###### Abstract
This connection export equipment has an \"outdoor unit (ODU) + indoor unit (IDU) + small cell\" hardware structure and is considered to be a terminal device with the following functions: (1) the \"ODU\" is an UE equipment that handles handovers and communications involving external SBSs; (2) the \"IDU\" is a connection device that provides Wi-Fi access to users in a car; and (3) the \"small cell\" is responsible for establishing connections with the UEs (of any telecoms operator) within a car (excluding the ODU), assumed to be equipped with a global positioning system (GPS) device with high positioning accuracy and assumed to provide coverage for a single car. For the sake of brevity, this connection export equipment is subsequently referred to as the OIS. All connected devices in a car communicate with external networks through the OIS, which performs handovers while the car is moving by selecting suitable SBSs from external networks. It is assumed that the OIS can maintain mutual communications with the SBSs deployed by all telecom operators. A new handover selection algorithm (applied to the OIS) is proposed in this study. This algorithm utilizes rail paths to categorize SBSs that are deployed in the vicinity of the railway track, automatically regulates the size of each SBS's coverage area by considering their respective loads and defines several modes to effectively manage these loads. If a handover is necessary, the OIS utilizes positioning to locate SBSs suitable for the handover at the next evaluation time point; after which, it scores these SBSs to identify the best candidate and send a message to the currently connected SBS to transfer all returning transmission data to the selected SBS with the best score. After the OIS is handed over to the most suitable SBS, it can then directly receive the returning transmission data. This process is continually repeated while the car is moving. Due to the \"toss (OIS \(\rightarrow\) currently connected SBS) and catch (next suitable SBS \(\rightarrow\) OIS)\" nature of the data transfer process when observed from the OIS's perspective, we therefore named the proposed algorithm the \"toss-and-catch algorithm\", as shown in Figure 1. By applying this toss-and-catch approach to calculations, data sent to the current location can be effectively redirected to an upcoming location, thereby achieving non-interruptible handovers and reliable data transmission. The simulation results showed that, in most scenarios, the toss-and-catch algorithm outperformed other methods in terms of signal quality and handover connection performance. In a typical fading channel environment (e.g., Nakagami-1 fading), the toss-and-catch algorithm produced, on average, better results than the random SBS selection method with respect to signal quality (approximately 28% improvement), disconnection rate for handover connections (approximately 50% reduction), and processable load ratio (approximately 71% improvement). These positive results open up the possibility for fixed-rail transport operators to provide free connection services (via this connection platform), which would attract more people to use their transport services and create more business opportunities. We believe that this is a good communication transmission approach for fixed-rail mobile terminal equipment in 5G and even more advanced network environments. This research incorporates efficiency designs derived from multiple viewpoints, and its primary contributions are as follows:  
* Use of OIS movement paths to effectively categorize SBSs that may be encountered: The OIS can identify, in advance, the SBSs located close to its movement path and categorize them effectively to optimize their performance. We can then avoid unnecessary handovers and provide a firm foundation for the OIS to perform data transmissions. * Automatic adjustment of each SBS's coverage area and definition of modes: Based on their respective loads, the coverage area of each SBS is automatically adjusted and several modes are defined.