Railway intelligent signal system based on visible light communication

Abstract

The application discloses a railway intelligent signal machine system based on visible light communication and belongs to the technical field of railway signals. The system comprises a ground signal machine end and a vehicle-mounted receiving end. The ground signal machine end modulates the LED light source by using a modulation frequency higher than the critical flicker frequency of the human eye while maintaining the normal color light display of the LED signal machine, and emits the real-time acquired line parameter information in a manner that cannot be perceived by the human eye. The vehicle-mounted receiving end is installed on a locomotive, receives and demodulates the visible light signal through a photoelectric detector, and provides the line parameter information to the train control vehicle-mounted unit after extraction. The application realizes the integration of the dual functions of the railway signal machine, i.e. "light signal display" and "optical wireless communication", greatly improves the vehicle-ground information transmission capacity and real-time performance without changing the existing infrastructure, and has the advantages of strong anti-electromagnetic interference, low deployment cost, good compatibility with the existing train control system and the like.

Description

Technical Field

[0001] This invention relates to the field of railway signaling technology, and more specifically to a railway intelligent signaling system based on visible light communication. Background Technology

[0002] Railway signaling systems are core infrastructure for ensuring train operation safety and improving railway transportation efficiency. Their vehicle-to-ground information transmission capabilities directly determine the control accuracy and response speed of the train control system. With the rapid development of my country's high-speed railway network and the continuous increase in train operating speeds, higher demands are placed on the real-time performance, reliability, and information capacity of vehicle-to-ground information transmission. In existing railway train control systems (such as the China Train Control System (CTCS), the transmission of track parameters and control information from the ground to onboard equipment mainly relies on point transponders, track circuits, and wireless communication.

[0003] Specifically, point-type transponders include two types: passive fixed transponders and active variable transponders. They are typically installed at specific locations on the track. When the train's onboard interrogator antenna passes over the transponder, it is activated by electromagnetic induction, thereby reading the basic information stored inside, such as fixed speed limits, gradients, and track carrier frequencies. Active transponders can also connect to the train control center to transmit dynamic control information such as temporary speed limits and routes. However, transponders are essentially point-based, discontinuous information sources, capable of transmitting data only in a very short instant as the train passes. They cannot achieve continuous coverage of information along the line, and the user information storage capacity of a single standard transponder is very limited, typically only about 830 bits. This is insufficient to handle large amounts of dynamic parameters or detailed information on temporary speed limit sections, failing to meet the transmission needs of high-speed trains for massive amounts of real-time data. Meanwhile, the ZPW-2000 series track circuits, a widely used continuous information transmission technology in my country's railways, can continuously transmit track occupancy status and basic speed level information to onboard equipment via the rails. However, the types of information transmitted are limited and the data granularity is coarse, only able to transmit limited speed level commands, and unable to transmit fine-grained line parameters such as track gradient and the length of temporary speed-limited sections. While mobile communication methods such as GSM-R / LTE-R can achieve two-way data interaction between the train and the ground and transmit complex control information such as mobile authorization, they suffer from signal coverage blind spots in complex terrain environments such as tunnels, mountains, and canyons, making transmission stability difficult to guarantee. Furthermore, radio frequency communication itself requires valuable radio spectrum resources, which are becoming increasingly scarce with the continuous growth of railway communication services. Additionally, radio frequency signals are susceptible to external electromagnetic interference, and their omnidirectional propagation characteristics can lead to signal leakage to adjacent lines, causing cross-interference and posing certain safety hazards.

[0004] On the other hand, the LED signals widely distributed along the railway line are the core information interface for train drivers to visually control the train, conveying passage instructions and speed level information to the drivers through different combinations of red, yellow, and green lights.

[0005] To overcome the limitations of traditional rail transit communication and train control systems, such as limited transmission capacity, visible light communication (VLC) technology has been explored for application in rail transit communication systems. The following existing technologies can be referenced:

[0006] CN118054852A, A visible light communication method and system for rail transit;

[0007] CN115432036A, Train operation control system and train positioning method based on visible light communication;

[0008] CN111845849A, Metro track section occupancy detection system and method based on visible light communication technology;

[0009] CN101938310A, A visible light communication control system and its implementation method;

[0010] CN104348546A, Visible light communication system for vehicles;

[0011] CN115432036A, Train operation control system and train positioning method based on visible light communication;

[0012] CN118054852A, A visible light communication method and system for rail transit;

[0013] CN106160859A, A CBTC system based on visible light communication;

[0014] CN118004240A, a signal controller control method, apparatus, equipment and medium;

[0015] JP2025141712A, Visible Light Communication System (This patent solves the problem of low communication rate through a novel sensor).

