频谱相关检测法在大频偏低信噪比扩频通信的载波频率提取中的应用

基于周期平稳信号特征和频谱相关密度,本文提出了利用频谱相关处理提取大频偏低信噪比扩频通信信号的载波频率的频谱相关检测方法.这种方法的检测性能优于常规经典方法,并有更好的抗噪声和干扰的能力.     

Clover-2000短波通信协议信号检测技术

如何快速检测具有特定协议的信号是无线电频谱监测领域的重要任务之一。针对短波频谱监测中的Clover-2000协议信号的宽带检测问题,提出了基于频谱模板匹配和瞬时谱自相关判别的Clover-2000协议信号检测技术,通过预先建立Clover-2000协议信号频谱模板,逐点滑动求最大保持谱与频谱模板的相关系数,构造检验统计量实现该协议信号的初步检测。之后针对模板匹配方法无法区分Clover-2000与2GALE信号的问题,应用瞬时谱自相关判别的方法,进一步区分Clover-2000与2GALE信号。最后通过仿真试验验证了算法的有效性。     

基于D-S证据理论的循环平稳频谱协作感知

为了避免干扰授权用户的正常通信,认知无线电系统需要较好的频谱检测性能。提出了基于循环平稳特征和D-S证据理论的多天线多用户频谱协作感知方法。分析了多天线接收信号的谱相关函数,在频域按照最大比合并的方法合并各天线接收信号,得到合并信号的谱相关函数。依据谱相关函数的能量,在多用户中采用D-S证据理论做协作频谱检测。仿真分析表明,基于循环平稳特征和D-S证据理论的多天线多用户频谱协作感知方法可有效改善认知无线电系统检测性能。     

基于相关标识符的频谱水印嵌入与提取方法

为有效标识无线电设备身份信息,快速确定无线电干扰,提出了一种基于相关标识符的频谱水印嵌入与提取方法.该方法中发射端在标识符嵌入控制模块的控制下将频谱水印嵌入位置标识符嵌入到通信信号中,然后通过对含有频谱水印嵌入位置标识符的通信信号小波分解低频系数进行量化来嵌入频谱水印;接收端通过分析相关标识符的自相关和互相关特性来检测频谱水印,对接收到的中频信号小波分解低频系数实施量化处理来提取频谱水印.理论分析与仿真结果表明:提出的方法能够在不对原始信号正常解调产生有害干扰的条件下,可有效提取频谱水印,不需解调原始信号,可有效减少频谱水印提取的复杂度,为有效标识和识别无线电设备身份提供了技术手段.     

基于循环前缀频域自相关的OFDM信号频谱感知

针对无线通信频谱资源有限并且利用率非常低的问题,研究了认知无线电系统中基于信号典型特征的频谱感知策略,并进行动态频谱检测.提出了一种基于循环前缀频域自相关的频谱感知算法,利用正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)信号的循环前缀具有循环平稳特性,在信号频域进行自相关运算,设定判决门限,完成对信号频谱的检测,同时具备较好的抑制平稳噪声和干扰的能力.在低信噪比或者噪声不确定度大的应用场景下,能够获得比能量检测方法更优、更稳定的频谱感知效果,增强了噪声鲁棒性.在算法中采用双门限检测,进一步减弱了噪声不确定度对检测性能的影响,提高了频谱感知性能.     

降噪自编码器用于频谱感知对抗防御模型

基于深度学习的频谱感知模型虽检测性能优异，但普遍具有脆弱性，容易受到频谱对抗攻击的干扰。为了防御这种攻击，提出使用降噪自编码器过滤对抗信号，并在此基础上提出了一种结合降噪自编码器和防御蒸馏的联合防御方法。利用对抗信号和干净信号预训练得到降噪自编码器，频谱信号经降噪自编码器过滤后用于训练感知分类器，在测试阶段，联合使用降噪自编码器和分类器。同时，为进一步缓解扰动对模型性能的影响，在分类器训练阶段，利用蒸馏算法平滑训练网络，提高模型泛化能力。实验结果表明，对于可以降低深度学习频谱感知模型检测概率的频谱对抗攻击，所提出的基于降噪自编码器的防御方法仍然能够拥有较高的检测概率和较低的攻击成功率。     

