Realistic Propagation Scenarios Research Articles

Laboratory validation of a new hydro-mechanical energy-based brittleness index model for hydraulic fracturing

Brittleness Index (BI) is a critical parameter characterising the deformation regime of geo-materials, covering the range from purely brittle (fractures) to ductile (plastic flow). A variety of BI models have been developed based on rock properties such as mineralogy, elastic parameters, or constitutive law. However, very few of them are based on the hydro-mechanical interactions emerging in underground engineering applications. In this study, we propose a BI model based on the partitioning of the injection energy EI into non-seismic deformation energy Ed associated with hydraulic fracture propagation. To calculate the Ed, we apply a model for temporal fracturing area (Ad) within the penny-shaped fracture; and we also correlate the wellbore pressure and the three-dimensional strain induced by hydraulic fracturing of the different types of rock samples subjected to true triaxial stress conditions (TTSC), either σv = 6.5 MPa, σH = 3 MPa, σh = 1.5 MPa or σv = 15 MPa, σH = 10 MPa, σh = 5 MPa. As a comparison, the BI is also quantified based on the existing models: (i) acoustic measurement from Rickman et al. (2008), and (ii) the Mohr-Coulomb’s criteria from Papanastasiou et al. (2016). The Ed ranges between 32.4% and 90.6% of the total injection energy EI, which is slightly higher than the value reported from field-scale data (15% to 80%), but comparable to laboratory-derived data (18% to 94%) from literature. The results show that the predictions based on our proposed energy-based BI model are qualitatively consistent with Papanastasiou et al.’s, but less so with Rickman et al.’s. Our BI model is shown to be stress-dependent and capable of capturing the brittle-to-ductile behaviour of geomaterials subjected to hydraulic fracturing. This study demonstrates that our BI model opens a new way for quantifying the brittleness index regarding to realistic fracture propagation scenarios in field.

Scintillation of partially coherent light in time-varying complex media.

We present a theory for wave scintillation in the situation of a time-dependent partially coherent source and a time-dependent randomly heterogeneous medium. Our objective is to understand how the scintillation index of the measured intensity depends on the source and medium parameters. We deduce from an asymptotic analysis of the random wave equation a general form of the scintillation index, and we evaluate this in various scaling regimes. The scintillation index is a fundamental quantity that is used to analyze and optimize imaging and communication schemes. Our results are useful to quantify the scintillation index under realistic propagation scenarios and to address such optimization challenges.

A probability-driven structure-aware algorithm for influence maximization under independent cascade model

Influence maximization (IM) is the problem of finding a set of nodes that can achieve the maximal influence spreads into the network, which faces two significant but intractable issues in latest studies: (i) Curse of scales: with the increase of the network scale, traditional methods cost extensive times in guaranteeing accuracy, which re-evaluate influence spread of every node in network, leading to significant computational overhead; (ii) Generalization issue: with more and more studies on various networks and propagation parameters, it is difficult to find a universally appropriate algorithm that performs well in each topology. In this paper, we propose a novel probability-driven structure-aware (PDSA) algorithm, which begins by cutting/updating network according to the edge activation probability parameters of the IC model, and then uses a graph traversal algorithm (e.g., breadth first search algorithm) to evaluate the influence spread scores of each node. Meanwhile, we adopt a kind of centrality-based independent cascade (CIC) model to approximate a more realistic propagation scenario. Through extensive experiments with six real-world/synthetic networks and six CIC/IC models, we demonstrate that PDSA achieves great performance over state-of-the-art algorithms in terms of effect and efficiency. Even facing various complex topologies and propagation parameters, PDSA exhibits excellent robustness in solving IM problems.

