JP6922795B2 - Receiver, 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. 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 and propagation delay, F (t) and F'(t) are described separately here. .. 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 converts the optical signal based on the modulation signal obtained by phase-shift keying the digital transmission signal into the charge stored in the samplers of a plurality of light receiving elements that are exposed at different exposure timings for half a cycle of the optical signal. Based on this, a plurality of received signals corresponding to each of the light receiving elements are generated. 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. Estimate the phase of the modulated signal.

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 block diagram which shows the structure of the visible light communication system 3 of Example 3. FIG. The sequence diagram which shows the operation of the visible light communication system 3 of Example 3. FIG. The block diagram which shows the structure of the visible light communication system 4 of Example 4. FIG. The sequence diagram which shows the operation of the visible light communication system 4 of Example 4. 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 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.

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. In this embodiment, it is assumed that the modulation method is binary phase shift keying and the exposure time τ is Tc / 2. Further, in this embodiment, Tf matches the symbol rate. For example, if 1000 bit / s communication is required, Tf = 1/1000. Also, by setting Ts to 1/1000, the time index i can be shared between transmission and reception. The carrier period Tc is usually set to an integral multiple of Tf. Further, in this embodiment, the exposure time τ is half of Tc.

As shown in the figure, the visible light communication system 1 of this embodiment includes a transmission device 91 and a reception device 12, and the transmission device 91 is the same as the transmission device 91 in the conventional visible light communication system 9. 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 and a transmission signal estimation unit 1232.

Hereinafter, input / output and operation of each part different from the conventional ones will be described with reference to FIG.
<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 converts the digital transmission signal S (i) into optical signals F1 (t), F2 (t), ... Based on the modulation signal M (i) phase-shift-modulated at different exposure timings. Multiple received signals B1 corresponding to each of the light receiving elements based on the charge stored in the samplers of the plurality of light receiving elements exposed over a half cycle of F1 (t), F2 (t), ... Generate'(t), B2'(t), ... (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 912 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. 13, 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. 13, 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 and a transmission signal estimation unit 1232. The phase signal estimation unit 1231 includes a memory, an arithmetic unit, and the like. Further, the reference phase information MI'is stored as an internal state in the memory of the demodulation unit 123 (described later).

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 generated values of the plurality of received signals and the normalized received signal values R1, R2, ... (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'(i).
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 (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 normalization received signal values R1 and R2 (see FIG. 14, and the luminance 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) as shown in FIG. 13, and determines the relative phase of the relative phase. Output as estimation result M'(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.

The transmission signal estimation unit 1232 of the demodulation unit 123 estimates the series S'(i) of symbols 0 or 1 from the series of relative phase estimation results M'(i) using the least squares method as shown below. (S1232). Specifically, the operation is performed based on the following mathematical formula (Equation 2).

However, the operator gmod (θ, π)

Means. Since M'(i) has only relative phase information as described above, the transmission signal estimation unit 1232 internally holds the reference phase information MI'(information indicating the phase shift between transmission and reception). There is a need. MI'holds the phase observed when the sign S (i) is 0. For example, if MI'is 0 and M'(1) = 0, M'(2) = π, M'(3) = π, M'(4) = π ... 1232 outputs the series S'(1) = 0, S'(2) = 1, S'(3) = 1, S'(4) = 1 ... If MI'is π, then M'(1) = 0, M'(2) = π, M'(3) = π, M'(4) = π ..., then the transmission signal estimation unit 1232 The series S'(1) = 1, S'(2) = 0, S'(3) = 0, S'(4) = 0 ... Is output.

