Abstract:
An interface device for interfacing a set of wayside systems with a radio transmitter includes a plurality of input ports each having at least one input for receiving a signal representing a state of a corresponding wayside system and first and second parallel data paths coupled to the plurality of input ports. Each data path includes input protection circuitry coupled to the inputs of the input ports for preventing short-circuit and open-circuit conditions from triggering a false input state, a multiplexer for selecting between the input port; and a processor for scanning the input ports with the multiplexer to determine the state of current signals appearing at the inputs. In response to determining the state of the current signals appearing at the inputs, the processor generates a message communicating a current state of the wayside systems for delivery to the radio transmitter.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/860,406, filed Nov. 21, 2006. 
    
    
     FIELD OF INVENTION 
     The present invention relates in general to railroad communications techniques, and in particular, to wayside monitoring systems. 
     BACKGROUND OF INVENTION 
     In any transportation industry, reliable communications systems are mandatory for avoiding serious, if not catastrophic, accidents. In the particular case of the railroads, reliable and secure communications must be maintained between railroad central offices, railroad locomotives, service vehicles operating on railway tracks, and wayside systems, among other things. 
     Railroad central offices normally communicate with a network of wireless base stations through wired telecommunications links. These base stations then support wireless communications with locomotives, service vehicles, and wayside systems. Electronic train management systems (ETMS) allow locomotives to communicate directly (peer-to-peer) with the wayside systems and base stations using on-board radios. The locomotives are therefore able to receive, for example, up-to-date wayside aspect information, track database updates, and track authorizations, well before the wayside systems (e.g. signals) are within sight. 
     Remote wayside interface systems monitor a corresponding set of wayside systems such as signals, switches, and track circuits and directly provide the locomotives with real-time critical aspect and status information. In addition to directly communicating with the locomotives, the wayside interface systems also provide this wayside status and aspect information to the central office via the network of base stations. 
     Given the criticality of the information being gathered and transmitted, reliability and security are key features in wayside interface system design and construction. Among other things, these systems must accurately ascertain the current state of the monitored signals, switches, and/or track circuits and then transmit that information to oncoming locomotives with minimal error. Furthermore, wayside interface systems must be substantially robust to withstand potentially severe field conditions, as well as be resistant to tampering and similar intentional human interference. 
     SUMMARY OF INVENTION 
     The principles of the present invention are embodied in one application in an interface device for interfacing a set of wayside systems with a radio transmitter, which includes a plurality of input ports each having at least one input for receiving a signal representing a state of a corresponding wayside system and first and second parallel data paths coupled to the plurality of input ports. Each data path includes input protection circuitry coupled to the inputs for preventing short-circuit and open-circuit conditions from triggering a false input state, a multiplexer for selecting between the input ports and a processor for scanning the input ports with the multiplexer to determine the state of current signals appearing at the inputs. In response to determining the state of the current signals appearing at the inputs, the processor generates a message for communicating a current state of the wayside systems to the radio transmitter. 
     Embodiments of the present principles advantageously minimize the chance of a catastrophic accident occurring through the use of redundant processing paths. Within a wayside interface module, dual parallel processing paths independently scan the input signals generated by monitoring devices monitoring a set of wayside systems and independently generate digital messages for transmitting to an associated radio. Opto-isolators or similar input protection circuitry protects against shorts and open-circuits at the interface module inputs from causing false input states. Moreover, the radio system processes the two independently derived messages to independently generate data representing the aspect of the monitored wayside systems (i.e. the current state of the signals, switches, and track circuits. Only if the independently derived aspect data match are those aspect data sent to the locomotives and central office. Hence, a failure of any component on either redundant processing path will cause an unknown aspect report to be generated thereby indicating that caution must be exercised by the train crews and dispatchers. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a high level diagram illustrating a small portion of a representative railroad communications system suitable for describing one particular embodiment of the principles of the present invention; 
         FIG. 2  is a more detailed block diagram of a wayside monitoring subsystem embodying the inventive principles; and 
         FIG. 3  is a block diagram illustrating a plurality of the wayside monitoring subsystems of  FIG. 3  chained together to increase the number of wayside systems that can be monitored. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The principles of the present invention and their advantages are best understood by referring to the illustrated embodiment depicted in  FIGS. 1-3  of the drawings, in which like numbers designate like parts. 
       FIG. 1  is high level diagram showing a small portion of a railroad communications system  100  embodying the principles of the present invention. Generally, system  100  supports wireless communications between a central office (network operating center)  101  and locomotives  102  located at various points around a rail system, direct communications between central office  101  and wayside monitoring systems, as well as direct communications between locomotives  102  and the electronic wayside monitoring subsystems, as discussed below in detail. 
     In communications system  100 , central office  101  communicates with packet radios on locomotives  102  through a wired telecommunications network and a series of packet radio base stations dispersed over thousands of square miles of geographical area through which the rail system operates. In the diagram of  FIG. 1 , two radio base stations  103   a  and  103   b  are shown for discussion purposes. 
