基于多电视台子孔径综合的无源雷达成像算法

该文提出一种基于多电视台子孔径综合的无源雷达成像算法。该算法通过单个接收机接收来自位于不同视线角的多个电视台的反射信号,将目标小角度转动时得到的各电视台回波形成的所有子孔径综合为等效大孔径的方法来对运动目标进行成像。该算法利用电视台的载频信号,相关计算简单,在电视台分布密集的区域,目标小角度转动即可成像。仿真结果证实了该算法的有效性。     

同航线双基聚束式SAR宽场景成像算法

该文在现有双基SAR成像研究的基础上,提出了同航线双基聚束式SAR成像的算法。该算法首先对回波信号进行方位预处理实现信号支撑区的不模糊,然后利用传统波数域的成像算法聚焦。该算法较双基极坐标算法有更高的聚焦精度并且没有几何形变。它不仅适用于平行航线的双基成像,其思路也完全适用于其它聚束模式的成像处理。最后通过仿真验证了算法的正确性。     

舰船目标实时一维距离像研究

针对线性调频脉冲信号提出了舰船目标一维距离像实时成像算法,给出了系统工作原理,并结合舰船目标的实测数据对该算法进行了仿真分析,同时讨论了该算法在信号处理中的具体实现流程,最后给出了实时成像结果。     

跳频脉冲雷达目标的距离-多普勒成像

该文采用跳频脉冲信号作为成像雷达信号形式,研究了一种雷达等效转台目标距离-多普勒成像的新算法。与常规步进频率雷达傅里叶变换成像算法相比,该算法具有多普勒不模糊范围大的特点,因而克服了步进频率雷达成像算法容易产生多普勒混叠的缺点。计算机仿真结果表明了该算法的有效性。     

基于单频连续波的无源雷达成像研究

该文提出一种新的单频连续波无源雷达成像时域算法。该算法先建立信号匹配矩阵,再将接收到的回波信号拓展为回波信号矩阵,然后将信号匹配矩阵和回波信号矩阵的Hadamard积在时间维上求和,实现回波信号的匹配积累,得到散射点目标的像。给出了算法成像分辨率,分析了影响成像质量的因素并综合得到算法聚焦能力的量度。算法完全在时域中进行成像处理,避免了频域的插值处理。在理论分析的基础上,仿真实验得到了较好成像结果,验证了所提算法有效性。     

基于去调频宽带LFM信号的二次距离压缩算法及其实时实现

该文在基于匹配滤波的二次距离压缩算法(SRC)基础上,通过对去调频的线性调频(LFM)信号的时、频域关系的分析,给出基于去调频LFM信号的SRC算法,与距离多普勒算法(RD)和普通LFM信号SRC算法对比,分析该算法的运算量,说明该算法适合于去调频体制SAR实时成像处理。对于去调频SAR数据采用该算法压缩得到清晰的图像,同时对比斜视下SRC与RD成像的结果。验证了在高分辨率实时成像时SRC算法优于RD算法。     

星载SAR等效斜视波数域算法的实现方法

等效斜视的波数域算法是一种适用于大距离徙动高分辨率星载合成孔径雷达成像的优化算法。该算法可以利用雷达发射信号的复制信号作为距离参考信号。由于该算法在频域插值,对插值精度要求高。多普勒参数的精度和加权处理对该算法的成像性能指标具有重要的影响。文中从距离参考函数、Stolt插值、多普勒参数估计和加权处理4个方面分析了等效斜视波数域算法的实现方法,并通过仿真测试对几种可能方法的成像质量指标进行了比较,实验结果验证了等效斜视波数域算法实现方法的有效性。     

跳频脉冲雷达目标的距离—多普勒成像

该文采用跳频脉冲信号作为成像雷达信号形式,研究了一种雷达等效转台目标距离－多普勒成像的新算法。与常规步进频率雷达傅里叶变换成像算法相比,该算法具有多普勒不模糊范围大的特点,因而克服了步进频率雷达成像算法容易发生多普勒混叠的缺点。计算机仿真结果表明了该算法的有效性。     

一种多体制兼容的微波成像新技术

虚拟透镜成像技术是一种可以兼顾远、中、近不同距离的成像新技术,但该技术是在被动成像的基础上发展起来的,适用于被动成像、半主动成像以及常规相控阵成像。在主动全息成像以及合成孔径成像系统中,由于天线单元依次工作并收发信号,目标回波信号具有不同的传播路径和相位延迟特性,因而不能直接采用虚拟透镜成像技术。文中对虚拟透镜成像技术进行扩展,针对主动全息成像和合成孔径成像的特点,引入了阵列属性参数,将其与信号传播路径和相位延迟特性进行关联,建立了一种多体制兼容的成像快速算法统一架构,并对相位加权算法进行了优化。所提出的新算法适用范围更广泛,且相位加权算法简洁易实现。最后进行了成像验证,实验及仿真结果证实了新算法的有效性。     

基于运动补偿的机载大斜视SAR成像算法

根据机载大斜视SAR信号的特点,研究了具有很强工程实用性的两维可分离大斜视SAR成像算法,分析了因速度不稳对大斜视SAR成像的影响,并给出了运动补偿算法.实测数据成像结果证明了该算法适合大斜视成像.     

基于参考距离史的多子阵SAS成像算法

为了解决现有多子阵合成孔径声呐(SAS)成像算法忽略了"非停走停"时间的孔径依赖性带来时延误差的问题,该文提出一种基于参考距离史的多子阵SAS成像算法.首先利用参考子阵与各子阵之间的平移关系,推导每个子阵的近似距离史,解决"非停走停"时间的孔径依赖性需要被近似的问题;然后将每个子阵信号搬移至相同的波束中心距离后,通过方...     

无源雷达成像的平动补偿

基于外辐射源的运动目标探测、定位与成像技术是目前新体制雷达研究的重点.讨论了无源雷达成像的平动补偿,建立目标回波模型,利用相邻回波包络的相关性进行运动补偿.将来自不同视线角的多个电视台的反射信号形成的子孔径综合为等效的大孔径的方法来对目标进行成像,并进行了仿真试验.     

多发多收SAR系统幅相误差定标方法

方位多通道SAR（Synthetic Aperture Radar）系统采用数字波束形成技术(Digital Beam-Forming, DBF),能够克服最小天线面积的限制,有效地解决了高分辨率与大测绘带之间的矛盾,实现了高分辨率宽测绘带对地观测,多发多收模式是方位多通道SAR未来的发展方向。对于方位多通道SAR系统,通道间的幅相误差对系统成像性能有很大影响,必须对其进行标定。利用子空间投影算法,提出了一种基于地面发射机和接收机的定标方法。其利用地面布设的发射机和接收机,分别估计出接收通道间的幅相误差和发射通道间的幅相误差,实现收发通道相位误差分离,从而估计出多发多收模式下各回波包含的幅相误差值。基于发射机和接收机估计方法的精度均得到了仿真验证。最后通过点目标仿真实验,对提出方法的有效性进行了仿真验证。实验表明,该方法通过布设地面发射机和接收机即可对多发多收模式下通道间的幅相误差进行标定,实现成像的校正。     

基于新型阵列结构的多波束SAS逐点成像算法研究

该文基于多波束测深和合成孔径技术原理,提出了多波束合成孔径声呐(Synthetic Aperture Sonar, SAS)的实现方案,设计了一种新型的多接收阵元阵列结构,有针对性地推导了相关数学模型,并仿真实现了逐点成像算法。计算机仿真结果表明：相比于传统多波束测深声呐,新方案的方位向分辨率有了明显的提高;相比于常规合成孔径声呐,新方案能够得到更多的目标信息,且能改善成像效果。     

多源宽带干扰对多阵元GPS接收机干扰效能分析

近年广泛使用的多阵元自适应调零天线抗干扰技术,大幅降低了单个GPS干扰源的干扰效能,如何对其实施有效干扰成为导航对抗的研究热点之一。本文首先使用干扰-信号比阈值分析了多阵元接收机失效机制,并使用单源干扰对其抗干扰效能进行了检验;其次建立了多源宽带高功率压制干扰模型,最后采用数值仿真研究了多源宽带高功率压制模式下,干扰4阵元线性约束最小方差(LCMV)自适应调零算法GPS接收机的工作效率。实验表明,适当布置的多源宽带高功率压制模式可以有效提升对多阵元GPS系统的干扰效能。      

