JP5925146B2 - Receiving device, receiving method, program - Google Patents

Description

  The present invention relates to a receiving device, a receiving method, and a program in visible light communication.

  In recent years, visible light sources have been used not only for illumination purposes for obtaining light but also for communication purposes. This contributes 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 have been conducted for use not only in lighting applications for obtaining light but also in signal transmission applications using blinking of visible light. For example, Non-Patent Document 1 proposes to perform communication by superimposing a signal on a household lighting fixture using a light emitting diode. In addition, since visible light is currently not subject to regulations of the Radio Law, there is no band or power limitation, and the band and power can be increased. Some studies have proposed to use it (see Non-Patent Document 2, for example). 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 light receiving element of a receiving device. In a photodetector, signals can usually be obtained continuously. On the other hand, the image sensor can acquire signals from a large number of photo detectors at a time, but normally it can only acquire signals sampled at the period Ts. In this specification, it is assumed that an image sensor is mainly used as the light receiving element. Hereinafter, a conventional visible light communication system will be outlined with reference to FIG. FIG. 1 is a block diagram showing a functional configuration of a conventional visible light communication system 9000. As shown in FIG. 1, a conventional visible light communication system 9000 includes a transmission device 8 and a reception device 9, and the transmission device 8 includes a modulation unit 81 and a light emitting unit 82. The reception device 9 includes a light receiving unit 91, A synchronization unit 93 and a decoding unit 94 are provided. The light emitting unit 82 includes a light emission signal control unit 821 and a light emitting element 822, the light receiving unit 91 includes a light receiving element 911, the synchronization unit 93 includes a clock element 931, a symbol timing reproduction circuit 932, and a luminance estimation element. 933.

  Hereinafter, signals used in the visible light communication system 9000 shown in FIG. 1 will be described with reference to FIG. 2 is a diagram illustrating signals used in the conventional visible light communication system 9000. FIG. 2A is an example of a transmission signal, FIG. 2B is an example of a modulation signal, and FIG. 2C is a case where the processing time is d = 0. 2D shows an example of an optical signal when the processing time d = 0, FIG. 2E shows an example of an electrical signal when the processing time d ≠ 0, and FIG. 2F shows an optical signal when the processing time d ≠ 0. Examples of

<Transmitter 8: Modulator 81>
The modulation unit 81 of the transmission device 8 receives the digital transmission signal S (i) (see FIG. 2A), modulates the transmission signal, and modulates the transmission signal only with 0 or 1 (whether the switch is on or off). i) is output (see FIG. 2B). Such a modulation method is called on-off modulation. Here, i is an index indicating time and is an integer indicating the number of the transmission signal. The modulation unit 81 generates a sequence M (1), M (2),... Of a modulation signal M (i) of the input transmission signal S (i), a sequence S (1), S (2),. , A sequence M (1), M (2),... Of the modulation signal M (i) is output. Both the transmission signal S (i) and the modulation signal M (i) are 1-bit information.

  For example, when the transmission signal sequence is S (1) = 0, S (2) = 1, S (3) = 1, S (4) = 1, the modulation unit 81 outputs M (1) as a modulation result. = 0, M (2) = 1, M (3) = 1, and M (4) = 1.

<Transmitter 8: Light Emitting Unit 82>
The light emission signal control unit 821 outputs an electric signal E (t) for driving the light emitting element according to M (i). However, E (t) is a temporally continuous signal with respect to the temporally discrete signal M (i) (see FIG. 2C). The light emitting element 822 repeats light emission / extinction according to E (t) and outputs an optical signal F (t) (see FIG. 2D). The output time of E (t) corresponding to the time-series index i is set to a predetermined time width Tf centered on the time indicated by the index i. Hereinafter, Tf is referred to as a blinking cycle.

  Specifically, when the input modulation signal M (i) is 1, the light emission signal control unit 821 is a time when a predetermined time Tf has elapsed from the time i × Tf−Tf / 2 + T (where T is a delay amount). An electric signal is given to the light emitting element 822 until i × Tf + Tf / 2 + T. When the input modulation signal M (i) is 0, the light emitting element 822 has a period from time i × Tf−Tf / 2 + T to time i × Tf + Tf / 2 + T after a predetermined time Tf (T ≦ Tf) has elapsed. Do not give an electrical signal. In the example of FIG. 2, the delay amount T = (− Tf / 2). The light emitting element 822 emits light according to an electric signal given from the light emission signal control unit 821. As a result, the light signal F (t) is output from the light emitting unit 82. Further, depending on the performance of the light emission signal control unit 821, it may take time to control the light emitting element 822, and light emission may not be possible during the processing time d. In such a case, when the input modulation signal M (i) is 1, a time i × Tf + Tf / when a predetermined time Tf−d (T ≦ Tf) has elapsed from the time i × Tf−Tf / 2 + d / 2 + T. An electric signal is given to the light emitting element 822 until 2-d / 2 + T. When the input modulation signal M (i) is 0, from time i × Tf−Tf / 2 + d / 2 + T to time i × Tf + Tf / 2−d / 2 + T when a predetermined time Tf−d (T ≦ Tf) has elapsed. In the meantime, no electrical signal is applied to the light emitting element 822 (see FIG. 2E). The light emitting element 822 outputs an optical signal F (t) in accordance with the electric signal E (t) given from the light emission signal control unit 821 (see FIG. 2F). The light emitting element 822 may be an LED, for example. With these operations, the light signal F (t) is output from the light emitting unit 82. As shown in FIG. 2, the index i has a predetermined time width Tf. However, when representing a discrete signal in time, one point having a time width indicated by the index i (for example, the central time) is also represented by i. For example, when a discrete signal is represented, the time difference represented by the index i and i + 1 is Tf. Further, as described above, it may take time to control the light emitting element 822. If the time required for processing is set to d, the light emission time per index is Tf−d.

