Angular Spread Research Articles

Measurement and Simulation for Vehicle-to-Infrastructure Communications at 3.5 GHz for 5G

Intelligent Transportation System (ITS) is more and more crucial in the modern transportation field, such as the applications of autonomous vehicles, dynamic traffic light sequences, and automatic road enforcement. As the upcoming fifth-generation mobile network (5G) is entering the deployment phase, the idea of cellular vehicle-to-everything (C-V2X) is proposed. The same 5G networks, coming to mobile phones, will also allow vehicles to communicate wirelessly with each other. Hence, 3.5 GHz, as the main sub-6 GHz band licensed in 5G, is focused in our study. In this paper, a comprehensive study on the channel characteristics for vehicle-to-infrastructure (V2I) link at 3.5 GHz frequency band is conducted through channel measurements and ray-tracing (RT) simulations. Firstly, the channel parameters of the V2I link are characterized based on the measurements, including power delay profile (PDP), path loss, root-mean-square (RMS) delay spread, and coherence bandwidth. Then, the measurement-validated RT simulator is utilized to conduct the simulations in order to supplement other channel parameters, in terms of the Ricean K-factor, angular spreads, the cross-correlations of abovementioned parameters, and the autocorrelation of each parameter itself. This work is aimed at helping the researchers understand the channel characteristics of the V2I link at 3.5 GHz and support the link-level and system level design for future vehicular communications of 5G.

Obtaining transverse cooling with nonmagnetized electron beam

The first electron cooling with rf-accelerated electron bunches was recently demonstrated at the low energy RHIC electron cooler (LEReC) at BNL. Successful cooling requires that the electrons in the cooling section have a small angular spread and are well aligned with respect to the copropagating ions. LEReC puts into practice a nonmagnetized cooling of the ions at Lorentz factors of $\ensuremath{\gamma}=4.1$ and 4.9. Hence, unlike in previous coolers, in which the transverse electron dynamics is constrained by longitudinal solenoid fields, the ion-electron focusing and steering strongly contribute to the average angular spread of the electron beam. In this paper we discuss the factors that affect the electron angles and describe the process of tuning the electron beam to maximize the cooling of ion bunches in RHIC.

Cluster-Based Millimeter-Wave Outdoor-to-Indoor Propagation Characteristics Based on 32 GHz Measurement Analysis

Although the fifth-generation (5G) networks are deployed at millimeter-wave (mmWave) frequencies, little information about the multipath clustering statistics for mmWave outdoor-to-indoor (O2I) propagation has been reported. This letter attempts to overcome this deficiency somewhat by investigating cluster-based propagation statistics for mmWave O2I that are based upon measurements. The measurements were conducted at 32 GHz at two office buildings. The multipath components (MPCs) were resolved by the space-alternating generalized expectation-maximization algorithm and the MPC clustering was performed by the K -power-means algorithm. We observed that numerous reflections bouncing back-and-forth between the windows cause large numbers of clusters. Other statistics such as the number of rays per clusters, cluster power and shadowing, cluster delay, and angular spread were also calculated.

DOA Tracking of Two-Dimensional Coherent Distribution Source Based on Fast Approximated Power Iteration

Aiming at two-dimensional (2D) coherent distributed (CD) sources, this paper has proposed a direction of arrival (DOA) tracking algorithm based on signal subspace updating under the uniform rectangular array (URA). First, based on the hypothesis of small angular spreads of distributed sources, the rotating invariant relations of the signal subspace of the receive vector of URA are derived. An ESPRIT-like method is constructed for DOA estimation using two adjacent parallel linear arrays of URA. Through the synthesis of estimation by multiple groups of parallel linear arrays within URA arrays, the DOA estimation method for 2D CD sources based on URA is obtained. Then, fast approximated power iteration (FAPI) subspace tracking algorithm is used to update the signal subspace. In this way, DOA tracking of 2D CD sources can be realized by DOA estimation through signal subspace updating. This algorithm has a low computational complexity and good real-time tracking performance. In addition, the algorithm can track multiple CD sources without knowing the angular signal distribution functions, which is robust to model errors.

