JP2012186521A - Optical communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical communication system having realized high-quality, high-speed, and large-capacity communication in an optical communication system using consecutive optical transmission frames such as OTN frames.SOLUTION: An optical communication system comprises a plurality of optical transmission devices 1, 2 connected to each other via a communication path 3, and performs communication using the number of frames about which m redundant frames are added to n transmission frames as a codeword of one symbol. Each of the plurality of optical transmission devices 1, 2 comprises the OTUk framer 10. The OTUk framer 10 performs disappearance correction corresponding to a burst error by use of an error correction code using the n+m frame number as a symbol number.

Description

  The present invention relates to an optical communication system using a continuous optical transmission frame such as an OTN (Optical Transport Network) frame.

  Conventionally, in an optical communication system, ITU-T (International Telecommunication Union Telecommunication Standardization Sector) Recommendation G. A technique for realizing long-distance and large-capacity transmission by applying an error correction code to the OTN frame shown in 709 to compensate for signal quality degradation due to optical SNR degradation has been proposed (for example, see Non-Patent Document 1). ).

  In addition, techniques for applying multi-level modulation such as phase modulation and digital coherent light reception processing as optical communication speeds up have been proposed (see, for example, Non-Patent Document 2).

  On the other hand, in wireless communication, by adding a redundant packet to a transmission information packet when performing packet communication, even if there is a packet that is not recognized due to a burst error on the receiving side, the lost packet An erasure correction technique for decoding the image is applied (see, for example, Patent Document 1).

  However, an example in which the erasure correction technique described in Patent Document 1 is applied to optical communication has not been proposed so far, and ITU-T Recommendation G. In FEC (Forward Error Correction) applied to an OTN frame such as 709, it has not been possible to cope with a large burst error such as several frames.

  In recent years, for example, the inter-satellite optical communication field in which inter-satellite communication is performed with light has been spotlighted. In addition, since it is expected that the optical communication business will be expanded to fields where large burst errors must be handled, it is necessary to make erasure correction applicable to optical communication.

JP 2009-55603 A

ITU-T Recommendation G. 709 “Cycle Slip Probability in 100G PM-QPSK Systems”, OWE2, OFC / NFOFC 2010.

  In conventional optical communication systems, signal quality degradation due to polarization mode dispersion and nonlinear optical effects can no longer be ignored as the wavelength multiplexing communication systems increase in number and transmission speed. Since a large burst error occurs due to these signal degradations, for example, there is a problem that the error correction code described in Non-Patent Document 1 may not be able to be corrected.

  Further, for example, although the multilevel signal transmission is progressing due to the advancement of the digital coherent optical receiving technology described in Non-Patent Document 2, the phase displacement modulation (PSK) is caused by the phase slip caused by the phase estimation of the multilevel signal. When the differential encoding applied to the above is not performed, a large burst error occurs. Especially in the optical space communication system between the satellite and the ground, the transmission quality varies significantly depending on the atmospheric conditions. As a result, there is a problem that a burst error occurs.

  In addition, the conventional ITU-T Recommendation G. In the OTN frame described in 709, FEC is applied to perform error correction, but there is a problem that FEC cannot cope with a large burst error ranging from several thousand bits to several frames.

  Further, in the technique described in Patent Document 1, for example, erasure correction is realized by adding redundancy to packet data using a low-density parity check (LDPC) code. There is a problem that it cannot be realized in an OTN frame that transmits a continuous signal.

  The present invention has been made to solve the above-described problems, and is an optical communication system that uses a continuous optical transmission frame such as an OTN frame, and realizes high-quality, high-speed and large-capacity communication. An object is to obtain a communication system.

  An optical communication system according to the present invention includes a plurality of optical transmission apparatuses connected via a communication path, and performs communication using a transmission frame between the plurality of optical transmission apparatuses. In an optical communication system that performs communication using the number of frames with m redundant frames added as one symbol codeword, each of a plurality of optical transmission apparatuses includes an OTUk framer, and the OTUk framer has n + m number of frames. By using an error correction code having the number of symbols, erasure correction corresponding to a burst error is performed.

