JP6289176B2 - Optical transmission apparatus and optical transmission method - Google Patents

Description

  The present invention relates to an optical transmission device that transmits and receives communication data using an optical transmission line, and a training sequence that is a known signal for estimating the chromatic dispersion characteristics of the optical transmission line is inserted into the communication data. The present invention relates to an optical transmission apparatus and an optical transmission method that can suppress an increase in the amount of transmission data.

  Conventional optical transmission / reception apparatuses and optical transmission / reception methods use On Off Keying (OOK), two-phase phase modulation (BPSK), or the like as an optical modulation method. In recent years, an increase in the capacity of an optical communication system has been demanded due to an increase in traffic on the Internet, and a method for handling a multilevel phase modulation signal using a digital signal processing technique has been studied. The multi-level modulation signal includes quadrature phase shift keying (QPSK), differential quadrature phase modulation (differential QPSK: DQPSK), and eight phase modulation (eight quadrature amplitude modulation: 8QAM).

  In contrast to the conventional method in which the on / off of the light intensity is assigned to the binary signal and directly detected, the digital coherent reception method extracts the light intensity and the phase information by the coherent reception method. The extracted intensity and phase information is quantized by an analog / digital converter, and demodulated by a digital signal processing unit.

  One advantage of the digital coherent reception system is that a mechanism for synchronizing the frequency and phase of the transmission light source and the local transmission light source with respect to the reception light can be implemented as digital signal processing. This makes it possible to synchronize the frequency and phase of the transmission light source and the local transmission light source with respect to the reception light without mounting an optical PLL (Phase Locked Loop) that is difficult to realize. Further, the digital coherent reception system has a feature that it has an optical signal-to-noise ratio (OSNR) tolerance and a waveform distortion tolerance of a transmission line.

  Waveform distortion includes a phenomenon called chromatic dispersion that occurs when the refractive index of an optical fiber that is a transmission path is a function of wavelength, and a phenomenon called nonlinear effect that occurs when the refractive index changes with the intensity of light. In the case of chromatic dispersion, since a signal generally has a certain wavelength band, the waveform is distorted due to the difference in refractive index perceived by each wavelength.

  In the digital coherent reception system, waveform distortion correction is performed by using a digital filter (dispersion compensator) having characteristics inverse to the waveform distortion. At this time, since the dispersion compensator needs to know the magnitude of chromatic dispersion of the optical fiber that is the transmission path, a training sequence that becomes a known signal is provided between the transmitter and the receiver. As a result, the coefficient of the digital filter that is a dispersion compensator can be obtained from the waveform distortion state of the training sequence (see, for example, Patent Document 1). As for the nonlinear effect, it is possible to correct waveform distortion from a training sequence that becomes a known signal (see, for example, Patent Document 2).

Japanese Patent Laid-Open No. 11-313013 JP-A-5-160865

ITU-T Recommendation G. 709

However, the prior art has the following problems.
In Patent Document 1 or Patent Document 2, there is a problem that the amount of data transmitted to the optical transmission path increases due to the insertion of the training sequence into the communication data, and the bandwidth of the optical transmission path or the optical transmission apparatus is insufficient. It was. Further, there is a problem that the signal is deteriorated due to the narrowing of the frequency band of the optical filter provided in the optical transmission repeater.

  The present invention has been made to solve the above-described problems, and an optical transmission line obtained by inserting a training sequence, which is a known signal for estimating the chromatic dispersion characteristic of an optical transmission line, into communication data. An object of the present invention is to obtain an optical transmission device and an optical transmission method capable of suppressing an increase in the amount of transmission data.

