Velocity compensation methods for LPRF modulated frequency stepped-frequency(MFSF) radar

In the high speed target environment,there exists serious Doppler effect in the low pulse repetition frequency（LPRF） modulated frequency stepped frequency（MFSF） radar signal.The velocity range of the target is large and the velocity is high ambiguous,so the single method is difficult to satisfy the velocity measurement requirement.For this problem,a novel method is presented,it is a combination of cross-correlation inner frame velocity measurement and range-Doppler coupling velocity measurement.The cross-correlation inner frame method,overcoming the low Doppler tolerance of the cross-correlation between frames,can obtain the coarse velocity of the high speed target,and then the precision velocity can be obtained with the range-Doppler coupling method.The simulation results confirm the method is effective,and also it is well real-time and easy to the project application.

NEW TYPE OF WINDOWS FOR DIGITAL PULSE COMPRESSION IN FREQUENCY DOMAIN FOR BROADBAND LFM SIGNALS

A new type of window called combined window is designed to get higher Ratio of Mainlobe to Sidelobes (RMS) and lower Mainlobe Widening Factor (MWF). Simulation results prove that the new window can solve the contradiction between RMS and MWF better than classic windows.

Lorentz force electrical impedance tomography using pulse compression technique

Lorentz force electrical impedance tomography （LFEIT） combines ultrasound stimulation and electromagnetic field detection with the goal of creating a high contrast and high resolution hybrid imaging modality. In this study, pulse compression working together with a linearly frequency modulated ultrasound pulse was investigated in LFEIT. Experiments were done on agar phantoms having the same level of electrical conductivity as soft biological tissues. The results showed that：（i） LFEIT using pulse compression could detect the location of the electrical conductivity variations precisely; （ii） LFEIT using pulse compression could get the same performance of detecting electrical conductivity variations as the traditional LFEIT using high voltage narrow pulse but reduce the peak stimulating power to the transducer by 25.5 dB; （iii） axial resolution of 1 mm could be obtained using modulation frequency bandwidth 2 MHz.

Analysis and Improvement of the Real-Time Segmented Pulse Compression-Detection Algorithm

Real-Time segmented pulse compression-detection is one of the key technologies of space-borne tracking receiver. Its implementation requires an optimized and dedicated hardware. The real-time processing places several constraints such as area occupied, power comumption, and speed. A number of segmented compression techniques have been proposed to overcome these limitations and decrease the processing latency. However, relatively high power loss in the partial field could limit their implementation in many current real-time systems. A good theoretical model was designed with intersection signal accumulation to enhance signal- noise-ratio （SNR） gain of detecting signal in the paper. From the experimental results it is known that this approach works well for pulse compression-detection, which is better suited for implementation in the high performance of current field programmable gate array （FPGA） with dedicated hardware multipliers.

基于分数阶傅里叶滤波的数字信道化储频

现代战场环境电磁日趋密集和复杂,各类信号相互混迭,同时各种相参雷达采用脉冲压缩技术以及相参处理方法,抗噪声和抗干扰能力大大增强,特别是采用线性调频(LFM)信号满足了雷达大威力、低截获的功能设计需求,抗干扰能力也得到提高。常规的数字储频(DRFM)采用宽带采集,在数字上对宽带信号进行调频、叠加等调制处理,在瞬时带宽内调制样式、参数是相同的,此处理方式导致瞬时带宽内多信号时,无法针对性施加不同的调制样式,以致干扰粗放、不够精确。为实现精确、有效的干扰相参脉冲压缩雷达,文中提出了采用频域子带处理与分数阶傅里叶滤波的数字信道化干扰设计,增强LFM信号去噪能力,通过DRFM技术形成假目标干扰信号,实施有效干扰。

