Invisible light communication system and signal processing device

Abstract

An invisible light communication system 100 comprises: a transmission unit TT that modulates and flashes invisible light-wavelength band light EL as invisible light and thereby transmits a signal; a light reception unit RR that receives the invisible light-wavelength band light EL; a first reading unit RU1 that reads a signal at a predetermined frame rate for a first range of an image acquired as a result of light reception by the light reception unit RR; and a second reading unit RU2 that reads a signal at a frame rate higher than that of the first reading unit RU1 for a second range more narrow than the first range.

Description

Non-visible light communication system and signal processing device

[0001] The present invention relates to a non-visible light communication system and a signal processing device that transmit and receive signal information using non-visible light and perform signal identification.

[0002] There is known a system that performs communication using light in a wavelength band outside the visible light range, that is, non-visible light, in which a plurality of types of signal information having different blinking periods are generated on the signal transmission side (see Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2024-17476

[0004] However, in Patent Document 1 above, it is premised that, for example, the blinking period on the transmission side is adjusted in consideration of the frame rate on the reception side (imaging side) so that identification of a plurality of types of signal information is maintained on the reception side (imaging side).

[0005] An object of the present invention is to provide a non-visible light communication system and a signal processing device that enable accurate information collection while suppressing an increase in processing load for processing on the side that receives optical communication, that is, the side that reads signals.

[0006] A non-visible light communication system for achieving the above object includes a transmission unit that modulates and blinks non-visible light to transmit a signal, a light reception unit that receives non-visible light, a first reading unit that reads a signal at a predetermined frame rate for a first range of an image acquired by light reception by the light reception unit, and a second reading unit that reads a signal at a frame rate higher than that of the first reading unit for a second range whose range is narrower than the first range.

[0007] In the non-visible light communication system, signal reading can be performed in two stages: reading by the first reading unit and reading by the second reading unit. Also, in the reading by the second reading unit, since the range of the image to be read is narrowed (more limited), reading can be performed at a frame rate higher than that of the reading by the first reading unit while suppressing an increase in processing load.

[0008] In a specific aspect of the present invention, the first reading unit reads the identification information of the transmitting unit, and the second range read by the second reading unit is narrowed to include the image of the transmitting unit to be processed based on the reading result of the first reading unit. In this case, the signal can be read at a higher frame rate over an appropriately limited range, and detailed signal reading from the image of the transmitting unit becomes possible.

[0009] In another aspect of the present invention, the exposure time in one frame in the second reading unit is shorter than the exposure time in one frame in the first reading unit. In this case, the difference in exposure time allows for more detailed signal reading in the second reading unit.

[0010] In yet another aspect of the present invention, the invisible light communication system includes a switching unit that switches from the frame rate and exposure time for reading in the first reading unit to the frame rate and exposure time for reading in the second reading unit. In this case, the frame rate and exposure time can be changed in conjunction with the switching operation in the switching unit.

[0011] In yet another aspect of the present invention, invisible light is light in a single wavelength band. In yet another aspect of the present invention, the transmitting unit emits infrared light in a specific frequency band as invisible light, and the receiving unit has a bandpass filter that transmits infrared light in a specific frequency band. In this case, the effects of ambient light and the like can be suppressed, and the necessary invisible light component can be accurately captured.

[0012] In yet another aspect of the present invention, the transmitting unit has an invisible light emitting unit that emits invisible light and a visible light emitting unit that emits visible light. In yet another aspect of the present invention, the transmitting unit has an invisible light emitting unit that emits invisible light and a visible light emitting unit that emits colored light, and the invisible light emitting unit and the visible light emitting unit share a power supply for each color of light. In this case, since the invisible light emitting unit and the visible light emitting unit share a power supply for each color of light, it is possible to reliably transmit signals with the desired modulated flashing with a simple configuration. In yet another aspect of the present invention, the transmitting unit is incorporated into a railway signal and transmits information regarding the progress of a train. In this case, it becomes possible to confirm the main type of signal regarding the progress of a train. In yet another aspect of the present invention, the transmitting unit is configured to change the flashing period of the invisible light.

[0013] A signal processing device for achieving the above objective includes a first reading unit that reads a signal at a predetermined frame rate for a first range of an image acquired by receiving modulated flashing invisible light, and a second reading unit that reads a signal at a higher frame rate than the first reading unit for a second range that is narrower than the first range.

[0014] The above signal processing device enables two-stage signal reading: reading in the first reading unit and reading in the second reading unit. Furthermore, since the reading range of the image to be read is narrowed (more limited) in the second reading unit, it is possible to perform reading at a higher frame rate than reading in the first reading unit while suppressing an increase in processing load.

