JP3194281B2 - Optical space transmission system - 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 spatial transmission system for spatially transmitting audio signals, video signals, and the like by optical signals.

[0002]

2. Description of the Related Art In an optical space transmission system, an optical signal including an audio signal, a video signal, or the like may be momentarily interrupted when a bird or the like blocks an optical space transmission path. in this case,
It is difficult to control the movement of the bird to prevent the instantaneous interruption, and all signals in the period in which the instantaneous interruption occurs are lost. The amount of signal lost increases as the transmission speed of the signal increases, and thus the effect on high-speed communication is greater. Conventionally, the following method has been adopted or proposed for such an instantaneous interruption phenomenon.

First, in the case of the analog system, for example, in image communication, there is a method in which an image for one frame is held at the moment of an instantaneous interruption to make it seem as if a signal is coming.

In the case of the digital system, there are a method of correcting error data by using an error correction code for a digital signal to be transmitted, and a method of correcting data by interleaving data.

[0005]

However, in the above-mentioned analog system, there is a problem that the image looks unnatural because the same image is continuous.

In the digital method, when error data is corrected by using an error correction code, when the burst error time is long, a complicated code is required to correct the error data, which increases the hardware scale and the cost. There was a problem of inviting. Further, when error data is corrected by data interleaving, a memory that is many times as long as the burst error time is required, which also causes a problem that the hardware scale and cost are increased.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to enable transmission data lost due to a momentary interruption of an optical signal caused by a bird or the like to be reproduced on a receiving side, and to further reduce the system scale. An object of the present invention is to provide an optical space transmission system that does not cause an increase in cost and increase in cost.

[0008]

According to the present invention, there is provided a transmission system for converting a signal to be transmitted into an optical signal and transmitting the signal, and a signal for converting the optical signal into an electric signal and transmitting the signal. A transmission system comprising: a first delay unit that delays an input transmission target signal by a predetermined time to obtain an first delay signal;
Transmission means for generating a transmission signal from the transmission target signal and the first delay signal, converting the transmission signal into an optical signal and transmitting the optical signal, wherein the receiving system receives the optical signal and Receiving means for obtaining the first delay signal; delaying the transmission target signal obtained by the reception means by a predetermined time; and delaying the first delay signal obtained by the reception means by a predetermined time. A second delay means for obtaining a second delayed signal, a signal to be transmitted, a delayed signal of the signal to be transmitted, a first delayed signal, and a delayed signal of the first delayed signal. Data comparison and selection means for selecting the delay signal and the first delay signal, instantaneous interruption detection means for detecting an instantaneous interruption of the optical signal, and a time slot corresponding to the period of the instantaneous interruption detection in the delay signal of the transmission target signal. , The instantaneous interruption detection in the l-th delayed signal Inserting the corresponding data between,
Alternatively, there is provided switching means for inserting data corresponding to the period of the instantaneous interruption detection in the delay signal of the transmission target signal into the time slot corresponding to the period of the instantaneous interruption detection in the first delay signal.

[0009]

In the transmission system 1 of the optical space transmission system (analog system) according to the present invention, as shown in FIG. 1, a first delay obtained by delaying the input transmission target signal A by a predetermined time τ. The signal B1 and the transmission target signal A are FM-modulated at different frequencies and added, and the added signal is subjected to electrical / optical conversion and transmitted as an optical signal.

In the receiving system 2, the optical signal is converted into an electric signal, and the added transmission target signal and the first delay signal are separated into a transmission target signal A and a first delay signal B1. Get. Either the second delay signal A1 or the first delay signal B1 obtained by delaying the transmission target signal A by the predetermined time τ is selected according to the result of the instantaneous interruption detection, and is selected as the transmission target signal A '. Is output.

In such an optical space transmission system, as shown in FIG. 2, when an optical signal is momentarily interrupted by a bird or the like during the period t1, the data a14 of the transmission target signal A is lost. In the case of the first delay signal B1 delayed by τ, the data all
Is being transmitted, data a11 is lost, but data a1
4 is not lost.

Therefore, the time slot (t) of the lost data a14 of the second delay signal A1 shown in FIG.
By inserting the data a14 of the first delay signal B1 into the 1st time slot), the transmission target signal A ′ output from the reception system 2 is changed to the same content as the transmission target signal A input to the transmission system 1. It can be.

