Visible light communication system

Abstract

To provide a visible light communication system that can increase communication speed in visible light communication.SOLUTION: A visible light communication system 100 includes a light-emitting device 11 that transmits signals by emitting visible light EL with differences provided between blinking periods and duty ratios, a light-receiving device 21 that reads a blinking period and a duty ratio from changes in luminance of the visible light EL from the light-emitting device 11, and a signal processing unit 22 that extracts transmission information from a transmitting side from the blinking period and the duty ratio read by the light-receiving device 21.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a visible light communication system that can be applied to, for example, signal lamps in railway facilities. [Background technology]

[0002] For example, when performing visible light communication by rapidly blinking illumination light, an optical transmission device is known that irradiates illumination light with a uniform amount of light so as to prevent flickering of the illumination light (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5196706 Summary of the Invention [Problem to be solved by the invention]

[0004] In order to prevent flickering in visible light communication, it is generally considered to shorten the blinking cycle by using, for example, an LED as illumination light. However, if a normal camera is used on the signal detection side, the blinking cycle on the illumination side can only be shortened to, for example, about 200 Hz due to the frame rate limitations of the camera. Therefore, the communication speed in visible light communication is also limited. However, the above-mentioned Patent Document 1 does not mention how to address the limit on communication speed due to constraints on the light receiving side of the optical transmitting device, for example.

[0005] The present invention has been made in view of the above-mentioned points, and has an object to provide a visible light communication system that can increase the communication speed in visible light communication. [Means for solving the problem]

[0006] To achieve the above objective, a visible light communication system includes a light-emitting device that transmits signals by emitting visible light with different blinking periods and duty ratios, a light-receiving device that reads the blinking period and duty ratio from changes in brightness of the visible light from the light-emitting device, and a signal processing unit that extracts transmission information from the transmitting side from the blinking period and duty ratio read by the light-receiving device.

[0007] In the above-mentioned visible light communication system, the light receiving side reads the blinking period and duty ratio from the change in brightness of the received visible light and extracts a signal, thereby avoiding the occurrence of flicker in visible light communication and achieving faster communication speeds.

[0008] In a specific aspect of the present invention, the signal processor extracts the light color information and traffic light ID of the transmitting side from the flashing period and duty ratio as transmission information, thereby enabling the necessary information to be obtained quickly.

[0009] In another aspect of the present invention, the signal processor extracts light color information from differences in the flashing cycles and extracts the traffic light ID from differences in the duty ratios. In this case, the light color information and the traffic light ID can be accurately extracted.

[0010] In yet another aspect of the present invention, the frame rate when continuously capturing visible light in the light receiving device is higher than the frequency of on / off switching for the blinking operation of the light emitting device, and in this case, the blinking operation of the light emitting device can be reliably captured by utilizing a sufficiently fast change in the frame rate.

[0011] In yet another aspect of the present invention, the light receiving device reads visible light using an image sensor that asynchronously detects changes in luminance of each pixel and outputs only the changed data in combination with information on the pixel position and time, thereby enabling processing at a speed sufficiently high to be required.

[0012] In yet another aspect of the present invention, the light emitting device changes the emission brightness of visible light in accordance with differences in duty ratio, thereby suppressing differences in brightness due to differences in duty ratio, i.e., communication content.

[0013] In yet another aspect of the present invention, the light-emitting device is provided on the ground side and emits visible light using an LED light source constituting a railway signal lamp to transmit a railway signal, and the light-receiving device and signal processing unit are provided on the train side and the signal processing unit obtains information on whether the train is proceeding or not based on the railway signal. In this case, accurate and rapid communication of the railway signal can be achieved. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a schematic diagram for explaining a visible light communication system according to an embodiment and a railway incorporating the system; [Figure 2] FIG. 1 is a conceptual block diagram for explaining an example configuration of a visible light communication system. [Figure 3] 10A to 10C are conceptual diagrams for explaining the differences in the on / off (blinking) operations of the color signal lamps. [Figure 4] 10(A) to 10(C) are conceptual diagrams for explaining differences in duty ratios in the on / off (blinking) operation of a yellow traffic light device. [Figure 5] 10A is a time chart showing the cycle of the blinking operation of the traffic light devices of each color, and FIG. 10B is a time chart showing the duty ratio when the yellow signal is lit. [Figure 6] FIG. 1 is a conceptual diagram illustrating an overview of a visible light communication system. DETAILED DESCRIPTION OF THE INVENTION

