原子钟两级驾驭算法及在建立GNSS时间基准中的应用

本文提出了一种原子钟驾驭算法,方法是使用等价于Kalman滤波器加延迟器的数字锁相环（DPLL）。本文完整地推导了DPLL的闭环系统传递函数和闭环误差传递函数,给出了其实现结构,和每次的对于被驾驭原子钟的调整量,并给出了使DPLL输出信号的频率稳定度最优的参数选取方法。在此基础上,提出了使用两个这样的DPLL级联起来的二级驾驭算法。理论分析和仿真实验都表明：该算法相比传统原子钟驾驭算法,参数选取更容易,可以保证输出信号的频率稳定度最优;并保证输出信号与第一级的参考输入保持时间同步。该两级驾驭算法可以应用于设计锁相振荡器,即先用铯钟驾驭氢钟,然后再驾驭数控振荡器（NCO）;也可以应用于建立 GNSS 时间基准,即先用 UTC （BSNC）驾驭产生BDT,然后再用BDT驾驭主控站主钟来产生BDT（MC）。     

零输入响应初始条件的处理

经典“信号与系统”教科书中,在时域部分为了强调零输入响应是由换路前0-瞬间系统储能产生的,大都将初始条件给定为y（k）（0-）,并表明因为激励为零时,系统的状态不会发生变化,所以有y（k）（0-）=y（k）（0＋）。因此可用y（k）（0-）直接求解零输入响应。在不涉及具体电路问题时,上述方法简洁明了。本文举例说明在激励为零时,求解具体电路零输入响应时,会有y（k）（0-）≠y（k）（0＋）,从而导致双解情况的出现。为此笔者建议将y（k）（0-）改为y（k）（0＋）,既可使求解具有物理意义或工程背景问题与一般数学问题一致,又有利于学生掌握零输入响应求解方法。     

时间与全球卫星导航

卫星导航定位系统能完成精密导航、定位和授时任务,都是建立在具有高精度的时间基准和时间同步基础之上的。因此,所有卫星导航定位系统都建有独立的内部时间系统GNSST,导航系统内部时间系统都溯源至其国家标准时间UTC(k),通过UTC(k)与国际标准时间UTC的常规比对功能实现其与国际法定标准时间的同步和统一(国际溯源),从而实现其授时应用功能。本文简要介绍了国际标准时间UTC的定义和发展,介绍了国际上全球卫星导航定位系统的时间基准、时间溯源和时间兼容互操作。     

一种优化的频率驾驭算法研究

为满足各应用领域对高精度时间性能不断提升的需求,该文设计实现了一种迭代的优化频率驾驭算法,主要分为纸面时间计算和实际物理信号实现两个部分。其中纸面时间计算采用ALGOS算法,利用实时原子钟数据和Circular T公报数据计算获得准确可靠的时间尺度,保障了驾驭参考的准确性和实时性。实时物理信号实现采用最优二次型高斯控制算法与Kalman算法综合,通过实时调整参数,计算出最优的频率驾驭量,将该驾驭量输送至频率调整设备,最终实现高精度时间信号的输出,整个驾驭系统是闭环的。该文基于我国时间基准保持系统和原子钟组,搭建试验平台,采用该算法对一台氢钟进行为期140天的频率驾驭,最终对输出的物理信号进行性能评估。试验结果表明,该算法有效提高了驾驭后物理信号的准确度和稳定度,驾驭后信号与国际标准时间协调世界时(UTC)相比,相位偏差保持在±3 ns以内,且30天稳定度优于5×10–16。     

一种优化的频率驾驭算法研究

为满足各应用领域对高精度时间性能不断提升的需求,该文设计实现了一种迭代的优化频率驾驭算法,主要分为纸面时间计算和实际物理信号实现两个部分。其中纸面时间计算采用ALGOS算法,利用实时原子钟数据和Circular T公报数据计算获得准确可靠的时间尺度,保障了驾驭参考的准确性和实时性。实时物理信号实现采用最优二次型高斯控制算法与Kalman算法综合,通过实时调整参数,计算出最优的频率驾驭量,将该驾驭量输送至频率调整设备,最终实现高精度时间信号的输出,整个驾驭系统是闭环的。该文基于我国时间基准保持系统和原子钟组,搭建试验平台,采用该算法对一台氢钟进行为期140天的频率驾驭,最终对输出的物理信号进行性能评估。试验结果表明,该算法有效提高了驾驭后物理信号的准确度和稳定度,驾驭后信号与国际标准时间协调世界时(UTC)相比,相位偏差保持在±3 ns以内,且30天稳定度优于5×10–16。     

