JP2019161484A - Receiving device, receiving method, and program - Google Patents

Abstract

To provide a receiving device capable of receiving a phase shift keying signal without sacrificing the number of pixels obtained by one sampling.SOLUTION: A receiving device includes a light-receiving unit that generates a plurality of reception signals respectively corresponding to light receiving elements on the basis of charges accumulated in samplers of a plurality of light receiving elements that expose an optical signal based on modulation signal obtained by phase shift keying of a digital transmission signal for one-half cycle of the optical signal at different exposure timings, and a demodulation unit that estimates the phase of the modulation signal on the basis of the generated multiple received signal values and a normalized received signal value by setting the value of the received signal when the phase difference between the optical signal and the exposure timing is zero at the normalized received signal value.SELECTED DRAWING: Figure 5

Description

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

  In recent years, visible light sources have been used not only for illumination purposes for obtaining light but also for communication purposes. This is due to the widespread use of light emitting diodes (LEDs) as visible light sources. The light emitting diodes are superior to conventional visible light sources in terms of their lifetime, size, and power consumption, although the amount of light emitted per element does not reach that of conventional visible light sources such as incandescent bulbs and fluorescent lamps. 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 characteristics described above, in recent years, research and development for use in signal transmission using flashing of visible light as well as lighting applications for obtaining light have been performed.

  For example, Non-Patent Document 1 discloses that communication is performed by superimposing a signal on a home lighting apparatus using a light emitting diode.

  In addition, since visible light is not subject to the regulations of the Radio Law at present, there is no band or power limitation, and these can be increased. Non-Patent Document 2 discloses that this is used to use a light emitting diode exclusively for communication. 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 that is an array thereof is used as a receiver. In a photodetector, signals can usually be obtained continuously. On the other hand, the image sensor can acquire signals from a large number of photodetectors at a time, but normally it can only acquire signals sampled at the period Ts due to its nature. Hereinafter, it is assumed that an image sensor is mainly used as a light receiving device.

  FIG. 1 shows the nature of signals used in visible light communication. First, a digital transmission signal S (i) (also referred to as a transmission symbol) is expressed by converting it into a phase value to obtain a modulation signal M (i). Such a modulation method is called phase shift modulation (phase shift keying). For example, when S (i) is expressed as a binary value, it is converted into a phase value such as 0 → 0, 1 → π (binary phase shift keying, BPSK). Here, i is an index indicating time. Next, the phase of the rectangular wave having the carrier frequency 1 / Tc is changed according to the modulation signal M (i), and an 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 an optical signal F (t). The output time of E (t) corresponding to the time index i is set from the time iTf−Tf / 2 to the time iTf + Tf / 2 based on the time iTf obtained by adding a certain delay from the time indicated by the index i. As shown in FIG. 1, the time indicated by the index i has a time width Tf.

  In a 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). Thereafter, the phase signal M ′ (i) is estimated from E ′ (t). Ideally F (t) = F '(t), but it may change depending on the performance of the image sensor and propagation delay, so here we describe F (t) and F' (t) separately. . It is assumed that approximately F (t + TL) = F ′ (t). TL represents 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 blinking of the light emitting element is received by the image sensor. Assume that the blinking of the transmitter (light emitting element) forms an image in the region Ω on the image sensor. The receiver views the total output value of all the photodetectors in the region Ω as the received signal from the transmitter.

  When transmitting information on a communication channel, it is common to encode the original information in some form. A minimum unit signal constituting encoded information is called a symbol. In a digital communication channel, it is important to detect a symbol clock (a time width used for transmitting one symbol) and a phase. 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, in general, there is no means for sharing the same oscillator between the receiver and the transmitter, and there is a possibility that synchronization will always shift.