In the transmission system 3 of the optical space transmission system (digital system) according to the present invention, as shown in FIG. 3, the first transmission target signal P obtained by delaying the input transmission target signal P by a predetermined time τ is obtained. The parallel data of the delay signal Q1 and the transmission target signal P is converted into serial data, and the converted signal is subjected to electrical / optical conversion and transmitted as an optical signal.

In the receiving system 4, the optical signal is converted into an electric signal, and the serial data is converted into two parallel data. When converting from serial to parallel, which one of the two data is delayed is signal Q
Since it is not possible to determine whether it is 1, it is determined by providing two delay circuits. After the determination, one of the second delay signal P1 and the first delay signal Q1 obtained by delaying the transmission target signal P by a predetermined time τ is selected according to the instantaneous interruption detection result, and the transmission target signal P 'Is output from the receiving system 4.

In such an optical free space transmission system, as shown in FIG. 4C, when an optical signal is momentarily interrupted by a bird or the like during period t1, the data a11 of the transmission target signal P is lost. However, in the case of the first delay signal Q1 delayed by τ, the data a8 is being transmitted during the period t1, and the data a8 is lost but the data a8 is lost.
11 is not lost.

Accordingly, the time slot (t) of the lost data a11 of the second delay signal P1 shown in FIG.
By inserting the data a11 of the first delay signal Q1 into the (1 ′ time slot), the transmission target signal P ′ output from the reception system 4 is changed to the transmission target signal P having the same content as the transmission target signal P input to the transmission system 3. Things.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of the free-space optical transmission system according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing an analog optical free-space transmission system according to an embodiment of the present invention.
In the figure, reference numeral 1 denotes a transmission system, and 2 denotes a reception system.

The transmission system 1 includes FM modulation circuits 11 and 13, a delay circuit 12, an addition circuit 14, and an electro-optical converter 15.
Consists of FM modulation circuit 11, excluding the delay circuit 12,
The adder 13, the adder circuit 14, and the electrical / optical converter 15 constitute a transmission unit. Also, the electric / optical converter 15 is an electric / optical converter.
It comprises a light converter 151 and a lens 152.

The receiving system 2 includes an optical / electrical converter 21, band pass filters 22, 25, FM demodulators 23, 26, a delay circuit 24, a switch circuit 27 as an insertion means, an envelope detection circuit 28, and an instantaneous interruption. It comprises a detection circuit 29. The above light
Electric conversion device 21, band-pass filter circuits 22, 25, and FM
The demodulation circuits 23 and 26 constitute a receiving means, and the envelope detection circuit 28 and the instantaneous interruption detecting circuit 29 constitute an instantaneous interruption detecting means. The optical-electrical conversion device 21 includes a lens 211 and an optical-electrical converter 212.

In FIG. 1, a signal A to be transmitted (FIG. 2A) input to a terminal T1 of the receiving system 1
1, the first carrier is FM-modulated, and the transmission target signal A is delayed for a predetermined time τ by a first delay signal B1 (FIG. 2).
(B)) the second carrier is FM-modulated by the FM modulation circuit 13. The frequencies of the first and second carriers are, for example, 100
MHz and 200 MHz.

A first FM modulated wave obtained by FM-modulating a first carrier with a signal A, and a second FM modulated wave obtained by FM-modulating a second carrier with a signal B1. Are added by the adder circuit 14 and input to the electrical-optical converter 151 of the electrical-optical converter 15 as an additive FM modulated wave. The added FM modulated wave input to the electro-optical converter 151 is converted into an optical signal, and this optical signal is
As a result, the light is emitted into space as parallel rays.

A part of the optical signal emitted into the space is an optical signal.
The light converged by the lens 211 of the electric conversion device 21
It is incident on the electric converter 212 and converted into an electric signal,
The added FM modulated wave is obtained.

The added FM modulated wave is supplied to band-pass filters 22 and 2
The signal is separated into first and second FM modulated waves at 5 and input to FM demodulation circuits 23 and 26. The FM demodulation circuits 23 and 26 demodulate the first and second FM modulated waves and output a transmission target signal A and a first delay signal B1.

