JP5896841B2 - Optical communication system - Google Patents

Description

  The present invention relates to an optical communication system, and more particularly to a reference signal encoding technique in a coherent optical communication system.

In general, in order to realize large-capacity optical transmission, overcoming the optical signal-to-noise power limit and high-density wavelength multiplexing have become issues.
As a technique for overcoming the optical signal power vs. noise power limit, binary phase-shift keying (BPSK) or quaternary PSK (QPSK) is compared to conventional on-off keying (OOK). : Quarterly Phase-Shift Keying) is used.

  As a specific example of high-density wavelength multiplexing, a technique for doubling the number of transmission bits per symbol by polarization multiplexing that assigns independent signals to two orthogonal polarization components X / Y, QPSK, There is known a technique of increasing the signal multiplicity and increasing the number of transmission bits per symbol, such as quadrature amplitude modulation (QAM).

In QPSK and 16QAM, an optical transmitter assigns signals to the same phase axis (I axis: In-Phase axis) and quadrature phase axis (Q axis: Quadrature-Phase axis) for transmission.
Further, a digital coherent optical communication system that receives these optical modulation signals by combining digital signal processing with a synchronous detection system has attracted attention (see, for example, Non-Patent Document 1 and Non-Patent Document 2).

In the digital coherent optical communication system described in Non-Patent Document 1 and Non-Patent Document 2, linear photoelectric conversion by synchronous detection and fixed, semi-fixed, and adaptive linear equalization by digital signal processing are performed. It is used.
This realizes excellent equalization characteristics and excellent noise tolerance against linear waveform distortion caused by chromatic dispersion and polarization mode dispersion (PMD) generated in the transmission path.

  On the other hand, in the above-described digital coherent optical communication system, as a technique for performing carrier phase offset compensation in the receiving unit, the M-power method (M: natural number indicating the phase number of PSK) (for example, refer to Non-Patent Document 3) A type algorithm (see, for example, Patent Document 1) has been used.

  However, in the carrier phase offset compensation techniques described in Non-Patent Document 3 and Patent Document 1, a phase slip of an angle “N × 2π / M” (N: natural number) occurs at the time of carrier phase recovery under conditions where noise and waveform distortion are large. As a result, large-scale continuous errors may occur.

Therefore, conventionally, differential encoding and differential decoding have been generally used as techniques for preventing phase slip.
On the other hand, techniques for avoiding phase slip without using differential encoding and differential decoding have also been studied (see, for example, Patent Document 2, Patent Document 3, and Patent Document 4).

  In Patent Document 2, in the carrier phase estimation of a coherent optical receiver, the period count (cycle count) value is increased or decreased on the condition that the transition of the estimated carrier phase between symbols exceeds a positive or negative threshold value. A technique for accurately estimating the carrier phase based on the above is disclosed.

  Further, in Patent Document 3, in coherent optical communication, a reference signal (pilot signal) is inserted between main signals on the transmission side, the carrier phase is estimated from the reference signal on the reception side, and the phase of the data signal is determined. For symbols with large fluctuations, it is disclosed that the carrier phase based on the reference signal is linearly interpolated to obtain the carrier phase, thereby guaranteeing the estimation accuracy of the carrier phase.

Furthermore, Patent Document 4 discloses that in coherent optical communication, a reference signal (SYNC burst) is inserted between main signals on the transmission side, and continuous errors that may occur due to phase slip are relieved by error correction. Yes.
Also, phase slip occurs by superimposing and collating bi-directional data decoding in time-series order and time-series reverse order, and then determining whether there is a mismatch in the decoding result of the same symbol decoded in each direction. Is also detected and corrected by error correction.

US Patent Application Publication No. 2011/0217043 US Patent Application Publication No. 2006/0245766 US Patent Application Publication No. 2011/0274442 US Pat. No. 7,522,841

Optical Internetworking Forum, “100G Ultra Long Haul DWDM Framework Document”, http: // www. oiforum. com / public / documents / OIF-FD-100G-DWDM-01.0. pdf, June 2009. Seb J.H. Savory, “Digital Filters for Coherent Optical Receivers”, Optics Express, vol. 16, no. 2, pp. 804-817, 2008. Andrew J. Viterbi and Audrey M. Viterbi “Nonlinear Establishment of PSK—Modulated Carrier Phase with Application to Burst Digital Transmission”, Trans Inf. Theory, vol. IT-29, no. 4, pp. 543-551, 1983.

  In a conventional optical communication system, when differential coding and differential decoding are used in order to prevent phase slip, since one symbol error propagates on the transmission line, almost two symbol errors are generated. Since the error rate is deteriorated, there is a problem that noise tolerance is impaired by error propagation particularly in a region where the code error rate is high.

  On the other hand, as described in Patent Document 2, in order to avoid the phase slip, when the carrier phase is estimated based on the period count value, the detection accuracy of the phase slip is insufficient and the missed phase slip is caused. There was a problem that large-scale continuous errors were inevitable.

Further, as described in Patent Document 3 and Patent Document 4, when error correction is performed by linearly interpolating a carrier phase based on a reference signal or inserting a reference signal between main signals on the transmission side However, since it is necessary to insert a completely known reference signal, there is a problem that it is necessary to increase the redundancy and increase the transmission speed.
Furthermore, the technique described in Patent Document 4 has a problem in that resistance to random errors is reduced because a restriction is added to the coding rule of the error correction code in order to increase the resistance to consecutive errors in error correction.

  The present invention has been made to solve the above-described problems, and eliminates the need for differential encoding and differential decoding, while reducing an increase in redundancy for obtaining a reference signal. An object of the present invention is to obtain an optical communication system that detects and compensates for phase slip and realizes improved noise tolerance.

  An optical communication system according to the present invention includes an optical unit configured by a transmission unit that transmits an optical signal, a transmission unit that transmits an optical signal from the transmission unit, and a reception unit that receives an optical signal via the transmission unit. In the communication system, a transmission unit encodes a part of an information bit string included in a main signal to be transmitted based on a reference signal encoding rule for generating a reference signal, and a reception unit refers to a reference in the transmission unit Based on the signal coding rule, a part of the information bit sequence encoded by the transmission unit is decoded and treated as a reference signal, and communication quality changes due to transmission characteristics with respect to the main signal in the transmission unit, transmission unit, and reception unit The compensation is performed using the reference signal.

  According to the present invention, the redundancy for obtaining the same amount of the reference signal can be suppressed to be smaller than that in the case where the known signal is inserted into the main signal as in Patent Document 3 and Patent Document 4, for example.

It is a functional block diagram which shows the optical communication system which concerns on Embodiment 1 of this invention. It is explanatory drawing which shows the bit allocation operation | movement of a conventional system as a comparative example. It is explanatory drawing which shows the bit allocation operation | movement by Embodiment 1 of this invention. It is explanatory drawing which shows the bit allocation operation | movement by Embodiment 2 of this invention. It is explanatory drawing which shows the bit allocation operation | movement by Embodiment 3 of this invention. It is explanatory drawing which shows the bit allocation operation | movement by Embodiment 4 of this invention. It is a functional block diagram which shows the optical communication system which concerns on Embodiment 5 of this invention. It is a functional block diagram which shows the optical communication system which concerns on Embodiment 6 of this invention.

Embodiment 1 FIG.
Hereinafter, an optical communication system according to Embodiment 1 of the present invention will be described in detail with reference to the drawings. In addition, Embodiment 1-6 demonstrated below is an example at the time of actualizing this invention, Comprising: This invention is not limited within the range of these specific examples.

1 is a functional block diagram showing an optical communication system according to Embodiment 1 of the present invention.
In FIG. 1, the optical communication system includes a transmission unit 10 and a reception unit 30 connected to the transmission unit 10 via a transmission unit 20.