An optical transmission device according to the present invention is configured to include a first optical transmission device and a second optical transmission device that are arranged to face each other via an optical transmission line and transmit / receive communication data to / from each other using the optical transmission line. Each of the first optical transmission device and the second optical transmission device arranged opposite to each other transmits a training sequence, which is a known signal for estimating the chromatic dispersion characteristic of the optical transmission path, to communication data at the time of transmission in advance. The transmission unit is equipped with a training sequence insertion unit to be inserted, and when the communication data transmitted from the other optical communication device is received via the optical transmission path, the wavelength dispersion of the optical transmission path from the waveform distortion of the training sequence by estimating the characteristics, a dispersion compensator for compensating the wavelength dispersion of the communication data, the wavelength dispersion characteristics of the optical transmission path dispersion compensator is estimated, against the training sequence insertion portion in the other optical communication device Provided in the receiving unit and a wavelength dispersion characteristic notification section for notifying Te, training sequence insertion portion in each of the transmission unit of the first optical transmission device and the second optical transmission apparatus, the insertion frequency of the communication data of the training sequence, itself Is variably set according to the chromatic dispersion characteristic of the optical transmission line notified from the chromatic dispersion characteristic notifying unit in the other optical communication apparatus as a response to the communication data transmitted by the other .

The optical transmission method according to the present invention is an optical transmission method executed by two optical transmission devices that are arranged to face each other via an optical transmission path and transmit / receive communication data to / from each other using the optical transmission path, In either one of the two optical transmission apparatuses, communication data in which a training sequence, which is a known signal for estimating the chromatic dispersion characteristics of the optical transmission path, is inserted in advance is transmitted to either of the two optical transmission apparatuses. Communication data transmission step for transmitting to the other optical transmission device, and in the other optical transmission device, when receiving communication data transmitted from one optical transmission device by the communication data transmission step, the optical transmission path from the waveform distortion of the training sequence by estimating the wavelength dispersion characteristics, the wavelength dispersion compensating step of compensating the chromatic dispersion of the communication data, in the other optical transmission apparatus, a wavelength dispersion compensation step A constant with wavelength dispersion characteristics of the optical transmission path, and the wavelength dispersion characteristic notification step notifies the one of the optical transmission device, at one of the optical transmission device, the insertion frequency of the communication data of the training sequence, the communication data transmitting step itself is one having a training sequence insertion step of variably set in accordance with the wavelength dispersion characteristic of the optical transmission line to thus notified wavelength dispersion characteristics notifying step by the other optical communication apparatus as a response to the communication data transmitted in.

  According to the present invention, in an optical transmission device that transmits and receives communication data using an optical transmission line, the frequency of insertion of a training sequence, which is a known signal for estimating the chromatic dispersion characteristics of the optical transmission line, into the communication data is It is set according to the wavelength dispersion characteristic of the transmission line. As a result, it is possible to obtain an optical transmission device and an optical transmission method that can suppress an increase in the amount of transmission data on the optical transmission line due to the insertion of a training sequence into communication data.

It is a block diagram which shows the optical communication system using the optical transmission apparatus in Embodiment 1 of this invention. It is an illustration figure which shows the structure of the optical transmission apparatus in Embodiment 1 of this invention. It is an illustration figure which shows the structure of the reception front end in Embodiment 1 of this invention. In the second embodiment of the present invention, the training sequence is referred to as ITU-T Recommendation G. 7 is an explanatory diagram illustrating an example of insertion into a TS of an ODTU frame defined in 709. FIG.

  Hereinafter, preferred embodiments of an optical transmission device and an optical transmission method according to the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected and demonstrated about the part which is the same or it corresponds in each figure.

Embodiment 1 FIG.
FIG. 1 is a configuration diagram showing an optical communication system using the optical transmission apparatus according to Embodiment 1 of the present invention. The optical communication system shown in FIG. 1 includes optical transmission devices 1 a and 1 b and an optical transmission path 3. The optical transmission devices 1 a and 1 b illustrated in FIG. 1 have a transmission function or a reception function of communication data, and can exchange communication data via the optical transmission path 3.

  FIG. 2 is an exemplary diagram illustrating a configuration of the optical transmission devices 1a and 1b illustrated in FIG. 1, and illustrates a detailed configuration diagram when the optical transmission device 1a is a transmission side and the optical transmission device 1b is a reception side. First, the function and data flow of each component of the optical transmission devices 1a and 1b in the first embodiment will be described. For simplicity, in the following description, the optical transmission device 1a performs only transmission, The transmission apparatus 1b performs only reception.

