【作者】 李强；

【导师】 苏涛；

【作者基本信息】 西安电子科技大学 ， 信号与信息处理， 2020， 博士

【摘要】 共形阵列是阵列流形和其安装载体保持一致的阵列。除了机械结构方面的优势外,共形阵列还提供了360度空间的全方向快速扫描和覆盖能力,这是传统阵列天线所不具备的特点。作为新一代雷达和通信等领域的关键,毫米波技术是当前研究的热点,而毫米波的波长极短和强耗损特点,使得毫米波结合大规模阵列成为重要的技术解决途径。作为当下阵列信号处理的两个研究热点,共形阵列和毫米波阵列的结合在可预见的未来会成为一个重要的研究方向,其应用场景包括基于无人机群的毫米波5G通信组网以及毫米波卫星通讯系统等,而快速且精确的波达方向(Direction-of-Arrival,DOA)估计是毫米波共形阵列得以充分发挥其优势的关键和前提。本文针对毫米波大规模共形阵列的特点,重点研究低复杂度、快速迭代、高精确的DOA估计算法,本文的主要工作及创新包括:1.针对大规模均匀圆阵(Uniform Circular Array,UCA),提出了一种基于序列相关和最佳偏转相位搜索的复杂度低、精度高的单快拍DOA估计方法。该方法利用UCA阵列响应的相关性,构造了用于DOA粗估计的匹配系数序列,并通过循环互相关获得信号源DOA的粗估计;利用偏转相位重构匹配系数序列,从而通过搜索最佳偏转相位得到精确的DOA估计结果。具体创新包括:(1)提出并证明了大规模UCA的阵列响应具有良好的自相关性,并基于此设计了匹配系数序列,利用循环卷积高效实现DOA的粗估计;(2)提出了适用于UCA的相位偏转设计,利用相关运算的互易性质,将阵列响应的相位偏转转化至匹配系数序列,然后通过对最佳偏转相位的快速搜索实现DOA的精细化估计;(3)引入序贯干扰相消算法,实现了多信源的DOA估计。并将提出的单快拍方法扩展到多快拍场景,进一步提高了算法性能;(4)评估了本方法的运算量,和基于子空间的多种算法相比较,具有数量级上的优势;(5)推导了所提估计方法的克拉美-罗下界(Cramér-Rao Lower Bound,CRLB)的闭式解,并通过仿真实验验证了所提方法能够在高信噪比(Signal to Noise Ratio,SNR)下逼近CRLB。2.针对大规模均匀圆柱阵列,提出了一种基于离散傅里叶变换(Discrete Fourier Transform,DFT)、匹配相关和最佳偏转相位搜索的低复杂度、高精度的单快拍DOA估计方法。该方法利用均匀圆柱阵列的对称性特点,将二维角度估计解耦。首先,利用DFT和最佳偏转相位搜索实现基于均匀线阵(Uniform Linear Array,ULA)的俯仰维DOA初步估计。然后,基于匹配相关和最佳偏转相位搜索实现方位维DOA的估计。最后,借助方位维DOA估计结果对俯仰维DOA进行精确估计,从而最终得到大规模均匀圆柱阵列的二维DOA估计结果。具体创新包括:(1)基于空间矢量运算构建了均匀圆柱阵列的接收信号模型,并将均匀圆柱阵列的阵列响应分解成ULA和UCA的阵列响应的克罗内克积的形式;(2)利用相干积累将均匀圆柱阵的接收信号降维合成单个的虚拟UCA,从而可利用前文方法实现方位维DOA的估计,极大地提高了估计SNR和DOA估计精度;(3)利用相干积累将均匀圆柱阵的接收信号降维合成单个的虚拟ULA,进一步提高了俯仰维的估计SNR和DOA估计精度;(4)分析了偶极子极化模型下信号的特点以及对所提出算法的影响;(5)开展了大量仿真实验,验证了本章方法的高性能和相比于已有算法的优越性。3.针对大规模巴特勒矩阵收发器(Butler Matrix-based Transceiver,BMT)混合共形阵列,提出了基于宽波束合成、快速区间迭代和二进制编码的多种快速DOA估计方法。该类方法首先根据BMT的探测能力和排布方式对阵列探测角度空间进行了划分;然后利用BMT的宽波束合成方法合成多个宽波束,以覆盖整个探测角度空间;通过各个宽波束检测到的信号功率确定DOA所在的角度区间,迭代不断缩小角度区间范围直到将DOA定位到某个特定的DFT波束上。具体创新包括:(1)基于空间矢量运算建立了BMT共形阵列的信号模型;(2)提出了空间角度域的BMT宽波束合成方法;(3)提出了快速区间迭代的方案,包括密铺宽波束法和重叠宽波束法,计算和分析了其运算量和迭代速度;(4)提出和证明了BMT非重叠宽波束的自由叠加原理;(5)提出了基于等长二进制编码的DOA快速定位方法,计算和分析了其迭代速度;(6)针对DOA非等概率分布的情况,提出了基于哈夫曼编码的DOA快速定位方法。4.针对大规模BMT混合共形阵列,提出了基于DOA快速定位和高阶差分波束的精确DOA估计方法,以及基于极大似然准则的DOA估计结果融合方法。该方法首先进行前文所述的快速DOA估计,将DOA定位到特定的DFT波束上;再利用差分波束或高阶差分波束的方法,使用多个BMT分别进行DOA估计;最后利用极大似然估计的方法将多个BMT的估计结果进行融合,得到最终的精确DOA估计结果。具体创新包括:(1)分析了基于DFT波束的测角方法存在的缺点,据此提出了差分波束的概念,并推导了基于差分波束的DOA估计方法的闭式解;(2)构造并提出了高阶差分波束的概念,并讨论了其用于DOA估计的优势和存在的问题;(3)分析了硬件可实现的二阶差分波束的两种形式,推导了用于DOA估计的闭式解,对比讨论了各自的优缺点,以及和已有算法在DOA估计性能上的差异;(4)分析了差分波束和高阶差分波束在不同DOA下均方误差的差异性,并据此提出了基于极大似然法则的多BMT的DOA估计结果的融合方法;(5)通过仿真实验验证了所提方法的有效性,并通过对差分波束和高阶差分波束的性能仿真验证了其相较于DFT波束的优势和特点。更多还原

【Abstract】 Conformal arrays refer to the arrays whose array manifolds conform to the carrier platform due to the limitation of aerodynamics and underwater environment,etc..Conformal arrays not only have the advantages of mechanical structure,but also can provide omnidirectional fast scanning and large spatial coverage,hence outperforming traditional array antennas in certain applications.As a key technology of the future radar and communication systems,millimeter wave(mm Wave)is has been a hot research topic in recent years.Due to its ex-tremely short wavelength and severe path loss,mm Wave is generally used in combination with large-scale arrays.As two current research hotspots in array signal processing,the combination of conformal arrays and mm Wave arrays will become an important research direction in the foreseeable future.Its application scenarios include mm Wave 5G commu-nication networking based on UAV swarms and mm Wave satellite communication systems,etc.,and fast and accurate