Radio Receiver Research Articles

On Performance of a SWIPT Enabled FD CRN With HIs and Imperfect SIC Over α–μ Fading Channel

This paper investigates the performance of overlay full-duplex cooperative cognitive radio network in the presence of imperfect self interference cancellation over generalized <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\alpha -\mu $ </tex-math></inline-formula> fading channels effected by nonlinearity of the propagation medium. In practice, physical transceivers create distortion which degrades the performance, hence, the impact of transceiver hardware impairments (HIs) is considered. To overcome the energy constraint problem, a hybrid simultaneous wireless information and power transfer receiver is adopted that includes both the time switching and the power splitting protocols. To improve reliability of the communication link, we employ a hybrid relaying protocol that combines both the decode-and-forward and amplify-and-forward relaying protocols. The closed-form expressions of outage probability and asymptotic outage probability are derived for both the primary and the secondary networks over <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\alpha -\mu $ </tex-math></inline-formula> fading channels. The diversity order, throughput, and energy efficiency of the considered network are derived. Optimal values of time switching factor is obtained for which the considered network exhibits optimum outage probability, maximum throughput and energy efficiency. Further, optimal value of power splitting factor is obtained for which the considered network shows maximum throughput and energy efficiency. Finally, the Monte-Carlo simulations validate correctness of the derived closed-form expressions.

The Minimum Principle of SINR: A Useful Discretization Tool for Wireless Communication

Theoretical study of optimization problems in wireless communication often deals with tasks that concern a single point. For example, the power control problem requires computing a power assignment guaranteeing that each transmitting station s i is successfully received at a single receiver point r i . This paper aims at addressing communication applications that require handling two-dimensional tasks (e.g., guaranteeing successful transmission in entire regions rather than at specific points). The natural approach to two-dimensional optimization tasks is to discretize the optimization domain, e.g., by sampling points within the domain. The straightforward implementation of the discretization approach, however, might incur high time and memory requirements, and moreover, it cannot guarantee exact solutions. The alternative proposed and explored in this paper is based on establishing the minimum principle 1 for the signal to interference and noise ratio (SINR) function with free space path loss (i.e., when the signal decays in proportion to the square of the distance between the transmitter and receiver). Essentially, the minimum principle allows us to reduce the dimension of the optimization domain without losing anything in the accuracy or quality of the solution. More specifically, when the two-dimensional optimization domain is bounded and free from any interfering station, the minimum principle implies that it is sufficient to optimize the SINR function over the boundary of the domain, as the “hardest” points to be satisfied reside on the boundary and not in the interior. We then utilize the minimum principle as the basis for an improved discretization technique for solving two-dimensional problems in the SINR model. This approach is shown to be useful for handling optimization problems over two dimensions (e.g., power control, energy minimization); in providing tight bounds on the number of null cells in the reception map; and in approximating geometric and topological properties of the wireless reception map (e.g., maximum inscribed sphere). The minimum principle, as well as the interplay between continuous and discrete analysis presented in this paper, are expected to pave the way to future study of algorithmic SINR in higher dimensions.

In situ ground-based mobile measurement of lightning events above central Europe

Abstract. This article describes the equipment (and the advantages of the equipment) used for in situ ground measurements of thunderstorm phenomena with measuring cars. By using all-sky high-speed cameras, radio receivers, and electric field measurements, typical lightning discharges in the central European region have been characterized. Measurements of ionizing radiation during storms using a gamma spectrometer were also performed. At ground level, no ionizing radiation originating from storm clouds was detected, although during other experiments (using the same equipment at lower altitudes corresponding to the lower part of storm clouds) ionizing radiation was detected. We showed that radio antennas with appropriately constructed receivers and all-sky high-speed cameras are devices that can significantly contribute to the understanding of processes taking place in storm clouds during lightning discharges. On the contrary, measurements of the vertical electric field did not provide any new information about the processes occurring in thunderclouds.

A Roadmap for Gigabit to Terabit Optical Wireless Communications Receivers.

Silicon photomultipliers' relatively large areas and ability to detect single photons make them attractive as receivers for optical wireless communications. In this paper, the relative importance of the non-linearity and width of SiPMs' fast output in their performance in receivers is investigated using Monte Carlo simulations. Using these results, the performances of receivers containing different SiPMs are estimated. This is followed by a discussion of the potential performances of arrays of existing SiPMs. Finally, the possible dramatic improvements in performance that could be achieved by using two stacked integrated circuits are highlighted.