  The transmission unit 10 includes a transmission bit string generation unit 11 that generates a transmission bit string from input data from an external communication device (not shown), a reference bit string insertion unit 12 that inserts a reference bit string into the transmission bit string, and a transmission signal (optical signal). ) To the transmission unit 20.

  The reception unit 30 includes a signal reception unit 31 that receives a transmission signal via the transmission unit 20, a reference bit string analysis unit 32 that analyzes a reference bit string from the reception signal (optical signal), and a bit string that receives the analyzed reference bit string And a receiving unit 33.

  Here, a case where a polarization multiplexed QPSK (DP-QPSK) signal is assumed as a modulation target is assumed, but the modulation of the application destination is not limited, and a DP-BPSK signal, DP- It can be easily extended to 16QAM signals and other signals.

The DP-QPSK signal has orthogonal X / Y polarization and four lanes (XI, XQ, YI, YQ) composed of I / Q phases.
It should be noted that the expression by four lanes of XI, XQ, YI, and YQ is general. DP-BPSK has a part thereof, a part of a single polarized signal, and DP-16QAM has an I / Q of 2 respectively. Think of it as an extension with bits assigned.

The operation of the optical communication system according to the first embodiment of the present invention shown in FIG. 1 will be described below with reference to FIG. 3 while comparing with the conventional operation shown in FIG.
FIG. 2 is an explanatory diagram showing a bit allocation operation of a conventional system as a comparative example, and shows a bit allocation operation when a known signal is inserted as a reference signal.

  FIG. 3 is an explanatory diagram showing a bit allocation operation according to the first embodiment of the present invention, and shows a bit allocation operation in the case where a reference signal is encoded by a reference signal and decoded on the receiving side to be a reference signal. .

2 and 3, the horizontal axis corresponds to the time axis (time slot), and the vertical axis corresponds to the four lanes of the DP-QPSK signal.
2 and 3, the four lanes include an XI lane 101, an XQ lane 102, a YI lane 103, and a YQ lane 104.

  In the horizontal axis of FIG. 2, the known bits 201, 202, 203, and 204 and information bits 211, 212, 213, and 214 arranged following the known bits 201 to 204 are allocated.

  On the other hand, on the horizontal axis of FIG. 3, as reference signal encoding frame 300 (reference signal encoding frame), reference signal encoded information bits 301 and 302 and reference signal encoded redundant bits 311 and 312 are shown. The information bits 321, 322, 323, and 324 that are not encoded with the reference signal are bit-allocated.

  Information bits 321 and 322 not coded with reference signal are arranged following information bits 301 and 302 coded with reference signal, and information bits 323 and 324 not coded with reference signal are coded with reference signal code. The redundant bits 311 and 312 are arranged next to each other.

In FIG. 1, first, the transmission bit string generation unit 11 allocates bit strings to four lanes on the transmission path side based on input data from an external communication device. At this time, it is also assumed that, for example, an error correction coding sequence or a frame synchronization sequence is inserted as necessary.
The transmission bit string generated from the transmission bit string generation unit 11 is input to the reference bit string insertion unit 12.

Subsequently, the reference bit string insertion unit 12 inserts a reference bit string into the transmission bit string input from the transmission bit string generation unit 11 as illustrated in FIG. 3, and transmits the transmission bit string after insertion of the reference bit string to the signal transmission unit 13. input.
The feature of the first embodiment of the present invention is that the bit allocation operation (FIG. 3) by the reference bit string insertion unit 12 in the transmission unit 10 and the decoding and analysis processing operation by the reference bit string analysis unit 32 in the reception unit 30 are as follows. is there.

  In the conventional bit allocation operation, as shown in FIG. 2, known bits 201 to 204 are simply added to information bits 211 to 214 as an alternating pattern of “0, 1”, for example. In the example of FIG. 2, known bits 201 to 204 are additionally inserted at a rate of 1 time slot in 10 time slots, and the redundancy is 10%. As a result, the transmission speed on the transmission line side increases 1.1 times.

The insertion of the known bits 201 to 204 has been actively performed especially in wireless communication. However, in wireless communication, increase in redundancy is not disliked and even 100% redundancy has been allowed.
However, in the optical communication system, in view of the point that the transmission quality deterioration due to the narrowing of the band by the optical branching multiplex apparatus becomes serious and the hardware operation speed of the analog / digital converter needs to be increased. Therefore, it is desired to perform transmission with as little redundancy as possible, and it is required to suppress the increase in redundancy.

  Therefore, as shown in FIG. 3, in the bit allocation operation according to the first embodiment of the present invention, a known signal (known bits 201 to 204 in FIG. 2) is not simply inserted as a reference bit. A reference bit string is composed of information bits 301 and 302 encoded with reference signals and redundant bits 311 and 312 encoded with reference signals.

  Further, the reference signal encoded frame 300 is composed of information bits 301 and 302 encoded with reference signals, redundant bits 311 and 312 encoded with reference signals, and information bits 321 to 324 not encoded with reference signals. Composed.

  Note that the information bits 301 and 302 encoded with the reference signal are not inserted into bits in the reference bit string insertion unit 12, but the bits input from the transmission bit string generation unit 11 are used as they are, or some code conversion is performed. Only redundant bits are not inserted.

  On the other hand, the reference bit-encoded redundant bits 311 and 312 are obtained by selecting a specific bit from the bit sequence input from the transmission bit sequence generation unit 11 and encoding the reference signal in the reference bit sequence insertion unit 12. In order to protect the information bits 301 and 302 encoded with the reference signal, they are additionally inserted as redundant bits.

Thereby, according to the operation example shown in FIG. 3, the redundancy by reference bit sequence insertion is suppressed to half of the conventional system (FIG. 2).
That is, the bit allocation operation in FIG. 3 corresponds to coding information bits of one time slot in 10 time slots at the coding rate (= 1/2) of the reference signal. 5.26% ", which corresponds to almost half of the redundancy (= 10%) in the conventional operation (FIG. 2). Thereby, the transmission speed on the transmission line side is suppressed to “1.0526 times” lower than the conventional transmission speed (1.1 times).

As reference signal encoding in the reference bit string insertion unit 12, for example, an error correction code or a space-time code can be used.
Further, with respect to redundant bits to be additionally inserted, it is possible to further increase the reliability by using a known signal in part.

  In this way, the reference bit string insertion unit 12 performs reference bit string insertion processing on the bit string input from the transmission bit string generation unit 11 and inputs the transmission bit string of four lanes after the reference bit string is inserted to the signal transmission unit 13. To do.

  Hereinafter, the signal transmission unit 13 generates a DP-QPSK signal based on the 4-lane bit string input from the reference bit string insertion unit 12 and inputs the DP-QPSK signal to the transmission unit 20. The specific configuration of the signal transmission unit 13 is described in Non-Patent Document 1 described above, and detailed description thereof is omitted here.

The transmission unit 20 transmits the DP-QPSK signal input from the signal transmission unit 13 and inputs the DP-QPSK signal to the signal reception unit 31 in the reception unit 30.
At this time, an optical fiber, an optical amplifier, a multiplexer / demultiplexer, or the like is usually used as a transmission medium in the transmission unit 20, and noise superposition or waveform distortion occurs in the transmission process.

  In the reception unit 30, the signal reception unit 31 receives the DP-QPSK signal input from the transmission unit 20, restores the 4-bit transmission bit string generated by the reference bit string insertion unit 12, and refers to the restored signal Input to the bit string analyzer 32. The specific configuration and processing contents of DP-QPSK signal reception are described in Non-Patent Document 1 and Non-Patent Document 2 described above, and will not be described in detail here.

  In general, an error is included in the 4-lane bit string input to the reference bit string analysis unit 32 due to noise or waveform distortion superimposed on the transmission unit 20. In addition, the above-described phase slip may occur.