Sparse Channel Estimation via Hierarchical Hybrid Message Passing for Massive MIMO-OFDM Systems

In this paper, we investigate a sparse channel estimation problem for broadband massive multiple-input-multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems. We propose a hidden Markov model to capture the structured sparsity and temporal dependency characteristic of massive MIMO-OFDM channels in the angle-delay domain, and this probability model exhibits extensive adaptability to different realistic propagation scenarios. Then we solve the channel estimation problem based on a novel optimization framework named constrained Bethe free energy (BFE) minimization, which is valid for a generic statistical model. Under this systematic theoretical framework, a hierarchical hybrid message passing (HHMP) algorithm is proposed to track dynamic channel parameters recursively. The proposed method can adaptively learn the sparse structure and temporal correlation of multiuser channels without requiring the knowledge of hidden Markov channel parameters. Numerical simulations demonstrate that the proposed HHMP algorithm can accurately estimate angle-delay domain channels with reduced iteration times and pilot overhead.

Comparison of probability density functions for aperture-averaged irradiance fluctuations of a Gaussian beam with beam wander.

Over the years, there has been much interest in the use of optical wavelengths for communication because of the potential for high data rates. However, the performance of these systems can become significantly degraded due to turbulence-induced signal fluctuations. These fluctuations can be minimized by enlarging the receiving aperture, thereby averaging the fluctuations. There is extensive interest in developing probability density functions (PDFs) describing these intensity fluctuations so as to accurately predict system performance. This work examines several PDF models that have been suggested to represent fluctuations by comparing them to simulations of realistic propagation scenarios of a collimated Gaussian beam with centroid wander. Unlike with an infinite plane or spherical wave, the empirical PDF shape in these simulations changed significantly with increased aperture, going from a positively skewed to a negatively skewed distribution; therefore, the PDF model that describes it also must change. This change in skew can have serious consequences on the metrics of an optical communication system, e.g., number of fades and bit-error rate. In this work, we examine the evolution of the empirical PDF with aperture size and the fit of potential PDF models under various strengths of turbulence. We show that the change in skew with increasing aperture size occurred for all strengths of turbulence and that the currently used PDF models do not adequately characterize this for realistically sized apertures where beam wander is present.

PETOOL v2.0: Parabolic Equation Toolbox with evaporation duct models and real environment data

A new version of PETOOL (Parabolic Equation Toolbox) is introduced with various additional capabilities. PETOOL is an open-source and MATLAB-based software tool with a user-friendly graphical user interface (GUI) for the analysis and visualization of electromagnetic wave propagation over variable terrain and through arbitrary atmosphere. Four novel features of the second version are as follows: (i) Several evaporation duct models have been developed. (ii) Real atmosphere data have been included in the form of “Binary Universal Form for Representation (BUFR)” data developed by “World Meteorological Organization (WMO)”. (iii) Real terrain data have been incorporated into the toolbox in the form of “Digital Terrain Elevation Data (DTED)” developed by “National Imagery and Mapping Agency (NIMA)”. (iv) A special add-on has been developed to generate a 3D coverage map of propagation factor/loss on real terrain data. The toolbox can be used for research and/or educational purposes to analyze more realistic propagation scenarios in an easier and flexible manner. Program summaryProgram title: PETOOL v2.0 (Parabolic Equation Toolbox v2.0)CPC Library link to program files:http://dx.doi.org/10.17632/v8f42rn2zs.1Licensing provisions: GNU General Public License 3Programming language: MATLAB (MathWorks Inc.) R2019a. Partial Differential Toolbox, Curve Fitting Toolbox and Mapping Toolbox required.Journal Reference of previous version: O. Ozgun, G. Apaydin, M. Kuzuoglu, and L. Sevgi, PETOOL: MATLAB-based one-way and two-way split-step parabolic equation tool for radiowave propagation over variable terrain, Computer Physics Communications 182 (2011) 2638–2654.Does the new version supersede the previous version?: YesReasons for the new version: The new version of the toolbox has been enriched with several add-ons which allow the toolbox to make more realistic analyses with real terrain and atmospheric data. The toolbox has the ability to read real atmospheric data in the form of BUFR data and real terrain data in the form of DTED data. A wide range of evaporation duct models has been incorporated into the toolbox. A special add-on has been developed to generate a 3D coverage map of propagation factor/loss on real terrain data. Hence, the toolbox can be used to analyze more realistic propagation scenarios in an easier and flexible manner.Summary of revisions: (i) Several evaporation duct models have been included with real atmospheric data in BUFR format. (ii) Real terrain data in DTED format have been incorporated into the toolbox. (iii) A special add-on has been developed to generate a 3D coverage map of propagation factor/loss on real terrain data.Nature of problem: This program is designed with a user-friendly GUI for the analysis and visualization of radio-wave propagation over variable terrain on the Earth’s surface, and through homogeneous and inhomogeneous atmosphere by using real atmosphere and terrain data. It can easily model both horizontally- and vertically-varying atmospheric refraction (especially ducting) and multipath effects.Solution method: The program employs one-way and two-way Split-Step Parabolic Equation (SSPE) algorithms with a wide-angle propagator. The SSPE is an initial-value problem starting from a reference range (typically from an antenna), and marching out in range by obtaining the field along the vertical direction at each range step, through the use of step-by-step Fourier transformations. The two-way algorithm incorporates the backward-propagating waves into the standard one-way SSPE by utilizing an iterative forward–backward scheme for modeling multipath effects over a staircase-approximated terrain.