一种面向低成本轻量级雷达的单比特复用阵列信号收发框架

面向低成本轻量级雷达的应用需求,该文提出了一种联合单比特采样量化和时分复用接收机的雷达信号收发框架。首先,通过介绍该框架的工作原理,阐述其在节省接收机数量方面的优势。从雷达资源配置的角度,分析了单比特采样量化在该框架中的重要性,并提出了该框架可利用时间换空间,获得比经典线性调频连续波雷达更好的探测性能。接着,推导了雷达测距、测速和测角公式,以及目标参数估计的克拉美罗界。在此基础上,验证了该框架的性能优势,同时也给出了其稳定工作的信噪比条件。最后,利用一种基于单比特二维多重信号分类的速度维配对算法,验证了该框架获取目标原理的正确性,以及性能分析的可靠性。

超短基线在低频基阵指向性测量中的应用

随着水声换能器工作频率的降低,实验室空间很难达到自由场和远场测量的要求。而开阔水域的水下环境复杂,基阵很难实现更深层次的吊放,需要安装价格昂贵的吊装平台来获取标准声源与待测基阵之间的相对位姿,效率低且维护成本高。文章采用超短基线定位技术,信号选用线性调频脉冲信号与伪随机编码脉冲信号,并分别基于脉冲压缩法和复相关算法实现距离和相位测量。比对湖上定位精度试验和基阵指向性标定静态试验的结果显示:角度误差为2.5°以内;-6 dB波束宽度在2~10 kHz频率范围内测量误差在5.38%以内。证明超短基线定位在低频基阵指向性标定的可行性。

Chirp-DS-BPSK雷达通信一体化波形设计

针对线性调频-二进制相移键控(Chirp-Binary Phase Shift Keying,Chirp-BPSK)雷达通信一体化信号存在模糊函数受通信数据严重影响的问题,分析了传统周期扩频、混沌序列扩频及Logistic映射混沌序列的自相关性能,设计了一种扩频信号与线性调频脉冲相结合的雷达通信一体化共用波形,即Chirp-DS-BPSK一体化信号。该一体化波形分别采用混沌序列和BPSK方式对通信数据进行直接序列扩频与调制,以线性调频信号作为载波,并采用脉冲成型滤波器来提高频谱利用率,降低脉压旁瓣。最后,通过仿真分析证明了所提波形具有良好的模糊函数特性和误码率性能。在扩频比为7的条件下,与传统的Chirp-BPSK波形相比,Chirp-DS-BPSK波形的脉压峰值旁瓣比降低了约2.69 dB,通信误码率下降约8.45 dB,表明Chirp-DS-BPSK比Chirp-BPSK更适合作为雷达通信一体化共用波形。

基于FPGA的多相频域脉冲压缩实现方法

随着高速ADC器件的发展及雷达系统性能需求,宽带线性调频信号在雷达系统中取得广泛应用。高速采样使得频域脉冲压缩点数增大,增加了处理延时与工程实现难度。FPGA接收ADC采样的宽带信号为时域抽取的多相分量的形式,采用多相的方法实现基于时域抽取与频域抽取的二维FFT与IFFT,能够节省FPGA存储资源,降低脉冲压缩的处理延时。

转发式干扰条件下LFM雷达的检测概率估计

对多雷达干扰效果评估的难点在于分析干扰机对非目标雷达的影响。针对干扰机转发一部线性调频(linear frequency modulation,LFM)雷达的信号无意干扰另一部LFM雷达时的检测概率估计问题,首先计算了被干扰雷达对干扰信号在空域、频域和时域上的接收增益;其次将干扰信号在判决单元中的统计特性建模为非中心卡方分布,并给出了检测概率和虚警概率的计算方法。仿真结果表明,在一部干扰机的无意干扰下,估计的检测概率可作为被干扰雷达检测概率的上限;为达到同样的干扰效果,转发非目标雷达的信号实施干扰,比转发目标雷达的信号进行干扰所需的干扰功率更少。

MSK-LFM一体化信号波形相关性分析与参数选择

以二进制数字信号最佳接收准则为依据,分析了MSK-LFM雷达通信一体化信号不同码元对应波形的相关性。利用fresnel函数得到了波形相关系数的表达式;通过数值仿真得到了相关系数随LFM信号的初始频率、调频率、脉冲内码元调制速率等参数的变化关系;构建MSK-LFM信号正交调制、解调仿真模型进行验证。研究表明,通过增大初始频率、调频率或减少调制速率可降低信号误码率;当初始频率远大于脉冲内码元调制速率时可认为不同码元波形正交。