  In order to perform symbol timing synchronization, it is necessary to use a symbol timing recovery circuit as in Non-Patent Document 3, for example. This detects the phase difference between two input signals and applies feedback control to synchronize the phases. One of the two signals is an input from an oscillator, and the other is a signal to be synchronized. When a photodetector is used as a receiver, it is easy to use a symbol timing recovery circuit because signals can be obtained continuously. On the other hand, when an image sensor is used, a signal that can be used for reception processing is a sampled signal, and thus becomes a discrete-time signal. In this case, a certain sampling frequency is required to perform symbol timing synchronization by the symbol timing recovery 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, a conventional visible light communication system 9 includes a transmission device 91 and a reception device 92. The transmission device 91 includes a modulation unit 911 and a light emission unit 912. The light emission unit 912 includes a light emission signal control unit. 9121 and a light emitting element 9122 are included. The receiving device 92 includes a light receiving unit 921, a synchronizing unit 922, and a demodulating unit 923. The light receiving unit 921 includes a light receiving element 9211 and a received signal generating unit 9212. The synchronizing unit 922 includes a clock element 9221, a symbol, The timing recovery circuit 9222 is included, and the demodulation unit 923 includes a phase signal estimation unit 9231 and a transmission signal estimation unit 9232. Hereinafter, input / output and operation of each unit will be described with reference to FIG.

<Modulation unit 911>
Input: Modulation unit 911 receives a sequence S (1), S (2),... Of digital transmission signal S (i). The digital transmission signal S (i) is 1-bit information, and i is an integer representing the number of the digital transmission signal.
Output: Modulation section 911 outputs a sequence M (1), M (2),... Of modulated signal M (i). The modulation signal M (i) is phase information having a value of 0 or π. I is also used as an index representing time.
Operation: The modulation unit 911 modulates the sequence S (1), S (2),... Of the input digital transmission signal S (i) to modulate the sequence 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,. The results are 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 the light emission signal control unit 9121 and the light emitting element 9122. The light emitting element 9122 is, for example, an LED.
Input: A sequence M (1), M (2),... Of the modulation signal M (i) is input to the light emitting unit 912.
Output: The light 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 emission unit 912 is between time iTf−Tf / 2 and time iTf + Tf / 2 after a predetermined time Tf has elapsed. , A rectangular wave (electrical signal) having a frequency of 1 / Tc and a phase of 0 is generated and applied to the light emitting element 9122. When the input modulation signal M (i) is π, a predetermined value is obtained from time iTf−Tf / 2. A rectangular wave (electric signal) having a frequency 1 / Tc and a phase π is applied to the light emitting element 9122 until the time iTf + Tf / 2 when the time Tf has passed (S9121). The light emitting element 9122 emits light according to the electrical signal given from the light emission signal control unit 9121 (S9122). As a result, an optical signal is output from the light emitting unit 912. However, the electric signal generated by the light emission 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 the light receiving element 9211 and the reception signal generating unit 9212. The light receiving element 9211 is, for example, a photo detector. 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 photodetectors are arranged in a grid pattern.
Input: The light signal F (t) output from the light emitting unit 912 is input to the light receiving unit 921.
Output: The light receiving unit 921 outputs a temporally continuous reception signal E ″ (t).
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 reception signal generating 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).

<Synchronizer 922>
As described above, the synchronization unit 922 includes the clock element 9221 and the symbol timing recovery circuit 9222.
Input: The reception signal E ″ (t) output from the light receiving unit 921 is input to the synchronization unit 922.
Output: The synchronization unit 922 outputs phase information and frequency information.
Operation: The clock element 9221 of the synchronization unit 922 outputs clock information (S9221). The symbol timing recovery 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. The phase is synchronized, and phase information and frequency information are output (S9222).

<Demodulation unit 923>
As described above, demodulation section 923 includes phase signal estimation section 9231 and transmission signal estimation section 9232. The phase signal estimation unit 9231 and the transmission signal estimation unit 9232 include a memory, an arithmetic device, and the like.
Input: The demodulator 923 receives the received signal E ″ (t) output from the light receiver 921 and the phase information and frequency information output from the synchronizer 922.
Output: From the demodulator 923, the estimation result S ′ (i) is output.
Operation: The phase signal estimation unit 9231 of the demodulation unit 923 generates the phase signal M ′ (i) using the received signal E ″ (t), the phase information, and the frequency information (S9231). The transmission signal estimation unit 9232 of the demodulation unit 923 estimates a digital transmission signal based on the phase signal M ′ (i) and outputs an estimation result S ′ (i) (S9232).

