JP4652211B2 - Optical communication apparatus, optical communication system, and optical communication method - Google Patents

Description

  The present invention relates to an optical communication device, an optical communication system, and an optical communication method, and more particularly to a technique for performing optical communication using illumination light.

  In recent years, visible light communication for performing communication by weighting a signal to illumination light has been studied. In addition, LEDs have been developed as a light source device with a large amount of light and are used for illumination purposes. On the other hand, communication using infrared light has been put into practical use, and its communication devices are widely used for digital home appliance control and simple transmission applications.

  By the way, although the LED for illumination can be used for communication as described above, it is originally not a device suitable for communication because it is originally a device for illumination. For example, factors that make communication quality such as stability as a carrier, a spectrum spread over a wide band, etc. worse, and modulation / demodulation are difficult, driving requires a large current, and switching of direct modulation is difficult to speed up, etc. There is a problem to be solved.

  In addition, as described above, infrared light communication devices are widely used for control of digital home appliances and simple transmission applications, but are limited to these applications, and have advanced communication functions and multi-channel communication. Is not suitable.

On the other hand, with the popularization of digital home appliances, digital communication technology and digital signal processing technology have become common, and general-purpose digital communication devices can be used at low cost. For example, Patent Document 1 discloses a technique for performing stable communication using normal light such as an illumination LED.
JP 2004-221747 A

  However, even with the technique disclosed in Patent Document 1, specific specifications as a communication device, for example, a specific technique regarding a modulation method and a signal processing method is not described. It has been difficult to perform stable visible light communication using LEDs for illumination.

  The present invention has been made in view of this point, and an object thereof is to provide an optical communication device, an optical communication system, and an optical communication method capable of performing communication using illumination light in a stable and simple manner. And

The relative problems, the present invention provides an optical communication apparatus for transmitting an optical signal corresponding to the information, the primary modulation signal obtained by performing primary modulation by pairs to the base band signal of the information There are input secondary modulation means for performing secondary modulation with a pseudo-random signal and light emission means for emitting an optical signal corresponding to the signal subjected to the secondary modulation.

  With this configuration, when illumination light is used as communication, not only the primary modulation but also the secondary modulation using a pseudo-random code is performed on the information baseband signal. Communication is possible.

  In the optical communication apparatus of the present invention, the light emitting means controls to emit an optical signal corresponding to a signal obtained by superimposing the signal subjected to the secondary modulation and a driving signal for illuminating the light emitting means. You may have a control means.

  In the optical communication apparatus of the present invention, the secondary modulation unit may include a calculation unit that calculates the primary modulation signal and the pseudo-random signal.

  Further, the present invention is an optical communication device that receives an optical signal corresponding to information, wherein the optical signal received by the optical signal and the optical signal received by the optical receiver are input, and the pseudo-random signal is used to input the optical signal. Demodulating means for demodulating a primary modulation signal obtained by performing primary modulation on a baseband signal of information.

  With this configuration, it is possible to receive an optical signal corresponding to a signal subjected to secondary modulation and obtain an original primary modulation signal.

  Further, in the optical communication device of the present invention, the demodulating means slides the pseudo-random signal and outputs it, a photoelectric converting means for converting the optical signal received by the light receiving means into an electrical signal, Computation means for computing the pseudo-random signal output by the sliding means and a signal subjected to secondary modulation included in the electrical signal, and detection means for detecting the primary modulation signal obtained by the computation. May be.

  In the optical communication apparatus of the present invention, the sliding means outputs the pseudo random signal while shifting the pseudo random signal by predetermined bits at predetermined time intervals, and the level of the primary modulation signal detected by the detecting means is not less than a predetermined value or When exceeding, sliding of the pseudo-random signal may be stopped, and further, the output timing of the pseudo-random signal may be adjusted so that the level of the primary modulation signal detected by the detection means becomes maximum.

  In addition, the present invention is an optical communication system having an optical communication device that transmits an optical signal corresponding to the above-described information and an optical communication device that receives an optical signal corresponding to the information.

