EP0274650B1 - Bidirectionnel information transmission system between a monitor station on the ground and a mobile station - Google Patents

Abstract

The exchange of information takes place at hyperfrequency, the ground station being connected to a waveguide (25), and the station on the railway vehicle being connected to an antenna (26). Each station comprises a hyperfrequency generator (19) supplying a carrier, emitters (3 to 7) supplying subcarriers, receivers (28 to 32) and a pilot generator (1). The carrier and the subcarriers have frequencies which are multiples of the pilot frequency, the frequency deviation between two successive subcarriers being equal to the pilot frequency. An emission mixing unit (MTX) receives the carrier and the subcarriers and is connected to a circulator (24) which is itself connected to the waveguide (25) in the ground station and to the antenna on the vehicle. <??>A reception mixing unit (MRX) is connected by a filter (23) to the circulator (24) and receives the hyperfrequency generator carrier; it is connected to the receivers (28 to 32) to which it supplies the subcarriers emitted by the other station. <IMAGE>

Description

The invention relates to a bidirectional information transmission system between a mobile station and a ground control station; by information it must be understood that these are analog and / or digital signals, corresponding generally to sounds, images, instructions, measurements, etc.

The mobile station which travels along a known path, is for example a train, a funicular, an elevator, a motor car, an enclosure monitoring cart, etc., and the control station is fixed, on the ground .

The transmissions are made for example using a waveguide arranged along the path followed by the mobile station provided with a transmitting and receiving antenna moving along the waveguide. A waveguide transmission device can be found in the publication "Wave guide communication system for centralized railway traffic control" by T. KAWAKAMI et al, IEEE trans. on vehicular communications, Sept. 1964, p.1-18. The article "High frequency guided electromagnetic waves in application to railway signaling and control" by HM BARLOW, the radio and electronic engineer May 1967, p, 275-281, also deals with the use of microwaves for locating trains and telephone communications. These articles essentially concern the problem of the transmission of a microwave wave by waveguide along a railway track and an antenna on the railway vehicle, and do not deal with the transmission system, that is to say transmission / reception units on the ground and on the mobile vehicle. It is only indicated that the frequencies assigned to the direction of vehicle / ground transmission are lower than those assigned to the direction of ground / vehicle transmission, and that a separate channel is assigned to the transmission of television in the ground / vehicle direction.

The presence of several frequencies corresponding to the transmission channels assigned to the different transmissions causes interference which disturbs the transmissions, so that these can become unusable.

The object of the invention is to avoid such interference.

The invention also aims to transmit, in each direction of ground / vehicle transmission, a signal allowing the control of transmissions in each direction.

The subject of the invention is a bidirectional information transmission system between a ground control station connected to a waveguide and a mobile station of a vehicle connected to an antenna moving along the waveguide, each station comprising a transmitter / receiver unit, the stations transmitting in different frequency bands and the ground station transmitting in the band with the highest frequencies, characterized in that each transmitter / receiver unit comprises a pilot generator delivering a pilot frequency, a microwave generator delivering a frequency carrier multiple of the pilot frequency, a coupler connected as an input to the microwave generator and having an output connected to a transmit mixer and another output connected to a receive mixer, circuits transmitters each connected to the pilot generator and each delivering a frequency subcarrier multiple of the pilot frequency, the subcarriers having different frequencies, regularly spaced, the frequency difference between two successive subcarriers being equal to the pilot frequency and the frequencies of the subcarriers being less than the frequency of the carrier , a transmitting coupler connected at the input to the transmitting circuits and at the output at the transmitting mixer, a circulator connected to the waveguide, at the transmitting mixer and by a filter at the receiving mixer, and a receiving coupler connected at the input to the reception mixer and at the output to receivers on which it switches subcarriers which it receives from the reception mixer.

The bidirectional exchange of information between two stations, in this case a ground control station and a mobile station on board a vehicle, takes place in both directions, that is to say from the station on the ground to the on-board station and vice versa, which requires that each station can transmit and receive, the ground station transmitting on a higher frequency channel than the mobile station.

Among the various signals to be transmitted, there are video signals whose manipulation is delicate, because they are particularly sensitive to interference. These are reflected on the screen by moire, even in the case of low amplitude signals.

To eliminate this interference and in accordance with the invention, the various signals to be transmitted are synchronized with one another and frequency controlled. For this, a pilot frequency fp equal to the difference in frequency between the image carrier and the sound carrier in television is used.

In France, this difference is 6.5 MHz; the transmission system is therefore controlled by this frequency or its multiples.

