JP3049307B2 - Receiver for spatial transmission optical communication - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical receiver for receiving signal light in spatial transmission optical communication.

[0002]

2. Description of the Related Art Conventionally, in space transmission optical communication,
The following measures are taken in order to reduce the degradation of communication quality due to noise due to disturbance light mixed into signal light.
(Measure 1) Disturbance light is removed by a wavelength filter.
(Measure 2) Prevent disturbance light from entering the light receiving element by the shield. (Measure 3) Modulate the carrier wave to make it easy to distinguish from disturbance light.

[0003]

However, in the above-described method of removing disturbance light by the wavelength filter, if the disturbance light contains a component having the same wavelength as the signal light, the component cannot be removed. In some cases, noise removal cannot be performed effectively. Also, in measures to prevent disturbing light from entering the optical antenna with a shield, if the incident direction of the disturbing light to the optical antenna is substantially the same as the incident direction of the signal light, only the disturbing light is used. Can't block. Further, even in a method of modulating a carrier wave to facilitate distinction from disturbance light, when disturbance light includes a component that cannot be distinguished from a modulation signal, noise cannot be distinguished from signal light, and thus is not necessarily. It could not be said that effective noise removal was expected.

[0004] The problem to be solved by the present invention is to provide a receiving apparatus that effectively reduces the influence of noise due to disturbance light, which cannot be removed by the above-described measures or a combination thereof, on signal light. It is in.

[0005]

In order to solve the above problems, the present invention has a technical feature in that adaptive signal processing technology is applied to spatial propagation optical communication. The adaptive signal processing technique described above is a sum signal of a signal and noise (hereinafter, referred to as a sum signal).
Recorded as "observed signal". ) Is filtered by an adaptive filter to reproduce another noise (hereinafter, referred to as a “reference signal”) that is correlated with the noise included in the observation signal, and the reproduced signal is subtracted from the observation signal to reduce the observation signal. This is a method of canceling the noise in the middle, and good noise cancellation can be performed by changing the filter coefficient according to the changing noise. Although known as an adaptive signal processing technique, it has not been known whether this technique can be applied to space propagation optical communication.

In order to apply the above-described adaptive signal processing technique to perform noise cancellation, it is necessary to be able to acquire an observation signal and a reference signal. As a precondition, an electric field in which an observation signal exists and an electric field in which a reference signal exists exist. Must exist. Such a field exists in a sound field, and an example in which howling is successfully reduced by an adaptive signal processing technique is known. However, no clear suggestion has been made that a similar field exists in the case of light waves.

On the other hand, the inventor of the present invention generally disposes the position where the transmitter is installed and the position where disturbance light is generated, and the propagation range of signal light and disturbance light emitted from the transmitter.
Since the direction is different and the light wave has a higher straightness than the sound wave, the electric field of the observation signal and the electric field of the reference signal are clearly present in the propagation space, and as a result, an efficient noise cancellation result is obtained. I thought I could get it. Then, it was confirmed by experiments that these electric fields existed, and a detection signal obtained by arranging a light receiving element in each electric field was subjected to adaptive signal processing to obtain a signal in which noise due to disturbance light was canceled. It was.

That is, in the optical receiving apparatus according to the present invention, the light receiving surface of the light receiving element (for example, the first light receiving element 11f) is arranged at a position where the signal light (S) for communication propagating in the space can be received. A first light receiving section (1f), a first analog-to-digital conversion processing section (2f) for converting the detection signal of the first light receiving section from analog to digital and outputting a digital observation signal (Df), It is possible to receive disturbance light (for example, disturbance light Ns incident on the second light receiving unit) correlated with disturbance light that can be received by the unit (for example, disturbance light incident on the first light receiving unit Nf), but not signal light. The light receiving surface of the light receiving element (for example, the second light receiving unit 11s) is disposed at a proper position.
The detection signal from the light receiving section (1s) and the detection signal from the second light receiving section are converted from analog to digital to a digital reference signal (D
s) and a second analog-to-digital conversion processing section (2
s) and an estimated noise signal (Dm) obtained by filtering the digital reference signal output from the second analog-to-digital conversion processing unit with an adaptive filter and subtracting the estimated noise signal (Dm) from the digital observation signal to thereby cancel the noise. And a noise canceling function section (3) for outputting (Do).