Toshihiko Kobuchi, Yuichi Tanaka, Masao Nakagawa, “Fusion System of White LED Lighting Signal Transmission and Power Line Signal Transmission”, IEICE Technical Report, The Institute of Electronics, Information and Communication Engineers, March 12, 2002, Vol.101, No.726, pp.99-104 Masanori Ishida, Shinichiro Haruyama, Masao Nakagawa, “Examination of Communication Speed Limit in Parallel Visible Light Wireless Communication System”, IEICE Technical Report CS Communication System, The Institute of Electronics, Information and Communication Engineers, 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 a frequency that is at least twice as large as the carrier frequency. On the other hand, in an image sensor, generally, the upper limit of the product of the number of pixels obtained by one imaging and the number of imaging per time, that is, the sampling frequency, is restricted to be constant. Therefore, when a large sampling frequency is used for demodulation using an image sensor as the light receiving unit of the system as described above, the number of pixels obtained by one sampling must be sacrificed.

  Accordingly, an object of the present invention is to provide a receiving apparatus that can receive a phase shift keying signal without sacrificing the number of pixels obtained by one sampling.

  The receiving apparatus of the present invention includes a light receiving unit and a demodulating unit. The light receiving unit converts the charges accumulated in the samplers of the plurality of light receiving elements that are exposed to the optical signal based on the modulation signal obtained by phase shift modulation of the digital transmission signal at half the period of the optical signal at different exposure timings. Based on this, a plurality of reception 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 based on the generated multiple received signal values and the normalized received signal value Estimate the phase of the modulation signal.

  According to the receiving apparatus of the present invention, it is possible to receive a phase shift keying signal without sacrificing the number of pixels obtained by one sampling.

The figure which shows the example which converted the digital transmission signal into the modulation signal, the electric signal, and the optical signal sequentially. The figure explaining a mode that the image sensor light-receives blinking of a light emitting element. The block diagram which shows the structure of the conventional visible light communication system 9. FIG. The sequence diagram which shows operation | movement of the conventional visible light communication system 9. FIG. 1 is a block diagram illustrating a configuration of a visible light communication system 1 according to a first embodiment. FIG. 3 is a sequence diagram illustrating an operation of the visible light communication system 1 according to the first embodiment. FIG. 3 is a block diagram illustrating a configuration of a visible light communication system 2 according to a second embodiment. FIG. 6 is a sequence diagram illustrating an operation of the visible light communication system 2 according to the second embodiment. FIG. 4 is a block diagram illustrating a configuration of a visible light communication system 3 according to a third embodiment. FIG. 10 is a sequence diagram illustrating an operation of the visible light communication system 3 according to the third embodiment. FIG. 6 is a block diagram illustrating a configuration of a visible light communication system 4 according to a fourth embodiment. FIG. 10 is a sequence diagram illustrating an operation of the visible light communication system 4 according to the fourth embodiment. The figure which shows the difference in the exposure timing of a 1st light receiving element and a 2nd light receiving element. The figure which shows the example of the change of the pixel value observed by the 1st light receiving element accompanying the change of a relative phase. The figure which shows the theoretical locus | trajectory which made the pixel value by a 1st light receiving element the horizontal axis and the pixel value by a 2nd light receiving element made the vertical axis | shaft.

  Hereinafter, embodiments of the present invention will be described in detail. In addition, the same number is attached | subjected to the structure part which has the same function, and duplication description is abbreviate | omitted.

  Hereinafter, the configuration of the visible light communication system according to 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. 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 cycle Tc is normally set to an integer multiple of Tf. In this embodiment, the exposure time τ is half of Tc.

  As shown in the figure, the visible light communication system 1 of the present 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. The light receiving unit 121 includes a first light receiving element 1211, a second light receiving element 1212, a first received signal generating unit 1213, and a second received signal generating unit. The demodulator 123 includes a phase signal estimator 1231 and a transmission signal estimator 1232.

Hereinafter, input / output and operation of each part different from the conventional one will be described with reference to FIG.
<Light receiving unit 121>
As described above, in this embodiment, the light receiving unit 121 includes two sets of light receiving elements and reception signal generation units, but the number of sets of light receiving elements and reception signal generation units is not limited to two. When the operation of the light receiving unit 121 is generally expressed, it can be expressed as follows. The light receiving unit 121 converts the optical signal F1 (t), F2 (t),... Based on the modulation signal M (i) obtained by phase shift modulation of the digital transmission signal S (i) into optical signals at different exposure timings. A plurality of received signals B1 corresponding to each of the light receiving elements based on the charges accumulated in the samplers of the plurality of light receiving elements that are exposed over a half period of F1 (t), F2 (t),. '(t), B2' (t), ... are generated (S121).