direction-of-arrival(DOA)estimation is the key and substitute for mm Wave conformal array to give full play to its advantages.According to the characteris-tics of mm Wave large-scale conformal array,this dissertation focuses on developing DOA estimation algorithms with low complexity and high accuracy.1.For large-scale uniform circular arrays(UCAs),a low complexity and accurate single-snapshot DOA estimation method based on sequence correlation and optimal phase compen-sation is proposed.Taking advantage of the excellent auto-correlation property of the array response of a UCA,the coarse-resolution estimation of the DOA is obtained through a cyclic cross-correlation between the matching coefficient sequence and the array received signal.Then the DOA refinement is obtained by searching the optimal phase compensation which maximizes the inner product of matching coefficient sequence and the phase-compensated array received signal.The specific contributions include:(1)It is proved that the array re-sponse of large-scale UCA has good correlation.Based on this,the matching coefficient sequence is designed,and the cyclic cross-correlation operation of two cyclic sequences is developed and turned into cyclic convolution;(2)The idea of fast phase compensation is proposed.It is illustrated that compensating the phases of the matching coefficient sequence is equivalent to performing the same processing on the array response vector,which is due to the reciprocity of the two sequences in correlation.Then,the DOA refinement is obtained by searching the optimal phase compensation;(3)The successive interference cancellation algorithm is introduced to estimate the DOAs of multiple impinging signals;(4)The com-putational complexity of the proposed algorithm is analyzed and compared with numerous existing methods,which shows up to orders of magnitude decrease of the computational complexity;(5)The closed-form expression of the Cramér-Rao lower bound(CRLB)for the proposed algorithm is derived.Extensive simulation results are provided,showing that the RMSE of the proposed method is much better than that of the existing methods and able to approach CRLB in high signal to noise ratio(SNR)regions.2.For large-scale uniform cylindrical array,a low complexity and accurate single-snapshot DOA estimation method based on discrete Fourier transform(DFT),matching correlation and optimal phase compensation is proposed.In this method,the two-dimensional angle estimation is decoupled by using the symmetry of uniform cylindrical array.Firstly,the pre-liminary estimation of elevation DOA based on uniform linear arrays(ULAs)is obtained through DFT and optimal phase compensation.Then the estimation of azimuth DOA is ob-tained through matching correlation and optimal phase compensation.Finally,the accurate elevation DOA is obtained by the estimation of azimuth DOA,and the results of 2D DOA estimation for large-scale uniform cylindrical array are obtained.The specific innovations include:(1)The received signal model of uniform cylindrical array is constructed by space vector operation,and the array response of uniform cylindrical array is decomposed into the Kronecker product of array response of ULA and UCA;(2)The received signals of uniform cylindrical array are reduced to a single virtual UCA by coherent integration to estimate the azimuth DOA by the previous method,which greatly improves the estimation SNR and DOA estimation