JP2004349888A - Optical receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize low-cost and high-quality high-speed/large-capacity transmission without increasing the transmission speed nor making an optical receiver large-sized. <P>SOLUTION: In the optical receiver which corrects errors of an optical receive signal and outputs the error-corrected signal as a receive signal, a soft decision means that the optical receiver is equipped with selects (2<SP>n</SP>-k-j) (where (j) is an integer satisfying 0≤j≤(2<SP>n</SP>-k-1)) of (2<SP>n</SP>-k) (where (n) is a natural number and (k) is an integer satisfying 0≤k≤(2n-1)) results of multilevel discrimination based upon the data pattern of the optical receive signal and then generates a hard decision result and reliability information for soft decision decoding from those selected multilevel discrimination results. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical receiver, and more particularly, to an optical receiver that can compensate for signal quality degradation after optical transmission and provide high-quality transmission services.
[0002]
[Prior art]
As an optical receiving device applied to an optical transmission device that performs long-distance and large-capacity transmission, for example, an error correction code based on a multi-level identification signal is performed according to the optical receiving quality indicated by the reliability information, and the optical receiving quality is improved. An optical receiving device capable of correcting an error with a high probability even when deteriorated has been disclosed (for example, Patent Document 1).
[0003]
The optical receiving apparatus disclosed in Patent Document 1 includes an optical-electrical conversion unit, a multi-level identification unit, an optical reception quality determination unit, and an error correction decoding unit, and the optical-electrical conversion unit is connected via a transmission path. The input optical reception signal is converted into a first electric reception signal and a second electric reception signal, and the multi-level identification means generates the first electric reception signal as a multi-value identification signal identified by a plurality of identification levels. The optical reception quality determining means generates reliability information indicating the quality of the optical reception signal based on the second electrical reception signal, and the error correction decoding means refers to the reliability information to determine the reliability of the multilevel identification signal. An error-corrected received signal is output.
[0004]
Therefore, this optical receiver can perform error correction with a high probability even when the optical reception quality is degraded, and can obtain a received signal with a good bit error rate.
[0005]
In addition, high-speed A / D conversion can be performed by arranging a plurality of high-speed binary decision circuits in parallel in place of the multi-level discrimination unit of Patent Document 1 described above, and a soft decision error correction process similar to that of Patent Document 1 is performed. There is disclosed an example of an optical receiving apparatus for performing the method (for example, Patent Document 2).
[0006]
In addition, the threshold control circuit uses the threshold value of the high-speed binary decision circuit controlled so that the number of errors detected by the hard-decision error correction decoding circuit is minimized. There is disclosed an example of an optical receiver that can maintain reception characteristics with respect to fluctuations in transmission characteristics in an optimum state by performing correction (for example, Patent Document 3).
[0007]
[Patent Document 1]
JP-A-2002-330104 (page 5-7, FIG. 1)
[Patent Document 2]
JP-A-2003-18023 (page 3-4, FIG. 1)
[Patent Document 3]
JP-A-2000-341344 (page 3-7, FIG. 1)
[0008]
[Problems to be solved by the invention]
However, in the optical receivers disclosed in Patent Documents 1 and 2, sufficient compensation can be made for deterioration of optical signal quality due to noise or the like received on a transmission line by determination at a multi-level identification level. Although it could be performed, the optical signal quality degradation caused by the propagation delay in the waveform after reception due to the speed difference of the polarization plane at the same signal wavelength such as chromatic dispersion, nonlinear optical effect and polarization dispersion As a result, sufficient compensation could not be provided.
[0009]
In addition, as the transmission distance becomes longer, not only the above-mentioned chromatic dispersion and noise alone cause, but also the interaction between these factors themselves and the nonlinear optical effect causes rapid deterioration of optical signal quality. It is.
[0010]
In order to improve the optical signal quality in response to the sudden deterioration of the optical signal quality, it is conceivable to apply a conventional method of improving the correction capability by increasing the ratio of redundant bits of the error correction code. The increase in speed leads to deterioration of optical signal quality, and furthermore, a device or the like capable of operating at higher speed is required, and there is a problem in cost reduction.
[0011]
As an example of equalizing distorted waveforms, a digital signal after AD conversion is converted from time-domain data to frequency-domain data by Fourier transform, and a filter is installed that has the opposite characteristic to the transmission path characteristics by frequency analysis. There is also a method of compensating for. Although this method is widely used in the field of wireless communication, a dedicated high-speed circuit such as a control circuit and a compensation circuit is additionally required, and it is not possible to avoid high cost and an increase in the size of the device.
