JP2002198914A - Digital optical relay system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical transmission relay system which can reduce the power consumption for the digital process measure to the utmost by resolving the problem that the consumption power increases according to the filtering process which is carried out by the digital process measures like DSP at transponder against base transceiver station or mobile base transceiver in conventional optical transmission relay system. SOLUTION: An optical transmission transponder consists of a control measure 27, 33 which controls the degree of the digital filter, a FFT measure 26, 32 which output a predetermined frequency spectrum information processing the digital signal which is output by the digital filter by the first Fourier transform and a measure to calculates the signal strength ratio of the requested and other than requested signal components based on the frequency spectrum information which is output by the FFT measure. The optical transmission transponder is characterized by the control of the degree of the digital filter in order to maintain over the predetermined value of the signal strength ratio by the control part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical transmission repeater system for mobile communication.

[0002]

2. Description of the Related Art In recent years, mobile phones, PHSs, MCAs (Mu
Mobile communication businesses such as lti Channel Access) have been developed nationwide, and their service areas are rapidly expanding. Along with this, behind the building, inside the tunnel,
It is necessary to take measures in areas where radio waves are difficult to reach and communication is difficult, such as underground shopping malls.

As a countermeasure, a wireless relay system as shown in FIG. 3 has been constructed. That is, the base station repeater 2 is installed at a place where radio waves transmitted by the base station 1 can be received at a relatively high level, and the mobile station repeater 3 is installed at a place where communication is difficult such as behind a building. An optical repeater system in which the two are connected by an optical fiber 4 to optically transmit a signal. According to such an optical transmission repeater system, communication between the base station 1 and the mobile station 5 can be performed via the base station repeater 2, the optical fiber 4, and the base station repeater 3.

FIG. 4 is a block diagram of a base station repeater for a downlink (base station 1 → mobile station 5) in a conventional optical transmission relay system proposed in Japanese Patent Application No. 11-305070. It should be noted that the base station repeater and the mobile station repeater for the uplink (from the mobile station 5 to the base station 1) have the same block diagram as that for the downlink, and therefore are omitted.

In FIG. 4, a downlink repeater for base station 2 includes an antenna 6 for receiving a radio signal from the base station 1, a BPF 7 for selecting the radio signal and limiting the band,
RF amplifier 8 for amplifying the high-frequency signal output of the BPF 7
An A / D converter 9 for converting a high-frequency signal amplified by the RF amplifier 8 into a digital signal; and an LPF (Low Pass) for filtering the digital signal.
A filter (Filter) 10, a DS (Down Sampler) 11 for sampling the filtered digital signal and converting the digital signal into a predetermined transmission rate,
An S / P converter 12 for converting the digital signal output from the parallel signal 11 from a parallel signal to a serial signal; an E / O converter 13 for converting the serial signal output from the S / P converter 12 into a digital optical signal; It is provided with.

[0006] The mobile station repeater 3 for the downlink is
An O / E converter 14 that converts a digital optical signal supplied from the E / O converter 13 via the optical fiber 4 into an electric signal and outputs a digital signal, and converts the digital signal from a serial signal to a parallel signal S / P converter 15
And a US (Up S) that samples the digital signal output from the S / P converter 15 and converts it to a predetermined transmission rate.
amplifier 16 and a BPF (Band P) for filtering the digital signal output from the US 16.
as filter), a D / A converter 18 for converting the filtered digital signal into an analog signal (high-frequency signal), a BPF 19 for selecting the high-frequency signal and limiting the band, and a high-frequency signal selected by the BPF 19. An RF amplifier 20 for amplification and an antenna 21 for transmitting a high-frequency signal amplified by the RF amplifier as a wireless signal are provided.

[0007] The conventional optical transmission repeater system shown in FIG. 4 operates as follows. First, a radio signal (frequency fRF: 400 MHz, for example) transmitted from the base station 1 is received by the antenna 6 of the base station repeater 2, and the BPF 7 and R
After the required band limitation and amplification by the F-amplifier 8 (FIG. 5)
(See (a)), and is converted into a digital signal by the A / D converter 9. The sampling frequency fs at this time is sufficient if it is at least twice the signal bandwidth (for example, 200 kHz) of the high-frequency signal that is the input signal when only the sampling theorem is taken into consideration. Yes, and A /
The effect of reducing the quantization error of the D-converter 9 to lower the quantization noise density (oversampling effect) is to make the sampling frequency as high as possible (for example, 2
(About 0 MHz) is effective.

