JP2006165966A - Light-receiving device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light-receiving device for suppressing the deterioration of error correcting capability due to fluctuation of the input signal, and for applying soft decision result change, even when there is no region into which training bytes are inserted in a transmission frame. <P>SOLUTION: This light receiving device is provided with a front end 12 for converting an optical signal from an optical fiber 11 into an electrical signal, a multi-level identifier 13 for identifying a soft decision identification level, a binary encoder 14 for converting the output of the multi-level identifier 13 into reliability information of a q-bit binary signal, a weighting circuit 15 for rewriting the reliability information, a serial/parallel converting circuit 16, a block turbo decoding part 17 for executing q-bit soft decision decoding and a selector 18 for selecting the soft decision decoding result. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical receiver having an error correction function.

  Due to the rapid increase in demand for the Internet in recent years, technology development for high speed and large capacity is progressing in order to cope with the increasing traffic volume. In submarine cable systems responsible for international communications, etc., high-speed, large-capacity data is transmitted over long distances, so transmission quality deteriorates due to chromatic dispersion and bit errors are likely to occur. For this reason, in a submarine cable system, it is common to add FEC (Forward Error Correction) as a high-efficiency error correction code for transmission. As an error correction method of FEC, hard decision error correction in which received data is identified by a single classifier has been used. Recently, in order to improve error correction capability, received data is identified by a plurality of classifiers. Soft decision error correction using an identification threshold has been studied. Furthermore, the transmission speed of optical signals transmitted through an optical fiber has been increased year by year, so that waveform distortion due to a non-linear effect tends to occur, and the transmission quality further deteriorates due to the influence. At this time, the signal waveform has a phenomenon of interfering with adjacent bits due to waveform distortion. This is called pattern dependency. The conventional soft decision decoding apparatus is configured to include a changing unit that changes the soft decision result output from the soft decision unit in consideration of the preceding and following codes, so that the accuracy can be improved even when the reliability information of the soft decision result is low. Some are configured so that error correction can be performed well (see, for example, Patent Document 1).

JP 2003-78422 A

  In conventional optical receivers, the soft decision result change due to the pattern dependence of the input signal remains at the fixed setting at the time of start-up of the device, or the training byte is inserted into the transmission frame at the time of transmission beforehand. However, there is a problem in that it cannot be applied when there is no area for inserting a training byte in a transmission frame.

  The present invention has been made in order to solve the above-described problems. The object of the present invention is to suppress a decrease in error correction capability due to fluctuations in an input signal, and there is no region for inserting a training byte in a transmission frame. Even in such a case, an optical receiver capable of applying the soft decision result change is obtained.

  An optical receiving apparatus according to the present invention is an optical receiving apparatus having a soft decision error correction function, wherein the optical signal from the transmission path is converted into an electric signal, and the electric signal is identified by a plurality of threshold values. An identification means for identifying based on the value and outputting an identification result; an identification signal corresponding to the identification result; and an encoding means for outputting reliability information indicating the reliability of the identification signal; and the identification signal and reliability information The weighting means for outputting a plurality of types of data having different weights, and performing error correction on the plurality of types of output data from the weighting means in accordance with a predetermined decoding algorithm, thereby correcting the errors of the plurality of types of output data. Decoding means for outputting the data with the lowest error rate from the results as the optimum weighting is provided.

  The optical receiving apparatus according to the present invention can suppress a decrease in error correction capability due to fluctuations in an input signal, and has an effect that a soft decision result change can be applied even when there is no region for inserting a training byte in a transmission frame.

Embodiment 1 FIG.
An optical receiver according to Embodiment 1 of the present invention will be described with reference to FIG. FIG. 1 is a block diagram showing a configuration of an optical receiving apparatus according to Embodiment 1 of the present invention. In addition, in each figure, the same code | symbol shows the same or equivalent part.

