JP2007281817A - Communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a communication system which makes a level of a sub-signal smaller than before, and can detect deterioration of communication quality by multiple optical reflection at an early stage by a simple composition. <P>SOLUTION: A detection circuit detects the sub-signal input from a separating unit 23, and outputs the detected signal to a DC amplifier. A comparator creates demodulated data based on the DC signal input from the DC amplifier and reference voltage V1, an ASK (amplitude shift keying) demodulation unit 26 outputs the demodulated data to a discrimination unit 27. The discrimination unit 27 decodes the input demodulated data in a decoder, and discriminates whether the decoded data agree with predetermined original data or not. If the decoded data agree with the original data, the discrimination unit 27 discriminates that multiple optical reflection does not occur. Moreover, if the decoded data do not agree with the original data, the discrimination unit 27 discriminates that multiple optical reflection occurs since data error occurs under impact of noise by the multiple optical reflection. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a communication system capable of detecting deterioration in communication quality due to multiple light reflection of an optical signal transmitted and received through an optical fiber.

  In mobile radio communication systems represented by mobile phones, between the master station and slave stations as a countermeasure for dead areas such as indoors, underground malls, behind buildings such as buildings, and tunnels where radio waves from radio base stations do not reach. An optical transmission system that installs an optical fiber and transmits and receives an optical signal through the optical fiber is used. In addition, it is also used as a broadcast wave relay system between broadcast stations to distribute broadcast waves to areas where broadcast radio waves do not reach.

  Since such an optical transmission system can efficiently realize broadband transmission by using an optical fiber, analog signals such as radio signals and broadcast wave signals (UHF / VHF) are converted into optical signals as they are and transmitted. An analog optical transmission system is used.

  However, when constructing an optical line using optical fibers, the optical fibers are fused and connected, or optical fibers are connected using optical components such as connectors, so that a plurality of connection points on the optical line. Exists. Therefore, an optical signal transmitted through the optical fiber is reflected at each connection point, and multiple light reflection occurs in which the reflected optical signal is reflected again at the connection point. When multiple light reflection occurs, there is a problem that the reflected optical signal appears as noise in the transmission signal and the communication quality deteriorates.

Therefore, a sub-signal having a frequency different from that of the main signal is superimposed on the main signal, and the main signal on which the sub-signal is superimposed is converted to electrical / optical, sent to the optical fiber, and the harmonics of the sub-signal are monitored. An optical transmission system that detects light reflection has been proposed (see Patent Document 1).
JP 2005-229372 A

  However, the system of Patent Document 1 has a problem that a filter for extracting a harmonic component or a third-order intermodulation wave component of the sub-signal is required, and the circuit configuration is complicated. In addition, since the harmonic component or third-order intermodulation wave component of the sub-signal becomes smaller in proportion to the square or the third power of the input level of the sub-signal, the harmonic component or the third-order intermodulation wave component is accurately extracted. In order to achieve this, it is necessary to increase the input level of the sub signal. On the other hand, since there is an upper limit on the signal level that can be transmitted by the optical transmission system, there is a problem that when the input level of the sub signal is increased, the level of the main signal that can be transmitted to the optical fiber is limited. In particular, in mobile phone or broadcast wave optical transmission systems, when radio waves with degraded communication quality are output, there is a risk of system failure to other communication channels, leading to early degradation of communication quality due to multiple light reflections. There has been a desire for a communication system capable of detection.

  The present invention has been made in view of such circumstances, and a transmission apparatus includes a modulation unit that generates a sub-signal obtained by modulating a carrier wave with a data signal having a predetermined data rate, and has a main signal having information to be transmitted and received And the sub signal are combined into an optical signal, and the converted optical signal is transmitted to the receiving device through an optical fiber. The receiving device converts the received optical signal into an electric signal and is converted. Multiplexing of optical signals transmitted / received through an optical fiber based on the data rate of the data signal obtained by separating the electrical signal into a main signal and a sub signal and demodulating the separated sub signal and the predetermined data rate By providing means for determining light reflection, it is not necessary to use the harmonic component of the sub-signal, and the level of the sub-signal can be made lower than before, and communication by multiple light reflection with a simple configuration. And to provide a communication system capable of detecting deterioration in quality at an early stage.

  Another object of the present invention is to provide a communication system in which the modulation means can determine the multiple light reflection using a signal sufficiently smaller than the main signal by modulating with the amplitude modulation method. is there.

  Another object of the present invention is that the modulation means modulates a carrier wave with a data signal having predetermined data and demodulates a sub-signal, and the data signal obtained by demodulating the sub-signal is multiplexed with a multiple light reflection. It is an object of the present invention to provide a communication system capable of accurately determining deterioration of communication quality due to multiple light reflections by providing a means for determining that there is an abnormality.

  Another object of the present invention is a means for detecting the signal level of the separated sub-signal and determining the presence / absence of abnormality due to multiple light reflection based on the comparison result obtained by comparing the detected signal level with a predetermined signal threshold value. By providing the communication system, it is possible to provide a communication system that can categorize deterioration of communication quality due to factors other than multiple light reflection and determine the deterioration of communication quality due to multiple light reflection more accurately.

  A communication system according to a first aspect of the invention converts an electrical signal into an optical signal, transmits the converted optical signal through an optical fiber, receives the optical signal transmitted by the transmission device, and converts the received optical signal into electrical In a communication system including a receiving device that converts a signal into a signal, the transmitting device includes a modulation unit that generates a sub signal obtained by modulating a carrier wave with a data signal having a predetermined data rate, a main signal having information to be transmitted and received, and the sub signal. Combining means for combining the signal and conversion means for converting the electric signal combined by the combination means into an optical signal, the receiving device converting the received optical signal into an electric signal; Separating means for separating the electric signal converted by the means into a main signal and a sub signal, a demodulating means for demodulating the sub signal separated by the separating means, and a data signal obtained by demodulating by the demodulating means Data rate and based on the predetermined data rate, characterized in that it comprises means for determining multiple light reflections of the optical signal transmitted and received through an optical fiber.

  A communication system according to a second invention is characterized in that, in the first invention, the modulation means is configured to modulate by an amplitude modulation method.

  A communication system according to a third invention is the communication system according to the first or second invention, wherein the modulating means is configured to modulate a carrier wave with a data signal having predetermined data, and is obtained by demodulating with the demodulating means. When the data of the received data signal is different from the predetermined data, there is provided means for determining an abnormality due to multiple light reflection.

  A communication system according to a fourth aspect of the present invention is the communication system according to any one of the first to third aspects, wherein the detection means for detecting the signal level of the sub signal separated by the separation means, and the signal level detected by the detection means. Comparing means for comparing with a predetermined signal threshold, and means for determining the presence or absence of abnormality due to multiple light reflection based on the comparison result of the comparing means.

  In the first invention, the transmission device converts an electric signal obtained by synthesizing a main signal (for example, 2 GHz band) having information to be transmitted and received and a sub signal (315 MHz band) into an optical signal, and converts the optical signal through an optical fiber. The transmitted optical signal is transmitted to the receiving device. When multiple light reflection occurs in an optical transmission line such as an optical fiber, Gaussian noise is generated in the transmitted optical signal. In the case of a modulated sub-signal, noise due to multiple light reflection occurs in the sideband of the sub-signal. The optical signal received by the receiving device is converted into an electric signal, and the converted electric signal is separated into a main signal and a sub signal. When multiple light reflections occur in the optical transmission line, noise is included in the sidebands of the separated sub-signals. An error occurs in the data signal obtained by demodulating the separated sub-signal due to the influence of noise generated in the sideband (for example, when the high level becomes low level, the low level becomes high level) Case). For this reason, the data rate of a data signal becomes high compared with the time of transmission. Based on the data rate of the data signal obtained by demodulation and the predetermined data rate at the time of transmission, it is possible to determine the multiple light reflection of the optical signal transmitted and received through the optical fiber. As a result, it is not necessary to use the harmonic component of the sub-signal, and the level of the sub-signal can be made smaller than before, and communication quality deterioration due to multiple light reflections can be quickly achieved with a simple configuration without forming a complicated filter. Can be detected.

  In the second invention, the carrier wave is amplitude-modulated with the data signal to generate the sub signal. Compared to the case where the harmonic component of the sub-signal is extracted, the signal level of the sub-signal is sufficient so that the amplitude can be demodulated. Therefore, the signal level can be used sufficiently smaller than the main signal. The level of the main signal that can be transmitted to the fiber is not limited, and the main signal can occupy most of the signal level input to the transmitter.

  In the third invention, the transmission device modulates the carrier wave with a data signal having predetermined data that is predetermined and decipherable on the reception device side, and generates a sub-signal. If the data signal obtained by demodulating the received sub-signal is different from the predetermined data, the receiving apparatus determines that communication quality is deteriorated due to multiple light reflection. On the other hand, if the data signal obtained by demodulating the received sub-signal is the same as the predetermined data, the receiving apparatus determines that communication quality deterioration due to multiple light reflection has not occurred. Since the presence / absence of abnormality due to multiple light reflection is determined based on the mismatch between the data at the time of transmission and the data at the time of reception, it is possible to accurately determine deterioration in communication quality due to multiple light reflection.

  In the fourth invention, the receiving device detects the signal level of the separated sub-signal. In addition to the multiple light reflections in the optical transmission path, the electrical / optical conversion unit that converts the electrical signal of the transmission device into the optical signal or the optical signal of the reception device can cause errors in the original data obtained by demodulation. A decrease in the signal level of the sub-signal is assumed due to a failure of the optical / electrical conversion unit that converts it into an electrical signal or an increase in loss of the optical line. Based on the comparison result obtained by comparing the signal level of the sub-signal detected by the receiving apparatus with a predetermined signal threshold value, the presence / absence of abnormality due to multiple light reflection is determined. For example, when the signal level is smaller than the signal threshold, it is determined that the degradation of communication quality is caused by factors other than multiple light reflection. When the signal level is larger than the signal threshold, other than multiple light reflection is determined. It is determined that the communication quality is not deteriorated due to multiple light reflection. As a result, it is possible to stratify communication quality deterioration due to factors other than multiple light reflection, and to determine communication quality deterioration due to multiple light reflection more accurately.

  In the present invention, the transmission device includes modulation means for generating a sub signal obtained by modulating a carrier wave with a data signal having a predetermined data rate, and combines the main signal having information to be transmitted and received with the sub signal. The signal is converted into an optical signal, the converted optical signal is transmitted to a receiving device through an optical fiber, the receiving device converts the received optical signal into an electric signal, and the converted electric signal is converted into a main signal, a sub signal, and And a means for determining multiple optical reflections of an optical signal transmitted and received through an optical fiber based on the data rate of the data signal obtained by demodulating the separated sub-signal and the predetermined data rate. Therefore, it is not necessary to use the harmonic component of the sub-signal, the level of the sub-signal can be made smaller than before, and a simple configuration without using a complicated filter can be used for the transmission by multiple light reflection. It is possible to detect the deterioration of quality at an early stage.

Embodiment 1
Hereinafter, the present invention will be described with reference to the drawings illustrating embodiments thereof. FIG. 1 is a block diagram showing a communication system 100 according to the present invention. The communication system 100 includes a transmission device 1, a reception device 2, an optical fiber 3, and the like. The transmission device 1 includes a combining unit 11, an E / O (electric / optical converter) 12, a carrier wave generating unit 13, a data generating unit 14, an ASK (Amplitude Shift Keying) modulating unit (amplitude modulating unit) 15, and the like. . The receiving device 2 includes an O / E (optical / electrical converter) 21, amplifiers 22 and 24, a separation unit 23, an ASK demodulation unit 26, a determination unit 27, and the like. In the case of an optical repeater system in which a master station (or broadcast station) and a slave station (or broadcast station) are connected by an optical fiber to relay a radio signal, a broadcast wave signal, etc., the master station and the slave station (or broadcast station) Each of them is configured to include a transmission device 1 and a reception device 2.

  The communication system 100 includes a main signal having information to be transmitted / received through the optical fiber 3 (for example, a radio signal of a cellular phone having a 2 GHz band) and a sub signal having a frequency band different from the frequency band of the main signal (for example, a 315 MHz band). Is an optical transmission system for transmitting a signal as an analog optical signal.

  The carrier generation unit 13 includes an oscillator, for example, generates a 315 MHz sinusoidal carrier wave (unmodulated signal), and outputs the generated carrier wave to the ASK modulation unit 15. The data generation unit 14 includes an encoding circuit and the like, for example, generates a data signal composed of a bit string (for example, “1”, “0”, etc.) having a data rate of 1 kbps, and the generated data signal is ASK modulated. To the unit 15. The data signal may be data in any format and format, and is encoded according to a predetermined rule by an encoder (not shown).

  The ASK modulation unit 15 includes a wideband operational amplifier, a mixer (modulator), a diode, and the like, modulates a carrier wave with a data signal, and outputs a sub signal (modulation signal) obtained by the modulation to the synthesis unit 11. More specifically, for example, the ASK modulation unit 15 outputs a carrier wave while “1” data is input, and stops outputting the carrier wave while “0” data is input. By doing so, a sub-signal is generated.

  The synthesizer 11 includes a broadband synthesizer, synthesizes the main signal and the sub signal, and outputs the synthesized electric signal to the E / O 12. A configuration using a duplexer instead of the combiner may be used.

  The E / O 12 includes a semiconductor laser that outputs laser light of a predetermined wavelength band, and converts an electrical signal (combined main signal and sub signal) input from the combining unit 11 into an optical signal of a predetermined wavelength band. The converted optical signal is transmitted to the receiver 2 through the optical fiber 3.

  The O / E 21 includes a photodiode, converts the optical signal transmitted from the transmission device 1 through the optical fiber 3 into an electrical signal, and outputs the converted electrical signal to the separation unit 23 via the amplifier 22.

  The separation unit 23 includes a duplexer that combines a filter that passes the main signal in the 2 GHz band, a filter that passes the sub signal in the 315 MHz band, and the like, and the electrical signal input from the O / E 21 is used as the main signal. Separated into sub-signals. The separation unit 23 outputs the separated main signal to the amplifier 24 and outputs the separated sub signal to the ASK demodulation unit 26. Note that the separation unit 23 may be configured to include a required filter, a distributor, and the like instead of the duplexer.

  FIG. 2 is a schematic diagram illustrating an example of the frequency spectrum of the main signal and the sub signal. FIG. 2A shows a main signal and a sub signal (electric signal) that are combined by the combining unit 11 and input to the E / O 12. In the figure, fm is the frequency of the main signal, for example, the 2 GHz band, and fs is the frequency of the sub signal, for example, the 315 MHz band. The sub signal is a modulation signal, and there are sidebands on both sides of fs.

  2B shows the main signal separated by the separation unit 23 and inputted to the amplifier 24, and FIG. 2C shows the sub-signal separated by the separation unit 23 and inputted to the ASK demodulation unit 26. As shown in the figure, by widening the frequency interval between the main signal and the sub signal (for example, 2 GHz and 315 MHz), the main signal and the sub signal can be easily separated and the main signal and the sub signal are separated. Therefore, the filter characteristics can be simplified, and the cost and size of the filter can be reduced.

  The amplifier 24 amplifies the main signal input from the separation unit 23, and the amplified main signal is transmitted as a radio signal via the antenna 25.

  FIG. 3 is a block diagram showing the configuration of the ASK demodulator 26. The ASK demodulator 26 includes a detection circuit 261, a DC amplifier 262, comparators 263 and 266, buffers 264 and 267, a peak hold 265, a synchronization circuit 268, and the like.

  The detection circuit 261 detects the sub-signal input from the separation unit 23 by half-wave or both-wave rectification with a diode or a rectifier, and outputs a detection signal (DC signal) to the DC amplifier 262.

  The DC amplifier 262 amplifies the DC signal input from the detection circuit 261 and outputs the amplified DC signal to the comparator 263 and the peak hold 265.

  The comparator 263 compares the DC signal input from the DC amplifier 262 with the reference voltage V1, for example, outputs a high level signal when the voltage level of the DC signal is higher than the reference voltage V1, and When the voltage level is lower than the reference voltage V1, a data signal is generated from the DC signal based on the reference voltage V1 by outputting a low level signal. The comparator 263 outputs the generated data signal to the buffer 264.

  The buffer 264 performs level conversion (voltage level conversion) of the data signal input from the comparator 263, and outputs the level-converted data signal to the synchronization circuit 268.

  The synchronization circuit 268 extracts sampling timing from the data signal input from the buffer 264 according to the data rate (for example, 1 kbps), and outputs the demodulated data obtained by sampling the data signal at 1 msec intervals to the determination unit 27.

  The peak hold 265 holds the maximum value of the DC signal input from the DC amplifier 262 (a level corresponding to the high level of the demodulated data) for a predetermined time, and outputs the held signal to the comparator 266.

  The comparator 266 compares the hold signal input from the peak hold 265 with the reference voltage V2. For example, when the voltage level of the hold signal is higher than the reference voltage V2, the high level signal is determined via the buffer 267. When the voltage level of the hold signal is smaller than the reference voltage V 2, the low level signal is output to the determination unit 27 via the buffer 267.

  As a result, the signal level of the sub-signal is sufficient to enable ASK demodulation, so that a sufficiently low signal level (for example, about −20 dB) can be used as compared with the main signal, and the signal level can be sent to the optical fiber. The level of the main signal is not limited, and the main signal can occupy most of the electrical signals that can be used in the transmission apparatus.

  FIG. 4 is a schematic diagram showing an example of the voltage waveform of each part of the ASK demodulator 26. FIG. 4A shows a detection signal detected by the detection circuit 261. FIG. 4B shows a binarized waveform obtained by binarizing the detection signal based on the reference voltage V1. As shown in the drawing, the high level of the binarized waveform is represented by data “1”, and the low level of the binarized waveform is represented by data “0”. Furthermore, the data signal is sampled in accordance with the data rate of the data signal generated by the transmitter 1 in the synchronization circuit 268 as shown in the figure, and demodulated data is generated. FIG. 4C shows the hold signal held by the peak hold 265. FIG. 4D shows the signal level of the sub signal obtained by binarizing the detection signal based on the reference voltage V2.

  The determination unit 27 includes a CPU, a memory, a decoder, and the like, and determines the presence or absence of multiple light reflections in the optical fiber 3 based on the demodulated data input from the ASK demodulation unit 26 and the signal level of the sub signal. Detects degradation of communication quality. When the determination unit 27 detects the deterioration of communication quality due to the multiple light reflection generated in the optical fiber 3, it notifies this and outputs a stop signal to the amplifier 24 so that the main signal is transmitted from the antenna 25. Stop.

  More specifically, the determination unit 27 uses a decoder to decode the demodulated data input from the ASK demodulation unit 26, and determines whether or not the decoded data matches predetermined original data. The determination unit 27 determines that multiple light reflection has not occurred when the decoded data matches the original data. Further, when the decoded data does not match the original data, the determination unit 27 determines that multiple light reflection has occurred, assuming that a data error has occurred due to the influence of noise due to multiple light reflection.

  Further, when the determination unit 27 determines that multiple light reflection has occurred based on the demodulated data input from the ASK demodulation unit 26, the signal level of the sub-signal input from the ASK demodulation unit 26 is high. When it is a signal, it is determined that multiple light reflection has occurred, and it is finally determined that multiple light reflection has occurred.

  In addition, when the determination unit 27 determines that multiple light reflection has occurred based on the demodulated data input from the ASK demodulation unit 26, the signal level of the sub-signal input from the ASK demodulation unit 26 is low. If it is a signal, it is finally determined that an abnormality due to factors other than the multiple light reflection has occurred.

  Possible causes of errors in the original data obtained by demodulation include failure of the E / O 12 of the transmission device 1 or O / E 21 of the reception device 2 or loss of the optical line in addition to the multiple optical reflection in the optical transmission line. A decrease in the signal level of the sub-signal due to an increase or the like is assumed. Based on the comparison result obtained by comparing the signal level (hold signal) of the sub-signal separated by the receiver 2 with the reference voltage V2, the presence / absence of abnormality due to multiple light reflection is determined. For example, when the signal level is lower than the reference voltage V2, it is determined that the communication quality is deteriorated due to a factor other than the multiple light reflection. When the signal level is higher than the reference voltage V2, the communication quality is deteriorated. It is determined that the deterioration is not due to multiple light reflection but due to multiple light reflection. As a result, it is possible to stratify communication quality deterioration due to factors other than multiple light reflection, and to determine communication quality deterioration due to multiple light reflection more accurately.

  As a result, the occurrence of multiple light reflections can be detected at an early stage while transmitting / receiving the main signal, and when multiple light reflections occur, the influence on other communication channels can be prevented and It is possible to respond quickly.

  Next, the operation of the communication system 100 of the present invention will be described. The transmission device 1 converts an electrical signal obtained by combining the main signal and the sub signal into an optical signal, and transmits the converted optical signal to the reception device 2 through the optical fiber 3. When multiple light reflections occur in an optical transmission line such as the optical fiber 3, Gaussian noise is generated in the transmitted optical signal. In the case of a sub signal that is a modulation signal, noise due to multiple light reflection occurs in the sideband of the sub signal.

  FIG. 5 is a schematic diagram showing an example of the frequency spectrum of the sub-signal when multiple light reflection occurs. As shown in the figure, when multiple light reflection occurs, noise is generated around the carrier.

  The receiving device 2 converts the received optical signal into an electric signal, and separates the converted electric signal into a main signal and a sub signal. An error occurs in the data signal obtained by demodulating the separated sub-signal due to the influence of noise generated in the sideband.

  6 and 7 are schematic diagrams showing examples of detection signals of the ASK demodulator 26 depending on whether or not multiple light reflection occurs. FIG. 6A shows an example of a data signal waveform and data generated and transmitted by the transmission apparatus 1. In the example of the figure, the data (bit string) is “1” “0” “1” “0” “0” “1” “0”.

  FIG. 6B shows an example of a detection signal when no multiple light reflection occurs, and FIG. 6C shows an example of an output signal (binarized waveform) of the buffer 264 when no multiple light reflection occurs. It is. When multiple light reflections are not generated, noise is not superimposed at the time when sampling is performed by the synchronization circuit 268. Therefore, the demodulated data is “1” “0” “1” “0” “0” “1” “0”. ", Which is the same as the transmitted data.

  FIG. 7A shows an example of a detection signal when multiple light reflection occurs. When multiple light reflection occurs, noise is superimposed on the detection signal, and the waveform of the portion that should be at a low level (reference voltage V1 or less) becomes larger than the reference voltage V1. FIG. 7B is an example of the output signal (binarized waveform) of the buffer 264 when multiple light reflection occurs. At the time of sampling by the synchronization circuit 268, an error occurs in the data at a portion where the voltage level of the detection signal exceeds the reference voltage V1 due to noise. For example, as shown in FIG. 7B, the demodulated data is “1” “1” “1” “0” “0” “1” “1”, which is different from the transmitted data. FIG. 7C shows the signal level of the sub signal.

  The determination unit 27 determines that multiple light reflection has occurred based on the result that the demodulated data input from the ASK demodulation unit 26 does not match the transmission data, and the signal level of the sub signal is a high level signal. Finally, it is determined that multiple light reflections in the optical fiber 3 have occurred, the deterioration of communication quality is detected, this is notified, a stop signal is output to the amplifier 24, and the main signal is transmitted from the antenna 25. To stop. In the above-described embodiment, since the occurrence of multiple light reflection is determined based on the demodulated data obtained by sampling the output signal of the buffer 264 by the synchronization circuit 268, the determination can be made only at the sampling point, which is realized by simple processing. can do.

  FIG. 8 is a schematic diagram illustrating an example of a frequency spectrum of a transmission signal. The frequency of the transmission signal (unmodulated wave) is 315 MHz, and the length of the optical fiber is about 10 km. FIG. 8A shows a frequency spectrum when no multiple light reflection occurs, and FIG. 8B shows a frequency spectrum when multiple light reflection occurs. For example, when the difference between the level of noise and the level of the transmission signal (sub signal) as shown in the figure is less than about 20 dB, there is a high possibility that communication quality will deteriorate due to the occurrence of multiple light reflections.

Embodiment 2
The first embodiment uses a data signal having data (for example, determination data) composed of a predetermined bit string, and determines the occurrence of multiple light reflection based on whether the demodulated data matches the original data. However, the present invention is not limited to this, and in order to determine the occurrence of multiple light reflections, it is possible to use only the data rate of the data signal instead of the determination data.

  FIG. 9 is a block diagram showing a configuration of the ASK demodulator 26 of the second embodiment. The ASK demodulator 26 includes a detection circuit 261, a DC amplifier 262, comparators 263 and 266, buffers 264 and 267, a peak hold 265, and the like. The difference from the first embodiment is that the synchronization circuit 268 is not provided.

  The detection circuit 261 detects the sub-signal input from the separation unit 23 by half-wave or both-wave rectification with a diode or a rectifier, and outputs a detection signal (DC signal) to the DC amplifier 262.

  Since the DC amplifier 262, the comparator 263, the buffer 264, the peak hold 265, the comparator 266, and the buffer 267 are the same as those in the first embodiment, the same reference numerals are given and the description thereof is omitted.

  FIG. 10 is a schematic diagram illustrating an example of a detection signal detected by the detection circuit 261. FIG. 10A shows a detection signal obtained by detecting the sub signal by the detection circuit 261. FIG. 10B shows a binarized waveform obtained by binarizing the detection signal based on the reference voltage V1. As shown in the drawing, the high level of the binarized waveform is represented by data “1”, and the low level of the binarized waveform is represented by data “0”. FIG. 10C shows a hold signal held by the peak hold 265. FIG. 10D shows the signal level of the sub signal obtained by binarizing the detection signal based on the reference voltage V2.

  The determination unit 27 determines the occurrence of multiple light reflections based on the data rate of the data signal obtained by demodulation and a predetermined data rate at the time of transmission. More specifically, when the data rate at the time of transmission is 1 kbps, the duration time of the demodulated data in the on state (high level) and the off state (low level) is always 1 msec ± predetermined value (for example, 0.1 msec) If it is within the range, it is determined that multiple light reflection has not occurred. On the other hand, if the on-state (high level) and off-state (low level) duration of the demodulated data obtained by demodulating the sub signal is outside the range of 1 msec ± predetermined value (for example, 0.1 msec), It is determined that multiple light reflection has occurred.

  FIG. 11 is a schematic diagram showing an example of a detection signal of the ASK demodulator 26 when multiple light reflection occurs. FIG. 11A shows an example of a data signal waveform and data generated and transmitted by the transmission apparatus 1. For example, the data rate of the data signal is 1 kbps, the data “1” and “0” are alternately repeated, and the time during which the data is “1” and “0” is 1 msec, respectively. In the illustrated example, the data (bit string) is “1” “0” “1” “0”.

  FIG. 11B shows an example of a detection signal when multiple light reflection occurs. When multiple light reflection occurs, noise is superimposed on the detection signal, and the waveform of the portion that should be at a low level (reference voltage V1 or less) becomes larger than the reference voltage V1. As shown in FIG. 11C, the demodulated data becomes high level (“1”) when the voltage level of the detection signal exceeds the reference voltage V1 due to noise, and the voltage level of the detection signal is equal to or lower than the reference voltage V1. It becomes a low level (“0”) in the part. That is, due to the occurrence of multiple light reflections, the time “0” of the demodulated data does not continue for about 1 msec.

  The determination unit 27 determines whether the high level (“1”) time and the low level (“0”) duration of the demodulated data are within a range of, for example, 1 msec ± 0.1 msec. As shown in FIG. 10 (c), the determination unit 27 first determines that the time “0” should continue for about 1 msec after the time “1” continues for about 1 msec. By detecting that it does not continue for about 1 msec, it is determined that multiple light reflection has occurred.

  Compared to the first embodiment, by detecting the durations of “1” and “0” of the demodulated data, when noise is superimposed on the detection signal due to the occurrence of multiple light reflection, any part of the detection signal is detected. Noise can be detected even when superimposed on the light, and the occurrence of multiple light reflection can be determined with high accuracy.

  In the second embodiment described above, multiple light reflections are generated based on whether or not the durations of demodulated data “1” and “0” are within a range of 1 msec ± predetermined value (for example, 0.1 msec). However, the present invention is not limited to this. For example, the times “1” and “0” of the demodulated data are accumulated and added to obtain “1” and “ The configuration may be such that the presence or absence of occurrence of multiple light reflections is determined based on whether or not the duration of “0” is in the range of n times 1 msec ± predetermined value (for example, 0.1 msec). However, n is a natural number.

  As described above, in the present invention, it is not necessary to use the harmonic component of the sub-signal, the level of the sub-signal can be made smaller than before, and multiplexing can be performed with a simple configuration without forming a complex filter. It is possible to detect early deterioration of communication quality due to light reflection. Further, since the signal level of the sub signal is sufficient so that the amplitude can be demodulated, the signal level can be used sufficiently smaller than the main signal, and the level of the main signal that can be transmitted to the optical fiber is limited. The main signal can occupy most of the signal level input to the transmitter. Further, since the presence / absence of abnormality due to multiple light reflection is determined based on the mismatch between the data at the time of transmission and the data at the time of reception, it is possible to accurately determine deterioration in communication quality due to multiple light reflection. Further, it is possible to stratify communication quality deterioration due to factors other than multiple light reflection, and to determine communication quality deterioration due to multiple light reflection more accurately.

  In the above-described embodiment, the frequency of the main signal is 2 GHz and the frequency of the sub signal is 315 MHz. However, the frequency band is not limited to this, and the required main signal and the frequency differ from the main signal. Side signals can be used.

  In the above-described embodiment, the case where the main signal and the sub signal are transmitted from the transmission device 1 to the reception device 2 has been described. However, the present invention is an optical transmission system that transmits an optical signal in both directions of upstream and downstream. It can also be applied to. For example, when the frequency of the main signal is different between the uplink direction and the downlink direction, it is possible to use an uplink sub-signal and a downlink sub-signal having different frequencies from each other, as well as different frequencies of the main signal.

  In the above-described embodiment, when it is determined that there is an abnormality due to multiple light reflection, the reception device 2 is configured to stop the transmission of the main signal via the antenna 25. However, the present invention is not limited to this. The determination result of the multiple light reflection may be transmitted to the device 1, and the transmission device 1 may stop the transmission of the main signal.

  In the above-described embodiment, the configuration using the amplitude modulation method is used. However, the modulation method is not limited to this, and other modulation methods such as a frequency modulation method and a phase modulation method are used. There may be. When the amplitude modulation method is adopted, it is easy to be influenced by noise, and therefore it is possible to determine the presence / absence of the occurrence of multiple light reflection with higher accuracy than other modulation methods.

It is a block diagram which shows the communication system which concerns on this invention. It is a schematic diagram which shows the example of the frequency spectrum of a main signal and a subsignal. It is a block diagram which shows the structure of an ASK demodulation part. It is a schematic diagram which shows the example of the voltage waveform of each part of an ASK demodulation part. It is a schematic diagram which shows the example of the frequency spectrum of the subsignal when multiple light reflection generate | occur | produces. It is a schematic diagram which shows the example of the detection signal of the ASK demodulation part according to the presence or absence of multiple light reflection. It is a schematic diagram which shows the example of the detection signal of the ASK demodulation part according to the presence or absence of multiple light reflection. It is a schematic diagram which shows the example of the frequency spectrum of a transmission signal. 6 is a block diagram showing a configuration of an ASK demodulator according to Embodiment 2. FIG. It is a schematic diagram which shows the example of the detection signal detected by the detection circuit. It is a schematic diagram which shows the example of the detection signal of an ASK demodulation part when multiple light reflection generate | occur | produces.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Transmission apparatus 2 Reception apparatus 3 Optical fiber 11 Synthesis | combination part 12 E / O
13 Carrier generation unit 14 Data generation unit 15 ASK modulation unit 21 O / E
22, 24 Amplifier 23 Separation unit 26 ASK demodulation unit 27 Determination unit 261 Detection circuit 262 DC amplifier 263, 266 Comparator 264, 267 Buffer 265 Peak hold 268 Synchronization circuit

Claims (4)

A transmission device that converts an electrical signal into an optical signal, transmits the converted optical signal through an optical fiber, and a reception device that receives the optical signal transmitted by the transmission device and converts the received optical signal into an electrical signal. In a communication system,
The transmitter is
Modulation means for generating a sub-signal obtained by modulating a carrier wave with a data signal having a predetermined data rate;
Combining means for combining the main signal having information to be transmitted and received and the sub-signal;
Conversion means for converting the electrical signal synthesized by the synthesis means into an optical signal,
The receiving device is:
Conversion means for converting the received optical signal into an electrical signal;
Separating means for separating the electric signal converted by the converting means into a main signal and a sub-signal;
Demodulating means for demodulating the sub-signal separated by the separating means;
Means for determining multiple light reflections of an optical signal transmitted / received through an optical fiber based on a data rate of a data signal obtained by demodulation by the demodulating means and the predetermined data rate. system. The modulating means includes
The communication system according to claim 1, wherein the communication system is configured to perform modulation using an amplitude modulation method. The modulating means includes
It is configured to modulate a carrier wave with a data signal having predetermined data,
3. The communication according to claim 1, further comprising means for determining that an abnormality is caused by multiple light reflection when data of a data signal obtained by demodulating by the demodulating means is different from the predetermined data. system. Detecting means for detecting a signal level of the sub signal separated by the separating means;
Comparing means for comparing the signal level detected by the detecting means with a predetermined signal threshold;
The communication system according to any one of claims 1 to 3, further comprising: a unit that determines presence / absence of abnormality due to multiple light reflection based on a comparison result of the comparison unit.

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