Select 1. System Introduction 2. System Configuration 3. System Specification 1. System Introduction The system is a train tunnel optic distribution system designed to remove shaded areas and provide quality service to subscribers by relaying BTS signals through train tunnels. It is a single system that saves cost by relaying real-time cellular signals. Since the system transmits signals via optic lines, it can relay BTS signals for long-distance transmission without damaging signal quality. The system provides two types of interfaces between the BTS and repeater. One is the RF method (relaying with the base station), and the other is the optic method (relaying via optic lines). The system allows for an efficient network configuration as it can use up to nine remotes per donor. Furthermore, since the system is designed to provide future CDMA2000 1C EV-DO services, network extension or additional installation is relatively easy.