Optoelectronic Device for Measuring Radio Signal Samples and Evaluating Its Accuracy Characteristics

When using quadrature signals in radio channels, flat and selective fading, multipath radio reception, intersymbol interference, and jitter occur. In addition to the need to accurately estimate the value of the phase difference at the current and previous clock intervals, a critical factor in receiving and demodulating such signals is the accuracy of measuring the amplitude of their samples. When demodulating such signals, an approach is possible, the basis of which is to measure the values of individual signal samples at discrete time points with higher accuracy than in existing electronic devices. Such an approach can be implemented by an optoelectronic device in which a coherent luminous flux is formed, the parameters of which are modulated by a voltage proportional to the readings of the received radio signal. Using a modulated light flux, an interferogram is formed, the parameters of which are directly related to the parameters of this light flux and accordingly to the parameters of the received radio signal. This makes it possible, by increasing the accuracy of estimating radio signal samples, to increase the base of the alphabet used for code manipulation, the efficiency of using the allocated frequency band for transmitting information and reduce the probability of a bit error. The article presents a mathematical model for converting the parameters of the received radio signal into the parameters of the generated interferogram. By mathematical modeling the accuracy characteristics of an optoelectronic device for measuring radio signal samples were evaluated. The results of mathematical modeling illustrating the relationship of the parameters of the optical elements of the device with the accuracy of estimates of the radio signal counts are presented. The practical significance of the proposed optoelectronic device can be used as an independent device for analog-to-digital conversion of radio signals, as well as part of demodulators for QAM and OFDM signals in networks and communication systems of 5G and the next generations.

Carrier Phase Ranging with DTMB Signals for Urban Pedestrian Localization and GNSS Aiding

China developed its Digital Television (DTV) standard in 2006, known as Digital Television Terrestrial Multimedia Broadcasting (DTMB), which employs time-domain synchronous orthogonal frequency division multiplexing (TDS-OFDM) as the modulation method. In contrast to Global Navigation Satellite Systems (GNSSs), DTV signals have higher transmitting power, wider coverage, larger bandwidth, and fixed transmitter location. This paper explores the positioning performance of DTMB signals, and the potential to improve GNSS positioning accuracy in urban environments. Specifically, a solution is proposed, and a software-defined radio receiver is developed for wireless localization. Without changing the current signal structure, the pseudorandom noise (PN) sequences in the signal are used for signal acquisition and carrier phase ranging. The carrier phase of the first arrived path is extracted by the least squares matching pursuit method. Both static and dynamic field tests were conducted to verify the proposed ranging and positioning method. Centimeter-level ranging accuracy was achieved in the static scenario, while meter-level ranging accuracy was achieved in the dynamic scenario. As one possible application, the proposed ranging method was combined with GPS pseudorange measurements to achieve higher accuracy position results in an urban pedestrian scenario, especially when there is only a limited number of visible satellites.

A Design of Wireless Power Receiver With Gate Charge Recycled Dual-Mode Active Rectifier and Step-Down Converter With 88.2% System Efficiency for Power Management IC

This article presents a power management integrated circuit for a wireless power receiver unit. A dual-mode high-efficiency active rectifier design is based on alliance for wireless power (A4WP) and wireless power consortium (WPC) standards. A gate charge recycling technique is proposed in the dual-mode active rectifier so that the current generated by the switching of the high side gate driver can be recycled to the rectifier output voltage in order to enhance efficiency. A step-down dc–dc converter with a proposed bootstrap circuit and dynamic pull-up resistor gate driver circuit is designed. The chip is implemented in a 0.18-μm bipolar-CMOS double-diffused metal-oxide-semiconductor process. The total die area, including the pad, is 2.64 mm × 2.6 mm. The measurement results show that the active rectifier achieves peak power conversion efficiency (PCE) of 94.7% and generates an output voltage of 7.68 V in WPC mode and 9.1 V with 93.4% efficiency in A4WPC mode. The input voltage varies from 10 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P-P</sub> –12 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P-P</sub> . Similarly, the step-down dc–dc converter obtains a peak PCE of 93.2% at a load current of 500 mA while producing an output voltage of 5 V. The overall system efficiency at A4WP and WPC mode are 86.7% and 88.2%, respectively.