  According to the present invention, it is possible to realize high-quality, high-speed and large-capacity communication by applying a erasure correction technique and correcting a large burst error.

1 is a block configuration diagram schematically showing an optical communication system according to Embodiment 1 of the present invention. FIG. It is a block block diagram which shows the detailed function of the optical transmission apparatus in FIG. It is explanatory drawing which shows the operation | movement by Embodiment 1 of this invention. It is explanatory drawing which shows the structure of the OTUk frame to which Embodiment 1 of this invention is applied. It is explanatory drawing which expands and shows the OH part in FIG. It is explanatory drawing which shows the frame number display operation | movement by Embodiment 2 of this invention. It is explanatory drawing which shows concretely the structure of FASOH to which Embodiment 3 of this invention is applied.

Embodiment 1 FIG.
1 is a block diagram schematically showing an optical communication system according to Embodiment 1 of the present invention.
In FIG. 1, the optical communication system is a communication such as optical transmission devices 1 and 2 that transmit and receive a client signal Sc and an optical fiber that is inserted between the optical transmission device 1 and the optical transmission device 2 and transmits an optical signal So. Road 3 is provided.

  The optical transmission apparatuses 1 and 2 perform, for example, mapping processing and demapping processing between the client signal Sc and the optical transmission frame, error correction coding processing, and decoding as mutual conversion processing between the client signal Sc and the optical signal So. Processing, electrical / optical (E / O) conversion processing and optical / electrical (O / E) conversion processing, and bidirectional communication between the optical transmission apparatuses 1 and 2 via the communication path 3 Do.

FIG. 2 is a block diagram showing the detailed functions of the optical transmission apparatuses 1 and 2 in FIG.
In FIG. 2, the configuration of one optical transmission device 1 in FIG. 1 is representatively shown, but the configuration of the other optical transmission device 2 is also the same as that in FIG. It is only.

  In FIG. 2, the optical transmission device 1 includes an OTUk (Optical channel Transport Unit-k) framer 10 arranged on the transmission / reception side of the client signal Sc and an optical transceiver 20 arranged on the transmission / reception side of the optical signal So. ing.

  The OTUk framer 10 transmits the client signal Sc as an SFI (Serdes Framer Interface) signal Sf to the other optical transmission device 2 and the SFI signal Sf from the optical transmission device 2 as the client signal Sc. And an OTUk frame termination unit 14 for reception.

  The OTUk frame generation unit 11 includes an erasure correction encoding unit 12 and an error correction encoding unit 13, and maps the client signal Sc (transmission signal) to the OTUk frame and adds information necessary for frame synchronization and maintenance control. Then, an optical transmission frame is generated and transmitted to the optical transceiver 20 as the SFI signal Sf.

  The OTUk frame termination unit 14 includes an error correction decoding unit 15 and an erasure correction decoding unit 16, and is necessary for frame synchronization and maintenance control with respect to the SFI signal Sf received from the optical transceiver 2 by the optical transceiver 20. Such information is terminated, and the client signal Sc (received signal) is demapped from the OTUk frame and output.

At this time, the error correction decoding unit 15 in the OTUk frame termination unit 14 corrects the random error by applying the FEC described in the above ITU-T.
It should be noted that the error correction decoding unit 15 notifies the erasure correction decoding unit 16 of an uncorrectable flag FL for a frame that cannot be corrected by the error correction decoding unit 15.
As a result, the erasure correction decoding unit 16 performs erasure correction decoding by determining what frame is lost from the frame position and frame number where the uncorrectable flag FL is set.

  The optical transceiver 20 includes a D / A (digital / analog) converter 21 and an E / O (electric / optical) converter 22 inserted on the transmitting side, and an O / E (optical / electrical) inserted on the receiving side. A conversion unit 23 and an A / D conversion unit 24 are provided.

