Optical transmitting device, optical receiving device, optical transmission system, and optical transmission method

Abstract

The optical transmitting device for transmitting a multi-level modulated optical transmission signal comprises a control coding unit (27) for performing error correction coding processing on control information including information on a multi-level modulation method used for a main signal information sequence and outputting an encoded control information sequence; a main coding unit (25) for performing error correction coding processing on the main signal information corresponding to the multi-level modulation method indicated by the control information and generating an encoded main signal information sequence; a selection circuit (28) for inserting a control information sequence into a main signal information sequence so that the control information sequence indicates the multi-level modulation method to be used for the main signal information sequence immediately following, and a mapping unit (29) for performing mapping processing on the control information sequence output by the selection circuit (28) using a predetermined multi-level modulation method, and for performing mapping processing on the main signal information sequence output by the selection circuit using the multi-level modulation method indicated by the control information sequence, thereby generating a multi-level modulated optical transmission signal.

Description

[Technical field]

[0001] The present disclosure relates to an optical transmitting device, an optical receiving device, an optical transmission system, and an optical transmission method for transmitting a multi-level modulated optical transmission signal. [Background technology]

[0002] Conventionally, in optical transmission systems, error correction codes are used to realize high transmission capacity and long distance transmission. In optical transmission systems that transmit multi-level modulated optical transmission signals, error correction codes corresponding to the multi-level modulation method used are used. For example, Patent Document 1 discloses an error correction coding device corresponding to the multi-level modulation method. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2021 / 199690 Summary of the Invention [Problem to be solved by the invention]

[0004] However, according to the above conventional technology, the multi-level modulation method used is assumed to be one predetermined method, and the code format for error correction is determined to be one type. Therefore, when data shorter than the code format is input, a fixed value is inserted into the information bit sequence to match the data length to the code format, which causes a problem of reduced transmission efficiency.

[0005] The present disclosure has been made in view of the above, and has an object to provide an optical transmitting device capable of improving transmission efficiency. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems and achieve the object, an optical transmission device according to the present disclosure is an optical transmission device that transmits a multi-level modulated optical transmission signal, and includes: a control encoding unit that performs an error correction encoding process on control information including information on a multi-level modulation method used for a main signal information sequence, and outputs an encoded control information sequence; For the transmitted information bit sequence, The multi-level modulation method indicated by the control information A fixed bit corresponding to the number of bits is inserted according to the multi-level modulation method used, and the main signal information, which is a bit sequence corresponding to the maximum multi-level symbol of the multi-level modulation method used, is encoded according to the same parameters regardless of the multi-level modulation method. Error correction coding process I'll do it a main coding unit for generating an uncoded main signal information sequence; a selection circuit for inserting a control information sequence into a main signal information sequence so that the control information sequence indicates the multi-level modulation scheme to be used for the main signal information sequence immediately following, and outputting the control information sequence; and a mapping process for the control information sequence output by the selection circuit using a predetermined multi-level modulation scheme, Encoded and a mapping unit that performs mapping processing on the main signal information sequence using the multi-level modulation method indicated by the control information sequence to generate a multi-level modulated optical transmission signal. Effect of the Invention

[0007] The optical transmission device according to the present disclosure has an effect of improving transmission efficiency. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram showing a configuration of an optical transmission system according to a first embodiment; [Diagram 2] FIG. 2 is a diagram showing a configuration example of the optical transmission device shown in FIG. 1; [Diagram 3] FIG. 3 is a diagram showing a detailed configuration example of the encoding circuit shown in FIG. [Figure 4] 3 is a flowchart illustrating the operation of the optical transmitter shown in FIG. 2. [Diagram 5] FIG. 2 is a diagram showing the configuration of a decoding circuit included in the optical receiving device shown in FIG. 1; [Figure 6] 1 is a flowchart illustrating the operation of the optical receiving device shown in FIG. [Figure 7] FIG. 2 shows dedicated hardware for implementing the functions of the optical transmitter and the optical receiver shown in FIG. 1. [Figure 8] FIG. 2 is a diagram showing the configuration of a control circuit for implementing the functions of the optical transmitter and the optical receiver shown in FIG. 1; [Figure 9] Diagram showing the frame format of 256QAM (Quadrature Amplitude Modulation) [Figure 10] Diagram showing the 64QAM frame format [Figure 11] Diagram showing the 16QAM frame format [Figure 12] Diagram showing QPSK frame format DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] An optical transmitting device, an optical receiving device, an optical transmission system, and an optical transmission method according to embodiments of the present disclosure will be described below in detail with reference to the drawings.

[0010] Embodiment 1 FIG. 1 is a diagram showing a configuration of an optical transmission system 1 according to a first embodiment. The optical transmission system 1 includes an optical transmitter 2 and an optical receiver 3. The optical transmitter 2 and the optical receiver 3 are connected by an optical fiber or the like. The optical transmission system 1 transmits a multi-level modulated optical transmission signal. The optical transmitter 2 generates a multi-level modulated optical transmission signal and transmits the generated optical transmission signal. The optical receiver 3 receives the optical transmission signal transmitted by the optical transmitter 2.

