JP6922796B2 - Receiver, visible light communication system, receiving method, program - Google Patents

Description

The present invention relates to a receiving device, a receiving method, and a program for receiving visible light and electromagnetic waves in the peripheral band thereof.

In recent years, visible light sources have been used not only for lighting to obtain light but also for communication. This is due to the widespread use of light emitting diodes (LEDs) as visible light sources. Although the amount of light emitted per element of the light emitting diode is not as high as that of the conventional visible light source such as an incandescent lamp or a fluorescent lamp, the light emitting diode is superior to the conventional visible light source in terms of its life, size and power consumption. In addition to the above characteristics, the light emitting diode has a characteristic that the response speed is very fast. Moreover, it is easy to electrically control the light emission of the light emitting diode. Since light emitting diodes have the above characteristics, in recent years, research and development have been carried out not only for lighting applications for obtaining light but also for signal transmission using blinking of visible light.

For example, Non-Patent Document 1 discloses that a signal is superimposed on a household lighting fixture using a light emitting diode to perform communication.

In addition, since visible light is not subject to the regulations of the Radio Law at present, there are no restrictions on the band or power, and these can be taken large. Non-Patent Document 2 discloses that a light emitting diode is used exclusively for communication by utilizing this fact. Communication performed using a visible light source such as a light emitting diode is called visible light communication. In visible light communication, a photodetector or an image sensor, which is an array thereof, is used as a receiver. Photodetectors can usually obtain signals continuously. On the other hand, an image sensor can acquire signals from a large number of photodetectors at one time, but due to its nature, it can usually acquire only signals sampled with a period Ts. Hereinafter, it is assumed that an image sensor is mainly used as a light receiving device.

FIG. 1 shows the properties of signals used in visible light communication. First, the digital transmission signal S (i) (also referred to as a transmission symbol) is expressed by converting it into a phase value to obtain a modulated signal M (i). Such a modulation method is called phase shift modulation (phase shift keying). For example, when S (i) is represented by two values, it is converted into a phase value such as 0 → 0, 1 → π (binary phase shift modulation, BPSK). Here, i is an index indicating time. Next, the phase of the square wave having the carrier frequency 1 / Tc is changed according to the modulation signal M (i), and the electric signal E (t) for driving the light emitting element is obtained. Here, t is a real number indicating time. However, the signal E (t) is a temporally continuous signal with respect to the temporally discrete signal M (i). The light emitting element repeatedly turns on and off according to the signal E (t) and outputs the optical signal F (t). The output time of E (t) corresponding to the time index i is from time iTf-Tf / 2 to time iTf + Tf / 2 with reference to time iTf with a certain delay added from the time indicated by index i. As shown in FIG. 1, the time indicated by the index i has a time width Tf.

In the conventional technique (for example, Non-Patent Document 1), an optical signal F'(t) in which noise is superimposed on F (t) captured by a light receiving element is converted into an electric signal E'(t). After that, the phase signal M'(i) is estimated from E'(t). Ideally, F (t) = F'(t), but since it may change depending on the performance of the image sensor, propagation in the medium, and delay, F (t) and F'(t) are separated here. Describe. It is assumed that approximately F (t + TL) = F'(t). TL represents the propagation delay.

An example of signal exchange in visible light communication will be described with reference to FIG. FIG. 2 is a diagram illustrating a state in which the blinking of the light emitting element is received by the image sensor. It is assumed that the blinking of the transmitter (light emitting element) is imaged in the region Ω on the image sensor. The receiver captures the sum of the output values of all the photodetectors in the region Ω as the received signal from the transmitter.

When transmitting information on a communication path, it is common to encode the original information in some way. The smallest unit of signal that constitutes encoded information is called a symbol. In a digital channel, it is important to detect the clock (time width used when transmitting one symbol) and the phase of the symbol. Doing this is called symbol timing synchronization between the receiver and the transmitter. It is desirable that symbol timing synchronization is always performed during communication. This is because there is generally no way to share the same oscillator between the receiver and the transmitter, which can lead to constant out-of-sync.

In order to perform symbol timing synchronization, it is necessary to use a symbol timing reproduction circuit as in Non-Patent Document 3, for example. This synchronizes the phase by detecting the phase difference between the two input signals and applying feedback control. One of the two signals is the input from the oscillator, and the other is the signal that you want to synchronize. When a photodetector is used as a receiver, it is easy to use a symbol timing reproduction circuit because signals can be continuously obtained. On the other hand, when an image sensor is used, the signal that can be used for reception processing is a sampled signal, so that it is a discrete-time signal. In this case, a certain sampling frequency is required to perform symbol timing synchronization by the symbol timing reproduction circuit.

With reference to FIG. 3, a configuration of a visible light communication system using phase shift keying using a conventional technique will be described. As shown in the figure, the conventional visible light communication system 9 includes a transmitting device 91 and a receiving device 92, the transmitting device 91 includes a modulation unit 911 and a light emitting unit 912, and the light emitting unit 912 is a light emitting signal control unit. Includes 9121 and light emitting element 9122. The receiving device 92 includes a light receiving unit 921, a synchronization unit 922, and a demodulation unit 923, the light receiving unit 921 includes a light receiving element 9211 and a received signal generation unit 9212, and the synchronization unit 922 includes a clock element 9221 and a symbol. The timing reproduction circuit 9222 is included, and the demodulation unit 923 includes a phase signal estimation unit 9231 and a transmission signal estimation unit 9232. Hereinafter, the input / output and operation of each part will be described with reference to FIG.

<Modulation unit 911>
Input: The series S (1), S (2), ... Of the digital transmission signal S (i) are input to the modulation unit 911. The digital transmission signal S (i) is 1-bit information, and i is an integer representing the number of the digital transmission signal.
Output: The modulation unit 911 outputs the series M (1), M (2), ... Of the modulation signal M (i). The modulated signal M (i) is phase information having a value of 0 or π. In addition, i is also used as an index representing time.
Operation: The modulation unit 911 modulates the series S (1), S (2), ... Of the input digital transmission signal S (i) to modulate the series M (1), M (2) of the modulated signal M (i). ), ... Are generated (S911). For example, the modulation unit 911 generates a modulation signal with M (i) = 0 if S (i) = 0 and M (i) = π if S (i) = 1.
Specific example: For example, when the sequence of the digital transmission signal S (i) is S (1) = 0, S (2) = 1, S (3) = 1, S (4) = 1, ..., Modulation The result is M (1) = 0, M (2) = π, M (3) = π, M (4) = π, ...

