Patent Publication Number: US-2023138011-A1

Title: Dual Band Radio for Railway Communications Applications

Description:
RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application 63/273,094, filed Oct. 28, 2021, which is incorporated herein in its entirety by reference for all purposes. 
    
    
     FIELD OF INVENTION 
     The invention generally relates to radio communication systems for applications supporting railroads and, more particularly, wireless messaging between an end of train and a head of train. 
     BACKGROUND 
     Modern railway operations, particularly those of class I freight railroads with long trains, require various electronic devices for monitoring, signaling, and controlling trains and devices located on trains. One such device is an “end of train” (EOT) unit or device attached to the rear of the last car of a train. Because the final car in a train may change at any point in a trip, the EOT unit needs to be relatively easily and quickly removed by train personnel and attached to the new final car. 
     An EOT unit is, therefore, typically an integrated device with a structure and enclosure that facilitates its attachment and removal from the train car, protects the equipment, and discourages unauthorized access to the equipment. Initially, EOT units were relatively simple devices with a signal light for the end of the train. However, EOT units have evolved to handle more functions and are now required by regulation on trains that go over 30 miles per hour and operate on heavy grades. EOT units now include additional equipment or components that monitor or interoperate with one or more subsystems on the train and perform signaling and communication functions. 
     For example, one of the functions of modern EOT units is to monitor the train&#39;s braking system pressure at the last car and report it or a loss of pressure to a head of train (HOT) unit or device located in, for example, the lead locomotive. If there is adequate pressure at the train&#39;s last car, the cars in front of it will have adequate pressure. Another function of an EOT is to provide emergency braking control to the rear section of a train. EOT units are thus capable of receiving an emergency braking signal from a HOT device. EOTs may also, for example, include GPS or other components for detecting geolocation to identify the end of train, train movement, and train speed. 
     A HOT unit will usually be capable of communicating over the local area network with other systems in a train&#39;s locomotive. HOT units are typically capable of communicating with computers and other circuits used to control the operation of the train and its various subsystems. 
     The HOT unit and EOT unit typically use radios to communicate wirelessly. Each unit will have a radio capable of transmitting to and receiving a wireless signal from the radio in the other unit. Wireless messages between EOT and HOT in North America are sent over a radio frequency (RF) link in the 450 MHz band and are expected to conform to the S-9152 standard in the Manual of Standards and Recommended Practices published by the Association of American Railroads (AAR). 
     SUMMARY 
     The invention pertains to improvements to radio frequency communications for railway applications and can offer additional advantages when used for radio frequency communications with an end of train (EOT) unit. 
     The 450 MHz band used for communication with an EOT unit does not provide a sufficiently robust communication channel between an EOT unit and the HOT for RF links conforming to the S-9152 standard when a train is very long. In certain situations, the RF link can have insufficient throughput or bandwidth to carry the amount of data that must be reliably transported for such communications. 
     Disclosed below are representative examples of a radio useful for an EOT unit and, optionally, a HOT unit that supports three RF link types. In the representative examples, the radio supports legacy S-9152 RF links in the 450 MHz band, ITCR (Interoperable Train Control Radio) links in the 220 MHz band, and RF links in the 450 MHz band that uses a higher-order modulation and coding scheme than provided by S-9152. Each radio integrates the capability of supporting all three link types into one radio that allows for simultaneous reception of a message on any of the three RF link types. 
     ITCR networks using the 220 MHz band are currently deployed in the United States and elsewhere for use by railroads to transport positive train control (PTC) messages between base stations and train locomotives using RF links specified by the ITCR standard. At the lower frequencies used by ITCR, RF signals exhibit better propagation and less susceptibility to noise. ITCR radio frequency links also allow for higher-order modulation, which allows for higher throughput. However, 220 MHz radios cannot be deployed immediately and ubiquitously for EOT to HOT communications, nor do all railroads operate 220 MHz ITCR networks. 
     Deploying a new radio in a HOT or EOT unit that supports three RF link types for transporting of EOT/HOT messages enable the unit to interoperate with legacy radios that support only S-9152 RF links, units that have radios that support ITCR RF links, and, in the future, units that use an enhanced RF link type for the 450 MHz band, with higher-order modulation and coding. With the ability for the radio to receive a message on any of the three RF link types, an EOT with the radio can receive emergency messages from a HOT unit on any one or all of the three links simultaneously. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1   a    is a schematic diagram of a first, nonlimiting, representative example of a dual-band radio for EOT communication. 
         FIG.  1 B  a schematic diagram of a variation of the first, nonlimiting, representative example of a dual-band radio for EOT communication of  FIG.  1     a.    
         FIG.  2    is a schematic diagram of a second, nonlimiting, representative example of a dual-band radio for EOT communication. 
         FIG.  3    is a schematic diagram of a third, nonlimiting, representative example of a dual-band radio for EOT communication. 
         FIG.  4    is a schematic diagram of a fourth, nonlimiting, representative example of a dual-band radio for EOT communication. 
