Data Processing System Design
The master radio at the REL is connected to a personal computer running custom software designed by TransLink. Efficient information transfer over the wireless link is accomplished via an ASCII-based data protocol developed specifically for the wireless system. Similar software runs on the field controller at each collection site. As the data arrives at TransLink it is logged and made available for real-time feeds. All incoming train movement data is timestamped and stored in a file indexed to the train event. Train event files are accessible from the World Wide Web using nothing more than a generic web browser or FTP client and are in a textual format for easy reading or computer analysis. In addition to archival data, users can link into the system from anywhere in the world and get a live data feed from the railroad sensors along the corridor. This functionality allows the corridor to become a data collection and test system for researchers removed from College Station and Texas A&M University. Several standard Internet communication protocols are supported (UDP and TCP). A user can even link into the system with a server push capable browser (Netscape) and get a real-time printout of data as it arrives at the lab. TransLink master software also acts as a watchdog or early warning device for the sensor network. Battery voltages and heartbeat messages are monitored for signs of system degradation. Maintenance personnel can be dispatched to the site before performance issues become critical. The master station software also can control or change the operation of the data collection station. The master can set field unit’s heartbeat rate, provide a programmed pinging or interrogation of a site and dynamically set the sense direction of unidirectional detectors. The latter service is used in conjunction with the George Bush unidirectional sensor to change the system’s sense direction after a northbound train is detected at F. M. 2818. After the train departs the George Bush detector the master sends a command to change the sensor’s direction for southbound movements. This capability can easily be expanded to automatically control other network devices such as a changeable message sign, or provide additional train arrival information to downstream traffic signal controllers.