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Any wireless system communication system used in an IPTC system must not only meet the requirements and goals of the Rail Safety Improvement Act of , but also must meet the transmission band requirements mandated by the Federal Communications Commission FCC , including, for example, those related to frequency band allocation, channel width and spacing.

Moreover, in addition to meeting all of the government imposed requirements, an IPTC system must also meet all of the engineering demands placed on any system being deployed in the harsh railroad operating environment.

The principles of the present invention are embodied in methods and systems for supporting railroad communications, particularly interoperability positive train control systems. According to one representative embodiment, a method is disclosed for implementing communications in a railroad communications system having a base station radio and remote radios, the remote radios including a mobile radio and a wayside radio.

A common radio communications channel is assigned for allowing a remote radio to connect with the base station radio using a carrier sense multiple access CSMA communications protocol. A local channel is assigned for allowing communications between the radio base station and the remote radios and between the remote radios, wherein communications on the local channel utilizes a selected one of fixed time division multiple access FTDMA and dynamic time division multiple access DTDMA communications protocols.

According to another representative embodiment, a method of messaging in a railroad communications system is disclosed, which includes generating a message with at an application layer, the message associated with a message handling code. The message and the message handling codes are passed to a transport layer and the message is fragmented.

The fragmented message and the message handling code are passed to a network layer implemented, where the fragmented message is selectively segmented as indicated by the message handling code.

The selectively segmented message and the message handling code are passed to a link layer and a packet is formed, which includes packet type information and data parts. The packet is passed to a physical layer and a preamble is added.

The preamble and packet are transmitted with a radio. The embodiments of the principles of the present invention realize a number of significant advantages. Embodiments of the principles of the present invention are particularly advantageous in implementing ITPC systems, since they support multi-channel communications, prioritized messaging, wayside monitoring, and unicast and broadcast transmissions, among other things.

These principles can be implemented using different radio frequency waveforms and data bit rates. Messages can be forward error correction encoded or transmitted without forward error correction encode, as required to optimize efficiency. 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:.

The principles of the present invention and their advantages are best understood by referring to the illustrated embodiment depicted in FIGS. Definitions of selected terms and acronyms used in the present text and drawings are provided in Table 1 of the Appendix. Generally, system supports wireless communications between a central office network operating center and locomotives and other railroad vehicles located at various points around a rail system, as well as direct communications between locomotives and the electronic wayside monitoring subsystems, discussed below in detail.

In communications system , central office communicates with packet data radios on locomotives 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. Communications system 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 within the corresponding wireless coverage area, as well as to central office , though base stations As examples of typical uses of wayside monitoring subsystems , wayside monitoring subsystem a is shown monitoring a switch and a signal , and wayside monitoring subsystem b is shown monitoring a hand-throw switch Also for illustrative purposes, two parallel sections of track a and b and a connecting section are shown in FIG.

Mobile remote radios are those radios disposed on locomotives and other railroad vehicles. The present inventive principles are generally embodied in wireless communications systems for IPTC applications. One challenge with such IPTC applications is the need to maintain multiple communications paths between various communications nodes within the system.

In addition, these multiple communications paths must support the exchange of different types of information while still meeting all of the wireless regulatory requirements imposed by the FCC.

For example, a communication path must be maintained between mobile remote radios on locomotives and central office to support the exchange of such information as locomotive location reports, locomotive health and diagnostic data, movement authorities, files, and network management data. Another communication path must be established between the mobile remote radios on railroad non-locomotive vehicles not shown and the central office The data traffic in this path includes vehicle location reports, work reports, email, and material requisitions.

Another set of communication paths are required for maintaining communications with the fixed remote radios at railroad waysides In this case, a communication path is required between the radios at waysides and central office for supporting signal system health and status monitoring, centralized control of control points, and wayside defect detector system data and alarms.

A further communication path is required between the mobile radios on locomotives and the radios at waysides , which supports wayside status updates provided to locomotives in the proximity of a given set of waysides. In a PTC system, trains require a status update from each approaching wayside. For each wayside within 3. It is also desirable that the wayside status updates are forwarded to central office Finally, another communications path is required between the mobile remote radios on locomotives and non-locomotive railroad vehicles and the mobile remote radios on other locomotives and non-locomotive railroad vehicles.

