Optical transmission device and likelihood generation circuit

Abstract

The optical transmission device comprises: a symbol demapping unit, which converts a received signal into a signal of an I-axis component, a signal of a Q-axis component, and a signal formed by connecting the signal of the I-axis component and the signal of the Q-axis component on a phase plane; a likelihood generating circuit, which generates a likelihood related to the received signal; and an error correction decoding unit, which implements soft decision decoding, wherein the likelihood generating circuit comprises: a first one-dimensional modulation lookup table, which takes the signal of the I-axis component as an independent variable and outputs a first likelihood; a second one-dimensional modulation lookup table, which takes the signal of the Q-axis component as an independent variable and outputs a second likelihood; and a two-dimensional modulation lookup table, which takes the signal of the I-axis component and the signal of the Q-axis component as an independent variable and generates a third likelihood, and the error correction decoding unit implements soft decision decoding based on the first likelihood, the second likelihood, and the third likelihood.

Description

Technical Field

[0001] The present invention relates to an optical transmission device that implements soft decision decoding and a likelihood generating circuit used in the optical transmission device. Background Art

[0002] In recent years, as the bit rate of transmitted data has increased, the modulation methods used in optical transmission systems have become increasingly multi-valued. Furthermore, the realization of large-scale digital circuits based on the miniaturization of semiconductor manufacturing processes and the emergence of ultra-high-speed ADCs (Analog Digital Converters) and DACs (Digital Analog Converters) with sampling speeds of tens of Gsps (sample per second) have made it possible to generate and demodulate complex optical signals.

[0003] Therefore, multi-value modulation methods such as 64QAM (Quadrature Amplitude Modulation), 128QAM, and 256QAM have been developed that are extremely multi-valued and cannot be realized in conventional optical communications.

[0004] In these multi-value modulation methods, the configuration interval of the signal points on the phase plane is narrow, and a higher signal-to-noise ratio (SNR) is required to achieve the required transmission distance and signal speed. In order to compensate for the lack of SNR, the importance of powerful error correction coding such as LDPC (Low Density Parity Check) that can achieve high speed and high coding gain has further increased. Therefore, LDPC is used in combination with other error correction codes.

[0005] In error correction coding, there is soft decision decoding that also uses analog information of the signal as a method of enhancing performance in contrast to hard decision decoding that uses 1 or 0 to judge the received information sequence and perform decoding. In soft decision decoding, the likelihood indicating the reliability of the bit assigned to the signal point is calculated based on the coordinates on the phase plane of the received signal, and error correction is performed.

[0006] In the likelihood calculation in soft decision decoding, it is necessary to perform a lot of arithmetic operations on the quantized multi-bit information, which increases the circuit scale when implemented. Therefore, in the past, the following method was adopted: instead of the many arithmetic operations, the circuit scale was reduced by using an approximation of the calculation formula used in the likelihood calculation, or a LUT (Look Up Table) that stores the likelihood calculated in advance and outputs the value by taking the coordinates as input, etc. (see, for example, Patent Document 1).

[0007] In the method described in Patent Document 1, the quadrant on the phase plane where the coordinates of the received signal point exist is detected using bits that have been hard-determined decoded based on the I (In-phase) axis and the Q (Quadrature-phase) axis of the received signal point on the phase plane. In addition, in the method described in Patent Document 1, the likelihood information obtained once is converted into the final likelihood information based on its quadrant information. Thus, Patent Document 1 shows the following method: the range in which the likelihood value varies according to the received signal point is limited only to the adjacent signal points containing the hard-decision threshold, thereby reducing the scale of the likelihood generation circuit and achieving miniaturization.

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: International Publication No. 2008 / 038749 Summary of the invention

[0011] Problems to be solved by the invention

[0012] However, the conventional technology has the following problems.

[0013] The emergence of digital coherent technology has led to the development of optical communication systems with transmission capacity exceeding 1Tbps per channel. As a result, the scale of digital circuits for signal processing has approached the limit of LSI (Large Scale Integration) integration.

[0014] On the other hand, as the application area of ​​optical communication systems in data centers and the like expands, it is required to transmit and receive signals of various modulation methods, from QPSK (Quadrature Phase Shift Keying) to 128QAM, using the same LSI.

