基于信噪比测量的欺骗干扰检测方法

在捕获北斗信号的过程中,接收机根据预先设定好的信号搜捕策略和门限值来捕获信号;欺骗干扰源通过产生虚假的相关峰和增加噪声基底,可以有效地干扰普通型北斗接收机正常的捕获工作;针对欺骗信号检测问题,在分析欺骗信号入侵对接收机噪声基底影响的基础上,提出了在捕获阶段利用信噪比(SNR)检测技术识别欺骗干扰信号的方法,并对其有效性进行了分析;仿真结果表明,采用该方法的接收机具有一定程度的欺骗干扰识别能力,为提高GNSS接收机抗干扰能力提供了有益的参考 。     

北斗B1信号捕获跟踪算法的软件仿真研究

针对北斗B1频率的I支路信号,设计并实现了北斗软件接收机的基带处理部分。阐述了北斗B1频点信号的扩频体制和产生过程,并行码相位搜索捕获策略以及鉴相辅助跟踪环路,并设计了二阶数字环路滤波器,滤波器参数取ζ=0.707,B_n=25(Hz)。同时采用Matlab软件,仿真北斗中频数字信号,编码实现捕获跟踪算法,并分别通过对仿真信号和真实卫星信号的捕获跟踪,验证捕获跟踪算法的可行性,并提出锁频环辅助锁相环算法的改进思路。为进一步开展北斗软件接收机相关技术研究打下了基础。     

转发式北斗导航卫星信号性能评估的研究与实现

北斗一代在使用过程中存在隐蔽性不良,定位实时性差等问题,为了实现北斗导航信号的性能评估,相对于以往的硬件形式,如硬件接收机、频谱分析仪、矢量网络分析仪等,提出了以软件接收机的方法对北斗导航信号进行性能评估。首先分析了转发式北斗导航信号评估的意义、内容与方法,并采用软件接收机的形式进行评估;然后研究了转发式北斗导航的信号性能评估关键技术,给出了捕获、跟踪、评估参数计算的程序流程;最后根据实测数据在Linux高性能集群系统上进行了测试验证,实现了北斗导航信号的捕获、跟踪以及评估中的评估参数计算。测试结果表明,文章中的设计方法可实现北斗导航信号性能的评估,效果良好,评估内容、指标易于调整,便于软件算法参数的测试、升级,可为后续的卫星导航信号评估以及算法测试等提供了一定的依据。     

水声瞬态信号短时谱形态及谱相关法检测

通过对海上记录时间大于4h的几十条水声目标噪声进行归一化短时谱图即船谱图方法分析,归纳出一些典型的瞬态信号的时频分布形态。有竖条分布、横条分布、“麻花状”的共振峰滑动型和能量集中的正方型分布等,为进一步研究和识别瞬态信号打下基础。文章还调查了谱相关技术（二阶累积量谱）在干扰噪声中检测水声瞬态信号的性能。计算机模拟和对18个实际瞬态信号的分析说明用谱相关技术检测瞬态信号的有效性,近80％的实际信号比常规功率谱检测有3～6dB的增益。文章最后研究用谱相关提取瞬态信号模态的技术,给出了3个无源目标瞬态信号模态较清晰的图像,为识别瞬态信号提供特征。     

一种光电容积脉搏信号的峰值点自动识别方法

光电容积脉搏信号的峰值点自动识别直接关系到无创血氧饱和度测量与脉搏波峰-峰间期提取的准确率。提出一种小波联合识别方法：基于小波多分辨率分析原理校正影响脉搏波峰值点幅值的基线干扰,再利用二次样条小波模极大算法自动识别峰值点。将该方法应用到自行研制的光电容积脉搏波测量系统中,对采集的信号进行了校正与峰值点识别,通过在信号中增加随机噪声以评价方法的稳定性与可靠性,然后利用10组实测数据,对比本方法与传统差分阈值法的峰值点识别准确率,进一步评价方法的有效性。结果表明：本方法在较好地消除了基线干扰的基础上,在染噪的信号中仍然会较精确地检测出脉搏波主波峰,具有较好的抗干扰能力,有利于提高血氧饱和度检测及峰-峰间期提取的准确性,从而有助于后期人体呼吸功能评价与心率变异性分析。     