Further, disturbance light (disturbance light Ns incident on the second light receiving unit) from an angle different from the disturbance light (disturbance light Nf incident on the first light receiving unit) received by the first light receiving unit (1f). When the light receiving element is located near the light receiving element of the second light receiving unit, the light receiving surface direction of the light receiving element of the second light receiving unit is provided so as to be different from the light receiving surface direction of the light receiving element of the first light receiving unit. The second light receiving unit may receive the disturbance light having the irregularity. This has the advantage that the second light receiving section (1s) can be arranged near the first light receiving section (1f).

[0010]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an exploded perspective view of a receiver for spatial transmission optical communication according to the present invention.

FIG. 1 is a functional block diagram showing a schematic configuration of a first embodiment of a spatial transmission optical communication receiving apparatus according to the present invention. FIG. It is the perspective view which showed the specific example of arrangement | positioning of a source.

As shown in FIG. 1, the first light receiving portion 11
The signal light S for communication and the first light-receiving unit incident disturbance light Nf which becomes noise enter f, and the second light-receiving unit light-receiving element 11s has a correlation with the first light-receiving unit incident disturbance light Nf. In order that only the disturbance light Ns incident on the second light receiving unit as disturbance light is incident,
By adjusting the direction of the light receiving surface of the first light receiving element 11f and the direction of the light receiving surface of the second light receiving element 11s, the first light receiving section 1f is adjusted.
And the second light receiving section 1s. Then, the signals received by the first and second light receiving sections 1f and 1s are supplied to the noise processing section 5, and the noise is canceled from the noise processing section 5 with high probability (it can be estimated that the noise has been removed). The estimation signal Do is obtained.

In the first light receiving portion 1f, the first light receiving portion light receiving element 11f is connected to the first light receiving portion electronic circuit 12f, and the signal light S and the first light receiving portion incident disturbance light Nf are formed on the light receiving surface.
The weak light signal photoelectrically converted by the first light receiving element 11f that has received the light is appropriately amplified and output by the first light receiving section electronic circuit 12f. Further, the first light receiving section electronic circuit 12 f is connected to the noise processing section observation signal input section 51 of the noise processing section 5.

In the second light receiving section 1s, the second light receiving section light receiving element 11s is connected to the second light receiving section electronic circuit 12s, and the second light receiving section receives the second light receiving section incident disturbance light Ns on the light receiving surface. The weak electric signal photoelectrically converted by the second light receiving unit 11s is appropriately amplified and output by the second light receiving unit electronic circuit 12s. Further, the second light receiving section electronic circuit 12s is connected to the noise processing section reference signal input section 52 of the noise processing section 5.

Next, the configuration of the noise processing section 5 will be described. A noise processing unit observation signal input unit 51 receiving a signal from the first light receiving unit 1f is connected to a noise processing unit reference signal input receiving a signal from the second light receiving unit 1s to an input unit of the first analog-to-digital conversion processing unit 2f. The section 52 is connected to the input section of the second analog / digital conversion processing section 2s, and the analog observation signal Sf from the noise processing section observation signal input section 51 is supplied to the first analog / digital conversion processing section 2f.
The analog reference signal Ss from the noise processing unit reference signal input unit 52 is transmitted to the second analog / digital conversion processing unit 2s.
To each of them.

The first analog / digital conversion processing unit 2
The output part of f is connected to the noise cancellation function part observation signal input part 31 of the noise cancellation function part 3, and the output part of the second analog-to-digital conversion processing part 2s is connected to the noise cancellation function part reference signal input part 32 of the noise cancellation function part 3. A digital observation signal Df obtained by converting the analog observation signal Sf into a digital signal is connected to the noise cancellation function unit observation signal input unit 31 from the first analog / digital conversion processing unit 2f. The digital observation signal Ds converted into a signal is supplied from the second analog-digital conversion processing unit 2s to the noise cancellation function unit reference signal input unit 32.

The noise canceling function section 3 includes an adaptive filter 4 and a difference detecting section 6. The noise canceling function section observation signal input section 31 is connected to an addition input section of the difference detecting section 6 to provide a noise canceling function. The reference signal input section 32 is connected to the adaptive filter input section 41 of the adaptive filter 4, and the adaptive filter output section 42 of the adaptive filter 4 is connected to the subtraction input section of the difference detection section 6. Thus,
When the digital observation signal Df from the noise cancellation function unit observation signal input unit 31 and the estimated noise signal Dm as the digital reference signal filtered by the adaptive filter 4 are supplied to the difference detection unit 6, the digital observation signal Df From which the estimated noise signal Dm is reduced,
Estimated signal Do that can be estimated to have noise components removed
Is obtained.