Comparing Channel Emulation Algorithms by Using Plane Waves and Spherical Vector Waves in Multiprobe Anechoic Chamber Setups

This paper evaluates the performances of channel emulation algorithms in the multiprobe anechoic chamber (MPAC) by using plane wave (PW) and spherical vector wave (SVW) theories. Channel emulation in MPAC enables the over-the-air (OTA) testing of performances of wireless devices under realistic propagation scenarios, through setting excitation voltages of probes and utilizing the polarized radiation patterns, locations, and orientations of probe antennas to emulate desired fields in test zone. Accurate emulation of radio wave propagation in target scenario guarantees that the device under test (DUT) be assessed fairly in the laboratory. Dynamic multipath scenario and orthogonal polarization can be emulated by exciting the multiple probes in such a way that the total fields from probes resemble the target impinging field in the test zone. The excitation voltages can be either calculated by PW or SVW theories. Despite the fact that PW and SVW are mathematically equal in the far field, different treatments on rotation and translation of waves as well as different linear equations used in two methods result in different computed voltages, hence, different emulated fields. The emulation performances of the two methods with different MPAC setups (e.g., test zone size, probe number, probe sphere radius, and probe directivity) are investigated. Both scenarios of the 2-D field emulation with the 2-D probe configuration and the 3-D (or 2.5-D) field emulation with the 3-D probe configuration are discussed, and instructions on how to wisely use the emulation algorithm are provided.

Low-Complexity Massive MIMO Subspace Estimation and Tracking From Low-Dimensional Projections

Massive MIMO is a variant of multiuser MIMO, in which the number of antennas $M$ at the base-station is very large. It has been observed that in many realistic propagation scenarios, although the user channel vectors have a very high-dim $M$ , they lie on low-dim subspaces because of their limited angular spread (spatial correlation). This low-dim subspace structure remains stable across several coherence blocks and can be exploited to improve the system performance. In a recent work, we addressed this problem and proposed a very effective novel algorithm referred to as Approximate Maximum-Likelihood (AML), which was formulated as a semi-definite program (SDP). In this paper, we address two problems left open in our previous work, namely, computational complexity and tracking. We propose a new algorithm that is reminiscent of Multiple Measurement Vectors (MMV) problem in Compressed Sensing and prove that it is equivalent to the AML Algorithm for sufficiently dense angular grids. It has also a very low computational complexity and is able to track the sharp transitions in the channel statistics very quickly. We provide numerical simulations to assess the estimation/tracking performance of our proposed algorithm, with a particular emphasis on situations where a direct implementation of the SDP is infeasible in real-time. Our proposed algorithm is of independent interest in applications other than massive MIMO. We provide numerical simulations to compare the performance of our algorithm with that of other related subspace estimation algorithms in the literature.