This path supports peer-to-peer proximity position reports so that one mobile radio is aware of the locations of nearby mobile radios. In particular, the frequency channels in the MHz band are paired into base radio frequency channels and mobile radio frequency channels, with each base radio transmit frequency taken from the MHz range and paired with a mobile radio frequency from the MHz range.

Currently, according to FCC regulations, a mobile radio may transmit or receive on either a mobile radio or base radio frequency, while a base radio can transmit only on a base radio frequency. In the future, the FCC may also allow a base radio to transmit on a mobile radio frequency, subject to certain to antenna height and power restrictions.

For example, a base radio transmitting on a mobile radio frequency may be restricted to antennas of less than 7 meters in height or to powers less that 50 Watts ERP.

The multi-channel capability of a software defined radio SDR provides several advantages, particularly in railroad applications. Among other things, with multi-channel capability, a locomotive can receive information from a base station and a wayside monitoring subsystem simultaneously.

Additionally, locomotives and base stations can receive status messages from multiple wayside monitoring subsystems simultaneously. This in turn provides the ability to support communications with a high density of waysides in city areas, which is highly desirable in IPTC systems.

The subsystems within railroad communications system operate in conjunction with external link manager ELM , which is a software application that is the bridge between an ITC Messaging System, running on a host computer and the ITC MHz wireless network.

For example, in the office area, the ELM will run on an office server, and in the locomotive and wayside areas, the ELM will run on a processor within equipment local to the area. In railroad communications system , all primary communications to and from a given radio are made through an ELM.

The ITC Messaging System preferably expects each non-IP underlying transport to provide an ELM that will hide the details of the underlying transport and provide a consistent interface into that transport. It should be recognized, however, that different radios, as well as different configurations of SDR , could be utilized to practice these principles, depending on the needs of the particular application.

Among other things, SDR realizes the significant advantage of allowing multiple information voice and data channels to be simultaneously received on multiple radio frequency RF input bands and then simultaneously demodulated using multiple parallel data processing paths. Particularly advantageous is the fact that these information channels can have different frequencies, channel spacing, modulation types, and bit rates.

In other words, SDR performs multiple simultaneous receive operations typically requiring a corresponding number of single-channel receivers.

Furthermore, SDR also supports simplex data transmission on a selected transmission channel and RF frequency band. In exemplary system of FIG. As discussed below, because of its file ability, SDR can be particularly configured as required to meet the requirements of each of these particular applications.

Various communications protocols have been used to support data communications in railroad communications systems. For railroad communications, analog voice is typically In order to meet the requirements of the various communications protocols, SDR supports multiple both linear and constant envelope modulation waveforms. These modulation techniques, which are well known in the art, can be generally be described as follows.

Differential Quadrature Phase Shift Keying DQPSK is a linear modulation waveform that relies on the difference between successive phases of a signal rather than the absolute phase position. DQPSK modulation uses 2 bits per symbol and a symbol rate of half the bit rate. In particular, in 4FM signaling the carrier is shifted in frequency at a particular rate to a particular location around a center frequency.

This allows for each of the four states to represent a binary number, with each state representing a symbol that contains two bits of information. The symbol rate of 4FM signal is half the bit rate. Gaussian Minimum Shift Keying GMSK uses a constant envelope and continuous phase modulation to carry information in the frequency of the signal. Specifically, the GMSK waveform is a continuous-phase frequency-shift keying modulation scheme with a Gaussian pulse shaping filter and a frequency separation of one-half the bit rate i.

A shift of half the bit rate corresponds to the modulation index of 0. The symbol rate of a GMSK signal is the same as the bit rate. The GMSK waveform also provides a bit rate of 9. The symbol rate of a GFSK signal is the same as the bit rate. The frequency deviation is 1. As shown in FIG. In the illustrated embodiment, BPFs a - c have a passband of approximately MHz, IF amplifiers a - c provide approximately 21 dB of gain with bypass, and ADCs a - c operate at a sampling rate of Filters a - c reduce spurious noise generated elsewhere in the system and suppress energy that would otherwise be sampled outside the first two 2 Nyquist zones.

