Security Performance Analysis of a NOMA-Assisted Underwater VLC System Under Imprecise Channel Estimations

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.

Solution for Self-Interference of NOMA-Based Wireless Optical Communication System in Underwater Turbulence Environment

“…It can be observed from Fig. 3(a) that the minimum distances between the receiver constellation points of the two users are respectively [27] (14) (15) Based on the analysis above, the BER of User 1 can be calculated by (16) The solution of  function in (16) can be referred to in Appendix A.…”

“…Thus, the demodulation error of User 1 will be hardly causing the demodulation error of User 2. According to the analysis above, the BER judgment region of User 1 remains unchanged, and thus the BER of User 1 can still be calculated by (16). It is noted that the interference cancellation method based on the fixed sorting of power-graded magnitudes is employed in this paper for the sake of interference cancellation efficiency.…”

“…[13] provided a calculation method for the interference cancellation factor under incomplete SIC, and addressed the effect of the interference factor on the robustness and effectiveness of the NOMAbased optical communication system. The design of power allocation schemes for the NOMA-based UWOC system mostly makes reference to existing terrestrial wireless communication technologies, and the most commonly used are the fixed power allocation algorithm and the distancebased fixed-proportional power allocation algorithm [14][15][16]. Both of the two algorithms are easy to be implemented, and however they are not flexible enough to deal with the complex oceanic channel environments, which makes it challenging to achieve the optimal efficiency of the NOMAbased UWOC system.…”