New analytical expressions for the performance metrics of wireless communication system over Weibull/Lognormal composite fading

A realistic propagation scenario is more frequently characterized by a composite multipath/shadowed fading. In this work, a class of Weibull/Lognormal (W-LN) composite fading channel has been analysed and investigated. New analytical approximations to various important performance metrics of wireless communication systems such as the average symbol error probability (SEP), the outage probability, the amount of fading (AF), and the channel capacity are derived. Further, an asymptotic analysis of the composite fading channel is carried out and closed form expressions of the average SEP with and without maximal ratio combining (MRC) diversity along with the coding and diversity gain are presented. The solutions are presented in terms of Fox H-function and are valid for both the integer and non-integer values of the multipath and shadowing parameters. The results are validated via Monte-Carlo simulations and exact numerical results.

A tunable 3‐D statistical channel model for spatio‐temporal characteristics of wireless communication networks

AbstractA new 3‐dimensional geometric channel model is proposed with multiple degrees of freedom in its scattering volume geometry, which enables accurate modeling of realistic propagation scenarios for emerging machine‐to‐machine wireless networks. Analytical expressions for the joint and marginal statistics in delay and angular domains are derived, and we present the impact of various physical channel parameters such as link distance, antenna height, size and position of the scattering region, as well as shape and orientation of the scattering region on the delay and angular spread of the proposed model. The derived analytical results are validated with simulations and are also shown to provide a good fit to published empirical data sets. Relative to existing models, the proposed model is shown to more accurately adapt to different propagation environments envisioned for emerging communication scenarios such as in indoor picocellular and vehicle‐to‐vehicle communication applications.

Effect of atmospheric anisoplanatism on earth-to-satellite time transfer over laser communication links.

The need for an accurate time reference on orbiting platforms motivates study of time transfer via free-space optical communication links. The impact of atmospheric turbulence on earth-to-satellite optical time transfer has not been fully characterized, however. We analyze limits to two-way laser time transfer accuracy posed by anisoplanatic non-reciprocity between uplink and downlink. We show that despite limited reciprocity, two-way time transfer can still achieve sub-picosecond accuracy in realistic propagation scenarios over a single satellite visibility period.

A Non-Stationary Mobile-to-Mobile Channel Model Allowing for Velocity and Trajectory Variations of the Mobile Stations

In mobile-to-mobile (M2M) communication systems, both the transmitter and the receiver are moving with a certain velocity, which is usually assumed to be constant over time. However, in realistic propagation scenarios, the velocity of the mobile stations (MSs) is subject to changes resulting in a non-stationary fading process. In this paper, we develop a non-stationary narrow-band M2M multipath fading channel model, where the transmitter and the receiver experience changes in their velocities and trajectories. For this model, we derive expressions for the local autocorrelation function (ACF), the Wigner–Ville spectrum, the local average Doppler shift, and the local Doppler spread under isotropic scattering conditions. In addition, we investigate the correlation properties of the proposed model assuming non-isotropic scattering around the MSs. By relaxing the standard assumption of constant velocities of the MSs, this paper shows that the local ACF and the Wigner–Ville spectrum differ completely from known expressions derived for wide-sense stationary M2M channel models. Furthermore, it is shown that our model provides consistent results with respect to the Doppler spread. The proposed channel model is useful for the performance analysis of M2M communication systems under non-stationary conditions caused by velocity variations of the MSs.

Indoor cognitive radio operation within the broadcast TV protection contour

Although the broadcast television (TV) spectrum is currently open for unlicensed operation in the USA, a considerably large geographic area still remains excluded from the unlicensed operation due to potential interference to the licensed users. However, it might be possible to reuse primary spectrum within the protection contour if the frequency reuse occurs inside a building that shields radio signals and reduces interference to the primary system. Interference to outdoor licensed users from the indoor operations can be minimized if the unlicensed users adjust their transmit power according to their locations in the building. This paper presents an analysis and effectiveness evaluation of a novel cognitive radio (CR) system which enables CRs to access the licensed spectrum inside a building in the area within the protection contour. The system utilizes an indoor sensor network for (i) interference sensing, (ii) CR transmit power control, to limit the interference to the outdoor primary receiving antennas. Power control model of the indoor system has been developed to estimate safe transmit power for the indoor users. Two cases have been considered; single-user single-sensor (single indoor user and single sensor), and multi-user multi-sensor. Based on the power control model, a power control algorithm has been developed and its effectiveness is assessed through simulations. The algorithm is effective in realistic propagation scenarios, e.g. when internal partition walls and multipath fading are present. The outage probabilities in these propagation scenarios are found and the procedure of determining the transmit powers for CRs is presented.