<Receiving device: light receiving unit 91>
The light receiving element 911 receives (receives) an optical signal F ′ (t) in which noise is superimposed on the optical signal F (t) output from the transmitter 8 (the light emitting element 822). Ideally, F (t) = F ′ (t). However, since it may change depending on the performance and delay of the photodetector, F (t) and F ′ (t) are described separately here. It is assumed that approximately F (t + T) = F ′ (t). As described above, T represents the delay amount. The light receiving element 911 is, for example, a photo detector, an image sensor in which photo detectors are arranged in a grid, a high-speed camera, or the like. Further, an optical lens may be provided before the light receiving element 911.

  A realization example of a light emitting element and a light receiving element in a conventional visible light communication system 9000 will be described with reference to FIG. FIG. 3 is a diagram illustrating a light emitting element and a light receiving element in a conventional visible light communication system 9000. As shown in FIG. 3, in the conventional visible light communication system 9000, for example, the light emitting element 822 can be an LED element. In addition, the light receiving element 911 can be realized as an image sensor including the photodetectors 911-a, b, c,. As shown in FIG. 3, it is assumed that the blinking of the transmission device 8 represented by the index i forms an image in the region Ωk (the knitted portion in FIG. 3) on the image sensor. The receiving device 8 captures the total output value of all the photodetectors in the region Ωk as a received signal from the transmitting device 8.

<Symbol clock synchronization>
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, a symbol clock (information indicating a time width used when transmitting one symbol) of the transmitter is received in order to correctly decode the encoded information transmitted from the transmitter by the decoder. It is important to detect on the device side. This is called symbol clock synchronization between the receiving device and the transmitting device. It is desirable that symbol clock synchronization is always performed during communication. This is because, in general, there is no means for sharing the same oscillator between the receiving device and the transmitting device, and therefore synchronization may always shift.

<Synchronizer 93>
The synchronization unit 93 estimates and outputs parameters necessary for correctly decoding the information F (t) transmitted from the transmission apparatus 8 (synchronization parameter TI and maximum luminance parameter R). Specifically, parameters (TI, R) necessary for decoding are generated by the following operations of the clock element 931, the symbol timing recovery circuit 932, and the luminance estimation element 933.

<Clock element 931>
The clock element 931 generates a clock.

<Symbol Timing Recovery Circuit 932>
The symbol timing recovery circuit 932 uses the clock obtained from the clock element 931 and the electric signal E ′ (t) obtained from the light receiving unit 91 to set the parameter TI of the synchronization deviation between the clock of the clock element 931 and the clock of the transmission device 8. Is output. As the symbol timing recovery circuit 932, for example, Non-Patent Document 5 is known. In Non-Patent Document 5, the phase is synchronized by detecting the phase difference between two input signals and applying feedback control. One of the two signals is an input from an oscillator, and the other is a signal to be synchronized.

<Luminance estimation element 933>
The luminance estimation element 933 estimates the parameter (maximum luminance value) R of the maximum luminance using the electric signal E ′ (t) obtained from the light receiving unit 91.

<Decryption unit 94>
The decoding unit 94 decodes the electric signal E ′ (t) output from the light receiving unit 91 using the least square method or the like using the synchronization deviation parameter TI and the maximum luminance parameter R as clues, and the decoding result M ′. ⁺ (I) is output. The least square method can be performed by a digital circuit by discretizing the electric signal E ′ (t) in some form. Note that the receiving device 9 may be provided with a demodulation unit, and the demodulation unit may demodulate the decoding result M ′ ⁺ (i) and output the demodulation result S ′ (i). In this case, the demodulation unit needs to be configured to correspond to the modulation unit 81.

Toshihiko Komine, 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 Miyauchi, S .; Komine, T .; Haruyama, S .; Nakagawa, M .; “Analysis of LED-allocation algorithm for high-speed parallel wireless optical communication system,” Proc. IEEE 2006 Radio and Wireless Symposium, pp. 191 -194. Nagura, T .; Yamazato, T .; Katayama, M .; Yendo, T .; Fujii, T .; Okada, H .; “Improved Decoding Methods of Visible Light Communication System for ITS using LED Array and High-Speed Camera, ”Proc. IEEE 71st Vehicular Technology Conference 2010, pp. 1-5. 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

  When a photodetector is used as the light receiving element, it is easy to use a symbol timing reproduction circuit as described in Non-Patent Document 5 because signals can be obtained continuously. However, when it is desired to perform symbol clock synchronization by a digital circuit, a somewhat large sampling frequency is required. For example, when an image sensor is used, the obtained signal is a sampled signal (discrete time signal). In this case, the frequency necessary for performing symbol clock synchronization by the symbol timing recovery circuit becomes larger than the sampling frequency necessary for the original communication, which is a problem.

