With the ongoing trends in the energy sector such as vehicular electrification and renewable energy, smart grid is clearly playing a more and more important role in the electric power system industry. One essential feature of the smart grid is the information flow over the high-speed, reliable and secure data communication network in order to manage the complex power systems effectively and intelligently. Smart grids utilize bidirectional communication to function where traditional power grids mainly only use one-way communication. The communication requirements and suitable technique differ depending on the specific environment and scenario. In this paper, we provide a comprehensive and up-to-date survey on the communication technologies used in the smart grid, including the communication requirements, physical layer technologies, network architectures, and research challenges. This survey aims to help the readers identify the potential research problems in the continued research on the topic of smart grid communications.

Communication Technologies for Smart Grid: A Comprehensive Survey

This paper presents a secrecy performance analysis of a parallel free-space optical/millimeter-wave (mm-wave) communication system with a selection-combining receiver over a unified Fisher-Snedecor $\mathcal{F}$-distribution channel. The $\mathcal{F}$-distribution model, with the proper parameters, may be used to describe both the mm-wave and optical channels. The security performance is specifically evaluated by deriving closed-form expressions for the average secrecy capacity, secrecy outage probability, and strictly positive secrecy capacity. We examine the three following distinct security scenarios: 1) An FSO-link eavesdropping attack, 2) mm-wave-link eavesdropping attacks, and 3) eavesdropping attacks on FSO and mm-wave links at the same time. Furthermore, to better understand the influence of various system and channel parameters, asymptotic analysis is performed at high signal-to-noise ratio values. Our developed analytical expressions provide an efficient tool for examining the influence of various system and channel parameters on the secrecy performance, including the atmospheric turbulence severity, pointing errors of the FSO link, fading severity, the shadowing parameters, as well as the number of diversity branches of the mm-wave links. Monte-Carlo simulations are used to verify the correctness of the numerical findings.

/pdf/secrecy-performance-analysis-of-parallel-fso-mm-wave-system-2mkrlifx.pdf

Secrecy Performance Analysis of Parallel FSO/mm-wave System Over Unified Fisher-Snedecor Channels

Intelligent reflecting surface (IRS) is an emerging key technology for the fifth-generation (5G) and beyond wireless communication systems to provide more robust and reliable communication links. In this letter, we propose a mixed dual-hop free-space optical (FSO)-radio frequency (RF) communication system that serves the end user via a decode-and-forward (DF) relay employing hybrid automatic repeat request (H-ARQ) protocols on both hops. Novel closed-form expressions of the probability density function (PDF) and cumulative density function (CDF) of the equivalent end-to-end signal-to-noise ratio (SNR) are computed for the considered system. Utilizing the obtained statistics, we derive the outage probability (OP) and packet error rate (PER) of the proposed system by considering generalized detection techniques on the source-to-relay (S-R) link with H-ARQ protocol and IRS having phase error. We obtain useful insights into the system performance through the asymptotic analysis which aids to compute the diversity gain. The derived analytical results are validated using Monte Carlo simulation. 

/pdf/mixed-dual-hop-irs-assisted-fso-rf-communication-system-with-3y667p93.pdf

Mixed Dual-Hop IRS-Assisted FSO-RF Communication System With H-ARQ Protocols

In this paper, an artificial noise (AN) injection technique is incorporated in a free-space optical (FSO) communication system with the aim of enhancing the secrecy performance of the system. An intensity modulated direct detection (IM/DD) FSO link which is subjected to Malaga ( $\mathcal {M}$ ) distributed turbulence with pointing errors is considered in this paper. The performance of FSO systems is evaluated by deriving novel closed-form expressions for the secrecy outage probability (SOP), strictly positive secrecy capacity (SPSC), and throughput of the system. By formulating a constrained optimization problem, we discuss an optimal power allocation strategy for throughput maximization in the considered system. It is shown through the results that the proposed technique is very effective in improving the secrecy performance of FSO systems.

