JPH08242209A - Optical transmission equipment - Google Patents

Abstract

PURPOSE: To make it possible to transmit both of outgoing high frequency communication information from a master stastion to a slave station and incoming base band control information from the slave station to the master station through one optical cable in respect to an optical transmission equipment for executing subcarrier analog optical transmission through the optical cable connected between the master station on the central base station side and the slave station on the radio base station side. CONSTITUTION: Received light from the slave station 20 is inputted to a photoelectric converter 23 through two directional couplers 21, 22. An optical signal 50 distributed by the coupler 22 is inputted to an external converter 26 and modulated based upon control information 52 and output light 48 is synthesized by the coupler 21 and sent to the optical cable 30. A directional coupler 13 is connected to the output side of an electrooptical converter 12 in the master station 10, an outgoing optical signal 41 is sent to the cable 30, an optical signal 46 received from the station 20 and distributed is converted into an electric signal 51, and control information from the station 20 is extracted through a low pas filter 15.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a relay transmission apparatus for wireless communication using subcarrier analog optical transmission, and more particularly, to an optical cable connecting a central base station apparatus and peripheral wireless base station apparatuses arranged in each zone with an optical cable. The present invention relates to a transmission device.

[0002]

2. Description of the Related Art Generally, an optical transmission device of a relay transmission device for wireless communication using subcarrier analog optical transmission is constructed as shown in FIG. In the figure, 1 is a central base station side device (referred to as a master station), 2 is a peripheral radio base station side device (referred to as a slave station), 3 and 4 are optical fibers, and 11 is a high frequency amplifier for a downlink from the master station to the slave station. , 12 is an electro-optical converter (E / O), 14 is an opto-electric converter (O / E) that converts the received light from the slave station into an electric signal, 16 is an uplink high frequency amplifier, and 23 is a downlink. An optical-electrical converter for converting the light of the line into an electric signal, 24 is a high frequency amplifier of the down line,
Reference numeral 27 is an upstream high-frequency amplifier, and 28 is an electro-optical converter. The central base station side device (master station) 1 and the peripheral radio base station side device (slave station) 2 of the optical transmission device are connected by two optical fibers 4 and 3 for upstream and downstream, respectively, and a high frequency input (R
(FIN) is amplified by amplifiers 11 and 27, converted into optical signals by electro-optical converters 12 and 28 and transmitted through optical fibers 3 and 4, and the transmitted optical signals are converted into optical-electrical converters 14 and The signal is converted into a high frequency electric signal again by 23 and amplified by the amplifiers 16 and 24 to output a high frequency signal (RF OUT). In the case of FIG. 1 described above, bidirectional transmission is performed between the master station and the slave station. For example, in the case of one-way communication from the master station to the slave station such as a radio calling (pager radio) system, the transmission is performed. Since the path need only be in the downstream direction for transmitting communication information, the optical transmission device uses one optical fiber 3 in the downstream direction as shown in FIG. 2 for the master station 1'and the slave station 2 '.
It becomes a system configuration that is tied.

[0003]

However, in an actual system, it is necessary to transmit a low bit rate digital signal which is a control information signal from the slave station in the upstream direction.
In the case of the bidirectional transmission configuration as shown in FIG. 1, this digital signal can be subjected to some modulation to be multiplexed with the upstream high frequency signal for transmission. However, in the case of the one-way transmission configuration as shown in FIG. 2, the control information signal of the slave station cannot be sent to the master station. Therefore, there is a problem that an upstream transmission path is installed only for transmitting the control information signal, and as a result, the system configuration becomes exactly the same as that in FIG.

An object of the present invention is to enable transmission of a control information signal from the slave station to the master station even if there is one transmission optical fiber between the master station and the slave station. An object of the present invention is to provide an optical transmission device that is compact and lightweight.