激光告警接收机灵敏度和信噪比分析及实验验证

为了对抗现代战争中日趋严重的激光威胁,激光告警技术已成为亟需研究的课题之一。灵敏度和信噪比是激光告警系统重要的性能指标,它直接影响告警系统整体的探测性能。文中根据信号统计检测理论,提出了一种计算相干探测光谱识别型激光告警接收机灵敏度和信噪比的方法。首先,分析了激光信号和接收机噪声的概率分布。然后,基于阈值探测理论和奈曼—皮尔逊准则,通过引入探测概率因子和虚警概率因子,建立了信号电流方程,进而得到了灵敏度和信噪比的计算表达式。最后,利用该方法对自行研制的光栅衍射激光告警接收机的探测灵敏度和信噪比进行了理论计算和相关的实验验证, 结果表明：由该方法计算的灵敏度和信噪比与实验结果基本相符。     

高荧光及强背景噪声情况下表面增强拉曼散射光谱提取方法研究

试提出一种高荧光及强背景噪声情况下表面增强拉曼散射光谱的提取方法。该方法从分析荧光谱及背景噪声信号的组成入手,构建相应模型对荧光谱及噪声信号进行估计,通过比较估计结果与实际数据的差别识别谱峰信号,并定位谱峰的基底位置。通过在若丹明6G、前列腺特异抗原测量及pH值传感实验中的实际应用检验可知,该方法可提高表面增强拉曼散射光谱信号的分辩率和测量准确度,在微量物质鉴别及物质含量定量测量方面有较好的应用前景。     

一种基于粒子滤波的雷达抗欺骗干扰方法

针对雷达的抗欺骗干扰问题,利用欺骗干扰信号强于目标信号的特点,基于粒子滤波进行了抗欺骗干扰研究。当存在欺骗干扰时,粒子滤波中各粒子的重要性权值会明显减小,据此可以检测干扰,并对受到干扰的数据点进行置零处理,使得欺骗干扰不再与匹配滤波器匹配,从而达到抑制干扰的目的。设计的粒子滤波算法不需要估计系统状态转移函数、系统量测噪声,从而使得算法更具实用性。仿真结果表明,该算法能有效地抑制欺骗干扰,且对干信比不敏感。     

卫星导航接收机自动测试系统

为了满足卫星导航接收机整机性能快速、精确测试的需求,实现对导航接收机性能的自动测试,构建了一种基于NI PXI硬件平台,采用导航信号模拟器、虚拟仪器技术和Microsoft Visual Studio 2008软件进行开发的卫星导航接收机自动测试系统。系统实现了多导航接收机的定位精度、冷启动首次定位时间、热启动首次定位时间、捕获灵敏度、速度精度的并行自动测试。良好的人机交互界面与多接收机并行测试的稳定运行,大大缩短了测试时间,提高了测试效率。通过对北斗导航接收机大量测试,结果表明该卫星导航接收机快速测试系统对于导航接收机整机性能并行测试快速、有效。     

电力系统故障的微弱信号检测方法的研究

为了确保电力系统能够安全稳定的运行,实时检测故障中的微弱信号。通过噪声干扰情况下微弱信号的不同变化进行研究,得到了一种微弱信号的DUFFING混沌检测模型。系统发生故障时会产生相应的微弱信号,运用DUFFING混沌振子法分析不同情况下微弱信号的时域波形和相平面轨迹变化规律,并建立数学检测模型,对其幅值进行混沌检测仿真。结果表明,当r=0.8264V,w=1rad/s时将白噪声和微弱正弦信号同时加入后,此时,混沌状态、大尺度周期状态的相平面运行轨迹依然在进行有规律的运行,可以清晰的观察出需要检测的微弱信号。在强噪声存在于系统中时,该方法明显克服了噪声对信号稳定性的干扰,能精确有效检测微弱信号。系统在应对不同工作环境、仪器设备老化等情况时,提高了检测效率,保证系统的稳定运行。     

