The dependence of the noise equivalent temperature difference (NETD) of a superconducting integrated receiver (SIR) on the receiver noise temperature and the inputsignal level has been investigated. An unprecedented NETD of 13±2 mK has been measured at a SIR noise temperature of 200 K, intermediate-frequency bandwidth of 4 GHz, and time constant of 1 s. With a decrease in the input signal, an improvement in the NETD is observed. This effect is explained by a reduction in the influence of the instabilities of the receiver power supply and the amplification circuit that occur when the input signal is decreased.
Nowadays, many devices require a wireless Internet connection, while the available frequency spectrum is limited. The nonorthogonal multiple access (NOMA) is a multiplexing technology that can significantly improve spectral efficiency and thus solve this problem. In this paper, the use of NOMA in Wi-Fi networks with two traffic types, Web traffic and Internet of Things (IoT) traffic, is investigated. Web traffic is one of the main Internet traffic types. It consists of relatively small data flows that need to be quickly delivered to users. IoT traffic consists of very short data flows compared to Web traffic, but there can be a lot of IoT flows due to a large number of IoT devices. In this paper, we propose an algorithm for resource allocation in Wi-Fi networks with the NOMA. This algorithm takes into account the traffic of both types and its performance is investigated by simulation.
Numerical simulation of interaction processes in the electron–positron matter (EPM) is numer ically simulated in the framework of the specific research area, gammaelectronics, which is concerned with the problem of creation and long existence of an EPM with extremely high energy, which is released in the process of delayed annihilation. Interaction processes in the EPM are studied by the methods of the classical largeparticle model and a quantum model using macroscopic wave functions of electrons and positrons. In contrast to the point kinematic approach used in quantum electrodynamics, large particles are considered as deformed bunches of charge.
The error exponent of the regular graph-based binary low-density parity-check (LDPC) codes under the maximum likelihood (ML) decoding algorithm in the binary symmetric channel (BSC) is analyzed. Unlike most other papers where error exponents are considered for the case when the length of LDPC codes tends to infinity (asymptotic analysis), the finite length case (finite length analysis) is considered. In this paper, a method of deriving the lower bound on the error exponent for a regular graph-based LDPC code with finite length under ML decoding is described. Also we analyze Dependences of the error exponent on various LDPC code parameters are also analyzed. The numerical results obtained for the considered lower bound are represented and analyzed at the end of the paper.
Fifth generation (5G) networks should use millimeter-wave (mmWave) frequencies to provide high data transmission rate. However, the performance of such networks significantly suffers from the Transmission Control Protocol (TCP) used by various applications for data transmission. In this article, it is shown that the data download rate in 5G networks is much lower than the capacity of the mmWave link because of the Slow Start algorithm used in the TCP. We analyze various approaches to the problem and propose to use the xStream platform for adjusting TCP parameters. This approach significantly increases the download rate and does not require any changes to the software of client devices, which simplifies the implementation of the proposed approach in real systems.
A phonetic approach to the problem of automatic recognition of isolated words is investigated.The phonetic encoding method whereby each word from a vocabulary is associated with the code sequenceof stable phonemes is proposed. The informationtheoretical estimate of vocabulary confusability, the calcuations of which rely on the phonetic database of a speaker and the communications channel SNR, is synthesized using the Kullback–Leibler divergence properties. In the experimental study of the proposed method,the mutual influence between the recognition quality and the proposed estimate of confusability is demonstrated by solving the problem of recognition of words in the Russian speech. It is established that the introduced requirement to isolated syllable pronunciation makes it possible to attain the 90–95% accuracy of recognition for vocabularies containing 2000 words.
We consider the regression problem, i.e. prediction of a real valued function. A Gaussian process prior is imposed on the function, and is combined with the training data to obtain predictions for new points. We introduce a Bayesian regularization on parameters of a covariance function of the process, which increases quality of approximation and robustness of the estimation. Also an approach to modeling nonstationary covariance function of a Gaussian process on basis of linear expansion in parametric functional dictionary is proposed. Introducing such a covariance function allows to model functions, which have non-homogeneous behaviour. Combining above features with careful optimization of covariance function parameters results in unified approach, which can be easily implemented and applied. The resulting algorithm is an out of the box solution to regression problems, with no need to tune parameters manually. The effectiveness of the method is demonstrated on various datasets.