[0005]

According to the present invention, a slave station 20 is provided with an external modulator 26 having an electric-optical signal converting function, a downlink optical signal 50 is modulated with control information 52, and an uplink system of a master station 10 is provided. A filter 15 is inserted into the optical fiber to extract an upstream signal, and an optical directional coupler (c) is used at each signal distribution / coupling point, so that the transmission path by the optical fiber 30 between the master station and the slave station becomes 1 This book also allows the control information signal from the slave station to be sent to the master station.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 3 is a block diagram showing an embodiment of the present invention, which is an example applied to a communication device of a radio calling (pager radio) system. In the figure, the same parts as those in FIG. 1 are designated by the same reference numerals. 10 is a master station, 20 is a slave station, 1
3 and 21, 22 are directional couplers (C), 15 is a low-pass filter, 26 is an external modulator, 30 is an optical fiber, 41-5.
0 is an optical signal, and 51 and 52 are digital baseband electric signals. Directional couplers (C) 13, 21 and 22 for distributing / combining optical signals to the transmission path of the downstream signal are inserted at three locations in total in the master station and the slave stations. A radio frequency electric signal (RF IN), which is communication information sent from the master station to the slave station, is amplified by an amplifier 11 and then converted into an optical signal by an electro-optical converter 12 and then converted into an optical signal in the optical fiber 30 via a directional coupler 13. And the transmitted optical signal is a directional coupler 2
It is converted into a high frequency electric signal (RF OUT) again by the opto-electric converter 23 via 1 and 22. on the other hand,
For the upstream signal, the digital baseband signal (Digital IN), which is the control information signal of the slave station, is transferred to the external modulator (E
OM) 26 to the modulation signal input section. External modulator 2
In 6, the downlink signal distributed by the directional coupler 22 is modulated with a digital baseband signal, and this modulated light is output to the directional coupler 21. The modulated optical signal coupled in the upward direction by the directional coupler 21 is
It is transmitted from the slave station 20 to the master station 10 through the optical fiber 30 and distributed by the directional coupler 13. The distributed modulated optical signal is converted into an electric signal by the optical-electrical converter 14. Since this electric signal is a signal obtained by digitally modulating the downstream signal by the external modulator 26, the low-pass filter 15 extracts the upstream signal. As described above, the upstream signal is transmitted via the downstream transmission path.

The system configuration will be described in more detail. The downstream optical signal 41 converted by the electro-optical converter 12 passes through the directional coupler 13 and the optical fiber 30.
The optical signal 42 is transmitted through the inside (optical signal 42) and is divided into an optical signal 43 and an optical signal 49 by the directional coupler 21. The optical signal 49 reaches the external modulator 26 and terminates. The optical signal 43 is distributed by the directional coupler 22 into an optical signal 44 and an optical signal 50,
The optical signal 44 is converted into an electric signal by the optical-electrical converter 23 and amplified by the amplifier 24 to generate a high frequency electric signal (RF
OUT). On the other hand, the optical signal 50 is input to the external modulator (EOM) 26, and is a digital baseband signal (Digital) that is control information from the slave station to the master station.
IN) is digitally modulated by the electric signal 52 amplified by the amplifier 25, and is output as the upstream modulated optical signal 48.
The modulated optical signal 48 is coupled in the upstream direction by the directional coupler 21 and transmitted through the optical fiber 30 (optical signal 4
7), the optical signal 45 and the optical signal 4 by the directional coupler 13.
It is divided into six. The optical signal 45 reaches the electro-optical modulator 12 and terminates. On the other hand, the optical signal 46 is the optical-electrical converter 14
Is converted into an electric signal 51 by the low-pass filter 1
Only the upstream signal is taken out by 5. The above is the distribution / coupling of optical signals by the directional coupler C and the series of signal flows resulting therefrom.

FIG. 4 shows a Mach-Zehnder type modulator showing an example of the external modulator (EOM) 26. This is an element that modulates through an optical signal in a modulation crystal to which a modulation voltage is applied.

FIG. 5 is an explanatory diagram of the operation of this system. In the external modulator (EOM) 26, the upstream baseband signal 52 (digital electric signal) is used as the downstream optical signal 50.
(Modulated by a high frequency signal) is directly modulated and output as an optical signal 48. These signals have waveforms as shown in FIG. Therefore, the optical signal 48 becomes the optical signal 47 → the optical signal 46 → the electric signal 51, the high-frequency component is removed by the low-pass filter 15, and the upstream baseband signal 5
The same signal (Digital OUT) as 2 can be obtained.

Both the optical signal 45 and the optical signal 49 are one of the signals distributed by the directional coupler, but they are unnecessary signals for the system itself. Therefore, the signals reaching the E / O 12 and EOM 26 affect the operation of the E / O 12 and EOM 26 as return light. Therefore, "terminating with ..." means this E / O12, EOM
In FIG. 26, an element called an optical isolator that allows light to pass in the forward direction but does not pass in the reverse direction is used.
5, it means that the optical signal 49 is removed. This optical isolator is generally built in the E / O 12 and EOM 26, but if it is not built in, it must be provided outside.

[0011]

According to the present invention, by using the external modulator in the upstream electro-optical conversion unit of the slave station, the electro-optical converter including the semiconductor laser and its peripheral circuits becomes unnecessary, and It is possible to reduce the size, weight and cost of the station. Also, since the optical signal is distributed / coupled by the directional coupler, the transmission between the master station and the slave station can be realized with one optical fiber, which simplifies the system configuration and installs the upstream optical fiber. Cost can be reduced.

[Brief description of drawings]

FIG. 1 is a system configuration example diagram of a conventional optical transmission device.

FIG. 2 is a system configuration example diagram of a conventional optical transmission device for a radio paging system.

FIG. 3 is a diagram showing a system configuration example of an embodiment of the present invention.

FIG. 4 is a structural example diagram of an external modulator used in the present invention.

FIG. 5 is an explanatory diagram of an upstream signal modulation operation of the present invention.

[Explanation of symbols]

 1 master station 2 slave station 3,4 optical fiber 10 master station 11 amplifier 12 electric-optical converter 13 directional coupler 14 optical-electrical converter 15 low-pass filter 16 amplifier 20 slave station 21, 22 directional coupling Device 23 Optical-electrical converter 24, 25 Amplifier 26 External modulator 30 Optical fiber 41-50 Optical signal 51, 52 Electric signal

Claims (1)

[Claims] 1. A master station on the side of a central base station, which sends out a downstream optical signal obtained by converting a high-frequency electric signal, which is communication information from the central base station to a wireless base station, into an optical signal by an electro-optical converter, on a transmission line of an optical cable. And a sub-carrier analog optical transmission optical signal composed of a downstream optical signal received through the optical cable and a slave station on the radio base station side which converts the downlink optical signal into a high frequency electric signal by a first optical-electrical converter and outputs the high frequency electric signal. In the transmission device, the slave station distributes a downlink optical signal output from the first directional coupler for distributing and synthesizing downlink optical signals received through the optical cable. A second optical signal which inputs one of the downstream optical signals to the first optical-electrical converter
Of the directional coupler and the other downlink optical signal output from the second directional coupler, and the modulated light modulated by the digital baseband signal which is the control information from the radio base station for the central base station. And an external modulator which outputs to the first directional coupler, and the master station uses the downstream optical signal output from the electro-optical converter as one input to the downstream optical signal to the optical cable. A third directional coupler that sends out a signal and distributes and outputs the modulated light received from the slave station through the optical cable, and electrically supplies the modulated light that is distributed and output from the third directional coupler. A second optical-electrical converter for converting into a signal; and a low-pass filter for receiving the electric signal output from the second optical-electrical converter and extracting the digital baseband signal. You Optical transmission equipment.