[0015] The LUT used for likelihood generation is installed in a circuit so that the received signal coordinates of a RAM (Random Access Memory) are used as input addresses, and the likelihood for the coordinates is accumulated as RAM data and output. In the circuit reduction method using the LUT, when LUTs for multiple modulation methods are made consistent individually, there is a problem that the circuit scale is large, especially in a modulation method with super-multi-values.

[0016] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an optical transmission device and a likelihood generation circuit capable of suppressing an increase in the circuit scale when likelihood generation is performed using an LUT.

[0017] Means for solving problems

[0018] The optical transmission device of the present invention comprises: a symbol demapping section that converts a received signal into a signal of an I-axis component, a signal of a Q-axis component, and a signal obtained by connecting the signal of the I-axis component and the signal of the Q-axis component on a phase plane; a likelihood generating circuit that generates a likelihood related to the received signal based on the signal of the I-axis component, the signal of the Q-axis component, and the signal obtained by connecting the signal of the I-axis component and the signal of the Q-axis component converted by the symbol demapping section; and an error correction decoding section that performs soft decision decoding on the received signal based on the likelihood generated by the likelihood generating circuit, the likelihood generating circuit comprising: a first one-dimensional modulation lookup table that takes the signal of the I-axis component as an independent variable and outputs a first likelihood; a second one-dimensional modulation lookup table that takes the signal of the Q-axis component as an independent variable and outputs a second likelihood; and a two-dimensional modulation lookup table that takes the signal of the I-axis component and the signal of the Q-axis component as an independent variable and generates a third likelihood, and the error correction decoding section performs soft decision decoding based on the first likelihood, the second likelihood, and the third likelihood.

[0019] The likelihood generating circuit of the present invention comprises: a first one-dimensional modulation lookup table, which uses the signal of the I-axis component in the signal formed by converting the received signal into the signal on the phase plane as an independent variable and outputs the first likelihood; a second one-dimensional modulation lookup table, which uses the signal of the Q-axis component in the signal formed by converting the received signal into the signal on the phase plane as an independent variable and outputs the second likelihood; and a two-dimensional modulation lookup table, which uses the signal formed by connecting the signal of the I-axis component and the signal of the Q-axis component in the signal formed by converting the received signal into the signal on the phase plane as an independent variable and generates the third likelihood.

[0020] Effects of the Invention

[0021] According to the present invention, it is possible to obtain an optical transmission device and a likelihood generation circuit, and it is possible to suppress an increase in the circuit scale when likelihood generation is performed using an LUT. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a configuration diagram of a 128QAM likelihood generation circuit according to Embodiment 1 of the present invention.

[0023] Figure 2 This is an example of a constellation diagram showing the relationship between 128QAM signal points and allocated bits in Embodiment 1 of the present invention.

[0024] Figure 3 This is a diagram showing the likelihood values ​​of the received signal point coordinates of the coded bit 0 (b0) of 128QAM in Embodiment 1 of the present invention.

[0025] Figure 4 This is a diagram showing the relationship between the I-axis direction and the likelihood value of a signal point related to 128QAM coded bit 0 (b0) in Embodiment 1 of the present invention.

[0026] Figure 5 This is a diagram showing the likelihood values ​​of the received signal point coordinates of the coded bit 1 (b1) of 128QAM in Embodiment 1 of the present invention.

[0027] Figure 6 This is a diagram showing the relationship between the Q-axis direction and the likelihood value of a signal point related to coded bit 1 (b1) of 128QAM in Embodiment 1 of the present invention.

[0028] Figure 7 This is a diagram showing the likelihood values ​​of the received signal point coordinates of the coded bit 2 (b2) of 128QAM in Embodiment 1 of the present invention.

[0029] Figure 8 This is a diagram showing the likelihood values ​​of the received signal point coordinates of the coded bit 3 (b3) of 128QAM in Embodiment 1 of the present invention.

[0030] Fig. 9 This is a diagram showing the likelihood values ​​of the received signal point coordinates of the coded bit 4 (b4) of 128QAM in Embodiment 1 of the present invention.

[0031] Fig.10 This is a diagram showing the likelihood value of the received signal point coordinates of the coded bit 5 (b5) of 128QAM in Embodiment 1 of the present invention.

