JP2014064174A - Error correction system and error correction method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an error correction system and an error correction method that hold a FAS structure in an overhead while applying interleaving on a transmission line side, and reduce latency or improve burst tolerance.SOLUTION: A first transmitting side interleaver applies interleaving to m transmission frames (m is a positive integer). A transmitting side error correction encoding section performs error correction encoding on an output of the first transmitting side interleaver. A second transmitting side interleaver applies interleaving to n transmission frames (n is a positive integer different from m) output from the transmitting side error correction encoding section and cooperates with the first transmitting side interleaver to recover a FAS structure in an overhead.

Description

  The present invention relates to an error correction system and an error correction method applied to, for example, an optical communication system.

  In recent ultrahigh-speed optical communications, the transmission rate per wave is increased by applying a multi-level modulation method or a polarization multiplexing method. However, by applying the multi-level modulation method or the polarization multiplexing method, there arises a problem that the transmission performance is deteriorated or the transmission distance is shortened due to the influence of the noise tolerance reduction and the transmission deterioration factor.

  As a method for solving such a problem, an error correction technique for correcting an error after transmission by adding a redundant sequence to an information sequence has been actively studied. In the error correction technique, the correctable number is determined according to the information sequence length to be error correction encoded and the redundant sequence length added by the error correction encoding. Therefore, when a burst error occurs, there is a possibility that the error correction is disabled.

  Therefore, as a method for improving burst tolerance, there is a method of applying interleaving by an interleaver (interleave circuit) to an encoded sequence after error correction coding. Here, interleaving refers to switching the order of signal sequences input to the interleaver and outputting the replaced signal sequence.

  In other words, by applying interleaving to a transmission sequence having an encoded sequence length equal to or greater than the combined sequence length of an information sequence and a redundant sequence, burst errors are distributed to a plurality of encoded sequences, and errors within one encoded sequence are detected. It is possible to reduce the number, and it is possible to prevent the error correction from occurring.

  Note that burst tolerance improves as the number of encoded sequences to be interleaved increases (the depth of the interleaver increases). On the other hand, as the number of encoded sequences increases, the decoding start timing is delayed, so that the latency in the interleaver increases. For this reason, an interleaver design that takes into account the balance between burst strength and latency is required.

  Here, in the current optical communication, an optical channel transmission unit (OTU: Optical-Channel Transport Unit) frame structure is adopted as a frame format on the transmission line side. In the OTU frame, an overhead holding various setting information, a payload including an information sequence, and a parity that is a redundant sequence by error correction coding are defined as a predetermined format.

  Further, the receiver performs error correction coding and decoding by synchronizing the OTU frame using a frame alignment signal (FAS) within the overhead. Therefore, an error correction system including an interleaver that can maintain the FAS structure while applying interleaving is required on the transmission line side.

  Therefore, an interleaver is arranged before and after the error correction coding unit, and the preceding interleaver converts the OTU frame format into a format for error correction coding and cooperates with the subsequent interleaver for the purpose of improving burst tolerance. Thus, an error correction system for restoring the OTU format on the transmission line side has been proposed (see, for example, Patent Document 1).

  Specifically, the error correction system of Patent Document 1 includes a transmitter and a receiver that are connected to each other via a transmission path. The transmitter interleaves n number of OTU frames together (depth n), a previous stage interleaver, a transmission side encoder that performs error correction coding, and interleaves n number of OTU frames together (depth n). Interleaver.

  Further, the optical signal transmitted from the transmitter passes through the transmission path and is received by the receiver. The receiver interleaves n OTU frames together (depth n), a preceding interleaver, a receiving decoder that performs error correction decoding, and interleaves n OTU frames together (depth n). Interleaver.

  In such an error correction system, as interleaving processing at the transmitter, first, a signal having an OTU frame structure is input to the preceding interleaver every nOTU frames. Subsequently, the signals for nOTU frames are converted into a format for encoding by the transmission side encoder and output.

  Next, the post-conversion format encoded by the transmission-side encoder is deinterleaved so as to restore the OTU frame format in a subsequent interleaver, and is output as an encoded OTU frame. Thereby, the overhead of the OTU frame is restored, and an output signal to which interleaving is applied is obtained while maintaining the FAS structure in the overhead.

  As described above, in the conventional error correction system, the overhead of the OTU frame, that is, the FAS structure is maintained by applying the interleaver having the same depth (the same number of OTU frames) as the front-stage interleaver and the rear-stage interleaver in the transmitter. Was. In the receiver, decoding is performed by the reverse procedure of the above-described encoding.

