# Beyond the Horizon, Backhaul Connectivity for Offshore IoT Devices
###### Abstract  
The prevalent use of the Internet of Things (IoT) devices over the Sea, such as, on oil and gas platforms, cargo, and cruise ships, requires high-speed connectivity of these devices. Although satellite based backhaul links provide vast coverage, but they are inherently constrained by low data rates and expensive bandwidth. If a signal propagated over the sea is trapped between the sea surface and the Evaporation Duct (ED) layer, it can propagate beyond the horizon, achieving long-range backhaul connectivity with minimal attenuation. This paper presents experimental measurements and simulations conducted in the Industrial, Scientific, and Medical (ISM) Band Wi-Fi frequencies, such as 5.8 GHz to provide hassle-free offshore wireless backhaul connectivity for IoT devices over the South China Sea in the Malaysian region. Real-time experimental measurements are recorded for 10 km to 80 km path lengths to determine average path loss values. The fade margin calculation for ED must accommodate additional slow fading on top of average path loss with respect to time and climate-induced ED height variations to ensure reliable communication links for IoT devices. Experimental results confirm that 99% link availability of is achievable with minimum 50 Mbps data rate and up to 60 km distance over the Sea to connect offshore IoT devices. a 27 September 2021 18 October  
necessary for smart platforms used in remote monitoring and surveillance. Backhaul is a reliable, high data-rate link to provide remote connectivity over the Sea surface. Trade vessels approaching seaports need to be connected well in advance to reduce ship lane queuing time. With digitization of oil and gas platforms over the Sea, IoT devices are installed to provide smart production operations. IoT improves energy efficiency, remote monitoring, security, and control of physical assets on offshore platforms [8; 9]. However, the conventional over the sea communication techniques are not appropriate for such sophisticated actions on remote offshore platforms. In tropical regions of the World, occurrence of Evaporation Duct (ED) layer over the sea is a common phenomenon. Wireless signal trapped in the ED can propagate beyond the horizon and cover vast distances with very less attenuation. In [10; 11; 12], Australian Institute of Marine Science (AIMS) has performed experiments at 10 GHz frequency band to establish long-range communication links utilizing ED. In addition, many articles are published on ED based measurements and predictions to establish a long-range radio link using ED [13; 14; 15]. Limited measurements in ED are also performed and path loss variations are predicted through machine learning algorithms [16; 17]. The climatology of ED and its percentage of occurrence is important for the signal propagation in ED. Therefore in [18], a new ED climatology measured within the Malaysian Sea region of South China Sea is presented. However, the average height of the evaporation duct was 12.42 m and its occurrence vary from 4 m to 20 m [18]. The authors conducted an experimental study in Malaysian region of South China Sea using ED climatology. The authors reported that the ED availability and capacity based on fade margin can be estimated correctly using path loss measurements [15]. Therefore, it is necessary to extend high-speed connectivity range between the seaports and the moving vessels with low altitude antennas. A reliable backhaul link via ED can provide high data rate connectivity to IoT based network on an offshore platform, cargo vessel, or cruise ships, as shown in Figure 1.  
Another advantage of propagating in ED is that we require low antenna height compared to conventional line of sight based backhaul links. Due to this fact, we require a low-cost infrastructure and low power to achieve beyond the horizon offshore IoT devices connectivity. The energy is trapped between the sea surface and the ED layer with very less attenuation and enhanced signal strength.