[0016] US7949259B2, Visible light communication system and method therefor.

[0017] However, the inventors discovered that these existing technologies generally suffer from the following drawbacks:

[0018] (1) The existing VLC modulation technology for trains separates "communication and display" and does not take into account the core principle of "display priority and safety first" of railway signaling. High-speed modulation is prone to light flux fluctuations, causing abnormal visual recognition by the driver. Traditional point transponders can only transmit a maximum of 830 bits of raw data (1023 bits of message after encoding) instantaneously when the train passes by, which cannot meet the needs of large-capacity safety information interaction. The existing VLC scheme based on CCD / CMOS sensors is limited by the frame rate and it is difficult to obtain complete data within the short communication window of high-speed trains.

[0019] (2) The existing train operation system requires significant modifications, such as installing a dedicated ground visible light transceiver and adding wheel sensors to trigger modulation start-up, which results in high system upgrade costs.

[0020] (3) Fault degradation strategy was not considered. If a train proximity triggering mechanism is used, a sensor failure will cause the communication function to fail completely, which will greatly reduce safety.

[0021] It is evident that existing vehicle-to-ground information transmission technologies all have their inherent defects and cannot simultaneously meet the comprehensive requirements of high-speed railways for information transmission capacity, real-time performance, continuity, anti-interference capability, and low-cost deployment. This has become a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0022] To alleviate or partially alleviate the above-mentioned technical problems, the solution of the present invention is as follows:

[0023] A railway intelligent signaling system based on visible light communication includes:

[0024] The ground signal terminal includes an LED signal and a drive control unit. The drive control unit is configured to: while maintaining the normal color light display of the LED signal, use a modulation frequency of 500~5kHz to modulate the LED light source with OOK, OFDM or DMT, and superimpose the real-time acquired line parameter information into the visible light signal for transmission.

[0025] The onboard receiver, installed on the locomotive, includes a photodetector and a signal processing unit. It is configured to receive and demodulate visible light signals from the ground signal terminal, extract the line parameter information, and provide it to the train control onboard unit.

[0026] The photodetector is a PIN photodiode array or an avalanche photodiode array, and is equipped with an optical focusing system;

[0027] The LED light source has a lighting rise time and a extinguishing fall time of less than 1 microsecond after modulation, so as to respond to the modulation frequency and maintain a constant average luminous flux.

[0028] Furthermore, when the LED signal controller malfunctions, experiences power supply abnormalities, or enters a degraded mode, the drive control unit prioritizes ensuring the normal color light display function and automatically silences or switches the visible light communication function to the lowest speed mode.

[0029] After multiple consecutive frame verification failures, the vehicle-mounted receiver automatically switches to the previously successfully received valid data as a backup data source.

[0030] Furthermore, the drive control unit includes an information receiving module, a channel coding module, and a modulation drive module:

[0031] The information receiving module is connected to the train control center in real time to obtain the line parameter information;

[0032] The channel coding module is used to perform forward error correction coding on the line parameter information;

[0033] The modulation driving module is used to generate LED driving control signals based on the encoded information.

[0034] Furthermore, the signal processing unit includes an analog front-end module, a demodulation synchronization module, and a decoding verification module:

[0035] The analog front-end module is used to sequentially amplify, bandpass filter, and automatically control the electrical signal output by the photodetector.

[0036] The bandpass filter is used to filter out the DC component of ambient light and high-frequency noise interference;

[0037] The demodulation and synchronization module is used for clock synchronization recovery, frame synchronization detection, and signal demodulation.

[0038] The decoding and verification module is used to perform error correction decoding and cyclic redundancy check to extract valid line parameter information.

[0039] Furthermore, the line parameters include: fixed permissible speed in the block section ahead, temporary speed limit value and effective section length, line gradient value and track circuit reference carrier frequency.

[0040] Furthermore, the line parameters are transmitted between the ground signal terminal and the vehicle-mounted receiver using information frames;

[0041] The total length of the information frame ranges from 128 bits to 192 bits, and includes a preamble, frame header, data payload, and checksum.

[0042] The data payload includes at least the code transmission information, fixed permissible speed, temporary speed limit value, length of temporary speed limit section, track gradient, and track carrier frequency field.