[0015] This is a conceptual side view showing how a non-visible light communication system of one embodiment is employed in a train signaling system. This is a diagram illustrating the configuration of a non-visible light communication system that includes a signal processing device of one embodiment on the vehicle side. This is a circuit diagram of a signal lamp that constitutes the transmitting unit. This is a block diagram illustrating an example configuration of a non-visible light communication system including a signal processing device. This is an image diagram illustrating an overview of image processing in the signal processing device. This is a waveform diagram showing the operating status on the transmitting side. This is a waveform diagram showing the operating status on both the transmitting and receiving (light-receiving) sides. This is a conceptual diagram illustrating an example of a signal reading method at high frame rates. This is a conceptual diagram illustrating one mode of ending and starting signal reading at high frame rates, and a conceptual diagram illustrating a modified example of the signal reading method at high frame rates. This is a flowchart illustrating a series of operation processes related to signal reading on the receiving side of a non-visible light communication system. This is a conceptual diagram illustrating an overview of a non-visible light communication system.

[0016] Hereinafter, with reference to Figure 1 and other figures, an example of a signal processing device and a non-visible light communication system including the same according to one embodiment will be described. Figure 1 is a conceptual side view showing how the non-visible light communication system 100 of this embodiment is used in a train signaling system, Figure 2 is a diagram for explaining the configuration in which the signal processing device SD of the non-visible light communication system 100 is located on the vehicle side, and Figure 3 is a circuit diagram of the signal lamp that constitutes the transmitting unit. In this example, as shown in each figure, the signal processing device SD is built into a receiving device 10 that performs reception (light reception) in non-visible light communication on the vehicle side.

[0017] First, Figure 1 illustrates a non-visible light communication system 100 applied to signal communication processing between the onboard and ground sides during train operation (including automatic operation). Specifically, Figure 1 shows an example in which the non-visible light communication system 100 is introduced as a system for railway signaling, to transmit and receive multiple types of signal information that constitute signal indications in railway signaling equipment RS, and to perform signal identification. It should be noted that various forms of automatic operation of trains can be envisioned. That is, automatic operation of trains includes various forms of automatic operation, from fully unmanned automatic operation without a driver, to automatic operation that assists with some of the driver's operations.

[0018] As shown in the figure, the invisible light communication system 100 consists of a receiving device 10 and a transmitting device 20. The receiving device 10 is mounted on a train TR and functions as an on-board device that receives signals from the ground. On the other hand, the transmitting device 20 is incorporated into a railway signal RS installed around the track RL and functions as a ground-side device, or functions as part of the railway signal RS.

[0019] The receiving device 10 includes a camera (image sensor), etc., and functions as a light receiving unit RR for receiving light as signal information transmitted from the transmitting device 20. Furthermore, the receiving device 10 incorporates a signal processing unit SD, and the signal processing unit SD can identify the signal indication in the railway signal RS by reading the signal generated by the modulated flashing invisible light from the transmitting device 20.

[0020] The transmitter 20 is a ground-side device that functions as a transmitter TT that transmits information regarding the progress of the train TR, and outputs various commands to the train TR. In other words, the transmitter 20 functions as a railway signal RS or a part thereof. In the illustrated example, the transmitter 20 has a plurality (four in this case) of signal lights 20α to 20δ. Each signal light 20α to 20δ is configured to emit light in the visible light wavelength band (visible light), such as yellow, blue, and red, and to emit light in the non-visible light wavelength band (non-visible light: light in the light wavelength band other than visible light) by modulating and flashing. Non-visible light (light in the light wavelength band other than visible light) is assumed to be infrared light (IR light) emitted from an infrared emitter or ultraviolet light (UV light) emitted from an ultraviolet emitter. In this example, the transmitter 20 as the transmitter TT emits IR light (infrared light) in a specific frequency band as non-visible light. For a more detailed configuration of each signal lamp 20α to 20δ, please refer to Figure 2 and see the following description.

[0021] Furthermore, in the following, light in the visible light wavelength band will be referred to as visible light wavelength band light VL, and light in the non-visible light wavelength band will be referred to as non-visible light wavelength band light EL. In this example, the transmitting device 20 performs normal illumination for the visible light wavelength band light VL, while blinking the non-visible light wavelength band light EL (e.g., IR light), thereby transmitting a signal.

[0022] In particular, in this embodiment, a sufficiently long period of blackout is interspersed between the modulated flashing of the transmitter 20, so that when the receiving device 10 reads the modulated flashing of the transmitter 20, it is possible not only to read each on / off by reading with a short exposure time, but also to detect blackout by reading with a long exposure time.

[0023] The configuration of the receiving device 10, the configuration of the transmitting device 20, and the transmission (emission) and reception (reception) of light will be explained below with reference to Figure 2. Further details of the signal lights 20α to 20δ that constitute the transmitting device 20 will be explained here. Note that the figure shows the configuration of signal light 20α, and although the colors emitted differ, the mechanical configuration of the other signal lights 20β to 20δ is the same, so their illustration and explanation are omitted.

