Global timing systems of nanosecond accuracy using satellite references
High accuracy timing systems using satellite atomic clocks
Osborne, E. F.↗
SEARCH · Engineering Papers
Results for “timing system”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Stochastic approximation algorithms for linear discrete-time system identification.
Stochastic approximation algorithms for identification of linear discrete time systems
Saridis, G. N.↗
All covariance controllers for linear discrete-time systems
The set of covariances that a linear discrete-time plant with a specified-order controller can have is characterized. The controllers that assign such covariances to any linear discrete-time system are given explicitly in closed form. The freedom in these covariance controllers is explicit and is parameterized by two orthogonal matrices. By appropriately choosing these free parameters, additional system objectives can be achieved without altering the state covariance, and the stability of the closed-loop system is guaranteed.
Hsieh, Chen↗
Methodology for object-oriented real-time systems analysis and design: Software engineering
Successful application of software engineering methodologies requires an integrated analysis and design life-cycle in which the various phases flow smoothly 'seamlessly' from analysis through design to implementation. Furthermore, different analysis methodologies often lead to different structuring of the system so that the transition from analysis to design may be awkward depending on the design methodology to be used. This is especially important when object-oriented programming is to be used for implementation when the original specification and perhaps high-level design is non-object oriented. Two approaches to real-time systems analysis which can lead to an object-oriented design are contrasted: (1) modeling the system using structured analysis with real-time extensions which emphasizes data and control flows followed by the abstraction of objects where the operations or methods of the objects correspond to processes in the data flow diagrams and then design in terms of these objects; and (2) modeling the system from the beginning as a set of naturally occurring concurrent entities (objects) each having its own time-behavior defined by a set of states and state-transition rules and seamlessly transforming the analysis models into high-level design models. A new concept of a 'real-time systems-analysis object' is introduced and becomes the basic building block of a series of seamlessly-connected models which progress from the object-oriented real-time systems analysis and design system analysis logical models through the physical architectural models and the high-level design stages. The methodology is appropriate to the overall specification including hardware and software modules. In software modules, the systems analysis objects are transformed into software objects.
Schoeffler, James D.↗
A Computer Aided Optimization Technique for Digital Systems Timing
Computer-aided optimization using Monte Carlo techniques for digital systems timing
COMPUTER SIMULATION↗
Remarks on Astrodata timing system
Redundant solid state digital clocks and code generators for reliable timing system
Laios, S. C.↗
On the periodicity of symbolic observations of piecewise smooth discrete-time systems
A study is made of the behavior of discrete-time systems composed of a set of smooth transition maps coupled by a quantized feedback function. The feedback function partitions the state space into disjoint regions and assigns a smooth transition function to each region. The main result is that under a constraint on the norm of the derivative of the transition maps, a bounded state trajectory with limit points in the interior of the switching regions leads to a region index sequence that is eventually periodic. Under these assumptions, it is shown that eventually the feedback function is determined by a finite state automaton. A similar result is proved in the case of finite state dynamic feedback.
Ramadge, Peter J.↗
The integrated-circuit control and timing system of the high-altitude rocket-radar project
Integrated circuit control and timing system of high altitude rocket radar
TIMING APPARATUS↗
Design of a compensation for an ARMA model of a discrete time system
The design of an optimal dynamic compensator for a multivariable discrete time system is studied. Also the design of compensators to achieve minimum variance control strategies for single input single output systems is analyzed. In the first problem the initial conditions of the plant are random variables with known first and second order moments, and the cost is the expected value of the standard cost, quadratic in the states and controls. The compensator is based on the minimum order Luenberger observer and it is found optimally by minimizing a performance index. Necessary and sufficient conditions for optimality of the compensator are derived. The second problem is solved in three different ways; two of them working directly in the frequency domain and one working in the time domain. The first and second order moments of the initial conditions are irrelevant to the solution. Necessary and sufficient conditions are derived for the compensator to minimize the variance of the output.
Mainemer, C. I.↗
Sources of unbounded priority inversions in real-time systems and a comparative study of possible solutions
In the design of real-time systems, tasks are often assigned priorities. Preemptive priority driven schedulers are used to schedule tasks to meet the timing requirements. Priority inversion is the term used to describe the situation when a higher priority task's execution is delayed by lower priority tasks. Priority inversion can occur when there is contention for resources among tasks of different priorities. The duration of priority inversion could be long enough to cause tasks to miss their dead lines. Priority inversion cannot be completely eliminated. However, it is important to identify sources of priority inversion and minimize the duration of priority inversion. In this paper, a comprehensive review of the problem of and solutions to unbounded priority inversion is presented.
