Patent Publication Number: US-6034646-A

Title: Information transmission device and method for systems using radiating waveguides

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention concerns information transmission devices and methods in general and, more particularly, an information transmission device and method for systems using radiating waveguides. 
     2. Description of the Prior Art 
     The IAGO system is an information and automation system using radiating waveguides and is described, for example, in &#34;THE USE OF RADIATING WAVEGUIDES IN GUIDED TRANSPORTATION SYSTEMS&#34;, by Marc HEDDEBAUT and Marion BERBINEAU, special issue No. 8, published by the Institut National de Recherche sur les Transports et leur Securite. 
     This system is able to locate mobiles traveling along the radiating waveguide. 
     This location is based on the use of dedicated location slots. 
     These location slots are complementary and perpendicular to slots disposed regularly and continuously along the radiating waveguide. 
     The regular slots are used for high bit rate transmission of information and to measure the speed of the mobiles. 
     The information relating to the location of the mobiles is only available when the mobile is moving along the radiating waveguide, however. 
     In some applications, the mobile is in a workshop area or in a parking area or at the entry to a station. For these applications it is necessary to provide an information transmission device that can be read when the mobile is stopped or even parked above the information transmission device. 
     For applications in which the mobile moves along the radiating waveguide, it is necessary to provide a high bit rate information transmission device. 
     One aim of the invention is therefore an information transmission device for systems using radiating waveguides. 
     Another aim of the invention is an information transmission method for systems using radiating waveguides. 
     SUMMARY OF THE INVENTION 
     The invention consists in an information transmission device for systems using radiating waveguides along which a mobile travels, including: 
     means for injecting an unmodulated carrier wave into said radiating waveguide, 
     means for localized sampling along said radiating waveguide of some of the energy of said unmodulated carrier wave, 
     modulator means for modulating said unmodulated carrier wave using a local modulation signal representing information addressed to said mobile, and 
     means for radiating a modulated carrier wave to said mobile. 
     The information transmission device of the invention for systems using radiating waveguides can also have any of the features of the accompanying subsidiary claims. 
     The invention also consists in an information transmission method for systems using radiating waveguides along which a mobile travels, including the following principal steps: 
     injecting an unmodulated carrier into said radiating waveguide, 
     localized sampling along said radiating waveguide of some of the energy of said unmodulated carrier wave, 
     modulating said unmodulated carrier wave using a local modulation signal representing information addressed to said mobile, and 
     radiating the modulated carrier wave to said mobile. 
     The information transmission method of the invention for systems using radiating waveguides can also have any of the features of the accompanying subsidiary claims. 
     The information transmission device of the invention for systems using radiating waveguides may be entirely implemented using a short straight section of radiating waveguide, for example, its length being similar to the wavelength in air of the signals propagated in the radiating waveguide. 
     A technology of this kind was used to build a prototype originally constructed in the laboratories of the Institut National de Recherche sur les Transports et leur Securite. 
     One advantage of the information transmission device and method of the invention for systems using radiating waveguides is that it samples only a very small amount of energy, around 0.02 dB, from the radiating waveguide, so that transmission devices may be provided as often as the operation of the mobiles along the radiating waveguide makes necessary. 
     Another advantage of the information transmission device and method of the invention for systems using radiating waveguides is that they provide a simple and autonomous system with the minimum of components and connections. 
     Another advantage of the information transmission device and method of the invention for systems using radiating waveguides is that they do not require a continuous power supply. 
     Another advantage of the information transmission device and method of the invention for systems using radiating waveguides is that they can provide a precise location pulse signal. 
     Another advantage of the information transmission device and method of the invention for systems using radiating waveguides is that they can indicate the direction of movement of the mobile without ambiguity. 
     Other aims, features and advantages of the invention will emerge from a reading of the description of the preferred embodiment of the information transmission device and method for systems using radiating waveguides given with reference to the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a general view of a preferred embodiment of the information transmission device of the invention for systems using radiating waveguides. 
     FIG. 2 shows the radiating waveguide and its directional coupler of the transmission device of FIG. 1. 
     FIG. 3A shows the resonant cavity of the transmission device from FIG. 1. 
     FIG. 3B shows the top face of the resonant cavity and its modulator device. 
     FIG. 3C shows the resonant cavity and its device generating the signal representing the information to be transmitted. 
     FIG. 4 is a general view of the information transmission device and its remote power feed device. 
     FIG. 5 shows one embodiment of the modulated carrier wave receiver device on the mobile. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The IAGO system uses the great bandwidth of a TE 01  mode microwave waveguide for high bit rate transmission of information between mobiles and the ground. 
     The great bandwidth also enables an unmodulated additional carrier wave to be transmitted in the radiating waveguide. 
     This unmodulated carrier wave is emitted at a low level and propagates all along the radiating waveguide. 
     The unmodulated carrier wave is not strongly attenuated and it is amplified by the same in-line repeaters as are used to regenerate the other signals transmitted in the radiating waveguide. 
     The unmodulated carrier wave is therefore present over all the length of the radiating waveguide, and essentially inside the waveguide. 
     The unmodulated carrier wave is not discernible from the mobile and initially does not carry any identifiable signature or information. 
     In accordance with the invention, the information transmission device and method for systems using radiating waveguides, for example the IAGO system, sample some of the energy propagating in the waveguide in a manner that is not discernible in the overall energy balance at locations along the radiating waveguide that are strategic in terms of operation of mobiles. 
     The energy sampled is radiated to the mobile. 
     At this time, a local modulation signal that is required to be delivered to the mobile traveling along the waveguide is applied to the unmodulated carrier wave. 
     FIG. 1 is a general view of a preferred embodiment of the information transmission device of the invention for systems using radiating waveguides. 
     In the preferred embodiment of the information transmission device of the invention for systems using radiating waveguides, the mobile (not shown) is a rail vehicle. 
     It is clear that in other applications the mobiles can be waggons or any other mobile means. 
     As shown in FIG. 1, there is a resonant cavity 1 on one side of the radiating waveguide 2. 
     The radiating waveguide 2 and the resonant cavity 1 each comprise a respective directional coupler 3 and 4, on their sides facing towards each other. 
     The directional couplers are, for example, two circular apertures the dimensions of which are large in comparison to the period of the unmodulated carrier wave. 
     FIG. 2 shows the radiating waveguide of the transmission device from FIG. 1 and its directional coupler. 
     FIG. 3A shows the resonant cavity of the transmission device from FIG. 1 and its directional coupler. 
     In the IAGO system, the radiating waveguide operates in TE 01  mode. There is therefore virtually no electric field to the lateral sides of the radiating waveguide. 
     The apertures must therefore be large to achieve the required level of coupling; accordingly, this dimension is not very critical from the mechanical point of view. 
     A construction of this kind provides repetitive coupling coefficients in the order of -40 dB relative to the power level transmitted in the radiating waveguide. 
     The length of the resonant cavity 1 is made as small as possible so that the interior volume of the resonant cavity resonates in a TE 011  fundamental mode. In this type of embodiment of the resonant cavity, all directional characteristics are eliminated and the coupling coefficient remains exactly the same whether the radiating waveguide is fed from the upstream or downstream end. 
     The TE 011  fundamental mode resonant cavity is short-circuited at its ends and incorporates a half-wave resonant slot 5. 
     The half-wave resonant slot is formed on the large exterior face of the resonant cavity facing towards the rail vehicle. 
     The half-wave resonant slot is perpendicular to the slots 6 of the radiating waveguide. 
     The half-wave resonant slot radiates the energy coupled from the radiating waveguide towards the TE 011  mode resonant cavity. 
     The half-wave resonant slot radiates with linear polarization perpendicular to the regular slots of the radiating waveguide. 
     These regular slots are the transmission and speed measurement slots of the waveguide. 
     This radiation provides approximately 15 dB of decoupling relative to the signals transmitted by the transmission and speed measurement slots of the waveguide. 
     The carrier wave propagating in the waveguide, which is a pure sinusoidal signal, is locally coupled to the rail vehicle by means of the resonant cavity and its half-wave resonant slot. 
     This sinusoidal signal is modulated locally. 
     To achieve this a modulator device 7 such as a Schottky type diode, for example, is disposed between the edges of the half-wave resonant slot at a point which has a high impedance at the required frequency. 
     FIG. 3B shows the resonant cavity and its modulator device 7. 
     This diode is biased by a direct current applied to its terminals and when so biased short-circuits the half-wave resonant slot, the slot having a high impedance at this point at the working frequency in question. 
     This causes amplitude modulation of the pure sinusoidal signal sampled along the radiating waveguide. 
     The coupling coefficient between the radiating waveguide and the resonant cavity being in the order of -40 dB, the mismatch associated with this short-circuit at the timing rate of the modulation is not detectable in the radiating waveguide. 