噪声源非均匀分布海洋环境噪声水平声能流理论分析

研究水平非均匀分布噪声源所产生的各向异性海洋环境噪声场声能流。提出一种混合型非均匀分布噪声源模型,理论分析并数值计算了此模型情况下的环境噪声场水平声能流。结果表明:非均匀分布噪声源引起的海洋环境噪声场具有显著非零平均水平声能流;不同接收点的水平声能流明显不同;其幅度和方向取决于各个局部海域不等强度声源产生的合成噪声声能流矢量和。研究了两接收点间噪声的声压和振速水平分量、振速水平分量归一化相关系数随两接收点间距的关系,各量之间表现出较强相关性,为分析水下矢量声场目标探测技术性能提供理论依据。      

Noise Stability of SIS Receivers

There is a strong interest in the submillimeter astronomy community to increase the IF bandwidth of SIS receivers in order to better facilitate broad spectral linewidth and continuum observations of extragalactic sources. However, with an increase in receiver IF bandwidth there is a decrease in the mixer stability. This in turn effects the integration efficiency and quality of the measurement. In order to better understand the noise mechanisms responsible for reducing the receiver stability, we employed a technique first described by D.W. Allan and later elaborated upon by Schieder et al. In this paper we address a variety of factors that degrade the noise stability of SIS receivers. The goal of this exercise is to make recommendations aimed at maximizing SIS receiver stability.     

激光位置探测器的角位移测量精度分析

作为激光光斑位置探测器,象限探测器和位敏探测器被广泛应用于激光光斑跟踪、监控、位置检测和定位等领域。对这两种探测器的角位置测量精度进行了探讨,分析了影响精度的主要噪声源,推导出两者的角位移精度表达式,并通过计算进行了模拟。结果显示,两者的测量精度决定于信号的信噪比,且随作用距离的增加而降低;象限探测器的角位移测量精度明显高于位敏探测器。在忽略背景光噪声的情况下,象限探测器的精度约为位敏探测器的40倍。     

A sixteen-channel multiplexing upgrade for single channel receivers

With the increasing interest in phased arrays in magnetic resonance imaging, imaging system receivers capable of acquiring larger number of parallel signals are needed. Suggested techniques for rapid imaging propose the use of arrays with as many as 128 elements. While simply duplicating the number of receiver chains as needed is a viable technique, it quickly becomes both cumbersome and expensive.Time domain multiplexing offers an alternative solution to this problem. By using RF multiplexing switches, a single receiver can be upgraded to an array receiver capable of multi-channel data acquisition giving users array capability. Additionally, it can be used to dramatically increase acquisition capability of multiple receiver systems.This paper reports results from a multiplexing system upgrade, which converts a single channel standard clinical imaging system to a 16-channel array system. The upgrade includes both the RF multiplexing front-end and an external data acquisition system with image processing capability. Issues concerning the implementation of high channel-count multiplexers are also discussed.     

利用海浪噪声自相关实现散射体无源探测

提出了一种利用海浪噪声自相关实现散射体无源探测的新方法.将各接收器记录噪声信号的自相关减去所有接收器记录噪声信号自相关的平均值,得到散射信号的到达结构,然后结合基尔霍夫移位算法实现对散射体的探测.与利用背景噪声互相关提取格林函数从而实现散射体探测的方法不同,自相关无需考虑各个接收器之间的大量数据传输及时间同步问题,这为相距较远的多接收器和移动平台目标探测提供了极大的方便.将所提出的方法应用于实验数据中,最终探测结果与实际测量结果相比差别不大,验证了方法的有效性.     

