Signal Propagation Delay Research Articles

A comprehensive approach for optimizing controller placement in Software-Defined Networks

Software-Defined Networks (SDNs) are characterized by dividing a network architecture in a data plane (i.e., any packet-relaying nodes like switches or routers) and a control plane, where specialized controllers assign forwarding decisions to the underlying data plane, and must do so in a very short timeframe. Thus, controllers play a key role in SDNs and the Controller Placement Problem (CPP) becomes a critical issue, affecting network delays and synchronization. If there are significant propagation delays between controllers and nodes, or among controllers, their ability to quickly react to network events is affected, degrading reliability. In this work, we propose a comprehensive mathematical formalization of the CPP, which constrains propagation latency and controller capacity, and determines simultaneously the minimum number of controllers, their location and the assignment of nodes to each, while keeping a balanced load distribution among controllers. As CPP is NP-hard, a heuristic approach is also presented. Simulations for 60 network scenarios show that this approach obtains balanced and resilient solutions, in negligible time, which are proven to be optimal or near optimal for 90% of the evaluated cases.

Reducing the Measurement Error of Signal Propagation Delays Using an Optical Reflectometer with Picosecond Resolution

Reducing the Measurement Error of Signal Propagation Delays Using an Optical Reflectometer with Picosecond Resolution

Underwater angle-only tracking with propagation delay and time-offset between observers

Due to the existence of signal propagation delay, the time interval between two consecutive signal emission times from the same target is varying and unknown, it will not be equal to the sampling interval of the observer. This phenomenon occurs more apparently in acoustic sensor surveillance system and complicates angle-only target tracking problems. As a result, the current state of the target kinematic information is difficult to estimate. For the double observer systems, even if they are synchronized, there is a time-offset between the observers due to signal propagation delay. So each observer receives signals from the same target at different emission times. In this paper, we propose a new algorithm to deal with this time-offset by building a set of constraints for a centralized double observer system in a three-dimensional environment, and using the Gauss-Helmert model for the state transition of two adjacent consecutive states. Furthermore, we consider the varying underwater sound speed and apply a sound speed profile model. Also, a novel algorithm is developed for the underwater environment, and its convergence condition is mathematically derived. Simulation results clearly validate that our proposed algorithm has better estimation accuracy in the underwater environment with comparison to other existing methods.

Design of Attenuation loss and Multipath propagation Model for Underwater Acoustic Communication in Tank

The wireless sensor network uses some sort of sensors to detect in general physical quantity of interest. The wireless sensor network has potential to explore difficult-to access area on the earth and the concept is extended to underwater applications in future. Past several years studies has been focused on development of reliable and robust communication systems for underwater wireless sensor network for various underwater applications. The scenario of communication is different in underwater compared to that on land as environment is completely different. Also radio waves cannot propagate for longer distance, so instead of that acoustic waves are used. The efforts are made to devise a model for acoustic frequency ranges in the environment for underwater tanks using basic equations governing various physical phenomena occurring during acoustic wave propagation. The model uses scenario of underwater tank filled with raw water diluted with sodium chloride with communicating devices placed at various distances. Attenuation model can be proposed for such communication scenario with respect to distance between transmitter and receiver for acoustic frequency ranges. The acoustic wave travelling through propagating medium suffers from multiple reflections resulting into multipath propagation. The multipath propagation model is proposed for calculation of length of multipath signals propagating in bounded shallow water. Propagation delays of each multipath signals are proposed. Empirical relationship is developed between number of multipath components and distance between transmitter and receiver. Arrival time lag jitter of various multipath signals are developed with respect to distance between transmitter and receiver and height of transmitter and receiver with respect to water bottom is also proposed.

