JP2005094630A - Analog optical transmission system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect abnormality in a circuit (RF circuit) of an electric signal at a slave station side when transmitting an optical signal via an up optical fiber from a slave station to a master station. <P>SOLUTION: In a slave station 2, a carrier signal (RF signal) and a pilot signal that is generated by a pilot signal generator 2, of a frequency close to that of the carrier signal are composed by a synthesizer 27, and the synthesized signal is transmitted to a master station 1 via an optical fiber 4 by emitting an optical signal in a semiconductor laser (LD) 29. In the master station 1, the optical signal from the slave station is received by a photo-diode (PD) 14, the pilot signal separated by a filter 19, a level of the pilot signal is detected by a detection circuit 20, and a control part detects abnormality in the RF circuit on the basis of the level of the pilot signal. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an analog optical transmission system that transmits an analog optical signal from a master station to a slave station via a downstream optical fiber, while transmitting an analog optical signal from the slave station to the master station via an upstream optical fiber. The present invention relates to a technique that makes it possible to detect an abnormality in a circuit of an electric signal on a station side.

  For example, in the communication method using subcarrier analog transmission, an optical fiber that can be used as a transmission line has a wide band and low loss, or a radio frequency signal (RF signal) is directly modulated and transmitted by the analog optical transmission method. For example, it is used as a communication method for a relay amplification device or the like provided in a mobile phone system or a CATV system.

  In an analog optical transmission system using such a system, as shown in FIG. 2, there are a master station 31 and a slave station 32, and a plurality of slave stations are placed in a dead zone of service such as a mobile phone (inside a building or in a tunnel). The base station 31 and the slave station 32 are connected by the upstream and downstream optical fibers 34 and 35, and the radio frequency signal (RF signal) from the base station 30 is optically transmitted by the master station. The slave station 32 converts the received optical signal into an RF signal and outputs this RF signal, thereby existing in the service area of the slave station 32. The RF signal from the base station 30 can be output to the mobile phone 33, and the slave station 32 converts the RF signal from the mobile phone 33 existing in the service area into an optical signal, and transmits this optical signal. Master station 3 with optical fiber 34 Transmitted to the master station 31, the optical signal received by that converts the RF signal to the base station 30, an analog optical transmission system enabling services such as a cellular phone to dead zones.

  Further, the master station and the slave station of such an analog optical transmission system are configured by an electric signal circuit (RF circuit) for processing an RF signal and an optical signal circuit (optical circuit) for processing an optical signal. Since the optical signal from the master station to the slave station (downlink from the base station to the mobile phone) is always output, the detection circuit that detects the carrier signal is installed in the slave station. By providing, the monitoring of the RF circuit can be confirmed, and by providing the detection circuit for monitoring the optical level at the slave station, the received light level and the optical transmission part can be confirmed, and abnormality of the RF circuit and the optical signal can be confirmed. Can be easily monitored. By detecting the light reception level of the optical signal from the slave station at the master station, it is possible to detect an abnormality in the optical fiber.

In such an analog optical transmission system, the optical signal transmitted from the slave station at the master station is received via the optical fiber, the received light level of the received optical signal is detected, and the detected received light level fluctuations are detected. There are analog optical transmission systems that detect optical fiber anomalies based on the above.
JP 2000-91993 A JP 2000-151511 A

  However, in the analog optical transmission system described above, the optical signal from the slave station to the master station (uplink from the mobile phone to the base station) is not always transmitted at a constant level depending on the distance from the mobile phone. Therefore, even if a carrier signal detection circuit is provided in the master station, it is difficult to determine whether or not the characteristics such as the gain of the apparatus are normal.

  Under such circumstances, conventionally, a method of monitoring only an optical circuit without performing monitoring of an RF circuit in the uplink has been performed. Therefore, it is desired to monitor the RF circuit and the optical circuit separately.

  The present invention has been made to solve such a conventional problem. When an analog optical signal is transmitted from a slave station to a master station via an upstream optical fiber, a circuit ( An object of the present invention is to provide an analog optical transmission system that can detect an abnormality in an RF circuit.

  An analog optical transmission system in which a master station and a slave station are connected by an optical fiber, and the slave station has an electric signal circuit for processing a carrier signal (RF signal), pilot signal generating means for generating a pilot signal, A combining unit configured to combine the electrical signal to be transmitted to the base station and the pilot signal; and a light emitting unit configured to transmit the combined signal as an optical signal to the parent station via an optical fiber. A light receiving means for receiving the optical signal via the optical fiber, a filter means for separating the pilot signal from the signal received by the light receiving means, a pilot signal detecting means for detecting the level of the pilot signal separated by the filter means, And a control unit that detects an abnormality in the circuit of the electric signal based on the level detected by the pilot signal detecting means.

  In the analog optical transmission system of the present invention, an optical circuit and an electric circuit are obtained by synthesizing a pilot signal with an RF signal at a slave station and determining a light reception level of the optical signal and a pilot signal level at the master station. And the entire uplink can be monitored.

  The RF signal in which the pilot signal is injected on the slave station side is converted into an optical signal and transmitted to the master station via an optical fiber. The master station detects the pilot signal injected into the RF signal, thereby detecting the RF signal of the slave station. Realized to monitor the circuit of electrical signal processing signal.

  An analog optical transmission system according to an embodiment of the present invention will be described with reference to FIG. 1. FIG. 1 shows an example of an analog optical transmission system according to this example. This analog optical transmission system is an upstream optical fiber. 3 and a master station 1 and a slave station 2 connected via a downstream optical fiber 4. An analog optical signal is bidirectionally communicated between the master station 1 and the slave station 2 via the optical fibers 3 and 4.

  The master station 1 includes a master station side RF signal input terminal 10 for inputting an RF signal from a base station (not shown), an RF amplifier 11 for amplifying the RF signal input from the base station, and an optical signal. A semiconductor laser (LD) 12 that emits light, an optical connector 13 that connects the upstream optical fiber 4, a photodiode (PD) 14 that receives an optical signal and converts it into an RF signal, and an output voltage of the optical signal received by the PD 14 A detection unit 15 that detects the level of the signal, an amplification unit 16 that amplifies the RF signal output from the PD 14, a distribution unit 17 that distributes the amplified RF signal, and a filter unit 19 that identifies the pilot signal and the carrier signal And a detection circuit 20 that detects the level of the output voltage of the pilot signal, and a control unit 21 that detects an abnormality based on the levels of the detection unit 15 and the detection circuit 20.

  The slave station also receives a light signal from the downstream optical fiber 3 and converts it into an RF signal, an amplifying unit 23 for amplifying the RF signal, and an RF signal output for outputting the RF signal. An RF signal input terminal 25 for inputting a carrier frequency, a pilot signal generator 26 for transmitting a pilot signal having a frequency close to the carrier pivot number, and a carrier frequency and pilot signal generator 26 from the RF signal input terminal 25. Are combined with a pilot unit 27, an RF amplifier 28 for amplifying the synthesized signal, and a semiconductor laser (LD) 29 for emitting an optical signal. The electrical signal circuit includes a synthesizer 27 and an RF amplification unit 28, and the optical signal circuit includes a semiconductor laser (LD) 29 and the like.

  Next, the operation of the analog optical transmission system of the present invention will be described. In the master station 1, the optical signal is received by the PD 14 by connecting the upstream optical fiber 4 that transmits the optical signal output from the slave station 2 and the optical connector 13. The detection unit 15 detects an output voltage (output voltage = light reception level × PD conversion efficiency × a voltage proportional to the light reception level) from the received light signal, and the control unit 21 detects this output voltage. Based on the output voltage, the normality / abnormality of the received light level is determined. For example, when the light reception level is lower than a predetermined threshold value, it is possible to detect an abnormality such as a failure of a circuit portion of an optical signal (for example, LD of a slave station), disconnection of an optical fiber, or disconnection of an optical fiber. .

  In the slave station 2, a carrier signal (RF signal) input to the RF signal input terminal 25 and a pilot signal having a frequency close to the frequency of the carrier signal are injected and combined, and the carrier is combined by the RF amplifier 28. The signal is amplified, converted into an optical signal by the LD 29, and transmitted to the master station through the upstream optical fiber 4.

  In the master station 1, the combined optical signal is received by the PD 14, amplified by the RF amplifying unit 16, and only the pilot signal among the signals combined by the filter unit 19 is passed, and the output voltage proportional to the pilot signal Is detected by the detection circuit 20, and the control unit 21 determines whether or not the gain of the entire system is normal based on the output voltage of the detection circuit 20.

Thus, by determining the light reception level of the optical signal and determining the level of the pilot signal, it is possible to determine whether the optical portion or the RF signal portion is separated, and further, the RF signal and the optical signal can be determined. It is possible to determine the entire uplink including it.

It is a figure which shows the structural example of the analog optical transmission system which concerns on one Example of this invention. It is a figure which shows the structural example of the communication system using an analog optical transmission system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Master station, 2 ... Slave station, 3 ... Upstream optical fiber, 4 ... Downstream optical fiber, 10, 25 ... RF signal input terminal, 11, 16, 23, 28 ... RF amplification part, 12, 29 ... Semiconductor laser ( LD), 13 ... Optical connector, 14, 22 ... Photodiode (PD), 15 ... Detection unit, 17 ... Distribution unit, 18, 24 ... RF signal output end, 19 ... Filter unit, 20 ... Detection circuit, 21 ... Control , 26 ... pilot signal generator, 27 ... synthesizer

Claims (1)

An analog optical transmission system in which a master station and a slave station are connected by an optical fiber,
The slave station processes an electric signal, an electric signal circuit, pilot signal generating means for generating a pilot signal, combining means for combining the electric signal to be transmitted to the base station and the pilot signal, and the combining Light emitting means for converting the signal into an optical signal and transmitting it to the master station via the optical fiber,
The master station receives a light signal from the slave station via the optical fiber, a filter means for separating a pilot signal from the signal received by the light receiving means, and a pilot separated by the filter means An analog optical transmission comprising: pilot signal level detection means for detecting a signal level; and a control unit for detecting an abnormality in the circuit of the electric signal based on the level detected by the pilot signal level detection means. system.

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