JP2010032267A - Light receiver and optical communication system - Google Patents

Abstract

Disclosed is a simple apparatus configuration that can measure a distance without reducing transmission efficiency.
An LED array of an optical transmitter is imaged by a high-speed camera of an optical receiver, an image captured by the high-speed camera is acquired (100), and received data is demodulated based on the acquired image (102). ). When the demodulated received data is synchronization preamble data (104), the stored synchronization preamble data is read (108), the demodulated synchronization preamble data and the read reference are read The number of error data is measured by comparing with the synchronization preamble data, and the error bit rate is calculated (110). Then, the distance determination table is read (112), the distance corresponding to the calculated error bit rate is determined from the read distance determination table, and the distance to the LED array of the optical transmitter is measured (114).
[Selection] Figure 8

Description

  The present invention relates to an optical receiver and an optical communication system, and more particularly to an optical receiver and an optical communication system that receive data transmitted by blinking a plurality of light emitting elements and measure a distance from the optical transmitter.

Conventionally, a position detection system is known as a system that performs distance measurement by optical communication (for example, Patent Document 1). In this position detection system, the transponder receives the identification information transmitted from the base station and the distance measurement signal by means of optical communication, and the received identification information and the transponder-specific identification information match the base information. Means for transmitting to the station by radio waves. In addition, three or more base stations respectively receive transmission identification information and ranging signals from the transponder, measure the distance to the transponder based on the received information, transponder identification information and distance Means for transmitting information to the management terminal. Then, the management terminal detects at least three base stations that are close to the transponder based on the transponder identification information and distance information received from the base station, and based on the detected base station position information, the transponder Is identified by triangulation. As described above, the transponder receives the identification information and the distance measurement signal transmitted from the base station by optical communication, and transmits the information to the base station by radio waves, thereby realizing distance measurement.
JP2005-241301

  However, in the technique described in Patent Document 1, in order to perform ranging, it is necessary to perform signal transmission from the receiving apparatus to the transmitting apparatus, and thus the receiving apparatus requires a device for signal transmission. There is a problem.

  In addition, since a ranging signal is transmitted for ranging, there is a problem in that information data cannot be transmitted while the ranging signal is transmitted, and transmission efficiency is reduced.

  The present invention has been made to solve the above-described problems, and provides an optical receiver and an optical communication system capable of measuring a distance with a simple apparatus configuration without reducing transmission efficiency. With the goal.

  In order to achieve the above object, an optical receiving apparatus according to the present invention includes: an imaging unit that images the plurality of light emitting elements of a light source in which a plurality of light emitting elements that are turned on according to transmission data are arranged; and the imaging unit Calculated by the demodulation means for demodulating the transmission data, the error calculation means for calculating the error rate or the number of errors of the transmission data demodulated by the demodulation means, and the error calculation means. Measuring means for measuring the distance to the light source based on the error rate or the number of errors.

  According to the optical receiver of the present invention, the imaging unit captures the plurality of light emitting elements of the light source in which the plurality of light emitting elements that are turned on according to the transmission data are arranged, and the demodulation unit captures the images. The transmission data is demodulated based on the received image.

  Then, the error calculation means calculates the error rate or the number of errors of the transmission data demodulated by the demodulation means, and the measurement means calculates the distance to the light source based on the error rate or the error number calculated by the error calculation means. measure.

  As described above, by measuring the distance to the light source based on the error rate or the number of errors of the demodulated transmission data, the distance can be measured with a simple apparatus configuration without reducing the transmission efficiency. .

  The error calculation means according to the present invention can calculate the error rate or the number of errors by comparing the transmission data demodulated by the demodulation means with the transmission data stored in the storage means storing the transmission data. As a result, it is possible to calculate the error rate or the number of errors by comparing the transmission data known on the receiving side with the demodulated transmission data.

  The optical receiver according to the present invention further includes error correction means for performing error correction on the transmission data demodulated by the demodulation means, and the error calculation means includes the transmission data demodulated by the demodulation means and the error correction means. The error rate or the number of errors can be calculated by comparing with transmission data subjected to error correction. Thus, the error rate or the number of errors can be calculated by comparing the transmission data subjected to error correction with the transmission data not subjected to error correction.

  The measuring unit according to the present invention can measure the distance to the light source based on the relationship between the distance obtained in advance and the error rate or the number of errors, and the error rate or the number of errors calculated by the error calculating unit.

  The above light source has a light emitting element group consisting of at least one light emitting element to be lit for each of the spatial frequency stages divided into a plurality of stages, and corresponds to the spatial frequency stage of the lighting pattern according to the transmission data The light emitting elements of the light emitting element group to be turned on according to the transmission data, the error calculating means calculates the error rate or the number of errors of the transmission data for each stage, and the measuring means is a stage calculated by the error calculating means The distance to the light source can be measured based on the error rate or the number of errors for each. This makes it possible to accurately measure the distance to the light source in consideration of the error rate or the number of errors that fluctuate according to the stage of the spatial frequency.

  An optical communication system according to the present invention includes an optical transmission device that turns on a plurality of light emitting elements of a light source in which a plurality of light emitting elements are arranged in accordance with transmission data, and the above-described optical reception device.