/pdf/artificial-noise-injection-based-secrecy-improvement-for-fso-346wz7qpu5.pdf

Artificial Noise Injection–Based Secrecy Improvement for FSO Systems

Analysis of selection combining hybrid FSO/RF systems considering physical layer security and interference

In this article, we study the physical layer security of free-space optical (FSO) communications under different eavesdropping scenarios. More specifically, the secrecy performance of FSO communication employing intensity modulation/direct detection detection is analyzed for the well-established Malaga channels. Three different realistic scenarios of eavesdropping are considered by assuming different placement locations for the eavesdropper in the paper. Novel expressions for the average secrecy capacity (ASC) and secrecy outage probability (SOP) are derived for the considered scenarios, and useful insights are also provided through asymptotic analysis. The results show: (1) When the eavesdropper is placed near the transmitter, atmospheric condition imposes a less significant impact on secrecy performance; (2) Certain level of correlation can potentially enhance the secrecy performance for FSO communications; (3) The correlation imposes opposite impacts on the ASC and SOP of FSO communications; and the secrecy performance metrics exhibit a non-monotonic impact with the increase of correlation; (5) When the correlation of the FSO links is too small or too large (i.e., the correlation parameter around 0 or 1), the correlation plays a more significant impact on secrecy performance; and (6) The asymptotic slope of the SOP is 0.5 for all eavesdropping scenarios under practical FSO channels.

/pdf/comprehensive-physical-layer-security-analysis-of-fso-336wnmx565.pdf

Comprehensive Physical Layer Security Analysis of FSO Communications Over Málaga Channels

Secrecy performance of FSO communication systems with non-zero boresight pointing errors

In release 16 of the third-generation project partnership, it has been suggested that hybrid-automatic repeat request (H-ARQ) protocols can be used to ensure robust communications. In this paper, we incorporate H-ARQ in the free-space optical (FSO) communication systems to improve their performance and communication link reliability. We derive novel, to the best of our knowledge, closed-form expressions for the outage probability of the FSO systems under the combined impact of gamma–gamma distributed atmospheric turbulence and pointing errors (PEs) for heterodyne detection and intensity modulation and direct detection techniques. This is accomplished using various H-ARQ protocols, such as, at least once, chase combing, and incremental redundancy (INR). Further, using outage probability expressions, we calculate throughput for the FSO systems using H-ARQ protocols. Useful insights into the FSO system performance are obtained through the asymptotic analysis for the considered H-ARQ protocols and detection techniques. It is observed through the numerical results that H-ARQ with INR performs better than the other considered H-ARQ protocols. We also draw a comparison between the outage performance of an FSO system with boresight PE and without boresight PE.

Performance improvement of FSO communication systems using hybrid-ARQ protocols.

Free space optical (FSO) communication systems are a promising candidate for beyond-5G (B5G) wireless communication systems because of their merits, such as high data rate, huge bandwidth, low latency, less power consumption, and no electromagnetic interference. In this paper, we develop the experimental setup of a 10 Gigabits/second (Gb/s) FSO communication system in a laboratory controlled environment. An atmospheric turbulence chamber is designed for introducing the effects of turbulence and fog to the transmitted signal. We experimentally evaluate the bit error rate (BER) and the received power profile fluctuations under various conditions such as with and without turbulence. Further, we also demonstrate the effect of heat and fog on the received power profile. Additionally, we exemplify the role of cyclic redundancy check (CRC) to mitigate the deteriorating effects of atmospheric conditions on the FSO link.

Experimental Investigation of FSO Systems Under the Effect of Atmospheric Turbulence, Heat, and Fog

Intelligent reflecting surface (IRS) is an emerging key technology for the fifth-generation (5G) and beyond wireless communication systems to provide more robust and reliable communication links. In this paper, we propose a mixed dual-hop free-space optical (FSO)-radio frequency (RF) communication system that serves the end user via a decode-and-forward (DF) relay employing hybrid automatic repeat request (HARQ) protocols on both hops. Novel closed-form expressions of the probability density function (PDF) and cumulative density function (CDF) of the equivalent end-to-end signal-to-noise ratio (SNR) are computed for the considered system. Utilizing the obtained statistics functions, we derive the outage probability (OP) and packet error rate (PER) of the proposed system by considering generalized detection techniques on the source-to-relay (S-R) link with H-ARQ protocol and IRS having phase error. We obtain useful insights into the system performance through the asymptotic analysis which aids to compute the diversity gain. The derived analytical results are validated using Monte Carlo simulation.

Gyan Deep Verma

Papers

Comprehensive Physical Layer Security Analysis of FSO Communications Over Málaga Channels

Secrecy performance of FSO communication systems with non-zero boresight pointing errors

Performance improvement of FSO communication systems using hybrid-ARQ protocols.

Experimental Investigation of FSO Systems Under the Effect of Atmospheric Turbulence, Heat, and Fog

Mixed Dual-Hop IRS-Assisted FSO-RF Communication System with H-ARQ Protocols.