The results of numerical simulation of electrodynamic characteristics of a slow-wave structure shaped as a folded waveguide and an electron–optical system of a three-millimeter-band pulse travelling wave tube with an output pulsed power of up to 50 W are presented. The matching devices, the interaction space, and the electron–optical system are calculated, which allows determination of their constructive parameters. The effect of loss caused by the roughness of the surfaces of the walls of the electrodynamic system on the output characteristics of the device is estimated.
The electrodynamic characteristics of the helical slow-wave structure of a high-power pulse traveling-wave tube operating in the centimeter wavelength range are calculated by means of the solution of the dispersion equation and simulation. Special attention is focused on the effect of a helix wire profile on the electrodynamic characteristics of the system. The results of the theoretical study are compared with the experimental data.
A numerical simulator of the interaction processes in helical traveling-wave tubes is developed on the basis of the method of large particles in the 1D approximation with the use of the calculation methods developed previously. The output characteristics (frequency dependences of the output power and gain factor) of high-power traveling wave tubes based on helical slow-wave structures for operation in the C and Ku wave bands are studied theoretically and experimentally. It is shown that the results of numerical simulation are in satisfactory agreement with experimental data.
The self-excitation of electron generators based on the flows of nonlinear excited oscillators obtained by a centrifugal electrostatic focusing is analyzed. The possibility of the master–slave synchronization of the generators is demonstrated. It is shown that the mutual synchronization leads to the narrowing of the spectral line.
The article is devoted to studying the properties of a suboptimal sequential procedure of testing hypotheses when the set of possible distributions is nonparametric. It is assumed that the tails of the distributions exponentially decrease at infinity but the exact value of the rate of the decrease in not known. Procedures are considered as admissible if they provide for a given upper bound for the maximum error probability. The risk function of the procedure is the maximum expectation duration of observations for all distributions from the true hypothesis.
Results of the numerical simulation of the slowwave structure and the electronoptical system of a wideband continuouswave travelingwave tube with an output power of 250 W and gain of 23 dB, which is designed for operation in an X/Kuband vacuum solidstate amplifying module, are given.
Light diffraction in a nonuniform acoustic field induced by a wedge shaped piezoelectric trans ducer is theoretically studied. Electric, acoustic, and acoustooptic characteristics of cells with such transducers are calculated. The emphasis is on the features of cell operation in the case when a piezoelectric plate is excited at the third harmonic. The acoustic field is shown to possess a complex amplitude and phase structure varying with the ultrasound frequency. The efficiency of acoustooptic diffraction depending on the acoustic wave amplitude and phase mismatch is studied. It is established that the efficiency of the Bragg diffraction can approach 100% despite a noticeable phase mismatch. Optimal values for the ultrasound power and angles of light incidence onan acoustooptic cell are found.
A model of the slowwave cavity structures that can be used for the analysis of electrodynamic parameters and excitation by the fixed current is electrodynamically substantiated. A possibility of the calcu lation of electrodynamic parameters using the 3D simulation is demonstrated for the slowwave cavity struc tures. The calculated electrodynamic parameters of the two and fourport slowwave structures are pre sented.
Microwave devices designed on the basis of multipole lenses (ring electromagnetic structures using resonant sections of slow-wave structures) are analyzed. The possibility of development on the basis of these lenses of a low-noise amplifier and a microwave multiplier, which ensure long-term interaction of the electron beam and the transversely extended electromagnetic field with continuous extraction of energy, is shown.
The suppression of the nonlinear distortions in amplifier using the effect of the envelope signal of the amplified HF oscillations on the amplifier parameters is analyzed. A slow (on the time scale of the HF oscillations) variation in the parameters gives rise to additional frequency components of oscillations that compensate for the nonlinear distortions of the original signal. Several variants to employ the compensating signal using the feedback circuits in the transistor amplifiers and variations in the electron-beam current in TWT in the absence of such circuits are considered. The suppression of the nonlinear intermodulation distortions (IMDs) of the test two_frequency signal is studied for the above variants and the suppression of the third_order IMD by 6–19 dB corresponds to the known experimental data on the microwave transistor amplifier. The generalization of the quasistationary method for the analysis of the nonlinear transformation of signals allows the analysis of the amplification and suppression of IMD for more complicated multifrequency signals that are used in radio systems.