Showing papers on "Fading distribution published in 2021"

An experimentally validated fading model for THz wireless systems.

Abstract: As the wireless world moves towards the sixth generation (6G) era, the demand of supporting bandwidth-hungry applications in ultra-dense deployments becomes more and more imperative. Driven by this requirement, both the research and development communities have turned their attention into the terahertz (THz) band, where more than [Formula: see text] of contiguous bandwidth can be exploited. As a result, novel wireless system and network architectures have been reported promising excellence in terms of reliability, massive connectivity, and data-rates. To assess their feasibility and efficiency, it is necessary to develop stochastic channel models that account for the small-scale fading. However, to the best of our knowledge, only initial steps have been so far performed. Motivated by this, this contribution is devoted to take a new look to fading in THz wireless systems, based on three sets of experimental measurements. In more detail, measurements, which have been conducted in a shopping mall, an airport check-in area, and an entrance hall of a university towards different time periods, are used to accurately model the fading distribution. Interestingly, our analysis shows that conventional distributions, such as Rayleigh, Rice, and Nakagami-m, lack fitting accuracy, whereas, the more general, yet tractable, [Formula: see text]-[Formula: see text] distribution has an almost-excellent fit. In order to quantify their fitting efficiency, we used two well-defined and widely-accepted tests, namely the Kolmogorov-Smirnov and the Kullback-Leibler tests. By accurately modeling the THz wireless channel, this work creates the fundamental tools of developing the theoretical and optimization frameworks for such systems and networks.

Security at the Physical Layer Over GG Fading and mEGG Turbulence Induced RF-UOWC Mixed System

Abstract: With the rapid evolution of communication technologies, high-speed optical wireless applications under the water surface as a replacement or complementary to the conventional radio frequency (RF) and acoustic technologies are attracting significant attention from the researchers. Since underwater turbulence (UWT) is an inevitable impediment for a long distance underwater optical wireless communication (UOWC) link, mixed RF-UOWC is being considered as a more feasible solution by the research community. This article deals with the secrecy performance of a variable gain relay-based mixed dual-hop RF-UOWC framework under the intercepting attempt of a potential eavesdropper. The RF link undergoes Generalized Gamma (GG) fading distribution, whereas the UOWC link is subjected to mixture Exponential Generalized Gamma (mEGG) distribution. The eavesdropper is capable of wiretapping via a RF link that also experiences the GG fading. The secrecy analysis incorporates the derivations of closed-form expressions for strictly positive secrecy capacity, average secrecy capacity, and exact as well as lower bound of secrecy outage probability in terms of univariate and bivariate Meijer’s $G$ and Fox’s $H$ functions. Based on these expressions, impacts of heterodyne and intensity modulation/direct detection techniques along with weak, moderate, and severe UWT conditions due to air bubbles, temperature, and salinity gradients are quantified. To the best of authors’ knowledge, the proposed model is the first of its kind that addresses the secrecy analysis of a temperature gradient RF-UOWC system along with air bubbles, as opposed to the existing models that considered thermally uniform scenarios only. Finally, the derived expressions are verified via Monte-Carlo simulations.

Composite Fading Models Based on Inverse Gamma Shadowing: Theory and Validation

Abstract: We introduce a general approach to characterize composite fading models based on inverse gamma (IG) shadowing. We first determine to what extent the IG distribution is an adequate choice for modeling shadow fading, by means of a comprehensive test with field measurements and other distributions conventionally used for this purpose. Then, we prove that the probability density function and cumulative distribution function of any IG-based composite fading model are directly expressed in terms of a Laplace-domain statistic of the underlying fast fading model and, in some relevant cases, as a mixture of well-known state-of-the-art distributions. Also, exact and asymptotic expressions for the outage probability are provided, which are valid for any choice of baseline fading distribution. Finally, we exemplify our approach by presenting several application examples for IG-based composite fading models, for which their statistical characterization is directly obtained in a simple form.

PLS for V2I Communications Using Friendly Jammer and Double kappa-mu Shadowed Fading

Abstract: The concept of intelligent transportation systems (ITS) is considered to be a highly promising area of research due to its diversity of unique features. It is based mainly on the wireless vehicular network (WVN), where vehicles can perform sophisticated services such as sharing real-time safety information. To ensure high-quality service, WVN needs to solve the security challenges like eavesdropping, where malicious entities try to intercept the confidential transmitted signal. In this paper, we are going to provide a security scheme under the Double kappa-mu Shadowed fading. Our solution is based on the use of a friendly jammer that will transmit an artificial noise (AN) to jam the attacker’s link and decrease its eavesdropping performances. To evaluate the efficiency of our solution, we investigated the outage probability for two special cases: Nakagami-m and Rician shadowed while taking into consideration the density of the blockage and the shadowing effects. We also studied the average secrecy capacity via deriving closed-form expressions of the ergodic capacity at the legitimate receiver and the attacker for the special case: Nakagami-m fading distribution.

