Samir Ahmed, Elsayed Mohamed, El-Banna Ahmad A Aziz, Shafique Ansari Imran, Rabie Khaled, ElHalawany Basem M
Faculty of Engineering at Shoubra, Benha University, Cairo 13511, Egypt.
James Watt School of Engineering, University of Glasgow, Glasgow G12 8QQ, UK.
Sensors (Basel). 2022 Jun 15;22(12):4521. doi: 10.3390/s22124521.
The hybrid combination between underwater optical wireless communication (UOWC) and radio frequency (RF) is a vital demand for enabling communication through the air-water boundary. On the other hand, non-orthogonal multiple access (NOMA) is a key technology for enhancing system performance in terms of spectral efficiency. In this paper, we propose a downlink NOMA-based dual-hop hybrid RF-UOWC with decode and forward (DF) relaying. The UOWC channels are characterized by exponential-generalized Gamma (EGG) fading, while the RF channel is characterized by Rayleigh fading. Exact closed-form expressions of outage probabilities and approximated closed-form expressions of ergodic capacities are derived, for each NOMA individual user and the overall system as well, under the practical assumption of imperfect successive interference cancellation (SIC). These expressions are then verified via Monte-Carlo simulation for various underwater scenarios. To gain more insight into the system performance, we analyzed the asymptotic outage probabilities and the diversity order. Moreover, we formulated and solved a power allocation optimization problem to obtain an outage-optimal performance. For the sake of comparison and to highlight the achievable gain, the system performance is compared against a benchmark orthogonal multiple access (OMA)-based system.
水下光无线通信（UOWC）与射频（RF）的混合组合是实现通过空气 - 水边界进行通信的关键需求。另一方面，非正交多址接入（NOMA）是一种在频谱效率方面提升系统性能的关键技术。在本文中，我们提出了一种基于下行链路NOMA的具有解码转发（DF）中继的双跳混合RF - UOWC。UOWC信道具有指数广义伽马（EGG）衰落特性，而RF信道具有瑞利衰落特性。在不完全连续干扰消除（SIC）的实际假设下，推导了每个NOMA用户以及整个系统的中断概率的精确闭式表达式和遍历容量的近似闭式表达式。然后通过蒙特卡罗模拟对各种水下场景验证了这些表达式。为了更深入了解系统性能，我们分析了渐近中断概率和分集阶数。此外，我们制定并解决了一个功率分配优化问题以获得最优中断性能。为了进行比较并突出可实现的增益，将该系统性能与基于正交多址接入（OMA）的基准系统进行了比较。
