Railway switches and signals – Block-signal systems – Automatic
Patent
1993-12-15
1996-03-05
Le, Mark T.
Railway switches and signals
Block-signal systems
Automatic
246 8, 246 63C, B61L 300
Patent
active
054960037
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns the field of information transmission between the ground and moving objects. More specifically, it concerns, but is not limited to, the transmission of information between the ground and moving railway objects, pulling engines, cars, and train components.
Prior art encompasses various means allowing such communications. These means may be categorized according to various criteria, one of these criteria being the range of the area they make it possible to cover.
Some of these means have a localized zone of coverage; that is, an area restricted to several tens of centimeters or meters. Accordingly, they cannot be used when the moving object travels in certain determinate locations. Some of these means are unidirectional, such as conventional light signalling or its repetition in the car by means of metal contact or inductive loop. More recent techniques, such as ultrahigh frequencies or optics (infrared) permit the establishment of two-directional links between a moving object and a "beacon" having a high rate of output.
Other means have a larger coverage area. These means are basically radioelectrical. The transceiver with which the moving object maintains information exchanges (which, in some cases, are unidirectional) is found either in space (telecommunications satellites) or on the ground. In this latter case, there is, on an extraordinary basis, a station having a vast coverage area and, most often, by virtue of the frequency band used, a series of fixed stations whose range is limited to several kilometers, these stations thus being organized into a network. The informational output of these radio links is normally restricted by the relative narrowness of the available frequency band. More restricted yet than the overall output, the output per moving object is limited by the number of moving objects located in the coverage zone, among which the available output is shared.
A third category of communications means has a coverage area which is neither localized nor extended to a relative vast zone in its two dimensions. These means have a coverage zone which is, so to speak, linear, in order to cover a section of highway or railway. The means used might include a radiating cable, a loss waveguide, or even, in the case of the railroad, the rails themselves. However, in this instance, transmission is unidirectional.
The disadvantages of localized transmissions have long resided in their unidirectional nature. Recent progress has made it possible to provide two-way transmissions having a high output rate and at low cost. There remain disadvantages tied to the narrowness of the coverage zone, and, first of all, the impossibility of establishing contact with a moving object halted outside the coverage area. This is particularly bothersome in the case of sending to a stopped train the authorization to continue its progress, since the level of stopping accuracy makes it difficult for an engineer to stop within the coverage area of a beacon, even if this area is indicated. In the second place, there is the difficulty involved in sending to a stopping train the authorization to resume speed, so as to make traffic flow more smoothly and to save energy, except by multiplying the number of beacons. In the third place, the overall output rate available for ensuring transmission with a moving object is proportional not only to the output rate of the link once it is established, but also to the proportion of the time during which said link is established, i.e., to the ratio between the length of the area covered by a localized link and the spacing separating two successive coverage zones. Fourthly, even if the average output rate is sufficient, its discontinuous nature in time dictates that, for service such as the telephone, which requires continuity a priori, there be temporary storage, and thus a high apparent response time.
The disadvantages attaching to transmissions over a vast coverage area are basically of two kinds. First, the obligation to share among all of the moving objects s
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Le Mark T.
Societe Nationale Des Chemins De Fer Francais
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