However, when a high sampling frequency fs is adopted, the amount of information increases, so that it is necessary to increase the information transmission speed. For example, when the A / D converter 9 is 12 bits, the information transmission speed is 20 MHz × 12 bits =
240 Mbps. Therefore, E / O converter 13 and O
The / E converter 14 may be expensive, and the relayable distance is shortened.

In order to avoid this, a conventional LPF 10
After extracting only necessary signal components in step (see FIG. 5 (b)), downsampling is performed by DS11.
For example, when downsampling of 1/10 is performed, the sampling frequency fs becomes 20 MHz / 10 = 2 MHz (see FIG. 5C). The band that can be transmitted at this time is Nyquist's theorem (maximum transmission frequency = sampling frequency /
2) to 1 MHz, but the signal bandwidth is 200 kHz
It is enough to transmit a high frequency signal of z.

Furthermore, if the LPF 10 sufficiently attenuates unnecessary signal components of 1 MHz or more, the unnecessary signal components will not be turned back at the sampling frequency.
No folding distortion occurs. like this. When downsampling is performed, the information transmission speed when converted to a serial signal by the P / S converter 12 is 2 MHz × 12 bits = 24 Mbps. This serial signal is E /
The optical signal is converted into a digital optical signal by the O converter 13 and input to the optical fiber 4.

The digital optical signal transmitted by the optical fiber 4 is converted into an electric signal by the O / E converter 14 of the repeater 3 for mobile stations, and is converted into a parallel signal by the S / P converter 15. This parallel signal is up-sampled by US16 (10 times upsampling when 1/10 downsampling is performed),
, Only necessary signal components are extracted, and are converted into analog signals (high-frequency signals) by the D / A converter 18. The high-frequency signal output from the D / A converter 25 is supplied to the BPF 19 and R
After the necessary band limitation and amplification are performed by the F amplifier 20, the signal is transmitted to the mobile station 5 by the antenna 21.

As described above, the conventional optical transmission repeater converts a radio signal into a digital signal to perform filtering and transmission speed conversion, and also converts the radio signal into a digital optical signal using the E / O converter 13 and converts this into an optical signal. Since the signal is transmitted through the fiber 4, the signal-to-noise ratio (C / N) is not degraded as much as possible during the relay, and the transmission speed of the digital optical signal can be suppressed low.

[0013]

However, the conventional optical transmission repeater has the following problems. That is, the filtering by the LPF 10 and the BPF 17 is performed after the A / D converter 9 and before the D / A converter 18, respectively. These filters are inserted to remove unnecessary components such as spurious components (harmonics) and noises other than the desired signal, but the filtering process uses digital processing means such as a DSP to perform a huge amount of processing. This is usually done. In particular, if the order of the filter (the number of taps of the digital filter) is increased in order to make the attenuation characteristic of the filter steep, the D
The amount of processing that must be performed by the SP increases.
For this reason, the DS processing should be performed so that the
Usually, a method of increasing the driving clock of the P is adopted, but if the driving clock of the DSP is increased, the power consumption of the DSP increases and the amount of heat generated increases, which is not desirable. .

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and it is intended to reduce spurious and noise to a predetermined value or less, reduce the amount of operation by digital processing means such as a DSP, and reduce power consumption. It is an object of the present invention to provide a digital optical repeater transmitter capable of suppressing the above problem.

[0015]

In order to solve the above-mentioned object, an optical transmission repeater according to the present invention has an A / D converter for converting an analog signal received via an antenna into a digital signal. Conversion means, a digital filter for filtering the digital signal converted by the A / D conversion means, down-sampling means for reducing the transmission rate of the digital signal output from the digital filter to a predetermined transmission rate, In an optical transmission repeater having an electro-optical converter for converting a down-sampled signal output from a sampling unit into a digital optical signal and outputting the digital optical signal to a predetermined optical fiber, a control unit for controlling an order of the digital filter, and the digital filter Process the digital signal output by An FFT means for outputting, the FF
T means for calculating a signal intensity ratio between a desired signal component and other unnecessary signal components based on frequency spectrum information output by the T means, wherein the control unit maintains the signal intensity ratio at a predetermined value or more. The order of the filter is controlled.

