## 1 Introduction  
Today, the use of mobile nodes such as autonomous underwater vehicles (AUVs) for underwater exploration and cluster searches is increasing [1; 2; 3]. To effectively coordinate AUVs involved in underwater tasks and transmit collected data to the surface station, an underwater wireless communication network is established by employing floating structures such as buoys [4; 5; 6]. Acoustic communication, preferred for its reliability in transmitting data over longer distances (ranging from hundreds of meters to tens of kilometers), is the main method employed, as opposed to radio frequency (RF) and optical communications [7; 8]. To extend network coverage beyond the communication range of a single buoy, deploying multiple buoys on the water surface allows AUVs to move from one buoy network to another. Buoys, serving as base stations (BSs) akin to terrestrial cellular networks, provide AUVs with network services, with such networks defined as BS-based underwater wireless acoustic networks (B-UWANs). Existing communication and network technologies for B-UWANs have been well developed, with established international standards [9; 10; 11]. The movement of an AUV between cells may result in temporary channel disconnections or data transmission interruptions. Furthermore, underwater acoustic communication often encounters frequent transmission failures caused by various interferences (e.g., vessel noises, sonar, or dolphins) and environmental conditions, including currents and sea temperature variations [12; 13]. Joining a new network under these environments can result in increased network overhead, transmission delays, and extended service unavailability. Therefore, it is necessary to establish measures that guarantee continuous quality of service (QoS), highlighting the need for integrating handover technology within B-UWANs [14]. While studies targeting underwater networks have mainly focused on fixed network topologies, such as underwater acoustic sensor networks, recent trends have shifted towards exploring mobile underwater communication networks, with a particular emphasis on media access control and routing technologies [15; 16; 17; 18; 19; 20; 21]. A review of several studies concerning underwater handover over the past five years indicates that this field is still in its early stages, despite its necessity. Noteworthy research includes machine learning-based handover prediction [22; 23], along with the design of handover technologies using underwater RF or optical communication [24; 25]. In addition, studies have proposed methods for tracking and predicting the paths of mobile nodes in underwater cellular networks to enhance handover performance [26], as well as addressing the necessity of handover in underwater Internet of Things (IoT) environments [27]. As with the existing handover technologies, underwater handover is also broadly categorized into horizontal and vertical handovers [28; 29]. However, underwater communication candidates other than acoustic communication (e.g., RF and optical communications) pose challenges in AUV-based networks characterized by relatively high mobility, attributable to severe communication losses and distance constraints. Accordingly, handover technology for B-UWANs primarily focuses on horizontal handover using exclusively acoustic communication. In contrast to terrestrial handover technology, the development of underwater handover needs to consider the following distinctive factors:  
* Since the underwater acoustic frequency band is an open spectrum, it is strongly susceptible to a variety of interferences. Most of them are uncontrollable, with unpredictable locations, operating frequencies, times of occurrence, and durations [30; 31; 32]. Consequently, frequent communication failures during handovers can result in poor spectrum utilization, high energy consumption, and increasing message overheads. * The propagation delay of approximately 1 s for a 1.5-km transmission using underwater acoustic signals can significantly boost handover delay [33].