The transmission target signal A becomes a second delay signal A1 (FIG. 2 (c)) delayed by a predetermined time τ by the delay circuit 24 and is input to the switch circuit 27. Further, the first delay signal B1 is directly input to the switch circuit 27.

The added FM modulated wave converted into an electric signal from the optical / electrical converter 212 is output to the envelope detection circuit 2.
8, the signal is envelope-detected and becomes a signal C1 (FIG. 2 (i)). The level of the signal C1 is compared by the instantaneous interruption detection circuit 29, and when the level falls below the threshold value TH (see FIG. 2 (i)), the instantaneous interruption detection circuit 29 determines that an instantaneous interruption has occurred. In the case of FIG. 2 (i), the instantaneous interruption period is W. The instantaneous interruption detection circuit 29 outputs a pulse signal of the width W as an instantaneous interruption detection signal C2 (FIG. 2 (j)) after a lapse of a predetermined time τ after detecting the instantaneous interruption.

The switch circuit 27 functioning as a data inserting means operates while the instantaneous interruption detection signal C2 is at "H" level.
The common terminal 27c of the switch circuit 27 is connected to the contact 27b to output the signal B1 as the output signal A 'of the receiving system 2. During the period when the instantaneous interruption detection signal C2 is at the “L” level, the switch circuit 27 connects the common terminal 27c and the contact 27a and outputs the signal A1 as the output signal A ′ of the receiving system 2. In this way, a correct signal is inserted into the momentarily interrupted signal portion.

Next, a specific example of the instantaneous interruption will be described. First,
As shown in FIGS. 2A and 2B, a case where an instantaneous interruption occurs in the period t1 will be described. If an instantaneous interruption occurs in the period t1, data a1
4 and the data a1 for the first delayed signal B1
One is lost.

The reason why the lost data differs between the transmission target signal A and the first delay signal B1 is that the signal B1 is delayed by the delay circuit 12 by a predetermined time τ. The signal A is subjected to the FM demodulation circuit 23
After that, the signal is delayed by a predetermined time τ in the delay circuit 24 to become the second delayed signal A1 in FIG. 2C, which has the same phase as the demodulated signal B1.

The second delay signal A1 and the first delay signal B1
Although the same data value is obtained in the same phase as the above, the instantaneously interrupted data has the signal a1 as the data a14 and the signal B1 as the data a11 as described above, and the instantaneously interrupted data is temporally shifted by τ. Therefore, if the data a14 of the signal B1 is inserted into the time slot of the data a14 of the momentarily interrupted signal A, the second delay signal A1 will be identical in content to the transmission target signal A.

This insertion is performed by the switch circuit 27. That is, the switch circuit 27 operates at the time t shown in FIG.
During 1 ', the common terminal 27c and the contact 27b are switched so as to be connected, and the signal B1 is output from the terminal T2 as an output signal A' during that time. Therefore, the output signal A '
Has a delay of a predetermined time τ from the transmission target signal A, but has the same contents as the signal A.

In the specific example of the instantaneous interruption described above, the data of the first delay signal B1 is inserted into the time slot corresponding to the second delay signal A1. The data of the second delay signal A1 may be inserted into the corresponding time slot of.

FIGS. 2 (e) and 2 (f) show FIGS.
FIG. 9 is a data diagram showing a case where an instantaneous interruption occurs for a period t2 shown in FIG. In the same figure, it is interrupted just by τ = t2. Also in this case, the data a10 to a12 of the signal B1 are inserted into the time slot of the period t2 'shown in FIG.

FIGS. 2 (g) and 2 (h) correspond to FIGS.
FIG. 9 is a data diagram showing a case where an instantaneous interruption occurs for a period t3 shown in FIG. In the same figure, it is momentarily interrupted for a period t3 exceeding a predetermined time τ. Also in this case, the period t shown in FIG.
In the 3 'time slot, data a9 to a12 of signal B1
Is inserted. However, as shown in FIG. 2 (h), even in the signal B1, the data a9 is lost due to the instantaneous interruption of the optical signal. Therefore, the signal B is added to the time slot of the period t3 '.
Even if data 1 is inserted, data a9 is not recovered. This is because the period t3 '= t3 has exceeded the predetermined time τ.

