Receiving device, visible light communication system, receiving method, program

Abstract

To provide a visible light communication system, a transmitter, a receiver, a method, and a program that more accurately detect a redundant frame including a transitory frame.SOLUTION: In the visible light communication system, a receiver 12 includes: a light reception unit 121 that receives an optical signal based on a modulated signal that is created by phase shift modulating and connecting together a training sequence having a predetermined value and a digital transmit signal, and generates a plurality of receive signals that correspond to light receiving elements, respectively, on the basis of the electrical charges accumulated in a plurality of sampling instruments that are exposed to light through a half cycle of the optical signal at different timing, respectively; and a demodulation unit 123 that estimates the phase of the modulated signal and estimates, on the basis of a section corresponding to the training sequence in the estimation result, the estimate value of a relative phase that represents a misalignment of phase between transmission and reception and the index of a redundant frame that includes a transitory frame at an exposure timing when symbols are switched. The demodulation unit adopts a frame closer to a timing at which symbols are switched, as the redundant frame.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to a technique for performing communication using visible light and electromagnetic waves in its surrounding band.

Background Art

[0002] In recent years, visible light sources are used not only for lighting applications to obtain light but also for communication applications. The spread of light-emitting diodes (LEDs) as visible light sources has contributed to this. Although the amount of light emitted per element of a light-emitting diode is less than that of conventional visible light sources such as incandescent bulbs and fluorescent lamps, it is superior to conventional visible light sources in terms of its lifespan, size, and power consumption. In addition to the above characteristics, a light-emitting diode has a characteristic of a very fast response speed. Also, it is easy to electrically control the light emission of a light-emitting diode. Because of the above characteristics of light-emitting diodes, in recent years, research and development have been conducted not only for lighting applications to obtain light but also for use in signal transmission using the blinking of visible light.

[0003] For example, Non-Patent Document 1 discloses performing communication by superimposing a signal on a household lighting fixture using a light-emitting diode.

[0004] Also, currently, since visible light is not subject to the regulations of the Radio Law, there are no restrictions on the band and power, and these can be taken largely. Non-Patent Document 2 discloses using a light-emitting diode exclusively for communication by utilizing this fact. Communication performed using a visible light source such as a light-emitting diode is called visible light communication. In visible light communication, a photodetector or an image sensor which is an array thereof is used as a receiver. Usually, a signal can be continuously obtained with a photodetector. On the other hand, an image sensor can acquire signals from a large number of photodetectors at once, but due to its nature, usually only signals sampled at a period Tf can be acquired. Hereinafter, it is mainly assumed that an image sensor is used as a light-receiving device.

[0005] Figure 1 shows the properties of signals used in visible light communication. First, the digital transmission signal S(i) (also called the transmission symbol) is converted to a phase value to obtain the modulated signal M(i). This type of modulation is called phase-shift modulation (phase-shift modulation). For example, if S(i) is represented as a binary value, it is converted to a phase value such as 0→0 and 1→π (binary phase-shift modulation, BPSK). Here, i is an index representing time. Next, the phase of a square wave with a carrier frequency of 1 / Tc is changed according to the modulated signal M(i) to obtain an electrical signal E(t) for driving the light-emitting element. Here, t is a real number representing time. However, while the signal M(i) is a temporally discrete signal, the signal E(t) is a temporally continuous signal. 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 time iTs-Ts / 2 to time iTs+Ts / 2, with a reference to time iTs, which is a certain delay from the time indicated by index i. As shown in Figure 1, the time represented by index i has a time width Ts.

[0006] Conventional techniques (for example, Non-Patent Document 1) convert the optical signal F'(t), which is obtained by superimposing noise on F(t) captured by a photodetector, into an electrical signal E'(t). Subsequently, the phase signal M'(k) is estimated from E'(t). Ideally, F(t) = F'(t), but this may change depending on the performance of the image sensor, propagation in the medium, and delay, so here we will describe F(t) and F'(t) separately. It is assumed that approximately F(t+TL) = F'(t), where TL represents the propagation delay.

[0007] Referring to Figure 2, an example of signal exchange in visible light communication will be explained. Figure 2 illustrates how the blinking of a light-emitting element is received by an image sensor. Assume that the blinking of the transmitter (light-emitting element) is imaged in region Ω on the image sensor. The receiver captures the sum of the output values ​​of all photodetectors in region Ω as the received signal from the transmitter.

