JP2015088981A - Visible light communication system and visible light communication method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a visible light communication system and a visible light communication method, reduced in the generation of transmission errors.SOLUTION: A transmission device 100 includes: a light emitting part 106; a color coordinate modulation part 102 that converts each bit stream of transmission data into an order of signal points on a color coordinate on the basis of a predetermined regulation, and converts the order of signal points into an order of color coordinate values; and a transmission coordinate system conversion part 104 that converts the order of color coordinate values into an order of light emitting intensities at the light emitting part 106. A reception device 130 includes: a light receiving part 132; a reception coordinate system conversion part 134 that converts an order of light receiving intensities at the light receiving part 132 into an order of color coordinate values; and a color coordinate demodulation part 136 that converts the order of color coordinate values into an order of signal points on a color coordinate, and converts the order of signal points into each bit stream of reception data on the basis of the predetermined regulation.

Description

  The present invention relates to a visible light communication system and a visible light communication method.

  In recent years, with the widespread use of LEDs, visible light communication using LED light sources such as traffic lights and lighting has attracted attention. Patent Documents 1 and 2 disclose CSK (Color Shift Keying), which is one of the modulation methods of visible light communication. In CSK, (1) communication connectivity is ensured by chromaticity coordinates that are not directly influenced by the wavelength of the light source, (2) there is no flicker due to luminance changes, and the total emission intensity is constant, (3) chromaticity coordinates There is an advantage that the communication speed can be increased by increasing the number of the upper signal points.

JP 2008-252570 A JP 2010-098574 A

  While CSK has the advantages as described above, the chromaticity coordinates on the transmission side and the chromaticity coordinates of the received signal are affected by the influence of disturbance light, wavelength variation of optical elements, nonlinearity of analog circuits between transmission and reception, and the like. There was a case where a transmission error occurred due to a difference. In particular, when the number of signal points is increased, or when the RGB triangles in the chromaticity coordinates are intentionally reduced and biased to a certain color in order to communicate with a specific color even if the number of signal points is small, each signal point There is a problem in that the distance between them becomes small and transmission errors are likely to occur.

  The present invention has been made to solve such problems, and an object of the present invention is to provide a visible light communication system and a visible light communication method with less transmission errors.

  The visible light communication system according to the present invention includes a transmission device and a reception device, and the transmission device converts a sequence of signal points on chromaticity coordinates based on a predetermined rule for each bit string of transmission data and a transmission unit. A chromaticity coordinate modulation unit that converts the sequence of the signal points into a sequence of chromaticity coordinate values; and a transmission coordinate system conversion unit that converts the sequence of the chromaticity coordinate values into a sequence of emission intensity of the light emitting unit. The receiving apparatus includes: a light receiving unit; a receiving coordinate system converting unit that converts a sequence of received light intensities of the light receiving unit into a sequence of chromaticity coordinate values; and a sequence of the chromaticity coordinate values of signal points on the chromaticity coordinates. And a chromaticity coordinate demodulator that converts the sequence of the signal points into each bit string of the received data based on the predetermined rule.

  A visible light communication method according to the present invention is a visible light communication method in a visible light communication system including a transmission device and a reception device, wherein the transmission device colors each bit string of transmission data based on a predetermined rule. A step of converting a sequence of signal points on a chromaticity coordinate; a step of converting a sequence of the signal points into a sequence of chromaticity coordinate values; a step of converting a sequence of chromaticity coordinate values into a sequence of luminescence intensity; and the luminescence intensity. A step of emitting visible light according to the sequence of: the receiving device generating a sequence of received light intensity from the received visible light; a step of converting the sequence of received light intensity into a sequence of chromaticity coordinate values; Converting a sequence of chromaticity coordinate values to a sequence of signal points on the chromaticity coordinate; converting the sequence of signal points to each bit string of received data based on the predetermined rule; Those having.

  According to the present invention, it is possible to provide a visible light communication system and a visible light communication method with less occurrence of transmission errors.