Shared Impedance Noise Coupling in Radio Receivers

Shared Impedance Noise Coupling in Radio Receivers

Mattering the Invisible: Technologies, Bodies, and the Realm of the Spectral ed. by Diana Espírito Santo and Jack Hunter

Reviewed by: Mattering the Invisible: Technologies, Bodies, and the Realm of the Spectral ed. by Diana Espírito Santo and Jack Hunter Claire Fanger diana espírito santo and jack hunter, eds. Mattering the Invisible: Technologies, Bodies, and the Realm of the Spectral. New York: Berghahn Books, 2021. Pp. 329. This book focuses on the way matter and material technologies are involved in making paranormal experiences possible. The word "paranormal" is not used in the title but appears in the first sentence and recurs frequently thereafter. The book shares a basic theoretical framework with other work that has been done on material religion, the introduction citing sources starting with Alfred Gell leading to Karen Barad with nods at Bruno Latour in the middle—a familiar theoretical pantheon. The editors argue that in these accounts, we need to think not about "the meanings of messages" (11)—that is, not about what the dead or other discarnate entities may communicate within such experiences, but rather about how these experiences convey presence—they are all at least in part about a sense of contact with a numinous reality. For this reader it was something of a problem that the word "paranormal" was not defined anywhere, not in the introduction, the conclusion, nor in the essays. A large array of very different sorts of materials seems to be subsumed under the heading in this book, which nevertheless offers some very interesting reading. Many if not most of the chapters concern things that might elsewhere be categorized as "anthropology of religion." But how does "religion" intersect with the "paranormal?" What is the advantage of using the word "paranormal" here? I will return to these questions later. One reason I wanted to review this book is that I know Diana Espírito Santo is good at writing about the paranormal. In her work, the idea of what constitutes the "paranormal" is somehow transparent in a way that seems connected with the kinds of stories she tells: she can stun readers with marvels and lure them into the human dimension of stories that challenge credibility and yet escape disproof. Her chapter in this book is no exception. The rest of the book is a bit of a mixed bag inasmuch as not all the chapters constitute stories of clearly paranormal experiences as far as I can see—neither in its ordinary colloquial sense of something that is "above or beyond normal," nor in the storyteller's way that Espírito Santo does (if those are in fact distinct). The book comprises ten chapters, with an introduction and conclusion. I will summarize the chapters before returning to the issues of definition. In Chapter 1, "Organicism and Psychical Research: Where Mediums and Mushrooms Meet," Jack Hunter begins by describing how, in his work with mediums of the Bristol Spirit Lodge, instruments are used to coax the [End Page 459] reluctant spirits into speech—a slow halting process which "does not seem to be so much a case of turning the medium on like a radio receiver and then tuning in with a dial but rather is more like a process of nurturing—a participatory process of encouragement and growth, gradually enabling the spirit to manifest" and "is perhaps better understood using an organic rather than technological metaphor" (38). This is interesting and feels useful, though most of chapter is theoretical, in fact concerned with the superiority of organic to machine metaphors for a general idea of what the world is about, which I found dry and in spots implausible. Chapter 2, by Miguel M. Algranti, "Semantics of the Suffering: Torture Technologies and Mediumship in Buenos Aires," gives a brief history of Esoteric and Spiritist groups in Argentina ending with a group among whom the author conducted fieldwork: the Basilio Scientific School Association (BSSA). He discusses how Martha, his informant in this context, channels a young man who says that his spirit was broken when he was tortured with a cattle prod; he gave away information that he should have kept to himself. The point of Martha's channeling is to offer healing to the spirit of this dead youth through Martha's replication of the physical condition of his...

Batteryless, Wireless, and Secure SoC for Implantable Strain Sensing

The past few years have witnessed a growing interest in wireless and batteryless implants, due to their potential in long-term biomedical monitoring of in-body conditions such as internal organ movements, bladder pressure, and gastrointestinal health. Early proposals for batteryless implants relied on inductive near-field coupling and ultrasound harvesting, which require direct contact between the external power source and the human body. To overcome this near-field challenge, recent research has investigated the use of RF backscatter in wireless micro-implants because of its ability to communicate with wireless receivers that are placed at a distance outside the body ( 0.5 m), allowing a more seamless user experience. Unfortunately, existing far-field backscatter designs remain limited in their functionality: they cannot perform biometric sensing or secure data transmission; they also suffer from degraded harvesting efficiency and backscatter range due to the impact of variations in the surrounding tissues. In this paper, we present the design of a batteryless, wireless and secure system-on-chip (SoC) implant for in-body strain sensing. The SoC relies on four features: 1) employing a reconfigurable in-body rectenna which can operate across tissues adapting its backscatter bandwidth and center frequency; 2) designing an energy efficient 1.37 mmHg strain sensing front-end with an efficiency of 5.9 mmHg·nJ/conversion; 3) incorporating an AES-GCM security engine to ensure the authenticity and confidentiality of sensed data while sharing the ADC with the sensor interface for an area efficient random number generation; 4) implementing an over-the-air closed-loop wireless programming scheme to reprogram the RF front-end to adapt for surrounding tissues and the sensor front-end to achieve faster settling times below 2 s.