[0032] Fig.11 This is a diagram showing the likelihood values ​​of the received signal point coordinates of the coded bit 6 (b6) of 128QAM in Embodiment 1 of the present invention.

[0033] Fig.12 It is a constellation diagram showing the relationship between 64QAM signal points and allocated bits in Embodiment 1 of the present invention.

[0034] Fig.13 This is a diagram showing the likelihood value of the reception signal point coordinates of the 64QAM coded bit b0 (b0) in Embodiment 1 of the present invention.

[0035] Fig.14 This is a diagram showing the likelihood value of the reception signal point coordinates of the 64QAM coded bit b1 (b1) in Embodiment 1 of the present invention.

[0036] Fig.15This is a diagram showing the likelihood value of the reception signal point coordinates of the 64QAM coded bit b2 (b2) in Embodiment 1 of the present invention.

[0037] Fig.16 This is a diagram showing the likelihood value of the reception signal point coordinates of the 64QAM coded bit b3 (b3) in Embodiment 1 of the present invention.

[0038] Fig.17 This is a diagram showing the likelihood value of the reception signal point coordinates of the 64QAM coded bit b4 (b4) in Embodiment 1 of the present invention.

[0039] Fig.18 This is a diagram showing the likelihood value of the reception signal point coordinates of the 64QAM coded bit b5 (b5) in Embodiment 1 of the present invention.

[0040] Fig.19 This is a diagram showing the structure of a 64QAM likelihood generation LUT in Embodiment 1 of the present invention.

[0041] Fig. 20 It is a constellation diagram showing the relationship between 32QAM signal points and allocated bits in Embodiment 1 of the present invention.

[0042] Fig.21 This is a diagram showing the likelihood values ​​of the reception signal point coordinates of the 32QAM coded bit b0 (b0) in Embodiment 1 of the present invention.

[0043] Fig. 22 This is a diagram showing the likelihood value of the reception signal point coordinates of the 32QAM coded bit b1 (b1) in Embodiment 1 of the present invention.

[0044] Fig.23 This is a diagram showing the likelihood value of the reception signal point coordinates of the 32QAM coded bit b2 (b2) in Embodiment 1 of the present invention.

[0045] Fig.24 This is a diagram showing the likelihood value of the reception signal point coordinates of the 32QAM coded bit b3 (b3) in Embodiment 1 of the present invention.

[0046] Fig.25 This is a diagram showing the likelihood value of the reception signal point coordinates of the 32QAM coded bit b4 (b4) in Embodiment 1 of the present invention.

[0047] Fig.26 This is a diagram showing the structure of a 32QAM likelihood generation LUT in Embodiment 1 of the present invention.

[0048] Fig. 27This is a configuration diagram showing a case where each function of the optical transmission device according to Embodiment 1 of the present invention is realized by a processing circuit as dedicated hardware.

[0049] Fig.28 This is a configuration diagram showing a case where each function of the optical transmission device according to Embodiment 1 of the present invention is realized by a processing circuit having a processor and a memory. DETAILED DESCRIPTION

[0050] Hereinafter, preferred embodiments of the optical transmission device and likelihood generation circuit of the present invention will be described with reference to the drawings.

[0051] Implementation Method 1

[0052] Figure 1 This is a diagram showing the configuration of a 128QAM likelihood generation circuit according to Embodiment 1 of the present invention. The symbol mapping unit 12 determines the coordinates on the phase plane based on the coded bits output from the error correction coding unit 11, and transmits the mapped signal.

[0053] In the symbol demapping unit 14, the signal transmitted through the transmission path channel 13 is converted into a signal of an I-axis component with a 6-bit resolution obtained according to the coordinates of the received signal point, a signal of a Q-axis component with a 6-bit resolution, and a signal formed by connecting the I-axis component and the Q-axis component with a 6-bit resolution.

[0054] Then, the signal of the I-axis component with a 6-bit resolution is input to the one-dimensional modulation likelihood generation LUT 15. In addition, the signal of the Q-axis component with a 6-bit resolution is input to the one-dimensional modulation likelihood generation LUT 16. Furthermore, the signal obtained by connecting the I-axis component and the Q-axis component with a 6-bit resolution is input to the two-dimensional modulation likelihood generation LUT 17.

