Syntactic Modeling and Signal Processing of Multifunction Radars: A Stochastic Context-Free Grammar Approach

Multifunction radars (MFRs) are sophisticated sensors with complex dynamical modes that are widely used in surveillance and tracking. This paper demonstrates that stochastic context-free grammars (SCFGs) are adequate models for capturing the essential features of the MFR dynamics. Specifically, MFRs are modeled as systems that ldquospeakrdquo a language that is characterized by an SCFG. The paper shows that such a grammar is modulated by a Markov chain representing radar's policy of operation. The paper also demonstrates how some well-known statistical signal processing techniques can be applied to MFR signal processing using these stochstic syntactic models. We derive two statistical estimation approaches for MFR signal processing-a maximum likelihood sequence estimator to estimate radar's policies of operation, and a maximum likelihood parameter estimator to infer the radar parameter values. Two layers of signal processing are introduced in this paper. The first layer is concerned with the estimation of MFR's policies of operation. It involves signal processing in the CFG domain. The second layer is concerned with identification of tasks the radar is engaged in. It involves signal processing in the finite-state domain. Both of these signal processing techniques are important elements of a bigger radar signal processing problem that is often encountered in electronic warfare applications-the problem of the estimation of the level of threat that a radar poses to each individual target at any point in time.     

Likelihood ratios for sequential hypothesis testing on Markov sequences

A variety of likelihood ratios are derived for detecting Gauss-Markov and finite-state Markov sequences in additive Gaussian noise. The Bayesian recursions appropriate to related filtering problems are exploited, together with "known-form" likelihood ratios, to obtain the desired results. In the derivation of a discrete-time Gauss-Markov likelihood ratio, a "pure" causal estimator-correlator structure is sought and a "locally stable" state estimator is encountered that is of some interest in its own right. The likelihood ratio is "pure" in the sense that the locally stable estimator is used in precisely the same manner as the stored replica is used in known-form signal detection problems to form the likelihood ratio. Consequently, the likelihood ratio is devoid of the extra data-dependent term that arises whenever one uses least squares state estimators to form the likelihood ratio statistic. The locally stable estimator equalizes, within a constant related to the {em a priori} and {em a posteriori} filtering error covariances, the {em a priori} and {em a posteriori} filtering densities. Heuristically, the estimator is a compromise between the one-step predictor and the filtered estimator of a discrete-time Kalman filter. When the observation noise covariance is unknown, a generalization of the so-called unknown level problem, then a Wishart prior is assigned to the innovations covariance and an integral representation is obtained for the desired likelihood ratio. The representation suggests a parallel structure for approximating the likelihood ratio when the observation noise covariance is unknown. Finally, the likelihood ratio for detecting finite-state Markov sequences is derived to illustrate that in general no "pure" estimator-correlator structure can exist when the state-space is finite.     

基于文法派生解析表的多功能雷达快速参数估计方法

随机上下文无关文法(SCFG)在多功能雷达(MFR)状态识别和威胁估计中具有良好的应用前景.为了减少常规算法的运算复杂度,本文提出一种基于解析表构造的多功能雷达参数快速估计方法.该方法通过对截获的每个雷达数据序列构造库克-杨-卡塞米(CKY)解析表,排除了大量未参与序列派生过程的产生式,随后在解析表的基础上采用改进的Inside-Outside(IO)算法对雷达文法产生式概率和多功能雷达状态进行快速估计.理论分析与实验仿真证明,该算法在参数估计精度相同的条件下,其运算时间相对于常规IO算法和Viterbi-Score(VS)算法减少了50%以上.     

FSK-FMCW雷达通信一体化信号设计与处理方法研究

在未来的智能交通系统中,车载雷达通信一体化信号可使智能车辆同时完成雷达探测和通信信息传输功能,然而现有的基于调频连续波（Frequency Modulated Continuous Wave, FMCW）的车载雷达通信一体化信号的通信数据率较低,难以满足未来智能交通的需求。为了提高雷达通信一体化系统的通信数据率,本文提出了一种频移键控（Frequency-Shift Keying, FSK） FMCW雷达通信一体化信号设计方法,该方法通过在每个线性调频（Linear Frequency Modulation, LFM）信号上调制多个通信符号,以提高一体化信号的通信数据率。此外,在雷达接收端,将差拍处理和二维快速傅里叶变换（Fast Fourier Transformation, FFT）相结合,对接收到的目标回波进行处理,以获取目标的距离与速度估计。在通信接收端,通过差拍和一维FFT处理,对接收到的FSK-FMCW雷达通信一体化信号进行通信信息解调。最后,通过仿真实验验证了所提方法的有效性。      

生物基因技术在多功能雷达信号解析中的应用

多功能雷达作为一个大规模动态系统,具有复杂的信号形式.对其信号进行解析,揭示系统内部的运行规律,是当今电子侦察领域面临的严重挑战.本文借鉴生物基因工程的思想,提出了多功能雷达信号解析的研究框架和研究手段.详细分析了多功能雷达的工作机制,从系统的角度,将其与生物体的细胞做类比,指出两者在系统结构和运行机制上的高度相似性.对生物基因工程中的逆向工程等关键技术进行了总结,在此基础上,讨论了其在多功能雷达信号解析领域的应用前景.前期的研究成果表明了本文方法的合理性.     

