Signal Propagation Effects Research Articles

Propagation of spin waves in a lattice of laterally and vertically coupled YIG microwaveguides by changing the magnetization angle in linear and nonlinear modes

Purpose. Investigation of the joint manifestation of the effects of anisotropic signal propagation, coupling, and nonlinear power dependence of the medium parameters in a lattice of laterally and vertically coupled spin-wave (SW) microwaveguides. Consideration of the case of the influence of the rotation of the magnetization angle and the change of the lateral gap between microwaveguides located on the same substrate on the transverse profile of the spin-wave beam and the spatial localization of the SW amplitude. Methods. The method of micromagnetic modeling based on the numerical solution of the Landau–Lifshitz–Hilbert equation shows the possibility of controlling the direction of propagation of SW in an ensemble of laterally and vertically coupled iron yttrium garnet (YIG) microwaveguides by changing the magnetization angle. By the method of numerical integration of the system of coupled discrete nonlinear Schrodinger equations, the possibility of changing the transverse profile of the spin-wave beam by changing the level of the initial signal amplitude is shown. Results. The spatial distributions of the components of the dynamic magnetization of the SW excited in two microwaveguides located on the same substrate obtained in micromagnetic simulations indicate a change in the character of localization of the SW power in the output sections of the microwaveguides. At variation of the lattice magnetization angle, a shift of the threshold power value is observed, at which a characteristic curbing of the transverse width of the spin-wave beam in the nonlinear mode appears. Conclusion. When excitation of surface magnetostatic SW in a lattice of laterally and vertically coupled microwaveguides, a transformation of the transverse profile of the wave is observed at a deviation of the magnetization angle of the structure by 15º , which is manifested in the change of the SW length and its localization in each of the microwaveguides. The combined effects of dipole coupling, gyrotropy, and nonlinearity of the medium make it possible to control the value of the threshold power of the SW, at which the mode of diffractionless propagation of the spin-wave beam is realized in a single layer of the structure.

Improved QoT estimations through refined signal power measurements and data-driven parameter optimizations in a disaggregated and partially loaded live production network

Accurate quality of transmission (QoT) estimations are essential enablers for future low-margin dynamic optical network operations. However, physical parameter measurement uncertainties and other intractable signal propagation effects degrade the accuracy of QoT estimation, especially in live production networks. The recent trend of network disaggregation further exacerbates the issue, and a vendor-agnostic accurate QoT estimator is much needed. In this paper, we study Gaussian-noise-model-based QoT estimation in a large-scale disaggregated and partially loaded live production network with monitored physical layer data spanning across 8 months. We first propose refining the signal power measurements by combining the inline amplifier and optical channel monitor (OCM) power measurements, followed by estimating the gain and noise power profiles of each inline amplifier, which in turn improves QoT estimation accuracy. We further introduce an optical multiplex section and frequency bias to the analytical model to incorporate intractable location-specific and spectral effects in the network and proposed data-driven parameter optimizations to learn the biases as well as erbium-doped fiber amplifier noise figures. The (mean, standard deviation) of the QoT estimation errors were reduced from (−0.1043, 0.6037) dB using average amplifier power and (−0.7875, 0.6337) dB using OCM power to (−0.0964, 0.4649) dB after input parameter refinements and were further reduced to (0.0046, 0.2377) dB with data-driven parameter optimization. The proposed methodologies are simple procedures that network operators can adopt to optimize analytical-model-based QoT estimators and/or serve as feature engineering procedures preceding machine-learning-based QoT in realistic disaggregated live production networks.

An acoustic tracking model based on deep learning using two hydrophones and its reverberation transfer hypothesis, applied to whale tracking

Acoustic tracking of whales’ underwater cruises is essential for protecting marine ecosystems. For cetacean conservationists, fewer hydrophones will provide more convenience in capturing high-mobility whale positions. Currently, it has been possible to use two hydrophones individually to accomplish direction finding or ranging. However, traditional methods only aim at estimating one of the spatial parameters and are susceptible to the detrimental effects of reverberation superimposition. To achieve complete whale tracking under reverberant interference, in this study, an intelligent acoustic tracking model (CIAT) is proposed, which allows both horizontal direction discrimination and distance/depth perception by mining unpredictable features of position information directly from the received signals of two hydrophones. Specifically, the horizontal direction is discriminated by an enhanced cross-spectral analysis to make full use of the exact frequency of received signals and eliminate the interference of non-source signals, and the distance/depth direction combines convolutional neural network (CNN) with transfer learning to address the adverse effects caused by unavoidable acoustic reflections and reverberation superposition. Experiments with real recordings show that 0.13 km/MAE is achieved within 8 km. Our work not only provides satisfactory prediction performance, but also effectively avoids the reverberation effect of long-distance signal propagation, opening up a new avenue for underwater target tracking.

