JP3813860B2 - Received signal processing apparatus and method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a transmission line monitoring apparatus in a wavelength-division-multiplexed optical repeater transmission system, and in particular, long-distance transmission in which the received signal transmitted to the far end of the transmission line is deteriorated, for example, long-distance transmission system length exceeding 8000 km In transmission, the present invention relates to a received signal processing apparatus and method capable of compensating for an expanded out-of-band signal component of a spectrum waveform even when the bandwidth of the spectrum waveform is widened and the received signal level is lowered.
[0002]
[Prior art]
When performing optical fiber cable loss measurement using OTDR, which is used as a transmission line monitoring method in a wavelength division multiplexing optical repeater transmission system, the signal receiving unit A / D converts the received signal after detecting the monitoring optical signal At this time, the signal transmitted through the transmission line having a system length of about 3000 km does not cause the waveform deterioration of the transmission signal at the near end of the transmission line, and the spectrum is almost the same as the reception bandwidth of the receiving unit of the transmission line monitoring device. The width signal returns from the near end of the transmission line to the receiving unit of the transmission line monitoring device.
[0003]
Here, conventionally, in a received signal processing apparatus for transmission path monitoring, the reception bandwidth of the receiving unit of the transmission path monitoring apparatus is determined according to the bandwidth of the spectrum of the monitoring signal transmitted by the transmission path monitoring apparatus. ing.
[0004]
As described above, in a transmission line having a system length of about 3000 km, a signal having a spectrum width substantially the same as the reception bandwidth of the receiving part of the transmission line monitoring apparatus is received from the near end of the transmission line to the receiving part of the transmission line monitoring apparatus. Therefore, there is no reduction in the level of the received signal for signal processing at the receiving unit of the transmission line monitoring device.
[0005]
Hereinafter, a conventional received signal processing apparatus will be described with reference to FIG. FIG. 3 is a block diagram showing a configuration of a received signal processing apparatus in a conventional transmission line monitoring system. The received signal processing device 31 performs the following processing on the received signal. The band-pass filter 32 having a reception bandwidth of F (MHz) sends a monitoring optical signal from the OTDR of the transmission line monitoring device that measures the cable loss of the optical fiber of the transmission line, and returns after transmitting the transmission line. A signal obtained by detecting the monitoring light signal and converting it to an electrical signal is received, and the received signal is filtered. The filtered received signal is amplified by the amplifier 3. The amplified signal is converted from an analog signal to a digital signal by the A / D converter 4. The converted digital signal is stored in the memory 35 at the sampling point number A. The CPU 6 performs graphing processing.
[0006]
[Problems to be solved by the invention]
In recent years, the system length of transmission lines has been required to be transmitted over a longer distance. If the reception bandwidth of the receiver is determined from the bandwidth of the spectrum of the monitoring signal transmitted as in the past, for example, long-distance transmission (transmission path system length exceeds 8000 km) is performed across the Pacific Ocean. In such a case, the waveform degradation of the transmission signal occurs remarkably at the far end of the transmission path, and the bandwidth of the spectrum waveform of the transmission signal is smaller than the signal transmitted to the near end of the transmission path having a system length of about 3000 km. It spreads.
[0007]
Therefore, a signal having a spectrum width that has been expanded beyond the reception bandwidth of the reception unit of the transmission line monitoring device comes back from the far end of the transmission line to the reception unit of the transmission line monitoring device, and has spread. Since the received signal is subjected to signal processing by the receiving unit of the transmission line monitoring device, there has been a problem that the signal level is lowered.
[0008]
The object of the present invention is that the influence of signal degradation, which has not been a problem with the system length of transmission lines up to about 3000 km, appears in long-distance transmission of about 8000 km, and the signal component whose bandwidth has been expanded accordingly. However, an object of the present invention is to provide a received signal processing apparatus and method capable of compensating an out-of-band signal component of a signal.
[0009]
[Means for Solving the Problems]
According to the present invention, a signal transmitted from a transmission line monitoring device for measuring a cable loss of an optical fiber in a transmission line, detected from the monitoring light signal returned through the transmission line, and received as a signal converted into an electrical signal is received. In the received signal processing device,
In order to compensate the out-of-band signal component of the spectrum waveform of the monitoring signal transmitted to the far-end transmission path, it is m times larger than the first reception bandwidth (F (MHz)) of the received signal from the near-end of the transmission path. A bandpass filter having a second reception bandwidth (m × F (MHz)) and filtering the received signal;
An amplifier that amplifies the filtered signal;
An A / D converter for converting the amplified signal from an analog signal to a digital signal;
A memory for storing the converted digital signal at a sampling point number (n × A) that is n times the sampling point number A corresponding to the first reception bandwidth;
A received signal processing apparatus is provided, comprising a central processing unit for performing a graphing process after performing a process of taking a moving average from a digital signal having the number of sampling points stored in the memory.
[0010]
Further, according to the present invention, the signal transmitted from the transmission line monitoring device that measures the cable loss of the optical fiber in the transmission line, and detected by the monitoring light signal returned through the transmission line and converted into an electrical signal In the received signal processing method for receiving
In order to compensate the out-of-band signal component of the spectrum waveform of the monitoring signal transmitted to the far end, the second larger m times than the first reception bandwidth (F (MHz)) of the received signal from the near end of the transmission path Filter the received signal with a band-pass filter with a receiving bandwidth (m x F (MHz)),
Amplifies this filtered signal,
This amplified signal is converted from an analog signal to a digital signal,
The converted digital signal is accumulated at a sampling point number (n × A) that is n times the sampling point number A corresponding to the first reception bandwidth,
A received signal processing method is characterized in that a graphing process is performed after a process of taking a moving average from the stored digital signal of the number of sampling points.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described. FIG. 1 is a block diagram showing the configuration of a received signal processing apparatus in a transmission line monitoring system according to the present invention. The reception signal processing device 1 sends out a monitoring optical signal from the OTDR of the transmission line monitoring device that measures the cable loss of the optical fiber in the transmission line, detects the monitoring optical signal that has returned through the transmission line, and detects the electrical signal. Receive the converted signal. The reception signal processing device 1 has a reception bandwidth (m × F (MHz)), a band-pass filter 2 that filters the reception signal, an amplifier 3 that amplifies the filtered signal, and an amplified signal. An A / D converter 4 for converting an analog signal into a digital signal, a memory 5 for storing the converted digital signal in the number of sampling points (n × A), and a number of sampling points (n × A) stored in the memory 5 A CPU 6 that performs a graphing process after performing a process of taking a moving average from a digital signal is provided.
[0016]
FIG. 2 is a diagram showing a spectrum waveform of a received signal in the present embodiment. A spectrum waveform 11 shows a spectrum waveform of a received signal from the near end of the transmission path. The reception bandwidth 12 represents the reception bandwidth F (MHz) of the conventional bandpass filter, and the reception bandwidth 13 is the reception bandwidth (m × x) of the bandpass filter having a width of m times the conventional reception bandwidth. F (MHz)). A region 14 indicates an out-of-band signal component that cannot be captured by a conventional band-pass filter in the spectrum of the received signal from the near end of the transmission path. A spectrum waveform 15 shows an example of a spectrum waveform of a received signal from the far end of the transmission path. A region 16 indicates an out-of-band signal component that cannot be captured by a conventional bandpass filter in the spectrum of the received signal from the far end of the transmission path. The reception bandwidth 12 and the reception bandwidth 13 in (B) are the same as the reception bandwidth 12 and the reception bandwidth 13 in (A), respectively.
[0017]
Hereinafter, the operation of the received signal processing apparatus 1 will be described. The received signal processing device 1 is a signal obtained by detecting a monitoring optical signal transmitted from the OTDR of a transmission line monitoring device that performs cable loss measurement of an optical fiber in the transmission line and returning after transmitting through the transmission line and converting it to an electrical signal. Receive. The received signal after the monitoring light signal is detected has a noise component reduced by the band-pass filter 2 having a reception bandwidth of m × F (MHz). For the received signal from the near end of the transmission line shown in FIG. 2A, the amount of signal component obtained even if it is a conventional bandpass filter having a reception bandwidth of F (MHz) is m × F ( The amount of signal component obtained by a bandpass filter having a reception bandwidth of (MHz) is almost the same as that of the received signal from the far end of the transmission line shown in FIG. A band pass filter 2 having a reception bandwidth (m × F (MHz)) that is m times (F (MHz)) is used.
[0018]
As a result, the signal component 16 that cannot be captured by the bandpass filter having the reception bandwidth (F (MHz)) of the reception signal from the near end of the conventional transmission path can be captured, and the far end transmission path can be obtained. The out-of-band signal component corresponding to the deterioration of the transmitted signal is compensated.
[0019]
On the other hand, the signal component compensation is realized by setting the reception bandwidth to m times the reception bandwidth (m × F (MHz)) from the conventional reception bandwidth (F (MHz)), but the noise component is also captured. The amount will increase and the signal to noise ratio (S / N) will degrade. In order to compensate for this S / N degradation, the A / D converter 4 converts the analog signal into digital data, and the converted digital data is stored in the memory 5 at a sampling point number n times the conventional sampling point number A ( n × A). The CPU 6 reduces the noise component by performing the moving average process using n times the number of sampling points as compared with the prior art, thereby realizing S / N improvement.
[0020]
【The invention's effect】
As a first effect, by expanding the reception bandwidth of the receiver of the transmission line monitoring device, it is possible to compensate for out-of-band signal components of the signal that has been transmitted to the farthest end transmission line and the signal has deteriorated In addition, the influence of the degradation that was not a problem with the system length of the transmission line up to about 3000 km is caused by the signal component of the signal component in which the signal degradation in the long-distance transmission of about 8000 km has occurred and the bandwidth is widened. The out-of-band signal component can be compensated.
[0021]
As a second effect, by increasing the reception bandwidth, increasing the reception bandwidth also increases the noise component and degrades the S / N. However, the increase in the noise component is reduced after A / D conversion. The S / N improvement can be performed by increasing the number of sampling points of the digital data and taking a moving average.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a received signal processing apparatus in a transmission line monitoring system according to the present invention.
FIG. 2 is a diagram showing a spectrum waveform of a reception signal in the present embodiment.
FIG. 3 is a block diagram showing a configuration of a received signal processing apparatus in a conventional transmission path monitoring system.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Reception signal processing apparatus 2 Band pass filter 3 Amplifier 4 A / D converter 5 Memory 6 CPU

Claims (2)

In a received signal processing device that receives a signal that is transmitted from a transmission line monitoring device that measures a cable loss of an optical fiber in a transmission line and that is returned through the transmission line and converted into an electrical signal ,
In order to compensate the out-of-band signal component of the spectrum waveform of the monitoring signal transmitted to the far-end transmission path, it is m times larger than the first reception bandwidth (F (MHz)) of the received signal from the near-end of the transmission path. A bandpass filter having a second reception bandwidth (m × F (MHz)) and filtering the received signal;
An amplifier that amplifies the filtered signal;
An A / D converter for converting the amplified signal from an analog signal to a digital signal;
A memory for storing the converted digital signal at a sampling point number (n × A) that is n times the sampling point number A corresponding to the first reception bandwidth;
A received signal processing apparatus comprising: a central processing unit that performs a graphing process after performing a process of taking a moving average from a digital signal having the number of sampling points stored in the memory. In a received signal processing method for detecting a monitoring optical signal transmitted from a transmission line monitoring device for measuring a cable loss of an optical fiber of a transmission line and returning through the transmission line and receiving a signal converted into an electric signal ,
In order to compensate the out-of-band signal component of the spectrum waveform of the monitoring signal transmitted to the far end, the second larger m times than the first reception bandwidth (F (MHz)) of the received signal from the near end of the transmission path Filter the received signal with a band-pass filter with a receiving bandwidth (m x F (MHz)),
Amplifies this filtered signal,
This amplified signal is converted from an analog signal to a digital signal,
The converted digital signal is accumulated at a sampling point number (n × A) that is n times the sampling point number A corresponding to the first reception bandwidth,
A received signal processing method comprising: performing a graphing process after performing a process of taking a moving average from the stored digital signals of the number of sampling points.

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