  At this time, since the interleaver stores n OTU frames and outputs them after interleaving, the deeper the interleaver, the greater the latency at the interleaver. Also, the latency is doubled by applying two interleavers of the same size.

JP 2011-146932 A

However, the prior art has the following problems.
In the error correction system of Patent Document 1, as described above, in order to maintain the FAS structure in the overhead of the OTU frame, it is necessary to apply two interleavers having the same size, thereby doubling the latency.

  Therefore, when a deep interleaver is applied to improve burst strength, the effect of the doubled latency increases, and the depth of the interleaver is reduced to reduce the influence of the latency. When the depth is shallow, there is a problem that the influence due to the decrease in burst strength increases.

  The present invention has been made to solve the above-described problems, and while maintaining the FAS structure in the overhead while applying interleaving on the transmission line side, the latency is reduced or the burst strength is improved. An object of the present invention is to obtain an error correction system and an error correction method that can be performed.

  An error correction system according to the present invention is an optical communication system in which a transmitter and a receiver are connected to each other via a transmission line and transmit a transmission frame formed by adding an overhead and an error correction code to an information sequence. An error correction system that performs error correction coding and decoding, wherein a transmitter includes a first transmission side interleaver that applies interleaving to m (m is a positive integer) transmission frames, and a first transmission side interleaver. Transmission-side error correction coding unit that performs error-correction coding on the output of, and n (n is a positive integer different from m) transmission frames output from the transmission-side error correction coding unit A second transmission side interleaver that applies interleaving and cooperates with the first transmission side interleaver to restore the FAS structure in the overhead, and the receiver is input from the transmission path. Further, a first receiving side interleaver that applies interleaving to n transmission frames, a receiving side error correction decoding unit that performs error correction decoding on the output of the first receiving side interleaver, and a receiving side error correction decoding unit And a second receiving-side interleaver that applies interleaving to the m transmission frames that are output.

  The error correction method according to the present invention is executed by an error correction system that performs error correction coding and decoding in an optical communication system that transmits a transmission frame formed by adding overhead and an error correction code to an information sequence. A first transmitting side interleaving step for applying interleaving to m (m is a positive integer) number of transmission frames, and error correction coding for the output of the first transmitting side interleaving step And applying interleaving to n (n is a positive integer different from m) transmission frames output by the transmission-side error correction coding step and the transmission-side error correction coding step. Second transmission side interleaving step for restoring the FAS structure in the overhead in cooperation with the interleaving step, and input from the transmission line A first reception side interleaving step for applying interleaving to the n transmission frames, a reception side error correction decoding step for performing error correction decoding on the output of the first reception side interleaving step, and a reception side error correction. And a second receiving-side interleaving step for applying interleaving to the m transmission frames output by the decoding step.

According to the error correction system and the error correction method of the present invention, the first transmission side interleaver (interleaving step) applies interleaving to m (m is a positive integer) number of transmission frames, and transmits side error correction. The encoding unit (step) performs error correction encoding on the output of the first transmission side interleaver (interleaving step), and the second transmission side interleaver (interleaving step) outputs from the transmission side error correction encoding unit (step). The interleaving is applied to n (n is a positive integer different from m) transmission frames, and the FAS structure in the overhead is restored in cooperation with the first transmitting side interleaver.
Therefore, on the transmission line side, while maintaining the FAS structure in the overhead while applying the interleaving, the latency can be reduced or the burst strength can be improved.

It is a block block diagram which shows the error correction system which concerns on Embodiment 1 of this invention. It is explanatory drawing which shows the function of the error correction system which concerns on Embodiment 1 of this invention. It is a block block diagram which shows the error correction system which concerns on Embodiment 2 of this invention.

  Hereinafter, preferred embodiments of an error correction system and an error correction method according to the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts will be described with the same reference numerals.

Embodiment 1 FIG.
1 is a block diagram showing an error correction system according to Embodiment 1 of the present invention. Here, an error correction system using a single code when different interleaver sizes are employed is shown.

  In FIG. 1, this error correction system includes a transmitter 20 and a receiver 30 connected to each other via a transmission line 10. The transmitter 20 includes a client port 21, a first transmission side interleaver 22, an error correction (FEC: Forward Error Correlation) encoder (transmission side error correction coding unit) 23, a second transmission side interleaver 24, and a line port 25. ing.

  The client port 21 is a client signal input or communication data generation circuit. The first transmission side interleaver 22 interleaves m OTU frames (transmission frames) together (depths m and m are positive integers).

  The FEC encoder 23 performs error correction coding. The second transmitting side interleaver 24 interleaves n OTU frames together (depth n, n is a positive integer different from m). The Line port 25 converts to a format for sending to the transmission line 10.