IF amplifiers a - c improve the noise figure at the inputs to ADCs a - c. The particular receive hardware parameters may change based on the specific design and application of SDR The RF transmit path includes a direct data synthesizer DDS , which performs digital sinusoidal carrier frequency generation and digital to analog conversion, and an analog lowpass filter LPF Generally, FPGA and accompanying firmware act as a multi-channel receiver tuner and transmit modulator interpolator.

FPGA implements, for example, signal routing, channel turning, frequency down conversion, gain control, and CORDIC rotation Cartesian to polar conversion independently and simultaneously on multiple input channels. The sixteen 16 channels of data are processed by sixteen 16 corresponding direct data converters DDCs a - p , which will be discussed in detail in further conjunction with FIG. The simultaneous processed channels can be made up of data channels, voice channels, or a combination of voice and data.

Additionally, each channel can be set for a different channel frequency and spacing, modulation type, and bit rate, for example, bps GMSK data in a Two antennas may be used for each frequency channel to implement receive diversity. The DDC output vectors from each DDC a - d include Cartesian I and Q , along with magnitude, phase, and instantaneous frequency, which support data and voice demodulators operating on polar data.

FPGA operates in conjunction with a bus and digital signal processor DSP also runs digital signal coding for forward error correction FEC and privacy, and can support digital voice decoding using commercially available vocoder firmware applications.

A direct memory access DMA system implemented with DSP enables the transfer and buffering of blocks of data samples between buffers within buffers block and the DSP memory space. For example, when a prescribed block length of receive data processed by a DDC a - d has been collected within buffer, DSP retrieves those data blocks using DMA and performs the balance of the data or voice demodulation tasks.

DSP then outputs from one 1 to four 4 user data streams to host processor via host port interface One 1 of those data streams can be a voice channel routed to an audio codec after preprocessing by DSP Audio codec emits an analog voice audio signal. This clock signal is also provided as a reference signal to clock generation circuitry Clock generation circuitry includes a Clock generation circuitry provides a set of clock signals, and in particular, a NCO oscillator is controlled by frequency control data loaded into frequency register Frequency register , gain register , decimation rate register , and filter coefficient register are loaded from bus by DSP In the illustrated embodiment, host sends DSP digital receive and transmit values in Hz, which are then validated and converted into appropriate numerical values, and then stored in the corresponding register.

The I and Q signals are shifted in barrel shifters a - b , under the control of data stored within gain register Generally, barrel shifters a - b selectively shift the bits of each value output from the corresponding mixer a - b to double the digital gain for each bit shifted with sign bits maintained in their current states.

The I and Q signals are then filtered and decimated by corresponding cascaded integrator-comb CIC filters a - b , under the control of clock enable signals generated by clock enable circuit block and the data loaded into decimation rate register In the preferred embodiment, where the input data stream is received at After decimation, the I and Q data streams are lowpass filtered and further decimated by lowpass filters LPFs a and b , also enabled by clock enable block The FIR filter coefficients are selected through filter coefficient select register Each DDC a - d also includes CORDIC rotation and phase differentiation circuitry , which generates digital magnitude, phase, and instantaneous frequency information.

This feature advantageously supports demodulation algorithms running on DSP that utilize polar data. During data transmission processing, data packet bits received by DSP through host port from host processor are converted to bipolar format and then passed to buffers within FPGA The resulting data are combined with the carrier frequency data and sent to DDS for conversion into analog form and ultimate transmission as an RF signal.

In the illustrated embodiment, DSP implements analog voice processing operations including pre-emphasis filtering, amplitude limiting, and a FIR filtering for voice frequency band limiting.

As discussed above, the DSP implemented functions, for example modulation and demodulation, generate or operate on blocks of samples that are contained in sample buffers within buffers block of FPGA In the preferred embodiment, the DMA system supports up to eighteen 18 simultaneously active DMA channels, allocated as sixteen 16 receive channels, one 1 transmit channel, and one 1 audio channel. In particular, the DMA system generates a real time interrupt when a new block of samples is ready in the receive mode or data are needed in the transmit mode for processing by DSP Generally, the interrupt rate is derived from the system clock and is integrally related to the sampling frequencies, which can range from two 2 to ten 10 times the bit rate of the data stream being processed.

In the case of transmission processing, the sample buffers are at the output of the signal processing chain, while during reception processing, the sample buffers are at the input of the signal processing chain.