[0012]
Further, in the optical receiving device disclosed in Patent Document 3, as described above, the threshold value of the high-speed binary decision circuit is set so that the number of errors corrected by the error correction decoding circuit is minimized. Since this configuration controls the threshold value of the binary decision circuit, it cannot be applied to soft decision and cannot cope with quality degradation that changes for each received bit.
[0013]
SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has been made in view of the fact that optical transmission that enables low-cost, high-quality, high-speed / large-capacity transmission without increasing the transmission speed and without increasing the size of the device. An object is to provide a receiving device.
[0014]
[Means for Solving the Problems]
In order to solve the above-mentioned problems and achieve the object, an optical receiving apparatus according to the present invention includes: an optical-electrical conversion unit configured to generate an electrical reception signal by performing an optical-electrical conversion on an optical reception signal; Soft-decision means for outputting a multi-valued identification digital signal in which a signal is identified at a plurality of identification levels; Separating means, in the optical receiving device that performs error correction based on the reliability information and the hard decision result included in the multi-level parallel digital signal, and outputs the error-corrected signal as a received signal, the soft decision means (2 ⁿ −k) (n is a natural number and k is 0 ≦ k ≦ (2 ⁿ Each of the electric received signals is identified by an integer) thresholds satisfying -1), and the identified (2) ⁿ -K) variable bit multi-valued discriminators for generating binary discrimination results, and (2) output from the variable bit multi-valued discriminator. ⁿ −k) (2) ⁿ −kj) (j is 0 ≦ j ≦ (2 ⁿ −k−1), a selection circuit for generating binary identification results, and (2) output from the selection circuit. ⁿ -Kj) one-bit delay circuit for generating a binary identification result obtained by delaying the binary identification result by one bit, and (2) output from the one-bit delay circuit. ⁿ -Kj) a reliability information generation circuit that generates a hard decision result and a plurality of pieces of reliability information based on one binary identification result selected from the binary identification results. And
[0015]
According to the present invention, the soft decision means includes a variable bit multi-valued discriminator, a selection circuit, a 1-bit delay circuit, and a reliability information generation circuit. In the variable bit multi-value discriminator, the electric reception signal is (2 ⁿ −k) (n is a natural number and k is 0 ≦ k ≦ (2 ⁿ (2) thresholds (integer satisfying -1) ⁿ -K) binary identification results are generated. In the selection circuit, (2) ⁿ −k) (2) ⁿ −kj) (j is 0 ≦ j ≦ (2 ⁿ −k−1) binary identification results are generated. In the one-bit delay circuit, (2) ⁿ −k−j binary identification results are generated by delaying the binary identification results by one bit. In the reliability information generation circuit, the output from the one-bit delay circuit (2 ⁿ A hard decision result and a plurality of pieces of reliability information are generated based on one binary identification result selected from -kj) binary identification results.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of an optical receiver according to the present invention will be described in detail with reference to the drawings. It should be noted that the present invention is not limited by the embodiment.
[0017]
Embodiment 1 FIG.
First, the configuration of the optical receiving device according to the first embodiment of the present invention will be described. FIG. 1 is a block diagram illustrating a configuration of the optical receiving apparatus according to the first embodiment of the present invention. The optical receiving device shown in FIG. 1 includes an optical-electrical conversion unit 2, a soft decision unit 3, a demultiplexing unit 4, and an error correction unit 6. In the figure, the output end of the photoelectric conversion means 2 is connected to the soft decision means 3. The output end of the soft decision means 3 is connected to the error correction means 6 via the demultiplexing means 4.
[0018]
Next, the operation of the optical receiver will be described with reference to FIG. The photoelectric conversion unit 2 converts an optical signal received from an optical transmission line (not shown) into an electric signal and outputs the electric signal to the soft decision unit 3. The soft decision unit 3 outputs to the demultiplexing unit 4 a digital signal obtained by identifying the electric signal (electric reception signal) converted by the photoelectric conversion unit 2 at a plurality of identification levels. The demultiplexing means 4 outputs to the error correction means 6 a multi-level parallel digital signal obtained by developing the digital signals (multi-level identification digital signals) identified at the plurality of identification levels in parallel to a speed at which large-scale logic processing is possible. . The error correction means 6 performs error correction based on the reliability information and the hard decision result included in the demultiplexed multilevel parallel digital signal, and outputs the error-corrected parallel signal as a received signal.