Hereinafter, the configuration of the visible light communication system of the second embodiment will be described with reference to FIG. 7. In this embodiment, it is assumed that the modulation method is differential binary phase shift keying (DBPSK) and the exposure time τ = Tc / 2. As shown in the figure, the visible light communication system 2 of the present 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 912, and the light emitting unit 912 is a conventional unit. It is the same as the light emitting unit 912 in the transmission device 91. The receiving device 22 includes a light receiving unit 121 and a demodulating unit 223, and the light receiving unit 121 is the same as the light receiving unit 121 in the receiving device 12 of the first embodiment. The demodulation unit 223 includes a phase signal estimation unit 1231 and a transmission signal estimation unit 2232, and the phase signal estimation unit 1231 is the same as the phase signal estimation unit 1231 in the receiving device 12 of the first embodiment. 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. The internal state MI (i) is stored in the memory of the modulation unit 211. MI (i) is 0 degree or π degree phase information.
Input: The series S (1), S (2), ... Of the digital transmission signal S (i) are input to the modulation unit 211. 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 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 of 0 degree or π degree. In addition, i is also used as an index representing time.
Operation: If the digital transmission signal S (i) is 0 and the internal state MI (i-1) is 0, the modulation unit 211 generates a modulated signal with M (i) set to 0, and the internal state MI (i). Is set to 0. Further, if the digital transmission signal S (i) is 1 and the internal state MI (i-1) is 0, the modulation unit 211 generates a modulation signal with M (i) as π, and the internal state MI (i). Let be π. Further, if the digital transmission signal S (i) is 0 and the internal state MI (i-1) is π, the modulation unit 211 generates a modulated signal with M (i) as π, and the internal state MI (i) ) Is π. Further, if the digital transmission signal S (i) is 1 and the internal state MI (i-1) is π, the modulation unit 211 generates a modulated signal with M (i) set to 0, and the internal state MI (i). Is 0 (S211).

For example, in the modulation unit 211, the sequence of digital transmission signals is S (1) = 0, S (2) = 1, S (3) = 1, S (4) = 1, ..., And the initial internal state MI ( When 0) is 0, a modulated signal is generated as M (1) = 0, M (2) = π, M (3) = 0, M (4) = π, ..., and the internal state of each index is generated. Let MI (1) = 0, MI (2) = π, MI (3) = 0, M (4) = π, ...

<Demodulation unit 223>
The demodulation unit 223 includes a memory, an arithmetic unit, and the like. The internal state MI'(i) is stored in the memory of the demodulation unit 223. MI'(i) represents the phase information estimated at the previous index (i-1) (described later).
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 223.
Output: From the demodulation unit 223, the symbol sequence S'(i) (estimation result) is output.
Operation: The transmission signal estimation unit 2232 of the demodulation unit 223 receives the sequence of the relative phase estimation result M'(i) and outputs the symbol sequence S'(i) (S2232). Further, the transmission signal estimation unit 2232 has an internal state MI'(i). Specifically, the transmission signal estimation unit 2232 selects a series S'(i) of symbols 0 or 1 from the series of relative phase estimation results M'(i) using the least squares method as shown below. presume. Specifically, the operation is performed based on the following mathematical formula (Equation 3).

MI'(i) records the phase information of the phase information M'(i-1) estimated at the previous index (i-1). If the absolute value of the difference between M'(i) and MI'(i) is less than π, 0 is output, and if it is π or more, 1 is output. For example, if MI'(0) is 0, then M'(1) = 0, M'(2) = π, M'(3) = π, M'(4) = π, ... The transmission signal estimation unit 2232 outputs the series S'(1) = 0, S'(2) = 1, S'(3) = 0, S'(4) = 1, ... If MI'(0) is π, then M'(1) = 0, M'(2) = π, M'(3) = π, M'(4) = π, ... The estimation unit 2232 outputs the series S'(1) = 1, S'(2) = 1, S'(3) = 0, S'(4) = 0, ...

Hereinafter, the configuration of the visible light communication system of the third embodiment will be described with reference to FIG. In this embodiment, it is assumed that the modulation method is multi-value phase shift keying (M-PSK) and the exposure time τ = Tc / 2. As shown in the figure, the visible light communication system 3 of this embodiment includes a transmitting device 31 and a receiving device 32, the transmitting device 31 includes a modulation unit 311 and a light emitting unit 912, and the light emitting unit 912 is a conventional unit. It is the same as the light emitting unit 912 in the transmission device 91. The receiving device 32 includes a light receiving unit 121 and a demodulating unit 323, and the light receiving unit 121 is the same as the light receiving unit 121 in the receiving device 12 of the first embodiment. The demodulation unit 323 includes a phase signal estimation unit 1231 and a transmission signal estimation unit 3232, and the phase signal estimation unit 1231 is the same as the phase signal estimation unit 1231 in the receiving device 12 of the first embodiment. 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 311>
The modulation unit 311 includes a memory, an arithmetic unit, and the like. The gradation information G is stored in the memory of the modulation unit 311.
Input: The series S (1), S (2), ... Of the digital transmission signal S (i) are input to the modulation unit 311. The digital transmission signal S (i) is log2 (G) bit information, and i is an integer representing the number of the digital transmission signal.
Output: The modulation unit 311 outputs the series M (1), M (2), ... Of the modulation signal M (i). The modulated signal M (i) is phase information having values of 0 degrees, 2 * π / G * 1, 2 * π / G * 2, ... 2 * π / G * (G-1). In addition, i is also used as an index representing time.
Operation: The modulation unit 311 generates a sequence of modulation signals of the sequence M (1), M (2), ... Of the sequence of the modulation signal M (i) of the input digital transmission signal S (i). If S (i) is L, the modulation unit 311 generates a modulation signal with M (i) as 2 * π / G * L (S311).

