Radio communication apparatus for rail and tram vehicles

Abstract: Radio communication apparatus for rail and tram vehicles comprising at least one transmission unit (T) and at least one reception unit (R) mounted on corresponding coaches (3) of a vehicle formed by a plurality of coaches (3), each of said transmission (T) and reception units (R) being associated to at least a corresponding antenna (1; 2) able to transmit and respectively receive radio signals exchanged by said units (T, R) within the space said signals propagate, characterized in that the propagation space of said signals consists of a wave guide delimited on top by the platform or underbody (30) of the coaches (3) which form the vehicle, at the bottom by the rails plane (4) and, laterally by the trucks and wheels (31) of the coaches (3).

Description: The present invention refers to a radio communication apparatus for rail and tram vehicles. As it is known to those skilled in the art, the communications on board of trains take place mainly via cable, with an array of connections which can be found only on special vehicles, having a strictly fixed composition or configuration, such as the underground and the so-called "Eurostar" trains. In case of vehicles whose composition or configuration may be varied, such as the express or local passenger trains and goods trains, no means or system of communication is provided for exchanging communications, that is, signals forwarding information of a preset nature and type to and from the components of the vehicle and able, for example, to control the coaches being pulled, that is, to control identification data of the individual coaches, as well as diagnostics and automation data of on-board subsystems among which, for example, bu not exclusively, the braking subsystem. Moreover, it should be noted that the adoption of this type of system, allowing the transmission of signals through dedicated cables, implies a standardization of elements, such as cables and connectors, to ensure a perfect continuity of the transmission line during the formation of trains, especially those traveling on international routes and subject to variations of composition in the number and type of wagons and/or locomotives along the routes to be covered. The standardization of the transmission material brings about also some drawbacks of economic character, inasmuch as all the wagons and locomotives must be provided with the same transmission equipment and materials. To overcome the above drawbacks, typical of via-cable transmissions, radio connections have been experimented based on the use of standard radiotelephones or microwave directional systems. In the first case, the connection between locomotives and coaches or wagons requires the use of higly powerful transceivers whose antennae are usually positioned on the roof. This system is essentially based on the so-called brute-force principle, which provides for considerable powers to counteract the fading effect (drastic attenuation of the transmitted signals) correlated to the multipath phenomenon (according to which, the electromagnetic waves travel on multiple paths due to reflections from obstacles). The said system is exclusively suitable for so-called "head-tail" and "head-mid-tail" transmissions, that is, for transmission between the leading and trailing locomotives, as weel as mid locomotives if any, and allows a correct transmission and reception of signals only on open spaces. In fact, within tunnels and on lengths delimited by walls taller than the vehicle the transmissions are ineffective and characterized by long periods of blackout, that is, by a connection interruption (fading). To overcome the said drawbacks a solution has been proposed which provides for using a plurality of microwave transceivers associated to directional antennae located on both sides of each wagon to prevent interruption of connection between curved lengths. Said transceivers form relay terminals in the same way as ground radio links do, to allow the sequential passage of signals from one wagon to the other. Associated to each signal is a code representing the address of the target wagon. This known system for transmissiona and reception of signals on railway vehicles is to meet the same standardization requirements as for the wired systems, inasmuch as all the wagons must be likewise equipped. Moreover, the use of microwaves implies a greater attenuation of transmitted signals in the presence of such obstacles as heaps of snow sideway of the rails. US 4,207,569 discloses a waveguide for conducting radio frequency signals along a railroad line comprising the ballast, ties and rails of the railroad line. The main object of the present invention is to provide a radio communication apparatus for railway vehicles which is of high reliability, applicable to existing rolling equipment, without requiring heavy standardization and with no need of providing each wagon or coach with a transceiver unit. This result has been achieved, according to the invention, by providing an apparatus having the features indicated in claim 1. Further characteristics being set forth in the dependent claims. The advantages deriving from the present invention