Uplink NOMA With QoS-Based SIC for Mixed Underwater-Terrestrial Communication System

This work investigates the outage behavior of an uplink decode-and-forward (DF) based mixed underwater optical wireless-RF communication (UOW-RFC) system utilizing non-orthogonal multiple access (NOMA) for underwater transmission. A water surface vehicle (WSV), acting as relay, forwards the data of the underwater devices (UDs) to a terrestrial access point (AP) by utilizing the quality of service (QoS) based successive interference cancellation (SIC) schemes. In particular, we consider three different QoS-based SIC schemes at the WSV, namely (i) Basic QoS-based SIC (BQ-SIC), (ii) Advanced QoS-based SIC (AQ-SIC), and (iii) Enhanced QoS-based SIC (EQ-SIC), which are different from conventional channel state information (CSI)-based SIC. Moreover, we employ partial relaying over the RF hop, i.e., the relay forwards the data to AP even if it is able to decode the data of one UD only. Considering the mixture-Extended Generalized Gamma (mEGG) distribution with lab channel scenario and non-zero boresight pointing error model for underwater links and Nakagami-
$m$
distribution for RF link, we obtain the expressions for outage probability under all the three QoS-based SIC schemes in terms of bivariate and multivariate Fox-H functions. It is shown through the numerical results that, in comparison with the BQ-SIC scheme, the AQ-SIC scheme provides significant improvement in the outage performance of low-QoS UD only, whereas the EQ-SIC scheme outperforms both BQ-SIC and AQ-SIC schemes for high-QoS and low-QoS UDs. The numerical results also reveal that employing EQ-SIC at WSV enables to overcome the error floor problem of UL-NOMA. Further, we perform the asymptotic outage analysis and derive analytical diversity order for all the QoS-based SIC schemes considered in this work. We also compare the proposed DF-based system with its AF counterpart to demonstrate the superiority of the proposed model. The impact of various other system and underwater channel parameters such as, threshold, bubble level, salinity, temperature gradient, and link lengths is shown on the outage performance of UDs. The derived results have also been compared with the benchmark scheme without partial relaying.