[0055] The likelihood generation LUT 15 for one-dimensional modulation uses the signal of the I-axis component as an independent variable to generate the likelihood of the coded bit 0 (b0). The likelihood generation LUT 16 for one-dimensional modulation uses the signal of the Q-axis component as an independent variable to generate the likelihood of the coded bit 1 (b1). Furthermore, the likelihood generation LUT 17 for two-dimensional modulation uses the signal obtained by connecting the I-axis component and the Q-axis component as an independent variable to generate the likelihood of the coded bit 2 (b2) to the coded bit 6 (b6).

[0056] That is, the one-dimensional modulation likelihood generation LUT 15 is equivalent to the one-dimensional modulation lookup table used to generate the first likelihood. In addition, the one-dimensional modulation likelihood generation LUT 16 is equivalent to the one-dimensional modulation lookup table used to generate the second likelihood. Furthermore, the two-dimensional modulation likelihood generation LUT 17 is equivalent to the two-dimensional modulation lookup table used to generate the third likelihood.

[0057] Furthermore, three lookup tables, namely, the one-dimensional modulation likelihood generation LUT 15 , the one-dimensional modulation likelihood generation LUT 16 , and the two-dimensional modulation likelihood generation LUT 17 , which generate likelihoods from the signals converted by the symbol demapping unit 14 , correspond to likelihood generation circuits.

[0058] Then, the error correction decoding unit 18 performs soft decision decoding based on the likelihood values ​​generated by the likelihood generation circuit including the three lookup tables.

[0059] Figure 2 FIG. 1 is an example of a constellation diagram showing the relationship between the signal points of 128QAM and the allocated bits in Embodiment 1 of the present invention. Figure 2 As shown, the signal points of 128QAM form a non-rectangular constellation that is not arranged in a square on the phase plane.

[0060] Figure 3 This is a diagram showing the likelihood values ​​of the received signal point coordinates of the coded bit 0 (b0) of 128QAM in Embodiment 1 of the present invention. Figure 4 1 is a diagram showing the relationship between the I-axis direction of the signal point and the likelihood value related to the coded bit 0 (b0) of 128QAM in Embodiment 1 of the present invention. The grid portion of the constellation is an area where the likelihood value is positive. The coded bit 0 (b0) is only allocated to the I-axis direction of the signal point, so it can be processed by a one-dimensional modulation LUT that generates the likelihood using only the coordinate information of a single axis. Regarding the likelihood value, the larger the absolute value of the I-axis of the received signal point coordinate, the higher the likelihood value of the coded bit being 1 or 0.

[0061] Figure 5 This is a diagram showing the likelihood values ​​of the received signal point coordinates of the coded bit 1 (b1) of 128QAM in Embodiment 1 of the present invention. Figure 6 This is a diagram showing the relationship between the Q-axis direction and the likelihood value of a signal point related to 128QAM coded bit 1 (b1) in Embodiment 1 of the present invention. The grid portion of the constellation is an area where the likelihood value is positive.

[0062] Coded bit 1 (b1) is assigned only to the Q-axis direction of the signal point, so it can be processed by a one-dimensional modulation LUT that generates likelihood using only the coordinate information of a single axis, just like coded bit 0. Regarding the likelihood value, the larger the absolute value of the Q-axis of the received signal point coordinate, the higher the likelihood value of the coded bit being 1 or 0.

[0063] Figure 7 This is a diagram showing the likelihood values ​​of the received signal point coordinates of the coded bit 2 (b2) of 128QAM in Embodiment 1 of the present invention. Figure 8This is a diagram showing the likelihood values ​​of the received signal point coordinates of the coded bit 3 (b3) of 128QAM in Embodiment 1 of the present invention. Fig. 9 This is a diagram showing the likelihood values ​​of the received signal point coordinates of the coded bit 4 (b4) of 128QAM in Embodiment 1 of the present invention.

[0064] Fig.10 1 is a diagram showing the likelihood value of the received signal point coordinates of the coded bit 5 (b5) of 128QAM in Embodiment 1 of the present invention. Fig.11 This is a diagram showing the likelihood values ​​of the received signal point coordinates of the coded bit 6 (b6) of 128QAM in Embodiment 1 of the present invention.

