JP2015220639A - Optical radio transmitter, optical radio receiver and optical radio communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical radio transmitter, an optical radio receiver and an optical radio communication system reducing the influence of multiple-reflected light and preventing the deterioration of communication quality.SOLUTION: The optical radio transmitter includes means for generating and composing a signal for canceling a multiple-reflected light component which arrives at the receiver after multiple-reflected by glass etc. in an optical space through the glass in which the glass etc. are existent on a transmission path. This enables the suppression of the influence of the glass etc. on the transmission path. Also, the optical radio transmitter includes means for feeding back information of delay, attenuation, etc. related to the multiple-reflected light component from the reception side to the transmitter.

Description

  The present invention relates to a transmission / reception technique in optical wireless communication.

  In recent years, with an increase in communication speed, an optical wireless communication technique known as FSO (Free Space Optics) has attracted attention. Optical wireless is a method of communicating using laser light through a medium. This optical radio has the advantage that communication can be performed only by installing a transmitter / receiver like a radio without laying an optical fiber, and that, unlike radio, no license is required and broadband communication is possible. However, it is characterized by being more susceptible to attenuation and diffusion due to a passing medium such as the atmosphere than radio.

  As one of the application destinations of optical wireless communication, communication in which an optical wireless signal passes through a medium such as glass installed in a window or the like (hereinafter referred to as communication through glass) has been proposed (for example, Patent Document 1 or non-patent). (Refer to Reference 2.) In communication through glass, communication between rooms partitioned by walls, etc., and communication between indoors and outdoors, etc., do not make a hole in the wall and make optical wireless transmission through glass such as windows. It is what is used.

JP 2007-228466 A

Proposal of optical space communication system through glass (Ken Sasamura et al., IEICE Technical Report. OFT, Optical Fiber Application Technology 107 (52), 19-24, 2007-05-17)

  However, in communication through glass, intersymbol interference due to reflection becomes a quality deterioration factor in addition to the quality deterioration factor of signal light decrease due to loss caused by a medium such as glass. That is, as shown in FIG. 1, the signal light from the optical wireless transmitter passes through the glasses 1 and 2 to the optical wireless receiver and there are components that reach directly, whereas the optical wireless transmitter as shown in FIG. There is a component (hereinafter referred to as a multiple reflection component) that is reflected once by the glass 1 and returns in the opposite direction, reflected again by the glass 2, and received by the optical receiver. The space between the optical receiver and the glass 1, between the glass 1 and the glass 2, and between the glass 2 and the optical wireless transmitter is filled with air that can be regarded as free space, or with a medium having a different dielectric constant from the glass 1 and the glass 2. Yes. In FIG. 2, the signal light for each reflection is not arranged in the same straight line for convenience of explanation, but is actually a signal light in the same straight line. In practice, glass has a thickness, and multiple reflection occurs even with a single glass.

Here, if the direct signal light S _direct (t) and the multiple reflected light S _reflect (t) are taken, the signal light of S _direct (t) + S _reflect (t) is incident on the optical wireless receiver and directly received by the light receiving element. Since only the signal light S _direct (t) cannot be separated, an error may occur during signal identification. That is, the prior art document has a problem of possibility of communication quality degradation.

  In order to solve such a problem, an object of the present invention is to provide an optical wireless transmitter, an optical wireless receiver, and an optical wireless communication system that reduce the influence of multiple reflected light and prevent deterioration in communication quality. To do.

  In order to achieve the above object, the optical wireless transmitter according to the present invention superimposes in advance an information signal for transmitting a signal that cancels a multiple reflected light component that is multiple-reflected by glass or the like.

Specifically, an optical wireless transmitter according to the present invention is an optical wireless transmitter for optical wireless communication that transmits an information signal by passing an optical signal through a plurality of media having different dielectric constants,
A signal generator for generating the information signal;
A predistortion unit that superimposes on the information signal a compensation signal that is generated when the optical signal passes through the medium and compensates for a component of multiple reflected light that enters the optical wireless receiver that is the destination of the information signal;
It is characterized by providing.