[0011] The optical transmitting device 2 can perform multi-level modulation processing corresponding to a plurality of types of multi-level modulation methods. The optical transmitting device 2 can select and use a multi-level modulation method with good transmission efficiency according to the length of the information bit sequence to be transmitted. The optical receiving device 3 needs to perform reception processing according to the modulation method used for the optical transmission signal to be received. For this reason, the optical transmitting device 2 has a function of transmitting a control signal for notifying the optical receiving device 3 of the modulation method used, to the optical receiving device 3, before transmitting the main signal including the information bit sequence to be transmitted. The specific configuration and operation will be described below.

[0012] Fig. 2 is a diagram showing an example of the configuration of the optical transmission device 2 shown in Fig. 1. The optical transmission device 2 includes a modulation method determination unit 20, a fixed value insertion unit 21, a control information generation unit 22, and an encoding circuit 23. Note that the optical transmission device 2 may include components other than those shown in Fig. 2.

[0013] The modulation scheme determination unit 20 determines the multi-level modulation scheme to be used for the main signal information including the information bit sequence based on the sequence length of the information bit sequence to be transmitted. The modulation scheme determination unit 20 selects the multi-level modulation scheme so as to improve the transmission efficiency. The modulation scheme determination unit 20 outputs the information bit sequence to be transmitted to the fixed value insertion unit 21, and outputs the determined multi-level modulation scheme to both the fixed value insertion unit 21 and the control information generation unit 22.

[0014] The fixed value insertion unit 21 inserts fixed values ​​into bit positions that are not to be transmitted in accordance with the multi-level modulation scheme determined by the modulation scheme determination unit 20, thereby generating main signal information which is an information bit sequence corresponding to the maximum multi-level symbol, and outputs the main signal information to each of the control information generation unit 22 and the encoding circuit 23.

[0015] The control information generator 22 generates control information including information indicating the multi-level modulation scheme determined by the modulation scheme determiner 20, and outputs the generated control information to the encoder 23. The control information may include frame information of the main signal information after processing by the fixed value inserter 21. The frame information includes, for example, information on the sequence length of the information bit sequence to be transmitted, which is included in the main signal information.

[0016] The encoding circuit 23 executes error correction encoding processing and modulation processing on the main signal information and the control information. A specific configuration will be described below.

[0017] Fig. 3 is a diagram showing a detailed configuration example of the encoding circuit 23 shown in Fig. 2. The encoding circuit 23 receives main signal information and control information including information on the modulation method used for the main signal information.

[0018] The encoding circuit 23 includes an interleaver 24, a main encoding unit 25, a deinterleaver 26, a control encoding unit 27, a selection circuit 28, and a mapping unit 29. Main signal information is input to the interleaver 24, and control information is input to the control encoding unit 27.

[0019] The interleaver 24 rearranges the order of the bit sequence of the main signal information in units of multi-level modulation symbols. The interleaver 24 rearranges the order of the bit sequence of the main signal information in accordance with the processing in the main encoding unit 25. The interleaver 24 outputs the main signal information after rearrangement to the main encoding unit 25.

[0020] The main coding unit 25 performs coding processing on the main signal information output by the interleaver 24 based on the control information, and generates a coded main signal information sequence. The main coding unit 25 has an HD (Hard Decision)-FEC (Forward Error Correction) coding unit 251, a multilevel coding unit 252, and an SD (Soft Decision)-FEC coding unit 253.

[0021] The HD-FEC encoding unit 251 performs encoding processing using an error correction code that assumes that the optical receiving device 3 performs hard decision decoding on the main signal information based on the frame information included in the control information. The encoding processing performed by the HD-FEC encoding unit 251 may be referred to as a first encoding processing. In the first encoding processing, for example, a BCH (Bose Chaudhuri Hocquenghem) code, an RS (Reed Solomon) code, or the like is used, and encoding processing is performed assuming the maximum multi-level modulation symbol. That is, the HD-FEC encoding unit 251 performs error correction encoding on the symbol bits of the fixed 0 row as an information sequence. The HD-FEC encoding unit 251 outputs the main signal information sequence, which is the encoded sequence after the encoding processing, to the multilevel encoding unit 252.

[0022] The multilevel coding unit 252 divides the main signal information sequence output by the HD-FEC coding unit 251 in accordance with the multilevel modulation method included in the control information, and performs multilevel coding processing. The multilevel coding unit 252 outputs some bits to be processed by the SD-FEC coding unit 253 out of the multiple bits included in the main signal information sequence after the multilevel coding processing to the SD-FEC coding unit 253, and outputs the remaining bits to the deinterleaver 26. It is preferable that the bits to be processed by the SD-FEC coding unit 253 are bits with a high error rate. For example, depending on the multilevel modulation method, the error rate of each bit of the multilevel modulation symbol is different. For this reason, a bit with a high error rate among the multiple bits of the multilevel modulation symbol, for example, a least significant bit (LSB), can be the bit to be processed by the SD-FEC coding unit 253.

