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BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to systems for informing users of urban public
transport about the real positions at each instant of the transport
vehicles that they are considering taking.
2. The Prior Art
The vehicles concerned in this case are more particularly self-propelled
surface urban public transport vehicles and they are referred to below by
the word "buses".
It is recalled that in general it is not possible to predict exactly the
instants at which the buses serving a given line in an urban transport
network will serve each of the bus stops or "stops" of the line.
Although the instants at which the various buses leave the departure depot
of the line can be determined accurately, it is not possible to know in
advance what difficulties each bus will encounter as it travels along the
corresponding line, essentially because of the unpredictable formation of
more or less dense "holdups" along the line that may slow traffic down or
even stop it temporarily.
Thus, in general, users going to one of the various stops of the line for
the purpose of taking one of the buses serving it do not know how long
they will have to wait for the next bus to arrive.
They are therefore reduced to waiting for the next bus to arrive without
knowing whether their wait will be short or otherwise.
This ignorance constitutes a serious drawback for surface urban public
transport.
For fear of being obliged to wait a long time for a bus, which time may
reach or even exceed quarter of an hour, and may sometimes take place
under conditions of relative discomfort, e.g. standing and exposed to bad
weather, numerous potential users use some other form of transport, such
as an underground railway or a taxi, while regretting that they cannot
benefit from the advantages of surface transport such as a pleasant trip
associated with a cheap fare.
To remedy this drawback, proposals have already been for certain bus stops
to display information relating to the waiting time expected before the
next bus arrives.
That constitutes real progress.
However, to obtain such information, a user must actually go to a bus stop
that has been improved in that way.
The information then acquired concerning the waiting time for the next bus
is certainly advantageous in that it helps the user to be patient if the
time is long.
However it loses much of its advantage since the user still has practically
no opportunity of avoiding wasting time, since the range of activities
that a user can undertake on the spot is generally extremely limited.
To remedy that new drawback, proposals have already been made to made
portable appliances available to the users of buses in a network, the
appliances including, inter alia, means for displaying the waiting times
associated with buses that can be taken (see document EP-A-0 451 756).
That concept is advantageous.
However, in the implementations proposed, each appliance is associated with
a single bus stop, such that the problem of informing the user is solved
in part only.
Thus, the portable appliance enables the user to be informed remotely about
the waiting time for buses at the usual bus stop from which the user makes
bus trips, which bus stop is generally close to home, assuming that the
appliance is associated with that bus stop.
However, the appliance is incapable of giving any information about the
waiting times for buses serving other bus stops in the network.
Unfortunately, it is often for a user's return journey that the information
in question would be the most useful, in particular such information would
enable a user to spend a few more minutes performing activities away from
home, e.g. examining goods on sale in a shop, with such examination
possibly also being associated with consulting a specialist.
In addition to the above limitation on performance due to the fact that
each appliance is associated with a single bus stop, information systems
that have been proposed in the past also suffer from the drawback of being
of complex organisation, and therefore slow, thus making it difficult to
update the displayed information accurately, with this being for reasons
that are explained below.
In said systems, the information transmitted over an electromagnetic path
and made use of by bus stops and by portable appliances associated with
said stops is the same, and it is generated by a common facility required
to serve all of the various stops in the network in question, such that
each item of data is associated with an encoded address representative of
one of the stops.
The receivers included respectively in a given bus stop and in the
appliances associated with said bus stop are therefore of the same type,
with the main difference between these two receivers lying in that one of
them is fixed while the other one is portable.
The addressed items of information in question relate in particular to the
approximate waiting times for the two "approaching" buses expected at the
stop in question: the fixed or portable receivers located at said bus stop
or in the vicinity thereof then merely decode and display those waiting
times.
That kind of organization constitutes considerable overhead since it
requires:
a very large number of different signals to be transmitted in succession
over the electromagnetic path, which number is theoretically equal to the
total number N of stops included throughout the network in question; and
for each signal "addressed" to a given stop, a large number P of
constituent information units (generally "binary digits" or "bits"), each
signal being required to provide, for example, sufficient data to identify
the waiting times for the next two buses expected at the stop in question.
The total number NP of information units to be transmitted over the
electromagnetic path in known solutions is therefore very high, and this
presents the drawback of requiring a long duration or a high data rate for
transmitting all of the information useful to the network.
The long duration means a long period before the transmission is renewed,
which transmission is preferably renewed cyclically: a result of the
length of this period is a long overall response time, and thus
information for display may be updated very late, and this can make the
system unusable in practice if the observed delays reach or exceed one
minute.
A high data rate means that it is difficult for the transmission considered
herein to make use of the sidebands left available by urban radiotelephone
transmissions, since said sidebands are too narrow for excessively high
rates of transmission.
SUMMARY OF THE INVENTION
A particular object of the invention is to remedy the above drawbacks, and
in particular:
to propose "universal" portable appliances, i.e. appliances capable of
selecting and displaying bus waiting times corresponding to any stop in
the network under consideration; and
to do that while greatly reducing the number of information units required
to make up all of the useful information signals of the network, and
thereby firstly reducing the duration of electromagnetic transmission of
the information and thus the overall response time that stems therefrom,
and secondly reducing the bandwidth required for the transmission
channels.
To this end, according to the invention, information systems of the kind in
question still comprise, firstly a management facility including means for
receiving data identifying the instantaneous positions of the various
buses travelling over the various lines of the network, means for
responding to said data by generating electrical information signals
concerning said positions, and means for transmitting said signals over an
electromagnetic path, and secondly a plurality of receivers, including
portable receivers, each receiver having means for receiving said signals
and for selecting from them those that have a relationship with a given
stop, and means responding to the signals selected in this way by
displaying information relating to the waiting times for buses at said
stop, and they are essentially characterized in that firstly each of the
electrical information signals transmitted by the electromagnetic path is
associated with a given bus and is tied to the distance between said bus
and a stop of the corresponding line, and in that, secondly, the portable
receivers are in the form of appliances comprising firstly interrogation
means suitable for actuation by users and capable of identifying any given
stop of the network, and secondly means suitable for causing the above
electrical signals to be selected in response to said interrogations and
with the help of signals selected in this way successively to operate
means for calculating the waiting times to be displayed, and means for
displaying said times.
In preferred embodiments, use is also made of one and/or the other of the
following dispositions:
the signals emitted via the electromagnetic path form a signal sequence
that is transmitted cyclically, and each portable appliance includes
memory means designed to record the data relating to the complete
transmission cycle preceding each instant so that the data corresponding
to any particular interrogation can be made available instantly as soon as
said interrogation has been performed; and
the signals transmitted by the electromagnetic path are made secret by
suitable encrypting and the portable receiver appliances include means for
decrypting at least some of said signals.
The invention also provides the portable receiver appliances included in
the above information systems.
Apart from the main dispositions explained above, the invention further
includes certain other dispositions that are preferably used
simultaneously therewith and that are explained in greater detail below.
Preferred embodiments of the invention are described below with reference
to the accompanying drawing, naturally in non-limiting manner.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 of the drawing is a highly diagrammatic fragmentary map of a bus
network together with an installation for informing users of buses of the
network, which installation is set up in accordance with the invention.
FIG. 2 is a diagram of a portable receiver appliance included in such an
installation.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The portion of bus network shown in FIG. 1 shows two lines of the network,
given respective references a and b, and each line having two
opposite-direction "paths" or "parts" (respectively a.sub.1 & a.sub.2 ;
and b.sub.1 & b.sub.2).
By way of example, path b.sub.1 of line b extends from a departure depot A
to an arrival depot E and includes three intermediate bus stops or "stops"
1 more particularly referenced herein by the letters B, C, and D.
Naturally, in reality, the number N of stops corresponding to each bus line
is much greater than three, and generally of the order of several tens.
The buses serving the various lines of the network are represented by small
triangles 2 pointing in their travel directions.
Here again, the number n of buses serving each line has been greatly
reduced for reasons of clarity.
However the number n of buses is always much less than the number N of
stops served.
Rectangle 3 designates a central station for managing the network.
Means represented diagrammatically by dashed lines 4 are provided for
generating and conveying to the station 3 information i enabling the real
positions of the various buses 2 at each instant to be identified.
Each item of information i comprises an "address" .alpha. allocated to a
bus under consideration, which address itself includes data suitable for
identifying the "path" being followed by the bus.
These means are implemented in any appropriate manner.
For example, they may be implemented by telephone messages sent by the bus
drivers to the station 3.
However, it is generally preferred to adopt automatic means that do not
require any intervention on the part of the bus drivers and that make use
of radio links between transmitters mounted on said buses and the station
3.
The station 3 includes memory means in which data is recorded enabling the
various lines of the network to be identified and also enabling the
various stops 1 of each of the lines to be identified.
The station 3 also includes calculation means capable, at each instant, of
comparing each item of information i suitable for identifying the position
of a given bus 2 of address .alpha. with the data stored in the memory
means so as to generate an electrical signal s representing the distance
between said bus 2 and the "next" stop 1 that is to be served by the bus.
All of the electrical signals s as generated in this way are sent from the
station 3 to a transmitter 6 that includes a transmit antenna 7 from which
the electrical signals are transmitted into space in the form of
electromagnetic waves.
These waves are represented by dashed lines 8 in FIGS. 1 and 2.
A certain number of receivers are organized to receive and make use of the
signals 8 transmitted in this way.
Some of the receivers 9 may be fixed and be intended for installing in the
stops 1.
Other receivers 10 are portable and are made available to users.
