Effect Of Propagation Delay Research Articles

Asynchronous Cell-Free Massive MIMO With Rate-Splitting

In practical cell-free (CF) massive multiple-input multiple-output (MIMO) networks with distributed and low-cost access points, the asynchronous arrival of signals at the user equipments increases multi-user interference that degrades the system performance. Meanwhile, rate-splitting (RS), exploiting the transmission of both common and private messages, has demonstrated to offer considerable spectral efficiency (SE) improvements and its robustness against channel state information (CSI) imperfection. The signal performance of a CF massive MIMO system is first analyzed for asynchronous reception capturing the joint effects of propagation delays and oscillator phases of transceivers. Taking into account the imperfect CSI caused by asynchronous phases and pilot contamination, we derive novel and closed-form downlink SE expressions for characterizing the performance of both the RS-assisted and conventional non-RS-based systems adopting coherent and non-coherent data transmission schemes, respectively. Moreover, we formulate the design of robust precoding for the common messages as an optimization problem that maximizes the minimum individual SE of the common message. To address the non-convexity of the design problem, a bisection method is proposed to solve the problem optimally. Simulation results show that asynchronous reception indeed destroys both the orthogonality of the pilots and the coherent data transmission resulting in poor system performance. Besides, thanks to the uniform coverage properties of CF massive MIMO systems, RS with a simple low-complexity precoding for the common message obtained by the equal ratio sum of the private precoding is able to achieve substantial downlink sum SE gains, while the application of robust precoding to the common message is shown to be useful in some extreme cases, e.g., serious oscillator mismatch and unknown delay phase.

The Effect of Signal Propagation Delay on the Measured Vibration in Planetary Gearboxes

Modulation of the gear mesh vibration is a major field of research for the condition monitoring of planetary gearboxes. The modulation creates sidebands around the gearmesh frequency in the vibration spectrum, and the distribution of these sidebands has been researched in numerous papers. All publications on the subject assume that the effect of the time varying signal propagation delay between the main vibration source – the gear mesh point(s) – and the (usually fixed) transducer can beneglected. This paper investigates the validity of this assumption. To do so, a planetary gearbox with a transducer mounted on the (fixed) ring gear is studied, and the effect of the propagation delay is modelled as a phase modulation of the gear mesh vibration. General expressions are then derived for the distribution and strength of the modulation sidebands, and these expressions are applied to quantify the effect of the propagation delay on five industrial gearboxes. The results show that the amplitude of the sidebands is negligible and would not interfere with condition assessment based on analysis of the modulation of the gear mesh frequency, and thus the propagation delay can be neglected for practical purposes.

Development of InSAR Neutral Atmospheric Delay Correction Model by Use of GNSS ZTD and Its Horizontal Gradient

Interferometric Synthetic Aperture Radar (InSAR) often suffers from atmospheric disturbances due to the microwave propagation delay effect, which limits the surface displacement detection accuracy to an order of centimeters or more. Here I developed a new neutral atmospheric delay correction model for InSAR by using the global navigation satellite system (GNSS) zenith total delay (ZTD) and its horizontal gradient data. The proposed model at first retrieves the regularly gridded ZTD distribution at sea level and the linear height dependence from GNSS ZTD and gradient observations by the least squares method. Then, the gridded ZTD is projected onto the InSAR coordinate to correct the neutral atmospheric delay. I evaluated the correction model performance by applying it to L-band ALOS-2/PALSAR-2 ScanSAR interferograms over the Kanto plain in Japan. The correction result showed that by applying the proposed delay correction the phase standard deviation decreased by 33.87 % on average. By comparing it with the generic atmospheric correction online service for InSAR (GACOS) model and the correction by the Japanese regional mesoscale weather model (MSM), the proposed GNSS-based model outperformed others in my test case. The sensitivity test indicated that including the delay gradient could improve delay reproducibility under situations with fewer available GNSS stations. Although the proposed correction model’s applicability depends on the number of available GNSS stations at the area of interest, the proposed model has a potential to effectively mitigate the neutral atmospheric delay and to improve the detection ability for smallamplitude surface displacements.

Effects of propagation delay in coupled oscillators under direct–indirect coupling: Theory and experiment

Propagation delay arises in a coupling channel due to the finite propagation speed of signals and the dispersive nature of the channel. In this paper, we study the effects of propagation delay that appears in the indirect coupling path of direct (diffusive)–indirect (environmental) coupled oscillators. In sharp contrast to the direct coupled oscillators where propagation delay induces amplitude death, we show that in the case of direct–indirect coupling, even a small propagation delay is conducive to an oscillatory behavior. It is well known that simultaneous application of direct and indirect coupling is the general mechanism for amplitude death. However, here we show that the presence of propagation delay hinders the death state and helps the revival of oscillation. We demonstrate our results by considering chaotic time-delayed oscillators and FitzHugh–Nagumo oscillators. We use linear stability analysis to derive the explicit conditions for the onset of oscillation from the death state. We also verify the robustness of our results in an electronic hardware level experiment. Our study reveals that the effect of time delay on the dynamics of coupled oscillators is coupling function dependent and, therefore, highly non-trivial.