[0065] The grid part of the constellation is the area where the likelihood value is positive. These coded bits are assigned to the signal points, making it impossible to make a decision using only the information of the I axis or only the information of the Q axis. Therefore, it is necessary to process it using a two-dimensional modulation LUT that generates the likelihood using the coordinate information of the I axis and the Q axis.

[0066] Fig.12 : is a constellation diagram showing the relationship between the signal points of 64QAM and the allocated bits in Embodiment 1 of the present invention. Fig.12 As shown, the signal points of 64QAM form a rectangular constellation arranged in a square shape on the phase plane.

[0067] Fig.13 This is a diagram showing the likelihood value of the reception signal point coordinates of the 64QAM coded bit b0 (b0) in Embodiment 1 of the present invention. Fig.14 This is a diagram showing the likelihood value of the reception signal point coordinates of the 64QAM coded bit b1 (b1) in Embodiment 1 of the present invention. Fig.15 This is a diagram showing the likelihood value of the reception signal point coordinates of the 64QAM coded bit b2 (b2) in Embodiment 1 of the present invention.

[0068] Fig.16 This is a diagram showing the likelihood value of the reception signal point coordinates of the 64QAM coded bit b3 (b3) in Embodiment 1 of the present invention. Fig.17 : is a diagram showing the likelihood value of the received signal point coordinates of the 64QAM coded bit b4 (b4) in Embodiment 1 of the present invention. Fig.18 This is a diagram showing the likelihood value of the reception signal point coordinates of the 64QAM coded bit b5 (b5) in Embodiment 1 of the present invention.

[0069] Since the coded bits b0 to b2 are allocated only to the I-axis direction of the signal point, they can be processed by a one-dimensional modulation LUT that generates likelihood using only the coordinate information of the single axis. On the other hand, since the coded bits b3 to b5 are allocated only to the Q-axis direction of the signal point, they can be processed by a one-dimensional modulation LUT that generates likelihood using only the coordinate information of the single axis, similarly to the coded bits b0 to b2.

[0070] Fig.19 This is a structural diagram of the 64QAM likelihood generation LUT in Embodiment 1 of the present invention. The 6-bit resolution I-axis component obtained from the received signal point coordinates is input to the one-dimensional modulation likelihood generation LUT 121. On the other hand, the 6-bit resolution Q-axis component is input to the one-dimensional modulation likelihood generation LUT 122.

[0071] Furthermore, the one-dimensional modulation likelihood generation LUT 121 generates the likelihoods of coded bit 0 (b0), coded bit 1 (b1), and coded bit 2 (b2) based on the I-axis component with a 6-bit resolution. On the other hand, the one-dimensional modulation likelihood generation LUT 122 generates the likelihoods of coded bit 3 (b3), coded bit 4 (b4), and coded bit 5 (b5) based on the Q-axis component with a 6-bit resolution.

[0072] Fig. 20 : is a constellation diagram showing the relationship between the signal points of 32QAM and the allocated bits in the first embodiment of the present invention. Fig. 20 As shown, the signal points of 32QAM form a non-rectangular constellation that is not arranged in a square on the phase plane.

[0073] Fig.21 This is a diagram showing the likelihood values ​​of the reception signal point coordinates of the 32QAM coded bit b0 (b0) in Embodiment 1 of the present invention. Fig. 22 This is a diagram showing the likelihood value of the reception signal point coordinates of the 32QAM coded bit b1 (b1) in Embodiment 1 of the present invention. Fig.23 This is a diagram showing the likelihood value of the reception signal point coordinates of the 32QAM coded bit b2 (b2) in Embodiment 1 of the present invention.

[0074] Fig.24 : is a diagram showing the likelihood value of the received signal point coordinates of the coded bit b3 (b3) of 32QAM in Embodiment 1 of the present invention. Fig.25 This is a diagram showing the likelihood value of the reception signal point coordinates of the 32QAM coded bit b4 (b4) in Embodiment 1 of the present invention.

[0075] Figure 21 to Figure 25 The grid area in shows the area where the likelihood value is positive. Figure 21 to Figure 25As shown, there are signal points that cannot be determined using only the information of the I axis or only the information of the Q axis. Therefore, it is necessary to perform processing using a two-dimensional modulation LUT that generates likelihood using the coordinate information of the I axis and the Q axis.