Reducing the measurement error of signal propagation delays using an optical reflectometer with picosecond resolution

The problems requiring high-precision measurements of signal propagation delays in optical fibers are considered. Design features of a pulsed optical reflectometer with a picosecond resolution designed for measuring propagation delays of a signal are considered. It is shown that the error of such a reflectometer includes the additive and multiplicative components. A method for determining the additive component of the optical reflectometer error based on measurements of signal delays introduced by individual optical fiber coils and the total delay introduced by series-connected coils is proposed. The requirements to the measurement conditions are formulated and the results of the error estimation of the proposed method are presented. To exclude the multiplicative component of the reflectometer error, a method for determining corrections to the reflectometer readings is proposed. The method is based on measuring the propagation delays of the signal in the coils of the optical fiber, first using reference equipment (installation for measuring the propagation delay of the signal), and then using an optical reflectometer, and then calculating the differences of the obtained measurement results. The scheme of installation for measurements of a propagation delay of signal in a coil of optical fiber is presented, the principle of operation of measuring installation is described. The results of the estimation of the error in determining the corrections to the reflectometer readings by the proposed method are presented. It is shown that the exclusion of the additive and multiplicative components of the error will reduce the error of optical reflectometers to values less than ± 100 ps.

УСТАНОВКА ДЛЯ ИЗМЕРЕНИЙ ЗАДЕРЖЕК РАСПРОСТРАНЕНИЯ СИГНАЛОВ В ОПТИЧЕСКИХ ЭЛЕМЕНТАХ

The results of the development of an installation for measuring signal propagation delays in optical elements and optical fibers are presented. Measuring the delays of signal propagation in optical elements and optical fibers required for the development of various instruments, in particular, the development of fiber-optic systems, the synchronization time scales for complexes of metrological support of the global navigation satellite system GLONASS and measuring means of ground-based GLONASS, the development of metrological maintenance of fiber-optic communication systems, the development radiophonic systems (e.g., phased arrays with fiber-optical channels, measuring systems with remote antennas). It is shown that the installation allows to implement phase and pulse methods for measuring signal propagation delays introduced by optical elements, as well as a modified pulse method designed to determine the delays in optical elements with a large signal attenuation, when the accuracy of measurements by other methods is reduced due to the increasing influence of noise measuring equipment. The developed method is based on registration of the pulse shape with the help of analog-to-digital Converter, the approximation was a data taking into account information about the original form of pulses to reduce random error caused by the influence of noise, and subsequent determination of temporal characteristics of pulses using parameters approximating functions. The application of the developed method for various forms of laser pulses is considered, the scheme of the installation implementing these methods is presented, and the results of experimental studies of the installation are presented. It is shown that the modified pulse method allows to reduce the measurement error of signal propagation delays in optical fibers and optical elements by 15–20% or more, depending on the introduced attenuation, and the installation for measuring signal propagation delays can be used to control the characteristics of optical fibers and optical elements of various fiber-optic systems.

A Digital Power Factor Controller for Primary-Side-Regulated LED Driver

In this study, a digital primary-side controller for a flyback light-emitting diode driver with superior line regulation, high power factor (PF), and low total harmonic distortion (THD) was proposed. Conventional constant on-time control is hampered by input current distortion, leading to high THD. To achieve high PF and low THD, a digital switching frequency limiter with quasi-resonant control was proposed. In addition, owing to the turn-off delay of the MOSFET and propagation delay of the feedback signals, a primary-side-controlled flyback converter experiences poor line regulation. To achieve superior line regulation, delay compensation was proposed and analyzed. A digital controller was realized using a field-programmable gate array and was applied to an input voltage of 90– $264~V_{\mathrm {ac}}$ and an output current of 1 A in a hardware prototype to verify the feasibility of the proposed control solution. The experimental results indicate that line regulation was within ±3%, PF was higher than 0.95, and THD was lower than 5% at universal input voltage.

Can Signal Delay be Functional? Including Delay in Evolved Robot Controllers.

Engineers, control theorists, and neuroscientists often view the delay imposed by finite signal propagation velocities as a problem that needs to be compensated for or avoided. In this article, we consider the alternative possibility that in some cases, signal delay can be used functionally, that is, as an essential component of a cognitive system. To investigate this idea, we evolve a minimal robot controller to solve a basic stimulus-distinction task. The controller is constrained so that the solution must utilize a delayed recurrent signal. Different from previous evolutionary robotics studies, our controller is modeled using delay differential equations, which (unlike the ordinary differential equations of conventional continuous-time recurrent neural networks) can accurately capture delays in signal propagation. We analyze the evolved controller and its interaction with its environment using classical dynamical systems techniques. The analysis shows what kinds of invariant sets underlie the various successful and unsuccessful performances of the robot, and what kinds of bifurcations produce these invariant sets. In the second phase of our analysis, we turn our attention to the parameter θ, which describes the amount of signal delay included in the model. We show how the delay destabilizes certain attractors that would exist if there were no delay and creates other stable attractors, resulting in an agent that performs well at the target task.

