Fading Characteristics Of Channel Research Articles

Cooperative Spacing Control of Vehicle Platoon via Relative Output Feedback Considering Analog Fading Networks

ABSTRACTThe influence of analog fading channels on platoon control performance is studied via relative output feedback. The main goal is to determine the existence of a distributed output feedback controller capable of achieving mean square stability (MSS) for the underlying vehicle platoon systems over analog fading channels. First, the conditions, closely associated with the statistical characteristics of fading channels, for achieving platoon MSS are derived for three cases: undirected information flow (UIF) topology with identical fading channels, balanced directed information flow (BDIF) topology with identical fading channels, and general information flow topology (IFT) with nonidentical fading channels, respectively. These conditions explicitly reveal how the statistical characteristics of fading channels and IFT jointly affect vehicular stability. Second, in order to mitigate the impact of fading channels on platoon MSS, some feasible dynamic observer‐based controllers by using the relative output feedback, are proposed for each one of the former two situations by solving the corresponding modified Riccati inequalities (MRIs); and in the last situation, by employing edge Laplacian to model the vehicle platoon dynamics, a sufficient condition based on the solution of an LMI, and a feasible state‐based controller based on the solution of an MRI, are provided. Finally, simulations are carried out to compare three distinct fading channels, namely the Nakagami channel, Rician channel, and Rayleigh channel. The outcomes substantiate the superior and effective performance of the implemented control methods in guaranteeing the platoon MSS.

Non-orthogonal Multiple Access (NOMA) Channel Estimation for Mobile & PLC-VLC Based Broadband Communication System

Background: The paper focuses on enhancing the performance of 5G wireless mobile communication systems. Furthermore, it addresses the increasing demand for high data rates, improved channel capacity, and spectrum efficiency outlined by the 3rd Generation Partnership Project (3GPP) protocol. Objective: To develop an innovative Non-Orthogonal Multiple Access (NOMA)-based channel estimation (CE) model aimed at improving the performance of 5G wireless mobile communication systems Methods: A proportionate recursive least squares (PRLS) algorithm is utilized for estimating the characteristics of practical Rayleigh fading channels. The applicability of the PRLS algorithm is investigated in Lambertian channels for indoor broadband communication systems such as power line communication (PLC) and visual light communication (VLC) systems. Results: The assessment of evaluation metrics, including mean square error (MSE), bit error rate (BER), spectral efficiency (SE), energy efficiency (EE), capacity, and data rate, have been analysed. Faster convergence and higher accuracy compared to existing state-of-the-art approaches have been demonstrated. Conclusion: The NOMA-based channel estimation model presents significant promise in enhancing the performance of 5G wireless communication systems. The demands for higher data rates and improved spectral efficiency as per 3GPP standards have been addressed.

Effective Energy Efficiency under Delay-Outage Probability Constraints and F-Composite Fading.

The paradigm of the Next Generation cellular network (6G) and beyond is machine-type communications (MTCs), where numerous Internet of Things (IoT) devices operate autonomously without human intervention over wireless channels. IoT's autonomous and energy-intensive characteristics highlight effective energy efficiency (EEE) as a crucial key performance indicator (KPI) of 6G. However, there is a lack of investigation on the EEE of random arrival traffic, which is the underlying platform for MTCs. In this work, we explore the distinct characteristics of F-composite fading channels, which specify the combined impact of multipath fading and shadowing. Furthermore, we evaluate the EEE over such fading under a finite blocklength regime and QoS constraints where IoT applications generate constant and sporadic traffic. We consider a point-to-point buffer-aided communication system model, where (1) an uplink transmission under a finite blocklength regime is examined; (2) we make realistic assumptions regarding the perfect channel state information (CSI) available at the receiver, and the channel is characterized by the F-composite fading model; and (3) due to its effectiveness and tractability, application data are found to have an average arrival rate calculated using Markovian sources models. To this end, we derive an exact closed-form expression for outage probability and the effective rate, which provides an accurate approximation for our analysis. Moreover, we determine the arrival and required service rates that satisfy the QoS constraints by applying effective bandwidth and capacity theories. The EEE is shown to be quasiconcave, with a trade-off between the transmit power and the rate for maximising the EEE. Measuring the impact of transmission power or rate individually is quite complex, but this complexity is further intensified when both variables are considered simultaneously. Thus, we formulate power allocation (PA) and rate allocation (RA) optimisation problems individually and jointly to maximise the EEE under a QoS constraint and solve such a problem numerically through a particle swarm optimization (PSO) algorithm. Finally, we examine the EEE performance in the context of line-of-sight and shadowing parameters.