[0019]
FIG. 2 is a block diagram showing a configuration of the soft decision means 3 shown in FIG. The soft decision means 3 shown in FIG. 1 includes a variable bit multi-value discriminator 101, a selection circuit 102, a 1-bit delay circuit 103, and a reliability information generation circuit 104.
[0020]
In FIG. 2, the variable bit multi-value discriminator 101 converts the electric reception signal output from the photoelectric conversion unit 2 into (2 ⁿ −k) (k is 0 ≦ k ≦ (2 ⁿ (Integer satisfying -1)) thresholds, and (2) ⁿ -K) output the binary identification results to the selection circuit 102; The selection circuit 102 outputs the variable bit multi-valued discriminator 101 based on the output of the one-bit delay circuit 103 (2 ⁿ -K) out of the binary identification results, (2 ⁿ -Kj) (j is 0 ≦ j ≦ (2 ⁿ −k−1) are selected and output to the one-bit delay circuit 103. The one-bit delay circuit 103 outputs (2 ⁿ −k−j binary identification results are delayed by one bit, output to the reliability information generation circuit 104, and delayed (2 ⁿ -Kj) is output to the selection circuit 102 as a selection signal. The reliability information generation circuit 104 outputs the delayed (2 ⁿ −k−j) Output the hard decision result and m pieces of reliability information from the binary identification results to the demultiplexing means 4 at the next stage.
[0021]
Note that n shown above is the minimum number of bits (number of bits required for identification) required to represent the identification state identified by the threshold. Now, the number of bits required for identification will be briefly described with reference to FIGS. FIG. 3 is an explanatory diagram for explaining the operation when the received 1-bit waveform is identified at the multi-value level, and FIG. 4 is a table showing the identification result at each threshold value and the identification state. .
[0022]
As shown in FIG. 3, the seven threshold values are “D” from the higher identification level, respectively. ₊₃ "," D ₊₂ "," D ₊₁ "," D _C "," D _-1 "," D _-2 "," D _-3 When "1" is set, the identification result at each threshold value is as shown in FIG. 4. For example, the level of the received 1-bit waveform is "D". ₊₃ "And" D ₊₂ ”And“ D ₊₃ The identification result corresponding to "" is "0", and "D" ₊₂ The identification result below is "1" and the identification state is "7." Similarly, the level of the 1-bit received waveform is "D." _C "And" D _-1 If the threshold value is present between "4" and "4", then if the number of thresholds is seven, eight identification states appear as shown in FIG. In the example shown in (1), the number of identification required bits for expressing these eight identification states is 3. If the number of thresholds is p (p is a natural number), the number of identification required bits is n Is n = log ₂ It can be represented by (p + 1).
[0023]
FIG. 5A is a diagram for explaining the signal waveform (eye pattern) of the electric reception signal and the threshold value of the variable bit multi-value discriminator 101, and FIG. 5B is a diagram illustrating a one-bit delay circuit. 10 is a chart showing a relationship between a value of an output Dc of FIG. 103 and a selected identification data group. A set of thresholds (identification data groups) shown in FIG. 2A is obtained by calculating eight thresholds when n = 3, k = 0, and j = 1 in each processing unit shown in FIG. The figure shows an example in which identification is performed using a plurality of identification data groups (in this example, two identification groups) including seven threshold values.
[0024]
Signal quality deterioration due to propagation delay in the waveform after reception due to the speed difference of the polarization plane at the same signal wavelength such as chromatic dispersion and nonlinear optical effect received in the optical transmission line, and the polarization difference in the same signal wavelength such as polarization dispersion When this occurs, the eye opening of the eye pattern of the electric reception signal after photoelectric conversion is deteriorated depending on the data pattern as shown in FIG. For example, a space ("0") after a continuous mark ("1") does not fall to the space side, and conversely, a mark ("1") after a continuous space ("0") is a mark ("1"). I can not go up to the side.
[0025]
For this reason, the error rate for the space is smaller for the result of discrimination at the plus-side discrimination-level (TH + α) than for the result of discrimination at the center of the eye pattern. The result of identification at the minus identification level (TH-α) is smaller than the result of identification at the center (THc).