  Furthermore, when an image sensor is used as the light receiving element, the throughput (data transmission amount per unit time) between the image sensor and a general processing device at the subsequent stage is generally limited, so the number of pixels × sample The conversion frequency cannot exceed a certain value. For this reason, if the sampling frequency is increased, the number of pixels must be reduced, and as a result, the number of light receiving elements provided in one receiving apparatus must be reduced. On the other hand, when a receiving apparatus having an upper limit on the sampling frequency is used, it is necessary to increase the blinking period of the transmitter (decrease the blinking frequency) in order to perform accurate symbol clock synchronization. Therefore, an object of the present invention is to provide a receiving apparatus that can make the sampling frequency required for symbol timing reproduction smaller than the conventional one.

  The receiving apparatus of the present invention is a receiving apparatus that performs visible light communication with a transmitting apparatus, and includes a light receiving element, a received signal generation unit, a provisional decoding unit, and a synchronization unit.

  The light receiving element receives an optical signal from the transmission device and outputs an electrical signal corresponding to the optical signal. The reception signal generation unit measures the intensity of the electrical signal at predetermined time intervals and outputs the measurement result as a series of reception signals for each index. The tentative decoding unit generates a tentative decoding result sequence by using the received signal sequence, the synchronization deviation parameter and the maximum luminance parameter in the previous sequence of the received signal. The synchronization unit updates the synchronization error parameter and the maximum luminance parameter using the received signal sequence and the provisional decoding result sequence.

  According to the receiving apparatus of the present invention, the sampling frequency required for symbol timing reproduction can be made smaller than before.

The block diagram which shows the function structure of the conventional visible light communication system. The figure which illustrates the signal used with the conventional visible light communication system. The figure which illustrates the light emitting element and light receiving element in the conventional visible light communication system. The block diagram which shows the function structure of the visible light communication system which concerns on Example 1 of this invention. The sequence diagram which shows operation | movement of the visible light communication system which concerns on Example 1 of this invention. The block diagram which shows the function structure of the visible light communication system which concerns on Example 2 of this invention. The sequence diagram which shows operation | movement of the visible light communication system which concerns on Example 2 of this invention. The block diagram which shows the function structure of the visible light communication system which concerns on Example 3 of this invention. The sequence diagram which shows operation | movement of the visible light communication system which concerns on Example 3 of this invention. The figure which shows the example of a received signal when it is Tf = Ts and each exposure time is not settled in each blinking period. The figure which shows the example of a received signal when it is Tf = Ts and each exposure time is settled in each blinking period. The figure which shows the example of the received signal in case of Tf / 2 <Ts <Tf and d = 0. It shows a specific example of a ^{- I +} and I in the example of FIG. 12. The figure which shows the example of the received signal in case of d <> 0. The figure which shows about 6 types of case classification which arises by the shift | offset | difference of blinking period and exposure time. The figure explaining the definition of time tm, tp, Tmm, Tmp, Tpm, Tpp.

  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 visible light communication system 1000 according to the first embodiment will be described with reference to FIGS. 4, 5, 10, and 11. FIG. 4 is a block diagram illustrating a functional configuration of the visible light communication system 1000 according to the present embodiment. FIG. 5 is a sequence diagram showing the operation of the visible light communication system 1000 of the present embodiment. FIG. 10 is a diagram illustrating an example of a reception signal when Tf = Ts and each exposure time does not fall within each blinking cycle. FIG. 11 is a diagram illustrating an example of a received signal when Tf = Ts and each exposure time is within each blinking period.

  As shown in FIG. 4, the visible light communication system 1000 of this embodiment includes a transmission device 8 and a reception device 1, and the transmission device 8 is the same as the transmission device 8 included in the above-described visible light communication system 9000. . The receiving device 1 includes a light receiving unit 11, a provisional decoding unit 12, a synchronization unit 13, a decoding unit 14, and a storage unit 15. The light receiving unit 11 includes a light receiving element 111 and a reception signal generating unit 112.

  A measurement cycle of a reception signal generation unit 112 described later is Ts, an exposure time of the light receiving element 111 is τ, and in this embodiment, the case where the blinking cycle Tf is equal to the measurement cycle Ts and the processing time d = 0 is handled.

<Light receiving unit 11>
The light receiving element 111 can be, for example, a photo detector as in the prior art. Further, an optical lens may be provided in front of the light receiving element 111. Further, the light receiving element 111 may be an image sensor in which photodetectors are arranged in a grid pattern. The reception signal generation unit 112 includes a sampling element, a memory, an arithmetic device, and the like. The light receiving element 111 receives the optical signal F ′ (t) from the transmission device 8 and outputs an electrical signal E ′ (t) corresponding to the optical signal F ′ (t) to the reception signal generation unit 112 ( SS111).