  Further, the optical signal sent from the transmitter 20 passes through the transmission line 10 and is received by the receiver 30. The receiver 30 includes a line port 31, a first receiving side interleaver 32, an FEC decoder (receiving side error correction decoding unit) 33, a second receiving side interleaver 34, and a client port 35.

  The Line port 31 receives a signal input from the transmission line 10 and converts it into a predetermined format. The first receiving side interleaver 32 interleaves n OTU frames together (depth n). The FEC encoder 33 performs error correction decoding. The second receiving side interleaver 34 interleaves m OTU frames together (depth m). The client port 35 is a circuit for receiving output or communication data to the client.

  In such an error correction system, as interleaving processing at the transmitter, first, a signal 1 having an OTU frame structure output from the Client port 21 is input to the first transmitting side interleaver 22 for each mOTU frame. Subsequently, the signal for the mOTU frame is converted into the format 2 for error correction coding by the FEC encoder 23 and output.

  Next, the converted format 2 that has been error correction encoded by the FEC encoder 23 is input to the second transmitting interleaver 24 every nOTU frames, interleaved, and output as an encoded OTU frame 3 Is done.

  Here, since the depth of the first transmitting interleaver 22 and the depth of the second transmitting interleaver 24 are different from each other, in the second transmitting interleaver 24, the overhead (OH), payload (pay load), and parity in the OTU frame. All of (parity) cannot be completely restored.

  However, by selecting a combination of the first transmission side interleaver 22 and the second transmission side interleaver 24 (values of m and n, the configuration of the interleaver, etc.), interleaving in the second transmission side interleaver 24 results in an FAS structure in overhead. Can be restored.

  In the receiver 30, decoding is performed by the reverse procedure of the above-described encoding. That is, after the signals are synchronized using the FAS structure, the first receiving side interleaver 32 rearranges the signals into the decoding format (format at the time of encoding).

  Subsequently, after error correction decoding is performed by the FEC decoder 33, the OTU frame format is restored by the second receiving side interleaver 34. Here, the first transmission side interleaver 22 and the second reception side interleaver 34 are in a relationship between an interleaver and a deinterleaver, and the second transmission side interleaver 24 and the first reception side interleaver 32 are an interleaver and a deinterleaver. Become a relationship.

  Further, the depth (size) m of the first transmission side interleaver 22 and the depth (size) n of the second transmission side interleaver 24 are set to m <n, thereby improving the burst strength on the transmission line 10 side. In addition, the latency can be made smaller than that of Patent Document 1 using two interleavers of the same size.

  The depth (size) m of the first transmitting interleaver 22 and the depth (size) n of the second transmitting interleaver 24 are as long as these interleavers can cooperate to restore the FAS structure in the overhead. Takes an arbitrary value.

  FIG. 2 is an explanatory diagram showing functions of the error correction system according to Embodiment 1 of the present invention. Here, a construction example of the FAS structure by the first transmission side interleaver 22 and the second transmission side interleaver 24 is shown. As an example, a case will be described in which the sizes of the first transmission side interleaver 22 and the second transmission side interleaver 24 are m = 1 and n = 4, respectively.

  In FIG. 2, an OTU frame 41 for one OTU includes a FAS structure 42 in the overhead. The OTU frame 41 is rearranged into the error correction frame format 43 (FEC frame) in the first transmission side interleaver 22 (m = 1 OTU interleaver).

  The OTU frame 41 corresponds to an OTU frame for one OTU of the signal 1 having the OTU frame structure shown in FIG. 1, and the error correction frame format 43 is the format 2 for error correction encoding shown in FIG. Corresponds to a part of

  Here, as an example, it is assumed that the OTU frames 41 are sampled in the direction of the arrow in the drawing (from top to bottom, from left to right) and arranged in order from the left of the FEC frame. Thereafter, the parity bit sequence generated by the FEC encoder 23 is overwritten in the parity bit area.

  Subsequently, 4 (= n) FEC frames for one OTU frame output from the FEC encoder 23 are collected, and interleaving is performed in the second transmission side interleaver 24. Here, it is assumed that the four FEC frames are OTU # 1 44, OTU # 2 45, OTU # 3 46, and OTU # 4 47, respectively.

  Further, regarding the bit sequence 48 of the bits in the FAS block, the bits in the FAS of OTU # 1 44 are represented as index 1-1, index 1-2, index 1-3, and index 1-4, and The bits in the FAS are represented as index 2-1, index 2-2, index 2-3, and index 2-4.

