Receiving apparatus, receiving method, and program

Abstract

A sampling frequency required for symbol timing recovery is made smaller than that of the related art. A receiver 1 performs visible light communication with a transmitter 8. A received signal generating unit 112 measures an intensity of an electrical signal corresponding to an optical signal received from a transmitter 8 at a predetermined time interval to generate a sequence of received signals. A parameter estimation unit 12 uses a distribution of received signals estimated from the sequence of received signals to estimate any one or more parameters of a maximum luminance value, a synchronization shift, and a steady noise level, the one or more parameters including at least the maximum luminance value.

Claims

1. A receiver for performing visible light communication with a transmitter, the receiver comprising: a received signal generator configured to measure an intensity of an electrical signal corresponding to an optical signal received from the transmitter at a predetermined time interval to generate a sequence of received signals; and a parameter estimator configured to use a distribution of received signals estimated from the sequence of received signals to estimate any one or more parameters of a maximum luminance value, a synchronization shift, and a steady noise level, the one or more parameters including at least the maximum luminance value.

2. The receiver according to claim 1, wherein the parameter estimator includes: a received signal distribution estimator configured to generate a histogram representing a frequency of the received signals per luminance from the sequence of received signals; and a distribution estimation result interpreter configured to determine the one or more parameters from an average of each of peaks appearing in the histogram.

3. The receiver according to claim 2, wherein the distribution estimation result interpreter, when R is taken as the maximum luminance value, g.sub.c is taken as the synchronization shift, d is taken as the steady noise level, and an average of each of peaks appearing in the histogram is taken as any of d, R*g.sub.c+d, R(1−g.sub.c)+d, and R+d, determines the maximum luminance value R, the synchronization shift g.sub.c, and the steady noise level d.

4. The receiver according to claim 3, further comprising: a decoding unit configured to decode the received signals based on the one or more parameters estimated by the parameter estimator.

5. The receiver according to claim 2, further comprising: a decoding unit configured to decode the received signals based on the one or more parameters estimated by the parameter estimator.

6. The receiver according to claim 1, further comprising: a decoder configured to decode the received signals based on the one or more parameters estimated by the parameter estimator.

7. The receiver according to claim 1, the receiver further comprising: a light receiver configured to receive visible light communication from the transmitter.

8. A receiving method performed by a receiver configured to perform visible light communication with a transmitter, the method comprising: measuring, by a received signal generator, an intensity of an electrical signal corresponding to an optical signal received from the transmitter at a predetermined time interval to generate a sequence of received signals; and using, by a parameter estimator, a distribution of received signals estimated from the sequence of received signals to estimate any one or more parameters of a maximum luminance value, a synchronization shift, and a steady noise level, the one or more parameters including at least the maximum luminance value.

9. The receiving method according to claim 8, wherein the parameter estimator includes: generating, by a received signal distribution estimator, configured to generate a histogram representing a frequency of the received signals per luminance from the sequence of received signals; and determining, by a distribution estimation result interpreter configured to determine the one or more parameters from an average of each of peaks appearing in the histogram.

10. The receiving method according to claim 9, wherein the distribution estimation result interpreter, when R is taken as the maximum luminance value, g.sub.c is taken as the synchronization shift, d is taken as the steady noise level, and an average of each of peaks appearing in the histogram is taken as any of d, R*g.sub.c+d, R(1−g.sub.c)+d, and R+d, determines the maximum luminance value R, the synchronization shift g.sub.c, and the steady noise level d.

11. The receiving method according to claim 10, further comprising: decoding, by a decoder, the received signals based on the one or more parameters estimated by the parameter estimator.

12. The receiving method according to claim 9, further comprising: decoding, by a decoder, the received signals based on the one or more parameters estimated by the parameter estimator.

13. The receiving method according to claim 8, the method further comprising: decoding, by a decoder, the received signals based on the one or more parameters estimated by the parameter estimator.

14. The receiving method according to claim 8, the method further comprising: receiving, by a light receiver, visible light communication from the transmitter.

