星基增强系统接收机中的导航比特同步设计与性能仿真

星基增强系统(SBAS)中导航电文速率为500符号/秒,针对其弱信号时找导航比特边界难的特点,提出了基于最大似然算法的比特同步算法,给出了在SBAS接收机中比特同步的应用公式和实现方法,并进一步创新性地设计了包含有软判决和多次判决的比特同步综合流程;最后在多种导航比特分布的情形下,对最大似然比特同步算法进行了不同载噪比下的性能仿真,确认了此算法在接收信号很弱时仍然有效。     

群时延的新概念、测量方法及其应用

 群时延是衡量传输网络对信号传输时间延迟及信号失真影响的重要参数.基于微分(差分)的传统群时定义和测量存在如下缺点:存在分辨率与精度之间的矛盾,不能反映一定带宽内的整体相位特性,难以定量描述相位的非线性畸变.为了解决这些问题,本文从相频特性整体出发,基于Taylor展开给出了一种新的群时延的定义和测量方法.在GPS授时接收机电缆传输特性测试中的实验结果表明,新测量方法测得的群时延达到了0.01ns的测量精度,与GPS授时接收机测得的信号传输时延之间最大偏差不超过0.3ns,具有良好的对应关系.     

基于电热模型的SNSPD响应过程模拟与时间抖动分析

超导单光子探测器(SNSPD)具有高探测效率,低时间抖动、低暗计数率、高计数率等优点.文章通过对纳米线电热过程的建模,分析了纳米线的电热响应过程,探讨了负载电阻、偏置电流和动态电感对SNSPD响应时间的影响,结合蒙特卡洛方法来模拟研究了纳米线空间不均匀性对于SNSPD时间抖动的影响,结果表明随着纳米线空间不均匀性的增加,纳米线的时间抖动不断增加,并求出了典型的时间抖动约为7.73 ps.     

利用正弦幅值时间转换的脉冲激光测距方法

提出了一种利用正弦幅值时间转换的高精度脉冲激光测距方法,该方法以正弦信号作为时间基准,采用倍频和时钟分相技术,通过调节脉冲发射延时,控制回波脉冲定时点落在基准正弦波的0~∏/4区间,然后对这一区间进行分段线性插值处理,将正弦幅值的变化转换为定时时间,实现高精度测距。该方法原理结构简单、容易实现。实验结果表明:在激光发射平均功率为1 mW时,在无合作目标测程300 m内,测距精度为±(5 mm+3 ppm)。     

Graph-based STA for asynchronous controllers

We present a Graph-based Asynchronous Static Timing Analysis (ASTA) methodology for Asynchronous Control Circuits, which pessimistically computes Critical Cycle(s), instead of Critical Paths, without cycle cutting. Its additional requirement over STA is a graph-based Event Model, Marked Graph or Petri Net. We contrast STA, ASTA results for 23 asynchronous circuit benchmarks, and demonstrate significant timing differences between the ASTA critical cycle and STA critical path, with cut cycles. We also demonstrate our correlation to SPICE level simulations, for 20 of the 23 circuits. Our ASTA flow effectively upper bounds critical cycle delay over SPICE, and is orders of magnitude faster.     

Analysis of K-Transmit Dual-Receive Diversity with Cochannel Interferers over a Rayleigh Fading Channel

The need to combat the severe effects of fading and interferencein the rapidly increasing number of communication systemsproviding wireless services has motivated the study of diversityin the presence of interference.Hence the analysis of wireless systems with both transmit andreceive diversity and subject to cochannel interference is animportant tool for system design.We consider here a K-transmit dual-receive diversitycommunication systememploying K antennas for transmission and two antennasfor reception. The desired signal is corruptedby N interfering sources apart from additive whiteGaussian noise. The channel is Rayleigh fading.As a result, the channel matrix for the desired signaland the propagation vectors of the interferers havezero-mean complexGaussian entries; the entries are assumedto be independent and identically distributed.The complex receive weight vectorused for combining the received signalsis chosen so as to maximize the outputsignal-to-interference-plus-noiseratio (SINR).From the statistics of the channel matrix and thepropagation vectors of the interferers,we derive a closed-form expressionfor the probability density function (p.d.f.)of the maximum outputSINR. This p.d.f. can be used to obtainthe symbol errorprobability for different digital modulation schemes.     

湍流系统中的阵发非完美位相同步和能量爆发

湍流现象广泛地存在于自然界的各个领域，关于湍流发生的机制成为一个多世纪以来人们不断探索但尚未完全解决的难题之一，在强湍状态下，系统不时地会突然聚集起巨大的能量，这对人类活动可能产生重大影响，作者利用一个典型的模型说明，在适当的参照系下，湍流波动可以等价地变换为在势阱中相互耦合的一组振子的运动；作为非线性系统自组织的结果，不同空间尺度的振子可以阵发地调节到非完美的位相同步，在同步发生的瞬间，虽然每个振子的位相和振幅的运动看起来仍很紊乱，但振子间的位相差却很小，并且它们的振幅几乎同时达到极大，引起系统整体能量爆发。     

Stability of incoherence in a population of coupled oscillators

We analyze a mean-field model of coupled oscillators with randomly distributed frequencies. This system is known to exhibit a transition to collective oscillations: for small coupling, the system is incoherent, with all the oscillators running at their natural frequencies, but when the coupling exceeds a certain threshold, the system spontaneously synchronizes. We obtain the first rigorous stability results for this model by linearizing the Fokker-Planck equation about the incoherent state. An unexpected result is that the system has pathological stability properties: the incoherent state is unstable above threshold, butneutrally stable below threshold. We also show that the system is singular in the sense that its stability properties are radically altered by infinitesimal noise.     

A position- and time-sensitive particle detector with subnanosecond time resolution

A microchannel plate/CCD-camera particle detector is described that utilises gold strips deposited upon the surface of a MCP to provide particle arrival time information. The uncertainty in the timing is assessed to be ∼500 ps (FWHM) for a measured time interval between adjacent strips. The main contribution of which is the result of the slow response time of the CFD compared to the signal. The application of timing measurement is shown to be of particular benefit in the accurate determination of product state branching ratios from the dissociative recombination of diatomic ions. Finally, the possibilities of such a detector are assessed. This revised version was published online in July 2006 with corrections to the Cover Date.     

ATM的扰码技术(Ⅰ)

扼要地介绍了扰码的基本概念，并重点地论述了在ＰＤＨ／ＳＤＨ以及以信元为基础的ＡＴＭ传输环境下的扰码技术，指出了在以信元为基础的ＡＴＭ传输环境下所采用的ＤＳＳ扰码方案，虽然复杂了一些，但可只进行一次扰码，并有一定的自由度，因此可以选择ＤＳＳ的扰码方案。