The D / A converter 21 performs D / A conversion on the SFI signal Sf (transmission signal) from the error correction encoder 13 in the OTUk framer 10 to generate an analog signal.
The E / O converter 22 converts the analog signal from the D / A converter 21 into an optical signal So (transmission signal) and outputs the optical signal So (transmission signal) to the communication path 3.

The O / E converter 23 converts the optical signal So (received signal) from the communication path 3 into an analog signal.
The A / D conversion unit 24 performs A / D conversion on the analog signal from the O / E conversion unit 23, generates q-bit soft decision reception data (reception signal) including a digital signal, and generates an OTUk framer. 10 is input to the error correction decoding unit 15.

  FIG. 3 is an explanatory diagram showing the operation according to the first embodiment of the present invention. Transmission information and reception information before and after processing in the erasure correction encoding unit 12 and erasure correction decoding unit 16 in the optical transmission apparatuses 1 and 2 are shown. The transmission frame structure is shown.

FIG. 4 is an explanatory diagram showing the structure of an OTUk frame to which the first embodiment of the present invention is applied, and shows a known OTUk frame structure (for example, see Non-Patent Document 1 described above).
FIG. 5 is an explanatory diagram showing, in an enlarged manner, the OH (OverHead) section 40 in FIG.

  In FIG. 3, for example, the erasure correction encoding unit 12 (see FIG. 2) in the optical transmission device 1 performs n (n = 5) transmission frames (OTUk frames # 1 to # 5) before encoding. , M (m = 4) redundant frames (# 6 to # 9) for encoding erasure correction are added, and the number of encoded n + m (n + m = 9) frames is one symbol code. Word (transmission information).

  On the other hand, the reception information received by the optical transmission apparatus 2 has lost, for example, OTUk frames # 2, # 5, and # 7 before decoding due to the occurrence of a burst error. The erasure correction decoding unit 16 (see FIG. 2) transmits n (n = 5) transmissions using non-erased OTUk frames # 1, # 3, # 4, # 6, # 8, and # 9. Play the frame.

As illustrated in FIG. 3, the optical transmission device 1 adds m redundant frames to n transmission frames, and performs communication with the optical transmission device 2 that is regarded as one symbol of a codeword. .
Here, as an example, a transmission frame forming one symbol with five transmission frames and four redundant frames is shown, but the values of n and m can be arbitrarily set.

In FIG. 4, the OTUk frame includes a payload (Payload) 30 (238 × 16 bytes) for storing actual communication data such as the client signal Sc and an OH unit 40 (16 bytes).
Further, the OTUk frame has an FEC redundant area 50 (16 × 16 bytes) for storing information of an error correction code for correcting a bit error caused by quality deterioration of the optical signal So after transmission.

  The OH unit 40 includes an FAOH (Frame Alignment OverHead) 41 for frame synchronization, an OTUkOH 42 and an ODUkOH (Optical channel Data Unit-k OverHead) 43 for maintenance monitoring information, and an OPUkOH (Optical) for mapping the payload 30. channel Payload Unit-k OverHead) 44.

As shown in FIG. 4, in an optical communication system, an OTUk frame in which an OH unit 40 and an FEC redundant area 50 (error correction code) are added to a payload 30 that is information data to be actually transmitted is formed as a transmission frame. This is transmitted at high speed and long distance.
Normally, a known RS (Reed-Solomon) code (255, 239) is used as the error correction code.

In FIG. 5, the FAOH 41 in the OH unit 40 is configured by a FAS (Frame Alignment Signal) OH 45 and a MFAS (Multiframe Alignment Signal) OH 46.
The FASOH 45 is defined by a row number “1” and a column number “1-6”, and the MFASOH 46 is defined by a row number “1” and a column number “7”.

  The OTUkOH 42 is defined as a row number “1” and a column number “8-14”, the ODUkOH 43 is defined as a row number “2-4” and a column number “1-14”, and the OPUkOH 44 is defined as a row number “1-14”. 4 ”and column numbers“ 15, 16 ”.