采用低秩稀疏建模的盲频谱检测算法

频谱检测技术是认知无线电的一项关键技术,传统的频谱检测方法或依赖于相关的先验信息,或受限于低信噪比和运算复杂度的影响,在实际应用中均有一定的缺陷。针对此问题,本文基于协方差矩阵的检测算法,结合低秩稀疏建模理论,建立了频谱检测的低秩稀疏模型,提出了一种改进的频谱检测新方法。所提方法不需要事先获取主用户信号和噪声功率等先验信息,对信号样本的协方差矩阵进行低秩稀疏分解,以低秩矩阵之间的特征差异来判决当前是否存在主用户信号。仿真实验验证了所提方法具有较好的检测性能和鲁棒性。      

NI PXIe-5667接收器具备一流的测量性能

美国国家仪器公司近日发布NI PXIe-5667频谱监测接收器，可用于无线电监测、干扰检测、频谱规则以及ITU推荐的相关应用。该NI PXIe-5667结合NI FlexRIO与NI LaBVIEW FPGA模块，可在FPGA硬件中进行实时射频信号分析，如连续频谱监测、谱图和高级信号处理，无需再延迟等待数据在主控制器或PC之间的传输。     

一种采用卡尔曼滤波与正则匹配的信号盲检测法

信号检测是电磁频谱感知的有效手段之一，但受电磁环境非平稳特性、样本数据有限性及傅里叶变换全域能量分布特性等诸多因素影响，使得基于快速傅里叶变换(Fast Fourier Transform, FFT)的频谱数据抖动较大，无法适应低信噪比、大动态范围的信号检测。为了提高信号检测性能，提出了一种采用卡尔曼滤波的频谱累积平滑方法，在此基础上提取了能够反映信号能量分布变化的曲率特征，设计了基于符号正则匹配的方法，实现对信号能量分布特征的检测。介绍了处理方法的主要原理并进行了仿真分析，结果表明在信噪比大于2 dB时，信号检测准确率达到100%,且相比能量检测门限法具有更优的搜索动态范围。     

基于压缩感知的通信信号频谱检测方法

频谱感知是无线通信网络中提高频谱利用率的关键。针对现有通信信号频谱检测方法抗噪性低的问题,文中提出一种基于压缩感知的频谱检测方法。该方法首先利用压缩感知理论对通信信号的宽频带进行稀疏采样,其次采用改进的平滑范数重构算法对信号循环谱进行重构,提高了信号循环谱的重构性能,最后在循环谱域实现频谱检测。仿真实验结果表明,改进的平滑范数重构算法对信号的重构精度优于正交匹配追踪算法,压缩感知信号频谱检测算法的抗噪性优于传统能量检测算法。     

Cyclostationarity-based filtering for narrowband interferencesuppression in direct-sequence spread-spectrum systems

This paper addresses the problem of narrowband interference suppression in direct-sequence spread-spectrum (DS/SS) techniques, which have been adopted to implement code division multiple access (CDMA) systems for wireless mobile communications. The theory of cyclic Wiener filtering, based on the cyclostationarity assumption for the signals involved in the reception problem, is applied to design single-channel adaptive frequency-shift filters which exploit both temporal and spectral correlation properties, i.e., the correlation between time- and frequency-shifted versions of the received signal. The numerical results show that receiving structures based on the proposed cyclostationarity-based interference suppression schemes largely outperform receivers that utilize conventional linear time-invariant suppressors, when they operate in highly contaminated interference environments     

A CDMA overlay system using frequency-diversity spread spectrum

The frequency bands currently used by existing narrow-band users might be shared with a code-division multiple-access (CDMA) spread-spectrum (SS) overlay system. Thus, the spectral efficiency is improved, providing more capacity for future personal communications services. Since both narrow- and wide-band signals interfere with each other, an SS modulation scheme with a good resistance to narrow-hand interference results in an increased number of acceptable overlay users. We study a frequency-diversity SS modulation scheme for which optimal detection in the presence of narrow-band interference is easy to implement. The acceptable number of overlay users is evaluated and compared to that of conventional direct-sequence SS (DS-SS) modulation schemes with and without interference rejection filters. The proposed system also presents the following advantage: by suppressing transmission of replicas where narrow-band signals (NBSs) are present, the mutual interference can be avoided completely     

直接序列扩频信号的检测方法研究与仿真

直接序列扩频信号(DSSS)具有很强的抗干扰能力、很低的被截获概率和良好的码分多址能力,在个人通信网、无线局域网、第三代移动通信、卫星通信以及军事战术通信等领域得到了广泛应用,因此对它的研究是宽带微弱信号检测与估计以及通信对抗领域的一个重要研究课题。本文针对直扩信号,以双相移相键控(Binary Phase Shift Keying,BPSK)为例,运用小波变换和循环谱相关方法相结合,在非合作情况下,从干扰的角度出发,给出了BPSK信号的参数检测方法和Matlab的仿真结果,为直扩信号的检测探讨了一种更有效的方法。     