15. A computer-readable non-transitory recording medium storing computer-executable program instructions for performing visible light communication with a transmitter when executed by a processor cause a computer to: measure, by a received signal generator, an intensity of an electrical signal corresponding to an optical signal received from the transmitter at a predetermined time interval to generate a sequence of received signals; and use, by a parameter estimator, a distribution of received signals estimated from the sequence of received signals to estimate any one or more parameters of a maximum luminance value, a synchronization shift, and a steady noise level, the one or more parameters including at least the maximum luminance value.

16. The computer-readable non-transitory recording medium according to claim 15, wherein the parameter estimator includes: a received signal distribution estimator configured to generate a histogram representing a frequency of the received signals per luminance from the sequence of received signals; and a distribution estimation result interpreter configured to determine the one or more parameters from an average of each of peaks appearing in the histogram.

17. The computer-readable non-transitory recording medium according to claim 16, wherein the distribution estimation result interpreter, when R is taken as the maximum luminance value, g.sub.c is taken as the synchronization shift, d is taken as the steady noise level, and an average of each of peaks appearing in the histogram is taken as any of d, R*g.sub.c+d, R(1−g.sub.c)+d, and R+d, determines the maximum luminance value R, the synchronization shift g.sub.c, and the steady noise level d.

18. The computer-readable non-transitory recording medium according to claim 17, the computer-executable instructions when executed further causing the system to: decode, by a decoder, the received signals based on the one or more parameters estimated by the parameter estimator.

19. The computer-readable non-transitory recording medium according to claim 16, the computer-executable instructions when executed further causing the system to: decode, by a decoder, the received signals based on the one or more parameters estimated by the parameter estimator.

20. The computer-readable non-transitory recording medium according to claim 15, the computer-executable instructions when executed further causing the system to: decode, by a decoder, the received signals based on the one or more parameters estimated by the parameter estimator.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a diagram illustrating a functional configuration of a related-art visible light communication system.

(2) FIG. 2 is a diagram illustrating signals transmitted in visible light communication.

(3) FIG. 3 is a diagram illustrating a light emitting element and a light receiving element.

(4) FIG. 4 is a diagram illustrating a functional configuration of a visible light communication system according to an embodiment.

(5) FIG. 5 is a diagram illustrating an operation of the visible light communication system according to the embodiment.

(6) FIG. 6 is an illustrating signals received in visible light communication.

DESCRIPTION OF EMBODIMENTS

(7) Embodiments of the present invention will be described in detail below with reference to the drawings. Note that components having the identical function are given the identical reference numerals, and redundant descriptions are omitted.

First Embodiment

(8) FIG. 4 is a block diagram illustrating a functional configuration of a visible light communication system 100 according to a first embodiment. As illustrated in FIG. 4, the visible light communication system 100 of the first embodiment includes a transmitter 8 and a receiver 1. The transmitter 8 is the identical as the transmitter 8 included in the related-art visible light communication system 900 described above. The receiver 1 includes a light receiving unit 11, a parameter estimation unit 12, and a decoding unit 13. The light receiving unit 11 included in the receiver 1 includes a light receiving element 111 and a received signal generating unit 112. The parameter estimation unit 12 included in the receiver 1 includes a received signal distribution estimation unit 121 and a distribution estimation result interpretation unit 122. The visible light communication system 100 performs processing of each of steps illustrated in FIG. 5 to realize a visible light communication method of the first embodiment. Note that, in the visible light communication method of the first embodiment, a series of steps performed by the receiver 1 is referred to as a receiving method according to the first embodiment.

(9) The receiver 1 is a special apparatus constituted by, for example, a known or dedicated computer including a central processing unit (CPU), a random access memory (RAM), and the like into which a special program is read. The receiver 1, for example, executes each processing under control of the central processing unit. Data input to the receiver 1 and data obtained in each processing are stored in the main memory, for example, and the data stored in the main memory is read out as needed to the central processing unit to be used for other processing. At least a portion of processing units of the receiver 1 may be constituted with hardware such as an integrated circuit.

(10) Hereinafter, a measuring period (hereinafter, also referred to as “sampling period”) of the received signal generating unit 112 is T.sub.RX, an exposure time of the light receiving element 111 is τ, and in the present embodiment, a case in which a flashing period T.sub.TX and a measuring period T.sub.RX are approximately equal (T.sub.TX≈T.sub.RX) and a processing time T.sub.P equals to 0 will be described.

(11) Receiver 1: Light Receiving Unit 11

(12) The light receiving element 111 may be a photodetector, for example, as in the related art. An optical lens may also be provided at the preceding stage of the light receiving element 111. Furthermore, the light receiving element 111 may be an image sensor in which photodetectors are arranged in a lattice shape. The received signal generating unit 112 includes a sampling element, a memory, a computing device, and the like.

(13) Receiver 1: Light Receiving Element 111

(14) The light receiving element 111 receives an optical signal F′(t) obtained by superimposing noise on an optical signal F(t) output from the transmitter 8, and outputs an electrical signal E′(t) corresponding to the optical signal F′(t) to the received signal generating unit 112 (step S111).

(15) Receiver 1: Received Signal Generating Unit 112

(16) The received signal generating unit 112 measures an intensity of the electrical signal E′(t) at a predetermined time interval T.sub.RX (≈T.sub.TX) (step S112). When the light receiving element 111 is a single photodetector, as illustrated in FIG. 6, the received signal generating unit 112 measures charges accumulated in the sampling element from a time g.sub.c*τ+j*T.sub.RX−T.sub.RX/2−τ/2 to a time g.sub.c*τ+j*T.sub.RX−T.sub.RX/2+τ/2, and outputs the measurement result as a sequence of received signals B′(j) per index j. On the other hand, when the light receiving element 111 is an image sensor, as illustrated in FIG. 6, the received signal generating unit 112 measures charges accumulated in the sampling element from a time g.sub.c*τ+j*T.sub.RX−T.sub.RX/2−τ/2 to a time g.sub.c*τ+j*T.sub.RX−T.sub.RX/2+τ/2 and outputs a result obtained by adding the measurement results within a predetermined range Ω.sub.k as a sequence of received signals B′(j) per index j.

(17) Receiver 1: Parameter Estimation Unit 12

(18) The parameter estimation unit 12 includes a memory, a computing device, or the like. The parameter estimation unit 12 acquires the sequence of the received signal B′(j) from the received signal generating unit 112, uses the received signal distribution estimation unit 121 and the distribution estimation result interpretation unit 122 to estimate a parameter, and outputs the estimated parameter to the decoding unit 13. Here, the parameter is any one or more parameters of a maximum luminance parameter R, a synchronization shift parameter g.sub.c, and a steady noise level parameter d, the one or more parameters including at least the maximum luminance parameter R.

(19) Receiver 1: Received Signal Distribution Estimation Unit 121

(20) The signal distribution estimation unit 121 stores the received signal B′(j) as an input sequentially in the memory. Next, the signal distribution estimation unit 121 estimates a distribution of received signals from a histogram of J received signals B′(j), B′(j+1), . . . , B′(j+J) (step S121). Here, J is an amount determined depending on the flashing period T.sub.TX, the measuring period T.sub.RX, the exposure time τ, a magnitude of non-steady noise, and the like. The received signal B′(j) corresponds to a luminance at the time indicated by the time index j. Thus, the distribution of received signals is a distribution representing a frequency of received signals per luminance.

(21) Receiver 1: Distribution Estimation Result Interpretation Unit 122

(22) The distribution estimation result interpretation unit 122 estimates and outputs the maximum luminance parameter R, the synchronization shift parameter g c, and the steady noise level parameter din the model of Equation (1) from the distribution of received signals estimated by the received signal distribution estimation unit 121 (step S122).
B′(j)=R(g.sub.c*S(i)+(1−g.sub.c)*S(i+1))+d  (1)

(23) More specifically, transmission signals S(i), S(i+1) each take 0 or 1, and thus the possible value of the received signal B′(j) when there is no noise is any one of four values: d (when S(i)=0 and S(i+1)=0); R*g.sub.c+d (when S(i)=1 and S(i+1)=0); R (1−g.sub.c)+d (when S(i)=0 and S(i+1)=1); and R+d (when S(i)=1 and S(i+1)=1). This is utilized to determine the above parameters R, g.sub.c, and d from the average of each of 2 to 4 peaks appearing in the histogram of received signals.