         FIG.  5    is a schematic diagram of a fifth, nonlimiting, representative example of a dual-band radio for EOT communication. 
         FIG.  6    is a schematic diagram of a sixth, nonlimiting, representative example of a dual-band radio for EOT communication. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, like numbers refer to like elements. 
     The examples of radios described below are digital radios implemented as a software defined radio (SDR). An SDR implements some conventional components of a radio, such as modulators, demodulators, filters, mixers, etc., using software running on a processer or other programmable hardware circuit, examples of which a digital signal processor (DSP), field-programmable gate arrays (FPGA), and general-purpose processors. In addition to hardware for executing the processes, an SDR will also have additional hardware, such as memory for storage, analog amplifiers and filters for its RF stage, analog to digital (ADC) and digital to analog (DAC) converters, interfaces, and power supplies. An SDR provides several possible advantages, including multi-channel capability and the ability to adapt to different channel conditions. 
     For example, a digital radio receiver functions or acts like a conventional radio but processes a digitized version of an RF or IF frequency division multiplexed (FDM) signal for an entire band. After the received RF or IF frequency signal is processed by a radio frequency stage, the digital receiver samples the FDM signal using an analog-to-digital converter to generate a discrete, time-invariant signal representing a continuous sequence of samples. The digitized FDM signal is then demodulated and decoded according to the modulation and coding scheme being used by the RF link using a processor that will, in effect, down-convert and filter the sampled FDM signal into separate baseband digital signals corresponding to different predefined channels within the band for detection of data that was transmitted. Similarly, a digital baseband signal (usually as in-phase and quadrature-phase signals) generated according to a particular modulation and coding scheme is used to modulate the phase and/or amplitude of a carrier frequency. 
       FIGS.  1   a ,  1   b   ,  2 ,  3 ,  4 ,  5 , and  6  illustrate schematically representative examples of embodiments for a radio capable of supporting three RF link types for use by an end of train (EOT) or a head of train (HOT) unit with separate RF stages for signals in a first RF band and signals in a second RF band. In these examples, the first RF band is the 450 MHz RF band, and the second RF band is the 220 MHz band. 
     Radios  100 ,  200 ,  300 ,  400 ,  500 , and  600  shown in  FIGS.  1   a  and  1   b    to  6 , each have two RF stages, one for the first RF band and one for the second RF band. Each RF stage has a receiving path for receiving signals in the corresponding RF band and a transmission path for transmitting a signal in the corresponding RF band. In the examples of radios  100 ,  200 ,  300 ,  400 , and  500 , the first RF stage includes a first band RF transceiver  102 , and a second RF stage includes a second band transceiver  104 . Each transceiver has both a receiver and a transmitter integrated as a single unit, with separate receiving and transmission paths within the unit. Radio  600 , of  FIG.  6   , uses separate receivers and transmitters. Two RF stage receiving paths are implemented by a first RF band receiver  616  and second RF band receiver  618 , and two RF stage transmission paths provided by a first RF band transmitter  604  and second RF band transmitter  606 . Unlike the transceivers used in radios  100  to  500 , separating the transmitter and receiver can allow different configurations that permit certain benefits or advantages, and possibly disadvantages. Each of these radios is an example of a radio with at least two, independent RF stage paths corresponding to each of the RF bands, allowing the radio to be capable of independent RF stage operation in each frequency band. Therefore, the transmission and receiving operations in each RF band do not interfere with either other. 
     For each of these examples, a shared baseband processor  106  coordinates the operation of the RF stages. The baseband processor is programmed to handle frequency conversion to and from baseband for both 220 MHz signals and 450 MHz band signals and channel filtering. It is also programmed to handle modulation/demodulation for baseband signals with legacy S-9152 coding and modulation schemes for the 450 MHz band, enhanced modulation and coding schemes for the 450 MHz band that might be adopted in the future for communications with an EOT unit, and modulation and coding schemes specified by the ITCR standard for RF links in the 220 MHz band. In this example, the shared baseband processor  106  is implemented by a field-programmable gate array (FPGA) and is labeled as such in the figures. However, as explained above, the shared baseband processor could be implemented using a digital signal processor or another type of processor. References to FPGA should be understood to include alternative implementations such as DSPs or other processors capable of being programmed as described unless explicitly stated otherwise. 
     Applications software for the EOT application running on microprocessor  120  processes data streams produced by the demodulation and decoding of the baseband processor  106 . Although not shown, the microprocessor may be connected to nonvolatile storage in the form of EEPROM to store configuration data; memory for storing application and operating system code, such as flash memory; a working memory, such as RAM; an Ethernet network interface, and a USB data interface. It communicates with the FPGA over, for example, a serial peripheral interface (SPI). 
     Referring now to  FIGS.  1   a  and  1   b   , each RF transceiver  102  and  104  has a converter (represented by converters  108  and  110 , respectively) for converting analog to digital signals (for received signals) and digital to analog signals (for transmission). The analog to digital conversion samples a RF or IF analog signal from the receiving path in the RF stage of the transceiver to generate a digital signal that is communicated to the shared baseband processor  106 . The digital to analog conversion process converts a digital baseband signal to an analog signal for the transmission path in the RF stage of the transceiver. 