Regarding the phase slip, depending on the implementation form of the digital signal processing in the signal receiving unit 31, when the carrier phase estimation is performed synchronously with the X polarization and the Y polarization, the phase slip is also the X polarization and the Y polarization. It occurs in synchronization with the polarization.
On the other hand, when the carrier phase estimation is performed independently for the X polarization and the Y polarization, the phase slip also occurs independently for the X polarization and the Y polarization.

The reference bit string analyzer 32 synchronously extracts the reference signal encoded frame 300 (see FIG. 3) from the restored 4-lane bit string input from the signal receiver 31.
The reference bit string analysis unit 32 extracts the information bits 301 and 302 encoded with the reference signal and the redundant bits 311 and 312 encoded with the reference signal, and performs the reference signal encoding performed in the reference bit string insertion unit 12. Decrypt based on the rule.

  At this time, in the decoding process of each bit 301, 302, 311 and 312, if a combination of codes with high likelihood is found and it is determined that “decoding succeeded”, it is inferred that no phase slip has occurred. Is done.

  On the other hand, when a combination of codes with high likelihood is not found, there is a possibility that a phase slip has occurred in the reference signal encoded frame 300. Depending on the code configuration, there is a possibility that the phase slip can be detected even when the phase slip occurs in the entire reference signal encoding frame 300.

In DP-QPSK (polarization multiplexing QPSK), phase slips of +90 degrees, 180 degrees, and -90 degrees may occur in each polarization.
For example, when slipping +90 degrees, lane switching between I-ch and Q-ch occurs, and logical polarity inversion of Q-ch occurs.

Further, at the time of 180 degree slip, lane switching does not occur, but logic polarity inversion occurs in both I-ch and Q-ch.
Further, when slipping at -90 degrees, lane switching between I-ch and Q-ch occurs, and logical polarity inversion of I-ch occurs.

The lane change due to the phase slip or the logical polarity inversion occurs definitely when the value of the phase slip is determined.
Therefore, it is possible to perform decoding more easily and with high probability by performing code search in decoding in the reference bit string analysis unit 32 in consideration of lane replacement due to phase slip and logic polarity inversion.

  When the decoding in the reference bit string analysis unit 32 is successful, the information bits 301 and 302 encoded with the reference signal and the redundant bits 311 and 312 encoded with the reference signal are all the same as in the conventional known signal. It can be used as a reference signal.

  Alternatively, based on the comparison between the result of decoding the reference signal encoded information bits 301 and 302 as “reference bits” and the result of decoding the reference signal encoded information bits 301 and 302 as “main signal”, For example, it is possible to estimate a phase slip state having a high correlation value.

Similarly, a comparison between the result of decoding the redundant bits 311 and 312 encoded with the reference signal as the “reference signal” and the result of decoding the redundant bits 311 and 312 encoded with the reference signal as the “main signal” is as follows: It is applicable to estimation of the state of phase slip.
In this way, the reference bit string analyzer 32 substantially compensates for “phase slip”, and a received bit string in which many of the remaining errors are “random errors” is input to the bit string receiver 33.

  The bit string receiving unit 33 is used to input the received bit string to the external communication device through a process reverse to the transmission bit string generating unit 11 in the transmitting unit 10 with respect to the received bit string input from the reference bit string analyzing unit 32. Performs bit allocation.

For example, it is assumed that a random error remaining by decoding by error correction decoding is corrected or a frame synchronization pattern is removed.
In this way, the bit string generated from the bit string receiving unit 33 of the receiving unit 30 is input to the external communication device.

  As described above, the optical communication system according to Embodiment 1 (FIGS. 1 and 3) of the present invention includes a transmission unit 10 that transmits an optical signal, and a transmission unit 20 that transmits an optical signal from the transmission unit 10. And a receiving unit 30 that receives an optical signal via the transmission unit 20, and the transmitting unit 10 generates a reference signal for a part (301, 302) of an information bit string included in the transmitted main signal. Encoding based on a reference signal encoding rule.

  The receiving unit 30 treats a part of the information bit sequence encoded by the transmitting unit 10 as a reference signal based on the reference signal encoding rule in the transmitting unit 10, and handles the transmitting unit 10, the transmitting unit 20, and the receiving unit. The communication quality change caused by the transmission characteristic of the main signal at 30 is compensated by using the reference signal. In particular, the phase slip included in the communication quality change is detected and compensated.

  Specifically, the transmission unit 10 includes a reference bit string insertion unit 12 for encoding a part of the information bit string, and the reception unit 30 decodes a part of the information bit string and uses the reference signal. A reference bit string analyzing unit 32 for compensating for a change in communication quality is provided.

In the transmission unit 10, a part of the information bit sequence encoded based on the reference signal encoding rule includes four main signals based on the orthogonal polarization component X / Y and the orthogonal phase component I / Q in the polarization multiplexing orthogonal phase modulation. Data lanes XI, XQ, YI, and YQ (XI lane 101, XQ lane 102, YI lane 103, and YQ lane 104) are allocated equally.
Also, a part of the information bit sequence encoded based on the reference signal encoding rule is allocated to the same time slot for the four main signal data lanes XI, XQ, YI, YQ.

As described above, the reference bit string insertion unit 12 in the transmission unit 10 encodes and transmits a part of the information bit string of the main signal as a reference signal, and converts a part of the information bit string encoded with the reference signal into a reference bit. Allows handling as if it were transmitted.
On the other hand, in the reference bit string analysis unit 32 in the receiving unit 30, a part of the information bits encoded by the reference signal is decoded by the reference signal, and the part of the decoded information bits is handled like a known reference signal. To detect and compensate for phase slip.

  As a result, transmission quality deterioration due to phase slip can be avoided without using differential encoding and differential decoding as in the conventional system, and a reference bit string (known bit signal in FIG. 2) is added to the main signal. Compared with the case of inserting, the redundancy for obtaining the same amount of reference signals is suppressed to be small, so that the increase in redundancy can be reduced and the transmission quality can be improved.

Embodiment 2. FIG.
In the first embodiment (FIG. 3), the information bits 301 simultaneously encoded with the reference signal are preceded by the information bits 321 to 324 not encoded with the reference signal for each of the four lanes 101 to 104. 302 and redundant bits 311 and 312 encoded with reference signals are inserted, but as shown in FIG. 4, information bits 421 to 424 that are not encoded with reference signals in XI lane 101 and XQ lane 102 and YI The information bits 423 to 427 that are not coded in the reference signal in the lane 103 and the YQ lane 104 are shifted by a half period (5 time slots), and the reference signal is coded before each information bit 421 to 427. The information bits 401 to 404 and the redundant bits 411 to 414 encoded with the reference signal may be inserted.

FIG. 4 is an explanatory diagram showing a bit allocation operation according to the second embodiment of the present invention. As in the above (FIG. 3), the horizontal axis corresponds to the time axis (time slot), and the vertical axis represents the DP-QPSK signal. Correspond to the four lanes.
FIG. 4 is a modification of FIG. 3 and shows a bit allocation operation in the case where a reference signal is encoded by a reference signal and decoded on the receiving side to obtain a reference signal.

  The configuration of the optical communication system according to the second embodiment of the present invention is the same as that of FIG. 1, and only the operations of the reference bit string insertion unit 12 in the transmission unit 10 and the reference bit string analysis unit 32 in the reception unit 30 are performed. Different from the above.

  In the bit allocation operation according to the second embodiment of the present invention, as shown in FIG. 4, information bits 401, 402, 403, 404 encoded with reference signals and redundant bits 411, 412, 413, encoded with reference signals, 414 constitutes a reference bit string.

  Further, a reference bit string composed of information bits 401 to 404 encoded with reference signals and redundant bits 411 to 414 encoded with reference signals, and information bits 421, 422, 423, 424, 425 not encoded with reference signals, 426 and 427 constitute a reference signal encoded frame 400.