Two-Dimensional Angular Parameter Estimation for Noncircular Incoherently Distributed Sources Based on an L-Shaped Array

In this paper, a two-stage reduced-rank estimator is proposed for two-dimensional (2D) direction estimation of incoherently distributed (ID) noncircular sources, including their center directions of arrival (DOAs) and angular spreads, based on an L-shaped array. Firstly, based on the first-order Taylor series approximation, a noncircularity-based extended generalized array manifold (GAM) model is established. Then, the 2D center DOAs of incident ID signals are obtained separately with the noncircularity-based generalized shift-invariance property of the array manifold and the reduced-rank principle. The pairing of the two center DOAs is completed by searching for the minimum value of a cost function. Secondly, the 2D angular spreads can be obtained in closed-form solution from the central moments of the angular distribution. The proposed estimator achieves higher accuracy in angle estimation that manages more sources and shows promising results in the general scenario, where different sources possess different angular distributions. Furthermore, the approximate noncircular stochastic Cramer-Rao bound (CRB) of the concerned problem is derived as a benchmark. Numerical analysis proves that the proposed algorithm achieves better estimation performance in both 2D center DOAs and 2D angular spreads than an existing estimator.

Beyond the acceptance limit of DRAGON: The case of the [formula omitted]Li([formula omitted])[formula omitted]B reaction

Radiative capture reactions play a pivotal role for our understanding of the origin of the elements in the cosmos. Recoil separators provide an effective way to study these reactions, in inverse kinematics, and take advantage of the use of radioactive ion beams. However, a limiting factor in the study of radiative capture reactions in inverse kinematics is the momentum spread of the product nuclei, which can result in an angular spread larger than the geometric acceptance of the separator. The DRAGON facility at TRIUMF is a versatile recoil separator, designed to study radiative capture reactions relevant to astrophysics in the A∼10–30 region. In this work we present the first attempt to study with DRAGON a reaction, 6Li(α,γ)10B, for which the recoil angular spread exceeds DRAGON’s acceptance. Our result is in good agreement with the literature value, showing that DRAGON can measure resonance strengths of astrophysically important reactions even when not all the recoils enter the separator.

Dynamic carotid plaque imaging using ultrasonography

ObjectiveDynamic image analysis of carotid plaques has demonstrated that during systole and early diastole, all plaque components will move in the same direction (concordant motion) in some plaques. However, in others, different parts of the plaque will move in different directions (discordant motion). The aim of our study was (1) to determine the prevalence of discordant motion in symptomatic and asymptomatic plaques, (2) to develop a measurement of the severity of discordant motion, and (3) to determine the correlation between the severity of discordant motion and symptom prevalence. MethodsA total of 200 patients with 204 plaques resulting in 50% to 99% stenosis (112 asymptomatic and 92 symptomatic plaques) had video recordings available of the plaque motion during 10 cardiac cycles. Video tracking was performed using Farneback's method, which relies on frame comparisons. In our study, these were performed at 0.1-second intervals. The maximum angular spread (MAS) of the motion vectors at 10-pixel intervals in the plaque area was measured in degrees. Plaques were classified as concordant (MAS, <70°), moderately discordant (MAS, 70°-120°), and discordant (MAS, >120°). ResultsMotion was discordant in 89.1% of the symptomatic plaques but only in 17.9% of asymptomatic plaques (P < .001). The prevalence of symptoms increased with increasing MAS. For a MAS >120°, the hazard ratio for the presence of symptoms was 47.7 (95% confidence interval, 18.1-125.6) compared with the rest of the plaques after adjustment for the degree of stenosis and mean pixel motion. The area under the receiver operating characteristic curve for the prediction of the presence of symptoms using the MAS was 0.876 (95% confidence interval, 0.823-0.929). The use of the median MAS (120°) as a cutoff point classified 86% of the plaques correctly (sensitivity, 81.4%; specificity, 91.2%; positive predictive value, 90.2%; and negative predictive value, 83.0%). ConclusionsThe use of the MAS value to identify asymptomatic plaques at increased risk of developing symptoms and, in particular, stroke should be tested in prospective studies.