<Light emitting unit 912>
As described above, the light emitting unit 912 includes a light emitting signal control unit 9121 and a light emitting element 9122. The light emitting element 9122 is, for example, an LED.
Input: The series M (1), M (2), ... Of the modulation signal M (i) are input to the light emitting unit 912.
Output: An optical signal F (t) is output from the light emitting unit 912.
Operation: When the input modulation signal M (i) is 0, the light emission signal control unit 9121 of the light emitting unit 912 is between the time iTf-Tf / 2 and the time iTf + Tf / 2 when the predetermined time Tf has elapsed. , Frequency 1 / Tc, phase 0 square wave (electric signal) is generated and given to the light emitting element 9122, and if the input modulation signal M (i) is π, it is determined from time iTf-Tf / 2. A square wave (electric signal) having a frequency of 1 / Tc and a phase of π is applied to the light emitting element 9122 until the time iTf + Tf / 2 elapses (S9121). The light emitting element 9122 emits light by an electric signal given from the light emitting signal control unit 9121 (S9122). As a result, an optical signal is output from the light emitting unit 912. However, it is assumed that the electric signal generated by the light emitting signal control unit 9121 is controlled so that the light signal F (t) of the light emitting element becomes a desired value in consideration of the performance and characteristics of the light emitting element.

<Light receiving unit 921>
As described above, the light receiving unit 921 includes a light receiving element 9211 and a received signal generation unit 9212. The light receiving element 9211 is, for example, a photodetector. Further, an optical lens may be provided in front of the light receiving element 9211. The light receiving element 9211 may be an image sensor in which photo detectors are arranged in a grid pattern.
Input: The optical signal F (t) output from the light emitting unit 912 is input to the light receiving unit 921.
Output: A time-continuous reception signal E'' (t) is output from the light receiving unit 921.
Operation: The light receiving element 9211 of the light receiving unit 921 outputs an electric signal E'(t) corresponding to the input optical signal F (t) to the received signal generation unit 9212 (S9211). The reception signal generation unit 9212 of the light receiving unit 921 outputs the reception signal E''(t) to the synchronization unit 922 and the demodulation unit 923 based on the input electric signal E'(t) (S9212).

<Synchronization unit 922>
As described above, the synchronization unit 922 includes a clock element 9221 and a symbol timing reproduction circuit 9222.
Input: The reception signal E''(t) output from the light receiving unit 921 is input to the synchronization unit 922.
Output: Phase information and frequency information are output from the synchronization unit 922.
Operation: The clock element 9221 of the synchronization unit 922 outputs clock information (S9221). The symbol timing reproduction circuit 9222 of the synchronization unit 922 detects the phase difference between the two signals based on the clock information input from the clock element 9221 and the input received signal E'' (t) and applies feedback control. Then, the phase is synchronized and the phase information and the frequency information are output (S9222).

<Demodulation unit 923>
As described above, the demodulation unit 923 includes a phase signal estimation unit 9231 and a transmission signal estimation unit 9232. The phase signal estimation unit 9231 and the transmission signal estimation unit 9232 include a memory, an arithmetic unit, and the like.
Input: The reception signal E''(t) output from the light receiving unit 921, the phase information output from the synchronization unit 922, and the frequency information are input to the demodulation unit 923.
Output: The demodulation unit 923 outputs the estimation result S'(i).
Operation: The phase signal estimation unit 9231 of the demodulation unit 923 generates a phase signal M'(i) using the received signal E'' (t), phase information, and frequency information (S9231). The transmission signal estimation unit 9232 of the demodulation unit 923 estimates the digital transmission signal based on the phase signal M'(i) and outputs the estimation result S'(i) (S9232).

Toshihiko Komine, Yuichi Tanaka, Masao Nakagawa, "Integrated System of White LED Illumination Signal Transmission and Power Line Signal Transmission", IEICE Technical Report, IEICE Technical Report, March 12, 2002, Vol.101, No.726, pp.99-104 Masanori Ishida, Shinichiro Haruyama, Masao Nakagawa, "Examination of Communication Speed Limits in Parallel Visible Optical Wireless Communication System", IEICE Technical Report CS Communication System, IEICE Technical Report, January 4, 2007, Vol. .106, No.450, pp.37-41 Bertrand, C .; Sehier, P .;, "A novel approach for full digital modems implementing asynchronous sampling techniques," Global Telecommunications Conference, 1996. GLOBECOM '96.'Communications: The Key to Global Prosperity, vol.2, no. , pp.1320-1324 vol.2, 18-22 Nov 1996

In the system described above, the sampling frequency required for phase demodulation is at least twice as large as the carrier frequency. On the other hand, in an image sensor, the upper limit of the product of the number of pixels obtained in one imaging and the number of imagings per hour, that is, the sampling frequency, is generally constrained to be constant. Therefore, when an image sensor is used as the light receiving unit of the system as described above and a large sampling frequency is adopted for demodulation, the number of pixels obtained by one sampling must be sacrificed.

Therefore, an object of the present invention is to provide a receiving device capable of receiving a phase shift keying signal without sacrificing the number of pixels obtained by one sampling.

The receiving device of the present invention includes a light receiving unit and a demodulating unit. The light receiving unit receives an optical signal based on a modulation signal formed by phase-shifting and connecting a training series having a predetermined value and a digital transmission signal, and the optical signal is combined with an optical signal at different exposure timings. A plurality of received signals corresponding to each of the light receiving elements are generated based on the charges accumulated in the samplers of the plurality of light receiving elements exposed over a half cycle of the above. The demodulator uses the value of the received signal when the phase difference between the optical signal and the exposure timing is zero as the normalized received signal value, and is based on the generated multiple received signal values and the normalized received signal value. The phase of the modulated signal is estimated, and the reference phase information, which is information representing the phase shift between transmission and reception, is estimated based on the portion of the phase estimation result corresponding to the training sequence.

