Transmitting and receiving device

Abstract

To select the optimal transmission mode from transmission modes defined by combinations of a plurality of parameters related to transmission performance.SOLUTION: A transmitter-receiver comprises: a transmission mode candidate transmitting unit that transmits transmission mode candidate information including transmission mode information to a transmission device to be communicated; a transmission mode candidate receiving unit that receives the transmission mode candidate information including the transmission mode information of the transmission device to be communicated; a transmission mode selection unit that selects transmission mode information to be used for the communication from the plurality of pieces of common transmission mode information; and a signal transmitting and receiving unit that transmits and receives signals based on the selected transmission mode information. The transmission mode selection unit selects, from the plurality of pieces of common transmission mode information, pieces of candidate transmission mode information to be candidates for transmission capacity required during the transmitting and receiving, and selects, in the selected pieces of transmission mode information, pieces of transmission mode information in which power consumption is reduced or pieces of transmission mode information in which optical frequency utilization efficiency is increased in a descending order of priority.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a transmitting / receiving device. This application claims priority based on Japanese Patent Application No. 2018-148290, filed on August 7, 2018, the contents of which are incorporated herein by reference. [Background technology]

[0002] As digital signal processing (hereinafter referred to as "DSP") for optical transmission becomes more sophisticated, not only modulation methods but also various parameters related to transmission performance such as baud rate, types of error correction codes such as FEC (Forward Error Correction), and number of carriers have increased, resulting in a diversification of transmission modes. For example, Patent Document 1 discloses a method for selecting an optimal modulation method based on a training signal. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5753604 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the technique described in Patent Document 1 has a problem in that it is not possible to select an optimum transmission mode in response to various parameters related to transmission performance, such as the baud rate, the type of error correction code, and the number of carriers, other than the modulation method.

[0005] In view of the above circumstances, an object of the present invention is to provide a technique that can select an optimal transmission mode from among transmission modes determined by a combination of multiple parameters related to transmission performance. [Means for solving the problem]

[0006] One aspect of the present invention is an optical transmission system comprising an optical transmitting device and an optical receiving device that receives a signal transmitted from the optical transmitting device via an optical transmission path, the optical transmission system comprising: a transmission mode selection unit that selects transmission mode information, which is a combination of a plurality of parameters related to transmission performance, from a plurality of pieces of transmission mode information that are common to the transmission performance of the optical transmitting device and the optical receiving device in order of priority; a signal transmitting unit that transmits a signal modulated based on the selected transmission mode information to the optical receiving device; and a signal receiving unit that receives the signal and demodulates the received signal based on the transmission mode information selected by the transmission mode selection unit.

[0007] One aspect of the present invention is the above-mentioned optical transmission system, further comprising a signal quality detection unit that detects the signal quality of the received signal, and a signal quality judgment unit that judges whether the signal quality of the signal is acceptable based on information indicating the signal quality detected by the signal quality detection unit, and the transmission mode selection unit selects the transmission mode information with the next highest priority when the signal quality judgment unit judges that the signal quality of the signal is unacceptable.

[0008] One aspect of the invention is the above-mentioned optical transmission system, wherein the optical transmitting device comprises a transmission mode candidate transmitting unit that transmits transmitting side transmission mode candidate information including the transmission mode information of the optical transmitting device to the optical receiving device, a transmission mode candidate receiving unit that receives receiving side transmission mode candidate information including the transmission mode information of the optical receiving device from the optical receiving device, and the transmission mode selecting unit; and the optical receiving device comprises a transmission mode candidate receiving unit that receives the transmitting side transmission mode candidate information from the optical transmitting device, a transmission mode candidate transmitting unit that transmits the receiving side transmission mode candidate information to the optical transmitting device when the transmission mode candidate receiving unit receives the transmitting side transmission mode candidate information, and the transmission mode selecting unit.

[0009] One aspect of the present invention is the optical transmission system described above, wherein the transmission mode candidate transmitter of the optical transmitting device superimposes the transmitting-side transmission mode candidate information on a pilot tone signal, which is a signal sequence in which power is concentrated at one or more specific frequencies, and transmits the superimposed information to the signal transmitter, and the transmission mode candidate receiver of the optical receiving device receives the transmitting-side transmission mode candidate information superimposed on the pilot tone signal received by the signal receiver.

[0010] One aspect of the present invention is the optical transmission system described above, wherein the transmission mode candidate sending unit of the optical sending device writes the sending-side transmission mode candidate information into a reserved field of a signal frame of a main signal included in the signal and causes the signal sending unit to send it, and the transmission mode candidate receiving unit of the optical receiving device reads out the sending-side transmission mode candidate information included in the reserved field of the signal frame of the main signal.

[0011] One aspect of the present invention is the above-mentioned optical transmission system, further comprising a control device, wherein the control device comprises the transmission mode selection unit, and when the transmission mode selection unit selects the transmission mode information, it generates a transmission mode designation signal that designates the selected transmission mode information and transmits the generated transmission mode designation signal to the optical transmitting device and the optical receiving device, and the optical transmitting device and the optical receiving device operate in a transmission mode corresponding to the transmission mode designation signal transmitted from the transmission mode selection unit.

[0012] One aspect of the present invention is the optical transmission system described above, further comprising a management device, wherein the management device comprises a transmission design information storage unit that stores information on physical property parameters of various modules provided on the optical transmission path, the optical transmitting device, and the optical receiving device, and the transmission mode information of the optical transmitting device and the optical receiving device, and a transmission design processing unit that calculates transmission quality for each piece of transmission mode information based on the physical property parameters, generates a transmission mode candidate list including multiple pieces of transmission mode information to be selected based on the calculated transmission quality, and transmits the generated transmission mode candidate list to the control device, and the transmission mode selection unit of the control device selects the transmission mode information from the received transmission mode candidate list in descending order of priority.

[0013] One aspect of the present invention is a transmission mode selection method in an optical transmission system including an optical transmitting device and an optical receiving device that receives a signal transmitted from the optical transmitting device via an optical transmission path, the transmission mode selection method comprising: selecting transmission mode information, which is a combination of a plurality of parameters related to transmission performance, from a plurality of pieces of transmission mode information that are common to the transmission performance of the optical transmitting device and the optical receiving device in descending order of priority; transmitting a signal modulated based on the selected transmission mode information to the optical receiving device; receiving the signal; and demodulating the received signal based on the transmission mode information selected by the transmission mode selection unit.

[0014] One aspect of the present invention is the optical transmission system described above, further comprising a management device, the management device comprises: a transmission design information storage unit that stores information on physical property parameters of various modules provided on the optical transmission path, the optical transmitting device, and the optical receiving device, and the transmission mode information of the optical transmitting device and the optical receiving device; a transmission design processing unit that calculates transmission quality for each of the transmission mode information based on the physical property parameters, and generates a transmission mode candidate list including multiple pieces of transmission mode information to be selected based on the calculated transmission quality; a network design information storage unit that collects network information including any or all of topology information, node information, and path information of the optical transmission path, and stores the collected network information; and a network design processing unit that performs, for each of the transmission mode information, an accommodation design process that uses the network information to determine an optical path that improves network utilization efficiency, and transmits the transmission mode candidate list to the control device, to which information indicating priority for each piece of transmission mode information has been added, and the transmission mode selection unit of the control device selects the transmission mode information from the received transmission mode candidate list in descending order of priority.