Performance Analysis for Downlink NOMA Over $\alpha$ - $\mu$ Generalized Fading Channels

Abstract: This work presents a performance analysis for downlink non-orthogonal multiple accesses (DL-NOMA) systems where the channel gains follow the $\alpha$ - $\mu$ fading distribution Specifically, closed-form expressions are derived for DL-NOMA in terms of the outage probability (OP), bit error rate (BER), and ergodic capacity (EC) The OP analysis considers two main scenarios, the first is when the individual user's rate is required to satisfy a certain quality of service (QoS), while the second is when the individual user's NOMA rate is less than that of the conventional orthogonal multiple access (OMA) rate Moreover, the derived BER performance is generalized for the case of $M$ -ary quadrature amplitude modulation (MQAM) The results demonstrate the interplay between the system performance, the power allocation coefficients, target data rates, and the channel fading parameters Moreover, the OP results reveal that NOMA users with OMA data rate experience higher outage compared to NOMA with fixed target data rate The accuracy of the derived expressions is validated using extensive Monte Carlo simulation

Energy detection investigation over composite α-μ/inverse-gamma wireless channel

Abstract: Proper utilization of the unused spectrum hole facilitates the expanding necessity of the elevated data rate in the upcoming 5th Generation (5G) wireless communication technology. Energy detection is a widely worked technique to fulfill this requirement with minimal time, cost, and efforts. With this motivation, this work develops an analytical framework to analyze the functioning of an energy detector (ED) based cognitive radio (CR) system over a composite fading distribution, characterized by α - μ /Inverse-Gamma (I-Gamma) composite fading channel. To begin with, closed-form expressions for the probability density function (PDF) are developed for single-input single-output (SISO) and single-input multiple-output (SIMO) channels. Exploiting these expressions, analytical results for the average probability of detection (PD) and the average area under the receiver operating characteristic curve (AUC) are obtained. Further, the breakdown is extended in determining average PD under high and very low signal-to-noise ratio (SNR) regime. Finally, the results are utilized as an application in analyzing the cooperative spectrum sensing (CSS) under different shadowing conditions. The optimization of the number of cognitive radios is carried out using the r-out-of-N voting rule. The validation of all the proposed results and their accuracy is determined using the Monte-Carlo simulations.

Reconfigurable Intelligent Surface in Wireless-Powered Interference-Limited Communication Networks

Abstract: The commercialization of future wireless communication systems faces crucial problems in terms of reduced network cost of deployment and high power consumption. As a result, reconfigurable intelligent surfaces (RIS) have been suggested as a promising approach to overcome these existing challenges. In this paper, the performance of RIS in a wireless-powered interference-limited communication network is investigated. In this network, an energy-constrained access point (AP) is powered by a dedicated multiantenna power beacon (PB) and communicates to a destination limited-interference node via the RIS. It is assumed that the RIS experiences generalized-K fading distribution while the PB and interferers links are subjected to Nakagami-m fading distributions. To evaluate the system performance, the analytical closed-form expression of the probability distribution function (PDF) for the concerned system is derived. Through this, the exact closed-form expressions of the systems outage probability, average delay-tolerance throughput and average bit error rate are obtained. The analysis quantifies the effects of the number of reflecting elements in the RIS, number of interferer nodes, fading parameters on the AP and interferer links and number of antennas on the PB. It is deduced from the results that there is a kind of symmetry relationship between the analytical and simulation results. Additionally, the results illustrate that the proposed system with an RIS outperforms the conventional system without an RIS. Finally, the accuracy of the derived analytical expressions is validated through a Monte-Carlo simulation.

Capacity of Backscatter Communication under Arbitrary Fading Dependence.

Abstract: We analyze the impact of arbitrary dependence between the forward and backward links in backscatter communication systems. Specifically, we quantify the effect of positive and negative dependence between these fading links on channel capacity, using Copula theory. The benefits of this approach are highlighted over the classical framework of linear dependence based on Pearson's correlation coefficient, which is also analyzed. Results show that for a fixed transmit power budget, capacity grows with positive dependence as well as with fading severity in the low signal-to-noise ratio (SNR) regime. Conversely, fading dependence becomes immaterial in the high SNR regime.

