Adaptive Waveform Design In Ultra-wideband MIMO Radar

Ultra wideband multiple-input multiple-output(UWB-MIMO)radar is a new type radar system blending UWB and MIMO technologies in recent years.The UWB-MIMO radar has the ultra-high capabilities of resolution and imaging.Meanwhile,the new system also brings great challenges to radar signal processing,especially in intelligent radar signal design and processing.Cognitive radar is considered to be an important direction of radar development and the adaptive-waveform optimization design is its basis and main point of research.It radically changes the open loop information processing mode of the traditional radar system and exhibits significant performance improvements and adaptivity to the varing environments.It is one of the important way to realize radar intelligence and has important theory and application value.Therefore,taking UWB-MIMO radar as research background,this dissertation aims to optimize and design radar-transmitting waveforms adaptively for improving the performances of detection,information acquisition and clutter suppressing.The mainly contents of the dissertation are summarized as follows:1)Two distributed UWB-MIMO radar system models are established for backgrounds of single transmit diversity and full transmit-receive diversity respectively.According to different antenna structures and the corresponding signal processing methods,the influences on radar output SNR and detection probability have been studied based on the models.The research conclusion indicated that when output SNR(SCNR)is lower,the radar with only transmit diversity architecture has better performance on target detection and clutter suppression than the radar with full transmit-receive diversity architecture.The research laid the foundation of the follow-up work about adaptive UWB-MIMO radar waveform design.2)Based on the need of radar same frequency interference suppression,after studying several design methods of UWB pulse compression radar orthogonal waveform under different types of modulation,an orthogonal waveform design method that adopts time-hopping and frequency-hopping modulation is proposed.By using the analogy randomicity of chaos sequence and Costas sequence,lots of transmit waveforms with excellent orthogonal performance can be generated,this method can avoid the complicated optimization process and decrease the complexity of system.The designed dual-modulation signal has lower auto-correlation peak side-lobe level and peak cross-correlation level,which are good for improving the target accuracy of measurement and resisting interference between received signals.The superiority of the design is validated through the comparison with the conventional orthogonal waveforms(for example:orthogonal phase coding waveform,orthogonal frequency coding waveform).3)Considering the time varying character of the radar clutter environment,an adaptive waveform design method based on information theory for UWB-MIMO radar is proposed.Two design criterions are taken in this method,which are maximizing the mutual information between the target signal and the clutter and minimizing the mutual information between successive received signals.According to the target prior angle information,the received signals from target and clutter are obtained by using beamforming technology based on only transmit diversity antenna architecture in this design.Then the optimal transmit signal can be acquired by calculating mutual information value between the received signals.Compared with the traditional waveform design method,the signal designed by this method is more effective to acquire target information and suppress clutter signal.4)In the same time-varying environment,an adaptive waveform design based on optimum detection criterion is proposed.A mixture model that satisfies multivariate Dirichlet distribution is applied in which the received signal contaminated by noise and clutter.Then the information from different targets can be separated and identificated by using Dirichlet process mixture model algorithm.According to the information,the transmission power is concentrated on frequency range that is the maximized difference between target and clutter frequency responses to acquire maximum SCNR and target detection probability.In the time-varying environment,according to UWB signal frequency richness,the method can adjust transmit signal adaptively to achieve the goal of suppressing clutter interference and optimizing detection performance.The results of simulations and theoretical analysis have proved the feasibility of the proposed method.