[0015] An example of a visible light communication system according to an embodiment will be described below with reference to FIG. 1 and other figures. FIG. 1 is a schematic diagram for explaining the visible light communication system 100 according to this embodiment, and illustrates a railway incorporating the visible light communication system 100 as an application example. More specifically, the example shown in FIG. 1 illustrates the visible light communication system 100 when applied to signal communication processing between the on-board side (on-board side) and the ground side (traffic light side) during automatic operation of a train TR. In particular, the visible light communication system 100 according to this embodiment, configured as described above, receives visible light EL from the ground side (transmitting side) on the on-board side (receiving side) and analyzes the emission state of the visible light, thereby enabling visible light communication for multiple types of signal information.

[0016] It should be noted that various modes of automatic operation of the train TR mentioned above are assumed, and this includes a wide range of modes, from completely unmanned automatic operation with no driver present, to automatic operation where the driver performs driving operations and partially assists with the operation.

[0017] A more detailed description will now be given of an example of the configuration of the visible light communication system 100 of this embodiment. First, as shown in Fig. 1, the visible light communication system 100 includes a ground-side device 10 on the transmitting side and an on-board device 20 on the receiving side.

[0018] The ground-side device 10 is fixedly installed on the ground and includes a light-emitting device 11 that emits visible light EL using an LED light source, and a lighting control unit 12 that controls the light-emitting operation of the light-emitting device 11. In this example, the light-emitting device 11 controls the lighting of light in the visible light wavelength band to display signals and transmit signal content, i.e., a railway signal light, and constitutes a railway signal light. From another perspective, a typical railway signal light is flashed to perform visible light communication, but the flashing is performed at a high speed so that it appears to the naked eye as a normal lighting state. Note that, as shown in the figure, the light-emitting device emits each color of visible light EL (red light ELr, yellow light ELy, and blue light ELg), allowing for normal visual confirmation of the signal, while controlling the operation of the colored lights ELr, ELy, and ELg to also perform visible light communication. More specifically, the light-emitting device 11 is composed of a red signal light 11r that emits red light ELr as visible light EL, a yellow signal light 11y that emits yellow light ELy, and a blue signal light 11g that emits blue light ELg. Each of the emitted colored lights ELr, ELy, and ELg has a predetermined blinking cycle and duty ratio, which the receiver can read to identify the content of the visible light communication. In other words, by setting the blinking cycle and duty ratio of the light emission to be different depending on the content of the information to be transmitted, signal transmission based on the emission of visible light is possible. In the ground-side device 10, the lighting control unit 12 controls the operation of each of the colored light signals 11r, 11y, and 11g that constitute the light-emitting device 11 so that the colored lights ELr, ELy, and ELg are emitted at the predetermined blinking cycle and duty ratio.

[0019] The on-board device 20 includes a light receiving device 21 that receives visible light EL (red light ELr, yellow light ELy, blue light ELg) and a signal processing unit 22 that performs processing to extract a signal from the received visible light EL, and as described above, receives (receives) the visible light EL emitted by the ground-side device 10 from the ground side, analyzes it, and extracts (takes out) information such as the flashing period and duty ratio.

[0020] Here, an EVS (Event-Based Vision Sensor) camera 21e is adopted as an example of the light receiving device 21, and the light receiving device 21 analyzes and processes continuous images as the light receiving results of the EVS camera 21e in an image processing unit 21g.