一种类线性调频雷达波型自动识别方法

随着电子技术的发展,雷达信号调制方式趋于复杂化,对雷达信号波形进行可靠的识别是雷达侦察系统面临的一个难题。其中,类线性调频雷达信号(LFM、Frank码、P1~P4码)是识别难度较大的一类信号。针对该问题,论文提出了一种基于深度学习的雷达波形自动识别方法,首先计算类线性调频雷达的基于S-method的时频分布,在此基础上计算信号时频分布的Zernike矩,然后通过卷积神经网络进行分类识别。实验表明,在-2dB信噪比下,信号的整体识别率达到94.33%,能够有效识别雷达波形。

线性调频和MSK雷达通信一体化波形设计

在通信领域,许多物联网设备对于信息传输速率的要求越来越高,导致无线通信相关的电子产品所使用的带宽越来越高,进而使得无线通信在工作频段上与雷达的使用频率出现了重叠。无线通信类的电子产品越来越多,因而未来电磁频谱会越来越紧张。对此,设计出一个一体化波形,使该波形同时具有雷达探测和无线通信功能是非常有价值的研究。文章将线性调频信号与最小频移键控(Minimum Shift Keying,MSK)调制相结合设计一体化波数学模型,通过研究其模糊函数和相干解调验证了一体化波形具有雷达和通信的良好工作性能。

Adaptive digital self-interference cancellation based on fractional order LMS in LFMCW radar

Adaptive digital self-interference cancellation(ADSIC)is a significant method to suppress self-interference and improve the performance of the linear frequency modulated continuous wave(LFMCW)radar.Due to efficient implementation structure,the conventional method based on least mean square(LMS)is widely used,but its performance is not sufficient for LFMCW radar.To achieve a better self-interference cancellation(SIC)result and more optimal radar performance,we present an ADSIC method based on fractional order LMS(FOLMS),which utilizes the multi-path cancellation structure and adaptively updates the weight coefficients of the cancellation system.First,we derive the iterative expression of the weight coefficients by using the fractional order derivative and short-term memory principle.Then,to solve the problem that it is difficult to select the parameters of the proposed method due to the non-stationary characteristics of radar transmitted signals,we construct the performance evaluation model of LFMCW radar,and analyze the relationship between the mean square deviation and the parameters of FOLMS.Finally,the theoretical analysis and simulation results show that the proposed method has a better SIC performance than the conventional methods.

HIGH RESOLUTION RANGE PROFILE FORMATION BASED ON LFM SIGNAL FUSION OF MULTIPLE RADARS

This paper presents a new method of High Resolution Range (HRR) profile formation based on Linear Frequency Modulation (LFM) signal fusion of multiple radars with multiple frequency bands. The principle of the multiple radars signal fusion improving the range resolution is analyzed. With the analysis of return signals received by two radars,it is derived that the phase difference between the echoes varies almost linearly with respect to the frequency if the distance between two radars is neg-ligible compared with the radar observation distance. To compensate the phase difference,an en-tropy-minimization principle based compensation algorithm is proposed. During the fusion process,the B-splines interpolation method is applied to resample the signals for Fourier transform imaging. The theoretical analysis and simulations results show the proposed method can effectively increase signal bandwidth and provide a high resolution range profile.