[0024] First, the receiving device 10 includes an imaging device 11, which is composed of, for example, a camera (image sensor) CA, a bandpass filter 12 that transmits light in a specific wavelength band, and a control / processing device 13. Of these, the control / processing device 13 incorporates a signal processing device SD.

[0025] Various cameras (image sensors) can be used as the camera (image sensor) CA that constitutes the imaging device 11 within the receiving device 10. For example, an image sensor for IR light can be used depending on the invisible light wavelength band EL to be captured. In this example, a bandpass filter 12 is further attached to the front of the camera CA, which is the imaging device 11. The bandpass filter 12 is configured to efficiently transmit light in the wavelength band of the component of the invisible light wavelength band EL incident from the transmitting device 20. That is, the receiving device 10 as the light receiving unit RR has a bandpass filter 12 that transmits IR light (infrared light) in a specific frequency band. By adapting the bandpass filter 12 to the invisible light wavelength band EL, the receiving device 10 (light receiving unit RR) can efficiently capture the component of the invisible light wavelength band EL in the imaging device 11. It is also conceivable that the transmitting device 20 is configured to transmit the invisible light wavelength band EL as light in a single wavelength band. By focusing the non-visible light wavelength band EL on a single wavelength band in this way, the effects of ambient light can be further suppressed (improving resistance to ambient light).

[0026] The control / processing device 13 performs processing to read the signal from the transmitter 20 by analyzing the image data acquired by the imaging device 11. In this case, the control / processing device 13 is configured to read the content of the signal from the blinking pattern of the modulated blinking non-visible light wavelength band EL by analyzing the results of continuous image acquisition by the imaging device 11 in the signal processing device SD. In particular, in this embodiment, the control / processing device 13 is configured to perform a first stage of reading in which the signal is read from the entire image at a predetermined frame rate, and a second stage of reading in which the range of the image to be read is narrowed, and the signal is read from the narrowed range of the image at a frame rate higher than the predetermined frame rate.

[0027] The signal lamp 20α, which constitutes the transmitting device 20 that is the source of the light signal, includes a large number of LED elements EE, EE, ... arranged planarly, as shown in the figure. In particular, in this embodiment, as shown by the difference in patterns (hatching, white outline) in the figure, the large number of LED elements EE, EE, ... of the signal lamp 20α include a mixture of visible light LED elements EEv, EEv, ... and invisible light LED elements EEi, EEi, ... In other words, the signal lamp 20α is formed by a visible light emitting section VP composed of a large number of visible light LED elements EEv, EEv, ... and an invisible light emitting section IP composed of a large number of invisible light LED elements EEi, EEi, ...

[0028] As previously described, the visible light wavelength band light VL emitted from the visible light emission unit VP, which is composed of visible light LED elements EEv, EEv, ..., is normally illuminated (illuminated without intended flashing modulation) when lit. Each signal lamp 20α to 20δ, as a railway signal RS, transmits information about the progress of the train TR to detectable people or sensors, etc., based on the color of the visible light emitted by the visible light emission unit VP at each placement location. On the other hand, the invisible light wavelength band light EL emitted from the invisible light emission unit IP, which is composed of invisible light LED elements EEi, EEi, ..., transmits a signal by flashing in a modulated manner when lit. That is, each signal lamp 20α to 20δ transmits information about the progress of the train TR to detectable sensors, etc., based on the way the invisible light emission unit IP flashes in a modulated manner (differences in modulated flashing).

[0029] Figure 3(A) shows a circuit diagram of one of the signal lights 20α to 20δ that constitute the transmitting device 20 (for example, signal light 20α). In the above configuration, the timing of power supply for normal illumination of visible light and modulated flashing of invisible light can be the same. Therefore, the invisible light emitting unit IP and the visible light emitting unit VP can share a power supply PW for each color of light, that is, for each signal light 20α to 20δ. In the illustrated example, power is supplied from a single power supply PW to the visible light side, i.e., the visible light emitting unit VP side, which is enclosed by a dashed line in Figure 3(B), and to the invisible light side, i.e., the invisible light emitting unit IP side, which is enclosed by a dashed line in Figure 3(C). As shown in the illustration, on the visible light emitting unit VP side, a circuit is formed for normal illumination operation of each color for each signal light 20α to 20δ. On the other hand, on the non-visible light emitting section IP side, a modulation circuit and the like are provided, and a circuit is formed to perform a desired modulated flashing operation for each signal lamp 20α to 20δ. In particular, in this embodiment, it is possible to include various information such as the ID information of the transmitting device 20 in addition to the indication display in the information transmitted by modulated flashing.

