Noise-like Signals Research Articles

RADIO RELAY STATIONS WITH IMPROVED CHARACTERISTICS

Despite the variety of modern means of communication, radio relay lines of information are not lost due to the possibility of their creation in hard-to-reach mountain regions and in conditions of dense development of large cities. One-way radio relay lines have been widely used to transmit information between the central office and branches of the enterprise in corporate networks, between base stations and switching center in mobile communication networks, between military structures for operational management, in emergency situations. When creating radio relay links, the basic tasks are to use the minimum possible transmitter power sufficient to ensure the required quality of information transmission. At the same time minimum influence of electromagnetic radiation on health of people in the area of station operation, better electromagnetic compatibility of equipment with equipment of neighboring regions, duration of station operation at power supply from accumulator battery are achieved. In this paper are reviewed the methods to improve the energy, noise immunity and confidential microwave link using the 4-way signal of PM-4. The advantages of microwave links with noise-like signals generated using pseudorandom sequences based on chaos are shown here.

An analysis the mutual influence of channels in radiotechnical information-measuring system

The development of new radiotechnical information-measuring systems (IMSs) of the ground control complex of flying objects should be aimed at increasing their capabilities for accurate and reliable control of signals navigation parameters. This is especially important in a time-limited communication session, as well as for ensuring the operational control of the trajectories of ballistic objects during their flight along unequipped routes.In recent years, wideband noise-like signals (WNLSs) are often used in radio systems ‒ complex discrete signals, modulated by a harmonious signal in frequency, phase and amplitude by a pseudo-random sequence code. The use of the WNLSs is explained by a number of their properties: better noise immunity and concealment, greater accuracy in measuring the speed and range of moving objects, the prospect of more efficient use of such signals in the allowed frequency ranges, and the possibility of their multipath propagation.IMSs with WNLSs have several advantages: increased noise immunity, secrecy, the ability to measure the motion parameters of an aircraft object with one signal and transmit information, sufficient accuracy and high reliability of in­formation transfer. In the future, this may lead to the construction of unified, mobile information-measuring systems, the tactical and technical characteristics of which will meet modern requirements. However, the main reasons preventing the wider implementation of complex pseudo-random signals in the practice of radio engineering IMSs are the difficulties as­sociated with their optimal processing.In this paper, the analysis of information-measuring systems with wideband noise-like signals was performed to determine the degree of mutual influence of the channels, when filtering interrelated parameters of signal. It is established, that the errors caused by the mutual influence of the channels are minimal if the parameter estimate coincides with its true value, and there are no divergences on the filtered parameter. Thus, the filtering accuracy of each of the parameters depends on the degree of their correlation, on the signal-to-noise ratio, and on the steepness of autocorrelation function the input signal complex envelope.

CHARACTERISTICS IMPROVEMENT OF THE WIDEBAND TELECOMMUNICATION SYSTEM APPLYING CHAOS BASED PSEUDORANDOM SEQUENCE

Background. Telecommunication systems with a broadband signal have undoubted advantages: increased noise immunity with narrowband and wideband interference, confidentiality of information transmission, as well as improved electromagnetic compatibility with neighboring radio-electronic devices. A broadband signal is usually formed by direct spread spectrum using well-known classical pseudo-random sequences (PRS): m-sequences, Kasami, Gold, Walsh sequences, which can be decoded and received at the receiver.Objective. The aim of the paper is creating PRS on the basis of chaos, which the subscriber is practically unable to decode, and thus ensure increased confidentiality of information transmission.Methods. Using the mathematical model of chaotic logistic mapping, which, as shown by preliminary studies, provides the best results, as well as referring to the bifurcation diagram of Feigenbaum, the parameters of 3-secret keysare defined and the PRS of the selected length is created. Based on the application of the graphical user interface developed in the MATLAB system, a correlation analysis of the resulting PRS is performed and the PRS is determinedwith the minimum side lobes of the autocorrelation function.Results. By empirical decision of 3 secret keys of the dynamic parameter of the Feigenbaum diagram, the initial value of the sequence and the number of the initial pulse of the PRS, as well as the study of the autocorrelation function,we obtained a PRS with a side lobe level of the autocorrelation function acceptable for practical use of no more than 0.25.Conclusions. The use of well-known pseudo-random sequence: Walsh’s, Kasami’s, Gold’s, creating a system with a noise-like signal doesn’t ensure complete confidentiality of information transmission, since they can be decoded.The most acceptable by the criterion of the side lobe minimum of the autocorrelation function – no worse than 0.25 – is the use of chaos based on the Feigenbaum logistic map. When creating pseudo-random sequences based on chaos, the best results are obtained by choosing the maximum value of the dynamic parameter of the Feigenbaum diagram at the level of the boundary value equal to 4, with an accuracy of 0.05.