一个用于背板通信的24Gb/s高速自适应组合均衡器

本文介绍了应用于背板通信系统中均衡器的设计与实现.该均衡器采用连续时间线性均衡器（Continuous Time Linear Equalizer,CTLE）和2抽头判决反馈均衡器（Decision Feedback Equalizer,DFE）的组合结构来消除信道码间干扰中的前标分量和后标分量.在设计中,CTLE采用双路均衡器结构补偿信道不同频率的损耗,减小了电路的面积和功耗;DFE采用半速率预处理结构来缓解传统DFE结构中关键反馈路径的时序限制,并采用模拟最小均方（Least Mean Square,LMS）算法电路控制DFE系数的自适应.电路采用IBM 0.13μm BiCMOS工艺设计并实现,测试结果表明对于经过18英寸背板后眼图完全闭合的24Gb/s的信号,均衡后的眼图水平张开度达到了0.81UI.整个均衡器芯片包括焊盘在内的芯片面积为0.78×0.8mm²,在3.3V的电源电压下,功耗为624mW.     

HLA/RTI时间管理的一种优化算法

 时间管理服务是HLA与以前分布式仿真标准最主要区别内容之一,也是RTI实现的重点和难点.其性能直接影响到仿真的效率和正确性.时间管理服务实现的关键是最大可用逻辑时间GALT的计算.论文针对目前GALT算法存在的可能死锁问题,提出了计算GALT的递归式算法——R-GALT算法和递归式推进检测方法,并给出了R-GALT算法无死锁证明.R-GALT算法不但解决了时间管理实现中可能出现的联盟时间推进死锁问题,而且能够提高盟员时间推进的效率.该算法在作者等人研制的遵循IEEE1516标准的RTI软件StarLink中已经得到了实现,测试表明,其性能优于国际上同类软件.     

电离层闪烁对北斗增强系统影响的建模研究

电离层闪烁严重影响了北斗及其增强系统的性能.为了评估电离层闪烁影响下北斗系统的可用性,需建立闪烁影响下的北斗及其增强系统性能模型,并进行仿真分析.文章系统地建立了电离层闪烁影响下的卫星导航接收机模型、用户定位算法和系统性能模型,利用电离层闪烁模型给出电离层闪烁分布,利用建立的北斗系统性能影响模型,实现对电离层闪烁影响下北斗增强系统性能的可用性分析.利用上述方法,仿真分析了中国中低纬地区强电离层闪烁影响下北斗增强系统的可用性.结果表明:电离层闪烁将引起用户接收机测量误差的增大,对于中国低纬地区而言,强电离层闪烁影响下,存在系统可用性低于95％的性能严重影响区域,北斗系统性能受影响区域与电离层强闪烁的发生 区域具有密切关系.     

基于索引调制OTFS系统的应用

正交时频空（Orthogonal Time Frequency Space,OTFS）调制技术和索引调制（Index Modulation,IM）技术适用于高移动性场景,具有高频谱效率等优势,在图像传输领域应用前景广泛。然而,结合索引调制的正交时频空（Orthogonal Time Frequency Space with Index Modulation,OTFS-IM）调制技术的算法实现复杂度较高。对此,在广义近似消息传递（Generalized Approximate Message Passing,GAMP）的基础上改进,提出一种基于概率排序的阻尼广义消息传递算法。实验结果表明,在图像传输应用中,与传统的最小均方误差结合最大似然方案（Minimum Mean Squared Error with Maximum Likelihood,MMSEML）相比,所提的算法具有更低的复杂度,性能也优于传统的MMSE-ML传输方案。     

Cu CMP工艺对薄膜介电常数的影响机制

研究了使用不同研磨液的Cu CMP工艺对超低介电常数(ULK)薄膜介电常数k值的影响.实验结果表明经过Cu CMP工艺,ULK薄膜的介电常数k均有不同程度的增加.XPS成分分析结果表明,ULK薄膜表面C含量的增加是造成介电常数k值升高的主要原因.这主要是由于CMP工艺中,化学品溶液进入多孔的ULK薄膜.而退火工艺可以使得化学品挥发,从而使ULK薄膜表面C含量降低,由此介电常数k基本上得以恢复.初步建立了Cu CMP工艺对介电常数k影响的物理模型.根据模型计算的k结果为2.75,与实测值2.8基本符合.     

用WSF算法实现机扫雷达多维超分辨估计

针对传统扫描体制雷达(机扫雷达)无法分辨半功率波束宽度内存在多目标的问题,基于阵列信号处理的思想,应用加权子空间拟合(WSF)方法实现了机扫雷达超分辨估计.首先分析了机扫雷达幅度调制的导向矢量模型,然后推导了基于此导向矢量的WSF DOA估计方法.仿真结果表明,该方法具有较高的估计精度.     