Geometry-Cluster-Based Stochastic MIMO Model for Vehicle-to-Vehicle Communications in Street Canyon Scenarios

Vehicle-to-vehicle (V2V) wireless communications have many envisioned applications for ensuring traffic safety and for addressing traffic congestion. However, developing suitable communication systems and standards for this purpose requires developers to have accurate models for the V2V propagation channel. Likewise, the dynamic evolution of multipath components (MPCs) in V2V channels has not been well modeled in existing models. In this paper, we propose a geometry-based stochastic channel model for a lightly built-up urban environment and then parametrize the model from measurements. The MPCs are extracted based on a high-resolution parameter estimation; they are tracked and clustered through a joint algorithm. The identified clusters are classified as line-of-sight, reflections from static scatterers, reflections from mobile scatterers, multiple-bounce reflections, and diffuse scattering. Specifically, the multiple-bounce reflections are modeled as twin clusters that follow the COST 273/COST2100 approach. The paper gives a full parameterization of the channel model and supplies a step-by-step implementation recipe. We verify the model by comparing two second-order statistics, i.e., the root-mean-square (RMS) delay spread and the angular spreads of arrival/departure derived from the channel model, to the results obtained directly from the measurements. Furthermore, we also identify several key factors that strongly impact the synthetic channel performance.

Multidimensional Channel Characteristics Analysis in High‐Speed Train Scenarios

AbstractLTE for Railways (LTE‐R) is a next‐generation communication network dedicated to railway services, enabling high‐speed, reliable, and intelligent communications to ensure safety and efficiency for rail passengers. The wireless channel between the train and the ground is a key challenge in network design and optimization. The high‐speed train (HST) and its surrounding scenarios bring nonstationarity and unique radio propagation characteristics to the HST channel. A comprehensive and in‐depth analysis of channel characteristics is the basis of channel modeling. In this paper, based on the measurement‐validation ray tracing (RT) simulator, the quasi‐stationary intervals are presented first to reasonably quantify channel statistical parameters. Next, the time‐varying multidimensional spectra of the channels in three typical HST scenarios are shown, including the power delay profile (PDP), the arrival/departure angular spectrum, and the Doppler spectrum. Moreover, the corresponding channel characteristic parameters are extracted, such as the root‐mean‐square (RMS) delay spread, angular spread, and Doppler spread. Based on multidimensional channel characteristic analysis, combined with multipath geometric parameters provided by RT, we extract significant scatterers and mine key physical factors that affect radio propagation in HST scenarios. This work lays a solid foundation for accurate time‐varying HST channel modeling.

Spatial Filtering Based Random Access for Machine-Type Communications in Massive MIMO Cellular Networks

Machine-type communication (MTC) is one of the most important enabling technologies for the emerging Internet of Things (IoT). However, the potential massive access will significantly degrade the access performance of MTC. To meet the massive access requirement of MTC, we propose a spatial filtering based random access (SFRA) scheme in massive MIMO cellular networks. Specifically, the angle of arrival (AOA) information provided by massive MIMO is utilized to distinguish collided MTC devices (MTDs). To improve the preamble utilization as possible, we further propose a novel preamble reuse scheme to eliminate the influence of multipath angular spread on preamble detection at the base station (BS). Theoretical analysis and simulation results both show that the proposed SFRA scheme can efficiently reuse preambles and considerably improve the access capacity. In typical urban environments, preambles can be perfectly reused for 9 times at most. Moreover, the average access delay of SFRA is only about one seventh of that of the conventional random access scheme when 10000 MTDs attempt to access the network simultaneously.

