Effect Of Doppler Shift Research Articles

A Climatological Study of the Frequency Spectra of Vertical Winds From MU Radar Data (1987–2022)

AbstractIn this paper, we present a statistical analysis of the frequency spectra of vertical velocity W based on data collected by the VHF middle and upper atmosphere (MU) radar from 2.025 to 19.875 km altitude during several days per month over 36 years (1987–2022). We analyzed the mean spectral slopes in the band [0.5–6 hr], which is in the core of the period range for internal gravity waves at the MU radar latitude (∼36° N). First, we tested the performance of several spectral estimators when data are missing to minimize estimation bias on and variance. Second, we analyzed the properties of . We found a dependence on radar echo power aspect ratio and power imbalance between oblique beams maybe due to contaminations of measurements by the horizontal wind . After corrections, we found that: (a) in the troposphere ( is almost seasonally invariant (∼−0.8) despite the strong variability of and (b) is highly variable in the stratosphere ( from ∼0 to −1.2 and shows a clear exponential dependence on at least up to . An empirical expression of the apparent frequency spectra in the stratosphere is with, for example, and . From numerical simulations, we show that Doppler shift effects cannot explain the dependence on . Therefore, the variation of with may represent a real change in the shape of the intrinsic frequency spectrum, which is not considered in the theoretical models.

Optical appearance of numerical black hole solutions in higher derivative gravity

The optical appearance of the numerically black hole solutions within the higher derivative gravity illuminated by an accretion disk context is discussed. We obtain solutions for non-Schwarzschild black holes with r0=1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$r_0=1$$\\end{document}, r0=2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$r_0=2$$\\end{document}, and r0=3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$r_0=3$$\\end{document}. Further analysis of spacetime trajectories reveals properties similar to Schwarzschild black holes, while the r0=2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$r_0=2$$\\end{document} black hole exhibits significant differences. The results reveal the presence of a repulsive potential barrier for the black hole, allowing only particles with energies exceeding a certain threshold to approach it, providing a unique gravitational scenario for non-Schwarzschild black holes. Additionally, the optical images are derived through numerical simulations by discussing the trajectories of photons in the black hole spacetime. The distribution of radiation flux and the effects of gravitational redshift and Doppler shift on the observed radiation flux are considered. Interestingly, previous analyses of the optical appearance of black holes were conducted within the framework of analytic solutions, whereas the analysis of numerical black hole solutions first appears in our analysis.

Wave trapping by porous breakwater near a rigid wall under the influence of ocean current

The present work investigates the water wave interaction with bottom-standing thick porous trapezoidal-shaped structures and shore-side vertical rigid wall in the presence of uniform ocean currents. This study has been done to understand the impact of different physical parameters like friction, porosity, and ocean currents along with different structural parameters (width and height) on different phenomena like wave energy reflection, wave forces, wave energy dissipation, etc. The quadratic boundary element method-based numerical technique has been used to solve the boundary value problem. The structural porosity is modeled using Sollitt and Cross’s model of water wave interaction with thick porous structures. Several results associated with the wave energy reflection and energy dissipation have been analyzed. Also, the wave force exerted by the incoming waves has been investigated to check the stability and sustainability of the right vertical rigid wall and porous structure. The Doppler-shift effect is observed in wave transformation characteristics due to the presence of ocean currents. The impact of following and opposing ocean currents can be seen in the graph of wave energy reflection, dissipation, and wave forces. The periodic patterns can be observed clearly in wave characteristics like wave energy reflection, dissipation, and wave forces when plotted against the non-dimensional separation gap between the porous breakwater and shore-side rigid seawall.

Doppler-enhanced quantum magnetometry with thermal Rydberg atoms

We report experimental measurements showing how one can combine quantum interference and thermal Doppler shifts at room temperature to detect weak magnetic fields. We pump 87 Rb atoms to a highly-excited, Rydberg level using a probe and a coupling laser, leading to narrow transmission peaks of the probe due to destructive interference of transition amplitudes, known as Electromagnetically Induced Transparency. While it is customary in such setups to use counterpropagating lasers to minimize the effect of Doppler shifts, here we show, on the contrary, that one can harness Doppler shifts in a copropagating arrangement to produce an enhanced response to a magnetic field. In particular, we demonstrate an order-of-magnitude bigger splitting in the transmission spectrum as compared to the counterpropagating case. We explain and generalize our findings with theoretical modeling and simulations based on a Lindblad master equation. Our results pave the way to using quantum effects for magnetometry in readily deployable room-temperature platforms.