[0043] Furthermore, the information frame includes: a preamble, a frame header, a signal ID, a code transmission information, a fixed permissible speed, a TSR speed limit value, a TSR section length, a track gradient, a track carrier frequency, as well as a reserved field and a CRC-32 checksum.

[0044] Furthermore, the preamble is 16 bits long and uses a fixed synchronization sequence for carrier synchronization and frame boundary detection at the receiver.

[0045] The frame header is 16 bits long, containing a 4-bit frame type, a 4-bit version number, and an 8-bit sequence number, which are used for frame type identification, protocol version management, and frame sequence number tracking.

[0046] The signal ID is 24 bits long and is used to uniquely identify the number of the ground signal. The vehicle-mounted receiver can use this ID to access the route database and obtain more auxiliary information.

[0047] Furthermore, the code transmission information is 8 bits long and is used to transmit the speed code of the current segment;

[0048] The fixed permissible speed length is 10 bits, used to indicate the maximum permissible operating speed of the block section ahead;

[0049] The TSR speed limit value is 10 bits long and is used to represent the currently valid temporary speed limit value.

[0050] The TSR segment length is 16 bits long and is used to represent the effective segment length of the temporary speed limit.

[0051] The line gradient length is 16 bits, represented by a 1-bit sign bit plus a 15-bit value bit.

[0052] The track carrier frequency has a length of 4 bits and is represented by enumerated values, corresponding to four reference carrier frequencies of the ZPW-2000 series track circuits: 1700Hz, 2000Hz, 2300Hz, and 2600Hz.

[0053] Furthermore, the reserved field has a length of 8 bits, currently filled with 0x00 by default, for future functional expansion, and can carry additional content such as tunnel identification and station area information;

[0054] The CRC-32 checksum is 32 bits long and covers all fields of the entire information frame.

[0055] The technical solution of the present invention has one or more of the following beneficial technical effects:

[0056] (1) Multiple technical features work together to solve security and efficiency problems:

[0057] Addressing the unique safety requirement of "integrated display and communication" in railway signaling, a pioneering dedicated modulation frequency range of 500~5kHz was proposed. This physically ensures constant luminous flux and imperceptible brightness fluctuations under high-speed modulation, completely resolving the compatibility issue between general VLC drivers and railway signaling. High-speed communication is achieved without affecting traditional signal display functions (reflecting the principle of "display priority, safety first"). Relatedly, the LED light source's lighting rise time and extinguishing fall time after modulation are both less than 1 microsecond, responding to the modulation frequency and maintaining a constant average luminous flux.

[0058] Based on this, an OOK+OFDM / DMT dual-mode modulation architecture is constructed: the data rate in the basic OOK mode can reach tens of kbps, which meets the needs of conventional signal command transmission, while the OFDM / DMT high-order modulation technology can achieve a transmission rate of more than 1Mbps. The amount of data transmitted in a single transmission is more than a thousand times that of a traditional transponder, and it can simultaneously transmit multi-dimensional safety information such as signal status, line parameters, temporary speed limits, and fault warnings.

[0059] By combining a PIN photodiode array or avalanche photodiode array receiving solution, the response speed is improved by an order of magnitude compared to the existing CCD / CMOS sensor solution. It can continuously transmit multiple frames of complete data within the 100-300 meter line of sight commonly seen by trains (with only a very short communication window of 1-3 seconds), completely solving the inherent defect of point transponders that can only transmit instantaneously, and ensuring that high-speed trains obtain enough driving safety information in a limited time.

[0060] In other words, this application abandons the conventional and common practice of "separating communication and display", and improves driving safety and ease of operation: because it realizes the integration of signal display and information transmission, while the locomotive driver observes the signal light color, the on-board system has automatically analyzed and presented the complete line parameters, realizing the effect of "seeing the signal and obtaining the complete line parameters", reducing the reliance on the driver's visual judgment and reducing the driving safety risks caused by misreading information.

[0061] Furthermore, this invention also brings cost benefits: for the first time, it proposes that without changing the appearance, installation location, and control logic of the existing LED signal, only a communication modulation driver board and an on-board receiver module need to be added. It is highly compatible with the existing train control system architecture, supports gradual promotion and deployment, and significantly reduces the system transformation cost. It can realize the dual functions of "visual signal display" and "digital information transmission" without the need to install a dedicated ground visible light transceiver, add wheel sensors to trigger modulation start, or make large-scale modifications to the existing system such as changing the appearance, installation location, and control logic of the signal.