[0015] One aspect of the present invention is the optical transmission system described above, wherein the control device further includes a transmission design information storage unit that stores information on physical property parameters of various modules provided on the optical transmission path, the optical transmitting device, and the optical receiving device, and the transmission mode information of the optical transmitting device and the optical receiving device, and a transmission design processing unit that calculates transmission quality for each piece of transmission mode information based on the physical property parameters, generates a transmission mode candidate list including multiple pieces of transmission mode information to be selected based on the calculated transmission quality, and outputs the generated transmission mode candidate list to the transmission mode selection unit, and the transmission mode selection unit selects the transmission mode information from the output transmission mode candidate list in descending order of priority.

[0016] One aspect of the present invention is the above-mentioned optical transmission system, wherein the control device comprises a signal quality detection unit that detects the signal quality of the received signal, and a signal quality judgment unit that judges whether the signal quality of the signal is acceptable based on information indicating the signal quality detected by the signal quality detection unit, and the transmission mode selection unit selects the transmission mode information with the next highest priority when the signal quality judgment unit judges that the signal quality of the signal is not acceptable. [Effects of the Invention]

[0017] According to the present invention, it is possible to select an optimum transmission mode from among transmission modes determined by a combination of multiple parameters related to transmission performance. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a block diagram showing a configuration of an optical transmission system according to a first embodiment. [Figure 2] 1 is a block diagram showing the internal configuration of an optical transmission device according to a first embodiment and the connection relationship with other devices. [Figure 3] FIG. 2 is a diagram (part 1) showing the configuration of an OTN frame according to the first embodiment. [Figure 4] 3 is a block diagram showing the internal configuration of an error correction coding unit and the connection relationship with other functional units in the first embodiment. FIG. [Figure 5] FIG. 2 is a diagram (part 2) illustrating the configuration of an OTN frame according to the first embodiment. [Figure 6] FIG. 2 is a diagram illustrating a configuration of a transmission signal format according to the first embodiment. [Figure 7] FIG. 4 is a diagram illustrating a data configuration of a transmission mode information table according to the first embodiment. [Figure 8] FIG. 4 is a diagram illustrating a data configuration of a transmission mode information table on a transmitting side according to the first embodiment. [Figure 9] 1 is a block diagram showing the internal configuration of an optical receiving device according to a first embodiment and the connection relationship with other devices. [Figure 10]3 is a block diagram showing the internal configuration of an error correction decoding unit and the connection relationship with other functional units of the first embodiment. FIG. [Figure 11] FIG. 4 is a diagram illustrating a data configuration of a receiving-side transmission mode information table according to the first embodiment. [Figure 12] FIG. 1 is a diagram (part 1) showing the connection relationship between an optical receiving device and an optical transmitting device in a receiving-side system according to the first embodiment. [Figure 13] FIG. 1 is a diagram (part 1) showing the connection relationship between an optical transmitting device and an optical receiving device in a transmitting-side system of the first embodiment. [Figure 14] 5 is a flowchart showing the flow of a transmission mode selection process according to the first embodiment. [Figure 15] FIG. 2 is a diagram (part 2) showing the connection relationship between the optical transmitting device and the optical receiving device in the transmitting-side system of the first embodiment. [Figure 16] FIG. 2 is a diagram (part 2) showing the connection relationship between the optical receiving device and the optical transmitting device in the receiving-side system of the first embodiment. [Figure 17] FIG. 10 is a block diagram showing the internal configuration of an optical transmitting device in another configuration example of the first embodiment and the connection relationship with other devices. [Figure 18] FIG. 10 is a block diagram showing the internal configuration of an optical receiving device in another configuration example of the first embodiment and the connection relationship with other devices. [Figure 19] FIG. 10 is a block diagram showing the configuration of an optical transmission system according to a second embodiment. [Figure 20] 10 is a flowchart showing the flow of a transmission mode selection process according to the second embodiment. [Figure 21] FIG. 10 is a block diagram showing a configuration of an optical transmission system according to a third embodiment. [Figure 22] 10 is a flowchart showing a processing flow of a management device according to a third embodiment. [Figure 23] 10 is a flowchart showing the flow of a transmission mode selection process according to the third embodiment. [Figure 24] FIG. 10 is a block diagram showing a configuration of an optical transmission system according to a fourth embodiment. [Figure 25]13 is a flowchart showing a processing flow of a management device according to a fourth embodiment. [Figure 26] FIG. 10 is a block diagram showing the configuration of an optical transmission system according to a fifth embodiment. [Figure 27] FIG. 10 is a block diagram showing a configuration of an optical transmission system according to a sixth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0019] (First embodiment) Hereinafter, embodiments of the present invention will be described with reference to the drawings. Fig. 1 is a block diagram showing the configuration of an optical transmission system S according to a first embodiment. The optical transmission system S includes a transmitting system T, a receiving system R, and an optical transmission line 3. The transmitting system T includes an optical transmitting device 1t, an optical receiving device 2t, and a multiplexing unit 4T. The receiving system R includes an optical receiving device 2r, an optical transmitting device 1r, and a multiplexing unit 4R.

[0020] The optical transmission path 3 physically connects the transmitting system T and the receiving system R. The optical transmission path 3 transmits signal light between the transmitting system T and the receiving system R. The optical transmission path 3 is, for example, an optical fiber 300. The multiplexing units 4T and 4R are connected to both ends of the optical fiber 300. The multiplexing unit 4T is connected to the optical transmitting device 1t and the optical receiving device 2t of the transmitting system T. The multiplexing unit 4R is connected to the optical receiving device 2r and the optical transmitting device 1r of the receiving system R. The optical signal transmitted from the optical transmitting device 1t of the transmitting system T is transmitted to the optical receiving device 2r of the receiving system R via the optical transmission path 3. The optical signal transmitted from the optical transmitting device 1r of the receiving system R is also transmitted to the optical receiving device 2t of the transmitting system T via the optical transmission path 3. The multiplexing units 4T and 4R may be functional units that perform wavelength multiplexing, or may not perform wavelength multiplexing. For example, the application of the present invention also includes a configuration in which the transmitting system T and the receiving system R are opposed to each other and only one wavelength is used, without wavelength multiplexing. In other words, the multiplexing units 4T and 4R may be included in the transmitting system T and the receiving system R as a unit (multiplexing unit) that multiplexes the optical transmitting device 1t and the optical receiving device 2r, rather than wavelength multiplexing.

[0021] In the optical transmission system S, an optical transmitter 1t and an optical receiver 2r are in a facing relationship, i.e., they have the same transmission mode and transmit signal light from the optical transmitter 1t to the optical receiver 2r. Similarly, the optical transmitter 1r and the optical receiver 2t are in a facing relationship.

