The Communication Systems
Punctual or Balise-Based Communication Systems
These systems using balises rely on the transmission of information between two points close to each other. These short range communications are locally valid only in the transmission area of the balise. Such systems operate at frequency range from few kHz to several GHz for applications, such as vehicle identification, localization, integrity control or embedded control automation. For instance, ERTMS/ETCS system (level 1) relies on Eurobalise operating at 27 MHz.
Track circuits are electrical circuits obtained by isolating a section of track known as “Block”, used to detect the presence of a train, transmit side signals on trains as well as maximum authorized speed instructions, the next speed limit and the distance to this limitation.
Continuous Communication Systems Using Magnetic Coupling
Although gradually replaced by radio, these systems are still widely used. The core technology consists of a two-wire line. The electric current flowing in the wires induces a magnetic field which allows the continuous transmission of information detected by a magnetic antenna on board the train. They are economical but are subject to limitations, such as low useful bandwidth and poor Signal-to-Noise Ratio (SNR). The wires can be crossed regularly or not. These systems are widely used for automatic metros.