JP2998365B2 - Data transmission equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data transmission apparatus using an optical fiber, and more particularly to a data transmission apparatus of a system for transmitting a radio band signal in a microwave band as it is through an optical fiber.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 2, for example, a data transmission apparatus of this type modulates an input data signal into a signal in an intermediate frequency band, and modulates a signal output from the modulator 12. A frequency converter 13 for converting a signal into a microwave band, and an electro-optical converter (E / E) for converting the microwave output from the frequency converter 13 into an optical signal.
O) 15, an optical fiber 17 for transmitting an optical signal output from the electro-optical converter 15, and an optical fiber 17
And an optical-electrical converter (O / E) 19 for converting the frequency of the optical signal transmitted in the microwave band into a microwave band.
9, a frequency converter 21 for returning the microwave output to the intermediate frequency band, an AGC amplifier 29 for amplifying the signal in the intermediate frequency band output from the frequency converter 21, and a return for the amplified signal to a data signal. A demodulator 30 is connected between the transmission signal input terminal 11 and the reception signal output terminal 31 in series.

In the data transmission device having such a configuration, the data signal input from the transmission signal input terminal 11 is
2, the signal is modulated into an intermediate frequency band signal by a frequency converter 2, and then converted into a microwave band by a frequency converter 13, and then converted into an electric signal.
The light is converted into an optical signal by an optical converter (E / O) 15.
After the converted optical signal passes through the optical fiber 17, the optical signal
After being returned to the microwave band again by the electric converter (O / E) 19, further subjected to frequency conversion to the intermediate frequency band by the frequency converter 21, amplified by the AGC amplifier 29, and then demodulated into a data signal by the demodulator 30 Is done.

In a data transmission apparatus using an optical fiber as described above, the wavelength of an optical signal changes depending on the input current to a laser diode used as a light emitting element of the electro-optical converter 15. It has been known. Therefore, when trying to increase the reliability of the transmission path,
It is necessary to use a high-quality light-emitting element for use in the optical converter 15, and thus there has been a problem that the entire apparatus becomes expensive.

[0005] For these reasons, a dual transmission system has conventionally been adopted as a data transmission device. FIG. 3 shows an example of an apparatus according to this method. The same components as those of the apparatus shown in FIG. 2 are denoted by the same reference numerals, and description thereof will be omitted.

This data transmission device has a transmission signal input terminal 1
1 between the transmission signal input terminal 11 and the reception signal output terminal 31.
(Branch device) 1 that branches the input signal from
4 and two electro-optical converters 15 and 16 for converting the signals branched by the hybrid 14 into optical signals, respectively.
And optical fibers 17 and 18 for transmitting the optical signals converted by the electro-optical converters 15 and 16, respectively, and an optical-electric converter for converting the signals transmitted by the optical fibers 17 and 18 to electric signals. 19 and 20, and a selection switch 32 whose movable contact is switched to one of the output terminals of the optical-electrical converters 19 and 20.

In the data transmission apparatus based on the dual transmission system, an input signal is branched into two and each is separated into separate electro-optical converters 1.
5, 16, optical fibers 17, 18, optical-electrical converter 1
9 and 20 are transmitted, and either output signal is selected by the selection switch 32.

[0008]

However, in this conventional data transmission apparatus, the optical-to-electrical converters 19, 20
Each time the selection switch 32 in the output unit operates, a shock is applied to the transmission signal, which causes noise, which causes an error in the data signal.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has as its object to eliminate the impact on the data signal due to the conventional switching operation, improve the signal-to-noise ratio,
An object of the present invention is to provide a data transmission device with improved reliability.

[0010]

A data transmission apparatus according to the present invention comprises: a frequency converter for converting an input data signal into a microwave band; a splitter for splitting an output signal of the frequency converter into two; Two electro-optical converters for converting the output signal of each of the devices into an optical signal;
Two optical fibers respectively transmitting optical signals output from the optical converters, two optical-electrical converters respectively converting the optical signals transmitted by these optical fibers into electric signals, and Two frequency converters for converting the output signal of the electric converter into an intermediate frequency band, a phase control unit for controlling the phase so that the output signals of the two frequency converters are in phase with each other, and a local oscillation signal. A local oscillator that supplies the frequency converter directly to the one frequency converter and supplies the other frequency converter via the phase controller, and the two phase-shifted in-phase by the phase controller. A synthesizer for synthesizing output signals of the two frequency converters,
And a demodulator for demodulating the output signal of the synthesizer.