Experimental Study on a Modified Method for Propagation Delay of Long Wave Signal

The propagation of a long wave signal is influenced by many factors, such as topography, geology, and weather. How to get the accuracy signal propagation delay has always been the bottleneck restricting the realization of high-precision timing of a long wave system. Now, there are two methods to obtain the signal delay, the calculation and the measurement. The error of the calculation value is caused by the propagation path condition including of topography, geology, and weather. For users in a range, the conditions are similar on the path, and there is the correlation in the error. The relevance of the error is analyzed in theory, and a correction method of signal propagation delay is proposed. Similar to the local area differential Global Position System (GPS), in the reference station, we measure time delay, calculate the error, and send to users. The users around the reference station receive the value and modify the calculation value to get the accuracy delay. The results show that it can effectively improve the accuracy of propagation delay. For the users, the closer it is to the differential station, the higher the correction accuracy is. For the reference stations, if it is farther away from the transmitter, the users’ correction accuracy around it will be higher than others users around with the same distance.

Networking in Interstellar Dimensions: Communicating With TRAPPIST-1

The recent discovery of potentially habitable planets orbiting the TRAPPIST-1 system intensified interest in interstellar exploration. In these challenging mission concepts, communication protocols would need to cope with unprecedented signal propagation delays. In this paper, we propose and explore delay tolerant networking (DTN) technologies and analyze in a case study based on the TRAPPIST-1. Results suggests that DTN protocols features could become a valuable means to achieve data delivery in future interstellar networks.

Nonlinear dynamics of delay systems: an overview

Time delays play an important role in many fields such as engineering, physics or biology. Delays occur due to finite velocities of signal propagation or processing delays leading to memory effects and, in general, infinite-dimensional systems. Time delay systems can be described by delay differential equations and often include non-negligible nonlinear effects. This overview article introduces the theme issue 'Nonlinear dynamics of delay systems', which contains new fundamental results in this interdisciplinary field as well as recent developments in applications. Fundamentally, new results were obtained especially for systems with time-varying delay and state-dependent delay and for delay system with noise, which do often appear in real systems in engineering and nature. The applications range from climate modelling over network dynamics and laser systems with feedback to human balancing and machine tool chatter. This article is part of the theme issue 'Nonlinear dynamics of delay systems'.

Small contact resistance and high-frequency operation of flexible low-voltage inverted coplanar organic transistors

The contact resistance in organic thin-film transistors (TFTs) is the limiting factor in the development of high-frequency organic TFTs. In devices fabricated in the inverted (bottom-gate) device architecture, staggered (top-contact) organic TFTs have usually shown or are predicted to show lower contact resistance than coplanar (bottom-contact) organic TFTs. However, through comparison of organic TFTs with different gate-dielectric thicknesses based on the small-molecule organic semiconductor 2,9-diphenyl-dinaphtho[2,3-b:2’,3’-f]thieno[3,2-b]thiophene, we show the potential for bottom-contact TFTs to have lower contact resistance than top-contact TFTs, provided the gate dielectric is sufficiently thin and an interface layer such as pentafluorobenzenethiol is used to treat the surface of the source and drain contacts. We demonstrate bottom-contact TFTs fabricated on flexible plastic substrates with record-low contact resistance (29 Ωcm), record subthreshold swing (62 mV/decade), and signal-propagation delays in 11-stage unipolar ring oscillators as short as 138 ns per stage, all at operating voltages of about 3 V.

Thermally conductive nanostructured, aramid dielectric composite films with boron nitride nanosheets

The rapid development of modern electronics and high-frequency and high-speed circuits sets stringent requirements of low dielectric permittivity and efficient heat removal of thermal-management materials to reduce the time delay of signal propagation and ensure the long lifetime of the electronics. In this work, we report a novel thermally conductive and minimally dielectric nanocomposite film by vacuum filtering aramid nanofibers (ANFs) on nylon filter with boron nitride nanosheets (BNNSs). To obtain a continuous, uniform, freestanding composite film with both low dielectric permittivity and strong thermal conductivity, ANF suspensions were dialyzed and then absorbed into a BNNSs/Isopropanol (IPA) dispersion by bath-sonication. The advantage of the nanocomposite film lies in that it possesses an out-plane thermal conductivity up to 0.6156 (w·m−1·k−1) at BNNSs mass percent of 50 wt%, a conductivity that is almost 5 times that of the pure nano-aramid film. The nanocomposite film also boasts a low dielectric permittivity (∼2.4 at 108 Hz) along with excellent mechanical flexibility and strength (∼62 MPa).

