No abstract

We investigate the physical layer security of decode-and-forward-relayed free space optics (FSO)/radio frequency (RF) communication system. In this network, the eavesdropper exists after relay node and overhears RF transmission.Further, FSO being a line-of-sight transmission is assumed to be secure from eavesdroppers. Here, we have the Gamma-Gamma (ΓΓ) distribution for FSO link and generalized − distribution for RF link. The security for information transmission to the legitimate user in the presence of an eavesdropper is measured in terms of secrecy capacity and secrecy outage probability. Deriving the probability density function and cumulative distribution function of end-to-end signal-to-noise ratio, the closed-form expressions for security parameters are achieved. The numerical analysis of the proposed system is done under the influence of atmospheric turbulence effects and various fading conditions. The results have been verified through simulation. KEYWORDSdual hop, FSO/RF system, physical layer security, secrecy capacity, secrecy outage probability Int J Commun Syst. 2018;31:e3468.wileyonlinelibrary.com/journal/dac to confuse eavesdropper. They provide secure transmission but require higher transmitting signal power to generate artificial noise. Moreover, the design of beamformer is a bit difficult due to computational complexity. The situation when main link condition is worse than the eavesdropper link creates hassle in security analysis of RF system. This limitation can be improved by using the multiple-input multiple-output (MIMO), 5 multiple-input and single-output (MISO), 6 and single-input and multiple-output (SIMO) 7 systems. However, due to high cost and size limitations, the designing of the network system with multiple antennas becomes difficult. The free space optics (FSO) has emerged as an effective solution to provide secured transmission with high data rate because it is a line-of-sight (LoS) transmission. 8 However, it has a limited transmission distance of the order of few kilometers only. It is a license-free transmission, but atmospheric turbulence effects (ie, smoke, snow, and fog) are main factors in deteriorating the performance of an FSO system. The PLS analysis of single hop FSO system investigated in 9 in which the secrecy performance was evaluated for data transmission consisting of single source and destination in the presence of an eavesdropper.Because of the complementary properties of FSO and RF communications, mixed FSO/RF systems have gained the attention of various researchers. These systems are more economical and save unnecessary modifications in existing system networks. They also avoid significant interference as both communications operate on different frequency bands. 10 It has been found that RF link can be a wiretapping link in mixed FSO/RF systems. Hence, the secure and legitimate transmission via mixed systems remains impossible before applying PLS. Recently, trade-off analysis on security-reliability is investigated for multiuser SIMO based RF/FSO relay networks...

No abstract

The accurate estimation of underwater Visible Light Communication (VLC) channel conditions is challenging due to its widespread attenuation and scattering effects. The channel attenuation is a linear function of frequency and causes exponential signal power loss whereas due to the scattering effect, numerous photons are statistically generated as light beams strike water molecules and there arise security concerns. Assuming realistic underwater conditions, this paper investigates the security performance of a typical Non-Orthogonal Multiple Access (NOMA)-assisted underwater VLC system. It consists of a Floating Vehicle Transmitter (FVT), equipped with multiple Light Emitting Diodes (LEDs) to transmit the signal to two legitimate near-end and far-end Underwater Vehicles (UVs) in presence of an active/passive eavesdropper. The Channel State Information (CSI) of each transmitting link is estimated with the use of a Minimum Mean Square Error (MMSE) technique. Furthermore, we propose a LED selection mechanism to select an LED that can achieve the highest secrecy rate defined under the constraints of known and unknown CSI of legitimate and/or eavesdropping links. Using the Successive Interference Cancellation (SIC) technique, a novel closed-form secrecy outage probability expressions for the conventional single-LED and multi-LED NOMA-VLC links for both known and unknown CSI scenarios is derived. The security performance of the proposed multi-LED NOMA-VLC system is compared with the conventional single-LED NOMA-VLC system under the effect of air bubbles for both fresh and salty water. Finally, we verify the validity of the numerical results through Monte-carlo simulation analysis.INDEX TERMS Non-orthogonal multiple access, physical layer security, secrecy capacity, secrecy outage probability and underwater visible light communication.

No abstract

No abstract

The complexity of successive interference cancellation at the receiver's end is a challenging issue in conventional non-orthogonal multiple access assisted massive wireless networks. The computational complexity of decoding increases exponentially with the number of users. Further, under realistic channel conditions, a synchronous non-orthogonal multiple access scheme is impractical in the uplink deviceto-device communications. In this paper, an asynchronous non-orthogonal multiple access-based cyclic triangular successive interference cancellation scheme is proposed for a massive device-to-device network. The proposed scheme reduces the decoding complexity, energy consumption, and bit error rate of a superimposed signal received in an outband device-to-device network. More specifically, the scheme follows three consecutive stages; optimization, decoding, and re-transmission. In the optimization stage, a dual Lagrangian objective function is defined to maximize the number of data symbols decoded at the receiver by determining an optimal interference cancellation triangle, under the co-channel interference and data rate constraints. In the decoding stage, the data in the optimal interference cancellation triangle is decoded using a conventional triangular successive interference cancellation technique. Next, the remaining users' data are decoded in sequential iterations of the proposed scheme, using the retransmissions from such users. Utilizing the successive interference cancellation characteristics, the performance of the proposed deviceto-device network is defined in terms of energy efficiency, bit error rate, computational complexity, and decoding delay metrics. Moreover, the performance of the proposed decoding scheme is compared with the conventional triangular successive interference cancellation decoding scheme to demonstrate the superiority of the proposed scheme.

We present a first detailed survey that focuses on the security challenges faced by the underwater and air-water (A-W) wireless communication networks (WCNs), as well as the countermeasures proposed to date. Specifically, we provide a detailed literature review of the various kinds of active and passive attacks which hamper the confidentiality, integrity, authentication and availability of both underwater and A-W WCNs. For clarity of exposition, this survey paper is mainly divided into two parts. The first part of the paper is essentially a primer on underwater and A-W WCNs whereby we outline the benefits and drawbacks of the three promising underwater and A-W candidate technologies: radio frequency (RF), acoustic, and optical, along with channel modelling. To this end, we also describe the indirect (relay-aided) and direct mechanisms for the A-W WCNs along with channel modelling. This sets the stage for the second part (and main contribution) of the paper whereby we provide a thorough comparative discussion of a vast set of works that have reported the security breaches (as well as viable countermeasures) for many diverse configurations of the underwater and A-W WCNs. Finally, we highlight some research gaps in the open literature and identify some open problems for the future work.