Vol 50, No 6 (2016)

The possibility of using asynchronous sigma-delta modulation in primary signal converters for precision event timers is considered. A demodulation method based on the moving averaging of a signal and on using the measurements of zero-crossing instants is investigated. The moving averaging of a signal is shown to minimize the effect of timing errors on the accuracy of recovering the waveform of demodulated signals.

The paper analyzes high energy concealment factor techniques for satellite communications systems by lowering the carrier frequency (to f₀ = 100…30 MHz) is carried out. According to research experiments, fading in communication channels with diversity reception is also determined by the influence of small-scale variations of the ionospheric total electron content. A procedure is developed for calculating the dependence of the energy concealment factor on carrier frequency selection for satellite communications system using space-diversity signal reception by two antennas. The calculation procedure is based on the standard deviation of small-scale variations of the ionospheric total electron content.

It is often desirable to have statistical tolerance limits available for the distributions used to describe time-to-failure data in reliability problems. For example, one might wish to know if at least a certain proportion, say β, of a manufactured product will operate at least T hours. This question cannot usually be answered exactly, but it may be possible to determine a lower tolerance limit L(X), based on a random sample X, such that one can say with a certain confidence γ that at least 100β% of the product will operate longer than L(X). Then reliability statements can be made based on L(X), or, decisions can be reached by comparing L(X) to T. Tolerance limits of the type mentioned above are considered in this paper, which presents a new approach to constructing lower and upper tolerance limits on order statistics in future samples. Attention is restricted to invariant families of distributions under parametric uncertainty. The approach used here emphasizes pivotal quantities relevant for obtaining tolerance factors and is applicable whenever the statistical problem is invariant under a group of transformations that acts transitively on the parameter space. It does not require the construction of any tables and is applicable whether the past data are complete or Type II censored. The proposed approach requires a quantile of the F distribution and is conceptually simple and easy to use. For illustration, the Pareto distribution is considered. The discussion is restricted to one-sided tolerance limits. A practical example is given.

This paper addresses an adaptive method for designing a sensorless trajectory tracking control scheme for a wheeled mobile robot. In order to reduce the cost of the robot, a new Nonlinear Observer (NOB) is used to leave out velocity sensors in the robot. Also, an adaptive model reference technique is used for designing the dynamic controller. In order to ensure the implementability of proposed controller, dynamic controller and nonlinear observer are designed in the presence of uncertainties. In addition, the Observer-based Kinematic Controller (OKC) is designed in the presence of sliding velocity. In order to improve the performance of the kinematic controller, sliding velocity is estimated and used for modification of kinematic controller. Finally, the effectiveness of the proposed method is demonstrated by simulations.