  The present invention is also an optical communication method for transmitting an optical signal corresponding to information, wherein a secondary modulation signal is input to a baseband signal of the information and subjected to secondary modulation using a pseudo-random signal. A modulation step and a light emission step of emitting an optical signal corresponding to the signal subjected to the secondary modulation.

  In the optical communication method of the present invention, the light emitting step may emit an optical signal corresponding to a signal obtained by superimposing the signal subjected to the secondary modulation and a driving signal for illuminating the light emitting means.

  Further, in the optical communication method of the present invention, the secondary modulation step may perform calculation of the primary modulation signal and the pseudo random signal.

  The present invention is also an optical communication method for receiving an optical signal corresponding to information, wherein the information base is based on a light receiving step for receiving the optical signal and an optical signal received by the light receiving step by a pseudo-random signal. A demodulation step for demodulating the primary modulation signal with respect to the band signal.

  Further, in the optical communication method of the present invention, the demodulation step includes a sliding step for sliding and outputting the pseudo-random signal, a photoelectric conversion step for converting the optical signal received by the light receiving means into an electrical signal, A calculation step of calculating the sliding pseudo-random signal output by the sliding step and a signal subjected to secondary modulation included in the electrical signal, and a detection step of detecting the primary modulation signal obtained by the calculation You may have.

  Further, in the optical communication method of the present invention, the sliding step outputs the pseudo random signal while shifting the pseudo random signal by predetermined bits at predetermined time intervals, and the level of the primary modulation signal detected by the detection step is equal to or higher than a predetermined value or When exceeding, sliding of the pseudo-random signal may be stopped, and further, the output timing of the pseudo-random signal may be adjusted so that the level of the primary modulation signal detected by the detection means becomes maximum.

According to the present invention, simply adding a small-scale circuit that can be realized by a general-purpose device to an illumination light source such as an illumination LED enables simple and stable optical communication.

  Hereinafter, the present invention will be described in detail with reference to the drawings. It should be noted that the present invention is not limited to the following examples, and modifications and improvements can be made without departing from the spirit of the present invention.

  FIG. 1 is a diagram showing a configuration of an optical communication system according to the present invention. The optical communication system shown in FIG. 1 includes a transmitter 1 and a receiver 2 as optical communication devices.

  The transmitter 1 includes a modulation unit 4 that performs secondary modulation based on a spreading code of a pseudo-random signal on a baseband signal that has been subjected to primary modulation input via a terminal 3, and an illumination light source such as an LED. A light emitting unit 6 that emits light for illumination, a drive unit 5 that drives the light emitting unit 6 based on a signal that has been subjected to secondary modulation by the modulation unit 4, and light emitted by the light emitting unit 6 is emitted. And an injection unit 7.

  On the other hand, the receiver 2 includes a light receiving unit 8 that receives light from the transmitter 1, a photoelectric conversion unit 9 that converts light received by the light receiving unit 8 into an electrical signal, and the photoelectric conversion unit 9. And a demodulator 10 that demodulates a baseband signal that is first-order modulated from the converted electrical signal.

  Hereinafter, the operation of the optical communication system will be described. The modulation unit 4 in the transmitter 1 receives a signal (baseband signal subjected to primary modulation) obtained by performing primary modulation on the information baseband signal via the terminal 3. . The modulation unit 4 performs secondary modulation with a pseudo-random signal that is a spreading code on the baseband signal subjected to the primary modulation. The signal subjected to the secondary modulation is input to the drive unit 5. The drive unit 5 adds the signal of the drive current of the illumination light source to the signal subjected to the secondary modulation, and drives the light emitting unit 6 using the added signal as a drive signal. Thereby, the light emission part 6 drives and emits light. Since the drive signal is obtained by adding the signal of the drive current of the light source for illumination to the signal subjected to the secondary modulation, the light emitted from the light emitting unit 6 includes the light component corresponding to the signal subjected to the secondary modulation, And a normal illumination light component. The emitting unit 7 emits the light emitted from the light emitting unit 6 to the outside.

  The light receiving unit 8 in the receiver 2 receives a part of the light emitted from the emitting unit 7 in the transmitter 1 and outputs it to the photoelectric converter 9. The photoelectric converter 9 converts the input light into an electrical signal and outputs it to the demodulator 10. The demodulator 10 demodulates the input electrical signal, converts it to a baseband signal subjected to primary modulation, and outputs it via the terminal 11.