  The reception signal generation unit 112 measures the intensity of the electric signal E ′ (t) every predetermined time interval Ts = Tf (SS112). When the light receiving element 111 is a single photodetector, the reception signal generation unit 112 specifically samples from time TI + iTs−Ts / 2−τ / 2 to TI + iTs−Ts / 2 + τ / 2 as shown in FIG. The charge accumulated in the element is measured, and the measurement result is output as a series of reception signals B ′ (i) for each index. On the other hand, when the light receiving element 111 is an image sensor, the reception signal generation unit 112 measures the electric charge accumulated in the sampling element, adds the measurement results within a predetermined range Ωk, and uses the addition result as the reception signal for each index. Output as a sequence of B ′ (i).

<Tentative decoding unit 12>
The temporary decoding unit 12 includes a memory, an arithmetic device, and the like. The temporary decoding unit 12 acquires the sequence of the reception signal B ′ (i) from the reception signal generation unit 112, and the previous sequence of the reception signal B ′ (i) (the received signal of the first frame among the frames included in the current sequence). When the time index is i, the synchronization sequence parameter TI and the maximum luminance parameter R obtained by the synchronization unit 13 in the previous sequence (for example, the sequence before i-1) are acquired from the storage unit 15, and A sequence of provisional decoding results M ′ (i) obtained by decoding the transmission signal of the transmitting apparatus corresponding to B ′ (i) is generated (S12). Note that when there is no previous sequence from the received signal B ′ (i), a predetermined initial value (stored in the storage unit 15 in advance) is used. It is assumed that maximum likelihood estimation such as the Viterbi algorithm is used as the initial value decoding method in the temporary decoding unit 12. Normally, the provisional decoding unit 12 performs decoding by collectively collecting a certain number L (L is a positive integer) of received signals B ′ (i). The number of temporary decoding results M ′ (i) output at this time is K (K is a positive integer). K is a value determined by L and TI. K = L only when each exposure time is within each blinking period as shown in FIG. 11, and K = L−1 in other cases of FIG. Become. Specifically, the temporary decoding unit 12 updates the temporary decoding result M ′ with the sequence M ^ ′ _i calculated by the following equation (1) (S12).

Equation (1) corresponds to obtaining the sequence M ^ ′ _i by the least square method using the observed received signal B ′ (i) and the parameter TI of the synchronization error as a clue. However, ‖-‖ ₂ represents the L2 norm, Ω is a set of L consecutive time index.

<Synchronizer 13>
The synchronization unit 13 includes a memory, an arithmetic device, and the like. The synchronization unit 13 obtains the sequence of the reception signal B ′ (i) from the reception signal generation unit 112 and the sequence of the provisional decoding result M ′ (i) from the provisional decoding unit 12, and uses the least square method or the like. Then, the synchronization deviation parameter TI and the maximum luminance parameter R are calculated for each index, stored in the storage unit 15, and the TI and R are output to the decoding unit 14 (S13). Specifically, the synchronization unit 13 calculates the parameters TI and R using the following equation (2). Accordingly, the storage unit 15 stores the synchronization deviation parameter TI and the maximum luminance parameter R for each index.

In Equation (2), TI and R are estimated by the least square method using the sequence M ′.

<Decoding unit 14>
The decoding unit 14 decodes the reception signal B ′ (i) using the TI and R obtained by the synchronization unit 13 and the sequence of the reception signal B ′ (i) acquired from the reception signal generation unit 112. ' ⁺ (I) is output (S14). The decoding method is the same as that of the provisional decoding unit 12. Note that the decoding unit 14 is not an essential component. The temporary decoding result M ′ (i) obtained by the temporary decoding unit 12 may be output as it is as the decoding result without using the decoding unit 14. Further, as described above, the receiving apparatus 1 may be provided with a demodulating unit, and the demodulating unit may demodulate the decoding result M ′ ⁺ (i) and output the demodulating result S ′ (i). In this case, the demodulation unit needs to be configured to correspond to the modulation unit 81.

  According to the receiving apparatus 1 of the present embodiment, the sampling frequency required for symbol timing reproduction can be made smaller than before. Moreover, according to the receiving apparatus 1 of the present embodiment, it is possible to realize accurate symbol clock synchronization of a transmission signal having a higher blinking period than when a conventional receiving apparatus having the same sampling frequency is used.

Hereinafter, the visible light communication system 2000 according to the second embodiment will be described with reference to FIGS. 6, 7, 12, and 13. FIG. 6 is a block diagram illustrating a functional configuration of the visible light communication system 2000 according to the present embodiment. FIG. 7 is a sequence diagram showing the operation of the visible light communication system 2000 of this embodiment. FIG. 12 is a diagram illustrating an example of a received signal when Tf / 2 <Ts <Tf and d = 0. FIG. 13 is a diagram showing a specific example of I ⁺ and I ^{− in} the example of FIG. In the first embodiment, since it is assumed that Tf and Ts are synchronized (Tf = Ts), the time index of the transmission signal (transmission signal) of the transmission device and the time index of the reception signal of the reception device are the same. (I) It was described as a thing. However, since Tf and Ts are not synchronized in the second embodiment, the time index of the transmission signal is different from the time index of the reception signal. Assuming that the time index of the transmission signal is j and the time index of the reception signal is i, the reception signal B ′ (i) of the index i receives the light emitted from the light emitting element corresponding to the transmission signal M (j) of the index j. It was acquired with the element. Since the receiving device cannot know the exact value of j, the receiving device uses I ⁺ and I ⁻ as estimated values of the index j of the transmission signal.