The invention also provides for the transmission in each direction of a safety signal serving for the control of transmissions, this safety signal being an unmodulated carrier, of well defined frequency.

The various transmissions currently defined relate to images (television), the accompanying sound of images (television sound), sounds in general and in particular telephone conversations, data in digital form, in particular for exchanges of instructions, data, or orders between the ground station and the vehicles, the safety signal.

• d'une voie vidéo (images seules),
• d'une voie son d'accompagnement (son télévision),
• d'une voie son multiplex,
• d'une voie numérique,
• d'une voie signal de sécurité.

It is therefore necessary to have in each direction:

• a video channel (images only),
• an accompanying sound channel (its television),
• a multiplex sound channel,
• a digital channel,
• a safety signal channel.

The multiplex sound channel transmits the various sounds, in particular the transmission of telephone conversations, according to a multiplexing technique, and for example according to the well known pulse modulation and coding technique, MIC.

• porteuse vidéo à fp = 6,5 MHz,
• porteuse son d'accompagnement à 2 fp = 13 MHz,
• porteuse son multiplex à 3 fp = 19,5 MHz,
• porteuse numérique à 4 fp = 26 MHz,
• porteuse signal de sécurité à 5 fp = 32,5 MHz.

This gives a baseband in which the video channel occupies the low frequencies, its width being equal to 2 x 6 MHz, the accompanying sound being transmitted by a carrier whose frequency is higher by fp, ie 6.5 MHz. to that of the video carrier. The baseband width of a transmission channel is 5 fp, or 32.5 MHz within which the distribution of the channel carriers is as follows, starting from the low frequency of the transmission channel, which '' this is the transmission channel in the ground / vehicle direction or the transmission channel in the vehicle / ground direction:

• video carrier at fp = 6.5 MHz,
• accompanying sound carrier at 2 fp = 13 MHz,
• sound carrier multiplex at 3 fp = 19.5 MHz,
• digital carrier at 4 fp = 26 MHz,
• safety signal carrier at 5 fp = 32.5 MHz.

The different carriers are separated by a constant difference equal to fp, pilot frequency, the carrier of the safety signal having the highest frequency.

The transmissions being made in microwave we will also adopt for the central frequency Fo of all the transmissions, that is to say for the two directions of transmission, a value multiple of the pilot frequency fp = 6.5 MHz, by example Fo = 2450.5 MHz.

By taking a safety margin of fp between the central frequency and the two channels situated on either side of it, the channel allocated to vehicle / ground transmissions is between 2411.5 MHz and 2444 MHz, the video channel being at 2418 MHz, and the channel assigned to ground / vehicle transmissions is between 2457 MHz and 2489.5 MHz, the video channel being at 2463.5 MHz.

Each of the different frequencies of the transmission channels of each channel is obtained by the addition of an intermediate frequency called a subcarrier, with a frequency F of a carrier delivered by a microwave generator, the frequencies of the subcarriers and the frequency F being multiples of the pilot frequency fp.

Depending on requirements, these intermediate frequencies will be located in VHF band III, and CATV super-band (CATV for community antenna Television), or in UHF bands IV and V. To allow use standard televisions, the UHF IV and V bands will be used, so that the intermediate frequencies will be of the order of 600 MHz.

In the vehicle / ground direction the intermediate frequencies will be; 572 MHz, 578.5 MHz, 585 MHz, 591.5 MHz and 598 MHz, the intermediate frequency of 572 MHz being that of the video channel.

In the ground / vehicle direction the intermediate frequencies will be: 617.5 MHz, 624 MHz, 630.5 MHz, 637 MHz and 643.5 MHz, the intermediate frequency of 617.5 MHz being that of the video channel. The frequency F of the microwave carrier is then 1846 MHz for each direction of transmission, which gives a central frequency Fo of 2450.5 MHz.

In each direction of transmission, the signal levels undergo significant fluctuations during their transmission by the waveguide and the antenna. On reception it is therefore interesting to be able to control the gain of the receivers as a function of the levels received, and this gain control will be all the better if we are dealing with an unmodulated signal. To this end, the safety signal subcarrier is used in each direction of transmission so that an automatic gain control circuit delivers a port voltage at said subcarrier, the level of which has undergoes the same fluctuations as the levels of the other subcarriers which are transmitted in the same channel.

• la figure 1 est un schéma d'un ensemble émission/réception de l'invention, pour la station au sol,
• la figure 2 est un schéma d'un ensemble émission/réception de l'invention, pour un véhicule.

