Average Fade Research Articles

Pyrrolic nitrogen-doped carbon sandwiched monolayer MoS2 vertically anchored on graphene oxide for high-performance sodium-ion battery anodes

In this work, a novel pyrrolic nitrogen-doped carbon sandwiched monolayer MoS2 hybrid was prepared. This sandwiched hybrid vertically anchors on graphene oxide as anode materials for sodium-ion batteries. Such electrode was fabricated by facile ionic liquid-assisted reflux and annealing methods. Owing to rational structure and enhancement from pyrrolic nitrogen dopant, this unique MoS2/C-graphene hybrid exhibits reversible specific capacity of 486 mAh g−1 after 1000 cycles with a low average fading capacity of 0.15 mAh g−1 (fading cyclic rate of ca. 0.03% per cycle). A capacity of 330 mAh g−1 is remained at the current densities of 10.0 A g−1. The proposed strategy provides a convenient way to create new pyrrolic nitrogen-doped hybrids for energy field and other related applications.

Performance Analysis of Interference-Limited Mobile-to-Mobile κ–μ Fading Channel

In this paper, a wireless cooperative network, with two sections, operating over multipath mobile-to-mobile interference-limited fading channel is considered. The desired signal and the cochannel interference experience κ–μ short term fading. The source and destination mobile stations are connected by an amplify-and-forward relay mobile station. The destination station signal-to-interference ratio probability density function and the outage probability closed-form expressions are derived. The closed form approximate expressions for the average fade duration and the level crossing rate are also derived. The influence of the fading channel parameters on these statistical measures are studied. The Monte-Carlo simulations are used to validate the theoretical results.

An Extension of the <inline-formula> <tex-math notation="LaTeX">$\kappa$</tex-math> </inline-formula>-<inline-formula> <tex-math notation="LaTeX">$\mu$</tex-math> </inline-formula> Shadowed Fading Model: Statistical Characterization and Applications

We here introduce an extension and natural generalization of both the \kappa-\mu$\,$shadowed and the classical Beckmann fading models: the Fluctuating Beckmann (FB) fading model. This new model considers the clustering of multipath waves on which the line-of-sight (LoS) components randomly fluctuate, together with the effect of in-phase/quadrature power imbalance in the LoS and non-LoS components. Thus, it unifies a variety of important fading distributions as the one-sided Gaussian, Rayleigh, Nakagami-m, Rician, \kappa-\mu, \eta-\mu, \eta-\kappa, Beckmann, Rician shadowed and the \kappa-\mu$\,$shadowed distribution. The chief probability functions of the FB fading model, namely probability density function, cumulative distribution function and moment generating function are derived. The second-order statistics such as the level crossing rate and the average fade duration are also analyzed. These results can be used to derive some performance metrics of interest of wireless communication systems operating over FB fading channels.

Wireless Powered Cooperative Communication Using Two Relays: Protocol Design and Performance Analysis

This paper develops an adaptive cooperative transmission scheme with relays harvesting wireless energy. Two relays are adopted to alternately forward source data to the destination using the two-path successive relaying (TPSR) protocol. When one relay forwards previous data along with source transmitting current data, using the power-splitting technique, the other relay will harvest energy and decode the current data from the received composite signal. If the TPSR cannot be performed due to the failure of data decoding at either relay, the decode-and-forward (DF) protocol will be performed by selecting a better relay. If one relay joins in the DF relaying, it will harvest energy and decode source data using the PS technique, while the other relay will always harvest energy from the received signal. If neither TPSR nor DF relaying can be performed, the source will transfer wireless power to both relays. The transmit powers of relays and the PS ratio are judiciously determined through analyzing the occurrence probability, average power fading, and success probability of each case. Numerical results show that our adaptive relaying scheme can achieve a much higher throughput than the single-relay DF scheme and the TPSR-only scheme.

A WINNER+ Based 3-D Non-Stationary Wideband MIMO Channel Model

In this paper, a three-dimensional (3D) non-stationary wideband multiple-input multiple-output (MIMO) channel model based on the WINNER+ channel model is proposed. The angular distributions of clusters in both the horizontal and vertical planes are jointly considered. The receiver and clusters can be moving, which makes the model more general. Parameters, including number of clusters, powers, delays, azimuth angles of departure (AAoDs), azimuth angles of arrival (AAoAs), elevation angles of departure (EAoDs), and elevation angles of arrival (EAoAs) are time-variant. The cluster time evolution is modeled using a birth-death process. Statistical properties, including spatial cross-correlation function (CCF), temporal autocorrelation function (ACF), Doppler power spectrum density (PSD), level-crossing rate (LCR), average fading duration (AFD), and stationary interval are investigated and analyzed. The LCR, AFD, and stationary interval of the proposed channel model are validated against the measurement data. Numerical and simulation results show that the proposed channel model has the ability to reproduce the main properties of real non-stationary channels. Furthermore, the proposed channel model can be adapted to various communication scenarios by adjusting different parameter values.