According to the receiving device of the present invention, the phase shift keying signal can be received without sacrificing the number of pixels obtained by one sampling.

The figure which shows the example which sequentially converted the digital transmission signal into a modulation signal, an electric signal, and an optical signal. The figure explaining the state of receiving the blinking of a light emitting element by an image sensor. The block diagram which shows the structure of the conventional visible light communication system 9. The sequence diagram which shows the operation of the conventional visible light communication system 9. The block diagram which shows the structure of the visible light communication system 1 of Example 1. FIG. The sequence diagram which shows the operation of the visible light communication system 1 of Example 1. FIG. The block diagram which shows the structure of the visible light communication system 2 of Example 2. FIG. The sequence diagram which shows the operation of the visible light communication system 2 of Example 2. FIG. The figure which shows the difference of the exposure timing of the 1st light receiving element and the 2nd light receiving element. The figure which shows the example of the change of the pixel value observed by the 1st light receiving element with the change of a relative phase. The figure which shows the example of the modulation signal generated by the modulation part of Example 2. FIG. The figure which shows the theoretical locus which the pixel value by the 1st light receiving element is a horizontal axis, and the pixel value by a 2nd light receiving element is a vertical axis. The figure which shows the theoretical locus which the pixel value by the 1st light receiving element is a horizontal axis, and the pixel value by a 2nd light receiving element is a vertical axis. The figure which illustrates the training series for normalization used in the modification 5.

Hereinafter, embodiments of the present invention will be described in detail. The components having the same function are given the same number, and duplicate explanations will be omitted.

Hereinafter, the configuration of the visible light communication system of the first embodiment will be described with reference to FIG. As shown in the figure, the visible light communication system 1 of this embodiment includes a transmitting device 11 and a receiving device 12, the transmitting device 11 includes a modulation unit 111 and a light emitting unit 112, and the light emitting unit 112 emits light. The signal control unit 1121 and the light emitting element 9122 are included, and the light emitting element 9122 is the same as the light emitting element 9122 in the conventional transmission device 91. The receiving device 12 includes a light receiving unit 121 and a demodulating unit 123, and the light receiving unit 121 includes a first light receiving element 1211, a second light receiving element 1212, a first received signal generation unit 1213, and a second received signal generation unit. 1214 is included, and the demodulation unit 123 includes a phase signal estimation unit 1231, a frame interpretation unit 1232, and a transmission signal estimation unit 1233.

Hereinafter, input / output and operation of each part different from the conventional ones will be described with reference to FIG.
<Modulation unit 111>
The modulation unit 111 includes a memory, an arithmetic unit, and the like.
Input: The series S (1), S (2), ..., S (J) of the digital transmission signal S (j) are input to the modulation unit 111. The transmission signal S (j) is 1-bit or log2G-bit information, and j is an integer representing the number of the transmission signal.
Output: The modulation unit 111 outputs the series M (1), M (2), ... Of the modulation signal M (i). The modulated signal M (i) is phase information having a value corresponding to the digital transmission signal S (j) and the value specified in the predetermined training sequence. Further, i is a number representing the number of the modulated signal. i is also used as an index representing time.
Operation: The modulation unit 111 generates the series MM (1), MM (2), ..., MM (J) of the modulation signal MM (j) of the input digital transmission signal S (j) (S111). .. For example, if the value of S (j) is L, the modulation unit 111 generates a modulation signal with MM (j) as 2 * π / G * L. Further, the modulation unit 111 generates the series MT (1), MT (2), ..., MT (JJ) of the modulation signal MT (jj) of the training series (S111). The series MT (1), MT (2), ..., MT (JJ) are predetermined phase ΘR modulation signals. The modulation unit 111 sets the modulation signal sequences MT (1), MT (2), ..., MT (JJ) of JJ training sequences as M (1), M (2), ..., M (JJ), and J The sequence MM (1), MM (2), ..., MM (J) of the modulated signals is output as M (JJ + 1), M (JJ + 2), ..., M (JJ + J). That is, the modulation unit 111 generates the series MM and MT of the two modulation signals as shown in the table below, and then concatenates them to form the modulation signal M, which is the series M (1), ..., Of the modulation signal M (i). Outputs M (JJ), M (JJ + 1), ..., M (JJ + J).

<Light emitting unit 112>
As described above, the light emitting unit 112 includes a light emitting signal control unit 1121 and a light emitting element 9122. The light emitting element 9122 is, for example, an LED.
Input: The series M (1), M (2), ... Of the modulation signal M (i) are input to the light emitting unit 112.
Output: An optical signal F (t) is output from the light emitting unit 112.
Operation: When the input modulation signal M (i) is ΘM (M is an arbitrary value), the light emission signal control unit 1121 of the light emitting unit 112 is the time iTf at which a predetermined time Tf has elapsed from the time iTf-Tf / 2. Until + Tf / 2, a square wave (electric signal) having a frequency of 1 / Tc and a phase of ΘM is generated and given to the light emitting element 9122 (S1121). The light emitting element 9122 emits light by an electric signal given by the light emitting signal control unit 1121 (S9122). As a result, the optical signal F (t) is output from the light emitting unit 112. However, it is assumed that the electric signal generated by the light emitting signal control unit 1121 is controlled so that the light signal F (t) of the light emitting element becomes a desired value in consideration of the performance and characteristics of the light emitting element.

<Light receiving unit 121>
As described above, in the present embodiment, the light receiving unit 121 includes two sets of the light receiving element and the received signal generating unit, but the set of the light receiving element and the received signal generating unit is not limited to two sets.

The operation of the light receiving unit 121 can be generally expressed as follows. The light receiving unit 121 is an optical signal F1 (t), F2 ( After receiving t), ..., the optical signals F1 (t), F2 (t), ... are given to the optical signals F1 (t), F2 (t), ... at different exposure timings. A plurality of received signals B1'(t), B2'(t), ... Generate (S121).