[0011] Specifically, the phase control unit includes a phase detector for detecting a phase difference between two intermediate frequency band output signals respectively output from the two frequency converters, and the other frequency converter. A phase shifter that changes the phase of the supplied local oscillation signal, and the phase shifter is controlled based on a phase difference detected by the phase detector, so that the outputs of the two frequency converters have the same phase. , And a phase controller for controlling

In the data transmission apparatus according to the present invention, the input data signal is frequency-converted into the microwave band by the frequency converter, and then branched into two by the branching device. Each output signal of the splitter is converted into an optical signal by two electro-optical converters, transmitted by two optical fibers, and converted into an electric signal in a microwave band by the two optical-electric converters. Is converted. After that, these electric signals are frequency-converted to the intermediate frequency band by the two frequency converters, respectively, and controlled by the phase control unit so that the phases of these signals become the same. The output signals of the two frequency converters shifted in phase by the phase control unit are combined by a combiner, and then demodulated to an original signal by a demodulator.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a configuration of a data transmission apparatus according to one embodiment of the present invention. The same components as those shown in FIGS. 2 and 3 are denoted by the same reference numerals, and description thereof will be omitted.

The data transmission apparatus according to the present embodiment has a modulator 12 at a transmission signal input terminal 11, a frequency converter 13,
Further, a hybrid (branch) 14 is connected,
In this hybrid 14, the data transmission system is branched into two. The transmission system branched into two by the hybrid 14 is connected in series with electro-optical converters 15 and 16, optical fibers 17 and 18, optical-electric converters 19 and 20, and frequency converters 21 and 22. The transmission system that has been branched into two by the hybrid (combiner) 28 is integrated to combine data. The hybrid 28 includes an AGC amplifier 29 for amplifying the output of the hybrid 28 to a certain level, and an AGC amplifier 2
9, a demodulator 30 for demodulating the signal amplified in step 9 is connected in series.
Output from

The output terminals of the frequency converters 21 and 22 are connected by a phase control unit 23 for controlling the two phases to be in phase. The phase control unit 23 includes a phase detector 24 that detects a phase difference between the intermediate frequency band output signals output from the frequency converters 21 and 22, and two phase detectors based on the phase difference detected by the phase detector 24. A phase controller 25 for controlling the phases of the intermediate frequency band output signals to be in phase, and a phase shifter 26 controlled by the phase controller 25
It is composed of The frequency converter 21 and the frequency converter 22 are each supplied with a local transmission signal from a local transmitter 27. Here, the local transmission signal supplied to the frequency converter 22 passes through the phase shifter 26 of the phase control unit 23, and the phase is controlled by the phase shifter 26.

Next, the operation of the data transmission apparatus having the above configuration will be described. A signal input from the transmission signal input terminal 11 is modulated into an intermediate frequency band signal by a modulator 12, frequency-converted into a microwave band signal by a frequency converter 13, and then branched into two by a hybrid 14.
The microwave signal divided into two is converted into an electric-optical converter 1 respectively.
After being converted into optical signals by the optical fibers 5 and 16,
7 and 18. These optical fibers 17, 1
The optical signal transmitted by 8 is converted into a microwave band signal by optical-electrical converters 19 and 20, respectively, and then converted into an intermediate frequency band signal by frequency converters 21 and 22. The two converted intermediate frequency band signals are combined by the hybrid 28, amplified to a certain level by the AGC amplifier 29, demodulated by the demodulator 30, and output from the reception signal output terminal 31.

Here, the intermediate frequency band signal synthesized by the hybrid 28 is always synthesized in the same phase by the following operation of the phase controller 23.