For example, in the modulation unit 311, when G = 4, the sequence of digital transmission signals is S (1) = 0, S (2) = 3, S (3) = 2, S (4) = 1, ... In this case, a modulated signal is generated with M (1) = 0, M (2) = 3 * π / 2, M (3) = π, M (4) = π / 2, and so on.

<Demodulation unit 323>
The demodulation unit 323 includes a memory, an arithmetic unit, and the like. The reference phase information MI'is stored as an internal state in the memory of the demodulation unit 323.
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 323.
Output: From the demodulation unit 323, the symbol sequence S'(i) (estimation result) is output.
Operation: The transmission signal estimation unit 3232 of the demodulation unit 323 receives the sequence of the relative phase estimation result M'(i) and outputs the symbol sequence S'(i) (S3232). Further, the transmission signal estimation unit 3232 has the reference phase information MI'as an internal state. Specifically, the transmission signal estimation unit 3232 uses the least squares method or the like as shown below from the sequence of the relative phase estimation result M'(i) to sequence S'(i) of symbols from 0 to G-1. ) Is estimated. Specifically, the operation is performed based on the following mathematical formula (Equation 4).

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

Means. Since M'(i) has only relative phase information as described above, the transmission signal estimation unit 3232 needs to separately hold the reference phase information MI'internally. MI'holds the phase observed when the sign S (i) is 0. For example, if MI'is 0, then M'(1) = 0, M'(2) = 3 * π / 2, M'(3) = π, M'(4) = π / 2, ... If so, the transmission signal estimation unit 3232 outputs the series S'(1) = 0, S'(2) = 3, S'(3) = 2, S'(4) = 1, ... If MI'is π, then M'(1) = 0, M'(2) = 3 * π / 2, M'(3) = π, M'(4) = π / 2, ... , Transmission signal estimation unit 3232 outputs series S'(1) = 2, S'(2) = 1, S'(3) = 0, S'(4) = 3, ...

Hereinafter, the configuration of the visible light communication system of the fourth embodiment will be described with reference to FIG. In this embodiment, it is assumed that the modulation method is differential multi-value phase shift keying (DM-PSK) and the exposure time τ = Tc / 2. As shown in the figure, the visible light communication system 4 of this embodiment includes a transmitting device 41 and a receiving device 42, the transmitting device 41 includes a modulation unit 411 and a light emitting unit 912, and the light emitting unit 912 is a conventional unit. It is the same as the light emitting unit 912 in the transmission device 91. The receiving device 42 includes a light receiving unit 121 and a demodulating unit 423, and the light receiving unit 121 is the same as the light receiving unit 121 in the receiving device 12 of the first embodiment. The demodulation unit 423 includes a phase signal estimation unit 1231 and a transmission signal estimation unit 4232, and the phase signal estimation unit 1231 is the same as the phase signal estimation unit 1231 in the receiving device 12 of the first embodiment. 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 411>
The modulation unit 411 includes a memory, an arithmetic unit, and the like. The gradation information G is stored in the memory of the modulation unit 411. Further, the internal state MI (i) is stored in the memory of the modulation unit 411. MI (i) is the phase information of 0 degree, 2 * π / G * 1, 2 * π / G * 2, ... 2 * π / G * (G-1).
Input: The series S (1), S (2), ... Of the digital transmission signal S (i) are input to the modulation unit 411. The digital transmission signal S (i) is log2 (G) bit information, and i is an integer representing the number of the digital transmission signal.
Output: The modulation unit 411 outputs the series M (1), M (2), ... Of the modulation signal M (i). The modulated signal M (i) is phase information having values of 0 degrees, 2 * π / G * 1, 2 * π / G * 2, ... 2 * π / G * (G-1). In addition, i is also used as an index representing time.
Operation: The modulation unit 411 generates a sequence of modulation signals of the sequence M (1), M (2), ... Of the sequence of the modulation signal M (i) of the input digital transmission signal S (i). If S (i) is L and MI (i) is L', the modulation signal M (i) is generated as 2 * π / G * L'+ 2 * π / G * L. However, if 2 * π / G * L'+ 2 * π / G * L is larger than 2 * π, the modulation signal M is set as 2 * π / G * L'+ 2 * π / G * L-2 * π. (i) is generated (S411).