Synthesis of Signals with Zero Width of Autocorrelation Function

This article presents examples of probing functions construction with a small width of autocorrelation function (a noise-like signal, a chirp signal) of long duration, which allows to obtain a reflectivity profile along a high resolution path. Attention is drawn to the fact that space in the process of probe pulse propagation returns to the receiver in an almost mutual correlation function of reflectivity and probe pulse. This approach opens up new possibilities for filtering signals and recognizing targets with appropriate selection and changing shape of the probe pulse right during measurements.

An Electrooptic Chaotic System Based on a Hybrid Feedback Loop

An electrooptic chaos source is proposed based on phase-modulation-to-intensity-modulation conversion theory and an analog–digital hybrid time-delay feedback loop. The analog part takes the digital binary sequences from shift registers as input and converts them into an analog noise-like signal, from which new bits are determined. The dynamical characteristic of the generated waveform is studied in detail by means of spectrum analysis, periodicity analysis, correlation performance, and complexity analysis. Moreover, the evolution between chaos and stochastic noise is observed and measured by adopting the complexity–entropy curves when a random perturbation is introduced. Such a perturbation can help with recovering chaotic dynamics from degradation. Based on this chaotic source, a secure and robust synchronization scheme that can exactly reproduce the signal is put forward. The effect of parameters’ mismatch and noise level on the synchronization quality is also investigated. The scheme has the potential to be applied in various applications when a robust random source is needed.

Координатный базис на основе псевдослучайных последовательностей

Broadband data transmission systems are used noise-like signals derived from pseudorandom sequences. The most widely used m-sequences have good correlation properties. However, M-sequences are not orthogonal sequences. In this work the methods of creation of orthogonal bases on the basis of M-sequences are proved. Two theorems on the linear independence of the functions obtained by cyclic shift of some of the original discrete functions are provide. For orthogonalization of M-sequences, the method of orthogonalization is used, which consists in determining the weight of orthogonality of linearly independent functions.

Investigation of the energy hiddenness of noise-free timer signal structures

The features of the formation of noise-like timer signals are considered. The estimation of the energy concealment of the functioning of radio engineering systems based on direct spreading of the spectrum is given. To assess the energy secrecy, it is suggested to use the efficiency criterion, according to which the maximum effect is achieved on masking the signal energy against the noise background in the channel.The use of a variable signal structure makes it difficult to identify its parameters in the event of a message being intercepted by radio engineering intelligence. Therefore, timer coding creates a good premise for developing effective methods for protecting information from unauthorized access at the channel level of the OSI model. However, the potentially high structural concealment of signals based on timer signal constructions does not solve the problem of energy concealment with narrowband transmission methods. Therefore, a promising solution to this problem is the expansion of the spectrum of timer signal constructions, the study of the appropriate characteristics of transmission and reception of noise signals in conditions of interference.The purpose of the work is to study the energy concealment of noise-like timer signals.The results of the research have shown that the probability of distortion of the timer signal structure is influenced by the value of the signal base and the type of modulation. Increasing the efficiency of the bandwidth due to the increase of the multipositional modulation system (FM-8, FM-16) does not give the desired result even at high values of the base. The FM-2 and FM-4 modulation systems are more disturbing.