  Since this optical wireless transmitter superimposes in advance on an information signal for transmitting a signal that cancels the multiple reflected light component in the predistortion unit, the multiple reflected light component contained in the optical signal received by the optical wireless receiver is small. Therefore, the present invention can provide an optical wireless transmitter that reduces the influence of multiple reflected light and prevents deterioration in communication quality.

  The predistortion unit of the optical wireless transmitter according to the present invention is characterized by receiving a parameter representing the component of the multiple reflected light from the optical wireless receiver and generating the compensation signal. By receiving the parameter from the optical wireless receiver, it is possible to follow the fluctuation of the multiple reflected light component.

  The predistortion unit further includes a compensation circuit unit that receives reflected light reflected by the optical wireless receiver of the optical wireless transmitter according to the present invention and discriminates a parameter representing a component of the multiple reflected light. Receives a parameter representing the component of the multiple reflected light from the compensation circuit unit, and generates the compensation signal. By determining the parameter based on the optical signal reflected by the optical wireless receiver, it is possible to follow the variation of the multiple reflected light component.

  On the other hand, in order to achieve the above object, the optical wireless receiver according to the present invention superimposes a signal for canceling multiple reflected light components that are multiple-reflected by glass or the like on the received signal.

Specifically, an optical wireless receiver according to the present invention is an optical wireless receiver for optical wireless communication that transmits an information signal by passing an optical signal through a plurality of media having different dielectric constants,
A light receiving unit that receives the optical signal and converts it into an electrical reception signal;
A distortion compensation unit that outputs a distortion compensation signal by superimposing a compensation signal for compensating a multiple reflected light component of multiple reflected light generated by the optical signal passing through the medium on the reception signal output by the light receiving unit; ,
An identification unit for identifying the information signal from the optical wireless transmitter that has transmitted the optical signal, from the distortion compensation signal output by the distortion compensation unit;
It is characterized by providing.

  Since the optical wireless receiver superimposes a signal for canceling the multiple reflected light component in the distortion compensating unit on the received signal, the multiple reflected light component included in the signal received by the identifying unit is small. Therefore, the present invention can provide an optical wireless receiver that reduces the influence of multiple reflected light and prevents deterioration in communication quality.

  The identification unit of the optical wireless receiver according to the present invention compares the distortion compensation signal and the information signal to detect a deterioration amount, and the distortion compensation unit detects the multiplex from the deterioration amount received from the identification unit. The compensation signal is generated by discriminating the parameter of the reflected light component. By receiving the deterioration amount from the identification unit and discriminating the parameters, it is possible to follow the variation of the multiple reflected light component.

  The optical wireless receiver according to the present invention further includes a reflection unit that reflects the optical signal and outputs reflected light. By reflecting the optical signal received by the optical wireless receiver to the optical wireless transmitter, the optical wireless transmitter can determine the parameter, and can follow the variation of the multiple reflected light component.

  Furthermore, the optical wireless communication system according to the present invention is a system in which an optical wireless transmitter receives parameters of multiple reflected light components determined by an optical wireless receiver and superimposes a compensation signal on an information signal to be transmitted.

  The optical wireless communication system according to the present invention is a system in which an optical signal reflected by an optical wireless receiver is received by an optical wireless transmitter, a parameter of a multiple reflected light component is determined, and a compensation signal is superimposed on an information signal to be transmitted. It may be.

  The present invention can provide an optical wireless transmitter, an optical wireless receiver, and an optical wireless communication system that reduce the influence of multiple reflected light and prevent deterioration in communication quality.

It is a figure explaining the optical component which arrives directly from an optical wireless transmitter to an optical wireless receiver in optical wireless communication. It is a figure explaining the optical component which arrives in an optical wireless communication, carrying out multiple reflection from an optical wireless transmitter to an optical wireless receiver. It is a figure explaining the optical wireless transmitter which concerns on this invention. It is a figure explaining the signal generation part which produces | generates a compensation signal in the optical wireless transmitter which concerns on this invention. It is a figure explaining the optical wireless transmitter which concerns on this invention. It is a figure explaining the signal generation part which produces | generates a compensation signal in the optical wireless transmitter which concerns on this invention. It is a figure explaining the optical wireless transmitter which concerns on this invention. It is a figure explaining the signal generation part which produces | generates a compensation signal in the optical wireless transmitter which concerns on this invention. It is a figure explaining the optical wireless transmitter which concerns on this invention. It is a figure explaining the signal generation part which produces | generates a compensation signal in the optical wireless transmitter which concerns on this invention. It is a figure explaining the optical wireless receiver and optical wireless communication system which concern on this invention. It is a figure explaining the optical wireless receiver and optical wireless communication system which concern on this invention. It is a figure explaining the optical wireless receiver which concerns on this invention.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are embodiments of the present invention, and the present invention is not limited to the following embodiments. In the present specification and drawings, the same reference numerals denote the same components.

