Noise amplitude modulation jamming signal suppression based on weighted-matching pursuit

To suppress noise amplitude modulation jamming in a single-antenna radar system, a new method based on weighted-matching pursuit （WMP） algorithm is proposed, which can achieve underdetermined blind sources separation of the jamming and the target echo from the jammed mixture in the single channel of the receiver. Firstly, the presented method utilizes a prior information about the differences between the jamming component and the radar transmitted signal to construct two signal-adapted sub-dictionaries and to determine the weights. Then the WMP algorithm is applied to remove the jamming component from the mixture. Experimental results verify the validity of the presented method. By comparison of the pulse compression performance, the simulation results shows that the presented method is superior to the method of frequency domain cancellation （FDC） when the jamming-to-signal ratio （JSR） is lower than 15 dB.

Cognitive anti-jamming receiver under phase noise in high frequency bands

This paper investigates the jamming sensing performance of the simultaneous transmit and receive based cognitive anti-jamming(SCAJ) receiver impaired by phase noise in local oscillators(LO) over fading channels. Firstly, energy detection(ED)based on the jamming to noise ratio(JNR) of the high frequency bands SCAJ receiver with phase noise under different channels is analyzed. Then, the probabilities of jamming detection and false alarm in closed-form for the SCAJ receiver are derived. Finally,the modified Bayesian Cramer-Rao bound(BCRB) of jamming sensing for the SCAJ receiver is presented. Simulation results show that the performance degradation of the SCAJ system due to phase noise is more severe than that due to the channel fading in the circumstances where the signal bandwidth(BW) is kept a constant. Moreover, the signal BW has an effect on the phase noise in LO, and the jamming detection probability of the wideband SCAJ receiver with lower phase noise outperforms that of the narrowband receiver using the same center frequency. Furthermore,an accurate phase noise estimation and compensation scheme can improve the jamming detection capability of the SCAJ receiver in high frequency bands and approach to the upper bound.

Low noise,continuous-wave single-frequency 1.5-μm laser generated by a singly resonant optical parametric oscillator

We report a low noise continuous-wave （CW） single-frequency 1.5-μm laser source obtained by a singly resonant optical parametric oscillator （SRO） based on periodically poled lithium niobate （PPLN）. The SRO was pumped by a CW single-frequency Nd：YVO4 laser at 1.06μm. The 1.02 W of CW single-frequency signal laser at 1.5 μm was obtained at pump power of 6 W. At the output power of around 0.75 W, the power stability was better than ±l.5% and no mode-hopping was observed in 30 min and frequency stability was better than 8.5 MHz in 1 min. The signal wavelength could be tuned from 1.57 to 1.59 μm by varying the PPLN temperature. The 1.5-μm laser exhibits low noise characteristics, the intensity noise of the laser reaches the shot noise limit （SNL） at an analysis frequency of 4 MHz and the phase noise is less than 1 dB above the SNL at analysis frequencies above 10 MHz.

The Response to Arbitrarily Bandlimited Gaussian Noise of the Complex Stretch Processor Using a Conventional Range-Sidelobe-Reduction Window

This paper derives a mathematical description of the complex stretch processor’s response to bandlimited Gaussian noise having arbitrary center frequency and bandwidth. The description of the complex stretch processor’s random output comprises highly accurate closed-form approximations for the probability density function and the autocorrelation function. The solution supports the complex stretch processor’s usage of any conventional range-sidelobe-reduction window. The paper then identifies two practical applications of the derived description. Digital-simulation results for the two identified applications, assuming the complex stretch processor uses the rectangular, Hamming, Blackman, or Kaiser window, verify the derivation’s correctness through favorable comparison to the theoretically predicted behavior.

A Probable Short Decimetric Type Ⅰ-like Noise Storm: Associated with Type Ⅲ Bursts?

