Needs for wireless transmissions in the railway environment are quite growing since several years. But it is important to distinguish the different needs depending on intended applications, required throughputs and railway sectors.
The Wireless Communication Needs Depending on Intended Applications
Two main kinds of applications can be identified:
- • The operational services, that include:
- - The safety-related applications for control and command of trains and signaling, also called “operation control system”, aiming to control and monitor the traffic: it includes the control and command of automations, the remote control of trains, the obstacle detection, the driving assistance or the reversal of the trains for metros without driver . It is a safety application that must meet security requirements;
- - The robust operational voice communication systems: these systems allow trains to communicate with the rail traffic control centers, but also trains drivers, rail traffic and maintenance agents to communicate with each others in conference mode (group calls). It can be noted that some National Safety Administration (e.g. Sweden) also characterize voice communication systems as safety-related, in the sense their unavailability is considered an unacceptable risk for safety;
- - The image transmission for video surveillance (CCTV), the TV-platform or Television Semi-Embarquee (TVSE) and the Public Announcement (PA): the first one is a system of cameras disposed in the trains and image transmission to the control center. The second one is a system of cameras disposed on the platform and image transmission to the train driver. TV-platform is used for metro applications, TVSE systems are currently developed for the railway applications. All these systems perform remote monitoring to ensure the conditions of safety and exist mainly for metro applications;
- - The maintenance and diagnosis: these two systems allow the monitoring of infrastructure and rolling-stock. Several systems can be developed, such as track monitoring systems and health monitoring systems;
- - The information to passengers: it consists of information transmission from the ground to passengers in trains, such as train related environment information and train schedule.
- • The services to passengers: it comprises mainly the Internet access on board trains, but also infotainment (information + entertainment), Video on Demand (VoD), video streaming and Passenger Information System (PIS).
These applications have access to appropriate services and traffic classes and can even share a same medium. CCTV was initially classified as a non-critical application, that is related to embedded surveillance. However, video is also used more recently for remote control of trains or for other safety-related applications for control of trains, such as reversal of metro trains, and driverless metro.