An optical wireless communication system according to the present embodiment described below includes an optical transmitter and an optical receiver, and can be regarded as a free space such as air (hereinafter referred to as free space), one or more glasses, and the like. Communication is performed using a medium having a dielectric constant different from that of the space (FIGS. 1 and 2). 1 and 2 show a case where there are two glasses. The signal light transmitted from the optical wireless transmitter is a direct signal light S _direct (t) that reaches the optical wireless receiver through the free space 3, the glass 2, the free space 2, the glass 1, the free space 1, etc. Reflected by glass 1 through free space 3, glass 2, free space 2, etc., reflected by glass 2 through free space 2, etc., and again reflected through free space 2, glass 1, free space 1, etc. It is divided into S _reflect (t). The free space 1, the free space 2, the free space 3, the glass 1, and the glass 2 that are routed here are not limited to air or glass, but may be media that have different dielectric constants and reflect on their boundary surfaces. Good.

An optical wireless transmitter according to the present invention is an optical wireless transmitter for optical wireless communication that transmits an information signal by passing an optical signal through a plurality of media having different dielectric constants,
A signal generator for generating the information signal;
A predistortion unit that superimposes on the information signal a compensation signal that is generated when the optical signal passes through the medium and compensates for a component of multiple reflected light that enters the optical wireless receiver that is the destination of the information signal;
It is characterized by providing.
This optical wireless transmitter has the configuration described in the first to fourth embodiments.

(Embodiment 1)
FIG. 3 is a diagram for explaining the optical wireless transmitter 101 according to the present embodiment. The optical wireless transmitter 101 generates a signal generation unit 11 that generates a component of signal light S (t) of information to be transmitted, and S _c (t) corresponding to a component that is a reverse phase of multiple reflected light. The signal generating unit 12 includes a combining unit 13 that combines the signal S (t) from the signal generating unit 11 and the signal S _c (t) of the signal generating unit 12. A signal generating unit 12 and a combining unit 13 are predistortion units 14.

Here, S _c (t) = − kS (t + τ), k is an intensity ratio of reflected light to direct light, and generally k << 1. τ is the delay time of the reflected light with respect to the direct light, and τ> 0. k and τ are parameters representing components of multiple reflected light.

Therefore, the optical wireless receiver receives S _direct (t) = S (t) + S _c (t) as direct light and S _reflect (t) = kS (t + τ) + kS _c (t + τ) as reflected light. Will be. As a result, the optical wireless receiver receives S _direct (t) + S _reflect (t) = S (t) −k ² St (t + 2τ). since it is k << 1, term of k ² becomes small enough, it is possible to greatly reduce the influence of multiple reflection light component. In addition, as S _c (t), k is generated in a form including k and second order components as S _c (t) = − kS (t + τ) + k ² S (t + 2τ), and k in the optical wireless receiver is You may make it cancel the component after the secondary. In addition, assuming a plurality of multiple reflection paths, a component corresponding to multiple reflected light is generated as S _c (t) = − k ₁ S (t + τ ₁ ) −k ₂ S (t + τ ₂ ). It doesn't matter.

The signal generating section 12 is made of, for example, reversed phase and damping unit 19 for attenuating S c _{(t) is} and the k delay unit 18 and the reverse phase delaying time τ the S _{c (t)} (FIG. 4). However, FIG. 4 is an example, and the signal generator 12 may have a configuration other than that of FIG. 4 in order to generate S _c (t).