[0022] 1, the transmission mode is determined between the transmitting system T and the receiving system R, but since the same transmission mode is normally used in both directions in the above-mentioned opposing relationship, the line between the optical transmitting device 1t of the transmitting system T and the optical receiving device 2r of the receiving system R, which will be mainly described, is shown by a solid line, and the optical receiving device 2t and the optical transmitting device 1r are shown by a dashed line. Note that, when the transmitting system is considered to be downstream and the receiving system is considered to be upstream, if the transmission modes for the uplink from the transmitting side to the receiving side and the downlink from the receiving side to the transmitting side are different, the optimal transmission mode may already be determined between the optical receiving device 2t and the optical transmitting device 1r of the downlink and the normal operating state may be established, or the transmission mode may be determined by performing the same processing as between the optical transmitting device t1 and the optical receiving device 2r.

[0023] The terms "transmitting side" of transmitting system T and "receiving side" of receiving system R are names used for convenience of explanation. This means that optical transmitting device 1t is the side that transmits a pilot tone signal when selecting a transmission mode between optical transmitting device 1t and optical receiving device 2r, and optical receiving device 2r is the side that receives the pilot tone signal. Therefore, conversely, when selecting a transmission mode between optical transmitting device 1r and optical receiving device 2t, as shown by the dashed line, receiving system R becomes the transmitting system, and transmitting system T becomes the receiving system.

[0024] (Configuration of the optical transmitter of the first embodiment) The optical transmitter 1t of the transmitting system T and the optical transmitter 1r of the receiving system R have the same configuration. The optical transmitter 1t of the transmitting system T will be described below as an example with reference to FIG.

[0025] The optical transmitter 1t modulates a main signal, which is information to be transmitted, to generate signal light and transmits the generated signal light to the optical transmission line 3. As shown in Fig. 2, the optical transmitter 1t has a configuration in which it transmits the main signal in parallel using two orthogonal polarized waves, i.e., X polarized wave and Y polarized wave.

[0026] The optical transmitting device 1t includes a framing unit 11t, an error correction coding unit 12t, main signal modulation units 13t-1 and 13t-2, multiplexing units 14t-1 and 14t-2, electrical-to-optical conversion units 15t-1 and 15t-2, a polarization multiplexing unit 16t, a clock control unit 17t, a control information modulation unit 18t, and a control unit 10t. In Fig. 2, the configuration including the framing unit 11t, the error correction coding unit 12t, main signal modulation units 13t-1 and 13t-2, the multiplexing units 14t-1 and 14t-2, electrical-to-optical conversion units 15t-1 and 15t-2, the polarization multiplexing unit 16t, and the clock control unit 17t is referred to as a signal transmitting unit 110t.

[0027] The framing unit 11t receives client signals transmitted by IP (Internet Protocol) devices such as IP routers and Ethernet (registered trademark) switches connected to the optical transmitting device 1t, and forms a signal frame including the received client signals. For example, an OTN (Optical Transport Network) frame 40 of the ITU-T G.709 recommendation, as shown in FIG. 3, is used as the signal frame. The framing unit 11t writes information used for monitoring and the like into an overhead section 41 of the OTN frame 40, and writes the received client signal into a payload section 42.

[0028] The error correction encoder 12t receives an error correction code designation signal from the controller 10t and generates an error correction code by encoding the signal frame output from the framing unit 11t using the error correction coding method indicated by the error correction code designation signal. The error correction encoder 12t also writes the generated error correction code to the error correction encoder 43 of the OTN frame 40. For example, as shown in FIG. 4, the error correction encoder 12t includes an outer code error correction encoder 121t, an inner code error correction encoder 122t, and a main signal separator 123t.

[0029] The inner code error correction encoder 122t performs encoding based on, for example, a soft-decision error correction technique. Here, the soft-decision error correction technique is a technique that classifies signals using multiple thresholds and makes judgments that also include likelihood information that represents "likelihood," such as "1 close to 0" or "1 close to 1," and can achieve error correction capabilities close to the ideal Shannon limit.

[0030] The outer code error correction encoder 121t performs encoding based on, for example, a hard-decision error correction technique. Here, hard-decision technique is a technique that classifies a signal using a single threshold and determines it as either a 0 or a 1. The soft-decision error correction technique used by the inner code error correction encoder 122t tends to produce an error floor where the bit error rate after correction tails off, in exchange for achieving error correction capability close to the ideal Shannon limit. Therefore, by eliminating this error floor using the hard-decision error correction technique used by the outer code error correction encoder 121t, it is possible to achieve extremely high error correction capability. This method of concatenating soft-decision error correction coding for the inner code and hard-decision error correction coding for the outer code is called a concatenated encoding method.

[0031] As a soft decision error correction technique, for example, a low density parity check code (hereinafter referred to as "LDPC" (Low-Density Parity Check)) is applied. As a hard decision error correction technique, for example, a Reed-Solomon (hereinafter referred to as "RS" (Reed-Solomon)) code, a BCH (Bose-Chaudhuri-Hocquenghem) code, or the like, which are block coding techniques, is applied. In each of the inner code error correction coding unit 122t and the outer code error correction coding unit 121t, bit rearrangement, i.e., interleaving, may be performed to improve burst error tolerance. For example, a bit error rate (hereinafter referred to as "BER" (Bit Error Rate)) for a BPSK signal of "10 -12 In this case, the NCG (Net Coding Gain) is 8.35 dB and the FEC overhead is 6.7%.

[0032] 4 shows a case where a concatenated coding method including an outer code error correction coding unit 121t and an inner code error correction coding unit 122t is applied, assuming that high error correction capability is required. In this case, an outer code error correction code 43-1 coded by the outer code error correction coding unit 121t and an inner code error correction code 43-2 coded by the inner code error correction coding unit 122t are written to the error correction coding unit 43 of the OTN frame 40 shown in FIG. 5, as shown in FIG.

[0033] On the other hand, if the required error correction capability is not so high, it is possible to provide only one of them, for example, the outer code error correction coding unit 121t that performs coding using hard decision error correction technology, and in that case, only the outer code error correction code 43-1 coded by the outer code error correction coding unit 121t will be written to the error correction coding unit 43.

[0034] In the error correction encoder 12t, the main signal separator 123t converts the serial signal output by the inner code error correction encoder 122t into a parallel signal to generate two binary sequence information main signals for X polarization and Y polarization. The main signal separator 123t outputs the generated main signal for X polarization to the main signal modulator 13t-1, and outputs the generated main signal for Y polarization to the main signal modulator 13t-2.

[0035] Each of the primary signal modulation units 13t-1 and 13t-2 receives a modulation scheme signal from the control unit 10t and modulates the corresponding X-polarized primary signal and Y-polarized primary signal output from the error correction coding unit 12t based on the modulation scheme indicated by the modulation scheme signal, i.e., the mapping rule. Furthermore, the primary signal modulation units 13t-1 and 13t-2 generate transmission symbol sequences through modulation and output the generated transmission symbol sequences to the multiplexing units 14t-1 and 14t-2 connected to each other. Examples of modulation schemes that may be used include binary phase shift keying (BPSK), quadrature phase shift keying (QPSK), and quadrature amplitude modulation (QAM). Note that other modulation schemes may also be used.

