An improved cyclostationary feature detection based on the selection of optimal parameter in cognitive radios

Spectrum sensing is an important part of cognitive radio systems to find spectrum hole for transmission which enables cognitive radio systems coexist with the authorized radio systems without harmful interference. In this paper, an improved cyclostationary feature detection method is proposed to reduce computational complexity without loss of good performance based on the optimal parameter selection strategy for choosing detection parameters of cyclic frequency and lag. Taking binary phase shift keying (BPSK) and quadrature phase shift keying (QPSK) signals as examples, the theoretical analyses are presented for choosing the optimal parameters. Simulation results are given to certify the correctness of the proposed parameter selection strategy and show the performance of the proposed method.     

A selection scheme for optimum number of cooperative secondary users in spectrum sensing

An optimization scheme for choosing the optimum number of secondary users in cooperative spectrum sensing based on the cyclostationary feature detection with Neyman-Pearson criterion is proposed in this paper. The optimal soft combination test statistic for the cooperative spectrum sensing based on cyclostationary feature detection is derived according to the generalized likelihood ratio test and its corresponding detection performance is deduced. A target function, considering two important parameters as the resource use efficiency and the number of samples employed by each cooperative secondary user in the system design, is constructed to obtain the optimum number of cooperative secondary users. It can be found that the selection scheme is to make a tradeoff between the system complexity of the cognitive radio network and the global sensing performance of the cooperative spectrum sensing.     

BLIND DIFFERENTIAL ADAPTIVE MULTIUSER DETECTION

IntroductionThe problem of combating multi- access interfer-ence ( MAI) in CDMA systems has receivedgreat attention recently[1～ 3] . In Ref. [4 ] ,M.Honig employed a blind adaptive multiuser de-tector based on the minimization of mean- out-put- energy( MOE) to overcome MAI,and itre-quired no more knowledge than did the conven-tional single- user receiver.Surplus energy wasemployed to suppress the effects of multi- accessinterference and thus provided an optimal detec-tion solution. The…     

基于小波变换的频谱检测算法分析

文章分析了认知无线电频谱检测中匹配滤波检测、能量检测、周期平稳过程特征检测的性能,指出了噪声对各自检测性能的影响,给出了一种基于小波变换的信号频谱检测算法,着重对含噪2FSK、2PSK信号进行分离仿真。仿真结果表明,该算法可以有效地进行信号的成分分离,降低了噪声的频谱检测的影响。     

Multi-channel spectrum sensing in cognitive ad-hoc networks: An energy-efficient manner

Cognitive radio,which is capable of enabling dynamic spectrum access,is a promising technology in future wireless communication.The feasibility of cognitive radio network greatly depends on the energy efciency and reliability of spectrum sensing technology.In this paper,spectrum sensing in cognitive ad-hoc network（CAN）with wide-band dynamic spectrum is considered.A cognitive cluster head（CCH）is set and responsible for dividing the wide-band spectrum into multiple sub-channels;it can either sense sub-channels in a centralized manner,or make use of sensing modules to sense sub-channels in a distributed manner.Then cognitive users（CUs）can get sensing results and access to the available sub-channel.We take the cost of control message into consideration and formulate the energy consumption of CAN in terms of sub-channel sampling rate and whole-band sensing time.We define energy efciency intuitively and solve the energy efciency optimization problem with sensing reliability constraints by constructing a parametric problem and obtain the optimal sampling rate and the wholeband sensing time.Power dissipation model of a practical A/D convertor（ADC）is introduced,and numerical results are given to show the energy efciency performance of two diferent sensing manners.     

一种新的循环谱统计量频谱感知算法

为了提高认知无线电中感知用户对授权用户（主用户）的检测概率,提出一种新的基于循环谱统计量的主用户信号检测算法．该算法利用循环谱离散频域平滑方法,对信号的循环谱在循环频率处建立合理的检测统计量,然后求解得到对应不同虚警概率的判决门限,以使感知用户能检测信噪比更低的授权用户信号．该算法具有检测结构简单,易实现的特点．仿真结果表明,在高斯白噪声信道中,虚警概率为0．1,频域平滑累积次数为255,在信噪比为-16dB的条件下,与Dandawate-Giannakis（DG）方法相比,本文算法的检测概率提高23％．     