  According to the optical communication system of the present invention, the plurality of light emitting elements of the light source in which the plurality of light emitting elements are arranged are turned on according to the transmission data by the optical transmitter.

  In the optical receiver, the imaging unit images the plurality of light emitting elements of the light source, and the demodulation unit demodulates the transmission data based on the captured image. Then, the error calculation means calculates the error rate or the number of errors of the transmission data demodulated by the demodulation means, and the measurement means calculates the distance to the light source based on the error rate or the error number calculated by the error calculation means. measure.

  As described above, by measuring the distance to the light source based on the error rate or the number of errors of the demodulated transmission data, the distance can be measured with a simple apparatus configuration without reducing the transmission efficiency. .

  As described above, according to the optical receiver and the optical communication system of the present invention, by measuring the distance to the light source based on the error rate or the number of errors of the demodulated transmission data, the simple apparatus configuration can be obtained. The effect is obtained that the distance can be measured without reducing the transmission efficiency.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the present embodiment, a case where the present invention is applied to an optical communication system that transmits and receives data by optical communication between an in-vehicle camera mounted on a vehicle and an LED traffic light will be described as an example.

  As shown in FIG. 1, the optical communication system 10 according to the first embodiment is configured using, for example, an LED traffic light, and an optical transmission device 12 that transmits data by blinking LEDs of the LED traffic light at high speed. And an optical receiver 14 that is configured using an in-vehicle camera mounted on a vehicle and that receives data by imaging an LED of the optical transmitter 12 by the in-vehicle camera.

  As shown in FIG. 2, the optical transmission device 12 is provided in an LED traffic light, and an LED array 16 as a light source in which a plurality of LEDs are two-dimensionally arranged (for example, 16 × 16), and a transmission data generation device 18. The interface 20 for inputting transmission data from the signal generator, the signal generation unit 22 for generating a drive signal for driving each LED of the LED array 16 based on the transmission data input by the interface 20, and the signal generation unit 22 And a drive circuit 24 for driving each LED of the LED array 16 on the basis of the drive signal generated by. Each LED is switched (on / off) at high speed in order to transmit a large amount of data.

  The plurality of LEDs of the LED array 16 of the optical transmitter 12 are arranged in an arbitrary shape. Also, the data to be transmitted is modulated to the change in brightness of each LED. The luminance of the LED changes depending on whether it is turned on or off. In this embodiment, the luminance is changed at high speed, so that the change in luminance cannot be clearly seen by human eyes. Moreover, it is not necessary to use all the arranged LEDs, and the luminance of only some of the LEDs may be changed.

  Here, the luminance of the LED represents the intensity of light, and information is transmitted using a change in luminance of each of the plurality of LEDs. The change in the luminance of the LED is realized by a change in the lighting time of the LED.

  The signal generation unit 22 of the optical transmission device 12 is configured by a computer, and is connected to a CPU, a ROM that stores programs, a RAM that stores data, an HDD, an I / O port for inputting and outputting data, and the like. It is configured to include a bus.

The signal generation unit 22 calculates the luminance coefficient x _{u, v} based on the transmission data generated by the transmission data generation device 18. Here, the subscripts u and v represent LEDs arranged at the position of u rows and v columns. In accordance with the luminance coefficient x _{u, v} , the luminance of the LED arranged at the position of u row and v column is driven, and light transmission is performed.

The signal generator 22 calculates a luminance value for driving the LED based on the input transmission data. Here, this operation is called encoding. Further, considering the case where the transmission data generated by the transmission data generation device 18 is simultaneously processed by 64 bits, the transmission data is represented as dm _{, n} . However, m, n = 1, 2,...

  In encoding, transmission data is arranged in an 8 × 8 matrix as shown in the following equation (1).

  However, D11, D12, D21, and D22 are 4 × 4 square matrices, respectively, and dm, n = {− 1, 1}.

  The signal generation unit 22 performs encoding using a two-dimensional high-speed Haar wavelet transform (2D FHWT). If the signal generation unit 22 is described with function blocks divided for each function realization means determined based on hardware and software, as shown in FIG. 3, each transmission data is transmitted according to the spatial frequency component of the data. Mapping unit 30 assigned to LEDs, wavelet inverse transform unit 32 that performs two-dimensional high-speed wave red inverse transform (2D IFHWT) on transmission data assigned to each LED, and data subjected to two-dimensional high-speed wave red inverse transform And a normalizing bias adding unit 34 for adding a bias, and a driving signal generating unit 36 for generating a driving signal based on the output data of the normalizing bias adding unit 34.

  The mapping unit 30 divides the transmission data into data having lighting patterns of three stages of spatial frequency components and allocates the data to a plurality of LEDs. For example, data having a lighting pattern with a low spatial frequency component is assigned to the LED group corresponding to the portion D11 in the equation (1), and the total data rate of this portion is, for example, 16 Rb. Further, the LED group corresponding to the portions of D12 and D21 is assigned data having a lighting pattern of a spatial frequency component that is not so high, and the total data rate of this portion is, for example, 32 Rb. Further, data having a lighting pattern with a high spatial frequency component is assigned to the LED group corresponding to the portion D22, and the total data rate of this portion is, for example, 16 Rb.

