Owing to the growth of Internet of Things (IoT) technologies, the scale of issues and applications has increased in various areas. For better network connectivity, many studies have been conducted to determine the optimal power consumption strategies to increase the lifetime of each node [1]. With IoT technologies, a massive number of nodes equipped with communication devices and sensors require access to the internet and long-distance communication with limited energy.

Recently, data control and analysis of ships have been required to improve efficiency and safety. Data-driven management in a ship increasingly needs a networking solution that should satisfy the requirements of a ship. Passenger and non-passenger ships of 3000 gross tonnages and upwards constructed on or after July 1, 2002, must carry voyage data recorders (VDRs) to assist in accident investigations under regulations adopted in 2000, which entered into force on July 1, 2002 [2]. The VDR is a data recording system designed for all vessels required to comply with the IMO's International Convention Safety of Life at Sea (SOLAS) Requirements (IMO Res. A. 861 (20)) to collect data from various sensors onboard a vessel [3].

New challenges arise from maintaining a stable connection in a ship for IoT-based data-driven management while reducing energy consumption and extending communication coverage. Therefore, there have been limitations in the application of legacy short-distance wireless communication methods, such as Wi-Fi and Bluetooth. To satisfy the requirements of IoT networking, many studies on low-power wide area networks (LPWAN) have been actively conducted. As a result, several approaches, such as LoRaWAN, Sigfox, narrowband Internet of Things (NB-IoT), and long-term evolution (LTE) machine-to-machine (M2M) (LTE-M), are commercially available.

LoRaWAN [4]-[5] is a promising candidate for use in many applications in ships. Figure 1 shows an example of the LoRaWAN network implementation for data-driven management in a ship. This paper focuses on presenting suitable standard protocols as IoT solutions for data-driven management in a ship and proposes an application strategy that considers these requirements.

Figure 1: 
LoRaWAN network architecture

This paper is organized as follows: Section 2 explains the applicable solutions for IoT in a ship. In Section 3, the IoT strategy for ships is described. In Section 4, candidate technologies are compared and discussed to propose a more suitable onboard IoT technology. Finally, concluding remarks are presented in Section 5.

Wireless communication technologies proposed for IoT are classified into licensed and unlicensed band technologies. The first category includes the LoRaWAN and Sigfox, and the second category includes NB-IoT and LTE-M [6].

Table 1 presents the features of several LPWAN technologies that consider the best solution for data-driven management of a ship.

Regarding the data rate requirement, power efficiency, and communication coverage, Figure 2 shows a comparison of the features of each technology. NB-IoT and Sigfox show almost the same performance levels, whereas LTE-M and LoRaWAN technologies show superior overall performance. Although LTE-M supports the highest data rate, its performance is inferior to that of the other technologies in terms of power efficiency. The supported data rate of LoRaWAN is lower than that of LTE-M. However, it satisfies the interface requirements for VDR, such as IEC 61162-1 and IEC 61162-2. In terms of power efficiency, it exhibits excellent performance, which makes it suitable for IoT applications.

Figure 2: 
LoRaWAN network architecture

Although there are tradeoffs between LTE-M and LoRaWAN in terms of data speed and power efficiency, LoRaWAN can be said to be a more suitable technology for onboard IoT, considering the communication bands of LoRaWAN and LTE-M and the in-ship environment. IoT communication methods with unlicensed spectra can conflict with other business flows with respect to channel collisions [9]. However, unlicensed band communication technologies within a ship are relatively free from the problem of collisions between heterogeneous communication technologies.

Potential use cases in ships using LoRaWAN are as follows: in domestic use cases, smart leakage detectors of gas and water using LoRaWAN have been installed in cities such as Seoul, Busan, and Daegu. Germany and Switzerland applied LoRaWAN to monitor containers at ports. By analyzing these application cases, data-based vessel management will become possible by applying LoRaWAN to the part that collects and monitors the ship's engine system or various navigation information.

This study analyzes several promising IoT technologies for data-driven enhancement in ships. Considering requirements such as the IMO regulations, data rate, power efficiency, cost reduction, etc., and the onboard communication environment, LoRaWAN is suitable technology for onboard IoT. Because the LoRaWAN protocol has been applied in various areas and meets the requirements for safety and efficiency, it can easily be adopted in the onboard IoT strategy.