From the above description, the predetermined time (delay time)
τ is set to a time such that the number of occurrences of data that cannot be recovered is a number that does not hinder communication.

In FIG. 1, the first and second FMs are shown.
Although the modulated waves are added and converted into an optical signal, the first and second FM modulated waves may be converted into optical signals by different optical systems and transmitted. In this case, the addition circuit 14 becomes unnecessary.

FIG. 3 is a block diagram showing a digital optical space transmission system according to a second embodiment of the present invention. In the figure, 3 is a transmission system, and 4 is a reception system.

The transmission system 3 comprises a delay circuit 31, a parallel / serial conversion circuit 32, and an electro-optical conversion device 33. The parallel-to-serial conversion circuit 32 and the electro-optical conversion device 33 excluding the delay circuit 31 constitute transmission means. The electric-optical converter 33 is an electric-optical converter 33.
1 and a lens 332.

The receiving system 4 includes an optical / electrical conversion device 41, a serial / parallel conversion circuit 42, delay circuits 43 and 45, a data comparison / selection circuit 44, a switch circuit 46, and an instantaneous interruption detecting circuit 47 as instantaneous interruption detecting means. Consists of The above-mentioned optical / electrical conversion device 41, serial / parallel conversion circuit 4
2. The delay circuits 43 and 45, the data comparison / selection circuit 44, and the switch circuit 46 constitute reception means. The optical-electrical conversion device 41 includes a lens 411 and an optical-electrical converter 412.

In FIG. 3, the transmission target signal P (FIG. 4A) input to the terminal T3 of the receiving system 3 is input to the parallel / serial conversion circuit 32. The transmission target signal P
Delay signal Q1 obtained by delaying
(FIG. 4B) also shows the parallel / serial conversion circuit 3
2 is input.

The signals P and Q1 input to the parallel / serial conversion circuit 32 are converted into a serial signal PQ1 as shown in FIG. The data of the signal PQ1 is, for example, a
The order is 4, a1, a5, a2, a6, a3, and so on.

The serial signal PQ1 is input to the electrical / optical converter 331 of the electrical / optical converter 33. The serial signal PQ1 input to the electro-optical converter 331 is converted into an optical signal, and this optical signal is emitted into space as a parallel light beam by the lens 332.

A part of the optical signal emitted into the space is converged by the lens 411 of the optical-electrical conversion device 41 of the receiving system 4 and is incident on the optical-electrical converter 412 to be converted into an electric signal. It becomes the serial signal PQ1.

The serial signal PQ1 input to the serial / parallel conversion circuit 42 is separated into parallel signals of the signals P and Q1, and output from the terminal 42a or 42b. However, in this case, the signal P is applied to the terminal 42a or 42b.
Is unknown, and therefore the signal P
Is unknown to which of the delay circuits 43 and 45 is input. The data comparison / selection circuit 44 detects this.
It is. That is, there are two delay circuits 43 and 45, and the signals P and Q1 are delayed signals P1 and Q1, respectively.
2 and two signals P and Q1 which are not delayed are input to the data comparison / selection circuit 44.

The data comparison / selection circuit 44 compares the signal on the output line of the delay circuit 43 with the signal on the output line L2 from the terminal 42b of the serial / parallel conversion circuit 42. When the signal P is output from the terminal 42a and the signal Q1 is output from the terminal 42b, the compared signals are the signal P1 and the signal Q obtained by delaying the signal P by τ.
And 1. Since the signal P is advanced by τ from Q1 (see FIGS. 4A and 4B), the signals P1 and Q1 have the same phase. Therefore, as shown in FIGS. 5A and 5B, the signals P1 and Q1 completely match. As a comparison at this time, for example, data A456 and A789 of the period τ are compared with each other.

Next, a signal P is output from the terminal 42b,
The case where the signal Q1 is output from the terminal 42a will be described. In this case, the signals to be compared are the signal Q2 and the signal P obtained by delaying the signal Q1 by τ. Signal Q1
Is delayed by τ from the signal P, the signal Q2 is delayed by 2τ from the signal P. Therefore, FIG.
As shown in (d), data in the same period is data A1
23 and A789, and data A456 and A101112. That is, the signal Q2 and the signal P do not match. The data A123 and A789 may rarely coincide with each other, but the data amount to be compared may be set so that the probability falls within a range that does not hinder the data processing.