  FIG. 2 is a diagram illustrating a detailed configuration of the modulation unit 4 in the transmitter 1. The modulation unit 4 illustrated in FIG. 2 includes a pseudo random signal generator 13, a calculator 14, and a terminal 15. The pseudo random signal generator 13 generates a pseudo random signal assigned to the baseband signal. The pseudo-random signal and the baseband signal subjected to the primary modulation input via the terminal 3 are input to the computing unit 14. The computing unit 14 performs a logical operation on these input signals, performs secondary modulation with a pseudo-random signal on the baseband signal subjected to the primary modulation, and outputs the baseband signal subjected to the secondary modulation to the terminal 15. Is output to the drive unit 5 via.

  FIG. 3 is a diagram showing a detailed configuration of the demodulator 10 in the receiver 2. 3 includes a terminal 16, a secondary filter 17, a branching unit 18, a clock extraction circuit 19, a pseudo random signal generator 20, a sliding circuit unit 21, arithmetic units 22a, 22b, and 22c (hereinafter, arithmetic units). 22a, 22b, and 22c are collectively referred to as “calculator 22”) and primary filters 23a, 23b, and 23c (hereinafter, the primary filters 23a, 23b, and 23c are collectively referred to as “primary filter 23” as appropriate). , Branching unit 25, detectors 26a, 26b, and 26c (hereinafter, detectors 26a, 26b, and 26c are collectively referred to as “detector 26” as appropriate), control unit 27, and branching unit 38.

  An electrical signal obtained by photoelectric conversion by the photoelectric conversion unit 9 is input to the secondary filter 17 via the input terminal 16. The secondary filter 17 extracts only the component of the signal subjected to the secondary modulation generated in the modulation unit 4 from the input signal. The signal subjected to the secondary modulation is branched by the branching unit 18, and one is input to the clock extraction circuit 19. The clock extraction circuit 19 extracts the clock of the pseudo random signal used for the secondary modulation in the modulation unit 4 from the input signal subjected to the secondary modulation. The extracted clock is branched by the branching unit 38 and supplied to the pseudo random signal generator 20, the sliding circuit unit 21 and the control unit 27.

  On the other hand, the signal subjected to the secondary modulation branched by the branching unit 18 and the output signal of the sliding circuit unit 21 are input to the calculators 22a, 22b, and 22c, respectively. These computing units 22a, 22b, and 22c perform despreading of the input signal. The output signal of the calculator 22a is input to the primary filter 23a, the output signal of the calculator 22b is input to the primary filter 23b, and the output signal of the calculator 22c is input to the primary filter 23c. Here, only when the pseudo-random signal and the pseudo-random signal included in the signal subjected to the secondary modulation coincide with each other, a correlation is obtained by despreading in the computing unit 22 and the primary modulation is performed from the primary filter 23. The baseband signal made is output. On the other hand, in a state where the pseudo-random signal and the signal subjected to the secondary modulation are almost orthogonal, the baseband signal subjected to the primary modulation by the despreading in the computing unit 22 is further spread, and the signal from the primary filter 23 is further spread. There is no output signal.

  The output signal of the primary filter 23a is input to the detector 26a, the output signal of the primary filter 23b is input to the detector 26b, and the output signal of the primary filter 23c is input to the detector 26c. The detectors 26 a, 26 b, and 26 c each detect an input signal and output the detection signal to the control unit 27. The control unit 27 controls the sliding circuit unit 21 according to the level of the detection signal, thereby capturing and maintaining synchronization of the signal subjected to the secondary modulation. When acquisition and synchronization hold are established, the best communication state is obtained. At this time, the baseband signal subjected to the primary modulation is output from the primary filter 23 c, further branched at the branch point 25, and output from the terminal 11.

  FIG. 4 is a diagram showing a detailed configuration of the sliding circuit unit 21 related to acquisition and synchronization holding, and FIG. 5 is a diagram showing a detailed configuration of the control unit 27 related to acquisition and synchronization holding. In the following, it is assumed that one bit length of the pseudo random signal is Ts.

