defined according to the space-time interaction characteristic of clutter.Then,based on the quadratic uncertainty constraints of clutter steering vector covariance matrixes,a max-min optimization problem is established.Finally,an iterative algorithm involved power-method iteration is adopted to solve the optimization problem.Numerical results demonstrate the effectiveness of the robust designs and algorithms introduced above.Compared to the optimal designs considering the precise knowledge,the robust designs proposed above can against the uncertainties in target and environment,and also obviously improve the worste-case SNR or SINR under the imprecise apriori information.