[0062] (2) The density of dynamic information between the train and the ground is greatly improved. This invention transforms the LED signal along the line into a dynamic information transmission node, which breaks through the limitation of the traditional train control system that can only transmit dynamic information through active transponders at key locations such as the station entrance. It can update data such as temporary speed limits and route changes in real time, significantly improving the accuracy and responsiveness of the train control system.

[0063] (3) A robust fault safety mechanism has been designed: when the signal malfunctions, the power supply is abnormal, or the signal enters a degraded mode, the drive control unit automatically cuts off the communication function to prioritize the correctness of the light color display; after multiple consecutive frame verification failures, the vehicle terminal automatically switches to the last valid data as a backup.

[0064] Furthermore, other beneficial effects of the present invention will be mentioned in the specific embodiments. Attached Figure Description

[0065] Figure 1 This is a general architecture diagram of one embodiment of the present invention;

[0066] Figure 2 This is a schematic diagram of the LED visible light communication signal modulation and demodulation process in one embodiment of the present invention;

[0067] Figure 3 This is a schematic diagram of the VLC information frame structure of one embodiment of the present invention. Detailed Implementation

[0068] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0069] To facilitate a clear description of the technical solutions in the embodiments of the present invention, the terms "first" and "second" are used to distinguish identical or similar items with essentially the same function and effect. Those skilled in the art will understand that the terms "first" and "second" do not limit the quantity or execution order.

[0070] Through investigation and research, the inventors discovered that existing LED signal controllers only possess simple visual display functions, typically indicating six to eight light color states. They cannot directly transmit extended information such as digitized track parameters, temporary speed limits, track gradients, or track carrier frequencies to the locomotive's onboard equipment. This results in the underutilization of this most widely distributed infrastructure resource, closest to train operating lines, causing significant resource waste. The inventors' starting point for considering and proposing a solution was to find a way to improve the capacity, real-time performance, continuity, and anti-interference capabilities of train-to-ground information transmission while fully utilizing existing railway infrastructure and without altering the existing train control system architecture.

[0071] Figure 1 This is a general architecture diagram of one embodiment of the present invention. As shown in the figure, the railway intelligent signal system based on visible light communication (VLC) of the present invention mainly consists of two parts: a ground signal terminal and an onboard receiver terminal. The ground signal terminal is deployed within the control cabinet of an existing railway LED signal, achieving integrated signal display and visible light communication functions without altering the original appearance, installation location, or control logic of the signal. The onboard receiver terminal is installed at the front of the locomotive or in front of the windshield of the driver's cab, used to receive and demodulate the modulated light signal emitted by the ground signal, reconstruct the line parameter information, and output it to the train control onboard unit.

[0072] The ground signal terminal mainly includes an information receiving module, a channel coding and modulation module, and an LED high-speed drive circuit. The information receiving module is integrated inside the signal control unit (SCU) and establishes a real-time connection with the train control center (TCC) through a standard communication interface to continuously acquire the current track operation status parameters. The track parameters that need to be transmitted include, but are not limited to, the fixed permissible speed (fixed speed limit) of the block section ahead, the current effective temporary speed restriction (TSR) value and effective section length, the track gradient value (expressed in per mille), and the reference carrier frequency of the track circuit (e.g., 1700Hz, 2000Hz, 2300Hz, or 2600Hz).

[0073] The information receiving module encapsulates the acquired parameters according to a predefined frame format, generates a complete information frame, and then sends it to the channel coding and modulation module. The channel coding and modulation module performs forward error correction coding on the encapsulated information frame. In one embodiment, Reed-Solomon code (RS code) or low-density parity check code (LDPC code) is preferably used to improve transmission reliability.

[0074] The encoded data is modulated using on-off keying (OOK) to generate LED drive control signals. The modulation frequency is set in the range of 500Hz to 5kHz. Since the critical flicker fusion frequency of the human eye is about 70 to 100Hz, this modulation frequency is much higher than the threshold that the human eye can perceive. Therefore, the driver cannot detect the flickering of the LED lights, which can ensure the normal visual display effect of the signal.

[0075] The modulated electrical signal is sent to the high-speed LED driver circuit, which is specifically designed for the high-power LED arrays commonly used in railway signals (typically composed of dozens to hundreds of LED chips connected in parallel). This ensures that the LEDs' on / off response speed at the modulation frequency meets the requirements. In one embodiment, the high-speed LED driver circuit uses a high-speed metal-oxide-semiconductor field-effect transistor (MOSFET) as the switching device to drive the high-power LED array specifically designed for railway signals. Since the typical rise / fall time of an LED device is less than 1 microsecond, much shorter than the modulation period, it can reliably respond to high-speed modulation signals while maintaining a relatively constant average luminous flux, without altering the original color and brightness of the signal light. This ensures that the LED array's response speed at the modulation frequency meets the requirements for high-speed data transmission.