  As shown in FIG. 6, the visible light communication system 2000 according to the present embodiment includes a transmission device 8 and a reception device 2, and the transmission device 8 is the same as the transmission device 8 described above. The receiving device 2 includes a light receiving unit 11, a provisional decoding unit 22, a synchronization unit 23, a decoding unit 14, and a storage unit 15. Since each function component other than the provisional decoding unit 22 and the synchronization unit 23 is the same as each mechanism component having the same number in the first embodiment, a description thereof will be omitted.

In this embodiment, a case where Tf and Ts are different will be described. Specifically, the case where Tf / 2 <Ts <Tf and d = 0 is handled. Similar to the temporary decoding unit 12 of the first embodiment, the temporary decoding unit 22 of the present embodiment acquires the sequence of the reception signal B ′ (i) from the reception signal generation unit 112, and the received signal B ′ (i) The synchronization deviation parameter TI and the maximum luminance parameter R obtained by the synchronization unit 23 in the previous sequence are acquired from the storage unit 15, and a sequence of temporary decoding results M ′ (i) is generated (S22). When there is no series before B ′ (i), a predetermined initial value (stored in the storage unit 15 in advance) is used. As the decoding method, it is assumed that maximum likelihood estimation such as the Viterbi algorithm (reference non-patent reference 1) is used.
(Reference Non-Patent Document 1) CM Bishop (Author), Hiroshi Motoda (Director), Takio Kurita (Director), Tomoyuki Higuchi (Director), Yuji Matsumoto (Director), Noboru Murata (Director), “Pattern Recognition and Machine Learning ”Maruzen Publishing, 2012

Normally, the provisional decoding unit 22 performs decoding by collecting a certain number K of B ′ (i). The number of temporary decoding results M ′ (j ^) output at this time is L, which is determined by the relationship between Tf and Ts and the parameter TI for synchronization deviation. Here, j ^ is an estimated value of the index of the transmission signal.
The temporary decoding unit 22 updates the temporary decoding result sequence M ′ with the sequence M ′ ′ _i calculated by the following equation (3) (S22).

However, I ⁺ (i, TI, Ts, Tf, τ) and I ⁻ (i, TI, Ts, Tf, τ) are functions that output estimated values (values of j ^) of transmitted signal indexes, respectively. ,

Is defined. The role of Expression (3) is the same as Expression (1), but since Tf and Ts are asynchronous (different values), which slot of sequence M ′ corresponds to B ′ (i) in i Is added to calculate I by I ⁺ and I ⁻ depending on the value of i. Specific examples of I ⁺ and I ⁻ defined by the formulas (4) and (5) are shown in FIG.

<Synchronizer 23>
The synchronization unit 23 acquires the sequence of the received signal B ′ (i) and the sequence of the provisional decoding result M ′ (j ^), and uses the least square method or the like to set the parameter TI of synchronization deviation for each index. The maximum brightness parameter R is calculated (S23). Specifically, the synchronization unit 23 calculates the parameters TI and R using K M ′ (j ^) and L B ′ (i) using the following equation (6).

  According to the receiving apparatus 2 of the present embodiment, the sampling frequency required for symbol timing reproduction can be made smaller than before. Further, according to the receiving apparatus 2 of the present embodiment, it is possible to realize accurate symbol clock synchronization of a transmission signal having a higher blinking period than when a conventional receiving apparatus having the same sampling frequency is used.

  Hereinafter, the visible light communication system 3000 according to the third embodiment will be described with reference to FIGS. 8, 9, 14, 15, and 16. FIG. 8 is a block diagram showing a functional configuration of the visible light communication system 3000 according to the present embodiment. FIG. 9 is a sequence diagram showing the operation of the visible light communication system 3000 according to the present embodiment. FIG. 14 is a diagram illustrating an example of a received signal when d ≠ 0. FIG. 15 is a diagram showing six case classifications caused by the difference between the blinking period and the exposure time. FIG. 15A is a diagram showing six case classifications in T ≦ Tf−d, and FIG. These are figures which show about six cases classification in T> Tf-d. FIG. 16 is a diagram for explaining the definitions of times tm, tp, Tmm, Tmp, Tpm, and Tpp.

  As shown in FIG. 8, the visible light communication system 3000 according to the present embodiment includes a transmission device 8 and a reception device 3, and the transmission device 8 is the same as the transmission device 8 described above. The receiving device 3 includes a light receiving unit 11, a provisional decoding unit 32, a synchronization unit 33, a decoding unit 14, and a storage unit 15. Since each function component other than the provisional decoding unit 32 and the synchronization unit 33 is the same as each mechanism component having the same number in the first embodiment, a description thereof will be omitted.