Analysis of Propagation Delay Effects on Bearings-Only Fusion of Heterogeneous Sensors

Analysis of Propagation Delay Effects on Bearings-Only Fusion of Heterogeneous Sensors

Age-Optimal HARQ Design for Freshness-Critical Satellite-IoT Systems

In this article, we consider the satellite Internet of Things (IoT) system, in which the IoT device observes physical processes and transmits the status updates to the monitor node over an error-prone channel with nontrivial propagation delay. The freshness of status updates is characterized by Age of Information (AoI), a novel metric that is defined as the time that elapsed since the freshest received status update was generated. Channel coding is used to combat the burst channel errors and feedback is available through hybrid automatic repeat request (HARQ) protocols. By adopting both the simple-HARQ and incremental redundancy HARQ (IR-HARQ) transmission schemes, we study the age-optimal redundancy allocation problems under the constraint of reliability. As we put special interests on the satellite-IoT scenarios in which the propagation delays are nonnegligible, there exists a threshold of the propagation delay only below which using retransmissions is beneficial to AoI. However, the characterization of such a threshold has received little attention in the literature. By formulating and solving the age-optimal redundancy allocation problems for the adopted HARQ schemes, explicit expressions of the optimal codeword length for each transmission round are derived, and then the threshold of the propagation delay for beneficial retransmissions is obtained. Extensive numerical analysis is conducted to show the effects of propagation delay and channel state on the redundancy allocation results and the optimal AoI. The threshold is also demonstrated by numerical analysis. The results shed important light on the age-optimal HARQ design for freshness-critical satellite-IoT systems in the presence of nontrivial propagation delay.

The effect of propagation delay on the dynamic evolution of the Bitcoin blockchain

This paper analyzes the selfish-mine strategy in the Bitcoin blockchain introduced in 2013 by I. Eyal and E. G. Sirer. This strategy could be used by a colluding pool of miners to earn more than their fair share of the mining revenue and in consequence to force other honest miners to join them to decrease the variance of their revenues and make their monthly revenues more predictable. It is a very dangerous dynamic that could allow the rogue pool of miners to go toward a majority by accumulating powers of news adherents and control the entire network. Considering that the propagation delay of information between any two miners in the network, which is not negligible and follows a normal distribution with mean proportional to the physical distance between the two miners, and a constant variance independent of others' delays, we prove that no guarantee can be given about the success or failure of the selfish-mine attack because of the variability of information propagation in the network.

The Propagation Delay Effect of the Expansion and Inflation of the Universe

The effect of the propagation delay of gravitational interactions results in a singularity of the normalized acceleration of the radius of a sphere representing the Universe. Stephen Hawking in his Inflation Model also discusses a delay type interaction. This term can be used to model the inflationary rapid expansion of the early Universe. Since the Universe is thought to occupy all of space-time, one cannot define a boundary or radius of the Universe. Therefore, the properties of a sphere in the Universe are analyzed. It is assumed that the Universe will behave similarly to this sphere. This analysis is performed by including the effect of the propagation delay of gravitational interactions in Einstein’s equation.

Detection localization and tracking of aircraft using Sparse distributed passive acoustic system

Stevens Institute of Technology has conducted extensive long-term testing of acoustic systems designed to track low-flying small aircraft in remote location and recorded over 2 years of data. The system consisted of 4 nodes placed in difficult remote terrain with separation ranging 1–4 km, each node comprising a pyramid-shaped volumetric cluster of 5 microphones an embedded computer, and a pan-tilt-zoom camera steered to detected targets in real time. and communication device. Each nodes' computer performed direction of arrival finding communicated to a central computer collected that data and processed it to generate tracks and classify targets. The duration and the scale of the deployment allowed to identify and solve many problems, including the effects of propagation delays between station and on cooperative localization and tracking, the seasonal changes in environmental noise, persistent and transient noise sources, and the diversity of targets of opportunity and their signatures. The propagation de...