Statistical Properties of the Dual-Polarization Differential Reflectivity (ZDR) Radar Signal

The statistical characteristics of three estimators of the differential reflectivity (ZDR) radar signal are examined theoretically and compared with pulse-to-pulse measurements of reflectivity at horizontal and vertical polarizations. The square-law and log-ratio estimators provide satisfactory means for measuring ZDR while the log-ratio estimator does not. In addition, the theory is consistent with radar data, clearly showing that ZDR could be measured accurately from a sequence of alternately polarized waves.     

间歇采样转发干扰信号分析

间歇采样转发干扰是一种新型的相干干扰方法，可以使线性调频脉压雷达受到相干假目标串的干扰。文章从时域和频域分别对这种干扰样式产生的干扰信号进行计算分析，从而揭示了这种新型干扰样式可以对线性调频脉压雷达产生相干假目标串干扰的本质原因，即干扰信号是相干脉间步进跳频、脉内线性调频的脉冲串。     

Multiuser Detection Using Hidden Markov Model

Many existing multiuser detection algorithms assume that the user sequences are independent and identically distributed (i.i.d.). These algorithms, however, may not be efficient when the user sequences sent to a multiuser system are time correlated due to signal processing procedures such as channel coding. In this paper, we assume that the user sequences are time correlated and can be modeled as first-order, finite-state Markov chains. The proposed algorithm applies the decision feedback framework in which a linear filter based on the maximum target likelihood (MTL) criterion is derived to remove the interferences. A hidden Markov model (HMM) estimator is applied to the output of the MTL filter to estimate the user data, noise variance, and state transition probabilities. The estimated user data in turn are applied to update the parameters of the MTL filter. By exploiting the transmission of training symbols, the proposed algorithm requires neither knowledge of the user codes nor the timing information. Simulation results show the performance improvement of the proposed algorithm by exploiting the time-correlated redundancy of the Markov sources.     

Optimization of trajectory signal processing in a radar system with digital synthesis of antenna aperture using hidden Markov models

Function of radar relief in the space of states is determined using hidden Markov models. An optimal algorithm for processing of trajectory signal of radar system with digital synthesis of antenna aperture is developed with allowance for equivalent discrete representation of the continuous function of radar relief. The application of the Gaussian approximation of the conditional a posteriori probability density of the radar-relief function yields an acceptable quasi-optimal filtering algorithm. The efficiency of the synthesized recurrence algorithm is proven with the aid of statistical simulation.     

参数调制多载波雷达通信共享信号设计

雷达通信一体化是减少电子平台体积与电磁干扰的一种有效途径,而共享信号的研究是实现雷达通信一体化的关键技术。该文提出了一种基于Chirp信号的多载波雷达通信共享信号,其主载波采用唯一Chirp信号实现雷达功能,副载波通过改变调频率和初始频率参数组合的Chirp信号调制通信信息。分析了共享信号的模糊函数以及参数设计方法,并对其处理过程及系统性能进行了研究。仿真结果表明,该信号具有较低误码率和高稳健性特性,使用该共享信号可在微量降低雷达性能的前提下实现通信数据的传输。      

Maximum Likelihood Sequence Estimation of Binary Sequences Transmitted Over Bandlimited Nonlinear Channels

The problem of designing and evaluating the performance of a maximum likelihood sequence receiver for binary PSK transmission over bandlimited nonlinear channels is considered in this paper. The effects of intersymbol interference followed by AM/AM and AM/PM conversions are taken into account while optimizing the performance in the presence of white Gaussian noise. A new representation for the output of a bandpass nonlinearity is given when the input consists of a carrier signal modulated by a sum of binary overlapping pulses. The structure of a maximum likelihood sequence receiver for a bandlimited nonlinear channel is derived using this representation. The receiver uses a modified Viterbi algorithm to determine the most likely sequence of data symbols transmitted. An upperbound on the probability of symbol error for this receiver is obtained. Numerical results illustrating the applicability of the present work to optimizing the performance of a digital satellite communications link are also presented.     