The wavelet inverse transform unit 32 performs scale 1 two-dimensional high-speed Haar wavelet inverse transform on the transmission data in the form of the above equation (1). After the inverse transformation, an 8 × 8 matrix is obtained as with the transmission data, and each element x ′ _{u, v} of the output matrix is expressed by the following equation (2).

Here, H ⁸ _{m, n} represents an element of m rows and n columns of an 8 × 8 matrix H ⁸ as shown in the following equation (3).

The range of values that x ′ _{u, v} can take is −2 ≦ x ′ _{u, v} ≦ 2. In order to make the value of x ′ _{u, v} take a range from 0 to 1, the normalization bias adding unit 34 normalizes after applying a bias as shown in the following equation (4).

As a result of the processing described above, there are five possible values of x _{u, v} {0, 1/4, 1/2, 3/4, 1}.

  The drive circuit 24 blinks the LED array 16 based on the drive signal generated by the signal generator 22 and transmits data to be transmitted.

  As shown in FIG. 4, the optical receiver 14 is composed of an in-vehicle optical communication camera (two-dimensional image sensor), and the high-speed camera 40 that continuously captures the LED array 16 of the optical transmitter 12 at high speed. And an image processing unit 42 that performs various image processing on the image data captured by the high-speed camera 40 to generate an image that is digital data, and that performs data demodulation based on the generated image. It has. The optical receiving device 14 outputs the output data of the image processing unit 42 to the output device 60.

  The high-speed camera 40 includes an optical system 44 such as a lens, an image sensor 46 composed of a CCD image sensor or a CMOS image sensor, and signal processing for generating captured image data based on an output signal from the image sensor 46. Circuit 48.

  The high-speed camera 40 captures the blinking of the LED array 16 of the optical transmission device 12, and the brightness of each LED of the LED array 16 is represented by a change in the lighting time of the LED. The high-speed camera 40 detects the luminance of the LED by detecting the change in lighting during one symbol period.

  The image processing unit 42 is configured by a computer, and connects a CPU, a ROM storing programs, a RAM storing data, an HDD, an I / O port for inputting / outputting data to / from the high-speed camera 40, and the like. It is configured to include a bus.

The image processing unit 42 performs appropriate processing to obtain a relative position regarding the LED (information regarding u rows and v columns) and information R _{u, v} regarding the luminance value. Hereinafter, the reproduction of transmission data from this R _{u, v} is referred to as demodulation.

  When the image processing unit 42 is described by function blocks divided for each function realization means determined based on hardware and software, the position of each LED is determined from the image captured by the high-speed camera 40 as shown in FIG. A luminance value acquisition unit 62 that detects and acquires a luminance value of each LED, a reverse bias unit 64 that applies a reverse bias to the acquired luminance value of each LED, and a luminance value of each LED to which the reverse bias is applied Then, the wavelet transform unit 66 that performs the two-dimensional high-speed Haar wavelet transform (2D FHWT) and the luminance value of each LED that has performed the two-dimensional high-speed Haar wavelet transform determine whether the value is greater than 0, Based on the threshold value determination unit 68 that converts the luminance of the LED into output data represented by +1 and −1, and the output data represented by ± 1 And a data generation unit 70 for generating a reception data sequence.

  The luminance value acquisition unit 62 detects the position of the LED array 16 from the captured image, finds the range where one LED is shining, detects the position of the LED, and detects the luminance value from the found range. To do.

If R _{u, v} obtained from the captured image is an 8 × 8 square matrix, the reverse bias unit 64 reverses each element x ′ _{u, v} of the matrix as shown in the following equation (5). Add a bias.

However, b is a bias value, and is a value calculated from the average value of R _{u, v} as shown in the following equation (6). In this embodiment, since it is necessary to average over time in order to obtain an appropriate bias value, the calculation is performed in consideration of the time parameter i.

  The wavelet transform unit 66 performs two-dimensional high-speed Haar wave red transform (2D FHWT) on the matrix to which the reverse bias is applied, as shown in the following equation (7).

The threshold determination unit 68 performs threshold determination and obtains output data. If the value of _d'm, hat _n is positive above _(7), d _m, estimates _d'm hat of _n, and 1 hat _{n, d'm,} hat _n is negative if the value, d _m, an estimate of hat _n d _m, a hat of _n as -1, into an output data.

  In addition, the image processing unit 42 includes a data storage unit 72 that stores predetermined transmission data (for example, synchronization preamble data), reception data generated by the data generation unit 70, and transmission stored in the data storage unit 72. An error rate calculation unit 74 that compares the data and calculates the bit error rate as the quality of the received data, and distance determination table data that represents the relationship between the bit error rate and the distance to the LED array 16 of the optical transmission device 12 The stored table storage unit 76 and a distance measurement unit 78 that measures the distance to the LED array 16 of the optical transmission device 12 based on the calculated bit error rate and distance determination table data are provided.