ENDPOINT DETECTOR OF NOISY SPEECH SIGNAL USING A RECURRENT NEURAL NETWORK

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多特征多阈值级联AdaBoost行人检测器

为了满足更快、更准、更鲁棒的行人检测需求, 考虑交通监控视频图像质量不高与局部特征不明显的缺点, 采用简单的行人特征来实现行人检测。除矩形度、高宽比、轮廓复杂度、宽度比、行人面积特征外, 特定选用了对遮挡等干扰具有强鲁棒性的头部圆形度这一简单的局部特征。考虑交通监控视频图像中行人的尺寸变化, 引入区域划分策略划分图像区域。兼顾高检测率和低误检率, 根据分类误差最小原则与正样本分类率最大原则训练多个单特征多阈值AdaBoost行人检测器。为了优化多个行人检测器级联后的检测性能, 在兼顾检测性能和检测速度的基础上, 定义了以贡献率作为行人检测器的级联规则, 依据贡献率大小确定的级联次序为基于高宽比、宽度比、矩形度、行人面积、轮廓复杂度和头部圆形度的行人检测器, 依次进行级联, 建立了新的多特征多阈值级联AdaBoost行人检测器。选用3个交通场景对行人检测器进行测试, 并与单级AdaBoost行人检测器与现有2种级联AdaBoost行人检测器进行比较。分析结果表明: 在3个交通场景的检测中, 相比其他几种行人检测器, 多特征多阈值级联AdaBoost行人检测器具有较高检测率、较快的检测速度和较低误检率, 检测率最低为96.70%, 误检率最高为0.67%, 检测时间小于5s, 满足交通场景中对行人检测实时性和可靠性的要求。     

EFFECTIVE PITCH ESTIMATION ALGORITHM UNDER LOW SNR CIRCUMSTANCE

ＥＦＦＥＣＴＩＶＥＰＩＴＣＨＥＳＴＩＭＡＴＩＯＮＡＬＧＯＲＩＴＨＭＵＮＤＥＲＬＯＷＳＮＲＣＩＲＣＵＭＳＴＡＮＣＥＬｕＷｅｉ（陆伟）ＣｈｅｎＪｉａｎ（陈健）ＣｈｅｎＹａｊｕｎ（陈亚骏）（ＤＳＰＲｅｓｅａｒｃｈＩｎｓｔｉｔｕｔｅ，Ｄｅｐｔ．ｏｆＥｌｅｃｔ...     

Magnetic Tile Surface Defect Detection Based on Texture Feature Clustering

In the field of magnetic tile surface detection, artificial detection efficiency is low, and the traditional image segmentation algorithm cannot show good performance when the gray scale of the magnetic tile itself is small, or the image is affected by uneven illumination. In view of these questions, this paper puts forward a new clustering segmentation algorithm based on texture feature. This algorithm uses Gabor function spectra to represent magnetic tile surface texture and then uses a user-defined local product coefficient to modify Gabor energy spectra to get the center number of fuzzy C-means(FCM) clustering. Moreover, the user-defined Gabor energy spectra image is segmented by clustering algorithm. Finally, it extracts the magnetic tile surface defects according to the changes of regional gray characteristics. Experiments show that the algorithm effectively overcomes the noise interference and makes a good performance on accuracy and robustness, which can effectively detect crack,damage, pit and other defects on the magnetic tile surface.     

Reputation-based collaborative spectrum sensing scheme in cognitive radio networks

Collaborative spectrum sensing is proposed to improve the detection performance in cognitive radio (CR) networks. However, most of the current collaborative sensing schemes are vulnerable to the interference of the malicious secondary users (SUs). In this paper we propose a reputation-based collaborative spectrum sensing scheme to improve the security of cooperative sensing by mitigating the impacts of misbehaviors. The fusion center calculates the reputation rating of each SU according to their history reports to weight their sensing results in the proposed scheme. We analyze and evaluate the performance of the proposed scheme and its advantages over previous schemes in expansibility and integrity. Simulation results show that the proposed scheme can minimize the harmful influence from malicious SUs.     

改进SSD模型在高分二号遥感影像中高速公路收费站位提取的应用

以高分二号遥感影像中的高速公路收费站为研究对象,选取了北京、山西、河南、广东、福建5个省市2019年的高速公路收费站点位和0.8 m遥感影像,通过图像预处理、样本标注、裁切、数据增强、样本集划分的步骤制作训练样本集;引入“多尺度特征融合”的方法对SSD目标检测模型进行改进,通过增加“转置卷积”和“拼接”操作,将高层次特征图像的语义特征赋予低层次特征图像,以增强上采样质量与特征融合能力,从而提升了模型对小目标收费站的检测效果;将改进SSD模型用于2019年福建省高分二号影像中的收费站点位提取,沿福建省高速公路路网矢量对影像进行自动切片,将切片输入模型中进行目标检测;保留有收费站的切片,使用非极大值抑制去除多余的检测框,将剩余的检测框的坐标变换为中心点的坐标,可以直接输出得到高速公路收费站的中心点矢量,从而实现对于收费站点位的端到端自动化提取。研究结果表明：改进SSD模型的精度、召回率及二者的调和平均数分别为0.86、0.88和0.87,均优于传统的SSD, VGG, Faster R-CNN和特征金字塔网络模型。可见,对收费站点位的自动提取可以大大提高公路管理者的工作效率,有效满足公路管理者的实际工作需求。     