For example, in the modulation unit 411, when G = 4 and MI (0) = π / 2, the sequence of digital transmission signals is S (1) = 0, S (2) = 3, S (3) = 2, S. If (4) = 1, ..., M (1) = π / 2, M (2) = 0, M (3) = π, M (4) = 3 * π / 2, ... To generate.

<Demodulation unit 423>
The demodulation unit 423 includes a memory, an arithmetic unit, and the like. The phase information MI'(i) is stored as an internal state in the memory of the demodulation unit 423.
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 423.
Output: From the demodulation unit 423, the symbol sequence S'(i) (estimation result) is output.
Operation: The transmission signal estimation unit 4232 of the demodulation unit 423 receives the sequence of the relative phase estimation result M'(i) and outputs the symbol sequence S'(i) (S4322). Further, the transmission signal estimation unit 4232 has the phase information MI'(i) as an internal state. Specifically, the transmission signal estimation unit 4232 uses the least squares method or the like as shown below from the sequence of the relative phase estimation result M'(i) to sequence S'(i) of symbols from 0 to G-1. ) Is estimated. Specifically, the operation is performed based on the following mathematical formula (Equation 5).

MI'(i) records the phase information of M'(i-1). For example, if MI'(0) is π / 2, M'(1) = 0, M'(2) = π, M'(3) = 3 * π / 2, M'(4) = π If / 2, ..., the transmission signal estimation unit 4232 outputs the series S'(1) = 3, S'(2) = 2, S'(3) = 1, S'(4) = 2, ... do.

[Modification 1]
In Examples 1 to 4, 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 to 4. 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 2]
In Examples 1 to 4, the phase signal estimation unit 1231 estimated the phase using Equation 1, but as the processing in the previous stage, as shown in FIG. 15, the value of the received signal expected in advance is subjected to the least squares method or the like. You may do this after mapping.

[Modification 3]
Even when there are a plurality of transmission devices (H), the system described in Examples 1 to 4 can be applied. In this case, a plurality of received signal generation units and demodulation units of Examples 1 to 4 may be prepared. In this case, the estimation of the demodulated signal is performed corresponding to each transmitting device.

<Supplement>
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 (8)

Based on the charge stored in the sampler of a plurality of light receiving elements that expose the digital transmission signal to the optical signal based on the modulation signal phase-shift-modulated at different exposure timings for half the cycle of the optical signal. A light receiving unit that generates 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 receiver including a demodulator that estimates the phase of the modulated signal. The receiving device according to claim 1.
The demodulation unit
A receiving device that estimates the digital transmission signal based on the estimated phase and reference phase information representing a phase shift between transmission and reception. The receiving device according to claim 1.
The phase shift keying is a differential binary phase shift keying.
The demodulation unit
A receiving device that estimates the digital transmission signal based on the estimated phase and the information of the phase estimated at the previous index. The receiving device according to claim 2.
A receiving device in which the phase shift keying is multi-valued phase shift keying. The receiving device according to claim 1.
The phase shift keying is a differential multi-value phase shift keying.
The demodulation unit
A receiving device that estimates the digital transmission signal based on the estimated phase and the information of the phase estimated at the previous index. The receiving device according to any one of claims 1 to 5.
A receiving device in which the exposure timings of two light receiving elements whose exposure timings are close to each other are shifted by a quarter of the period of the optical signal among the plurality of light receiving elements. It is a receiving method executed by the receiving device.
Based on the charge stored in the sampler of a plurality of light receiving elements that expose the digital transmission signal to the optical signal based on the modulation signal phase-shift-modulated at different exposure timings for half the cycle of the optical signal. A step of generating a plurality of received signals corresponding to each of the light receiving elements, and
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 comprising the step of estimating the phase of the modulated signal. A program that causes a computer to function as the receiving device according to any one of claims 1 to 6.

Images