Millimeter‐wave propagation modeling and characterization at 32 GHz in indoor office for 5G networks

Since it has a great bandwidth that supports gigabit communication, it is considered to use the millimeter-wave (mmWave) band in the fifth generation (5G) wireless communication. Therefore, an efficient, reliable, and accurate channel model is of vital importance in mmWave bands for indoor environments, especially in the 31.8 to 33.4 GHz band allocated by ITU for 5G communications. In this article, we performed modeling and characterization campaign at the 32 GHz in a typical indoor office environment on fourth floor of the Engineering Faculty in University of Karabuk, Turkey. The obtained results provide large-scale fadings such as path loss, shadowing, root mean square (RMS) delay spread, RMS angular spread, power angular spectrum, number of clusters, and Ricean K-factor in an open-plan indoor environment. Power angular spectrum is used to comprehend the propagation structure. We propose that the results obtained in this study will play a key role in simulating and planning systems at 32 GHz for 5G wireless communication.

An Efficient Near-Field Localization Method of Coherently Distributed Strictly Non-circular Signals.

For the near-field localization of non-circular distributed signals with spacial probability density functions (PDF), a novel algorithm is proposed in this paper. The traditional algorithms dealing with the distributed source are only for the far-field sources, and they need two-dimensional (2D) search or omit the angular spread parameter. As a result, these algorithms are no longer inapplicable for near-filed localization. Hence the near-filed sources that obey a classical probability distribution are studied and the corresponding specific expressions are given, providing merits for the near-field signal localization. Additionally, non-circularity of the incident signal is taken into account in order to improve the estimation accuracy. For the steering vector of spatially distributed signals, we first give an approximate expression in a non-integral form, and it provides the possibility of separating the parameters to be estimated from the spatially discrete parameters of the signal. Next, based on the rank-reduced (RARE) algorithm, direction of arrival (DOA) and range can be obtained through two one-dimensional (1-D) searches separately, and thus the computational complexity of the proposed algorithm is reduced significantly, and improvements to estimation accuracy and identifiability are achieved, compared with other existing algorithms. Finally, the effectiveness of the algorithm is verified by simulation.

Parameter Estimation for Two-Dimensional Incoherently Distributed Source with Double Cross Arrays.

A direction of arrival (DOA) estimator for two-dimensional (2D) incoherently distributed (ID) sources is presented under proposed double cross arrays, satisfying both the small interval of parallel linear arrays and the aperture equalization in the elevation and azimuth dimensions. First, by virtue of a first-order Taylor expansion for array manifold vectors of parallel linear arrays, the received signal of arrays can be reconstructed by the products of generalized manifold matrices and extended signal vectors. Then, the rotating invariant relations concerning the nominal elevation and azimuth are derived. According to the rotating invariant relationships, the rotating operators are obtained through the subspace of the covariance matrix of the received vectors. Last, the angle matching approach and angular spreads are explored based on the Capon principle. The proposed method for estimating the DOA of 2D ID sources does not require a spectral search and prior knowledge of the angular power density function. The proposed DOA estimation has a significant advantage in terms of computational cost. Investigating the influence of experimental conditions and angular spreads on estimation, numerical simulations are carried out to validate the effectiveness of the proposed method. The experimental results show that the algorithm proposed in this paper has advantages in terms of estimation accuracy, with a similar number of sensors and the same experimental conditions when compared with existing methods, and that it shows a robustness in cases of model mismatch.

Best Fit for Complex Peaks (BFCP) in Matlab® for quantitative analysis of in situ 2D X-Ray diffraction data and Raman spectra