Hereinafter, the operation of the light receiving unit 121 will be described in detail with reference to FIG. Similar to the prior art, the first and second light receiving elements 1211 and 1212 are, for example, photodetectors. Further, an optical lens may be provided in front of the first and second light receiving elements 1211 and 1212. Furthermore, the first and second light receiving elements 1211 and 1212 may be image sensors 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, a calculation device, 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 reception signal B1 ′ (i) and the sequence B2 ′ (1), B2 ′ (1) of the second reception signal B2 ′ (i), B2 '(2), ... is output.
Operation: The first light receiving element 1211 of the light receiving unit 121 outputs a first electric signal E1 ′ (t) corresponding to the input first optical signal F1 ′ (t) to the first received signal generating unit 1213. (S1211). In the case where the first light receiving element 1211 is an image sensor, specifically, as shown in FIG. 13, each photodetector has accumulated in the sampler from time TI + iTs-Ts / 2 to TI + iTs-Ts / 2 + τ. Measure the charge. Here, TI is a relative phase (offset), iTs is a time corresponding to the center of the i-th symbol, iTs-Ts / 2 is a time corresponding to the head of the i-th symbol, and τ is an exposure time.

  Similarly, the second light receiving element 1212 of the light receiving unit 121 outputs a second electric signal E2 ′ (t) corresponding to the input second optical signal F2 ′ (t) to the second received signal generating unit 1214. (S1212). In the case where the second light receiving element 1212 is an image sensor, specifically, as shown in FIG. 13, each photodetector detects from time TI + iTs-Ts / 2 + Tc / 4 to TI + iTs-Ts / 2 + τ + Tc / 4. Measure the charge that has accumulated in the sampler. Tc / 4 represents a difference in exposure timing between the first light receiving element 1211 and the second light receiving element 1212 and is a quarter of the carrier wave period Tc.

  The first reception 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 reception signal B1 ′ (i) (S1213). When the first light receiving element 1211 is an image sensor, the first reception signal generation unit 1213 calculates the sum of the measurement results of charges over a predetermined range Ω, and calculates the sum of the measurement results as the first reception signal B1 ′ (i). (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 the second received signal B2 ′ (i) as a second received signal B2 ′ (i) (S1214). . When the second light receiving element 1212 is an image sensor, the second reception signal generation unit 1214 calculates the sum of the charge measurement results over a predetermined range Ω, and the sum of the measurement results is used as the second reception signal B2 ′ (i). It outputs (S1214).

<Demodulation unit 123>
As described above, the demodulator 123 includes the phase signal estimator 1231 and the transmission signal estimator 1232. The phase signal estimation unit 1231 includes a memory, an arithmetic device, and the like. Further, the reference phase information MI ′ is stored in the memory of the demodulation unit 123 as an internal state (described later).

When the operation of the demodulator 123 is generally expressed, it can be expressed as follows. The demodulator 123 normalizes the received signal values R1, R2,... When the phase difference between the optical signals F1 (t), F2 (t),... And the exposure timing is zero. Then, the phase of the modulation signal is estimated based on the generated values of the plurality of reception signals and the normalization reception signal values R1, R2,... (S123). Hereinafter, the operation of the demodulation unit 123 will be described in detail with reference to FIG. 6 on the assumption that two sets of light receiving elements and reception signal generation units are included.
Input: The sequence of the first reception signal B1 ′ (i) and the sequence of the second reception signal B2 ′ (i) are input from the light receiving unit 121 to the demodulation unit 123.
Output: The estimation result S ′ (i) is output from the demodulation unit 123.
Operation: The phase signal estimating unit 1231 of the demodulating unit 123 performs the 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 the received signal when the phase difference between the exposure timing and the carrier wave is 0 for each of the first received signal B1 ′ (i) and the second received signal B2 ′ (i). Are previously stored as normalization received signal values R1 and R2 (see FIG. 14, the luminance value (pixel value) when TI = 0 in the figure is R1). These normalization received signal values are assumed to be given from the outside in some form or estimated in advance. The phase signal estimation unit 1231 estimates the relative phase of the reception signal based on the first reception signal B1 ′ (i) and the second reception signal B2 ′ (i) as shown in FIG. Output as an estimation result M ′ (i).