According to a second aspect of the present invention, there is provided an optical transmission repeater which converts an analog signal received by the antenna into an intermediate frequency signal and outputs the intermediate frequency signal to the A / D conversion means. It further comprises conversion means. The invention according to claim 3 of the optical transmission repeater according to the present invention further comprises a clock generation means for supplying an operation clock to the digital filter according to claim 1 or 2, wherein the clock generation means is provided for the control unit. The frequency of the operation clock is controlled in accordance with the designated digital filter order.

According to a fourth aspect of the present invention, there is provided an optical transmission repeater for converting a digital optical signal into a digital signal by an optical-electrical converting means, and a digital signal converted by the optical-electrical converting means. Upsampling means for increasing a transmission rate to a predetermined transmission rate, a digital filter for filtering a digital signal output from the upsampling means, and a D / A conversion means for converting a digital signal output from the digital filter into an analog signal And an optical transmission repeater having an antenna for transmitting the analog signal converted by the D / A conversion means, a control means for controlling an order of the digital filter, and a digital processing signal output from the digital filter. FFT means for performing fast Fourier transform processing and outputting predetermined frequency spectrum information; Means for calculating a signal intensity ratio between a desired signal component and other unnecessary signal components based on frequency spectrum information output by the FFT means, wherein the control unit maintains the signal intensity ratio at a predetermined value or more. The order of the digital filter is controlled.

According to a fifth aspect of the present invention, there is provided an optical transmission repeater according to the fourth aspect, wherein the analog signal output by the D / A conversion means is converted into a high-frequency signal, and the frequency conversion is output to the antenna. Means are further provided. The invention according to claim 6 of the optical transmission repeater according to the present invention further comprises a clock generation means for supplying an operation clock to the digital filter according to claim 4 or 5, wherein the clock generation means is provided for the control unit. The frequency of the operation clock is controlled according to the order of the designated digital filter.

According to a seventh aspect of the present invention, there is provided an optical transmission repeater according to the present invention, wherein the first optical transmission repeater according to any one of the first, second, and third aspects is provided. Claim 5
Alternatively, the second optical transmission repeater according to claim 6 and an optical fiber that inputs a digital optical signal output from the first optical transmission repeater to the second optical transmission repeater. It is configured to be provided.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail. FIG. 1 is a block diagram showing a base station repeater and a mobile station repeater for a downlink (base station 1 → mobile station 5) in the optical transmission repeater system according to the present invention. Here, the base station repeater for the uplink (mobile station 5 → base station 1) and the repeater for the mobile station will not be described because they have the same block diagram as that for the downlink. The overall configuration of the relay system according to the present embodiment is shown in FIG.
And the communication between the base station 1 and the mobile station 5 is performed via the base station repeater 2, the mobile station repeater 3, and the optical fiber 4. It is.

As shown in FIG. 1, the downlink base station repeater 2 includes an antenna 6 for receiving a radio signal, a BPF 7 for selecting and band limiting the radio signal,
7, an RF amplifier 8 for amplifying the high-frequency signal output from the A / D converter 7, an A / D converter 9 for converting the high-frequency signal amplified by the RF amplifier 8 into a digital signal, a DSP 22 for filtering the digital signal, and the DSP 22 A DS11 for down-sampling the processed digital signal and converting it to a predetermined transmission speed, an S / P converter 12 for converting the digital signal output by the DS11 from a parallel signal to a serial signal, and the S / P converter 12 An E / O converter 13 for converting a serial signal output by the device into an optical signal;
Clock oscillator 2 for generating a clock signal of a predetermined frequency
3, and the DSP 2 divides the clock signal by a predetermined number.
And a variable frequency divider 24 for supplying a drive clock to the second frequency divider 2.

The DSP 22 performs an LPF 25 for filtering the digital signal supplied from the A / D converter 9 and a high-speed Fourier transform of the digital signal output from the LPF 25 to output frequency spectrum information. And a signal intensity ratio between the desired signal component and the unnecessary signal component based on the frequency spectrum information output from the FFT unit 26.
The control unit 25 outputs a PF control signal and a frequency division ratio control signal. The LPF supplied by the control unit 27
The control signal controls the filter order of the LPF unit 25, and the frequency division ratio control signal controls the frequency division ratio of the variable frequency divider 24.