Analytical model OFDM-MIMO signal in a radio channel with frequency-time selective fading

One of the main problems in modern wireless electronic communication networks is the transmission and reception of signals in multipath propagation. Due to the imperfect impulse response of the communication channel, frequency-selective fading of the transmitted signal occurs. This can cause waveform distortion and inter-symbol interference, which can seriously degrade the performance of the communication system. Thus, increasing the noise immunity of wireless electronic communication networks in real-world conditions is one of the most important tasks of modern communication technologies. Orthogonal frequency division multiplexing is known for its resistance to multipath fading and is used to reduce the impact of inter-symbol interference. Multi-antenna systems are a key technology for increasing bandwidth and improving communication reliability. The combination of these two technologies in wireless electronic communication networks can reduce the impact of negative phenomena on the transmitted signal in difficult interference conditions. An analytical model of the signal transmitted by a nonstationary frequency-selective radio channel in a wireless electronic communication network with orthogonal frequency multiplexing and a multi-antenna system is proposed. Analytical expressions are presented that allow us to jointly take into account the influence of interchannel and inter-symbol interference (the effect of multipath signal propagation and Doppler shift on the transmitted signal) against the background of fluctuating noise. Taking into account the factors affecting the transmitted signal makes it possible to bring the model closer to the real processes that occur in the vast majority of radio channels of wireless electronic communication networks.

Gravitational signal propagation in the double pulsar studied with the MeerKAT telescope

The double pulsar PSR J0737−3039A/B has offered a wealth of gravitational experiments in the strong-field regime, all of which general relativity has passed with flying colours. In particular, among current gravity experiments that test photon propagation, the double pulsar probes the strongest spacetime curvature. Observations with MeerKAT and, in the future, the Square Kilometre Array (SKA) can greatly improve the accuracy of current tests and facilitate tests of next-to-leading-order (NLO) contributions in both orbital motion and signal propagation. We present our timing analysis of new observations of PSR J0737−3039A, made using the MeerKAT telescope over the last three years. The increased timing precision offered by MeerKAT yields a measurement of Shapiro delay parameter s that it twice as good, and an improved mass measurements compared to previous studies. In addition, our results provide an independent confirmation of the NLO signal propagation effects and already surpass the previous measurement from 16 yr data by a factor of 1.65. These effects include the retardation effect due to the movement of the companion and the deflection of the signal by the gravitational field of the companion. We also investigate the novel effects that have been expected. For instance, we search for potential profile variations near superior conjunctions caused by shifts of the line of sight due to latitudinal signal deflection, and we find insignificant evidence with our current data. With simulations, we find that the latitudinal deflection delay is unlikely to be measured with timing because of its correlation with Shapiro delay. Furthermore, although it is currently not possible to detect the expected lensing correction to the Shapiro delay, our simulations suggest that this effect may be measured with the full SKA. Finally, we provide an improved analytical description for the signal propagation in the double pulsar system that meets the timing precision expected from future instruments such as the full SKA.

Minimizing the Destructive Effects of Multipath Signal Propagation on Wireless Radio Signal

Minimizing the Destructive Effects of Multipath Signal Propagation on Wireless Radio Signal

A review on uncertainty quantification of shadowing reconstruction and signal measurements in Radio Tomographic Imaging