Hereinafter, the operation of the light receiving unit 121 will be described in detail with reference to FIG. 6, assuming that two sets of the light receiving element and the received signal generating unit are included. Similar to the prior art, the first and second light receiving elements 1211, 1212 are, for example, photodetectors. Further, an optical lens may be provided in front of the first and second light receiving elements 1211, 1212. Further, the first and second light receiving elements 1211, 1212 may be an image sensor in which photodetectors are arranged in a grid pattern. The first and second received signal generation units 1213 and 1214 include a sampling element, a memory, an arithmetic unit, and the like.
Input: The first optical signal F1'(t) and the second optical signal F2'(t) output from the light emitting unit 112 are input to the light receiving unit 121.
Output: From the light receiving unit 121, the sequence B1'(1), B1'(2), ... Of the first received signal B1'(i) and the sequence B2'(1), of the second received signal B2'(i), B2'(2), ... is output.
Operation: The first light receiving element 1211 of the light receiving unit 121 outputs the first electric signal E1'(t) corresponding to the input first optical signal F1'(t) to the first received signal generation unit 1213. (S1211). When the first light receiving element 1211 is an image sensor, specifically, as shown in FIG. 9, each photodetector has accumulated in the sampler from the time TI + iTs-Ts / 2 to TI + iTs-Ts / 2 + τ. Measure the charge. However, TI is the relative phase (offset), iTs is the time corresponding to the center of the i-th symbol, iTs-Ts / 2 is the time corresponding to the beginning of the i-th symbol, and τ is the exposure time.

Similarly, the second light receiving element 1212 of the light receiving unit 121 outputs the second electric signal E2'(t) corresponding to the input second optical signal F2'(t) to the second received signal generation unit 1214. (S1212). When the second light receiving element 1212 is an image sensor, specifically, as shown in FIG. 9, each photodetector has a time of TI + iTs-Ts / 2 + Tc / 4 to TI + iTs-Ts / 2 + τ + Tc / 4. Measure the charge accumulated in the sampler by. Tc / 4 represents the difference in exposure timing between the first light receiving element 1211 and the second light receiving element 1212, and is one-fourth of the period Tc of the carrier wave.

The first received signal generation unit 1213 measures the intensity of the input first electric signal E1'(t) at each time interval Ts and outputs it as the first received signal B1'(i) (S1213). When the first light receiving element 1211 is an image sensor, the first received signal generation unit 1213 sums the charge measurement results over a predetermined range Ω, and the sum of the measurement results is the first received signal B1'(i). Is output as (S1213). Similarly, the second received signal generation unit 1214 measures the intensity of the input second electric signal E2'(t) at each time interval Ts and outputs it as the second received signal B2'(i) (S1214). .. When the second light receiving element 1212 is an image sensor, the second reception signal generation unit 1214 takes the sum of the charge measurement results over a predetermined range Ω, and the sum of the measurement results is taken as the second reception signal B2'(i). Output (S1214).

<Demodulation unit 123>
As described above, the demodulation unit 123 includes a phase signal estimation unit 1231, a frame interpretation unit 1232, and a transmission signal estimation unit 1233. The phase signal estimation unit 1231, the frame interpretation unit 1232, and the transmission signal estimation unit 1233 include a memory, an arithmetic unit, and the like.

The operation of the demodulation unit 123 can be generally expressed as follows. The demodulation unit 123 normalizes the values of the received signals when the phase difference between the optical signals F1 (t), F2 (t), ... And the exposure timing is zero, and the received signal values R1, R2, ... Then, the phase of the modulated signal is estimated based on the values of the generated multiple received signals B1'(t), B2'(t), ... and the normalized received signal values R1, R2, ... , The reference phase information MI'(k), which is information representing the phase shift between transmission and reception, is estimated based on the portion of the phase estimation result M'(i) corresponding to the training sequence (S123).

Hereinafter, the operation of the demodulation unit 123 will be described in detail with reference to FIG. 6, assuming that two sets of the light receiving element and the reception signal generation unit are included.
Input: A sequence of the first received signal B1'(i) and a sequence of the second received signal B2'(i) are input to the demodulation unit 123 from the light receiving unit 121.
Output: The demodulation unit 123 outputs the estimation result S'(j).
Operation: The phase signal estimation unit 1231 of the demodulation unit 123 has a relative phase estimation result M'based on the sequence of the first received signal B1'(i) and the sequence of the second received signal B2'(i). (i) is generated and output to the frame interpretation unit 1232 and the transmission signal estimation unit 1233 (S1231).

Specifically, the phase signal estimation unit 1231 receives signals when the exposure timing and the phase difference of the carrier wave are 0 for each of the first received signal B1'(i) and the second received signal B2'(i). The values of are held in advance as the reception signal values R1 and R2 for normalization (see FIG. 10, and the brightness value (pixel value) when TI = 0 in the figure is R1). These normalized received signal values shall be given from the outside in some way or estimated in advance. The phase signal estimation unit 1231 estimates the relative phase of the received signal based on the first received signal B1'(i) and the second received signal B2'(i), and the relative phase estimation result M'(. Output as i).

Normally, the phase signal estimation unit 1231 estimates the phase using a certain number of pairs of B1'(i) and B2'(i) (assuming = LL). The number of relative phase estimation results M'(i) output at this time is also LL. Specifically, the above relative phase estimation can be performed by the following mathematical formula (Equation 1).

However, B1'' (i) is a value obtained by dividing B1'(i) by R1, and B2'' (i) is a value normalized by dividing B2'(i) by R2.

Next, the frame interpretation unit 1232 of the demodulation unit 123 generates and controls the control signal C'(k) and the reference phase information MI'(k) based on the relative phase estimation result M'(i). The signal C'(k) and the reference phase information MI'(k) are output to the transmission signal estimation unit 1233 (S1232). k is an integer representing the number of the control signal C'(k). It is assumed that the frame interpretation unit 1232 holds in advance the predetermined phase information ΘR, the length JJ of the modulation signal sequence of the training sequence, and the length J of the modulation signal sequence of the symbol. The frame interpreter 1232 estimates the reference phase information MI'(k) based on JJ pieces from the beginning of the series of relative phase estimation results M'(i). Specifically, the operation is performed based on the following mathematical formula (Equation 2).

Reference phase information MI'(k) is information representing a phase shift between transmission and reception. Further, the frame interpretation unit 1232 holds the indexes of JJ training sequences and uses them as control signals C'(k).