[0008] When transmitting information over a communication channel, it is common practice to encode the original information in some form. The smallest unit of signal that constitutes the encoded information is called a symbol. In digital communication channels, it is important to detect the symbol's clock (the time width used when transmitting one symbol) and phase. This process is called symbol timing synchronization between the receiver and the transmitter. It is desirable that symbol timing synchronization is always maintained during communication. This is because, generally, there is no means of sharing the same oscillator between the receiver and the transmitter, so there is always a possibility that the synchronization will be out of sync.

[0009] To perform symbol timing synchronization, it is necessary to use a symbol timing regeneration circuit, such as the one described in Non-Patent Document 3. This circuit detects the phase difference between two input signals and synchronizes their phases by applying feedback control. One of the two signals is the input from the oscillator, and the other is the signal to be synchronized. When a photodetector is used as the receiver, it is easy to use a symbol timing regeneration circuit because the signal can be obtained continuously. On the other hand, when an image sensor is used, the signal that can be used for reception processing is a sampled signal, and therefore a discrete-time signal. In this case, a certain sampling frequency is required to perform symbol timing synchronization using a symbol timing regeneration circuit.

[0010] In the system described above, the sampling frequency required for phase demodulation is more than twice the carrier frequency. On the other hand, image sensors generally have a fixed upper limit on the product of the number of pixels obtained in a single image and the number of images taken per unit time, i.e., the sampling frequency. Therefore, if an image sensor is used as the light-receiving part of the system described above and a large sampling frequency is adopted for demodulation, the number of pixels obtained in a single sample must be sacrificed.

[0011] Incidentally, by using two cameras and capturing images at different timings, as illustrated in Figure 3, the relative phase of the transmitted signal can be determined. It is known that this allows for communication using phase shift modulation even if the number of images captured per unit time is approximately the same as the number of symbols transmitted per unit time.

[0012] However, this method has the following two problems a) and b).

[0013] a) The correspondence between the phase of a phase-shift modulated codeword and the observable relative phase is not trivial. When trying to determine the phase of a transmitted signal using the results of imaging performed at different timings using two cameras, it is necessary to know the reference phase, that is, which phase the phase-shift modulated codeword corresponds to. However, it is not possible to determine the reference phase by simply using two cameras.

[0014] b) The symbol switches during the exposure time. As illustrated in Figure 4, if imaging is performed at the moment the symbol switches, the pixel values ​​will not be the expected values, making it impossible to determine the relative phase. Below, frames captured at such timings will be referred to as "transition frames".

[0015] To address these two challenges, the technology described in Patent Document 1 has been proposed (see, for example, Patent Document 1).

[0016] The technology described in Patent Document 1 addresses problem a) above by enabling the receiving device to periodically acquire an estimated value Θrel of the relative phase θrel. Furthermore, the technology described in Patent Document 1 addresses problem b) above by inserting redundant frames. [Prior art documents] [Patent Documents]

[0017] [Patent Document 1] Japanese Patent Publication No. 2019-161485 [Overview of the Initiative] [Problems that the invention aims to solve]

[0018] The method described in Patent Document 1 is effective for clear transition frames where the phase changes at the center of the exposure time. However, if two consecutive detected phases within a frame take similar values, there was a possibility of making an incorrect determination.

[0019] For example, in the example shown in Figure 5, the upper frame should be identified as Pattern 2 and the lower frame as Pattern 3. Patterns such as Pattern 2 and Pattern 3 will be discussed later. In this time relationship, even in a completely noise-free environment, almost identical pixel value sets can be obtained in frame 2 and frame 3. Therefore, even slight noise can alter the detection results for redundant frames. Here, the actual pixel values ​​include noise such as thermal noise from the camera and ambient light noise. Consequently, in situations like the one shown in Figure 5, there is a possibility of detecting an incorrect pattern.

[0020] As a result, if the transition frame is incorrectly determined, the wrong frame may be discarded within a single packet, and demodulation may be performed using pixel values ​​that should have been discarded, potentially increasing the number of symbol errors per packet.