Second-Order Statistics for Indoor Wireless Joint Fading/Shadowing Channels

In this letter, we consider the joint fading and two-path shadowing (JFTS) channel model, which has been found suitable for characterizing indoor large open office environments with low mobility and stationary users. We derive useful expressions of fundamental channel statistics such as the number of level crossings in time, frequency, and space as well as average fade duration, bandwidth, and length for the JFTS faded/shadowed link. We also compare numerical results and their impact on system design over a variety of realistic propagation scenarios, which can be modeled by varying the JFTS parameters.

A New Approximate Closed-Form Distribution and Performance Analysis of a Composite Weibull/Log-Normal Fading Channel

The presence of both the fading and shadowing effects (also called composite multipath/shadowed fading) is often encountered in a realistic radio propagation scenario, thus, making it necessary to consider the simultaneous effect of fading and shadowing on the received signal. The multipath effect is captured using models such as Rician, Nakagami-m, Weibull distribution and shadowing effect is modeled using Log-normal distribution. In this paper we present the closed-form expression of composite (Weibull/log-normal shadowed) fading using the efficient tool proposed by Holtzman. Using this result, the closed-form expression of combined (time-shared) shadowed/unshadowed fading is presented. The performance measures of fading communication systems such as probability density function of signal to noise ratio, amount of fading, outage probability (Pout) and channel capacity are analyzed and expressed in closed form.

Error Analysis and Comparative Study of Numerical Methods for the Parabolic Equation Applied to Tunnel Propagation Modeling

Parabolic equation (PE) methods have been widely applied to the modeling of wireless propagation in tunnel environments. However, the relevant literature does not include concrete guidelines for the choice of the parameters of these methods and the tradeoffs involved. This paper provides a comprehensive analysis of the two sources of error that arise when PE methods are employed for the modeling of radio-wave propagation scenarios: the well-known numerical dispersion error stemming from the finite-difference solvers for PE and the approximation error stemming from the use of PE for the solution of wave propagation problems that are subject to Maxwell's equations. The analysis is performed for four methods, three of which have been already used in PE-based propagation studies, namely, the Crank-Nicolson (CN) scheme, the alternative-direction-implicit (ADI) method, and its locally one-dimensional (LOD-ADI) version. The fourth method is the Mitchell-Fairweather (MF)-ADI scheme that has been recently shown to be a promising alternative technique for tunnel propagation modeling. The proposed method leads to robust criteria for the choice of spatial discretization in realistic propagation scenarios, as shown via numerical examples.

Dynamic Configuration and Optimization of WiMAX Networks with Relay Power Saving Modes: Measurement-Based Scenario in a Hilly Region

This paper investigates the performances achievable by WiMAX networks deployed in various sectorization configurations, with and without relay stations (RSs). Further, it studies the dynamic adjustment of the configuration to serve traffic loads at different times of the day while maximising the use of opportunistic sleep modes by relays in conjunction with cell zooming, thereby saving energy. The configuration changes and invocation of opportunistic sleep modes also take into account coverage constraints. This paper first reports extensive propagation measurements that have been undertaken in Covilha, a hilly area of Portugal which presents a realistic and challenging propagation scenario. Using this scenario as the topographical basis, practical cellular planning results are then obtained and compared, using the dominant path and ray tracing (RT) functionalities of Winprop™. It is shown that without RSs present, the supported throughput is lower in practice because coverage is not 100 %. Further, for the case with omnidirectional cells, coverage reduces to only approximately 60 % if RSs go into sleep mode, and for the tri-sectored cells case coverage drops from 95.75 to 81.90 % (based on RT calculations) if RSs go into sleep mode. There is, however, still a reasonable economic performance in all cases. Additional results demonstrate that savings typically of 47.6 % in RSs' average power consumption can be achieved. These savings are shown to result in a financial saving for the operator of 10 % of the combined operational and maintenance cost. However, it is observed that such solutions have to be used cautiously in hilly regions due to challenges in maintaining coverage.

