OFDM雷达通信一体化波形相参积累研究

传统雷达系统不同脉冲发射相同的波形,而在OFDM雷达通信一体化系统中,为了最大化通信数据率,不同脉冲需要发射不同的OFDM雷达通信一体化波形。在进行多脉冲相参积累时,一体化波形不同脉冲间的差异可能会导致目标能量积累性能下降。针对该问题,本文从理论上推导发现,当通信调制信息服从相位均匀分布时,不同脉冲波形在脉冲压缩处理后,主瓣内的相位与时间延迟成线性关系。此外,不同脉冲间,由多普勒引入的相位变化占主导因素,而时域非完全匹配所造成的相位改变可忽略。理论分析和仿真实验表明,OFDM雷达通信一体化波形不会影响目标在主瓣内能量的相参积累。      

Nonsinusoidal radar signal design for stealth targets

The detection of stealth point targets challenges the design of conventional radars using sinusoidal carriers since the objective of stealth technology is to reduce the radar cross section (RCS) of targets to a level where the radar receiver cannot detect the target. While there are a number of techniques employing different technologies to reduce the RCS of targets, shaping and coating the target with absorbing material are the most useful ones. The analysis and design of nonsinusoidal radar signals is based on modeling stealth point targets by a two-layer structure consisting of a metal surface covered with a coat of absorbing material. The design is presented for two classes of signals: uncoded signals and pulse compression signals using Barker codes. The relationship between target response, absorbing material time delay, time variation of transmitted pulses and coding features are determined and analyzed. While sliding correlators are used for detection and selection of various target responses, their output autocorrelation functions are determined analytically in terms of transmitted signal autocorrelation functions. Thumbtack range-velocity resolution functions are obtained for transmitted signal characters with a single pulse and characters with coded waveforms, for different pulse duration. It is shown that the range resolution can be improved by the proper choice of the transmitted signal duration relative to absorbing material time delay. Thumbtack range-velocity resolution functions similar to those of conventional point targets can also be realized     

脉冲压缩技术在数字侦察接收机中的应用仿真分析

提出了基于匹配滤波器线性调频压缩技术的数字侦察接收机模型。该模型克服了传 统的基于色散延迟线等模拟器件的脉冲压缩接收机精度低、受环境影响大等缺点,采用了匹 配滤波器技术使在相同输入条件下输出信噪比最大;同时解决了普通超外差体制全景显示搜 索接收机搜索速度、频率分辨率和灵敏度之间的矛盾。实现了中频滤波器和压缩滤波器的设 计。仿真结果表明,基于数字化压缩技术的侦察接收机在侦察频段内高速搜索时保持了 很高的信号接收灵敏度和频率分辨率,性能稳定,能有效检测到跳频信号。     

Analysis of HF pulse reflection from a randomly varying ionosphere

The reflection of high-frequency (HF) pulses by a randomly inhomogeneous, dispersive, and absorbing ionosphere is considered. The distortion of the transmitted pulses due to the intrinsic ionosphere dispersion, multipath effects, and frequency incoherence is related to the spatial, temporal, and frequency dependent characteristics of both the ionosphere and the troposphere. The envelope broadening of a constant-carrier pulse due to the dispersion (delay distortion) and randomness of the media (diffuse multipath) is seen to be small compared to the discrete mulfipath spread resulting from variations of the ionosphere's index of refraction with height. In the case of chirp-pulse transmission, pulse compression in the range of 20-30 dB may be achieved provided the frequency sweep of the transmitted pulse is matched to the slope of the delay of the channel and the bandwidth of the chirp pulse is large enough (0.1-10% of the center frequency).     

Interaction of Electromagnetic Transient Radiation with Biological Materials

The transmission characteristics of transient electromagnetic pulses in biological material are studied using a plane wave pulse incident normally on a semi-infinite layer model. With the dispersion properties of complex tissue dielectric constants taken into account, the steady state transfer function was examined as a function of frequency. Integral solutions for the transmitted field of a Gaussian pulse were obtained through Fourier transformation. The transmitted waveforms inside muscle were determined numerically for various depths pertinent to biological situations. The results suggest that incident pulse experiences severe reflection at the airtissue interface and, shorter pulses are transmitted more readily than longer ones. For an incident pulse of 50 kV/m and 1 us in pulsewidth, the transmitted amplitude is 221 V/m.     