lie essentially in that it is possible to ensure a perfect continuity of radio link under any travel condition, for any composition and length of the vehicle, also under particularly adverse environmental conditions, as well inside tunnels and closed spaces; that the connection is ensured even when not all the wagons or coaches of the vehicle are equipped with the apparatus according to the invention; that it is possible to establish a connection with one or more stationary posts located along the vehicle route, also when the vehicle is running; that an apparatus according to the invention is relatively simple to make, lightweight and easily installable on existing rolling equipment without any structural modification of the latter. These and other advantages and characteristics of the invention will be best understood by anyone skilled in the art from a reading of the following description in conjunction with the attached drawings given as a practical exemplification of the invention, but not to be considered in a limitative sense, wherein: Fig. 1 is a schematic back elevation view of a railway wagon provided with an apparatus according to the invention; Fig. 2 is a schematic view in longitudinal section of a railway vehicle showing the pattern of field lines in the space surrounding the wagons of the same vehicle; Fig. 3 is a block diagram of a possible embodiment of an apparatus according to the invention; Fig. 4 is a schemativ representation of the connections between the antennae of the transmitting and, respectively, receiving units of the apparatus of Fig. 3; Fig. 5 is a graph showing the subdivision in four-channel bands of the available spectrum. Reduced to its basic structure, and reference being made to the figures of the attached drawings, a radio communication apparatus for railway vehicles according to the invention comprises at least one transmission unit (T) mounted on a corresponding locomotive or coach or wagon, and at least one reception unit (R) mounted on a corresponding locomotive or coach or wagon, to said units (T, R) being associated at least a corresponding antenna (1; 2) to allow them to be radio-linked. The said antennae (1, 2) have longitudinal development and are vertically mounted in correspondence of the bottom metal platform or underbody (30) of the respective coaches (3) and oriented toward the plane (4) of the rails, so that the waves transmitted by at least one antenna (1) of said at least one transmission unit (T) will propagate in a wave guide delimited on top by the platforms or underbodies (30) of the coaches (3) that form the vehicle, at the bottom by the surface (4) of the rails and laterally by the metal trucks and wheels (31) of the same coaches (3). In practice, the vehicle, cooperatively delimited by the rails surface and the vehicle coaches, is used as a wave guide for the signals exchanged between said transmission and reception units, the antennae of said units being permanently positioned inside this guide. As described later on in greater detail, by a proper selection of the such factors as frequency and polarization of the signals, mode of transmission and reception, configuration and positioning of the antennae, and processing of received signals, it is possible to obtain each time the optimal configuration of the system in relation to the vehicle composition, without this constituting a limitation of the operation of the same system. By using the wave guide above defined, the wavelength of the signals exchanged between said transmission and reception units may be in the range of about one tenth to few times the height of the platform (30) of the coaches (3) from the plane (4) of the rails. In practice, since the diameter of the wheels (31) of coaches (3) is in the order of one meter, it is believed that the optimal wavelength value could be between fifty and one hundred centimeters. However, given the geometrical characteristics of the transmission channel formed by the wave guide, it is possible to resort to wavelenghts ranging from five centimeters to ten meters. The considerable extent of the interval of usable frequences allow to skip those already intended for other telecommunication applications and/or services. As far as the signal polarization is concerned, it should be noted that the wave guide being used supports preferably the vertical polarization, especially when the height of the propragation channel is less than half a wavelength. Hoever, upon using lower wavelengths, it is possible to resort also to the circular polarization. As far as the mode of signal transmission and reception is concerned, a higher reliability and a reduced cost of the connections are ensured by adopting transmissions of enlarged, or so-called wide band spectrum, such transmissions allowing an improvement in the quality of the received signal and exhibiting a marked characteristic of immunity over any interference and of compatibility with neighboring transceiver units. For example, according to the invention, the available band may be subdivided into two or more subands to each of which a transceiver unit is made to correspond - as illustrated in the diagram of Fig. 5 which indicates the case of transmission