1. Technical Field
The present disclosure includes embodiments that relate to a communication system and apparatus. The present disclosure includes embodiments that relate to a method of communication involving a channel equalizer.
2. Discussion of Art
Conventional track circuits may use signaling points to monitor a block of railroad track for the presence of trains and broken rails. Signals transmitted and/or received by the signaling points indicating the block state (e.g., whether occupied, empty, or containing a broken rail) may be used to directly control the wayside signal aspects and to send information to the train (via cab signals in the rail) or a central office (via remote communication links). The electrical current sensed at a receiving signal point may be compared to a threshold value, and decisions about track occupancy, broken rails, and bits (e.g., codes, or signal aspects) can be made based on this threshold value comparison.
High-speed communications using track circuits can be difficult because of distortion introduced by the rail inductance. This inductance, combined with current leakage between the rails, limits the communication rate to less that 10 bits-per-second (bps) over a 3 mile range. Track circuit communication has involved using different modulation approaches. These approaches may include frequency shift key, amplitude shift key, and frequency modulation. These modulation approaches may not address adequately issues of signal distortion and slow communication rates. Train detection and broken rail detection may be performed in a fixed amount of time (e.g., 1.4 seconds), it may be desired that a communications scheme for transmitting signals/bits over the track circuits be provided that allows for a relatively faster communication rate to allow more time for train and broken rail detection.
It may be desirable to have a system that can provide a faster communication rate for signals. It may be desirable to have a method for affecting signal communication rates. It may be desirable to reduce signal distortion in the transmitted signals and provide for transmission of signals over track circuits having an increased length.
In accordance with one aspect of the invention, a signaling system includes a track including a pair of rails spaced apart in a parallel orientation, a first signaling point electrically connected to the track, and a second signaling point electrically connected to the track and separated from the first signaling point, the first and second signaling points capable of communicating track data therebetween. The second signaling point further includes a channel equalizer configured to filter the track data received from the first signaling point.
In accordance with one aspect of the invention, a method includes the step of feeding a modulated voltage from a transmitter to a track to generate a data packet, the data packet representing at least one of a voltage and a current. The method also includes the steps of receiving the data packet at a receiver that is electrically connected to the track, and applying the data packet to an adaptive channel equalizer in the receiver to reduce distortion in the data packet introduced by the track. The method further includes the steps of recording an amount of voltage or current represented by the data packet after application to the channel equalizer and detecting a presence of one or both of a vehicle in contact with a section of the track, and a break within the section of railroad track using the amount of voltage or current.
In accordance with one aspect of the invention, a track circuit apparatus includes a track having a first rail and a second rail, a track circuit transmitter electrically connected to the track and configured to generate a signal transmitted into the track, and a track circuit receiver electrically connected to the track and separated from the track circuit transmitter and having an adaptive channel equalizer. The track circuit receiver is configured to detect the signal, apply the detected signal to the adaptive channel equalizer, and determine a presence of one of a vehicle within a section of the track, and a break within the section of track based on one of a voltage or current level and a received signal level in the equalized signal.
Various other features will be made apparent from the following detailed description and the drawings.
The drawings illustrate embodiments contemplated for carrying out the invention.
In the drawings:
The present disclosure includes embodiments that relate to a communication system and apparatus. The present disclosure includes embodiments that relate to a method of communication involving a channel equalizer.
According to one embodiment of the invention, a signaling system includes a track including a pair of rails spaced apart in a parallel orientation, a first signaling point electrically connected to the track, and a second signaling point electrically connected to the track and separated from the first signaling point by a determined distance, the first and second signaling points capable of communicating track data therebetween. The second signaling point further includes a channel equalizer configured to filter the track data received from the first signaling point.
According to one embodiment of the invention, a method includes the step of feeding a modulated voltage from a transmitter to a track to generate a data packet, the data packet representing at least one of a voltage and a current. The method also includes the steps of receiving the data packet at a receiver that is electrically connected to the track, and applying the data packet to an adaptive channel equalizer in the receiver to reduce distortion in the data packet introduced by the track. The method further includes the steps of recording an amount of voltage or current represented by the data packet after application to the channel equalizer and detecting a presence of one or both of a vehicle in contact with a section of the track, and a break within the section of railroad track using the amount of voltage or current.