[0023] The SD-FEC encoding unit 253 performs encoding processing on the bits output by the multilevel encoding unit 252 using an error correction code that is premised on performing soft decision decoding at the time of decoding in the optical receiving device 3. The encoding processing performed by the SD-FEC encoding unit 253 may be referred to as a second encoding processing. In the second encoding processing, for example, an LDPC (Low Density Parity Check) code or the like is used. The SD-FEC encoding unit 253 outputs the encoded sequence after the encoding processing to the deinterleaver 26.

[0024] The deinterleaver 26 rearranges the order of the main signal information sequence output by the main encoding unit 25 to return it to the original order. In other words, the deinterleaver 26 rearranges the order of the bits contained in the main signal information sequence so that the order is the same as before the rearrangement by the interleaver 24. The deinterleaver 26 outputs the rearranged main signal information sequence to the selection circuit 28.

[0025] The control coding unit 27 performs coding processing on the control information, and outputs the control information sequence after the coding processing to the selection circuit 28. The control information includes information indicating the multi-level modulation method used for the main signal information sequence, frame information, and the like. The control coding unit 27 can hold information included in the control information and provide it to the main coding unit 25. The control coding unit 27 can error-correction code the control information using an error-correction code different from the error-correction code used for the main signal information. It is preferable that the control coding unit 27 performs coding processing using an error-correction code having a higher error-correction ability than the error-correction code used for the main signal information. For example, examples of the error-correction code used for the control information include a block code, an LDPC code, and a polar code. Since the control information sequence has a short information bit length, a polar code is preferable because it has a high error-correction ability even with a short code length and the coding rate can be flexibly configured. By the control coding unit 27 using the polar code, it is possible to improve the decoding performance of the control information. In addition, since polar codes can reduce processing delays, the time required for encoding control information can be shortened, and it becomes possible to perform the encoding process of the control information in parallel with the error correction encoding process of the main signal information.

[0026] The selection circuit 28 selects either the main signal information sequence output by the deinterleaver 26 or the control information sequence output by the control coding unit 27, and outputs the selected sequence to the mapping unit 29. Specifically, the selection circuit 28 inserts a control information sequence into the main signal information sequence so that the control information sequence indicates the multi-level modulation scheme for the main signal information sequence immediately following, and outputs the selected sequence.

[0027] The mapping unit 29 performs mapping processing on the coded sequence output by the selection circuit 28 to generate a multi-level modulation symbol sequence. At this time, the mapping unit 29 performs mapping processing on the control information sequence using a predetermined multi-level modulation method, and performs mapping processing on the main signal information sequence using a multi-level modulation method indicated by the control information. It is preferable that the mapping unit 29 uses a modulation method that is resistant to transmission noise, such as a BPSK (Binary Phase Shift Keying) modulation method or a QPSK (Quaternary PSK) modulation method, for the control information sequence. Furthermore, when the mapping unit 29 performs mapping processing on the main signal information sequence, the mapping unit 29 excludes fixed bit rows that are not transmitted from the multi-level modulation symbols. The mapping unit 29 transmits an optical transmission signal including the multi-level modulation symbol sequence after the mapping processing.

[0028] Fig. 4 is a flow chart for explaining the operation of the optical transmitter 2 shown in Fig. 2. The modulation scheme determining unit 20 of the optical transmitter 2 determines the multi-level modulation scheme to be used for the main signal information sequence based on the sequence length of the information bit sequence to be transmitted (step S101). The fixed value inserting unit 21 inserts a fixed value into the information bit sequence to be transmitted according to the determined multi-level modulation scheme (step S102). The fixed value is preferably set to, for example, "0".

[0029] The control information generator 22 generates fixed-length control information (step S103) that includes at least information indicating the multi-level modulation scheme determined by the modulation scheme determiner 20. The control information may further include frame information of the main signal.

[0030] Following the control information, main signal information is input to the encoding circuit 23. The control encoding unit 27 of the encoding circuit 23 performs error correction encoding processing on the control information (step S104). The control encoding unit 27 performs error correction encoding processing with high error correction capability.

[0031] In parallel with the error correction coding process for the control information in step S104, the interleaver 24 performs interleaving process for the main signal information when the main signal information is input (step S105). Next, the HD-FEC coding unit 251 of the main coding unit 25 performs a first error correction coding process for the main signal information output by the interleaver 24 (step S106). When the HD-FEC coding unit 251 outputs the main signal information after the first error correction coding process, the multilevel coding unit 252 performs a multilevel coding process for the main signal information (step S107). The multilevel coding unit 252 outputs the bits to be processed by the SD-FEC coding unit 253 to the SD-FEC coding unit 253, and outputs the remaining bits to the deinterleaver 26. The SD-FEC coding unit 253 performs a second error correction coding process for the main signal information for the input bits (step S108). The deinterleaver 26 performs a deinterleaving process on the main signal information output by the multilevel encoding unit 252 and the SD-FEC encoding unit 253 (step S109).

[0032] In this embodiment, the process of step S104 and the process of steps S105 to S109 are performed in parallel. However, the process of steps S105 to S109 may be performed following the process of step S104.