  Normally, the phase signal estimation unit 1231 performs phase estimation using a certain number (= LL) of pairs of B1 ′ (i) and B2 ′ (i). The number of relative phase estimation results M ′ (i) output at this time is still LL. Specifically, the relative phase estimation can be executed by the following mathematical formula (Formula 1).

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

  The transmission signal estimation unit 1232 of the demodulation unit 123 estimates a sequence S ′ (i) of 0 or 1 symbols from the sequence of relative phase estimation results M ′ (i) using the least square method as described below. (S1232). Specifically, an operation based on the following formula (Formula 2) is performed.

However, the operator gmod (θ, π) is

Means. Since M ′ (i) has only relative phase information as described above, the transmission signal estimation unit 1232 internally holds reference phase information MI ′ (information indicating a phase shift between transmission and reception) separately. There is a need. MI ′ holds the phase observed when the code S (i) is zero. For example, when MI ′ is 0, if M ′ (1) = 0, M ′ (2) = π, M ′ (3) = π, M ′ (4) = π, and so on, the transmission signal estimation unit 1232 outputs the sequence S ′ (1) = 0, S ′ (2) = 1, S ′ (3) = 1, S ′ (4) = 1. When MI ′ is π, if M ′ (1) = 0, M ′ (2) = π, M ′ (3) = π, M ′ (4) = π, the transmission signal estimation unit 1232 The sequence S ′ (1) = 1, S ′ (2) = 0, S ′ (3) = 0, S ′ (4) = 0.

  Hereinafter, the configuration of the visible light communication system according to the second embodiment will be described with reference to FIG. In this embodiment, the modulation method is assumed to be differential binary phase shift keying (DBPSK) and exposure time τ = Tc / 2. As shown in the figure, the visible light communication system 2 of the present embodiment includes a transmission device 21 and a reception device 22, and the transmission device 21 includes a modulation unit 211 and a light emission unit 912. The light emission unit 912 is a conventional one. This 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 demodulator 223 includes a phase signal estimator 1231 and a transmission signal estimator 2232, and the phase signal estimator 1231 is the same as the phase signal estimator 1231 in the receiving device 12 of the first embodiment. Hereinafter, input / output and operation of each part different from those of the conventional example and Example 1 will be described with reference to FIG.

<Modulation unit 211>
The modulation unit 211 includes a memory, an arithmetic device, 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: Modulation section 211 receives a sequence S (1), S (2),... Of digital transmission signal S (i). 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 a sequence M (1), M (2),... Of the modulation signal M (i). The modulation signal M (i) is phase information having a value of 0 degree or π degree. I is also used as an index representing time.
Operation: Modulator 211 generates a modulated signal with M (i) as 0 if digital transmission signal S (i) is 0 and internal state MI (i-1) is 0, and internal state MI (i) Is 0. Further, the modulation unit 211 generates a modulation signal with M (i) as π if the digital transmission signal S (i) is 1 and the internal state MI (i−1) is 0, and the internal state MI (i) Is π. In addition, if the digital transmission signal S (i) is 0 and the internal state MI (i−1) is π, the modulation unit 211 generates a modulation signal with M (i) as π and generates the internal state MI (i ) Is π. Further, the modulation unit 211 generates a modulation signal with M (i) as 0 if the digital transmission signal S (i) is 1 and the internal state MI (i−1) is π, and the internal state MI (i) Is set to 0 (S211).

  For example, the modulation unit 211 has a digital transmission signal sequence of S (1) = 0, S (2) = 1, S (3) = 1, S (4) = 1,. If (0) is 0, a modulation signal is generated as M (1) = 0, M (2) = π, M (3) = 0, M (4) = π, and so on, and the internal state of each index Are MI (1) = 0, MI (2) = π, MI (3) = 0, M (4) = π,.