Level Crossing Rate and Average Fade Distance of Signal Scattering From Rough Layered Interfaces

In this paper, we study the level crossing rate (LCR) and the average fade distance (AFD) of signal scattering from layered rough surfaces. First, we implement the first-order perturbation method, and we establish the analytical expression of the joint probability density function (PDF) of the modulus of the field filtered by a sensor and its spatial derivative. We also consider the case of the field intensity. Then, we derive from the joint PDF the closed-form formulas for the LCR and the AFD as functions of the statistical parameters of rough interfaces. Numerical simulations are conducted to validate the theoretical results and show that the second-order descriptors are very sensitive to the values of cross-correlation parameters of rough interfaces.

A Sulfur-Limonene-Based Electrode for Lithium-Sulfur Batteries: High-Performance by Self-Protection.

The lithium-sulfur battery is considered as one of the most promising energy storage systems and has received enormous attentions due to its high energy density and low cost. However, polysulfide dissolution and the resulting shuttle effects hinder its practical application unless very costly solutions are considered. Herein, a sulfur-rich polymer termed sulfur-limonene polysulfide is proposed as powerful electroactive material that uniquely combines decisive advantages and leads out of this dilemma. It is amenable to a large-scale synthesis by the abundant, inexpensive, and environmentally benign raw materials sulfur and limonene (from orange and lemon peels). Moreover, owing to self-protection and confinement of lithium sulfide and sulfur, detrimental dissolution and shuttle effects are successfully avoided. The sulfur-limonene-based electrodes (without elaborate synthesis or surface modification) exhibit excellent electrochemical performances characterized by high discharge capacities (≈1000 mA h g-1 at C/2) and remarkable cycle stability (average fading rate as low as 0.008% per cycle during 300 cycles).

Effect of Matrix Partitioning on Second Order Statistics of Fading Channels

In this paper, the expressions for level crossing rate and average fade duration of two-branch selection combining are derived using the proposed matrix partitioning based method for a space-diversity system using a two-branch horizontal linear antenna array at the mobile station. It has been observed that when the antennas are perpendicular to the direction of the vehicle motion, the average fade duration is not very much dependent on the antenna spacing and is almost identical to that for independent fading except for very small antenna spacing. On the other hand, when the antennas are parallel to the direction of the vehicle motion, the level crossing rate can be reduced below the value obtained for independent fading, although the average fade duration deteriorates, especially for small antenna spacing. Numerical results are presented and compared with the existing characteristic function based methods including Gaussian fluctuation effects.

Analysis and Simulation of Second-Order Statistics with Modified Characteristic Function Parameters in a Multipath Fading Environment

In this paper, we analyse and implement a modified low pass filtering based characteristic function for a multipath Rayleigh fading channel. A new class of this modified filtering sequence based statistical simulation model is proposed for a Rayleigh fading environment. Comparing with the sum-of-sinusoids (SOS) deterministic model and its modifications as a new SOS model, the proposed model reintroduces the randomness to Doppler frequency and initial phase of the sinusoids to have non-deterministic simulators with desired statistical properties. The expressions and simulation results of level crossing rate (LCR) and average fade duration are derived and shown in this paper. Comparison of power spectra reveals that the spectrum spread is much less for our proposed method. Therefore, we would expect reduction in the rapidity of fading which is observed in LCR calculations.

On the Double-Generalized Gamma Statistics and Their Application to the Performance Analysis of V2V Communications

Important statistical properties of the double-generalized Gamma (dGG) distribution are studied in this paper. The dGG distribution is suitable for modeling non-homogeneous double-scattering radio propagation fading conditions, which can be frequently observed in vehicle-to-vehicle (V2V) communications. In this context, important statistical metrics for the bivariate dGG distribution, such as the joint probability density function, cumulative distribution function, and the moments, are derived for the first time, while simplified expressions for the corresponding marginal statistical metrics are presented. Moreover, the second-order statistics of this distribution are also analytically studied. The derived analytical framework has been employed to analyze the performance of a transmit antenna selection system operating in V2V communication channels modeled by the dGG distribution. In this scenario, the impact of outdated channel state information (CSI) to the system’s performance is investigated in terms of various metrics, including the level crossing rate and the average fade duration. Furthermore, simplified asymptotic closed-form expressions for the outage probability have been derived to examine the achievable diversity and coding gains. Based on our analysis, insightful discussions are provided. It is shown that the diversity gain is independent from the number of transmit antennas when the available CSI becomes outdated.

Bivariate Rician Shadowed Fading Model

In this paper we present a bivariate Rician shadowed fading model where the shadowing is assumed to follow a Nakagami-$m$ distribution. We derive exact expressions involving a single integral for both the joint probability density function (PDF) and the joint cumulative distribution function (CDF) and we also derive an exact closed-form expression for the moment generating function (MGF). As a direct consequence we obtain a closed-form expression for the power correlation coefficient between Rician shadowed variables as a function of the correlation coefficient between the underlying variables of the model. Additionally, in the particular case of integer $m$ we show that the PDF can be expressed in closed-form in terms of a sum of m Meijer G-functions of two variables. Results are applied to analyze the outage probability (OT) of a dual-branch selection combiner (SC) in correlated Rician shadowed fading and the evaluation of the level crossing rate (LCR) and average fade duration (AFD) of a sampled Rician shadowed fading envelope.

V2V Radio Channel Performance Based on Measurements in Ramp Scenarios at 5.9 GHz

This paper focuses on vehicle-to-vehicle (V2V) radio channel properties under ramp scenarios with different structures. Ramps are categorized according to different construction structures into: 1) viaduct ramp with soundproof walls in an urban area and 2) a general ramp without soundproof walls in a suburban region. Furthermore, considering whether the line of sight is available, the entire propagation process of the radio signal is divided into various propagation zones. Propagation characteristics, including the distribution of fading, fading depth (FD), level crossing rate, average fade duration, Root-Mean-Square (rms) delay spread, propagation path loss, and shadow fading, have been estimated and extracted. In particular, the radio channel properties in different types of ramp scenarios are compared and some interesting findings are obtained: 1) an abrupt fluctuation of the received signal level (RSL) in the urban viaduct ramp scenario indicates the nonignorable impact of soundproof walls on V2V radio channel and 2) continuous changes of RSL and different FD values in various propagation zones can be observed in suburban ramp scenarios. Furthermore, the statistical characteristics of RMS delay spread are fitted using a generalized extreme value model with a good fit. Furthermore, propagation path loss is modeled, demonstrating the difference of path loss values in the transition region owing to the impact of soundproof walls. Overall, the research results emphasize the significance of the V2V radio channel modeling under ramp scenarios.

Statistical Properties of Double Hoyt Fading With Applications to the Performance Analysis of Wireless Communication Systems

In this paper, we investigate the statistical properties of double Hoyt fading channels, where the overall received signal is determined by the product of two statistically independent but not necessarily identically distributed single Hoyt processes. Finite-range integral expressions are first derived for the probability density function (PDF), cumulative distribution function (CDF), level-crossing rate (LCR), and average duration of fades of the envelope fading process. A closed-form approximate solution is also deduced for the LCR by making use of the Laplace approximation theorem. Applying the derived PDF of the double Hoyt channel, we then provide analytical expressions for the average symbol error probability of both coherent M-ary phase-shift keying and square M-ary quadrature amplitude modulation schemes. It is shown that all the obtained theoretical results include those that are already known for double Rayleigh channels as a special case. In addition, simplified expressions for the Hoyt $\times $ Rayleigh, Rayleigh $\times $ one-sided Gaussian, and double one-sided Gaussian channels are presented. Moreover, the applicableness of the proposed model to measured real-world propagation channels is examined and discussed by comparing the derived CDF and LCR with published measurement data collected in inter-vehicular propagation environments. Numerical and simulation results are also provided to confirm the validity of the derivations.

Statistical properties of single-mode fiber coupling of satellite-to-ground laser links partially corrected by adaptive optics.

In the framework of satellite-to-ground laser downlinks, an analytical model describing the variations of the instantaneous coupled flux into a single-mode fiber after correction of the incoming wavefront by partial adaptive optics (AO) is presented. Expressions for the probability density function and the cumulative distribution function as well as for the average fading duration and fading duration distribution of the corrected coupled flux are given. These results are of prime interest for the computation of metrics related to coded transmissions over correlated channels, and they are confronted by end-to-end wave-optics simulations in the case of a geosynchronous satellite (GEO)-to-ground and a low earth orbit satellite (LEO)-to-ground scenario. Eventually, the impact of different AO performances on the aforementioned fading duration distribution is analytically investigated for both scenarios.