According to one embodiment of the invention, a track circuit apparatus includes a track having a first rail and a second rail, a track circuit transmitter electrically connected to the track and configured to generate a signal transmitted into the track, and a track circuit receiver electrically connected to the track and separated from the track circuit transmitter and having an adaptive channel equalizer. The track circuit receiver is configured to detect the signal, apply the detected signal to the adaptive channel equalizer, and determine a presence of one of a vehicle within a section of the track, and a break within the section of track based on one of a voltage or current level and a received signal level in the equalized signal.
Referring to
Referring to
During training, the tap weight update algorithm 18 estimates the channel impulse response by cross-correlating the training signal as received with a stored version of the known training signal. If s[k] is defined as the stored known training sequence for k=0 . . . (L−1), and if u[k] is defined as received data sampled at the symbol rate, with u[o] being the first received training symbol in the received signal, the cross-correlation is given by the following equation:
where Nc is the length of the causal response of the channel (post ghosts), and Na is the length of the anti-causal channel response (pre-ghosts).
The tap weight update algorithm 18 then determines the Z-transform of h[i] and inverts the Z-transform in order to determine the tap weights that are supplied to the multipliers 161 through 16n.
Referring now to
Each block of railroad track 40, 44, 46 includes two spaced-apart parallel rails 48, 50. The metal rails 48, 50 rest on a plurality of spaced apart railroad ties 52, each of which is positioned orthogonal to the rails 48, 50. Ballast 54, such as gravel, occupies the spaces between the rails 48, 50 that are bounded on either side by the railroad ties 52. Each of the blocks of railroad track 40, 44, 46 includes a transmitter/receiver pair 34, 36 positioned between the insulated joints 41 defining the block, with pairs of connections 56 electrically connecting the transmitter/receiver 34, 36 to the rails 48, 50.
As shown in
According to one embodiment of the invention, an adaptive channel equalizer 60 (such as an adaptive channel equalizer configured in the same manner as equalizer 10 in
In an exemplary embodiment, the adaptive channel equalizer 60 is configured as zero-forcing linear equalizer that acts as an adaptive digital filter (e.g., a finite impulse response (FIR) filter). The zero-forcing equalizer removes all ISI, and is ideal when the channel is noiseless. However, when the channel is noisy, the zero-forcing equalizer amplifies the noise at frequencies where the channel response has a small magnitude (i.e. near zeros of the channel) in the attempt to invert the channel completely. As such, the filter response is adapted (i.e., adapting filter coefficients/tap weights) to adequately compensate for channel distortions. While several algorithms are available for adapting the filter coefficients and thereby the filter response, in an exemplary embodiment, a least mean squares (LMS) algorithm (e.g., signed LMS algorithm) is employed. In this algorithm, by varying coefficient values as a function of a representative error signal, the equalizer output signal is forced to approximate a reference data sequence. This error signal is formed by subtracting the equalizer output signal from the reference data sequence. As the error signal approaches zero, the adaptive channel equalizer 60 approaches convergence, whereby the equalizer output signal and the reference data sequence are approximately equal.
As set forth above with respect to
After adaptation with the training signal, the “eye” has opened considerably and the adaptive equalizer 60 is switched to a decision-directed operating mode. In this mode, final convergence of the filter tap weights is achieved by using the actual values of symbols from the output of the equalizer 60 instead of using the training signal. That is, when acting in decision-directed mode, adaptive equalizer 60 receives track data and automatically adapts to any changes in the rails 48, 50, such as a change in inductance. The decision-directed equalizing mode allows for the tracking and cancelling of time varying channel distortions in the rails 48, 50 more rapidly than were periodically transmitted training signals continually sent.
While channel equalizer 60 is described above as an adaptive channel equalizer, according to another embodiment of the invention, it is also recognized that the channel equalizer could have fixed coefficient values/filter tap weights through the duration of its operation. That is, upon an initial convergence of the equalizer coefficients by way of the training signals, the coefficients would be set in channel equalizer 60. In such an embodiment, channel equalizer 60 would not adapt to changes in the rails 48, 50, but maintain its fixed coefficient values/filter tap weights and operate to cancel channel distortions in a constant manner.
