Performance Analysis of Integrated Air-Ground-Underwater Hybrid RF/FSO Communication System Using HAPS Based Relaying

In this paper, the distant source communicates with the underwater destination using High Altitude Platform Station (HAPS) and a triple-hop relay setup. In this setup, the source transmits information using hybrid Radio Frequency (RF)/Free Space Optical Communication (FSO) link to the decode-and-forward (DF) based relay at HAPS, which forwards the signal to the relay at the water surface using FSO link, which further transmits the signal to the underwater destination using Under Water Optical Communication (UWOC) link. Both the relays use DF relaying protocols. HAPS are used to increase the reliability of the system and range of transmission. FSO links offers a high bandwidth and better data rates than the RF links. But they often get affected by the atmospheric conditions, turbulence, and pointing errors. RF link on the other hand acts as a good complement to FSO links, thereby increasing the reliability of the system when both are used in parallel to transmit the information. UWOC link has several benefits like higher data rates, less attenuation and low power consumption in comparison to acoustic links. New statistical characteristics for the signal-to-noise-ration (SNR) of the proposed system are developed using which the outage probability of the system is derived. The numerical results shows that the outage probability of the system proposed gets affected by the RF shadowing, FSO turbulence parameters and turbulence parameters of UWOC links such as salinity, temperature gradient and bubble level concentration. Also the asymptotic analysis matched with the analytical results.