Transmitter and receiver for a rail circuit

Abstract

The invention consists of a transmitter (1) and a receiver (2) for a rail circuit of a section (SC) of a transport line, wherein said transmitter (1) comprises output means (13,14) for transmitting a signal (ST) on said rail circuit, input means (11) adapted to receive a transmission message (MT), processing means (12) configured for receiving, via the input means (11), the transmission message (MT), encoding said transmission message (MT), thereby generating said signal (ST), and transmitting, via the output means (13,14), said signal (ST) on said rail circuit, wherein the signal (ST) transmitted on said rail circuit is generated by using a linear-variation continuous-phase modulation.

Description

[0001] TRANSMITTER AND RECEIVER FOR A RAIL CIRCUIT

[0002] DESCRIPTION

[0003] The present invention relates to a transmitter and a receiver for a rail circuit of a section of a transport line, in particular a rail circuit of the audio frequency type used for detecting the presence of rolling stock in a section of a railway line, a tramway line, or the like.

[0004] It is known that, in order to guarantee the safety of a railway line, said line is typically divided into a plurality of sections by means of joints (which may be either mechanical or electrical) allowing drive current to flow and preventing the signals used for detecting the presence of rolling stock from passing from one section to another. With each section a rail-circuit transmitter and a rail-circuit receiver are associated (whether directly or via an impedance bond or an electrical joint), which operate in different audio frequencies. That is, a first section is delimited by a first joint and by a second joint, which are respectively connected to a first transmitter and a first receiver operating in a first audio frequency, while a second section is delimited by the second joint and by a third joint, which are respectively connected to a second transmitter and a second receiver operating in a second audio frequency.

[0005] As can be easily inferred, such a solution requires the use of at least two distinct audio frequencies, so that at least two distinct types of transmitters and receivers need to be produced. Moreover, the need for using at least two distinct audio frequencies leads to considerably longer times when designing and constructing a new railway line or renovating an existing one, also because it will be necessary to verify that the different types of transmitters and receivers have been placed into the correct positions.

[0006] The use of a single audio frequency would, however, make it very likely that a receiver might detect a signal emitted by a transmitter of a neighbouring section even when rolling stock is present in the section of that receiver, which might result in a false negative (i.e. it might be detected that the section is clear even when there is rolling stock on it), which might consequently lead to a railway accident.

[0007] For this reason, at least two audio frequencies must be used at present. This situation makes it particularly difficult to fabricate the joints, especially due to the large number of reactive and capacitive components required. Such joints must, in fact, have an adequate passband allowing for signal transmission and / or reception in two distinct sections, i.e. directing most of the energy of a first signal centred in a first frequency towards a first section and most of the energy of a second signal centred in a second frequency towards a second section.

[0008] In addition, the risk of a false negative (when detecting if there is any rolling stock in one of the sections of a line) is further increased when joint components (e.g. reactive and / or capacitive components) fail or degrade and / or when environmental conditions (e.g. temperature and humidity) are significantly different from the design values and the joints may undergo reactance and / or capacity variations, so that, disadvantageously, a signal having a particular audio frequency might pass from one section to another. It must also be pointed out that joint elements are installed manually on rails, and therefore installation errors are possible (e.g. imperfect connection to rails, damaged insulation, insufficient or excessive length, etc.). Therefore, additional time is required for proper installation and verification after a line has been constructed or serviced.

[0009] The present invention aims at solving these and other problems by providing a transmitter for a rail circuit.

[0010] Furthermore, the present invention aims at solving these and other problems by providing a receiver for a rail circuit.

[0011] The basic idea of the present invention is to modulate an output signal of a transmitter for a rail circuit by means of a linear-variation continuous-phase (MSK, Minimum-Shift Keying) modulator, and to demodulate the input signal of a receiver of said rail circuit by means of a continuous-phase (MSK, Minimum-Shift Keying) demodulator, which can demodulate signals transmitted by said transmitter.

