Path Loss Fading Research Articles

Accuracy-Enhanced IRS-Aided Target Sensing with RSS by Exploiting Path-Loss Fading

Accuracy-Enhanced IRS-Aided Target Sensing with RSS by Exploiting Path-Loss Fading

Energy-Efficient Federated Learning Over Cell-Free IoT Networks: Modeling and Optimization

To leverage massive distributed data and computation resources in the Internet-of-Things (IoT) networks, federated learning (FL) is considered to be a promising technique with benefits of improved data privacy and communication efficiency. Meanwhile, cell-free massive multiple-input multiple-output (cell-free massive MIMO) is a promising technology to enable the IoT networks to support FL. By deploying the access points (APs) closer to the IoT devices, path loss attenuation can be reduced. However, the performance of FL is still constrained by the limited power resources of IoT devices. To address this issue, we design an energy-efficient FL scheme over cell-free IoT networks by formulating an optimization problem to minimize the total energy consumption of the IoT devices participating in the FL process. To solve the intractable problem in hand, by exploiting its unique structure, we decompose it into three sub-problems that facilitate the development of the proposed scheme. First, we derive the optimal central processing unit (CPU) operating frequency for IoT devices. Then, we design an optimal power allocation scheme to mitigate the straggler effect. Next, nonlinear programming method is adopted to obtain a sub-optimal solution for the reformulated problem. Finally, a three-stage algorithm is proposed for energy consumption minimization by considering these sub-problems. Simulation results demonstrate the close-to-optimal performance of the proposed algorithm for energy savings compared with three baseline algorithms and the capability to support large numbers of IoT device access by mitigating the straggler effect.

Low-Power IoT for Monitoring Unconnected Remote Areas.

This paper deals with IoT devices deployed in remote areas without terrestrial Internet connectivity. We consider connecting IoT devices on the ground to the Internet through an aerial system based on an Unmanned Aerial Vehicle (UAV) for smart agriculture and environmental monitoring. The UAV flying over the remote area receives data from distributed IoT devices. The transmissions between the ground sensors and the UAV are carried out via LoRa. We have proposed a synchronization protocol for the opportunistic communication of LoRa IoT devices with a gateway onboard the UAV to save node battery life. Class A LoRa nodes on the ground transmit only when the UAV is expected to pass close to them; otherwise, they stay in the sleeping state most of the time. This paper provides a detailed description of the formulation of the synchronization protocol. The UAV's flying dynamics have been considered for characterizing its speed and the time of visibility of each IoT sensor. Our model has allowed an analytical approach that can help to determine the best settings for LoRa transmissions. Finally, experiments have been carried out to assess the path loss attenuation, and a laboratory setup of the synchronization protocol has been implemented for the preliminary validation of our scheme.

Performance Evaluation of Reconfigurable Intelligent Surface against Distributed Antenna System at the Cell Edge

In small spaces in which typical cell towers cannot be constructed, distributed antenna systems (DASs) are the preferable approach for increasing network coverage, as they are a superior solution for congested, high-volume areas. However, due to their high cost and complexity in backhaul routing, reconfigurable intelligent surfaces (RISs) are a promising solution to overcome the major drawbacks of DAS systems while improving network coverage. Thus, this work investigated a correlation of execution in an RIS-aided system cell framework and DAS-aided system cell framework where a simple and precise structure for the performance measurement of area spectral efficiency (ASE) and energy efficiency (EE) under realistic channel presumptions was introduced. The analysis started with the downlink ergodic capacity with regards to the RIS framework and DAS framework under a generalized Nakagami-m fading channel with the presence of path-loss attenuation and interference from co-channel base stations (BSs), and was simplified further by utilizing a moment-generating function (MGF)-based approach. From the computed expression, the effects of traffic activity, EE and ASE were derived and analyzed for both systems in the presence of co-channel interference. The results were then verified by comparing them with Monte Carlo simulations, and the findings show that the two outcomes generally match. Based on these, it is demonstrated that the ASE performance of the RIS-assisted system in various traffic activity conditions outperforms the DAS-aided system; however, in high signal-to-noise (SNR) regions with full traffic activity, the ASEs are highest for both systems; by only 0.005 bits/s/Hz/km2.

