## 1 Introduction
This interference can lead to an increase in errors and collisions among AIS messages, resulting in unreliable maritime communication and unnecessary delays. Therefore, the standard recommends that when operating VDES in duplex mode co-located with AIS, there should be sufficient isolation between the AIS receiver and VDE transceiver to protect the AIS function from interference. It also suggests implementing a mechanism to synchronize VDE with AIS and ASM. However, the standard does not specify a particular methodology for achieving these requirements. To reduce collisions of AIS messages in coastal areas, various studies have been conducted previously. [PERSON] et al. proposed an improved version of the self-organized TDMA-based medium access control (MAC) protocol to reduce the collision probability of ASM channels during data transmission in VDES [25]. This approach aims to minimize interference by optimizing slot allocation. However, it has a limitation in terms of compatibility with AIS. [PERSON] et al. introduced a collision feedback-based MAC protocol, which attempts retransmission after delaying data transmission for a certain period when a collision is detected by the transmitting station [26]. However, this approach results in long delays and resource wastage due to repeated retransmissions. [PERSON] et al. proposed a feedback-based MAC protocol that employs the concept of cognitive radio to reduce collisions in dynamic maritime environments [27]. However, due to the unpredictable characteristic of AIS, which allocates resources and transmits messages in a self-organized TDMA (SOTDMA), collisions between VDES message transmissions among various ship and shore stations remain a challenging issue. In this paper, we propose a slot occupancy-based collision avoidance algorithm (SOCA) for a VDES network in the MIoT. SOCA is designed to mitigate the impact of interference caused by transmissions of AIS messages on transmissions of VDE-TER data in coastal areas. For this purpose, unlike the existing VDES, SOCA estimates transmission intervals of AIS messages for neighboring stations and updates the expected slot occupancy probabilities of slots in the VDES frame in real time. This allows ship stations to adaptively allocate slots, considering the dynamic changes in the surrounding maritime environment. SOCA includes four steps: (1) construction of the neighbor information table (NIT) and VDES frame maps, (2) construction of the candidate slot list, (3) TDMA channel selection, and (4) slot selection for collision avoidance. In the first step, the ship station constructs the neighbor information table and the VDES frame maps by monitoring VDES channels. The neighbor information table includes the navigational-related information. The VDES frame maps provides transmission schedules of the ship station and its neighboring stations. In the second step, the ship station constructs the candidate slot list of VDE-TER channels and classifies the candidate slots into interference and non-interference slots. In the TDMA channel selection, it selects the TDMA channel that minimizes the impact of VDE-TER data transmission on AIS message transmission. In the collision avoidance slot selection, the ship station selects candidate slots on the chosen TDMA channel that have a low probability of being used by itself or neighboring stations for transmitting AIS messages. To verify the superiority of SOCA, we conducted an experimental simulation. The simulation results demonstrated that SOCA is 13.58%, 11.50%, 33.60%, and 22.64% superior to the existing VDES in aggregate throughput, average latency, collision ratio, and packet delivery ratio, respectively. The remainder of this paper is organized as follows: Section 2 provides the overview of VDES and discusses the related works. Section 3 describes a design of SOCA in detail. Section 4 shows the simulation configuration and results. Finally, we conclude this paper in Section 5.