Exploiting Temporal Correlation in Wireless Channel for Energy-Efficient Communication

Widespread adoption of Internet-of-Things (IoT) technology depends on cost-affordability of the devices and convenience of their usage in terms of long life. Energy-efficiency of the miniaturized wireless IoT devices is a key to the cost and convenience factors. While there have been a few prior studies on wireless channel adaptive communication strategies, in this paper we relook at the problem aiming at effectively characterizing the wireless fading channel and devising energy-efficient link-layer retransmission strategy suitable for IoT devices. In particular, we propose a new channel-adaptive strategy that depends on the rate of variation of wireless channel irrespective of the underlying channel fading distribution. We further show that the concept of average fade duration dependent retransmission is a special case of the proposed strategy. Extensive simulations show that the proposed scheme most effectively characterizes the temporal variations of wireless channel in comparison with the other existing schemes. Performance of the proposed retransmission strategy is compared with the competitive protocols using the Markov model. Numerical results demonstrate that, the proposed scheme offers a gain of about 9% in terms data throughput and about 12% in terms of energy efficiency in comparison to its nearest existing benchmark scheme.

A Three-Dimensional Geometrical Scattering Model for Cellular Communication Environment

Geometrical channel modeling has been one of the hot topics in wireless communication systems since the last two decades. It has been used for variety of scattering model characterizations like spatial and temporal statistical behavior of the channel, level crossing rate of the fading channel along with the analysis of average fade duration etc. In this paper, we propose a three dimensional (3D) semi-ellipsoid geometric scattering model for cellular mobile communication systems, where, elevated base station is considered in scattering free region while the mobile station is assumed to be surrounded by uniformly distributed scatterers in the proposed geometrical shape. Exploiting the proposed geometry, expressions for the joint and marginal probability density functions for angle-of-arrival and time-of-arrival in azimuth and elevation planes are derived. This model is suitable for macro-cellular environment.

Second-Order Statistics Channel Model for 5G Millimeter-Wave Mobile Communications

Millimeter waves (mmWs) are considered as one of the most promising technologies for future 5G networks. The current study presents a three-dimensional (3D) geometry-based channel model for a fixed-to-mobile non-isotropic Ricean mmW scattering environment. According to this 3D reference model, the mmW complex faded envelope impulse response has been derived. This impulse response has been employed in estimating the second-order statistics of the mmW channel model. These statistics comprise both the 3D faded envelope level crossing rate (LCR) and the average fade duration (AFD). As a consequence, these statistics may contribute to the 5G network planning and engineering, especially for studying the phenomenon of fading with time, the 5G system characteristics, the handoff scenarios, and the relationship between the mobile user velocity and the fading rate. Furthermore, this study also provides a stochastic sum-of-sinusoids mmW channel simulator for comparison with analytical results. Numerical results validated the proposed analytical model and revealed the effect of channel parameters on both LCR and AFD in the mmW bands.

STATISTICS OF SIGNAL TO INTERFERENCE RATIO PROCESS AT OUTPUT OF MOBILE-TO-MOBILE RAYLEIGH FADING CHANNEL IN THE PRESENCE OF COCHANNEL INTERFERENCE

Dual-hop cooperative communications in interference-limited Rayleigh fading channel will be investigated in this paper. The paper considers the first- and second-order statistics of the signal to interference ratio process at the input of the destination mobile station. The exact closed-form expressions for the first-order statistical measures, the probability density function and cumulative distribution function, will be derived. We will also derive approximate closed form expressions for the second-order statistics, the level crossing rate and the average fade duration. The obtained theoretical results will be verified by the Monte-Carlo simulations.

LEVEL CROSSING RATE OF MACRODIVERSITY OUTPUT PROCESS IN THE PRESENCE OF η-μ SHORT TERM FADING AND GAMMA LONG TERM FADING

In this paper macrodiversity reception with macrodiversity selection combining (SC) receiver and two microdiversity MRC receivers operating over shadowed multipath fading channel is studied. Received signal experiences short term fading and correlated Gamma long term fading resulting in system performance degradation. Level crossing rate (LCR) of η-μ random process and level crossing rate of signals at outputs of microdiversity MRC receivers are efficiently calculated. By using these derived formulas, level crossing rate of macrodiversity SC receiver output signal process is calculated. By using this result, average fade duration (AFD) of the proposed wireless communication system can be calculated. The influence of η-μ short term fading severity parameter, Gamma long term fading severity parameter and Gamma long term correlation coefficient on level crossing rate is analysed and studied.

Second-Order Measures of Performance of Dual SC Macro-Diversity System with Unbalanced BSs Exposed to CCI in Composite Fading Channels

ABSTRACTThis paper provides infinite-series expressions for both second-order performance measures, level crossing rate, and average fade duration of dual macro-diversity system employing signal processing from unbalanced base stations (BSs). The main characteristic of those expressions is their rapid convergence. Selection combining algorithm is applied at both micro and macro levels. The general case that assumes different shadowing severities and average powers of the desired signal and co-channel interference (CCI) on BS's branches is explored. The performance degradation due to shadowing and CCI is illustrated and discussed in detail.