Modeling the Atmospheric Phase Effects of a Digital Antenna Array Communications System

In an antenna array system such as that used in the Deep Space Network (DSN) for satellite communication, it is often necessary to account for the effects due to the atmosphere. Typically, the atmosphere induces amplitude and phase fluctuations on the transmitted downlink signal that invalidate the assumed stationarity of the signal model. The degree to which these perturbations affect the stationarity of the model depends both on parameters of the atmosphere, including wind speed and turbulence strength, and on parameters of the communication system, such as the sampling rate used. In this article, we focus on modeling the atmospheric phase fluctuations in a digital antenna array communications system. Based on a continuous-time statistical model for the atmospheric phase effects, we show how to obtain a related discrete-time model based on sampling the continuous-time process. The effects of the nonstationarity of the resulting signal model are investigated using the sample matrix inversion (SMI) algorithm for minimum mean-squared error (MMSE) equalization of the received signal. I

Kinematyka dwupunktowego kontaktu koła z szyną

The railway transport in a maximum degree is conservative. For example, the design of wheelsets, practically, has not changed for the last 150 years. Such a long life was given to this tendency by its high reliability and simplicity of the design. It is considered, that the rigid connection of wheels by means of an axis provides a self-centering of wheelset within the limits of a cross backlash of a railway. The tread contact surfaces have a difficult profile. Researches of many scientists, dealing with the questions of interaction of wheels with rails, show that the classical approach to the wheelset design leads to many problems of the railway transport. Therefore, the authors of this article strived for deeper consideration of kinematics of a movement of vehicle by a railway

Data-Rate Estimation for Autonomous Receiver Operation

In this article, we present a series of algorithms for estimating the data rate of a signal whose admissible data rates are integer base, integer powered multiples of a known basic data rate. These algorithms can be applied to the Electra radio currently used in the Deep Space Network (DSN), which employs data rates having the above relationship. The estimation is carried out in an autonomous setting in which very little a priori information is assumed. It is done by exploiting an elegant property of the split symbol moments estimator (SSME), which is traditionally used to estimate the signal-to-noise ratio (SNR) of the received signal. By quantizing the assumed symbol-timing error or jitter, we present an all-digital implementation of the SSME which can be used to jointly estimate the data rate, SNR, and jitter. Simulation results presented show that these joint estimation algorithms perform well, even in the low SNR regions typically encountered in the DSN. I