Receive and transmit band and channel control is implemented by a set of tables accessed by DSP and populated by host processor on system start-up. The channel palette defines, in the preferred embodiment, up to twenty one 21 receive and transmit frequency pairs, along with the modulation parameter value that selects modulation type, FCC designated channel spacing, and bit rate.

A channel palette validate routine validates the channel palette contents at system start up and whenever called by host processor after a channel palette change. Generally, valid and invalid receive channels are marked, with the corresponding transmit channel of the pair similarly assumed valid or invalid. Unused channels are indicated by zeros. A channel assignment table, which is a subset of the channel palette, identifies up to sixteen 16 active assigned receive channel numbers from the validated channel palette.

The active assigned channels tune DDCs a - p. For signal reception on the sixteen 16 assigned receive channels, sixteen 16 corresponding sets of dual sample receive buffers are established in buffers block of FPGA Each pair of buffers stores either the I and Q output data or the phase, magnitude, and instant frequency output data generated by the associated DDC a - p.

In a ping-pong fashion, one dual sample buffer is filled by the DMA system while the other dual sample buffer is accessed to provide a sample block to the appropriate DSP demodulator routine.

Whenever a sample block buffer is filled, a DMA interrupt occurs and its service routine moves the ping-pong buffer pointer s to the alternate buffer of the pair. During voice operations, audio data samples are transferred by DMA between audio codec and one of a pair of ping-pong audio sample buffers. Specifically, a single ping-pong buffer pair is used to transfer modulation samples from DSP to FPGA while the transmitter is keyed.

In the illustrated embodiment, host processor can initiate transmission on one 1 active transmit channel defined in the channel assignment table. Specifically, a transmit key command, which indicates which of the assigned channels to transmit on, initiates a transmit operation. A receive stop routine interrupts reception on the selected channel. The corresponding modulation routine e. On data channels, either individual transmit packet bytes or the entire packet is transferred to DSP from host processor via host processor interface Tasks being executed by DSP are put into a task buffer, with each task indicating that an incoming block of samples is ready for processing by the given modulation routine being executed or that the samples in the current transmit buffer have been expended.

Once the oldest task is begun, it runs to completion before the next oldest task is called. When the task loop calls it, the modulator subroutine runs using packet data bits as input.

DSP , through the DMA system, fills one of the data transmit sample block ping-pong buffers, as its output and then returns to the task buffer to start the next task. Generally, the baseband modulation routine running on DSP implements data pre-coding. The resulting output samples are scaled to generate a precise frequency offset that is interpolated by a FIR pre-modulation filter and then added to the carrier frequency phase increment in FPGA The phase increment information is used by transmit DDS to generate the desired carrier frequency.

During transmit of analog voice, audio codec quantizes the voice or audio tone input from a microphone not shown into bit pulse code modulation PCM samples at a fixed rate of around 8 ksps. These samples are collected by the DMA system into audio sample blocks.

The baseband voice processor implemented by DSP provides audio pre-emphasis band-limited differentiation , amplitude limiting clipping , and lowpass band limiting to about 3 kHz. The resulting samples are scaled for proper frequency deviation and placed in one of the transmit block sample buffers for use by FPGA During reception, if the desired reception channel has a valid entry in the channel table, the channel is activated.

The applicable RF front end circuitry not shown is energized and initialized, as required. An interrupt service routine enters receive tasks each time a complete block of either I and Q or magnitude, phase, and instantaneous frequency data has been received in the corresponding receive ping-pong buffer. When the receive task is called, the receive sample block is operated on by the demodulation subroutines running on DSP During analog voice reception, the sample blocks from the given DDC a - p are passed through a de-emphasis filter band-limited integrator.

DSP implements a separate high pass filter that selects only the high frequency noise output from the discriminator samples, performs amplitude detection, low pass filtering, and threshold detection. The result of the threshold detection is used as a voice audio output SINAD squelch decision for controlling audio gates downstream in the audio path.

A more complete description of SDR radio is provided in co-pending and co-assigned U. ITCNET protocol provides some functionalities of the OSI transport layer, which in the OSI model layer is responsible for transparent transfer of data between end users and for providing reliable data transfer services to the upper layers e.

An ITCNET transport layer protocol provides the means for transferring data between lower layers in the radios and higher layers outside the radios. An ITCNET network layer is responsible for source-to-destination packet delivery including routing through intermediate hosts. ITCNET network layer provides node connectivity, routing, congestion control, flow control, segmentation, and packet sequencing between nodes.