  Here, the principle of the present embodiment will be described. In order to simplify the description, consider a case where transmission is performed by the optical transmitter 12 using the following two lighting patterns. The two lighting patterns are a lighting pattern with a high spatial frequency component as shown in FIG. 6 (A) and a lighting pattern with a low spatial frequency component as shown in FIG. 6 (B). These lighting patterns are generated by controlling the luminance value of each LED of the LED array 16 of the optical transmitter 12. That is, the lighting pattern depends on the transmission data.

  When the lighting pattern having a high spatial frequency component is transmitted, the high-speed camera 40 of the optical receiver 14 captures an image having a high spatial frequency component as shown in FIG. When a low lighting pattern is transmitted, the high-speed camera 40 of the optical receiver 14 captures an image with a low spatial frequency as shown in FIG.

  As described above, when the individual LEDs of the LED array 16 are individually modulated, the spatial frequency of the image to be captured may be increased or decreased depending on the spatial frequency component of the lighting pattern.

  Next, the case where the transmission data by each lighting pattern is received by changing the distance from the LED array 16 of the light transmission device 12 will be described.

  When the distance from the LED array 16 of the optical transmission device 12 is short, the individual LEDs of the LED array 16 of the optical transmission device 12 can be clearly discriminated by the image captured by the high-speed camera 40. For this reason, as shown to FIG. 6 (A), the lighting pattern with a high spatial frequency can be caught firmly.

  Further, when the LED array 16 of the optical transmission device 12 is imaged by the high-speed camera 40 from a position 15 m away, as shown in FIG. Each LED can be clearly distinguished. Thus, a lighting pattern having a high spatial frequency can be accurately received. Note that the lighting pattern of the LED array 16 in FIG. 7A is a pattern in which all LEDs are lit.

  On the other hand, when the distance from the LED array 16 of the optical transmission device 12 is long, it is difficult to clearly distinguish the individual LEDs of the LED array 16 of the optical transmission device 12 from the image captured by the high-speed camera 40. It is. When the distance from the LED array 16 is far, even if the LED array is arranged with a certain distance, the high-speed camera 40 captures a plurality of LEDs as only one point light source. This is because they cannot.

  In other words, when the optical receiver 14 receives data at a position far from the LED array 16, a plurality of point light sources are captured and overlapped in the captured image of the high-speed camera 40, so that the high-frequency component of the spatial frequency is It will be lost.

  When the LED array 16 of the optical transmission device 12 is imaged by the high-speed camera 40 from a position 50 m away, as shown in FIG. Therefore, the high frequency component of the spatial frequency is lost.

  As described above, it can be seen that there is a relationship between the communication distance and the spatial frequency of the captured image in which the higher spatial frequency component decreases in the captured image as the communication distance increases. This means that the communication path can be modeled with a low-pass filter corresponding to the communication distance. That is, the communication distance can be estimated by analyzing the spatial frequency component of the image captured by the high-speed camera 40 of the optical receiver 14.

  Also, between the quality of the received data demodulated by the optical receiver 14 and the spatial frequency component of the image captured by the high-speed camera 40, the lower the received data quality, the lower the spatial frequency component of the captured image. Thus, the higher the quality of the received data, the higher the spatial frequency component of the captured image.

  Therefore, in the present embodiment, the image processing unit 42 measures the distance to the LED array 16 of the optical transmission device 12 based on the reliability of the demodulated reception data. For example, when the distance to the LED array 16 of the light transmission device 12 is long, the quality of the reception data is low, and when the distance to the LED array 16 of the light transmission device 12 is short, the quality of the reception data is high. . Thus, the distance to the LED array 16 of the optical transmitter 12 is measured by obtaining the quality of the received data.

  The data storage unit 72 stores synchronization preamble data as transmission data serving as a reference for comparison.

  The error rate calculation unit 74 compares the synchronization preamble data of the demodulated received data with the stored synchronization preamble data to obtain the number of erroneous data, and calculates the number of error data as the total number of received data. By dividing, a bit error rate as reception data quality is calculated.

  The table storage unit 76 stores a distance determination table that represents the relationship between the bit error rate obtained in advance by experiments or the like and the distance to the LED array 16 of the optical transmitter 12.

  Next, the operation of the optical communication system 10 according to the first embodiment will be described. First, transmission data is generated by the transmission data generation device 18 and input to the optical transmission device 12. Then, in the optical transmission device 12, the LED array 16 is blinked in a blinking pattern corresponding to the input transmission data, and data is transmitted.

  In the optical receiver 14, the LED array 16 of the optical transmitter 12 is continuously imaged by the high-speed camera 40. Then, the image processing unit 42 executes a communication distance measurement processing routine shown in FIG.

  First, in step 100, an image captured by the high-speed camera 40 is acquired, and in step 102, received data is demodulated based on the image acquired in step 100.

  In step 104, it is determined whether or not the received data demodulated in step 102 is synchronization preamble data. If the received data is not synchronization preamble data, it is decoded in step 106 in step 106. The received data is output to the output device 60 as a received data series, and the process returns to step 100.

  On the other hand, if the demodulated reception data is the synchronization preamble data in step 104, the reference synchronization preamble data stored in the data storage unit 72 is read in step 108.

  In step 110, the synchronization pre-angle data demodulated in step 102 is compared with the reference synchronization preamble data read in step 108, and the number of error data is measured. The error bit rate is calculated based on the total number of received data.