Radio Tomographic Imaging (RTI) is a novel technology to reconstruct the target-induced shadowing effect of signal propagation in the Radio-Frequency (RF) sensing network, through the Received Signal Strength (RSS) measurements in the RF propagation links. As a novel wireless-signal reconstruction technology, RTI is widely utilized in the Device-Free Localization (DFL) and Location-Based Services (LBS) applications. However, the multipath interference in RF sensing network often induces serious uncertainty in RTI system, including the RSS measurement noise and the RTI reconstruction degradation. Addressing this problem, as the RTI system is to reconstruct the probability image of shadowing by using the RSS measurements, from the perspective of probabilistic modeling, the RTI reconstruction issue is modeled as the Maximum a Posterior Probability (MAP) of the reconstructed shadowing image from the RSS measurements. Then lots of RTI reconstruction methods for uncertainty quantification, have been developed to improve the RSS measurement accuracy and the RTI reconstruction quality. Therefore, for the first time, this article conducts a comprehensive survey of the recent RTI methods from the viewpoint of uncertainty quantification. At first, the uncertainty quantification in these RTI methods of the shadowing image and RSS measurements are united into the Epistemic uncertainty and Aleatoric uncertainty respectively. Besides, these methods are further classified into different categories based on their technical commonalities. Moreover, the presenting challenges of uncertainty quantification in the actual RTI applications are also discussed, and based on that, the potential development directions of these methods for improving the RSS measurement accuracy and RTI reconstruction performance in future are reasonably predicted.

Propagation and Parametric Amplification in Four-Wave Mixing Processes: Intramolecular Coupling and High-Order Effects

A strong pump-power dependence of the four-wave mixing (FWM) signal for an aqueous solution of Malachite green is reported. The characteristics of the pump-power dependence of the nonlinear signal are reproduced by a theoretical model based on the coupling between pump-probe, considering signal fields and propagation effects. The effect of the intramolecular coupling on the nonlinear intensity of the FWM signal is studied using a model molecule consisting of two-coupled harmonic curves of electronic energies with minima displaced in energy and nuclear positions. Two-vibrational states are considered while including non-adiabatic effects for the two-state model. Moreover, the coupling among the field components, as well as the propagation effects, are studied by considering a constant pump-intensity. Our calculation scheme, considering both the intramolecular coupling effects in the description of the molecular structure and the effects produced by the propagation of the FWM signal along the optical length, allows the exponential dependence of the latter, as the intensity of the pumping beam increases. Our treatments do not require the inclusion of other non-resonant processes outside the RWA approximation, due to the consideration of an adiabatic basis.

Effect of remote signal propagation in an empirical brain network.

Increasing evidence has shown that brain functions are seriously influenced by the heterogeneous structure of a brain network, but little attention has been paid to the aspect of signal propagation. We here study how a signal is propagated from a source node to other nodes on an empirical brain network by a model of bistable oscillators. We find that the unique structure of the brain network favors signal propagation in contrast to other heterogeneous networks and homogeneous random networks. Surprisingly, we find an effect of remote propagation where a signal is not successfully propagated to the neighbors of the source node but to its neighbors' neighbors. To reveal its underlying mechanism, we simplify the heterogeneous brain network into a heterogeneous chain model and find that the accumulation of weak signals from multiple channels makes a strong input signal to the next node, resulting in remote propagation. Furthermore, a theoretical analysis is presented to explain these findings.

Estimation of laminar BOLD activation profiles using deconvolution with a physiological point spread function

BackgroundThe specificity of gradient echo (GE)-BOLD laminar fMRI activation profiles is degraded by intracortical veins that drain blood from lower to upper cortical layers, propagating activation signal in the same direction. This work describes an approach to obtain layer specific profiles by deconvolving the measured profiles with a physiological Point Spread Function (PSF). New methodIt is shown that the PSF can be characterised by a TE-dependent peak to tail (p2t) value that is independent of cortical depth and can be estimated by simulation. An experimental estimation of individual p2t values and the sensitivity of the deconvolved profiles to variations in p2t is obtained using laminar data measured with a multi-echo 3D-FLASH sequence. These profiles are echo time dependent, but the underlying neuronal response is the same, allowing a data-based estimation of the PSF. ResultsThe deconvolved profiles are highly similar to the gold-standard obtained from extremely high resolution 3D-EPI data, for a range of p2t values of 5–9, which covers both the empirically determined value (6.8) and the value obtained by simulation (6.3). -Comparison with Existing Method(s) Corrected profiles show a flatter shape across the cortex and a high level of similarity with the gold-standard, defined as a subset of profiles that are unaffected by intracortical veins. ConclusionsWe conclude that deconvolution is a robust approach for removing the effect of signal propagation through intracortical veins. This makes it possible to obtain profiles with high laminar specificity while benefitting from the higher efficiency of GE-BOLD sequences.