Therefore, if the data on the output line of the delay circuit 43 matches the data on the output line L2 from the terminal 42b of the serial / parallel conversion circuit 42,
The signal P is output from the terminal 42a, and the signal Q1 is output from the terminal 42a.
b can be determined. When the data do not match, it can be determined that the signal P is output from the terminal 42b and the signal Q1 is output from the terminal 42a.

Thus, the signals output from the terminals 42a and 42b of the serial / parallel conversion circuit 42 are determined. This is because the second delay signal P1 and the first delay signal Q1 obtained by delaying the transmission target signal P by τ are used as the output signal P ′.

The serial signal PQ1 converted into an electric signal from the optical / electrical converter 412 and output is converted to an instantaneous interruption detection circuit 4.
7, and the level is compared with the threshold value TH (FIG. 4).
(Refer to (j).) When the following occurs, the instantaneous interruption detection circuit 47 determines that an instantaneous interruption has occurred. In the case of FIG. 4 (j), the instantaneous interruption period is W. The instantaneous interruption detection circuit 47 detects the instantaneous interruption for a predetermined time τ
After the elapse, the pulse signal having the width W is changed to the instantaneous interruption detection signal D1.
(FIG. 4 (k)). When data "0" continues, a noise-like signal as shown by NL in FIG. 4 (j) appears, but the period during which such a signal is generated is short. Therefore, an erroneous determination can be prevented by not considering a short-term instantaneous interruption as an instantaneous interruption.

The switch circuit 46 is provided with the instantaneous interruption detection signal D1.
Is at “H” level, the common terminal 4 of the switch circuit 46
6c and the contact 46b are connected to output the signal Q1 as the output signal P 'of the receiving system 4. Instantaneous interruption detection signal D1 is "L"
During the level period, the switch circuit 46 is connected to the common terminal 4.
6c and the contact 46a are connected to output the signal P1 as the output signal P 'of the receiving system 4. In this way, a correct signal is inserted into the momentarily interrupted signal portion.

Next, a specific example of the instantaneous interruption will be described. First,
As shown in FIG. 4C, a case where an instantaneous interruption occurs in the period t1 will be described. When an instantaneous interruption occurs in the period t1, the data a11 is lost for the transmission target signal P, and the data a8 is lost for the first delay signal Q1.

The data lost as described above differs between the transmission target signal P and the first delay signal Q1 because the signal Q1 is delayed by the delay circuit 31 for a predetermined time τ. The signal P is converted from a serial signal to a parallel signal by a serial / parallel conversion circuit 42 in order to match the phase, and then delayed by a predetermined time τ by a delay circuit 43 or 45 to become a signal P1 in FIG. It has the same phase as the signal Q1 converted into a parallel signal.

The signals P1 and Q1 output from the data comparison / selection circuit 44 have the same data value in the same phase, but the instantaneously interrupted data is the signal P1 as the data a1 as described above.
1. The signal Q1 is data a8, and each instantaneous interruption data is temporally shifted by τ. Therefore, the data a11 of the signal Q1 is added to the time slot of the data a11 of the signal P that has been momentarily interrupted.
Is inserted, the output signal P 'completely matches the signal P to be transmitted. The only difference is that the signal P 'lags behind the signal P by τ.

This insertion is performed by the switch circuit 46. That is, the switch circuit 46 operates at the time t shown in FIG.
During 1 ', switching is performed so that the common terminal 46c and the contact 46b are connected, and during that time, the signal Q1 is output from the terminal T4 as an output signal P'.

In the specific example of the instantaneous interruption, the data of the first delay signal Q1 is inserted into the time slot corresponding to the second delay signal P1, but conversely, the data of the first delay signal Q1 is inserted. The data of the second delay signal P1 may be inserted into the corresponding time slot.