Spectrally Efficient Frame-Format-Aided Turbo Equalization With Channel Estimation

Chained turbo equalization (CHATUE) has been recently recognized as a low-complexity frequency-domain turbo equalization technique that eliminates the necessity of transmitting the cyclic prefix (CP), and hence allows for spectrally efficient signaling in wireless communications. However, two issues arise from the original version of CHATUE (referred to as CHATUE1) as a consequence of eliminating the CP, which are the noise enhancement and the latency due to the time-concatenated structure. This paper proposes a new version of CHATUE (referred to as CHATUE2) to solve the noise enhancement problem. CHATUE2 retrieves the circulant structure of the channel matrix, originally inherent within the CP transmission, by utilizing composite replica signals that combine the received signals and the soft reference signals replicated from the log-likelihood ratio (LLR) fed back from the decoder. For this purpose, this paper determines the optimal combining ratio based on the minimum-mean-square-error (MMSE) criterion. CHATUE2 is hence able to achieve an improvement in bit-error-rate (BER) performance over CHATUE1. In addition, this paper provides a solution to solving the latency problem by making a practical assumption on the training sequence (TR) transmission, which is required to perform channel estimation generally, in practical systems. Furthermore, this paper proposes a new channel estimation technique, i.e., chained turbo estimation (CHATES), which improves the spectrum efficiency and asymptotically achieves the Cramer–Rao bound (CRB). CHATES assumes that the TR length is exactly equal to the channel impulse response (CIR) length, although the conventional technique requires twice as long or even longer TR lengths. Numerical results show that CHATUE2 with CHATES achieves a gain of 1 dB over conventional turbo equalization with a CP at a BER of $\hbox{10}^{-5}$ in realistic propagation scenarios represented by channel sounding measurement data and in model-based frequency-selective fading channels.

Computationally Efficient MR-FDPF and MR-FDTLM Methods for Multifrequency Simulations

We propose a modification of the multi-resolution frequency domain ParFlow (MR-FDPF) method that allows simulating radio propagation channels in a frequency range. The performance of the proposed MR-FDPF implementation has been analyzed based on different realistic propagation scenarios. We also analyze the possibility of applying the multi-resolution frequency domain approach to the well-known transmission-line matrix method. The proposed multi-resolution frequency domain transmission-line matrix method provides a computationally efficient way of modeling radio wave propagation in three-dimensional space at multiple frequencies.

Going realistic and optimal: A distributed multi-hop broadcast algorithm for vehicular safety

A subject of great interest and important investments by governments, navigation system companies and street management authorities is highway safety. In this context, an important role is played by applications designed to warn drivers of upcoming dangers. An example is vehicular accident warning systems, which advertise accident events to approaching vehicles. The effectiveness of currently in use vehicular accident warning systems can be jeopardized by their: (a) inability to provide an accident warning to the closest approaching vehicles; and, (b) high delays in advertising an event. In fact, such systems are unable to reach the vehicles that are closest to an accident site due to the absence of any deployed automatic detection and broadcast mechanisms. The future deployment of Vehicular Ad hoc Networks (VANETs) can fill this gap. By leveraging on the distributed nature of ad hoc networks, accident warning systems can rapidly alert the vehicles which most risk their involvement in a crash. To reach this goal, VANET-based accident warning systems require the design of efficient broadcast algorithms. A number of solutions have been proposed in the past few years. However, no such proposals, to the best of our knowledge, assume realistic wireless propagation scenarios. The scope of this paper is to present an optimal distributed algorithm, working at the application layer, for the broadcast of safety messages in VANETs. Optimality, in terms of delay, is achieved in unidimensional highway scenarios and under realistic wireless propagation assumptions. This is the only algorithm, to this date, capable of reaching all vehicles with the minimum number of transmissions within a realistic setting.