Small-scale Fading Model Research Articles

Joint Learning and Optimization-Based Resource Management in Hybrid Network of Cooperative and Non-Cooperative Massive MIMO Systems

Multi-cell multiple-input multiple-output (MIMO) systems have the potential to significantly improve wireless network throughput. However, the cooperative MIMO network experiences the limited backhaul capacity, while the non-cooperative MIMO network requires high fronthaul bandwidth. To overcome these issues, we consider the hybrid MIMO networks to take advantages of both non-cooperative and cooperative MIMO network. In such hybrid system, the decision of whether cells operate in non-cooperative or cooperative mode, as well as the allocated bandwidth for cells are challenging due to the unavailability of channel state information (CSI). Furthermore, cells operating in the cooperative mode should optimize the quantized level selection and power allocation when the backhaul capacity is limited. To address this problem, we propose a joint learning-based and optimization-based framework. Particularly, we employ both large-scale and small-scale fading models to formulate the optimization problems, and then use the obtained solutions of these problems to determine fixed-size features in dynamic networks for the learner. Our numerical results show when the placement decision and the bandwidth assignment for cells are determined, the proposed algorithm can compute the quantized level and allocate power to significantly improve the system performance. Moreover, the proposed hybrid network model controlled by our algorithms outperforms both the non-cooperative and the cooperative MIMO systems in term of net throughput.

AI-Generated Incentive Mechanism and Full-Duplex Semantic Communications for Information Sharing

The next generation of Internet services, such as Metaverse, rely on mixed reality (MR) technology to provide immersive user experiences. However, limited computation power of MR headset-mounted devices (HMDs) hinders the deployment of such services. Therefore, we propose an efficient information-sharing scheme based on full-duplex device-to-device (D2D) semantic communications to address this issue. Our approach enables users to avoid heavy and repetitive computational tasks, such as artificial intelligence-generated content (AIGC) in the view images of all MR users. Specifically, a user can transmit the generated content and semantic information extracted from their view image to nearby users, who can then use this information to obtain the spatial matching of computation results under their view images. We analyze the performance of full-duplex D2D communications, including the achievable rate and bit error probability, by using generalized small-scale fading models. To facilitate semantic information sharing among users, we design a contract theoretic AI-generated incentive mechanism. The proposed diffusion model generates the optimal contract design, outperforming two deep reinforcement learning algorithms, i.e., proximal policy optimization and soft actor-critic algorithms. Our numerical analysis experiment proves the effectiveness of our proposed methods.

Outdoor THz fading modeling by means of gaussian and gamma mixture distributions

Terahertz (THz) band offers a vast amount of bandwidth and is envisioned to become a key enabler for a number of next generation wireless applications. In this direction, appropriate channel models, encapsulating the large and small-scale fading phenomena, need to be developed for both indoor and outdoor communications environments. The THz large-scale fading characteristics have been extensively investigated for both indoor and outdoor scenarios. The study of indoor THz small-scale fading has recently gained the momentum, while the small-scale fading of outdoor THz wireless channels has not yet been investigated. Motivated by this, this contribution introduces Gaussian mixture (GM) distribution as a suitable small-scale fading model for outdoor THz wireless links. In more detail, multiple outdoor THz wireless measurements recorded at different transceiver separation distance are fed to an expectation-maximization fitting algorithm, which returns the parameters of the GM probability density function. The fitting accuracy of the analytical GMs is evaluated in terms of the Kolmogorov-Smirnov, Kullback-Leibler (KL) and root-mean-square-error (RMSE) tests. The results reveal that as the number of mixtures increases the resulting analytical GMs perform a better fit to the empirical distributions. In addition, the KL and RMSE metrics indicate that the increase of mixtures beyond a particular number result to no significant improvement of the fitting accuracy. Finally, following the same approach as in the case of GM, we examine the suitability of mixture Gamma to capture the small-scale fading characteristics of the outdoor THz channels.

An Improved Modelling of User Clustering for Small Cell Deployment in Heterogeneous Cellular Network

Users in practical cellular geographical areas are found to be non-uniformly distributed. Small cell (SC) deployments in heterogeneous user distribution in a cellular geographical area help to meet high data rate user demands for multimedia data communications in hot spots. SCs help to offload traffic burden from the macro cell (MC) base station, and also cater the data traffic need for the edge users where signal strength from the MC base station (BS) is very weak. For deployments of SCs along with the central MC BS (hence called HetNet) in such spatial heterogeneous user distribution, effective user grouping or clustering algorithm is required for appropriate and satisfactory service coverage. We call it service grouping or clustering of users to be put under a SC for data transmission and reception. It does not disturb the spatial positions of users in clustered non-uniform distribution. Efficient grouping or clustering of users and then deploying a SC at optimal location enhances the performance of the HetNet. It is found that the K-means algorithm used for such grouping of users to position SCs is not efficient. A novel and improved user grouping algorithm is proposed in this paper which performs much better compared to the k-means algorithm. The proposed algorithm of modelling of user clustering results in increase in the number of users under SCs, increase in more offloading of data traffic from MC BS thereby increasing data throughput of MC users. The algorithm also increases in the energy efficiencies of the SCs which is considered as one important performance metric. A doubly stochastic poison process (DSPP), also called Cox process, is assumed here for simulation of non-uniform user distributions. We consider Rayleigh distributed small scale fading model, large scale fading factor representing shadow fading, and users’ geographical distances from BSs to evaluate users’ data rates.