Large mineral grains that have undergone shock metamorphism or tectonic stress can exhibit plastic deformation. Using in situ micro X-Ray diffraction, such deformation is revealed in a 2D detector image by distortion of diffraction spots into an angular spread or ‘streaking’ along Debye ring or chi (χ) dimension; this can provide a quantitative measurement of plastic deformation via full width at half maximum (FWHMχ) measurement of the diffraction profile along χ. Often the X-ray intensity is not a single homogeneous streak, but is partitioned into discrete orientationally-related spots along the Deybe ring, called asterism. These complex peaks require more sophisticated fitting. This study introduces a user-friendly, high efficiency data fitting program, Best Fit for Complex Peaks (BFCP), executed within Matlab®. Using XRD data as examples, we fit the integrated complex peaks by a Pseudo-Voigt function and assess the BFCP fitting ability on arbitrarily-generated complex peaks simulating XRD peaks with and without observable noise. In addition, we test BFCP with representative highly-deformed terrestrial and meteoritic samples: quartz in the Concord Granite, olivine in ureilite meteorite Larkman Nunatak 04315, and plagioclase in martian meteorite Northwest Africa 8171. We further test BFCP on Raman spectra from a plagioclase clast in martian meteorite Northwest Africa 11220. Fitting results are monitored by the Normalized Root-Mean-Squared Error (NRMSE), the sum of full width at half maximum (∑(FWHM)) and Modified-∑(FWHM). BFCP is designed for XRD data where there is contribution from both Lorentzian and Gaussian components, but it can be applied where appropriate to peak-fitting of other intensity-versus-quantity data, including spectra.

Two-Dimensional Localization: Low-Rank Matrix Completion With Random Sampling in Massive MIMO System

In this paper, random sampling is considered for direction-of-arrival (DOA) estimation with reduced hardware complexity in massive multiple-input-multiple-output (MIMO) systems. The resulting problem is that the accuracy of the existing DOA estimators will significantly degrade with the availability of only a small subset of data entries as the low date rate is employed to reduce the system power consumption. To address that, an efficient approach based on the variant of matrix factorization is devised to complete the underlying data matrix. As a result, the nominal azimuth and elevation DOAs with the corresponding angular spreads are estimated from the underlying data matrix. Numerical results demonstrate that even in the case of missing entries, the proposed method is superior to the existing approaches with full data.

Experimentally validated computations of simultaneous ion and fast neutral energy and angular distributions in a capacitively coupled plasma reactor

Accurate predictions of the ion energy and angular distribution functions (IEADFs) and fast neutral energy and angular distribution functions (FNEADFs), are essential for a range of critical applications in the plasma processing of thin film etching and deposition. Computationally efficient methods that can be applied to industrial reactor systems that are also validated across a range of operating conditions are essential for prediction of IEADFs and FNEADFs. In this work, we present a hybrid model where a capacitively coupled plasma (CCP) solution was computed using a fluid model and the IEADF/FNEADF was generated using a particle transport model with a multi-species Monte Carlo Collision model. We first compare the computed IEADFs across a range of pressures with experimental measurements for a CCP reactor. We predict FNEADFs that are typically difficult to measure experimentally but are believed to have a significant effect on etch/deposition process phenomena. Across a large pressure range, we observe significant fast neutral bombardment of the electrode surface with at least half the energy of the most energetic ions as well as an angular spread that is larger than that of the ions.

In-building coverage of millimeter-wave wireless networks from channel measurement and modeling perspectives

To progress cost-effective deployment of millimeter-wave (mmWave) wireless networks for indoor users, the prediction of indoor-to-indoor (I2I) and outdoor-to-indoor (O2I) coverage based on field measurement studies is of great interest to the future generation mobile communication system. First, measurements in I2I and O2I scenarios, which have advantages in terms of achieving a fair comparison of channel characteristics across different mmWave bands and bandwidths, are performed. Next, the developed dual-slope path loss model with a break-point distance is found to well fit omnidirectional and directional measured I2I data, especially at 39.5 GHz, revealing that the transition from lit or shadow regions to totally blocked regions is abrupt. Combined with space-time propagation characteristics, the indoor blockage effect on path loss and angular spread is investigated, therein being essential for the design of beam-steering and tracking algorithms. Double-directional measurement results show that most dominant paths arrive along the line-of-sight path, and only a few in-building reflections can be detected in higher frequency bands. Based on the joint analysis of channel measurement and modeling results, several mmWave network design and in-building coverage enhancement insights are presented.

