Home Engineering Broadband Wireless Communications for Railway Applications: For Onboard Internet Access and Other Applications
The Needs for Operational Applications
The operational applications relying on wireless communications can be divided into three main categories:
The Communication and Signaling Systems
The Different Strategies for Signaling Applications
A large number of techniques and strategies for signaling applications are deployed around the world. They all have the same basic objective: to keep a safe distance between trains. This safe distance can be maintained by measuring the current train position, its relative velocity to other trains and the other trains locations and directions of movement in the same area. All these data are continuously transmitted to other trains via wireless links. These continuous informations about trains’ close area allow to reduce inter-train intervals and thus increase traffic capacity without infrastructure investments.
Several such signaling systems are deployed depending on country: the Communication Based Train Control (CBTC), the Advanced Train Control System (ATCS), the Command, Control and Communication System (C3S), the Incremental Train Control System (ITCS), the Positive Train Control (PTC), the Positive Train Separation (PTS) or the European Train Control System (ETCS). The standard IEEE 1474 establishes the performance and functional requirements for a CBTC system .
The main operational functions, often linked to each others, can be identified below:
A CBTC or an ETCS system is described as an ATC system using high resolution train location determination; continuous, high-capacity, bidirectional train- to-wayside data communications; and train-borne and wayside processors capable of implementing ATP functions, and optional ATO and ATS functions . CBTC applications include the train localization, the train-to-ground transmission and all the communications between the computers in the train and the ground computers .
Safety-critical applications generally rely on low throughput (10-100 kbps) but require a high availability (at least 99.999 % of the time) and high levels of robustness and reliability (typically a packet error rates of 10-3 for 200 ko length packets) . Furthermore, KPI have to be checked regardless of the mobility conditions: handover times below 10 ms, time of communication establishment, etc. All these KPI are described in the IEEE 1474 standard .
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