[0026]
Therefore, when the value of the Dc output of the one-bit delay circuit 103 is “1”, that is, when the value of Dc identified one bit before is “1”, the selection circuit 102 sets the value of the identification data group (DG1). Seven identification results are selected. On the other hand, when the value of the Dc output of the one-bit delay circuit 103 is “0”, that is, when the value of Dc identified one bit before is “0”, the selection circuit 102 sets the 7th of the identification data group (DG2). Individual identification results are selected. At this time, the reliability information generation circuit 104 sets, for example, Dc as a hard decision result from each of the selected identification data groups, and sets “1” or “1” for the hard decision result from the binary identification result of the selected identification data group. Probability of “0” is generated as reliability information. The hard decision result and the reliability information are parallel-developed by the demultiplexing means 4 to a speed at which large-scale logical processing is possible, and then the soft correction decoding processing is performed by the error correction means 6.
[0027]
FIG. 6 is a diagram illustrating an example of a case where the number of thresholds is increased in FIG. The example shown in FIG. 6 is an example where n = 4, k = 5, and j = 4, and the number of thresholds existing in one set of identification data groups is 7 (= 2 ⁴ −5-4), which is the same as the example shown in FIG. 5, but the number of discriminators (not shown) provided in the variable bit multi-value discriminator 101 is 11 (= 2). ⁴ -5), which increases the number of classifiers. As in the example of FIG. 6, by increasing the number of discriminators, the difference between the Dc output values of the discrimination data groups can be increased, so that the quality of the optical reception signal deteriorates and the eye opening is closed. However, highly accurate error correction is possible.
[0028]
As described above, according to the optical receiver of this embodiment, the soft decision means provided in the optical receiver is identified according to the data pattern of the optical reception signal (2). ⁿ −k) From the multi-valued identification results, (2 ⁿ −k−j), the hard decision result for performing soft decision decoding and the reliability information are generated, so that various optical signal qualities such as chromatic dispersion and polarization dispersion of the transmission path can be obtained. Even in the presence of a factor that causes deterioration, high-quality services can be provided with a low-cost and small-sized device without increasing the size of the device.
[0029]
Further, according to the optical receiver of this embodiment, the variable bit multi-valued discriminator is (2 ⁿ −k) (n is a natural number and k is 0 ≦ k ≦ (2 ⁿ Each of the electrical received signals is identified by (integer satisfying -1) thresholds (2). ⁿ -K) binary discrimination results are generated, and the selection circuit outputs (2) ⁿ −k) (2) ⁿ −kj) (j is 0 ≦ j ≦ (2 ⁿ −k−1) binary identification results are generated, and the 1-bit delay circuit outputs (2 ⁿ -Kj) binary identification results are generated by delaying the binary identification results by one bit, and the reliability information generation circuit outputs (2) ⁿ −k−j) The hard decision result and the plurality of pieces of reliability information are generated based on one binary identification result selected from the binary identification results. Even in the presence of various factors that degrade optical signal quality, such as polarization dispersion, high-quality services can be provided with low-cost and small-sized devices without increasing the size of the devices.
[0030]
Embodiment 2 FIG.
FIG. 7 is a block diagram illustrating a configuration of a soft decision unit of the optical receiver according to the second embodiment of the present invention. The soft decision means shown in the drawing has a configuration in which a one-bit delay circuit 106 for generating a one-bit delay signal is added immediately after the output terminal of the one-bit delay circuit 103 in the soft decision means shown in FIG. . The other configuration is the same as or equivalent to the configuration shown in FIG. 2, and these portions are denoted by the same reference numerals.
[0031]
FIG. 8A is a diagram showing an example in which the number of identification data groups is increased in FIG. 6, and FIG. 8B shows the value of the output Dc of the 1-bit delay circuit 103 and the 1-bit delay. 9 is a table showing a relationship between the value of an output Dc of the circuit 106 and an identification data group selected.
[0032]
The example shown in FIG. 8 is an example where n = 4, k = 5, and j = 4, as in FIG. 6, and the number of thresholds existing in one set of identification data groups is 7 (= 2 ⁴ −5-4), and the number of discriminators (not shown) provided in the variable bit multi-value discriminator 101 is 11 (= 2). ⁴ -5). On the other hand, there are four identification data groups (DG1 to DG4), and one of these identification data groups is selected according to the value of the output Dc of the 1-bit delay circuit 103 and the value of the output Dc of the 1-bit delay circuit 106. Will be.