It is a figure for demonstrating 4CSK which has arrange | positioned four signal points on chromaticity coordinates. It is a figure which shows the specific arrangement | positioning of the signal point of 4CSK. 1 is a diagram showing a system configuration of a visible light communication system 10 according to a first embodiment. 6 is a diagram showing a signal flow in transmitting apparatus 100 according to Embodiment 1. FIG. 6 is a diagram showing a signal flow in receiving apparatus 130 according to Embodiment 1. FIG. It is a figure which shows the relationship between the bit string of the input data of the visible light communication system which concerns on Embodiment 2, and the two-dimensional arrangement | positioning in the surface which cross | intersects the transmission / reception direction of the visible light corresponding to each signal point.

Embodiments of the present invention will be described below with reference to the drawings.
Embodiment 1 of the Invention
First, the transmission data modulation method and demodulation method of the visible light communication system according to the first embodiment will be described.

  FIG. 1 is a diagram for explaining 4CSK in which four signal points C1, C2, C3, and C4 are arranged on chromaticity coordinates. In CSK, transmission data is converted into color information of visible light by multi-value color modulation, and communication is performed. The transmission data is defined by xy coordinate values of chromaticity coordinates (xy color coordinate) of a predetermined color system. In the visible light communication system according to the first embodiment, the chromaticity coordinates of the color plane expressed by the hue and saturation of the XYZ color system are used as the chromaticity coordinates of the predetermined color system.

The xy coordinate values are converted into values R, G, and B representing the light emission intensities of the three color LED light sources according to the following equation (1). The result of mixing the light of the three color light sources is the color indicated by the chromaticity coordinates.

x _i = R · x _R + G · x _G + B · x _B
y _i = R · y _R + G · y _G + B · y _B (1)
R + G + B = 1

  That is, the CSK symbol is defined by the color of visible light generated by the three color light sources. The transmission data is transmitted according to the ratio of the emission intensity of the three color light sources. Since CSK can freely set signal points as information points on the chromaticity coordinates, it has a degree of freedom in setting the emission color and transmission speed, and is resistant to the influence of attenuation and disturbance in the light propagation path.

  FIG. 2 is a diagram showing a specific arrangement of 4CSK signal points. Signal points are arranged at three vertices of an equilateral triangle and the position of the center of gravity thereof, and the colors of the respective signal points are represented by C1, C2, C3, and C4.

  In the conventional 4CSK, each color (each signal point) transmits 2-bit data. For example, if it is C1, bit string [00] is transmitted. At this time, it is the distance between the signal points, that is, the distance between the signals, that determines the resistance to various noises in the transmission path. In the signal point arrangement shown in FIG. 2, the minimum distance between signals is the distance d between C2 (or C1, C3) and C4, and when the noise is larger than d / 2 which is half the distance d. A transmission error occurs on the receiving side.

  Therefore, in the visible light communication system according to the first embodiment, the transmission apparatus transmits the signal points defined on the chromaticity coordinates based on a predetermined order, that is, a predetermined rule. A bit string or digital value of data is associated with a temporal order of signal points, that is, a sequence of signal points according to a predetermined rule. For transmission data, a sequence of signal points is associated with each bit string having a predetermined number of bits, and the transmission data is encoded in the format of the sequence of signal points. Here, one section in which a sequence of signal points corresponding to a bit string having a predetermined number of bits is transmitted is called a frame.

In the visible light communication system according to the first embodiment, as a predetermined rule, four signal points are transmitted in the following order according to a transmission signal as follows. For a 2-bit input signal, a frame that is an array of a set of signal points is given.

Input data bit string Frame symbol Signal point transmission order (transmission frame)
[0 0] A [C1 C2 C3 C4]
[0 1] B [C2 C1 C4 C3]
[1 0] C [C3 C4 C1 C2]
[1 1] D [C4 C3 C2 C1]

  In the transmission order according to the predetermined rule, the order of each transmission point within a frame is not the same between frames. For example, the transmission order of the signal point C1 is first in frame A, second in frame B, third in frame C, and fourth in frame D. The signal points with the first transmission order of frames A, B, C, and D are C1, C2, C3, and C4, and the signal points with the first transmission order are different for each frame. For this reason, the cross correlation between frames can be lowered. In this transmission order, the cross-correlation becomes 0, and the reception gain can be increased.

