added a research item
Предложены вычислительные процедуры, позволяющие осуществить частотное уплотнение узкополосных каналов связи на основе неортогональной частотной дискретной модуляции сигналов.
The phase multifrequency methods of radar range measurements from the viewpoint of solving the problem of digital spectral analysis are proposed in this study. At present, the OFDM type orthogonal signals have gained widespread use for solving the range finding problems. However, the measurement methods based on using these signals lead to errors in range finding in the presence of Doppler frequency shift. In addition, such methods feature limited spectral efficiency and noise immunity. All this in full measure can be referred to the well-known methods of superresolution. The fundamental distinction of the approach proposed in this paper is the use of multifrequency nonorthogonal signals (N-OFDM) in which the location of frequencies of harmonic components is not tied to maximums of the amplitude-frequency characteristics (AFC) of filters synthesized by using the fast Fourier transform (FFT). The non-orthogonal signal based methods considered in this paper could be viewed as a more general case with respect to OFDM. An advantage of the proposed method is the possibility of arbitrary variations of multifrequency signal parameters, including frequencies of harmonic components (subcarriers) and the length of sample observed. It allows us to take into account the Doppler shift of subcarriers, provide for the control of range resolution magnitude and the attainable signal-to-noise ratio. Such an approach makes it possible to implement an adaptive offset from frequency concentrated interference by the selection of values of subcarrier frequencies that are least susceptible to negative impact, to reduce the peak factor of a multifrequency signal mixture, and improve the electromagnetic compatibility of radar equipment at the expense of signal frequency bandwidth narrowing. In addition, the nonorthogonal frequency plan prevents the communications surveillance means to determine the distance to radar using the same phase difference of subcarriers that is possible, in principle, while using the fixed frequency grid in the case of OFDM signals. Based on the theory of multichannel analysis, the paper presents a system of equations derived that ensures the system solution in the case of several targets. The range estimation method proposed in this paper and based on the maximum likelihood can potentially guarantee the attainment of the lower Cramer-Rao bound for dispersions of unbiased estimates of signal parameters. In this case, all the other methods of superresolution with respect to the maximum likelihood method are known to be quasi-optimal. You can read the full text at the link: https://rdcu.be/cycvi
This report is considered different aspects of the concept of the networked distributed engine control system (DECS) of future air vehicles. These aspects include the following: the structure of multiple networks similar to NATO Generic Vehicle Architecture (NGVA), the role of Artificial Intelligence (AI) in DECS, and the use Augmented Reality (AR) as Human-Machine Interface between AI and pilots. Deployment of AI solutions for monitoring equipment in on-board infrastructure can be provided on physical or virtual servers and in the clouds. In this case, it is possible to use various methods of alerting the pilot and ground personnel on the basis of AR. The use of AI allows covering an unlimited set of scenarios, to provide an assessment of the likelihood of equipment failure, classification alarm is normal, and recognition of the development of defects. To collect Big Data from sensors and the pre-processing of this data before a machine learning (ML) procedure it is proposed to form data sets with the help of the face-splitting matrix product. To decrease the time of reaction of Neural Networks it has been suggested the implementation of advanced tensor-matrix theory on the basis of penetrating face product of matrices. Other important results of the report are a possible version of the AR data format for DECS and a proposal about the use of non-orthogonal frequency discrete multiplexing (N-OFDM) signals to data transfer via fibre optics.
Multistage versions of I/Q-demodulation of OFDM signals which allow to secure noise-immunity to the communication channel are considered in this article.
A method of synthesis of odd-order I/Q demodulators based on replacing the multistage demodulation schemes with equivalent single-stage ones is proposed. The calculation of coefficients of single-stage odd-order I/Q demodulator, which is equivalent to multistage scheme in terms of the waveform of its amplitude-frequency characteristic (AFC), is based on the sample-wise analysis of the process of forming the response of the demodulator output stage that involves the sampling the harmonic signal voltages at the output of analog-to-digital converter (ADC). An example of synthesis of 11-sample former of quadrature components is considered for illustrating the application peculiarities of the method proposed for synthesis of odd-order I/Q demodulators. The comparative results of its AFC calculations are presented. The analytical description of the response of the specified unit in terms of the coefficients of even-order I/Q demodulators forming the multistage scheme has been derived. A number of regularities intrinsic to coefficients of odd-order I/Q demodulators was established, including the regularities characterizing the dependence of their dynamic range on values of weighting coefficients of the initial multistage scheme.
The Kramer-Rao bound for amplitude estimations of N-OFDM signals was investigated in the case of the usning of a digital antenna array.
The method of the space-time encoding of signals of troposphere communication with use of the improved technology of multi-МІМО is presented in the article. The resulted method differs from the known formulas of signal processing by generalisation on outputs of the receiving channels and the account of directional diagrams of antenna elements. The new approach to the formalized representation of the response of the linear digital antenna array which fundamental advantage is the accounts of the determined component in a matrix of transmit characteristics of the channel is offered.
In article the method of non-orthogonal frequency division multiplexing (N-OFDM) on the basic of the Hartley transform with quadrature amplitude modulation (QAM) of the frequency carriers is considered. Application of a real kernel of functions Hartley provides calculations without use of complex numbers and, as consequence, allows to reduce computing expenses, to simplify hardware realisation of method N-OFDM. Modulation of separate frequency carriers signals N-OFDM with use of QAM modulation raises throughput of communication channels.
Two-step processing of OFDM (N-OFDM) signals in digital antenna array was proposed
Рассмотрены сущность и результаты имитационного моделирования передачи тестового сообщения, модулированного по методу N-OFDM на основе базисных функций Хартли. Дано описание эксперимента передачи и приема гармонического сигнала на основе преобразования Хартли. Полученные результаты подтверждают возможность реализации метода N-OFDM на основе преобразования Хартли.
In this work it has been done the analysis of possible variants of the method of non-orthogonal frequency division multiplexing (N-OFDM) realization. As a base conversion it's offered to use the Hartley transform, which will allow essentially to reduce calculating expenses and to simplify the method N-OFDM realization.
In this report the question about using the increasing of carring capathity of radio relay communication systems owing to using the method of non-orthogonal frequency descret modulation(N-OFDM) with usage the orthogonally polarized rays is studied.During the research the synthesis of the demodulation procedure N-OFDM signals was made taking into account the cross-polarized hindrance.To analize maximum capabilities of the presented method it has been proposed to use the well-known methodology of calculating the lower barrier of Kramer-Rao(LBKR)for the potentially achieving dispersion of mistakes in measuring the amplitude ingrediens.