Secrecy Performance Analysis of Half/Full Duplex AF/DF Relaying in NOMA Systems Over κ - μ Fading Channels

Abstract: Although the progress in understanding 5G and beyond techniques such as Non-Orthogonal Multiple Access (NOMA) and full-duplex techniques has been overwhelming, still analyzing the security aspects of such systems under different scenarios and settings is an important concern that needs further exploration. In particular, when considering fading in wiretap channels and scenarios, achieving secrecy has posed many challenges. In this context, we propose to study the physical layer security (PLS) of cooperative NOMA (C-NOMA) system using the general fading distribution $$\kappa $$ - $$\mu $$ . This distribution facilitates mainly the effect of light-of-sight as well as multipath fading. It also includes multiple distributions as special cases like: Rayleigh, Rice, Nakagami-m which help to understand the comportment of C-NOMA systems under different fading parameters. The use of Half-Duplex and Full-Duplex communication is also investigated for both Amplify-and-forward (AF) and Decode-and-Forward (DF) relaying protocols. To characterize the secrecy performance of the proposed C-NOMA systems, closed form expressions of the Secrecy Outage Probability (SOP) and the Strictly Positive Secrcey Capacity (SPSC) metrics for the strong and weak users are given for high signal-to-noise ratio (SNR) due to the intractable nature of the exact expressions. Based on the analytical analysis, numerical and simulation results are given under different network parameters. The results show, for low eavesdropper SNR, the positive effect of fading on the secrecy of the NOMA system. Whereas, fading deteriorates more the system secrecy with high eavesdropper SNR. We also deduce that FD relaying gives better secrecy to the weak user. While, more secrecy is granted to the strong user when using HD relaying.

Measurement and analysis of fading characteristics of V2V propagation channel in two tunnels

Abstract: In order to fulfill the requirement of vehicle-to-vehicle communication system for wireless channel fading characteristics and corresponding models, vehicle to vehicle(V2V) wireless channel measurement activities are carried out at the frequency bands of 5.9 GHz and 5.2 GHz in two kinds of tunnel scenes. And small-scale fading characteristics are analyzed for outside the tunnel, inside the tunnel and their junction part. Based on the close-in(CI) log-distance model and ABG (α-β-γ) model, the distance dependent received power models are established. The received power inside and outside the tunnel in the two scenarios are evaluated and compared, and the path loss index is 1.83 and 1.9, respectively. The results show that the CI model with a reference distance of 1 m has higher fitting degree. In addition, the fading distribution of measured data amplitude is compared with five typical theoretical fading distributions, and it is found that its characteristic is closer to the Rice distribution with the minimum goodness of fit value, and the Rice K-factor in the tunnel is smaller than that outside the tunnel. Further, distance-based K-factor models for the tunnel and the junction part are presented. We find that the K-factor at the conjunction area are independent of the distance, while the K-factor inside the tunnel decreases with the increase of the distance.

Physical Model Based Method to Generate Channel Coefficients for Nakagami-m Distribution

Abstract: In this paper, we discuss physical model based method to generate channel coefficients for Nakagami-m distribution. We consider the phase envelope joint distribution so that the phase of the faded signal is also considered. Mainly, the coefficients are generated by exploring the physical model that relates the Nakagami-m fading distribution with Gaussian and gamma distributions for which generation of coefficients is available in commonly used simulation tools. The empirical probability density function (PDF) of generated coefficients are compared with the theoretical values and they are found in excellent agreements. The empirical PDFs for envelope and phase of the generated coefficients are validated using the Kolmogorov–Smirnov test.

Performance Analysis of OTFS Modulation in Vehicular Networks

Abstract: Consider the vehicular network comprising of a fixed source hub, a fixed destination hub with single antenna. Assume that the source-to destination Vehicle Equipment (VE) channel is modelled as Rayleigh fading distribution and Eavesdropper Vehicle (EV) channel link from Source is modelled as Nagakami fading distribution. In this paper, we newly propose Orthogonal Time Frequency Modulation (OTFS) modulation at the transmitter for high speed vehicular networks. The Significance of OTFS modulation is to multiplex the information through two dimensional symmetrical basis capacities regarding postponement and Doppler areas valuable for rapid vehicles. We infer the tight shut structure expression for ergodic secrecy capacity of the proposed system model. It is observed that analytical and simulation result showed that the secrecy capacity improved significantly when compared with the existing system models.