[0036] The multiplexer 14t-1 for X polarization receives the transmission symbol sequence for X polarization output from the main signal modulator 13t-1 and receives the predetermined signal output from the control information modulator 18t. The multiplexer 14t-1 also performs time division multiplexing by inserting the received predetermined signal into each of the received transmission symbol sequences for X polarization to generate a signal sequence for X polarization.

[0037] The Y-polarized wave multiplexer 14t-2 receives the Y-polarized wave transmission symbol sequence output by the main signal modulator 13t-2 and receives the control signal output by the control information modulator 18t. The multiplexer 14t-2 also performs time division multiplexing by inserting the received control signal into each received Y-polarized wave transmission symbol sequence to generate a Y-polarized wave signal sequence.

[0038] The electro-optical converter 15t-1 performs electro-optical conversion on the signal sequence for X polarization output by the multiplexer 14t-1, and outputs the optical signal for X polarization to the polarization multiplexer 16t. The electro-optical converter 15t-2 performs electro-optical conversion on the signal sequence for Y polarization output by the multiplexer 14t-2, and outputs the optical signal for Y polarization to the polarization multiplexer 16t.

[0039] The polarization multiplexing unit 16t is connected to the multiplexing unit 4T of the optical transmission line 3, and generates polarization-multiplexed time-division multiplexed signal light by polarization-multiplexing the X-polarized optical signal and the Y-polarized optical signal output from each of the electrical-optical conversion units 15t-1 and 15t-2. The polarization multiplexing unit 16t outputs the generated signal light to the optical transmission line 3. As shown in FIG. 6, the transmission signal format of the signal light 50 output by the polarization multiplexing unit 16t is formed by time-division multiplexing Nt (Nt≧1, Nt is a positive integer) pieces of control information 45-1 to 45-Nt between main signal information 40-1 to 40-Ns, which are Ns (Ns≧1, Ns is a positive integer) transmission symbol sequences. Note that the control information 45-1 to 45-Nt are predetermined signals for the X-polarized wave of the signal light 50, and are control signals for the Y-polarized wave of the signal light 50.

[0040] The clock control unit 17t receives a baud rate control signal from the control unit 10t and sets the clock frequency of the clock provided inside the optical transmitting device 1t so that the baud rate of the main signal becomes the baud rate specified by the baud rate control signal. For example, when the clock control unit 17t receives a baud rate control signal from the control unit 10t that sets the baud rate of the main signal to 32 GBaud, it sets the clock frequency to that baud rate. When the clock control unit 17t receives a baud rate control signal that changes the baud rate of the main signal from 32 GBaud to 64 GBaud, it clocks up, i.e., increases the clock frequency, to set the baud rate of the main signal to 64 GBaud. Conversely, when the clock control unit 17t receives a baud rate control signal that changes the baud rate of the main signal from 64 GBaud to 32 GBaud, it clocks down, i.e., decreases the clock frequency, to set the baud rate of the main signal to 32 GBaud.

[0041] The control unit 10t includes a transmission mode information storage unit 100t, a transmission mode candidate transmitter 101t, a transmission mode candidate receiver 102t, and a transmission mode selector 103t. The transmission mode information will now be described with reference to FIG. 7. The transmission mode information is information that combines various parameters related to transmission performance, such as parameters for a modulation method, a baud rate, and an error correction code type. The transmission mode information table 1000 shown in FIG. 7 shows 24 types of transmission mode information, which combine, for example, parameters for six types of modulation methods, two types of baud rates, and two types of error correction code types. In this example, the transmission mode information also describes the transmission capacity for each of the 24 combinations. Each piece of transmission mode information is assigned a transmission mode number, such as "mode 1" or "mode 2," as shown in the "transmission mode" section.

[0042] As shown in Figure 7, the six modulation methods are BPSK, QPSK, 8QAM, 16QAM, 32QAM, and 64QAM, as shown in the "Modulation Method" section. The two baud rates are 32GBaud and 64GBaud, as shown in the "Baud Rate" section. The two error correction code types are, as shown in the "Error Correction Code Type" section, one is a concatenated code FEC with Reed-Solomon (RS) code as the outer code and a low-density parity check code (LDPC) as the inner code. The other is a concatenated code FEC with BCH code as the outer code and a low-density parity check code (LDPC) as the inner code.

[0043] By storing a table with a data structure similar to the transmission mode information table 1000 shown in FIG. 7 in each of the optical transmitting device 1t and the optical receiving device 2r, the optical transmitting device 1t and the optical receiving device 2r can exchange only the transmission mode number between them to check the table and identify the modulation method, baud rate, and error correction code type. For example, in the case of "mode 5," the modulation method can be identified as QPSK, the baud rate as 32 GBaud, and the error correction code type as RS+LDPC. In the case of "mode 16," the modulation method can be identified as 16QAM, the baud rate as 64 GBaud, and the error correction code type as BCH+LDPC. The information stored in the transmission mode information table 1000 is not limited to 24 as shown in FIG. 7 and may be changed as appropriate due to technological advances or the addition of new functions. For example, the transmission mode information table 1000 may be configured with more than 24 modes based on combinations of the modulation method, baud rate, and error correction code type, or new information other than the modulation method, baud rate, and error correction code type may be added.

[0044] In the control unit 10t, the transmission mode information storage unit 100t stores in advance a transmitting side transmission mode information table 1001t having the data configuration shown in Fig. 8, for example. The transmitting side transmission mode information table 1001t stores transmission mode information that can be transmitted in the optical transmitting device 1t. Fig. 8 shows an example of the transmitting side transmission mode information table 1001t that stores transmission mode information in which the error correction code type is RS+LDPC as a function possessed by the transmitting side in the transmission mode information table 1000 shown in Fig. 7.

[0045] The transmission mode candidate transmitter 101t generates, as transmission information, transmission mode candidate information on the transmission side that includes all transmission mode numbers stored in the "transmission mode" item of the transmission side transmission mode information table 1001t stored in the transmission mode information storage unit 100t. When information is provided from the outside, the transmission mode candidate transmitter 101t takes in the provided information as transmission information.

[0046] The transmission mode candidate transmitter 101t also uses transmission information as a signal sequence, differentially encodes the signal sequence bit by bit, and outputs the differentially encoded signal to the control information modulator 18t. The transmission mode candidate transmitter 101t also generates a signal sequence in which power is concentrated at one or more specific frequencies, and outputs the generated signal sequence to the control information modulator 18t as a default signal.

[0047] The transmission mode candidate receiver 102t receives, from the optical receiver 2t of the transmitting system T, receiving-side transmission mode candidate information including transmission mode numbers indicating transmission mode information that can be transmitted in the optical receiver 2r of the receiving system R. This receiving-side transmission mode candidate information of the optical receiver 2r of the receiving system R is information that the optical receiver 2r of the receiving system R transmitted to the optical transmitter 1r, and that the optical transmitter 1r transmitted to the optical receiver 2t of the transmitting system T via the optical transmission path 3. The transmission mode candidate receiver 102t also outputs the received receiving-side transmission mode candidate information to the transmission mode selector 103t.