The limits of extended Kalman filtering for pulse traindeinterleaving

Some signals are transmitted as periodic pulse trains. If more than one pulse train is transmitted over the same communication channel, a challenge is to separate them for source identification at the receiver. This is known as pulse train deinterleaving and is clearly a fundamental problem in the study of discrete-event systems. Frequently, the only relevant information at the receiver is the time of arrival (TOA) data, which is usually contaminated by jitter noise. Perhaps there are also missing or overlapping pulses. In this paper, we present an approach for deinterleaving pulse trains and estimating their periods using an extended Kalman filter (EKF). A naive application of EKF theory is not attractive because of discontinuities in the signal model. Here, a form of smoothing of the discontinuities is proposed so that the EKF approach becomes attractive. The advantage of this EKF approach is that it is less computationally expensive than most previously proposed methods, which are of order N², where N is the number of pulses being processed. The computation required here is of order N. The method proposed appears to give useful results for up to seven or so pulse trains, particularly when there is some a priori information on the pulse frequencies, which can be obtained using computations of order N log N     

Faraday tarotion: New parameter for electromagnetic pulse propagation in magnetoplasma

Extreme distortion and time-dependent Faraday rotation occur for propagation of short electromagnetic pulses in magneto-plasma, for some ranges of plasma parameters. In order to relate pulse and monochromatic waves for propagation-path diagnostic purposes, we introduce a new parameter for the transmitted pulse train which has properties that correspond very accurately to results that would be expected for Faraday rotation of a continuous wave having the central frequency of the incident pulse spectrum. Results for 5-ns pulses (10 GHz) are presented for varying propagating length, static magnetic field, electron density, and collisional absorption.     

DFT扩展OFDM系统中降低信号峰均比的频域成型方法

OFDM(正交频分复用)技术的主要缺点之一是其发送信号具有较高的峰均比。DFT(离散傅里叶变换)扩展OFDM系统的发送方案可以有效降低信号的峰均比。在该系统中,频域成型方法不仅对系统有无码间干扰的特性和抗噪声性能有重要影响,而且对发送信号的峰均比也有重要影响。文中首先在加性高斯白噪声信道下推导了无码间干扰和接收机最大输出信噪比条件下发送频域成型函数及接收频域成型函数所要满足的条件,然后根据该条件设计了几种频域成型方法。仿真结果表明,频域成型方法能进一步有效降低发送信号的峰均比。     

1064nm激光诱导等离子体开关控制355nm脉宽可调输出

为得到脉宽可控的355nm紫外脉冲激光输出,采用1064nm脉冲激光诱导等离子体开关技术,控制355nm激光脉冲宽度,在激光电离Cu小孔内壁表面及空气击穿共同作用下,获得了2.8ns～10ns的脉宽可调输出.讨论了1064nm单脉冲输出能量对脉宽压缩的影响,在无延时情况下得到了脉宽最短达2.8ns的脉冲激光输出.在此基础上,保持1064nm单脉冲输出能量不变,采用延时装置改变两光路间的光程差,以控制等离子体开关相对于355nm激光脉冲的形成时间,最终得到脉宽可调的脉冲激光输出.结果表明,等离子体开关结构简单、操作方便、适用范围广,是一种较好的脉冲整形手段.     