[0033]
For example, as shown in FIG. 8B, when both the output Dc of the 1-bit delay circuit 103 and the output Dc of the 1-bit delay circuit 106 are “1”, DG1 is selected and the 1-bit delay circuit 103 and the 1-bit delay circuit When both the values of the output Dc of the delay circuit 106 are “0”, DG4 is selected. That is, when “1” is continuously output, the value of the Dc output level of the identification data group is set to a higher value (on the mark level side). Conversely, when “0” is output continuously. , The value of the Dc output level of the identification data group is set to a lower value (space level side).
[0034]
In this embodiment, the case where there are two 1-bit delay circuits is described, but a configuration including a plurality of 1-bit delay circuits may be employed. In this case, the number of identification data groups selected by the selection circuit 102 can be further increased.
[0035]
As described above, according to the optical receiver of this embodiment, the variable bit multi-valued discriminator is (2 ⁿ −k) (n is a natural number and k is 0 ≦ k ≦ (2 ⁿ Each of the electrical received signals is identified by (integer satisfying -1) thresholds (2). ⁿ -K) binary discrimination results are generated, and the selection circuit outputs (2) ⁿ −k) (2) ⁿ −kj) (j is 0 ≦ j ≦ (2 ⁿ -K-1) binary identification results are generated, and the first 1-bit delay circuit outputs (2) ⁿ -Kj) The binary identification results are generated by delaying the binary identification results by one bit, and the second one-bit delay circuit outputs (2) ⁿ -Kj) binary identification results are further delayed by one bit to generate a binary identification result delayed by a total of two bits, and the reliability information generation circuit is output from the first one-bit delay circuit. (2 ⁿ -Kj) binary identification results selected from the binary identification results, and (2) output from the second 1-bit delay circuit. ⁿ -Kj) Since the hard decision result and the plurality of pieces of reliability information are generated based on one binary identification result selected from the binary identification results, selectable identification data can be selected. Since the number of groups can be increased and more optimal soft decision identification can be selected according to the identification result, higher performance error correction can be performed.
[0036]
The first bit delay circuit described above corresponds to the one-bit delay circuit 103, and the second bit delay circuit corresponds to the one-bit delay circuit 106.
[0037]
Embodiment 3 FIG.
FIG. 9 is a block diagram illustrating a configuration of the optical receiving apparatus according to the third embodiment of the present invention. The optical receiving apparatus shown in the figure is different from the optical receiving apparatus according to the first embodiment shown in FIG. 1 in that the threshold setting means 14 is added to the configuration and the control output (threshold setting information and And / or threshold sweep information). The other configuration is the same as or equivalent to the configuration shown in FIG. 1, and these portions are denoted by the same reference numerals.
[0038]
FIG. 10 is a block diagram showing the configuration of the soft decision means 13 shown in FIG. The soft decision means 13 shown in FIG. 10 is a configuration obtained by adding a variable threshold value discriminator 107 to the configuration shown in FIG. 2, and the other configuration is the same as or equivalent to the configuration shown in FIG. Are given the same reference numerals.
[0039]
Next, the operation of the optical receiver will be described with reference to FIGS. Variable threshold identifier 107 shown in FIG. 10 sweeps a plurality of thresholds at predetermined time intervals based on a threshold sweep signal from threshold setting means 14 and Is output as noise distribution information. This noise distribution information is parallel-expanded by the demultiplexing means 4 shown in FIG. 9 to a speed at which large-scale logic processing is possible, and is input to the threshold setting means 14 shown in FIG.
[0040]
The threshold setting unit 14 performs statistical processing on the noise distribution information that has been developed in parallel, and estimates the noise distribution on the mark side and the space side of the received electric signal. This estimation can be realized, for example, by accumulating “1” and “0” of the identification result at each threshold and performing histogram analysis. The threshold setting unit 14 outputs threshold setting information generated based on the estimated noise distribution and the error correction information output from the error correction unit 6 to the variable bit multi-value discriminator 101 shown in FIG. In the variable bit multi-value discriminator 101, the threshold discrimination level and the like are controlled based on the threshold setting information output from the threshold setting unit 14.