[0048] The transmission mode selection unit 103t extracts a transmission mode number that is common to all transmission mode numbers stored in the "Transmission Mode" item of the transmission side transmission mode information table 1001t stored in the transmission mode information storage unit 100t and the reception side transmission mode candidate information output by the transmission mode candidate reception unit 102t.

[0049] Furthermore, the transmission mode selection unit 103t selects the transmission mode number with the highest priority from among the extracted common transmission mode numbers. Here, priority is information indicating a predetermined level of priority, and for example, transmission mode information including a modulation method with a higher multi-level and a higher baud rate has a higher priority. For example, in the transmission mode information shown in the transmission mode information table 1000 shown in FIG. 7, a transmission mode number with a large transmission capacity (high multi-level and high baud rate) has a higher priority.

[0050] The transmission mode selection unit 103t also has an internal storage area, and writes and stores the selected transmission mode number in the internal storage area. The transmission mode selection unit 103t also performs the following processing. For example, if the notification included in the notification signal is a signal quality unacceptable notification, the transmission mode selection unit 103t refers to the internal storage area and selects the transmission mode number of the transmission mode information with the next highest priority after the transmission mode information selected at that time. The notification signal is transmitted inline from the optical transmission device 1r in the receiving system R to the optical reception device 2t in the transmitting system T without going through an external line.

[0051] The transmission mode selection unit 103t also reads information indicating the modulation method from the "Modulation method" field of the transmission mode information corresponding to the selected transmission mode number, the baud rate value from the "Baud rate" field, and information indicating the error correction coding method from the "Error correction code type" field. The transmission mode selection unit 103t also generates a modulation method signal including the read information indicating the modulation method and outputs it to the main signal modulation units 13t-1 and 13t-2. The transmission mode selection unit 103t also generates a baud rate control signal including the read baud rate value and outputs it to the clock control unit 17t. The transmission mode selection unit 103t also outputs an error correction code designation signal including the read information indicating the error correction coding method to the error correction coding unit 12t.

[0052] The control information modulator 18t receives the predetermined signal and the differentially encoded signal output from the transmission mode candidate transmitter 101t, modulates the predetermined signal with the differentially encoded signal to generate a control signal, and outputs the predetermined signal to the multiplexer 14t-1 for X polarization and the control signal to the multiplexer 14t-2 for Y polarization.

[0053] The predetermined signal and the control signal are time-division multiplexed with the main signal by the multiplexing units 14t-1 and 14t-2, and then converted into optical signals by the electrical-to-optical conversion units 15t-1 and 15t-2. The signal generated by polarization multiplexing the optical signals of the predetermined signal and the control signal by the polarization multiplexing unit 16t becomes a pilot tone signal, which is a signal sequence in which power is concentrated at one or more specific frequencies.

[0054] In addition, the control information modulator 18t may output the control signal to the multiplexer 14t-1 for X polarization and the default signal to the multiplexer 14t-2 for Y polarization, inversely to the above-described configuration. In this case, the control information 45-1 to 45-Nt become the control signal in the X polarization of the signal light 50 and the default signal in the Y polarization of the signal light 50.

[0055] (Configuration of the optical receiving device of the first embodiment) The optical receiving device 2r of the receiving system R and the optical receiving device 2t of the transmitting system T have the same configuration. The optical receiving device 2r of the receiving system R will be described below as an example with reference to FIG.

[0056] The optical receiving device 2r receives the signal light sent by the optical transmitting device 1t and transmitted through the optical transmission line 3. The optical receiving device 2r also performs coherent reception of the received signal light using a local oscillation laser provided inside, and demodulates the original signal from the signal light.

[0057] The optical receiving device 2r has the internal configuration shown in Fig. 9 and includes a polarization separation unit 21r, optical-electrical conversion units 22r-1 and 22r-2, AD (Analog-to-Digital) conversion units 23r-1 and 23r-2, main signal demodulation units 24r-1 and 24r-2, an error correction decoding unit 25r, a deframing unit 26r, a clock control unit 27r, a control information demodulation unit 210r, and a control unit 20r. In Fig. 9, the configuration including the polarization separation unit 21r, optical-electrical conversion units 22r-1 and 22r-2, AD conversion units 23r-1 and 23r-2, main signal demodulation units 24r-1 and 24r-2, error correction decoding unit 25r, deframing unit 26r, and clock control unit 27r is referred to as a signal receiving unit 220r.

[0058] The polarization separation unit 21r is connected to the multiplexing unit 4R of the optical transmission line 3, and receives the signal light sent by the optical transmitter 1t and transmitted by the optical transmission line 3. The signal light is signal light obtained by polarization multiplexing a time-division multiplexed signal as described above. The polarization separation unit 21r also performs polarization separation on the received signal light in the optical domain, separating it into two orthogonal X-polarized waves and Y-polarized waves, and outputs the separated X-polarized wave and Y-polarized wave to the optical-electrical conversion units 22r-1 and 22r-2, respectively.

[0059] Specifically, the polarization separation unit 21r includes, for example, a polarization diversity 90-degree hybrid coupler and a local oscillation laser, and performs polarization separation using these. The polarization separation unit 21r outputs the separated X-polarized wave to the optical-electrical conversion unit 22r-1 and outputs the separated Y-polarized wave to the optical-electrical conversion unit 22r-2.

[0060] The optical-electrical conversion unit 22r-1 on the X-polarized side receives the X-polarized signal light output by the polarization separation unit 21r, converts it into an electrical analog signal, and outputs the converted electrical analog signal to the AD conversion unit 23r-1. The optical-electrical conversion unit 22r-2 on the Y-polarized side receives the Y-polarized signal light output by the polarization separation unit 21r, converts it into an electrical analog signal, and outputs the converted electrical analog signal to the AD conversion unit 23r-2.

[0061] Each of the AD conversion units 23r-1 and 23r-2 generates a digital received signal by converting an electrical analog signal output by the optical-electrical conversion units 22r-1 and 22r-2 connected to the AD conversion units 23r-1 and 23r-2 into a digital signal. Each of the AD conversion units 23r-1 and 23r-2 outputs the generated digital received signal to the main signal demodulation units 24r-1 and 24r-2 connected to the AD conversion units 23r-1 and 23r-2. Each of the AD conversion units 23r-1 and 23r-2 outputs the generated digital received signal to the control information demodulation unit 210r and the control unit 20r.

[0062] The main signal demodulators 24r-1 and 24r-2 receive a modulation scheme signal from the controller 20r and demodulate the main signals included in the digital received signals output from the AD converters 23r-1 and 23r-2 connected to them in accordance with a demodulation scheme corresponding to the modulation scheme indicated by the modulation scheme signal, i.e., a demapping rule. The main signal demodulated by the main signal demodulator 24r-1 becomes the main signal corresponding to the X-polarized signal light, and the main signal demodulated by the main signal demodulator 24r-2 becomes the main signal corresponding to the Y-polarized signal light.

[0063] The error correction decoder 25r receives an error correction code designation signal from the controller 20r and performs decoding processing on the main signals demodulated by the main signal demodulators 24r-1 and 24r-2 in accordance with the error correction coding method designated by the error correction code designation signal. The error correction code used by the error correction decoder 25r when performing the decoding processing may be information on the error correction code included in the error correction code unit 43 of the OTN frame 40 of the main signal.

[0064] The error correction decoding unit 25r includes, for example, an inner-code error correction decoding unit 251r and an outer-code error correction decoding unit 252r, as shown in FIG. 10 , corresponding to the outer-code error correction coding unit 121t and the inner-code error correction coding unit 122t included in the error correction coding unit 12t of the optical transmitting device 1t. The inner-code error correction decoding unit 251r performs decoding using, for example, a soft-decision error correction technique such as LDPC, and the outer-code error correction decoding unit 252r performs decoding using, for example, a hard-decision error correction technique such as RS-FEC or BCH-FEC. Note that if the error correction coding unit 12t of the optical transmitting device 1t only includes the outer-code error correction coding unit 121t, the error correction decoding unit 25r will also only include the outer-code error correction decoding unit 252r.

[0065] In the error correction decoding unit 25r, the main signal synthesis unit 253r converts a parallel signal consisting of a main signal corresponding to the X-polarized signal light output by the main signal demodulation unit 24r-1 and a main signal corresponding to the Y-polarized signal light output by the main signal demodulation unit 24r-2 into a serial signal and outputs it to the inner code error correction decoding unit 251r.

[0066] The deframing unit 26r reads the client signal from the payload portion 42 of the OTN frame 40 shown in FIG. 3, and outputs the read client signal to an IP device such as an IP router or an Ethernet (registered trademark) switch connected to the optical receiving device 2r.

[0067] The clock control unit 27r receives a baud rate control signal from the control unit 20r and sets the clock frequency of the clock of the optical receiving device 2r so that the baud rate when receiving the main signal is the baud rate specified by the baud rate control signal. For example, when the clock control unit 27r receives a baud rate control signal from the control unit 20r specifying a baud rate of 32 GBaud, it sets the clock frequency to that baud rate. When the clock control unit 27r receives a baud rate control signal to change the baud rate from 32 GBaud to 64 GBaud, it clocks up, i.e., increases the clock frequency, to set the baud rate to 64 GBaud. Conversely, when the clock control unit 27r receives a baud rate control signal to change the baud rate from 64 GBaud to 32 GBaud, it clocks down, i.e., decreases the clock frequency, to set the baud rate to 32 GBaud.

[0068] The control information demodulator 210r includes a control information detector 211r, control information extractors 212r-1 and 212r-2, and a differential decoder 213r. In the control information demodulator 210r, the control information detector 211r captures the digital received signals output by the AD converters 23r-1 and 23r-2, in which main signal information and control information are time-division multiplexed, and detects the positions of the control information 45-1, 45-2, ..., 45-Nt included in the optical signal 50 shown in FIG. 6 based on a specific frequency of a pilot tone signal from the captured digital received signal. Note that the specific frequency of the pilot tone signal transmitted by the optical transmitter 1t is provided to the optical receiver 2r in advance. The control information detector 211r also outputs the detected positions of the control information 45-1, 45-2, ..., 45-Nt to the control information extractors 212r-1 and 212r-2 as timing information.

[0069] As described above, the control information 45-1 to 45-Nt is a predetermined signal for the X polarization and a control signal for the Y polarization, so the control information of the digital reception signal output by the AD conversion unit 23r-1 includes the predetermined signal, and the control information of the digital reception signal output by the AD conversion unit 23r-2 includes the control signal.

[0070] Based on the timing information output by the control information detection unit 211r, each of the control information extraction units 212r-1 and 212r-2 detects a section including control information 45-1, 45-2, ..., 45-Nt from the digital received signals output by the AD conversion units 23r-1 and 23r-2 connected to it, and outputs the signal of the detected section to the differential decoding unit 213r. The differential decoding unit 213r generates a differentially decoded signal by performing differential decoding processing using the signals output by the control information extraction units 212r-1 and 212r-2, and outputs the generated differentially decoded signal to the control unit 20r.

[0071] The control unit 20r includes a transmission mode information storage unit 200r, a transmission mode candidate receiving unit 201r, a transmission mode candidate transmitting unit 202r, a transmission mode selecting unit 203r, a signal quality detecting unit 204r, and a signal quality determining unit 205r.

[0072] In the control unit 20r, the transmission mode information storage unit 200r pre-stores a receiving-side transmission mode information table 2001r having the data configuration shown in Fig. 11. The receiving-side transmission mode information table 2001r stores transmission mode information available for transmission in the optical receiving device 2r. Fig. 11 shows an example of the receiving-side transmission mode information table 2001r that stores transmission mode information with transmission mode numbers "mode 1," "mode 5," "mode 9," and "mode 13" in the transmission mode information table 1000 shown in Fig. 7.

[0073] The transmission mode candidate receiver 201r demodulates the differentially decoded signal output by the differential decoder 213r and acquires transmitting-side transmission mode candidate information for the optical transmitter 1t from the differentially decoded signal. The transmission mode candidate receiver 201r also outputs the acquired transmitting-side transmission mode candidate information to the transmission mode selector 203r. Upon acquiring the transmitting-side transmission mode candidate information, the transmission mode candidate receiver 201r outputs a receiving-side transmission mode candidate information transmission instruction signal for transmitting the receiving-side transmission mode candidate information to the transmission mode candidate transmitter 202r.

[0074] When the transmission mode candidate transmitter 202r receives a receiving side transmission mode candidate information transmission instruction signal from the transmission mode candidate receiver 201r, it generates receiving side transmission mode candidate information including all transmission mode numbers stored in the "transmission mode" item of the receiving side transmission mode information table 2001r stored in the transmission mode information storage unit 200r.

[0075] The transmission mode candidate transmitter 202r is connected to the transmission mode candidate transmitter 101r of the optical transmitter 1r in the receiving system R, and transmits the generated receiving-side transmission mode candidate information to the transmission mode candidate transmitter 101r of the optical transmitter 1r. After transmitting the generated receiving-side transmission mode candidate information to the transmission mode candidate transmitter 101r of the optical transmitter 1r, the transmission mode candidate transmitter 202r outputs a signal quality detection instruction signal for detecting signal quality to the signal quality detector 204r.

[0076] The transmission mode selection unit 203r extracts a transmission mode number that is common to all transmission mode numbers stored in the "transmission mode" item of the receiving side transmission mode information table 2001r stored in the transmission mode information storage unit 200r and the transmitting side transmission mode candidate information of the optical transmitting device 1t output by the transmission mode candidate receiving unit 201r.

[0077] Furthermore, the transmission mode selection unit 203r selects the transmission mode number with the highest priority from the extracted common transmission mode numbers. The priority used as a basis for selection by the transmission mode selection unit 203r is the same as the priority of the transmission mode selection unit 103t of the optical transmission device 1t. Therefore, the transmission mode number selected by the transmission mode selection unit 203r according to the priority and the transmission mode number selected by the transmission mode selection unit 103t of the optical transmission device 1t according to the priority are the same transmission mode number.

[0078] Furthermore, the transmission mode selection unit 203r has an internal storage area, and writes and stores the selected transmission mode number in the internal storage area. Furthermore, when the transmission mode selection unit 203r receives a notification signal from the signal quality determination unit 205r, if the notification signal contains a signal quality unacceptable notification, the transmission mode selection unit 203r refers to the internal storage area and selects the transmission mode number of the transmission mode information with the next highest priority after the transmission mode information selected at that time.