     In the example of  FIG.  1   a   , the first band RF transceiver is adapted to transmit and receive frequency division multiplexed (FDM) signals in the 450 MHz band used by S-9152 using a dedicated antenna  112 . The second bandwidth transceiver is adapted to transmit and receive radio frequency signals in the 220 MHz band used by ITCR using antenna  114 . 
     In  FIG.  1 B , the transceivers  102  and  104  share a dual-band antenna  116  capable of transmitting and receiving signals in the 220 MHZ and 450 MHz bands. Transceivers  102  and  104  are coupled to antenna  116  through a duplexer filter circuit represented by bandpass filters  118  and  119  to allow the RF stages for each transceiver  102  and  104  to share the antenna. This circuit is controlled by, for example, the baseband processor  106 . The duplexer filter circuit allows the paths of the two transceivers to be combined in the RF stage to share a single dual-band antenna. However, adding a duplexer filter circuit will introduce signal loss and increase the cost and size of the radio. 
     Referring now to  FIG.  2   , radio  200  is similar to radio  100  except that it utilizes a dual ADC/DAC  202  that receives the output of the RF stage of transceivers  102  and  104 , thus avoiding separate ADC/DACs for each transceiver as shown in  FIGS.  1   a    and  1   b.    
     In  FIG.  3   , radio  300  is another representative and nonlimiting example of a radio configured for supporting three RF link types in which the received signal of one or both the transceivers are mixed to produce outputs for both transceivers that are adjacent to one another in frequency before digitization. In this example, the received signal output from transceiver  102  is mixed by mixer  306  with a signal from oscillator  307  to produce a signal that is frequency adjacent with the received output signal from transceiver  104 . These signals are then combined using combiner  308  before being digitized by analog to digital converter (ADC)  302 . The combining can be done at the radio frequency or an intermediate frequency, depending on the sampling frequency and the use of under-sampling or oversampling. This arrangement allows both bands to be processed simultaneously with a single ADC. The two signals can be separated again in the baseband processor  106  using digital filtering. 
     In  FIG.  4   , radio  400  resistively splits the received signal from dual-band antenna  116  using splitter/combiner  402  and tunes one circuit to 450 MHz for first band transceiver  102  and the other circuit to 220 MHz for second transceiver  104 . Similarly, the splitter/combiner  402  combines the transmitted signal before amplification. This configuration allows for the use of a single dual-band antenna but at the cost of a 3 dB loss when the signal from the antenna is split, thus reducing the sensitivity of the receiver circuit in each of the transceivers  102  and  104 . A dual ADC/DAC  404  coupled with the first band transceiver  102  and the second band transceiver  104  converts between analog and digital signals for processing by baseband processor  106 . 
     Radio  500  in  FIG.  5    is an example of a radio that supports three RF links in which the receiver and/or transmitter are switched between 450 MHz and 220 MHz operations. The switching is represented by switches  502  and  504 , which are controlled by baseband processor  106 , to connect in an alternating fashion either first band transceiver  102  or second band transceiver  104  in series with the dual-band antenna  116  and ADC  506 . This arrangement allows for a single dual-band antenna and a single ADC/DAC, and thus less circuitry and lower cost. However, it achieves these benefits at the expense of creating a “deaf” receiver during the portion of time the transceiver is operating on the opposite band. 
     Radio  600  in  FIG.  6    is a representative example of an embodiment of a radio for railway applications that is configured for and is capable of simultaneously supporting three RF link types. This embodiment allows the sharing of a broadband RF power amplifier  602  by the first band transmitter  604  and the second band transmitter  606  by switching transmit paths through the radio. Switch  608  connects the first RF band transmitter  604  or the second RF band transmitter  606  to the broadband power amplifier  602 . Switch  610  connects the output of the digital to analog converter DAC  612 , which converts the digital baseband signal generated by the baseband processor  106  into an analog signal for modulating the carrier signal of the transmitter to which it is connected by switch  610 . A transmit/receive switch  614  connects the dual-band antenna  116  to the broadband power amplifier for transmission mode to broadcast the transmitted signal. The transmit/receive switch  614  connects the dual-band antenna  116  to the first RF band receiver  616  and second RF band receiver  618  through a splitter  620 , which splits the signal between the two receivers. In this example, the output signals from the first band and second band receivers are digitized using a dual ADC  622 . However, the outputs of the first and second band receivers could be, for example, digitized as shown in the other examples of radios described above. 
     The preceding description is of exemplary and preferred embodiments. The invention is defined by the appended claims and is not limited to the described embodiments. The embodiments are, unless otherwise noted, nonlimiting examples. Alterations and modifications to the disclosed embodiments may be made without departing from the invention. Furthermore, unless expressly defined otherwise, the meaning of terms used in this specification that are not explicitly defined are intended to have their ordinary and customary meaning to those in the art and not be limited by any of the characteristics or features of the example or embodiment that is being described using the term.