  In Embodiment 2 of the present invention, as shown in FIG. 4, reference bits encoded information bits 401 to 401 that are used as reference signals in the X polarization and Y polarization of four lanes 101 to 104 are used. 404 and redundant bits 411 to 414 encoded with reference signals are shifted by a half period (5 time slots) with respect to the reference signal period (10 time slots) in each polarization. Different from the first embodiment.

The features of the second embodiment of the present invention are the bit allocation operation (FIG. 4) by the reference bit string insertion unit 12 in the transmission unit 10 and the reference bit string analysis unit in the reception unit 30 as in the first embodiment. 32 for decoding and analyzing processing.
In this case, the reference bit string insertion unit 12 in the transmission unit 10 performs a reference signal encoding process having the characteristics shown in FIG.

With the above feature, it is possible to apparently double the frequency of the reference signal when viewed on the time axis with the same redundancy as in the first embodiment.
Alternatively, even if the reference signal period is set to double (20 time slots), the frequency of the reference signal can be kept apparently the same (1 time).

As described above, depending on the implementation form of the digital signal processing in the signal receiving unit 31, when the carrier phase estimation is performed synchronously with the X polarization and the Y polarization, the phase slip is also X polarization. And Y-polarized wave.
On the other hand, when the carrier phase estimation is performed independently for the X polarization and the Y polarization, the phase slip also occurs independently for the X polarization and the Y polarization.

When the carrier phase estimation is performed in synchronization with the X polarization and the Y polarization, the reference bit string analysis unit 32 can detect and compensate for the phase slip in synchronization with the X polarization and the Y polarization. is there.
On the other hand, when the carrier phase estimation is performed independently for the X polarization and the Y polarization, the reference bit string analysis unit 32 needs to detect and compensate for the phase slip independently for the X polarization and the Y polarization.

When carrier phase estimation is performed synchronously with X polarization and Y polarization, there is a possibility that the redundancy of reference signal encoding can be halved.
That is, even if the reference signal period is doubled by referring to one signal of X polarization or Y polarization in one time slot and applying the reference result to the other polarization, the frequency of the reference signal Can be kept the same.

  Furthermore, as a further modification of the reference signal encoding, it goes without saying that the reference signal encoding time slots of I-ch and Q-ch can also be set as different time slots.

  As described above, according to the optical communication system according to Embodiment 2 (FIGS. 1 and 4) of the present invention, a part of the information bit sequence encoded based on the reference signal encoding rule in the transmitter 10 is Reference signal for two main signal data lanes XI, XQ out of four main signal data lanes XI, XQ, YI, YQ (XI lane 101, XQ lane 102, YI lane 103, YQ lane 104) The encoded information bits 401 and 402 and the reference signal encoded redundant bits 411 and 412 are assigned to the first time slot.

  Also, for the other two main signal data lanes YI and YQ, the first time slot, as shown by reference signal encoded information bits 403 and 404 and reference signal encoded redundant bits 413 and 414 Is assigned to a second same time slot different from.

  Alternatively, a part of the information bit sequence encoded based on the reference signal encoding rule in the transmission unit 10 is allocated to a different time slot for each of the four main signal data lanes XI, XQ, YI, YQ. .

  As a result, in the same manner as in the first embodiment, in the transmission unit 10, a part of the information bit string of the main signal is encoded by the reference signal and transmitted, and a part of the information bit string encoded by the reference signal is referred to Bits can be handled as if they were transmitted, and the receiving unit 30 can detect and compensate for a phase slip by handling a part of the decoded information bits like a known reference signal. .

  Therefore, transmission quality deterioration due to phase slip can be avoided without using differential encoding and differential decoding as in the conventional system, and a reference bit string (known bit signal in FIG. 2) is inserted into the main signal. Compared with the case of performing the above, the redundancy for obtaining the same amount of reference signals is suppressed to be small, so that the increase in redundancy can be reduced and the transmission quality can be improved.

Embodiment 3 FIG.
In the first embodiment (FIG. 3), the modulation target is a polarization multiplexed QPSK (DP-QPSK) signal. However, as shown in FIG. 5, the DP-16QAM signal is used. However, it can be similarly applied.

FIG. 5 is an explanatory diagram showing a bit allocation operation according to the third embodiment of the present invention.
The configuration of the optical communication system according to the third embodiment of the present invention is the same as that of FIG. 1, and only the operations of the reference bit string insertion unit 12 in the transmission unit 10 and the reference bit string analysis unit 32 in the reception unit 30 are performed. Different from the above.

  In addition, here, it is assumed that the DP-16QAM signal is applied as the modulation signal, but the present invention is not limited to this, and the same form can be applied to QAM having a higher multilevel.

In FIG. 5, the vertical axis indicates a state in which four lanes (XI, XQ, YI, YQ) are expanded to DP-16QAM, and each lane has 2-bit information.
On the vertical axis, XI0 lane 111, XQ0 lane 112, YI0 lane 113, and YQ0 lane 114, XI1 lane 121, XQ1 lane 122, YI1 lane 123, and YQ1 lane 124 are shown.

  Here, “0” of each lane 111 to 114 indicates the MSB (Most Significant Bit) of each lane, and “1” of each lane 121 to 124 indicates the LSB (Least Significant Bit) of each lane. .

  Further, on the horizontal axis of FIG. 5, the reference signal encoded frame 500 includes reference bits encoded information bits 501 and 502, reference signal encoded redundant bits 511 and 512, and reference signal encoded. Information bits 521, 522, 523, and 524.

  The information bits 521 and 522 that are not encoded by the reference signal are arranged following the information bits 501 and 502 that are encoded by the reference signal, and the information bits 523 and 524 that are not encoded by the reference signal are the reference signal codes. The redundant bits 511 and 512 are arranged after the redundant bits.

  In the bit allocation operation according to the third embodiment of the present invention, as shown in FIG. 5, a reference bit string is composed of information bits 501 and 502 encoded with reference signals and redundant bits 511 and 512 encoded with reference signals. Is done.

  Further, the reference signal encoded frame 500 is composed of information bits 501 and 502 encoded with the reference signal, redundant bits 511 and 512 encoded with the reference signal, and information bits 521 to 524 not encoded with the reference signal. Composed.

In the third embodiment of the present invention, as shown in FIG. 5, information bits encoded by reference signals used as reference signals are expanded by expressing 4 lanes (XI, XQ, YI, YQ) with 2 bits each. The numbers of 501 and 502 and the number of redundant bits 511 and 512 encoded with reference signals are each doubled.
With the above feature, the number of bits of the reference signal can be doubled with the same redundancy as in the first embodiment.

  As described above, according to Embodiment 3 (FIGS. 1 and 5) of the present invention, as described above, in transmission unit 10, a part of the information bit string of the main signal is encoded by reference signal and transmitted. , It is possible to treat a part of the information bit sequence encoded with the reference signal as if the reference bit was transmitted, and in the receiving unit 30, the part of the decoded information bit is treated as a known reference signal. The phase slip can be detected and compensated.

  Therefore, transmission quality deterioration due to phase slip can be avoided without using differential encoding and differential decoding as in the conventional system, and a reference bit string (known bit signal in FIG. 2) is inserted into the main signal. Compared with the case of performing the above, the redundancy for obtaining the same amount of reference signals is suppressed to be small, so that the increase in redundancy can be reduced and the transmission quality can be improved.

Embodiment 4 FIG.
In the third embodiment (FIG. 5), information bits 501 and 502 encoded with reference signals are inserted into the lanes 101 to 104 and 111 to 114. However, as shown in FIG. Information bits 601 and 602 encoded with reference signals are inserted into the lanes 101 to 104, and the reference signals are transmitted to the lower lanes 111 to 114 at the same timing as the information bits 601 and 602. Encoded redundant bits 613 and 614 may be inserted.