Evaluation of Wet Mapping Functions Used in Modeling Tropospheric Propagation Delay Effect on GPS Measurements

Background:The author compares several methods to map the a priori wet tropospheric delay of GNSS signals in Egypt from the zenith direction to lower elevations.Methods and Materials:The author compared the following mapping techniques against ray-traced delays computed for radiosonde profiles under the assumption of spherical symmetry: Saastamoinen, Hopfield, Black, Chao, Ifadis, Herring, Niell, Moffett, Black and Eisner and UNBabc mapping functions. Radiosonde data were computed from radiosonde stations at the Egyptian stations; in the south of Egypt, near the Mediterranean Sea, and near the Red Sea over a period of 5 years (2000-2005), most of the stations launched radiosonde twice daily, every day of the year. Moreover, data is received from the Egyptian Meteorology Authority.Results and Conclusion:The results indicate that currently, the saastamoinen mapping function should be used for all geodetic applications in Egypt, and if necessary, the Chao and Moffett mapping functions can serve as an acceptable replacement without introducing a significant bias into the station position.

Replication-Based Load Balancing

Load balancing of large distributed server systems is a complex optimization problem of critical importance in cloud systems and data centers. Existing schedulers often incur a high communication overhead when collecting the data required to make scheduling decisions, hence delaying job requests on their way to the executing servers. We propose a novel scheme that incurs no communication overhead between the users and the servers upon job arrival, thus removing any scheduling overhead from the job's critical path. Our approach is based on creating several replicas of each job and sending each replica to a different server. Upon the arrival of a replica to the head of the queue at its server, the latter signals the servers holding replicas of that job, so as to remove them from their queues. We show, through analysis and simulations, that this scheme significantly improves the expected queuing overhead over traditional schemes under various load conditions and different job length distributions. In addition, we show that our scheme remains efficient even when the inter-server signal propagation delay is significant (relative to the job's execution time). We provide a heuristic solution to the performance degradation that occurs in such cases and show, by simulations, that it efficiently mitigates the detrimental effect of propagation delays.

The Repulsive Force Within Ampère’s Bridge Explained by Coulomb’s Law and Special Relativity Theory, Taking into Account the Effects of Propagation Delay

It has been previously proved that the repulsive force between the two parts of Ampere's bridge, measured in experiments performed by Pappas and Moyssides, can be explained by Coulomb's law, if the effects of propagation delay are correctly taken into account. Special relativity theory is also necessary to estimate the extent to which it may affect the result. Otherwise it might be unnecessary to involve special relativity theory in the case of DC currents carried by electric conductors, because the velocities of conduction electrons are usually very small compared to the speed of light. However, in this paper, the force between the two parts of Ampere's Bridge has been calculated, taking into account special relativity theory, particularly the Lorentz transformation which brings about a change in the lengths of moving bodies. The result is that the repulsive force between the two parts of Ampere's bridge remains repulsive, displaying dependence on the thickness of the branches, decreasing with increasing thickness. This was also the case when analysis was conducted without taking into account the special relativity theory. In fact, the predictions are in complete agreement with physical measurements.

Delay stabilizes stochastic motion of bumps in layered neural fields

We study the effects of propagation delays on the stochastic dynamics of bumps in neural fields with multiple layers. In the absence of noise, each layer supports a stationary bump. Using linear stability analysis, we show that delayed coupling between layers causes translating perturbations of the bumps to decay in the noise-free system. Adding noise to the system causes bumps to wander as a random walk. However, coupling between layers can reduce the variability of this stochastic motion by canceling noise that perturbs bumps in opposite directions. Delays in interlaminar coupling can further reduce variability, since they couple bump positions to states from the past. We demonstrate these relationships by deriving an asymptotic approximation for the effective motion of bumps. This yields a stochastic delay-differential equation where each delayed term arises from an interlaminar coupling. The impact of delays is well approximated by using a small delay expansion, which allows us to compute the effective diffusion in bumps’ positions, accurately matching results from numerical simulations.

Delay and crosstalk reliability issues in mixed MWCNT bundle interconnects

Multi-walled carbon nanotube (MWCNT) bundles have potentially provided attractive solution in nanoscale VLSI interconnects. In current fabrication process, it is not trivial to grow a densely packed bundle having MWCNTs with similar number of shells. A realistic nanotube bundle, in fact, is a mixed CNT bundle consisting of MWCNTs of different diameters. This research paper presents an analytical model of mixed CNT bundle wherein MWCNTs having different number of shells are densely packed. Two different types of MWCNT bundles are presented: (1) MB that contains MWCNTs with similar number of shells (i.e., uniform diameters) and (2) MMB wherein MWCNTs having different number of shells (i.e., non-uniform diameters) are mixed. Multi-conductor transmission line theory is used to present an equivalent single-conductor (ESC) model of different MB and MMB configurations. Using the ESC model, performance is analyzed to address the effect of propagation delay, crosstalk and power dissipation that explores the reliability of an interconnect wire. It is observed that using an MMB arrangement, the overall reduction in delay and crosstalk are 15.33% and 29.59%, respectively, compared to the MB for almost similar power dissipation.