  The transmission unit 10 of the optical transmission device 1a includes an OTUk frame generation unit 11, an error correction encoding unit 12, a symbol mapping unit 13, an MLD frame generation unit 14, a training sequence insertion unit 15, a multiplexing / D / A conversion unit 16, And an optical modulation unit 17.

  The receiving unit 20 of the optical transmission device 1b includes a receiving front end 21, an A / D conversion / demultiplexing unit 22, a dispersion compensation unit 23, a polarization separation / phase estimation unit 24, a chromatic dispersion characteristic notification unit 25, an MLD frame. A synchronization unit 26, an error correction decoding unit 27, and an OTUk frame termination unit 28 are provided.

  First, in the transmission unit 10, an OTUk frame generation unit 11 uses an OTU (Optical channel Transport Unit, see Non-Patent Document 1) k frames (k = 0, 1, 2, 3, 4,. ..) And information necessary for frame synchronization and maintenance control is added to generate an optical transmission frame (hereinafter referred to as “communication data”).

  The error correction encoding unit 12 generates redundant bits for error correction in the FEC (Forward Error Correction) unit of the generated OTUk frame. The symbol mapping unit 13 generates a multilevel modulation signal from the OTUk frame. The MLD frame generation unit 14 distributes the OTUk frame to a plurality of lanes (Multi-Lane Distribution).

  The training sequence insertion unit 15 inserts in advance into the communication data a training sequence that becomes a known signal for estimating the chromatic dispersion characteristic of the optical transmission path 3 on the receiving side. The multiplexing / D / A conversion unit 16 multiplexes communication data and performs D / A (digital / analog) conversion. The optical modulation unit 17 performs E / O (electrical / optical) conversion of the analog electric signal and transmits it to the optical transmission line 3.

  Next, in the reception unit 20, the reception front end 21 performs O / E (optical / electrical) conversion on the optical signal transmitted via the optical transmission path 3. The A / D conversion / demultiplexing unit 22 performs A / D (analog / digital) conversion and demultiplexing of communication data converted into an analog electrical signal. The dispersion compensation unit 23 compensates the chromatic dispersion of communication data by estimating the chromatic dispersion characteristic of the optical transmission line 3 from the waveform distortion of the training sequence.

  The polarization separation / phase estimation unit 24 separates two or more polarizations orthogonal to each other in the optical transmission path 3 and estimates the phase state of communication data. The chromatic dispersion characteristic notification unit 25 notifies the chromatic dispersion characteristic of the optical transmission line 3 estimated by the dispersion compensation unit 23 to the training sequence insertion unit 15 of the transmission unit 10, so that the transmission unit 10 and the reception unit 20 perform optical transmission. Information on wavelength dispersion characteristics of the path 3 is shared.

  The MLD frame synchronization unit 26 corrects the skew state of the MLD distributed to the plurality of lanes. The error correction decoding unit 27 performs error correction using redundant bits added on the transmission side. The OTUk frame termination unit 28 terminates information necessary for frame synchronization and maintenance control with respect to the OTUk frame, demaps communication data from the OTUk frame, and outputs it as a client reception signal.

  FIG. 3 is an exemplary diagram illustrating a configuration of the reception front end 21 according to the first embodiment. The reception front end 21 includes a polarization beam splitter (PBS) that separates the X polarization and Y polarization of the optical signal received from the optical transmission path 3, a local oscillator (LO) for coherent reception, and LO. PBS for polarization separation, 90 ° optical hybrid for mixing polarization-separated optical signal and LO signal, O / E converter for converting received optical signal into electric signal, and O / E converted And an AMP for amplifying a signal.

  As described above, in the optical transmission device 1 according to the first embodiment, the training sequence insertion unit 15 converts the training sequence, which is a known signal for estimating the chromatic dispersion characteristics of the optical transmission path 3, into communication data at the time of transmission in advance. I try to insert it. As a result, the dispersion compensator 23 can estimate the chromatic dispersion characteristic of the optical transmission line 3 from the waveform distortion of the training sequence when receiving the communication data, and can compensate the chromatic dispersion of the communication data.