[0021] The present invention aims to provide a receiving device, a visible light communication system, a receiving method, and a program that can detect redundant frames, which may include transition frames, with greater accuracy than conventional methods. [Means for solving the problem]

[0022] A receiving apparatus according to one aspect of the present invention receives an optical signal based on a modulation signal formed by phase-shift modulating and connecting a training sequence having a predetermined value and a digital transmission signal, and exposes the optical signal to a plurality of light-receiving elements at different exposure timings over a half cycle of the optical signal. A light-receiving unit that generates a plurality of received signals corresponding to each of the light-receiving elements based on the charge stored in the sampler of the light-receiving elements; when the phase difference between the optical signal and the exposure timing is zero, the value of the received signal is used as a received signal value for normalization, and the phase of the modulation signal is estimated based on the values of the plurality of generated received signals and the received signal value for normalization, and among the estimation results of the phase, based on the part corresponding to the training sequence, an estimated value of the relative phase, which is the phase shift between transmission and reception, and an index of a redundant frame that may include a transition frame, which is a frame at the exposure timing when the symbol switches, are estimated. A demodulation unit, and the demodulation unit uses a frame closer to the timing when the symbol switches as the redundant frame.

Advantages of the Invention

[0023] It is possible to detect a redundant frame that may include a transition frame more accurately than in the prior art.

Brief Description of the Drawings

[0024] [Figure 1] FIG. 1 is a diagram for explaining the background art. [Figure 2] FIG. 2 is a diagram for explaining the background art. [Figure 3] FIG. 3 is a diagram for explaining the background art. [Figure 4] FIG. 4 is a diagram for explaining the background art. [Figure 5] FIG. 5 is a diagram for explaining the background art. [Figure 6] FIG. 6 is a diagram showing a configuration example of a visible light communication system, a transmission apparatus, and a reception apparatus. [Figure 7] FIG. 7 is a diagram showing an example of a processing procedure of a visible light communication system. [Figure 8] FIG. 8 is a diagram showing an example of a sequence of a modulation signal. [Figure 9] Figure 9 shows an example of a packet. [Figure 10] Figure 10 shows an example of the symbol period (Tsymbol), frame period (Tframe), and exposure timing. [Figure 11] Figure 11 shows an example of a pattern. [Figure 12] Figure 12 shows an example of a computer's functional configuration. [Modes for carrying out the invention]

[0025] Embodiments of the present invention will be described in detail below. In the drawings, components having the same function are given the same number, and redundant explanations are omitted.

[0026] The configuration of an embodiment of the visible light communication system will be described below with reference to Figure 6. As shown in the figure, the visible light communication system 1 of this embodiment includes a transmitting device 11 and a receiving device 12. The transmitting device 11 includes a modulation unit 111 and a light-emitting unit 112. The light-emitting unit 112 includes a light-emitting signal control unit 1121 and a light-emitting element 9122. The receiving device 12 includes a light-receiving unit 121 and a demodulation unit 123. The light-receiving unit 121 includes a first light-receiving element 1211, a second light-receiving element 1212, a first received signal generation unit 1213, and a second received signal generation unit 1214. The demodulation unit 123 includes a phase signal estimation unit 1231, a frame interpretation unit 1232, and a transmission signal estimation unit 1233.

[0027] The inputs, outputs, and operation of each part will be explained below with reference to Figure 7.

[0028] <Modulation section 111> The modulation unit 111 consists of a memory, an arithmetic unit, and the like.

[0029] Input: The modulation unit 111 receives a sequence of digital transmission signals S(j) S(1), S(2), ..., S(J). The transmission signal S(j) contains 1 bit or log2G bits of information, and j is an integer representing the transmission signal number.

[0030] Output: The modulation unit 111 outputs a sequence of modulated signals M(i) M(1), M(2), ... The modulated signal M(i) is phase information with values ​​corresponding to the digital transmission signal S(j) and predetermined training sequences. i is a number representing the modulation signal number. i is also used as an index representing time.

[0031] Operation: The modulation unit 111 generates a series of modulated signals MM(j) MM(1), MM(2), ..., MM(J) of the input digital transmission signal S(j) series (S111). For example, if the value of S(j) is L, the modulation unit 111 generates the modulated signal MM(j) as 2*π / G*L. Furthermore, the modulation unit 111 generates a series of training sequence modulated signals MT(jj) MT(1), MT(2), ..., MT(JJ) (S111). The series MT(1), MT(2), ..., MT(JJ) are modulated signals with a predetermined phase ΘR. The modulation unit 111 converts the sequence of modulated signals MT(1), MT(2), ..., MT(JJ) of JJ training sequences into M(1), M(2), ..., M(JJ), and outputs the sequence of modulated signals MM(1), MM(2), ..., MM(J) of J sequences into M(JJ+1), M(JJ+2), ..., M(JJ+J). That is, as shown in Figure 8, the modulation unit 111 generates two sequences of modulated signals MM and MT, concatenates them to form a modulated signal M, and outputs the sequence M(1), ..., M(JJ), M(JJ+1), ..., M(JJ+J) of the modulated signal M(i).