(Embodiment 2)
FIG. 5 is a diagram for explaining the optical wireless transmitter 102 of the present embodiment. The optical wireless transmitter 102 generates a signal generation unit 21 that generates a component of s (t) of information to be transmitted, and a signal generation that generates s _c (t) corresponding to a component that is the reverse phase of the multiple reflected light. Unit 22, combining unit 23 that combines signal s (t) from signal generating unit 1 and signal s _c (t) from signal generating unit 2, and an electrical signal from combining unit 23 as an optical wireless signal The modulation unit 25 converts the signal light into S (t) + S _c (t). The signal generation unit 22 and the multiplexing unit 23 are the predistortion unit 24. The modulation unit 25, s signal light S with respect to the modulation signal (t) _(t), for the modulated signal _s c (t) and outputs the signal light _S c (t) .

Here, S _c (t) = − kS (t + τ), k is an intensity ratio of reflected light to direct light, and generally k << 1. τ is the delay time of the reflected light with respect to the direct light, and τ> 0. k and τ are parameters representing components of multiple reflected light.

Therefore, the optical wireless receiver receives S _direct (t) = S (t) + S _c (t) as direct light and S _reflect (t) = kS (t + τ) + kS _c (t + τ) as reflected light. Will be. As a result, the optical wireless receiver receives S _direct (t) + S _reflect (t) = S (t) −k ² St (t + 2τ). since it is k << 1, term of k ² becomes small enough, it is possible to greatly reduce the influence of multiple reflection light component. In addition, as s _c (t), k is generated so as to include components after the second order as s _c (t) = − ks (t + τ) + k ² s (t + 2τ), and k in the optical wireless receiver is You may make it cancel the component after the secondary. Further, assuming a plurality of multiple reflection paths, a component corresponding to the multiple reflected light is generated as s _c (t) = − k ₁ s (t + τ ₁ ) −k ₂ s (t + τ ₂ ). It doesn't matter.

The signal generating section 22 is made of, for example, s c _(t) and s _{c (t)} the time τ by a delay unit 28 for delaying reverse phase and negative-phase-attenuation section 29 for attenuating the k (FIG. 6). However, FIG. 6 is an example, and in order to generate s _c (t), the signal generator 22 may have a configuration other than that of FIG.

(Embodiment 3)
FIG. 7 is a diagram for explaining the optical wireless transmitter 103 of the present embodiment. The optical wireless transmitter 103 generates a signal generator 31 that generates a component of signal light S (t) of information to be transmitted, and a signal generator 32 that generates -S _c (t) corresponding to a component of multiple reflected light. And a multiplexing unit 33 for multiplexing the signal S (t) from the signal generation unit 31 and the signal S _c (t) of the signal generation unit 32 in opposite phases. The signal generation unit 32 and the multiplexing unit 33 are the predistortion unit 34.

Here, −S _c (t) = kS (t + τ), k is an intensity ratio of reflected light to direct light, and generally k << 1. τ is the delay time of the reflected light with respect to the direct light, and τ> 0. k and τ are parameters representing components of multiple reflected light.

Therefore, the optical wireless receiver receives S _direct (t) = S (t) + S _c (t) as direct light and S _reflect (t) = kS (t + τ) + kS _c (t + τ) as reflected light. Will be. As a result, the optical wireless receiver receives S _direct (t) + S _reflect (t) = S (t) −k ² St (t + 2τ). since it is k << 1, term of k ² becomes small enough, it is possible to greatly reduce the influence of multiple reflection light component. In addition, as S _c (t), k is generated in a form including k and second order components as S _c (t) = − kS (t + τ) + k ² S (t + 2τ), and k in the optical wireless receiver is You may make it cancel the component after the secondary. Further, assuming a plurality of multiple reflection paths, a component corresponding to multiple reflected light such as -S _c (t) = k ₁ S (t + τ ₁ ) + k ₂ S (t + τ ₂ ). I do not care.

The signal generating unit 32 is made of, for _{example, S} c (t) and _S c (t) the time τ by the attenuation section 39. attenuate the delay unit 38 and k delaying (Figure 8). However, FIG. 8 is an example, and the signal generator 32 may have a configuration other than that of FIG. 8 in order to generate S _c (t).