  The pseudo random signal output from the pseudo random signal generator 20 in the receiver 2 is input to a predetermined bit shift circuit 28 in the sliding circuit unit 21 in FIG. The predetermined bit shift circuit 28 outputs the three series of pseudo-random signals 33a, 33b, and 33c with a delay shift of Ts, that is, one bit respectively. At this time, the predetermined bit shift circuit 28 repeats the operation of outputting the three series of pseudo-random signals 33a, 33b, and 33c for a certain time T1, respectively, and again outputting them for a certain time T1 after the elapse of 3Ts. At this time, since the capture is not yet established, the minute time adjustment circuit 29 is not operating, and the pseudo-random signals 33a, 33b, and 33c that are the input signals and the pseudo-signal that is the output signal to the computing unit 22 The random signals 35a, 35b, and 35c are equal.

  In a state where acquisition is not established, a pseudo random signal included in the signal subjected to the secondary modulation input to the calculator 22 and a pseudo random signal output from the pseudo random signal generator 20 to the sliding circuit unit 21; In other words, the pseudo-random signal output from the sliding circuit unit 21 to the computing unit 22 is almost orthogonal. For this reason, the output signal of the arithmetic unit 22 becomes a component of the despread signal as a result of multiplication of the pseudo-random signals, in other words, the component of the baseband signal subjected to the primary modulation does not appear. Therefore, there is no output signal from the primary filter 23.

  The time between any of the three sequences of pseudo-random signals output from the sliding circuit unit 21 to the computing unit 22 and the pseudo-random signals included in the second-order modulated signal that has passed through the second-order filter 17 as sliding proceeds. When the base shift is within 1 bit, a part of the component of the baseband signal subjected to the primary modulation is output from the corresponding computing unit 22. The detector 26 receives and detects the baseband signal subjected to the primary modulation, and outputs the detection signal to the control unit 27.

  The determination unit 32 in the control unit 27 in FIG. 5 inputs the three series of detection signals 24a, 24b, and 24c, and determines whether the level of any detection signal is equal to or higher than a predetermined value. When the level of the detection signal is equal to or higher than a predetermined value, the determination unit 32 generates a signal for stopping sliding and outputs the signal to the sliding circuit unit 21. As a result, the state of the predetermined bit shift circuit 28 in the sliding circuit unit 21 is fixed.

  In a state in which the predetermined bit shift circuit 28 is fixed, the determination unit 32 then compares the three series of detection signals 24a, 24b, and 24c, and the three series pseudo random signals output from the predetermined bit shift circuit 28. 33a, 33b, 33c and the time base relationship of the pseudo-random signal included in the second-order modulated signal are determined. Further, the determination unit 32 operates the predetermined bit shift circuit 28 again based on the determined result, and the time base relationship of the three series of pseudo random signals 33a, 33b, and 33c output from the predetermined bit shift circuit 28 is determined. The delay lock loop is shifted in time so that the initial values of the delay lock loop are + Ts, -Ts, and 0, respectively, and among the three series of pseudorandom signals 33a, 33b, and 33c, the pseudorandom signal 33c is subjected to secondary modulation. The time base of the pseudo-random signal included in the generated signal is made closest.

  In this state, the detection signals 24 a and 24 b branched by the branching units 31 a and 31 b are input to the differencer 30. The difference unit 30 outputs a difference signal between the detection signals 24 a and 24 b to the minute time adjustment circuit 29 via the adjustment signal generator 34. The minute time adjustment circuit 29 is controlled by the difference signal.

  In a state where the pseudo random signal included in the signal subjected to the secondary modulation matches the pseudo random signal 35c that is the output signal of the minute time adjustment circuit 29, the difference signal that is the output of the differentiator 30 becomes zero. Therefore, the adjustment signal generator 34 adjusts and controls the delay time of the minute time adjustment circuit 29 within a minute time within plus or minus 1 bit so that the output of the differencer 30 becomes zero. The adjustment signal generator 34 fixes the delay time of the minute time adjustment circuit 29 in a state where the difference signal that is the output of the differencer 30 becomes 0, and completes the capturing operation.