Secrecy Analysis of UAV-Based mmWave Relaying Networks

Employing unmanned aerial vehicles (UAVs) in millimeter-wave (mmWave) networks as relays has emerged as an appealing solution to assist remote or blocked communication nodes. In this case, the network security becomes a great challenge due to the presence of malicious eavesdroppers. In this paper, we perform a secrecy analysis for a UAV-based mmWave relaying network. We first investigate the relaying scheme without jamming where the UAV decodes and forwards the information from the source to the destination with malicious eavesdropping. Furthermore, to enhance the secrecy performance, we propose a cooperative jamming scheme via utilizing the destination and an external UAV to cooperatively disrupt the eavesdroppers at the two stages of relaying, respectively. Using the probability of line-of-sight (LoS) between the UAV and ground nodes, the three-dimensional (3D) antenna gain, and the Nakagami-m small-scale fading model, the secrecy outage probability (SOP) of the two schemes with and without jamming is analyzed. Closed-form expressions for the SOP of the two schemes are obtained by employing the Gauss-Chebyshev quadrature. Simulation results are presented to validate the theoretical expressions of SOP and to show the effectiveness of the proposed schemes.

A Generalized Framework for Connectivity Analysis in Vehicle-to-Vehicle Communications

In vehicular networks, the instantaneous connectivity between any two consecutive vehicles is a function of both the headway distance between them and the communication channel characteristics. We derive a generalized analytic expression for vehicle-to-vehicle link connectivity probability in highway vehicular networks that considers the change in vehicle headway distribution under different traffic conditions. The introduced formulation is derived under the Nakagami-m small-scale fading model which captures a wide range of small-scale fading conditions in freeway vehicular networks and was shown to well fit the empirical data. This formulation is of interest in analyzing and simulating vehicular communication systems.

Performance Analysis in Terms of Bit Error Rate Over Fluctuating Two-Ray (FTR) Fading Channels

The fluctuating two-ray (FTR) channel is currently taken as a suitable small-scale fading model for fifth-generation millimeter-wave communications. This paper analyzes the performance in terms of the average bit error rate (ABER). The expressions of ABER of coherent and non-coherent modulation are evaluated using probability density function over FTR fading channels. Moreover, the behaviors of each modulation schemes are also studied based on the fading parameters. A comparison of the modulation schemes is also presented over FTR fading channels. The evaluated expressions are then verified with expected outcomes and Monte Carlo simulation.

Effective Throughput Analysis of α-η-κ-μ Fading Channels

The $\alpha $ - $\eta $ - $\kappa $ - $\mu $ fading model is a very useful instrument to accurately describe various radio wave propagation scenarios. In this paper, we study the effective throughput performance of communication systems over the $\alpha $ - $\eta $ - $\kappa $ - $\mu $ fading channels. Novel and exact expressions for the effective throughput over $\alpha $ - $\eta $ - $\kappa $ - $\mu $ channels are derived, and the effective throughput of multiple-input single-output (MISO) and multiple-input multiple-output (MIMO) systems over some widely used small-scale fading models are presented based on the derived results. To obtain more understandings on the impact of physical channel characteristics and system configuration on the effective throughput, closed-form expressions for the asymptotic effective throughput at high signal-to-noise ratio (SNR) regimes are also obtained. The results reveal the underlying connections between different physical channel parameters (e.g., scattering level, phase correlation, channel nonlinearity, multipath clustering, and channel imbalance) and the effective throughput. It is found that the effective throughput improves with the increase of channel nonlinearity and number of multipath clusters, and the high-SNR slope is only dependent on the channel nonlinearity and the number of multipath clusters present in the physical channel.

Performance evaluation of OFDM systems over α – κ – μ fading

In this Letter, the authors derive the moment generating function-based BER expressions for binary phase shift keying and M-QAM signal for OFDM systems over –– fading. This fading model is known as the generalised fading model because it can accurately characterise all the well known small-scale fading models given in the literature. In order to validate the derived BER expressions, analytical and simulated BER curves for a variety of modulation formats at different values of fading parameters are also shown in the letter.