The switching speed of signal points in the frame is set according to the product incorporating the light source, for example, lighting, signboard, TV, etc.
Further, in the visible light communication system according to the first embodiment, the reception device is obtained by inversely converting the received light intensity values R, G, and B into xy coordinate values of chromaticity coordinates according to the equation (1). Become. Then, the type of the received frame is specified from the color change order, that is, the order of the received signal points and the predetermined rule, and the data is decoded and demodulated.

Next, the configuration of the visible light communication system 10 according to the first embodiment will be described.
FIG. 3 is a diagram showing a system configuration of the visible light communication system according to the first embodiment. The visible light communication system 10 includes a transmission device 100 and a reception device 130. The transmission device 100 includes a chromaticity coordinate modulation unit 102, a transmission coordinate system conversion unit 104, and a light emitting unit 106. The receiving device 130 includes a light receiving unit 132, a reception coordinate system conversion unit 134, and a chromaticity coordinate demodulation unit 136.

  The chromaticity coordinate modulation unit 102 converts the sequence of signal points on the chromaticity coordinates based on the above-mentioned predetermined rule for each bit string of the transmission data, and converts the sequence of the signal points into a sequence of chromaticity coordinate values x and y. To do. The transmission coordinate system conversion unit 104 converts the arrangement of the chromaticity coordinate values x and y into a sequence of the emission intensities R, G, and B according to the equation (1). The light emitting unit 106 emits visible light under light intensity modulation according to the arrangement of the light emission intensities R, G, and B. The light emitting unit 106 includes LEDs of three colors of R, G, and B.

  The light receiving unit 132 receives visible light, performs photoelectric conversion, and outputs an arrangement of received light intensity R, G, and B. The light receiving unit 132 includes a photodiode having photosensitivity corresponding to R, G, and B. The reception coordinate system conversion unit 134 reversely converts the arrangement of the received light intensities R, G, and B in accordance with the chromaticity coordinate values x and y according to the equation (1). The chromaticity coordinate demodulator 136 converts the sequence of chromaticity coordinate values x and y into a sequence of signal points, and converts the sequence of signal points into each bit string of received data based on the predetermined rule.

  FIG. 4 is a diagram illustrating a signal flow in the transmission device 100 according to the first embodiment. The chromaticity coordinate modulation unit 102 encodes the bit string [00] of the transmission data into the transmission frame A based on the predetermined rule. The transmission frame A is a sequence of signal points [C1 C2 C3 C4]. Here, the arrangement of signal points is the temporal order of transmission. Further, the chromaticity coordinate modulation unit 102 converts the signal point sequence [C1 C2 C3 C4] into a chromaticity coordinate value sequence [x1 x2 x3 x4], [y1 y2 y3 y4].

  The transmission coordinate system conversion unit 104 converts the chromaticity coordinate values [x1 x2 x3 x4] and [y1 y2 y3 y4] into the emission intensity sequences [R1 R2 R3 R4] and [G1 G2 G3 G4] according to the equation (1). , [B1 B2 B3 B4]. The light emission intensity sequences [R1 R2 R3 R4], [G1 G2 G3 G4], and [B1 B2 B3 B4] are temporal changes in numerical values R, G, and B representing the light emission intensities of the three colors of LEDs of the light emitting unit 106. It is. In response to temporal changes in the light emission intensities R, G, and B, each LED of the light emitting unit 106 undergoes light intensity modulation.

  The light emitting unit 106 converts the light emission intensity sequence [R1 R2 R3 R4], [G1 G2 G3 G4], and [B1 B2 B3 B4] from a digital signal to an analog signal, and R, G, B via an LED driver. The LEDs emit light as visible light. Visible light emitted by the R, G, and B LEDs is mixed to become visible light having a color corresponding to the chromaticity coordinates of the signal point.

  FIG. 5 is a diagram showing a signal flow in receiving apparatus 130 according to the first embodiment. The light receiving unit 132 receives visible light from the transmission device 100, performs photoelectric conversion, amplifies, converts the analog signal into a digital signal, and arranges the received light intensity [R1 R2 R3 R4], [G1 G2 G3 G4]. , [B1 B2 B3 B4] are output. At this time, the section of the transmission frame is recognized based on a synchronization signal sent in advance from the transmission apparatus 100. As the synchronization signal, a preamble signal used for channel matrix estimation can be used. The preamble signal includes a synchronization code component having a strong autocorrelation and used for timing synchronization.

  The reception coordinate system conversion unit 134 inversely converts the received light intensity arrangements [R1 R2 R3 R4], [G1 G2 G3 G4], and [B1 B2 B3 B4] according to the equation (1) to obtain the arrangement of chromaticity coordinate values [ x1 x2 x3 x4], [y1 y2 y3 y4].

  The chromaticity coordinate demodulator 136 converts the chromaticity coordinate value sequence [x1 x2 x3 x4] and [y1 y2 y3 y4] into a signal point sequence [C1 C2 C3 C4]. At this time, the chromaticity coordinate demodulation unit 136 performs conversion using the inter-code distance or the inter-coordinate distance.

  When converting using the inter-code distance, the chromaticity coordinate demodulator 136 first converts the chromaticity coordinate values [x1 x2 x3 x4] and [y1 y2 y3 y4] into the chromaticity coordinate values (x1, y1). ), (X2, y2), (x3, y3), and (x4, y4) are converted into a sequence [C1 C2 C3 C4] of signal points closest to each other.

  Next, the chromaticity coordinate demodulator 136 compares the sequence of converted signal points [C1 C2 C3 C4] with the sequence of signal points of each of the frames A, B, C, and D to determine whether the sequences match. Alternatively, the frame with the largest number of matching signal points that is closest in sequence is selected. In this case, the chromaticity coordinate demodulation unit 136 matches the sequence of chromaticity coordinate values [x1 x2 x3 x4] and [y1 y2 y3 y4] with the sequence of signal points of frame A, so The point arrangement [C1 C2 C3 C4] is determined.

Then, the chromaticity coordinate demodulation unit 136 decodes the signal point sequence [C1 C2 C3 C4] of the frame A into the bit string [00] of the received data based on the predetermined rule.
Note that the chromaticity coordinate demodulation unit 136 does not determine the signal point sequence [C1 C2 C3 C4] when the frame A that matches or is closest to the sequence is selected. The sequence of points [C1 C2 C3 C4] may be decoded as it is into the bit string [00] of the received data.

  Further, when converting using the inter-coordinate distance, the chromaticity coordinate demodulator 136 firstly converts the chromaticity coordinate values (x1, x2 x3 x4) and [y1 y2 y3 y4] of the chromaticity coordinate values (x1, x2 x3 x4). y1), (x2, y2), (x3, y3), (x4, y4) and each chromaticity coordinate value of the arrangement of signal points of each frame A, B, C, D, for example, each chromaticity coordinate of frame A For the values (x1, y1), (x2, y2), (x3, y3), (x4, y4), the sum of the distances between the corresponding chromaticity coordinate values is calculated.

Next, the chromaticity coordinate demodulating unit 136 uses the sequence of chromaticity coordinate values [x1 x2 x3 x4] and [y1 y2 y3 y4] as a frame in which the sum of the distances between the corresponding chromaticity coordinate values is smallest. In this case, the signal is converted into a sequence of signal points in frame A [C1 C2 C3 C4].
Then, the chromaticity coordinate demodulation unit 136 decodes the signal point sequence [C1 C2 C3 C4] of the frame A into the bit string [00] of the received data based on the predetermined rule.

  In the visible light communication system according to the first embodiment, data communication is performed using a temporal transmission order of four signal points of 4CSK as a predetermined rule. In 8CSK in which 8 signal points are arranged, data communication is performed using the transmission order of 4 signal points out of 8 signal points, and 16 signal points on chromaticity coordinates. In the 16CSK with the arrangement, data communication can be performed using the transmission order of four signal points among the 16 signal points. As a result, the transmission rate can be improved by increasing the number of transmission orders of signal points corresponding to the bit string.

The method of selecting the four signal points in the case of 8CSK and 16CSK can also be biased to a specific color or distributed so as not to be biased to a specific color.
Further, the number of signal points is not limited to four. In 16 CSK, 8 signal points out of 16 signal points can be used.
The predetermined number of bits is not limited to 2 bits.

  As described above, the visible light communication system according to the first embodiment includes the transmission device and the reception device, and the transmission device colors the light emitting unit and each bit string of the transmission data based on a predetermined rule. A chromaticity coordinate modulation unit that converts a sequence of signal points on a chromaticity coordinate and converts a sequence of signal points to a sequence of chromaticity coordinate values, and a transmission coordinate system that converts a sequence of chromaticity coordinate values to a sequence of luminescence intensity of a light emitting unit A receiving unit, a receiving coordinate system converting unit that converts a sequence of received light intensities of the light receiving unit into a sequence of chromaticity coordinate values, and a sequence of chromaticity coordinate values on a chromaticity coordinate. A chromaticity coordinate demodulating unit that converts the arrangement of the signal points and converts the arrangement of the signal points into each bit string of the received data based on a predetermined rule. With this configuration, it is possible to spread a signal in the chromaticity coordinate space, lower the correlation of the color change order between frames, increase the spreading gain, and perform transmission with few errors.

Further, in the visible light communication system according to the first embodiment, the arrangement of the emission intensity and the arrangement of the received light intensity are in the temporal order of transmission and reception.
Further, in the visible light communication system according to the first embodiment, the chromaticity coordinate demodulating unit selects the signal point closest to each of the chromaticity coordinate values by selecting the sequence of chromaticity coordinate values, and A sequence of signal points is compared with a sequence of signal points determined in advance according to a predetermined rule, and the sequence of signal points is a sequence of predetermined signal points that match or are closest to each other. It converts to a corresponding bit string.

  Further, in the visible light communication system according to the first embodiment, the chromaticity coordinate demodulating unit is configured so that each chromaticity coordinate value in the sequence of chromaticity coordinate values and each chromaticity coordinate in the sequence of signal points predetermined by a predetermined rule. The distance between the corresponding chromaticity coordinate values is calculated with respect to the value, the sequence of chromaticity coordinate values is converted into a sequence of predetermined signal points with the smallest sum of distances, and the predetermined sequence of signal points is converted. This is converted into a bit string based on a predetermined rule.

  With this configuration, even when the chromaticity coordinates of signal points in communication data are shifted due to noise during communication, the data can be correctly demodulated.

Embodiment 2 of the Invention
The visible light communication system according to Embodiment 1 transmits data by converting a bit string into a predetermined order of signal points in the time direction. On the other hand, the visible light communication system according to the second embodiment transmits the visible light of the color corresponding to the signal point from the light emitting unit in a two-dimensionally predetermined arrangement at the same time or almost simultaneously.

That is, in the visible light communication system according to the second embodiment, the light emitting unit includes three sets of LEDs of R, G, and B as one set, two sets in the direction intersecting the transmission direction, and two sets in the horizontal direction. Each LED set emits visible light of a color corresponding to a signal point.
The system configuration of the visible light communication system according to the second embodiment and the arrangement of four signal points of 4CSK on the chromaticity coordinate plane are the same as those of the visible light communication system according to the first embodiment. Description and illustration are omitted.

  FIG. 6 is a diagram showing a relationship between a bit string of input data of the visible light communication system according to the second embodiment and a two-dimensional arrangement in a plane intersecting the visible light transmission / reception direction corresponding to each signal point. . The chromaticity coordinate modulation unit converts the bit string [00] of the transmission data into a two-dimensional frame A based on a two-dimensional arrangement that is a predetermined rule. Also in the visible light communication system according to the second embodiment, the arrangement of the signal points C1, C2, C3, and C4 in the frames A, B, C, and D is the same among the frames A, B, C, and D. There is nothing.

  The light receiving unit receives visible light using a two-dimensional image sensor, and the chromaticity coordinate demodulation unit performs data demodulation according to the type of two-dimensional signal point arrangement. Specifically, a two-dimensional transmission frame displayed by a plurality of sets of LEDs of three colors is image-recognized, and each time each frame is received, the chromaticity coordinate demodulator receives the inter-code distance. A bit string corresponding to a frame in which the two-dimensional arrangement of signal points coincides or the closest to the two-dimensional arrangement is set as demodulated data. Further, the chromaticity coordinate demodulator uses the inter-coordinate distance to determine the inter-signal distance between each coordinate value of the received signal point in the two-dimensional frame and each coordinate value of each of the two-dimensional transmission frames A to D. And a bit string corresponding to a transmission frame having the smallest sum of distances between signals is set as demodulated data.

  In the visible light communication system according to the second embodiment, the two-dimensional arrangement of the three color LED sets is set to two sets × 2 sets using four signal points of 4CSK. Using signal points, it may be 2 sets x 2 sets, 3 sets x 3 sets, 4 sets x 4 sets, or 3 sets x 2 sets, 4 sets x 2 sets. Alternatively, they may be arranged side by side on a straight line.

  In the visible light communication system according to the second embodiment, communication is performed by combining the temporal order of the signal points according to the first embodiment and the spatial order of the signal points according to the second embodiment. Also good.

  As described above, in the visible light communication system according to the second embodiment, the two-dimensional visible light in the direction in which the light emission intensity sequence and the light reception intensity sequence intersect the transmission / reception direction in the light emission unit and the light reception unit. Arrangement. With this configuration, communication can be performed by displaying CSK signals on various display devices and illuminations.

DESCRIPTION OF SYMBOLS 10 Visible light communication system 100 Transmission apparatus 102 Chromaticity coordinate modulation part 104 Transmission coordinate system conversion part 106 Light emission part 130 Reception apparatus 132 Light reception part 134 Reception coordinate system conversion part 136 Chromaticity coordinate demodulation part

Claims (6)

A transmission device and a reception device;
The transmitter is
A light emitting unit;
A chromaticity coordinate modulation unit that converts a sequence of signal points on chromaticity coordinates based on a predetermined rule for each bit string of transmission data, and converts a sequence of the signal points in a sequence of chromaticity coordinate values;
A transmission coordinate system conversion unit that converts the sequence of the chromaticity coordinate values into a sequence of emission intensity of the light emitting unit;
The receiving device is:
A light receiver;
A reception coordinate system conversion unit that converts a sequence of received light intensities of the light receiving unit into a sequence of chromaticity coordinate values;
A visible light communication system comprising: a chromaticity coordinate demodulator that converts the sequence of chromaticity coordinate values into a sequence of signal points and converts the sequence of signal points into each bit string of received data based on the predetermined rule.   The visible light communication system according to claim 1, wherein the arrangement of the light emission intensity and the arrangement of the received light intensity is a temporal order of transmission and reception.   The visible light communication system according to claim 1 or 2, wherein the arrangement of the light emission intensity and the arrangement of the light reception intensity is a two-dimensional arrangement of visible light in a direction intersecting a transmission / reception direction in the light emission unit and the light reception unit. .   The chromaticity coordinate demodulating unit selects a signal point having the closest distance to each of the chromaticity coordinate values, converts the sequence of the signal points, and converts the sequence of the signal points and the sequence of the chromaticity coordinate values. A sequence of signal points is compared with a predetermined sequence of signal points according to a predetermined rule, and the sequence of the signal points is converted into a bit string corresponding to a sequence of the predetermined signal points that are aligned or closest to each other. Item 4. The visible light communication system according to any one of Items 1 to 3.   The chromaticity coordinate demodulating unit is a distance between chromaticity coordinate values corresponding to each chromaticity coordinate value of the sequence of chromaticity coordinate values and each chromaticity coordinate value of the sequence of signal points predetermined by the predetermined rule. The sequence of the chromaticity coordinate values is converted into a sequence of the predetermined signal points with the smallest sum of the distances, and the sequence of the predetermined signal points is converted into a bit string based on the predetermined rule. The visible light communication system according to any one of claims 1 to 3, wherein the visible light communication system is converted into a visible light. A visible light communication method in a visible light communication system comprising a transmitter and a receiver,
The transmitting device is
Converting a sequence of signal points on chromaticity coordinates based on a predetermined rule for each bit string of transmission data; and
Converting the sequence of the signal points into a sequence of chromaticity coordinate values;
Converting the sequence of chromaticity coordinate values into a sequence of emission intensities;
Emitting visible light according to the arrangement of the emission intensities;
The receiving device is
Generating an array of received light intensity from the received visible light;
Converting the sequence of the received light intensity into a sequence of chromaticity coordinate values;
Converting the sequence of chromaticity coordinate values into a sequence of signal points;
Converting the sequence of the signal points into bit strings of received data based on the predetermined rule.

Images