Part of the intermediate frequency band signal output from the frequency converters 21 and 22 is input to a phase detector 24,
The phase difference between the two intermediate frequency band signals is detected. FIG. 4 shows the characteristics of the phase detector 24. The phase controller 25 generates a control signal to rotate the phase shifter 26 in a direction in which the phase difference output from the phase detector 24 becomes zero. In response to this control signal, the phase shifter 26
7, the phase of the local transmission signal transmitted to the frequency converter 22 among the local transmission signals transmitted to the frequency converters 21 and 22 is changed. As a result, the phase of the intermediate frequency band output signal output from the frequency converter 22 changes so as to approach the phase of the intermediate frequency band signal output from the frequency converter 21. By continuously performing the above operations, the two intermediate frequency band signals are always in phase, and then combined by the hybrid 28.

As described above, according to the data transmission apparatus of the present embodiment, a dual transmission system is employed and a switch for selecting one of the two transmission systems is not required. Noise generated by switching could be eliminated. In addition, since the output signals of the two optical-to-electrical converters 19 and 20 are combined in phase, the signal-to-noise ratio (C / N ratio) is improved by 3 dB compared to transmission using a single optical fiber. Was done.

[0021]

As described above, according to the data transmission apparatus of the present invention, a frequency converter for converting the frequency of an input data signal into a microwave band, and a splitter for splitting an output signal of the frequency converter into two parts are provided. , Two electro-optical converters for converting the output signal of each of the splitters into an optical signal,
Two optical fibers respectively transmitting optical signals output from the two electro-optical converters, two optical-electric converters respectively converting the optical signals transmitted by these optical fibers into electric signals, and Two frequency converters for frequency-converting the output signal of the optical-electrical converter into an intermediate frequency band, a phase control unit for controlling the phase so that the output signals of the two frequency converters are in phase with each other, and a local unit. A transmission signal is supplied directly to the one frequency converter, and a local oscillator supplied to the other frequency converter via the phase control unit is phase-shifted to the same phase by the phase control unit. And a demodulator for demodulating the output signals of the two frequency converters, so that one of the conventional two transmission systems is selected. Do Because of the selection switch is not required,
Noise generated by conventional switching can be eliminated. In addition, since the outputs of the two optical-to-electrical converters are combined in phase, the signal-to-noise ratio is improved compared to transmission using a single optical fiber, and a high-quality transmission path can be provided. effective.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of a data transmission device of the present invention.

FIG. 2 is a block diagram illustrating an example of a conventional data transmission device.

FIG. 3 is a block diagram illustrating an example of a conventional data transmission device.

FIG. 4 is a characteristic diagram showing a relationship between a phase difference between two waveform signals and an output from a phase detector.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Transmission signal input terminal 12 Modulator 13,21,22 Frequency converter 14,28 Hybrid 15,16 Electric-optical converter 17,18 Optical fiber 19,20 Optical-electric converter 23 Phase control part 24 Phase detector 25 Phase controller 26 Phase shifter 27 Local oscillator 29 AGC amplifier 30 Demodulator 31 Received signal output terminal

Claims (2)

(57) [Claims] 1. A frequency converter for converting the frequency of an input data signal into a microwave band, a splitter for splitting an output signal of the frequency converter into two, and an output signal of each of the splitters is converted to an optical signal. Two electro-optical converters, two optical fibers respectively transmitting optical signals output from these two electro-optical converters, and optical signals transmitted by these optical fibers into electric signals, respectively. Two optical-to-electrical converters for converting, two frequency converters for frequency-converting the output signals of these optical-to-electrical converters to an intermediate frequency band, and the output signals of the two frequency converters are in phase with each other. And a local controller that supplies a local oscillation signal directly to the one frequency converter and supplies the other frequency converter to the other frequency converter via the phase controller. A synthesizer for synthesizing output signals of the two frequency converters shifted in phase by the phase control unit; and a demodulator for demodulating an output signal of the synthesizer. Data transmission device. 2. A phase detector for detecting a phase difference between two intermediate frequency band output signals respectively output from the two frequency converters, and the phase detector is supplied to the other frequency converter. A phase shifter that changes the phase of the local oscillation signal, and the phase shifter is controlled based on the phase difference detected by the phase detector, and the two frequency converters are controlled so that the outputs have the same phase. 2. The data transmission device according to claim 1, comprising a phase controller.