A Reconfigurable RF Filter With 1%–40% Fractional Bandwidth for 5G FR1 Receivers

This paper presents a radio frequency front-end (RFFE) for 5G New Radio (NR) receivers operating in Frequency Range 1 (FR1). The core of this RFFE is a synthetic fourth-order Q-enhanced RF filter employing gm-boosting, noise-cancelling, capacitive cross-coupling, and forward body-biasing techniques to achieve 1.7 GHz to 6.4 GHz operating range and 1 adjustable fractional bandwidth (FBW). The function of the filter is based on subtracting out-of-phase signals in the passband and in-phase signals in the stopband. Two Q-enhanced LC resonators are utilized for outphasing. The filter is preceded by a low-noise transconductance amplifier, and it is followed by a programmable gain amplifier and a differential buffer stage for the measurement purposes and gain equalization. The experimental results demonstrate that the voltage gain is tunable between 18 and 47 dB with 0.2 dB steps, which leads to an equalized output power in all the filter configurations. Fabricated in 22 nm Fully Depleted Silicon on Insulator (FD-SOI) technology, the RFFE achieves 4.6 dB NF, -14 dBm IB-IIP3, and 26 dBm IB-IIP2 at 4 GHz. Notably, the fourth-order steep roll-off provides 22 dBm OOB-IIP3 at 2WBW frequency offset. The entire RFFE draws 22-45 mA from a 1 V supply and the filter core occupies 0.11 mm2 chip area.

Опыт использования метода ГНСС-рефлектометрии для измерения высоты снежного покрова

Height of the snow cover is an important parameter used to predict crop yields and floods. The traditional method of measuring the height of the snow cover according to the readings of three snow gauges has the disadvantage that in open areas the snow cover is blown out and redistributed under the influence of the wind. The new method of GNSS reflectometry makes it possible to circumvent this disadvantage by averaging the height of the snow cover over a certain local area around the antenna of the ground-based GNSS radio signal receiver. The aim of the study is to assess the accuracy of determining the height of the snow cover using GNSS reflectometry using the example of the IRKM station (Irkutsk city) for the winter period 2021/2022. It has been established that the standard deviation of heights of the snow cover determined by reflectometry of GPS and GLONASS radio signals from heights of the snow cover recorded by the traditional method at a meteorological station was 3,2 cm. The standard deviation of heights of snow cover obtained from the results of processing only GLONASS radio signals was 5,6 cm. At the same time, for the GLONASS system, the dependence of the discrepancies with the reference data on the height of the snow cover is obvious: the greater the depth of the snow cover, the smaller the discrepancies. Thus, the standard deviation of discrepancies, calculated under conditions of the height of the snow cover above 10 cm, is only 3,0 cm. Thus, it can be preliminarily concluded that the GNSS refletometry method is able to supplement the traditional method of measuring the height of the snow cover.

ЕКОЛОГІЧНО БЕЗПЕЧНА ЗАГОРИЗОНТНА РЛС МЕТРОВОГО ДІАПАЗОНУ ДЛЯ ОХОРОНИ ТЕРИТОРІАЛЬНИХ ВОД

Subject and Purpose.Without regard to successes attained in the field of monitoring of territorial formations frontier areas and environment the problem of territorial waters guard and control of economic zone is as well as before actual for many states, that have the prolonged marine boundary. The aim of researches is an improvement of method of ecologically safe exposure of surface objects beyond the radiohorizon and development of ecologically safe meter wavelength radar for the guard of territorial waters with the use of active floating radio buoy. Methods and Methodology.Taking into account ecological requirements to the radiotechnical equipment and feature of beyond the horizon radio wave propagation the bistatic radar for surface objects exposure beyond the radiohorizon was proposed. One of the system features is the use of active radio buoy located on considerable distance from a shoreline. To estimate the system operationthe methods of analysis and numerical modelling are used. Results. Having conducted the analysis of basic mechanisms of radio wave propagation beyond the radiohorizon and existed experimental data, the necessary power features of proposed meter wavelength bistatic radar is calculated. For practical realization of this system the algorithms for finding the distance to the surface object and its speed are brought in details. The functional diagrams for both coastal and radio buoy receivers are worked out. Detailed description of their operation is given. Conclusion. The ecologically safe impulsively-coherent radar system is proposed, its transmission device is set on radio buoy beyond the radiohorizon, The radar true coherence is obtained due to the use of continuous signal of driving generator transmitter, that is irradiated in a period between sounding impulses and after a reception and treatment in the receiver serves as a reference signal, the coherenceinterval exceeds the period of pulse-repetition considerably. The use of speed difference of surface objects to be located and wind waves that create radar clutter will allow to carry out the radar exposure of surface objects on a background of marine surface clutter.