  In the next step 112, the distance determination table is read from the table storage unit 76. In step 114, the distance corresponding to the error bit rate calculated in step 110 is determined from the distance determination table read in step 112. The distance to the LED array 16 of the optical transmitter 12 is measured.

  In step 116, the distance measured in step 114 is output to the output device 60, and the process returns to step 100.

  Next, experimental results regarding the distance measurement method according to the present embodiment will be described.

  The experiment was performed using a prototype optical transmitter. This prototype optical transmission device is composed of an FPGA that realizes a transmission data generation device and a signal generation unit, a drive circuit (Driver Circuit), and an LED array.

  In the optical transmitter, the FPGA and the drive circuit are connected by an I / O port, and the drive circuit is connected to the LED array. The individual LEDs are the same as those used in actual LED traffic lights, the number of LEDs is smaller than that of actual LED traffic lights, and the LED spacing (2 cm) is the same as the LED layout of actual LED traffic lights. An array was used.

  In the optical transmission apparatus, transmission data is encoded every 64 bits. The 64-bit data was divided into three groups for each spatial frequency component of the lighting pattern corresponding to the data, and the scale 1 two-dimensional high-speed Haar wavelet inverse transform was performed to assign the data on the spatial frequency axis. Then, after normalization, a bias was added to modulate the brightness of the LED to a non-negative value.

  The optical receiver used in the experiment was composed of an optical communication camera and a PC as an image processing apparatus. In the optical receiver, first, an image of the LED array of the optical transmitter was taken with an optical communication camera. Then, image processing was performed on the photographed image to obtain a luminance value corresponding to each LED, and a reverse bias was applied to the luminance value. Then, a two-dimensional high-speed Haar wavelet transform with a scale of 1 was performed on the obtained numerical value, and then a threshold value was determined to obtain a received data series.

  The experimental specifications are shown below. The experiment was performed indoors, the LED lighting cycle was 1/2000 s, and the data rate was 128 kbps. In addition, the photographing speed of the optical communication camera was set to 4000 fps (twice the LED lighting frequency), the number of pixels of the optical communication camera was set to 160 × 128 pixels, and the focus of the lens was set to infinity. The focal length of the lens was 35 mm, the aperture of the lens was 3.5, and the communication distance was 10 to 50 m. The experiment was conducted with all the fluorescent lamps in the room turned on.

  Next, experimental results will be described. When the communication distance between the LED array of the optical transmission device and the optical reception device is 10 m, 30 m, and 50 m, the received images shown in FIGS. 9A to 9C are captured in the optical reception device. It was. The images in FIG. 9 are all taken when all 64 LEDs of the optical transmission device are lit at the maximum brightness.

  When the communication distance is 10 m, the number of pixels indicated by the 64 LED areas in the received image is 46 × 46 pixels, and when the communication distance is 50 m, the 64 LED areas in the received image indicate. The number of pixels was 11 × 11 pixels. When the communication distance is 30 m, the number of pixels indicated by the 64 LED regions in the received image is 15 × 15 pixels, and the size is about 2 × 2 pixels per LED.

  In the experiment, the focus of the camera lens was set to infinity and the zoom was fixed. For this reason, when the communication distance is increased, the size of the LED in the image is reduced.

  In the above experiment, data having a low spatial frequency component lighting pattern assigned to the LED group corresponding to the portion D11 in the above equation (1) by changing the communication distance, and the LED group corresponding to the portions D12 and D21 When the bit error rate is calculated for each of the data having the lighting pattern of the medium spatial frequency component assigned to, and the data having the lighting pattern of the high spatial frequency component assigned to the LED group corresponding to the portion D22, FIG. As shown in FIG. 10, the relationship between the communication distance and the bit error rate was obtained. When the communication distance was shorter than 30 m, no error occurred in the data having the lighting pattern of any spatial frequency component. That is, it was found that all data can be received without error up to a position where the communication distance is 30 m, and it is possible to estimate a communication distance farther than 30 m based on the bit error rate.

  In this embodiment, in order to calculate the bit error rate based on the received data demodulated based on the entire received image, the values for the data having the lighting pattern of each spatial frequency component are averaged in the relationship of FIG. The communication distance may be measured from the bit error rate using the relationship between the bit error rate and the communication distance obtained by doing so.

  As described above, according to the optical communication system according to the first embodiment, in the optical receiver, the distance to the LED array of the optical transmitter is measured based on the bit error rate of the demodulated transmission data. As a result, the distance can be measured with a simple apparatus configuration without reducing the transmission efficiency.

  In addition, the transmission data transmitted from the optical transmission device can be received by the optical reception device, and the distance to the LED array of the optical transmission device can be measured based on the received transmission data.

  In the above embodiment, the case where an LED array is used has been described as an example. However, the present invention is not limited to this, and a laser diode (LD) may be used as a light emitting element.

  Further, as an example of the case where the bit error rate is calculated as the quality of the received data and the distance to the LED array of the optical transmission device is measured based on the bit error rate, the optical data is calculated based on the number of error data. You may make it measure the distance to the LED array of a transmitter. In this case, a distance determination table indicating the relationship between the number of error data and the communication distance may be obtained in advance and stored in the table storage unit.