The transmission signal estimation unit 1233 of the demodulation unit 123 is a sequence M'(JJ) other than the JJ training sequences pointed out by the control signal C'(k) in the sequence of the relative phase estimation result M'(i). From the sequence of M'(JJ + J) from +1), the sequence of symbols S'(j) is estimated using the least squares method as shown below (S1233). Specifically, the operation is performed based on the following mathematical formula (Equation 3).

However, the operator gmod (θ, 2π / G)

Means.

Hereinafter, the configuration of the visible light communication system of the second embodiment will be described with reference to FIG. 7. As shown in the figure, the visible light communication system 2 of this embodiment includes a transmitting device 21 and a receiving device 22, the transmitting device 21 includes a modulation unit 211 and a light emitting unit 112, and the light emitting unit 112 is implemented. It is the same as the light emitting unit 112 in the transmission device 11 of Example 1. However, the carrier period Tc is (N + 1) times Tf. Where N is a natural number. The receiving device 22 includes a light receiving unit 221 and a demodulating unit 223, and the light receiving unit 221 includes a first light receiving element 1211, a second light receiving element 1212, a first received signal generation unit 2213, and a second received signal generation unit. The first and second light receiving elements 1211, 1212 including 2214 are the same as the first and second light receiving elements 1211, 1212 in the light receiving unit 121 of the first embodiment. The demodulation unit 223 includes a phase signal estimation unit 2231, a frame interpretation unit 2232, and a transmission signal estimation unit 2233.

Hereinafter, input / output and operation of each part different from the conventional one and the first embodiment will be described with reference to FIG.

<Modulation unit 211>
The modulation unit 211 includes a memory, an arithmetic unit, and the like.
Input: The series S (1), S (2), ..., S (J) of the digital transmission signal S (j) are input to the modulation unit 211. The transmission signal S (j) is 1-bit or log2G-bit information, and j is an integer representing the number of the transmission signal.
Output: The modulation unit 211 outputs the series M (1), M (2), ... Of the modulation signal M (i). The modulated signal M (i) is phase information having a value corresponding to the digital transmission signal S (j) and the value specified in the predetermined training sequence. Further, i is a number representing the number of the modulated signal. i is also used as an index representing time.
Operation: The modulation unit 211 generates a series MM (1), MM (2), ..., MM (J) of the modulation signal MM (j) of the input digital transmission signal S (j) (S211). For example, if the value of S (j) is L, the modulation unit 211 generates a modulation signal with MM (j) as 2 * π / G * L. Further, the modulation unit 211 generates the series MT (1), MT (2), ..., MT (JJ) of the modulation signal MT (jj) of the training series. MT (1), MT (2), ..., MT (JJ) are signals that are alternately modulated to the predetermined phases ΘR1 and ΘR2 (0 ° and 180 ° in the example of the figure) as shown in FIG. Is. The modulation unit 211 sets the sequence MT (jj) of JJ modulated signals as M (1), M (2), ..., M (JJ), and sets the sequence MT (1), MM (2) of J modulated signals. ,…, MM (J) is output as M (JJ + 1), M (JJ + 2),…, M (JJ + J). That is, the modulation unit 211 generates the sequences MM and MT of the two modulation signals and then concatenates them to form the modulation signal M, which is the sequence M (1), ..., M (JJ) of the modulation signal M (i). , M (JJ + 1),…, M (JJ + J) is output.

<Light receiving unit 221>
Similar to the first embodiment, the first and second received signal generation units 2213 and 2214 include a sampling element, a memory, an arithmetic unit, and the like. As described above, in the present embodiment, the light receiving unit 221 includes two sets of the light receiving element and the received signal generating unit, but the set of the light receiving element and the received signal generating unit is not limited to two sets.

The operation of the light receiving unit 221 can be generally expressed as follows. The light receiving unit 221 is an optical signal F1 based on a modulation signal M (i) formed by phase-shift keying and connecting a training sequence in which two predetermined values are alternately arranged and a digital transmission signal S (j). Upon receiving (t), F2 (t), ..., the optical signals F1 (t), F2 (t), ... are converted into optical signals F1 (t), F2 (t) at different exposure timings. Multiple received signals B1'(t), B2'(t) corresponding to each of the light receiving elements based on the charge stored in the sampler of the plurality of light receiving elements exposed over a half cycle of, ... ), ... are generated (S221).

Hereinafter, the operation of the light receiving unit 221 will be described in detail on the premise that two sets of the light receiving element and the received signal generation unit are included. Input: The first optical signal F1'(t) and the second optical signal F2'(t) output from the light emitting unit 112 are input to the light receiving unit 221.
Output: From the light receiving unit 221, the sequence B1'(1), B1'(2), ... Of the first received signal B1'(ii) and the sequence B2'(1), of the second received signal B2'(ii), B2'(2), ... is output.
Operation: The first received signal generation unit 2213 measures the intensity of the input first electric signal E1'(t) at each time interval Ts and outputs it as the first received signal B1'(ii) (S2213). Here, the index ii is an index representing the imaging number, and is different from the index i representing the modulation signal number. For example, ii = 1, ..., 6 is set for the optical signal corresponding to the five transmission symbols represented by the indexes i = 1, ..., 5, and a total of 6 imagings (exposures) are assigned. Can be done. When the first light receiving element 1211 is an image sensor, the first received signal generation unit 2213 sums the charge measurement results over a predetermined range Ω, and the sum of the measurement results is the first received signal B1'(ii). Is output as (S2213). Similarly, the second received signal generation unit 2214 measures the intensity of the input second electric signal E2'(t) at each time interval Ts and outputs it as the second received signal B2'(ii) (S2214). .. When the second light receiving element 1212 is an image sensor, the second reception signal generation unit 2214 takes the sum of the charge measurement results over a predetermined range Ω, and the sum of the measurement results is taken as the second reception signal B2'(ii). Output (S2214).

<Demodulation unit 223>
As described above, the demodulation unit 223 includes a phase signal estimation unit 2231, a frame interpretation unit 2232, and a transmission signal estimation unit 2233. The phase signal estimation unit 2231, the frame interpretation unit 2232, and the transmission signal estimation unit 2233 include a memory, an arithmetic unit, and the like.

