JP4156446B2 - Optical receiver - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical receiver used in an optical communication apparatus.
[0002]
[Prior art]
An optical receiver used in an optical communication device receives an optical signal and converts it into an electrical signal. When the electrical signal is at a fixed identification phase, the electrical signal is compared with a threshold value, and the electrical signal is received. The signal is binarized.
However, the optimum value of the threshold fluctuates due to the influence of, for example, an optical transmission path exceeding 9000 km or a change over time of the apparatus itself. If the optimum value of the threshold value varies, the quality of the transmission signal deteriorates. Therefore, it is necessary to change the threshold value according to the variation of the optical transmission path.
[0003]
As a method for changing the threshold value, a technique for changing the threshold value according to the magnitude of the occurrence of an error in the received signal is disclosed in the following Patent Document 1. The transmission characteristic of the optical transmission line is evaluated, and the threshold value is set according to the evaluation result. The technique to change is disclosed by the following patent document 2.
[0004]
[Patent Document 1]
JP-A-2-288640 (pages 4 to 6, FIG. 1)
[Patent Document 2]
JP 2000-341344 A (paragraph numbers [0013] to [0015], FIG. 1)
[0005]
[Problems to be solved by the invention]
Since the conventional optical receiver is configured as described above, the threshold value can be optimized in accordance with fluctuations in the optical transmission path. However, when distortion occurs in the waveform of the optical signal, the optimum value of the identification phase also fluctuates. Therefore, there is a problem that even if the threshold value is simply changed, deterioration of the quality of the transmission signal cannot be suppressed.
[0006]
The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an optical receiver that can suppress deterioration in the quality of a transmission signal even if distortion occurs in the waveform of the optical signal. To do.
[0007]
[Means for Solving the Problems]
An optical receiver according to the present invention includes a threshold value changing unit that changes a threshold value in a direction in which the code error rate detected by the detection unit decreases, and an identification phase in a direction in which the code error rate detected by the detection unit decreases. Phase changing means for changing is provided.
Further , the threshold value changing means and the phase changing means repeatedly perform the threshold value and identification phase changing processes separately until the code error rate detected by the detecting means converges. If the code error rate is reduced when the phases are changed simultaneously, the threshold value changing means and the phase changing means simultaneously execute the threshold value and identification phase changing processing.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described below.
Embodiment 1 FIG.
FIG. 1 is a block diagram showing an optical receiver according to Embodiment 1 of the present invention. In FIG. 1, a photodetector 2 receives conversion means for receiving an optical signal from a transmission line 1 and converting the optical signal into an electrical signal. It is composed. The discriminator 3 compares the electrical signal with the reception threshold Y when the electrical signal output from the photodetector 2 is at the set reception discrimination phase X, and binarizes the electrical signal. Means.
The code error detector 4 constitutes detection means for detecting the code error rate of the binary signal output from the discriminator 3. The threshold control unit 5 constitutes a threshold changing unit that changes the reception threshold Y in a direction in which the code error rate detected by the code error detection unit 4 decreases. The phase control unit 6 constitutes a phase changing unit that changes the reception identification phase X in a direction in which the code error rate detected by the code error detection unit 4 decreases.
[0009]
Next, the operation will be described.
When the photodetector 2 receives the optical signal from the transmission line 1, the photodetector 2 converts the optical signal into an electrical signal.
When the electrical signal output from the photodetector 2 is at the set identification phase X, the discriminator 3 compares the electrical signal with the reception threshold Y, binarizes the electrical signal, and outputs the binary value. Output a signal. That is, if the electrical signal is greater than the reception threshold Y, a signal having a value of “1” is output. If the electrical signal is not greater than the reception threshold Y, a signal having a value of “0” is output.
[0010]
Here, when the waveform of the optical signal received by the photodetector 2 has a relationship between time axis and intensity as shown in FIG. 2, the distribution of the code error rate of the received signal is as shown in FIG. It is represented by contour lines.
The contour line in FIG. 3 represents a state in which the code error rate decreases as it approaches the center. Therefore, the optimal reception threshold Y and reception identification phase X in the case of FIG. 3 are points of A0.