水中目标水压场信号特征提取与检测研究

利用目标信号功率主要集中在低频部分的特点，用功率谱估计方法提取低频信号的能量作为特征，提出了所谓的浮动阈值方法，对信号滑动地进行目标检测．通过对实验船模水压场信号进行检测验证。讨论了在各种不同情况下，目标信号的特征提取及目标检测方法的效果，验证了该方法的有效性．     

应用小波变换检测噪声中的信号

研究了基于小波变换的信号检测问题,提出了多分辨似然比的概述,表明对检测问题存在一些特定的时频空间,在其中信号的大部分能量得到保存,而噪声能量很快减少,因此应用小波变换,通过对特定的时频空间的似然比分析较容易判断噪声是否存在信号。     

SPEECH ENHANCEMENT BASED ON DYNAMIC NOISE ESTIMATION WITHIN AUTO-CORRELATION DOMAIN

IntroductionTo improve the robustness of recognition sys-tems in real environment,many theories and ap-proaches have been brought forward to suppressthe environmental noise ( background noise,chan-nel distortion,etc) ,and they can be divided intothree types according to their thoughts:speech en-hancement,robust feature vector and model com-position. The approach of speech enhancementconsiders extracting clean speech signal fromspeech signal corrupted by noise,typically as SSmethod[1] ( to supp…     

一种有效去除图像中脉冲噪声的滤波算法

为了抑制脉冲噪声,根据脉冲噪声点和边缘像素点的特征,提出了一种新的基于脉冲噪声点检测的滤波算法.实验结果表明,与传统中值滤波相比,这种新算法很好地保留了图像的细节,尤其在噪声密度较低时,滤波性能更加优越.     

窄带干扰条件下水声OFDM系统LMMSE信道估计算法

因为正交频分复用（OFDM）系统中强窄带干扰引起水声信道估计性能退化,因此,提出了一种可实用的线性最小均方误差（LMMSE）信道估计方法.该方法结合最小二乘（LS）信道估计结果对受窄带干扰（NBJ）和加性高斯白噪声（AWGN）噪声干扰的导频子载波进行辨别,从而获得最有效信道抽头;根据导出的理论模型,给出了信道自相关、窄带干扰信号和噪声功率等参数的近似估计方法;并采用傅里叶变换以避免矩阵的求逆运算,减少了计算复杂度.仿真结果表明,在强干扰信号条件下,文中提出的方法接近理想状态的LMMSE方法.     

高速列车气动噪声数值仿真

建立了高速列车组包括头车、中间车、尾车及外部空间在内的气动噪声计算物理模型,从声学理论出发,结合列车实际运行的边界条件,运用以稳态结果作为初始值进行瞬态计算,预测了高速列车气动噪声,并对采用直接瞬态法计算气动噪声的可行性进行了分析计算.研究结果表明气动噪声分布于很宽的频带内,无明显的主频,属于宽频噪声.在低频中气动噪声...     

PIC-MF-based Iterative Receiver for Multiuser Space Frequency Block Coding Systems

A novel low-complexity iterative receiver for multiuser space frequency block coding (SFBC) system was proposed in this paper. Unlike the conventional linear minimum mean square error (MMSE) detector, which requires matrix inversion at each iteration, the soft-in soft-out (SISO) detector is simply a parallel interference cancellation (PIC)-matched filter (MF) operation. The probability density function (PDF) of PIC-MF detector output is approximated as Gaussian, whose variance is calculated with a priori information fed back from the channel decoder. With this approximation, the log likelihood ratios (LLRs) of transmitted bits are under-estimated. Then the LLRs are multiplied by a constant factor to achieve a performance gain. The constant factor is optimized according to extrinsic information transfer (EXIT) chart of the SISO detector. Simulation results show that the proposed iterative receiver can significantly improve the system performance and converge to the matched filter bound (MFB) with low computational complexity at high signal-to-noise ratios (SNRs).     

自由表面射流迁移域流动结构研究

针对自由表面射流迁移域的流动结构的研究欠深入的问题，文中对具有喷针机构的轴对称无旋粘性射流进行数值解析，探究了射流迁移域的形成机理和表现形式，并分析不同喷针行程下射流迁移域的能量以及流动特征。