User Grouping and Imperfect CSI for Downlink NOMA over κ- µ Fading

Abstract: The massive increase in the utilization of mobile devices and communication networks has increased the requirement of massive connectivity and efficient spectrum utilization. Non-Orthogonal Multiple Access (NOMA) technique has been a promising technology towards the present day requirements of the users. In NOMA, the signals are superimposed with different power levels for each user and then transmitted to the receiver. The receiver performs Successive Interference Cancellation (SIC) to distinguish and obtain the required signal. Till now, various researches have focused on SIC with perfect characteristics whereas only few research focused on imperfect SIC (ipSIC). While perfect SIC (pSIC) acts an ideal case of no loss of information and external noises, the ipSIC acts as practical scenario of data transmission in real-time environment. In this paper, we aim to obtain the performance metrics of the considered NOMA system in presence of ipSIC and compare to the performance of pSIC of the same user. More importantly, we characterize channels as κ - µ fading distribution. We derive closed-form expressions of outage probability for two destinations. Meanwhile, we also perform the Monte-Carlo simulations to check the authenticity of obtained mathematical expressions.

Ultra‐wideband Channel Measurements and Modeling for Unmanned Aerial Vehicle‐to‐Wearables (UAV2W) Systems

Abstract: The characterization of ultra‐wideband (UWB) wireless channel is very important to design any UWB system for health‐related applications. This chapter focuses on the fundamental properties of the UWB channel and presents one of the first experimental off‐body studies between a human subject and an unmanned aerial vehicle (UAV) at 7.5 GHz of bandwidth. The study was conducted in two environments: indoors and outdoors, and the human subject in this work was patched at nine different body locations under line‐of‐sight (LoS) conditions, four different body locations under non‐line‐of‐sight (NLoS), and at two body locations for four different body postures (sitting, sleeping, standing, and bending). The idea is to determine the best patch antenna location from the captured measurement data. Akaike Information Criteria (AIC) was used for statistical testing to find the distribution that best characterizes the fading channels between different body locations and the UAV. It was found that lognormal distribution fits the fading distribution the best. Detailed time dispersion analysis is also conducted for these nine body locations and four postures channels. In conclusion, the forehead was concluded to be the best location with minimum path loss and minimum delay among all the body channels, and among all the different postures.

Stochastic Geometric Analysis of IRS-aided Wireless Networks Using Mixture Gamma Model

Abstract: An intelligent propagation environment is in massive demand to achieve ubiquitous connectivity for future wireless networks. One novel approach to resolve this demand is by utilizing passive intelligent reflective surfaces (IRS) that can operate with negligible energy and be deployed at low cost. Due to these properties, IRS has recently gained immense attention in the research community and has been studied extensively. However, most of the published work focused on link-level performance without incorporating the impact of the co-channel interference. These limitations motivated us to evaluate the IRS-aided wireless network’s network performance by using a stochastic geometric framework. We utilized the Mixture Gamma model to represent arbitrary fading distribution and derived its statistics. We derived the outage probability in a closed-form expression based on the proposed channel model and introduced a tight bound for asymptotic analysis. Our numerical results indicate that the Mixture Gamma model provides an excellent fit to diverse propagation environments, including the line of sight (LOS) and Non-LOS channel, and the majority of the well-known popular fading models.

On The Performance of NOMA with Bi-directional in Weibull-Channel

Abstract: Fading is considered to be one of the major issues in wireless communications. The non-Orthogonal Multiple Access (NOMA) technique proved to be efficient enough to overcome the fading issues if utilized efficiently. Since the signals transmitted in NOMA are superimposed, with the help of Channel State Information (CSI), the Successive Interference Cancellation (SIC) technique is applied to separate each user's signal. A lot of researches have been going on to study the performance of the NOMA system in various fading channels such as Nakagami-m channel distribution, Rayleigh channel distribution, Rician fading channel distribution, etc. Very few studies were conducted on Weibull-channel distribution applied in the NOMA network. This letter studies performance of the Weibull-channel fading distribution applied in the NOMA network in presence of two users and the presence of a bi-directional communication link between the devices. The analytical expressions were obtained to study the performance efficiency of the system and extensive simulations were generated comparing the performance in various parameters.