КОМП’ЮТЕРНИЙ АНАЛІЗ УМОВ ПРАЦЕЗДАТНОСТІ РАДІОКАНАЛУ VHF/UHF ДІАПАЗОНУ З УРАХУВАННЯМ ЗОН ЕЛЕКТРОМАГНІТНОЇ ДОСТУПНОСТІ ДЖЕРЕЛ РАДІОВИПРОМІНЮВАННЯ

The paper considers a technique for computer analysis of the working conditions of a VHF/UHF radio channel, taking into account the zones of electromagnetic accessibility of radio emission sources in relation to a topographic map, depending on the terrain characteristics. Based on the known models of radio signal propagation, mathematical relationships are obtained to determine the boundaries of the electromagnetic accessibility of a radio emission source as part of a mobile radio communication channel on a topographic map of the area. This takes into account the sensitivity of the receiver, the power of the transmitter and the shape of the digitized radiation pattern of its antenna, the scale of the map, and the loss of transmitter power depending on the characteristics of the terrain. On the basis of a modified wave algorithm, a method is proposed for calculating the boundaries of the zone of electromagnetic accessibility of radio facilities of a radio communication channel on a topographic map of the area. The method is characterized by simplicity, high speed and reliability of calculations. Already known techniques for modeling the propagation of a radio signal can be easily integrated into the proposed algorithm. The shape of the electromagnetic accessibility zone is determined by the digitized radiation pattern of the transmitter antenna, obtained using special software. The size of the EMI zone depends on the power and frequency of the radio transmitter, the power loss for signal propagation, and the sensitivity of the radio signal receiver. A technique for computer analysis of the working conditions of the VHF/UHF radio channel has been developed and implemented in the program for the operational support of the operation of mobile radio communications used in tactical levels of command and control of units and subdivisions of law enforcement agencies of Ukraine. Practical examples show the expediency of calculating the electromagnetic availability of radio facilities on a map of the area with a tactical situation in the tasks of assessing the performance of a mobile radio communication channel.

Modeling and Characterization of Pre-Charged Collapse-Mode CMUTs

Recently, the applications of ultrasound transducers expanded from high-end diagnostic tools to point of care diagnostic devices and wireless power receivers for implantable devices. These new applications additionally require that the transducer technology must comply to biocompatibility and manufacturing scalability. In this respect, Capacitive Micromachined Ultrasound Transducers (CMUTs) have a strong advantage compared to the conventional PZT based transducers. However, current CMUTs require a large DC bias voltage for their operation, which limits the miniaturizability of these devices. In this study, we propose a pre-charged collapse-mode CMUT for immersive applications that can operate without an external bias by means of a charge trapping Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> layer embedded in the dielectrics between the top and bottom electrodes. The built-in charge layer was analytically modeled and four layer stack combinations were investigated and characterized. The measurement results of the CMUTs were then used to fit the model and to quantify the amount and type of trapped charge. It was found that these devices polarize due to the ferroelectric-like behavior of the Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> , and the amount of charge stored in the charge-trapping layer was estimated to be approximately 0.02C/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Their acoustic performance shows a transmit and receive sensitivity of 8.8 kPa/V and 13.1V/MPa respectively. In addition, we show that increasing the charging temperature, the charging duration, and the charging voltage results in a higher amount of stored charge. Finally, results of ALT tests showed that these devices have a lifetime of more than 2.5 years at body temperature.