Referring now to
According to one embodiment of the invention, upon a determination that the length of block 40 allows for an acceptable SNR of the received signal, the channel equalizer 60 in receiver 36 enters a decision-directed mode to adapt to any changes in the rails 48, 50 during communication of track data between the signaling points, thus providing an adaptive channel equalization. Referring now to
As the transmitter 34 sends the data packet to the receiver 36, the technique 86 may further include a STEP 94 of receiving the data packet at the receiver 36. The STEP 94 may include STEP 96, at which the receiver 36 receives the modulated current provided by the transmitter 34, although it is recognized that voltage could also be received. It is recognized that the data rate of rail communication is slow (˜10 bps) and that an exact time at which a data packet is received by second signaling point 36 may be uncertain. Thus, according to one embodiment, receiver 36 samples the track data for a duration of a sampling window at STEP 94 (i.e., oversamples) so as to receive the transmitted data packet.
At STEP 98, the data packet sampled during the sampling window is applied to the adaptive channel equalizer 60 of receiver 36. Channel equalizer 60 in receiver 36 then equalizes the data packet received during the sampling window over the range of time offsets. A least mean squares value of the equalized track data obtained over the sampling window is estimated and is output at STEP 100 as an equalized data packet whose voltage or current level is recorded. At STEP 102, the content of the equalized data packet (i.e., current level) may be processed by a control device and/or compared with a data structure to determine one or more characteristics about a predetermined block of railroad track 40, such as the presence of a train in the block(s) or a break in the track in the block(s). That is, current and/or voltage detected by second signaling point 36 is compared with predetermined combinations of current/voltage that represent different situations. Such situations may include, for example: No-Train, Train, No Break, and Break.
At STEP 104, a result of processing the content of the data packet is outputted. STEP 104 may include a STEP 106 of outputting a result of “NO BREAK,” meaning that a block of railroad track 40, 44, 46 has no breaks. Alternatively, STEP 104 may include a STEP 108 of outputting a result of “BREAK,” meaning that a block of railroad track 40, 44, 46 has a break in one or both of its section of rails. STEP 104 may further include a STEP 110 of outputting a result of “NO TRAIN,” meaning that no train is present within a block of railroad track 40, 44, 46. Alternatively, STEP 104 may further include a STEP 112 of outputting a result of “TRAIN,” meaning that a train has been detected within a block of railroad track 40, 44, 46. After all results have been outputted, the technique 86 may end.
It is recognized that equalization of track data (i.e., data packets) transmitted along rails 48, 50 reduces distortion in the received data packets. Separate filters can be included in communication system 32 to filter out unwanted narrowband noise before the transmitted track data is received by the channel equalizer 60, such as 60 Hz noise inductively coupled into the track and/or grade crossing frequencies/noise. Additionally, other non-information carrying signals present in rails 48, 50 that are amenable to cancellation may also be removed by the adaptive channel equalizer 60. Equalization of the track data thus allows for a higher data communication/transmission rate to be achieved in the track circuit, such as speeds of around 100 bps. Additionally, equalization of the track data also allows for the track circuit/block length 40 (i.e., distance between insulating joints 41 and between transmitter/receiver 34, 36) to be increased and/or for poorer ballast 54 conditions, while still maintaining an acceptable signal quality. Increases in track circuit length can, for example, be approximately 1.5 times to 2 times farther than the typical distance (e.g., 2.5 miles) that separates signaling points today.
As set forth above, the channel equalizer 60 beneficially reduces distortion in track data transmitted along rails 48, 50. During a training or installation period of the channel equalizer 60, tap weights of the equalizer are determined and a performance measure is generated based on an error signal of the equalizer output. The performance measure is indicative of an acceptable circuit length in the railway signaling system. According to one embodiment of the invention, upon an initial configuring of the tap weights in the channel equalizer 60, the equalizer enters into a decision-directed mode to adapt to any changes in the rails 48, 50 during communication of track data between the transmitter/receiver 34, 36, thus providing an adaptive equalizer that allows for the cancellation of noise sources in the rails and for the reducing of distortion in the track data.
Embodiments of the adaptive equalization methods and system described herein are configured to co-exist with existing signaling systems. Consequently, signals to and from the signaling points are designed not to interfere with grade crossing and cab signals For example, embodiments of the invention can be implemented with various jointless track circuit systems, such as those employing passive signaling devices therein.
The invention has been described in terms of exemplary embodiments, and equivalents, alternatives, and modifications, aside from those expressly stated, are possible and within the scope of the appending claims.