Further, the output of the difference detection section 6 is connected to a noise canceling section estimation signal output section 33, and the noise cancellation section estimation signal output section 33 is connected to a noise processing section estimation signal output section 53. The estimation signal Do output from the difference detection unit 6 is output from the noise cancellation function unit 3 via the noise cancellation function unit estimation signal output unit 33.

On the other hand, the output of the difference detection unit 6 is also connected to a filter coefficient correction signal input unit 43 of the adaptive filter 4, and is based on the estimated signal Do fed back via the filter coefficient correction signal input unit 43. Then, the adaptive filter 4 corrects the filter coefficients so as to reproduce the noise included in the digital observation signal Df from the digital reference signal Ds. By repeating the correction of the filter coefficient as needed as described above, an estimated noise signal Dm that can satisfactorily remove a noise component corresponding to the first light-receiving unit incident disturbance light Nf from the digital observation signal Df is obtained.

In the first embodiment described above, for example, as shown in FIG. 2, indoor space transmission optical communication in which disturbance light is distributed over a wide range and signal light propagates in a part of the space. Light (disturbance light) from an illumination lamp that illuminates the entire room such as a fluorescent lamp 8 is incident on the first light receiving unit 1f and the second light receiving unit 1s, and the narrow signal light S from the transmitter 7 is the first signal light S. This is effective in a case where only the light receiving section 1f is irradiated. Of course, the communication space in which optical communication using the spatial transmission optical communication receiver according to the present invention is possible is not limited to indoors, and may be outdoors, optical communication between an artificial satellite and the ground, or between artificial satellites. It is also possible to apply the present invention to optical communication.

In FIG. 2, of the light from the fluorescent lamp 8, the light incident on the first light receiving portion 1f is converted into the first light receiving portion incident disturbance light Nf.
f, the light incident on the second light receiving unit 1s is a second light receiving unit incident disturbance light Ns, the light from the transmitter 7 is a signal light S, and the light is transmitted to the first light receiving unit 11f and the second light receiving unit 11s. The incident direction is indicated by each arrow. That is, by appropriately separating the first light receiving portion 1f and the second light receiving portion 1s, the light receiving surface of the first light receiving portion 11f of the first light receiving portion 1f and the second light receiving portion of the second light receiving portion 1s are provided. Even if the light receiving surface of the light receiving element 11s is arranged so as to be substantially parallel, the signal light S is not detected by the second light receiving portion 1s, and the disturbance light Ns incident on the second light receiving portion is incident on the first light receiving portion. This can be regarded as disturbance light having a correlation with the disturbance light Nf.

Next, a second embodiment of the spatial transmission optical communication receiver according to the present invention will be described with reference to FIG. The second embodiment is effective when the propagation direction of the signal light S and the propagation direction of the disturbance light are different in consideration of the point that the disturbance light is reflected by a surrounding object.

That is, as shown in FIG. 3, the direction of the light receiving surface of the first light receiving portion 11f and the second light receiving portion 11f
The first light receiving portion 1f and the second light receiving portion 1s are arranged so that the light receiving surface directions of s are different, and the first light receiving portion 1f detects the signal light S,
The second light-receiving unit incident disturbance light Ns having a correlation with the first light-receiving unit incident disturbance light Nf incident on the first light-receiving unit 1f in the second light-receiving unit 1s.
To be detected. With this arrangement, the first
The light receiving unit 1f can detect the signal light S and the first light receiving unit incident disturbance light Nf, and the second light receiving unit 1s can detect the second light receiving unit incident disturbance light Nf.
Only s can be detected. As a result, the analog observation signal Sf can be obtained from the first light receiving unit 1f,
An analog reference signal Ss can be obtained from s.

The analog observation signal Sf and the analog reference signal Ss obtained as described above are supplied to the noise processing unit observation signal input unit 51 and the noise processing unit reference signal input unit 52 of the noise processing unit 5, respectively. By the same operation as the noise processing unit 5 in the first embodiment described above, the noise processing unit estimation signal output unit 53 outputs the noise-cancelled estimation signal Do.

The spatial light transmission receiving apparatus according to the second embodiment includes a second light receiving unit incident disturbance light N having a different propagation direction from the first light receiving unit incident disturbance light Nf near the first light receiving unit 1f.
s is effective when the second light receiving unit 1s
Even if it is installed near the light receiving unit 1f, the second light receiving unit 1s
Without the light receiving element 11s receiving the signal light S,
There is an advantage that only the disturbance light Ns incident on the second light receiving unit can be received.