and reception of signals over four channels (C1, C2, C3, C4). The antennae (1, 2) that can be used for an apparatus according to the invention, both for the transmitting and receiving sections, may be of monopole quarter-wave stylus type, in their most simple constructional form. Use may however be made of flat or stripline antennae provided on printed circuits. Advantageously, for each transmitting unit (T) and for each receiving unit (R) use may be made, according to the example referring to the figures of the attached drawings, of four like antennae (1; 2) disposed in alignment with and equidistant from each other along an axis (r-r; r'-r') transversal to the direction of development of the coaches (3) which support the same antennae, so as to form curtains (CT; CR) inside the said wave guide which are orthogonal to the direction of advancement of the vehicle. The antennae (1, 2) of each transmitting (T) and receiving (R) unit may be spaced apart by at least half a wavelength. In the example of Figs. 3 and 4, the antennae (1) of the transmitting unit (T) are fed in parallel and in-phase, to obtain the effect of a single antenna with maximum directivity towards the receiving unit (R). The signals to be transmitted are fed to a modem (5) and from this to four radiotransmitters (6) associated to a duplexer (7) which, in turn, is connected to a power adder (8) which the antennae (1) lead to. Each of the antennae (2) of the receiving unit (R) feeds a corresponding receiver (60) via a diplexer (80). The output of the receivers (60) is connected to a logic adder (70) associated to a corresponding modem (50) whose output corresponds to the signals transmitted via the modem (5) of the transmitting unit (T). Each curtain of antennae (CT, CR) is easily reconfigurable by means of electronic switches to function both as transmitting and receiving means. According to the invention, provision is made, advantageously, for suitably processing the signals exchanged between said units (T, R) to prevent any fading phenomenon. More particularly, use is made of a redundant coding of the messages with repetition thereof at predetermined intervals, as well as of correlation techniques, so that the priority-messages result already acknowledged by the receing terminal and, therefore, able to be withdrawn and reconstructed by the same terminal even in the presence of disturbances. Due to the typical dimensions of a wave guide delimited by a railway vehicle in cooperation with the rails surface, the operating frequence may be conveniently in the range of 30 to 3000 MHz and more advantageously 100 to 1000 MHz. To avoid using frequencies already allocated to other applications experimental tests have been conducted in conformity to the law, with signals at 433.92 MHz. With this frequency it is possible to transmit up to 10 mW ERP (Equivalent Radiated Power) without needing any licence. Since the law provides for no restrictions to the fabrication of LPD (Low Power Devices), the fact of being able to use an apparatus radiating low-power signals is particularly advantageous in view of freely equipping, whith no law-enforced restrictions, a significant number of vehicles. The present apparatus is able to meet such requirement even if applied to transportation means such as goods trains longer than a kilometer, thanks to the low attenuation of the signals within the selected propagation channel which causes the same signals fading as in the free space. In the conventional transmission-reception systems said signals fading is far more marked owing to the presence of multiple obstacles like the tunnels. The antennae that can be used for this application may be of stylus type and as long as eighteen centimeters approximately, that is, of negligible dimensions with respect to the size of the coaches to which they are anchored. The anchorage of the antennae (1, 2) to the platform or underbody of the coaches may be made in the same way as for common antennae on vehicles, and the feeding thereof is ensured by means of common coaxial cables. Owing to the low losses in the cables and the selected operating frequencies, the transmission and reception units (T, R) of the apparatus can be housed in the respective coaches (3) under favourable environmental conditions. As previously mentioned, upon reception mode, the antennae (2) are associated to corresponding receivers (60), the latter being in a number equal to that of transmitters (6) of the transmitting unit (T). The output signal on the receiving curtain (CR) are sent to a processor able to discriminate the best signal and reconstruct the original message, transmitted by the unit (T), also by deriving it from the signals transmitted in parallel on the other channels. For example, assuming an operating band of 1.74 MHz, this band may be subdivided into four 400 kHz channels (C1, C2, C3, C4) of amplitude (A), while leaving a guard channel of about 40 kHz for each pair of adjacent operating channels. Under these conditions, signals can be transmitted with a speed up to 100 Kbit/s, so that a digital message of 100 bits can be transmitted in one thousandth of a second. The above example is indicative of the possibilities offered by the present