The invention will be clearly understood with the aid of the description which follows of an exemplary embodiment illustrated by the appended figures in which:

• FIG. 1 is a diagram of a transmission / reception assembly of the invention, for the ground station,
• FIG. 2 is a diagram of a transmission / reception assembly of the invention, for a vehicle.

FIG. 1 schematically represents a transmitter / receiver assembly of a ground station, connected to a waveguide 25 disposed along a railway track, 26 representing an antenna of a railway vehicle, said antenna moving along of the waveguide.

A circulator 24 is connected to the waveguide 25; it is connected directly to an MTX transmission mixer, and by a filter 23 to an MRX reception mixer; the two mixers are connected to a coupler 22 itself connected to a microwave generator 19 delivering a signal of frequency F = 1846 MHz. The transmission mixer MTX is connected to a transmission coupler 18 from which it receives signals each carried by a subcarrier; the MRX reception mixer is connected to a reception coupler 27 to which it delivers signals carried by subcarriers of the vehicle.

The transmission mixer MTX receives the frequency signal F from the coupler 22 and signals from the transmission coupler 18, the frequencies of the subcarriers of these signals being lower than the frequency F of the microwave signal; these frequencies are for example located in the V band of the UHF frequencies. In the emission mixer, the frequency of each signal delivered by the emission coupler is added to the frequency F, and the resulting signals are delivered to the circulator 24 which directs them to the waveguide 25.

In the vehicle there is also, as will be specified during the description of FIG. 2, a microwave generator which delivers a signal of the same frequency F = 1846 MHz as that of the ground station, and the frequencies of the subcarriers signals to be transmitted are lower than those of the ground station. The frequency of each signal is likewise added to the frequency F and the resulting signals are transmitted by the antenna 26 and transmitted by the waveguide 25 to the circulator 24 of the ground station, which directs them to the reception mixer. MRX. The reception mixer receiving the signal of frequency F = 1846 MHz from the coupler 22 delivers to the reception coupler 27, and by subtracting the frequency F from the frequencies of the received signals, signals whose frequencies are those of the subcarriers used in the vehicle.

In FIG. 1, a frequency generator 1, which is a very stable oscillator, delivers a signal with a frequency fp = 6.5 MHz, called the pilot frequency.

This pilot frequency is distributed by a coupler 2 to phase comparators, 8, 9, 10, 11, 12 and 20 of any known type, and for example of the MC 14152 type from the company MOTOROLA. The phase comparators 8 to 12 are connected at output to oscillator circuits 3 to 7, respectively, these oscillator circuits each having a modulation input and being for example of the TDA 5660 type from the company SIEMENS. The frequencies of these oscillator circuits are, for example 617.5 MHz, 624 MHz, 630.5 MHz, 637 MHz, 643.5 MHz; these frequencies are those of the subcarriers, and it will be noted that the subcarrier at 643.5 MHz which corresponds to the safety signal is not modulated.

The oscillator circuits 3 and 4 which correspond to the video and accompanying sound channels receive modulation signals corresponding respectively to the image and to the sound; the oscillator circuit 5 which is reserved for multiplex sound is modulated by a multiplex whose channels of a frame are each assigned to a distinct sound channel, such as for example a telephone conversation or the transmission of a sound program. The oscillator circuit 6 assigned to the digital transmission is modulated by a binary coded information multiplex.

Each oscillator circuit 3 to 7 is connected at the output to the emission coupler 18 on the one hand, and to the phase comparator which is associated with it by means of a frequency divider 13 to 17 on the other hand.

The frequency dividers 13 to 17 are dividers by 95, 96, 97, 98, 99, respectively. There is indeed at the output of each divider a signal at 6.5 MHz.

The phase comparator 20 is connected at the output to the microwave generator 19 itself connected at the output on the one hand to the coupler 22 and on the other hand to the phase comparator 20 by a frequency divider 21 which is a divider by 284; after dividing the frequency F = 1846 MHz, we find a signal at 6.5 MHz.

The reception coupler 27 outputs the various modulated subcarriers of the signals transmitted by the vehicle, to receivers 28, 29, 30, 31, 32. The frequencies of these subcarriers are for example 572 MHz for the video channel, 578.5 MHz for a reserve channel, 585 MHz for the multiplex sound channel, 591.5 MHz for the digital channel and 598 MHz for the safety signal channel.

The security receiver 28 receives the 598 MHz subcarrier from the security signal and is connected at the output on the one hand to a filter 33 and on the other to an automatic gain control circuit 34. The filter 33 is connected to a frequency divider 35 which is a divider by 92 delivering a safety signal at 6.5 MHz to a control circuit 36. The automatic gain control circuit 34 is connected at output to the receivers 29, 30, 31, 32.