Measurement-based fading characteristics analysis and modeling of UAV to vehicles channel

With the rapid development of unmanned aerial vehicle (UAV) and autonomous driving technology, wireless communication between UAV and vehicles has become one of the hotspots in the research of intelligent transportation systems (ITS). Particularly, link-level UAV-based communication requires correlation characteristics of propagation channel. In the current channel measurement, the transmitter or receiver of the ground is fixed, which ignores the high dynamics of the vehicle and the complexity of the environment in the ITS scene. Therefore, it is necessary to conduct a dynamic channel measurement and analysis for UAV. In this paper, we carry out an UAV-to-Vehicle (U2V) measurement campaign in S- and C-band for multiple scenarios of low-altitude UAV and mobile vehicles propagation and provide a comprehensive investigation of channel fading characteristics. Based on the measurement data, the statistics of large-scale fading (path loss, shadow fading and its autocorrelation) and small-scale fading (amplitude distribution) for several typical measurement scenarios are extracted first, which are compared with other air-to-ground (A2G) and standard terrestrial propagation scenarios to analyze the U2V propagation characteristics in various scenarios. A comprehensive analysis and comparative study of all considered channel parameters extracted is then performed to reflect the physical laws behind the measurements. The analysis results reveal that the Log-distance model outperforms the considered typical models in terms of predicting the path loss, and the proposed autocorrelation model shows better performance than traditional models. The quantitative results are essential for modeling and realizing reliable communications in U2V wireless systems and analyzing the performance for UAV-enabled ITS.

Experimental demonstration of a hybrid OFDMA/NOMA scheme for multi-user underwater wireless optical communication systems

In this work, a hybrid multiple access scheme for multi-user underwater wireless optical communication (UWOC) systems is proposed and presented. The scheme combines the respective advantages of orthogonal frequency-division multiple access (OFDMA) and non-orthogonal multiple access (NOMA) scheme to reduce the unfairness among users caused by the unique high-frequency fading characteristics of the underwater optical channel. Multi-verse optimizer (MVO) algorithm is further introduced for solving the nonlinear problem of user power allocation. Experimental results in different water quality environments demonstrate that the hybrid OFDMA/NOMA scheme with MVO effectively improves the communication performance of the established 4-user UWOC system compared to the pure NOMA scheme and the pure OFDMA scheme, and a system sum rate of 3.94 Gbit/s is achieved.

MultiNet: Deep unsupervised power control for industrial MU-MIMO networks

This paper presents Multinet, an unsupervised deep learning (DL) approach for power allocation in industrial environments and IIoT applications. Multinet extends the previously proposed singular value decomposition network (SVDNet), which utilizes supervised DL to approximate the performance of the WMMSE algorithm. While SVDNet requires labeled data for training, limiting its scalability and generalization performance, in contrast, Multinet employs unsupervised DL to directly optimize the sum rate maximization objective function, eliminating the need for labeled datasets and improving training efficiency. Simulation studies are conducted to evaluate Multinet’s performance in an industrial environment, utilizing parameters derived from measured large-scale fading characteristics of the industrial radio channel at 5200 MHz. The suitability of Multinet for industrial applications is thus assessed and numerical evaluations demonstrate that Multinet outperforms benchmark supervised and unsupervised DL-based power control schemes in terms of sum rate and energy efficiency.

