Visible light communications (VLC) have received significant attention as a way of moving part of the saturated indoor wireless traffic to the wide and unregulated visible optical spectrum. Nowadays, ...VLC are considered as a suitable technology, for several applications such as high-rate data transmission, supporting internet of things communications or positioning. The signal processing originally derived from radio-frequency (RF) systems such as cooperative or precoding schemes can be applied to VLC. However, its implementation is not straightforward. Furthermore, unlike RF transmission, VLC present a predominant line-of-sight link, although a weak non-LoS component may appear due to the reflection of the light on walls, floor, ceiling and nearby objects. Blocking effects may compromise the performance of the aforementioned transmission schemes. There exist several surveys in the literature focused on VLC and its applications, but the management of the shadowing and interference in VLC requires a comprehensive study. To fill this gap, this work introduces the implementation of cooperative and precoding schemes to VLC, while remarking their benefits and drawbacks for overcoming the shadowing effects. After that, the combination of both cooperative and precoding schemes is analyzed as a way of providing resilient VLC networks. Finally, we propose several open issues that the cooperative and precoding schemes must face in order to provide satisfactory VLC performance in indoor scenarios.
This paper studies and provides a performance analysis for the atmospheric influence on the visibility in Free Space Optical Communications (FSOC). With a focus on ground station-satellite links, it ...aims to present and analyse the most commonly used attenuation models for the main atmospheric events, establish relationships and dependence never analyzed before, such as for example in the case of rain and snow. As the characterisation of atmospheric attenuation is far from following a pattern in different locations, this work is intended to simplify and unify all the atmospheric events, proposing the visibility as the main single parameter to compare and analyze them. This parameter is available in most of the measurements, including in the fog scenarios. Besides, the effects of clouds are also analyzed, establishing relationships to visibility, in the case of attenuation calculations, suggesting the use of certain attenuation models and providing a new technique for the calculation of the link blockage in the presence of clouds, which are reported by aviation codes in meteorological stations. Besides, all the sites accessed to obtain the meteorological parameters and tools used for the study in this paper are listed in <xref ref-type="sec" rid="sec2">section II .
Fifth-generation (5G) networks have been deployed alongside fourth-generation networks in high-traffic areas. The most recent 5G mobile communication access technology includes mmWave and sub-6 GHz ...C-bands. However, 5G signals possibly interfere with existing radio systems because they are using adjacent and co-channel frequencies. Therefore, the minimisation of the interference of 5G with other signals already deployed for other services, such as fixed-satellite service Earth stations (FSS-Ess), is urgently needed. The novelty of this paper is that it addresses issues using measurements from 5G base stations (5G-BS) and FSS-ES, simulation analysis, and prediction modelling based on artificial neural network learning models (ANN-LMs). The ANN-LMs models are used to classify interference events into two classes, namely, adjacent and co-channel interference. In particular, ANN-LMs incorporating the radial basis function neural network (RBFNN) and general regression neural network (GRNN) are implemented. Numerical results considering real measurements carried out in Malaysia show that RBFNN evidences better accuracy with respect to its GRNN counterpart. The outcomes of this work can be exploited in the future as a baseline for coexistence and/or mitigation techniques.
In this paper, a novel cooperative transmission and reception scheme in Visible Light Communications (VLC) is proposed and evaluated. This new scheme provides improvements and reliability in large ...indoor scenarios, such as corridors, laboratories, shops or conference rooms, where the coverage needs to be obtained by using different access points when VLC is used. The main idea behind the proposal is a simple cooperative transmission scheme where the receiver terminal will obtain the signal from different access points at the same time. This proposal outperforms traditional VLC schemes, especially in Non-Line-of-Sight reception where around 3 dB of gain, with respect to traditional schemes, can be obtained for unoptimized parameters, and larger than 3 dB could easily be achieved. The cooperation is studied in terms of the percentage of light coming from the main access point and a parameter called sidelobes' amplitude level. The performance is evaluated according to the location within the atto-cell.
The Smart Grid is a modern power grid that relies on advanced technologies to provide reliable and sustainable electricity. However, its integration with various communication technologies and IoT ...devices makes it vulnerable to cyber-attacks. Such attacks can lead to significant damage, economic losses, and public safety hazards. To ensure the security of the smart grid, increasingly strong security solutions are needed. This paper provides a comprehensive analysis of the vulnerabilities of the smart grid and the different approaches for detecting cyber-attacks. It examines the different vulnerabilities of the smart grid, including system vulnerabilities and cyber-attacks, and discusses the vulnerabilities of all its elements. The paper also investigates various approaches for detecting cyber-attacks, including rule-based, signature-based, anomaly detection, and ma-chine learning-based methods, with a focus on their effectiveness and related research. Finally, prospective cybersecurity approaches for the smart grid, such as AI approaches and blockchain, are discussed along with the challenges and future prospects of cyberattacks on the smart grid. The paper's findings can help policymakers and stakeholders make informed decisions about the security of the smart grid and develop effective strategies to protect it from cyber-attacks.
Direct current-biased optical orthogonal frequency division multiplexing (DCO-OFDM) signals used in visible light communications suffer from high peak-to-average-power ratio (PAPR) or cubic metric ...(CM). It strongly degrades the performance due to the great back-off necessary to avoid the clipping effect in the light-emitting diode. Thus, PAPR and CM reduction techniques become crucial to improve the system performance. In this paper, an adaptive network-based fuzzy inference system (ANFIS) is used to obtain efficient DCO-OFDM signals with a low power envelope profile. First, signals specially designed for DCO-OFDM with very low CM, as the ones obtained from the raw cubic metric (RCM)-active constellation extension method, are used to train the fuzzy systems in time and frequency domains. Second, after the off-line training, the ANFIS can generate a real-valued signal in a one-shot way with 8.9 dB of RCM reduction from the original real-valued signal, which involves a gain in the input power back off larger than 2.8 dB, an illumination-to-communication conversion efficiency gain of more than 35% and considerable improvements in bit error rate.
Visible light communication (VLC) is capable of satisfying the escalating data rate demand in indoor scenarios. The lighting infrastructure may also be exploited in the downlink of a wireless local ...area network (WLAN), where light-emitting diodes are used for transmitting information. The backhaul of VLC access points (APs) constitutes a potential bottleneck in WLANs, especially in large rooms where the number of APs is high. Thus, an alternative reflection-based cooperative wireless system concept is proposed, where no wired connections are required for connecting the APs. Then, its data rate analysis is developed based on the signal-to-noise ratio attained. The results show that the performance of the cooperative wireless system advocated closely approximates the performance of the traditional wired backhaul. Finally, we demonstrate by using Jain's index of fairness that the proposed scheme provides fair coverage quality for all users.
In this paper, we investigate a novel channel estimation (CE) method for multiple-input and single-output (MISO) systems in visible light communication (VLC). Direct current biased optical orthogonal ...frequency division multiplexing (DCO-OFDM) is commonly used in VLC where half of the available subcarriers are spent to guarantee a real-valued output after the inverse fast Fourier transform operation. Besides, dedicated subcarriers are typically used for CE, thus, many resources are wasted and the spectral efficiency is degraded. We propose a superimposed training approach for CE in MISO DCO-OFDM VLC scenarios. Analytical expressions of mean squared error (MSE) and spectral efficiency are derived when the least squares estimator is considered. This analysis is valid for outdoor and indoor scenarios. For the CE error, simulation results of MSE show a perfect match with analytical expressions. Moreover, results prove that this technique guarantees a larger spectral efficiency than previous schemes where dedicated pilots were used. Finally, the optimal data power allocation factor is also analytically derived.
Visible light communication (VLC) is a promising ubiquitous design alternative for supporting high data rates. Its application has been primarily oriented to indoor scenarios, but the proliferation ...of light-emitting diodes in the streets warrants its investigation in outdoor scenarios as well. This paper studies the feasibility of VLC in a conventional outdoor scenario, when optical orthogonal frequency division multiplexing techniques are employed. The presence of sunlight reduces the system's performance, hence sophisticated adaptive techniques must be applied. Closed-form expressions of the signal-to-noise ratio and of the mean cell data rate are derived and our simulations demonstrate their accuracy. Besides, the outage probability when adaptive modulation and coding schemes are employed is analytically expressed. It is shown that, when modulation bandwidth adaptation is carried out depending on the time of day and the illuminance from ambient light, the mean cell data rate is increased and the outage probability is reduced.
Orthogonal Frequency Division Multiplexing (OFDM) is one of the key modulations for current and novel broadband communications standards. For example, Multi-band Orthogonal Frequency Division ...Multiplexing (MB-OFDM) is an excellent choice for the ECMA-368 Ultra Wideband (UWB) wireless communication standard. Nevertheless, the high Peak to Average Power Ratio (PAPR) of MB-OFDM UWB signals reduces the power efficiency of the key element in mobile devices, the High Power Amplifier (HPA), due to non-linear distortion, known as the non-linear saturation of the HPA. In order to deal with this limiting problem, a new and efficient pre-distorter scheme using a Neural Networks (NN) is proposed and also implemented on Field Programmable Gate Array (FPGA). This solution based on the pre-distortion concept of HPA non-linearities offers a good trade-off between complexity and performance. Some tests and validation have been conducted on the two types of HPA: Travelling Wave Tube Amplifiers (TWTA) and Solid State Power Amplifiers (SSPA). The results show that the proposed pre-distorter design presents low complexity and low error rate. Indeed, the implemented architecture uses 10% of DSP (Digital Signal Processing) blocks and 1% of LUTs (Look up Table) in case of SSPA, whereas it only uses 1% of LUTs in case of TWTA. In addition, it allows us to conclude that advanced machine learning techniques can be efficiently implemented in hardware with the adequate design.
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