The operation of the demodulation unit 223 can be generally expressed as follows. The demodulation unit 223 normalizes the values of the received signals when the phase difference between the optical signals F1 (t), F2 (t), ... And the exposure timing is zero, and the received signal values R1, R2, ... Then, the phase of the modulated signal is estimated based on the values of the generated multiple received signals B1'(t), B2'(t), ... and the normalized received signal values R1, R2, ... , Estimates the index of the error frame, which is the frame information at the exposure timing at which the symbols are switched, based on the part of the multiple received signals B1'(t), B2'(t), ... corresponding to the training series. (S223).

Hereinafter, the operation of the demodulation unit 223 will be described in detail on the premise that two sets of the light receiving element and the reception signal generation unit are included.
Input: A sequence of the first received signal B1'(ii) and a sequence of the second received signal B2'(ii) are input from the light receiving unit 221 to the demodulation unit 223.
Output: The demodulation unit 223 outputs the estimation result S'(j).
Operation: The phase signal estimation unit 2231 of the demodulation unit 223 has a relative phase estimation result M'based on the sequence of the first received signal B1'(ii) and the sequence of the second received signal B2'(ii). (ii) is generated and output to the frame interpretation unit 2232 and the transmission signal estimation unit 2233 (S2231).

Specifically, the phase signal estimation unit 2231 receives signals when the exposure timing and the phase difference of the carrier wave are 0 for each of the first received signal B1'(ii) and the second received signal B2'(ii). The values of are held in advance as the reception signal values R1 and R2 for normalization. These normalized received signal values shall be given from the outside in some way or estimated in advance. The phase signal estimation unit 2231 estimates the relative phase of the received signal based on the first received signal B1'(ii) and the second received signal B2'(ii), and the relative phase estimation result M'( ii) Output as.

Normally, the phase signal estimation unit 2231 estimates the phase using a certain number of pairs of B1'(ii) and B2'(ii) (assuming = LL). The number of relative phase estimation results M'(ii) output at this time is also LL. Specifically, the above relative phase estimation can be performed by the following mathematical formula (Equation 4).

However, B1'' (ii) is a value normalized by dividing B1'(ii) by R1, and B2'' (ii) is a value normalized by dividing B2'(ii) by R2.

Next, the frame interpretation unit 2232 of the demodulation unit 223 generates a control signal C'(k) based on the first reception signal B1'(ii) and the second reception signal B2'(ii), and the control signal C'(k) is generated. '(K) is output to the transmission signal estimation unit 2233 (S2322). k is an integer representing the number of the control signal C'(k). It is assumed that the frame interpretation unit 2232 holds in advance the predetermined phase information ΘR1 and ΘR2, the length JJ of the modulation signal sequence of the training sequence, and the length J of the modulation signal sequence of the symbol. The frame interpreter 2232 is based on JJ * (N + 1) / N from the beginning of the series of relative phase estimation results M'(ii) (however, the frequency of imaging is the transmission of the symbol of the original modulated signal). (Assuming that the frequency is (N + 1) / N times), the error frame is detected as follows. The frame interpretation unit 2232 holds the normalized reception signal values R1 and R2, and is appropriately used for the calculation of B1'' (ii) and B2'' (ii).

If B1'' (ii) and B2'' (ii) correspond to the same symbol in the training sequence, then near the locus represented by the square in Figure 12 (B1'' (ii), B2' '(ii)) is plotted. Therefore, of the first JJ * (N + 1) / N (that is, the number corresponding to the training series) B1'' (ii) and B2'' (ii) pairs, the one that is farther from this locus. Top JJ / N pairs (B1'' (ii_1), B2'' (ii_1)), (B1'' (ii_2), B2'' (ii_2)),…, (B1'' (ii_ {JJ) In / N}), B2'' (ii_ {JJ / N})), it is judged that the phase transition of the training series has occurred, and these indexes are regarded as the set of indexes of the error frame.

From the index set of the training series and the index set of the error frame, the frame interpreting unit 2232 has an index corresponding to the phase series corresponding to the symbol, ii ∈ {JJ * (N + 1) / N + 1,JJ. Of * (N + 1) / N + 2,…, JJ * (N + 1) / N + J * (N + 1) / N}, the results of estimating the index set that will be the error frame are combined. , Output as control signal C'(k).

The specific operation of the frame interpretation unit 2232 when the above parameters are set as follows will be described. When JJ = 5, N = 5, J = 20, the training series (B1'' (1), B2'' (1)), (B1'' (2), B2'' (2)) , ..., (B1'' (6), B2'' (6)), the index corresponding to the error frame is 2. At this time, the sequence related to the symbol sequence (B1'' (7), B2'' (7)), (B1'' (8), B2'' (8)),…, (B1'' (30), B2 Of the'' (30)), ..., the index of the error frame can be estimated to be 8, 14, 20, and 26. The frame interpretation unit 2232 sends this set of indexes {1,2,3,4,5,6,8,14,20,26} as the control signal C'(1) to the transmission signal estimation unit 2233.

Next, the transmission signal estimation unit 2233 of the demodulation unit 223 is an index corresponding to the training sequence and the error frame pointed to by the control signal C'(k) in the sequence of the relative phase estimation result M'(ii). The symbol sequence S'(j) is estimated from the sequence obtained by removing the estimation result of (S2232) by using the least squares method or the like as follows (S2232). Specifically, the operation is performed based on the following mathematical formula (Equation 5).

However, the operator gmod (θ, 2π / G)

Means.

[Modification 1]
The above-mentioned Example 1 and Example 2 may be combined. That is, the frame interpreter holds a predetermined set of phases ΘR1 and ΘR2, and refers to the reference phase information MI'(from the set of (B1'(ii), B2'(ii)) corresponding to this set of phases ΘR1 and ΘR2. You may estimate k) by Equation 2 and estimate the index of the error frame from the training sequence and output them to the transmission signal estimation unit.

[Modification 2]
In the second embodiment described above, differential phase shift keying may be used. Since the transmission signal estimation unit demodulates using the difference between adjacent phase signals such as M'(ii) and M'(ii + 1), it is not necessary to hold the reference phase information MI'(k).