Impact of Meteorological Attenuation on Channel Characterization at 300 GHz

Terahertz (THz) communication is a key candidate for the upcoming age of beyond-fifth-generation mobile networks (B5G) or sixth-generation mobile networks (6G) in the next decade and can achieve ultra-high data rates of dozens of gigabits or even terabits per second. As the carrier frequency increases from radio frequency (RF) to the THz band, the impact of meteorological factors on the wireless link is expected to become more pronounced. In this work, we first provide an overview of the attenuation caused by atmospheric gases, fog, and rain on terrestrial THz wireless communications using the recommendations of the International Telecommunication Union-Radiocommunication (ITU-R). Measured data from the literature are used to predict the attenuation caused by snow. Because unfavorable weather conditions may harm sensitive measurement equipment, ray-tracing (RT) simulations are sometimes used as an alternative to extend sparse empirical data. In this study, the terrestrial channel in an urban scenario at 300 GHz, with a bandwidth of 8 GHz, is characterized using RT simulations under different meteorological factors. The key performance parameters are explored, including path loss (PL), Rician K-factor (KF), root-mean-square (RMS) delay spread (DS), and four angular spreads. The channel characteristics under different meteorological conditions studied in this work are expected to aid the design of future outdoor terrestrial THz communications.

Distance to the Energetic Neutral Hydrogen Source from the Heliotail

Abstract The interaction of the solar wind (SW) with the partially ionized interstellar medium forms the heliosphere. As the supersonic SW flows away from the Sun and incorporates pickup ions (PUIs), they are slowed, compressed, and heated at a termination shock, creating an energetic ion population in the inner heliosheath. The neutralization of PUIs in the heliosheath creates energetic neutral atoms (ENAs) at ∼keV energies that travel ballistically and can be observed at 1 au by the Interstellar Boundary Explorer (IBEX). IBEX uses single-pixel cameras to map ENAs from the heliosphere. In this study, we analyze IBEX observations of &gt;1 keV ENAs from the heliotail during 2009–2017. The ENA spectral index maximizes near the ecliptic plane and decreases at higher latitudes, reflecting the latitudinal structure of the SW. We show that the angular spread of this structure can be used to derive the distance at which the observed ENAs originate, i.e., their cooling length. Using Ulysses observations of the SW we determine that the distance from the Sun to the source of ∼1–6 keV ENAs in the heliotail is ≥289 ± 35 au in 2009–2013 and ≥489 ± 56 au in 2014–2017, using the distance to the termination shock in the downwind direction as 160 au based on the analysis of McComas et al. The increase in ENA source distance over time suggests that IBEX is observing a fast/hotter plasma parcel propagating down the heliotail before being replaced by slow/cooler plasma as the solar cycle evolves.

Wind Wave Effects on Remote Sensing of Sea Surface Currents From SAR

AbstractWind waves contribute a significant component to the sea surface currents detected by synthetic aperture radar (SAR) systems via the orbital velocity; this component is typically referred to as the wind wave‐induced artifact surface velocity (WASV). Accordingly, it is essential to precisely describe the WASV effect, so that the real sea surface currents can be obtained from SAR measurements. In order to enhance our understanding about WASV, we carried out a numerical analysis of the sea state dependence of WASV under various radar configurations. The simulated WASV compares reasonably well with observations reported in the literature. It is found that WASV not only depends on the wind speed but also increases considerably with the development of the wind waves, as characterized by wave age. WASV may increase by two to three times, in fully developed wind wave conditions, as compared to young waves. The wave age dependence appears to largely account for the observed uncertainty in WASV at a given wind speed; moreover, swell is also found to significantly influence WASV through hydrodynamic modulation of wind wave properties. These effects are stronger at higher wind speeds and vary significantly with the different radar configurations that are possible, in terms of polarizations and incidence angles. The variations in WASV using different shortwave spectral functions and angular spreading functions are examined in this manuscript.