<Demodulation unit 223>
The demodulator 223 includes a memory, an arithmetic device, and the like. The internal state MI ′ (i) is stored in the memory of the demodulation unit 223. MI ′ (i) represents phase information estimated at the previous index (i−1) (described later).
Input: The demodulator 223 receives a sequence of the first received signal B1 ′ (i) and a sequence of the second received signal B2 ′ (i).
Output: The demodulator 223 outputs a symbol sequence S ′ (i) (estimation result).
Operation: The transmission signal estimation unit 2232 of the demodulation unit 223 receives a sequence of relative phase estimation results M ′ (i) and outputs a sequence of symbols S ′ (i) (S2232). The transmission signal estimation unit 2232 has an internal state MI ′ (i). Specifically, the transmission signal estimation unit 2232 obtains a sequence S ′ (i) of 0 or 1 symbols from the sequence of relative phase estimation results M ′ (i) using the least square method as described below. presume. Specifically, an operation based on the following mathematical formula (Formula 3) is performed.

  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 greater than or equal to π, 1 is output. For example, if MI ′ (0) is 0, if M ′ (1) = 0, M ′ (2) = π, M ′ (3) = π, M ′ (4) = π,. Transmission signal estimation section 2232 outputs sequences 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 sequences S ′ (1) = 1, S ′ (2) = 1, S ′ (3) = 0, S ′ (4) = 0,.

  The configuration of the visible light communication system according to the third embodiment will be described below with reference to FIG. In this embodiment, the modulation method is assumed to be multi-level phase shift keying (M-PSK) and exposure time τ = Tc / 2. As shown in the figure, the visible light communication system 3 of this embodiment includes a transmission device 31 and a reception device 32. The transmission device 31 includes a modulation unit 311 and a light emitting unit 912. The light emitting unit 912 is a conventional one. This 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 demodulator 323 includes a phase signal estimator 1231 and a transmission signal estimator 3232, and the phase signal estimator 1231 is the same as the phase signal estimator 1231 in the receiving device 12 of the first embodiment. Hereinafter, input / output and operation of each part different from those of the prior art and the first embodiment will be described with reference to FIG.

<Modulation unit 311>
The modulation unit 311 includes a memory, an arithmetic device, and the like. The memory of the modulation unit 311 stores gradation information G.
Input: Modulation unit 311 receives a sequence S (1), S (2),... Of digital transmission signal S (i). 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 a sequence M (1), M (2),... Of the modulation signal M (i). The modulation signal M (i) is phase information having values of 0 degrees, 2 * π / G * 1, 2 * π / G * 2,... 2 * π / G * (G−1). I is also used as an index representing time.
Operation: Modulation section 311 generates a sequence of modulated signals M (1), M (2),... Of modulated 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, when G = 4, the modulation unit 311 has a digital transmission signal sequence of S (1) = 0, S (2) = 3, S (3) = 2, S (4) = 1,. In this case, the modulation signal is generated as M (1) = 0, M (2) = 3 * π / 2, M (3) = π, M (4) = π / 2,.

<Demodulation unit 323>
The demodulator 323 includes a memory, an arithmetic device, and the like. The memory of the demodulator 323 stores reference phase information MI ′ as an internal state.
Input: The demodulator 323 receives a sequence of the first received signal B1 ′ (i) and a sequence of the second received signal B2 ′ (i).
Output: The demodulator 323 outputs a symbol sequence S ′ (i) (estimation result).
Operation: The transmission signal estimation unit 3232 of the demodulation unit 323 receives a sequence of relative phase estimation results M ′ (i) and outputs a symbol sequence S ′ (i) (S 3232). Further, the transmission signal estimation unit 3232 has reference phase information MI ′ as an internal state. Specifically, the transmission signal estimation unit 3232 uses a sequence of relative phase estimation results M ′ (i) using a least square method as described below, and a sequence of symbols S ′ (i) of 0 to G−1. ). Specifically, an operation based on the following mathematical formula (Formula 4) is performed.