  Here, it is known that the information amount of the training sequence necessary for estimating the chromatic dispersion characteristic of the optical transmission path 3 is generally correlated with the magnitude of the chromatic dispersion of the optical transmission path 3.

  Therefore, as shown in FIG. 2, the chromatic dispersion characteristic notifying unit 25 according to the first embodiment is estimated from the waveform distortion of the training sequence after receiving the communication data in the subsequent stage of the polarization separation / phase estimation unit 24. The chromatic dispersion characteristics of the optical transmission line 3 (for example, the frequency of occurrence of a phase slip indicating whether or not the symbol of the multilevel signal is rotated) is notified to the training sequence insertion unit 15 of the transmission unit 10. Here, as a notification means from the chromatic dispersion characteristic notification unit 25 to the transmission unit 10, it is possible to use a method of storing information in the overhead of the OTN used in the reverse communication or a Data Communication Channel.

  Then, the training sequence insertion unit 15 sets the insertion frequency (for example, the insertion period) of the training sequence in the communication data according to the wavelength dispersion characteristic of the optical transmission path 3. As a result, the amount of transmission data in the optical transmission line 3 can be suppressed by optimally controlling the frequency of inserting the training sequence into the communication data according to the chromatic dispersion characteristics of the optical transmission line 3.

  As a specific method for setting the training sequence insertion frequency, for example, the training sequence insertion unit 15 generates a phase slip in the optical transmission line 3 among the chromatic dispersion characteristics received from the chromatic dispersion characteristic notification unit 25. The insertion frequency (insertion cycle) of the training sequence may be proportional to the frequency. Alternatively, if the chromatic dispersion characteristic received from the chromatic dispersion characteristic notification unit 25 exceeds a predetermined threshold, the first insertion frequency is set, and if the chromatic dispersion characteristic is equal to or less than the predetermined threshold, the second You may make it set insertion frequency.

  The training sequence insertion frequency may be set only once when the optical transmission apparatus 1 is installed, or may be changed according to a change in the state of the optical transmission line 3 during operation of the optical transmission apparatus 1. You may make it change automatically.

  As described above, in the first embodiment, the insertion frequency of the training sequence, which is a known signal for estimating the chromatic dispersion characteristic of the optical transmission line, is set according to the chromatic dispersion characteristic of the optical transmission line. I am doing so. As a result, it is possible to obtain an optical transmission device and an optical transmission method that can suppress an increase in the amount of transmission data on the optical transmission line due to the insertion of a training sequence into communication data.

Embodiment 2. FIG.
In the first embodiment, a specific place where a training sequence is inserted is not particularly mentioned. Therefore, in the second embodiment, the invention of the present application is referred to as ITU-T Recommendation G. As an example of application to the 709 standard, a method of inserting a training sequence into a tributary slot (TS) of an optical channel data tributary unit (ODTU) frame will be described.

  FIG. 4 shows the training sequence as ITU-T Recommendation G. 7 is an explanatory diagram illustrating an example of insertion into a TS of an ODTU frame defined in 709. FIG. Communication data transmitted to the optical transmission line 3 in the second embodiment is stored in an ODTU frame as shown in FIG. The configuration and function of the optical transmission apparatus 1 are the same as those in the first embodiment.

  The ODTU frame shown in FIG. 4 includes an overhead (OH), a tributary slot (TS), and an FEC (Forward Error Correction) parity. Information for monitoring control is stored in OH. A TS can efficiently accommodate communication data having various bit rates. In the FEC parity, information of an error correction code for correcting a bit error due to deterioration of optical quality after transmission is stored.

  In addition to communication data, monitoring control information can be stored in the TS. Further, the number of TSs stored in the ODTU frame can be set freely (1 TS corresponds to a redundancy of 1.25%).