  Next, a second embodiment will be described. In addition, about the part which becomes the structure similar to 1st Embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  In the second embodiment, the error correction is performed on the received data using error correction coding, and the demodulated received data and the received data subjected to error correction are compared with each other to obtain a bit error rate. This is mainly different from the first embodiment.

  In the optical transmission apparatus according to the second embodiment, transmission data is encoded by error correction encoding, and the LED array 16 is driven according to the encoded transmission data to perform data transmission.

  As shown in FIG. 11, the image processing unit 242 of the optical receiver according to the second embodiment includes a luminance value acquisition unit 62, a reverse bias unit 64, a wavelet transform unit 66, a threshold determination unit 68, A data generation unit 70, an error correction unit 272 that performs error correction on the reception data generated by the data generation unit 70, received data that has not been subjected to error correction generated by the data generation unit 70, and error correction. An error rate calculation unit 274 that compares the received data and calculates a bit error rate as the quality of the reception data, a table storage unit 76, and a distance measurement unit 78 are provided.

  The error correction unit 272 performs error correction on the reception data sequence generated by the data generation unit 70 to obtain final reception data. It should be noted that a conventionally known technique may be used for the error correction coding method, and the description of the error correction coding method is omitted in this embodiment.

  The error rate calculation unit 274 sets the data obtained by the error correction unit 272 as correct reception data, compares the reception data generated by the data generation unit 70 with the reception data subjected to error correction, and determines the number of erroneous data. And the bit error rate is calculated by dividing the number of error data by the total number of received data.

  Since other configurations and other processes of the optical communication system are the same as those in the first embodiment, description thereof is omitted.

  In this way, in the optical receiver, the demodulated transmission data is compared with the transmission data subjected to error correction, the bit error rate is calculated, and the distance to the LED array of the optical transmitter is measured, With a simple device configuration, the distance can be measured without reducing the transmission efficiency.

  Further, even if transmission data is unknown on the optical receiver side, the distance to the LED array of the optical transmitter apparatus can be measured.

  Further, more accurate data quality can be obtained by performing error correction and demodulating transmission data.

  In the above embodiment, the case where the error correction capability is fixed has been described as an example. However, the present invention is not limited to this, and the error correction capability may be adjusted. Thereby, since the relationship between the communication distance and the bit error rate indicated by the distance determination table can be adjusted, the range of distance that can be measured can be adjusted.

  Next, a third embodiment will be described. Since the configuration of the optical communication system according to the third embodiment is the same as that of the first embodiment, the same reference numerals are given and description thereof is omitted.

  The third embodiment is mainly different from the first embodiment in that the bit error rate is calculated for each stage of the spatial frequency component of the lighting pattern corresponding to the data.

  In the optical receiver 14 according to the third embodiment, transmission data is stored in the data storage unit 72 for each stage of the spatial frequency component.

  The error rate calculation unit 74 divides the reception data generated by the data generation unit 70 into each step of the spatial frequency component of the lighting pattern corresponding to the data, and stores it in the data storage unit 72 for each step of the spatial frequency component. Compared with the known transmission data, the number of error data is obtained, and the bit error rate is calculated.

  As shown in FIG. 10, the table storage unit 76 includes a distance determination table that represents the relationship between the bit error rate obtained in advance through experiments or the like and the distance to the LED array 16 of the optical transmitter 12. It is stored for each stage of the spatial frequency component.

  Here, as shown in FIG. 10, the LED group corresponding to the portion D11 in the above equation (1) is assigned with the lighting pattern data having a low spatial frequency component. Even when the distance to the array 16 is long, the data quality is unlikely to deteriorate. That is, transmission data can be received without error even at a long distance. Therefore, the distance determination table for data having a lighting pattern with a low spatial frequency component shows a relationship in which the bit error rate does not easily increase even when the communication distance is increased.

  In addition, since the LED group corresponding to the portion D22 is assigned lighting pattern data with a high spatial frequency component, the data quality is low when the distance from the LED array 16 of the light transmission device 12 is long, Data quality increases at close range. Therefore, in the distance determination table for lighting pattern data having a high spatial frequency component, the bit error rate increases as the distance from the LED array 16 of the optical transmission device 12 increases, and the distance from the LED array 16 of the optical transmission device 12 increases. This shows a relationship in which the bit error rate decreases as the distance decreases.

  Also, since the LED group corresponding to the portions of D12 and D21 is assigned lighting pattern data having a medium spatial frequency component, the data quality characteristics with respect to the distance from the LED array 16 of the optical transmitter 12 Is an intermediate characteristic between the characteristic of the D11 part and the characteristic of the D22 part. Therefore, the distance determination table for the lighting pattern data having a medium spatial frequency component is the distance determination table for the lighting pattern data having a low spatial frequency and the relationship indicated by the distance determination table for the lighting pattern data having a high spatial frequency. This indicates an intermediate relationship with the relationship indicated by.

For example, when the bit error rate at each stage of the spatial frequency component of the data lighting pattern is 10 ⁻² , the LED array 16 of the optical transmission device 12 is arranged in ascending order of the spatial frequency component of the data lighting pattern. The distance is 28 m, 31 m, and 35 m.