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

Means. As described above, since M ′ (i) has only relative phase information, the transmission signal estimation unit 3232 needs to internally store reference phase information MI ′ separately. MI ′ holds the phase observed when the code S (i) is zero. For example, when MI ′ is 0, M ′ (1) = 0, M ′ (2) = 3 * π / 2, M ′ (3) = π, M ′ (4) = π / 2,. If there is, transmission signal estimation section 3232 outputs sequences 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, ... The transmission signal estimation unit 3232 outputs the sequences S ′ (1) = 2, S ′ (2) = 1, S ′ (3) = 0, S ′ (4) = 3,.

  Hereinafter, the configuration of the visible light communication system according to the fourth embodiment will be described with reference to FIG. In this embodiment, it is assumed that the modulation method is differential multilevel phase shift keying (DM-PSK) and exposure time τ = Tc / 2. As shown in the figure, the visible light communication system 4 of the present embodiment includes a transmission device 41 and a reception device 42. The transmission device 41 includes a modulation unit 411 and a light emitting unit 912. The light emitting unit 912 is a conventional one. This 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 those of the conventional example and Example 1 will be described with reference to FIG.

<Modulation unit 411>
The modulation unit 411 includes a memory, an arithmetic device, and the like. The memory of the modulation unit 411 stores gradation information G. In addition, the internal state MI (i) is stored in the memory of the modulation unit 411. MI (i) is information of any phase of 0 degree, 2 * π / G * 1, 2 * π / G * 2,... 2 * π / G * (G−1).
Input: Modulation unit 411 receives a sequence S (1), S (2),... Of digital transmission signal S (i). 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 a sequence M (1), M (2),... Of the modulation signal M (i). The modulation signal M (i) is phase information having values of 0 degrees, 2 * π / G * 1, 2 * π / G * 2,... 2 * π / G * (G−1). I is also used as an index representing time.
Operation: Modulation section 411 generates a series of modulation signals M (1), M (2),... Of 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 greater than 2 * π, the modulation signal M is expressed as 2 * π / G * L' + 2 * π / G * L-2 * π (i) is generated (S411).

  For example, when G = 4 and MI (0) = π / 2, the modulation unit 411 has a digital transmission signal sequence of 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, ... Is generated.

<Demodulation unit 423>
The demodulator 423 includes a memory, an arithmetic device, and the like. The memory of the demodulation unit 423 stores phase information MI ′ (i) as an internal state.
Input: The demodulator 423 receives a sequence of the first received signal B1 ′ (i) and a sequence of the second received signal B2 ′ (i).
Output: The demodulator 423 outputs a symbol sequence S ′ (i) (estimation result).
Operation: The transmission signal estimation unit 4232 of the demodulation unit 423 receives a sequence of relative phase estimation results M ′ (i), and outputs a symbol sequence S ′ (i) (S 4232). Further, the transmission signal estimation unit 4232 has phase information MI ′ (i) as an internal state. Specifically, the transmission signal estimation unit 4232 uses a sequence of relative phase estimation results M ′ (i) using a least square method or the like as described below to generate a symbol sequence S ′ (i ). Specifically, an operation based on the following mathematical formula (Formula 5) is performed.

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 ,..., The transmission signal estimation unit 4232 outputs the sequences S ′ (1) = 3, S ′ (2) = 2, S ′ (3) = 1, S ′ (4) = 2,. To do.

[Modification 1]
In the first to fourth embodiments, the number of the light receiving elements and the reception signal generation units is two, but the number may be three or more. Also in this case, the phase of the first light receiving element and the second light receiving element is estimated in the same manner as in the first to fourth embodiments by shifting the exposure timing by one-fourth of the carrier wave period Tc in the two light receiving elements whose exposure timings are close to each other. Noise tolerance can be increased by performing the operation 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 the first to fourth embodiments, the phase signal estimation unit 1231 estimates the phase using Equation 1, but as a process in the previous stage, as shown in FIG. You may do this after mapping.

[Modification 3]
Even when there are a plurality (H) of transmission apparatuses, the systems described in the first to fourth embodiments can be applied. In this case, a plurality of reception signal generation units and demodulation units according to the first to fourth embodiments may be prepared. In this case, the estimation of the demodulated signal is executed corresponding to each transmitting apparatus.