一种PCM相参脉冲序列多普勒频率变化率估计算法

相位编码调制信号是一种典型的脉冲压缩信号,广泛应用于脉冲压缩体制的低截获概率雷达中。来波信号中多普勒频率变化率的高精度估计是基于质点运动学原理的单站无源定位与跟踪的一个关键技术。该文针对信号脉内相位调制和多普勒频率变化率信息非常微弱的特点,提出了一种快速高精度估计算法,通过相邻脉冲间的时域相关消除了相位调制对参数估计的影响,频域积累增强了信噪比,利用脉冲间的相参特性进行频谱相关消除了相位模糊,并放大了多普勒频率变化率信息。算法计算量小,为实际应用提供了良好条件。计算机仿真结果证明了算法的有效性。     

Performance analysis of b-bit digital receivers for TR-UWB systems with inter-pulse interference

An ultra-wideband (UWB) transmitted reference (TR) system transmits an un-modulated pulse and a delayed modulated pulse pair. Then, a correlation receiver uses the former to demodulate the latter. Because of the long spread of a typical UWB channel, time delay between the two pulses is preferable to be larger than the channel delay spread for reduced noise at the receiver. However, for bandwidth efficiency, that delay should be made small, resulting in inter-pulse interference at the receiver. In this paper, digital receivers are constructed for TR-UWB systems including inter-pulse interference. A typical mean matching technique, appropriate for both PPM and PAM schemes, is implemented digitally to obtain a good template for symbol detection. Joint estimation and detection performance of this family of digital receivers, using finite number of bits in analog-to-digital conversion and finite noisy observations, is analyzed. Closed form results are derived and verified by computer simulations. In addition, the effect of time offset between the reference pulse and information carrying pulse is studied. Overlap of the two pulses does not incur noticeable performance degradation. The proposed analytical framework can be applied to study detection performance of other related digital receivers not covered in this paper     

基于窗函数的非均匀步进频信号设计

针对均匀步进频连续波信号脉冲压缩处理过程中加窗处理抑制旁瓣导致信噪比损失的问题,提出了一种基于窗函数的非均匀步进频信号设计方法。首先根据分辨率和最大作用距离要求设计了步进信号总带宽和步进脉冲数,然后根据旁瓣要求和选择的窗函数设计了非均匀频率步进,最后根据雷达作用范围设计了频率步进量化间隔。该步进频信号呈现中间脉冲步进频率间隔小,两边脉冲步进频率间隔大的特点,在非均匀傅里叶逆变换脉冲压缩处理过程中无须加窗处理即可获得较低旁瓣,避免了加窗处理导致的信噪比损失。点目标仿真结果和实测数据处理结果验证了该非均匀步进频信号设计方法的有效性。      

A simple transmit diversity system for fading channels using shaped sinusoidal functions

This paper proposes a transmit-diversity system using a pair of orthogonal pulses. The system uses a set of orthonormal-basic functions, which contains four shaped-sinusoidal pulses with the same frequency. The first two elements in the set are shaped sine and cosine pulses. The second two elements are the same sine and cosine pulses but they are shaped with the Hilbert transform of the shaping pulse of the first two elements. The modulator in the proposed system produces two modulated symbols for each data symbol. It uses the first two elements in the proposed set in modulating the first modulated symbol and the second two elements in modulating the second modulated symbol. The modulated symbols are transmitted though two antennas. The diversity order of the proposed system is twice the number of antennas in the receiver. In the proposed system, no space-time coding is used and the channel gains change every symbol period. This is different from the Multiple-Input-Multiple-Output (MIMO) system. The receiver of the proposed system consists of two matched filters for each receiving antenna. No special detectors or interference cancelation techniques are used because there is no interference between the outputs of the matched filters.     

Orthonormal pulses for high data rate communications in indoor UWB systems

In this letter, we propose novel pulses which not only meet the power spectral mask of the Federal Communications Commission (FCC) for indoor Ultra-wideband (UWB) systems but also preserve orthogonality at the correlation receiver. The proposed pulses are derived from a parametric closed-form solution. Thus, multiple orthonormal pulses that comply with the FCC mask without additional frequency shifting or bandpass filters can be generated for high data rate communications or multiple access schemes. Simulation results demonstrate that high data rate communication is achieved by the proposed orthonormal pulses via pulse shape modulation and pulse position modulation.     

