Journal of Communications Technology and Electronics最新文献

Abstract

The paper presents the results of studying the dark currents of nB(SL)n structures with a superlattice (SL) in the barrier region based on Hg_1 – xCd_xTe grown by molecular beam epitaxy (MBE) in a wide range of experimental conditions. Dark currents were measured in the temperature range from 11 to 300 K for mesa structures with different cross-sectional diameters. The temperature dependences of the bulk component of the dark current density and the surface leakage current density are determined. It is shown that in the studied structures the current-voltage characteristics (CVCs) are formed by both the bulk and surface components of the current depending on the temperature and bias voltage.

Abstract—Sparse code multiple access (SCMA) is a variation of the nonorthogonal multiple access (NOMA) technology. SCMA communication systems use codebooks based on multidimensional constellations, which are generated using original mother constellations. The properties of these constellations largely determine the efficiency of SCMA communication systems. This paper proposes new mother constellations for use in SCMA systems. The proposed constellations were synthesized using a new analytical method for describing tabular functions in the form of a functional dependence of the signal on the vector of binary variables. This representation made it possible to reveal some patterns and determine the characteristics of constellations that affect the efficiency of their use. In particular, a new type of two-dimensional constellation with a parametric description, called Arrow constellations, is proposed. The proposed constellations belong to the class of multidimensional constellations and can be used both independently and in codebook synthesis in SCMA systems. The best effect from using these constellations is observed in SCMA systems with a turbo receiver, in which both the demodulator and the decoder are operated with the same feedback.

Abstract

The classical structure of nBn photodiode based on InAsSb for the detection in the mid-wave infrared (MWIR) range is considered. The optical absorption in the heterostructure at any position is calculated with allowance for the features of absorption of the InAsSb active layer, in particular, the Burstein–Moss effect and the Urbach rule. The quantum efficiency and spectral response of the sensitivity are calculated taking into account multiple reflections at the interfaces of the heterostructure and the features of free-carrier absorption in the GaSb substrate. The optimal thickness of the active layer of the nBn photodiode is determined for various lifetimes of minority carriers. Relatively high BLIP detectivity of the FPA is shown.

Abstract

Studies and analysis of samples with heteroepitaxial structure based on a InGaAs solid solution grown by molecular beam epitaxy on a GaAs substrate are presented. The composition and thickness of the layers of the structure were determined by photoluminescent spectroscopy at room temperature and scanning electron microscopy, respectively. Transmission spectra were measured on an IR Fourier spectrometer. An analytical model of the spectral characteristics of the studied structures has been developed. By solving the inverse problem, the structural parameters of the structure and the composition of the InGaAs active layer were determined by the fitting method. A comparative analysis of experimental and theoretical data showed a small spread of values for the thickness (less than 65 nm) and the composition of the absorbing layer (less than 0.04). The correctness and speed of the developed method of characterization of semiconductor structures without plate destruction is shown.

Abstract

The effect of anomalous (with respect to noise power spectral density) TDI channels on the probability of detection of small objects by FPAs is considered. A series of FPA output images simulating the signals of TDI channels with four main types of noise PSDs is generated, the probability of detection of a small object is calculated, and the efficiency of various combinations of linear filters used in intraframe processing is evaluated. It is found that TDI channels with low-frequency noise most significantly affect the probability of detection of a small object, and the successive application of an adaptive recursive filter and a window filter that is quasi-matched with the signal leads to an increase in the probability by 22% even in the presence of 6% anomalous TDI channels in the FPA.

Abstract—

The problem of online probabilistic time series forecasting is considered. Probabilistic forecasts are obtained as a result of the application of conformal forecasting systems. The conformal forecasting system is defined on the basis of point forecasts of the regression algorithm. The corresponding probability distribution function is used to assess the degree of reliability of the algorithm’s predictions. The paper considers the case when at each moment of time several competing methods (experts) present their forecasts in the form of distribution functions. These distributions are constructed online from point predictions using the conformal prediction method. The probabilistic forecasts of experts are combined using an aggregating algorithm into one probabilistic forecast at each stage of the forecasting process, while expert forecasts can be used at a discount. A technology has been developed for constructing predictive expert algorithms and aggregation of their probabilistic forecasts on the example of the problem of forecasting the hourly load of an electric network depending on the temperature forecast. The results of numerical experiments on real data are presented; a comparative analysis of the method of conformal predictions and the method of Gaussian mixtures is carried out.

Abstract

The dynamics of the temperature of particles with a characteristic size of 10^–7–10^–6 m at the boundary of Earth’s atmosphere and outer space is considered. Using graphite as an example, it is shown that at an altitude of 80–90 km from Earth’s surface, particles with a size of ∼5 × 10^–7 m or less can be heated above the temperature of the beginning of the glow (~900 K), reaching temperatures of more than 2000 K with a light turquoise glow. Based on the results obtained, it is concluded that the silvery clouds observed in the false dawn and after sunset from Earth’s surface are a cluster of white-hot nanoparticles.

Abstract

A review analysis of the problematic aspects of creating high-power nanosecond frequency-pulse solid-state lasers for use in various technological fields, including the electronics industry, has been carried out. Considered installations with various pumping methods (lamp and diode) in the frequency (about 100 Hz) of generation in the micron region of the infrared range. The possibilities of increasing the energy potential of influencing pulses in master oscillator-amplifier circuits, including two-pass amplification, are analyzed. Discussed possibilities and prospects for the use of lasers with active elements (AEs) on glass, as well as the synthesis of large-sized garnet single crystals with an admixture of rare earth elements and optical ceramics for the production of AEs.

Abstract—5G cellular systems provide a new service called Ultra-Reliable Low-Latency Communications (URLLC). In many URLLC scenarios (e.g., intelligent transport systems), users move at high speed and transmit data in the uplink. The base station shall assign transmission parameters that satisfy the strict quality of service requirements of URLLC applications and consume the least amount of channel resources. At high speed, users often change the serving base station. In this case, the task of selecting transmission parameters is complicated by the fact that the base station does not have channel quality measurements for the new user. This paper proposes various methods for selecting the initial transmission parameters when user connects to the base station. Using simulations, the paper compares various methods for different user speeds. Recommendations are given on the selection of initial parameters that provide a low amount of consumed channel resources.

Abstract

A screen that absorbs electromagnetic radiation has been proposed, a micromachine technology for its production has been developed based on volumetric microprocessing of single-crystalline silicon, experimental samples have been manufactured, and their characteristics have been studied. It is shown that in the measurement frequency range of 14.7–26.7 GHz there is a smooth increase in the attenuation introduced by the absorbing screen with increasing frequency to a maximum value of 20–23 dB at a frequency of about 20 GHz, and then a smooth decline. The amount of attenuation increases as the length of the screen increases and can reach any value. The manufactured samples of the absorbing screen provide significant attenuation in the required frequency range with a small substrate thickness and can be successfully used in space equipment to ensure electromagnetic compatibility.