[0032] <Light-emitting part 112> As described above, the light-emitting unit 112 includes a light-emitting signal control unit 1121 and a light-emitting element 9122. The light-emitting element 9122 is, for example, an LED.

[0033] Input: The light-emitting unit 112 receives a sequence of modulated signals M(i) M(1), M(2), ... as input.

[0034] Output: The light-emitting unit 112 outputs an optical signal F(t).

[0035] Operation: The light emission signal control unit 1121 of the light emission unit 112 generates a rectangular wave (electrical signal) with period Tc, frequency 1 / Tc, and phase ΘM from time iTs-Ts / 2 to time iTs+Ts / 2, which is a predetermined time Ts after the input modulated signal M(i) is ΘM (where M is an arbitrary value), and supplies it to the light-emitting element 9122 (S1121). The light-emitting element 9122 emits light in response to the electrical signal supplied by the light emission signal control unit 1121 (S9122). As a result, an optical signal F(t) is output from the light emission unit 112. However, the electrical signal generated by the light emission signal control unit 1121 is controlled to take into account the performance and characteristics of the light-emitting element, so that the optical signal F(t) of the light-emitting element becomes a desired value.

[0036] Here, each modulated signal M(i) is represented by an electrical or optical signal with a time length of n × Tc. This time length is called the symbol period Tsymbol. n is a predetermined positive integer.

[0037] Figure 9 shows an example of a packet transmitted by the transmitter 91 through modulation by the modulation unit 111 and illumination by the light-emitting unit 112. In this example, the packet consists of a preamble and data (payload). The preamble consists of a leading part shown as A in Figure 9 and a training part shown as B in Figure 9. In this example, the leading part, which has a duration of 2 × T symbol, blinks at half the maximum brightness of the LED, which is the leading light-emitting unit 112. Then, in the training part, a symbol that blinks n times with phases of 0°, 180°, 0°, 180°, 0° is inserted. n is a predetermined positive integer, as will be described later. This sequence of symbols that blinks n times with phases of 0°, 180°, 0°, 180°, 0° is an example of a predetermined sequence of phase ΘR MT(1), MT(2), ..., MT(JJ). As shown in Figure 9, the data (payload) D[1], D[2], ..., D

[50] are symbols of the data. These D[1], D[2], ..., D

[50] are an example of a sequence of J modulated signals MM(1), MM(2), ..., MM(J).

[0038] <Light receiving section 121> As described above, in this embodiment, the light receiving unit 121 has a configuration that includes two sets of light receiving elements and receiving signal generation units, but the number of sets of light receiving elements and receiving signal generation units is not limited to two.

[0039] The operation of the light-receiving unit 121 can be generally described as follows: The light-receiving unit 121 receives optical signals F1(t), F2(t),... based on a modulated signal M(i) which is obtained by phase-shift modulating and concatenating a training sequence with predetermined values ​​and a digital transmission signal S(j). Based on the charge accumulated in the samplers of multiple photodetectors that are exposed to the optical signals F1(t), F2(t),... for half a period of the optical signals F1(t), F2(t),... at different exposure timings, the light-receiving unit 121 generates multiple received signals B1'(t), B2'(t),... corresponding to each of the photodetectors (S121).

[0040] The operation of the light-receiving unit 121 will be described in detail below, assuming that there are two sets of light-receiving elements and received signal generation units. Similar to the prior art, the first and second light-receiving elements 1211 and 1212 are, for example, photodetectors. An optical lens may also 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 also be an image sensor in which photodetectors are arranged in a grid. The first and second received signal generation units 1213 and 1214 consist of a sampling element, memory, arithmetic unit, etc.

[0041] Input: The light receiving unit 121 receives the first optical signal F1'(t) and the second optical signal F2'(t) output from the light emitting unit 112.

[0042] Output: The light receiving unit 121 outputs a sequence of first received signals B1'(k) B1'(1), B1'(2), ... and a sequence of second received signals B2'(k) B2'(1), B2'(2), ...

[0043] Operation: The first light-receiving element 1211 of the light-receiving unit 121 outputs a first electrical signal E1'(t) corresponding to the input first optical signal F1'(t) to the first received signal generation unit 1213 (S1211).