[0012] This makes it possible to transmit / receive an encoded message by using a very narrow band (i.e. with a ratio between bandwidth and central frequency much lower than 0.05), so as to improve noise rejection in the entire system, and hence the robustness thereof, advantageously ensuring a highly reliable transmission of digital signals. It is thus possible, in fact, to encode a message (e.g. containing section identification data identifying the line section to which the transmitter has been assigned) through a signal transmitted by the transmitter on the rail circuit in a very narrow band, thereby advantageously allowing the receiver to (after decoding the signal) read the message (which may, for example, contain the section identification data) and determine (with certainty) whether the signal comes from the transmitter in the same line section or from another line section. The receiver will thus be able to consider only those signals coming from its own section, discarding any signals coming from adjacent sections, thus avoiding any false negatives that might cause a railway accident. In this way, the level of safety of trains circulating in a railway network can be improved.

[0013] Further advantageous features of the present invention are set out in the appended claims.

[0014] These features as well as further advantages of the present invention will become more apparent in the light of the following description of a preferred embodiment thereof as shown in the annexed drawings, which are provided herein merely by way of non-limiting example, wherein:

[0015] - Fig. 1 shows a block diagram depicting a signalling system comprising a transmitter and a receiver for a rail circuit according to the invention;

[0016] - Fig. 2 shows a block diagram of the transmitter and the receiver of Fig. 1.

[0017] In this description, any reference to "an embodiment" will indicate that a particular configuration, structure or feature is comprised in at least one embodiment of the invention. Therefore, expressions such as "in an embodiment" and the like, which may be found in different parts of this description, will not necessarily refer to the same embodiment. Moreover, any particular configuration, structure or feature may be combined as deemed appropriate in one or more embodiments. The references below are therefore used only for simplicity's sake, and shall not limit the protection scope or extension of the various embodiments.

[0018] With reference to Fig. 1, the following will describe a signalling system S for controlling a railway network, a tramway network, or the like; in particular, said signalling system S controls the circulation of rolling stock (e.g. coaches, locomotives, electric trains, etc.) circulating in the network, which is divided into a plurality of sections SC. Each section is delimited by a first joint G1 and a second joint G2, preferably of the electrical or mechanical type, wherein each joint G1,G2 comprises reactive elements, such as, for example, a pair of transformers (when the joint is a mechanical one) or an inductive element and at least one capacitive element (for an electric joint) mutually connected to form a resonant circuit, so as to allow for transmission or reception of a signal at a given frequency without it propagating to the sections adjacent to the section SC, i.e. to those sections which follow or precede said section SC.

[0019] In more detail, the signalling system S comprises the following components:

[0020] - a transmitter 1 for a rail circuit, preferably configured to be connected to the first joint Gl, where the rail circuit is preferably associated with the section SC;

[0021] - a receiver 2 for said rail circuit, preferably configured to be connected to the second joint G2;

[0022] - supervision and control means 3, e.g. a server, in communication with the transmitter 1 and the receiver 2, and configured to detect if the receiver 2 receives a signal transmitted by the transmitter 1, so as to determine the presence of rolling stock in the section SC (where the transmitter 1 and the receiver 2 are preferably positioned) when the receiver does not receive the signal transmitted by the transmitter 1.

[0023] It must be pointed out that the transmitter 1 and the receiver 2 are preferably positioned near the joints G1,G2 to which they are connected (i.e. inside junction boxes positioned along the line), while the supervision and control unit 3 is generally positioned in premises such as a server room, a signal box, or the like.

[0024] The supervision and control unit 3 is connected to the transmitter 1 and to the receiver 2 through a data network, e.g. an Ethernet network, an RS485 network, or the like.

