Microwave Interference with the Function of an Implanted Cardiac Pacemaker

The effect of external microwave radiation on an implanted cardiac pacemaker is studied. Based on a clinical case history [1] indicating an effective blocking in a patient of the implanted pacing activity due to microwave radiation, the process by which microwave energy may cause this observed effect is analyzed. The problem is formulated in terms of thermoelastic theory in which the absorbed microwave energy of the biomedium containing the implanted pacemaker represents a volume of heat source and a resulting thermoelastic motion sets up acoustic waves; these in turn, cause microphonic oscillations in the pacemaker which correspond to the noisy high-frequency artifact recorded on the ECG tracings [11.     

Proposed Cardiac Pacemaker System Combining Unipolar Stimulation with Bipolar Sensing

Present cardiac pacemaker designs use either unipolar or bipolar electrode systems. Advantages of unipolar electrodes for stimulation are listed; then arguments in favor of bipolar electrodes for sensing are cited. A proposed system combines unipolar stimulation with bipolar sensing and may be implemented by adding a differential-input stage to the sensing amplifier.     

The Structure of General Interference Functions and Applications

This paper provides a theoretical framework for the analysis of interference-coupled multiuser systems. The fundamental behavior of such a system is modeled by interference functions, defined by axioms “nonnegativity, ”scale-invariance,” and “monotonicity.” It is shown that every interference function has an interpretation as the optimum of a min-max problem, where the optimization is over a closed comprehensive positive coefficient set. This provides new insight into the structure of general interference functions and its elementary building blocks. Conversely, it is shown that every closed comprehensive positive set can be expressed as a level set of an interference function. This shows a close connection between the analysis of interference functions and multiuser performance regions, which are typically closed comprehensive. The generality of this framework allows for a wide range of potential applications. As an example, we analyze the problem of interference balancing.      

基于压缩感知的窄带干扰重构与消除

提出了一种基于压缩感知的TDS-OFDM系统窄带干扰重构方法,通过利用相邻TDS-OFDM帧头的差分采样建立压缩感知模型,能够在不依赖信道估计及在高频谱效率的条件下,精确恢复窄带干扰信号并予以消除,显著提升传输系统传输鲁棒性。     

CMOS器件感受新机遇

在过去几年中,人们一直期望CMOS(互补金属氧化物半导体)感光器件能够获得快速发展,但面对CCD(电荷耦合器件)器件的压倒性优势,这种技术却遇到了巨大的挑战,在数字相机领域中就是如此。 iSuppli预测全球CMOS市场将从2001年的1800万美元增长到2005年的7200万美元。同时,CCD的增长将相当缓慢,只是从2000年的4900万     

稀疏信号结构性噪声干扰下的感知矩阵优化

针对具有结构性噪声干扰的稀疏信号处理问题,该文提出一种基于贝叶斯理论的感知矩阵优化设计方法。结合具有加性干扰的稀疏信号模型,通过对感知矩阵进行能量约束,最小化信号的后验协方差矩阵的迹,实现感知矩阵的优化设计。仿真不同信号稀疏度和重构算法时,感知矩阵优化对信号重构误差和重构时间的影响;分析信号先验信息存在偏差时,感知矩阵优化对重构效果的影响。仿真结果表明,优化后的感知矩阵能够更好地获取稀疏信号中的重要信息,信号重构精度的均方误差减小约15～25 dB,重构时间减少约40%。

     

极化干扰对星地遥感数据传输影响分析

针对极化干扰对星地数据传输系统的影响,归纳影响极化干扰的主要因素,推导星地数据传输系统极化干扰的理论模型,仿真数据传输系统在不同的调制体制和信道编码方式下的误码率恶化情况,比较在相同程度的极化干扰下各体制传输性能试验结果,分析在不同的Eb/N0工作门限下,星地遥感数据传输系统所受极化干扰影响的规律。     

Characteristic Functions for Optimum-Combining Output SINR With AWGN and Correlated Interference

Optimum combining (OC) is a powerful means for combatting co-channel interference. Its performance, however, is difficult to analyze. The prevailing methodology in current use is to neglect the influence of additive white Gaussian noise (AWGN). Inclusion of AWGN into the analysis usually leads to mathematical intractability, except for some extreme cases. In this letter, we formulate the problem in the framework of hypergeometric functions, so that their good properties can be exploited to enable the analysis to account for the influence of AWGN and co-channel interference simultaneously. We obtain closed-form solutions to the characteristic function (CHF) of the signal-to-interference-plus-noise ratio at the OC output for three important operational scenarios in Rayleigh fading, although the general solution still needs further effort to simplify. The assumptions made here are that both signal and interferers suffer from Rayleigh fading, and the number of interferers is not less than the number of antennas. The use of resulting CHF formulas is illustrated through their application to the bit-error and outage performance evaluation of OC     

单星多波束天线下基于压缩感知的多目标干扰定位

针对卫星干扰处理中的多目标定位问题,该文提出基于压缩感知的定位方法.该方法利用目标的空间稀疏性,以及多波束天线在不同信号源方向上的增益不同,仅需要测量接收信号强度便可实现多个干扰的位置识别.研究结果表明,定位性能与节点分布、目标个数、波束覆盖半径、判决门限有关.在给定参数及原对偶内点算法下,该方法可实现1～4个干扰源的空域定位,在信噪比为20 dB时定位精度达到7.7 km,优于经典的旋转干涉仪和空间谱估计测向方法.     

单星多波束天线下基于压缩感知的多目标干扰定位

针对卫星干扰处理中的多目标定位问题,该文提出基于压缩感知的定位方法.该方法利用目标的空间稀疏性,以及多波束天线在不同信号源方向上的增益不同,仅需要测量接收信号强度便可实现多个干扰的位置识别.研究结果表明,定位性能与节点分布、目标个数、波束覆盖半径、判决门限有关.在给定参数及原对偶内点算法下,该方法可实现1～4个干扰源的...     

有云层干扰的光学遥感图像舰船检测算法

针对海面光学卫星遥感图像舰船检测中云层干扰所产生高虚警率的情况,提出一种基于串并联混合多维特征融合判决的舰船目标检测算法。首先,利用高斯灰度阈值分割目标与海面云层背景,并对分割后的二值图像进行区域标记;然后,利用感兴趣区域的几何形态和边缘能量两类特征,包括中心偏移度、长宽比、面积变化比、曲折度和填充度,构建了串并联混合多维特征融合判决方法;最后,通过对感兴趣区域进行综合鉴别,有效剔除了云层干扰导致的虚警,解决了含云层背景检测结果虚警率高的问题。对多幅SPOT4光学遥感卫星图像的实验结果表明算法的有效性。     

噪声干扰背景下压缩感知雷达波形优化设计

为改善压缩感知雷达（Compressive Sensing Radar,CSR）在干扰噪声背景下目标检测及距离-多普勒参数的估计性能,该文提出一种感知矩阵平均相干系数（Averaged Coherence of the Sensing Matrix,ACSM）与信干噪比（Signal to Interference and Noise Ratio,SINR）联合优化的波形设计方法.文中首先建立了CSR距离-多普勒二维参数感知模型,推导了波形联合优化设计的目标函数,其次以多相编码信号作为优化码型并采用模拟退火（Simulated Annealing,SA）算法对目标函数进行优化求解.与传统CSR波形相比,优化设计的波形提高了CSR在低信干噪比条件下的成功检测概率,同时有效降低了目标距离-多普勒参数估计误差,由此改善了CSR在干扰噪声背景下的距离-多普勒成像质量.计算机仿真验证了该方法的有效性.     

联合两级滤波与压缩感知的测距仪干扰抑制方法

针对测距仪(Distance Measure Equipment , DME)脉冲信号对L频段数字航空通信系统1(L-band Digital Aeronautical Communication System 1 , L-DACS1)接收机产生干扰的问题,提出一种联合两级滤波与压缩感知的DME干扰抑制方法。首先,接收机通过高通滤波器估计出DME干扰,并在时域将其从接收信号中消除;然后,通过低通滤波器进一步滤除残留的DME干扰和噪声;最后,针对经过两级滤波后仍残留的DME干扰,基于其在时域中的稀疏特性应用压缩感知算法实现重构并消除。数值仿真表明,所提方法可获得的DME干扰功率衰减值约41dB,有效克服了DME脉冲干扰对L-DACS1系统接收机的影响。      

一种新非单调法求解压缩感知问题

提出了一种新的非单调线搜索Barzilai-Borwein梯度法,并证明了该算法的全局收敛性。通过Matlab数值试验表明,该算法对重构稀疏信号是可行有效的,与其他算法相比,具有迭代次数少,计算用时短等优点。     

Simplified Prediction of Conducted and Radiated Interference Levels for Pulses and Step Functions

A series of laboratory measurements were made by the Bell Aerosystems Company to measure the levels of interference conducted by and radiated from shielded and unshielded signal wires which carry pulses or step functions. These test data have been plotted into graphs which show the interference level in dB/1? V/Mc/s vs. frequency for many common rise/fall times, amplitudes, pulse widths, and wire lengths. These graphs provide a rapid method for comparing the interference spectrum of a pulse or step function with the limits specified by MIL-1-6181D and MIL-1-11748B. The necessary amount of wire or case shielding can then be easily determined by observation of the applicable graph.     

高清ENG摄像机的新功能

随着高清技术的不断深入,高清ENG摄像机功能不断细化.对于不同HD ENG摄像机的功能,是否全部可行而且适合操作,画面是否得到改善,新功能对于使用人员带来怎样的便利等等,文章将从CCD、DSP、应用等几个层面来进行分析.     

无线Ad hoc网络一种最小化链路干扰的载波监听机制设计

无线Ad hoc网络中,干扰产生于接收节点处的接收信号被其他无用信号叠加,干扰问题严重影响接收端解码信息的能力,导致数据包冲突和重传的增加.如何最小化链路干扰,减少数据包冲突概率,是提高网络性能的关键.MAC协议中,合理的载波监听机制是减小链路干扰的有效方式之一,通过合适的感知门限设计,可以有效地降低链路中的干扰和冲突...     

Interference Avoidance through Pilot‐Based Spectrum Sensing Algorithm in Overlaid Femtocell Networks

Co‐channel interference between macro–femtocell networks is an unresolved problem, due to the frequency reuse phenomenon. To mitigate such interference, a secondary femtocell must acquire channel‐state knowledge about a co‐channel macrocell user and accordingly condition the maximum transmit power of femtocell user. This paper proposes a pilot‐based spectrum sensing (PSS) algorithm for overlaid femtocell networks to sense the presence of a macrocell user over a channel of interest. The PSS algorithm senses the pilot tones in the received signal through the power level and the correlation metric comparisons between the received signal and the local reference pilots. On ensuring the existence of a co‐channel macrocell user, the maximum transmit power of the corresponding femtocell user is optimized so as to avoid interference. Time and frequency offsets are carefully handled in our proposal. Simulation results show that the PSS algorithm outperforms existing sensing techniques, even at poor received signal quality. It requires less sensing time and provides better detection probability over existing techniques.     

New Second-Preimage Attacks on Hash Functions

In this work, we present several new generic second-preimage attacks on hash functions. Our first attack is based on the herding attack and applies to various Merkle–Damgård-based iterative hash functions. Compared to the previously known long-message second-preimage attacks, our attack offers more flexibility in choosing the second-preimage message at the cost of a small computational overhead. More concretely, our attack allows the adversary to replace only a few blocks in the original target message to obtain the second preimage. As a result, our new attack is applicable to constructions previously believed to be immune to such second-preimage attacks. Among others, these include the dithered hash proposal of Rivest, Shoup’s UOWHF, and the ROX constructions. In addition, we also suggest several time-memory-data tradeoff attack variants, allowing for a faster online phase, and even finding second preimages for shorter messages. We further extend our attack to sequences stronger than the ones suggested in Rivest’s proposal. To this end we introduce the kite generator as a new tool to attack any dithering sequence over a small alphabet. Additionally, we analyse the second-preimage security of the basic tree hash construction. Here we also propose several second-preimage attacks and their time-memory-data tradeoff variants. Finally, we show how both our new and the previous second-preimage attacks can be applied even more efficiently when multiple short messages, rather than a single long target message, are available.     

Self-Synchronizing Cardiac Pacemaker

A new kind of cardiac pacemaker for direct heart stimulation in cases of intermittent or variable heart block is presented. The pacemaker is capable of providing stimuli either synchronously with ventricular depolarization or at a fixed rate when natural pacing fails. Thus any competition between artificial and physiological rhythm is avoided, while allowing the exploitation, from the hemodynamic viewpoint, of the surviving capability of physiologic control of the heart rate. The main features of the instrument are that the shifts from synchronous to free operation and vice versa take place in an automatic way, and no electrode besides those which provide stimulation are needed for synchronization. The mean power consumption of the pacemaker is comparable with that of conventional unsynchronized pacemakers. Thus the subcutaneous implantation is possible, with a theoretical lifetime of 30 000-hour autonomy. Schematic diagrams and waveforms are included.