[0033] The selection circuit 28 inserts a control information sequence before the main signal information sequence (step S110). At this time, the selection circuit 28 inserts the control information sequence before the main signal information sequence so that the control information sequence to be inserted indicates the multi-level modulation method to be used for the main signal information sequence immediately following it. Specifically, following the control information, the main signal information for which the multi-level modulation method indicated by the control information is to be used is input to the encoding circuit 23, and the order of input to the selection circuit 28 is also the same. The selection circuit 28 outputs a fixed-length control information sequence to the mapping unit 29, and then outputs a main signal information sequence corresponding to the control information sequence to the mapping unit 29.

[0034] The mapping unit 29 performs mapping processing on the input coded bit sequence (step S111). Specifically, the mapping unit 29 performs mapping processing on the control information sequence using a predetermined multi-level modulation method. Also, the mapping unit 29 performs mapping processing on the main signal information sequence using a multi-level modulation method indicated by the control information. The mapping unit 29 transmits the multi-level modulation symbol sequence after the mapping processing to the optical receiving device 3 as an optical transmission signal (step S112).

[0035] FIG. 5 is a diagram showing a configuration of the decoding circuit 30 included in the optical receiving device 3 shown in FIG.

[0036] The decoding circuit 30 includes a separation circuit 31, a control signal soft decision generator 32, a control decoding unit 33, an interleaver 34, a main decoding unit 35, and a deinterleaver 36. In addition to the decoding circuit 30, the optical receiving device 3 can include a demodulation circuit (not shown).

[0037] The separation circuit 31 separates the input demodulated symbols into demodulated symbols of control information and demodulated symbols of main signal information. The separation circuit 31 outputs the demodulated symbols of control information to a control signal soft decision generator 32, and outputs the demodulated symbols of main signal information to an interleaver .

[0038] The control signal soft decision generator 32 performs soft decision processing on the demodulated symbols of the control information according to a predetermined control signal modulation method to generate soft decision information. The control signal soft decision generator 32 outputs the generated soft decision information to the control decoder 33.

[0039] The control decoder 33 performs error correction decoding processing on the soft decision information of the control information and outputs a control signal. The control decoder 33 can also hold the control information included in the control signal and provide it to the main decoder 35.

[0040] The interleaver 34 performs interleaving on the demodulated symbols of the main signal information, and rearranges the order of the main signal in units of multi-level modulation symbols. The interleaver 34 outputs the main signal information sequence after the interleaving process to the main decoding unit 35.

[0041] The main decoding unit 35 has a main signal soft decision generation unit 351, an SD-FEC decoding unit 352, a multi-level / multi-stage decoding unit 353, and an HD-FEC decoding unit 354. The main decoding unit 35 performs decoding processing on the main signal in accordance with the control information held by the control decoding unit 33.

[0042] The primary signal soft decision generator 351 performs soft decision processing on the primary signal to generate soft decision information. The primary signal soft decision generator 351 outputs the generated soft decision information to each of the SD-FEC decoder 352 and the multi-level / multi-stage decoder 353.

[0043] The SD-FEC decoding unit 352 performs error correction decoding processing by soft decision decoding processing on a part of the main signal. The SD-FEC decoding unit 352 outputs the processed signal to the multi-level / multi-stage decoding unit 353. The decoding processing performed by the SD-FEC decoding unit 352 may be referred to as a second error correction decoding processing.

[0044] The multilevel / multistage decoding unit 353 performs multilevel / multistage decoding processing using the non-SD-FEC decoded part output by the primary signal soft decision generation unit 351 and the SD-FEC decoded information output by the SD-FEC decoding unit 352. The multilevel / multistage decoding unit 353 outputs the processed signal to the HD-FEC decoding unit 354.

[0045] The HD-FEC decoding unit 354 performs hard-decision decoding processing on the main signal. The HD-FEC decoding unit 354 outputs the signal after the hard-decision decoding processing to the deinterleaver 36. The error correction decoding processing by the HD-FEC decoding unit 354 may be referred to as a first error correction decoding processing.

[0046] The deinterleaver 36 restores the order of the interleaved main signal in units of hard-decision multi-level modulation symbols.

[0047] Fig. 6 is a flow chart for explaining the operation of the optical receiving device 3 shown in Fig. 1. The optical receiving device 3 performs demodulation processing of the multi-level modulated optical transmission signal, which is the received signal (step S201). Then, the separation circuit 31 separates the control signal and the main signal (step S202).

[0048] The control signal soft decision generator 32 generates soft decision information for the control signal (step S203). The control decoder 33 performs soft decision error correction decoding processing for the control signal (step S204). Here, the control decoder 33 outputs the control signal and holds the control information included in the control signal.

[0049] The interleaver 34 also performs interleaving on the primary signal (step S205). The interleaving on the primary signal can be performed in parallel with the soft decision error correction decoding on the control signal in step S204. The interleaver 34 outputs the interleaved signal to the primary signal soft decision generator 351.

[0050] The primary signal soft decision generator 351 generates soft decision information for the primary signal based on the multi-level modulation scheme included in the control information held in the control decoder 33 (step S206). A portion of the generated soft decision information that is a target of soft decision decoding processing is output to the SD-FEC decoder 352, and the remaining portion is output to the multi-level / multi-stage decoder 353.

[0051] The SD-FEC decoding unit 352 performs soft-decision decoding processing, which is a second error correction decoding processing, on the input portion of the primary signal (step S207). The SD-FEC decoding unit 352 outputs the processed primary signal to the multi-level / multi-stage decoding unit 353.

[0052] The multilevel / multistage decoding unit 353 performs multilevel / multistage decoding processing on the input main signal (step S208). Specifically, the multilevel / multistage decoding unit 353 determines hard decision bits from the hard decision results of the multilevel demodulation symbols that have not been subjected to SD-FEC decoding processing based on the SD-FEC decoding results, and outputs the result to the HD-FEC decoding unit 354 together with the multilevel demodulation symbols that have been subjected to SD-FEC decoding processing.

[0053] The HD-FEC decoder 354 performs hard-decision decoding, which is a first error correction decoding process, on the main signal (step S209). At this time, by inputting the modulation symbol bits that are not transmitted as fixed bits "0" based on the information included in the decoded control signal, it is possible to reduce the probability of correction failure without affecting the error correction process and by shortening the error correction code sequence. The HD-FEC decoder 354 outputs the information bit sequence decoded by the hard-decision decoding process to the deinterleaver 36.

[0054] The deinterleaver 36 performs deinterleaving processing on the main signal to restore the order of the information bit sequence to the original order in accordance with the rearrangement performed by the interleaver 34 (step S210).

[0055] Here, a description will be given of the hardware configuration of the optical transmitting device 2 and the optical receiving device 3. Each function of the optical transmitting device 2 and the optical receiving device 3 is realized by a processing circuit. These processing circuits may be realized by dedicated hardware, or may be a control circuit using a CPU (Central Processing Unit).

[0056] When the above processing circuits are realized by dedicated hardware, they are realized by a processing circuit 90 shown in Fig. 7. Fig. 7 is a diagram showing dedicated hardware for realizing the functions of the optical transmitting device 2 and the optical receiving device 3 shown in Fig. 1. The processing circuit 90 is a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or a combination of these.

[0057] When the above processing circuit is realized by a control circuit using a CPU, the control circuit is, for example, a control circuit 91 having a configuration shown in FIG. 8. FIG. 8 is a diagram showing the configuration of the control circuit 91 for realizing the functions of the optical transmitter 2 and the optical receiver 3 shown in FIG. 1. As shown in FIG. 8, the control circuit 91 includes a processor 92 and a memory 93. The processor 92 is a CPU, and is also called an arithmetic unit, a microprocessor, a microcomputer, a DSP (Digital Signal Processor), etc. The memory 93 is, for example, a non-volatile or volatile semiconductor memory such as a RAM (Random Access Memory), a ROM (Read Only Memory), a flash memory, an EPROM (Erasable Programmable ROM), an EEPROM (Electrically EPROM), a magnetic disk, a flexible disk, an optical disk, a compact disk, a mini disk, a DVD (Digital Versatile Disk), etc.

[0058] When the above processing circuit is realized by the control circuit 91, it is realized by the processor 92 reading and executing a program corresponding to the processing of each component, which is stored in the memory 93. The memory 93 is also used as a temporary memory for each process executed by the processor 92. The program executed by the processor 92 may be provided in a state stored in a storage medium, or may be provided via a communication path such as the Internet.

[0059] The division of the components shown in Figures 2, 3, and 5 is merely an example, and is not limited to the illustrated example. Each of the components shown in Figures 2, 3, and 5 may be realized by a different processing circuit, or the components shown in Figures 2, 3, and 5 may be realized by a single processing circuit. The components shown in Figures 2, 3, and 5 may also be realized by dividing them into multiple processing circuits.

[0060] Next, the frame format used by the optical transmission system 1 will be described for each multi-level modulation method. The optical transmission system 1 can encode the main signal information to be transmitted using a multi-level modulation method selected from a plurality of multi-level modulation methods such as 256QAM, 64QAM, 16QAM, and QPSK. Figure 9 is a diagram showing a frame format of 256QAM. As for the control information, it is assumed that the control information is transmitted with a fixed length by QPSK modulation, regardless of the modulation method used for the main signal information.

[0061] For the main signal portion, in the case of 256QAM, data that has been doubly coded using SD-FEC and HD-FEC is placed in a portion of the LSB (the least significant bit), and data coded only using HD-FEC is placed in the portion other than the LSB.

[0062] Fig. 10 is a diagram showing a frame format of 64QAM. For the main signal, in the case of 64QAM, data doubly coded by SD-FEC and HD-FEC is placed in a part of the LSB, data coded only by HD-FEC is placed in the remaining part of the LSB and two of the remaining three systems, the most significant bit MSB (Most Significant Bit), SSB (Second Significant Bit), and TSB (Third Significant Bit), and the remaining system, the TSB, is fixed to 0, and error correction coding processing is performed. Note that the part fixed to 0 is not transmitted during transmission.

[0063] Fig. 11 is a diagram showing the frame format of 16QAM. For the main signal, in the case of 16QAM, data that is doubly coded by SD-FEC and HD-FEC is placed in a part of the LSB, data that is coded only by HD-FEC is placed in the remaining part of the LSB and the MSB of one of the three systems other than the LSB, and the remaining two systems, SSB and TSB, are fixed to 0, and error correction coding processing is performed. The part that is fixed to 0 is not transmitted during transmission.