accuracy;(3)The received signals of uniform cylindrical array are reduced to a single virtual ULA by coherent integration,which further improves the estimation SNR and DOA estimation accuracy;(4)The polarization model of uniform cylindrical array based on dipole antenna and its influence on the proposed algorithm are analyzed;(5)Extensive simu-lation results are provided,showing the high performance and great advantages of proposed method.3.For large-scale hybrid conformal array based on Butler matrix-based transceivers(BMTs),a variety of fast DOA estimation methods based on wide beam combination,fast interval it-eration and binary coding are proposed.Firstly,the detection angle space of array is divided according to the detection ability and arrangement of BMTs.Then,the wide beam synthesis method of BMT is used to synthesize multiple wide beams and cover the whole detection an-gle space.The angle range of DOA is determined by the signal power detected by each wide beam,and the range of angle interval is reduced continuously until DOA is finally located at a specific DFT beam.The specific innovations include:(1)The signal model of conformal array based on BMT is established by space vector operation;(2)The wide beam synthesis method of BMT in spatial angle domain is proposed;(3)The fast interval iteration scheme is proposed,including the close spread wide beam method and the overlapped wide beam method;(4)The principle of free superposition of non-overlapping wide beams of BMT is proposed and proved;(5)A fast DOA location method based on equal length binary coding is proposed,and its iteration speed is calculated and analyzed;(6)Considering the unequal probability distribution of DOA,a fast DOA location method based on Huffman coding is proposed.4.For large-scale hybrid conformal array based on BMTs,an accurate DOA estimation method based on fast DOA location and higher-order DFT beam differential(DBD)and a synthesization method of DOA estimation results based on maximum likelihood estimation method are proposed.Firstly,the fast DOA estimation described above is carried out to lo-cate the DOA on a specific DFT beam.Then,DBD or higher-order DBD method is used to estimate the DOA by each BMT.Finally,the maximum likelihood estimation method is used to synthesize the estimation results of multiple BMTs to obtain the final accurate DOA estimation result.The specific innovations include:(1)By analysing the shortcomings of angle measurement method based on DFT beam,the concept of DBD is proposed,and the closed-form solution of DOA estimation method based on DBD is derived;(2)The concept of higher-order DBD is proposed and its advantages and disadvantages in DOA estimation are discussed;(3)Two forms of second-order DBD that can be easy realized by hardware are analyzed.The closed-form solutions for DOA estimation are derived.The advantages and disadvantages of each method are compared and discussed,as well as the difference in DOA estimation performance with the existing algorithms;(4)The mean square error with different DOA by DBD and higher-order DBD method is analyzed,and a method of synthesizing DOA estimation results of multiple BMTs based on maximum likelihood rule is proposed;(5)The effectiveness of proposed method is verified by simulation experiments.The performance simulations of DBD and higher-order DBD verifies its advantages and characteristics compared with DFT beam.更多还原