FIG. 6 is an explanatory diagram showing a bit allocation operation according to the fourth embodiment of the present invention.
The configuration of the optical communication system according to Embodiment 4 of the present invention is the same as that in FIG. 1, and only the operations of the reference bit string insertion unit 12 in the transmission unit 10 and the reference bit string analysis unit 32 in the reception unit 30 are performed. Different from the above.

  In addition, here, it is assumed that the DP-16QAM signal is applied as the modulation signal, but the present invention is not limited to this, and the same form can be applied to QAM having a higher multilevel.

  In FIG. 6, a reference signal encoded frame 600 includes information bits 601 and 602 encoded with reference signals, redundant bits 611, 612, 613, and 614 encoded with reference signals, and information not encoded with reference signals. It consists of bits 621, 622, 623, and 624.

  In the bit allocation operation according to the fourth embodiment of the present invention, as shown in FIG. 6, information bits 601, 602, 603, 604 encoded with reference signals, and redundant bits 611, 612, 613, encoded with reference signals, 614 constitutes a reference bit string.

  Furthermore, the reference signal encoded frame 600 is composed of information bits 601 and 602 encoded with reference signals, redundant bits 611 to 614 encoded with reference signals, and information bits 621 to 624 not encoded with reference signals. Is done.

In Embodiment 4 of the present invention, as shown in FIG. 6, by assigning redundant bits 613 and 614 encoded with reference signals as bits of the lower half lanes (XI1, XQ1, YI1, and YQ1), The coding rate of reference signal coding is 1/4.
Due to the above feature, the probability of successful decoding of the reference signal can be further improved although the redundancy is increased by about 1.5 times compared to the third embodiment (FIG. 5).

  The bit allocation operations shown in the first to fourth embodiments (FIGS. 3 to 6) are merely examples, and it is needless to say that there are almost infinite bit allocation operations for reference signal encoding. .

  As described above, according to the fourth embodiment of the present invention, as described above, in transmission unit 10, a part of the information bit string of the main signal is encoded by the reference signal and transmitted, and the reference signal is encoded. A part of the information bit string can be handled as if the reference bits were transmitted, and the receiving unit 30 treats a part of the decoded information bits like a known reference signal, thereby causing a phase slip. Can be detected and compensated.

  Therefore, transmission quality deterioration due to phase slip can be avoided without using differential encoding and differential decoding as in the conventional system, and a reference bit string (known bit signal in FIG. 2) is inserted into the main signal. Compared with the case of performing the above, the redundancy for obtaining the same amount of reference signals is suppressed to be small, so that the increase in redundancy can be reduced and the transmission quality can be improved.

Embodiment 5 FIG.
In Embodiments 1 to 4 (FIG. 1), error correction of an optical signal is not specifically mentioned. However, as shown in FIG. 7, a transmission unit 1100 that performs error correction coding and a transmission unit 1200 In addition, an optical communication system may be configured by the receiving unit 1300 that performs error correction decoding.

FIG. 7 is a functional block configuration showing an optical communication system according to Embodiment 5 of the present invention.
In FIG. 7, a transmission unit 1100 that constitutes an optical communication system includes a main signal error correction encoding unit 1101, a reference signal encoding unit 1102, a transmission end signal processing unit 1103, and an optical modulation unit 1104. ing.

  In addition, the reception unit 1300 includes an optical demodulation unit 1301, a reception end signal processing unit 1302, a reference signal frame synchronization unit 1303, a main signal buffer unit 1304, a main signal carrier phase estimation unit 1305, and a reference signal carrier phase estimation. Unit 1306, reference signal likelihood generation unit 1307, reference signal decoding unit 1308, main signal likelihood generation unit 1309, main signal frame synchronization unit 1310, and main signal error correction decoding unit 1311 Has been.

The optical signal emitted from the optical modulation unit 1104 in the transmission unit 1100 is input to the optical demodulation unit 1301 in the reception unit 1300 via the transmission unit 1200 and processed in the reception unit 1300.
The fifth embodiment of the present invention is characterized in that the bit allocation operation by the reference signal encoding unit 1102 in the transmission unit 1100, the decoding operation by the reference signal decoding unit 1308 in the reception unit 1300, and the main signal carrier phase estimation unit 1305. The phase slip due to the detection and compensation operation.

The operation of the optical communication system according to Embodiment 5 of the present invention shown in FIG. 7 will be described below.
First, in transmission section 1100, main signal error correction encoding section 1101 encodes a bit sequence input from an external communication device with an error correction code such as a low density parity check code, and is error correction encoded. A bit sequence is input to reference signal encoding section 1102.

  The reference signal encoding unit 1102 encodes the error correction encoded bit sequence input from the main signal error correction encoding unit 1101 as described in the first to fourth embodiments, and performs reference signal encoding. The signal-encoded bit sequence is input to transmission end signal processing section 1103.

  The transmission end signal processing unit 1103 performs waveform shaping (band compensation, chromatic dispersion compensation, etc.) by digital signal processing on the reference signal-encoded bit sequence input from the reference signal encoding unit 1102 to perform digital signal processing. The later electric signal is input to the light modulation unit 1104.

The optical modulation unit 1104 generates an optical signal based on the electric signal after the digital signal processing input from the transmission end signal processing unit 1103 and inputs the optical signal to the transmission unit 1200.
Note that a specific method for generating an optical signal is described in Non-Patent Document 1 and Non-Patent Document 2 described above, and detailed description thereof is omitted here.

The transmission unit 1200 transmits the optical signal input from the optical modulation unit 1104 and inputs the optical signal to the optical demodulation unit 1301 in the reception unit 1300.
At this time, the transmission unit 1200 normally uses an optical fiber, an optical amplifier, a multiplexer / demultiplexer, or the like as a transmission medium, and noise is superimposed or waveform distortion occurs in the transmission process.

  The optical demodulator 1301 mixes the optical signal input from the transmission unit 1200 with a local oscillation optical signal, performs coherent detection, further converts it to an electrical signal, and then samples and quantizes the received signal as a main signal. Input to 1302.

  Reception end signal processing section 1302 compensates for waveform distortion generated in transmission section 1100, transmission section 1200, and optical demodulation section 1301 by digital signal processing, and inputs the main signal after waveform distortion compensation to reference signal frame synchronization section 1303. .

  The reference signal frame synchronization unit 1303 ensures the synchronization of the reference signal encoded frame based on the main signal after waveform distortion compensation input from the receiving end signal processing unit 1302, and the reference signal frame synchronized main signal The signal is input to the signal buffer unit 1304 and the reference signal carrier phase estimation unit 1306.

  The reference signal carrier phase estimation unit 1306 estimates the carrier phase of the frame-synchronized main signal input from the reference signal frame synchronization unit 1303 based on a known M-power method or provisional determination method, and the reference signal after carrier phase estimation Is input to the reference signal likelihood generation unit 1307.

  Reference signal likelihood generation section 1307 calculates the likelihood of the reference signal after carrier phase estimation input from reference signal carrier phase estimation section 1306, and inputs the likelihood information to reference signal decoding section 1308.

  The reference signal decoding unit 1308 performs reference signal decoding based on the likelihood information input from the reference signal likelihood generation unit 1307 and the encoding rule in the reference signal encoding unit 1102 in the transmission unit 1100. The decoding result is input to the main signal carrier phase estimation section 1305. The details of the decoding are as described in the first embodiment.

  The main signal buffer unit 1304 holds the reference signal frame-synchronized main signal input from the reference signal frame synchronization unit 1303 over a period until the reference signal is decoded, and when the reference signal is decoded, the main signal Input to the carrier phase estimation unit 1305.

  Main signal carrier phase estimation section 1305 performs phase slip based on the reference signal frame-synchronized main signal input from main signal buffer section 1304 and the reference signal decoding result input from reference signal decoding section 1308. The carrier phase is estimated while being detected and compensated, and the main signal whose carrier phase is estimated is input to the main signal likelihood generator 1309.

  The main signal likelihood generation unit 1309 calculates the likelihood of the main signal whose carrier phase is estimated by the main signal carrier phase estimation unit 1305 and inputs the likelihood information of the main signal to the main signal frame synchronization unit 1310.

  The main signal frame synchronization unit 1310 secures synchronization of the main signal frame based on the likelihood information of the main signal input from the main signal likelihood generation unit 1309, and obtains the likelihood information of the main signal synchronized with the main signal frame. The result is input to the main signal error correction decoding unit 1311.

  Main signal error correction decoding section 1311 is performed by main signal frame synchronization main signal likelihood information input from main signal frame synchronization section 1310 and main signal error correction encoding section 1101 in transmission section 1100. Based on the error correction coding rule, error correction decoding is performed, and the decoding result is input to the external communication device.

At this time, error correction decoding by the main signal error correction decoding unit 1311 is performed ignoring redundant bits in reference signal encoding.
The main signal frame synchronization unit 1310 may have a function of removing redundant bits encoded based on the reference signal encoding rule.
The bit allocation operation in the fifth embodiment (FIG. 7) of the present invention is performed in the same manner as in the first to fourth embodiments (FIGS. 3 to 6).

  As described above, the optical communication system according to Embodiment 5 (FIG. 7) of the present invention includes a transmission unit 1100 that transmits an optical signal, a transmission unit 1200 that transmits an optical signal from the transmission unit 1100, and a transmission unit. And a receiver 1300 that receives an optical signal via 1200. The transmitter 1100 includes an optical modulator 1104, and generates a reference signal for a part of an information bit string included in a main signal to be transmitted. Encoding is performed based on a reference signal encoding rule, and the optical signal is converted into an optical signal via the optical modulation unit 1104 and transmitted.

  The reception unit 1300 includes an optical demodulation unit 1301, performs coherent detection of an optical signal received via the transmission unit 1200, and generates a signal in which a finite number of phase slips remain in the demodulation processing in the optical demodulation unit 1301. On the other hand, the main signal data lane replacement and the logic polarity inversion caused by the phase slip are used as prior information, and a part of the information bit string encoded in the transmission unit 1100 is decoded with high accuracy to be handled as a reference signal and transmitted. The reference signal is used to compensate for the communication quality change caused by the transmission characteristics of the main signal in the unit 1100, the transmission unit 1200, and the reception unit 1300. In particular, the phase slip included in the communication quality change is detected and compensated.

  Specifically, the transmission unit 1100 has a reference signal encoding unit 1102 for encoding a part of the information bit sequence, and the reception unit 1300 is for decoding a part of the encoded information bit sequence. A reference signal decoding unit 1308 and a main signal carrier phase estimation unit 1305 for compensating for a change in communication quality using the reference signal.

  Further, the reference signal encoding unit 1102 assigns redundant bits encoded based on the reference signal encoding rule to the information bit string, and the reference signal decoding unit 1308 decodes the redundant bits.

The transmission unit 1100 also includes a main signal error correction encoding unit 1101. The main signal error correction encoding unit 1101 corrects the main signal error before inserting a reference bit string in encoding based on the reference signal encoding rule. Encoding is performed.
On the other hand, the receiving unit 1300 includes a main signal error correction decoding unit 1311. After removing redundant bits encoded based on the reference signal encoding rule, the main signal error correction decoding unit 1311 performs error correction on the main signal. Decrypt.

  More specifically, the transmission unit 1100 includes a main signal error correction encoding unit 1101 that performs error correction encoding of the main signal based on data input from the external communication device, and a part of the main signal as a reference signal. A reference signal encoding unit 1102 that encodes a reference signal based on a reference signal encoding rule for generating a signal, and an optical modulation unit that generates an optical signal corresponding to a signal obtained by performing error correction encoding on the main signal and encoding the reference signal 1104.

  In addition, the receiving unit 1300 performs coherent detection of the optical signal input from the transmission unit 1200, and then generates an optical demodulation unit 1301 that generates a main signal that is discretized and sampled by analog / digital conversion, and the optical demodulation unit 1301. The reference signal frame synchronization unit 1303 that synchronizes the reference signal frame from the main signal, the main signal buffer unit 1304 that temporarily holds the main signal via the reference signal frame synchronization unit 1303, and the reference signal frame synchronization unit 1303 A reference signal carrier phase estimation unit 1306 that estimates a carrier phase for reference signal decoding from a main signal, and a reference signal likelihood that generates likelihood information of the reference signal whose carrier phase is estimated by the reference signal carrier phase estimation unit 1306 Degree generator 1307 and reference signal decoder 130 for decoding the reference signal based on the likelihood information of the reference signal And the main signal for detecting and compensating the phase slip of the main signal based on the estimation result of the carrier phase of the main signal and the decoding result of the reference signal, while estimating the carrier phase of the main signal in the main signal buffer unit 1304 Based on the carrier phase estimation unit 1305, the main signal likelihood generation unit 1309 that generates likelihood information of the main signal whose phase slip is detected and compensated by the main signal carrier phase estimation unit 1305, and the likelihood information of the main signal, A main signal frame synchronization unit 1310 that performs frame synchronization of the main signal, and a main signal error correction decoding unit that performs error correction decoding of the main signal based on likelihood information of the main signal frame-synchronized by the main signal frame synchronization unit 1310 1311.

Note that, in the transmission unit 1100, a part of the information bit string encoded based on the reference signal encoding rule may be encoded by the main signal error correction encoding unit 1101.
Further, some of the redundant bits encoded based on the reference signal encoding rule may be known signals.
Furthermore, the receiving unit 1300 can also use redundant bits as reference signals.

  As a result, in the same manner as described above, in the transmission unit 1100, a part of the information bit string of the main signal is transmitted after being encoded with the reference signal, and the reference bit is transmitted with a part of the information bit string encoded with the reference signal. The receiver 1300 can detect and compensate for the phase slip by handling a part of the decoded information bit like a known reference signal.

  Therefore, transmission quality deterioration due to phase slip can be avoided without using differential encoding and differential decoding as in the conventional system, and a reference bit string (known bit signal in FIG. 2) is inserted into the main signal. Compared with the case of performing the above, the redundancy for obtaining the same amount of reference signals is suppressed to be small, so that the increase in redundancy can be reduced and the transmission quality can be improved.

Embodiment 6 FIG.
In the fifth embodiment (FIG. 7), the reference signal carrier phase estimation unit 1306 is used in the reception unit 1300. However, as shown in FIG. 8, the main signal phase compensation unit 1312 is used in the reception unit 1300A. The insertion position of the main signal carrier phase estimation unit 1305A may be changed.

  FIG. 8 is a functional block configuration showing an optical communication system according to Embodiment 6 of the present invention. Components similar to those described above (see FIG. 7) are denoted by the same reference numerals as those described above or after “ Detailed description is omitted with “A”.

  In FIG. 8, a receiving unit 1300A includes an optical demodulation unit 1301, a receiving end signal processing unit 1302A, a main signal carrier phase estimation unit 1305A, a reference signal frame synchronization unit 1303A, a main signal buffer unit 1304A, and a main signal phase. Compensator 1312, reference signal likelihood generator 1307 A, reference signal decoder 1308 A, main signal likelihood generator 1309 A, main signal frame synchronizer 1310, and main signal error correction decoder 1311 It is configured.

  In this case, in the reception unit 1300A, a main signal phase compensation unit 1312 is provided instead of the reference signal carrier phase estimation unit 1306 described above (see FIG. 7), and the main signal carrier phase estimation unit 1305A includes reference signal frame synchronization. It is inserted on the input side of the section 1303A.

  Also, regarding the receiving end signal processing unit 1302A, the reference signal frame synchronization unit 1303A, the main signal buffer unit 1304A, the reference signal likelihood generation unit 1307A, the reference signal decoding unit 1308A, and the main signal likelihood generation unit 1309A, The processing operation is different from that described above (FIG. 7).

  The features of the sixth embodiment of the present invention are the bit allocation operation by the reference signal encoding unit 1102 in the transmission unit 1100 and the reference signal decoding unit after phase estimation by the main signal carrier phase estimation unit 1305A in the reception unit 1300A. The decoding operation by 1308A and the phase slip detection and compensation operation by the main signal phase compensation unit 1312 are included.

  Reception end signal processing section 1302A compensates for waveform distortion generated in transmission section 1100, transmission section 1200 and optical demodulation section 1301 by digital signal processing, and the main signal after waveform distortion compensation is sent to main signal carrier phase estimation section 1305A. input.

  The main signal carrier phase estimation unit 1305A estimates the carrier phase of the main signal after waveform distortion compensation input from the receiving end signal processing unit 1302A using the M-power method or the provisional determination method, and the carrier phase is estimated. The signal is input to reference signal frame synchronization section 1303A.

  The reference signal frame synchronization unit 1303A ensures synchronization of the reference signal encoded frame based on the main signal input from the main signal carrier phase estimation unit 1305A, and the main signal buffer unit 1304A The signal is input to the reference signal likelihood generation unit 1307A.

  The reference signal likelihood generation unit 1307A calculates the likelihood of the reference signal after carrier phase estimation based on the reference signal frame synchronized main signal input from the reference signal frame synchronization unit 1303A, and uses the likelihood information as a reference signal. The data is input to the decoding unit 1308A.

  The reference signal decoding unit 1308A performs reference signal decoding based on the likelihood information of the reference signal input from the reference signal likelihood generation unit 1307A and the coding rule in the reference signal coding unit 1102, and performs decoding. The result is input to the main signal phase compensation unit 1312. Details of the decoding are as described in the first embodiment.

  The main signal buffer unit 1304A holds the main signal synchronized with the reference signal frame input from the reference signal frame synchronization unit 1303A over a period until the reference signal is decoded, and the main signal is decoded when the reference signal is decoded. Input to the phase compensation unit 1312.

  The main signal phase compensation unit 1312 detects the phase slip based on the main signal synchronized with the reference signal frame input from the main signal buffer unit 1304A and the reference signal decoding result input from the reference signal decoding unit 1308A. Compensation is performed, and the main signal subjected to phase slip compensation is input to the main signal likelihood generation unit 1309A.

  At this time, if the modulation target is a DP-QPSK signal as in the first and second embodiments, the phase slip compensation amount may be 0, 90, 180, or -90 degrees. is there.

The main signal likelihood generation unit 1309A calculates the likelihood of the main signal subjected to phase slip compensation input from the main signal phase compensation unit 1312 and inputs the likelihood information of the main signal to the main signal frame synchronization unit 1310.
The bit allocation operation in the sixth embodiment (FIG. 8) of the present invention is performed in the same manner as in the first to fourth embodiments (FIGS. 3 to 6).

  As described above, the optical communication system according to Embodiment 6 (FIG. 8) of the present invention includes a transmission unit 1100 that transmits an optical signal, a transmission unit 1200 that transmits an optical signal from the transmission unit 1100, and a transmission unit. The transmission unit 1100 includes an optical modulation unit 1104, and generates a reference signal for a part of an information bit string included in a main signal to be transmitted. Encoding is performed based on a reference signal encoding rule, and the optical signal is converted into an optical signal via the optical modulation unit 1104 and transmitted.

  The receiving unit 1300A performs coherent detection of the optical signal input from the transmission unit 1200, and then generates an optical demodulator 1301 that generates a main signal that is discretized and sampled by analog / digital conversion, and a main demodulator via the optical demodulator 1301. A main signal carrier phase estimation unit 1305A for estimating the main signal carrier phase used for decoding both the signal and the reference signal, and a reference signal for synchronizing the reference signal frame from the main signal via the main signal carrier phase estimation unit 1305A The carrier phase of the main signal is estimated by the frame synchronization unit 1303A, the main signal buffer unit 1304A that temporarily holds the main signal via the reference signal frame synchronization unit 1303A, and the main signal carrier phase estimation unit 1305A, and the reference signal frame synchronization Generating likelihood information of the reference signal synchronized with the reference signal frame by unit 1303A Based on the reference signal likelihood generation unit 1307A, the reference signal decoding unit 1308A that decodes the reference signal based on the likelihood information of the reference signal, the estimation result of the carrier phase of the main signal, and the decoding result of the reference signal, The main signal phase compensation unit 1312 that detects and compensates for the phase slip of the signal, the main signal likelihood generation unit 1309A that generates the likelihood information of the main signal whose phase slip is detected and compensated, and frame synchronization of the main signal A main signal frame synchronization unit 1310; and a main signal error correction decoding unit 1311 that performs error correction decoding of the main signal based on likelihood information of the main signal frame-synchronized by the main signal frame synchronization unit 1310. .

  As a result, in the same manner as described above, in the transmission unit 1100, a part of the information bit string of the main signal is transmitted after being encoded with the reference signal, and the reference bit is transmitted with a part of the information bit string encoded with the reference signal. In the receiving unit 1300A, it is possible to detect and compensate for the phase slip by handling a part of the decoded information bits like a known reference signal.

  Therefore, transmission quality deterioration due to phase slip can be avoided without using differential encoding and differential decoding as in the conventional system, and a reference bit string (known bit signal in FIG. 2) is inserted into the main signal. Compared with the case of performing the above, the redundancy for obtaining the same amount of reference signals is suppressed to be small, so that the increase in redundancy can be reduced and the transmission quality can be improved.

  As described above, the optical communication system according to the present invention is useful for a coherent optical communication system, and is particularly suitable for an optical communication system with a low code error rate.

  10, 1100 Transmission unit, 11 Transmission bit string generation unit, 12 Reference bit string insertion unit, 13 Signal transmission unit, 20, 1200 Transmission unit, 30, 1300, 1300A Reception unit, 31 Signal reception unit, 32 Reference bit string analysis unit, 33 Bit string Receiver, 101 XI lane, 102 XQ lane, 103 YI lane, 104 YQ lane, 111 XI0 lane, 112 XQ0 lane, 11 13 YI0 lane, 114 YQ0 lane, 121 XI1 lane, 122 XQ1 lane, 123 YI1 lane, 124 YQ1 lane 300, 400, 500, 600 Reference signal coding frame, 301, 302, 401-404, 501, 502, 601, 602 Encoded information bits, 311, 312, 411-414, 511, 512, 611 614 Encoded redundant bits, 321 to 324, 421 to 427, 521 to 524, 621 to 624 Uncoded information bits, 1101 main signal error correction encoding unit, 1102 reference signal encoding unit, 1103 transmitting end signal Processing unit, 1104 Optical modulation unit, 1301 Optical demodulation unit, 1302, 1302A Reception end signal processing unit, 1303, 1303A Reference signal frame synchronization unit, 1304, 1304A Main signal buffer unit, 1305, 1305A Main signal carrier phase estimation unit, 1306 Reference signal carrier phase estimation unit, 1307, 1307A Reference signal likelihood generation unit, 1308, 1308A Reference signal decoding unit, 1309, 1309A Main signal likelihood generation unit, 1310 Main signal frame synchronization unit, 1311 Main signal error correction decoding Part, 1312 main signal phase compensation part.