[0021] The EVS camera 21e is configured with an image sensor (array-type light receiving elements) that asynchronously detects changes in luminance of each pixel and outputs only the changed data in combination with information on the pixel's position and time. The EVS camera 21e reads changes in luminance of visible light EL (red light ELr, yellow light ELy, and blue light ELg). The light receiving device 21, which includes the EVS camera 21e, is specialized for detecting changes in luminance on a pixel-by-pixel basis. While it detects the presence or absence of changes in luminance of visible light EL at each position on the light receiving elements arranged in an array, it does not detect, for example, which wavelength band of red light ELr, yellow light ELy, or blue light ELg the detected visible light EL belongs to. This specialized configuration enables the light receiving device 21 to capture images at a very fast frame rate. Here, the EVS camera 21e detects three types of changes: a change in luminance from positive to negative, a change in luminance from negative to positive, and no change in luminance. In the above configuration, the EVS camera 21e can continuously capture images at a much higher speed (e.g., 10,000 fps) than a normal camera. A change in brightness from positive to negative corresponds to a transition from on to off (fall) on the transmitting side, and a change in brightness from negative to positive corresponds to a transition from off to on (rise) on the transmitting side. No change in brightness corresponds to the transmitting side remaining on or remaining off.

[0022] Meanwhile, the ground side, i.e., the transmitting side, is also capable of very high-speed flashing switching (for example, about 100 Hz, which is imperceptible to the naked eye), and forms a flashing cycle by repeating a lighting period and a flashing period. In this example, the flashing cycles of the colored lights ELr, ELy, and ELg are set to be different from each other. Furthermore, the duty ratio of the lighting period within each cycle is adjusted, and the traffic light ID number of the ground-side device 10 is set according to the duty ratio. As described above, in the ground-side device 10, the light-emitting device 11, when emitting visible light, sets different flashing cycles and duty ratios for the colored lights ELr, ELy, and ELg. In this embodiment, the receiving side, i.e., the on-board device 20, receives light color information and a traffic light ID as transmitted information from the transmitting side. Of these, light color information is extracted from the difference in the flashing cycle, and the traffic light ID is extracted from the difference in the duty ratio. For this reason, the light receiving device 21 of the on-board device 20 reads the flashing period and duty ratio from the brightness change of the received light component, and the signal processing unit 22 extracts the transmission information from the transmitting side from the flashing period and duty ratio read by the light receiving device 21. In one example, the signal processing unit 22 obtains train progress information based on railway signals. Note that an example of these operational controls and specific settings of the flashing period and duty ratio will be described later. Furthermore, the above-mentioned high-speed flashing switching operation can be realized by using, for example, an LED signal that emits LED light in wavelength bands corresponding to the color lights ELr, ELy, and ELg as the light emitting devices 11 composed of the color light signal lamps.

[0023] Hereinafter, a more specific example of the configuration of the ground-side device 10 and the on-board device 20 that constitute the visible light communication system 100 will be described with reference to the block diagram shown in FIG.

[0024] As described above, the ground-side device 10, which is the transmitting side of the visible light communication system 100, is composed of a light-emitting device 11 and a lighting control unit 12. Of these, the light-emitting device 11 is composed of a red signal light 11r, a yellow signal light 11y, and a blue signal light 11g. Meanwhile, the lighting control unit 12 is provided with color signal control units 12r, 12y, and 12g corresponding to the color signal light units 11r, 11y, and 11g that make up the light-emitting device 11, as shown in the figure. The color signal control units 12r, 12y, and 12g are individually controlled so that the blinking cycle and duty ratio for each color differ according to the settings. That is, the red signal control unit 12r operates the red signal light 11r at a predetermined blinking cycle and duty ratio. Similarly, the yellow signal control unit 12y operates the yellow signal light 11y, and the blue signal control unit 12g operates the blue signal light 11g at a predetermined blinking cycle and duty ratio, respectively.