[0044] When the first photodetector 1211 is an image sensor, specifically as shown in Figure 3, each photodetector measures the charge accumulated in the sampler from time TI + iTf - Tf / 2 - τ / 2 to TI + iTf - Tf / 2 + τ / 2. Here, TI is the relative phase (offset), iTf is the time corresponding to the center of the i-th frame, iTf - Tf / 2 is the time corresponding to the beginning of the i-th frame, and τ is the exposure time. The relative phase TI is sometimes expressed as the relative phase θrel.

[0045] Similarly, the second photodetector 1212 of the light-receiving unit 121 outputs a second electrical signal E2'(t) corresponding to the input second optical signal F2'(t) to the second received signal generation unit 1214 (S1212). If the second photodetector 1212 is an image sensor, specifically as shown in Figure 3, each photodetector measures the charge accumulated in the sampler from time TI+iTf-Tf / 2-τ / 2+Tf / 4 to TI+iTf-Tf / 2+τ / 2+Tc / 4. Tc / 4 represents the difference in exposure timing between the first photodetector 1211 and the second photodetector 1212, and is one-quarter of the carrier wave period Tc.

[0046] The first received signal generation unit 1213 measures the intensity of the input first electrical signal E1'(t) at time intervals Tframe and outputs it as the first received signal B1'(k) (S1213). Tframe is the frame period, which will be explained later. If the first photodetector 1211 is an image sensor, the first received signal generation unit 1213 takes the sum of the charge measurement results over a predetermined range Ω and outputs the sum of the measurement results as the first received signal B1'(k) (S1213). Similarly, the second received signal generation unit 1214 measures the intensity of the input second electrical signal E2'(t) at time intervals Ts and outputs it as the second received signal B2'(k) (S1214). If the second light-receiving element 1212 is an image sensor, the second received signal generation unit 1214 takes the sum of the charge measurement results over a predetermined range Ω and outputs the sum of the measurement results as the second received signal B2'(k) (S1214).

[0047] Here, the frame period Tframe = (n-1) × Tc. As mentioned earlier, by setting the symbol period Tsymbol = n × Tc and the frame period Tframe = (n-1) × Tc, a periodic redundant frame appears every n frames. This redundant frame is called a "redundant frame". Figure 10 shows the symbol period Tsymbol, frame period Tframe, and exposure timing when n = 6. A redundant frame is either a frame in which the same symbol observed in the frame before or after the redundant frame is observed, or it is a transition frame. Under these conditions, where the symbol period Tsymbol = n × Tc and the frame period Tframe = (n-1) × Tc, it is possible to prevent continuously obtaining only transition frames. That is, under these conditions, even if a transition frame appears once, the phase of the same symbol can be correctly estimated in the frame before or after the transition frame.

[0048] Furthermore, if the predetermined sequence of phase ΘR is the training sequence 0°, 180°, 0°, 180°, 0° as exemplified in Figure 9, the receiver 92 can observe redundant frames that have the same pixel values ​​as the preceding or succeeding frame, or include symbol transition timings that cannot be used for correct demodulation, in addition to the 0°, 180°, 0°, 180°, 0° symbols shifted by relative phase θrel. If JJ=5, n=5, symbol period Tsymbol=n×Tc, frame period Tframe=(n-1)×Tc, and the predetermined sequence of phase ΘR is the training sequence 0°, 180°, 0°, 180°, 0°, the types of symbol patterns that can be observed are the six types from Pattern 1 to Pattern 6 shown in Figure 11. The frame interpretation unit 1232 of the demodulation unit 123, described later, determines which pattern is appropriate, thereby detecting redundant frames including transition frames. By removing redundant frames, a more appropriate relative phase θrel and signal can be obtained.

[0049] <Demodulation section 123> As described above, the demodulation unit 123 includes a phase signal estimation unit 1231, a frame interpretation unit 1232, and a transmission signal estimation unit 1233. The phase signal estimation unit 1231, the frame interpretation unit 1232, and the transmission signal estimation unit 1233 consist of a memory, a processing unit, and the like.

[0050] The operation of the demodulation unit 123 can be generally described as follows: The demodulation unit 123 uses the values ​​of the received signal when the phase difference between the optical signals F1(t), F2(t),... and the exposure timing is zero as normalized received signal values ​​R1, R2,..., estimates the phase of the modulated signal based on the values ​​of the generated multiple received signals B1'(t), B2'(t),... and the normalized received signal values ​​R1, R2,..., and estimates the relative phase value Θrel, which is the phase difference between transmission and reception, and the index of redundant frames which may include transition frames, which are frames at the exposure timing when the symbols switch (S123). At this time, the demodulation unit 123 designates frames closer to the timing when the symbols switch as redundant frames.