     Communications system  100  also includes a series of wayside monitoring subsystems, which monitor wayside systems such as signals, switches, and track circuits and communicate the monitored information directly to locomotives  102  within the corresponding wireless coverage area, as well as to central office  101  though base stations  103 .  FIG. 1  shows two representative wayside monitoring subsystems  104   a  and  104   b . As examples of typical uses of wayside monitoring subsystems  104 , wayside monitoring subsystem  104   a  is shown monitoring a switch  105  and a three-lamp signal  106 , and wayside monitoring subsystem  104   b  is shown monitoring a hand-throw switch  109 . Also for illustrative purposes, two parallel sections of track  108   a  and  108   b  and a connecting track section  109  are shown in  FIG. 1 , which represent only a very small part of the overall track system. 
     Communications system  100  also includes a hotbox monitoring subsystem  110  which uses rail-side sensors to allow central office  101  to monitor the axle status of passing trains through packet data radios and wireless base stations  103 . In particular, railcar wheels, brakes, and trucks can be monitored for stuck brakes or overheated bearings, such that trains can be slowed or stopped before a catastrophic failure occurs. 
       FIG. 2  is a functional block diagram of a representative wayside monitoring subsystem  104  embodying the principles of the present invention. Wayside monitoring subsystem  104  includes a redundant wayside interface module (RWIM)  201  and a packet radio  202 , both of which will be discussed in further detail below. In the preferred embodiment, packet radio  202  is based on either a Meteor Comm MCC 545C or MCC 6100 packet data radio, although applications of the present inventive principles are not limited thereto. 
     In the illustrated embodiment, RWIM  201  supports thirty-two (32) input ports of two (2) signal inputs each, or a total of sixty four (64) inputs. The input signals are independently processed in two processing paths or channels (Channels A and B). In exemplary system  100  of  FIG. 1 , one port could be used to monitor switch  105 , one port to monitor each of three lamps of signal  106 , and one port to monitor hand throw switch  107 . In the preferred embodiment, the inputs into RWIM  201  are provided by Hall Effect sensors or relay contact closures associated with the current paths of the given monitored devices. 
     In the preferred embodiment, the two signals for each channel are decoded as follows:
         0=OFF (not active)   1=ON (active always on)   2=ON Flashing (active and flashing)   3=Failed or Unknown       

     Generally, according to the principles of the present invention, the state of each input is assumed to be safety critical, since reporting of a wrong state may send a false permissive state message to an approaching locomotive resulting in a hazard that could possibly lead to a fatal accident. Advantageously, RWIM  201  utilizes two (2) independent hardware paths to measure and produce two (2) independent sets of status bits for each of two channels channel (Channel A and Channel B). Each set of status bits are then sent to packet radio  202  where two independent software routines compute (by different methods) two aspects representing the overall state of the monitored wayside systems. The aspects are then compared, and if equal, a safety critical message is created and sent to approaching locomotive  102  and central office  101 . 
     As shown in  FIG. 2 , the thirty-two (32) two-bit input ports of each channel drive corresponding opto-isolation diodes  203   a - 203   b . The signal path for each input signal has an input source path and an input return path from the corresponding Hall Effect sensor or relay contact closure. In the illustrated embodiment, opto isolation divides  203   a - 203   b  provide greater than 2000 VRMS of isolation between the input return path and board ground. To activate any single input, i.e. to make the corresponding output on isolator block  203   a - 203   b  transition to an ACTIVE (ON) state, current must flow from the input source path through the opto-isolation diode to the input return path. Hence, an input short (across the input source and return paths) or an input open (i.e. a broken wire) will not cause an ACTIVE state at the corresponding output of opto isolation diode blocks  203   a - 203   b.    
     In the illustrated embodiment, the input threshold voltage required to activate any input is five (5) volts: Specifically to ensure that the input state is OFF, the input voltage must be less than four (4) volts and to ensure the input state is ON, the voltage must be greater than six (6) volts. Input hysteresis is greater than one-half (½) volt. 
     The outputs from opto isolation diodes  203   a - 203   b  are provided to corresponding thirty-two (32) by two-bit input multiplexers  204   a - 204   b . Multiplexers  204   a - 204   b  are under the control of corresponding Channel A or Channel B PIC processor  205   a - 205   b . In particular, processors  205   a - 205   b  scan the corresponding thirty-two (32) input ports of each channel to determine the states of the inputs of that channel. In the preferred embodiment, processors  205   a - 205   b  scan the associated thirty-two (32) input ports over approximately two (2) milliseconds, dwelling on each input port for about sixty (60) microseconds. The scans are repeated approximately every eleven (11) milliseconds. Since some inputs may represent flashing signal lamps, approximately three (3) seconds is required to determine the state of the channels (based on an assumed flashing rate of one (1) to two (2) seconds and a flashing duty cycle of 40/60 to 60/40). 