The Use of Finite Differences on Electric Currents Gives Credit to Coulomb‟s Law as Causing Electromagnetic Forces, thereby Explaining Electromagnetic Induction

Using differential calculus rigorously on electric currents, thereby using the method of finite elements, it has been possible to derive expressions for the total electromagnetic force between two electric currents, based solely on Coulomb's law, thereby applying the effects of propagation delay. These results, explored in earlier publications, have been used in order to attain a new explanation to electromagnetic induction, thereby simultaneously rejecting Faraday's Law of Induction. It is being shown that Faraday's Law of Induction fails to account for the behavior of the induced signal in a secondary loop of a typical transformer circuit, since it has been found a mathematical deficiency in the traditional analysis of electric measurements, which implies a phase fault. Instead it is successfully being shown that the usage of the Displacement Current Density, based on Coulomb's Law, and the Continuity Equation of Electricity are able to account for the correct phase behavior.

Distributed entanglement generation between continuous-mode Gaussian fields with measurement-feedback enhancement

This paper studies a scheme of two spatially distant oscillator systems that are connected by Gaussian fields and examines distributed entanglement generation between two continuous-mode output Gaussian fields that are radiated by the oscillators. It is demonstrated that using measurement-feedback control while a non-local effective entangling operation is on can help to enhance the Einstein-Podolski-Rosen (EPR)-like entanglement between the output fields. The effect of propagation delays and losses in the fields interconnecting the two oscillators, and the effect of other losses in the system, are also considered. In particular, for a range of time delays the measurement feedback controller is able to maintain stability of the closed-loop system and the entanglement enhancement, but the achievable enhancement is only over a smaller bandwidth that is commensurate with the length of the time delays.

Inverse Singular Value Method for Enforcing Passivity in Reduced-Order Models of Distributed Structures for Transient and Steady-State Simulation

Reduced-order modeling of distributed structures for transient and steady-state circuit simulation transforms discrete frequency-domain network parameters to a set of rational functions. The models are ideally causal and passive with passivity being the most difficult property to assure, especially when the distributed structures incorporate propagation delay effects or the available network parameters have limited bandwidth. Small errors in the frequency-domain network parameters, or out-of-band assumptions, can yield models that result in unstable transient simulations. Here, an inverse singular value method is developed that imposes the smallest perturbation required to simultaneously modify the residues, poles, and coupling coefficients of the rational function-based model to achieve passivity. The process enables selection of the frequency ranges for which the model is required to be most accurate. The method is based on the observation that a macromodel is passive if the singular values of the scattering parameter matrix are less than unity at all frequencies.

A 20-Gb/s Quadrature Phase-Shift-Keying Real-Time Coherent System Based on a Subcarrier Optical Phase-Locked Loop

A 20-Gb/s quadrature phase-shift keying (QPSK) homodyne coherent system was analyzed and experimentally demonstrated. This system is based on subcarrier optical phase-locked loop (SC-OPLL) and it works in real time. In this letter, we present a brief optical receiver analysis and the transmission system performance in terms of simulations and experimental results. We also show that the QPSK system works but it is affected by loop propagation delay effects due to the prototypal implementation. The delay loop effects can be mitigated by an SC-OPLL integrated realization.

A GA-based PID active queue management control design for TCP/IP networks

In this paper, a genetic algorithm-based (GA-based) proportional-integral-derivative (PID) controller as an active queue manager for Internet routers is proposed to reduce packet loss and improve network utilization in TCP/IP networks. Based on the window-based nonlinear dynamics, the TCP network was modeled as a time-delayed system with a saturated input due to the limitations of packet-dropping probability and the effects of propagation delays in TCP networks. An improved genetic algorithm is employed to derive optimal or near optimal PID control gains such that a performance index of integrated-absolute error (IAE) in terms of the error between the router queue length and the desired queue length is minimized. The performance of the proposed control scheme was evaluated in various network scenarios via a series of numerical simulations. The simulation results confirm that the proposed scheme outperforms other AQM schemes.

GA-based PID active queue management control design for a class of TCP communication networks

Active queue management (AQM) is a key congestion control scheme for reducing packet loss and improving network utilization in TCP/IP networks. This paper proposes a proportional–integral-derivative (PID) controller as an active queue manager for Internet routers. Due to the limitations of packet-dropping probability and the effects of propagation delays in TCP networks, the TCP AQM network was modeled as a time-delayed system with a saturated input. An improved genetic algorithm is employed to derive optimal or near optimal PID controller gains such that a performance index of integrated-absolute error (IAE) is minimized, and thereby a stable queue length, low packet loss, and high link utilization for TCP networks are guaranteed. The performance of the proposed control scheme is evaluated in various network scenarios via a series of numerical simulations.