Digital implementations of spectral correlation analyzers

The issues involved in the design of computationally efficient algorithms for spectral correlation estimation and the resulting impact on high-speed digital realization are addressed. The spectral correlation analyzer is characterized as a periodically time-varying quadratic system with a kernel possessing certain gross properties. The mean and variance of the output are expressed in terms of the kernel and the spectral correlation function of the input. Three realizations are analyzed in detail. One is based on the frequency-smoothing method of cross spectral analysis. The others are variants of the time-smoothing method. For each of these realizations, an exact expression for the quadratic system kernel is given, the digital implementation is developed, and a detailed complexity analysis is presented. High-speed pipeline realizations of the algorithms are analyzed, and related special issues are discussed. Examples involving the calculation of the spectral correlation function in near-real-time for broadband communications signals are discussed     

对流层散射信号的循环谱分析

简要阐述了对流层散射通信的接收信号的形式。提出了对流层散射通信信号的循环谱分析算法,并给出了散射通信常用的调制信号形式(带内两频QPSK)的循环谱相关函数和循环谱密度函数。通过使用MATLAB软件对算法在散射QPSK信号在无噪声和信噪比为0dB时的计算结果。仿真结果证实,循环谱相关分析方法是进行对流层散射通信信号的最佳谱分析方法之一。     

直扩信号伪码的盲估计方法的研究

对直接序列扩频通信的信号检测方法进行了综述,重点讨论了自相关域检测方法、四阶累积量方法、谱分析与信号子空间分解法,其中四阶统积量方法和谱分析与信号子空间分解法的最低检测门限远低于相关算法,谱分析与信号子空间分解法在直接序列扩频(DS/SS)信号的伪码周期估计以及伪码序列盲估计中,利用功率谱二次处理结合信号子空间分解的方法可以实现对低信噪比DS/SS信号的估计。     

基于循环谱分析的航空通信干扰信号检测

随着现代通信技术在航空领域的广泛应用,在机场环境下如何避免各干扰信号对航空通信的危害成为人们广泛关注的焦点问题。本文基于机场环境下的信号感知模型,提出一种基于支持向量机（SVM）和谱相关性的干扰信号感知算法,有效避免了外界信号对航空通信信号的干扰。该算法采用信号循环谱进行分析的方法提取特征向量,进而结合SVM分类器对航空干扰信号进行检测。仿真结果表明,本文算法对干扰信号具有较高的分类检测精度和良好的识别性能。     

Spread-spectrum signals and the chaotic logistic map

Chaotic systems provide a simple means of generating deterministic signals that resemble white noise. It is this noise-like property that provides the potential for applying chaotic systems in communications. In this work, we report a detailed study of the logistic map for use as direct-sequence spread-spectrum (DS/SS) codes. The advantages of the chaotic DS/SS codes are the almost unlimited number of distinct sequences of arbitrary lengths, the ease of generating these sequences, and the increased privacy afforded by the noise-like appearance of these sequences. Some design criteria are provided from the correlation properties of these sequences, and bit-error rate (BER) results are generated by Monte Carlo simulations.     

Direct-sequence spread spectrum narrowband interference rejectionusing property restoration

A new method of rejecting narrowband interference in direct-sequence spread spectrum (DS/SS) communications is presented. A typical approach is to reject the interference using a filter with large attenuation at the interference frequencies before despreading. The interference rejection method presented incorporates vector space projection techniques to suppress the correlated interference. Several signal characteristics are formulated which lead to constraint surfaces in the vector space of possible solutions. These constraint surfaces describe interference rejection solutions which introduce minimal distortion to the spread spectrum signal and simultaneously remove the interference. The constraint surfaces essentially correspond to spread spectrum signal estimates which, after interference rejection, conform to known characteristics of the transmitted spread spectrum signal. The formulation of the surfaces relies on prior knowledge about the spread spectrum signal correlation and spectral properties     

一种高效的混合M元扩频通信方案

为进一步提高扩频通信系统的频带利用率和抗截获性能,将正交扩频技术与码相位循环移位调制技术相结合,提出了一种新的高效多进制扩频通信方案。在正交信道的每条支路上,首先采用M元双正交扩频调制,再以每一个扩频码为原型码进行码相位循环移位调制,选用专用的伪噪声码进行同步,在接收端用基于变换域处理的循环相关器进行解扩。计算机仿真表明,该方案易于实现同步,同时有较高的频带利用率和更强的抗截获性能。该方案在卫星隐蔽通信、数据链通信等领域有较大的应用价值。