  Therefore, in the second embodiment, a training sequence that is a known signal for phase slip detection / correction is stored in the TS of the ODTU frame. As a result, it is possible to flexibly secure a TS region for storing a training sequence necessary for estimating the chromatic dispersion characteristic of the optical transmission line 3 in accordance with the insertion timing. In addition, without adding extra information such as a header for a training sequence, ITU-T Recommendation G. Training sequences can be stored in a form compliant with the 709 standard.

  As described above, in the second embodiment, a training sequence, which is a known signal for estimating the chromatic dispersion characteristic of an optical transmission line, is used as an ITU-T Recommendation G. 709 is inserted into a tributary slot (TS) of an optical channel data tributary unit (ODTU) frame. As a result, it is possible to further suppress an increase in the transmission data amount of the optical transmission line without adding extra information such as a header for the training sequence.

  1, 1a, 1b optical transmission device, 3 optical transmission path, 10 transmission unit, 11 OTUk frame generation unit, 12 error correction coding unit, 13 symbol mapping unit, 14 MLD frame generation unit, 15 training sequence insertion unit, 16 multiplexing Conversion / D / A conversion unit, 17 optical modulation unit, 20 reception unit, 21 reception front end, 22 A / D conversion / demultiplexing unit, 23 dispersion compensation unit, 24 polarization separation / phase estimation unit, 25 chromatic dispersion characteristics A notification unit, a 26 MLD frame synchronization unit, a 27 error correction decoding unit, and a 28 OTUk frame termination unit.

Claims (3)

An optical transmission device that includes a first optical transmission device and a second optical transmission device that are arranged to face each other via an optical transmission line and that transmit and receive communication data to and from each other using the optical transmission line,
Each of the first optical transmission device and the second optical transmission device arranged to face each other,
The transmission unit includes a training sequence insertion unit that previously inserts a training sequence, which is a known signal for estimating the chromatic dispersion characteristics of the optical transmission path, into the communication data at the time of transmission,
The communication data transmitted from the other optical communication device, when receiving via the optical transmission path, by estimating the wavelength dispersion characteristics of the optical transmission path from the waveform distortion of the training sequence, the communication A dispersion compensator for compensating the chromatic dispersion of the data;
A chromatic dispersion characteristic notifying unit for notifying the chromatic dispersion characteristic of the optical transmission path estimated by the dispersion compensating unit to the training sequence inserting unit in the other optical communication device ;
The training sequence insertion unit in each of the transmission units of the first optical transmission device and the second optical transmission device returns the frequency of insertion of the training sequence into the communication data as a response to the communication data transmitted by itself. An optical transmission apparatus variably set according to the chromatic dispersion characteristic of the optical transmission line notified from the chromatic dispersion characteristic notification unit in the other optical communication apparatus. The optical transmission device according to claim 1,
The training sequence insertion unit converts the training sequence into an ITU-T Recommendation G. An optical transmission device to be inserted into the TS of the ODTU frame specified in 709. An optical transmission method executed by two optical transmission apparatuses that are arranged to face each other via an optical transmission path and transmit / receive communication data to / from each other using the optical transmission path,
In either one of the two optical transmission apparatuses, communication data in which a training sequence, which is a known signal for estimating chromatic dispersion characteristics of the optical transmission path, is inserted in advance is transmitted to the two optical transmission apparatuses. A communication data transmission step for transmitting to one of the other optical transmission devices ;
In the other optical transmission apparatus, estimating the chromatic dispersion characteristic of the optical transmission path from the waveform distortion of the training sequence when receiving the communication data transmitted from the one optical transmission apparatus in the communication data transmission step. A chromatic dispersion compensation step for compensating chromatic dispersion of the communication data,
In the other optical transmission device, a chromatic dispersion characteristic notification step of notifying the chromatic dispersion characteristic of the optical transmission path estimated in the chromatic dispersion compensation step to the one optical transmission device ;
In the one optical transmission device , the chromatic dispersion characteristic notification step by the other optical communication device as a response to the communication data transmitted by itself in the communication data transmission step, as the frequency of insertion of the training sequence into the communication data. optical transmission method and a training sequence insertion step of variably set in accordance with the result notified the wavelength dispersion characteristics of the optical transmission line.

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