[0030] Hereinafter, with reference to the block diagram shown in Figure 4, an example configuration of the invisible light communication system 100 including the signal processing device SD of this embodiment will be described.

[0031] First, in the non-visible light communication system 100, the transmitting device 20 (transmitter TT), which is the signal transmitting side, includes a plurality of signal lights (LED signal lights) 20α to 20δ, and each signal light 20α to 20δ is equipped with a control board 21 and an LED board 22. The control board 21 consists of a visible light lighting control unit 21v and a non-visible light modulation control unit 21i, and the LED board 22 consists of a visible light light emitting unit VP and a non-visible light light emitting unit IP. The visible light lighting control unit 21v of the control board 21 corresponds to the circuit section on the visible light side as described with reference to Figure 3, and receives power supplied from a shared power supply PW to light up (normally illuminate) the visible light light emitting unit VP of the LED board 22. The non-visible light modulation control unit 21i of the control board 21 corresponds to the circuit section on the non-visible light side as described with reference to Figure 3, and receives power supplied from a shared power supply PW to light up (modulated blinking) the non-visible light emitting unit IP of the LED board 22. The visible light emitting unit VP emits visible light wavelength band light VL according to the operation control by the visible light lighting control unit 21v, and the non-visible light emitting unit IP emits non-visible light wavelength band light EL according to the operation control by the non-visible light modulation control unit 21i.

[0032] Of the non-visible light communication system 100, the receiving device 10, which is the signal receiving side, comprises an imaging device 11, a bandpass filter (BPF) 12, and a control / processing device 13, as described above. Of these, the control / processing device 13 includes a signal processing device SD, which comprises an image acquisition unit GR, an imaging device control unit CC, an image analysis unit GA, and an output unit OT.

[0033] In the control / processing device 13, the signal processing device SD, specifically the image acquisition unit GR, acquires image data captured by the imaging device 11, which receives invisible light wavelength band light EL emitted by the invisible light emission unit IP and passed through the bandpass filter 12. The image acquisition unit GR outputs the acquired image data to the image analysis unit GA.

[0034] The imaging device control unit CC controls the operation of the imaging device 11 according to the commands and instructions from the image analysis unit GA. As a result, the desired image data is acquired by the image acquisition unit GR.

[0035] The image analysis unit GA performs the above-described operational control to acquire image data and also performs analysis processing on the acquired image data. For this reason, as shown in the enlarged portion of the figure, the image analysis unit GA includes a first reading unit RU1 and a second reading unit RU2 for signal reading, and further includes a switching unit SW for switching between signal reading by the first reading unit RU1 and signal reading by the second reading unit RU2.

[0036] The first reading unit RU1 reads the signal at a predetermined frame rate for a first range of the image acquired by the image acquisition unit GR, which is responsible for receiving light in the receiving device 10, which acts as a light receiving unit RR. As an example, the first reading unit RU1 processes a continuous image with the first range being the range of the entire image acquired by the image acquisition unit GR and the predetermined frame rate being 60 fps. The first reading unit RU1 also reads the identification information of the transmitting device 20, which acts as a transmitting unit TT, from the result of demodulating the modulated blinking based on the frame rate of 60 fps.

[0037] The second reading unit RU2 reads signals from a second range, which is narrower than the first range, i.e., the range of the entire image, at a higher frame rate than the first reading unit RU1. For example, the second reading unit RU2 defines the second range as a rectangular region extracted from the entire image, surrounding one target transmitter 20, and processes this region as a continuous image at a frame rate of 600 fps, higher than that of the first range. In other words, in the second reading unit RU2, the second range is narrowed to include the image of the one transmitter 20 to be processed, based on the reading result of the first reading unit RU1, that is, based on the identification information of the transmitter 20 that was read. Then, in the second reading unit RU2, processing is performed at 600 fps, which is faster than 60 fps, for the narrowed range (limited range). This makes it possible to acquire more detailed information while suppressing an increase in processing load.

[0038] Hereinafter, reading at a relatively low frame rate by the first reading unit RU1 will be referred to as low fps reading, and reading at a relatively high frame rate by the second reading unit RU2 will be referred to as high fps reading.

[0039] Furthermore, in the above embodiment, the exposure time in one frame in the second reading unit RU2 is consequently shorter than the exposure time in one frame in the first reading unit RU1. In other words, the shutter speed in the second reading unit RU2 is faster than the shutter speed in the first reading unit RU1.

[0040] The switching unit SW switches between reading by the first reading unit RU1 and reading by the second reading unit RU2. As an example of typical operation, when one transmitter 20 to be processed is narrowed down from the reading result of the first reading unit RU1, the switching unit SW performs a process to switch the frame rate and exposure time from the frame rate and exposure time for reading by the first reading unit RU1 to the frame rate and exposure time for reading by the second reading unit RU2.

[0041] Furthermore, the series of processes performed by the first reading unit RU1, the second reading unit RU2, and the switching unit SW in the image analysis unit GA described above can be composed of various programs that perform a series of data processing operations.

[0042] The output unit OT outputs various signal information, such as the display information resulting from the analysis in the image analysis unit GA, to, for example, the display device DP or the sounding device (voice notification device) VD.

[0043] The following describes the image processing in the signal processing unit SD, which constitutes the main part of the receiving device 10, with reference to the image shown in Figure 5. Here, if an image sensor for IR light is used as the camera CA constituting the imaging device 11 of the receiving device 10, the image shown in Figure 5 will be a grayscale image of IR light. Furthermore, depending on the properties of the bandpass filter 12 used on the front of the imaging device 11, it is conceivable that almost nothing but the light-emitting portion of the signal light emitting IR light in a specific wavelength band will be captured. However, for the sake of clarity, the image here shows the entire signal light, and even its surroundings, captured.

[0044] First, FIG. 5(A) is an image diagram showing the state of the overall image G0 acquired by the image acquisition unit GR. In the illustrated example, the overall image G0 includes a plurality of transmission devices 20, 20,.... One of these is the transmission device 20 that includes the signal lamp device to be read. Note that the plurality of transmission devices 20, 20,... in the image can be extracted in a state surrounded by the rectangular region RA by appropriately performing image processing on the overall image G0 as shown in FIG. 5(B).

[0045] The non-visible light wavelength band light EL transmitted from the non-visible light emitting portions IP (see FIG. 4 etc.) of the extracted respective transmission devices 20, 20,... flickers in modulation in different ways from each other. Therefore, by reading the overall image G0 as the first range RE1 in the first reading unit RU1, an image GG including one target transmission device 20 can be narrowed down as shown in FIG. 5(C). Particularly here, adjustments regarding signal creation have been made in advance so that the difference in modulation flicker between adjacent transmission devices 20, 20,... can be identified even in the reading at low fps by the first reading unit RU1. In the figure, among the differences in the created signal waveforms, the state shown as the difference in the results in the reading at low fps is indicated by a balloon, and further, each signal waveform is numbered.

[0046] Here, it is assumed that the number of transmission devices 20 that can be included in one overall image G0 is not so large. Therefore, even when the amount of information that can be acquired by reading at low fps is small, the difference in modulation flicker between the transmission devices 20, 20,... is sufficiently distinguishable. That is, as shown in FIG. 5(C), from among the plurality of extracted transmission devices 20, 20,... shown in FIG. 5(B), an image GG of a rectangular region including one transmission device 20 to be the processing target can be narrowed down from the reading result of the first range RE1 (overall image G0) in the first reading unit RU1.

[0047] As described above, when the target is narrowed down, i.e., specified, to one transmission device 20, and the range of the image GG of the rectangular area including one transmission device 20 as shown in FIG. 5(D) is limited as the second range RE2, the switching unit SW performs a process of switching from the reading by the first reading unit RU1 to the reading by the second reading unit RU2. Thereby, reading at a high fps is performed for the range of the image GG.

[0048] Hereinafter, an example of the operation status for signal transmission and reception on the transmission side and the reception (light reception) side will be described with reference to FIGS. 6 and 7.

[0049] First, the operation status on the transmission side will be described with reference to FIG. 6. FIG. 6(A) is a waveform diagram showing the transmission operation status on the transmission side, and FIG. 6(B) is a waveform diagram corresponding to an enlarged view of a part of FIG. 6(A).

[0050] As previously described, the modulated flashing in the transmitter 20 includes periods of extinction that are sufficiently longer than the exposure time. More specifically, in the modulated flashing of the transmitter 20, periods of extinction that are sufficiently longer than the exposure time at low fps (for example, a period of about 60 fps) by the first reading unit RU1 of the receiver 10 are inserted between modulated flashing cycles. Here, as shown in Figure 6A, such a long period of extinction (the time during which the off state is maintained) is defined as the first unit time t_Lo, and the on / off switching for low fps on the receiving (light-receiving) side is configured with the first unit time t_Lo as the period. However, as shown in Figure 6(B), which is a partially enlarged view of Figure 6(A), during the on period in one first unit time t_Lo, even finer on / off modulated flashing is performed. These modulated flashing cycles correspond to readings at high fps on the receiving (light-receiving) side. Here, as shown in Figure 6(B), the duration of one short blink for high fps is defined as the second unit time t_Hi. That is, the on / off switching for high fps on the receiving (light receiving) side is configured with the second unit time t_Hi as the period. The period for the second unit time t_Hi, i.e., the switching timing between on and off, may be such that the switching occurs at a frequency of, for example, 100 Hz or 120 Hz. The first unit time t_Lo is thought to be set to be long enough so that a sufficiently large number of on / off switchings based on the second unit time t_Hi can be performed (information can be included) within one first unit time t_Lo.

[0051] In the above case, when reading at low fps on the receiving (light receiving) side, the amount of information acquired per unit of time is limited, while when reading at high fps, it becomes possible to acquire detailed information.

[0052] The following describes an example of the operation status of the transmitting side, as well as an example of the operation status for sending and receiving signals between the transmitting side and the receiving (optical receiving) side, with reference to Figure 7.

[0053] Figure 7(A) shows the operation of the reading side at low fps on the receiving (light receiving) side, and Figures 7(B) and 7(C) are waveform diagrams to explain the reading of invisible light by the receiving (light receiving) side at low fps. Furthermore, Figure 7(D) is a waveform diagram corresponding to an enlarged portion of Figure 7(C). In addition, Figure 7(E) is a waveform diagram to explain the reading of invisible light by the receiving (light receiving) side at high fps.

[0054] First, in Figure 7(A), the period PT represents the shutter interval during reading by the first reading unit RU1 of the receiving device 10, i.e., during reading at low fps, and corresponds to the reciprocal of the frame rate. Also, the exposure time in one period PT is denoted as τ_Lo.

[0055] Figure 7(B) shows the reading of the transmitted signal illustrated in Figure 6(A) in the above embodiment. As shown in the figure, here the period PT and its exposure time τ_Lo shown in Figure 7(A) are shorter than the first unit time t_Lo, and multiple exposures can occur per first unit time t_Lo. For this reason, as shown in Figure 7(C), for example, at least one exposure time τ_Lo is received within one first unit time t_Lo, and the result is detected as the amount of light received on the receiving side. The magnitude of one amount of light received is determined by the on-off ratio (duty cycle) in which finer fluctuations and blinking occur within one first unit time t_Lo, as shown in Figure 7(D). Although not particularly limited, for example, by making the on ratio within one first unit time t_Lo half (50%) or more, a sufficient amount of light for detection can be secured. As a result, the receiving (light receiving) side reads (decodes) the signal for low fps based on one first unit time t_Lo.

[0056] Next, we will explain the reading on the receiving (light-receiving) side at high fps. As shown in Figure 7(D) and as explained with reference to Figure 6(B), in order to accommodate reading at high fps, the transmitting side performs multiple fluctuating blinks, i.e., on / off switching, per first unit time t_Lo, with the second unit time t_Hi as the period for this on / off switching. In this case, t_Hi < t_Lo. On the receiving device 10 side, in order to read the fluctuating blinks at the second unit time t_Hi, reading is performed by the second reading unit RU2, i.e., reading at high fps (for example, around 600 fps). In other words, the transmitting side performs high-speed fluctuating blinks to correspond to reading at high fps on the receiving (light-receiving) side.

[0057] In this case, as shown in Figure 7(E), light is received at least once for an exposure time τ_Hi within one second unit time t_Hi, and the result is detected as the amount of light received on the receiving side. As a result, the receiving (light-receiving) side reads (decodes) the signal for high fps based on one second unit time t_Hi.

[0058] Furthermore, in order to achieve the above configuration, in the receiving device 10, the exposure time τ_Hi in one frame in the second reading unit RU2 is set to be short, as is the exposure time τ_Lo in one frame in the first reading unit RU1. In addition, the relationship including the first unit time t_Lo and the second unit time t_Hi on the transmitting side is τ_Hi < t_Hi < τ_Lo < t_Lo.

[0059] Below, an example of a signal reading method at high fps will be explained with reference to the conceptual diagrams shown in Figures 8 and 9. Figure 9(A) is a conceptual diagram illustrating the manner of ending and starting signal reading at high fps, while Figures 9(B) and 9(C) are conceptual diagrams showing modified examples of the signal reading method at high fps.

[0060] In this example, as shown in Figure 8, two sets of blinking (on / off) in the second unit time t_Hi for the smallest unit of modulated blinking at the transmitting side are considered as one set, and each set is assumed to be either an on-off (Hi-Lo) or on-on (Hi-Hi) combination, with on-off (Hi-Lo) defined as "0" and on-on (Hi-Hi) as "1" when signal generation is performed. In this case, in one first unit time t_Lo, the "on" state will account for more than 50% of the total. Also, in this case, as shown enclosed by the dashed line in Figure 9(A), it is conceivable that the detection result of the fluctuation of the smallest unit of modulated blinking described above can be used to determine the boundary of the fluctuation per first unit time t_Lo corresponding to low fps at the transmitting side. In other words, as shown in the figure, if an off-off (Lo-Lo) state, which is not used for signal generation, occurs after an on (Hi) state, it can be determined that there is an end to one first unit time t_Lo (one signal transmission has finished). On the other hand, if an on (Hi) state occurs after an off-off (Lo-Lo) state, it can be determined that one first unit time t_Lo has started. For readings at high fps, a set of information may be incorporated into the modulated blinking during the on state in one first unit time t_Lo, but as shown in Figure 9(B), multiple (three in the illustrated example) modulated blinking during the on state in one first unit time t_Lo state may be combined. In other words, as in the example shown in Figure 9(A), as shown in Figure 9(C), the end and start of one first unit time t_Lo are determined, and by using this determination result to connect the previous end and the next start immediately after the blackout period, it becomes possible to perform the splicing shown in Figure 9(B). In this case, more information can be captured in the signal corresponding to one low fps read compared to a high fps read. However, in this case, the proportion of the second unit time t_Hi being ON (Hi) must be sufficiently large in order to enable low fps reads.

[0061] The following describes a series of operations related to signal reading on the receiving side of the invisible light communication system 100, with reference to the flowchart shown in Figure 10.

[0062] First, when the receiving device 10 is started up, settings are made to perform reading at a low fps as the imaging condition (step S101), and the imaging device 11 is operated by the control operation of the imaging device control unit CC (step S102), and an image is acquired in the image acquisition unit GR (step S103).

[0063] Next, based on the image acquired in step S103, the image analysis unit GA performs analysis processing (step S104). In the case of operation from the initial setting (step S101), at this point (step S104), the first reading unit RU1 performs reading at a low fps.

[0064] Subsequently, it is determined whether or not to process (continue) the imaging conditions at a low fps (step S105). If it is determined in step S105 that processing will be performed at a low fps (step S105: Yes), then low fps decoding processing is performed. That is, the signal is read by the first reading unit RU1 (step S106).

[0065] Next, it is determined whether or not to switch to high fps (step S107). If it is determined that a switch should be made (step S107: Yes), the switching unit SW switches from the first reading unit RU1 to the second reading unit RU2. On the other hand, if it is determined in step S107 that a switch should not be made (step S107: No), reading at low fps by the first reading unit RU1 is maintained. After that, the result of the signal reading is output as the reception result (step S109), and the operation returns to that of step S102.

[0066] On the other hand, if it is determined in step S105 that processing cannot be performed at low fps (step S105: No), then high fps decoding processing is performed. That is, signal reading is performed by the second reading unit RU2 (step S110). A typical example of this is when a switch to high fps is made in step S107 (step S107: Yes), and then various image processing steps are performed (steps S108, S109, S102-S104) before reaching the processing in step S105.

[0067] After step S110, it is determined whether or not to switch to a lower fps (step S111). If it is determined to switch (step S111: Yes), the switching unit SW switches from the second reading unit RU2 to the first reading unit RU1. On the other hand, if it is determined in step S111 not to switch (step S111: No), reading at high fps by the second reading unit RU2 is maintained. After that, the result of the signal reading is output as the reception result (step S109), and the operation returns to step S102.

[0068] The above process is repeated until signal reading is no longer necessary (for example, until the train has completed its run).

[0069] The following describes the outline of the invisible light communication system 100 with reference to the conceptual diagram shown in Figure 11.

[0070] As shown in the figure and as previously described, the invisible light communication system 100 including the signal processing device SD of this embodiment includes a transmitting unit TT that modulates and blinks invisible light wavelength band optical EL as invisible light to transmit a signal, a light receiving unit RR that receives invisible light wavelength band optical EL, a first reading unit RU1 that reads the signal at a predetermined frame rate for a first range RE1 of the image G acquired by receiving light at the light receiving unit RR, and a second reading unit RU2 that reads the signal at a higher frame rate than the first reading unit RU1 for a second range RE2 which is narrower than the first range RE1. In the invisible light communication system 100 described above, it is possible to read the signal in two stages: reading at the first reading unit RU1 and reading at the second reading unit RU2. Furthermore, since the reading range of the image is narrowed (more limited) when reading with the second reading unit RU2, it is possible to perform reading at a higher frame rate than when reading with the first reading unit RU1 while suppressing an increase in processing load.

[0071] Furthermore, in the above case, it is sufficient to apply a frame rate of, for example, 600 fps to a portion of the image, thus enabling the exchange of necessary information without the need for ultra-high-speed cameras such as EVS (Event-Based Vision Sensor) cameras. In addition, by targeting light in a specific wavelength range of non-visible light (IR light or UV light), problems that occur when using modulated flashing of visible light (such as flickering) can be avoided.

[0072] [Other] The present invention is not limited to the embodiments described above, and can be implemented in various forms without departing from its essence.

[0073] First, regarding the receiving device 10, if accurate light reception is possible, various types of light-receiving elements can be used, not limited to image sensors for IR light. For example, photodiodes can also be used. Alternatively, the bandpass filter 12 can be omitted by using a light-receiving element specialized for a specific wavelength band.

[0074] Furthermore, the information acquired at high fps can vary. For example, the information acquired at high fps may include identification information of the transmitting device 20 in addition to the display information, so that the success or failure of the information acquired at low fps can be confirmed.

[0075] Furthermore, the transmitting device 20 can also be configured to separately include a device that emits visible light wavelength band light VL and a device that emits non-visible light wavelength band light EL.

[0076] Furthermore, various types of signal information can be envisioned as the information to be handled. If the information concerns railways, in addition to the information regarding whether or not to proceed as described above, the invisible light communication system 100 may also be used to exchange signals regarding, for example, instructions for changing direction at a turnout.

[0077] Furthermore, the above example applies the invisible light communication system 100 to railways that run on tracks designated as dedicated tracks. However, it is not limited to this. For example, the invisible light communication system 100 can also be used for trams that run on tracks designated as dedicated tracks (newly constructed tracks, shared tracks), and for buses that run on dedicated roads designated as dedicated tracks.

[0078] Furthermore, the transmitter 20 may be configured to change the flashing period of the invisible light. In other words, the transmitter 20 may be configured to generate multiple types of signal information with different flashing periods of invisible light, and to transmit any one of the multiple types of signal information. In this way, it may be possible to identify more signals by utilizing the differences in flashing periods while suppressing the effects of ambient light.

[0079] 10...Receiver, 11...Imaging device, 12...Bandpass filter, 13...Control / processing device, 20...Transmitter, 20α-20δ...Signal lamp, 21...Control board, 21i...Non-visible light modulation control unit, 21v...Visible light illumination control unit, 22...LED board, 100...Non-visible light communication system, CA...Camera, CC...Imaging device control unit, DP...Display device (display), EE...LED element, EEi...Non-visible light LED element, EEv...Visible light LED element, EL...Non-visible light wavelength band, G...Image, G0...Overall image, GA...Image analysis unit, GG...Image, GR...Image acquisition Part, IP...Non-visible light emitting part, OT...Output part, PT...Period, PW...Power supply, RA...Rectangular area, RE1...First range, RE2...Second range, RL...Track, RR...Light receiving part, RS...Railway signal, RU1...First reading part, RU2...Second reading part, SD...Signal processing device, SW...Switching part, TR...Train, TT...Transmitter, VD...Sounding device (voice notification device), VL...Visible light wavelength band light, VP...Visible light emitting part

Claims

1. An invisible light communication system comprising: a transmitting unit that modulates and flashes invisible light to transmit a signal; a receiving unit that receives the invisible light; a first reading unit that reads a signal at a predetermined frame rate for a first range of an image acquired by receiving light at the receiving unit; and a second reading unit that reads a signal at a higher frame rate than the first reading unit for a second range that is narrower than the first range.

2. The invisible light communication system according to claim 1, wherein the first reading unit reads the identification information of the transmitting unit, and the second range read by the second reading unit is narrowed to include the image of the transmitting unit to be processed based on the reading result of the first reading unit.

3. The invisible light communication system according to claim 1, wherein the exposure time in one frame in the second reading unit is shorter than the exposure time in one frame in the first reading unit.

4. The invisible light communication system according to claim 1, further comprising a switching unit for switching from the frame rate and exposure time for reading in the first reading unit to the frame rate and exposure time for reading in the second reading unit.

5. The invisible light communication system according to claim 1, wherein the invisible light is light in a single wavelength band.

6. The invisible light communication system according to claim 1, wherein the transmitting unit emits infrared light in a specific frequency band as the invisible light, and the receiving unit has a bandpass filter that transmits infrared light in the specific frequency band.

7. The invisible light communication system according to claim 1, wherein the transmitting unit comprises an invisible light emitting unit that emits invisible light and a visible light emitting unit that emits visible light.

8. The invisible light communication system according to claim 1, wherein the transmitting unit comprises an invisible light emitting unit that emits invisible light and a visible light emitting unit that emits colored light, and the invisible light emitting unit and the visible light emitting unit share a power supply for each color of light.

9. The non-visible light communication system according to claim 1, wherein the transmitting unit is incorporated into a railway signal and transmits information regarding the progress of a train.

10. The invisible light communication system according to claim 1, wherein the transmitting unit is configured to change the flashing period of the invisible light.

11. A signal processing device comprising: a first reading unit that reads a signal at a predetermined frame rate for a first range of an image acquired by receiving modulated flashing invisible light; and a second reading unit that reads a signal at a higher frame rate than the first reading unit for a second range that is narrower than the first range.

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