(Embodiment 4)
FIG. 9 is a diagram for explaining the optical wireless transmitter 104 of the present embodiment. The optical wireless transmitter 104 includes a signal generator 41 that generates a component of s (t) of information to be transmitted, a signal generator 42 that generates -s _c (t) corresponding to a component of multiple reflected light, The signal s (t) from the signal generator 41 and the signal −s _c (t) of the signal generator 42 are combined in reverse phase, and the electrical signal from the combiner 43 is an optical wireless signal. The modulation unit 45 converts the signal light into S (t) + S _c (t). The signal generation unit 42 and the multiplexing unit 43 are the predistortion unit 44. The modulation unit 45, s signal light S with respect to the modulation signal (t) _(t), for the modulated signal _s c (t) and outputs the signal light _S c (t) .

Here, −S _c (t) = kS (t + τ), k is an intensity ratio of reflected light to direct light, and generally k << 1. τ is the delay time of the reflected light with respect to the direct light, and τ> 0. k and τ are parameters representing components of multiple reflected light.

Therefore, the optical wireless receiver receives S _direct (t) = S (t) + S _c (t) as direct light and S _reflect (t) = kS (t + τ) + kS _c (t + τ) as reflected light. Will be. As a result, the optical wireless receiver receives S _direct (t) + S _reflect (t) = S (t) −k ² St (t + 2τ). since it is k << 1, term of k ² becomes small enough, it is possible to greatly reduce the influence of multiple reflection light component. In addition, as s _c (t), k is generated so as to include components after the second order as s _c (t) = − ks (t + τ) + k ² s (t + 2τ), and k in the optical wireless receiver is You may make it cancel the component after the secondary. Further, assuming a plurality of multiple reflection paths, a component corresponding to multiple reflected light is generated as in -s _c (t) = k ₁ s (t + τ ₁ ) + k ₂ s (t + τ ₂ ). I do not care.

The signal generator 42 is made of, for _{example, s} c (t) and _s c (t) the time τ delayed delaying portion 48 and the negative-phase-attenuation section 49. attenuate the k (Figure 10). However, FIG. 10 is an example, and the signal generator 42 may have a configuration other than that of FIG. 10 in order to generate s _c (t).

(Embodiment 5)
An optical wireless receiver according to the present invention is an optical wireless receiver for optical wireless communication that transmits an information signal by passing an optical signal through a plurality of media having different dielectric constants,
A light receiving unit that receives the optical signal and converts it into an electrical reception signal;
A distortion compensation unit that outputs a distortion compensation signal by superimposing a compensation signal for compensating a multiple reflected light component of multiple reflected light generated by the optical signal passing through the medium on the reception signal output by the light receiving unit; ,
An identification unit for identifying the information signal from the optical wireless transmitter that has transmitted the optical signal, from the distortion compensation signal output by the distortion compensation unit;
It is characterized by providing.

  FIG. 13 is a diagram for explaining the optical wireless receiver 201 of this embodiment. The optical wireless receiver 201 includes an identification unit 51 that performs signal identification, and a delay / intensity adjustment / phase inversion combination unit 52 that combines the signal identified by the identification unit 51 with time delay, intensity adjustment, and phase inversion. And a light receiving unit 53 that receives an optical signal from the optical wireless transmitter. The delay / intensity adjustment / phase inversion combining unit 52 may be referred to as a distortion compensation unit.

The light receiving unit 53 receives the signal light of S _direct (t) + S _reflect (t) and generates s ′ (t) + ks _c ′ (t + τ). The delay / intensity adjustment / phase inversion synthesizer 52 generates −ks (t + τ) based on s (t) and multiplexes it with s ′ (t) + ks _c ′ (t + τ). Since ks _c ′ (t + τ) ≈ks (t + τ), the delay / intensity adjustment / phase inversion combining unit 52 outputs the s ′ (t) component. The identification unit 51 identifies s (t) from the s ′ (t) component. At this time, the identification unit 51 may once identify the code of the information source from the input s ′ (t) component and regenerate s (t).