Novel Measurement Method to Determine Optimum Reception Frequency of Electric Field Wireless Power Receiver

Novel Measurement Method to Determine Optimum Reception Frequency of Electric Field Wireless Power Receiver

Construction of a System That Links Treatment RIS Terminals and Smartphones to Facilitate Radiation Therapy Operations

Confirmation of patient information is required to ensure the safety of radiation therapy. The purpose of this study was to construct a system that facilitates radiation therapy operations by linking a radiation therapy information system to a smartphone. By linking a smartphone to a radiation therapy operation support system, without using a PC terminal, we were able to input information about the patient's position and fixation into images taken with a smartphone. In addition, patient information could be directly linked into the radiation therapy information system. In addition, patient information could be verified in the irradiation room by synchronizing the smartphone with the radiation therapy support system. The questionnaire was highly evaluated in terms of radio reception, usability, visibility and barcode reading. In this study, by linking a smartphone to a radiotherapy information system, it was possible to construct a system that facilitates radiotherapy operations by checking and registering patient information at hand.

Оценка электромагнитной доступности источников радиоизлучений ГСС Starlink

The full-scale deployment of the Starlink global satellite system has opened up wide opportunities for high-speed wireless access to Internet information resources throughout the Earth. In such conditions, the problem of user control over the provided traffic arises. This is due to the fact that the organizational and technical parameters of the Starlink system were initially chosen with the condition of minimizing mutual interference to subscribers located in limited areas. On the one hand, such a system opens up the prospect of access to the global network for subscribers located in remote, industrially unequipped areas of the globe, and on the other hand, the possibility of organizing communications for illegitimate users and the right of criminal organizations. Therefore, it is necessary to understand how accessible the communication channels organized by the Starlink system are for monitoring. Taking into account these circumstances, the purpose of the study, the materials of which are presented in this article, was to assess the probability of electromagnetic availability of subscribers of the Starlink global satellite system. Based on the analysis of the operational and technical characteristics of the Starlink system in available sources, the features of its construction were considered and the initial data were determined for the development of a method for the electromagnetic availability of radio emission sources operating in the Ku / K-frequency bands. The methodology is based on calculations of the provided excess of signal power over noise power at the input of the radio receiver, which ensures the required quality and reliability of reception. The stages of the methodology are substantiated, the analytical apparatus is modified, taking into account the conditions of monitoring. The results of calculating the electromagnetic availability of radio emission sources of the Starlink global satellite system for the most difficult case, when the subscriber terminal is located at the nadir of the spacecraft coverage area and at the same time in the center of the beam formed on the subscriber, are presented. Probabilistic estimates are obtained and proposals and recommendations are formulated to improve the reliability and quality of the ongoing monitoring. Conclusions and proposals for the practical implementation of the results obtained are formulated.

Compound Preselector for Multistatic Passive Radar Employed in Remote Sensing Applications

Passive radars and multistatic passive radars in particular are gaining increasing attention. It is due to their effectiveness in detecting, tracking and identifying targets. Multistatic passive radars are used in remote sensing observations of the Earth’s ionosphere, meteors, space junk, etc. Another application is the detection and tracking of manmade objects and vehicles in the atmosphere or on the surface of the Earth. The current paper discusses a hardware design approach applicable to the front-end of a multistatic passive radar receiver, namely a compound preselector. The preselector is a very important part of the radio receiver in cases where there are strong neighbouring signals in the radio band of operation. Such strong signals may overload the receiver or the low noise preamplifier and render the whole system dysfunctional. This article elaborates on a two-component preselector having very high rejection ratio to nearby emitters, still keeping the receiver simple and reliable. The authors have registered several utility models on innovations in multistatic passive radars at Patent Office of Republic of Bulgaria.

Application of spectral approximation to model the dynamic properties of wireless communication channels

This work is devoted to the application of approximation methods for modeling wireless radio communication channels. The rationale and prospects of the use of unmanned aerial vehicles as part of flying self-organizing networks for the transmission of high-speed information in the conditions of «smart cities» are demonstrated. The problem of using these networks is also referred, associated with the technical complexity of ensuring acceptable reliability and quality of wireless communication, associated with the multipath of signal propagation and a number of other factors. It is shown that in this aspect, the development of mathematical modeling methods of analyzing signals at the inputs of UAV radio receivers in order to evaluate their amplitude- phase transformations by a communication channel is of special significance. It has been established that the connection between the signals on the transmitting and receiving sides of an arbitrary wireless radio communication channel, assuming its linearity, can be uniquely determined by a complex transfer function in the frequency domain, which in practice is very complex and difficult to describe analytically. In this regard, an approach to its approximation by an equivalent model, described by fractional- rational functions of a complex variable, physically realized by mixed connections of various linear inertial and inertial links, is proposed, and for modeling dynamic characteristics, a numerical-a nalytical modeling technique based on the spectral method and piecewise linear approximation. A results of applying the proposed solutions are shown.