Radio Channel Measurements and Characterization in Substation Scenarios for Power Grid Internet of Things

Wireless communication technologies play a key role to support the implementation of power grid Internet of Things (PIoT). An in-depth knowledge of the radio channel is vital to the application of wireless communication technologies in PIoT. This paper investigates the radio channel measurements and characterization for PIoT substation scenarios. A novel channel sounder is designed for achieving omnidirectional measurements and phased array antennas based directional measurements, and a directional multipath components extraction algorithm is proposed. The channel sounding system is verified and is used to perform a series of 3.35 GHz omnidirectional and directional channel measurements in four substation scenarios, involving a 10 kV switch room, a 110 kV GIS room, a semi-indoor 110 kV substation and an outdoor 220 kV substation. Based on the measured channel impulse responses data, both large-scale and small-scale fading characteristics of substation channels are extracted and analyzed. Empirical models of path loss, shadow fading, Ricean K-factor and root-mean-square (RMS) delay spread are proposed. In addition, results of RMS angle spread of departure and RMS angle spread of arrival are presented. These results will provide useful reference for the deployment and optimization of wireless communication networks in PIoT substation scenarios.

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.

Channel Fading Characteristics of Hyperloop Scenarios Based on Ray-Tracing Model

Hyperloop is envisioned as the next generation of railway transportation mode, which can proceed at a speed of more than 1000 km/h. The safe operation of the Hyperloop depends heavily on the support of a stable communication system. In this paper, we propose a 3D channel model in vacuum tube scenarios based on the ray-tracing method. The reflection paths and line of sight (LoS) paths are considered. We derive the channel transfer function (CTF) expression for each multipath, and then the channel impulse response (CIR) is obtained. On this basis, the large-scale and small-scale channel characteristics, including path loss, shadow fading, correlation coefficient, delay spread, and angular spread, are investigated and analyzed. Simulation results show that the proposed channel model can characterize the wireless channel in the Hyperloop scenarios in detail, and the results maintain a high level of symmetry between the range of 0–250 m and 250–500 m. The relevant research results will contribute to the design of future Hyperloop wireless communication systems.

Cooperative Key Establishment Protocol for Full-Duplex Relay Systems

Using the fading channel characteristics, as a randomness source, for the secret key generation earns significant attention because of it’s computational less power and low energy consumption. Current researches focus on point-to-point reciprocal-based key extraction from these randomness sources. Most practical communication situations are non-line of sight, so endpoints use a relaying channel to improve communication performance. Besides that, in the upcoming 5G systems, the full-duplex (FD) communications will be one of the main techniques, which will remove the advantage of using the reciprocal feature in the randomness source common observation. In this paper, we consider the challenge of generating a symmetric secret key between two legitimate parties in the relaying channel with FD capability. We suggest an efficient key extraction protocol that accomplished an acceptable shared secret key rate compared to the direct channel traditional approach. Unlike similar schemes, we provide full statistical analysis for the construction of randomness source from the relaying channel with FD capability. Additionally, we investigate the performance analysis of the suggested key agreement protocol. We also analyze the effect of the curious-but-honest relay and an eavesdropper on the proposed protocol.

Alignment of transmitters in indoor visible light communication for flat channel characteristics

Visible light communication (VLC) systems incorporate ambient lighting and wireless data transmission, and the experienced channel in indoor VLC is a major topic that should be examined for reliable communication. In this study, it is realized that multiple transmitters in classical alignment are the forceful factors for channel characteristics. In the frequency band, fluctuations with sudden drops are observed, where the fluctuation shape is related to the source layout and receiver location. These varying frequency-selective channels need solutions, especially for mobile users, because sustained channel estimation and equalization are necessary as the receiver changes its location. It is proven that using light-emitting diodes (LEDs) with highly directional beams as sources or using a detector with a narrow field of view (FOV) in the receiver may help partially alleviate the problem; the frequency selectivity of the channel reduces in some regions of the room. For flat fading channel characteristics all over the room, LEDs should be aligned in hexagonal cellular structure, and detector FOV should be arranged according to the cell dimension outcomes.

On Maximizing the Sum Secret Key Rate for Reconfigurable Intelligent Surface-Assisted Multiuser Systems