FIG. 4 is a perspective view showing a specific arrangement example of the transmitting / receiving section and the noise source in the second embodiment described above. In FIG. 4, the signal light S from the transmitter 7 is the first signal.
The direct light from the fluorescent lamp 8 is incident on the first light receiving unit 1f as the first light receiving unit incident disturbance light Nf, and the light reflected by the partition 9 out of the light from the fluorescent lamp 8 is the second light. As a result of the presence of the disturbance light Ns incident on the light receiving unit near the first light receiving unit 1f and the light being incident on the second light receiving unit 1s, the second light receiving unit 1s may be installed near the first light receiving unit 1f. Will be possible. With this configuration, the distance between the first light receiving unit 1f and the second light receiving unit 1s can be reduced, so that the installation space can be reduced. In addition, a reflection plate or the like for disturbance light is provided in advance in the second light receiving unit 1s so that the disturbance light Ns incident on the second light receiving unit having an incident angle different from that of the disturbance light Nf incident on the first light receiving unit is intentionally generated. May be.

In the case where special conditions, such as a screen 9 or a reflector (reflective object) having a frequency characteristic, for guiding disturbance light to the second light receiving portion 1s, are prepared, the reflector 9 There is a possibility that the correlation between the light incident on the reflecting surface and the reflected light may be broken. This is because the correlation between the disturbance light incident on the first light receiving unit 1f and the disturbance light incident on the second light receiving unit 1s is broken, so that the disturbance light incident on the first light receiving unit is disturbed from the disturbance light incident on the second light receiving unit. It means that estimation may not be possible.

However, the case where the above-described phenomenon occurs is only an extremely rare case in which various conditions such as the wavelength of the disturbance light, the incident angle to the reflecting object, and the surface condition of the reflecting surface are uniform. The influence is assumed to be negligible, and even if such a phenomenon occurs, it is relatively easy to adjust the positional relationship between the reflecting object and the second light receiving unit 1s. Can be eliminated. In order to prevent such a situation from occurring, it is effective to make the reflecting surface of the reflecting object white or a mirror surface.

[0029]

When the receiving apparatus for space transmission optical communication according to the present invention is used, noise caused by disturbance light can be canceled even if signal light and disturbance light enter the light receiving element at the same time. Therefore, high-speed spatial transmission optical communication with few transmission errors can be performed.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a first embodiment of a spatial transmission optical communication receiver according to the present invention.
It is a functional block diagram showing a schematic structure of an embodiment.

FIG. 2 is a perspective view showing an example of the arrangement of each light receiving unit and a noise source in the first embodiment of the spatial transmission optical communication receiver.

FIG. 3 is a diagram illustrating a second embodiment of the spatial transmission optical communication receiver according to the present invention;
It is a functional block diagram showing a schematic structure of an embodiment.

FIG. 4 is a perspective view showing an example of the arrangement of each light receiving unit and a noise source in a second embodiment of the spatial transmission optical communication receiver.

[Explanation of symbols]

 1f First light receiving unit 11f First light receiving unit light receiving element 1s Second light receiving unit 11s Second light receiving unit light receiving element 2f First analog-to-digital conversion processing unit 2s Second analog-to-digital conversion processing unit 3 Noise canceling function unit 4 Adaptive filter Nf Disturbance light incident on 1 light receiving unit Ns Disturbance light incident on 2nd light receiving unit S Signal light Df Digital observation signal Ds Digital reference signal Dm Estimated noise signal Do Estimated signal

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification code FI H04B 10/22

Claims (2)

(57) [Claims] A first light receiving portion having a light receiving surface of a light receiving element arranged at a position capable of receiving a signal light for communication propagating in space; and a digital signal obtained by converting the detection signal of the first light receiving portion from analog to digital. A first analog-to-digital conversion processing unit that outputs an observation signal; and a light-receiving element that is capable of receiving disturbance light having a correlation with disturbance light that can be received by the first light-receiving unit and that cannot receive signal light. A second light receiving section having a light receiving surface, a second analog-to-digital conversion processing section for converting a detection signal of the second light receiving section from analog to digital and outputting a digital reference signal, and a second analog-to-digital conversion processing section. By subtracting the estimated noise signal obtained by filtering the output digital reference signal with an adaptive filter from the digital observation signal, the estimated signal with noise canceled Spatial transmission optical communication reception apparatus characterized by comprising: a noise canceling function section for outputting a. 2. A light-receiving surface direction of a light-receiving element of a second light-receiving section,
2. The spatial transmission optical communication receiver according to claim 1, wherein the direction is different from the direction of the light receiving surface of the light receiving element of the first light receiving unit.