Revisiting profile instability of PSR J1022+1001

ABSTRACT Millisecond pulsars in timing arrays can act as probes for gravitational wave detection and improving the Solar system ephemerides among several other applications. However, the stability of the integrated pulse profiles can limit the precision of the ephemeris parameters and in turn the applications derived from it. It is thus crucial for the pulsars in the array to have stable integrated pulse profiles. Here we present evidence for long-term profile instability in PSR J1022+1001 which is currently included in the European and Parkes pulsar timing arrays. We apply a new evaluation method to an expanded data set ranging from the Effelsberg Pulsar Observing System backend used in the 1990s to that of data from the current PSRIX backend at the Effelsberg Radio Telescope. We show that this intrinsic variability in the pulse shape persists over time-scales of years. We investigate if systematic instrumental effects like polarization calibration or signal propagation effects in the interstellar medium causes the observed profile instability. We find that the total variation cannot be fully accounted for by instrumental and propagation effects. This suggests additional intrinsic effects as the origin for the variation. We finally discuss several factors that could lead to the observed behaviour and comment on the consequent implications.

Analysis of a Sliding Mode DC–DC Boost Converter Through LPRS of a Nonlinear Plant

An exact analysis of sliding mode boost converter dynamics based on the locus of a perturbed relay system (LPRS) method is presented in this article. An LPRS representation of the dc–dc boost converter based on a full nonlinear model is developed. This is a first known attempt to apply the LPRS concept to an industrial process having a nonlinear model. The frequency and amplitude of the self-excited oscillations (chattering/ripple) are analyzed through the LPRS method. The LPRS is also used to analyze the effect of the propagation of an external disturbance (fluctuations in the source voltage). It is found that the effect of source voltage fluctuations on the system dynamics can be attributed to a combination of the effects of amplitude modulation and input signal propagation. Further, LPRS is used in the design problem of the dc–dc boost converter prototype to determine the required controller hysteresis value which ensures the desired operating switching frequency. Simulation and experimental results are presented to validate and illustrate the theoretical analysis.

Recurrent Model for Wireless Indoor Tracking and Positioning Recovering Using Generative Networks

Indoor person tracking attracts a considerable effort from the research community as it allows to perform Human Behaviour Analysis tasks, where wireless technologies play a key role. However, complex signal propagation effects in indoor environments are the main issue to face when performing accurate indoor positioning and tracking. The advances in machine and deep learning models, applied to improve the estimation of the position captured by wireless sensors, can provide a more precise tracking and positioning, an open field for research which has been used to improve the prior art. In this paper, a novel framework for Adaptive Indoor Tracking using Recurrent models, in combination with Generative networks for new data generation (recovery), is presented (RecTrack-GAN). Firstly, a Received Signal Strength Indicator RSSI Fingerprinting database is collected. Secondly, a Recurrent Neural Network (RNN) takes as input the RSSI parameters collected by a Wireless Sensor Network (WSN) and estimates of both orientation and velocity using devices equipped with Inertial Measurement Unit (IMU) sensors, and learns to model the human movement based on these parameters. Thirdly, a Conditional Generative Adversarial Network (CGAN) is used to perform data recovering when no measurements are received and to update the Fingerprinting database taking into account the day time. The experiments performed showed that RecTrack-GAN improves accuracy performance and reduces error deviation for tracking up to 15% compared to the prior art in the literature.

Unifying Long-Term Plasticity Rules for Excitatory Synapses by Modeling Dendrites of Cortical Pyramidal Neurons

SummaryA large number of experiments have indicated that precise spike times, firing rates, and synapse locations crucially determine the dynamics of long-term plasticity induction in excitatory synapses. However, it remains unknown how plasticity mechanisms of synapses distributed along dendritic trees cooperate to produce the wide spectrum of outcomes for various plasticity protocols. Here, we propose a four-pathway plasticity framework that is well grounded in experimental evidence and apply it to a biophysically realistic cortical pyramidal neuron model. We show in computer simulations that several seemingly contradictory experimental landmark studies are consistent with one unifying set of mechanisms when considering the effects of signal propagation in dendritic trees with respect to synapse location. Our model identifies specific spatiotemporal contributions of dendritic and axo-somatic spikes as well as of subthreshold activation of synaptic clusters, providing a unified parsimonious explanation not only for rate and timing dependence but also for location dependence of synaptic changes.

Influence of bidirectional cavity structure on the Brillouin Stokes signal characteristics in ring BFL

We experimentally demonstrate the effects of Brillouin amplifications on the stimulated Brillouin scattering threshold as well as the generated Stokes power. Brillouin fiber laser (BFL) ring cavity structure is used to show the effect of bidirectional signal propagation on threshold and Stokes power. The laser cavity is tested with conventional technique in which there is no signal circulation take place. Both structures are tested under the same experimental conditions using 5 km SMF length, threshold power for the 1 st Stokes signal is improved and reduced up to 90% in ring cavity structure compared to its value in conventional technique. The threshold is reduced, from the value of 16.2 mW in conventional structure to be 1.67 mW in ring laser cavity. Furthermore, different SMF lengths are tested and exhibits the same threshold reduction ratio. In addition, the 1 st and the 2nd Stokes signals within ring laser cavity are tested in terms of threshold and Stokes signals power. In addition, the induced Brillouin gain effect within a bidirectional ring cavity are studied on the maximum Brillouin Stokes signal power.

New Reconstructed Database for Cost Reduction in Indoor Fingerprinting Localization

Location fingerprinting is a technique widely suggested for challenging indoor positioning. Despite the significant benefits of this technique, it needs a considerable amount of time and energy to measure the Received Signal Strength (RSS) at Reference Points (RPs) and build a fingerprinting database to achieve an appropriate localization accuracy. Reducing the number of RPs can reduce this cost, but it noticeably degrades the accuracy of positioning. In order to alleviate this problem, this paper takes the interior architecture of the indoor area and signal propagation effects into account and proposes two novel recovery methods for creating the reconstructed database instead of the measured one. They only need a few numbers of RPs to reconstruct the database and even are able to produce a denser database. The first method is a new zone-based path-loss propagation model which employs fingerprints of different zones separately and the second one is a new interpolation method, zone-based Weighted Ring-based (WRB). The proposed methods are compared with the conventional path-loss model and six interpolation functions. Two different test environments along with a benchmarking testbed, and various RPs configurations are also utilized to verify the proposed recovery methods, based on the reconstruction errors and the localization accuracies they provide. The results indicate that by taking only 11% of the initial RPs, the new zone-based path-loss model decreases the localization error up to 26% compared to the conventional path-loss model and the proposed zone-based WRB method outperforms all the other interpolation methods and improves the accuracy by 40%.

Hunting for Radio Emission from the Intermittent Pulsar J1107-5907 at Low Frequencies

Abstract Rare intermittent pulsars pose some of the most challenging questions surrounding the pulsar emission mechanism, but typically have relatively minimal low-frequency (≲300 MHz) coverage. We present the first low-frequency detection of the intermittent pulsar J1107–5907 with the Murchison Widefield Array (MWA) at 154 MHz and the simultaneous detection from the recently upgraded Molonglo Observatory Synthesis Telescope (UTMOST) at 835 MHz, as part of an ongoing observing campaign. During a 30 minute simultaneous observation, we detected the pulsar in its bright emission state for approximately 15 minutes, where 86 and 283 pulses were detected above a signal-to-noise threshold of 6 with the MWA and UTMOST, respectively. Of the detected pulses, 51 had counterparts at both frequencies and exhibited steep spectral indices for both the bright main pulse component and the precursor component. We find that the bright state pulse energy distribution is best parameterized by a log-normal distribution at both frequencies, contrary to previous results that suggested a power law distribution. Further low-frequency observations are required in order to explore in detail aspects such as pulse-to-pulse variability and intensity modulations, as well as to better constrain the signal propagation effects due to the interstellar medium and intermittency characteristics at these frequencies. The spectral index, extended profile emission covering a large fraction of pulse longitude, and the broadband intermittency of PSR J1107–5907 suggest that future low-frequency pulsar searches—for instance, those planned with SKA-Low—will be in an excellent position to find and investigate new pulsars of this type.

Power Line based Data Communication (as A Cost Effective Solution to Traditional System) and Interleave Division Multiple Access

Objectives: This paper presents a novel generalized PLC transceiver architecture (in IDMA system) and also compares the Channel frequency response based performance of PLC (in IDMA system) by varying the number of channels. Methods: The Matlab software is used for Simulation of Power Line Communication model. Multipath channel model for PLC is the model employed for considering the effect of multipath fading, frequency selective fading, physical signal propagation effects in main network and effect of impedance mismatching. The dispersive nature of channel is the base approach used for considering the effect of Intersymbol Interference. Single carrier modulation, FSK, QPSK, or other modulation methods are used as the modulation technique for narrowband applications on power lines. Power Line model Simulated Result for 4 and 15 number of channels concludes the relation between the parameters frequency, magnitude and phase. Findings: It shows the improvement in attenuation (frequency-dependent) and the frequency selective fading in Power Line Channel. The deep notches in the Frequency Response of the channel get reduced hence resulting in the attenuation improvement. By using IDMA with PLC, we can achieve a communication system which inherits the advantages of both schemes IDMA as well as power line channel. Wide variation in the Data rates can be achieved using power line communication. PLC major advantage is that its uses an existing infrastructure, so the cost of communication will get reduced. With PLC which can work over the various frequencies, communication becomes easier and maximum bandwidth can be utilized. Power Line (carrier) Communication system can be preferred choice over wireless or other Home Networking technology because of its easy installation and availability. With PLC which can work over the various frequencies, communication becomes easier and maximum bandwidth can be utilized. PLC technology promotes data communication of medium and low voltage power lines. Application: It involves the delivery of Communication signal with maximum efficiency over PLC applications. Frequency selective fading gets improved with increase in the number of channels when the PLC is used as the media of communication in IDMA system. Keywords: BER (Bit Error Rate), CDMA (Code Division Multiple Access), IDMA (Interleave Division Multiple Access), Power Grid, Smart Grid, FSK, QPSK

Evidence of short-term groundwater recharge signal propagation from the Andes to the central Atacama Desert: a singular spectrum analysis approach

ABSTRACTThe effect of pressure-driven groundwater recharge signal propagation in the Andean-Atacamenian environment is investigated by assessing a record of 15 years of water table fluctuations of an unconfined–confined aquifer system. Based on a singular spectrum analysis of water table time series, it is shown that, in the given case, groundwater levels in the central Atacama Desert are hydraulically controlled by two distant recharge areas associated with the Andes. The maximum observed range of the pressure signal propagation is ~50 km over an elevation difference of more than 3000 m at a lag of ~25 months. Several findings indicate that an often-cited study misinterpreted a water level rise at the same site as an in-situ alluvial fan recharge. Thus, the effect’s impact on groundwater dynamics in complex aquifer systems can easily be overlooked. Singular spectrum analysis could be of use to investigate pressure effects at hydrologically comparable sites.

Low Probability of Detection for Underwater Acoustic Communication: A Review

Low probability of detection (LPD) is an extremely important characteristic of an underwater acoustic communication (UWAC) system when used for military-related applications, since the detection of a communication signal in the channel may reveal the presence of the transmitter or receiver. Furthermore, the recent advances in the understanding of the environmental effects of sound transmission in the ocean have led to a growing interest in LPD for UWAC also for civilian use. This is because systems that are designed for reliable communication at low signal power have a reduced environmental impact. In this paper, we identify the main challenges for the design of UWAC LPD systems. We describe and classify common approaches for transmission, reception, and interception of LPD signals, and we discuss their advantages and weaknesses. We also present several methods to determine the LPD capability of a system and suggest to adopt the range ratio test as a performance measure that captures the effects of signal propagation through the UWAC channel and the capabilities of the communication receiver and a signal interceptor. In light of the environmental benefits of LPD transmission and ongoing discussions about limiting the power spectral density of UWAC signals through regulations, we believe that LPD transmission is an area of growing importance for UWAC research and development. We hope that this paper serves as a motivation and a starting point for further research in this field.