Channel reciprocity-based key generation (CRKG) has recently emerged as a new technique to address the problem of key distribution in wireless networks. However, as this approach relies upon the characteristics of fading channels, the corresponding secret key rate may be low when the communication link is blocked. To enhance the applicability of CRKG in harsh propagation scenarios, this paper introduces a novel multiuser key generation scheme, which is referred to as RIS-assisted multiuser key generation (RMK) that leverages the reconfigurable intelligent surface (RIS) technology for appropriately shaping the environment and enhancing the sum secret key rate between an access point and multiple users. In the RMK scheme, an RIS-induced channel, rather than the direct channel, serves as the key source. We derive a general closed-form expression of the secret key rate and optimize the configuration of the RIS to maximize the sum secret key rate over independent and correlated fading channels in the presence of multiple users. In the presence of independent fading, we introduce a low-complexity algorithm based on the Karush-Kuhn-Tucker (KKT) condition. In the presence of correlated fading, the optimization problem is non-convex and challenging to solve. To tackle it, we propose a new optimization algorithm based on the semi-definite relaxation (SDR) and successive convex approximation (SCA) methods. Simulation results demonstrate that the proposed RMK scheme outperforms existing RIS-assisted algorithms and achieves a near-optimal sum secret key rate over independent and correlated fading channels.

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

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.

The impacts of weak links on topology discovery process in large-scale wireless multi-hop networks

In wireless multi-hop networks, especially large-scale wireless multi-hop networks, obtaining the network topology is of vital significance. In fact, in both proactive and reactive routing protocols, before establishing an appropriate end-to-end route, the source node needs to obtain the global or local topology. Our previous research has studied the impacts of weak links on reactive routing protocols, which can also be considered as local topology discovery process. In this article, in order to get insight of the impacts of weak links on topology discovery process, especially the global topology discovery on which the proactive routing protocols rely, we apply a Markov chain to model the most common used topology discovery process in large-scale wireless multi-hop networks. Considering the fading characteristics of wireless channel, we analyze the impacts of weak links on topology discovery algorithms. Simulation and theoretical results show that, with the increase in the network scale, the weak links have great impacts on the stability and even on the feasibility of wireless multi-hop networks.

Cooperative Key Establishment Protocol for Full-Duplex Relay Systems

Using the fading channel characteristics, as a randomness source, for the secret key generation earns significant attention because of it’s computational less power and low energy consumption. Current researches focus on point-to-point reciprocal-based key extraction from these randomness sources. Most practical communication situations are non-line of sight, so endpoints use a relaying channel to improve communication performance. Besides that, in the upcoming 5G systems, the full-duplex (FD) communications will be one of the main techniques, which will remove the advantage of using the reciprocal feature in the randomness source common observation. In this paper, we consider the challenge of generating a symmetric secret key between two legitimate parties in the relaying channel with FD capability. We suggest an efficient key extraction protocol that accomplished an acceptable shared secret key rate compared to the direct channel traditional approach. Unlike similar schemes, we provide full statistical analysis for the construction of randomness source from the relaying channel with FD capability. Additionally, we investigate the performance analysis of the suggested key agreement protocol. We also analyze the effect of the curious-but-honest relay and an eavesdropper on the proposed protocol.

A Non-WSSUS Channel Simulator for V2X Communication Systems

This paper presents a simulator of non-wide sense stationary uncorrelated scattering (non-WSSUS) multipath fading channels for the performance analysis of vehicle-to-everything (V2X) communication systems. The proposed simulator is constructed with the combination of the Monte Carlo and sum-of-cisoids (SOC) principles, and it is suitable for multicarrier transmission schemes such as those defined for dedicated short-range communications (DSRC) and cellular-based V2X (C-V2X) communications. The channel simulator provides an accurate and flexible solution to reproduce the time and frequency (TF) correlation properties of non-WSSUS vehicular channels under arbitrary isotropic and non-isotropic scattering conditions. Furthermore, the proposed simulator allows velocity variations and non-linear trajectories of the mobile stations (MSs). To demonstrate the practical value of the presented simulator, we evaluate the bit error rate (BER) performance of two channel estimation techniques that are considered for IEEE 802.11p transceivers, namely the least squares (LS) estimator and the spectral temporal averaging (STA) technique. The BER performance of both channel estimators was analyzed by considering three propagating scenarios for road safety applications. Our results show that the non-stationary characteristics of the vehicular multipath fading channel have nearly no effects on the LS estimator’s BER performance. In contrast, the performance of the STA estimator is significantly affected by the channel’s non-stationary characteristics. A variation of the original STA technique that applies only a temporal averaging is introduced in this work to improve the system’s BER in non-WSSUS channels.