<Supplementary note>
The apparatus of the present invention includes, for example, a single hardware entity as 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. Can be connected to a communication unit, a CPU (Central Processing Unit, may include a cache memory or a register), a RAM or ROM that is a memory, an external storage device that is a hard disk, and an input unit, an output unit, or a communication unit thereof , A CPU, a RAM, a ROM, and a bus connected so that data can be exchanged between the external storage devices. If necessary, the hardware entity may be provided with a device (drive) that can read and write a recording medium such as a CD-ROM. A physical entity having such hardware resources includes a general-purpose computer.

  The external storage device of the hardware entity stores a program necessary for realizing the above functions and data necessary for processing the program (not limited to the external storage device, for example, reading a program) It may be stored in a ROM that is a dedicated storage device). Data obtained by the processing of these programs is appropriately stored in a RAM or an external storage device.

  In the hardware entity, each program stored in an external storage device (or ROM or the like) and data necessary for processing each program are read into a memory as necessary, and are interpreted and executed by a CPU as appropriate. . As a result, the CPU realizes a predetermined function (respective component requirements expressed as the above-described unit, unit, etc.).

  The present invention is not limited to the above-described embodiment, and can be appropriately changed without departing from the spirit of the present invention. In addition, the processing described in the above embodiment may be executed not only in time series according to the order of description but also in parallel or individually as required by the processing capability of the apparatus that executes the processing. .

  As described above, when the processing functions in the hardware entity (the apparatus of the present invention) described in the above embodiments are realized by a computer, the processing contents of the functions that the hardware entity should have are described by a program. Then, by executing this program on a computer, the processing functions in the hardware entity are realized on the computer.

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

  The program is distributed by selling, transferring, or lending a portable recording medium such as a DVD or CD-ROM in which the program is recorded. Furthermore, the program may be distributed by storing the program in a storage device of the server computer and 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. When executing the process, this computer reads the program stored in its own recording medium and executes the process according to the read program. As another execution form of the program, the computer may directly read the program from a portable recording medium and execute processing according to the program, and the program is transferred from the server computer to the computer. Each time, the processing according to the received program may be executed sequentially. Also, the program is not transferred from the server computer to the computer, and the above-described 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. It is good. Note that the program in this embodiment includes information that is used for processing by an electronic computer and that conforms to the program (data that is not a direct command to the computer but has a property that defines the processing of the computer).

  In this embodiment, a hardware entity is configured by executing a predetermined program on a computer. However, at least a part of these processing contents may be realized by hardware.

Claims (8)

Based on the charge accumulated in the samplers of the plurality of light receiving elements that are exposed to the optical signal based on the modulation signal obtained by phase shift modulation of the digital transmission signal, each at a different exposure timing over a half period of the optical signal, A light receiving unit that generates a plurality of reception 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 defined as a received signal value for normalization, and based on the generated values of the received signals and the received signal value for normalization A receiving apparatus including a demodulator that estimates a phase of the modulated signal. The receiving device according to claim 1,
The demodulator
A receiving apparatus that estimates the digital transmission signal based on the estimated phase and reference phase information indicating a phase shift between transmission and reception. The receiving device according to claim 1,
The phase shift keying is differential binary phase shift keying,
The demodulator
A receiving apparatus that estimates the digital transmission signal based on the estimated phase and information on the phase estimated in the previous index. The receiving device according to claim 2,
The receiving device, wherein the phase shift keying is multilevel phase shift keying. The receiving device according to claim 1,
The phase shift keying is differential multilevel phase shift keying,
The demodulator
A receiving apparatus that estimates the digital transmission signal based on the estimated phase and information on the phase estimated in the previous index. The receiving device according to any one of claims 1 to 5,
The receiving apparatus in which the exposure timing is shifted by a quarter of the period of the optical signal in two of the light receiving elements that are close to each other in the exposure timing. A receiving method executed by the receiving device,
Based on the charge accumulated in the samplers of the plurality of light receiving elements that are exposed to the optical signal based on the modulation signal obtained by phase shift modulation of the digital transmission signal, each at a different exposure timing over a half period of the optical signal, 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 defined as a received signal value for normalization, and based on the generated values of the received signals and the received signal value for normalization A receiving method, comprising: estimating a phase of the modulated signal.   The program which makes a computer function as a receiver in any one of Claim 1 to 6.

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