Signal detection for frequency-shift keying via short-time stochastic resonance

A series of short-time stochastic resonance (SR) phenomena, realized in a bistable receiver, can be utilized to detect a train of information represented by signals that adopt frequency-shift keying (FSK). It is demonstrated that the values of noise intensity at resonance regions are close for adjacent periodic signals with an appropriate frequency separation. This establishes the possibility of decoding subthreshold or slightly suprathreshold M-ary FSK signals in bistable receivers. Furthermore, the mechanism of FSK signal detection via short-time SR effects is elucidated in terms of the receiver response speed. This phenomenon provides a possible mechanism for information processing in a bistable device operating in nonstationary noisy environments, where even the inputs appear over a short timescale or have a frequency shift.     

水下目标对幅度高斯相关海面环境噪声场扰动特性的研究

理论探讨了水下目标受海面环境噪声场激发产生的散射场对海洋环境噪声场的扰动特性,基于幅度高斯型相关海面噪声源模型,利用任意声源分布声场的积分表达式和单极子源半无限空间格林函数的球面波展开式,获得了刚性球目标在海面单极子和偶极子源海洋环境噪声“照射”下的直达噪声场、散射噪声场、总噪声场,以及二接收点直达、散射和总噪声协方差的理论表达式,表明总噪声场除了和目标阻抗特性、接收点的方向有关外,还受到海面噪声源相关特性,以及直达与散射噪声场之间干涉的较大影响。数值计算结果给出较近距离范围内,刚球目标声学可见度约为4~5dB,并指出在海洋环境噪声场中,刚球目标散射的方向特性明显不同于平面波入射。      

Arrival-time structure of the time-averaged ambient noise cross-correlation function in an oceanic waveguide

Coherent deterministic arrival times can be extracted from the derivative of the time-averaged ambient noise cross-correlation function between two receivers. These coherent arrival times are related to those of the time-domain Green's function between these two receivers and have been observed experimentally in various environments and frequency range of interest (e.g., in ultrasonics, seismology, or underwater acoustics). This nonintuitive result can be demonstrated based on a simple time-domain image formulation of the noise cross-correlation function, for a uniform distribution of noise sources in a Pekeris waveguide. This image formulation determines the influence of the noise-source distribution (in range and depth) as well as the dependence on the receiver bandwidth for the arrival-time structure of the derivative of the cross-correlation function. These results are compared with previously derived formulations of the ambient noise cross-correlation function. Practical implications of these results for sea experiments are also discussed.     

Analysis of noise immunity of OFDMA communication systems operated in the presence of interfering stations

We analyze noise immunity of high-speed data transmission systems operated in a complex communication channel with frequency-selective fadings and interference from the neighboring base stations. This problem is very topical for modern orthogonal frequency-division multiple-access (OFDMA) data transmission standards. Such digital communication systems allow one to measure the noise parameters on individual subcarriers simultaneously with reception useful signals. We perform comparative analysis of different methods for measuring the noise characteristics and using them for demodulating the coded signal. Four processing methods with different complexity and noise immunity degree are proposed for receiver signals. Characteristics of the considered receivers are compared for different channel loadings and algorithms of power control by interfering stations. Practical recommendations for using the considered receivers are given. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 50, No. 6, pp. 533–543, June 2007.     

Trading detection for resolution in active sonar receivers

This paper proposes an active sonar receivers that offers a smooth trade-off between detection and resolution. A matched filter is the optimal detector of known signals in white Gaussian noise but may fail to resolve the targets if the time separation of targets is less than the mainlobe width of the autocorrelation function of the transmitted signal. An inverse filter achieves optimal resolution performance for multiple targets in the absence of noise, but amplifies the noise outside the signal bandwidth in a manner that makes it impractical in many realistic scenarios. The proposed active sonar receiver, the variable resolution and detection receiver (VRDR) combines the matched and inverse filter properties to achieve a smooth trade-off between detection and resolution. Simulated receiver operating characteristics demonstrate that for a range of dipole sonar targets, the performance of the VRDR is superior to the matched and inverse filter, as well as another previously proposed bandlimited inverse filter.