Further, the downlink base station repeater 3 is
O / E converter 14, S / P (serial / parallel) converter 15, US (Up Sampler) 16, D
SP28, D / A converter 18, BPF19, RF
Amplifier 20, antenna 21, clock oscillator 29
And a variable frequency divider 30. In addition, the DSP
Reference numeral 28 denotes a BPF for performing band-pass filtering on the digital signal supplied from the US 15, similarly to the DSP 22.
Unit 31, an FFT unit 32 that performs fast Fourier transform processing on the digital signal output from the BPF unit 31 and outputs frequency spectrum information, and a power ratio between a desired signal and an unnecessary signal based on the frequency spectrum information output from the FFT unit 32. And a control unit 33 that outputs a BPF control signal and a frequency division ratio control signal in accordance with the calculation result. In addition,
The BPF control signal supplied by the control unit 33 is a BPF 24
And the frequency division ratio control signal controls the frequency division ratio of the variable frequency divider 30.

The optical transmission repeater system configured as described above operates as follows. First, a radio signal transmitted from the base station 1 is received by the antenna 6 in the base station repeater 2. The radio signal received by the antenna 6 is subjected to band limitation and amplification by the BPF 7 and the RF amplifier 8, then converted into a digital signal by the A / D converter 9 and supplied to the DSP 22. Here, a clock signal of a predetermined frequency (= fCL) supplied from the clock generator 23 is frequency-divided by a predetermined number (= M) by the variable frequency divider 24 and supplied as a drive clock of the DSP 22. ing.

The DSP 22 filters the digital signal in the LPF unit 25, and outputs the output of the digital signal to the DS 11 and the F
Each is supplied to the FT unit 2. Here, the LPF unit 2
5 is supplied with an LPF control signal from the control unit 27,
The filter order of the unit 25 (corresponding to the number of taps of the digital filter) is controlled. Further, the control unit 27 supplies a frequency division control signal to the variable frequency divider 24 to control the frequency division ratio of the frequency divider 24 in accordance with the filter order. Immediately after the power is turned on, the control unit 27 sets n = n0 (maximum value) and M = M0 (minimum value) with the filter order (= n) and the division ratio (= M) as initial values, respectively. You have set.

This is because the DSP 22 is in the L state in the initial state.
The filter selection characteristic of the PF 25 section is maximized, and the filter selection characteristics are in the steepest state. Therefore, since the amount of calculation as the DSP is maximum, the frequency of the drive clock is set to fC so that the processing time does not become longer accordingly.
It is set to the maximum value of L / M0. Therefore, in the initial state, the power consumed by the DSP 22 is maximum.

Therefore, the DSP 22 performs a fast Fourier transform process on the digital signal subjected to the filtering process in the LPF 25 in the FFT unit 26 and passes the signal intensity of the desired signal component passing through the pass band of the LPF 25 and the attenuation range of the LPF 25. The signal strength of unnecessary signal components such as spurious noise and noise is calculated, and the result is sent to the control unit 27 as frequency spectrum information. The control unit 27 calculates a signal strength ratio (dB) between the signal strength of the desired signal and the largest unnecessary signal based on the frequency spectrum information.

Further, the control section 27 supplies an LPF control signal while referring to the signal intensity ratio, sequentially reduces the order of the LPF 25 one by one, and sends the frequency division ratio control signal to the variable frequency divider 24. The supplied frequency division ratio is increased by a predetermined number. Then, when the signal intensity ratio falls below the predetermined value, the filter order is increased by one again and fixed, and the frequency division ratio is correspondingly reduced and fixed again by a predetermined number. As described above, the filter order and the frequency division ratio are set to optimal values so that the signal intensity ratio between the desired signal component and the unnecessary signal component of the digital signal output from the LPF unit 25 maintains a predetermined value. Accordingly, the DSP 22 performs a filtering process with an appropriate filter order according to the signal received by the antenna 6 and controls the frequency of the drive clock to an optimal value according to the filter order, so that the power consumption of the DSP 22 is minimized. Can be.