A family of fully integrated CMOS chaos generators with strictly 1-D linear-piecewise chaos maps

A family of three complementary metal-oxide semiconductor (CMOS) chaos generators is presented. The proposed scheme starts by obtaining strictly 1-D piecewise-linear chaos maps using a stroboscopic sampling method. The chaotic behavior is then analyzed with the help of numerical simulations using Mathematica. As required for practical applications, the robustness of the derived chaos maps was also confirmed by analyzing bifurcation and Lyapunov exponent diagrams. For verification, a tent-shape chaos generator was implemented using the 0.18- $$\upmu $$ m CMOS process. The simulation as well as measurement results confirmed the proposed scheme. The key advantages of the proposed chaos generators with varied fabrication parameters, including compact size, low power consumption, simple achievement of chaos, and robust chaos generation, recommend them as a solution in design of fully integrated chaotic circuits for applications where noise-like signal sources are required.

РЕЗУЛЬТАТИ МОДЕЛЮВАННЯСХЕМИ ВИЗНАЧЕННЯ СЕРЕДНЬОЇ ЧАСТОТИЛІНІЙНО-ЧАСТОТНО-МОДУЛЬОВАНОГО СИГНАЛУЗ НИЗЬКОЮ СПЕКТРАЛЬНОЮ ЩІЛЬНІСТЮ ПОТУЖНОСТІ

During last time noticed a trend to the implementation radio electronic systems (RES) for various purposes with a spread spectrum signals. For contraction RES with aggregated signals, wideband and noise-like signals very often utilized radio emission with chirp signals. The research some issues of determining the parameters of such signals are not solved yet for the present time. The author suggested a decisive rule of the algorithm measurement average frequency for a discrete model of an autocorrelation receiver with quadrature processing. In the article also considers options for reducing the error in its determination, which is confirmed by the results of the experiment.

Помехоустойчивость систем радиосвязи с бинарными фазоманипулированными шумоподобными сигналами при воздействии ретранслированных компенсационных помех типа инверсии огибающей сигнала.

Помехоустойчивость систем радиосвязи с бинарными фазоманипулированными шумоподобными сигналами при воздействии ретранслированных компенсационных помех типа инверсии огибающей сигнала.

Acoustic direction finding using single acoustic vector sensor under high reverberation

We propose a novel and robust method for acoustic direction finding, which is solely based on acoustic pressure and pressure gradient measurements from single Acoustic Vector Sensor (AVS). We do not make any stochastic and sparseness assumptions regarding the signal source and the environmental characteristics. Hence, our method can be applied to a wide range of wideband acoustic signals including the speech and noise-like signals in various environments. Our method identifies the “clean” time frequency bins that are not distorted by multipath signals and noise, and estimates the 2D-DOA angles at only those identified bins. Moreover, the identification of the clean bins and the corresponding DOA estimation are performed jointly in one framework in a computationally highly efficient manner. We mathematically and experimentally show that the false detection rate of the proposed method is zero, i.e., none of the time-frequency bins with multiple sources are wrongly labeled as single-source, when the source directions do not coincide. Therefore, our method is significantly more reliable and robust compared to the competing state-of-the-art methods that perform the time-frequency bin selection and the DOA estimation separately. The proposed method, for performed simulations, estimates the source direction with high accuracy (less than 1 degree error) even under significantly high reverberation conditions.

Noise-like signals in wireless information transmission systems

Предметом вивчення є процеси аналізу та оцінки ефективності використання шумоподібних сигналів в безпроводових системах передачі інформації. Мета – підвищення показників якості обслуговування абонентів мобільного зв’язку шляхом ущільнення каналів зв’язку за рахунок застосування складних сигнально-кодових конструкцій. Завдання: формування системного уявлення щодо технології передачі інформації надкороткими імпульсними сигналами із виділенням основних особливостей, які виникають на різних етапах проходження сигналів у безпроводній системі передачі інформації. Методами , що використовувались, є такі: секвентний аналіз, методи імітаційного моделювання та цифрового кодування сигналів. Отримані такі результати . Для ефективного випромінювання та прийому шумоподібних сигналів запропонована конструкція антени із щілиною, яка розширюється. Запропоновано метод керування діаграмою спрямованості цієї антенної решітки. Обґрунтовано використання у якості шумоподібного сигналу гаусівського моноциклу із кодуванням інформації за допомогою часової позиційно-імпульсної модуляції. Показано, що для організації незалежних каналів в одній смузі частот доцільно використовувати систему ортогональних кодів, наприклад, послідовність Уолша. Накопичені у кореляторі приймача імпульси корисного сигналу дають можливість суттєво підвищити співвідношення сигнал / шум, забезпечуючи цим можливість передачі інформації у широкому частотному діапазоні значно нижче рівня шуму. В результаті сформовано системне уявлення про технологію передачі інформації надкороткими імпульсами у безпроводових системах передачі інформації. Також проведені кількісні та якісні оцінки ефективності запропонованих технічних рішень. Висновки. Використання шумоподібних сигналів у безпроводових системах передачі інформації дозволяє забезпечити великі швидкості передачі інформації з одночасною високою завадозахищеністю та захистом його від перехоплення. Можливість працювати із малою потужністю випромінювання та висока проникливість шумоподібних сигналів крізь будь-які перешкоди, наприклад, стіни, дозволяють виконати вимоги щодо електромагнітної сумісності та забезпечити стійкий зв’язок в умовах багатопроміневого розповсюдження радіохвиль. Ці обставини створюють підґрунтя для розвитку та впровадження технології передачі інформації із застосуванням шумоподібних сигналів при створенні офісних мереж.

A FPGA-based Fast Converging Digital Adaptive Filter for Real-time RFI Mitigation on Ground Based Radio Telescopes

Radio Frequency Interference (RFI) is a growing concern in the radio astronomy community. Single-dish telescopes are particularly susceptible to RFI. Several methods have been developed to cope with RF-polluted environments, based on flagging, excision, and real-time blanking, among others. All these methods produce some degree of data loss or require assumptions to be made on the astronomical signal. We report the development of a real-time, digital adaptive filter implemented on a Field Programmable Gate Array (FPGA) capable of processing 4096 spectral channels in a 1 GHz of instantaneous bandwidth. The filter is able to cancel a broad range of interference signals and quickly adapt to changes on the RFI source, minimizing the data loss without any assumption on the astronomical or interfering signal properties. The speed of convergence (for a decrease to a 1%) was measured to be 208.1 μs for a broadband noise-like RFI signal and 125.5 μs for a multiple-carrier RFI signal recorded at the FAST radio telescope.

Quartz vein formation by local dehydration embrittlement along the deep, tremorgenic subduction thrust interface

Hydrothermal quartz veins are ubiquitous in exhumed accretionary complexes, including the Namibian Damara belt. Here, subduction-related deformation occurred at temperatures ≤550 °C, and vein geometry is consistent with plate interface shear, low effective normal stresses, and mixed-mode deformation. Quartz vein δ18O values relative to Standard Mean Ocean Water (SMOW) range from 9.4‰ to 17.9‰ (n = 30), consistent with precipitation from metamorphic fluids. A dominant subset of quartz veins away from long-lived high-strain zones and basaltic slivers have δ18O values in a smaller range of 14.9‰ ± 1‰, requiring precipitation from a fluid with δ18O of 12‰ ± 1‰ at 470–550 °C. This uniform fluid isotope value is consistent with progressive local breakdown of chlorite allowing extensive hydrofracture at temperatures typical of the plastic regime. In active subduction zones, brittle deformation within the plastic regime is inferred from observations of tectonic tremor, a noise-like seismic signal including overlapping low- and very low-frequency earthquakes, which occurs below the seismogenic zone. Both tremor and hydrothermal veins correlate with zones of inferred high fluid pressure, could represent a mixture of shear and dilatant failure, and may therefore be controlled by episodic hydrofracturing within a dominantly plastic and aseismic regime.