Propagation Models and Performance Evaluation for 5G Millimeter-Wave Bands

Fifth-generation (5G) wireless networks are expected to operate at both microwave and millimeter-wave (mmWave) frequency bands, including frequencies in the range of 24 to 86 GHz. Radio propagation models are used to help engineers design, deploy, and compare candidate wireless technologies, and have a profound impact on the decisions of almost every aspect of wireless communications. This paper provides a comprehensive overview of the channel models that will likely be used in the design of 5G radio systems. We start with a discussion on the framework of channel models, which consists of classical models of path loss versus distance, large-scale, and small-scale fading models, and multiple-input multiple-output channel models. Then, key differences between mmWave and microwave channel models are presented, and two popular mmWave channel models are discussed: the 3rd Generation Partnership Project model, which is adopted by the International Telecommunication Union, and the NYUSIM model, which was developed from several years of field measurements in New York City. Examples on how to apply the channel models are then given for several diverse applications demonstrating the wide impact of the models and their parameter values, where the performance comparisons of the channel models are done with promising hybrid beamforming approaches, including leveraging coordinated multipoint transmission. These results show that the answers to channel performance metrics, such as spectrum efficiency, coverage, hardware/signal processing requirements, etc., are extremely sensitive to the choice of channel models.

Wireless Channel Modeling Simulation and Hardware Implementation

Channel simulator is an important part of the accurate evaluation of the fading characteristics of wireless channel. Efficient design and implementation of wireless channel simulator is very important for the design and verification of wireless systems. The greatest impact on the wireless communication system is a small-scale fading variation. According to the transmission characteristics, this paper analyzed the small scale fading model, the mathematical modeling simulation and hardware implementation. The measured results show that the statistical characteristics of hardware simulators output decline signal in conformity with the theoretical value, can simulate the attenuation, decline of wireless communication system, and doppler frequency shift and other transmission characteristics.

Capacity Analysis of $\alpha $ - $\eta $ - $\kappa $ - $\mu $ Fading Channels

The $\alpha $ - $\eta $ - $\kappa $ - $\mu $ model was recently proposed as a generalized fading and can include all well-known small-scale fading models as special cases. In this letter, we investigate the channel capacity of wireless communications that operate in $\alpha $ - $\eta $ - $\kappa $ - $\mu $ fading channels. More specifically, novel and exact expressions for the channel capacity under different adaptive transmission policies are derived in terms of infinite series. Previous results can be obtained through our newly derived expressions by combining and/or specializing the various parameters of the $\alpha $ - $\eta $ - $\kappa $ - $\mu $ model. Moreover, our derived analytical expressions assess the impact of fading parameters on the channel capacity, and are illustrated by simulation results.

Study on Modeling of Communication Channel of UAV

It is essential to study a statistical model for UAV(Unmanned Aircraft Vehicle) communication channel for the design and performance analysis of data link for UAV. Based on different situation and environment of flight, the communication propagation channel model included large scale fading model and small scale fading model. This paper analyzes interrelated parameters and PDF (probability density function) of parameters. Discussed the performance of large scale fading as well as small scale fading, according to roughness path loss and free-space loss theoretic, the uniform UAV channel model has been designed, which is fit to different environment.

Energy Harvesting From Multiple RF Sources in Wireless Fading Channels

Energy-harvesting technologies are currently under development to provide power for wireless networks and devices. This paper investigates the usage of radio frequency (RF) signals emitted from wireless nodes as sources in energy-harvesting systems. The system we consider consists of multiple RF source nodes, multiple destination nodes, and an energy-harvesting node with a limited-capacity rechargeable battery. We observe that the total received power at the antenna of the harvesting node changes with the number of RF source nodes and the channel conditions. At the same time, the variation of instantaneous received power and the selected modulation type affect the required time for recharging battery. We study statistical models for the battery recharging time in the presence of multiple RF source nodes and focus on the generalized-K channels that include both large-scale and small-scale fading models. Then, we propose a distribution for the battery recharging time that provides a close and analytically tractable expression. We derive the associated fundamental statistical expressions for the battery recharging time in closed form. The simulations and numerical studies are used to verify the theoretical results. The Gamma distribution provides tight approximation to simulation results in fading wireless channel conditions. Additionally, we present battery recharging test results for two sources as a real-life application of energy harvesting with multiple RF sources. Our test results show close fit with the derived distribution equations, supporting theoretical analyses.

The Performance of Double-Binary Turbo Codes in the HAP-Based Communication System

The small-scale fading model for HAP-based communication channel is analyzed, the structure and algorithm of double-binary Turbo encoding and decoding are studied. Numerical results show the BER performance with different interleaving depth and interleaving length of double-binary Turbo codes using QPSK modulation over Rayleigh fading channel.

Progresses in on-body channel models for wireless body area networks

On-body communication channels are a physical basis for the establishment of an effective and reliable wireless link between on-body nodes in wireless body area networks (WBANs).Due to normally strict limitations in transmit power and power consumptions of on-body nodes as well as the human-centered characteristics of WBANs,on-body channels are prone to be affected by the electromagnetic properties of human tissues,human movements,application environments and transceiver antennas,which increase greatly the complexity of the research on channel models.The paper discusses the developments,mathematical expressions and application characteristics of five types of on-body channel models,such as the simple path loss model,the hybrid path loss model,the small-scale fading model,the scenario-based model and the ultra-wideband model,and reviews the current progress on the modeling on-body channels. Key words: Wireless body area network; On-body channel; Path loss; Fading

On the Connectivity of 2-D Random Networks with Anisotropically Radiating Nodes

We study the effect that anisotropic radiation has on the probability that a dense, two-dimensional (2-D) random network is fully connected. To this end, we provide a thorough analytical treatment of the connectivity of wireless ad hoc networks with beamforming using a newly established theory of connectivity reported in , where we assume the network experiences small-scale fading according to the well-known two-wave with diffuse power (TWDP) model. We calculate the connectivity mass related to various radiation patterns, and show that isotropic radiation is optimal when the path loss exponent is greater than two, but single-sector directed transmission yields superior performance for other cases. We exploit our analysis to design optimal radiation patterns in the sense that connectivity is maximized, which can be used as masks to perform antenna pattern synthesis. Our results exhibit a property of universality with respect to the small-scale fading model since they do not depend on the TWDP fading parameters.

Review of wideband MIMO channel measurement and modeling for IMT-Advanced systems

In October 2005, the next generation mobile communication system was officially named as the International Mobile Telecommunications-Advanced (IMT-Advanced) by the ITU Radiocommunication Sector (ITU-R). Wideband multiple input and multiple output (MIMO) channel models in multiple propagation environments are fundamental for IMT-Advanced systems and such research has been initiated since 2003. The research challenges come from the fact that the wider bandwidth (20–100 MHz) and the advanced multiple antenna technology have been proposed for the IMT-Advanced system, thus leading to higher sampling rates and multiple spatial propagation channels. In this review, four aspects of wideband MIMO channel measurement and modeling are discussed: (1) radio channel measurement procedure and equipment; (2) large scale fading models; (3) small scale fading models; and (4) MIMO channel models. In particular, the large scale fading affected by the carrier frequency is investigated for urban macrocells and it shows that the higher carrier frequency results in greater loss for non-line-of-sight (NLoS) conditions in the cities of China, for which the frequency dependent factor is 32.1. Moreover, the dense and the obviously higher buildings also lead to a larger angle spread (AS) of both the angle of arrival and angle of departure in urban macrocell scenarios. The results indicate that there is the potential to explore the MIMO technique for an IMT-Advanced system with larger ASs, which would lead to the high system capacity. The progress on MIMO models is described and some methods for simplifying geometry-based stochastic channel models (GBSM) are proposed. Finally future research topics on channel measurement and modeling are identified.

Simulation Performance of WAVE System with Combined DD-CE and LMMSE Smoothing Scheme in Small-Scale Fading Models

This paper investigates the performance of IEEE 802.11p wireless access in vehicular environments (WAVE) system in small-scale fading models reported by Georgia Institute of Technology (Georgia Tech). We redesign the small-scale fading models to be applied to the computer simulation and develop the IEEE 802.11p WAVE physical layer simulator to provide the bit error rate and packet error rate performances. Moreover, a new channel estimator using decision directed channel estimation and linear minimum mean square error smoothing is proposed in order to improve the performance of the conventional least square channel estimator using two identical long training symbols. The simulation results are satisfactorily coincident with the scenarios of Georgia Tech report, and the proposed channel estimator significantly outperforms the conventional channel estimator.

The α − λ − μ and α − η − μ Small-Scale General Fading Distributions: A Unified Approach

In this paper, a general small-scale fading model for wireless communications, that explores the nonlinearity and at the same time the inhomogeneous nature of the propagation medium, is presented, studied in terms of its first-order statistics of the envelope, and validated by means of field measurements and the Monte Carlo simulation. It is indeed a novel distribution with many advantages such as its generality, its physical interpretation that is directly associated with the propagation channel, and its mathematical tractability due to its simple and closed-form expression. By fitting to measurement data, it has been shown that the proposed distribution outperforms the widely known fading distributions. Namely, the α - λ - μ model, which can be in fact called α - η - μ format 2 model, can also be obtained from the α - η - μ format 1 model by a rotation of the axes. Both formats are combined, in order to result to a unified model in a closed form that may describe the propagation environment in a variety of different fading conditions. Its physical background is hidden behind the names of its parameters. The unified model includes the already known general distributions α - μ', η - μ, λ - μ (η - μ format 2), and their inclusive ones as special cases.