The network nodes can be base station radios, repeaters, or remote radios. The remote radios choose the best base radio or repeater as it roams the network. Direct message exchange between the remotes without relaying through the base can then be made. An ITCNET link layer provides the functional means to transfer data between nodes in the same communication link and provides the means to detect and possibly correct errors that may occur in the physical Layer ITCNET link layer also provides new-neighbor and neighbor-offline detection as well as reliably transmitting and receiving messages between neighbor nodes.

An ITCNET physical layer defines the means of sending raw bits over a physical wireless channel from one radio to another radio. In particular, ITCNET physical layer defines the properties of the modulation scheme, bit rate, bandwidth, frequency, synchronization, and multi-channel processing.

In ITCNET protocol , multiple access schemes are used by the base and remote radios to share available channel resources. The FTDMA slot size can be different from one slot to another, but the allocation of the channel time to each user is fixed. FTDMA communications are used to support constant periodic traffic from the users.

More particularly, a fixed number of FTDMA slots, each having a fixed slot size, are periodically reserved for a user at a fixed repetition rate. The FTDMA configuration is done in advance by a network engineer, who pre-determines the channel capacity and the channel frequency required to send FTDMA data for each user in the network. FTDMA channel configuration update is done, for example, by sending configuration update information from central office to the remote radio through the appropriate base station Such information travels with the message from the application layer , FIG.

For the message to be transmitted in the FTDMA cycle, the ELM generates a slot key from the source address in the message, and then sends the slot key together with the message to the radio. The radio has a table lookup that maps the slot key to the FTDMA slot configuration for that particular message. DTDMA is a centralized access scheme where the frequency channel is time slotted and a base station controls the allocation of time slots to users.

In particular, each slot in the DTDMA cycle can be allocated for a transmission of an RF packet also simply referred to in this disclosure as a packet from a base station or a remote radio. A slot for a remote radio transmission could be assigned to a particular remote radio or set as a contention slot. Contention slots are not assigned to specific remote radios but allow remote radios to access the channel through the slotted CSMA scheme discussed below.

DTDMA slot assignment, including slot size and the user that the slot is assigned to, is controlled by a base station Specifically, a DTDMA slot assignment is performed by a scheduler at the base station based on transmit queue information from the base station radio and the associated connected remote radios. In order for the scheduler to obtain knowledge on the remote transmit queues of the associated radios, each associated remote radio sends an update of its transmit queue information to the base station when necessary.

The remote radio can transmit its queue information in the assigned DTDMA slot or in a contention slot. At the end of each DTDMA cycle, the scheduler uses currently available queue information of every user i. CSMA is a contention-based access scheme where a physical channel is shared by users i.

The CSMA scheme requires that the users listen to the channel before starting to transmit to avoid possible collisions with other ongoing transmissions. Generally, when a user has a packet to transmit, the user waits for a random period of time during which the channel is sensed. If the channel is found idle, the user transmits the packet immediately. If the channel is found busy, the user reschedules the packet transmission to some other time in the future chosen with some randomization at which time the same operation is repeated.

The slot size can be shorter than the time required to transmit a packet. When a user has packet to transmit, the user picks a random integer number and waits for that number of slots to occur before scheduling a transmission. The user then senses the channel, and if the channel is found idle, transmits its packet at the beginning of the current slot.

If the channel is found busy, the user picks another random integer number and reschedules the packet transmission, as in the basic CSMA scheme. The maximum back-off time i. The back-off times for different data priorities can also be set to different numbers to improve the latency performance. The FCC channel plan describes 5 kHz channels; however, where a licensee is authorized on adjacent channels, the 5 kHz channels can be aggregated over the contiguous spectrum.

The wireless IPTC system is designed as a half-duplex system where each 25 kHz frequency channel is used to provide communication path in both directions between two connected radios, but only in one direction at a time. In other words, each frequency channel supports both transmissions from a base radio and transmissions from remote radios, but not simultaneously.

If more than one radio transmits in the channel at the same time, then a signal collision occurs which could result in the loss of all transmissions.

In the wireless IPTC system, the available 25 kHz frequency channels are divided into two groups: local channels and common channels. A common channel is shared by all base stations radios and remote radios.