BER Analysis of FRFT-OFDM System Over α-µ Fading Channel Under CFO

Abstract: For the 5G mobile wireless system, the orthogonal frequency-division multiplexing (OFDM) is being unique sought-after techniques. But in OFDM-based system “Carrier Frequency Offset” (CFO) is one out of various impairments, which gives rise to “Inter-Carrier Interference” (ICI). In this paper, mitigation of CFO has been analyzed for FrFT-OFDM-based model under α-µ fading distribution. The outcome of CFO mitigation has been presented in terms of BER. α-µ distribution contains Rayleigh, Nakagami-m and Weibull channel distribution for dissimilar values of α and µ. Therefore, it is worthy to mention that the proposed analysis is the generalization of results available (Kumari et al. in Electron Lett 49(20):1299–1301, 2013 [1]), in which BER of the FrFT-OFDM scheme has been presented over a Rayleigh channel distribution. Numerical analysis has been carried out in MATLAB-14.

Capacity analysis of cooperative amplify and forward–quadrature spatial modulation MIMO system

Abstract: Quadrature spatial modulation (QSM) multiple-input multiple-output system attracted substantial research interests lately driven by the several promised advantages. As well, cooperative communication is well-known to enhance the diversity gain and the overall system performance. In this paper, the theoretical capacity of amplify and forward (AF)-QSM system is derived and analyzed. In particular, the mutual information is first obtained and used to obtain the capacity. Derived formulas are corroborated through Monte Carlo simulation results over wide range of system and channel parameters. Besides, the impact of various parameters on the capacity and the mutual information of the studied system is investigated. The performance of AF-QSM is compared with AF-spatial modulation system and superior gains are reported. It is revealed that the capacity of AF-QSM is independent of the channel fading distribution where Rayleigh, Rician and Nakagami-m fading channels are considered. It is also reported that increasing the number of transmit antennas enhances the performance whereas increasing the number of relays degrades the performance.

Higher Order Statistics of channel capacity in κ- µ fading channel

Abstract: The frequency scarcity imposed by the fast-growing need for mobile data service requires promising spectrum aggregation systems. The so-called higher-order statistics (HOS) of the channel capacity (CC) is a suitable metric on the system performance. While prior relevant works have improved our knowledge of HOS characterization on the spectrum aggregation systems, an analytical framework encompassing generalized fading models of interest is not yet available. However, the expressions of HOS are not correct in several previous research works. In this paper, we present novel method by expressing the closed-form expression of CC as the sum of weighted exponential terms and then invoke multinomial expansion to obtain the required coefficients and utilize MGF (Moment Generating Function) based maximum ratio combining (MRC) diversity receivers technique over κ-µ fading distribution to compute higher order moments. Also, we provide correct, simplified and efficient HOS expressions for the asymptotically low and high signal-to-noise regimes and provide a detailed HOS analysis of κ-µ fading channel by obtaining vital statistical measures, such as the amount of dispersion, skewness, and kurtosis by the HOS results. Finally, all derived expressions are validated via the Semi-infinite Gauss Hermite quadrature method.

Alternative Formulations for the Fluctuating Two-Ray Fading Model.

Abstract: We present two alternative formulations for the distribution of the fluctuating two-ray (FTR) fading model, which simplify its statistical characterization and subsequent use for performance evaluation. New expressions for the probability density function (PDF) and cumulative distribution function of the FTR model are obtained based on the observation that the FTR fading distribution is described, for arbitrary $m$, as an underlying Rician Shadowed (RS) distribution with continuously varying parameter $K$, while for the special case of $m$ being an integer, the FTR fading model is described in terms of a finite number of underlying squared Nakagami-$m$ distributions. It is shown that the chief statistics and any performance metric that are computed by averaging over the PDF of the FTR fading model can be expressed in terms of a finite-range integral over the corresponding statistic or performance metric for the RS (for arbitrary $m$) or the Nakagami-$m$ (for integer $m$) fading models, which have a simpler analytical characterization than the FTR model and for which many results are available in closed-form. New expressions for some Laplace-domain statistics of interest are also obtained; these are used to exemplify the practical relevance of this new formulation for performance analysis.

MIMO-TDL Model Parameter Estimation from V2I Channel Sounding

Abstract: This contribution proposes modeling methods for MIMO-TDL channel models under new evaluation method, which is non-WSSUS. V2X channels cannot be assumed to follow the WSSUS assumption due to high inherent mobility. It can be extended to non-WSSUS by employing an ON/OFF process (persistence process). An algorithm to select taps and estimate their parameters from measured data is illustrated. Meanwhile, the slow and fast fading is separated from received signal to assess the fading distribution of taps. The analysis investigates correlation coefficient among taps persistence process, as well as, among taps amplitude. Additionally, an approach is discussed to develop a time varying MIMO-TDL model, whose parameters are varying over time.