  Further, regarding the bit sequence 48 of the bits in the FAS block, the bits in the FAS of OTU # 3 46 are expressed as index 3-1, index 3-2, index 3-3, and index 3-4, and OTU # 4 47 The bits in the FAS are represented as index 4-1, index 4-2, index 4-3, and index 4-4.

  At this time, the FAS sequence has the same configuration in each FEC frame (OTU # 1 44, OTU # 2 45, OTU # 3 46, and OTU # 4 47). Therefore, the indexes 1-1, 2-1, 3-1, and 4-1 have the same value, the indexes 1-2, 2-2, 3-2, and 4-2 have the same value, and the index 1 -3, 2-3, 3-3 and 4-3 have the same value, and the indexes 1-4, 2-4, 3-4 and 4-4 have the same value.

  Here, in the second transmission side interleaver 24, one row in the row direction and one in the column direction from the first bit of each FEC frame (OTU # 1 44, OTU # 2 45, OTU # 3 46, and OTU # 4 47). Sampling is performed while shifting column by column, and the values are rearranged (see sampling example 49 at the start of OTU # 1).

  Therefore, at the OTU # 1 start, the indexes 1-1, 2-2, 3-3, 4-4 are sampled. Similarly, at the OTU # 2 start, the indexes 2-1, 3-2, 4-3, 1-4, sampled at OTU # 3 start, sampled at indexes 3-1, 4-2, 1-3, 2-4, and at OTU # 4 start, indexed 4-1, 1-2, 2- 3, 3-4.

  That is, the FAS structure is maintained although the bit sequences are rearranged in the FEC frames for 4 OTU frames by the rearrangement by the second transmission side interleaver 24 (see the FEC frame 50 after the interleaving).

  Thereafter, the second transmitting side interleaver 24 converts each OTU frame unit into the OTU frame format 51, so that the burst strength is maintained while maintaining the FAS structure 52 even when the interleaver having a different depth is used. Can be improved. The OTU frame format 51 corresponds to one of the encoded OTU frames 3 shown in FIG.

As described above, according to the first embodiment, the first transmission-side interleaver applies interleaving to m (m is a positive integer) transmission frames, and the transmission-side error correction coding unit Error correction coding is performed on the output of one transmission side interleaver, and the second transmission side interleaver outputs n (n is a positive integer different from m) transmission frames output from the transmission side error correction coding unit. On the other hand, interleaving is applied, and the FAS structure in the overhead is restored in cooperation with the first transmitting side interleaver.
Therefore, on the transmission line side, while maintaining the FAS structure in the overhead while applying the interleaving, the latency can be reduced or the burst strength can be improved.
This makes it possible to improve the latency in the current error correction system, or to increase the interleaver size in order to improve the burst tolerance, and gives flexibility to transceiver design.

Embodiment 2. FIG.
FIG. 3 is a block diagram showing an error correction system according to Embodiment 2 of the present invention. Here, an error correction system using a concatenated code when different interleaver sizes are employed is shown.

  In FIG. 3, this error correction system includes a transmitter 20 </ b> A and a receiver 30 </ b> A that are connected to each other via a transmission line 10. The transmitter 20A includes a client port 21, an outer FEC encoder (outer code error correction coding unit) 26, a first transmission side interleaver 22A, an inner FEC encoder (transmission side error correction coding unit) 27, and a second transmission side interleaver 24A. And a Line port 25.

  The Outer FEC encoder 26 performs error correction coding as an outer code. The first transmitting-side interleaver 22A interleaves m OTU frames together (depths m and m are positive integers). The Inner FEC encoder 27 performs error correction coding as an inner code. The second transmitting-side interleaver 24A interleaves n OTU frames together (depth n, n is a positive integer different from m).

  Further, the optical signal transmitted from the transmitter 20A passes through the transmission line 10 and is received by the receiver 30A. The receiver 30A includes a line port 31, a first receiving side interleaver 32A, an inner FEC decoder (receiving side error correction decoding unit) 36, a second receiving side interleaver 34A, an Outer FEC decoder (outer code error correction decoding unit) 37, and a client. A port 35 is provided.

  The first receiving interleaver 32A interleaves the n OTU frames together (depth n). The Inner FEC encoder 36 performs error correction decoding as an inner code. The second receiving side interleaver 34A interleaves m OTU frames together (depth m). The Outer FEC encoder 37 performs error correction decoding as an outer code.

  Other configurations are the same as those shown in FIG. In addition, as described above, the FAS structure and the configuration of the OTU frame are realized by cooperation of interleavers having different sizes.

  Here, the depth (size) m of the first transmission side interleaver 22A and the depth (size) n of the second transmission side interleaver 24A are such that when the occurrence rate of burst errors in the transmission line 10 is low, m> By setting n, it is possible to improve the burst tolerance of the outer code and to have a strong advantage against the residual error in the inner code.

  On the other hand, the depth (size) m of the first transmission side interleaver 22A and the depth (size) n of the second transmission side interleaver 24A are set to m <n. It can be configured to be resistant. As described above, similarly to the first embodiment, the latency can be made smaller than that of Patent Document 1 using two interleavers having the same size.

  The depth (size) m of the first transmitting interleaver 22A and the depth (size) n of the second transmitting interleaver 24A are as long as these interleavers can cooperate to restore the FAS structure in the overhead. Takes an arbitrary value.

As described above, according to the second embodiment, as in the first embodiment, on the transmission line side, while maintaining the FAS structure in the overhead while applying the interleaving, the latency is reduced or the burst strength is increased. Can be improved.
This makes it possible to improve the latency in the current error correction system, or to increase the interleaver size in order to improve the burst tolerance, and gives flexibility to transceiver design.

  DESCRIPTION OF SYMBOLS 10 Transmission path, 20 and 20A transmitter, 21 Client port, 22, 22A 1st transmission side interleaver, 23 FEC encoder (transmission side error correction encoding part), 24, 24A 2nd transmission side interleaver, 25 Line port, 26 Outer FEC encoder (outer code error correction encoding unit), 27 Inner FEC encoder (transmission side error correction encoding unit), 30, 30A receiver, 31 Client port, 32, 32A first reception side interleaver, 33 FEC encoder ( Receiving side error correction coding unit), 34, 34A second receiving side interleaver, 35 Line port, 36 Outer FEC encoder (receiving side error correction coding unit), 37 Inner FEC encoder (outer code error correction decoding unit).

Claims (6)

Errors in error correction coding and decoding in an optical communication system in which a transmitter and a receiver are connected to each other via a transmission line and transmit a transmission frame formed by adding overhead and an error correction code to an information sequence. A correction system,
The transmitter is
a first transmitting-side interleaver that applies interleaving to m (m is a positive integer) transmission frames;
A transmission-side error correction encoding unit that performs error correction encoding on the output of the first transmission-side interleaver;
Interleaving is applied to n (n is a positive integer different from m) number of transmission frames output from the transmission side error correction coding unit, and the overhead is coordinated with the first transmission side interleaver. A second sender interleaver for restoring the FAS structure in
The receiver is
A first receiving interleaver that applies interleaving to the n transmission frames input from the transmission path;
A receiving-side error correction decoding unit that performs error-correcting decoding on the output of the first receiving-side interleaver;
An error correction system comprising: a second reception-side interleaver that applies interleaving to the m transmission frames output from the reception-side error correction decoding unit. The error correction system is an error correction system that performs error correction encoding and decoding with a single code, and
2. The error correction system according to claim 1, wherein a size m of the first transmitting interleaver and a size n of the second transmitting interleaver are m <n. The error correction system is an error correction system that performs error correction encoding and decoding with a concatenated code,
The transmitter further includes an outer code error correction encoding unit that performs error correction encoding with an outer code in a stage preceding the first transmission side interleaver,
The transmission-side error correction encoding unit performs error correction encoding with an inner code,
The receiver further includes an outer code error correction decoding unit that performs error correction decoding with an outer code after the second receiving side interleaver,
The receiving-side error correction encoding unit performs error correction decoding using an inner code,
The error correction system according to claim 1. 4. The error correction system according to claim 3, wherein a size m of the first transmitting interleaver and a size n of the second transmitting interleaver satisfy m> n. The error correction system according to claim 3, wherein a size m of the first transmission side interleaver and a size n of the second transmission side interleaver satisfy m <n. In an optical communication system for transmitting a transmission frame formed by adding overhead and an error correction code to an information sequence, an error correction method executed by an error correction system that performs error correction encoding and decoding,
a first transmitting-side interleaving step of applying interleaving to m (m is a positive integer) transmission frames;
A transmission side error correction coding step for performing error correction coding on the output of the first transmission side interleaving step;
Interleaving is applied to n (n is a positive integer different from m) output frames output by the transmitting side error correction encoding step, and in cooperation with the first transmitting side interleaving step, A second sender interleaving step to restore the FAS structure in overhead;
A first receiving side interleaving step for applying interleaving to n transmission frames input from a transmission path;
A receiving side error correction coding step for performing error correction decoding on the output of the first receiving side interleaving step;
And a second receiving side interleaving step for applying interleaving to the m transmission frames output by the receiving side error correction coding step.

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