[0064] Fig. 12 is a diagram showing the frame format of QPSK. In the case of QPSK, data that is doubly coded by SD-FEC and HD-FEC is placed in a part of the LSB, data that is coded only by HD-FEC is placed in the remaining part of the LSB, and error correction coding processing is performed with the remaining three systems other than the LSB, that is, MSB, SSB, and TSB, fixed to 0. The parts that are fixed to 0 are not transmitted during transmission.

[0065] With the above configuration, the SD-FEC portion can perform the same encoding and decoding processes regardless of the modulation method, and the HD-FEC portion can also perform the same encoding and decoding processes, except for manipulating the portion that is fixed to 0 according to the modulation method set by the control signal. Therefore, it is possible to reduce the circuit scale.

[0066] As described above, the optical transmitting device 2 according to the first embodiment is an optical transmitting device 2 that transmits a multi-level modulated optical transmission signal, and is characterized by including: a control encoding unit 27 that performs error correction encoding processing on control information including information on a multi-level modulation method used for a main signal information sequence to output an encoded control information sequence; a main encoding unit 25 that performs error correction encoding processing on the main signal information corresponding to the multi-level modulation method indicated by the control information to generate an encoded main signal information sequence; a selection circuit 28 that inserts a control information sequence into a main signal information sequence so that the control information sequence indicates the multi-level modulation method used for the immediately following main signal information sequence, and outputs the result; and a mapping unit 29 that performs mapping processing on the control information sequence output by the selection circuit 28 using a predetermined multi-level modulation method, and performs mapping processing on the main signal information sequence output by the selection circuit 28 using the multi-level modulation method indicated by the control information sequence to generate a multi-level modulated optical transmission signal. With this configuration, the optical transmitting device 2 can transmit control information including the multi-level modulation method used for the main signal information sequence to the optical receiving device 3 before transmitting the main signal information sequence to the optical receiving device 3. Therefore, the optical receiving device 3 can process the received main signal based on the control information, and can transmit the main signal by changing the multi-level modulation method according to the sequence length of the information bit sequence of the main signal information. When a fixed multi-level modulation method is used, it is necessary to use one code format for error correction that matches the multi-level modulation method, and when the sequence length of the information bit sequence is shorter than the code length, a measure such as inserting a fixed length into the information bit sequence to match the code format is taken, so that depending on the sequence length of the information bit sequence, it may be necessary to insert many unnecessary fixed values, which may reduce the transmission efficiency. In contrast, with the above configuration, it is possible to change the multi-level modulation method according to the information bit sequence to be transmitted, which makes it possible to improve the transmission efficiency.

[0067] Furthermore, it is preferable that the control encoder 27 generates the control information sequence using an error correcting code having a higher error correcting capability than the error correcting code used for the main signal information by the main encoder 25. If there is an error in the control information, it becomes difficult for the optical receiver 3 to correctly decode the main signal information based on the control information, and therefore it is important to correctly transmit the control information. For this reason, it is preferable that an error correcting code having a higher error correcting capability than the error correcting code used for the main signal information is used for the control information.

[0068] In addition, it is preferable that the control coding unit 27 performs the coding process of the control information using an error correction code, such as a Polar code, that is compatible with a short code length and can reduce the processing delay of coding and decoding. This can shorten the time required for the coding process of the control information. Therefore, even if the coding process of the control information is performed in parallel with the error correction coding process of the main signal information, the coding process of the control information can be completed before the error correction coding process of the main signal information is completed. Therefore, it is possible to shorten the time required for the transmission process compared to the case where the error correction coding process of the main signal information is started after the coding process of the control information is completed.

[0069] It is preferable that the mapping unit 29 performs mapping processing on the control information sequence using a multi-level modulation scheme with a smaller degree of multiplication than the multi-level modulation scheme used for the main signal information sequence. This makes it possible to transmit the control information to the optical receiving device 3 more reliably.

[0070] In addition, the bit sequence on which the main encoding unit 25 performs error correction encoding processing is a bit sequence in which fixed bits have been inserted as a bit sequence that is not transmitted into the information bit sequence of the main signal information to be transmitted, and can be a bit sequence corresponding to the maximum multi-level symbol of the multi-level modulation method used for the main signal information sequence.

[0071] Furthermore, the main encoding unit 25 can perform a first error correction encoding process on the main signal information sequence using an error correction code that assumes hard decision decoding, and can perform a second error correction encoding process on a part of the main signal information sequence that has been subjected to the first error correction encoding process, for example, a bit corresponding to the least significant bit of a multi-level modulation symbol, using an error correction code that assumes soft decision decoding. This allows double error correction encoding processes to be performed on bits with a high error rate, making it possible to reduce the error rate.

[0072] The control information can further include information indicating the sequence length of the main signal information sequence. This allows the optical receiver 3 to know the sequence length of the information bit sequence in advance even when short and long information bit sequences are mixed, making it possible to simplify the processing in the optical receiver 3.