  The optical receiving apparatus according to the first embodiment is based on FEC calculation results with different weights in an optical receiving apparatus having a soft decision error correction function in which an optical received signal is identified by a plurality of discriminators using a plurality of discrimination thresholds. By determining the optimum weighting, high-performance error correction is performed.

  In FIG. 1, the optical receiver according to the first embodiment includes a front end (photoelectric conversion means) 12 that converts an optical signal from an optical fiber 11 that is a transmission path into an electric signal, and soft decision at each identification level. A multi-level discriminator (identification unit) 13 for identifying, a binary encoder (encoding unit) 14 for converting the output of the multi-level discriminator 13 into reliability information of a q-bit binary signal, and rewriting of the reliability information A weighting circuit (weighting means) 15, a serial / parallel conversion circuit 16, a block turbo decoding unit (decoding means) 17 that performs q-bit soft decision decoding, and a selector 18 that selects a soft decision decoding result are provided. ing.

  Next, the operation of the optical receiving apparatus according to the first embodiment will be described with reference to the drawings.

  The optical signal input from the optical fiber 11 is input to the front end 12, and the front end 12 converts the optical signal into an electrical signal and outputs it to the multilevel discriminator 13.

  The multi-level discriminator 13 discriminates the electrical data input from the front end 12 as information data “0” if the electrical signal is lower than the threshold level based on the set threshold value. If it is higher, information data “1” is identified, and the identification result is output to the binary encoder 14. FIG. 1 shows the case of seven identification levels as an example.

  The binary encoder 14 indicates an identification signal as a result of performing hard decision identification based on the identification result output from the multi-level discriminator 13 for each electric signal, and the reliability of the hard decision identification signal. The reliability information is output to the weighting circuit 15 as a group. As shown in FIG. 1, when there are seven classifiers, the hard decision identification signal is 1 bit, and the reliability information indicating the reliability of the hard decision identification signal is 2 bits. For example, when there are three discriminators, the reliability information is 1 bit.

  When the weighting circuit 15 receives the q-bit binary signal input from the binary encoder 14, the weighting circuit 15 looks at the preceding and following codes and changes the reliability information of the soft decision result or the hard decision code. At this time, several types are output from those not weighted to those heavily weighted. For example, in FIG. 1, three types of data are output: those without weighting, those with weak weighting, and those with strong weighting.

  Hereinafter, the weighting will be briefly described. When q = 3, there are eight possible values of the q-bit binary signal output from the binary encoder 14: “111, 110, 101, 100,000, 001, 010, 011”. Here, the most significant bit is a hard decision code and the lower 2 bits are reliability information. When the weight change rule is applied by looking at the preceding and following codes, the reliability information of the corresponding bit is “01” or less and low (in the case of “001”, “000”, “100”, “101”) ), The reliability information of the corresponding bit or the hard decision code is changed. For example, when changing from “1” to “1”, “001” is changed to “000”, “000” is changed to “100”, “100” is changed to “101”, and “101” is changed to “110”. To do. Conversely, when changing from “0” in one step, “001” becomes “010”, “000” becomes “001”, “100” becomes “000”, and “101” becomes “100”. change.

  The serial / parallel conversion circuit 16 converts serial binary encoded data into parallel data to reduce the speed, and outputs the parallel data to the block turbo decoder 17. The reason why the speed is reduced is that the processing speed of the block turbo decoder 17 is low. Depending on the relationship between the transmission rate and the processing capability of the block turbo decoder 17, the serial / parallel converter circuit 16 may be unnecessary. In FIG. 1, the three types of data output from the weighting circuit 15 are converted into parallel data.

  The block turbo decoder 17 performs error correction according to a predetermined decoding algorithm. In FIG. 1, error correction is performed on the three types of data output from the serial / parallel conversion circuit 16 and output to the selector 18. In addition, a selection signal is output to the selector 18 assuming that the error correction result of the three types of data having the lowest error rate is the optimum weighting. Here, the error rate is obtained from the sum of the number corrected from “0” to “1” and the number corrected from “1” to “0”. The smaller the number of corrections in a certain time, the lower the error rate. It turns out that. The selector 18 selects and outputs the decoded data having the lowest error rate.

  As described above, in the first embodiment, when the reliability information or the hard decision code of the soft decision result is changed by looking at the preceding and following codes in the weighting circuit 15, there are several types from those not weighted to those heavily weighted Since the block turbo decoder 17 performs error correction, and the selector 18 selects the one having the lowest error rate as the optimum weighting, the state of the transmission path varies with time. Even in such a case, error correction can be performed with high accuracy.

  Note that the optical receiving apparatus according to the first embodiment may perform weighting processing after performing serial / parallel conversion as shown in FIG.

Embodiment 2. FIG.
An optical receiver according to Embodiment 2 of the present invention will be described with reference to FIG. FIG. 3 is a block diagram showing the configuration of the optical receiving apparatus according to Embodiment 2 of the present invention.

  The optical receiving apparatus according to the second embodiment is an optical receiving apparatus having a soft decision error correction function in which an optical received signal is identified by a plurality of discriminators using a plurality of discrimination thresholds. By determining the optimum weighting, high-performance error correction is performed.

  In FIG. 3, the optical receiving apparatus according to the second embodiment includes a front end (photoelectric conversion means) 12 that converts an optical signal from an optical fiber 11 serving as a transmission path into an electric signal, and soft decision at each identification level. A multi-level discriminator (identification unit) 13 for identifying, a binary encoder (encoding unit) 14 for converting the output of the multi-level discriminator 13 into reliability information of a q-bit binary signal, and rewriting of the reliability information A weighting circuit (weighting means) 15, a serial / parallel conversion circuit 16, a block turbo decoding unit (decoding means) 17 that performs q-bit soft decision decoding, and a weighting control circuit (weighting control means) 19 are provided. ing.

  However, the weighting circuit 15, the serial / parallel conversion circuit 16, and the block turbo decoding unit 17 are configured to output several types of data having different weights in FIG. 1, but in FIG. There are two types of outputs for control.

  Next, the operation of the optical receiver according to the second embodiment will be described with reference to the drawings.

  The operations of the optical fiber 11, the front end 12, the multilevel discriminator 13, and the binary encoder 14 are the same as those in the first embodiment. In the first embodiment, the weighting circuit 15, the serial / parallel conversion circuit 16, and the block turbo decoding unit 17 are configured to process several types of data with different weights. A circuit is required, resulting in an increase in circuit scale and power consumption. Therefore, in the second embodiment, a circuit for normal operation and two types of circuits for weighting control are configured to suppress an increase in circuit scale and power consumption.

  The weighting circuit 15 changes the weighting of the data from the binary encoder 14 and outputs it at regular intervals according to the timing signal from the weighting control circuit 19.

  In the serial / parallel conversion circuit 16, the weighting control circuit performs the same serial / parallel conversion as the normal operation circuit.

  The block turbo decoding unit 17 performs error correction on both the normal operation circuit and the weighting control circuit according to a predetermined decoding algorithm. The error correction results of the weighting control circuit are divided at regular time intervals that match the timings of the weighting circuit 15 and the weighting control circuit 19, and the one with the lowest error rate is the optimum weighting from the respective error correction results. To the weighting control circuit 19.

  The weighting control circuit 19 generates a timing signal for the weighting control circuit of the weighting circuit 15 and determines that the error correction result from the block turbo decoding unit 17 having the lowest error rate is the optimum weighting. Are output to the circuit for normal operation of the weighting circuit 15, and the circuit for normal operation of the weighting circuit 15 performs weighting with the weighting output from the weighting control circuit 19.

  As described above, in the second embodiment, when the reliability information of the soft decision result or the hard decision code is changed by looking at the preceding and succeeding codes in the weighting circuit 15, the circuit for normal operation and the circuit for weight control are changed. Two types of weighting control circuits are configured to change the weighting at fixed time intervals so that error correction can be performed accurately even when the transmission line condition changes over time. And an increase in circuit scale and power consumption can be suppressed.

  Note that the optical receiving apparatus according to the second embodiment may perform weighting processing after performing serial / parallel conversion first.

Embodiment 3 FIG.
An optical receiving apparatus according to Embodiment 3 of the present invention will be described with reference to FIG. FIG. 4 is a block diagram showing the configuration of the optical receiving apparatus according to Embodiment 3 of the present invention.

  The optical receiving apparatus according to the third embodiment is an optical receiving apparatus having a soft decision error correction function in which an optical received signal is identified by a plurality of discriminators using a plurality of discrimination thresholds. By determining the optimum weighting, high-performance error correction is performed.

  In FIG. 4, the optical receiver according to the third embodiment includes a front end (photoelectric conversion means) 12 that converts an optical signal from an optical fiber 11 serving as a transmission path into an electric signal, and soft decision at each identification level. A multi-level discriminator (identification unit) 13 for identifying, a binary encoder (encoding unit) 14 for converting the output of the multi-level discriminator 13 into reliability information of a q-bit binary signal, and rewriting of the reliability information A weighting circuit (weighting means) 15, a serial / parallel conversion circuit 16, a block turbo decoding unit (decoding means) 17 that performs q-bit soft decision decoding, and a weighting control circuit (weighting control means) 19 are provided. ing.

  The optical fiber 11, the front end 12, the multilevel discriminator 13, the binary encoder 14, the weighting circuit 15, the serial / parallel conversion circuit 16, the block turbo decoding unit 17, and the weighting control circuit 19 are the same as those in the second embodiment. It is a configuration. However, in the second embodiment, the weighting circuit 15, the serial / parallel conversion circuit 16, and the block turbo decoding unit 17 are configured to output two types of data, that is, an output for normal operation and an output for weighting control. However, in the third embodiment, one type is used.

  Next, the operation of the optical receiving apparatus according to the third embodiment will be described with reference to the drawings.

  The operations of the optical fiber 11, the front end 12, the multilevel discriminator 13, the binary encoder 14, and the weighting control circuit 19 are the same as those in the second embodiment. In the second embodiment, the weighting circuit 15, the serial / parallel conversion circuit 16, and the block turbo decoding unit 17 are configured by two types of circuits, a circuit for normal operation and a circuit for weighting control. Each circuit is required, resulting in an increase in circuit scale and power consumption. When applied to a location where the state of the transmission path does not vary with time, the circuit scale and power consumption are wasted. Therefore, in the third embodiment, two types of circuits, that is, a circuit for normal operation and a circuit for weight control are shared, and an increase in circuit scale and power consumption is suppressed.

  In the weighting circuit 15, first, according to the timing signal from the weighting control circuit 19, the weighting of the data from the binary encoder 14 is changed and output at regular intervals.

  The serial / parallel conversion circuit 16 performs serial / parallel conversion.

  The block turbo decoding unit 17 performs error correction according to a predetermined decoding algorithm. The error correction results are divided at regular time intervals that match the timings of the weighting circuit 15 and the weighting control circuit 19, and the weighting control circuit 19 assumes that the error correction result having the lowest error rate is the optimum weighting. Output.

  The weighting control circuit 19 generates a timing signal for the weighting circuit 15 and outputs to the weighting circuit 15 that the error having the lowest error rate from the error correction result from the block turbo decoding unit 17 is the optimum weighting. Then, the weighting circuit 15 continues the operation with the weighting fixed to the weighting output from the weighting control circuit 19.

  As described above, in the third embodiment, when changing the reliability information of the soft decision result or the hard decision code by looking at the preceding and following codes in the weighting circuit 15, first, the weight is changed at regular intervals to obtain the optimum. Since it is configured to operate after weighting is determined, error correction can be performed accurately when applied to locations where the state of the transmission path does not vary with time, and the circuit scale and power consumption are increased. Can be suppressed.

