EP0188925B1 - Method and arrangement for data transmission between moving vehicles on a road - Google Patents

Description

The invention relates to the transmission of data, without material support, between vehicles subject to travel on the same lane, in particular for the detection of the relative position of two successive vehicles and the transmission of the information necessary for the automatic control of one of the vehicles. The invention finds a particularly important, although not exclusive, application in public transport installations using vehicles of relatively low capacity (ten or twenty places for example), which can be coupled by means controlled electronically, so that the vehicles can be separated when passing over a divergent switch, then grouped according to a different arrangement.

It relates more particularly to a data transmission method without material support between vehicles subject to moving on a track, in particular for the detection of the relative position of two successive moving vehicles, according to which messages are transmitted to be transmitted, to from each vehicle in circulation, in the form of brief transmissions of bit sequences, by modulation of a microwave beam.

Such a method is known (GB-A-1 286 251), but with a view to transmission between road vehicles and in particular buses, that is to say in an environment different from the railway environment where the transmission of high-speed information presents problems that are difficult to solve. The rate of transmission faults (undetected error or absence of transmission) must be very low to be compatible with the requirements of security. The use of available material supports, such as usable transmission conductors (catenary, relay by ground transmission lines) of power, does not allow sufficient information transmission rates to be achieved for installations with automatic control, automatic separation and grouping of vehicles . At first glance, the use of transmission channels without material support seems to be excluded, due to the very variable nature of the environment and the risk of reflection, especially on the walls in sections in trenches or in tunnels and on vehicles in movement on a parallel track.

The invention aims to provide a method and a device for transmission by microwave, responding better than those previously used to the requirements of practice, in particular in that the risk of link failure is considerably reduced.

To this end, the invention notably proposes a data transmission method as defined by claim 1.

The number m is usually between 5 and 40. Each message being very brief, typically of an duration of an order of magnitude less than T / m, the probability of losing a message as a result of collisions between messages is very scaled down.

It can be provided to transmit the messages at a variable power according to the conditions encountered, for example by providing a nominal power and a reduced power. The nominal power is used only under conditions where high transmission security is required and under those where the attenuation is high.

The invention also proposes a data transmission device making it possible to implement the method defined above, according to claim 4.

The data processing means can comprise two microprocessors, one of which is assigned to the data the other to security data. The latter will advantageously be transmitted with coding for increased redundancy and error detection.

To limit the risks of message loss, the reception assembly preferably comprises several antennas arranged at different locations at the front of the vehicle. Two antennas are typically used, the distance of which is at least equal to ten times the wavelength of emission in air. Each antenna, generally made up of a horn, is associated with an amplification chain with frequency transposition.

• les Figures 1A et 1B montrent, respectivement depuis l'avant et en élévation, un véhicule d'installation de transport à laquelle est applicable l'invention;
• les Figures 2A, 2B et 2C sont des schémas destinés à faire apparaitre des opérations réalisables de façon automatique sur le réseau d'une installation mettant en oeuvre l'invention ;
• la Figure 3 est un synoptique de principe d'un dispositif suivant l'invention ;
• la Figure 4 est un diagramme temporel destiné à montrer la répartition dans le temps des émissions du dispositif de la Figure 3 ;
• les Figures 5 et 6 sont des synoptiques montrant respectivement un récepteur et un coupleur de réception utilisables dans le dispositif de la Figure 3.

The invention will be better understood on reading the following description of a device which constitutes a particular embodiment thereof given by way of non-limiting example. The description refers to the accompanying drawings, in which:

• Figures 1A and 1B show, respectively from the front and in elevation, a transport installation vehicle to which the invention is applicable;
• Figures 2A, 2B and 2C are diagrams intended to show operations that can be carried out automatically on the network of an installation implementing the invention;
• Figure 3 is a block diagram of a device according to the invention;
• Figure 4 is a time diagram intended to show the distribution in time of the emissions of the device of Figure 3;
• Figures 5 and 6 are block diagrams respectively showing a receiver and a reception coupler usable in the device of Figure 3.

Before describing a particular embodiment of the invention, it may be useful to give indications on a public transport installation to which it is likely to apply.

The installation may in particular comprise elementary transport units which can be grouped together in trains and which are fitted for this purpose with an electronically controlled coupling. The elementary unit can consist of an isolated vehicle, such as that shown in Figures 1A and 1B, or a doublet consisting of two vehicles connected by a mechanical coupling. Each vehicle has, for example, a capacity of ten seats.

The installation includes a network of fixed tracks fitted with switches and vehicle location devices. It is intended to allow operations of which simple versions are represented on Figures 2A, 2B and 2C in the particular case where vehicles departing from stations C and D must serve stations A and B.

Figures 2A and 2B show the meeting of two trains coming from two converging branches 10 c and 10 d to form only one train on a common trunk 10.

Figures 2B and 2C show the separation of vehicles when passing over a divergent switch 12 and then the grouping of vehicles into groups of the same destination on branches 10 a and 10 b . The vehicles are identified in the three figures by the assembly of letters identifying the departure station and the arrival station.

We see that this principle makes it possible to adapt the length of the train to transport demand and to operate a mesh network without breaking the load for the user and to maintain a high rate of passage, even during off-peak hours, the trains simply comprising a reduced number of vehicles.

For example, we can consider an installation in which the interval between trains can go down to 35 seconds, with a stop time of 15 seconds, the maximum speed being 60 km / h and the regrouping speed. and appointments that can range from 14 to 33 km / h depending on the configuration of the track.

With short vehicles, having a capacity of ten people, we can accept very small radii of curvature in switches, reducing the speed when passing over these switches.

The device which will now be described is intended in particular to allow the detection of a vehicle which will subsequently be described as a "target vehicle", by a vehicle which follows it, which will be called "the following vehicle", at a sufficiently large distance to ensure Security.

The device comprises, on each vehicle 14 (FIGS. 1A and 1B), a rear emission assembly and a reception assembly for the emissions originating from the target vehicle. The transmission takes place at microwave frequency, at a frequency greater than 300 MHz and which will generally be of the order of magnitude of the GHz. The link will advantageously be of the asynchronous type with a high-level protocol, such as the HDLC protocol. Zeros are automatically inserted to avoid the presence of an excessive number of consecutive "one". The coding is advantageously binary, of NRZ type. Among the NRZ codings, one can in particular use the NRZI coding, according to which the emission changes state when the bit to be transmitted is at zero while one does not change state when the bit to transmit is at one. The HDLC protocol and NRZI encoding in combination allow easy recovery of the clock.

The information transmitted may include a number identifying the section of track on which the vehicle is located, a vehicle identification number, an indication of the vehicle position, an indication of the vehicle speed, the number of vehicles contained in the train . All of this information, known as security, is transmitted after coding ensuring the required level of security. Additional information, which does not require the same level of security, can also be sent.

• comparaison du numéro du véhicule cible avec un numéro de consigne, transmis par la voie lorsque le véhicule suiveur entre sur le segment occupé par le véhicule cible,
• calcul de la distance entre le véhicule suiveur et le véhicule cible et de la vitesse relative de rapprochement.

The reception assembly is designed to perform in particular the following operations on the information received from the target vehicle:

• comparison of the target vehicle number with a setpoint number, transmitted by the track when the follower vehicle enters the segment occupied by the target vehicle,
• calculating the distance between the following vehicle and the target vehicle and the relative speed of reconciliation.

Each vehicle 14 will consequently comprise a transmission assembly and a reception assembly (FIG. 3) each connected to a "functional" microprocessor 16 which processes the information received to determine the control law to be applied during '' a grouping or an appointment and provides the sender with the information to be transmitted other than that relating to security. The transmitter and receiver assemblies are also connected to a "safe" microprocessor 18 which processes the information received to monitor the grouping or the meeting as well as the rowing and which supplies the transmitter with the information to be transmitted which relates to security and are coded to provide the required redundancy.

The transmitter assembly can be viewed as comprising an antenna 20, which will generally be a horn, a microwave source 22 and a transmission coupler 24 connected to a bus 26 for connection with the microprocessors by an interface not shown.

The lobe provided by the horn 20 has a width which constitutes a compromise between two contradictory requirements. This lobe must be wide enough for visibility to be ensured in all the relative positions that the target vehicle and the following vehicle can take, despite the movements of the vehicle (yaw and pitch) and of the lane structure, which has turns and slope breaks. However, the lobe must be thin enough for a vehicle traveling on a track other than the vehicles between which communication is to be established, in the same direction or in the opposite direction, not to disturb the microwave beam over the entire useful range; in addition, the beam must be thin enough so that the echoes on the walls are tolerable. This last condition will generally lead to placing the horn 20 along the vertical axis of symmetry, at a height of the order of 1.25 m for the usual sizes.

The angular width of the lobe in the vertical direction will naturally depend on the profile accepted for the track and the maximum pitch amplitude. In practice, an angular width of 20 ° will generally be satisfactory.

In the horizontal direction, the criteria to be taken into account to determine the minimum value will be the maximum yaw amplitude of the vehicle, the minimum radius of curvature of the track and the need for visibility when switching. The choice will be made according to each particular installation.

To improve reception, the receiver assembly advantageously comprises two channels, each having an antenna 28 and a receiver 30. The presence of two antennas makes it possible to achieve a variety of reception positions. The antennas 28 can in particular be located on either side of the vertical plane of symmetry of the vehicle 14 and at different heights (Figure 1A). The two chains are connected to the same microwave coupler 32 comprising an input member which either selects the most favorable channel, or performs the summation of the two channels.

• présence ou non dans une zone de regroupement,
• réception ou non d'une télécommande de regroupement avec le véhicule cible,
• détection ou non (par exemple par une liaison ultrasonore entre véhicules) de la présence d'un véhicule suiveur,
• reconnaissance de la présence ou non dans une zone d aiguillage divergent,
• réception ou non d'une télécommande d'activation.

The transmitter assembly is advantageously designed to be able to operate at several power levels, for example at zero power (extinction of the transmitter), at reduced power and at nominal power. The power level will be determined by an order developed locally based on the indications received from the track or other detection elements. The parameters taken into account may include the following:

• presence or not in a regrouping area,
• reception or not of a grouping remote control with the target vehicle,
• detection or not (for example by an ultrasonic link between vehicles) of the presence of a tracking vehicle,
• recognition of the presence or not in a divergent referral area,
• receipt or not of an activation remote control.

• 1. Regroupement entre véhicules, identifié par la reconnaissance d une zone de regroupement et la réception de la télécommande de regroupement.
• 2. Passage dans une zone d'aiguillage divergent avec possibilité de séparation des véhicules sur les deux branches de l'aiguillage, identifiée par la détection d'une présence arrière et la reconnaissance d'une zone d'aiguillage divergent (la configuration à puissance nominale rendant plus aisée le passage d un divergent grâce à la suppression de zones aveugles).
• 3. Mode dégradé de fonctionnement en cas de dislocation d'une rame et de reconfiguration automatique, la transmission à puissance nominale étant provoquée par télécommande.

The configuration at nominal power can in particular be carried out under the following conditions:

• 1. Grouping between vehicles, identified by the recognition of a grouping zone and the reception of the grouping remote control.
• 2. Passage in a divergent switch area with the possibility of separation of the vehicles on the two branches of the switch, identified by the detection of a rear presence and the recognition of a divergent switch area (the power configuration nominal making it easier for a divergent passage thanks to the elimination of blind zones).
• 3. Degraded mode of operation in the event of a train dislocation and automatic reconfiguration, the transmission at nominal power being caused by remote control.

The reduced power configuration will be chosen after a nominal grouping (switching from nominal power to reduced power) or after preparation of the element in the garage (switching from zero power to reduced power).

In general, the choice between the power levels (nominal or reduced) will be made taking into account two parameters, desired range and curvature of the track.

The transmitter assembly and the receiver assembly may consist of conventional components, but the implementation of which is carried out according to a process which reduces the risk and the consequences of collisions between messages.

One can in particular adopt a link at 9.9 GHz with amplitude modulation while nothing at a rate that can range from 20 Kbits per second to 2 Mbits per second.

The transmission microwave coupler 24, connected by an interface to the bus 26 of the microprocessors 16 and 18, has the function of encoding and formatting the data received from the microprocessors in coded form in NRZ, then of timing the sending of the packet d bits to the transmitter 22 according to an algorithm such that the transmission takes place at a high rate (typically 1 Mbit per second), repeatedly and randomly.

Encoding may in particular consist in passing the message from the NRZ code to the NRZI code. Formatting can in particular use the HDLC transmission protocol, which implies the automatic insertion of zeros. The association of NRZI encoding and the use of the HDLC protocol results in the presence of a transition each time the binary element (bit) to be transmitted is at zero and after five consecutive "one".

• un fanion de tête, permettant d effectuer la synchronisation d'horloge,
• le message proprement dit, de longueur indéterminée,
• une séquence de contrôle de trame, permettant la détection d'erreurs, occupant deux octets,
• un fanion de fin, occupant un octet.

In the case of the transmission of messages of at least 140 bits, including the coding bits associated with the security information, the message to be transmitted can have the following format:

• a head flag, allowing clock synchronization,
• the message itself, of indefinite length,
• a frame control sequence, allowing the detection of errors, occupying two bytes,
• an end flag, occupying one byte.

One can naturally, instead of using an asynchronous link with the HDLC protocol, adopt a two-phase synchronous transmission with repeating clock recovery patterns.

According to the invention, the transmission of the same message (occupying a maximum of 190 bits in the case envisaged here) is repeated several times during the same refresh period. This period will depend on the targeted performances, in particular those concerning the speed of regrouping. In a public transit installation with a high rate, it can range from a few milliseconds to a few tens of milliseconds.

As shown in Figure 4, the refresh period T is divided into m segments of the same duration T / m. Each of the messages to be transmitted, indicated in 34, must have a short duration in relation to each T / m segment. Each message is given a position in the segment which is random. By adopting a transmission rate greater than or equal to 1Mbit per second, it is easy to arrive at mp values exceeding 100 with a refresh period of 20 milliseconds, which reduces the probability of collisions to a very low value, even in the case a large number p of disruptive vehicles (that is to say vehicles which, at a given instant, by their position and by the power of their transmitter, can influence the receiver which receives the message).

The calculation makes it possible, in each particular case, to optimize the number m of segments in the refresh period, in particular as a function of the transmission rate, the length of the messages and the number of disruptive vehicles. Generally, m will be between 5 and 40.

The transmission microwave coupler will have a conventional constitution: it may include a microprocessor (INTEL 8044 for example) associated with a memory for storing all of the message to be transmitted and a memory containing the formatting and encoding program as well as the algorithm in form readable by the microprocessor. This coupler will be connected to the transmission bus by an interface constituted by a data exchange register, a command register written by the microprocessor of the coupler, a status register read by the microprocessor and an information register.

The microwave transmitter 22 comprises a source and an amplitude modulator which receives the message to be transmitted from the coupler 24 in the form of an NRZ signal.

The vehicle receiver assembly comprises, for each reception antenna, a complete chain 36 of which only one is shown in FIG. 5. Each chain receives the signal collected by the antenna, after transposition of frequencies by beating with a carrier provided by a local oscillator 38. The transposed frequency signal, at 70 MHz for example, is applied to a low noise preamplifier 40, followed by an amplifier 42 with automatic gain control by a signal supplied by a detector 44. The low signal frequency from the detector is applied to a video preamplifier 46. The outputs of the two video preamplifiers are applied to the inputs of a summing circuit 48. The resulting signal is applied to a low-pass filter 50, then shaped in a comparator 52 before being routed, in the form of an NRZ signal, to the reception coupler 32.

The reception microwave coupler 32 (FIG. 6), the role of which is to validate the message received before transmitting it by byte on the bus of the functional microprocessor 16, may include the same elements as the transmission coupler 24, that is ie a microprocessor 54 associated with a clock recovery circuit 56 and a random access memory 56. The interface 58 will also consist of registers. We have represented, on this interface, an input 60 coming from a maintenance aid device providing elements intended to be used by the microprocessor 16.

The essential difference between the two couplers consists in that the reception coupler 32 will have a dual access random access memory 56, structured in two distinct parts. One of the parts, dedicated to transmission, receives the message to be transmitted from the functional microprocessor 16; the other part, dedicated to reception, receives from the microprocessor 54 of the coupler the message received and validated, that is to say corresponding for example to one of the two potential targets of the vehicle. The microprocessor 54 can be provided for analyzing the HDLC frame received only if its initial part, constituting an address field, corresponds to one of these potential targets. The microprocessor 54 can thus quickly discriminate, among the messages received, those which relate to one of its targets.

Claims (8)

1. Process for data communication without a material support between vehicles forced to move on a track, for detection of the relative position of two successive travelling vehicles (14), wherein messages to be sent are transmitted, from the first travelling vehicle towards the second vehicle which follows it, as short bursts of bit sequences, by modulation of a microwave beam,
      caracterized in that:

   - each message, which represents data delivered by data processing means aboard the first vehicle and which identifies the vehicle and its location, is repeated m successive times during a refreshment period T, each time at a random instant within a specific segment of the period, of duration T/m, m being an integer greater than 1, and

   - the track being in a railway environment, the beam is directional with an angular opening in the horizontal direction just sufficient for maintaining communication in bends and switches and sufficient in the vertical direction for maintaining communication during changes in the profile of the track.
2. Process according to claim 1,
      caracterized in that m is between 5 and 40.
3. Process according to claim or 2,
      caracterized in that the messages are sent with a variable power which depends on the encountered conditions, for instance by providing a set power and a reduced power.
4. Data communication system without a material support between vehicles (14) forced to move on a track in a railway environment, for detection of the relative position of two successive travelling vehicles (14), comprising, on each vehicle, a unit for transmission by modulation of a microwave beam and a reception unit which are connected through respective interfaces to data processing means,
      caracterized in that the transmission unit comprises a horn antenna and a coupler (24) for encoding and formating, as multibit messages according to a HDLC protocol, data received from the data processing means (16, 18) and means for transmitting a same message m consecutive times, m being an integer greater than 1, during a same refreshment period T, each time at a random instant variable within a whole particular segment, of duration T/m, of said period.
5. Device according to claim 4,
      caracterized in that the data processing means comprise two microprocessors (16, 18) one of which is dedicated to the functional data regarding a vehicle control law, and the other to data regarding the safety of the vehicle.
6. Device according to claim 4 or 5,
      caracterized in that the reception unit comprises a plurality of antennas (28) located at different locations at the front of the vehicle.
7. Device according to claim 6,
      caracterized in that the distance between the antennas (28) is at least equal to ten times the transmission wavelength in air.
8. Device according to claim 6 or 7,
      caracterized in that each antenna (28) is associated with a frequency transposition amplification channel and in that a summer (48) is provided for applying the sum of the two channels to the reception coupler (32).

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