     Likewise, considering a microwave power frequency level in the radiating waveguide, the modulated signal is re-injected into the radiating waveguide at best only at a level of -80 dB relative to the reference level, that is to say -40 dB in the radiating waveguide to resonant cavity direction and -40 dB in the resonant cavity to radiating waveguide direction. 
     The modulated signal produced in the resonant cavity is therefore not transmitted along the radiating waveguide and does not have any effect upstream or downstream of the resonant cavity. 
     The device 8 generates the signal representing the information to be transmitted to the rail vehicle. 
     This signal representing the information to be transmitted is a bit stream, for example. 
     The possible bit rate is high and is limited only by the switching time of the Schottky diode and the frequency of the pure sinusoidal signal. 
     To give an idea of the order of magnitude, several megabits per second may be available. 
     The device 8 generating the signal representing the information to be transmitted may comprise a picocontroller type device storing a frame in an EEPROM type memory and generating the frame repetitively for application to the Schottky diode as soon as it is supplied with energy. 
     Other suitable devices able to bias the Schottky diode at the rate of application of the information to be transmitted may be used. 
     As the energy present in the resonant cavity is very low, in the order of 40 dB below the power level present in the radiating waveguide, it is possible to dispose the device 8 generating the signal representing the information to be transmitted judiciously within the resonant cavity without significantly disturbing either the operation of this electronic circuit or the fundamental mode resonance of the resonant cavity. 
     FIG. 3C shows the resonant cavity and its device for generating the signal representing the information to be transmitted. 
     The device 8 generating the signal representing the information to be transmitted may advantageously be supplied with power, for example with a current of a few milliamperes at a voltage of 5 V, by a remote power feeding arrangement using a low-frequency signal, i.e. a signal at a few hundred kilohertz or even a few megahertz. 
     FIG. 4 is a general view of the information transmission device and its remote power feed device. 
     The low-frequency signal is coupled magnetically to the resonant cavity by means of two resonant loops 9, 10A or 10B. 
     For example, a serial type first resonant loop 9 is associated with the emission of energy and a parallel type second resonant loop 10A, 10B is associated with the reception of energy, the energy being emitted and received at the remote power feed frequency. 
     The energy emitting loop 9 is attached to the rail vehicle (not shown) and generates continuously a low level of energy, for example less than 1 watt, to be picked up by at least one energy receiver loop 10A, 10B attached to the resonant cavity 1. 
     The energy receiver loop 10A, 10B provides a remote power feed to the device 8 generating the signal representing the information to be transmitted when the rail vehicle passes. 
     Despite the fact that the microwave radiation from the energy emitting loop 9 is not closely controlled and may propagate relatively far from the resonant cavity by reflection or diffraction, the signal representing the information to be transmitted to the rail vehicle is generated only when the device 8 generating the signal representing the information to be transmitted is supplied with power via the remote power feed. 
     Protection against crosstalk is obtained by the fact that the microwave radiation from the energy emitting loop 9 is a low-frequency signal the amplitude of which decreases in accordance with the laws of magnetostatics, that is to say in inverse proportion to the cube of the distance between the emitter and the receiver. 
     In one embodiment a first energy receiver loop 10A is disposed on the upstream side of the resonant cavity 1 and provides a DC supply voltage V 1  as the rail vehicle approaches or moves away and a second energy receiver loop 10B is disposed on the downstream side of the resonant cavity 1 and provides a DC supply voltage V 2  as the rail vehicle moves away or approaches. 
     The device 8 generating the signal representing the information to be transmitted can therefore be continuously energized by the remote power feed as the rail vehicle passes from the upstream side to the downstream side of the resonant cavity or vice versa. 
     The transition from the DC voltage V 1  to the DC voltage V 2  or vice versa can be used to provide a signal indicating passage of the rail vehicle over the resonant cavity. 
     The transition from the DC voltage V 1  to the DC voltage V 2  can also be used to provide a signal indicating that the rail vehicle passed in the upstream to downstream direction. 
     The transition from the DC voltage V 2  to the DC voltage V 1  can also be used to provide a signal indicating that the rail vehicle passed in the downstream to upstream direction. 
     FIG. 5 shows one embodiment of the modulated carrier wave receiver device disposed on the mobile. 
     This receiver device 11 comprises an antenna 12 connected to a system 13 providing amplification, filtering at the frequency of the pure sinusoidal signal and amplitude detection, and its function is to reconstitute the information transmitted.