Nominal GSM-R Radio Network Design for Signalling and Train Control Systems: Case Study Dar-Moro Electrified SGR Line in Tanzania

The recent development of High-Speed Trains (HST) operations requires real-time information transfer, high network capacity, and reliable communication for train signalling and control purposes. Rail operators face challenges as the high-speed railroad traffic grows. In a high-speed driving profile, the communication must be able to overcome fast handover, large Doppler shift, high penetration losses, limited visibility in tunnels, and the harsh electromagnetic environment. Global System for Mobile Communications for Railway (GSM-R) is still a standard-bearer for railway signalling communications. The link capacity and coverage prediction of the predefined Base Transceiver Station (BTS) locations are simulated using the Radio Planner RF planning tool and Matlab®. The terrain map and the signal levels along the railway corridor are observed. The analysis of the GSM-R for a fast-moving train is performed. Signal level coverage prediction, Doppler-shift effect and the received carrier frequencies due to Doppler shift along Dar–Pugu stations have been presented. The critical sites (locations) with weak signals of the first three BTSs have been identified. It is also observed that the Doppler effect may limit the proposed speed.

Suppression of effects of the synchronization error with adaptive down-conversion for underwater acoustic communication

In underwater acoustic communication, inaccurate synchronization can cause an incorrect estimation of the uniform Doppler shift and degrade the demodulation performance. In this paper, it is mathematically described how the inaccurate synchronization affects the demodulation procedure. Moreover, it is also shown theoretically that adaptive down-conversion, which has been proposed to suppress the effects of the nonuniform Doppler shift, reduces the degradation of the demodulation performance caused by the inaccurate synchronization. Furthermore, the improvement in the demodulation performance by the adaptive down-conversion is evaluated using experimental data. The demodulation results of the addition of intended synchronization errors clearly show that the adaptive down-conversion reduced the effects of the synchronization errors and improved the demodulation performance in the case of inaccurate synchronization.

MHD modelling of coronal streamers and their oscillations

Context. The present work investigates solar coronal dynamics in particular streamer waves. Streamer waves are transverse oscillations of the streamer stalk, often generated by the passage of a coronal mass ejection (CME). Recent observational studies infer that the streamer wave is an eigenmode of the streamer plasma slab and an excellent candidate for coronal seismology. Aims. In the present work, we aim to numerically investigate the theoretical concepts of the physics and properties of streamer waves and to complement the observational statistical analysis of these events. Methods. We used the magnetohydrodynamics (MHD) module of MPI-AMRVAC. An adaptive mesh refinement scheme was employed to achieve high resolution for the streamer structure. All the simulations were computed on the same base grid with the same numerical methods. We considered a dipole magnetic field on the Sun and a uniformly accelerating solar wind. We introduced a θ-velocity perturbation within our computational domain in the plane of a streamer to excite the transverse motion. Results. A numerical model for the streamer wave phenomena was constructed in the framework of 2.5D MHD. We performed a parameter study and identified a sensitivity of the streamer dynamics to the background solar wind speed, the characteristics of the perturbation, and the input parameters for the model, such as temperature and magnetic field. We performed a statistical analysis and compared the obtained modelling results with the database of such events from observations from three different coronagraphs. We observed a narrow range of phase speeds and a correlation between wavelength and period. This is consistent with the observations and supports the idea that the streamer wave is an eigenmode of the streamer plasma slab. The measured phase speed is consistently significantly higher than the speed calculated from the measured period and wavelength. The simple fit, when the difference between these two speeds is exactly the background solar wind speed, only matches a small fraction of the data. The obtained results indicate that further investigation is required into the Doppler shift effect in the MHD theory for coronal seismology.

Machine Learning Algorithm for a Link Adaptation strategy in a Vehicular Ad hoc Network

Vehicular Ad Hoc Networks (VANETs) were created more than eighteen years ago with the aim of reducing accidents on public roads and saving lives. Achieving this goal depends on VANET mobiles exchanging Road State Information (RSI) with their surroundings and acting on the received RSI. Therefore, it is essential to ensure that transmitted messages are accurately received. This requires controlling the quality of the sharing medium or link while considering Channel State Information (CSI), which provides information on channel quality and Signal to Noise Ratio (SNR). The process of adjusting the payload based on the CSI is known as Link Adaptation (LA). While several LA works have been published in VANETs, few have considered the effect of relative node mobility. This work presents a link adaptation strategy for VANETs that uses a Neural Network (NN) and the Levenberg-Marquardt Algorithm (LMA). While accounting for Doppler Shift effect induced by the relative velocity, the simulation results demonstrate that the NN approach outperforms its peers by 77%, 115% and 853% in terms of the transmitted errors, model efficiency and throughput respectively, compared to Cte, ARF, and AMC algorithms.