  When the capturing operation is completed, the control unit 27 maintains the relationship of + Ts, −Ts, 0 in the time base of the three series of pseudo random signals 33a, 33b, 33c, or the pseudo random signals 35a, 35b, 35c, The predetermined bit shift circuit 28 is operated so that a delay lock loop is formed and the state where the difference signal, which is the output of the differencer 30, becomes zero is maintained. Further, the control unit 27 generates a PLL control signal of the clock extraction circuit 19 to lock the PLL of the clock extraction circuit 19 to the pseudo random signal clock of the transmitter 1. As a result, synchronization is maintained.

  In this state, the baseband signal component in the output signal from the calculator 22c is maximized. Furthermore, since signals other than the baseband signal are orthogonal to the pseudo-random signal, the component of the signal after despreading is almost zero. The demodulated primary band baseband signal is output from the terminal 11.

  FIG. 6 is a diagram showing signal waveforms in the time domain in these series of operations. 6 (a) and 6 (b), the output 24 of the detector 26 at the predetermined time T1 is the pseudo random signal included in the signal on which the vertical modulation and quadratic modulation are performed, and the pseudo output output from the sliding circuit unit 21. It is the figure which showed time difference (tau) of the time base with a random signal on the horizontal axis. Taking one pseudo-random signal 35c from the three series of pseudo-random signals 35a, 35b, 35c from the sliding circuit unit 21 as an example, it is the output of the detector 26c on the vertical axis with respect to the time difference τ on the horizontal axis. The detection signal 24c is in the form of an autocorrelation function of a pseudo-random signal, and is usually a triangle having a duration of 2Ts when correlation is obtained. Since the time difference τ is a digital circuit, it cannot be a continuous value, and becomes a discrete value that is a multiple of Ts.

  As an example, when the pseudo-random signal 35c is shifted bit by bit, the time of x in FIG. There are two crosses in a triangle having a sustained length of 2Ts. Actually, the outputs of the sliding circuit unit 21 are three systems, and the time bases of the respective systems are shifted by Ts, so that the detection signals 24a, 24b, 24c at a predetermined time T1 are shown in FIG. Outputs indicated by ○, □, and Δ in a). In this example, the detection signals 24a and 24b exist in a triangle. At that time, the determination unit 32 determines whether the fine pseudo-random signal included in the signal further subjected to the secondary modulation and the sliding circuit unit 21 based on the values of the detection signal 24b indicated by □ and the detection signal 24a indicated by Δ. The time base time difference τ with respect to the output pseudo-random signal can be determined. Then, the determination unit 32 operates the predetermined bit shift circuit 28 again based on the determined result, and the time base relationship of the three series of pseudo random signals 33a, 33b, and 33c output from the predetermined bit shift circuit 28. Are shifted in time so that the initial values of the delay lock loop are + Ts, -Ts, and 0, respectively, and the pseudo-random signal 33c is second-order modulated among the three series of pseudo-random signals 33a, 33b, and 33c. Is made closest to the time base of the pseudo-random signal included in the signal.

  In this example, since the increment of the sliding time of the predetermined bit shift circuit 28 is 3Ts having a 3-bit length, the detection signals 24a, 24b, and 24c of the three series are detected at all other predetermined times T1 including before and after this. Both of these become zero.

  Here, when the predetermined bit shift circuit 28 stops its operation and then the minute time adjustment circuit 29 starts its operation, the minute delay time within ± Ts so that the difference signal that is the output of the differencer 30 becomes zero. As shown in FIG. 6B, the detected signal 24c becomes the maximum point indicated by ◯, where the delay time is fixed and the acquisition is completed.

  6 (c) and 6 (d) show the time between the pseudo-random signal included in the signal on which the output of the differencer 30 is plotted on the vertical axis and quadratic modulation, and the pseudo-random signal output from the sliding circuit unit 21. It is the figure which showed the time difference (tau) of the base on the horizontal axis. When the detection signal 24a and the detection signal 24b that is the inverse of the detection signal 24a are input to the differencer 30, the output of the differencer 30 is as shown in FIG. 6C or 6D. In the case of the S-shaped curve shown in FIG. 6D, since the middle of the simple gradient is zero cross, the minute time adjustment circuit 29 can be stably operated so that the output of the differencer 30 becomes zero.