As described above, the LPF 2 of the DSP 22
Digital signal (parallel signal) filtered by 5
Is down-sampled by the DS 11 and its transmission rate is once converted to a lower transmission rate. This is converted into a serial signal by a P / S converter 12, converted into an optical digital signal by an E / O converter 13, and transmitted to the mobile station repeater 3 by an optical fiber 4.

On the other hand, the repeater 3 for mobile stations is an optical fiber 4
The O / E converter 14 converts the optical digital signal supplied from the S / P converter into an electric signal (serial signal), and then converts the signal into a parallel signal by the S / P converter 15 and supplies the parallel signal to the US 16. US16
Converts the transmission rate to the same transmission rate as the DS11 input by up-sampling the parallel signal. DS
P28 performs a predetermined band filtering process on the BPF unit 31 and supplies a digital signal to the D / A converter 18.

Here, in the DSP 28, the filter order (the number of taps of the digital filter) of the BPF 31 and the DPF
Regarding the frequency of the drive clock of SP28,
22 is the same as the control example in FIG.
The filter order of 31 units and the frequency of the drive clock supplied from the variable frequency divider 30 are set to optimal values. And
The digital signal filtered by the DSP 28 (BPF unit 31) is converted into an analog signal (high-frequency signal) by the D / A converter 18. This can be band-limited and amplified by the BPF 19 and the RF amplifier 20, transmitted as a radio signal by the antenna 21, and relayed to the mobile station 5.

As described above, in the base station repeater 2 and the mobile station repeater 3, the radio signal received by the antenna is converted into a digital signal, which is then converted into the DSP 22 or DS signal.
When filtering at P28, the amount of filtering (filter order) and the frequency of the driving clock are controlled to maintain the signal strength ratio between the desired signal and the unnecessary signal at a predetermined value or more. It is possible to suppress power consumption as a whole.

In the optical repeater system described above,
The high-frequency signal received by the antenna 6 in the base station repeater 2 is A / D converted as it is, and the mobile station repeater 3
In the above, an analog signal after the D / A conversion is obtained as a high-frequency signal and transmitted from the antenna 21. However, the present invention is not limited to this. For example, the base station repeater 2 includes frequency conversion means between the RF amplifier 8 and the A / D converter 9 to generate a low frequency intermediate frequency signal from the high frequency signal received by the antenna 6. A / D
The data is supplied to the converter 9. The mobile station repeater 3 has frequency conversion means between the D / A converter 18 and the BPF, and converts an analog signal output from the D / A converter 18 into an intermediate frequency signal in a low frequency band. Generated as
This may be converted into a high-frequency signal of a predetermined frequency by the frequency conversion means. In this case, since the high-frequency signal is converted into the intermediate-frequency signal and then the optical-electrical conversion is performed, the condition of the frequency characteristics of the A / D converter 9 and the D / A converter 18 is relaxed, and the higher frequency range is obtained. Can be configured as a repeater.

In this embodiment, the output of the variable frequency divider is used as the drive clock, and the frequency of the drive clock is controlled by controlling the frequency division ratio of the frequency divider. Not limited to. For example, as shown in FIG. 2, an output signal of the clock generator 23 may be used as a reference signal and a phase-locked signal generated by the PLL circuit may be used as a drive clock. In this case, the output signal (frequency: fCL) of the clock generator 23 is frequency-divided by the frequency divider 31 by a predetermined number (frequency division ratio: fCL).
N), using this as a PLL reference signal
, A loop filter 33, and a VCO (voltage controlled oscillator)
And the variable frequency divider 35 to obtain a phase-synchronized signal. In this case, when the output signal of the VCO 34 is obtained as a drive clock, its frequency changes by fCL / N every time the frequency division ratio of the variable frequency divider 35 is changed by one. There is an advantage that the clock frequency can be set finely and the degree of freedom of design increases.

[0035]

As described above, according to the present invention, in an optical relay system composed of a base station repeater and a mobile station repeater, a digital processing such as a DSP is performed in the base station repeater or the mobile base station repeater. In the filtering process performed by the means, the filter order (the number of taps) of the digital means can be controlled, and the signal intensity ratio between a desired signal component and an unnecessary signal component included in the digital signal output from the digital processing means is predetermined. The filter order is controlled to be as small as possible so as to maintain the value, and the frequency of the drive clock of the digital processing means is controlled to be as small as possible according to the filter order. This is extremely effective in providing an optical transmission repeater system capable of minimizing noise.