The delay / intensity adjustment / phase inversion combining unit 52 may automatically adjust k and τ by obtaining information such as the signal deterioration amount from the identification unit 51. This will be specifically described. The identification unit detects the amount of deterioration by comparing the distortion compensation signal and the information signal, the distortion compensation unit determines the parameter of the multiple reflected light component from the amount of deterioration received from the identification unit, The compensation signal is generated. The optical wireless transmitter outputs an optical known signal S _direct (A) obtained by optically converting the known information signal s (A) to the optical wireless receiver 201. The light receiving unit 53 receives the multiple reflected light S _reflect (A) generated by the known light signal S _direct (A), and generates s ′ (A) + ks _c ′ (A + τ). The delay / intensity adjustment / phase inversion synthesizer 52 first outputs to the discriminator 51 without compensation. Since this signal is obtained by superimposing multiple reflected light components on a known information signal, the identification unit 51 can recognize the amount of signal degradation. Then, the delay / intensity adjustment / phase inversion combining unit 52 determines the parameters k and τ from the signal degradation amount and s ′ (A) + ks _c ′ (A + τ). As an actual discrimination method, the delay / intensity adjustment / phase inversion synthesizer 52 finds the optimum k and τ by changing k and τ so that the deterioration amount is reduced. The delay / intensity adjustment / phase inversion synthesizer 52 generates −ks (A + τ) from s (A) using the parameters found in this way, and s ′ (A) + ks _c ′ (t + τ) is multiplexed. And output to the identification unit 51. The parameter may be optimized by repeating this operation several times.

  The delay / strength adjustment / phase inversion synthesizer 52 compensates for a normal received signal using the determined parameters. Further, the above parameters may be reviewed periodically or constantly.

(Embodiment 6)
The optical wireless communication system of this embodiment includes any one of optical wireless transmitters 101 to 104 and an optical wireless receiver 201. In the present optical wireless communication system, the predistortion unit of the optical wireless transmitters 101 to 104 receives a parameter representing the component of the multiple reflected light from the optical wireless receiver, and generates the compensation signal. .

  FIG. 11 is a diagram illustrating the optical wireless system 301 of the present embodiment. The optical wireless receiver 201 in FIG. 11 has a determination unit 61 that determines the delay time τ and the attenuation constant k of the multiple reflected light, and sends the determination information to the optical wireless transmitters (101 to 104). The discriminating unit 61 may be the discriminating unit 51 and the delay / intensity adjustment / phase inversion combining unit 52 described with reference to FIG. The optical wireless transmitters (101 to 104) use the delay units (18, 28, 38, 48) in the signal generators (12, 22, 32, 42) based on τ and k notified from the optical wireless receiver 201. The delay amount and the attenuation amount of the negative phase / attenuation unit (19, 29, 49) or the attenuation unit 39 are adjusted and determined.

  There is no limitation on the means for transmitting τ and k from the optical wireless receiver to the optical wireless transmitter. In addition, the adjustment timing of the delay amount and the attenuation amount in the signal generation unit is arbitrary. In addition, the information transmitted from the optical wireless receiver to the optical wireless transmitter is not directly τ and k, but the degradation amount of the optical signal received by the optical wireless receiver, and the parameter regarding the multiple reflection determined from the degradation amount It doesn't matter. In this case, the signal generator changes k and τ so as to reduce the deterioration amount, and determines a value.

(Embodiment 7)
The optical wireless communication system of this embodiment includes any one of optical wireless transmitters 101 to 104 and an optical wireless receiver 201. In the optical wireless communication system, the optical wireless receiver further includes a reflection unit that reflects the optical signal and outputs reflected light, and the optical wireless transmitters 101 to 104 transmit the optical signal to the optical wireless A compensation circuit unit that receives reflected light reflected by the receiver and discriminates a parameter that represents the component of the multiple reflected light, and the predistortion unit includes a parameter that represents the component of the multiple reflected light as the compensation circuit unit. And generating the compensation signal.