apparatus, also when considering that for railway applications no such a wide band is required. Actually, should the signal band be reduced by one tenth, it would be possible, in one thousandth of a second, to transmit the same signal ten times and with such a redundancy as to ensure a correct reception thereof. On the other hand, with the above indicated signals' feeding speed and using the spread spectrum transmission technique allowing a power gain directly proportional to the ratio between the signal band and the band of the available radiofrequency channel - four channels of 400 kHz and a signal band of 10 kHz being available - the equivalent gain will be equal to 40, which corresponds to the result obtained by using a transmitter of 400 mW instead of 10 mW ERP. The contemporary use of more channels gives the transceiver system a great operating reliability. Although the number of usable channels is not a limiting factor over the correct operation of the apparatus according to the invention, it is assumed that the optimal number of channels is two to four. The present apparatus is intended in particular for application in rail and tram vehicles in which the need arises for radio-linking always a huge number of coaches belonging to the same train. Owing to the fact that the electromagnetic field (schematically represented by a plurality of vertical arrows oriented upwards in Fig. 2) is not fully confined inside the above defined wave guide, but it results partly scattered outside because of the wave-guide's side walls delimited by the trucks and the wheels of the coaches being discontinuous, the signals result capable of being received also by fixed stations located at predetermined sites of the railway line. Vice versa, one or more fixed stations may send signals for enquiries and data to one or more receiving units (R) of the present apparatus. Thanks to the wide band available, that is, to the possibility of exchanging data in digital form at high speed, the link between the vehicle and the fixed stations along the route can be ensured even if the running vehicle's speed is very high. For example, supposing that a guarded level-crossing be monitored by a television camera, the signals corresponding to the image taken by the TV camera can be sent, either via cable or radio, to a station located at a predetermined distance upstream of the level-crossing, in order to transmit the said signals to the vehicle upon the transit of the latter past the said station. In this way, the said image is made available to the engine driver a long way off from the monitored site. Again by way of example, the possibility of establishing a link with a fixed station allows transmitting, from the vehicle, data relevant to the identification and composition of the train. Besides, the transmission band available is more than sufficient for transmitting also vocal messages in digital form, which allows avoiding any fading and distorsion of the propagation channel.

Claims: Radio communication apparatus for rail and tram vehicles comprising at least one transmission unit (T) and at least one reception unit (R) mounted on corresponding coaches (3) of a vehicle formed by a plurality of coaches (3), each of said transmission (T) and reception units (R) being associated to at least a corresponding antenna (1; 2) able to transmit and respectively receive radio signals exchanged by said units (T, R) within the space said signals propagate, the propagation space of said signals consists of a wave guide being delimited on top by the platform or underbody (30) of the coaches (3) which form the vehicle, at the bottom by the rails plane (4) and laterally by the trucks and wheels (31) of the coaches (3), characterized in that the antennae (1, 2) of said transmitting (T) and receiving (R) units are supported by the platform or underbody (30) of the respective coaches (3) and that each of said transmission unit (T) and to each reception unit (R) is associated a corresponding plurality of equidistant antennae (1; 2) in alignment to each other and transversal to the longitudinal plane of development of the respective coaches (3). Apparatus according to claim 1, characterized in that the wavelength of the signals exchanged between said at least one transmission unit (T) and said at least one reception unit (R) being in the range of about one tenth to few times the height of the platform or underbody (30) of the coaches (3) from the plane (4) of the rails. Apparatus according to claims 1 and 2, characterized in that the wavelength of said signals is between fifty to one hundred centimeters. Apparatus according to claim 1, characterized in that the transmission of said signals is of a wide band type over a plurality of channels. Apparatus according to claim 1, characterized in that said signals are digital signals. Apparatus according to claim 1, characterized in that said antennae (1, 2) are reconfigurable by means of electronic switches to be suited for both transmission and reception of said signals.

Inventors: PIATTELLI MAURIZIO, PIATTELLI, MAURIZIO
Applicants: RAIL & RADIOPATENT L L C, RAIL & RADIOPATENT L.L.C.
Application year: 1999
Main classification: B61L15
IPC codes: B61L3, B61L15