[0051] The operation of the demodulation unit 123 will be explained in detail below, with reference to Figure 7, assuming that it includes two sets of light-receiving elements and received signal generation units.

[0052] Input: The demodulation unit 123 receives the sequence of the first received signal B1'(k) and the sequence of the second received signal B2'(k) from the light receiving unit 121.

[0053] Output: The demodulation unit 123 outputs the estimation result S'(j).

[0054] Operation: The phase signal estimation unit 1231 of the demodulation unit 123 generates a relative phase estimation result M'(k) based on the sequence of the first received signal B1'(k) and the sequence of the second received signal B2'(k), and outputs it to the frame interpretation unit 1232 and the transmission signal estimation unit 1233 (S1231).

[0055] Specifically, the phase signal estimation unit 1231 pre-stores the values ​​of the received signals when the phase difference between the exposure timing and the carrier wave is zero for each of the first received signal B1'(k) and the second received signal B2'(k) as normalized received signal values ​​R1 and R2. These normalized received signal values ​​are either provided externally in some form or estimated in advance. Based on the first received signal B1'(k) and the second received signal B2'(k), the phase signal estimation unit 1231 estimates the relative phase of the received signals and outputs the relative phase estimation result M'(k).

[0056] Typically, the phase signal estimation unit 1231 performs phase estimation using a certain number (let's call it LL) of pairs of B1'(k) and B2'(k). The number of relative phase estimation results M'(k) output at this time is also LL. The above relative phase estimation can be performed, for example, by the following formula.

number

[0057] The frame interpretation unit 1232 detects redundant frames by performing the following processing on the first JJ × n / (n-1) elements of M'(k). The frame interpretation unit 1232 is assumed to have predetermined values ​​of phase information ΘR, the length of the training sequence's modulated signal JJ, the length of the symbol's modulated signal J, and n.

[0058] First, the frame interpretation unit 1232 calculates the estimated relative phase θrel Θrel and the error Drel between the estimated Θrel and the observed relative phase M'(k) for each of the multiple assumed patterns. Examples of assumed patterns are Pattern 1 to Pattern 6 shown in Figure 11. The number of assumed patterns is, for example, JJ × n / (n-1). By inserting a "redundant frame" to the left of the c-th symbol from the left of the JJ symbols constituting the phase information ΘR (where c=1,...,JJ) and inserting a "redundant frame" to the right of the rightmost symbol of the JJ symbols constituting the phase information ΘR, JJ × n / (n-1) types of assumed patterns can be created.

[0059] For example, the frame interpretation unit 1232 sets the relative phase θrel that minimizes the squared error defined by the following equation as the estimated value Θrel of the relative phase θrel corresponding to pattern p. The frame interpretation unit 1232 also sets this squared error as the error Drel corresponding to pattern p.

[0060] Σ k=1 JJ×n / (n-1) (M'(k)-Pp(k)) 2 Here, Pp(k) is the phase corresponding to the k-th frame of pattern p. For example, in Pattern 2 (p=2) in Figure 11, P2(1)=θrel, P2(2)=M'(k), P2(3)=180+θrel, P2(4)=θrel, P2(5)=180+θrel, and P2(6)=θrel. As in this example, if the phase corresponding to the k-th frame of pattern p is redundant, the error Drel is calculated using that phase as M'(k).

[0061] Next, the frame interpretation unit 1232 selects the pattern that minimizes the error Drel and calculates the phase difference Θd between the phase Θred of the redundant frame in the selected pattern and the estimated relative phase Θrel of the preceding or succeeding frame. The frame interpretation unit 1232 can calculate the phase difference Θd based, for example, on the following equation: The phase Θred of the redundant frame in the selected pattern is the relative phase M'(k) of the redundant frame in the selected pattern.

[0062] Θd = |Θrel-Θred|, |Θrel-Θred| <180 Θd = 360 - |Θrel-Θred|, |Θrel-Θred| ≧180 The frame interpretation unit 1232 determines whether Θd > Θt. If Θd > Θt, it selects the pattern that minimizes the error Drel as the actual received signal pattern. The phase difference threshold Θt is a predetermined threshold.

[0063] If Θd > Θt is not true, the frame interpretation unit 1232 considers the pattern with the smallest error Drel and the pattern with the second smallest error Drel as candidates, and if the estimated relative phase Θrel > 45°, it selects the pattern with the redundant frame later as the actual received signal pattern, and if the opposite is true, it selects the pattern with the redundant frame earlier.