[0025] As a result of the above, in the light-emitting device 11, visible light EL (red light ELr, yellow light ELy, blue light ELg) with a predetermined blinking period and duty ratio is transmitted as transmission information (or as information including this information) as visible light communication from the transmitting side.

[0026] As described above, the on-board device 20 is composed of the light receiving device 21 and the signal processing unit 22. Of these, the light receiving device 21 is composed of the EVS camera 21e and the image processing unit 21g. Furthermore, the image processing unit 21g is composed of a visible light signal extraction unit VS, a blinking cycle extraction unit FC, and a duty ratio extraction unit DR, as shown in the figure.

[0027] The EVS camera 21e is an array-type light receiving element (image sensor) that captures images continuously at a very high speed, for example, at about 10,000 fps. The EVS camera 21e detects visible light EL for each light receiving element, i.e., for each pixel, but what is detected at this time is limited to the three types of luminance changes mentioned above (from positive to negative, negative to positive, and no change) and the positions of those changes on the image, and does not detect the wavelength bands of each color light.

[0028] The visible light signal extraction unit VS in the image processing unit 21g extracts, as a visible light signal, from the luminance changes captured by the EVS camera 21e on a pixel-by-pixel basis, those that should be attributed to luminance changes due to visible light EL from the light-emitting device 11. For example, the image processing unit 21g may store the shapes and the like of the color signal lights 11r, 11y, 11g, and determine whether or not the shapes and the like are due to visible light signals by comparing the shapes and the ranges of luminance changes captured by the EVS camera 21e.

[0029] The blinking cycle extraction unit FC extracts the blinking cycle from the visible light signal extracted by the visible light signal extraction unit VS.

[0030] The duty ratio extraction section DR extracts the duty ratio for the blinking period calculated by the blinking period extraction section FC, that is, the ratio of the signal ON state to the signal OFF state within one period.

[0031] As described above, the light receiving device 21 reads the blinking period and duty ratio from the change in luminance of the visible light EL.

[0032] Next, as shown in the figure, the signal processing unit 22 is composed of a database DB, a judgment unit JD, and a display unit DS, and the signal processing unit 22 extracts the transmission information from the sending side from the blinking period and duty ratio read by the light receiving device 21.

[0033] The signal processing unit 22 includes a database DB, which is configured from various storage devices, and stores various data for determining received information from the blinking cycles and duty ratios extracted based on image processing by the image processing unit 21g. For example, the database DB stores table data indicating correspondences between predetermined blinking cycles and duty ratios and light color information and traffic light IDs on the transmitting side. The signal processing unit 22 extracts transmitted information from the transmitting side based on the blinking cycles and duty ratios read by the light receiving device 21. In this example, the signal processing unit 22 extracts light color information from differences in the blinking cycles and extracts traffic light IDs from differences in the duty ratios. In other words, the table data associates light color information with each blinking cycle and traffic light IDs with each duty ratio.

[0034] The determination unit JD refers to the table data in the database DB and determines which light color information and traffic light ID the blinking period and duty ratio acquired (extracted) as a visible light signal by the image processing unit 21g correspond to. That is, the determination unit JD extracts the transmission information from the transmitting side from the blinking period and duty ratio read by the light receiving device 21.

[0035] The display unit DS is configured with various screen display devices such as a liquid crystal panel, and displays the determination results from the determination unit JD.

[0036] An example of the blinking behavior of emitted light will be described below with reference to FIGS.

[0037] First, the on / off (flashing) operation of each of the color signal lamps 11r, 11y, and 11g constituting the light-emitting device 11 will be described with reference to the conceptual diagram shown in Fig. 3. Fig. 3(A) shows a time chart of the flashing operation of the red light ELr in the red signal lamp 11r and its pulse wave LLr, Fig. 3(B) shows a time chart of the flashing operation of the yellow light ELy in the yellow signal lamp 11y and its pulse wave LLy, and Fig. 3(C) shows a time chart of the flashing operation of the blue light ELg in the blue signal lamp 11g and its pulse wave LLg. It should be noted that the rise (from off to on) and fall (from on to off) of each pulse wave LLr, LLy, and LLg are assumed to be very short compared to the on time, off (flashing) time, and flashing cycle.

