KEYWORDS: Free space optics, Turbulence, Ocean optics, Signal to noise ratio, Error analysis, Telecommunications, Wireless communications, Water, Systems modeling, Relays
We propose a multihop underwater wireless optical communication (UWOC) convergent with free-space optical (FSO) system for an optical internet of underwater things (O-IoUT) and underwater optical wireless sensor network (UOWSN) applications. A closed-form expression of outage probability was derived for the proposed system using the cumulative distribution functions gamma–gamma and hypertangent log-normal for FSO link and UWOC link, respectively. The outage performance of the proposed multihop UWOC convergent with FSO system was analyzed over various oceanic water types (clear ocean, coastal ocean, and turbid harbor) and different FSO weather conditions (clear air, haze, drizzle, and light fog). The results also depict the end-to-end system performance for different pointing errors (strong, moderate, and weak) and varying the number of hops. The maximum link range of ∼2.5 km, which includes 2 km of FSO link and 450 m of multihop UWOC link (nine hops with each of 50 m clear ocean), is considered.
For the first time, we propose a dual-hop multiple input multiple output (MIMO)-based convergent underwater wireless optical communication (UWOC)–free-space optical (FSO) system. The UWOC and FSO links are Gamma–Gamma (GG) distributed. Closed-form expression for the average bit error rate (ABER) is derived for the proposed MIMO-based dual-hop UWOC-FSO convergent system using the GG cumulative distribution function. The end-to-end system performance analysis is carried out by considering the turbulence, attenuation, and pointing error effects for UWOC and FSO links. For the UWOC link, different oceanic conditions, such as the clear ocean, coastal ocean, and turbid harbor, are considered. Various atmospheric effects, such as clear air, fog, rain, drizzle, and haze, are considered for the FSO link. The analytical results of the proposed MIMO-based convergent system are compared with single-input single-output (SISO) system. As a result, it is observed that the proposed MIMO 2 × 3 scheme offers an improvement of 35 dB in the average signal-to-noise ratio compared with the SISO system at ABER of 10 − 5 in the case of weak pointing error.
KEYWORDS: Free space optics, Error analysis, Turbulence, Telecommunications, Signal to noise ratio, Ocean optics, Signal attenuation, Fiber optic gyroscopes, Wireless communications, Air contamination
The differential phase-shift keying-based dual-hop underwater wireless optical communication-free-space optics (UWOC-FSO) convergent system is proposed for UOWSNs and Internet of Underwater Things (IoUT) applications. In the proposed system, the collected sensor data are transmitted to a decode-and-forward relay using underwater optical wireless communication links modeled as gamma–gamma distribution. The relay transmits the signal to the terrestrial destination using free-space optical link modeled as Malaga distribution. The end-to-end performance of the system (novel expression for asymptotic bit error rate) is derived and analyzed over combined channel model (including the effects of attenuation, turbulence, and pointing errors for both FSO and UWOC channels). The in-depth study is carried out for different weather conditions of FSO (attenuation—very clear, haze, rain, and fog; turbulence—weak and strong; and pointing error—weak and strong based on the g values 1, 2, and 6) and UWOC (attenuation—clear, coastal ocean, and turbid harbor; turbulence—weak, moderate, and strong; and pointing error—weak and strong based on the g values 1, 2, and 6), respectively. The proposed system is highly useful in coastal environments, where the climate is changing adequately as clear, rain, haze, and fog.
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