(24) Receiver 1: Decoding Unit 13

(25) In step S13, the decoding unit 13 decodes the received signal B′(j) output from the received signal generating unit 112 on the basis of the maximum luminance parameter R, the synchronization shift parameter g.sub.c, and the steady noise level parameter d output by the parameter estimation unit 12, and outputs the decoded result M′(j). The method of decoding is similar to that of the decoding unit 93 of the related-art receiver 9. A configuration may be employed in which a demodulation unit that is not illustrated in the identical manner as the related-art receiver 9 described above is provided to demodulate the decoded result M′(j) and output the demodulated result S′(j). In this case, the demodulation unit needs to be configured to correspond to the modulation unit 81.

Second Embodiment

(26) When there is a Plurality of Transmitters

(27) Even when a plurality of the transmitters are present (H (≥2)), the visible light communication system of the present invention can be constituted. In this case, it is only required to provide a plurality of sets (a total of H sets) each of which has the light receiving unit 11, the parameter estimation unit 12, and the decoding unit 13 corresponding to each of the transmitters 8. In this case, the maximum luminance parameter R, the synchronization shift parameter g.sub.c, and the steady noise level parameter d are calculated corresponding to each of the transmitters 8. With this configuration, even when there are a plurality of transmitters 8, synchronization can be independently performed on each of the transmitters 8.

(28) The embodiments of the present invention have been described above in detail with reference to the drawings. However, specific configurations are not limited to those embodiments, and include any design change or the like within the scope not departing from the gist of the present invention. The various processing described above in the embodiments may be executed not only in chronological order as described, but also in parallel or individually according to the needs or the processing capability of the apparatus executing the processing.

(29) Program and Recording Medium

(30) When each processing function of each apparatus described in the above embodiments is realized by a computer, processing content of a function that each apparatus should have is described by a program. Then, by executing the program on a computer, various processing functions of each apparatus described above are implemented on the computer.

(31) A program describing the processing content 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 apparatus, an optical disk, a magneto-optical recording medium, and a semiconductor memory may be used.

(32) Additionally, the distribution of the program is performed, for example, by selling, transferring, and lending a portable recording medium such as a DVD or CD-ROM on which the program is recorded. Further, the program may be stored in a storage unit of a server computer, and the program may be distributed by transferring the program from the server computer to another computer via a network.

(33) A computer that executes such a program, for example, first stores, in a storage unit of the computer, a program recorded on a portable recording medium or a program transferred from a server computer. Then, when executing the processing, the computer reads the program stored in its own storage unit and executes processing in accordance with the read program. Furthermore, as another execution aspect of this program, a computer may directly read a program from a portable recording medium, and execute processing in accordance with the program. Furthermore, each time a program is transferred from a server computer to the computer, processing in accordance with the program received may be sequentially executed. Additionally, a configuration may be employed in which the program is not transferred from the server computer to the computer, but the processing described above is executed by a so-called application service provider (ASP) type service that achieves a processing function only by instructing the execution and acquiring the result. It should be noted that the program of the present embodiment includes information which is used for processing by the electronic computer and which is similar to the program (such as data that is not a direct command to the computer but has a property that defines the processing of the computer).

(34) Additionally, in the present embodiment, although the present apparatus is configured by executing a predetermined program on a computer, at least a portion of these processing contents may be achieved by hardware.

REFERENCE SIGNS LIST

(35) 1, 9 Receiver 11, 91 Light receiving unit 12 Parameter estimation unit 92 Synchronization unit 13, 93 Decoding Unit 8 Transmitter 81 Modulation unit 82 Light emitting unit