[0038] As shown in the figure, constant blinking periods Tr, Ty, Tg (the time corresponding to the time from the start of one turn-on to the completion of turning off) are preset for each color among the color signal lamps 11r, 11y, 11g, and the operation is controlled by each color signal control unit 12r, 12y, 12g (see FIG. 2) so that the blinking periods are different among the colors. In the example shown in the figure, the blinking period of the red light ELr is the shortest, the blinking period of the yellow light ELy is the next shortest, and the blinking period of the blue light ELg is the longest. On board the train, the difference in the blinking periods is read from the light reception results to determine (identify) the color of the signal.

[0039] Next, with reference to the conceptual diagram shown in FIG. 4, differences in duty ratios during the on / off (blinking) operation of the color signal lamps 11r, 11y, and 11g constituting the light-emitting device 11, i.e., differences in the pulse duration of visible light EL (see FIG. 2), will be described. In the illustrated example, among the color signal lamps 11r, 11y, and 11g, the blinking operation of the yellow light ELy in the yellow signal lamp 11y and a time chart thereof are shown. More specifically, FIGS. 4(A) to 4(C) respectively show the blinking operation of the yellow light ELy in the yellow signal lamp 11y corresponding to ID numbers 1 to 3, which correspond to traffic light IDs for identifying the light-emitting device 11, and time charts of the pulse waves LLα, LLβ, and LLγ thereof. That is, FIG. 4(A) shows the operation of the yellow signal lamp 11y mounted on the light-emitting device 11 with ID number 1, FIG. 4(B) shows the operation of the yellow signal lamp 11y mounted on the light-emitting device 11 with ID number 2, and FIG. 4(C) shows the operation of the yellow signal lamp 11y mounted on the light-emitting device 11 with ID number 3.

[0040] As shown in the figure, the blinking cycle Ty of the yellow light ELy, which is the same color, is the same, but the duty ratios of the ID numbers 1 to 3 are different. In the example shown, the pulse width Wα indicating the duty ratio (the time the pulse of the yellow light ELy is on) of ID number 1 shown in FIG. 4(A) is the smallest, the pulse width Wβ indicating the duty ratio of ID number 2 shown in FIG. 4(B) is small, and the pulse width Wγ indicating the duty ratio of ID number 3 shown in FIG. 4(C) is the largest. The onboard device reads the difference in duty ratios from the light reception results to determine (identify) the traffic light ID, i.e., which traffic light it is.

[0041] In the illustrated example, the emission luminance of yellow light ELy, which is visible light EL, is changed between ID numbers 1 to 3 according to the difference in duty ratio so that the total brightness (amount of light) when turned on is the same or approximately the same even if the duty ratio is different. In the figure, the difference in the magnitude of the emission luminance is expressed by the difference in height Hα, Hβ, and Hγ of pulse waves LLα, LLβ, and LLγ, and is adjusted so that the area (integral value) of the pulse wave in the on state is the same or approximately the same. As described above, light emitting device 11 changes the emission luminance of visible light EL according to the difference in duty ratio.

[0042] Below, with reference to Figure 5, we will explain based on a more specific example (an example with various numerical settings) regarding the blinking operation and duty ratio adjustment of the light-emitting device 11 on the ground side (transmitting side) and the reading on the on-board side (receiving side) based on receiving this.

[0043] Figure 5(A) shows more specific operation details for the case illustrated in Figure 3, and is a time chart showing the flashing operation periods (flashing periods) Tr, Ty, and Tg of each colored light ELr, ELy, and ELg shown in Figures 3(A) to 3(C).