  In the present embodiment, a case where a finite processing time d is required for switching the light emission pattern due to the nature of the processing in the light emitting unit 82 (when d ≠ 0) will be described. Further, in the present embodiment, the provisional decoding unit 32 and the synchronization unit 33 are described based on the second embodiment in order to explain in a general format, but the receiving device 3 of the present embodiment is not limited to this. It is also possible to describe based on the first embodiment. The function of the light receiving unit 11 is the same as in the first and second embodiments. The state of light emission in the light emitting unit 82 is shown in FIG. 2F. The relationship between F '(t) and B' (i) is as shown in FIG. In this embodiment, the exposure time τ is longer than d.

<Light Emitting Unit 82>
When the input modulation signal M (j) is 1, the light emission signal generation unit 821 of the light emission unit 82 has passed a predetermined time Tf−d (T ≦ Tf) from the time j × Tf−Tf / 2 + d / 2 + T. An electric signal is given to the light emitting element 822 until time j × Tf + Tf / 2−d / 2 + T. When the input modulation signal M (j) is 0, from time j × Tf−Tf / 2 + d / 2 + T to time j × Tf + Tf / 2−d / 2 + T when a predetermined time Tf−d (T ≦ Tf) has elapsed. In the meantime, no electrical signal is given to the light emitting element 822. The light emitting element 822 emits light in accordance with an electric signal given from the light emission signal generation unit 821. As a result, the light signal F (t) is output from the light emitting unit 82.

<Tentative decoding unit 32>
The provisional decoding unit 32 obtains the sequence of the reception signal B ′ (i) from the reception signal generation unit 112, and obtains the synchronization deviation parameter TI and the maximum obtained by the synchronization unit 33 in the previous sequence of the reception signal B ′ (i). The luminance parameter R is acquired from the storage unit 15, and a sequence of temporary decoding results M ′ (j ^) is generated (S32). As the decoding method, it is assumed that maximum likelihood estimation such as the Viterbi algorithm (Reference Non-Patent Document 1) is used. Normally, the provisional decoding unit 32 performs decoding by collectively collecting a certain number K of B ′ (i). The number of temporary decoding results M ′ (j ^) output at this time is L, which is determined by the relationship between Tf and Ts and the parameter TI for synchronization deviation. The temporary decoding unit 32 updates the temporary decoding result sequence M ′ with the sequence M ^ ′ _i calculated by the following equation (7) (S32).

Here, if τ ≦ Tf−d, T ⁻ and T ⁺ are
When I ⁻ = I ⁺

When I ⁻ ≠ I ⁺

It can be written as Expressions (8) and (9) correspond to the six cases shown in FIG.
On the other hand, if τ> Tf−d, T ⁻ and T ⁺ are
When I ⁻ = I ⁺

When I ⁻ ≠ I ⁺

It can be written as
Expressions (10) and (11) correspond to the six cases shown in FIG.
However, here

It is. That is, the times tm, tp, Tmm, Tmp, Tpm, and Tpp represent the times shown in FIG.

<Synchronizer 33>
The synchronization unit 33 acquires the sequence of the reception signal B ′ (i) from the reception signal generation unit 112 and the sequence of the provisional decoding result M ′ (j ^) from the provisional decoding unit 12, and uses the least square method or the like. Then, the synchronization deviation parameter TI and the maximum luminance parameter R are calculated for each index, stored in the storage unit 15, and the TI and R are output to the decoding unit 14 (S33). Specifically, the synchronization unit 33 calculates each parameter TI and R by the following equation (18) using K M ′ (j ^) and L B ′ (i).

  According to the receiving apparatus 3 of the present embodiment, the sampling frequency required for symbol timing reproduction can be made smaller than before. Further, according to the receiving apparatus 3 of the present embodiment, it is possible to realize accurate symbol clock synchronization of a transmission signal having a higher blinking period than in the case of using a conventional receiving apparatus having the same sampling frequency.

<When there are multiple transmitters>
Even when there are a plurality (H) of transmission devices, the visible light communication system of the present invention can be configured. In this case, a plurality of sets (total H sets) of light receiving units, provisional decoding units, and synchronization units corresponding to the transmission device may be prepared. In this case, the parameter TI for synchronization loss and the parameter R for maximum luminance are calculated corresponding to each transmission apparatus. Even when there are a plurality of transmitting apparatuses, it is possible to synchronize each transmitting apparatus independently.

<Discrete optimization>
The estimation of the parameter TI performed in the synchronization unit may be optimized from (Equation 2), (Equation 4), (Equation 18), etc. by selecting from several candidates prepared in advance.
[Other variations, etc.]
The present invention is not limited to the above-described embodiment. For example, the temporary decoding units 12, 22, and 32 change α and β to α + β = τ
When the weight according to the synchronization deviation parameter TI satisfying

Can be generalized as a process for obtaining a sequence M ^ ' _i of the decoded signal based on. That is, the temporary decoding unit sets the index of the time of the reception signal of the current frame to i, and the index of the time of the transmission signal of the transmission device corresponding to the reception signal B ′ (i) (the index of the light emission time of the light emitting element). When the estimated value is j ^, a provisional decoding result M '(j ^) obtained by decoding the modulated signal M (j ^) in the transmitting apparatus corresponding to the received signal B' (i) and an index adjacent to the modulated signal At least one of the tentative decoding results M ′ (j ^ + 1) (that is, M ′ (j ^ −1) and / or M ′ (j ^ + 1)) is the maximum luminance in the previous sequence of the received signal (R {αM ′ (j ^ ± 1) + βM ′ (j ^)}) and received signal B ′ ( i) Temporary decryption signal based on a criterion that reduces the difference from i) Determination of the series M ^ '. Here, when the blinking cycle Tf of the transmission device and the measurement cycle Ts of the reception device are equal as in the first embodiment, j ^ = i. When Tf and Ts are not synchronized as in the second and third embodiments, the values of j ^ and i are different. The value of ^ j in such a case can be estimated by, for example, equations (4) and (5).