[0076] The onboard receiver mainly includes a photodetector array, analog front-end processing circuitry, digital demodulation and synchronization unit, and channel decoding and data output unit. The photodetector array can employ a PIN photodiode (PIN PD) or avalanche photodiode (APD) array, coupled with a specially designed optical focusing system, providing an effective receiving distance sufficient for safe train braking and enabling high-sensitivity acquisition of LED light signals emitted by distant signals. In one embodiment, the effective receiving distance of the photodetector system is designed to be 100–300 meters, meeting the requirements for safe braking distances of high-speed trains. Furthermore, the field of view (FOV) of the optical system is optimized to ensure reliable alignment with the target signal head when the train enters the signal's visible area, while effectively suppressing interference from adjacent line signals and ambient light.

[0077] The analog front-end processing circuit sequentially processes the weak current signal output from the photodetector through a transimpedance amplifier (TIA), a bandpass filter, and automatic gain control (AGC). Specifically, the TIA converts the current signal from the photodetector into a voltage signal and performs initial amplification; the bandpass filter removes the DC component of ambient light and high-frequency noise interference; and the automatic gain control circuit automatically adjusts the amplification factor based on the intensity of the received light signal, ensuring that the amplitude of the output signal remains stable within a range suitable for digital processing.

[0078] The signal processed by the analog front end is sent to the digital demodulation and synchronization unit. This unit first samples the signal output by the analog front end through an analog-to-digital converter (ADC) (converting the analog signal into a digital quantity), and then performs clock synchronization recovery and frame synchronization detection. It achieves bit synchronization and frame boundary positioning by identifying the preamble sequence in the information frame. After synchronization is completed, OOK decision demodulation is performed to restore the analog signal to the original digital bit stream.

[0079] The channel decoding and data output unit performs FEC error correction decoding on the demodulated bitstream corresponding to that of the ground transmitter, and performs Cyclic Redundancy Check (CRC). If the check passes, various line parameter information is extracted according to the predetermined frame format and output to the On-Board Control Unit (OBCU) via the Multifunction Vehicle Bus (MVB) or RS422 standard interface for train speed monitoring and operation decisions. If the check fails, the frame data is discarded and the system continues to wait for the next frame, while retaining the previously successfully received valid data as a backup to ensure the continuity and reliability of system operation.

[0080] Figure 2This is a schematic diagram of the LED visible light communication signal modulation and demodulation process in one embodiment of the present invention. As shown in the figure, the complete working process of the present invention is as follows: In the ground transmission link, the line parameter data source provides various line operation parameters, including speed code, temporary speed limit (TSR), line gradient, track carrier frequency, etc. After the information frame encapsulation module packages the preamble, frame header, data payload and cyclic redundancy check (CRC) code into a complete information frame according to the standard frame format, it is then sent to the forward error correction (FEC) encoding module, which uses Reed-Solomon code (RS code) or low-density parity check code (LDPC code) for forward error correction encoding. The encoded bit stream enters the on / off keying (OOK) modulation module, which generates a high-speed switching modulation control signal according to the rule of "0 corresponds to off, 1 corresponds to on". This signal controls the LED driving circuit, which uses high-speed metal-oxide-semiconductor field-effect transistor (MOSFET) as the switching device, to drive the high-power LED lamp head of railway signaling to perform high-speed modulation at a frequency of 500Hz to 5kHz, which is imperceptible to the human eye, and transmits the digital information superimposed on the normally displayed visible light signal. After being transmitted through a free-space visible light channel of 100 to 300 meters, the visible light signal is received by the photodetector (PD) array at the vehicle-mounted receiver. In the onboard receiver link, the photodetector performs photoelectric conversion, converting the incident light signal into a corresponding weak current signal. This signal is then processed by a transimpedance amplifier (TIA), bandpass filter, and automatic gain control (AGC). The bandpass filter eliminates the DC component generated by ambient light, while the automatic gain control dynamically adjusts the amplification factor based on the received light signal intensity to improve the signal-to-noise ratio (SNR), ultimately outputting a stable analog signal. This analog signal is then digitally sampled and converted into a digital signal by an analog-to-digital converter (ADC). Clock recovery and frame synchronization detection are then performed. Clock synchronization and frame boundary positioning are achieved by identifying the preamble sequence in the information frame. The original bit stream is then obtained through OOK decision demodulation. Finally, the signal undergoes FEC error correction decoding and CRC verification corresponding to the transmitter. If the verification passes, valid line parameter information is extracted; if the verification fails, the erroneous frame is discarded, and the system continues to wait for the next frame. The correct line parameter information is then output to the onboard control unit (OBCU) via the multifunction vehicle bus (MVB) or RS422 standard interface.

[0081] To improve channel capacity, excessively high modulation rates or excessively long LED lighting-up and lighting-down times can easily lead to luminous flux fluctuations. This invention effectively avoids luminous flux fluctuations and their impact on drivers' normal recognition of traffic signal colors by using a modulation frequency of 500Hz to 5kHz and a switching time of less than 1 microsecond.

[0082] Once the locomotive enters the signal's line of sight at a certain speed (for example, when the train's speed is 350 km / h, i.e., 97.2 m / s), it can continuously receive and accumulate multiple frames of data within a communication time window of approximately 1 to 3 seconds. The onboard receiver performs merging, verification, and error correction on the received multiple frames of data. After successful decoding, the parameter information is immediately provided to the train control unit for speed monitoring and train operation decisions, ensuring that the train can adjust its operating speed in a timely manner according to the real-time track conditions.

[0083] Figure 3 This is a schematic diagram of a VLC information frame structure according to one embodiment of the present invention. As shown in the figure, the present invention specifically designs a visible light communication (VLC) information frame protocol for high-speed railway scenarios. The total frame length is approximately 160 bits, and in the transmission order, it includes a preamble, frame header, signal ID, transmission information, fixed permissible speed, TSR speed limit value, TSR section length, track gradient, track carrier frequency, reserved fields, and CRC-32 checksum. Detailed descriptions of each field are shown in Table 1.

[0084] Table 1: Detailed Explanation of Each Field in VLC Information Frame

[0085]

[0086] The preamble is 16 bits long and uses a fixed synchronization sequence, such as a binary sequence of 0xAAAA, for carrier synchronization and frame boundary detection at the receiver. The frame header is 16 bits long and includes a 4-bit frame type, a 4-bit version number, and an 8-bit sequence number, used for frame type identification, protocol version management, and frame sequence number tracking. The signal ID is 24 bits long and is used to uniquely identify the ground signal number, which the onboard receiver can use to obtain more auxiliary information from the line database. The transmission code is 8 bits long and is used to transmit the speed code of the current section, such as standard track circuit speed codes U, HU, H, L, LL, etc., corresponding to the speed level of the track circuit. The fixed permissible speed is 10 bits long, with a value range of 0–511 km / h and an accuracy of 1 km / h, used to indicate the maximum permissible operating speed of the block section ahead. The TSR speed limit value is 10 bits long, with a value range of 0–511 km / h and an accuracy of 1 km / h, used to indicate the current speed limit. The effective temporary speed limit value; the TSR segment length is 16 bits long, ranging from 0 to 65535m with a precision of 1m, used to represent the effective segment length of the temporary speed limit; the track gradient length is 16 bits long, using a 1-bit sign bit plus 15-bit value bit representation, with a unit of 0.01‰ and a range of approximately ±327‰; the track carrier frequency length is 4 bits long, represented by enumerated values, corresponding to four ZPW-2000 series track circuit reference carrier frequencies of 1700Hz, 2000Hz, 2300Hz, and 2600Hz; the reserved field length is 8 bits long, currently filled with 0x00 by default, for future function expansion, and can carry additional content such as tunnel markings and station area information; the CRC-32 checksum length is 32 bits long, calculated using the standard CRC-32 algorithm, and the check range covers all fields of the entire information frame, effectively detecting errors generated during transmission. If the on-board receiver fails the check, it will directly discard the frame.

[0087] The VLC information frame format of this invention can be flexibly adjusted according to actual transmission requirements, with a total frame length ranging from approximately 128 to 192 bits, of which the data payload portion is approximately 64 to 128 bits long. Frame tail verification can be performed using either CRC-16 or CRC-32 verification methods depending on reliability requirements. At a base modulation frequency of 500 Hz, the transmission time of a single complete frame is approximately 256 to 384 ms. When a locomotive passes through a 100-meter line-of-sight area at a speed of 350 km / h, approximately 2 to 3 complete information frames can be received within this time window. Through multi-frame redundant transmission and error correction mechanisms, the attenuation and interference problems of optical signals in the complex environment of railway sites can be effectively overcome, providing reliable information transmission capabilities.

[0088] When a signal malfunctions, experiences a power supply failure, or enters degraded mode, the ground signal terminal prioritizes ensuring the correctness of the light color display. The visible light communication function is automatically muted or switched to the lowest rate mode to avoid the vehicle-mounted receiver receiving incorrect information. Simultaneously, after multiple consecutive frame verification failures, the vehicle-mounted receiver automatically switches to a backup data source (such as the previous valid data or transponder information) to ensure driving safety.

[0089] In other embodiments of the present invention, the modulation method (OOK in the foregoing embodiments) can be replaced according to actual needs. For example, Pulse Position Modulation (PPM) or Multi-Pulse Position Modulation (MPPM) can be used. These two modulation methods have higher energy efficiency and can achieve a lower bit error rate under the same signal-to-noise ratio conditions. They are suitable for application scenarios with weak optical signals or requiring low power consumption. Alternatively, advanced modulation techniques such as Orthogonal Frequency Division Multiplexing (OFDM) or Discrete Multi-Tone (DMT) can be used to achieve high-speed data transmission of more than 1 Mbps.

[0090] The receiver (PIN photodiode or APD point detector in the aforementioned embodiments) can also be replaced with a complementary metal-oxide-semiconductor (CMOS) image sensor or a charge-coupled device (CCD) image sensor. The modulation signal of the LED is identified through image acquisition and processing technology. This scheme has more relaxed requirements on the alignment angle of the receiver, but the communication rate is relatively low due to the frame rate of the image sensor. It is suitable for scenarios where the train runs at a low speed or where the communication rate requirement is not high.

[0091] Furthermore, the channel coding scheme (Reed-Solomon code or LDPC code in the aforementioned embodiments) can also be selected based on the system's signal-to-noise ratio requirements and computational complexity, such as using BCH code, Turbo code, or a simple CRC repetition code scheme. All of the above alternatives are within the scope of protection of this invention.

[0092] This invention discloses a railway intelligent signal system based on Visible Light Communication (VLC). The system consists of a ground signal terminal and an onboard receiver. The ground signal terminal integrates an information receiving module, a channel coding and modulation module, and a high-speed LED driving circuit based on existing railway LED signals. It acquires track parameters, including fixed speed limits, temporary speed limits, track gradient, and track carrier frequency, in real time through the train control center and encapsulates them according to a dedicated VLC information frame protocol designed for high-speed railway operation. Using a 500Hz–5kHz on / off keying modulation method, the digital information is superimposed on the normally displayed visible light signal with a high-speed flicker imperceptible to the human eye. The onboard receiver transmits the signal via optical... The electric detector array collects modulated optical signals within a range of 100 to 300 meters. After transimpedance amplification, bandpass filtering, automatic gain control, analog-to-digital conversion, clock and frame synchronization recovery, demodulation, and error correction, the effective line parameter information is restored. This information is then output to the train control onboard unit via a multi-functional vehicle bus or RS422 standard interface. This achieves the integrated fusion of the railway signal's dual functions of "optical signal display" and "optical wireless communication." It can effectively replace or supplement the information transmission function of traditional point transponders, significantly improving the capacity, real-time performance, and anti-electromagnetic interference capability of vehicle-to-ground information transmission. Furthermore, it is highly compatible with the existing train control system architecture and can be deployed gradually without large-scale infrastructure modifications.

[0093] In summary, this patent systematically solves the core problem of visible light communication technology in railway signal applications for the first time, and constructs a safe, reliable, low-cost, and highly compatible intelligent railway signal system. It effectively replaces and enhances the functions of traditional transponders, which is of great significance for improving the technical level of my country's railway train control system.

[0094] To better illustrate the present invention, numerous specific details have been provided in the detailed embodiments described above. Those skilled in the art should understand that the present invention can be practiced even without certain specific details. In some instances, methods, means, components, and circuits well known to those skilled in the art have not been described in detail in order to highlight the main points of the present invention.