Nonlinear electron properties of an InGaAs/InAlAs-based ballistic deflection transistor: Room temperature DC experiments and numerical simulations

We present a detailed experimental and numerical study of a novel device so-called ballistic deflection transistor (BDT). Based on InGaAs-InAlAs heterostructure on InP substrate, BDT utilizes a two dimensional electron gas (2DEG) supported by a gated microstructure to achieve nonlinear electron transport at room temperature. BDT channel is larger than the mean free path implying that electron transport is not purely ballistic in nature. However, the asymmetric geometrical deflection combined with the electron steering caused by the applied differential gate voltages ultimately results in an attractive nonlinear behavior of the BDT useful for the working of the large scale devices at room temperature. Device performance was studied by analyzing the effects of several modifications of the BDT geometry and biasing conditions, both experimentally and by numerical simulations.     

Space‐time diversity‐enhanced QoS provisioning for real‐time service over MC‐DS‐CDMA based wireless networks

In order to support the quality‐of‐service (QoS) requirements for real‐time traffic over broadband wireless networks, advanced techniques such as space‐time diversity (STD) and multicarrier direct‐sequence code division multiple access (MC‐DS‐CDMA) are implemented at the physical layer. However, the employment of such techniques evidently affects the QoS provisioning algorithms at the medium access control (MAC) layer. In this paper, we propose a space‐time infrastructure and develop a set of cross‐layer real‐time QoS‐provisioning algorithms for admission control, scheduling, and subchannel‐allocations. We analytically map the parameters characterizing the STD onto the admission‐control region guaranteeing the real‐time QoS. Our analytical analyses show that the proposed algorithms can effectively support real‐time QoS provisioning. Also presented are numerical solutions and simulation results showing that the STD can significantly improve the QoS provisioning for real‐time services over wireless networks. Copyright © 2007 John Wiley & Sons, Ltd.     

Analysis of Distributed DDQ for QoS Router

In a packet switching network, congestion is unavoidable and affects the quality of real‐time traffic with such problems as delay and packet loss. Packet fair queuing (PFQ) algorithms are well‐known solutions for quality‐of‐service (QoS) guarantee by packet scheduling. Our approach is different from previous algorithms in that it uses hardware time achieved by sampling a counter triggered by a periodic clock signal. This clock signal can be provided to all the modules of a routing system to get synchronization. In this architecture, a variant of the PFQ algorithm, called digitized delay queuing (DDQ), can be distributed on many line interface modules. We derive the delay bounds in a single processor system and in a distributed architecture. The definition of traffic contribution improves the simplicity of the mathematical models. The effect of different time between modules in a distributed architecture is the key idea for understanding the delay behavior of a routing system. The number of bins required for the DDQ algorithm is also derived to make the system configuration clear. The analytical models developed in this paper form the basis of improvement and application to a combined input and output queuing (CIOQ) router architecture for a higher speed QoS network.     

一种有效的平面曲线关键点检测新方法

平面曲线的关键点检测可用于数字曲线的直线段逼近,因此在很多图像识别、测量及分析的场合均有重要应用.由于一般的数字直线均为若干连续的水平、垂直、±45°夹角直线段合成,称之为四个基本方向,并将每个基本方向的最大直线段长度定义为其方向象素长度(directional pixel length,DPL).提出了四个定理,证明了在相互垂直方向上的DPL不会同时超过1个象素,而45°夹角方向上DPL不会同时超过2个象素.在此基础上,提出并设计了一种全自动关键点检测算法.通过和现有典型算法的实验对比,验证了该方法在减少关键点数和时空开销方面的显著优势.     

Frequency and time stability of GPS and glonass clocks

The frequency stability and reliability of the clocks are critical to the success of the GPS and GLONASS programs. We will show some of the similarities and differences between the clocks involved in these two systems. Because both systems plan to be operational in the next few years, the data leading up to this operational stage is of significant interest. On-board clocks and the stability of the master control clocks for these systems are analysed. We will discuss the attributes of these two systems as time and frequency references. Their relationship to UTC will also be illustrated. More data over a longer period of time was available for the authors from GPS than from GLONASS. Even so it is obvious that both systems have matured. Though the GLONASS system was developed later, its overall clock performance has improved more rapidly. Some of the more recent GLONASS clock performance is at about the same level as that of the GPS clocks. The analysis has yielded some very interesting contrasts, comparisons and changes in these systems that should be of great interest for time and frequency users, as well as for clock vendors and receiver vendors.     

Efficient non-data-aided carrier and clock recovery for satelliteDVB at very low signal-to-noise ratios

This paper deals with the analysis and design of efficient non-data-aided clock and carrier (frequency/phase) synchronization algorithms intended for use in satellite digital video broadcasting systems employing turbo-coding techniques to enhance the power efficiency. The above issue appears quite challenging in view of both the extremely low signal-to-noise ratio, typical of turbo-codes operation, and the very short time allocated to the acquisition of synchronization parameters. These constraints rule out most conventional clock/carrier recovery schemes and demand a careful search for specific, highly efficient algorithms. We propose and analyze a clock/carrier synchronization scheme capable of operating at values of E_b/N _o as low as 1 dB with lock-in delay not exceeding 50 ms