Reproducible optical noise-like signal generation subjected by digital sequences

We experimentally demonstrate a reproducible broadband optical noise-like signal generation scheme whereby dispersion induced phase modulation to intensity modulation conversion and an electro-optic nonlinear transform are utilized to post process a binary random sequence. A flat spectrum and a symmetrical distribution of the generated analog noise-like signal can be observed. Moreover, Gaussian-like probability distribution function can be obtained by using the central limit theorem. The influences of the digital input and the analog parameters on complexity performance of the generated analogue noise are discussed in detail. Finally, the impact of key parameters on the reproducibility of the system is discussed. The proposed scheme could be a more controllable way to generate broadband optical noise-like signal, and has potential to be applied in various real world applications.

Enhancing Secrecy With Multiantenna Transmission in Millimeter Wave Vehicular Communication Systems

Millimeter wave (mmWave) vehicular communication systems will provide an abundance of bandwidth for the exchange of raw sensor data and support driver-assisted and safety-related functionalities. Lack of secure communication links, however, may lead to abuses and attacks that jeopardize the efficiency of transportation systems and the physical safety of drivers. In this paper, we propose two physical layer (PHY) security techniques for vehicular mmWave communication systems. The first technique uses multiple antennas with a single radio-frequency (RF) chain to transmit information symbols to a target receiver and noise-like signals in nonreceiver directions. The second technique uses multiple antennas with a few RF chains to transmit information symbols to a target receiver and opportunistically inject artificial noise in controlled directions, thereby reducing interference in vehicular environments. Theoretical and numerical results show that the proposed techniques provide higher secrecy rate when compared to traditional PHY security techniques that require digital or more complex antenna architectures.

A Novel Noise Jamming Detection Algorithm for Radar Applications

In this letter, we devise and assess a new algorithm to detect a platform equipped with self-screening jamming systems. The latter illuminates the victim radar by means of noise-like signals leading to an increase of the constant false alarm rate threshold (at the detection stage) and a reduction of radar sensitivity. The problem is formulated in terms of a binary hypothesis test exploiting the rank-one modification of the interference covariance matrix introduced by the jammer and the generalized likelihood ratio test is derived. Performance analysis is conducted on simulated data and is aimed at highlighting the effectiveness of this new approach.

АЛГОРИТМ ОБНАРУЖЕНИЯ ПРОСТРАНСТВЕННО-ВРЕМЕННОГО ШУМОПОДОБНОГО СИГНАЛА С НЕИЗВЕСТНЫМИ ПАРАМЕТРАМИ ПРИ МНОГОКАНАЛЬНОМ ПРИЕМЕ

Considered characteristic task for radio astronomy, detection spatio-temporal noise-like signal emitted by extended radiation source, observations of which are conducted in a parametrically uncertain noise conditions. The methodology of its solution is given, the main basis of which is the likelihood ratio criterion. Based on the developed methodology for multichannel reception, a detection technology was synthesized, which, unlike known ones, does not require knowledge of the interference power for forming a threshold level. The technology uses well-designed computational operations and tabulated statistics, it allows to control the magnitude of the error probability of the first kind

Determination of surface reflectivity using radio signals of opportunity

ABSTRACTUse of a bistatic reflectometry technique which employs signals of the Global Navigation Satellite System (GNSS) scattered off the Earth surface opened new opportunities in the environmental remote sensing. At the same time, similar approach can be implemented with non-GNSS signals. Recently, it was demonstrated that other signals of opportunity can be used, such as produced by communication satellites in K-, X-, S- at VHF bands and even by the Sun. This paper presents a theoretical analysis of a possible use of a noise-like broadband radio signal emitted by a point source for measuring reflectivity properties of Earth’s surface.

A New Chaotic Electro-Mechanical Oscillator

In this paper, a new electro-mechanical chaotic oscillator is presented. The system is based on the motion of the metal tip of a beam in a double-well potential generated by two magnets, and works thanks to the vibrations generated in the flexible mechanical structure by two rotating coils that produce noise-like signals. As the source of vibration is internal, the system may be considered an autonomous oscillator. Chaotic motion is experimentally observed and verified with a mathematical model of the phenomenon.