Davari, Sadegh↗
Optimal control of nonlinear discrete time systems by mathematical programming
Nonlinear discrete time sampled systems optimal control by dynamic programming, with application to stochastic systems
Tabak, D.↗
Explicit asymmetric bounds for robust stability of continuous and discrete-time systems
The problem of robust stability in linear systems with parametric uncertainties is considered. Explicit stability bounds on uncertain parameters are derived and expressed in terms of linear inequalities for continuous systems, and inequalities with quadratic terms for discrete-times systems. Cases where system parameters are nonlinear functions of an uncertainty are also examined.
Gao, Zhiqiang↗
Intercontinental time and frequency transfer using a global positioning system timing receiver
The DSN has a requirement to maintain knowledge of the frequency offset between DSN stations with 3 x 10 to the minus 13th power and time offset within 10 microseconds. It is further anticipated that in the 1987-1990 era the requirement for knowledge of time offset between DSN stations will be less than 10 nanoseconds. JPL is using the Global Positioning System (GPS) Space Vehicles, as a development project, to transfer time and frequency over intercontinental distances between stations of the DSN and between the DSN and other agencies. JPL has installed GPS timing receivers at its tracking station near Barstow, California, and at its tracking station near Madrid, Spain. The details of the experiment and the data are reported. There is a discussion of the ultimate capabilities of these techniques for meeting the functional requirements of the DSN.
Clements, P. A.↗
Intercontinental time and frequency transfer using a global positioning system timing receiver
The Deep Space Network (DSN) has a requirement to maintain knowledge of the frequency offset between DSN stations within 3 x 10 to the -13th power and time offset within 10 microseconds. It is further anticipated that in the 1987-1990 era the requirement for knowledge of time offset between DSN stations will be less than 10 nanoseconds. The Jet Propulsion Laboratory (JPL) is using the Global Positioning System (GPS) Space Vehicles, as a development project, to transfer time and frequency over intercontinental distances between stations of the DSN and between the DSN and other agencies. JPL has installed GPS timing receivers at its tracking station near Barstow, California and at its tracking station near Madrid, Spain. The details of the experiment and the data are reported. There is a discussion of the ultimate capabilities of these techniques for meeting the functional requirements of the DSN.
Clements, P. A.↗
Stable feedback control of distributed parameter systems: Time and frequency domain conditions
Large space structures, or any mechanically flexible structures, are inherently distributed parameter systems (DPS) whose dynamics are modeled by partial, rather than ordinary, differential equations. Such DPS are described by operator equations on an infinite-dimensional Hilbert (or Banach) space. However, any feedback controller for such a DPS must be a finite-dimensional (and discrete-time) system in order to be implemented with on-line digital computers and a finite (small) number of actuators and sensors. There are many ways to synthesize such controllers; the Galerkin or finite-element approach is emphasized.
Balas, M. J.↗
A framework for software fault tolerance in real-time systems
A classification scheme for errors and a technique for the provision of software fault tolerance in cyclic real-time systems is presented. The technique requires that the process structure of a system be represented by a synchronization graph which is used by an executive as a specification of the relative times at which they will communicate during execution. Communication between concurrent processes is severely limited and may only take place between processes engaged in an exchange. A history of error occurrences is maintained by an error handler. When an error is detected, the error handler classifies it using the error history information and then initiates appropriate recovery action.
Anderson, T.↗
The effects of gravity on the circadian timing system
The physiological system responsible for the temporal coordination of an organism is the circadian timing system (CTS). This system provides two forms of temporal coordination. First, the CTS provides for synchronization of the organism with the 24 hour period of the external environment. This synchronization of the organism with the environment is termed entrainment. Second, this system also provides for internal coordination of the various physiological, behavioral, and biochemical events within the organism. When either of these two temporal relationships are disturbed, various dysfunctions can be manifest within the organism. Homeostatic capacity of other physiological systems may be reduced. Performance is decreased and sleep disorders, mental health impairment (e.g., depression), jet lag syndrome, and shift work maladaptation frequently occur. Over the last several years, several studies have evaluated the potential influence of gravity on this physiological control system by examining changes in rhythmic characteristics of organisms exposed to altered gravitational environments. The altered gravitational environments have included the microgravity of spaceflight as well as hyperdynamic fields produced via centrifugation.
Review↗
An Optimization Framework for Dynamic, Distributed Real-Time Systems
Abstract. This paper presents a model that is useful for developing resource allocation algorithms for distributed real-time systems .that operate in dynamic environments. Interesting aspects of the model include dynamic environments, utility and service levels, which provide a means for graceful degradation in resource-constrained situations and support optimization of the allocation of resources. The paper also provides an allocation algorithm that illustrates how to use the model for producing feasible, optimal resource allocations.
Eckert, Klaus↗