The receiver 29 is a conventional television receiver which receives a video signal from the receive coupler 27 on the frequency of 572 MHz.

It has been assumed in Figure 1 that the accompanying sound was transmitted by the vehicle in the 585 MHz multiplex sound channel, instead of being transmitted by a separate accompanying sound channel. The multiplex sound receiver 30 delivers a digital multiplex to a demultiplexer 38 which delivers the different sound channels on different links, in binary form; the link 39 corresponds to the accompanying audio channel of the video channel and is connected to a decoder 40 which outputs the accompanying sound in analog form at the television receiver 29.

The digital receiver 31 delivers information in binary form; receiver 32 is a reserve receiver operating at 578.5 MHz since this frequency is not used by the vehicle for the accompanying sound of the video channel at 572 MHz.

FIG. 2 schematically represents a transmitter / receiver assembly of a vehicle, said assembly being connected to the antenna 26 moving along the waveguide 25. As in the transmitter / receiver assembly of the ground station there are , in FIG. 2, a circuit constituted by a circulator 74, a filter 73, a reception mixer MRX1, a coupler 72, a microwave generator 69, a transmission mixer MTX1, a reception coupler 75 and a coupler show 68.

The microwave generator delivers a frequency signal F = 1846 MHz this frequency being the same as that delivered by the microwave generator 19 of the ground station. The circulator 74 is connected on the one hand to the emission mixer MTX1 and on the other hand to the reception mixer MRX1 by the filter 73; the microwave generator 69 is connected at the output to the coupler 72 itself connected at the output on the one hand to the transmission mixer MTX1 and on the other hand to the reception mixer MRX1; the transmission coupler 68 is connected at the output to the transmission mixer MTX1, and the reception coupler 75 is connected at the input to the reception mixer MRX1.

On reception, the circulator 74 routes the signals received to the reception mixer MRX1 which, by subtracting the frequency F, delivers the subcarriers at 617.5 MHz, 624 MHz, 630.5 MHz, 637 MHz and 643 to the reception coupler 75. , 5 MHz, with their modulation, only the safety subcarrier at 643.5 MHz not being modulated as indicated in the description of FIG. 1. The reception coupler 75 is connected to a safety receiver 76 which receives the subcarrier at 643.5 MHz, to a television receiver 77 which is a normal television set and receives the subcarriers at 617.5 and 624 MHz corresponding to the video channel and to the accompanying sound channel , to a multiplex sound receiver 78 which delivers a digital multiplex on a link 86, and to a digital receiver 79 which delivers information on a link 87 in binary form.

The safety receiver 76 is connected at the output on the one hand to a filter 81 and on the other hand to an automatic gain control circuit 80 itself connected at the output to the receivers 77, 78, 79. The filter 81 is connected to a frequency divider 82 which is a divider by 92 and delivers a signal at 6.5 MHz to a phase comparator 83. An oscillator 85, very stable, of the VCXO type, delivers a signal at 6.5 MHz, this signal being applied to the phase comparator 83, connected as an output to a control input of the oscillator 85 via a filter 84. The oscillator 85 is therefore subject to phase and frequency control at the pilot frequency fp = 6, 5 MHz from the ground station.

The oscillator 85 is also connected at the output to a coupler 52 itself connected at the output to phase comparators 58, 59, 60, 61, 62 and 70 of the same type as those of the ground station. The phase compartments 58 to 62 are connected at output to oscillator circuits 53, 54, 55, 56, 57, respectively, these oscillator circuits each having a modulation input and being of the same type as the oscillator circuits of the ground station , and each corresponding to a transmission channel. The frequencies of the oscillator circuits 53 to 57 are, for example, 572 MHz, 578.5 MHz, 591.5 MHz and 598 MHz; these frequencies are those of the subcarriers and it will be noted that the subcarrier at 598 MHz which corresponds to the safety signal is not modulated.

The oscillator circuit 53, of subcarrier at 572 MHz corresponds to the video channel; as previously indicated, the accompanying sound is transmitted at the same time as other sounds by the oscillator circuit 55 of subcarrier at 585 MHz corresponding to the multiplex sound channel. The oscillator circuit 54, of subcarrier at 578.5 MHz is therefore not used for the accompanying sound, and is in reserve, or else it may not exist. The oscillator circuit 56, with a subcarrier at 591.5 MHz corresponds to the digital channel and is modulated by a multiplex of binary coded information. The oscillator circuit 57, of subcarrier at 598 MHz corresponds to the safety signal channel and is not modulated.

Each oscillator circuit 53 to 57 is connected at the output to the emission coupler 68 on the one hand, and to the phase comparator which is associated with it by means of a frequency divider 63 to 67, on the other hand. The frequency dividers 63 to 67 are dividers by 88, 89, 90, 91, 92, respectively. There is indeed at the output of each divider a signal at 6.5 MHz.

The phase comparator 70 is connected at the output to the microwave generator 69 itself connected at the output on the one hand to the coupler 72 and on the other hand to the phase comparator 70 by a frequency divider 71 which is a divider by 284; after dividing the frequency F = 1846 MHz we find a signal at 6.5 MHz.

In the description of Figures 1 and 2, the oscillator circuits are five in number, but obviously this number can be different depending on the application, that is to say the type of mobile; for example in the case of enclosure monitoring, the mobile cart can include one or more television cameras, and possibly a digital channel, one or more microphones, but will not include a television set; the safety channel subcarrier always has the highest frequency of all the subcarriers. Of course the number of receivers will be increased accordingly. Similarly, the frequency F of the microwave carrier can be different from 1846 MHz, while remaining a multiple of the pilot frequency fp.

Claims (9)

1. A two-way information transmission system for communications between a ground control station connected to a wave-guide (25) and a vehicular mobile station connected to an antenna (26) moving alongside the waveguide, each station comprising a transmitter-receiver unit, the stations transmitting in different frequency bands and the ground station transmitting in the band with the higher frequencies, characterized in that each transmitter-receiver unit comprises a pilot signal generator (1; 85) supplying a pilot frequency, a microwave generator (19; 69) supplying a carrier at a frequency which is a multiple of the pilot frequency, a coupler (22; 72) with input connected to the microwave generator, one output connected to a transmitter mixer (MTX; MTX1) and another output connected to a receiver mixer (MRX; MRX1), transmitter circuits (3 to 7; 53 to 57), each connected to the pilot generator and each supplying a sub-carrier at a frequency which is a multiple of the pilot frequency, the subcarriers having different, evenly spaced frequencies, the difference between successive subcarrier frequencies being equal to the pilot frequency and the frequencies of the subcarriers being less than the carrier frequency, a transmission coupler (18; 68), input-connected to the transmitter circuits and output-connected to the transmitter mixer (MTX; MTX1), a circulator (24; 74), connected to the waveguide (25), to the transmitter mixer and, via a filter (23), to the receiver mixer, and a receiver coupler (27; 75), with an input connected to the receiver mixer and output connected to receivers (28 to 32; 76 to 79) to which it routes subcarriers that it receives from the receiver mixer.
2. A transmission system according to claim 1, characterized in that all the subcarriers except one are modulated, each by a different signal to be transmitted, and the unmodulated subcarrier constitutes a check signal.
3. A transmission system according to claim 1, characterized in that the pilot frequency is equal to the difference in television between a video carrier and an accompanying sound carrier.
4. A transmission system according to claim 1, characterized in that each transmitter circuit has its input connected to a phase comparator (8 to 12; 58 to 62) having an input connected to the pilot generator (1; 85) and another input connected via a frequency divider (13 to 17; 63 to 67) to the output of the transmitter circuit.
5. A transmission system according to claim 1, characterized in that the microwave generator's input is connected to a phase comparator (20; 70) having one input connected to the pilot generator and another input connected via a frequency divider (21; 71) to the output of the microwave generator.
6. A transmission system according to claim 1, characterized in that the carriers of the microwave generators of the communicating stations have the same frequency.
7. A transmission system according to claim 1, characterized in that the frequencies of the subcarriers of the stations are located in the same frequency band, selected from among VHF band III, CATV superband and UHF bands IV and V.
8. A transmission system according to claim 2, characterized in that a receiver (28; 76) in each station receives the unmodulated carrier and is connected to a frequency divider (35; 82) which delivers a signal at the same frequency as that supplied by the pilot generator, said frequency divider being connected, in the ground station, to a control circuit (36) and, in the station aboard the vehicle, to an input of a phase comparator (83) having another input connected to the output of the pilot generator (85) and an output connected to a control input of the said pilot generator.
9. A transmission system according to claim 2, characterized in that a receiver (28; 76) in each station receives the unmodulated carrier and is output-connected to an automatic gain control circuit (34; 80) that is itself output-connected to a control input of the other receivers.

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