Maximum likelihood carrier phase recovery for coherently orthogonalCPFSK signals

ML estimation of carrier phase for coherently orthogonal continuous-phase frequency-shift-keying (COCPFSK) signals is considered. Although the estimator, in general is nonimplementable, its high and low signal-to-noise-ratio approximations both lead to linear readily implementable receiver structures. The high SNR approximation yields a DA receiver, whereas the low SNR approximation yields an NDA receiver. The performance of both receivers in term of bit error probability is analyzed. The existence of an unmodulated component in the sufficient statistical representation of a COCPFSK signal is pointed out, and it is shown how this component enters directly into maximum-like carrier recovery. This leads to interpretation of the NDA receiver as a generalization of the conventional matched-filter envelope-detector receiver. The insights gained here are useful to the problem of ML carrier recovery for Viterbi decoding of continuous phase modulation signals     

现代雷达信号处理的数字脉冲压缩方法

脉冲压缩技术是雷达信号处理的关键技术之一。文中主要从信号形式、优势和不足、应用场合等方面介绍线性调频、巴克码、多相码、非线性调频等几类常用脉冲压缩信号，提出在时域和频域实现数字脉冲压缩的统一数学模型，推荐了相应的工程实现方法。根据具体雷达的目的和不同类脉压信号的特性，设计最佳脉冲压缩滤波器是提高雷达脉冲压缩性能的关键。     

基于循环相关的符号速率盲估计

本文阐述了未知符号序列经线性调制后,在接收端利用循环相关理论对符号速率进行盲估计的问题。对接收信号进行过采样,利用信号的循环平稳统计特性,在循环域对信号的循环相关估计的模平方之和进行最大化处理,从而导出本文描述的符号速率估计器。文中给出了基于循环相关的盲估计算法,并对核算法的统计一致性和渐进性能进行了分析,最后给出了该算法的仿真数据。     

基于稀疏信号表示的雷达目标成像技术

雷达目标成像本质上是对雷达目标散射特性进行信号表示的过程.在高频区,雷达目标散射特性可用少数几个散射中心来描述,利用散射中心稀疏分布的先验信息能有效增强雷达图像的分辨率.以稀疏信号表示为基础,针对雷达成像系统的结构特点,提出了一种基于FFT和分块Toeplitz系统的快速成像算法.该算法无需存储系数矩阵,极大地降低了存储量和运算量.仿真结果表明,该技术对雷达目标图像具有良好的分辨率增强能力.     

Signal Decomposition by Using the S-Method With Application to the Analysis of HF Radar Signals in Sea-Clutter

This paper presents a new approach to the time-frequency signal analysis and synthesis, using the eigenvalue decomposition method. It is based on the S-method, the time-frequency representation that can produce a distribution equal or close to a sum of the Wigner distributions of individual signal components. The new time-frequency signal decomposition method is evaluated on the simulated and experimental high-frequency surface-wave radar (HFSWR) data. Results demonstrate that it provides an effective way for analyzing and detecting maneuvering air targets with significant velocity changes, including target signal separation from the heavy clutter. The analysis shows that this method can provide additional insight into the interpretation and processing of radar signals, with respect to the traditional Fourier transform based methods currently used by the HFSWRs. The proposed method could also be used in other signal processing applications.     

一种新的低截获概率雷达信号的设计与分析

从信号频谱、模糊函数等方面对二相编码信号、步进频率信号两种典型的低截获概率雷达信号进行了分析,提出一种脉内二相编码——脉间步进频率复合调制雷达信号,并对其优缺点进行了比较。研究结果表明,复合调制信号既能克服步进频率信号较严重的距离——多普勒耦合和相位编码信号的多普勒频移敏感的缺点,同时又具备相位编码信号的大带宽特性和步进频率信号的高距离分辨率特性,是一种较理想的低截获概率雷达信号。     

基于电磁模型的宽带雷达海杂波信号建模与分析

该文针对时变海洋面雷达回波信号模拟问题,建立了一种包含电磁散射机理与雷达波形调制特征的海杂波雷达回波信号模型.该模型首先建立一组具有时变特征的海面几何样本,通过对改进双尺度面元模型的加速处理,实现各时刻海面散射数据的高效模拟,并通过与测试数据的对比证实了电磁计算方法的准确性,然后采用子脉冲形式建立宽带回波信号模型,并以...     

基于模糊函数的双基地雷达信号检测分析

在双基地雷达系统中,基于纽曼-皮尔逊准则的似然比检测不但与发射信号的波形有关,而且还与双基地雷达系统的几何布站及目标的空间位置有关.首先以单基地雷达信号检测过程为基础,推导了双基地雷达系统的信号检测统计量模型,该模型是双基地雷达系统模糊函数的理论基础.然后给出了双基地雷达系统目标时延和多普勒频移参量的数学形式,与单基地...