FIGS. 4 (f) and 4 (g) are data diagrams showing a case in which there is an instantaneous interruption for the period t2 shown in FIG. 4 (c). In the same figure, it is interrupted just by τ = t2. Also in this case, the data a7 to a9 of the signal Q1 are inserted into the time slot of the period t2 'shown in FIG.

FIGS. 4 (h) and 4 (i) are data diagrams showing a case in which an instantaneous interruption occurs during the period t3 shown in FIG. 4 (c). In the same figure, it is momentarily interrupted for a period t3 exceeding a predetermined time τ. Also in this case, the data a6 to a9 of the signal Q1 are inserted into the time slot of the period t3 'shown in FIG.
However, as shown in FIG. 4 (i), even in the signal Q1, the data a6 is lost due to the instantaneous interruption of the optical signal. Therefore, even if data of the signal Q1 is inserted into the time slot of the period t3 ', the data a6 is not recovered. This is the period t
This is because 3 ′ = t3 has exceeded the predetermined time τ.

Although FIG. 3 shows a case where the transmission target signal P and the first delay signal Q1 are converted into the serial signal PQ1, carrier waves (AM, FM) having different frequencies depending on the signals P and Q1 are shown. (Whichever may be used), and the modulated wave may be converted into an optical signal.
In this case, an adder for two modulated waves or two optical systems is required, but a parallel / serial converter is not required.

[0059]

As described above, in the optical free space transmission system according to the present invention, when the instantaneous interruption of the optical signal is detected, the first delayed signal delayed on the transmitting side or the second delayed signal delayed on the receiving side. The data corresponding to the period of the instantaneous interruption detection of the second delay signal or the first delay signal is inserted into the time slot of the delay signal corresponding to the period of the instantaneous interruption detection. Even if a part of the transmission data is lost due to a momentary interruption of the optical signal, the lost data can be reproduced on the receiving side, and the reproduction can be performed without using complicated error correction codes or interleaving. In addition, there is no increase in system scale and cost.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of an optical free space transmission system according to the present invention.

FIG. 2 is a data diagram showing a data state in each unit of the system of FIG.

FIG. 3 is a block diagram showing another embodiment of the free-space optical transmission system according to the present invention.

FIG. 4 is a data diagram showing a data state in each section of the system of FIG. 3;

FIG. 5 is a data diagram showing data used for signal discrimination in the system of FIG. 3;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 transmission system 2 reception system 11, 13 FM modulation circuit 12, 24 delay circuit 14 addition circuit 15 electric-optical conversion device 21 optical-electric conversion device 22, 25 band-pass filter circuit 23, 26 FM demodulation circuit 27 switch circuit 28 envelope Line detection circuit 29 Instantaneous interruption detection circuit T1, T2 terminals

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04B 10/00-10/28 H04J 14/00-14/08 H04B 7/00 H04B 7/02-7/12 H04L 1 / 02-1/06

Claims (1)

(57) [Claims] 1. An optical space transmission system comprising: a transmission system that converts a signal to be transmitted into an optical signal and transmits the signal; and a reception system that converts the optical signal into an electric signal and obtains a signal to be transmitted. Comprises: a first delay unit for delaying an input transmission target signal by a predetermined time to obtain an l-th delay signal; generating a transmission signal from the transmission target signal and the l-th delay signal; Transmitting means for converting the signal into an optical signal and transmitting the signal; receiving means for receiving the optical signal to obtain the signal to be transmitted and a first delay signal; And a second delay for obtaining a delay signal of the transmission target signal obtained by delaying the transmission target signal by the predetermined time and a second delay signal obtained by delaying the first delay signal obtained by the receiving means by the predetermined time. Means and the transmission target signal. Data comparing and selecting means for comparing the delay signal of the transmission target signal, the first delay signal, and the delay signal of the first delay signal to select the delay signal of the transmission target signal and the first delay signal; An instantaneous interruption detecting means for detecting an instantaneous interruption of the optical signal; and a time slot corresponding to the period of the instantaneous interruption detection in the delayed signal of the transmission target signal, the period of the instantaneous interruption detection in the first delay signal. Or data corresponding to the instantaneous interruption detection period in the delay signal of the transmission target signal is inserted into a time slot corresponding to the instantaneous interruption detection period in the first delay signal. And a switch unit.