# An Insight to the Outage Performance of Multi-Hop Mixed RF/FSO/IWOC System
###### Abstract  
In this paper, we investigate the outage performance of the three-hop mixed system integrating radio frequency (RF), free space optics (FSO), and under water optical communication (UWOC) system. The closed-form analytical expressions for the outage probability of the system are derived. In the considered system, the RF channel follows the Nakagami-\(m\) distribution, the FSO channel observes the Gamma-Gamma fading statistics, and the UWOC link experiences a mixture Exponential Generalized Gamma (EGG) fading distribution. To verify the derived analytical expressions, numerical simulations are also carried out, and we present the influence of the various link parameters such as path loss, atmospheric turbulence, pointing errors, angle-of-arrival fluctuations, water salinity, and scintillation on the performance of the decode and forward (DF) relayed multi-hop communication system. asymptotic outage probability; Gamma-Gamma distribution; exponential generalized gamma fading; Nakagami-\(m\) fading 2023  
[PERSON], [PERSON], H.  
to the FSO channel because it is relatively unresponsive to the weather and can easily pass through the fog, the FSO link offers much higher data rates than the RF link, but suffers from atmospheric loss due to the fog and scintillation [8]. The hybrid RF/FSO system can be viewed as a way to lessen the effects of turbulence in the atmosphere and pointing errors [9]. In mixed RF/FSO communication networks, the relays play a significant role in transferring the information signal from the source node to the destination. The study and performance evaluation of mixed RF/FSO systems has been carried out extensively in the literature. The performance of amplify and forward (AF) relay-based mixed RF/FSO systems is presented in [10; 11; 12; 13] considering intensity modulation/direct detection (IM/DD) and heterodyne modulation schemes. The decode and forward (DF) relay-based mixed RF/FSO systems are studied in [14; 15; 16]. The author in [17] considered a unmanned aerial vehicle (UAV)-assisted RF/FSO system and obtained the expression for the outage probability (OP) and the optimal altitude. In [18], the authors analyzed the performance of the UAV-based RF/FSO communication system by evaluating its asymptotic average secrecy rate. In recent years, optical signals have also gained a lot of attention in underwater wireless communication because of their various advantages like wider bandwidth, higher data transmission rate, etc., and hence they provide an efficient transmission solution for a variety of underwater applications [19] such as military defense, port security, seismic monitoring, etc. Underwater wireless optical communication (UWOC) is an emerging field of research nowadays. Due to the difficult communication features, exploring the deep environment is a challenging endeavor. The high data transfer rate of collected data to control stations is another challenge in ocean monitoring applications. Each individual RF, FSO, and UWOC system has its own drawbacks and difficulties. Therefore, the mixed system helps to provide better exploration, monitoring, and transmission of the ocean data between the source and the destination. There has been rapid growth in the implementation of mixed RF/FSO/UWOC systems over the past few years, because the mixed systems are able to fulfill the data bandwidth requirement and provide easy data transmission from the source to the destination under different fading conditions. It has become interesting to combine RF communication with optical wireless communication (including FSO communication and UWOC). The authors in [20] explored the performance of the relay-based mixed RF/UWOC system where the relay conveys the information to an autonomous underwater vehicle (AUV) which is acting as the destination. The DF relay-based dual-hop mixed RF/UWOC is proposed in [21] and the author derived the novel expressions of the average bit error rate (ABER) for the different modulation schemes.