  Thereafter, the output of the differencer 30 becomes 0, and as a result, the minute time adjustment circuit 29 continues to adjust ± ΔT so that the detection signal 24c, which is the output of the detector 26c, is held at the maximum point. A lock loop is formed, synchronization is maintained, and tracking is performed.

  When tracking is performed, a baseband signal subjected to primary modulation is output from the terminal 11 in FIG. 3, and thus a target baseband signal can be obtained by performing demodulation in a subsequent stage.

  A series of these operations are similar to the spread spectrum of the direct spread method adopted in CDMA and GPS. However, the present embodiment is different in that the carrier is not a coherent wave like the normal spread spectrum spread spectrum method but an illumination light. Since illumination light has a wide spectrum, it cannot be directly locked to a carrier modulated by a Costas loop PLL that can be used in CDMA, and a baseband signal subjected to secondary modulation is extracted by synchronous detection. I can't. However, in this embodiment, it is possible to lock the illumination light to a pseudo-random signal of a signal subjected to secondary modulation by using a delay lock loop.

  According to the present invention, optical communication can be easily performed only by adding a small-scale circuit that can be realized by a general-purpose device to a proof light source such as an illumination LED. Further, since not only primary modulation but also secondary modulation is performed on the information baseband signal, unstable elements can be diffused on the time axis and stabilized. Due to the diffusion on the time axis by the secondary modulation, the burden of a large current necessary for the direct modulation by switching is reduced on the time axis, and the modulation with a small current becomes possible. Further, the processing gain by correlation detection for the signal subjected to the secondary modulation increases the stability of the carrier of the illumination light and enables stable communication. Furthermore, signal correlation can be performed by correlation detection on a signal subjected to secondary modulation, the number of channels can be increased, and privacy of each channel can be ensured. Also, the speed of the baseband signal is limited at the cost of obtaining processing gain by spreading. However, if the frequency of the secondary modulation is set to several GHz, the speed of the baseband signal can be increased to about several tenths. This level of acquisition and synchronization processing circuit is realized by a general-purpose device and does not require any special technique or device. As a result, a visible light communication system can be realized with a simple configuration.

  As described above, the optical communication device and the optical communication method according to the present invention enable modulation and demodulation with a simple circuit in communication using an illumination light source such as an LED. Furthermore, by performing secondary modulation of the pseudo-random signal used in the spread spectrum communication method, it is possible to stabilize communication using an illumination light source that is unstable as a communication application. Further, in a Costas loop that is necessary in a normal spread spectrum system, a pseudo-random signal of secondary modulation is captured and held in synchronization using a delay lock loop instead of carrier reproduction. As a result, the same effect as the spread spectrum method can be obtained with a simple circuit, and illumination light that is not accurate as a carrier can be used for stable communication by processing gain. Furthermore, since correlation detection is performed, multiplexing and secret functions can be realized. For this reason, it can be used for communication in a place where multiplexing or a secret story is required such as a place where people gather.

It is a figure which shows the structure of an optical communication system. It is a figure which shows the detailed structure of the modulation | alteration part in a transmitter. It is a figure which shows the detailed structure of the demodulation part in a receiver. It is a figure which shows the detailed structure of a sliding circuit part. It is a figure which shows the detailed structure of a control part. It is a figure which shows the signal waveform in a time domain.

Explanation of symbols

  1 Transmitter, 2 Receiver, 3, 11, 15, 16 Terminal, 4 Modulator, 5 Drive, 6 Light Emitter, 7 Ejector, 8 Light Receiver, 9 Photoelectric Converter, 10 Demodulator, 13, 20 Pseudorandom signal generator, 14, 22a, 22b, 22c arithmetic unit, 17 secondary filter, 18, 25, 31a, 31b, 38 branching unit, 19 clock extraction circuit, 21 sliding circuit unit, 23a, 23b, 23c primary Filter, 26a, 26b, 26c detector, 27 control unit, 28 predetermined bit shift circuit, 29 minute time adjustment circuit, 30 subtractor, 32 determination unit, 34 adjustment signal generator.