  The distance measuring unit 78 determines the distance corresponding to the calculated bit error rate based on the distance determination table for the lighting pattern data having the spatial frequency component at any stage, and the LED array of the optical transmission device 12 Measure the distance up to 16.

  For example, with respect to lighting pattern data with a low spatial frequency component, when it is not possible to determine the communication distance corresponding to the calculated bit error rate based on the distance determination table (communication distance corresponding to the calculated bit error rate) If there is a plurality of or when there is no error in the demodulated reception data), the lighting pattern data of the medium spatial frequency component or the lighting pattern data of the high spatial frequency component, based on the distance determination table, The distance to the LED array 16 of the optical transmitter 12 corresponding to the calculated bit error rate is determined.

  Since other configurations and other processes of the optical communication system are the same as those in the first embodiment, description thereof is omitted.

  In this way, the bit error rate is calculated for each stage of the spatial frequency component of the lighting pattern according to the data, and the data of the lighting pattern of the spatial frequency component at any stage is stored in the bit error rate and the distance determination table. On the basis of this, by measuring the distance to the LED array of the optical transmission device, it is possible to select the lighting pattern data of the spatial frequency component capable of measuring the distance and measure the communication distance, so the communication distance is accurate. Can be measured.

  Next, a fourth embodiment will be described. In addition, about the part which becomes the structure similar to 1st Embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  The fourth embodiment is mainly different from the first embodiment in that a two-dimensional high-speed Walsh transform encoding method is used.

  As shown in FIG. 12, the signal generation unit 422 of the optical transmission apparatus according to the fourth embodiment performs encoding using a two-dimensional fast Walsh transform (2D FWT). The signal generation unit 422 includes a mapping unit 430 that assigns transmission data to each LED according to a spatial frequency component of the data transmission pattern, and a two-dimensional fast Walsh inverse transform (for the transmission data assigned to each LED). 2D IFWT), the normalization of the data subjected to the two-dimensional fast Walsh inverse transformation, the normalization bias addition unit 434 for adding a bias, and the output data of the normalization bias addition unit 434 And a drive signal generator 36 for generating a drive signal.

  The mapping unit 430 assigns the transmission data to a plurality of LEDs by dividing the transmission data into lighting pattern data having 10 stages of spatial frequency components. When 4 × 4 point two-dimensional high-speed Walsh transform is used, for example, as shown in FIG. 12, 4 × 4 data corresponds to 10 frequencies from a high frequency component to a low frequency component according to the frequency component of the lighting pattern. Divided into stages. As shown in FIG. 13, the lighting pattern data of the lowest frequency component, the lighting pattern data of the fifth lowest frequency component, the lighting pattern data of the third highest frequency component, and the lighting pattern of the highest frequency component. The total data rate of each of the data is 4Rb, and the total data rate of the lighting pattern data of the other frequency components is 8Rb.

The Walsh inverse transform unit 432 performs 4 × 4 point two-dimensional high-speed Walsh inverse transform on the transmission data in the form of the above equation (1) divided into four times. After the inverse transformation, an 8 × 8 matrix is obtained as with the transmission data. Each element x ′ _{u, v} of the output matrix is expressed by the following equation (8).

Here, W ⁴ _{m, n} represents an element of m rows and n columns of a 4 × 4 matrix W ⁴ as shown in the following equation (9).

_X'u, the range of possible values of _{v above,} -1 ≦ _x'u, a _v ≦ 1. In order to set the possible values of x ′ _{u, v} to a range from 0 to 1, the normalization bias adding unit 434 normalizes after applying a bias as shown in the following equation (10).

As a result of the above processing, possible values of x _{u, v} are {0, 1/16, 1/8, 3/16, 1/4, 5/16, 3/8, 7/16, 1/2. , 9/16, 5/8, 11/16, 3/4, 13/16, 7/8, 15/16, 1}.

  As shown in FIG. 14, the image processing unit 442 includes a luminance value acquisition unit 62, a reverse bias unit 464 that applies a reverse bias to the acquired luminance value of each LED, and a luminance value of each LED to which the reverse bias is applied. On the other hand, the Walsh transform unit 466 that performs the two-dimensional fast Walsh transform (2D FWT) and the brightness value of each LED that has undergone the two-dimensional fast Walsh transform determine whether the value is greater than 0. The threshold value determination unit 468 that converts the luminance of the output data into output data represented by +1 and −1, the data generation unit 70, the data storage unit 72, the error rate calculation unit 74, the table storage unit 76, and the distance measurement unit 78 And.

When R _{u, v} obtained from the captured image is an 8 × 8 square matrix, the reverse bias unit 464 applies a reverse bias to each element x ′ _{u, v} of the matrix as shown in the following equation (11). Add.

Here, b is a bias value, and is calculated from the average value of R _{u, v} as shown in the following equation (12). In this embodiment, since it is necessary to average over time in order to obtain an appropriate bias value, the time parameter i is calculated in consideration.

  The Walsh transform unit 466 performs 4 × 4 point two-dimensional fast Walsh transform (2D FWT) on the matrix to which the reverse bias is applied as shown in the following equation (13).