[Modification 3]
In the above-described examples and modifications, the number of light receiving elements and the number of received signal generation units are two, but the number may be three or more. In this case as well, by shifting the exposure timing by a quarter of the carrier period Tc in the two light receiving elements whose exposure timings are close to each other, the phase estimation of the first light receiving element and the second light receiving element is performed in the same manner as in Examples 1 and 2. The noise immunity can be increased by performing the process between the second light receiving element and the third light receiving element, between the third light receiving element and the fourth light receiving element, respectively.

[Modification example 4]
In the above-described embodiment and modification, the phase signal estimation unit estimates the phase using Equation 1 (Equation 4), but as the processing in the previous stage, as shown in FIG. 13, the value of the received signal expected in advance. This may be done after mapping to the least squares method or the like.

[Modification 5]
In the above-described embodiment and modification, a series of signal MB (jjj) whose carrier period is sufficiently larger than Tc, JJJ pieces of MB (1), MB (2), ..., MB (JJJ) are combined with other M (j). ) May be output (see FIG. 14). MB (jjj) is called a normalization training series. In the frame interpreting unit, the received signals B1'(ii) and B2'(ii) corresponding to MB (jjj) may be averaged to obtain the normalized received signal values R1 and R2, respectively. This eliminates the need to share the normalization received signal values R1 and R2 in advance.

[Modification 6]
Even when there are a plurality of transmission devices (H), the systems described in the above-described examples and modifications can be applied. In this case, a plurality of received signal generation units and demodulation units of the above-described embodiment and modification may be prepared. In this case, the estimation of the demodulated signal is performed corresponding to each transmitting device.

[Modification 7]
In the above-described embodiment and modification, in addition to the training sequence, a preamble that notifies the start of transmission may be inserted.

[Modification 8]
In the above-described embodiment and modification, the transmission signal estimation unit may be omitted from the configuration inside the demodulation unit. When the transmission signal estimation unit is omitted, the outputs from the receiving device are the relative phase estimation result M', the reference phase information MI'(k), and the control signal C'(k). These pieces of information may be transmitted to another device, and the other device may perform the same processing as the transmission signal estimation unit and acquire the estimation result S'(j).

<Supplement 1>
In visible light communication using an image sensor, it is desirable to reduce the number of images taken per hour as much as possible. Therefore, the relative phase of the transmission signal can be known by taking an image as shown in FIG. 9 using two cameras. Using this, even if the number of images taken per hour is set to be about the same as the number of times symbols are transmitted per hour, communication by phase shift keying can be performed. However, the above method has the following two problems a) and b).
a) The correspondence between the phase of a phase-shift-modulated codeword and the observable relative phase is not trivial. When trying to know the phase of a transmitted signal using the result of imaging as shown in FIG. 9, the reference phase, that is, which phase the phase-shift-modulated codeword corresponds to. Need to know. However, it is not possible to know the reference phase only by using two cameras.
b) The symbols are switched during the exposure time. When imaging is performed as shown in FIG. 9, when imaging is performed at the timing when the symbols are switched, the pixel value does not become the expected value, and the relative phase cannot be obtained.

According to the visible light communication system, the transmitting device, and the receiving device according to the above-described embodiment and the modified example, the modulation unit that inserts and modulates the training sequence MT having a predetermined phase value, the training sequence MT. The frame interpreter that estimates the reference phase information MI'(k) based on it, or the frame interpreter that estimates the index of the error frame based on the training series MT that alternately repeats two predetermined phases, described above. We were able to solve problems a) and b).

<Supplement 2>
The device of the present invention is, for example, as a single hardware entity, an input unit to which a keyboard or the like can be connected, an output unit to which a liquid crystal display or the like can be connected, and a communication device (for example, a communication cable) capable of communicating outside the hardware entity. Communication unit to which can be connected, CPU (Central Processing Unit, cache memory, registers, etc.), RAM and ROM as memory, external storage device as hard hardware, and input, output, and communication units of these , CPU, RAM, ROM, and has a connecting bus so that data can be exchanged between external storage devices. Further, if necessary, a device (drive) or the like capable of reading and writing a recording medium such as a CD-ROM may be provided in the hardware entity. A physical entity equipped with such hardware resources includes a general-purpose computer and the like.

The external storage device of the hardware entity stores the program required to realize the above-mentioned functions and the data required for processing this program (not limited to the external storage device, for example, reading a program). It may be stored in a ROM, which is a dedicated storage device). Further, the data obtained by the processing of these programs is appropriately stored in a RAM, an external storage device, or the like.

In the hardware entity, each program stored in the external storage device (or ROM, etc.) and the data necessary for processing each program are read into the memory as needed, and are appropriately interpreted, executed, and processed by the CPU. .. As a result, the CPU realizes a predetermined function (each configuration requirement represented by the above, ... Department, ... means, etc.).

The present invention is not limited to the above-described embodiment, and can be appropriately modified without departing from the spirit of the present invention. Further, the processes described in the above-described embodiment are not only executed in chronological order according to the order described, but may also be executed in parallel or individually depending on the processing capacity of the device that executes the processes or if necessary. ..

As described above, when the processing function in the hardware entity (device of the present invention) described in the above embodiment is realized by a computer, the processing content of the function that the hardware entity should have is described by a program. Then, by executing this program on the computer, the processing function in the above hardware entity is realized on the computer.

The program describing the processing content can be recorded on a computer-readable recording medium. The computer-readable recording medium may be, for example, a magnetic recording device, an optical disk, a photomagnetic recording medium, a semiconductor memory, or the like. Specifically, for example, a hard disk device, a flexible disk, a magnetic tape, or the like as a magnetic recording device is used as an optical disk, and a DVD (Digital Versatile Disc), a DVD-RAM (Random Access Memory), or a CD-ROM (Compact Disc Read Only) is used as an optical disk. Memory), CD-R (Recordable) / RW (ReWritable), etc., MO (Magneto-Optical disc), etc. as a magneto-optical recording medium, EEP-ROM (Electronically Erasable and Programmable-Read Only Memory), etc. as a semiconductor memory Can be used.