[0076] Fig.26 This is a structural diagram of the 32QAM likelihood generation LUT in Embodiment 1 of the present invention. A signal formed by connecting the I-axis component and the Q-axis component of the 6-bit resolution obtained based on the received signal point coordinates is input to the likelihood generation LUT 151 for two-dimensional modulation. Then, the likelihood generation LUT 151 for two-dimensional modulation generates the likelihood of coding bit 0 (b0), coding bit 1 (b1), coding bit 2 (b2), coding bit 3 (b3), and coding bit 4 (b4) based on the signal formed by connecting the I-axis component and the Q-axis component of the 6-bit resolution.

[0077] The 32QAM likelihood generation LUT and the 64QAM likelihood generation LUT are respectively the same as the one-dimensional modulation likelihood generation LUT and the two-dimensional modulation likelihood generation LUT constituting the 128QAM likelihood generation circuit. Therefore, the 32QAM likelihood generation circuit and the 64QAM likelihood generation circuit can be used together as the 128QAM likelihood generation circuit.

[0078] In other words, in the first embodiment, the high-order non-rectangular QAM is composed of a likelihood generation circuit for one-dimensional modulation and a likelihood generation circuit for two-dimensional modulation. By adopting this structure, the likelihood generation circuit used in the low-order non-rectangular QAM and rectangular QAM can be made common with the likelihood generation circuit used in the high-order non-rectangular QAM. As a result, a likelihood generation circuit that can suppress the increase in circuit scale when using LUT for likelihood generation is realized. This likelihood generation circuit can be applied to an optical transmission device that adopts a non-rectangular multi-value modulation method above 8QAM.

[0079] In addition, each function in the optical transmission device of the above-mentioned Embodiment 1 is realized by a processing circuit. The processing circuit realizing each function may be dedicated hardware or a processor that executes a program stored in a memory. Fig. 27 This is a structural diagram showing a case where each function of the optical transmission device in Embodiment 1 of the present invention is realized by a processing circuit 1000 as dedicated hardware. Fig.28 This is a configuration diagram showing a state where each function of the optical transmission device according to Embodiment 1 of the present invention is realized by a processing circuit 2000 including a processor 2001 and a memory 2002 .

[0080] When the processing circuit is dedicated hardware, the processing circuit 1000 is, for example, 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 thereof. The functions of each of the symbol demapping unit, the likelihood generation circuit, and the error correction decoding unit constituting the optical transmission device may be implemented by a separate processing circuit 1000, or the functions of each unit may be implemented by the processing circuit 1000 in a unified manner.

[0081] On the other hand, when the processing circuit is the processor 2001, the functions of each of the symbol demapping unit, the likelihood generation circuit, and the error correction decoding unit are implemented by software, firmware, or a combination of software and firmware. The software and firmware are recorded as programs and stored in the memory 2002.

[0082] The processor 2001 realizes the functions of each unit by reading and executing the program stored in the memory 2002. That is, the optical transmission device has the memory 2002 for storing the program which, when executed by the processing circuit 2000, results in the execution of each processing step.

[0083] These programs can also be said to be steps or methods for causing the computer to execute the above-mentioned parts. Here, the memory 2002 is, for example, a non-volatile or volatile semiconductor memory such as RAM (Random Access Memory), ROM (Read Only Memory), flash memory, EPROM (Erasable Programmable Read Only Memory), EEPROM (Electrically Erasable and Programmable Read Only Memory), etc. In addition, a magnetic disk, a floppy disk, an optical disk, a high-density disk, a mini disk, a DVD, etc. are also memories 2002.

[0084] Furthermore, the functions of the above-mentioned components may be partially realized by dedicated hardware and partially realized by software or firmware.

[0085] In this way, the processing circuit can realize the functions of the above-mentioned components through hardware, software, firmware or a combination thereof.

[0086] Description of symbols

[0087] 11: Error correction coding unit; 12: Symbol mapping unit; 13: Transmission path channel; 14: Symbol demapping unit; 15: I-axis component one-dimensional modulation likelihood generation LUT; 16: Q-axis component one-dimensional modulation likelihood generation LUT; 17: Two-dimensional modulation likelihood generation LUT; 18: Error correction decoding unit; 121: I-axis component one-dimensional modulation likelihood generation LUT; 122: Q-axis component one-dimensional modulation likelihood generation LUT; 151: Two-dimensional modulation likelihood generation LUT.