[0041]
As described above, according to the optical receiver of this embodiment, the threshold value of the variable threshold value identifier is swept, and the statistical information of the binary identification result for each threshold value is used to detect the received electric signal. Since the noise distribution is inferred and the threshold value of the variable bit multi-valued discriminator is controlled from the error correction information of the error correction means, the deterioration of the optical signal quality which changes at high speed for each bit of the received electric signal and Soft decision identification can be performed with high accuracy for both optical signal quality deterioration that fluctuates in a relatively long cycle, and a high quality service with excellent stability can be provided.
[0042]
Further, according to the optical receiver of this embodiment, the variable threshold discriminator outputs noise distribution information based on the binary discrimination result for each of the plurality of thresholds swept at predetermined time intervals. , The threshold setting means includes a variable bit multi-value discriminator based on noise distribution information output from the variable threshold discriminator via the demultiplexing means and / or error correction result information output from the error correction means. Output the threshold setting information and generate the threshold sweep signal and output it to the variable threshold discriminator, so that the optical signal quality deteriorates at a high speed for each bit of the received electric signal. The soft decision identification can be performed with high accuracy for both the optical signal quality degradation that fluctuates in a relatively long cycle and a high quality service with excellent stability can be provided.
[0043]
In the optical receiver of this embodiment, the threshold setting means 14 is added to the soft decision means 3 of the first embodiment shown in FIG. 2, but the configuration of the second embodiment shown in FIG. The threshold value setting means 14 may be added to the soft decision means 3, and in this case, the same operation and effect can be obtained.
[0044]
Embodiment 4 FIG.
FIG. 11 is a block diagram illustrating a configuration of the optical receiving apparatus according to the fourth embodiment of the present invention. The optical receiving apparatus shown in the figure has a configuration in which a sampling means 15 for sampling an electric received signal is added to the optical receiving apparatus according to the third embodiment shown in FIG. The other configuration is the same or equivalent to the configuration shown in FIG. 9, and these portions are denoted by the same reference numerals. Further, the configuration of the soft decision means 13 may be any of the configurations shown in the first to third embodiments.
[0045]
In FIG. 11, sampling means 15 identifies a received electric signal with a plurality of identification phases and a plurality of identification thresholds. These identification results output waveform information of the sampled received electric signal to the threshold setting unit 14 via the demultiplexing unit. Now, assuming that the signal speed is B [bit / s] and the time interval of each identification phase is Ts [s], the sampling interval for satisfying the sampling theorem is set so that Ts ≦ 1 / (2B). Is done. The threshold setting unit 14 converts the received electrical waveform information into frequency domain data by Fourier transform and performs spectrum analysis to determine a threshold value to be applied to the soft decision unit 13. Is output to the variable bit multi-value discriminator 101 of the soft decision means 13. In the variable bit multi-value discriminator 101, the threshold discrimination level and the like are controlled based on the threshold setting information output from the threshold setting means 14.
[0046]
As described above, according to the optical receiver of this embodiment, the threshold value setting unit sets the threshold value of the soft decision identification unit by sampling the received electric waveform and performing spectrum analysis. Therefore, high-precision soft-decision decoding can be performed, and a high-quality service can be provided.
[0047]
As realized in the optical receiving apparatus according to the third embodiment, the threshold level and the like may be controlled by using the noise distribution information and the error correction information together. Services can be provided.
[0048]
Embodiment 5 FIG.
FIG. 12 is a block diagram showing a configuration of the optical receiver according to the fifth embodiment of the present invention. The optical receiving apparatus shown in the figure is different from the optical receiving apparatus according to the fourth embodiment shown in FIG. 11 in that the adaptive equalizing means 16 is provided between the photoelectric conversion means 2 and the soft decision means 3. Is the same or equivalent to the configuration shown in FIG. 11, and these portions are denoted by the same reference numerals. Further, the configuration of soft decision means 13 may be any of the configurations shown in the first to fourth embodiments.
[0049]
In FIG. 12, the adaptive equalizer 16 is composed of, for example, a transversal filter, and can set a weighting factor to be assigned to the transversal filter based on the result of the spectrum analysis performed by the threshold setting unit 14. . At this time, since the waveform distortion of the electric received signal input to the soft decision means 13 is improved by the adaptive equalization means 16, even if the optical signal quality is significantly degraded, high-precision soft decision decoding processing can be performed. It is possible to provide high quality services.