[0064] The frame interpretation unit 1232 outputs the interval d of redundant frames and the index e of the frame that is estimated to be the first redundant frame after the training sequence as a control signal C'(K)=(d,e), based on the pattern selected as the received pattern and the index k of the relative phase M'(k).

[0065] In this way, the demodulation unit 123 may determine the estimated relative phase Θrel and the error Drel between the estimated Θrel and the estimated phase M'(k), which is the observed relative phase, for each of the multiple assumed patterns, and estimate the index of redundant claims determined by the pattern with the smallest error Drel or the pattern with the second smallest error Drel.

[0066] The specific behavior when parameters JJ and n are set as follows is described below. When JJ=5 and n=5, assume that the index corresponding to the redundant frame among (B1'(1), B2'(1)), (B1'(2), B2'(2)), ..., (B1'(6), B2'(6)) related to the training sequence is 2.

[0067] At this point, it can be inferred that the index of the first redundant frame is 8 and the interval between them is 6. Therefore, the frame interpretation unit 1232 outputs the control signal C'(K)=(6,8) to the transmission signal estimation unit 1233 (S1232).

[0068] Furthermore, the frame interpretation unit 1232 outputs an estimated value Θrel of the relative phase θrel, assuming the pattern of the received signal, to the transmission signal estimation unit 1233 (S1232).

[0069] The transmission signal estimation unit 1233 of the demodulation unit 123 estimates the symbol sequence S'(j) using the least squares method or the like, based on the sequence M'(JJ+1), ..., M'(JJ+J) consisting of J M'(k) other than the training sequence, excluding the M'(k) indicated by the control signal C'(K) (S1233).

[0070] The M'(k) indicated by the control signal C'(K) are M'(e), M'(e+d), M'(e+2d), M'(e+3d), ...

[0071] [Differentiation] Although embodiments of the present invention have been described above, the specific configuration is not limited to these embodiments, and it goes without saying that any design modifications or other changes made as appropriate without departing from the spirit of the present invention are still included in the present invention.

[0072] The various processes described in the embodiments may be executed not only in chronological order according to the sequence described, but also in parallel or individually as needed, depending on the processing capacity of the device performing the processes.

[0073] For example, data exchange between components of a transmitting device or a receiving device may occur directly, or it may occur via a storage unit (not shown).

[0074] The length of the packet preamble, or in other words, the JJ value, may be greater than a predetermined value. This can improve the stability of the estimation.

[0075] The training sequence, in other words, the predetermined sequence of phases ΘR, can be any sequence of predetermined phases such as 0°, 90°, 180°, 270°, 180°, 90°, ..., other than the example of 0°, 180°, 0°, 180°, 0° given above.

[0076] In the above explanation, the number of photodetectors and received signal generators was two each, but this can be increased to three or more. In this case as well, by shifting the timing of each photodetector's reception by one-quarter of the carrier period Tc, the phase estimation can be performed between 1 and 2, between 2 and 3, between 3 and 4, etc., as described above, thereby increasing noise immunity.

[0077] The above explanation required two or more photodetectors for each light-emitting element on a single transmitter. However, a similar effect can be achieved by using two or more light-emitting elements in the transmitter and arranging the phases of their respective emission timings to be different.

[0078] The method of the present invention can be applied even when there are multiple transmitting devices (for example, H devices). In this case, multiple receiving signal generation units and demodulation units should be provided. In this case, the estimation of the demodulated signal is performed in accordance with each transmitting device.

[0079] In addition to the training sequence, a preamble to signal the start of transmission may be inserted into the packet.

[0080] [Programs, recording media] The processing of each part of the above-mentioned devices may be implemented by a computer. In this case, the processing content of the functions that each device should have is described by a program. This program is then loaded into the memory unit 1020 of the computer 1000 shown in Figure 12, and the arithmetic processing unit 1010, input unit 1030, output unit 1040, display unit 1060, etc. are operated, thereby realizing the various processing functions of each of the above-mentioned devices on the computer.

[0081] The program describing this process can be recorded on a computer-readable recording medium. Computer-readable recording media are, for example, non-temporary recording media, specifically magnetic recording devices, optical discs, etc.

[0082] Furthermore, this program may be distributed, for example, by selling, transferring, or lending portable recording media such as DVDs or CD-ROMs on which the program is recorded. Alternatively, the program may be stored in the storage device of a server computer and distributed by transferring the program from the server computer to other computers via a network.