  Synchronizers 13, 23, and 33 set i to be the time index of the current received signal and j to be the estimated time index of the transmission signal of the transmitting apparatus corresponding to received signal B ′ (i). When the transmission signal M (j ^) is decoded, the temporary decoding result M ′ (j ^) and at least one of the temporary decoding results of the adjacent indexes are used as the maximum luminance in the previous sequence of the received signal. The decoded signal (R {αM ′ (j ^ ± 1) + βM ′ (j ^)}) and the received signal B ′ (i) are distributed by allocating them in proportion to the parameter R and the parameter TI of synchronization loss. Any processing may be used as long as the synchronization deviation parameter R and the maximum luminance parameter TI are updated so that the error with respect to For example, not only the least square error used in Equation (2), Equation (6), and Equation (18), but also based on absolute value error or decibel (logarithmic) error, the parameter of synchronization deviation so that the error is reduced The same effect can be obtained if the process updates the TI and the maximum luminance parameter R. In addition, the various processes described above are not only executed in time series according to the description, but may be executed in parallel or individually according to the processing capability of the apparatus that executes the processes or as necessary. Needless to say, other modifications are possible without departing from the spirit of the present invention.

  Further, when the above-described configuration is realized by a computer, processing contents of functions that each device should have are described by a program. The processing functions are realized on the computer by executing the program 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.

  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, the computer reads a program stored in its own recording medium and executes a 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, the present apparatus 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 (10)

A receiving device that performs visible light communication with a transmitting device,
A light receiving element that receives an optical signal from the transmitter and outputs an electrical signal corresponding to the optical signal;
A reception signal generation unit that measures the intensity of the electrical signal at predetermined time intervals and outputs the measurement result as a series of reception signals for each index;
A temporary decoding unit that generates a temporary decoding result sequence using the received signal sequence, a parameter of synchronization loss and a maximum luminance parameter in a previous sequence of the received signal;
A synchronization unit that updates the synchronization error parameter and the maximum luminance parameter using the received signal sequence and the temporary decoding result sequence;
Receiver device. The receiving device according to claim 1,
The provisional decoding unit
The index of the frame of the received signal is i,
Let j ^ be the estimated value of the index of the transmission signal of the transmission apparatus corresponding to the received signal of index i ,
The provisional decoding result obtained by decoding the transmission signal of the transmission apparatus corresponding to the reception signal B ′ (i) is M ′ (j ^) ,
The temporary decoding result M at least one hand 'and (j ^), provisional decoding result of frame adjacent M thereto' (j ^ ± 1), the maximum luminance in the previous sequence in the received signal a signal when the decoding by allocating a proportion corresponding to parameters of the parameters and synchronization shift and allocation decoded signal,
A receiving device that generates the temporary decoding result sequence based on a criterion that reduces a difference between the distributed decoded signal and the received signal at index i. The receiving device according to claim 1 or 2,
The synchronization unit is
The index of the frame of the received signal is i,
The estimated value of the index of the transmission signal of the transmission apparatus corresponding to the reception signal B ′ (i) of the index i is j ^ ,
A temporary decoding result obtained by decoding the transmission signal of the transmission device corresponding to the reception signal B ′ (i) is M ′ (j ^) ,
The temporary decoding result M at least one hand 'and (j ^), provisional decoding result of frame adjacent M thereto' (j ^ ± 1), the maximum luminance in the previous sequence in the received signal a signal when the decoding by allocating a proportion corresponding to parameters of the parameters and synchronization shift and allocation decoded signal,
A receiving apparatus that updates the synchronization error parameter and the maximum luminance parameter so that an error between the distributed decoded signal and the received signal B ′ (i) is reduced. The receiving device according to claim 1,
The blinking period of the light signal and Tf, the measurement period of the receive signal generator and Ts, the processing time required for the control of the light emitting element of the transmission device is d, the exposure time of the light receiving element and tau, wherein The synchronization parameter is TI, the maximum luminance parameter is R, the index of the received signal is i, the received signal at the index i is B ′ (i), and the received signal B ′ (i) corresponds to the received signal B ′ (i). M ′ (i) is a provisional decoding result obtained by decoding the transmission signal of the transmitting device
When Tf = Ts and d = 0,
The provisional decoding unit