3D Poisson-Based Neighborhood Capacity Analysis for Millimeter Wave Communications.

This paper proposes a theoretical model for evaluating the capacity of a millimeter wave (mmWave) source destination link when the nodes are distributed according to a three-dimensional (3D) homogeneous Poisson point process. In the presented analysis, different from the existing approaches, the destination lies in an arbitrary location with respect to the source; thus, the link performance can be evaluated for a neighbor of any order. Moreover, the developed model relies on a realistic propagation environment, characterized by path loss attenuation and shadowing in line of sight (LoS), non-LoS, and outage link state conditions. The derived formulas, which are calculated in closed-form and validated by independent Monte Carlo simulations, are used to investigate the influence of the intensity parameter, of the antenna gain, and of the mmWave frequency band on the link capacity for any possible neighbor in a practical 3D scenario.

Subcarrier Mapping for Underwater Video Transmission Over OFDM

We study the transmission of high-quality video underwater. The underwater acoustic medium pathloss attenuation depends not only on transmission distance but also on the frequency occupied by the signal, where lower frequencies have lower attenuation for a given distance. We propose cross-layer design algorithms that exploit this frequency-dependent attenuation by connecting channel reliability to the structure of the compressed video. The video data are categorized based on their importance. Orthogonal frequency-division multiplexing is adopted as the modulation technique, such that different data can be sent on different frequencies. The underlying communications system accompanied with a noise analysis is developed in this article. The signal and noise statistics are used in the simulations to represent the underwater channel. We propose three new techniques and compare them to three baseline techniques. In the proposed techniques, important video information is transmitted on the least attenuated frequencies while less important data are transmitted through higher frequencies. Simulation results show that at least one of our proposed techniques can achieve significant improvements in the peak signal-to-noise ratio in comparison to the baseline techniques.

Power control scheme for device‐to‐device communication using uplink channel in 5G mm‐Wave network

AbstractMm‐Wave communication ushers next‐gen communication to new heights guaranteeing higher speed and throughput. Enabling device‐to‐device (D2D) communication in next‐gen wireless communication is a Herculean task. This is due to introduction of pathloss attenuation by various environmental factors which deteriorates the signal. This article aims to minimize the effect of interference for quality reception of signals for D2D communication and increase system throughput. Thus, a power control scheme is proposed in underlay mode for uplink channel in mm‐Wave band. Here, D2D communication takes place through two modes namely, general mode and mm‐Wave mode. In presence of large number of proximity D2D users and increasing pathloss attenuation, it switches to mm‐Wave mode for communication. The formulated problem is converted to semiconvex form by expressing it into exponential form in Laplace domain. Our final objective is to maximize the energy efficiency (EE) of the proposed system under certain constraints. To reduce complexity of the problem, feasible regions of transmission power is introduced, that is, least and upper bounds which will ensure that power is maintained within a limit guaranteeing better throughput for D2D users. Enhanced EE and outage probability values also depict better performance of proposed system. Finally, fairness index (FI) shows that the proposed scheme yields better performance for the D2D users to communicate in the mm‐Wave band. A detailed comparison of FI for the proposed scheme is also done with other existing methods to prove the adequate performance of the proposed method. Simulation results also prove the efficacy of the proposed scheme.

Limiting Performance of Millimeter-Wave Communications in the Presence of a 3D Random Waypoint Mobility Model

This paper proposes a mathematical framework for evaluating the limiting capacity of a millimeter-wave (mmWave) communication involving a mobile user (MU) and a cellular base station. The investigation is realized considering a threedimensional (3D) space in which the random waypoint mobility model is used to probabilistically identify the location of the MUs. Besides, the analysis is developed accounting for path-loss attenuation, directional antenna gains, shadowing, and modulation scheme. Closed-form formulas for the received signal power, the Shannon capacity, and the bit error rate (BER) are obtained for both line-of-sight (LoS) and non-LoS scenarios in the presence of a noise-limited operating regime. The conceived theoretical model is firstly checked by Monte Carlo validations, and then employed to explore the influence of the antenna gain and of the cell radius on the capacity and on the BER of a fifth-generation (5G) link in a 3D environment, taking into account both the 28 and 73 GHz mmWave bands.