Claims

1. An optical transmission device, comprising: A symbol demapping section converts a received signal obtained through an optical transmission path, the received signal being selectively modulated for transmission according to: Low-order rectangular QAM, Low-order non-rectangular QAM, and High-order non-rectangular QAM; Each of the received signals is converted into a signal of an I-axis component, a signal of a Q-axis component, and a signal obtained by connecting the signal of the I-axis component and the signal of the Q-axis component on a phase plane; a likelihood generating circuit for generating a likelihood related to each of the received signals based on the signal of the I-axis component, the signal of the Q-axis component, and a signal obtained by connecting the signal of the I-axis component and the signal of the Q-axis component after conversion by the symbol demapping unit; as well as an error correction decoding unit that performs soft decision decoding on each of the received signals based on the likelihood generated by the likelihood generating circuit, The likelihood generation circuit has: a first one-dimensional modulation lookup table, which takes the signal of the I-axis component of each of the received signals as an independent variable and outputs a first likelihood; a second one-dimensional modulation lookup table that takes the signal of the Q-axis component of each of the received signals as an independent variable and outputs a second likelihood; as well as a two-dimensional modulation lookup table that generates a third likelihood by using a signal obtained by connecting the signal of the I-axis component and the signal of the Q-axis component of each of the received signals as an independent variable, The error correction decoding unit performs the soft decision decoding based on the first likelihood, the second likelihood, and the third likelihood. using the first one-dimensional modulation lookup table and the second one-dimensional modulation lookup table in generating a likelihood for each of the received signals modulated according to the low-order rectangular QAM, wherein the low-order rectangular QAM is formed by the first one-dimensional modulation lookup table and the second one-dimensional modulation lookup table, using the two-dimensional modulation lookup table in generating a likelihood for each of the received signals modulated according to the low-order non-rectangular QAM, wherein the low-order non-rectangular QAM is formed by the two-dimensional modulation lookup table, The first one-dimensional modulation lookup table, the second one-dimensional modulation lookup table and the two-dimensional modulation lookup table are commonly used in generating the likelihood of each of the received signals modulated according to the high-order non-rectangular QAM, wherein the high-order non-rectangular QAM is formed by the first one-dimensional modulation lookup table, the second one-dimensional modulation lookup table and the two-dimensional modulation lookup table.

2. An error correction decoding apparatus for performing soft decision decoding on a signal converted from a received signal obtained through an optical transmission path and selectively modulated for transmission in the following manner: Low-order rectangular QAM, Low-order non-rectangular QAM, and High-order non-rectangular QAM; Each of the received signals is converted into a signal of an I-axis component, a signal of a Q-axis component, and a signal obtained by connecting the signal of the I-axis component and the signal of the Q-axis component on a phase plane, and the error correction decoding device has: a first one-dimensional modulation lookup table which uses as an independent variable a signal of an I-axis component in a signal obtained by converting one of the received signals into a signal on a phase plane and outputs a first likelihood; a second one-dimensional modulation lookup table that uses as an independent variable a signal of a Q-axis component in a signal obtained by converting one of the received signals into a signal on the phase plane and outputs a second likelihood; as well as a two-dimensional modulation lookup table that generates a third likelihood using as an independent variable a signal obtained by connecting the signal of the I-axis component and the signal of the Q-axis component in a signal obtained by converting one of the received signals into a signal on the phase plane, using the first one-dimensional modulation lookup table and the second one-dimensional modulation lookup table in generating a likelihood for each of the received signals modulated according to the low-order rectangular QAM, wherein the low-order rectangular QAM is formed by the first one-dimensional modulation lookup table and the second one-dimensional modulation lookup table, using the two-dimensional modulation lookup table in generating a likelihood for each of the received signals modulated according to the low-order non-rectangular QAM, wherein the low-order non-rectangular QAM is formed by the two-dimensional modulation lookup table, The first one-dimensional modulation lookup table, the second one-dimensional modulation lookup table and the two-dimensional modulation lookup table are commonly used in generating the likelihood of each of the received signals modulated according to the high-order non-rectangular QAM, wherein the high-order non-rectangular QAM is formed by the first one-dimensional modulation lookup table, the second one-dimensional modulation lookup table and the two-dimensional modulation lookup table.

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