Whereas the fixed receivers 9 are associated solely with informing users at
the stops 1 that are fitted with said receivers, to tell the users about
the waiting times for the next buses at those stops, the receivers 10 are
more universal, being organized to inform users about the waiting times
for the buses approaching any of the stops in the network, with this being
done in response to appropriate interrogations by the users.
Each portable receiver 10 comprises:
an antenna 11 associated with a receiver device 12 for receiving
electromagnetic signals;
a circuit 13 for decoding these signals;
a memory circuit 14;
a microprocessor 15;
a data display device 16, including, in particular, a video screen;
an interrogation device 17, generally comprising a keypad; and
a source of electricity 18, generally constituted by a battery.
These components are associated in such a manner as to make the following
operation possible.
A user U (FIG. 1) possessing an appliance 10 desires to know the waiting
times for the buses approaching a stop 1 which is assumed in this case to
be the stop D on path b.sub.1 above.
The user presses in succession keys of the keypad 17 (FIG. 2) corresponding
to the characters b, 1, and D.
This simple interrogation immediately causes the screen 16 to display
information relating to the waiting times at stop D for the next two buses
expected to serve that stop.
This display may be achieved in any appropriate manner, e.g. by displaying
the times in question in the clear, as digits representing minutes and
seconds.
To obtain such a result, the microprocessor 15 is organized to respond to
the above-defined interrogation "b1D" by automatically selecting from the
signals 8 received by its antenna 11 those signals that correspond to the
two buses serving path b.sub.1 and to be found immediately upstream from
stop D.
The information actually received in this respect from the transmitter 6
corresponds to the distances between those two buses and the stop D.
In an advantageous variant, the distances that can be deduced from said
received information may be the "master distances" between each bus and
its departure depot A: the distance between each bus and the "next stop" D
served by that bus is easily calculated from said master distance by
subtracting therefrom a constant which is the fixed distance between the
departure depot and the "next stop" under consideration.
The calculation means included in the microprocessor 15 are designed to
deduce the waiting times to be displayed from the above distances.
To this end, they make use of a parameter tied to the average speed of
progress of buses along the path under consideration, which parameter may
be a constant that is determined once and forever or it may be a variable
that constitutes a closer approximation to reality and that can be
determined in any appropriate manner.
It should be observed that the interrogation of the appliance 10 is not
limited in any way to finding out about stop D on line b.
On the contrary, such consultation can relate to any of the various stops 1
included on the various lines of the network.
It should also be observed that in preferred embodiments, the total number
of information units contained in the information transmitted over the
electromagnetic path from the transmitter 6 and referenced 8 in the
drawing is relatively small.
This number is no longer tied to the total number N of stops included in
the various lines of the network, but is tied to the number n of buses 2
travelling along said lines, which number is generally at least three or
four times smaller than the number N.
In addition, the information tied to each of the buses 2 under
consideration relates solely to its own position, which may be defined by
the distance to the following stop to be served on the line on which the
bus is travelling or by the distance from the departure depot of the line,
as in the variant explained above.
Such information can be expressed by a number p of units of information
that is smaller than the number P required for identifying the positions
of a plurality of buses relative to a given stop.
It follows from the above that the total number np of units of information
that need to be transmitted over the electromagnetic path is much less in
this case than in the context of previously known information systems,
thereby making it possible to reduce the total time for transmitting all
of the information, and thus to reduce the cycle period of the
information: the information is preferably transmitted continuously and
renewed without interruption.
The resulting reduction in said period can be a deciding factor in
practical use of information systems of the kind under consideration.
Thus, if the updating period for information to be displayed is 1 minute,
then certain users may find that unacceptable, whereas if said period has,
on the contrary, a duration of only 10 seconds, the same users may find
that quite satisfactory.
To further improve the response time of information systems under
consideration, use may advantageously also be made of the following
improvement: the portable appliance includes memory means capable of
restoring all of the data concerning any cycle immediately preceding any
given reception instant ("First In First Out" type memories); using such
memory means, it is possible at any instant to recover from the recorded
data, the data which corresponds to the interrogation made by the user at
that instant, without there being any need to wait for the next
transmission of said data from the transmitter 6.
To reserve useful reception of the signals 8 to portable receiver
appliances 10 that are specially authorized, it is possible to make the
signals secret by suitable encrypting or encoding, and to cause said
appliances to include special means for decrypting at least some of the
signals encrypted in this way, with decrypting itself possibly being
restricted to signals concerning a single stop in a given network, or to a
plurality of said stops, or on the contrary extending to all of said
stops.
As a result, regardless of the implementation adopted, a system is obtained
enabling bus users to be informed on the waiting times for the buses, and
the structure, operation, and advantages of such systems can be seen
sufficiently clearly from the above.
Naturally, and as can already been seen from the above, the invention is
not limited in any way to those applications and embodiments that are
particularly described; on the contrary, it extends to all variants.
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