A local channel is used to support the traffic from all users within a base station coverage area and is centrally controlled by that base station using a master-slave architecture. Each base station controls only one local channel.

Each remote radio can listen to multiple base stations , but a remote radio can select only one base station to be its master; other base stations are considered as neighbor base stations of the remote radio. Different local channels can be assigned to adjacent base stations to prevent adjacent base stations from interfering with each other, and the same local channel can be reused by multiple base stations that are far apart from each other to increase spectral efficiency.

A set of 25 kHz channels in the base frequency are set as primary local channels. Since base stations can transmit with higher power in the base radio frequency, using channels in the base radio frequency for local channels provides larger coverage than by using channels in a mobile radio frequency. Based on the currently available MHz IPTC spectrum, at least three 25 kHz channels in a base radio frequency can be set as primary local channels.

In high density areas where three primary local channels are not sufficient to support the traffic, other local channels can be used.

One 25 kHz channel is preferably reserved for a common channel. The common channel should be in a base radio frequency that allows for both base stations and remote radios to transmit in the channel. In this example, seven 7 local channels are shown i.

Each local channel is divided in time into periodically repeating superframe of fixed duration. The superframe duration is the same for any local channel , and it is set to the wayside broadcast interval, as discussed further below.

The common channel is shared by every user using the CSMA scheme discussed above. A packet transmitted in the common CSMA channel is typically a short packet that carries very high priority data.

Common channel can also be used to transmit base beacon signals, which carry information necessary for remote radios to identify and select a base station radio, as well as to setup their receive frequencies. When transmitting in the FTDMA partition, a remote radio can use slot timing from a GPS pulse such that it is independent of the base radio transmission. Every FTDMA cycle in a channel has the same length, which depends on the amount of periodic traffic in at channel, although FTDMA cycles on different local channels can be of different lengths.

The DTDMA partition in a frequency channel can be controlled by one base station or shared by multiple base stations In case when the local channel is controlled by one base station , that base station has the control of the entire DTDMA partition.

In case when a local channel is shared by adjacent base stations , those base stations coordinate their transmissions in the DTDMA partition. For example, with N adjacent base stations sharing the local channel , the DTDMA partition is divided into N parts, one for each of the N base stations. FTDMA cycle repeats every superframe , although the size of each slot remains the same in every superframe In the example of FIG. Each slot carries one RF packet , i.

Notwithstanding, the FTDMA cycles in all local channels start at the same time, namely, the beginning of the superframe The size of an FTDMA slot is specified in time units, which is independent of the transmit bit rate. The default FSU is 1 millisecond ms , which allows a two-byte transmission at the bit rate of 16 kbps.

The slot size is preferably set based on the packet size plus the guard time required between packets. Such data handling information is included in the header of the message, which is generated in the application layer e. The message and message header are passed from the application layer down to the transport layer e. The transport layer obtains the data handling information from the message header, and passes that information to the link layer in the radio e. A periodic WIU status message is broadcast from wayside radios every wayside broadcast interval, which is the same as the length of the superframe The length of WIU status message itself depends on the number of devices connected to the given wayside In other words, the message length is fixed for each wayside radio, but it can differ from one wayside radio to another.

Generally, DTDMA cycles are used to support traffic from a base station and remote radios that are connected to that base station. Following the DTDMA control packet is the data traffic between the base station and the remote radios. CSMA slots are for the remote radios to request access to the channel by sending a queue status packet via a slotted CSMA scheme.

The transmission of one queue status packet requires one or two CSMA slots , depending on the transmit bit rate. The resolution of the slot size is called DTDMA slot unit DSU , which in the illustrated embodiment is by default is 4 ms, allowing the transmission of 8 bytes at a bit rate of 16 kbps or 16 bytes at a bit rate of 32 kbps. One B-TX slot supports base station transmission of one outbound packet and can vary in size, depending on the packet size.

Specifically, since the base station knows the size of the outbound packet to be transmitted, the slot size can be set to the packet size plus the guard time required between outbound packets. One R-TX slot supports the transmission of one packet by a remote radio.

This packet can be an inbound packet that the remote radio sends to a base station , a peer-to-peer packet that one remote radio sends to another remote radio, or an acknowledgement packet. The size of an R-TX slot can be varied, as is specified in the control field by the base station discussed further below.