However, when the waveform of the optical signal is distorted, for example, as shown in FIG. 4, the distribution of the code error rate of the received signal is represented by contour lines as shown in FIG.
[0011]
Hereinafter, optimization of the reception threshold Y and the reception identification phase X when the waveform of the optical signal is distorted will be described.
When receiving a binary signal from the discriminator 3, the code error detector 4 detects the code error rate of the binary signal. For example, since the Reed-Solomon code is added to the optical signal, the code error rate is detected by detecting the Reed-Solomon code.
Here, for convenience of explanation, it is assumed that the reception identification phase X is at point A0 in FIG.
[0012]
When the code error detection unit 4 detects the code error rate, the phase control unit 6 adds a predetermined step value ΔX to the current reception identification phase X, and changes the reception identification phase to point A1. Here, as the step value ΔX, in order to minimize the fluctuation of the code error rate due to the change of the reception identification phase X, the minimum step value that can be accepted by the hardware is adopted.
After that, when the code error detection unit 4 detects the code error rate at the point A1, the phase control unit 6 compares the code error rate at the point A0 with the code error rate at the point A1, and receives the signal having the lower code error rate. Adopt phase.
In the example of FIG. 6, since the code error rate at the point A1 is lower than the point A0, (X + ΔX) is adopted as the current reception identification phase.
[0013]
However, in the example of FIG. 6, the code error rate at the A1 point is lower than the A0 point, but if the code error rate at the A0 point is lower than the A1 point, a predetermined step value from the reception identification phase X is assumed. ΔX is subtracted, and the reception identification phase is changed to the F1 point.
After that, when the code error detection unit 4 detects the code error rate at the F1 point, the phase control unit 6 compares the code error rate at the A0 point with the code error rate at the F1 point, and the reception identification with the lower code error rate is performed. Adopt phase.
[0014]
Next, the phase controller 6 adds a predetermined step value ΔX to the current reception identification phase (X + ΔX), and changes the reception identification phase to point A2.
After that, when the code error detection unit 4 detects the code error rate at the point A2, the phase control unit 6 compares the code error rate at the point A1 with the code error rate at the point A2, and receives the signal having the lower code error rate. Adopt phase.
In the example of FIG. 6, since the code error rate at the point A2 is lower than the point A1, (X + 2ΔX) is adopted as the current reception identification phase.
[0015]
Next, the phase control unit 6 adds a predetermined step value ΔX to the current reception identification phase (X + 2ΔX), and changes the reception identification phase to point F2.
After that, when the code error detection unit 4 detects the code error rate at the point F2, the phase control unit 6 compares the code error rate at the point A2 with the code error rate at the point F2, and receives the signal having the lower code error rate. Adopt phase.
In the example of FIG. 6, since the code error rate at the point A2 is lower than the point F2, the predetermined step value ΔX is subtracted from the current reception identification phase (X + 3ΔX). As a result, the reception identification phase converges once.
[0016]
As described above, once the reception identification phase converges, the threshold control unit 5 adds a predetermined step value ΔY to the current reception threshold Y, and changes the reception threshold to the B0 point. Here, as the step value ΔY, in order to minimize the fluctuation of the code error rate due to the change of the reception threshold Y, the minimum step value acceptable by hardware is adopted.
After that, when the code error detection unit 4 detects the code error rate at the point B0, the threshold control unit 5 compares the code error rate at the point A2 and the code error rate at the point B0, and receives the reception threshold value with the lower code error rate. Is adopted.
In the example of FIG. 6, since the code error rate at the point B0 is lower than the point A2, (Y + ΔY) is adopted as the current reception threshold.
[0017]
Next, the threshold control unit 5 adds a predetermined step value ΔY to the current reception threshold (Y + ΔY), and changes the reception threshold to point F3.
Thereafter, when the code error detection unit 4 detects the code error rate at the point F3, the threshold control unit 5 compares the code error rate at the point B0 and the code error rate at the point F3, and receives the reception threshold value with the lower code error rate. Is adopted.
In the example of FIG. 6, since the code error rate at the point B0 is lower than the point F3, the predetermined step value ΔY is subtracted from the current reception threshold (Y + 2ΔY). As a result, the reception threshold converges.
[0018]
As described above, when the reception threshold converges, the phase control unit 6 adds a predetermined step value ΔX to the current reception identification phase (X + 2ΔX), and changes the reception identification phase to point F4.
After that, when the code error detection unit 4 detects the code error rate at the point F4, the phase control unit 6 compares the code error rate at the point B0 with the code error rate at the point F4, and receives the signal having the lower code error rate. Adopt phase.
In the example of FIG. 6, since the code error rate at the point B0 is lower than the point F4, a predetermined step value ΔX is subtracted from the current reception identification phase (X + 3ΔX). As a result, the reception identification phase converges.
[0019]
By repeatedly performing the above change process, it is found that the code error rate at the point B0 is the smallest in the example of FIG. 6, so that the reception identification phase (X + 2ΔX) and the reception threshold value (Y + ΔY) at the point B0 are finally obtained. Adopted.
Note that if the reception threshold Y is simply changed from the point A0, it will not move much closer to the center of the contour line by simply moving in the vertical direction in FIG. 6, but by changing the reception identification phase from the point A0, the center of the contour line will be increased. You can see that it approaches.
[0020]
As apparent from the above, according to the first embodiment, the threshold control unit 5 that changes the reception threshold Y in a direction in which the code error rate detected by the code error detection unit 4 decreases, and the code error detection unit 4 Since the phase control unit 6 that changes the reception identification phase X in a direction in which the code error rate detected by the method is reduced is provided, even if distortion occurs in the waveform of the optical signal, the quality of the transmission signal is deteriorated. The effect which can be suppressed is produced.
Further, according to the first embodiment, the threshold control unit 5 and the phase control unit 6 are configured to repeatedly perform the changing process until the code error rate converges. There is an effect that can be optimized.
[0021]
Embodiment 2. FIG.
7 is a block diagram showing an optical receiver according to Embodiment 2 of the present invention. In the figure, the same reference numerals as those in FIG.
When the simultaneous control unit 7 changes the reception threshold Y and the reception identification phase X at the same time after the code error rate has converged, if the code error rate becomes smaller, the threshold control unit 5 and the phase control unit 6 simultaneously perform the changing process. Thus, the threshold control unit 5 and the phase control unit 6 are controlled. The simultaneous control unit 7 constitutes a threshold changing unit and a phase changing unit.
9 and 10 are flowcharts showing the processing contents of the optical receiver according to the second embodiment of the present invention.
[0022]
Next, the operation will be described.
First, similarly to the first embodiment, the threshold control unit 5 and the phase control unit 6 repeatedly perform the process of changing the reception threshold Y and the reception identification phase X separately (steps ST1 to ST4).
As a result, the reception identification phase (X + 2ΔX) and the reception threshold value (Y + ΔY) at point B0 are once employed as in the first embodiment (see FIG. 8).
[0023]
When the separate change processing of the reception threshold value Y and the reception identification phase X is completed, the simultaneous control unit 7 adds + ΔX or −ΔX to the reception identification phase with reference to the reception identification phase at the B0 point, and at the B0 point As a reference, + ΔY or −ΔY is added to the reception threshold value, and the code error rate when the following eight patterns are combined is confirmed (steps ST5 and ST6).
Reception identification phase Reception threshold (1) X + ΔX Ｙ Y
(2) X + 2ΔX Ｙ Y
▲ 3 ▼ X + 3ΔX Ｙ Y
(4) X + ΔX Ｙ Y + ΔY
(5) X + 3ΔX ⇔ Y + ΔY
(6) X + ΔX Ｙ Y + 2ΔY
(7) X + 2ΔX ⇔ Y + 2ΔY
(8) X + 3ΔX ⇔ Y + 2ΔY
[0024]
Next, the simultaneous control unit 7 compares the code error rates when the eight patterns are combined with each other, and selects the pattern with the lowest code error rate. In the example of FIG. 8, it is assumed that the code error rate of the pattern (8) (code error rate at the point D0) is the smallest.
The simultaneous control unit 7 further compares the code error rate at the point D0 with the code error rate at the point B0. In the example of FIG. 8, since the code error rate at the point D0 is lower than the point B0, the reception identification phase (X + 3ΔX) and the reception threshold value (Y + Δ2Y) at the point D0 are adopted (step ST7), and the process returns to step ST5. .
However, if the code error rate at the point B0 is lower than the point D0, the reception identification phase (X + 2ΔX) and the reception threshold value (Y + ΔY) at the point B0 are maintained, and a series of processing is terminated (step ST8).
[0025]
As is apparent from the above, according to the second embodiment, since the threshold control unit 5 and the phase control unit 6 are configured to perform the changing process at the same time, the threshold control unit 5 and the phase control unit 6 are separately provided. As compared with the case where the change process is performed, the reception identification phase and the reception threshold value can be changed so that the code error rate is further reduced.
Further, according to the second embodiment, when the reception threshold Y and the reception identification phase X are simultaneously changed after the code error rate has converged, when the code error rate becomes smaller, the threshold control unit 5 and the phase control unit 6 Since the simultaneous control unit 7 for controlling the threshold control unit 5 and the phase control unit 6 is provided so as to perform the change processing at the same time, compared to the case where the threshold control unit 5 and the phase control unit 6 perform the change processing simultaneously from the beginning. Thus, the reception identification phase and the reception threshold can be optimized in a short time.
[0026]
【The invention's effect】
As described above, according to the present invention, the threshold value changing means for changing the threshold value in the direction in which the code error rate detected by the detection means is reduced, and the direction in which the code error rate detected by the detection means is reduced are identified. Since the phase changing means for changing the phase is provided, even if distortion occurs in the waveform of the optical signal, there is an effect that it is possible to suppress the quality deterioration of the transmission signal.
Further , the threshold value changing means and the phase changing means repeatedly perform the threshold value and identification phase changing processes separately until the code error rate detected by the detecting means converges. If the code error rate is reduced when the phase is changed simultaneously, the threshold changing unit and the phase changing unit are configured to perform the threshold value and identification phase changing process at the same time. However, the threshold value and the identification phase can be optimized in a short time.
[Brief description of the drawings]
FIG. 1 is a configuration diagram illustrating an optical receiver according to a first embodiment of the present invention.
FIG. 2 is an explanatory diagram showing a waveform of an optical signal.
FIG. 3 is an explanatory diagram showing a distribution of code error rates when the optical signal of FIG. 2 is received.
FIG. 4 is an explanatory diagram showing a waveform of an optical signal in which distortion occurs.
5 is an explanatory diagram showing a distribution of code error rates when the optical signal of FIG. 4 is received. FIG.
FIG. 6 is an explanatory diagram illustrating a process of changing a reception threshold value and a reception identification phase.
FIG. 7 is a block diagram showing an optical receiver according to a second embodiment of the present invention.
FIG. 8 is an explanatory diagram illustrating a process of changing a reception threshold value and a reception identification phase.
FIG. 9 is a flowchart showing processing contents of the optical receiver according to the second embodiment of the present invention.
FIG. 10 is a flowchart showing processing contents of the optical receiver according to the second embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Transmission path, 2 Photo detector (conversion means), 3 Discriminator (binarization means), 4 Code error detection part (detection means), 5 Threshold control part (threshold change means), 6 Phase control part (phase change means) , 7 Simultaneous control section (threshold changing means, phase changing means).

Claims (1)

When the optical signal is received, the converting means for converting the optical signal into an electric signal, and when the electric signal converted by the converting means is at the set identification phase position, the electric signal is compared with the threshold value. The binarization means for binarizing the electric signal, the detection means for detecting the code error rate of the binary signal output from the binarization means, and the code error rate detected by the detection means a threshold changing means for changing the threshold value in the small direction, the optical receiver and a phase changing means for changing the identification phase in the direction in which the detected bit error rate is reduced by the detection means, the detection means until the detected code error rate converges by, the threshold value changing means and said phase changing means is performed repeatedly change processing separately the threshold and the identification phase, after which the code error rate has converged, the Changing the value and the identification phase at the same time, if the bit error rate is reduced, an optical receiver the threshold value changing means and said phase changing means which comprises carrying out the process of changing the threshold and the identification phase at the same time .

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