[0073] Moreover, the optical receiving device 3 receives the multi-level modulated optical transmission signal transmitted by the optical transmitting device 2. The optical receiving device 3 includes a control decoding unit 33 that extracts control information from the optical transmission signal, and a main decoding unit 35 that performs error correction decoding processing on a main signal information sequence included in the optical transmission signal, based on the control information extracted from the optical transmission signal.

[0074] In addition, when the main encoding unit 25 of the optical transmitting device 2 performs error correction encoding processing on a bit sequence corresponding to the maximum multi-level symbol of the multi-level modulation method used for the main signal information sequence, in which fixed bits have been inserted as a bit sequence that is not transmitted into the information bit sequence of the main signal information to be transmitted, the main decoding unit 35 of the optical receiving device 3 inserts the missing fixed bits into the main signal information sequence included in the optical transmission signal based on the control information, and then performs error correction decoding processing.

[0075] Furthermore, when the main encoding unit 25 of the optical transmitting device 2 performs a first error correction encoding process on the main signal information sequence using an error correction code premised on hard decision decoding, and performs a second error correction encoding process on the bit of the main signal information sequence that has been subjected to the first error correction encoding process, which corresponds to the least significant bit of the multi-level modulation symbol, using an error correction code premised on soft decision decoding, the main decoding unit 35 of the optical receiving device 3 determines hard decision bits other than the least significant bit based on the soft decision decoding result of the least significant bit of the multi-level modulation symbol, and then performs hard decision decoding process on the main signal information sequence.

[0076] The optical transmitter 2 can configure an optical transmission system 1 together with the optical receiver 3. Also, an optical transmission method for transmitting a multi-level modulated optical transmission signal can be provided. The optical transmission method includes the steps of: the optical transmitter 2 performs an error correction coding process on control information including information on a multi-level modulation method used for a main signal information sequence to generate an encoded control information sequence; the optical transmitter 2 performs an error correction coding process on the main signal information corresponding to the multi-level modulation method indicated by the control information to generate an encoded main signal information sequence; the optical transmitter 2 inserts a control information sequence into the main signal information sequence so that the control information sequence indicates the multi-level modulation method for the main signal information sequence immediately following; the optical transmitter 2 performs a mapping process on the control information sequence using a predetermined multi-level modulation method; the optical transmitter 2 performs a mapping process on the main signal information sequence using the multi-level modulation method indicated by the control information sequence; and the optical transmitter 2 transmits the multi-level modulated optical transmission signal generated by the mapping process to transmit the control information before the main signal information.

[0077] The configurations shown in the above embodiments are merely examples, and may be combined with other known technologies, or the embodiments may be combined with each other. Also, parts of the configurations may be omitted or modified without departing from the spirit of the invention.

[0078] In the above embodiment, an optical transmitting device 2 having a transmitting function and an optical receiving device 3 having a receiving function are shown, but it is also possible to provide an optical transmission device that combines the functions of the optical transmitting device 2 and the optical receiving device 3 and is capable of bidirectional communication. [Explanation of symbols]

[0079] 1 Optical transmission system, 2 Optical transmitting device, 3 Optical receiving device, 20 Modulation method determination unit, 21 Fixed value insertion unit, 22 Control information generation unit, 23 Encoding circuit, 24, 34 Interleaver, 25 Main encoding unit, 26, 36 Deinterleaver, 27 Control encoding unit, 28 Selection circuit, 29 Mapping unit, 30 Decoding circuit, 31 Separation circuit, 32 Control signal soft decision generation unit, 33 Control decoding unit, 35 Main decoding unit, 90 Processing circuit, 91 Control circuit, 92 Processor, 93 Memory, 251 HD-FEC encoding unit, 252 Multilevel encoding unit, 253 SD-FEC encoding unit, 351 Main signal soft decision generation unit, 352 SD-FEC decoding unit, 353 Multilevel / multistage decoding unit, 354 HD-FEC decoding unit.

Claims

1. In an optical transmitting device for transmitting a multi-level modulated optical transmission signal, a control coding unit that performs an error correction coding process on control information including information on a multi-level modulation method used for a main signal information sequence and outputs a coded control information sequence; a main encoding unit that performs error correction encoding processing on main signal information using the same parameters regardless of the multi-level modulation scheme by changing the number of bits to be inserted into according to the multi-level modulation scheme indicated by the control information, thereby generating the main signal information sequence that has been encoded; a selection circuit that inserts the control information sequence into the main signal information sequence so that the control information sequence indicates the multi-level modulation scheme used for the main signal information sequence immediately following the control information sequence, and outputs the control information sequence; a mapping unit that performs mapping processing on the control information sequence output by the selection circuit using a predetermined multi-level modulation scheme, and performs mapping processing on the main signal information sequence output by the selection circuit using the multi-level modulation scheme indicated by the control information sequence, thereby generating the multi-level modulated optical transmission signal; Equipped 1. An optical transmitting device comprising:

2. The control coding unit generates the control information sequence by using an error correction code having a higher error correction capability than the error correction code used by the main coding unit for the main signal information.

2. The optical transmitter according to claim 1 .

3. The control coding unit performs error correction coding processing of the control information sequence in parallel with the error correction coding processing of the main coding unit.