[0044] In the figure, the top column corresponds to FIG. 3(A), the middle column corresponds to FIG. 3(B), and the bottom column corresponds to FIG. 3(C). For example, in the blinking cycle Tr for red shown in the top column, the period RR indicates the on period of the red light ELr, while the period between two periods RR indicates the off period. In the example shown, the blinking cycle Tr is 9 ms, half of which, 4.5 ms, is the period RR, i.e., the on period, and the other half, 4.5 ms, is the off period. In other words, the duty ratio is 1:1. Similarly, the blinking cycle Ty for yellow is 10 ms, and the blinking cycle Tg for blue is 11 ms. In both cases, the periods YY and GG are half of the total, i.e., the duty ratio is 1:1.

[0045] In this case, the blinking speed of each color is extremely fast, at around 100Hz (red: 10,000 / 9Hz, yellow: 100Hz, blue: 1,000 / 11Hz), and is recognized as normal lighting to the naked eye, with no visible blinking.

[0046] While the above-described lighting operation is performed on the transmitting side, the on-board device 20, which is the receiving side, employs the EVS camera 21e (see FIG. 2) in the light-receiving device 21 to perform high-speed imaging, as previously described. In this example, for the situation shown in FIG. 5(A), continuous imaging is performed at 10,000 fps, i.e., imaging (light reception) processing is performed at a time interval of 1 f (frame) per 100 μs. In this case, as shown in the figure, imaging (light reception) is performed approximately 90 to 110 f (frames) (i.e., approximately 100 times) in one flashing cycle Tr, Ty, Tg. From another perspective, the frame rate at which the EVS camera 21e of the light-receiving device 21 continuously captures visible light EL is sufficiently higher than the on / off switching frequency for the flashing operation of the light-emitting device 11.

[0047] In the above-described embodiment, for example, if the blinking period Ty is 10 ms, an ON state is detected for approximately 50 frames, followed by an OFF state for approximately 50 frames, and then an ON state is detected for approximately 50 frames, and so on. When the above-described blinking operation indicating the yellow light ELy is performed on the ground side, the on-board side receives this and analyzes and extracts the light reception results in the image processing unit 21g (see FIG. 2) constituting the light receiving device 21, thereby reading that the blinking period is 10 ms and that the duty ratio is 1:1. Note that, when reading the above, the light receiving device 21 captures brightness changes using the EVS camera 21e, as described above. In this case, the EVS camera 21e detects the rising edge of the pulse wave (e.g., pulse wave LLy) shown in FIG. 3 at the location surrounded by the dashed line DT. This change in brightness from positive to negative, i.e., from off to on, is detected as a 10-ms interval. This brightness change is detected from the vehicle's interior, revealing the flashing period and, therefore, the illumination color. Furthermore, based on the detection by the EVS camera 21e, the falling edge of a single pulse wave, i.e., the change in brightness from negative to positive, i.e., from off to on, is detected as a 10-ms interval between the positive-to-negative brightness changes. Additionally, the absence of a brightness change is detected as a 1:1 interval. From the above, in the example of operation shown in FIG. 5(A), it can be seen that the duty ratio is 1:1.

[0048] On the other hand, with regard to the detection on the receiving side as described above, the operational control is set so that there may be cases where the duty ratio is 1:1 and cases where it is not, as shown in the example of Figure 5(B).

[0049] Fig. 5(B) is a time chart showing how to identify ID numbers 1 to 3 shown in Fig. 4(A) to 4(C). In the figure, the upper column corresponds to Fig. 4(A), the middle column corresponds to Fig. 4(B), and the lower column corresponds to Fig. 4(C), and the difference in the magnitude of light emission brightness is expressed by the difference in the heights Hα, Hβ, and Hγ of sections YY1, YY2, and YY3 that indicate lighting.