  In Embodiment 1 (FIG. 2) of the present invention, erasure correction encoding section 12 in OTUk framer 10 adds a frame number to OH section 40 of the OTUk frame shown in FIGS. That is, the frame number is added to the MFASOH 46 (Byte 7: byte number 7) in the FAOH 41 shown in FIG.

Next, a specific operation according to the first embodiment of the present invention shown in FIGS. 1 and 2 will be described with reference to FIGS.
Error correction by FEC (forward error correction) is performed in each OTUk frame. Here, a case where a burst error that cannot be corrected by error correction processing occurs is considered.

  In FIG. 3, it is assumed that OTUk frames # 2, # 5, and # 7 are lost due to an error (error correction is impossible), and the function of the erasure correction decoding unit 16 does not delete OTUk frames # 1, It is assumed that the transmitted transmission frame can be reproduced using # 3, # 4, # 6, # 8, and # 9.

At this time, the OTUk framer 10 needs to recognize the lost frame number and the frame number decoded without being lost.
For example, in the conventional OTUk framer defined in ITU-T, the framer number for erasure correction was not added. However, the OTUk framer 10 (the erasure correction code in FIG. In the case of the conversion unit 12), as described above, the frame number is added to the OH unit 40 (MFASOH 46 in FIG. 5) of the OTUk frame.

  In other words, the OTUk frame generator 10 in the OTUk framer 10 rewrites the MFASOH 46 to rewrite n + m OTUk frames # 1 to # n + m (or # 0) consisting of the number n of transmission frames and the number m of redundant frames (see FIG. 3). ˜ # n + m−1) are newly allocated for each frame.

At this time, every time a codeword regarded as one symbol is transmitted, the value of MFASOH 46 is initialized to, for example, “00000000” (or “00000001”).
In the signal received by the optical transmission device 1 (or the optical transmission device 2), the number indicated at the position of the MFASOH 46 is the frame number of the transmission frame.

  Accordingly, the erasure correction decoding unit 16 in the OTUk framer 10 can perform erasure correction of the transmission frame in which the frame number is lost by using the frame in which the frame number is not lost.

  As described above, the optical communication system according to Embodiment 1 (FIGS. 1 to 5) of the present invention includes the plurality of optical transmission apparatuses 1 and 2 connected via the communication path 3, and includes a plurality of optical transmissions. In order to perform communication between the apparatuses 1 and 2 using transmission frames, communication is performed using the number of frames obtained by adding m redundant frames to n transmission frames as a code word of one symbol.

  Each of the plurality of optical transmission apparatuses 1 and 2 includes an OTUk framer 10 that performs erasure correction corresponding to a burst error by using an error correction code in which the number of n + m frames is the number of symbols.

  The OTUk framer 10 is an ITU-TR RecommendationG. The OTN frame defined in 709 is applied, and the encoded frame number necessary for erasure correction is added to the MFASOH 46 in the OH section 40 of the OTN frame.

In this way, in an optical communication system using a continuous optical transmission frame such as an OTN frame, high quality, high speed and large capacity communication is realized by applying a erasure correction technique and correcting a large burst error. be able to.
In particular, it is useful when it is necessary to deal with burst errors in the range of several thousand bits to several frames.

Embodiment 2. FIG.
In the first embodiment, the frame number is added to the MFASOH 46 in the OH unit 40. However, the frame number is not added separately and incremented for each frame as shown in FIG. The frame number may be displayed using the operation of the MFASOH 46.

  FIG. 6 is an explanatory diagram showing a frame number display procedure according to the second embodiment of the present invention. Normally, ITU-T Recommendation G. In the definition of 709, as shown in FIG. 6, the MFASOH 46 repeats incrementing every frame.

  As shown in FIG. 6, in the 1-byte (= 8 bits) MFASOH 46 defined in the column number “7”, by incrementing from “00000000” to “11111111” for each OTUk frame and ODUk frame, A multi-frame of 256 (= 2 ^ 8) frames is generated.