Speed-Direction Sensing under Multiple Vehicles Scenario Using Photonic Radars

Recent reports from World Health Organization(WHO)show the impact of human negligence as a serious concern for road accidents and casualties worldwide.There are number of reasons which led to this negligence;hence,need of intelligent transportation system(ITS)gains more attention from researchers worldwide.For achieving such autonomy different sensors are involved in autonomous vehicles which can sense road conditions and warn the control system about possible hazards.This work is focused on designing one such sensor system which can detect and range multiple targets under the impact of adverse atmospheric conditions.A high-speed Linear Frequency Modulated Continuous Wave(LFMCW)based Photonic Radar is proposed to detect multiple targets by integrating Mode division multiplexing(MDM).Reported results in terms of range frequency,Doppler frequency and range resolution are demonstrated using numerical simulations with the bandwidths of 1 and 4 GHz and under adverse atmospheric conditions carrying 75 dB/km of attenuation.To prove the effectiveness of the proposed photonic radar,moving targets are also demonstrated with different speed.System reported substantial range resolution of 15 cm using 1 GHz of bandwidth and 3 cm using 4 GHz of bandwidth.

Hard Decision-Based PWM for MIMO-OFDM Radar

For the purpose of target localization, Multiple Input Multiple Output-Orthogonal Frequency Division Multiplexing (MIMO-OFDM) radar has been proposed. OFDM technique has been adopted in order to a simultaneous transmission and reception of a set of multiple narrowband orthogonal signals at orthogonal frequencies. Although multi-carrier systems such as OFDM support high data rate applications, they do not only require linear amplification but also they complicate the power amplifiers design and increase power consumption. This is because of high peak-to-average power ratio (PAPR). In this work, a new proposition has been made based on the Pulse Width Modulation (PWM) to enhance the MIMO-OFDM radar systems’ performance. In order to check the proposed systems performance and its validity, a numerical analysis and a MATLAB simulation have been conducted. Nevertheless of the system characteristics and under same bandwidth occupancy and system’s specifications, the simulation results show that this work can reduce the PAPR values clearly and show capable results over the ones in the literature.

基于MR-MWC系统的载频与DOA联合估计

针对传统奈奎斯特采样会产生庞大的数据量以及现有的阵列压缩采样系统存在结构复杂、重构运算量大等问题,本文提出了一种基于均匀线型阵列的改进型调制宽带转换器(Modulated Wideband Converter,MWC)的阵列接收系统,无需重构即可直接对接收信号的压缩采样数据进行载频与波达方向(Direction Of Arrival,DOA)估计.所提系统在MWC测频支路中采用周期性循环移位伪随机序列作为混频函数以求得子带索引估计,采用基于快速傅里叶变换(Fast Fourier Transform,FFT)谱线插值法进行基带频率估计,且将MWC测向分支中混频函数设置为相同的伪随机序列,便可直接利用高分辨率的多重信号分类(MUltiple SIgnal Classification,MUSIC)算法对组合压缩采样数据完成DOA估计.实验仿真结果证明了所提系统能较好地从压缩采样数据中完成对目标的载频与DOA参数估计.

对步进线性调频成像雷达的间歇采样转发干扰方法

针对步进线性调频信号(stepped frequency-linear frequency modulation,SF-LFM)体制雷达对抗问题,提出了一种基于子脉冲间歇采样的干扰方法。通过对截获SF-LFM信号的子脉冲进行交替采样与转发,在雷达成像处理后可形成沿距离向延拓的逼真假目标。在此基础上对其干扰特性与参数设计问题进行了讨论,并分别通过一维理想散射点仿真与某型飞机二维成像数据仿真实验验证了所提方法有效性。

基于分段移频调制的间歇采样重复转发干扰

针对间歇采样重复转发干扰(Interrupted-Sampling Repetitive Repeater Jamming,ISRRJ)假目标群滞后于真目标,且各假目标在空间的规律性分布导致干扰效果单一的问题,分析了ISRRJ特性,重点推导了移频量与转发脉冲脉压幅度及空间位置之间的数学关系,在此基础上提出基于分段移频调制的干扰方法。该方法利用每个采样周期内多个转发子脉冲的移频特性,按照不同的干扰效果灵活分配移频量,改变假目标的空间分布。仿真结果表明,所提算法能够在空间中呈现欺骗和压制双重干扰效果,并较好保证欺骗假目标幅度。该算法可根据实际情况合理配置干扰样式,具有硬件资源少、灵活高效的特点。