基于GPS校准的皮卫星高精度时间系统方案

许多实际应用任务对皮卫星星上时间系统有较高的精度要求,传统采用实时时钟芯片（RTC）的时间系统方案难以满足需求,基于GPS的皮卫星星上时间系统应运而生。受能源限制,皮卫星携带的GPS接收机一般采用间歇性开机方式工作。本文设计实现了一种基于GPS校准的星上时间系统方案,提出了分级校正算法,并对算法中的参数进行了优化,实验表明,每天GPS接收机仅需开机1024 s,即可保证优于1 ms/d的星上时间精度。整个方案实现简单,且已应用于浙江大学研制的ZDPS-2皮卫星,满足了任务载荷5 ms时间精度的要求。     

GPS接收机数字基带信号处理算法研究

为了优化GPS接收机数字信号基带处理过程,提高伪距测量精度和GPS定位精度,需要从解扩解调的角度,建立相应同步环路的数学模型,分析GPS接收机基带数字信号处理算法.采用循环相关法作为信号捕获方法,采用Costas环作为信号跟踪方法,在MATLAB环境下实现了相应的算法设计、验证与仿真.验证结果表明这种算法能够为软件CPS接收机提供快速捕获及跟踪能力,是一种适用而高效的软件CPS接收机处理算法,对于开发GPS接收机产品以及开展相关领域的研究工作都具有重要的意义.     

GPS/GLONASS接收机信号捕获及其仿真

随着多星座系统的组建完成,双模接收机已经成为了研究的热点。给出了GPS/GLONASS双模接收机的总体设计方案,重点研究了低信噪比环境下GPS/GLONASS信号捕获,采用基于快速捕获的FFT算法和相关累加结合非相关累加捕获算法分别对GLONASS信号和GPS信号进行检测。利用真实数据对双模接收机的信号捕获算法进行了仿真分析,结果表明双模接收机能够捕获低信噪比环境下的卫星导航信号,提高了接收机的灵敏度。     

基于DSP+FPGA的多频GPS接收机系统设计

为提高GPS接收机的定位精度,提出了一种基于DSP+FPGA的导航型多频GPS接收机的设计方案;在简述了多频接收机优点和GPS民用信号特性的基础上,从整体结构方面设计了L1/L2/L5三个频段民用信号的GPS接收机,介绍了多频信号的射频前端的设计,给出了用DSP和FPGA实现信号处理算法的原理架构,重点分析了利用三个频段信号问频率关系的多频信号联合捕获和联合跟踪的基带信号处理;经初步验证该多频GPS接收机相对单频接收机在精度方面有较大改进.     

GPS软件接收机的频域相关捕获算法

GPS软件接收机在移植性、灵活性等方面具有很大的优势。本文从GPS软件接收机的角度讨论了GPS频域相关捕获算法。本文分析了算法的理论模型,并利用Matlab对算法进行仿真实现,成功地解算出GPS信号的码相位偏移和载波多普勒偏移。与传统的滑动相关算法进行了运算量的比较,证明了频域相关捕获算法的优越性。     

基于衰减记忆UKF的高精度GPS定位估计

目前单机GPS接收机定位精度较低,主要是由于定位模型的不完善和定位估计算法的误差造成的.为了提高识别精度,提出了伪距和多普勒频移相融合测量模型,采用一种将衰减记忆平淡卡尔曼滤波算法(MAUKF)进行GPS定位估计,来提高单机GPS的定位精度.MAUKF是一种改进的卡尔曼滤波算法,通过引进衰减因子加强对当前测量数据的利用,以减小历史数据埘滤波结果的影响.经过GPS单机静态定位实验验证,算法能够提供优于传统滤波算法的定位估计精度,并可用于提高单机GPS定位精度.     

基于载波频率辅助相位的GPS信号跟踪算法

针对传统全球定位系统(GPS)接收机在高动态环境下跟踪性能不理想,提出一种基于载波频率辅助相位的GPS信号跟踪算法。利用锁频环(FLL)辅助锁相环(PLL)的方式代替传统单一跟踪环路,通过卡尔曼(Kalman)滤波器对接收机各跟踪通道中频信号进行综合处理。根据多条跟踪通道的伪距和伪距率残差对系统状态参量进行综合估计,并搭建Kalman滤波器的状态方程和量测方程,给出了跟踪环路反馈量,与传统标量跟踪模式下的跟踪性能进行了对比。仿真结果表明,基于载波频率辅助相位的GPS信号跟踪算法进入稳态时间减小了100 ms,位置误差精度提高了5 m,速度误差精度提高了近3 m/s,在接收机用户快速运动的环境下,能够很好地处理高动态信号。     

基于GPS和神经网络的滑坡位移监测算法

针对使用GPS接收机进行滑坡位移监测时,单点GPS定位误差较大的问题,提出了一种基于GPS和神经网络的滑坡位移监测算法。GPS接收机在滑坡发生之前和滑坡发生之后测得的定位数据耦合在一起,不是线性可分的。采用具有非线性可分特性的神经网络,把耦合在一起的定位数据分成两类,一类属于未滑坡的GPS数据,另一类属于发生滑坡的GPS数据,避免了对GPS定位误差这一非线性非高斯问题进行准确建模的过程。利用GPS接收机测得的样本训练集训练神经网络,用训练后的神经网络模型来验证测试集的分类效果。实测实验结果表明,对于低精度的GPS接收机,当滑坡程度分别达到3米、5米、8米时,训练样本分类正确率分别是95.85%、99.23%、99.99%,测试样本分类正确率分别是82.94%、89.44%、91.05%,说明所提出的算法适用于较大程度的滑坡。     