A rare Type I-like noise storm was observed with the solar radio spectrometers (1.0-2.0 GHz and 2.60-3.8 GHz) at National Astronomical Observatories of China (NAOC) on September 23, 1998. We concentrate on checking the Type I-like noise storm occurred in the decay phase of a Type Ⅳ radio burst. This noise storm consists of many Type I bursts and isolated Type Ⅲ or Type Ⅲ pair bursts. It has a bandwidth of ≤0.5 GHz. The duration of each Type I burst is of the order of 100-300 ms. The total duration is greater than 11 minutes. The circular polarization degree of the components of Type Ⅰ and associated Type Ⅲ bursts are about 40%-100% and almost 100%, respectively, which is greater than that of the background continuum (nearly the precision of our instrument). This short decimetric Type Ⅰ-like storm may be another kind or the extension of the kind of metric Type Ⅰ storm, and may possess the duality of metric and decimetric radio emission. It may be in favor of an earlier emission mechanism of the fundamental plasma radiation due to the coalescence of Langmuir waves with low-frequency waves.

Performance Analysis of Outage Probability and Error Rate of Square M-QAM in Mobile Wireless Communication Systems over Generalized α-μ Fading Channels with Non-Gaussian Noise

This paper derives new and exact closed-form expressions for the average symbol error rate(SER) of square M-ary quadrature amplitude modulation(M-QAM) in wireless communication systems over theα-μfading channels subject to an additive non-Gaussian noise. The obtained expressions take into account static and mobile wireless receivers. In addition, a closed-form expression for the outage probability in mobile networks is obtained. Please note that all derived expressions in this paper a valid for integer and non-integer values of the fading parameters. Analytical results are presented to study the impact of noise shaping parameter, severity of fading, and mobility on the average SER. Monte-Carlo simulations results are also provided to validate the accuracy of the analytical results.

Suppressive Influence of Time- Space White Noise on the Explosion of Solutions of Stochastic Fokker- Planck Delay Differential Equations

It is generally known that the solutions of deterministic and stochastic differential equations （SDEs） usually grow linearly at such a rate that they may become unbounded after a small lapse of time and may eventually blow up or explode in finite time. If the drift and diffusion functions are globally Lipschitz, linear growth may still be experienced, as well as a possible blow-up of solutions in finite time. In this paper, a nonlinear scalar delay differential equation with a constant time lag is perturbed by a multiplicative Ito-type time - space white noise to form a stochastic Fokker-Planck delay differential equation. It is established that no explosion is possible in the presence of any intrinsically slow time - space white noise of Ito - type as manifested in the resulting stochastic Fokker- Planck delay differential equation. Time - space white noise has a role to play since the solution of the classical nonlinear equation without it still exhibits explosion.

Artificial Noise Aided Polar Codes for Physical LayerSecurity

The secrecy rates of the existing practical secrecy coding methods are relative low to satisfy the security requirement of 5 G communications.We propose an artificial noise(AN) aided polar coding algorithm to improve the secrecy rate.Firstly,a secrecy coding model based on AN is presented,where the confidential bits of last transmission code block are adopted as AN to inject into the current codeword.In this way,the AN can only be eliminated from the jammed codeword by the legitimate users.Since the AN is shorter than the codeword,we then develop a suboptimal jamming positions selecting algorithm with the goal of maximizing the bit error rate of the eavesdropper.Theoretical and simulation results demonstrate that the proposed algorithm outperforms the random selection method and the method without AN.

Semiannual velocity variations around the 2008 M_w 7.9 Wenchuan Earthquake fault zone revealed by ambient noise and ACROSS active source data

We continuously monitor the long-term seismic velocity variation of one of the major ruptured faults of the devastating 2008 Mw7.9 Wenchuan earthquake in China from July 2009 to January 2012,jointly using accurately controlled routinely operated signal system active source and seismic noise-based monitoring technique.Our measurements show that the temporal velocity change is not homogeneous and highly localized in the damaged fault zone and the adjacent areas.Velocity variations from the active and passive methods are quite consistent,which both are characterized by ±0.2 % seasonal variation,with peak and trough at winter and summer,respectively.The periodic velocity variation within fault zone exhibits remarkably positive correlation with barometric pressure with stress sensitivity in the order of 10-6Pa-1,suggesting that the plausible mechanism might be the crack density variation of the shallow subsurface medium of the damaged fault zone in response to the cyclic barometric pressure loading.

