ASVMR: Adaptive Support-Vector-Machine-Based Routing Protocol in the Underwater Acoustic Sensor Network for Smart Ocean  
[PERSON]  
1 College of Information Science and Electronic Engineering, Zhejiang University, Hangzhou 310027, China; [EMAIL_ADDRESS] (S.Z. ); [EMAIL_ADDRESS] (L.X. )1 College of Information Science and Electronic Engineering, Zhejiang University, Hangzhou 310027, China; [EMAIL_ADDRESS] (S.  
As the critical infrastructure in the UIoT, the underwater acoustic sensor network (UASN) collects data from remote areas of the ocean in real time, enabling the acquisition of rich and accurate ocean data [6]. By deploying numerous sensor nodes under water, the UASN plays a crucial role in improving remote sensing capability, understanding the complex dynamics of the ocean, and assessing the impact on the environment. Deploying the UASN poses challenges due to the demanding environmental conditions and substantial deployment costs. First, the sound signal propagates much more slowly in the water, at approximately 1500 m/s, leading to noticeable latency in signal propagation. Second, some factors, such as water absorption, scattering, and underwater noise interference, limit the data transmission rate of the underwater acoustic signal. Third, the complexity and uncertainty of the underwater environment further increase the difficulty of underwater acoustic communication. Hence, underwater sensor nodes consume much more energy than their terrestrial counterparts when transmitting data of the same size [7]. In order to optimize energy utilization and enhance data transmission efficiency in the UASN, the design of an appropriate routing protocol is of paramount importance. This routing protocol should possess the flexibility to adapt to the dynamic underwater environment. Over the past decade, many routing protocols specifically tailored for the UASN have been proposed [8; 9; 10]. Traditional routing protocols, which are typically based on a fixed routing table or static network topology, are not suitable for the UASN due to the dynamic nature of the underwater environment and the limitations of underwater acoustic signal transmission. The use of traditional routing protocols in the UASN can result in significant propagation latency, data transmission rate limitations, and increased energy consumption by underwater sensor nodes. These limitations bring about the routing void, long packet delay, and data packet loss, which can significantly degrade the network performance. Typically, two categories of conventional routing protocols exist in the UASN, namely the location-aware routing protocol and the depth-aware routing protocol. For the location-aware routing protocol, it is assumed that the sensor nodes have the knowledge of the location information with the assistance of the node positioning technology. In the vector-based forwarding (VBF) protocol proposed in [11], data packets are forwarded in a virtual pipeline with a pre-defined radius. The virtual pipeline is specified by the routing vector from the location of the source node to the destination. Figure 1: The schematic of the UIoT. For the dense network, the VBF protocol effectively manages the network flooding area size to mitigate potential issues. However, in spare networks, the VBF protocol exhibits poor performance and fails to address routing voids. Hence, an enhanced VBF protocol, named hop-by-hop vector-based forwarding (HH-VBF), was proposed in [12]. The HH-VBF protocol employs the notion of a virtual routing pipe. This involves the utilization of an individual virtual pipeline for each forwarding node, and at each intermediate node, a directional choice is made based on its current location. Therefore, despite the limited number of neighboring nodes, the HH-VBF protocol can still find a data delivery path as long as a sensor node is available in the forwarding path within the communication range. However, the hop-by-hop nature introduces much more signaling overhead for the HH-VBF protocol.