[Brief description of the drawings]

FIG. 1 is a block diagram of a base station repeater and a mobile station repeater for a downlink in an optical transmission repeater system according to the present invention.

FIG. 2 is a block diagram showing an embodiment of a driving clock supply unit.

FIG. 3 is a block diagram showing the overall configuration of the relay system.

FIG. 4 is a block diagram of a base station repeater and a mobile station repeater for a downlink in a conventional optical transmission repeater system.

FIG. 5 is a diagram showing a frequency spectrum of a transmission signal.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Base station 2 ... Repeater for base station 3 ... Repeater for mobile station 4 ... Optical fiber 5 ... Mobile station 6, 21 ... Antenna 7, 17, 19 ... BPF 8, 20 RF amplifier 9 A / D converter 10 LPF 11 DS 12 P / S converter 13 E / O converter 14 O / E converter 15 S / P converter 16 US 18 D / A converter 22 DSP 23, 29 Clock generator 24 Variable frequency divider 25: LPF unit 26, 32: FFT unit 27, 33: control unit 31: BPF unit

Claims (7)

[Claims] An A / D converter for converting an analog signal received via an antenna into a digital signal;
A digital filter for filtering the digital signal converted by the D conversion means, a downsampling means for reducing the transmission rate of the digital signal output from the digital filter to a predetermined transmission rate, and a downsampling output from the downsampling means In an optical transmission repeater having an electro-optical converter for converting a signal into a digital optical signal and outputting the signal to a predetermined optical fiber, a control means for controlling an order of the digital filter; FFT means for performing Fourier transform processing and outputting predetermined frequency spectrum information, and means for calculating a signal intensity ratio between a desired signal component and other unnecessary signal components based on the frequency spectrum information output by the FFT means, The control unit sets the signal strength ratio to a predetermined value or less. An optical transmission repeater, wherein the order of the digital filter is controlled so as to maintain the order. 2. The apparatus according to claim 1, further comprising frequency conversion means for converting an analog signal received by said antenna into an intermediate frequency signal and outputting said signal to said A / D conversion means.
An optical transmission repeater according to any of the preceding claims. 3. The apparatus according to claim 1, further comprising clock generation means for supplying an operation clock to said digital filter, wherein said clock generation means controls a frequency of said operation clock in accordance with an order of said digital filter specified by said control unit. The optical transmission repeater according to claim 1 or 2, wherein: 4. An optical-to-electrical converter for converting a digital optical signal into a digital signal, an up-sampling unit for increasing a transmission rate of the digital signal converted by the optical-to-electrical converter to a predetermined transmission rate, A digital filter for filtering a digital signal output from the upsampling unit, a D / A conversion unit for converting the digital signal output from the digital filter into an analog signal, and an analog signal converted by the D / A conversion unit An optical transmission repeater having an antenna for transmitting a digital filter, a control unit for controlling an order of the digital filter, and an FFT unit for performing a fast Fourier transform process on a digitally processed signal output from the digital filter and outputting predetermined frequency spectrum information And the frequency spectrum information output by the FFT means. Means for calculating a signal intensity ratio between a desired signal component and other unnecessary signal components, wherein the control unit controls the order of the digital filter so as to maintain the signal intensity ratio at a predetermined value or more. Optical transmission repeater. 5. An optical transmission repeater according to claim 4, further comprising frequency conversion means for converting an analog signal output by said D / A conversion means into a high-frequency signal and outputting said high-frequency signal to said antenna. . 6. The digital filter further includes clock generation means for supplying an operation clock to the digital filter, wherein the clock generation means controls the frequency of the operation clock according to the order of the digital filter specified by the control unit. The optical transmission repeater according to claim 4 or claim 5, wherein: 7. A first optical transmission repeater according to any one of claims 1, 2 and 3, and a fourth optical transmission repeater.
Or a second optical transmission repeater according to claim 6, and an optical fiber for inputting a digital optical signal output from the first optical transmission repeater to the second optical transmission repeater. An optical transmission repeater system characterized in that: