Performance Analysis of Relay Assisted Convergent Free Space Optical - Underwater Wireless Optical Communication System

Abstract

The growth in mobile networks from the second generation (2G) to the fifth generation (5G) and the evolution of broadband Internet access in- creased the services of communication systems. Hence, there is a require- ment for ultra-wideband and ultra-highspeed wireless networks to support people’s ever-increasing needs. Wireless optical communication (WOC) systems accomplish these requirements with high bandwidth, high secu- rity, cost-effectiveness, license-free operation, simple deployment, and free from interference. WOC is mostly used in the terrestrial applications that is named as free space optical (FSO) system. Most of the part of the earth is filled with water, and oceans hold around 97% of this water. Oceans play a crucial role in human life because peo- ple use these oceans for traveling, edibles, and communication. Humans have explored only 5% of the oceans, and discovering the large parts of the oceans is possible with the advanced communication systems. Un- derwater communication requires high speed and high bandwidth, similar to terrestrial communication, to establish communication links between remotely operated vehicles (ROVs) and underwater wireless sensor net- works (UWSNs). These ROVs collect the information and transfer it to a nearby offshore base station. Suitable technologies are acoustic, wired (fiber optic), and WOC systems for underwater communications. The un- derwater wireless optical communication (UWOC) system is attractive and highly preferred among these methods. UWOC has several advantages over acoustic and RF communications regarding data rate, latency, and cost. It is also helpful to recover, offload, download, or exchange a more massive collection of information in real-time while minimizing loss of energy and traffic congestion. The UWOC system has several applications such as environmental monitoring, oceanography, maritime archaeology, imaging, port security, live video streaming, disaster preparedness, offshore oil field exploration, high-performance UWSNs, IoUT, and military operations In this thesis, we proposed relay-assisted convergent FSO-UWOC systems. Even though the WOC systems have substantial advantages, the link range, reliability, and data rate are affected by atmospheric/underwater vscintillation, attenuation, and pointing errors. This thesis considers point- ing errors and turbulence as significant limitations and reviews the average bit error rate (ABER) performance of the end-to-end convergent FSO- UWOC systems. Under strong turbulence conditions, the dual-hop single input single output (SISO) system gives an ABER of 10−2 at 25dB of aver- age signal to noise ratio (SNR). Using the multiple-input multiple-output (MIMO) technique, we improved the end-to-end system’s ABER perfor- mance to 10−5 over strong turbulence with pointing errors at an average SNR of 25dB. We proposed multi-hop FSO-UWOC convergent systems for island com- munication, Internet of underwater things (IoUT), and underwater optical wireless sensor networks (UOWSN) applications. We analyzed the outage performance of the multi-hop FSO-UWOC systems. We also proposed multi-hop FSO convergent with the UWOC system for navy applications. Here we assumed (n-1) FSO links and one UWOC link to perform the ABER and outage performances. We did a case study for the proposed system with real-time values of the Arabian Sea (GPS coordinates: N 130 0’38.0988’, E 740 47’17.4876’) near Surathkal, located in Mangalore, Karnataka, India. We proposed a multi-hop UWOC convergent with an FSO system with an ’n’ number of links for navy applications and identifying the item of the wrecked cargo ship. We analyzed the outage performance of the end- to-end system by considering the turbulence, attenuation, and pointing losses. We used the decode and forward (DF) relaying technique in all the proposed works. In this thesis, we considered the coherent and non- coherent modulation schemes, such as binary phase-shift keying (BPSK), binary frequency-shift keying (BFSK), and differential phase-shift keying (DPSK).