Claims (17)

An optical communication system including a transmission unit that transmits an optical signal, a transmission unit that transmits an optical signal from the transmission unit, and a reception unit that receives an optical signal via the transmission unit,
The transmission unit encodes a part of an information bit string included in a main signal to be transmitted based on a reference signal encoding rule for generating a reference signal,
The receiver is
Based on the reference signal encoding rule in the transmitter, treat as the reference signal by decoding a part of the information bit sequence encoded by the transmitter,
An optical communication system, wherein a change in communication quality caused by transmission characteristics with respect to the main signal in the transmission unit, the transmission unit, and the reception unit is compensated using the reference signal. The receiving unit, an optical communication system according to claim 1, characterized in that detecting and compensating for position-phase slip that is part of the communication quality changes. The transmission unit includes a reference bit string insertion unit for encoding a part of the information bit string,
The reception unit includes a reference bit string analysis unit for decoding a part of the information bit string and compensating for the communication quality change using the reference signal. The optical communication system described. An optical communication system including a transmission unit that transmits an optical signal, a transmission unit that transmits an optical signal from the transmission unit, and a reception unit that receives an optical signal via the transmission unit,
The transmission unit includes an optical modulation unit, and encodes a part of an information bit string included in a main signal to be transmitted based on a reference signal encoding rule for generating a reference signal, and the optical modulation unit Is converted into an optical signal via
The receiving unit includes an optical demodulation unit, performs coherent detection of the optical signal received via the transmission unit, and
For the signal in which a finite number of phase slips remain in the demodulation process in the optical demodulator, the main signal data lane replacement and logical polarity inversion caused by the phase slip are used as prior information and encoded in the transmitter. Treating it as the reference signal by decoding a part of the information bit string,
An optical communication system, wherein a change in communication quality caused by transmission characteristics with respect to the main signal in the transmission unit, the transmission unit, and the reception unit is compensated using the reference signal.   The optical communication system according to claim 4, wherein the reception unit detects and compensates for the phase slip included in the communication quality change. The transmission unit includes a reference signal encoding unit for encoding a part of the information bit string,
The receiving unit is a reference signal decoding unit for decoding a part of the encoded information bit sequence, a main signal carrier phase estimation unit for compensating the communication quality change using the reference signal, The optical communication system according to claim 4, wherein the optical communication system includes: The reference signal encoding unit allocates redundant bits encoded based on the reference signal encoding rule to the information bit string,
The optical communication system according to claim 6, wherein the reference signal decoding unit decodes the redundant bits. The transmission unit includes a main signal error correction encoding unit, and before inserting a reference bit string in encoding based on the reference signal encoding rule, the main signal error correction encoding unit performs error correction code of the main signal. Make
The receiving unit includes a main signal error correction decoding unit, and after removing redundant bits encoded based on the reference signal encoding rule, the main signal error correction decoding unit performs error correction decoding of the main signal. The optical communication system according to claim 7, wherein the optical communication system is configured. In the transmitter,
A part of the information bit sequence encoded based on the reference signal encoding rule is:
9. The optical communication system according to claim 8, wherein the optical communication system is encoded by the main signal error correction encoding unit.   The optical communication system according to any one of claims 7 to 9, wherein some of the redundant bits encoded based on the reference signal encoding rule are known signals.   11. The optical communication system according to claim 7, wherein the reception unit also uses the redundant bit as the reference signal. 11. In the transmitter,
A part of the information bit sequence encoded based on the reference signal encoding rule is:
The four main signal data lanes XI, XQ, YI, YQ based on the orthogonal polarization component X / Y and the orthogonal phase component I / Q in the polarization multiplexing orthogonal phase modulation are equally allocated to each of the four main signal data lanes. The optical communication system according to any one of claims 1 to 11. In the transmitter,
A part of the information bit sequence encoded based on the reference signal encoding rule is:
13. The optical communication system according to claim 12, wherein the four main signal data lanes XI, XQ, YI, YQ are assigned to the same time slot. In the transmitter,
A part of the information bit sequence encoded based on the reference signal encoding rule is:
Of the four main signal data lanes XI, XQ, YI, YQ, two main signal data lanes XI, XQ are allocated to the first time slot,
13. The optical communication system according to claim 12, wherein the other two main signal data lanes YI and YQ are allocated to a second same time slot different from the first time slot. In the transmitter,
A part of the information bit sequence encoded based on the reference signal encoding rule is:
13. The optical communication system according to claim 12, wherein each of the four main signal data lanes XI, XQ, YI, YQ is assigned to a different time slot. An optical communication system including a transmission unit that transmits an optical signal, a transmission unit that transmits an optical signal from the transmission unit, and a reception unit that receives an optical signal via the transmission unit,
The transmitter is
Based on data input from an external communication device, a main signal error correction encoding unit that performs error correction encoding of the main signal;
A reference signal encoding unit that encodes a part of the main signal based on a reference signal encoding rule for generating a reference signal;
An optical modulation unit that generates an optical signal corresponding to a signal obtained by performing error correction encoding and reference signal encoding on the main signal, and
The receiver is
An optical demodulator that generates a main signal discretized and sampled by analog / digital conversion after coherent detection of the optical signal input from the transmission unit;
A reference signal frame synchronization unit that synchronizes a reference signal frame from a main signal via the optical demodulation unit;
A main signal buffer unit that temporarily holds a main signal via the reference signal frame synchronization unit;
A reference signal carrier phase estimation unit for estimating a carrier phase for decoding a reference signal from a main signal via the reference signal frame synchronization unit;
A reference signal likelihood generation unit that generates likelihood information of a reference signal whose carrier phase is estimated by the reference signal carrier phase estimation unit;
A reference signal decoding unit for decoding the reference signal based on likelihood information of the reference signal;
A main signal for estimating the carrier phase of the main signal in the main signal buffer unit and detecting and compensating for the phase slip of the main signal based on the estimation result of the carrier phase of the main signal and the decoding result of the reference signal A carrier phase estimation unit;
A main signal likelihood generation unit that generates likelihood information of the main signal in which phase slip is detected and compensated by the main signal carrier phase estimation unit;
A main signal frame synchronization unit that performs frame synchronization of the main signal based on likelihood information of the main signal;
A main signal error correction decoding unit that performs error correction decoding of the main signal based on likelihood information of the main signal frame-synchronized by the main signal frame synchronization unit;
An optical communication system comprising: An optical communication system including a transmission unit that transmits an optical signal, a transmission unit that transmits an optical signal from the transmission unit, and a reception unit that receives an optical signal via the transmission unit,
The transmitter is
Based on data input from an external communication device, a main signal error correction encoding unit that performs error correction encoding of the main signal;
A reference signal encoding unit that encodes a part of the main signal based on a reference signal encoding rule for generating a reference signal;
An optical modulation unit that generates an optical signal corresponding to a signal obtained by performing error correction encoding and reference signal encoding on the main signal, and
The receiver is
An optical demodulator that generates a main signal discretized and sampled by analog / digital conversion after coherent detection of the optical signal input from the transmission unit;
A main signal carrier phase estimation unit for estimating a main signal carrier phase used for decoding both the main signal and the reference signal via the optical demodulation unit;
A reference signal frame synchronization unit that synchronizes a reference signal frame from a main signal via the main signal carrier phase estimation unit;
A main signal buffer unit that temporarily holds a main signal via the reference signal frame synchronization unit;
A reference signal likelihood generation unit that generates a reference signal likelihood information in which a carrier phase of the main signal is estimated by the main signal carrier phase estimation unit and a reference signal frame synchronization is performed by the reference signal frame synchronization unit;
A reference signal decoding unit for decoding the reference signal based on likelihood information of the reference signal;
A main signal phase compensation unit that detects and compensates for a phase slip of the main signal based on an estimation result of a carrier phase of the main signal and a decoding result of the reference signal;
A main signal likelihood generating unit for generating likelihood information of the main signal in which the phase slip is detected and compensated;
A main signal frame synchronization unit for performing frame synchronization of the main signal;
A main signal error correction decoding unit that performs error correction decoding of the main signal based on likelihood information of the main signal frame-synchronized by the main signal frame synchronization unit;
An optical communication system comprising:

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