[0050] In all of the cases shown in the upper, middle, and lower columns of Figure 5(B), the blinking period is determined to be 10 ms, as in the case explained with reference to Figure 5(A). In other words, they all have in common the fact that the yellow light ELy has a blinking period Ty = 10 ms. However, the duty ratios are different. In other words, Figure 5(B) shows an example of a case where the ID numbers are different (when identifying traffic lights installed in different locations).

[0051] For example, the one shown in the middle column of Figure 5(B) corresponds to ID number 2, and the period YY2 indicating lighting and the period between them are the same width. In other words, the duty ratio is 1:1 (5:5). The one shown in the middle column also has a duty ratio of 1:1, which ultimately matches the one shown in the middle column of Figure 5(A).

[0052] On the other hand, for the signals shown in the upper and lower columns, the duty ratio is other than 1:1, as is clear from the relationship between the periods YY1 and YY3 indicating illumination and the periods therebetween. Specifically, in the case corresponding to ID number 1 shown in the upper column, the duty ratio is 4:6 (2:3), and in the case corresponding to ID number 3 shown in the lower column, the duty ratio is 6:4 (3:2). Even in the above-mentioned situations, the duty ratio is extracted by the on-board light receiving device 21 performing the same operation as described above during detection, etc. The duty ratio information is extracted on-board, making it possible to identify the traffic light.

[0053] In this way, the signal processor 22 extracts the information transmitted from the transmitting side, i.e., identifies the light color information and traffic light ID, based on the information on the blinking cycle and duty ratio extracted by the light-receiving device 21. In other words, on the ground, the light-emitting devices 11 are turned on (blinked) with a duty ratio and blinking cycle preset according to the installation locations of the light-emitting devices 11 located in various places and the light colors of the color signal lamps 11r, 11y, 11g that make up each light-emitting device 11, and this can be read on the train.

[0054] Furthermore, in the above, the identification of traffic light ID based on differences in duty ratios has only been explained for the case of yellow light ELy, and explanations have been omitted for cases where differences are made in the duty ratios of other colored lights ELr and ELg, but it is possible to do the same for other colored lights ELr and ELg as for yellow light ELy.

[0055] In the above case, the EVS camera 21e can capture (receive) about 100 frames during one blinking cycle Tr, Ty, Tg, so it is possible to set about 100 patterns for changing the duty ratio. In other words, it is possible to set up to about 100 patterns of ID for individual identification.

[0056] Below, an overview of the characteristics of the visible light communication system 100 will be summarized and explained with reference to the conceptual diagram shown in FIG.

[0057] As shown in the figure and as previously described, the visible light communication system 100 includes a light-emitting device 11 in the ground-side device 10 and a light-receiving device 21 and signal processing unit 22 in the on-board device 20. The ground-side light-emitting device 11 transmits signals by emitting visible light EL with different flashing periods and duty cycles, i.e., it serves as the transmitter of visible light communication. Meanwhile, the on-board (light-receiving) light-receiving device 21 receives (receives) the visible light EL from the light-emitting device 11 and reads the flashing period and duty cycle contained therein from the luminance changes of the received visible light EL. Furthermore, the signal processing unit 22 extracts transmission information from the transmitter from the flashing period and duty cycle read by the light-receiving device 21. In this case, the light-receiving device reads the flashing period and duty cycle from the luminance changes of the received visible light EL and extracts the signal, thereby avoiding flickering and achieving high-speed communication in visible light communication.

[0058] 〔others〕 The present invention is not limited to the above-described embodiment, and can be embodied in various forms without departing from the spirit and scope of the present invention.

[0059] First, in the above description, an LED is used as the light source of the light emitting device 11, but this is not limiting and various other devices can be used as long as they can be switched on and off as required.