2. The optical transmitter according to claim 1 .

4. The control coding unit performs an error correction coding process on the control information sequence by using a polar code.

4. The optical transmitter according to claim 3.

5. The mapping unit performs the mapping process on the control information sequence by using a multi-level modulation scheme with a lower multi-level degree than a multi-level modulation scheme used for the main signal information sequence.

2. The optical transmitter according to claim 1 .

6. The main encoding unit performs the error correction encoding process on a bit sequence corresponding to a maximum multi-level symbol of the multi-level modulation method used for the main signal information sequence, in which a fixed bit is inserted as a bit sequence not to be transmitted into an information bit sequence of the main signal information to be transmitted.

2. The optical transmitter according to claim 1 .

7. The main encoding unit A first error correction coding process is performed on the main signal information sequence using an error correction code that assumes hard decision decoding, and a second error correction coding process is performed on a bit of the main signal information sequence that has been subjected to the first error correction coding process, the bit corresponding to the least significant bit of a multi-level modulation symbol, using an error correction code that assumes soft decision decoding.

2. The optical transmitter according to claim 1 .

8. The control information further includes information indicating a length of the main signal information sequence.

2. The optical transmitter according to claim 1 .

9. 9. An optical receiving device for receiving the optical transmission signal transmitted by the optical transmitting device according to claim 1, the optical transmission signal does not include the fixed bit, a control decoder for extracting the control information from the optical transmission signal; a main decoding unit that performs error correction decoding processing on the main signal information sequence included in the optical transmission signal based on the control information extracted from the optical transmission signal; Equipped with The main decoding unit performs the error correction decoding process using the same parameters regardless of the multi-level modulation method indicated by the control information by inserting the missing fixed bits into the main signal information sequence included in the optical transmission signal based on the control information.

1. An optical receiving device comprising:

10. 8. An optical receiving device for receiving the optical transmission signal transmitted by the optical transmitting device according to claim 7, a control decoder for extracting the control information from the optical transmission signal; a main decoding unit that performs error correction decoding processing on the main signal information sequence included in the optical transmission signal based on the control information extracted from the optical transmission signal; Equipped with The main decoding unit performs the error correction decoding process using the same parameters regardless of the multi-level modulation scheme indicated by the control information by inserting the missing fixed bits into the main signal information sequence included in the optical transmission signal based on the control information, and determines hard-decision bits other than the least significant bit based on a soft-decision decoding result of the least significant bit of the multi-level modulation symbol, and then performs hard-decision decoding process on the main signal information sequence.

1. An optical receiving device comprising:

11. An optical transmitter for transmitting a multi-level modulated optical transmission signal; an optical receiving device for receiving the optical transmission signal transmitted by the optical transmitting device; Equipped with The optical transmitter comprises: a control coding unit that performs an error correction coding process on control information including information on a multi-level modulation method used for a main signal information sequence and outputs a coded control information sequence; a main encoding unit that performs error correction encoding processing on main signal information using the same parameters regardless of the multi-level modulation scheme by changing the number of bits to be inserted into according to the multi-level modulation scheme indicated by the control information, thereby generating the main signal information sequence that has been encoded; a selection circuit that inserts the control information sequence into the main signal information sequence so that the control information sequence indicates the multi-level modulation scheme used for the main signal information sequence immediately following the control information sequence, and outputs the control information sequence; a mapping unit that performs mapping processing on the control information sequence output by the selection circuit using a predetermined multi-level modulation scheme, and performs mapping processing on the main signal information sequence output by the selection circuit using the multi-level modulation scheme indicated by the control information sequence, thereby generating the multi-level modulated optical transmission signal; having the optical transmission signal does not include the fixed bit, The optical receiving device comprises: a control decoder for extracting the control information from the optical transmission signal; a main decoding unit that performs error correction decoding processing on the main signal information sequence included in the optical transmission signal based on the control information extracted from the optical transmission signal; Equipped with The main decoding unit performs the error correction decoding process using the same parameters regardless of the multi-level modulation method indicated by the control information by inserting the missing fixed bits into the main signal information sequence included in the optical transmission signal based on the control information.

1. An optical transmission system comprising:

12. 1. An optical transmission method for transmitting a multilevel modulated optical transmission signal, comprising: an optical transmitting device performing an error correction coding process on control information including information on a multi-level modulation scheme used for a main signal information sequence to generate an encoded control information sequence; a step in which the optical transmitting device performs error correction coding processing on main signal information using the same parameters regardless of the multi-level modulation scheme by changing the number of bits into which fixed bits are inserted according to the multi-level modulation scheme indicated by the control information, thereby generating the main signal information sequence that is coded; the optical transmitting device inserting the control information sequence into the main signal information sequence such that the control information sequence indicates the multi-level modulation scheme for the main signal information sequence immediately following; a step of performing a mapping process on the control information sequence by the optical transmitting device using a predetermined multi-level modulation method; a step of performing a mapping process on the main signal information sequence by the optical transmitting device using the multi-level modulation scheme indicated by the control information sequence; a step of transmitting the control information before the main signal information by transmitting the multi-level modulated optical transmission signal generated by the mapping process by the optical transmitting device; Includes 1. An optical transmission method comprising:

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