Keywords mobile communications, train communications, railways
Start Date: 01-NOV-90 / Duration: 12 months
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The objective of the ERWIN exploratory action was to investigate the domain of fixed-to-mobile communications with particular emphasis on ground-to-train communications. These communications involve the railway operator's requirements, railway services offered to passengers, and passenger services such as telephone or mobile office services. Three communication segments have been investigated:
While the basic ground-to-train services involve all three segments, it has seemed appropriate to also consider services that will only use one of them, namely purely on-board services and track-side communications.
Two applications account for the bulk of the demand or have specific requirements which strongly affect the functional specifications: train control, which has specific requirements in terms of coverage and response time, and passenger telephone services, which demand a continuous coverage and a fairly high data-rate or bandwidth.
Of the several physical architectures considered for the on-board segment, wire vehicle highways with fibre and wire train highways are thought to be the best in the near-term.
For the ground-to-train segment, there was a strong wish to use an existing or emerging system. The most promising candidates appeared to be TETRA, which seems better adapted to a scenario where only data services (train control) and speech transmission with good communication quality for the driver would be offered, and GSM, which seems better adapted to a scenario where telephone services are offered to passengers as well. There are, however, technical problems to be overcome, and an adapted system might significantly differ from its original. Alternative solutions have therefore been investigated.
An attractive one is a radio link with a modulation and equalising scheme that is compatible with the very high speed of some trains, with a connectionless response time appropriate for an efficient train control system, a fast handover of connection-oriented (telephone) services that matches the demand for quickly rerouting from cell to cell a fairly large number of calls-in-progress, and with a bandwidth efficiency that enables the railways to offer their clients a good quality of service while making the best use of the allocated frequencies. Another appealing avenue has been identified as the emerging short-range micrograph communication technology. Yet another solution, of interest on low-traffic routes where a specific investment would not appear to be justified (or on other routes as a back-up), would be based on a coming generation of low-orbit communication satellites.
For ground communications, the workability of a number of longer-distance LANs and metropolitan area networks (MANs) in a railway environment have been assessed. However, in view of the moderate volume of traffic, current drop-and-insert PCM technology may suffice for most if not all ground communication requirements.
Critical communications have to be carried along with less critical ones, which may give rise to conflicting requirements. Two interesting approaches have been identified. Static scheduling analysis is applicable when resources access needs are known in advance: this is the case of most embedded systems, such as train control. Dynamic scheduling analysis is applicable where resource access needs cannot be precisely determined: this is the case of most open systems, such as passenger services.
Mr Patrice Bernard
CER - COMMUNITY OF
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tel: + 33/ 142856503
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CER - B - C
ASCOM-AUTOPHON SA - F - P
SECRE - F - P
TRIALOG INFORMATIQUE - F - P
TELETTRA SPA - I - P
SIEMENS-PLESSEY CONTROLS LTD - UK - P
ENA TELECOMUNICACIONES SA - E - P
ERWIN - 5650, December 1993
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html version of synopsis by Nick Cook