[0025] Also with reference to Fig. 2, the transmitter 1 and the receiver 2 will now be described. The transmiter 1 comprises the following elements:

[0026] - input means 11, e.g. a data network interface (such as an Ethernet network, an RS485 network, or the like) or a serial interface (e.g. a USB® interface, an RS232 interface, or the like), adapted to receive a transmission message MT, preferably generated by the supervision and control unit 3;

[0027] - output means for transmitting a signal ST on the rail circuit of the section SC, wherein said output means preferably comprise a digital-to-analog converter (DAC) 13 and a power amplifier 14 (e.g. a MOSFET or transistor amplification stage, or the like), wherein the digital-to-analog converter 13 is configured to convert a bit sequence into an analog signal, and wherein an output of said digital-to-analog converter 13 is connected to an input of said power amplifier 14, so as to drive said power amplifier 14 and generate a signal having adequate characteristics for transmission on the rail circuit of the section SC;

[0028] - processing means 12, e.g. a CPU, a DSP, a CPLD, an FPGA, or the like, in signal communication with the input means 11 and the output means 13,14.

[0029] When the transmitter 1 is in an operating condition, the processing means 12 are configured to execute the following steps:

[0030] - receiving, via the input means 11, the transmission message (MT), preferably from the supervision and control unit 3;

[0031] - encoding said transmission message MT, thereby generating the signal ST, e.g. by executing a set of instructions or by using a dedicated hardware component;

[0032] - transmitting, via the output means 13,14, said signal ST on said rail circuit.

[0033] The processing means 12 are configured to generate the signal ST to be transmited on said rail circuit by using a linear-variation continuous-phase modulation (MSK, Minimum-Shift Keying), e.g. by executing a set of instructions implementing the operation of a linear-variation MSK encoder, or by using a dedicated electronic component (e.g. an FPGA) comprised in and / or in communication with said processing means 12 and configured to operate as a linear-variation MSK encoder.

[0034] Due to the use of linear-variation continuous-phase modulation, a very narrow band portion is occupied at a given frequency, advantageously making it possible to transmit the signal effectively also when the section SC is delimited by joints G1,G2 comprising resonant circuits, which have a very limited passband. Being resonant, such joints are frequency-selective, and the use of a very narrow band MSK modulation like the one proposed herein makes it possible to calibrate the joint for a single frequency, and to perform transmission / reception at that very point of maximum efficiency of the joint, thereby maximizing the energetic efficiency in comparison with prior-art solutions, which use a larger number of resonant circuits and / or more band, thus proving less efficient.

[0035] With the solution according to the invention, the same performance can be attained with fewer components to be kept in operation, installed in the field, etc., thus advantageously shortening the time necessary for installation and advantageously increasing the mean time between failures (MTBF).

[0036] Furthermore, with this solution a message can be encoded in the signal transmitted by the transmitter on the rail circuit, thus advantageously allowing the receiver 2 and / or the supervision and control unit 3 to read the message and determine whether the signal comes from the transmitter installed in the same line section or from another section. It is thus possible to increase the level of safety of trains circulating in a railway network, because the risk that a false negative might occur when determining the presence of rolling stock in a section of the railway network is completely avoided.

[0037] The receiver 2 comprises the following elements:

[0038] - emission means 21, e.g. a data network interface (e.g. an Ethernet network, an RS485 network, or the like), or a PCI or USB® bus interface, or the like, for outputting a reception message MR;

[0039] - reception means adapted to receive a signal SR from said rail circuit, wherein said reception means preferably comprise an analog-to-digital converter (ADC) 23 and a signal amplifier 24 (e.g. a MOSFET or transistor amplification stage, or the like), wherein the signal amplifier amplifies the signal coming from the rail circuit so that an amplified signal outputted by said signal amplifier 24 will have electric characteristics allowing the sampling thereof, and wherein the output of said signal amplifier 24 is in communication with an input of said analog-to- digital converter 23, which transforms the amplified signal into a bit string;

[0040] - computing means 22, e.g. a CPU, a DSP, a CPLD, an FPGA, or the like, in signal communication with the emission means 21 and the reception means 23,24.

[0041] When the receiver 2 is in an operating condition, the computing means 22 are configured to execute the following steps:

[0042] - receiving, via the reception means 23,24, the signal SR from said rail circuit, wherein said signal is preferably the result of an attenuation of the signal ST transmitted by the transmitter 1, combined with any noise that may be present in the rail circuit;

[0043] - decoding said signal SR, thereby generating the reception message MR;

[0044] - emitting, via the emission means 21, said reception message MR, preferably to send it to the supervision and control unit 3 or to another destination.

[0045] The computing means 22 are configured to generate the message MR encoded in the signal SR received on said rail circuit (i.e. to reconstruct the message MR) by using a continuous-phase demodulation (MSK, Minimum-Shift Keying) capable of demodulating the signal generated by the transmitter 1, e.g. by executing a set of instructions implementing the operation of an MSK decoder, or by using a dedicated electronic component (e.g. an FPGA) comprised and / or in communication with said computing means 22 and configured to operate as an MSK decoder capable of decoding signals generated by a signal generator (e.g. the transmitter 1) comprising a linear-variation continuous-phase (MSK, Minimum-Shift Keying) modulator.

[0046] In addition to the advantages offered by the use of linear-variation continuous- phase modulation already mentioned with reference to the above-described transmitter 1, a message encoded in the signal transmitted by said transmitter 1 on the rail circuit can thus be decoded, so that it is advantageously possible for the receiver 2 and / or the supervision and control unit 3 to read the message and determine whether the signal comes from the transmitter in the same line section or from another section. The level of safety of trains circulating in a railway network can thus be improved because the risk that a false negative might occur in determining the presence of rolling stock in a section of the railway line is completely avoided, while at the same time maximizing the energetic efficiency of the signalling system S.

[0047] When the supervision and control unit 3 is in an operating condition, said supervision and control unit 3 is preferably configured to execute the following steps:

[0048] - transmitting, by means of the transmitter 1, the transmission message MT to the receiver 2 through the rail circuit;

[0049] - receiving, by means of the receiver 2, the reception message MR through the rail circuit;

[0050] - determining if there is any rolling stock in the section SC on the basis of at least one comparison between the transmission message MT and the reception message MR. For example, if the reception message MR has not been received within a certain time interval or is different from the transmitted message MT, the supervision and control unit 3 will conclude that the section SC is occupied by rolling stock or that the reception message MR must be discarded; conversely, if the signal has been received within a certain time interval, it will conclude that the section SC is clear of rolling stock.

[0051] As an alternative or in combination with the above, some of the operations performed by the supervision and control unit may be delegated to one or more receivers according to the invention. In more detail, the processing means 12 of the transmitter 1 may be configured to transmit the transmission message MT cyclically, preferably received from the supervision and control unit 3 or set by an operator during the installation and / or configuration of the transmitter 1 (e.g. by means of a terminal connected to the input means 11), and wherein the computing means 22 of the receiver 2 may also be configured to execute the following steps:

[0052] - determining if there is any rolling stock in the section SC on the basis of at least the reception message MR, and generating a presence datum indicating whether or not there is any rolling stock in the section SC;

[0053] - transmitting, via the emission means 21, a section status change message indicating the entry or exit of rolling stock into / from the section SC, when the presence datum undergoes a change.

[0054] Advantageously, this makes it possible to reduce the number of messages exchanged between the supervision and control unit 3 and the pairs of transmitters 1 and receivers 2 along the line. Moreover, a larger number of transmitters 1 and receivers 2 can be made to operate simultaneously, i.e. the transmitters 1 do not have to perform transmission one at a time and / or in a synchronized manner, being allowed to cyclically transmit the messages MT autonomously, thereby increasing the scalability of the signalling system S. It is thus possible to improve the level of safety of trains circulating in a railway network (even a very large one), because the risk that a false negative might occur when determining the presence of rolling stock in a section of the railway network is completely avoided, while at the same time maximizing the energetic efficiency of the signalling system S.

[0055] In combination with the above, the transmission message MT encoded by the transmitter 1 preferably comprises a header including a predefined bit sequence, while the computing means of the receiver 2 are configured to synchronize the generation of the reception message MR according to such header, so that the receiver 2 will know when the message MR contained in the signal coming from the transmitter 1 starts being received. This advantageously avoids the use of external synchronization means, which would require, for example, the supervision and control unit 3 to continuously manage the communication between transmitter 1 and receiver 2, or the use of dedicated transmission lines between transmitter 1 and receiver 2, thus further increasing the scalability of the signalling system S. In this way it is possible to improve the level of safety of trains circulating in a railway network (even a very large one), while at the same time maximizing the energetic efficiency of the signalling system S.

[0056] In combination with or as an alternative to the above, the transmission message MT encoded by the transmitter 1 preferably comprises an identification datum identifying, preferably by encoding an integer, a section SC to which said transmission message MT refers, while the computing means 22 of the receiver 2 and / or the supervision and control unit 3 are configured to determine, based on said identification datum, whether the reception message MR has been emitted by the transmitter 1 of the section SC to which the receiver 2 belongs and / or which is currently of interest for the supervision and control unit 3, and to discard said message MR if said message MR refers to another section. This allows the receiver or the supervision and control unit 3 to determine with certainty the origin of the message MR, and thus to determine whether said message MR should be used or not to determine the presence or absence of rolling stock in the section SC on the basis of said identification datum. It is thus possible to improve the level of safety of trains circulating in a railway network (even a very large one), while at the same time maximizing the energetic efficiency of the signalling system S.

[0057] In combination with the above, the computing means 22 of the receiver 2 and / or the supervision and control unit 3 may be configured to determine the presence or absence of rolling stock in the section SC also on the basis of, in addition to the identification datum, an energy datum representing the energy (or the power, e.g. the average power) that is present (in the spectrum) at the frequency (i.e. within a frequency range which is preferably very narrow) at which the signal SR transporting the reception message MR was transmitted, e.g. by comparing said energy with a threshold value. This makes it possible to identify any echoes of the signal ST that may have been generated between the joints G1,G2 when electric joints (i.e. joints having a rather low resistance) are used to delimit a particularly short line section. In this manner, the level of safety of trains circulating in a railway network can be further improved, while at the same time maximizing the energetic efficiency of the signalling system S.

[0058] In combination with or as an alternative to the above, the transmission message MT encoded by the transmitter 1 preferably comprises error correction data that make it possible to correct at least one error when said transmission message MT is received (i.e. to correct at least one error in the reception message MR), wherein said correction data are preferably generated by executing a set of instructions implementing a cyclic redundancy check (CRC) algorithm. The computing means 22 of the receiver 2 and / or the supervision and control unit 3 are preferably configured to correct the reception message MR on the basis of said error correction data, preferably prior to transmitting said reception message MR to the supervision and control unit 3 or before determining if there is any rolling stock in the section SC. This makes the signalling system S more robust against message collisions. For example, when two or more transmitters according to the invention are transmitting messages (almost) simultaneously and the joints cannot ensure a perfect insulation between adjacent sections, the message MR received by the receiver will be subject to interference from a second message coming from an adjacent section. It is thus possible to improve the level of safety of trains circulating in a railway network (even a very large one), while at the same time maximizing the energetic efficiency of the signalling system S.

[0059] Of course, the example described so far may be subject to many variations.

[0060] Some of the possible variants of the invention have been described above, but it will be clear to those skilled in the art that other embodiments may also be implemented in practice, wherein several elements may be replaced with other technically equivalent elements. The present invention is not, therefore, limited to the above-described illustrative examples, but may be subject to various modifications, improvements, or replacements of equivalent parts and elements without however departing from the basic inventive idea, as specified in the following claims.

Claims

CLAIMS1. Transmitter (1) for a rail circuit of a section (SC) of a transport line, comprising- output means (13,14) for transmitting a signal (ST) on said rail circuit, and characterized in that it further comprises- input means (11) adapted to receive a transmission message (MT),- processing means (12) configured for• receiving, via the input means (11), the transmission message (MT),• encoding said transmission message (MT), thereby generating said signal (ST), and• transmitting, via the output means (13,14), said signal (ST) on said rail circuit, wherein the signal (ST) transmitted on said rail circuit is generated by using a linear- variation continuous-phase modulation (MSK).

2. Transmitter (1) according to claim 1, wherein the processing means (12) are configured to transmit the transmission message (MT) cyclically.

3. Transmitter (1) according to claims 1 or 2, wherein the transmission message (MT) comprises a header that comprises a predefined bit sequence.

4. Transmitter (1) according to any one of claims 1 to 3, wherein the transmission message (MT) comprises an identification datum that identifies the section (SC) to which said transmission message (MT) refers.

5. Transmitter (1) according to any one of claims 1 to 4, wherein the transmission message (MT) comprises error correction data that make it possible to correct at least one error when said transmission message (MT) is received.

6. Receiver (2) for a rail circuit of a section (SC) of a transport network, comprising- reception means (23,24) adapted to receive a signal (SR) from said rail circuit, characterized in that it further comprises- emission means (21) for outputting a reception message (MR), and- computing means (22) configured for• receiving, via the reception means (23,24), said signal (SR) from said railcircuit,• decoding said signal (SR), thereby generating said reception message (MR), and• emitting, via the emission means (21), said reception message (MR), wherein said reception message (MR) is generated by demodulating the signal (SR) received from said rail circuit by using a continuous-phase demodulation (MSK) capable of decoding a signal generated by a transmitter (1) according to any one of claims 1 to 5.

7. Receiver (2) according to claim 6, wherein the computing means (22) are configured for- determining if there is any rolling stock in the section (SC) on the basis of at least the reception message (MR), and generating a presence datum indicating whether or not there is any rolling stock in the section (SC);- transmitting, via the emission means (21), a section status change message indicating the entry or exit of rolling stock into / from the section (SC), when the presence datum undergoes a change.

8. Receiver (2) according to claims 6 or 7, wherein the reception message (MR) comprises a header that contains a predefined bit sequence, and wherein the computing means (22) are configured to synchronize the generation of the reception message (MR) on the basis of said header.

9. Receiver (2) according to any one of claims 6 to 8, wherein the reception message (MR) comprises an identification datum that identifies the section (SC) to which the reception message (MR) refers, wherein the computing means (22) are configured for- determining, on the basis of said identification datum, if the reception message (MR) was emitted by a transmitter (1) of the section (SC),- discarding said reception message if said message (MR) refers to a second section different from said section (SC).

10. Receiver (2) according to claim 9, wherein the computing means (22) are configured to determine if there is any rolling stock in the section (SC) on the basis ofthe identification datum and an energy datum representing energy that is present within a frequency range in which the signal (SR) was transmitted.

11. Receiver (2) according to any one of claims 6 to 10, wherein the reception message (MR) comprises error correction data that make it possible to correct at least one error in the reception message (MR), and wherein the computing means (22) are configured to correct the reception message (MR) on the basis of said error correction data.

12. Signalling system (S), comprising- a transmitter (1) according to any one of claims 1 to 5, - a receiver (2) according to any one of claims 6 to 11,- supervision and control means (3) in communication with the transmitter (1) and the receiver (2), and configured for• transmitting, by means of the transmitter (1), the transmission message (MT) to the receiver (2) through the rail circuit; • receiving, by means of the receiver (2), the reception message (MR) through the rail circuit, and• determining if there is any rolling stock in the section (SC) on the basis of at least one comparison between the transmission message (MT) and the reception message (MR).

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