[0050]
As described above, according to the optical receiver of this embodiment, the identification is performed according to the data pattern of the optical reception signal (2). ⁿ −k) (n is a natural number and k is 0 ≦ k ≦ (2 ⁿ -1) (integral) number of multi-valued identification results, (2 ⁿ −kj) (j is 0 ≦ j ≦ (2 ⁿ After selecting (integers satisfying −k−1), a hard decision result for performing soft decision decoding and reliability information are generated from the selected multi-valued identification results. Even when the signal quality is significantly degraded, high-precision soft-decision decoding can be performed, and a high-quality service can be provided.
[0051]
As realized in the optical receiving apparatus according to the third embodiment, the threshold level and the like may be controlled by using the noise distribution information and the error correction information together. Services can be provided.
[0052]
【The invention's effect】
As described above, according to the present invention, identification is performed according to the data pattern of the optical reception signal (2 ⁿ −k) (n is a natural number and k is 0 ≦ k ≦ (2 ⁿ -1) (integral) number of multi-valued identification results, (2 ⁿ −kj) (j is 0 ≦ j ≦ (2 ⁿ −k−1) is selected, and then a hard decision result for performing soft decision decoding and reliability information are generated from the selected multi-valued identification results. The number of possible identification data groups can be increased, and more optimal soft-decision identification can be selected in accordance with the identification result, so that higher performance error correction can be achieved.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of an optical receiving device according to a first embodiment of the present invention;
FIG. 2 is a block diagram showing a configuration of a soft decision means 3 shown in FIG.
FIG. 3 is an explanatory diagram for explaining an operation when a received 1-bit waveform is identified at a multi-level.
FIG. 4 is a table showing identification results at respective threshold values and their identification states.
5A is a diagram for explaining a signal waveform (eye pattern) of an electric reception signal and a threshold value of a variable bit multi-level discriminator 101, and FIG. 5B is a diagram for explaining a one-bit delay circuit; 10 is a chart showing a relationship between a value of an output Dc of FIG. 103 and a selected identification data group.
FIG. 6 is a diagram illustrating an example of a case where the number of thresholds is increased in FIG.
FIG. 7 is a block diagram showing an optical receiving apparatus according to a second embodiment of the present invention, showing a configuration of soft decision means of the optical receiving apparatus;
8A is a diagram illustrating an example in which the number of identification data groups in FIG. 6 is increased, and FIG. 8B is a diagram illustrating the value of the output Dc of the 1-bit delay circuit 103 and the 1-bit delay; 9 is a table showing a relationship between the value of an output Dc of the circuit 106 and an identification data group selected.
FIG. 9 is a block diagram illustrating a configuration of an optical receiving device according to a third embodiment of the present invention;
FIG. 10 is a block diagram showing a configuration of a soft decision unit 13 shown in FIG.
FIG. 11 is a block diagram illustrating a configuration of an optical receiving device according to a fourth embodiment of the present invention;
FIG. 12 is a block diagram illustrating a configuration of an optical receiving device according to a fifth embodiment of the present invention;
[Explanation of symbols]
2 photoelectric conversion means, 3,13 soft decision means, 4 demultiplexing means, 6 error correction means, 14 threshold setting means, 15 sampling means, 16 adaptive equalization means, 101 variable bit multi-value discriminator, 102 selection Circuit, 103, 106 1-bit delay circuit, 104 reliability information generation circuit, 107 variable threshold value discriminator.