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.

Asymmetry between Galaxy Apparent Magnitudes Shows a Possible Tension between Physical Properties of Galaxies and Their Rotational Velocity

Despite over a century of research, the physics of galaxy rotation is not yet fully understood, and there is a clear discrepancy between the observed mass of galaxies and their rotational velocity. Here, we report on another observation of tension between the physical properties of galaxies and their rotational velocity. We compare the apparent magnitude of galaxies and find a statistically significant asymmetry between galaxies that rotate in the same direction relative to the Milky Way and galaxies that rotate in the opposite direction relative to the Milky Way. While asymmetry in the brightness is expected due to the Doppler shift effect, such asymmetry is expected to be subtle. The observations shown here suggest that the magnitude difference is sufficiently large to be detected by Earth-based telescopes. The asymmetry is consistent in both the northern and southern galactic poles. The difference is also consistent across several different instruments such as DECam, SDSS, Pan-STARRS, and HST as well as different annotation methods, which include automatic, manual, or crowdsourcing annotations through “Galaxy Zoo”. The observation can also explain other anomalies such as the Ho tension. Analysis of Ia supernovae where the host galaxies rotate in the same direction relative to the Milky Way shows a much smaller tension with the Ho value as estimated by the CMB.

Two-stage frequency compensation for Doppler shift on BPSK transceiver with LDPC codes for free-space optical communication systems

The deployment of low earth orbits is seen as a promising way of enlarging data capacities as well as high data rates. Catering to these interests, optical communication presents possible ways of larger bandwidth than microwave communication. The current generation of mainstream communication systems are classified as coherent systems and incoherent systems, and in particular, coherent systems have received more attention owing to their high receiving sensitivity. This study investigates a digital coherent transceiver, based on binary phase-shift keying technology. As coherent demodulation will be affected by considering the Doppler shift effect in digital demodulation, Doppler shift of ± GHz can be compensated by adopting a two-stage frequency offset compensation. Moreover, by leveraging a fast filtering algorithm a considerable amount of resource consumption is saved in its engineering implementation, and its sensitivity can be significantly enhanced via a high-speed parallel error-correction codec based on low-density parity-check technology.

Importance of Background Vorticity Effect and Doppler Shift in Defining Near‐Inertial Internal Waves

AbstractNear‐inertial waves contain a significant fraction of the ocean's internal wave energy and can propagate long distances from their source before dissipating. However, a varying background flow velocity can alter the wave propagation in two ways. The background vorticity modifies the lower bound of the wave frequency bandwidth while Doppler shifts alter the wave intrinsic frequency. Both effects complicate the identification of the waves and the quantification of their energy content. This study analyses the output of a realistic simulation of the North Pacific using adaptive frequency filters to isolate the effects of vorticity and Doppler shift on the apparent wave energy. Spectral filters neglecting background vorticity effects results in apparent near‐inertial energy being underestimated by 40% in anticyclonic structures and overestimated by 100% in cyclonic structures. The asymmetry in energy bias is reinforced when both background vorticity and Doppler shift effects are omitted from the frequency filters.

Waveguide finite element modelling for broadband vibration analysis of rotating and prestressed circular structures: Application to tyres

This paper deals with the waveguide finite element (WFE) method for broadband vibration analysis of rotating and prestressed circular structures. The equilibrium equations governing the vibration problem are formulated by means of a mixed Eulerian–Lagrangian description, allowing to rigorously include the effects of Coriolis, centrifugal and prestress efforts. The inflation pressure is also rigorously described by a follower pressure load at the fluid–structure interface. Due to Coriolis acceleration, solving the free response of the rotating system leads to a quadratic eigenproblem, which can be transformed into a linear eigenvalue problem. The forced response relies on modal decomposition accounting for specific properties of the eigenproblem. A simplified form of viscous damping is proposed, enabling to set damping factors for each mode, while preserving the symmetry of the undamped problem matrices. The WFE model qualitatively compares with an analytical model of a rotating circular shell from the literature. The WFE model is applied to the vibration of a rotating tyre with heterogeneous cross-section up to a frequency of 4 kHz. With rotation the dispersion curves become asymmetric. The waves propagate faster downstream than upstream due to the combined effect of Coriolis acceleration and Doppler shift. The effect of rotation is also clearly pointed out with point and transfer mobility results, showing higher amplitude downstream than upstream. Some dominant mode shapes over the considered frequency range are finally presented and discussed. The results of this study exemplify the efficiency of the WFE approach for broadband vibration analysis of rotating tyres.

A Deep Learning-Based Robust Automatic Modulation Classification Scheme for Next-Generation Networks

Due to stochastic wireless environment, the process of modulation classification has become a challenging task. Because of its powerful feature extraction ability and promising performance over the conventional schemes, deep learning (DL) models are employed to automatic modulation classification (AMC) problems. Most of the conventional models proposed are tested for the limited set of modulation schemes transmitted over additive white Gaussian noise (AWGN) channels without considering the effect of multipath fading and Doppler shift. The next-generation networks use adaptive and higher-order quadrature amplitude modulation (QAM) schemes for higher spectral efficiency. The classification accuracy of conventional DL-based AMC schemes drastically reduces, when different order QAM modulation schemes are accommodated. In this work, different scaling factors are selected for the generation of [Formula: see text]-QAM frames. The combination of scaling factors, which maximize the classification accuracy is chosen. A convolutional neural network (CNN) with six stages is employed for AMC. The simulation results show that the classification accuracy of proposed scheme is higher than the conventional DL-based schemes under various signal-to-noise ratio (SNR) conditions. The proposed scheme shows at least 4% improvement in classification accuracy over the other DL-based schemes.

Theoretical Analysis of Adaptive Algorithm Modulation Scheme in 3D OFDM WiMAX System

The growth of wireless networking has contributed to the need for high-speed services and multimedia applications anywhere and at any time. OFDM WiMAX technology is now considered one of the most popular technologies capable of delivering faster implementation and lower cost than standard wired options for Broadband Wireless Connectivity in metropolitan areas. This paper proposes appropriate adaptive modulation to be used in wireless networks based on SISO and MIMO OFDM WiMAX, which allows the performance of the network to be improved in the case of non-line-of-sight communications that are typical in urban environments. The effects of several paths, signal attenuation, Doppler shift, and different mobility speeds on the performance of the system were investigated. Mathematical models analysis of adaptive modulation in SISO and MIMO systems is treated by using BER, SNR and noise components. Simulation results show that the adaptive algorithm would improve throughput. It can also be concluded that when processing signals in a receiving system under conditions of multi-path signal propagation, the use of adaptive algorithms has a positive effect on noise immunity.
 HIGHLIGHTS
 
 With the growing evolution of wireless communication technologies, there is still a need for higher data rates, increased system capacity, and improved service quality
 3D OFDM-MIMO WiMAX technology is now regarded as one of the most common solutions for Broadband Wireless Connectivity in Urban Areas, capable of offering faster implementation and lower costs than standard wired options
 Effective adaptive algorithm processing in 3D wireless networks based on SISO-OFDM and MIMO-OFDM WiMAX was proposed, enabling network performance to be enhanced in the case of non-LOS wireless communications, which are standard in urban conditions. On the performance of the system, signal attenuation, the effects of several paths, different mobility speeds and Doppler shift were studied
 The adaptive algorithm significantly reduces the probability of error and increases the throughput. It can be concluded that the use of adaptive spatio-temporal algorithms has a positive effect on noise immunity when processing signals in the receiving system under conditions of multipath signal propagation
 
 GRAPHICAL ABSTRACT

Effect of Doppler shift on preamplifier DPSK receivers using balanced detection for optical satellite networks.

Optical satellite networks using laser intersatellite links are recognized as being capable of satisfying the increasing broadband communication demands. However, the Doppler shift due to relative movement between satellites must be taken into consideration. A convenient method that does not require complicated mathematical calculation is adopted to derive the relationship between the residual Doppler shift and the bit error rate (BER) for the balanced differential phase-shift keying (DPSK) detection system. It is shown that the DPSK receiver is sensitive to the residual Doppler shift; when the residual Doppler shift Δfres/Rb is 0.05, 0.10, and 0.15, the BER is reduced from a level of 10-17 to a level of 10-14, 10-11, and 10-6, respectively. The BER of a certain node pair under different link assignment schemes is calculated in a typical multi-hop LEO constellation. The results show that the communication BER of the same node pair is not only related to the step change of the Doppler but also related to the accumulation of the Doppler shift in the optical path. The results obtained here will be helpful in routing selection, link assignment, topology design, and system compensation.

Temporally modulated one-dimensional leaky-wave holograms

Spatio-temporally modulated impedance surfaces can be good candidates for generation of radiating waves with arbitrary eigenstates by breaking momentum and energy conservations. Here, we present a theoretical framework based on the holographic technique and generalized Floquet-wave expansion to analyze spatio-temporally modulated impedance surfaces. The holographic technique estimates the required impedance distribution to achieve the desired momentum. Injecting temporal modulation deviates the eigenvalues and changes the radiation frequency. Using the proposed analytical model, the eigenvalues can be calculated accurately in the presence of space and time modulations. Consequently, it is possible to predict the propagation mechanism of bounded and radiation states. It has been shown that, imposition of temporal modulation causes the Doppler-shift effect and nonreciprocal responses in the hologram. By plotting the antenna dispersion diagram, and observing the asymmetric displacement of dispersion curve due to temporal modulation, the system nonreciprocity can be verified. The beam scanning properties of these structures have also been investigated.

Channel Propagation Characteristics on the Performance of 4G Cellular Systems from High Altitude Platforms (HAPs)

In this paper, we investigated the effect of different channel propagation characteristics on the performance of 4G systems from high altitude platforms (HAPs). The use of High-Altitude Platforms for communication purpose in the past focused mostly on the assumption that the platform is quasi stationary. The technical limitation of the assumption was that of ensuring stability in the positioning of the platform in space. The use of antenna steering and other approaches were proposed as a solution to the said problem. In this paper, we proposed a channel model which account for the motion of the platform. This was done by investigating the effect of Doppler shift on the carrier frequency as the signals propagate between the transmitter and receiver while the High-Altitude Platform is in motion. The basic free space model was used and subjected to the frequency variation caused by the continuous random shift due to the motion of the HAPs. The trajectory path greatly affects the system performance. A trajectory of 30km, 100km and 500km radii were simulated. An acute elevation angle was used in the simulation. The proposed model was also compared to two other channel models to illustrate its performance. The results show that the proposed model behave similar to the existing models except at base station ID 35 and 45 where the highest deviation of 20dBm was observed. Other stations that deviated were less than 2dBm.

Suppression of effects of Doppler shifts of multipath signals in underwater acoustic communication

In underwater acoustic communication, the Doppler shift can severely degrade demodulation performance. In addition, multipath signals can have the Doppler shifts that are different from that of a direct signal. Although conventional signal processing in underwater acoustic communication can deal with multipath signals with the Doppler shifts equal to that of the direct signal, they cannot sufficiently deal with multipath signals with different Doppler shifts. In this paper, we provide a mathematical description of how multipath signals with the different Doppler shifts degrade demodulation performance. Moreover, signal processing, which suppresses the effects of such multipath signals, has been proposed. In addition, to confirm the improvement due to the proposed processing, simulations of communication between a small surface vessel and an underwater vehicle were carried out in this study. The results show that the proposed processing yields a demodulation performance better than that of conventional processing. Furthermore, we investigated how the proposed processing improved the performance under some motional conditions. Finally, through simulations at various symbol rates, the motional and signal conditions under which the proposed processing can improve the performance efficiently are discussed.

Channel Propagation Characteristics on the Performance of 4G Cellular Systems from High Altitude Platforms (HAPs)

In this paper, we investigated the effect of different channel propagation characteristics on the performance of 4G systems from high altitude platforms (HAPs). The use of High-Altitude Platforms for communication purpose in the past focused mostly on the assumption that the platform is quasi stationary. The technical limitation of the assumption was that of ensuring stability in the positioning of the platform in space. The use of antenna steering and other approaches were proposed as a solution to the said problem. In this paper, we proposed a channel model which account for the motion of the platform. This was done by investigating the effect of Doppler shift on the carrier frequency as the signals propagate between the transmitter and receiver while the High-Altitude Platform is in motion. The basic free space model was used and subjected to the frequency variation caused by the continuous random shift due to the motion of the HAPs. The trajectory path greatly affects the system performance. A trajectory of 30km, 100km and 500km radii were simulated. An acute elevation angle was used in the simulation. The proposed model was also compared to two other channel models to illustrate its performance. The results show that the proposed model behave similar to the existing models except at base station ID 35 and 45 where the highest deviation of 20dBm was observed. Other stations that deviated were less than 2dBm.