A receiving apparatus that updates a sequence of provisional decoding results with the sequence M ^ ′ _i calculated by the above. The receiving device according to claim 1,
The blinking period of the light signal and Tf, the measurement period of the receive signal generator and Ts, the processing time required for the control of the light emitting element of the transmission device is d, the exposure time of the light receiving element and tau, wherein The synchronization loss parameter is TI, the maximum luminance parameter is R, the received signal index is i, the received signal at the index i is B ′ (i),
Tf / 2 <Ts <Tf and d = 0,
Functions I ⁺ (i, TI, Ts, Tf, τ), I ⁻ (i, TI, Ts) that output an estimated value of the transmitted signal index of the transmitting apparatus corresponding to the received signal B ′ (i) of the index i , Tf, τ) respectively

And a temporary decoding result obtained by decoding the transmission signal of the index I ⁺ (i, TI, Ts, Tf, τ) is M ′ (I ⁺ (i, TI, Ts, Tf, τ)), and the index I ^{- (i, TI, Ts,} Tf, τ) the decoding result of the provisional decoding the transmission signal ^{M '(I - (i,} TI, Ts, Tf, τ)) when a,
The provisional decoding unit

A receiving apparatus that updates a sequence of provisional decoding results with the sequence M ^ ′ _i calculated by the above. The receiving device according to claim 1,
The blinking period of the light signal and Tf, the measurement period of the receive signal generator and Ts, the processing time required for the control of the light emitting element of the transmission device is d, the exposure time of the light receiving element and tau, wherein The synchronization loss parameter is TI, the maximum luminance parameter is R, the received signal index is i, the received signal at the index i is B ′ (i),
d ≠ 0,
Functions I ⁺ (i, TI, Ts, Tf, τ), I ⁻ (i, TI, Ts) that output an estimated value of the transmitted signal index of the transmitting apparatus corresponding to the received signal B ′ (i) of the index i , Tf, τ) respectively

And a temporary decoding result obtained by decoding the transmission signal of the index I ⁺ (i, TI, Ts, Tf, τ) is M ′ (I ⁺ (i, TI, Ts, Tf, τ)), and the index I ⁻ Let M ′ (I ⁻ (i, TI, Ts, Tf, τ)) be a provisional decoding result obtained by decoding the transmission signal of (i, TI, Ts, Tf, τ),
Time tm, tp, Tmm, Tmp, Tpm, Tpp,

And define
When τ ≦ Tf−d and I ⁻ = I ⁺ , T ⁻ and T ⁺ are

And define
When τ ≦ Tf−d and I ⁻ ≠ I ⁺ , T ⁻ and T ⁺ are

And define
When τ> Tf−d and I ⁻ = I ⁺ , T ⁻ and T ⁺ are

And define
When τ> Tf−d and I ⁻ ≠ I ⁺ , T ⁻ and T ⁺ are

Defined as
The provisional decoding unit

A receiving apparatus that updates a sequence of provisional decoding results with the sequence M ^ ′ _i calculated by the above. A receiving method performed by a receiving device that performs visible light communication with a transmitting device,
A light receiving element step for receiving an optical signal from the transmitter and outputting an electrical signal corresponding to the optical signal;
A reception signal generation step of measuring the intensity of the electrical signal at predetermined time intervals and outputting the measurement result as a series of reception signals for each index;
A provisional decoding step of generating a series of provisional decoding results using the sequence of the received signal, the parameter of synchronization loss and the parameter of maximum brightness in the previous series of the received signal;
A receiving method comprising: a synchronization step of calculating the synchronization error parameter and the maximum brightness parameter using the received signal sequence and the temporary decoding result sequence. The reception method according to claim 7, comprising:
The provisional decoding step includes
The index of the frame of the received signal is i,
The estimated value of the index of the transmission signal of the transmission apparatus corresponding to the reception signal B ′ (i) of the index i is j ^ ,
A temporary decoding result obtained by decoding the transmission signal of the transmission device corresponding to the reception signal B ′ (i) is M ′ (j ^) ,
The temporary decoding result M at least one hand 'and (j ^), provisional decoding result of frame adjacent M thereto' (j ^ ± 1), the maximum luminance in the previous sequence in the received signal a signal when the decoding by allocating a proportion corresponding to parameters of the parameters and synchronization shift and allocation decoded signal,
A receiving method for generating the temporary decoding result sequence based on a criterion that reduces a difference between the distributed decoded signal and the received signal B ′ (i). The reception method according to claim 7 or 8, comprising:
The synchronization step includes
The index of the frame of the received signal is i,
The estimated value of the index of the transmission signal of the transmission apparatus corresponding to the reception signal B ′ (i) of the index i is j ^ ,
A temporary decoding result obtained by decoding the transmission signal of the transmission device corresponding to the reception signal B ′ (i) is M ′ (j ^) ,
The temporary decoding result M at least one hand 'and (j ^), provisional decoding result of frame adjacent M thereto' (j ^ ± 1), the maximum luminance in the previous sequence in the received signal a signal when the decoding by allocating a proportion corresponding to parameters of the parameters and synchronization shift and allocation decoded signal,
A receiving method for updating the parameter of synchronization deviation and the parameter of maximum luminance so that an error between the distributed decoded signal and the received signal B ′ (i) becomes small.   A program for causing a computer to execute each step of the receiving method according to claim 7.

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