     Data generated by each processor  205   a - 205   b  is formed into a packet that contains an address associated with that processor, the processed channel data, a sequence number used to identify current data, and a thirty-two (32) bit CRCC that covers the address, data, and sequence number. The sequence number increments every time new data are placed in the given processor output buffer, which is typically every three (3) seconds. Data are also placed in the processor output buffer whenever the given processor  205   a - 205   b  detects a state change on any input. 
     Data are transferred between RWIM  201  and packet radio  202  via a serial bus including a  DATA IN  line, a  CLOCK IN  line, and a  DATA OUT  line, along with ground. In the preferred embodiment, the serial bus is CMOS driven (either 5.0 V or 3.3 V depending on the particular embodiment) and supports a cable between RWIM  201  and packet radio  202  of up to fifteen (15) feet. 
     Packet radio  202  operates through a signal I/O driver  206  and includes two (2) parallel processes  207   a  and  207   b , which are implemented on a processor platform  214  and independently process the messages received from RWIM processors  205   a  and  205   b . Packet radio processes  207   a - 207   b  operate as the bus master for the serial bus by supplying the clock via the  CLOCK IN  line and control signals via the  DATA IN  line. Data are transmitted from RWIM processors  205   a  and  205   b  to packet radio processes  207   a  and  207   b  on the  DATA OUT  line. 
     Packet radio processes  207   a  and  207   b  operate on their respective messages using two (2) different processing algorithms. In the preferred embodiment, packet radio processes  207   a  uses a state machine to cycle through the status bits received in the messages from RWIP processor  205   a  to generate a set of aspect bits representing the current overall state of the monitored signals, switches, and track circuits. This state machine may, for example, operate in response to a script downloaded to packet radio  202  through a serial port. 
     The two sets of aspect bits respectively generated by processes  207   a  and  207   b  are then compared in aspect compare block  208 , and if they match, the aspect is validated. Otherwise, if the two sets of aspect bits do not match, the aspect is tagged as invalid (i.e. a “99” aspect). The results are packaged into a message and a key-hashed message authentication code (HMAC) key is appended using a digital certificate (X.509), provided through the serial port of CIM  211 , by HMAC block  209 . (Onboard locomotive computers match the HMAC key to their internal database to verify that the source of the data is indeed from the proper sending wayside monitoring subsystem  104 .) 
     The generated wayside message is placed in the transmit queue  210 . Messages are sent to the locomotives  102  whenever there is an aspect change or when polled by a locomotive  102 . Similarly, messages are sent to central office  101  whenever an aspect change occurs or when the central office  101  polls the wayside monitoring subsystem  104 . 
     Configuration Information Module (CIM)  211  is a memory device that stores site specific configuration files through the use of a script file associated with radio  202 . (Generally, a site can be a locomotive, hyrail vehicle, wayside subsystem, hot box, or the like.) In particular, CIM  211  is locked to the corresponding site and is connected to the associated radio  202 . CIM  211  then stores radio configuration information, which is specific to the particular needs of the site. 
     RWIM  201  can interface with any monitoring device capable of forcing current through the opto isolation diodes  203   a - 203   b , including, for example, mechanical switches and relays, solid state relays, and Hall Effect sensors. In the illustrated embodiment, RWIM  201  is provided with self-test circuitry  212 , which allows Hall Effect sensors, when used, to be tested by forcing a current through the sensor to attempt to cause their output to change state. 
     In the preferred embodiment, RWIM  201  also has six (6) opto isolated outputs (not shown), with greater than two thousand (2000) VRMS isolation that can be used to wake-up track circuits or turn on signals. These outputs are not considered safety critical and are implemented on only one of the two data processing channels. 
     The RWIM channel capacity can be expanded up to one hundred and twenty eight (128) inputs by daisy chaining up to four (4) RWIMs  201   a - 201   d , as shown in  FIG. 3 . In the illustrative embodiment of  FIG. 3 , RWIMs  201   a - 201   d  operate in conjunction with packet radio  202  and a power supply  301 . A corresponding set of jumpers  302   a - 302   d  allow each RWIM  201   a - 201   d  to be individually addressed. Standard RS  232  connections  303   a - 303   b  allow data from the corresponding RWIM processors  205   a - 205   b  to pass through to the signal drivers  206  of packet radio  202 . RWIMs  201   a - 201   d  may be separated up to the maximum allowed by RS232 signal levels (&gt;100 feet). 
     Advantageously, the redundant design of wayside monitoring subsystem  104  ensures that a failure of any component on either channel will cause an unknown aspect report to be generated. Hence, a receiving locomotive  102  or central office  101  is actively notified in real-time of a potential hazardous, rather than receiving erroneous information that could lead to a catastrophic accident. 
     Although the invention has been described with reference to specific embodiments, these descriptions are not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternative embodiments of the invention, will become apparent to persons skilled in the art upon reference to the description of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed might be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. 
     It is therefore contemplated that the claims will cover any such modifications or embodiments that fall within the true scope of the invention.