[0079] The transmission mode selection unit 203r also reads information indicating the modulation method from the "Modulation method" field of the transmission mode information corresponding to the selected transmission mode number, the baud rate value from the "Baud rate" field, and information indicating the error correction coding method from the "Error correction code type" field. The transmission mode selection unit 203r also generates a modulation method signal including the read information indicating the modulation method and outputs it to the main signal demodulation units 24r-1 and 24r-2. The transmission mode selection unit 203r also generates a baud rate control signal including the read baud rate value and outputs it to the clock control unit 27r. The transmission mode selection unit 203r also outputs an error correction code designation signal including the read information indicating the error correction coding method to the error correction decoding unit 25r.

[0080] When new transmission mode information is selected in the optical transmission device 1t, the signal quality detection unit 204r detects the signal quality of the signal light transmitted by the optical transmission device 1t in accordance with the newly selected transmission mode.

[0081] The signal quality detection unit 204r has an internal flag area, and the initial value of the flag is "OFF." Furthermore, upon receiving a signal quality detection instruction signal from the transmission mode candidate transmission unit 202r, the signal quality detection unit 204r sets the flag to "ON." Furthermore, the signal quality detection unit 204r detects signal quality while the flag is "ON." Note that the signal quality detection unit 204r does not need to use a flag. In this case, upon receiving the signal quality detection instruction signal, the signal quality detection unit 204r uses a pilot tone signal to detect OSNR from the control information based on the timing information detected by the control information detection unit 211r.

[0082] The signal quality detector 204r detects, for example, a signal-to-noise ratio (hereinafter referred to as "SN ratio") from the intensity of a specific frequency of the pilot tone signal, and uses the detected signal-to-noise ratio as information indicating the signal quality. Note that the information indicating the signal quality is not limited to the SN ratio, and the intensity of the specific frequency itself may be used as information indicating the signal quality. Also, the bit error rate (BER) may be used as information indicating the signal quality. Furthermore, the signal quality detector 204r may be connected to two output terminals of the polarization separator 21r, and may detect an optical signal-to-noise ratio (hereinafter referred to as "OSNR" (Optical Signal-to-Noise Ratio)) based on the optical signals obtained from the output terminals, and use the detected OSNR as information indicating the signal quality. Furthermore, the signal quality detection unit 204r may use information obtained from measuring instruments such as OTDRs (Optical Time Domain Reflectometers), optical spectrum analyzers, and power meters as a signal quality detection method. The information obtained from the measuring instruments enables identification of signal degradation locations and high-precision signal quality detection, making it possible to obtain information that cannot be obtained by conventional optical transmission systems alone. In this case, the measuring instruments may be provided separately from the optical transmission system S, or the optical transmission system S may be configured to have a measurement function.

[0083] The signal quality detector 204r outputs information indicating the detected signal quality to the signal quality determiner 205r and sets the flag to "OFF." If the signal quality detector 204r receives an output from the control information detector 211r while the flag is "OFF," the signal quality detector 204r does not detect the signal quality. This is because the digital received signal is not a signal for which a new transmission mode has been selected in the optical transmitter 1t.

[0084] The signal quality determining unit 205r determines whether the signal quality is acceptable or not based on information indicating the signal quality detected by the signal quality detecting unit 204r and a threshold value that is predetermined according to the detected signal quality.

[0085] Furthermore, if the signal quality determining unit 205r determines that the signal quality is acceptable, it transmits a notification signal of signal quality acceptance notification inline to the optical receiving device 2t of the transmitting system T via the optical transmitting device 1r of the receiving system R. Furthermore, the signal quality determining unit 205r outputs the notification signal of signal quality acceptance notification to the transmission mode selecting unit 203r.

[0086] Furthermore, if the signal quality determining unit 205r determines that the signal quality is unacceptable, it transmits a notification signal of signal quality unacceptability notification inline to the optical receiving device 2t of the transmitting system T via the optical transmitting device 1r of the receiving system R. Furthermore, the signal quality determining unit 205r outputs the notification signal of signal quality unacceptability notification to the transmission mode selecting unit 203r.

[0087] (Regarding the optical transmitter 1r of the receiving system R) As described above, the optical transmitting device 1r of the receiving system R has the same configuration as the optical transmitting device 1t of the transmitting system T. Therefore, in the following description, when referring to each functional unit of the optical transmitting device 1r, the letter "t" in the symbol will be replaced with "r." For example, when referring to the transmission mode selection unit of the optical transmitting device 1r, it will be referred to as the "transmission mode selection unit 103r."

[0088] As described above, the optical transmitting device 1r in the receiving system R receives the receiving-side transmission mode candidate information transmitted by the optical receiving device 2r. The optical transmitting device 1r then transmits the received receiving-side transmission mode candidate information of the optical receiving device 2r to the optical receiving device 2t in the transmitting system T via the optical transmission path 3. For this reason, the transmission mode candidate transmitter 101r of the optical transmitting device 1r in the receiving system R is connected to the transmission mode candidate transmitter 202r of the optical receiving device 2r, as shown in FIG. 12. The transmission mode candidate transmitter 101r then receives the receiving-side transmission mode candidate information of the optical receiving device 2r transmitted by the transmission mode candidate transmitter 202r of the optical receiving device 2r.

[0089] The transmission mode candidate transmitter 101r of the optical transmitter 1r takes in the received reception-side transmission mode candidate information of the optical receiver 2r as transmission information. The transmission mode candidate transmitter 101r of the optical transmitter 1r uses the transmission information as a signal sequence, differentially encodes the signal sequence bit by bit, and outputs the differentially encoded signal to the control information modulator 18r. The transmission mode candidate transmitter 101r also generates a signal sequence in which power is concentrated at one or more specific frequencies, and outputs the generated signal sequence to the control information modulator 18r as a default signal. As a result, the reception-side transmission mode candidate information of the optical receiver 2r is superimposed on a pilot tone signal and transmitted to the optical receiver 2t of the transmitting-side system T via the optical transmission path 3.

[0090] (Regarding optical receiving device 2t of transmitting system T) As described above, the optical receiving device 2t of the transmitting system T has the same configuration as the optical receiving device 2r of the receiving system R. Therefore, in the following description, when referring to each functional unit of the optical receiving device 2t, the letter "r" in the symbol will be replaced with "t." For example, when referring to the transmission mode selection unit of the optical receiving device 2t, it will be referred to as the "transmission mode selection unit 203t."

[0091] As described above, the optical receiving device 2t in the transmitting system T receives the receiving-side transmission mode candidate information for the optical receiving device 2r transmitted by the optical transmitting device 1r in the receiving system R. The optical receiving device 2t then transmits the received receiving-side transmission mode candidate information for the optical receiving device 2r to the optical transmitting device 1t in the transmitting system T. Therefore, the transmission mode candidate receiving unit 201t of the optical receiving device 2t in the transmitting system T is connected to the transmission mode candidate receiving unit 102t of the optical transmitting device 1t, as shown in FIG.