Spectrum and Energy Efficiency in Dynamic UAV-Powered Millimeter Wave Networks

This letter investigates a dynamic scheme to analyze and optimize unmanned-aerial-vehicle-(UAV)-to-ground millimeter-wave (MMW) networks. First, a downlink energy transfer is proposed, followed by the uplink information transfer process between the UAV base stations (BSs) and a ground Internet of things (IoT) network. The UAVs fly above the ground IoT network in the energy transfer phase with the dynamic regulation to minimize the path loss fading. Afterwards, the ground-based IoT devices use the received energy to transmit the uplink information using vertical links. The UAV BSs are modeled with gain from multiple three-dimensional uniform linear antenna arrays. After deriving new statistical properties, we analyze the spectrum efficiency and energy efficiency for the system. Our numerical results have shown that the dynamic scheme in UAV-to-ground IoT networks provides great advantages than a traditional static deployment.

Coverage Performance in MIMO-ZFBF Dense HetNets with Multiplexing and LOS/NLOS Path-Loss Attenuation

The performance of multiple-input multiple-output (MIMO) multiplexing heterogenous cellular networks are often analyzed using a single-exponent path-loss model. Thus, the effect of the expected line-of-sight (LOS) propagation in densified settings is unaccounted for, leading to inaccurate performance evaluation and/or inefficient system design. This is due to the complexity of LOS/non-LOS models in the context of MIMO communications. We address this issue by developing an analytical framework based on stochastic geometry to evaluate the coverage performance. We focus on the zero-forcing beamforming where the maximum signal-to-interference ratio is used for cell association. We analytically derive the coverage. We then investigate the cross-stream interference correlation, and develop two approximations of the coverage: Alzer Approximation (A-A) and Gamma Approximation (G-A). The former is often used in the single antenna and single-stream MIMO. We extend A-A to a MIMO multiplexing system and evaluate its utility. We show that the inverse interference is well-fitted by a Gamma random variable, where its parameters are directly related to the system parameters. The accuracy and robustness of G-A is higher than that of A-A. We observe that depending on the multiplexing gain, it is possible to attain the best coverage probability by proper densification.

An Accurate Empirical Path Loss Model for Heterogeneous Fixed Wireless Networks Below 5.8 GHz Frequencies

Great progress has been made in providing convenient wireless communications with easy connectivity for users everywhere. Many empirical path loss (PL) models have been developed to assess the performance of new radio networks. This article first studies the state-of-the-art of empirical PL models, along with vegetation effects on radio signal propagation. Next, an accurate empirical PL model is proposed for fixed wireless networks under challenging rural propagation conditions. The proposed model is based on a Canadian dataset from a wireless internet service provider, using the Wireless-To-The-Home technology in the unlicensed 900 MHz, 2.4 and 5.8 GHz ISM bands and in the licensed 3.65 GHz band. The proposed model considers several parameters, such as line-of-sight obstructions, frequency bands and dynamic link distance splitting, in addition to seasonal variations in PL attenuation. It outperforms other models in terms of accuracy when tested on a dataset from a different Canadian region, and it provides excellent and steady accuracy when tested on a largely different open-access dataset for mobile communication technology from seven different regions in England.

Dynamic In-band Self-backhauling for 5G Systems with Inter-cell Resource Coordination

5G systems are expected to utilize frequency bands above 6 GHz in the so-called millimeter-wave (mmWave) spectrum because of large bandwidths. It is well know that higher carrier frequency bands suffer from higher path loss attenuation. It addition, dynamic blockages can be a challenge for achieving good coverage. Therefore, millimeter-wave deployments require cell densification to achieve high data rates. However, densification further leads to challenges in the system design because of the need for low cost backhaul. The concept of wireless self-backhauling (sBH) aims to provide a provide a backhaul solution at reduced cost. Self-backhaul solution makes use of integrated access and backhaul (IAB) at each base station to realize on-demand flexible backhaul and access. In this paper, we investigate the performance of in-band self-backhauling with integrated access and backhaul in a real-life street canyon scenario. We consider centralized scheduling which can effectively allocate radio resources for backhaul and access on a time slot basis with half duplex constraint. The centralized scheduler further mitigates cross-interference between backhaul and access using a beam coordination and interference cancellation. Our results show that the proposed relaying concept offers good user throughput gains for cell edge users and is also robust to offloading of users to relay cells. Results also show that interference cancellation receivers can improve the uplink and backhaul spectral efficiency in IAB deployment by around 10%.

Packet Retransmission in Hybrid Millimeter-Wave and Microwave D2D Communication System

Millimeter-wave communication is one of the key candidate technologies to provide the high data rate expected in the 5G wireless systems. However, the high path loss and penetration attenuation in millimeter-wave band reduce the transmission distance and limit the operation to line-of-sight transmission, requiring the use of appropriate techniques and approaches to mitigate the effects of this typical poor propagation condition. In this paper, we consider a device-to-device wireless network in which terminals can operate in the millimeter-wave and in the microwave bands, combined with a packet retransmission scheme and beamforming. Terminals primarily operate in the millimeter-wave band, and when propagation conditions deteriorate, they can switch to the microwave band in an attempt to improve the overall performance. Assuming that terminals are distributed according to a Poisson Point Process, we derive expressions for some performance metrics involving parameters such as density of terminals, antenna parameters and maximum number of retransmission attempts. Based on this formulation, we investigate the interrelationship among some network parameters and determine the conditions to achieve a given desired communication performance.

3D Millimeter-Wave Peer-to-Peer Networks With Boundary Located Destination

This letter presents a theoretical analysis for estimating the coverage probability and the average link capacity of an interfered peer-to-peer millimeter-wave communication when the destination lies at the boundary of a three-dimensional cell. The proposed model provides closed-form expressions for the statistics of the desired and undesired signal powers, by accounting for the impact of directional antenna gains, path-loss attenuation, mid-scale fading, interference, and noise.

Coverage Analysis for 2D/3D Millimeter Wave Peer-to-Peer Networks

This paper presents a theoretical analysis for estimating the coverage probability in two-dimensional (2D) and three-dimensional (3D) peer-to-peer (P2P) millimeter-wave (mmWave) wireless networks. The analysis is carried out by adopting suitable link state models and realistic propagation conditions, involving path-loss attenuation, angular dispersion, mid- and small-scale fading, which comply with recent channel measurements. The presented framework accounts in detail for the actual shape of the transmitting/receiving antenna patterns and for the spatial statistic that describes the node location, by considering the widely adopted Poisson point process, the uniform distribution, and the random waypoint mobility model. Analytical expressions for the statistic of the received power and simple integral formulas for the coverage probability in the presence of interference and noise are derived. The accuracy of the obtained estimations and of the introduced approximations is checked by independent Monte Carlo validations. As possible applications in the 3D mmWave context, the conceived mathematical theory is used to discuss the impact of the interference model on the reliability of the noise-limited approximation, and to estimate the average link capacity of an interfered P2P communication.

A Clustering Approach for Multiband Neighbor Discovery on 60 GHz WLAN

The 60 GHz mmWave unlicensed band has a very large spectrum available, divided into four orthogonal channels, which allows up to 7 Gbps data rate. On the other side, the propagation in the 60 GHz band is subject to severe path loss attenuation, which can be mitigated using highly directional antennas. This high directionality brings a new challenge to neighbor discovery; the devices now need to know the exact neighbors’ physical location to successfully communicate with them. In order to expedite the neighbor discovery process, multiband protocols have been proposed in the literature in which a separate band is used for the exchange of control messages in an omnidirectional mode. Nonetheless, these proposals suffer from the control channel bottleneck problem due to the numerous messages that need to be exchanged in this channel. In this work, we propose a scheme that divides the network nodes in clusters and for each cluster we allocate one separate control channel and also a separate mmWave channel for beamforming only. The former separation allows decreasing the number of control messages exchanged in each control channel, and the latter allows the simultaneously execution of multiple beamforming. In conjunction to this clustering scheme, we propose a multiband protocol in which only the cluster leader performs beamforming and uses the control channel to propagate the information obtained during this process. We compare the existing protocols with our proposed clustering protocol in terms of average transmission time, overhead, and accuracy of neighbor discovery information.

On the performance of wireless sensor network time difference of arrival localization under realistic interference and timing estimation errors

The article addresses the modeling and performance analysis of wireless sensor network localization with direct-sequence spread-spectrum signals and network-based, time difference of arrival measurements. Realistic radio channel propagation and interference conditions are taken into account. Synchronization by means of a delay-locked loop is adopted for sensor signal tracking at the wireless sensor network anchor nodes. A comprehensive timing estimation analysis is presented with channel impairments, including pathloss attenuation, shadowing, multipath fading, and multi-access interference. The full statistics of the delay-locked loop tracking jitter are derived, which serves to assess the practically achievable synchronization accuracy and its variability with radio channel conditions and specific sensor location. The time difference of arrival measurements are then used for sensor localization based on an efficient iterative maximum likelihood estimation approach shown to outperform weighted least squar...

Effect of Pointing Errors on the Performance of Hybrid FSO/RF Networks

The performance of a free space optics (FSO) transmission suffers from the atmospheric turbulence and the attenuation in foggy environment. By employing relay nodes, the error rate and the coverage area of the FSO communication system can be significantly improved. However, the pointing errors, generated because of the building sway, have the potential to eradicate the benefits of the relay-based FSO communication system. The effect of pointing errors in the presence of Gamma Gamma atmospheric fading together with path loss attenuation is considered in this paper. To counteract the adverse affects of the FSO link, a reliable millimeter-wave radio frequency (MMW RF) link is used as a backup. In this context, this paper proposes a cooperative decode-and-forward (DF)-relaying-based hybrid FSO/RF system with maximal-ratio-combining (MRC) at the destination. The system consists of FSO and RF sub-systems, where FSO sub-system has the priority to transmit and RF sub-system serves as a back up when the FSO sub-system is in outage. The exact and asymptotic outage probability and average symbol error rate (SER) expressions for the proposed system are derived in closed-form and the diversity order is determined. The effect of pointing errors on the system performance is analyzed extensively. The optimum values of transmit beam waist and radius of receiver aperture are determined. The theoretical results, which are validated by Monte-Carlo simulations, show that the proposed cooperative hybrid FSO/RF system drastically improves the system performance compared to single hop (SH) hybrid FSO/RF and cooperative FSO systems especially for large pointing errors scenario.

Closed-Form Expressions of Ergodic Capacity in Cloud Radio Access Networks With Nakagami-m Fading

We investigate a C-RAN model based on single nearest RRH association with Nakagami- m fading and path-loss fading. In the analysis the parameter $mL$ is not restricted to be an integer, where L is the number of antennas per RRH. We derive several closed-form expressions for the ergodic capacity, not restricted to the high SNR regime, for two classes of power path loss exponents. Moreover, the closed-form expression of a tight lower bound is provided for general scenarios. Finally, the results of simulation and numerical integration are provided to show the cross-verification.

Millimeter Wave Communications With OAM-SM Scheme for Future Mobile Networks

The orbital angular momentum (OAM) technique provides a new degree of freedom for information transmissions in millimeter wave communications. Considering the spatial distribution characteristics of OAM beams, a new OAM spatial modulation (OAM-SM) millimeter wave communication system is first proposed for future mobile networks. Furthermore, the capacity, average bit error probability, and energy efficiency of OAM-SM millimeter wave communication systems are analytically derived for performance analysis. Compared with the OAM-based multi-input multi-output (MIMO) millimeter wave communication systems, the maximum energy efficiency of OAM-SM millimeter wave communication systems is improved by 227.2%. Moreover, numerical results indicate that the proposed OAM-SM millimeter wave communication systems are more robust to path-loss attenuations than the conventional MIMO millimeter wave communication systems, which makes it suitable for long-range transmissions. Therefore, OAM-SM millimeter wave communication systems provide a great growth space for future mobile networks.