Further, the distribution of this program is performed, for example, by selling, transferring, renting, or the like a portable recording medium such as a DVD or a CD-ROM in which the program is recorded. Further, the program may be stored in the storage device of the server computer, and the program may be distributed by transferring the program from the server computer to another computer via a network.

A computer that executes such a program first stores, for example, a program recorded on a portable recording medium or a program transferred from a server computer in its own storage device. Then, when the process is executed, the computer reads the program stored in its own recording medium and executes the process according to the read program. Further, as another execution form of this program, a computer may read the program directly from a portable recording medium and execute processing according to the program, and further, the program is transferred from the server computer to this computer. Each time, the processing according to the received program may be executed sequentially. In addition, the above processing is executed by a so-called ASP (Application Service Provider) type service that realizes the processing function only by the execution instruction and result acquisition without transferring the program from the server computer to this computer. May be. The program in this embodiment includes information to be used for processing by a computer and equivalent to the program (data that is not a direct command to the computer but has a property of defining the processing of the computer, etc.).

Further, in this form, the hardware entity is configured by executing a predetermined program on the computer, but at least a part of these processing contents may be realized in terms of hardware.

Claims (7)

A training sequence having a predetermined value and a digital transmission signal are phase-shift-modulated and connected to receive an optical signal based on a modulated signal, and the optical signal is subjected to 2 of the optical signal at different exposure timings. A light receiving unit that generates a plurality of received signals corresponding to each of the light receiving elements based on the charge accumulated in the sampler of the plurality of light receiving elements exposed over a fractional cycle.
The value of the received signal when the phase difference between the optical signal and the exposure timing is zero is used as the normalized received signal value, and is based on the generated plurality of received signal values and the normalized received signal value. A receiving device including a demodulation unit that estimates the phase of the modulated signal and estimates reference phase information that is information representing a phase shift between transmission and reception based on the portion of the phase estimation result corresponding to the training sequence. A training series in which two predetermined values are alternately arranged and an optical signal based on a modulation signal formed by phase-shift-modulating and connecting a digital transmission signal are received, and the optical signals are exposed to different exposure timings. A light receiving unit that generates a plurality of received signals corresponding to each of the light receiving elements based on the charges accumulated in the samplers of the plurality of light receiving elements exposed over a half cycle of the optical signal.
The value of the received signal when the phase difference between the optical signal and the exposure timing is zero is used as the normalized received signal value, and is based on the generated plurality of received signal values and the normalized received signal value. A reception including a demodulator that estimates the phase of the modulated signal and estimates the index of the error frame, which is the information of the frame at the exposure timing at which the symbol is switched, based on the portion of the plurality of received signals corresponding to the training sequence. Device. A visible light communication system that includes a transmitter and a receiver.
The transmitter is
A modulation unit that generates a modulation signal formed by phase-shifting and connecting a training sequence having a predetermined value and a digital transmission signal, and a modulation unit.
A light emitting unit that outputs an optical signal based on the modulated signal is included.
The receiving device is
A plurality of received signals corresponding to each of the light receiving elements are based on the charges accumulated in the samplers of the plurality of light receiving elements that expose the optical signals to the optical signals at different exposure timings over a half cycle of the light signals. And the light receiving part that generates
The value of the received signal when the phase difference between the optical signal and the exposure timing is zero is used as the normalized received signal value, and is based on the generated plurality of received signal values and the normalized received signal value. Visible light communication including a demodulator that estimates the phase of the modulated signal and estimates reference phase information that is information representing the phase shift between transmission and reception based on the portion of the phase estimation result corresponding to the training sequence. system. A visible light communication system that includes a transmitter and a receiver.
The transmitter is
A modulation unit that generates a modulation signal formed by phase-shifting and connecting a training series in which two predetermined values are alternately arranged and a digital transmission signal, and a modulation unit.
A light emitting unit that outputs an optical signal based on the modulated signal is included.
The receiving device is
A plurality of received signals corresponding to each of the light receiving elements are based on the charges accumulated in the samplers of the plurality of light receiving elements that expose the optical signals to the optical signals at different exposure timings over a half cycle of the light signals. And the light receiving part that generates
The value of the received signal when the phase difference between the optical signal and the exposure timing is zero is used as the normalized received signal value, and is based on the generated plurality of received signal values and the normalized received signal value. Visible including a demodulator that estimates the phase of the modulated signal and estimates the index of the error frame, which is the information of the frame at the exposure timing at which the symbol is switched, based on the portion of the plurality of received signals corresponding to the training sequence. Optical communication system. It is a receiving method executed by the receiving device.
A training sequence having a predetermined value and a digital transmission signal are phase-shift-modulated and connected to receive an optical signal based on a modulated signal, and the optical signal is subjected to 2 of the optical signal at different exposure timings. A step of generating a plurality of received signals corresponding to each of the light receiving elements based on the charge accumulated in the sampler of the plurality of light receiving elements exposed over a fractional cycle, and a step of generating a plurality of received signals corresponding to each of the light receiving elements.
The value of the received signal when the phase difference between the optical signal and the exposure timing is zero is used as the normalized received signal value, and is based on the generated plurality of received signal values and the normalized received signal value. A receiving method including a step of estimating the phase of the modulated signal and estimating reference phase information which is information representing a phase shift between transmission and reception based on the portion of the phase estimation result corresponding to the training sequence. It is a receiving method executed by the receiving device.
A training series in which two predetermined values are alternately arranged and an optical signal based on a modulation signal formed by phase-shift-modulating and connecting a digital transmission signal are received, and different exposure timings are applied to the optical signal. A step of generating a plurality of received signals corresponding to each of the light receiving elements based on the charges accumulated in the samplers of the plurality of light receiving elements exposed over a half cycle of the optical signal.
The value of the received signal when the phase difference between the optical signal and the exposure timing is zero is used as the normalized received signal value, and is based on the generated plurality of received signal values and the normalized received signal value. A reception method including a step of estimating the phase of the modulated signal and estimating the index of the error frame, which is the information of the frame at the exposure timing at which the symbol is switched, based on the portion of the plurality of received signals corresponding to the training sequence. .. A program that causes a computer to function as the receiving device according to claim 1 or 2.

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