The threshold determination unit 468 performs threshold determination and obtains output data. _If the hat of d ′ _{m, n} is a positive value, the estimated value d ′ _{m, n} of the hat of d _{m, n} is set to 1, and _if the hat of d ′ _{m, n} is a negative value, d _m, an estimate of hat _n d _m, a hat of _n as -1, into an output data.

  Since other configurations and other processes of the optical communication system are the same as those in the first embodiment, description thereof is omitted.

  In the first to fourth embodiments, the case where the two-dimensional fast Haar wavelet transform is used or the case where the two-dimensional fast Walsh transform is used has been described. However, the present invention is not limited to this. Instead, the transmission data may be encoded and demodulated using two-dimensional orthogonal transform such as two-dimensional fast Fourier transform and two-dimensional discrete cosine transform.

It is the schematic which shows the structure of the optical communication system which concerns on the 1st Embodiment of this invention. It is the schematic which shows the structure of the optical transmitter which concerns on the 1st Embodiment of this invention. It is a block diagram which shows the structure of the signal generation part of the optical transmission apparatus which concerns on the 1st Embodiment of this invention. It is the schematic which shows the structure of the optical receiver which concerns on the 1st Embodiment of this invention. It is a block diagram which shows the structure of the image process part of the optical receiver which concerns on the 1st Embodiment of this invention. (A) An image diagram showing a lighting pattern with a high spatial frequency, (B) An image diagram showing a lighting pattern with a low spatial frequency, (C) An image diagram showing an image obtained by imaging a lighting pattern with a high spatial frequency, and (C) The spatial frequency is It is an image figure which shows the image which imaged the low lighting pattern. (A) It is an image figure which shows the image imaged from the position 15m away from the LED array, (B) It is an image figure which shows the image imaged from the position 50m away from the LED array. It is a flowchart which shows the content of the communication ranging process routine in the optical receiver which concerns on the 1st Embodiment of this invention. (A) Image diagram showing an image taken from a position 10 m away from the LED array in the experiment, (B) Image diagram showing an image taken from the position 30 m away from the LED array in the experiment, and (C) 50 m from the LED array in the experiment. It is an image figure which shows the image imaged from the distant position. It is a graph which shows the relationship between a bit error rate and the distance to the LED array of an optical transmitter. It is a block diagram which shows the structure of the image process part of the optical receiver which concerns on the 2nd Embodiment of this invention. It is a block diagram which shows the structure of the signal generation part of the optical transmission apparatus which concerns on the 4th Embodiment of this invention. It is a table | surface which shows the data and data rate in each step of a spatial frequency component at the time of using 4x4 point two-dimensional high-speed Walsh transform. It is a block diagram which shows the structure of the image process part of the optical receiver which concerns on the 4th Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Optical communication system 12 Optical transmitter 14 Optical receiver 16 LED array 18 Transmission data generation device 22, 422 Signal generation part 24 Drive circuit 40 High-speed camera 42,242,442 Image processing part 62 Luminance value acquisition part 64,464 Reverse bias Unit 66 wavelet transform unit 68, 468 threshold determination unit 70 data generation unit 72 data storage unit 74, 274 error rate calculation unit 76 table storage unit 78 distance measurement unit 272 error correction unit 464 reverse bias unit 466 Walsh transform unit

Claims (6)

Imaging means for imaging the plurality of light emitting elements of a light source in which a plurality of light emitting elements that are turned on according to transmission data are arranged;
Demodulating means for demodulating the transmission data based on an image captured by the imaging means;
Error calculating means for calculating an error rate or number of errors of the transmission data demodulated by the demodulating means;
Measuring means for measuring the distance to the light source based on the error rate or the number of errors calculated by the error calculating means;
An optical receiver comprising:   The error calculation unit compares the transmission data demodulated by the demodulation unit with the transmission data stored in a storage unit that stores the transmission data, and calculates the error rate or the number of errors. The optical receiver according to 1. Error correction means for performing error correction on the transmission data demodulated by the demodulation means;
2. The error calculation means calculates the error rate or the number of errors by comparing the transmission data demodulated by the demodulation means with the transmission data subjected to error correction by the error correction means. Optical receiver.   The measuring means measures a distance to the light source based on a relationship between the distance obtained in advance and the error rate or the number of errors and the error rate or the number of errors calculated by the error calculating means. The optical receiver according to any one of claims 1 to 3. The light source has a light emitting element group composed of at least one light emitting element to be lit for each stage of spatial frequency divided into a plurality of stages, and corresponds to a spatial frequency stage of a lighting pattern according to the transmission data. The light emitting elements of the light emitting element group to be turned on according to the transmission data,
The error calculating means calculates an error rate or the number of errors of the transmission data for each stage,
5. The light according to claim 1, wherein the measuring unit measures a distance to the light source based on the error rate or the number of errors for each stage calculated by the error calculating unit. Receiver device. An optical transmitter that turns on the plurality of light emitting elements of a light source in which a plurality of light emitting elements are arranged according to transmission data;
The optical receiver according to any one of claims 1 to 5,
An optical communication system including: