Mathur, Aashish

Wireless communications and power line communications (PLC) are essential components for smart grid communications. This paper analyses the performance of a dual-hop wireless-power line mixed communication setup employing a decode-and-forward relay in terms of analytical average bit error rate (BER), outage probability, and average channel capacity. The Nakagami- m distribution captures the wireless channel fading; whereas the PLC channel gain is characterized by the Log-normal distribution. The additive PLC channel noise is assumed to be Bernoulli-Gaussian distributed. Approximate closed-form expression of the average BER and exact closed-form expression of the outage probability are derived for the considered system. Further, we obtain an approximate closed-form expression of the capacity of the wireless-power line mixed system in terms of the Meijer-G function. It is observed that the system performance deteriorates as the impulsive noise index and the arrival probability of the impulsive component of the PLC additive noise increase.

Reconfigurable intelligent surface (RIS) is an emerging technology that can result in a dynamically controllable radio propagation environment by smartly tuning the signal reflections via a large number of low-cost passive reflecting elements. In this paper, we investigate the effect of RIS-aided jammer on distributed RIS-based dual-hop mixed free-space optical (FSO)-radio frequency (RF) communication systems. The channel distribution of the FSO link is assumed to follow a Gamma-Gamma (GG) distributed atmospheric turbulence (AT) model with pointing errors (PEs). The relay-RIS and RIS-destination links are assumed to follow Rayleigh distributions. The received signal at the destination node is corrupted by a RIS-aided jammer. It is assumed that the jammer-RIS and RIS-destination links follow a Rayleigh distribution. Novel closed-form expressions for the outage probability (OP) and bit error rate (BER) of the considered system are derived considering two types of detection schemes, namely intensity modulation/direct detection (IM/DD) and heterodyne detection (HD). Through numerical results, it is shown that the presence of the RIS-aided jammer severely degrades the performance of distributed RIS-based dual-hop mixed FSO-RF systems. Finally, the improvement in performance of dual-hop mixed FSO-RF systems with the use of distributed RIS is also validated through results.

Reconfigurable intelligent surface (RIS) is a recently emerged promising technology for beyond-5G (B5G)/6G wireless networks. In this letter, we propose to employ a signal space diversity (SSD) technique to improve the performance of distributed RIS-aided dual-hop mixed radio frequency (RF)-free-space optical (FSO) communication systems. The source-relay, source-RIS, and RIS-relay links are assumed to undergo independent but not identically distributed (i.n.i.d.) Nakagami-m fading. The destination node is equipped with multiple FSO apertures and the relay-destination links follow Gamma-Gamma (GG) distributed atmospheric turbulence (AT) model with pointing errors (PEs). Novel approximate closed-form expressions for the system's symbol error rate (SER) are derived for both the exhaustive RIS-aided (ERA) and opportunistic RIS-aided (ORA) configurations. The numerical results show that using the SSD technique at both the RF and FSO links significantly improves the spectral efficiency and the diversity order of the system considered.

Power line communications (PLC) are susceptible to interception due to their broadcast nature. In this letter, we study the impact of random pulse jamming attacks in PLC systems assuming M-ary phase shift keying (M-PSK) over Log-normally distributed channel gain. The nature of PLC channel noise is described by the Bernoulli-Gaussian random process. Additionally, the state of the jammer is characterized by the Bernoulli random variable. Conditioned upon the jamming activity, we evaluate the probability density function (PDF) of the instantaneous signal-to-jamming-plus-noise ratio (SJNR) and the instantaneous signal-to-noise ratio (SNR). Capitalizing on the statistical characterization of the SJNR and SNR, we derive the series-based expressions of the average symbol error rate (ASER) and outage probability (OP) for the considered PLC system. Further, the asymptotic ASER analysis is performed in terms of the coding gain and diversity order in the high SNR regime. In order to gain more insights into ASER and OP analysis of the considered PLC system, we demonstrate the effect of the different system parameters through the numerical results.

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 Málaga 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.

Artificial noise (AN) injection is one of the promising techniques for improving the secrecy performance of a communication system. In this paper, AN injection scheme is incorporated in free-space optical (FSO) communication system for improving the secrecy performance of free-space optical (FSO) communication systems. The FSO link is subjected to Gamma-Gamma (GG) distributed atmospheric turbulence (AT) with pointing errors (PEs). It is assumed that legitimate transmitter has only one FSO aperture while the legitimate receiver as well as an eavesdropper are equipped with multiple FSO apertures. The performance of the considered system is investigated by deriving novel series-based expressions for secrecy outage probability (SOP), secrecy throughput, and strictly positive secrecy capacity (SPSC) of the system. Finally, through numerical results, it is shown that the number of FSO apertures along with the proposed AN injection scheme and GG distributed AT with PEs have a significant impact on the performance of the considered system.

Power line communications (PLC) system performance is severely affected by the presence of impulsive noise and channel gain. Many communication systems employ a combination of forward error correction and automatic repeat request (ARQ) to detect transmission errors known as hybrid ARQ (HARQ). Thus, HARQ can be used to improve the reliability of a PLC system. In this paper, we evaluate the performance of a PLC system under the influence of impulsive noise over Rayleigh and Log-Normal channel gains using HARQ with chase combining scheme. Closed-form expressions of the analytical outage probability are derived for these two channel gain scenarios. Using the expression for outage probability, we also compute the average throughput for the PLC system under the given channel gain scenarios. It is observed by the analysis that the outage performance of the considered PLC system is significantly improved with the use of HARQ.

In the past two decades, chaotic modulation schemes have drawn much attention for their significant advantages over other traditional modulation techniques. One of the noticeable advantages is the capability of providing secure communication in the presence of an eavesdropper. In this article, we study the physical layer security (PLS) performance of low-frequency power line communication (PLC) systems against multiple eavesdroppers by employing differential chaos shift keying based modulation technique. A wiretap power line channel model is investigated by considering two different cases: 1) when all the channels are assumed to be independent and identically distributed (IID) following Log-normal distribution; and 2) the wiretap channels are considered to be identical but correlated Log-normally distributed and independent of the main channel. Contemporaneously, the Bernoulli-Gaussian random process models the PLC noise. Further, a comprehensive PLS study of the considered PLC system is characterized in terms of the average secrecy capacity, secure outage probability, and strictly positive secrecy capacity. We also propose an algorithm to maximize the secrecy throughput under security and reliability constraints. Moreover, to obtain essential insights, we reveal the impact of various crucial parameters onto the proposed system.

This paper presents experimental results for a free-space optical-fiber converged (FSO-FC) communication system under varying turbulence and foggy conditions. Based on the experimental measurements, we statistically characterize the FSO channel under different levels of turbulence and fog in terms of their respective probability density functions (PDFs). Our experimental PDFs fit well with the theoretical PDFs proposed in the literature. We experimentally evaluate the average bit error rate (ABER) of the considered FSO-FC communication system under different levels of turbulence and fog. Further, to compensate for the effects of turbulence and fog, we use multimode fiber as the receiver and compare the results with single-mode fiber as the receiver. Finally, we show the improvement in ABER under varying turbulence and fog by adding cyclic redundancy check bits to data bits.

In this paper, we propose to compensate the effects of imperfect channel state information (CSI) through the use of a reconfigurable intelligent surface (RIS)-assisted radio frequency (RF) communication system with hybrid automatic repeat request (H-ARQ) protocols thereby enhancing coverage and improving link reliability of the RF system. We derive novel series-based expressions of the probability density function (PDF) and cumulative distribution function (CDF) for the signal-to-interference-plus-noise ratio (SINR) at the destination (D) node, which is valid for an arbitrary number of RIS reflecting plates and various transmission rounds of H-ARQ protocols. Capitalizing on the derived CDF of SINR, we compute the outage probability (OP) and throughput for at least once (ALO), chase combining (CC), and incremental redundancy (INR) H-ARQ protocols. We analyze the impact of various H-ARQ rounds, number of RIS reflecting elements, and channel correlation coefficient on the performance of the considered system. The numerical results demonstrate that the proposed communication system shows remarkable performance improvement compared to the traditional RF communication systems.