The Equilibrium Range of Wind Wave Spectra: an Explanation Based on White Noise

Laboratory experiments and field observations show that the equilibrium range of wind wave spectra presents a – 4 power law when it is scaled properly. This feature has been attributed to energy balance in spectral space by many researchers. In this paper we point out that white noise on an oscillation system can also lead to a similar inverse power law in the corresponding displacement spectrum, implying that the – 4 power law for the equilibrium range of wind wave spectra may probably only reflect the randomicity of the wind waves rather than any other dynamical processes in physical space. This explanation may shed light on the mechanism of other physical processes with spectra also showing an inverse power law, such as isotropic turbulence, internal waves, etc.

Automatic estimation and removal of noise on digital image

An spatially adaptive noise detection and removal algorithm is proposed.Under the assumption that an observed image and its additive noise have Gaussian distribution,the noise parameters are estimated with local statistics from an observed degraded image,and the parameters are used to define the constraints on the noise detection process.In addition,an adaptive low-pass filter having a variable filter window defined by the constraints on noise detection is used to control the degree of smoothness of the reconstructed image.Experimental results demonstrate the capability of the proposed algorithm.

FDA-MIMO雷达噪声卷积式干扰抑制方法

基于数字射频存储器(digital radio frequency memory,DRFM)产生的噪声卷积灵巧干扰兼具压制式和欺骗式干扰的效果,严重降低了雷达系统的探测性能。为解决此问题,本文提出了一种采用频率分集阵(frequency diversity array,FDA)-多输入多输出(multiple-input-multiple-output,MIMO)雷达的噪声卷积灵巧干扰对抗方法。经由雷达发射信号和噪声信号卷积调制所得的干扰信号在距离-多普勒维与目标回波呈现不同的分布特性。据此,首先利用干扰信号在多普勒域的白噪声特性获取多普勒清晰区的干扰样本,然后在此基础上逐距离门挑选样本以获得干扰协方差矩阵,最后通过距离-角度二维匹配滤波器抑制距离不匹配的主瓣干扰信号。仿真试验验证了本文所提抗干扰方法的有效性。

Optimal Periodic Pulse Jamming Signal Design for QPSK Systems

The problem of optimal periodic pulse jamming design for a quadrature phase shift keying（QPSK）communication system is investigated.First a closed-form bit-error-rate（BER）of QPSK system under the jamming of pulse signal is derived.Then the asymptotic performance of the derived BER is analyzed as the signal-to-noise ratio（SNR）grows to infinity.In order to maximize the BER of the QPSK system,the optimal parameters of periodic pulse jamming signal,including the duty cycle and signal-tojamming power ratio（SJR）,are found out.Numerical results are presented to verify our analytical results and the optimality of our design.

Nonstationary Filtering for Markov Jumping Systems with Fading Channel and Multiplicative Noises

This paper studies the nonstationary filtering problem of Markov jump system under l2 - l∞ performance. Due to the difference in propagation channels, signal strength and phase will inevitably change randomly and cause the waste of signals resources. In response to this problem, a channel fading model with multiplicative noise is introduced. And then a nonstationary filter, which receives signals more efficiently is designed. Meanwhile Lyapunov function is constructed for error analysis. Finally, the gain matrix for filtering is obtained by solving the matrix inequality, and the results showed that the nonstationary filter converges to the stable point more quickly than the traditional asynchronous filter, the stability of the designed filter is verified.

智能反射面辅助的抗干扰安全通信系统鲁棒资源分配算法

为了解决恶意干扰攻击、窃听和不完美信道状态信息造成的通信质量降低和安全性差等问题,该文提出一种智能反射面(IRS)辅助的抗干扰安全通信系统鲁棒资源分配算法。首先,基于合法用户的最小安全速率约束、最大发射功率约束和IRS相移约束,在非法节点不完美信道状态信息、干扰器波束成形向量未知的情况下,构建了一个联合优化基站的波束成形向量、人工噪声的协方差矩阵和IRS的相移矩阵的鲁棒资源分配问题。其次,为了求解该非凸问题,利用交替优化、Cauchy-Schwarz不等式、连续凸逼近和泰勒级数展开等方法,将原问题转化为易于求解的凸优化问题。仿真结果表明,与传统算法相比所提算法能有效提高系统安全性、降低功率开销、提高抗干扰裕度,且在一定信道误差范围内能够减低约35%的保密中断概率,具有较强的鲁棒性。