分频段RWR/ESM脉冲重叠概率分析

当前战场电磁环境非常复杂,雷达脉冲信号非常密集,脉冲重叠是雷达告警器/电子支援(RW R/ESM)接收机面 临的重要问题之一。从理论上对分频段RWR/ESM接收机的脉冲重叠概率进行了分析,推导 出多频段RWR/ESM接收机的脉冲重叠概率计算公式。仿真结果虽然验证了分频段可以降低RWR /ESM接收机的脉冲重叠概率,然而固定的分频段方式并不能使得脉冲重叠概率最小;对于确 定分频段数量的RWR/ESM接收机,在特定的电磁环境下,存在最佳的频段划分方式可使RWR /ESM接收机的脉冲重叠概率取得最小值。     

超结构光纤光栅的正交波分复用系统实现方案及接收机串扰分析

解释了超结构光纤光栅(SSFBG)作为脉冲成型滤波器的特性,说明SSFBG能够产生规则的时域矩形光脉冲,在频域上功率谱密度表现为sinc函数的形式.当光波道的频率间隔为码元速率的整数倍时,相邻波长的功率谱零点位于信号波长的中心频率处,频谱正交交叠.研究了一种基于SSFBG的正交波分复用(OWDM)系统,发送端用SSFBG进行脉冲整形,接收端采用窄带滤波器.给出基于理想窄带滤波器和高斯窄带滤波器两种接收机的串扰噪声模型,并得出了仿真结果.结果显示,两种窄带滤波器均可抑制严重的信道串扰,当接收机窄带滤波器通带足够窄时,接收机串扰比信道串扰降低约10 dB;理想窄带滤波器优于高斯窄带滤波器2～5 dB.     

The effect of laser chirping on lightwave system performance

Directly modulated semiconductor lasers exhibit a dynamic wavelength shift (chirping) arising from gain-induced variations of the laser refractive index. The effect of laser chirping on the performance of multi-Gb/s lightwave systems operating at a wavelength of 1550 nm is investigated. Models suitable for computer-aided analysis are used to describe the dynamic response of the laser and the propagation of chirped optical pulses through a step-index single-mode optical fibre. A truncated pulse train, Gauss quadrature rule method is used to evaluate the average bit error rate of the receiver. This permits pattern effects in the transmitted optical waveform due to the laser dynamics and nonlinear optical power transmission properties of optical fibers to be included in the system model. The influence that modulation and device parameters have on the receiver sensitivity is assessed     

Performance analysis and tradeoffs for dual-pulse PPM on optical communication channels with direct detection

The performance and tradeoffs of multipulse position modulation (MPPM) are investigated and compared with that of the traditional (single) pulse position modulation (PPM) scheme typically employed on the optical direct-detection channel. While the primary motivation for the consideration of the problem is to provide performance improvement for deep-space optical communications where narrow high-peak-power transmitted pulses offer significant advantages in terms of detection probabilities and background suppression capabilities at the receiver, the results obtained are sufficiently generic as to apply to other applications.     

光子晶体光纤中基于交叉相位调制的脉冲压缩

为了研究飞秒双脉冲在光子晶体光纤不同色散区的非线性传输过程,采用分步傅里叶方法求解耦合的非线性薜定谔方程组,并进行了理论分析。讨论了不同抽运功率、不同抽运脉冲啁啾参量以及不同脉宽比对信号脉冲压缩的影响。结果表明,基于交叉相位调制效应,弱信号脉冲不仅能够被压缩,而且光纤存在最佳压缩长度。增大抽运脉冲输入功率,选取正啁啾抽运脉冲,可以得到更大的信号脉冲压缩因子,同时最佳光纤长度减小。另外,不同的脉冲宽度对信号脉冲的压缩产生大的影响,较窄脉宽的抽运脉冲易于产生较短的压缩信号脉冲。这一结果对用光子晶体光纤压缩弱信号脉冲提供了理论参考。     

Influence of noise in optical pulse source on soliton transmission

This paper performed a 10-Gb/s optical soliton transmission experiment in a sliding frequency recirculating loop and found that the noise in the optical pulse source decreased error-free distance. This is because the mean frequency of soliton at the pulse source is modulated by the noise which results in the increase of timing jitter at the receiver even in a strong sliding frequency controlled soliton transmission line. Jitter in arrival time of transmitted solitons was theoretically analyzed to verify experimental results