  Note that the optical receiving apparatus according to the third embodiment may perform the weighting process after performing serial / parallel conversion as shown in FIG.

Embodiment 4 FIG.
An optical receiving apparatus according to Embodiment 4 of the present invention will be described with reference to FIGS. FIG. 6 is a block diagram showing a configuration of an optical receiving apparatus according to Embodiment 4 of the present invention.

  The optical receiving apparatus according to the fourth embodiment has a pattern dependence from an FEC calculation result in an optical receiving apparatus having a soft decision error correction function in which an optical received signal is identified by a plurality of discriminators using a plurality of discrimination thresholds. Is determined, and an optimum threshold value arrangement is determined to perform high-performance error correction.

  In FIG. 6, the optical receiver according to the fourth embodiment includes a front end (photoelectric conversion means) 12 that converts an optical signal from an optical fiber 11 serving as a transmission path into an electrical signal, and soft decision at each identification level. A multilevel discriminator (identification unit) 13 for identifying, a binary encoder (encoding unit) 14 for converting the output of the multilevel discriminator 13 into reliability information of a q-bit binary signal, and a serial / parallel conversion circuit 16 , A block turbo decoding unit (decoding unit) 17 that performs q-bit soft decision decoding, and a threshold control circuit (threshold control unit) 20 are provided.

  The optical fiber 11, the front end 12, the multilevel discriminator 13, the binary encoder 14, the serial / parallel conversion circuit 16, and the block turbo decoding unit 17 have the same configuration as that of the third embodiment. However, the multi-level discriminator 13 is configured so that threshold control can be performed from the threshold control circuit 20.

  Next, the operation of the optical receiving apparatus according to the fourth embodiment will be described with reference to the drawings. FIG. 7 is a diagram for explaining an example of a waveform and threshold arrangement in the optical receiving apparatus according to Embodiment 4 of the present invention.

  The operations of the optical fiber 11, the front end 12, the binary encoder 14, the serial / parallel conversion circuit 16, and the block turbo decoding unit 17 are the same as those in the third embodiment. In the above-described third embodiment, the weighting circuit 15 is necessary, and this increases the circuit scale and power consumption. Therefore, in the fourth embodiment, the weighting circuit 15 is not required, and the increase in circuit scale and power consumption is suppressed.

  The threshold control circuit 20 inputs an error correction result from the block turbo decoding unit 17 and determines the strength of pattern dependence. When the pattern dependency is strong, many bit errors occur. Therefore, it is determined that the pattern dependency is weak when the error rate is small, and it is determined that the pattern dependency is strong when the error rate is large.

  An example of a waveform depending on the intensity of pattern dependence is expressed as shown in FIG. When the pattern dependency is weak as shown in FIG. 7A, the reliability information is distributed in a well-balanced manner by increasing the threshold interval setting. When the pattern dependence is strong as shown in FIG. 7B, the reliability information is distributed in a balanced manner by narrowing the threshold interval setting. The threshold of the multi-level discriminator 13 is set according to the pattern dependence determined by the threshold control circuit 20.

  As described above, in the fourth embodiment, the weighting is not changed, the pattern dependency is determined from the FEC calculation result, and the optimum threshold arrangement is determined. An increase in circuit scale and power consumption can be suppressed.

  The optical receiver according to the present invention is useful for application to a digital optical transmission system such as a submarine cable system for transmitting high-speed and large-capacity data over a long distance, but the application is not limited thereto. For example, the present invention can be applied to an external storage device using an optical disk such as a CD (compact disk) or a DVD (digital video disk) as a recording medium.

  In addition, the optical receiving apparatus according to the present invention is not limited to one using block turbo as a decoding algorithm as long as it uses a soft decision.

It is a block diagram which shows the structure of the optical receiver which concerns on Embodiment 1 of this invention. It is a block diagram which shows another structure of the optical receiver which concerns on Embodiment 1 of this invention. It is a block diagram which shows the structure of the optical receiver which concerns on Embodiment 2 of this invention. It is a block diagram which shows the structure of the optical receiver which concerns on Embodiment 3 of this invention. It is a block diagram which shows another structure of the optical receiver which concerns on Embodiment 3 of this invention. It is a block diagram which shows the structure of the optical receiver which concerns on Embodiment 4 of this invention. It is a figure for demonstrating an example of a waveform and threshold value arrangement | positioning in the optical receiver which concerns on Embodiment 4 of this invention.

Explanation of symbols

  11 optical fiber, 12 front end, 13 multi-level discriminator, 14 binary encoder, 15 weighting circuit, 16 serial / parallel conversion circuit, 17 block turbo decoding unit, 18 selector, 19 weighting control circuit, 20 threshold control circuit.

Claims (4)

An optical receiver having a soft decision error correction function,
Photoelectric conversion means for converting an optical signal from the transmission path into an electrical signal;
Identifying means for identifying the electrical signal based on a plurality of identification thresholds and outputting an identification result;
An encoding means for outputting an identification signal corresponding to the identification result and reliability information indicating the reliability of the identification signal;
Weighting means for outputting a plurality of types of data having different weights when changing the identification signal and the reliability information;
Decoding means for performing error correction on each of a plurality of types of output data from the weighting means according to a predetermined decoding algorithm, and outputting data having the lowest error rate from the error correction results of the plurality of types of output data as optimal weighting An optical receiver characterized by comprising: An optical receiver having a soft decision error correction function,
Photoelectric conversion means for converting an optical signal from the transmission path into an electrical signal;
Identifying means for identifying the electrical signal based on a plurality of identification thresholds and outputting an identification result;
An encoding means for outputting an identification signal corresponding to the identification result and reliability information indicating the reliability of the identification signal;
Weighting means for outputting two types of data for normal operation and weighting control when changing the identification signal and reliability information;
The two types of output data from the weighting means are respectively subjected to error correction in accordance with a predetermined decoding algorithm, and the data having the lowest error rate from the error correction results for each predetermined time of the output data for weighting control are weighted optimally. Decoding means for outputting as being,
A weighting control means for outputting a predetermined timing signal and outputting an optimum weighting having the lowest error rate from the decoding means;
The weighting means weights the data for normal operation with the optimum weighting, and outputs the weighting control data by changing the weighting at regular intervals according to the predetermined timing signal. An optical receiver. An optical receiver having a soft decision error correction function,
Photoelectric conversion means for converting an optical signal from the transmission path into an electrical signal;
Identifying means for identifying the electrical signal based on a plurality of identification thresholds and outputting an identification result;
An encoding means for outputting an identification signal corresponding to the identification result and reliability information indicating the reliability of the identification signal;
When changing the identification signal and the reliability information, first, weighting means for changing the weighting at regular intervals according to a predetermined timing signal and outputting data,
Decoding means for performing error correction on the output data from the weighting means according to a predetermined decoding algorithm, and outputting the data with the lowest error rate from the error correction results for each predetermined time of the output data as optimum weighting; ,
First, the predetermined timing signal is output, and weighting control means for outputting the optimum weighting with the lowest error rate from the decoding means,
The weighting means performs weighting with the optimum weighting and outputs data when the optimum weighting is outputted. An optical receiver having a soft decision error correction function,
Photoelectric conversion means for converting an optical signal from the transmission path into an electrical signal;
Identifying means for identifying the electrical signal based on a plurality of identification thresholds and outputting an identification result;
An encoding means for outputting an identification signal corresponding to the identification result and reliability information indicating the reliability of the identification signal;
Decoding means for performing error correction according to a predetermined decoding algorithm for the output data from the encoding means, and outputting an error correction result for each predetermined time of the output data;
Threshold value control means for determining the strength of pattern dependence from the error rate based on the error correction result, and setting the identification threshold based on the strength of the pattern dependence. Receiver device.

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