Modeling and Analysis of Hybrid ARQ Scheme for Incremental Cooperative Communication in Underwater Acoustic Sensor Networks

Underwater acoustic sensor network (UASN) is a vast network, in which the neighborhood of a transmitting node consists of many operating sensor nodes. By considering this as an advantage, we propose a hybrid automatic repeat request scheme for incremental cooperative communication (HARQ-INCC) in UASNs. The proposed scheme utilizes neighborhood sensor nodes during the instance of packet retransmission. It combines HARQ scheme with incremental cooperative communication; to enhance reliability and to optimize the energy efficiency. In this article, we present an analytical model to calculate the energy efficiency in UASNs for deep and shallow water scenarios, by examining the influence of acoustic fading, ambient noises and underwater channel characteristics. The analytical results show that HARQ-INCC outperforms the existing techniques for considerable distances between the source and destination nodes. We further propose an optimization algorithm to maximize the energy efficiency, by adjusting the modulation level and packet size as a function of the distance between source and destination nodes. The proposed optimization algorithm significantly enhances the energy efficiency of HARQ-INCC scheme. Finally, we analyze the energy efficiency of UASNs with respect to the variation in environmental parameters like waves and shipping noises. We validate the analytical results using ns-3 simulations.

Performance of Integrated Satellite-Terrestrial Relay Network With Relay Selection and Outdated CSI

Satellite communication plays an important role in future wireless network. In this article, we investigate the outage performance of the integrated satellite-terrestrial relay network (ISTRN) with relay selection based adaptive decode-and-forward (RSADF), where the relay selection is based on outdated channel state information (CSI), and the multiple-antenna relays conduct maximum-ratio receiving and transmitting for decoding and forwarding, respectively. Particularly, we first obtain a novel closed-form expression for the outage probability of the considered ISTRN with RSADF. Furthermore, to get further insights of the effect of key system parameters, e.g., the number of relays, the number of antennas, the CSI outdating level, and the channel fading characteristics, on the system performance, we conduct asymptotic analysis for three typical high average signal-to-noise-ratio (SNR) scenarios, i.e., 1) all satellite and terrestrial links are with high average SNR, 2) the satellite-to-relay link and the relay-to-user link are with high average SNR, and 3) only the relay-to-user link is with high average SNR. The derived high SNR approximations of outage probability explicitly reveal the impact of key system parameters in the form of diversity gain and coding gain. Finally, numerical simulations are presented to validate the analytical results.

Performance Analysis of Opportunistic Relay Selection Cooperative Communication in Cascaded Fading Channels

Cooperative communication enables users to transmit information in a cooperative way, which is one of the key technologies used in wireless communication systems to improve spectral efficiency. A cascade Nakagami-m fading function is proposed to describe the fading characteristics of complex wireless channels, and a communication model of decoding-and-forward opportunistic relay selection (DF-ORS) cooperative communication under total power constraints is established. Theoretical analysis and simulation results show that DF-ORS cooperative communication can effectively reduce outage probability and improve spectrum efficiency under total power constraints and complex cascade Nakagami-m fading channels. The transmission power allocation of source node and relay node has an important impact on communication performance. Equal power allocation scheme cannot guarantee the optimal system performance, and the obtained conclusions have more general applicability.

Outage Analysis of Ground-Aerial NOMA With Distinct Instantaneous Channel Gain Ranking

Future wireless networks envision to provide seamless connectivity to a multitude of devices including unmanned aerial vehicles (UAVs). This paper investigates a unique case where we aim to serve ground users and a UAV, with distinct channel characteristics and access environments in three-dimensional (3D) space, based on non-orthogonal multiple access (NOMA). Unlike traditional distance-based ranking or channel-gain-based ranking, we apply NOMA in uplink and downlink transmissions by evaluating instantaneous channel gain and distance-dependant path-loss together. The communication links of ground and aerial users have different fading environments and path losses which make it crucial to analyse instantaneous channel gain before applying NOMA. To this end, we derive new mathematical expressions of outage probabilities in downlink and uplink transmissions based on instantaneous distinct signal power (IDSP) for each user, verified by simulations. Next, we investigate the impact of different system parameters, e.g. data rate, path loss exponent, channel fading characteristics and UAV height, on outage behaviour. The results confirm that ground-aerial NOMA can be successfully employed in future wireless networks to provide cellular connectivity with improved spectral efficiency to a broader range of devices with individual data rate requirements.