Physical Layer Security for Multihop Underwater Wireless Optical Communications Using Optical CDMA

Abstract

For secure communications, the authors propose an underwater wireless optical communications code-division multiple-access (UOWC/CDMA) system with multiple relay assistance. Relay nodes employ the Chip Detect-and-Forward (CDF) technique to prevent the difficult multiuser decoding procedure. The proposed system performance, in terms of bit-error rate (BER) and transmission confidentiality, is analyzed in our study over fading channels. Therein, oceanic turbulence and beam misalignment between transmitters (Txs) and receivers (Rxs) have a significant negative impact on the reliability of a UWOC network. Additionally, changes in the water refractive index brought on by changes in pressure, water, and temperature can have an impact on the operation of UWOC systems. The performance analysis of a vertical UWOC link subject to Multiple-access interference and background noise is examined in this work. Additionally, we explore optical code-division multiple access (CDMA), which is used to facilitate simultaneous and asynchronous data transmission between sources (such as ships, buoys, unmanned underwater vehicles, divers, and so forth) and the destination. Based on a precise mathematical framework for link modeling that takes into consideration realistic Tx/Rx and channel parameters while accounting for the effects of oceanic turbulence and beam spreading loss conditions, this study was conducted. Moreover, it is shown that choosing the best Tx/Rx parameters is necessary to meet service quality requirements such as BER and transmission confidentiality. The provided findings provide insightful information about the practical considerations of deploying UWOC/ CDMA systems.