An Online Monitoring Method of Circuit Parameters for Variable On-Time Control in CRM Boost PFC Converters

This paper proposes an improved zero current detection for critical conduction mode (CRM) control, which can compensate the input current distortion caused by the signal propagation delay and the existence of the negative resonance current. A unified variable on-time calculation method is also proposed to unify the formulas under the zero-voltage-switching condition and the valley-switching condition. Since these two methods are dependent on the boost inductance and device junction capacitance, which may be different from the nominal values, effort is needed to compensate the deviation on these two parameters. In this paper, an online monitoring method is proposed to compensate the numerical deviation. The proposed method only needs to sense the input voltage, output voltage, and the reverse flow time of the inductor current, leading to a high power quality in the entire input and load conditions. The experimental results of the proposed methods are demonstrated on a 200-W GaN-based CRM boost power factor correction prototype. With the proposed methods, the input current total harmonic distortion is only 0.78% at 110 VAC input with full load and 2.1% at 220 VAC input with full load.

Geometric Modeling of the Z-Surface and Z-Curve of GNSS Signals and Their Solution Techniques

This paper presents a novel geometric model to characterize the zero-crossing surface ( $z$ -surface) and its z-curve for signals emitted by a pair of Global Navigation Satellite System satellites ( ${\mathcal{A}}$ , ${\mathcal{B}}$ ). The $z$ -surface is the surface of points which have zero difference in pseudorange to ( ${\mathcal{A}}$ , ${\mathcal{B}}$ ), and the $z$ -curve is the intersection of $z$ -surface with the earth’s surface. As a form of time difference of arrival, modeling of the $z$ -surface/ $z$ -curve benefits from the elimination of common error terms (e.g., receiver clock offset) shared by the pair of pseudoranges, so that the resulting model can be used for design of advanced applications, such as timing and positioning integrity monitors and tools for geodetic and atmospheric measurements. The derivation of the $z$ -curve starts with the shape modeling of the terrestrial service volume and the earth’s surface. Then, an equi-pseudorange surface of ( ${\mathcal{A}}$ , ${\mathcal{B}}$ )’s signals can be placed within these shape models. The $z$ -curve can be derived as a boundary condition of the $z$ -surface. The model can represent the morphing of $z$ -curves with respect to the changes in satellite positions and signal propagation delays. As a result, the $z$ -models can be readily generalized into a k-surface and k-curve, where k represents the pseudorange difference between ( ${\mathcal{A}}$ , ${\mathcal{B}}$ ). Solutions for modeling and analysis of the $z(k)$ -surface/curve are based on a system of quadratic Cartesian equations. We propose an algebraic method to parameterize them in terms of geocentric latitude and longitude.

Principles for reducing the phase shift between instantaneous analogue and discrete signals and the corresponding values in the sampled values (SV) stream of a digital substation

There are numerous publicly available articles on digital substations, including those dedicated to current and voltage measurements, time synchronization, test systems development, principles of substation design, and other aspects of this topic. But the phase shift between instantaneous signals and the corresponding values in the SV (sampled values) stream has been little discussed. We can list the following principles to reduce the phase shift between instantaneous analogue and discrete signals and the corresponding values in the SV stream. 1) Exclusion from the device, of non-essential elements that introduce additional propagation delays of analogue and discrete signals, provided that such exclusion does not adversely affect the device performance or characteristics. 2) Reduction of the delay time for the other device elements to the minimum values. 3) Adjustment of the delay time of some device elements or addition of special delay elements to equalize the time of signal propagation over analogue and discrete channels. 4) Consideration of the total delay time of signal propagation over analogue and discrete channels and adjustment of the time stamp in the SV frame. The article provides examples of application of these principles in signal generation and measuring devices and phase shift meters.