For a given R-TX slot size, the remote radio knows the maximum packet size that can be transmitted in the slot, such that transmitted packet can be of any size less than the maximum allowable size for the slot. CSMA slots are for CSMA transmission of queue status packets from a remote radio to a base station to request access to the local channel and have a fixed size of 2 DSU or 8 ms.

The transmission of queue status packet requires one 1 CSMA slot if it is sent at a bit rate of 32 kbps, and requires two 2 CSMA slots if it is sent at a bit rate of 16 kbps.

DTDMA control packets , transmitted from the base station within control field , convey information that the associated remote radios require to decode the DTDMA cycle structure.

DTDMA control packets also include acknowledgement information whereby the base station acknowledges the reception of inbound transmissions in the previous DTDMA cycle Information in a control packet includes packet type, transmitter ID, frame number, packet length, number of slots in each field, acknowledgement to inbound transmissions, and assignment of slots for remote transmission.

The length of control field depends on the size of control packet , which in turn depends on the assignments in the DTDMA cycle. B-TX fields , used to carry data traffic from the base station , comprise B-TX slots , each supporting a base station transmission of an RF packet. Packets transmitted in a B-TX slot can be outbound data packets sent to a specific remote radio or broadcast data packet sent to any remote radio within the coverage area of the base station The base station can perform continuous transmission when the base station radio transmit key is on the entire time allocated for both the control and B-TX fields.

R-TX field and R-TX slots carry data traffic from the remote radios that are connected to the base station , with one R-TX packet transmitted from one remote radio transmitted in each R-TX slot A scheduler at the base station determines the size and the assignment of each R-TX slot. An R-TX packet transmitted in the assigned R-TX slot could be an inbound packet sent to the base station , a peer-to-peer data packet sent to another remote radio, or a broadcast data packet.

For example, an inbound R-TX packet could carry inbound data that the remote radio is sending to central office , an acknowledgement that the remote radio acknowledges the reception of a corresponding base station data packet, or both.

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. 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.

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. 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.

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:. The principles of the present invention and their advantages are best understood by referring to the illustrated embodiment depicted in FIGS.

Generally, system supports wireless communications between a central office network operating center and locomotives located at various points around a rail system, direct communications between central office and wayside monitoring systems, as well as direct communications between locomotives and the electronic wayside monitoring subsystems, as discussed below in detail.

In communications system , central office communicates with packet radios on locomotives 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. Communications system 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 within the corresponding wireless coverage area, as well as to central office though base stations As examples of typical uses of wayside monitoring subsystems , wayside monitoring subsystem a is shown monitoring a switch and a three-lamp signal , and wayside monitoring subsystem b is shown monitoring a hand-throw switch Also for illustrative purposes, two parallel sections of track a and b and a connecting track section are shown in FIG.

Communications system also includes a hotbox monitoring subsystem which uses rail-side sensors to allow central office to monitor the axle status of passing trains through packet data radios and wireless base stations 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. Wayside monitoring subsystem includes a redundant wayside interface module RWIM and a packet radio , both of which will be discussed in further detail below.

In the preferred embodiment, packet radio is based on either a Meteor Comm MCC C or MCC packet data radio, although applications of the present inventive principles are not limited thereto. In the illustrated embodiment, RWIM 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 of FIG. In the preferred embodiment, the inputs into RWIM 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:. 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 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 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 and central office As shown in FIG.

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 a - b provide greater than VRMS of isolation between the input return path and board ground. To activate any single input, i.

Hence, an input short across the input source and return paths or an input open i. 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.

The outputs from opto isolation diodes a - b are provided to corresponding thirty-two 32 by two-bit input multiplexers a - b. In particular, processors a - 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 a - 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.

Data generated by each processor a - 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. We are fully committed to Equal Employment Opportunity. Web design by efelle creative.

My Meteorcomm. My Meterocomm. Product Technology. Interoperability Systems made to exchange data seamlessly across railroads.

Reliability Reducing risk of operational interruptions with solutions developed to support up to s reliability. Scalability Solutions built to accommodate new services and applications. Maintainability Products designed to make maintenance easier and faster. Availability Products and solutions built to maximize uptime through high reliability and ease of maintenance. Unrivaled expertise for the highest standard of PTC support.