Claims (5)

An optical communication device that receives an optical signal corresponding to information,
A light receiving means for receiving the optical signal;
Demodulating means for demodulating a primary modulation signal obtained by inputting an optical signal received by the light receiving means and performing primary modulation on the baseband signal of the information by a pseudo-random signal;
Have
The demodulating means includes
Pseudo-random signal generating means for generating the pseudo-random signal;
Sliding means for sliding and outputting the pseudo-random signal generated by the pseudo -random signal generating means ;
An arithmetic operation that performs an operation of a photoelectric conversion unit that converts an optical signal received by the light receiving unit into an electrical signal, a pseudo-random signal output by the sliding unit, and a signal subjected to secondary modulation included in the electrical signal. Means,
Detecting means for detecting a primary modulation signal obtained by the calculation,
The sliding means outputs the pseudo random signal while shifting it by predetermined bits at predetermined time intervals, and when the level of the primary modulation signal detected by the detection means exceeds or exceeds a predetermined value, the pseudo random signal The sliding is stopped, and further, the delay time of the output of the pseudo-random signal is adjusted by a minute time corresponding to within plus or minus 1 bit so that the level of the primary modulation signal detected by the detection means becomes maximum. ,
An optical communication device. It said demodulation means,
Secondary filter means for extracting the second-order modulated signal based on the electrical signal;
Further seen including a clock extracting means for extracting a clock of the pseudo random signal from the signal the secondary filter means 2 primary modulation extracted by the is made,
The pseudo random signal generating means generates the pseudo random signal in synchronization with the clock,
The sliding means slides the pseudo random signal generated by the pseudo random signal generating means for a time corresponding to the clock and corresponding to the predetermined bit, and outputs the result.
The computing means computes the pseudo-random signal output by the sliding means and the signal subjected to the secondary modulation extracted by the secondary filter means.
The optical communication apparatus according to claim 1. An optical communication device that transmits an optical signal corresponding to information,
Secondary modulation means for inputting a primary modulation signal obtained by performing primary modulation on the baseband signal of the information and performing secondary modulation with a pseudo-random signal;
An optical communication device having light emitting means for emitting an optical signal corresponding to the signal subjected to the secondary modulation;
An optical communication device according to claim 1 or 2,
An optical communication system comprising: An optical communication method for receiving an optical signal corresponding to information,
A light receiving step for receiving the optical signal;
A demodulation step of demodulating a primary modulation signal with respect to the baseband signal of the information from the optical signal received by the light reception step by a pseudo-random signal;
The demodulation step includes
A pseudo-random signal generating step for generating the pseudo-random signal;
A sliding step of sliding and outputting the pseudo-random signal generated in the pseudo -random signal generation step ;
A photoelectric conversion step for converting the optical signal received by the light receiving step into an electrical signal;
A calculation step of calculating a sliding pseudo-random signal output by the sliding step and a signal subjected to secondary modulation included in the electrical signal;
A detection step of detecting a primary modulation signal obtained by the calculation,
The sliding step outputs the pseudo random signal while shifting the pseudo random signal by predetermined bits at predetermined time intervals, and when the level of the primary modulation signal detected by the detection step exceeds or exceeds a predetermined value, The sliding is stopped, and further, the delay time of the output of the pseudo random signal is adjusted by a minute time corresponding to within plus or minus 1 bit so that the level of the primary modulation signal detected by the detection step becomes maximum. ,
An optical communication method characterized by the above. The demodulation step,
A secondary filtering step of extracting the signal subjected to the secondary modulation from the electrical signal;
Further comprising a clock extracting a clock of the pseudo random signal from the extracted secondary modulation is made signals by the secondary filtering step,
The pseudo random signal generation step generates the pseudo random signal in synchronization with the clock,
In the sliding step, the pseudo-random signal generated in the pseudo-random signal generation step is output according to a time corresponding to the clock and corresponding to the predetermined bit.
The calculation step calculates the pseudo-random signal output in the sliding step and the signal subjected to the secondary modulation extracted in the secondary filtering step.
The optical communication method according to claim 4.

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