[0060] Furthermore, the light source of the light-emitting device 11 and the imaging equipment of the light-receiving device 21, as well as their performance and specifications, are merely examples, and various other configurations are possible as long as the required communication speed and reliability are ensured while sufficiently suppressing flicker as in normal illumination light. For example, the manner and degree of differentiation between the color lights and duty ratios on the transmitting side, and the frame rate on the receiving side can be changed in various ways as long as they do not cause confusion or false detection.

[0061] In addition, in the above, the lighting color (light color information) is read from the flashing cycle and the traffic light ID is read from the duty ratio, but this is not limited to this, and it is also possible to read the traffic light ID from the flashing cycle and the lighting color (light color information) from the duty ratio.

[0062] Furthermore, as a possible scenario for performing the above-described visible light communication, in the case of use in a railway such as the above, a train TR stopped at a station platform or the like may perform readings when communicating with a traffic light ahead. Another possible scenario is, for example, communication with a traffic light ahead while the train TR is running. In this case, the imaging range in the image of the target light may change from moment to moment. To address this, for example, a possible scenario is to also measure the outline as the light receiving range, and compare the light receiving range (outline) between before and after consecutively captured images to determine their identity.

[0063] In the above, as an example, the present invention has been described as being used in railways, where the present invention is read as a railway signal (for example, a signal for automatic operation of a railway), but the present invention is not limited to this. For example, the visible light communication system 100 can be used for streetcars running on tracks (new tracks, dual-use tracks) and buses running on dedicated roads. Furthermore, it is also conceivable to use the present invention for traffic signals (in automobile signal lamps), for example. [Explanation of symbols]

[0064] 10...ground side device, 11...light emitting device, 11g...blue signal lamp, 11r...red signal lamp, 11y...yellow signal lamp, 12...lighting control unit, 12g...blue signal control unit, 12r...red signal control unit, 12y...yellow signal control unit, 20...on-board device, 21...light receiving device, 21e...EVS camera, 21g...image processing unit, 22...signal processing unit, 100...visible light communication system, DB...database, DR...duty ratio Extraction unit, DS...display unit, DT...dashed line, EL...visible light, ELg...blue light, ELr...red light, ELy...yellow light, FC...blinking cycle extraction unit, Hα,Hβ,Hγ...height, JD...judgment unit, LLg,LLr,LLy...pulse wave, LLα,LLβ,LLγ...pulse wave, RR,YY,GG,YY1-YY3...period, TR...train, Tr,Ty,Tg...blinking cycle, VS...visible light signal extraction unit, Wα,Wβ,Wγ...pulse width

Claims

1. a light-emitting device that transmits signals by emitting visible light with different blinking periods and duty ratios; a light receiving device that reads the blinking period and the duty ratio from a change in luminance of the visible light from the light emitting device; a signal processing unit that extracts transmission information from a transmitting side from the blinking period and the duty ratio read by the light receiving device; A visible light communication system comprising:

2. The visible light communication system according to claim 1 , wherein the signal processing unit extracts, as the transmission information, light color information and a traffic light ID on the transmitting side from the blinking period and the duty ratio.

3. The visible light communication system according to claim 2 , wherein the signal processing unit extracts the light color information from the difference in the blinking period and extracts the traffic light ID from the difference in the duty ratio.

4. The visible light communication system according to claim 1 , wherein a frame rate at which the light receiving device continuously captures the visible light is higher than an on / off switching frequency for blinking the light emitting device.

5. 2. The visible light communication system according to claim 1, wherein the light receiving device reads the visible light using an image sensor that asynchronously detects changes in luminance of each pixel and outputs only the changed data in combination with information on the pixel's position and time.

6. The visible light communication system according to claim 1 , wherein the light emitting device changes the emission luminance of the visible light in accordance with the difference in the duty ratio.

7. the light-emitting device is provided on the ground side, and emits the visible light using an LED light source constituting a railway signal lamp, and transmits the signal for the railway signal; the light receiving device and the signal processing unit are provided on the vehicle top side, The visible light communication system according to claim 1 , wherein the signal processing unit acquires train progress information based on the railway signal.

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