[0083] A computer executing such a program first stores the program recorded on a portable recording medium or transferred from a server computer in its own non-temporary storage device, the auxiliary recording unit 1050. Then, when processing is to be executed, the computer reads the program stored in the auxiliary recording unit 1050 into the storage unit 1020 and executes the processing according to the loaded program. Alternatively, the computer may directly read the program from the portable recording medium into the storage unit 1020 and execute the processing according to that program. Furthermore, each time a program is transferred to this computer from a server computer, it may sequentially execute the processing according to the received program. Alternatively, the above processing may be executed by a so-called ASP (Application Service Provider) type service, where the server computer does not transfer programs to this computer, but the processing function is realized only by execution instructions and result acquisition. In this embodiment, the program includes information used for processing by an electronic computer that is equivalent to a program (data that is not a direct instruction to the computer but has the property of defining the processing of the computer).

[0084] Furthermore, in this configuration, the device is configured by executing a predetermined program on a computer, but at least a part of these processing contents may be implemented in hardware. For example, the modulation unit 111, the first received signal generation unit 1213, the second received signal generation unit 1214, and the demodulation unit 123 may be configured by processing circuits.

[0085] It goes without saying that the invention may be modified as appropriate without departing from its spirit.

Claims

1. A light receiving unit receives an optical signal based on a modulated signal obtained by coupling a training sequence with predetermined values ​​and a digital transmission signal by phase shift modulation, and generates a plurality of received signals corresponding to each of the photodetectors based on the charge accumulated in the sampler of a plurality of photodetectors that are exposed to the optical signal for half a period of the optical signal at different exposure timings, A receiving device comprising: a demodulation unit that takes 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, estimates the phase of the modulated signal based on a plurality of generated received signal values ​​and the normalized received signal value, and estimates an estimated relative phase, which is the phase difference between transmission and reception, and an index of redundant frames, which may include transition frames, which are frames at the exposure timing when symbols switch, based on the portion of the phase estimation results that corresponds to the training sequence, The demodulation unit selects the frame closest to the timing when the symbol switches as the redundant frame. Receiving device.

2. A receiving device according to claim 1, The demodulation unit calculates an estimated relative phase for each of the assumed multiple patterns, and the error between the estimated value and the observed relative phase, which is the estimated phase. It then estimates the index of the redundant frame determined by the pattern with the smallest error or the pattern with the second smallest error. Receiving device.

3. A visible light communication system including a transmitting device and a receiving device, The transmitting device is A modulation unit generates a modulated signal by linking a training sequence, which consists of two predetermined different values ​​arranged alternately, with a digital transmission signal using phase shift modulation. Includes a light-emitting unit that outputs an optical signal based on the modulated signal, The receiving device is, A light-receiving unit generates a plurality of received signals corresponding to each of the photodetectors based on the charge accumulated in the sampler of a plurality of photodetectors that are exposed to the optical signal for half a period of the optical signal at different exposure timings, The demodulation unit includes a function that takes 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, estimates the phase of the modulated signal based on a plurality of generated received signal values ​​and the normalized received signal value, and estimates an estimated relative phase, which is the phase difference between transmission and reception, and an index of redundant frames, which may include transition frames, which are frames at the exposure timing when symbols switch, based on the portion of the phase estimation result that corresponds to the training sequence. The demodulation unit selects the frame closest to the timing when the symbol switches as the redundant frame. Visible light communication system.

4. A receiving method performed by a receiving device, A light receiving step involves receiving an optical signal based on a modulated signal obtained by phase-shift modulating and concatenating a training sequence with predetermined values ​​and a digital transmission signal, and generating a plurality of received signals corresponding to each of the photodetectors based on the charge accumulated in the samplers of a plurality of photodetectors that are exposed to the optical signal for half a period of the optical signal at different exposure timings, The demodulation step includes: setting 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; estimating the phase of the modulated signal based on a plurality of generated received signal values ​​and the normalized received signal value; and estimating an estimated relative phase, which is the phase difference between transmission and reception, and an index of redundant frames, which may include transition frames, which are frames at the exposure timing when symbols switch, based on the portion of the phase estimation results corresponding to the training sequence. In the demodulation step, frames closer to the timing of the symbol change are designated as redundant frames. Reception method.

5. A program that causes a computer to function as a component of the receiving device according to claim 1 or 2.

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