Prediction of the EM signal delay in the ionosphere using neural model

Neural model capable to accurately and efficiently predict a propagation delay of electromagnetic signal in the ionosphere is proposed in this paper. The model performs this prediction for a given geographic location in Europe between 40?(N) and 70?(N) latitude and 10?(W) and 30?(E) longitude, according to the following parameters: particular day in a year, time during the day and frequency of a signal carrier. Architecture of the model consists of four multilayer perceptron (MLP) networks with the task to estimate, for the known values of the previously mentioned input parameters of the model, the approximate value of free ions concentration in the atmosphere along the signal propagation path above the geographic location of the receiver. Based on the estimated ions concentration and taking into account the considered frequency of the signal carrier, the model calculates the time delay of signal propagation in the ionosphere. The developed neural model is applicable on the whole territory of Republic of Serbia, for all four weather seasons in the period of low solar activity. The results of using the proposed model for the prediction of time delay of the GPS (Global Positioning System) signal in the area of city of Nis are provided in the paper.

Reconfigurable RO-Path Delay Sensor

In this brief, we propose a method of analyzing signal propagation delay in certain digital circuits and a delay-sensing architecture. Based on controllability probabilities, we present a graph model that is useful for path delay analysis, derivation of test vectors that sensitize paths of interest, and reconvergent path detection. A delay-sensing architecture is illustrated that offers different accuracy levels and provides a nearly-on-the-fly measurement of the delay. The synergy of the introduced model with the introduced architecture is demonstrated by means of an example. The proposed technique can be used for delay estimation, delay characterization and on-demand, real-time, nearly-on-the-fly estimation of the delay of cell-based array logic units, such as multipliers. FPGA measurements show that a better estimation of the delay is possible, compared to simulations, and an increase by 30% of operation frequency is feasible in certain cases, compared to simulation-based frequency estimation.

Disentangling the effects of high permittivity materials on signal optimization and sample noise reduction via ideal current patterns.

To investigate how high-permittivity materials (HPMs) can improve SNR when placed between MR detectors and the imaged body. We used a simulation framework based on dyadic Green's functions to calculate the electromagnetic field inside a uniform dielectric sphere at 7 Tesla, with and without a surrounding layer of HPM. SNR-optimizing (ideal) current patterns were expressed as the sum of signal-optimizing (signal-only) current patterns and dark mode current patterns that minimize sample noise while contributing nothing to signal. We investigated how HPM affects the shape and amplitude of these current patterns, sample noise, and array SNR. Ideal and signal-only current patterns were identical for a central voxel. HPMs introduced a phase shift into these patterns, compensating for signal propagation delay in the HPMs. For an intermediate location within the sphere, dark mode current patterns were present and illustrated the mechanisms by which HPMs can reduce sample noise. High-amplitude signal-only current patterns were observed for HPM configurations that shield the electromagnetic field from the sample. For coil arrays, these configurations corresponded to poor SNR in deep regions but resulted in large SNR gains near the surface due to enhanced fields in the vicinity of the HPM. For very high relative permittivity values, HPM thicknesses corresponding to even multiples of λ/4 resulted in coil SNR gains throughout the sample. HPMs affect both signal sensitivity and sample noise. Lower amplitude signal-only optimal currents corresponded to higher array SNR performance and could guide the design of coils integrated with HPM.

Modeling Optimal Retransmission Timeout Interval for Bundle Protocol

Delay/disruption tolerant networking (DTN) was proposed as a networking architecture for reliable data delivery despite an extremely long propagation delay and frequent/lengthy link disruptions. The challenging problem of mission control and data delivery in deep-space explorations is a typical application scenario of the DTN technology. Reliable data delivery of DTN relies heavily on its core bundle protocol (BP). Performance evaluation and improvement of BP for deep-space communications are presently underway. The setting of the retransmission time-out (RTO) timer of BP is critical for reliable and highly efficient file transfer in a deep-space communication environment. In this paper, we present analytical modeling of an optimal RTO timer interval for the best goodput performance of BP in deep-space communications characterized by a very long signal propagation delay and lossy data links. A model is developed to compute the RTO timer interval that will result in the best goodput performance of BP normalized with respect to the total data load transmitted in order to achieve successful delivery of an entire file. Experimental validation using a PC-based testbed indicates that the RTO timer interval indicated by the model achieves the best normalized goodput performance of BP. The model predicts performance in all the experimented scenarios.