基于多维小波特征的有源雷达欺骗干扰识别

针对跟踪工作模式下常见雷达有源欺骗干扰识别问题,通过分析雷达信号和干扰模型,提出一种基于多维小波特征的识别算法。对目标回波多个相干处理间隔中的首个脉冲重复间隔内信号采样累积,构成一维离散序列,利用Mallat算法提取多尺度小波系数,计算不同尺度下小波系数的移位相关系数,并组成特征向量用于分类识别。构建不同参数的信号样本仿真,在信噪比为-5 dB时仍有高于80%的识别正确率。该算法能将距离假目标干扰和距离拖引干扰有效识别,证明了算法的准确性、通用性和严谨性。此外,针对实际情况,可以调整特征向量维度,选择更适合的母小波函数,进一步优化干扰识别效果。

基于噪声卷积调制的SAR多区域灵巧干扰方法

针对传统噪声卷积干扰存在的压制区域位置在方位向上不能灵活控制的缺陷,提出一种基于噪声卷积调制的SAR多区域灵巧干扰方法。该方法对截获信号进行距离向移频、方位向移相以及与噪声模板的卷积调制处理,以控制压制区域的位置;后对截获信号进行不同频率、相位的噪声卷积调制处理,以控制压制区域的数量。理论和仿真结果表明,所提方法实现了压制区域位置在方位向、距离向上的灵活控制,并实现了单一干扰机对多个待掩护区域的干扰,提高了干扰增益,干扰效果较好,对实际工程应用具有一定的参考价值。

Adaptive Threshold Clipper Combining Receiver for Fast Frequency Hopping Systems during Partial-Band Noise Jamming

Diversity combining technologies are analyzed for fast frequency-hopping spread spectrum systems during partial-band noise jamming to develop a novel combining receiver called an Adaptive Threshold Clipper Combining Receiver (ATCCR). The optimal clipping level for an ATCCR is analyzed, computed, and compared with several other diversity combining technologies. Since the ATCCR can estimate the power of the jamming and the number of jammed frequency cells to adaptively adjust the clipper's threshold, the system performance using the adaptive threshold clipper combining technique can be greatly improved.

16-QAM信号的最佳干扰分析

依托高效能电子战的背景,针对其缺乏理论依据的问题,本文从理论上分析了正交幅度调制(quadrature amplitude modulation,QAM)的最佳干扰样式,推导了信道为AWGN信道时M-QAM在二维数字调制干扰下的误码率通式,研究了基于凸分析的16-QAM通信系统的最佳干扰样式以及在最佳干扰下16-QAM通信系统的传输性能,分析了相位差、时延差对干扰效能的影响。仿真实验结果验证了M-QAM在二维数字调制干扰下的误码率公式的准确性,且理论分析和仿真实验均表明了当干信比大于-3 dB时,16-QAM通信系统的最佳干扰样式为QPSK。

利用接收机载噪比测量值的GNSS干扰源定位技术

由于GNSS信号在抵达地面时信号强度较低,极易遭受无意或蓄意的人为干扰,严重时甚至会导致导航和定位服务不可用,因此,定位和消除干扰源显得尤为重要.面向常见的压制式干扰,针对目前的定位方法主要是对原始采样信号进行处理,实现起来往往具有设备复杂、计算量大、成本高的问题.本文提出了一种利用普通商用接收机的载噪比(carrier-to-noise ratio,C/N0)测量值进行GNSS干扰源定位的方法,通过C/N0测量值估计干扰信号强度差,进而解算出干扰源位置.实测结果表明:视距条件下,在约11400 m2的监测区域中,该方法能够达到13.17 m的平均绝对定位误差,且耗时较少,可实现干扰源的有效定位.所提方法无需对接收机进行软硬件的改动,实现简单,成本低,利于工程应用.