Research On Waveform Design And Signal Processing For Transmit Diversity MIMO Radar

Comparing to the conventional phased-array radar,Multiple Input Multiple Output(MIMO)radar can change the working mode flexibly by exploring the transmit degree of freedom(DOF)provided by the transmit diversity technique.Due to this property,MIMO radar gains better performance in varied complex environment.In recent years,new types of MIMO radar gain distinct characteristics by applying time increment or frequency increment into the traditional array configuration.DOFs in dimensions other than conventional spatial and Doppler dimensions can be provided in MIMO radar configurations with time or frequency increment.These DOFs offer potential ways to solve the current MIMO radar problems such as bad Doppler shift tolerance,high waveform design computational complexity and undistinguishable false targets in the mainlobe.This disertation focuses on the MIMO radar waveform design and signal processing for different tasks.The addressed main problems include transmit beampattern synthesis,slow-time range profile synthesis,space-time matched filter design for circulating code array radar and deceptive jamming suppression for Frequency Diverse Array(FDA)-MIMO radar.The main contents of this thesis are summarized as follows:1.The existing MIMO radar transmit beampattern synthesis methods via waveform optimization have high computational complexity.Besides,it is difficult to guarantee the constant envelope property in these methods.To deal with above problems,an extended circulating code(ECC)is proposed to achieve the arbitrary transmit beampattern.Firstly,from the spectral-spatial analysis of basic circulating code,it has been shown that a partially overlapped sub-band of transmit signal has been distributed to each angle.Due to this property,the transmit beampattern synthesis problem is transformed into a spectral shaping problem.A gapped Linear Frequency Modulation(LFM)signal has been applied to meet the spectral shape determined by the desired angle coverage and then the extended circulating code is derived.Compared to the existing methods,a multiple waveform optimization problem is simplified into a single waveform design issue which acheives much lower computational complexity.Besides,constant modulus is satisfied since the waveform is based on the basic LFM signal.2.To deal with the range resolution loss problem caused by the circulating code,a simple transmit diversity technique based on joint slow-time coding with circulating code(STCC)has been proposed.Following the space-frequency coupling characteristics,proposed technique changes the frequency band illuminated to a specific angle pulse to pulse while providing a wide angular coverage for each pulse.With the full bandwidth achieved by synthesis of the pulse train at the receiver,the range resolution degradation problem caused by circulating code is solved.According to the analyses of ambiguity function,the synthesized range profile is irrelevant to slow-time codes.Moreover,a receive processing procedure is shown to meet the practical requirement.The superior performance of the STCC is validated by extensive simulation results.Compared with the existing methods,the combination of the circulating code and the slow time coding achieves a lower range sidelobe while improving the range resolution.3.The current matched filter for circulating code can not effectively use the coupled spatial DOF in the echoes.To suppress coherent interferences and clutters,a space-time dependent match filter has been designed for circulating code.By constraining the target range-angle mainlobe loss and gains of the spatial interference in range mainlobe,a non-convex optimization model for a space-time coupled matched filter is established.By loosen quadratic equality and quadratic greater-than inequality constraints,the problem can be efficiently solved by second-order cone programming.Then,the filter is combined with the slow-time coding technique to jointly improve the range resolution.Compare with the conventional matched filters,the proposed space-time filter can effectively suppress strong clutters coming from sidelobes without any range resolution loss.Besides,the proposed filter can be combined with transmit beampattern synthesis,slow-time range profile synthesis and other techniques to achieve a general transmit-receive processing chain.4.For FDA-MIMO radar,the deceptive jamming suppression performance loss dramatically without interference prior information when using adaptive beamforming technique.To deal with this problem,a detector using conic model is proposed to suppress false targets.By using additional resolvability in range domain due to the frequency diversity,the true target can be distinguishable from the false ones in FDA-MIMO radar,especially when facing mainlobe deceptive jamming.As a result,the proposed detector can effectively detect true target while rejecting deceptive jamming signal.Moreover,a two-pulse detection scheme is proposed so that high rejection probability of false target is guaranteed.Compared with the traditional method of adaptive beamforming,this method does not require any priori interference information and integrates detection and jamming suppression into one step,which reduces the time complexity of signal processing in radar systems.