FIG. 12 is a diagram illustrating the optical wireless system 302 according to the present embodiment. The optical wireless receiver 201 in FIG. 11 has a reflection unit 62 that reflects light from the light receiving unit 53, and sends the received signal light back to the optical wireless transmitters (101 to 104). The optical wireless transmitters (101 to 104) include a light receiving unit 63 that receives the reflected light S _reverse (t) sent back, and a determination unit 64 that determines the delay time τ and the attenuation constant k of the multiple reflected light from the reflected light. A compensation circuit 65 is further provided. Based on the determined τ and k, the determination unit 64 uses the delay amount of the delay unit (18, 28, 38, 48) and the reverse phase / attenuation unit (19, 29) in the signal generation unit (12, 22, 32, 42). 49) or the attenuation amount of the attenuation unit 39 is adjusted and determined.

For example, since the compensation circuit 65 can recognize the optical signal S _direct (t) + S _reflect (t) or S _direct (t) transmitted by the optical wireless transmitters (101 to 104), the reflected light S _reverse (t) is deteriorated. The amount can be judged. For this reason, the determination unit 64 determines k and τ so that the deterioration amount of the reflected light is reduced. Note that the amount of deterioration of the reflected light is due to the round trip between the optical wireless transmitter and the optical wireless receiver, so the deterioration amount of the reflected light is not minimized, for example, the current deterioration amount and the minimum deterioration amount. K and τ may be determined to be between.
The adjustment timing of τ and k is arbitrary.

(Effect of embodiment)
In the optical wireless transmitter, the optical wireless receiver, and the optical wireless communication system according to the first to seventh embodiments, in the optical wireless communication path in which multiple reflections such as glass occur, the signal degradation due to the multiple reflections is reduced. This can be improved by reducing the influence of, and higher speed and stable communication becomes possible.

11, 12, 21, 22, 31, 32, 41, 42: signal generators 13, 23, 33, 43: multiplexers 14, 24, 34, 44: predistortion units 25, 45: modulation units 18, 28 , 38, 48: delay units 19, 29, 49: reverse phase / attenuation unit 39: attenuation unit 51: identification unit 52: delay / intensity adjustment / phase inversion synthesis unit 53: light receiving unit 61: determination unit 62: reflection unit 63 : Light receiving unit 64: discrimination unit 65: compensation circuit units 101 to 104: optical wireless transmitter 201: optical wireless receiver 301, 302: optical wireless communication system

Claims (8)

An optical wireless transmitter for optical wireless communication that transmits an information signal by passing an optical signal through a plurality of media having different dielectric constants,
A signal generator for generating the information signal;
A predistortion unit that superimposes on the information signal a compensation signal that is generated when the optical signal passes through the medium and compensates for a component of multiple reflected light that enters the optical wireless receiver that is the destination of the information signal;
An optical wireless transmitter comprising:   The optical wireless transmitter according to claim 1, wherein the predistortion unit receives a parameter representing the component of the multiple reflected light from the optical wireless receiver and generates the compensation signal. The optical signal further includes a compensation circuit unit that receives reflected light reflected by the optical wireless receiver and discriminates a parameter representing a component of the multiple reflected light.
The optical wireless transmitter according to claim 1, wherein the predistortion unit receives a parameter representing the component of the multiple reflected light from the compensation circuit unit and generates the compensation signal. An optical wireless receiver for optical wireless communication that transmits an information signal by passing an optical signal through a plurality of media having different dielectric constants,
A light receiving unit that receives the optical signal and converts it into an electrical reception signal;
A distortion compensation unit that outputs a distortion compensation signal by superimposing a compensation signal for compensating a multiple reflected light component of multiple reflected light generated by the optical signal passing through the medium on the reception signal output by the light receiving unit; ,
An identification unit for identifying the information signal from the optical wireless transmitter that has transmitted the optical signal, from the distortion compensation signal output by the distortion compensation unit;
An optical wireless receiver comprising: The identification unit detects the amount of deterioration by comparing the distortion compensation signal and the information signal,
The optical wireless receiver according to claim 4, wherein the distortion compensator determines a parameter of the multiple reflected light component from the deterioration amount received from the identification unit, and generates the compensation signal.   The optical wireless receiver according to claim 4, further comprising a reflection unit configured to reflect the optical signal and output reflected light. An optical wireless transmitter according to claim 2,
An optical wireless receiver according to claim 5;
An optical wireless communication system comprising: An optical wireless transmitter according to claim 3,
An optical wireless receiver according to claim 6;
An optical wireless communication system comprising:

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