Claims (8)

Opto-electrical conversion means for converting an optical reception signal into an electric reception signal to generate an electric reception signal, soft decision means for outputting a multi-value identification digital signal which identifies the electric reception signal at a plurality of identification levels, A demultiplexing means for outputting a multi-level parallel digital signal obtained by expanding the digital signal in parallel to a speed capable of large-scale logic processing, and performing error correction based on the reliability information and the hard decision result contained in the multi-level parallel digital signal In the optical receiving device that performs the error-corrected signal as a received signal,
The soft decision means,
⁽² n -k) (n is a natural number, k is ^{0 ≦ k ≦ (2 n -1} ) to meet integer) the electrical received signal at the threshold identifies each the identified ^{(2 n} - k) a variable bit multi-valued discriminator for generating binary discrimination results;
Integer satisfying the output from the variable bit multi-level discriminator ⁽² n -k) number from the binary identification result ^{(2 n -k-j) (} j is ^{0 ≦ j ≦ (2 n -k} -1) A) selection circuit for generating binary identification results;
A 1-bit delay circuit for generating a binary identification result obtained by delaying the (2 ⁿ -kj) binary identification results output from the selection circuit by 1 bit;
A hard decision result and a plurality of pieces of reliability information are generated based on one binary identification result selected from the (2 ⁿ -kj) binary identification results output from the one-bit delay circuit. A reliability information generation circuit;
An optical receiving device comprising: The soft decision means includes a variable threshold value discriminator that sweeps a plurality of threshold values at predetermined time intervals and outputs the result as noise distribution information based on a binary discrimination result for each of the plurality of threshold values. And
Threshold setting for the variable bit multi-valued discriminator based on noise distribution information output from the variable threshold discriminator through the demultiplexing means and / or error correction result information output from the error correction means. The optical receiving device according to claim 1, further comprising a threshold setting unit that outputs information. 3. The variable threshold discriminator sweeps a plurality of thresholds at predetermined time intervals, and outputs a binary discrimination result for each of the thresholds as noise distribution information. The optical receiving device as described in the above. The optical receiving device according to claim 3, wherein the threshold setting unit generates a threshold sweep signal and outputs the generated signal to the variable threshold discriminator. Opto-electrical conversion means for converting an optical reception signal into an electric reception signal to generate an electric reception signal, soft decision means for outputting a multi-value identification digital signal which identifies the electric reception signal at a plurality of identification levels, A demultiplexing means for outputting a multi-level parallel digital signal obtained by expanding the digital signal in parallel to a speed capable of large-scale logic processing, and performing error correction based on the reliability information and the hard decision result contained in the multi-level parallel digital signal In the optical receiving device that performs the error-corrected signal as a received signal,
The soft decision means,
⁽² n -k) (n is a natural number, k is ^{0 ≦ k ≦ (2 n -1} ) to meet integer) the electrical received signal at the threshold identifies each the identified ^{(2 n} - k) a variable bit multi-valued discriminator for generating binary discrimination results;
Integer satisfying the output from the variable bit multi-level discriminator ⁽² n -k) number from the binary identification result ^{(2 n -k-j) (} j is ^{0 ≦ j ≦ (2 n -k} -1) A) selection circuit for generating binary identification results;
A first 1-bit delay circuit that generates a binary identification result obtained by delaying the (2 ⁿ −k−j) binary identification results output from the selection circuit by 1 bit;
A second 1-bit that further delays the (2 ⁿ -kj) binary identification results output by the first 1-bit delay circuit by 1 bit to generate a binary identification result delayed by a total of 2 bits A delay circuit;
One binary identification result selected from the (2 ⁿ -kj) binary identification results output from the first one-bit delay circuit, and an output from the second one-bit delay circuit A reliability information generation circuit for generating a hard decision result and a plurality of pieces of reliability information based on one binary identification result selected from the (2 ⁿ -kj) binary identification results obtained When,
An optical receiving device comprising: Sampling means for identifying the electrical reception signal with a plurality of identification phases and a plurality of identification thresholds,
The threshold setting means outputs threshold setting information to the soft decision means based on a spectrum analysis result obtained by spectrally analyzing received electric waveform information output from the sampling means via the demultiplexing means. The optical receiving device according to claim 1, wherein: Further provided is an application equivalent unit connected between the opto-electric equalization unit and the soft decision unit, for improving waveform distortion of an electric reception signal output from the opto-electric equalization unit,
The optical receiving device according to claim 6, wherein the threshold setting unit outputs a weight coefficient determined based on the spectrum analysis result to the application equivalence unit. Opto-electrical conversion means for converting an optical reception signal into an electric reception signal to generate an electric reception signal, soft decision means for outputting a multi-value identification digital signal which identifies the electric reception signal at a plurality of identification levels, A demultiplexing means for outputting a multi-level parallel digital signal obtained by expanding the digital signal in parallel to a speed capable of large-scale logic processing, and performing error correction based on the reliability information and the hard decision result contained in the multi-level parallel digital signal performed, an optical receiver for outputting a signal after error correction as the received signal, the soft decision unit, the light is identified in accordance with the data pattern of the received signal (2 n ^-k) (n is a natural number, k is (2 ⁿ −k−j) (j is an integer satisfying 0 ≦ j ≦ (2 ⁿ −k−1)) pieces from the multivalued identification results of 0 ≦ k ≦ (2 ⁿ −1) After selecting these selected multiples An optical receiving apparatus and generates a hard decision result and the reliability information for performing soft decision decoding the identification result.

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