Therefore, in the second embodiment of the present invention, the frame number is displayed using the defined normal operation instead of the frame number adding process to the MFASOH 46.
That is, as shown in FIG. 3, the code word by the OTUk frame generation unit 11 is displayed as the sum “n + m” of the transmission frame and the redundant frame. For example, the number of frames that can be displayed by incrementing the MFASOH 46 such as a multiple of 8 Set the codeword to.
Thereby, for example, the frame number for erasure correction can be displayed together with the display of the multi-frame (256) using the MFASOH 46.

Embodiment 3 FIG.
In the first and second embodiments (FIGS. 1 to 6), the MFASOH 46 is used to display the number of frames. However, a portion not used for frame synchronization in the FASOH 45 may be used.
FIG. 7 is an explanatory diagram specifically showing the structure of FASOH 45 to which the third embodiment of the present invention is applied.
In FIG. 7, FASOH 45 defined in row number “1” and column numbers “1-6” is composed of FASOH (Byte 1) to FASOH (Byte 7) of byte numbers 1 to 7, and FASOH (Byte 1 to Byte 3) includes , “11110110” is defined as OA1, and “00101000” is defined as OA2 in FASOH (Byte4 to Byte6).

  Of FASOH (Byte1 to Byte6), FASOH (Byte3, Byte4) is always used for frame synchronization, FASOH (Byte2, Byte5) may be used for frame synchronization, and FASOH (Byte1, Byte6) is It is not used for frame synchronization.

  Therefore, in the third embodiment of the present invention, the frame number is displayed using FASOH (Byte1, Byte6) that is not used for frame synchronization among FASOH (Byte1 to Byte6) shown in FIG.

  As described above, according to the third embodiment of the present invention, by adding a framer number using a location not used for frame synchronization in FASOH 45, for example, FASOH (Byte1, Byte6) in FIG. The framer number for erasure correction can be displayed without using the MFASOH 46.

Embodiment 4 FIG.
In the first to third embodiments (FIGS. 1 to 7), the MFASOH 46 or the FASOH 45 is used to display the number of frames. A portion not used for frame synchronization may be used.

  Thus, ITU-T Recommendation G. In the OH section 40 defined in 709, the erasure correction framer number is added to the undefined areas other than the areas (FASOH45, MFASOH46) used in the first to third embodiments, thereby Similar effects can be obtained.

  1 optical transmission device, 2 optical transmission device, 3 communication path, 10 OTUk framer, 11 OTUk frame generation unit, 12 erasure correction encoding unit, 13 error correction encoding unit, 14 OTUk frame termination unit, 15 error correction decoding unit, 16 erasure correction decoding unit, 20 optical transceiver, 21 D / A conversion unit, 22 E / O conversion unit, 23 O / E conversion unit, 24 A / D conversion unit, 30 payload, 40 OH unit, 41 FAOH, 50 FEC Redundant area, FL uncorrectable flag, m number of redundant frames, n number of transmitted frames, Sc client signal, So optical signal.

Claims (4)

A plurality of optical transmission devices connected via a communication path are provided, and m redundant frames are added to n transmission frames in order to perform communication using the transmission frames between the plurality of optical transmission devices. In an optical communication system that performs communication using the number of frames as a code word of one symbol,
Each of the plurality of optical transmission devices includes an OTUk framer,
The optical communication system, wherein the OTUk framer performs erasure correction corresponding to a burst error by using an error correction code in which n + m frames are used as symbols. The OTUk framer is
As the transmission frame, ITU-T Recommendation G. Apply the OTN frame defined in 709,
The optical communication system according to claim 1, wherein a frame number after encoding necessary for the erasure correction is added to an OH part of the OTN frame.   The optical communication system according to claim 2, wherein the OH part to which the frame number is added is MFAS.   The optical communication system according to claim 2, wherein the OH portion to which the frame number is added is a portion of the FAS that is not used for frame synchronization.

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