Abstract
A key challenge in free space optics/underwater wireless optical communication (FSO/UWOC) hybrid systems is maintaining the adequate power budget and signal to noise ratio (SNR), which necessitates wavelength translation (WT) between visible and infrared spectra at the water-air interface, thus increasing both the cost and complexity. In this work, we propose and simulate a hybrid free space optics/single-mode fiber (FSO/SMF) ring network supporting simultaneous downstream (DS) and upstream (US) transmissions to multiple terrestrial and underwater nodes without requiring local optical sources and WT scheme. The proposed architecture employs differential phase shift keying modulation for downstream channels to enhance turbulence tolerance and reuses the same optical carriers for US on-off keying channels through a dual-drive Mach-Zehnder modulator (DD-MZM) and sinusoidal radio frequency source based pulse carving scheme. The performance of the DS and US channels is analyzed using Bit-error rate (BER) results obtained for different values of refractive index structure parameter (
C
n
2
) and atmospheric attenuation coefficient
(
α
atm
)
using Gamma-Gamma channel model. Simulation results clearly show that forward-error correction target Bit-error rate of
3.8
×
1
0
−
3
is achieved both for DS and US channels under different turbulence strengths and weather conditions. Node survivability and link inflation analysis are performed for different scenarios. These findings reflect that the proposed ring topology based hybrid FSO/SMF system is flexible and resilient to the adverse channel effects, making it a promising solution for high-speed, long-range future Internet of underwater things (IoUTs) applications.