基于INS辅助的高动态GPS接收机算法研究

通过对弹载GPS接收机在实际应用中遇到问题的分析,提出了INS(inertialnavigationsystem)辅助GPS接收机的算法。采用不同性能的INS直接辅助GPS接收机,可以使弹载GPS接收机在多普勒频率发生较大变化时仍然保持锁定,而且陀螺漂移误差为0.01°/h的INS辅助GPS接收机后的动态应力误差比未辅助时减小了90%以上,提高了跟踪性能。对陀螺漂移误差为25.2°/h的INS进行紧耦合校正,并用校正后的结果辅助GPS接收机,动态应力误差比未校正前减小了20%以上。仿真结果表明,该算法在高动态环境下仍然可以使环路带宽足够小,在满足接收机动态性能的情况下,也保证了噪声性能。     

软件GPS接收机捕获算法的研究

数字信号捕获是软件GPS接收机的重要组成部分,同时也影响软件GPS接收机的工作性能指标。通过对GPS信号结构的分析后,通过对GPS导航信号进行仿真,分别在时域和频域范围对信号搜索捕获进行了算法仿真,根据信号搜索捕获理论结合仿真试验结果,对时域/频域两类处理方法进行了分析和比较,不同捕获方法各有优点,针对不同的情况应采用不同的算法或者对不同的算法进行适当的组合以实现快速捕获的目的。     

Modularising the specification of a small database system in extended ML

A case study in the modular specification and refinement of a small database system is presented in Extended ML. Two similar requirements specifications are given and a program development step from each these is presented. The structure resulting from the first program development step is similar to that given in [FiJ90] and is presented as an answer to the challenge problem given in that paper, while the second development step is presented as a possible alternative which is more suited to the Extended ML style of program development. In the context of these two development steps the module facilities of Extended ML, their role in specification and program development and their ability to meet the challenge of [FiJ90] are examined.This research was supported by SERC grant GR/E 78463     

Computer implementation of the constraint method

A computer program based on the constraint method approach to finite elements is described. The program permits the user to select arbitrarily polynomial orders for the various fields to be approximated. A set of nodal variables enforcing C¹ continuity for arbitrary polynomial order is presented, and those aspects of the program algorithm which differ from conventional finite element programs are described, including the numerical determination of a set of independent variables. An example is presented and the results obtained by the constraint method program compared with results from a conventional program. The constraint method approach is seen to be competitive with the conventional approach.     

Automated software test data generation

An alternative approach to test-data generation based on actual execution of the program under test, function-minimization methods and dynamic data-flow analysis is presented. Test data are developed for the program using actual values of input variables. When the program is executed, the program execution flow is monitored. If during program execution an undesirable execution flow is observed then function-minimization search algorithms are used to automatically locate the values of input variables for which the selected path is traversed. In addition, dynamic data-flow analysis is used to determine those input variables responsible for the undesirable program behavior, significantly increasing the speed of the search process. The approach to generating test data is then extended to programs with dynamic data structures and a search method based on dynamic data-flow analysis and backtracking is presented. In the approach described, values of array indexes and pointers are known at each step of program execution; this information is used to overcome difficulties of array and pointer handling     

Concurrent runtime monitoring of formally specified programs

A methodology for continuously monitoring a program for specification consistency during program execution is described. Prior development of the formal specification and program is assumed. The program is annotated with constructs from a formal specification language, and the formal specification constructs are transformed into checking code, which is then inserted into the underlying program. Calls to this checking code are inserted into underlying program wherever it can potentially become inconsistent with its specification. If an inconsistency does in fact occur, diagnostic information is provided. The implementation of such a system for Anna (annotated Ada) subtype annotations is presented     

A NEW GENERATOR FOR PARAMETRIC DRAFTING PROGRAM

In this paper a new generator for parametric drafting program is presented.The func-tions and the syntax of the parametric drafting program are described.This software has been suc-cessfully used to generate a parametric drafting program for designs of motors.     

Design of cellular cofferdams by the ccell computer program

CCELL is a computer program for the analysis and design of cellular cofferdams and mooring cells. The theoretical basis of the program is explained in sufficient detail to enable a designer to determine if the program is appropriate for his or her needs. Two design examples are presented.     

On a class of algebraic models of programs of practical interest

Algebraic program models are designed for the study of the semantic properties of programs on models—program schemas. The design concepts of these models are presented, and a class of models is considered that approximate real sequential programs. Algorithms are constructed that recognize the equivalence of program schemas in models of a given class with practically acceptable complexity. The validity of these algorithms for constructing equivalent transformations (ETs) of program schemas is established.     

监控系统中控制软件的工程化设计与实现

主要探讨微机监控系统中控制软件的工程化设计方法,介绍了模块化程序设计和结构化程序设计的基本原理,具体分析了在电锅炉微机控制系统中,采用模块化程序设计和结构化的程序设计相结合的设计思路,给出了程序框图。实践证明,这是一种行之有效的方法,取得了很好的实际效果。     

Colour: a computer program for QCD colour factor calculations

A computer program for evaluating colour factors of QCD Feynman diagrams is presented, and illustrative examples on how to use the program to calculate nontrivial colour factors are given. The program and the discussion in this paper is based on a diagrammatic approach to colour factors.     

基于LabVIEW的任意波形发生器编程与控制

介绍了广泛应用于虚拟仪器程序设计的LabVIEW图形化集成开发平台，指出了它相对于传统程序设计语言的优点。介绍了NIPXI-5421任意波形发生器及其任意波形产生原理，提出了任意波形发生器的通用程序控制流程，并编写了相应的控制程序。该程序采用基于数据流和基于事件响应相结合的程序设计方法，实现了波形载入、增益控制、直流偏移调节、滤波器状态设置和错误处理等功能，具有操作简单、人机界面友好、软件可读性、可维护性好和系统易于升级等特点。