[0095] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A railway intelligent signaling system based on visible light communication, characterized in that, include: The ground signal terminal includes an LED signal and a drive control unit. The drive control unit is configured to: while maintaining the normal color light display of the LED signal, use a modulation frequency of 500~5kHz to modulate the LED light source with OOK, OFDM or DMT, and superimpose the real-time acquired line parameter information into the visible light signal for transmission. The onboard receiver, installed on the locomotive, includes a photodetector and a signal processing unit, and is configured to receive and demodulate visible light signals from the ground signal terminal, extract the line parameter information, and provide it to the train control onboard unit. and, The photodetector is a PIN photodiode array or an avalanche photodiode array, and is equipped with an optical focusing system; The LED light source has a lighting rise time and a extinguishing fall time of less than 1 microsecond after modulation, so as to respond to the modulation frequency and maintain a constant average luminous flux.

2. The railway intelligent signal system based on visible light communication according to claim 1, characterized in that: When the LED signal device malfunctions, experiences power supply abnormalities, or enters degraded mode, the drive control unit prioritizes ensuring the normal color light display function and automatically silences or switches the visible light communication function to the lowest speed mode. After multiple consecutive frame verification failures, the vehicle-mounted receiver automatically switches to the previously successfully received valid data as a backup data source.

3. The railway intelligent signal system based on visible light communication according to claim 2, characterized in that, The drive control unit includes an information receiving module, a channel coding module, and a modulation drive module: The information receiving module is connected to the train control center in real time to obtain the line parameter information; The channel coding module is used to perform forward error correction coding on the line parameter information; The modulation driving module is used to generate LED driving control signals based on the encoded information.

4. The railway intelligent signal system based on visible light communication according to claim 1 or 3, characterized in that, The signal processing unit includes an analog front-end module, a demodulation synchronization module, and a decoding and verification module. The analog front-end module is used to sequentially amplify, bandpass filter, and automatically control the electrical signal output by the photodetector. The bandpass filter is used to filter out the DC component of ambient light and high-frequency noise interference; The demodulation and synchronization module is used for clock synchronization recovery, frame synchronization detection, and signal demodulation. The decoding and verification module is used to perform error correction decoding and cyclic redundancy check to extract valid line parameter information.

5. The railway intelligent signal system based on visible light communication according to claim 4, characterized in that, The line parameters include: The fixed permissible speed, temporary speed limit, effective section length, track gradient, and reference carrier frequency of the track circuit in the block section ahead.

6. The railway intelligent signal system based on visible light communication according to claim 1, characterized in that: The ground signal terminal and the vehicle-mounted receiver transmit the line parameters using information frames. The total length of the information frame ranges from 128 bits to 192 bits, and includes a preamble, frame header, data payload, and checksum. The data payload includes at least the code transmission information, fixed permissible speed, temporary speed limit value, length of temporary speed limit section, track gradient, and track carrier frequency field.

7. The railway intelligent signal system based on visible light communication according to claim 1 or 6, characterized in that: The information frame includes: preamble, frame header, signal ID, code transmission information, fixed permissible speed, TSR speed limit value, TSR section length, track gradient, track carrier frequency, as well as reserved fields and CRC-32 checksum.

8. The railway intelligent signal system based on visible light communication according to claim 7, characterized in that: The preamble is 16 bits long and uses a fixed synchronization sequence for carrier synchronization and frame boundary detection at the receiver. The frame header is 16 bits long, containing a 4-bit frame type, a 4-bit version number, and an 8-bit sequence number, which are used for frame type identification, protocol version management, and frame sequence number tracking. The signal ID is 24 bits long and is used to uniquely identify the number of the ground signal. The vehicle-mounted receiver can use this ID to access the route database and obtain more auxiliary information.

9. The railway intelligent signal system based on visible light communication according to claim 1, characterized in that: The code transmission information is 8 bits long and is used to transmit the speed code of the current segment; The fixed permissible speed length is 10 bits, used to indicate the maximum permissible operating speed of the block section ahead; The TSR speed limit value is 10 bits long and is used to represent the currently valid temporary speed limit value. The TSR segment length is 16 bits long and is used to represent the effective segment length of the temporary speed limit. The line gradient length is 16 bits, represented by a 1-bit sign bit plus a 15-bit value bit. The track carrier frequency has a length of 4 bits and is represented by enumerated values, corresponding to four reference carrier frequencies of the ZPW-2000 series track circuits: 1700Hz, 2000Hz, 2300Hz, and 2600Hz.

10. The railway intelligent signal system based on visible light communication according to claim 1, characterized in that: The reserved field is 8 bits long and is currently filled with 0x00 by default. It is intended for future function expansion and can carry additional content such as tunnel identification and station area information. The CRC-32 checksum is 32 bits long and covers all fields of the entire information frame.

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