基于SSCANL译码器的联合迭代检测译码算法

为了提升基于极化码的稀疏码多址接入（sparse code multiple access,SCMA）系统接收机性能,提出了基于简化软消除列表（simplify soft cancellation list,SSCANL）译码器的循环冗余校验（cyclic redundancy check,CRC）辅助联合迭代检测译码接收机方案。该方案中极化码译码器使用SSCANL译码算法,采用译码节点删除技术对软消除列表（soft cancellation list,SCANL）算法所需要的L次软消除译码（soft cancellation, SCAN）进行简化,通过近似删除冻结位节点,简化节点间软信息更新计算过程,从而降低译码算法的计算复杂度。仿真结果表明,SSCANL算法可获得与SCANL算法一致的性能,其计算复杂度与SCANL算法相比有所降低,码率越低,算法复杂度降低效果越好;且基于SSCANL译码器的CRC 辅助联合迭代检测译码接收机方案相较基于SCAN译码器的联合迭代检测译码（joint iterative detection and decoding based on SCAN decoder, JIDD-SCAN）方案、基于SCAN译码器的CRC辅助联合迭代检测译码（CRC aided joint iterative detection and decoding based on SCAN decoder,C-JIDD-SCAN）方案,在误码率为10^-4时,性能分别提升了约0.65 dB、0.59 dB。     

Adaptive Hybrid Beamformer for Mobile Reception of ATSC DTV

An adaptive hybrid beamformer is proposed to improve the reception performance of the advanced television system committee (ATSC) digital television (DTV) in a mobile environment. Dynamic multipaths and Doppler shifts severely degrade the reception performance of the ATSC DTV receiver. Accordingly, a hybrid beamformer, called a Capon and least mean square (CLMS) beamformer, is presented that uses direction of arrival (DOA) information and the least mean square (LMS) beamforming algorithm. The proposed CLMS algorithm efficiently removes dynamic multipaths and compensates for the phase distortion caused by Doppler shifts in mobile receivers. When the CLMS beamformer has an insufficient degree of freedom (DOF), the subsequent use of an equalizer removes any residual multipath effects, thereby significantly improving the performance of DTV receivers. The performances of the proposed CLMS, Capon, and LMS beamformers are compared based on computer simulations. In addition, the overall performance of the CLMS beamformer followed by an equalizer is also considered.     

Adaptive DFE Multiuser Receiver for CDMA Systems using Two-Step LMS-Type Algorithm: An Equalization Approach

This paper presents an adaptive decision feedback equalizer (DFE) based multiuser receiver for code division multiple access (CDMA) systems over smoothly time-varying multipath fading channels using the two-step LMS-type algorithm. The frequency-selective fading channel is modeled as a tapped-delay-line filter with smoothly time-varying Rayleigh-distributed tap coefficients. The receiver uses an adaptive minimum mean square error (MMSE) multiuser channel estimator based on the reduced Kalman least mean square (RK-LMS) algorithm to predict these tap coefficients (Kohli and Mehra, Wireless Personal Communication 46:507–521, 2008). We propose the design of adaptive MMSE feedforward and feedback filters by using the estimated channel response. Unlike the previously available Kalman filtering algorithm based approach (Chen and Chen, IEEE Transactions on Signal Processing 49:1523–1532, 2001), the incorporation of RK-LMS algorithm reduces the computational complexity of multiuser receiver. The computer simulation results are presented to show the substantial improvement in its bit error rate performance over the conventional LMS algorithm based receiver. It can be inferred that the proposed multiuser receiver proves to be robust against the nonstationarity introduced due to channel variations, and it is also beneficial for the multiuser interference cancellation and data detection in CDMA systems.     

Fast stochastic power control algorithms for nonlinear multiuser receivers

Uplink communication in a cellular radio network is considered where the base station in each cell employs linear or nonlinear (decision feedback) multiuser receivers. For any such receiver, the problem of interest is that of minimizing the total transmit power under the constraint that all the users of the network achieve their quality-of-service objective in terms of signal-to-interference ratio (SIR). When the solution is feasible for the desired SIR requirements, the optimum powers are computed with a distributed iterative power control strategy suitable for implementation at each base station. While the deterministic algorithm requires both in-cell and out-of-cell user information, the stochastic algorithm proposed in this paper can be implemented at the base stations in a truly distributed manner requiring knowledge of only in-cell parameters. Such an algorithm was proposed previously for the case where base stations use linear (single user) matched filter (MF) receivers. However, the feasibility region in terms of attainable SIRs for a well-designed multiuser receiver, particularly for a nonlinear receiver that employs decision feedback, is generally much larger than it is for the linear MF receiver. The stochastic power control algorithm in this paper, for linear or nonlinear multiuser receivers, converges in the mean-square sense to the minimal powers when the target SIRs are feasible. The second major focus of this paper is to improve the convergence properties of the conventional stochastic approximation based power control strategy by using the more recent results on averaging. Convergence issues of both the "nonaveraged" and "averaged" algorithms are investigated, and numerical examples are presented to demonstrate the performance improvement due to averaging.