[0092] The transmission mode candidate receiver 201t of the optical receiving device 2t demodulates the differentially decoded signal output by the differential decoder 213t and acquires receiving-side transmission mode candidate information for the optical receiving device 2r from the differentially decoded signal. The transmission mode candidate receiver 201t then transmits the acquired receiving-side transmission mode candidate information for the optical receiving device 2r to the transmission mode candidate receiver 102t of the optical transmitting device 1t. This allows the transmission mode candidate receiver 102t of the optical transmitting device 1t in the transmitting-side system T to acquire receiving-side transmission mode candidate information for the optical receiving device 2r in the receiving-side system R.

[0093] (Transmission mode selection process in the first embodiment) FIG. 14 is a flowchart showing the flow of a transmission mode selection process by the optical transmission system S of the first embodiment, and the dashed arrows indicate transmission and reception of information between the optical transmitter 1t and the optical receiver 2r.

[0094] (Processing of step ST1 of optical transmitter 1t) The transmission mode candidate sending unit 101t of the control unit 10t of the optical transmitting device 1t starts processing in response to a user operation or at the timing of startup of the optical transmitting device 1t. The transmission mode candidate sending unit 101t generates transmitting side transmission mode candidate information including all transmission mode numbers stored in the "transmission mode" item of the transmitting side transmission mode information table 1001t stored in the transmission mode information storage unit 100t.

[0095] The transmission mode candidate transmitter 101t uses the generated transmission mode candidate information on the transmitting side as a signal sequence, differentially encodes the signal sequence bit by bit, and outputs the differentially encoded signal to the control information modulator 18t. The transmission mode candidate transmitter 101t generates a signal sequence in which power is concentrated in one or more specific frequencies, and outputs the generated signal sequence to the control information modulator 18t as a default signal.

[0096] Here, we will explain the differential encoding performed by the transmission mode candidate transmitter 101t. In differential encoding, when the nth (n≧0, n is an integer) setting information is C(n) (C(n) is a binary value of 1 or 0), the nth output (differentially encoded signal) D(n) can be expressed as the exclusive OR of C(n) and D(n-1), as shown in the following equation (1). However, in equation (1), D(-1)=1.

[0097]

number

[0098] Next, we will explain the predetermined signal, i.e., a signal sequence in which power is concentrated at a specific frequency. As a signal sequence in which power is concentrated at a specific frequency, for example, an alternating signal that is point-symmetric with respect to the origin on the IQ plane can be used. As an example, when generating a BPSK signal, an alternating signal in which two signal points are alternately repeated, such as -S, S, -S, S, ..., -S, S, can be used.

[0099] Furthermore, when generating a QPSK signal, if the signal points are expressed as (real part, imaginary part), an alternating signal that alternates between two signal points can be used, such as (S,S),(-S,-S),(S,S),(-S,-S),...,(S,S),(-S,-S) or (S,-S),(-S,S),(-S,S),(S,-S),(-S,S),...,(S,-S),(-S,S). Here, S represents any real number. Furthermore, (real part α, imaginary part β) can be expressed as a complex number, α+jβ, where j is the imaginary unit. This alternating signal can generate power concentrated at two specific frequencies.

[0100] Alternatively, an alternating signal in which one signal is repeated twice, such as -S, -S, S, S, -S, -S, S, S, ..., -S, -S, S, S, S, may be used, or an alternating signal in which one signal is repeated M times (M > 0, a positive number). In this way, by multiplying or convolving alternating signals with multiple repetitions, it is possible to concentrate power at four or more specific frequencies. Furthermore, by superimposing multiple sine waves with different periods, it is also possible to generate a signal in which power is concentrated at two or more specific frequencies. Furthermore, a signal having a specific frequency can be generated by superimposing a signal only on specific subcarriers using Orthogonal Frequency Division Multiplexing (OFDM). Furthermore, by spreading a specific frequency band signal sequence with other signal sequences, it is possible to widen the frequency band in which power is concentrated.

[0101] The control information modulation unit 18t receives the default signal and the differentially encoded signal output by the transmission mode candidate transmission unit 101t, and generates a control signal by modulating the default signal with the differentially encoded signal. Specifically, when the default signal output by the transmission mode candidate transmission unit 101t is -S, S, -S, S, ..., -S, S, and the differentially encoded signal is D(n)=1, the control information modulation unit 18t outputs -S, S, -S, S, ..., -S, S as control signals. Furthermore, when the differentially encoded signal is D(n)=0, the control information modulation unit 18t inverts the sign and outputs S, -S, S, -S, ..., S, -S as control signals. Note that the sign inversion may be reversed between D(n)=1 and D(n)=0, i.e., when D(n)=1, S, -S, S, -S, ..., S, -S may be output, and when D(n)=0, -S, S, -S, S, ..., -S, S may be output.

[0102] Control information modulator 18t outputs the predetermined signal to X-polarized wave multiplexer 14t-1 and outputs the control signal to Y-polarized wave multiplexer 14t-2. X-polarized wave multiplexer 14t-1 performs time division multiplexing by inserting the predetermined signal output by control information modulator 18t into each X-polarized wave transmission symbol sequence output by main signal modulator 13t-1, thereby generating an X-polarized wave signal sequence. Y-polarized wave multiplexer 14t-2 performs time division multiplexing by inserting the control signal output by control information modulator 18t into each Y-polarized wave transmission symbol sequence output by main signal modulator 13t-2, thereby generating a Y-polarized wave signal sequence.

[0103] The electrical-optical conversion units 15t-1 and 15t-2 perform electrical-optical conversion on the signal sequences for X polarization and Y polarization output from the multiplexing units 14t-1 and 14t-2, respectively, and output the optical signals for X polarization and Y polarization to the polarization multiplexing unit 16t.

[0104] The polarization multiplexing unit 16t generates polarization-multiplexed time-division multiplexed signal light by polarization-multiplexing the optical signal for X polarization and the optical signal for Y polarization output from each of the electrical-optical conversion units 15t-1 and 15t-2. In this case, if the differentially encoded signal D(n)=0, the control information in the signal output from one polarization becomes a signal with the phase reversed from the control information in the other polarization.

[0105] The polarization multiplexing unit 16t transmits the generated signal light to the optical transmission line 3. As a result, the signal light including the pilot tone signal on which the transmission side transmission mode candidate information of the optical transmitting device 1t is superimposed is transmitted to the optical receiving device 2r via the optical transmission line 3.

[0106] (Processing of step SR1 of optical receiving device 2r) The polarization separation unit 21r of the optical receiving device 2r receives an optical signal including a pilot tone signal transmitted via the optical transmission line 3. The polarization separation unit 21r performs polarization separation on the received optical signal in the optical domain to separate it into two orthogonal X-polarized and Y-polarized waves, and outputs the separated X-polarized and Y-polarized waves to the optical-electrical conversion units 22r-1 and 22r-2. Each of the optical-electrical conversion units 22r-1 and 22r-2 takes in the X-polarized and Y-polarized optical signals output by the polarization separation unit 21r, converts them into electrical analog signals, and outputs the converted electrical analog signals to the corresponding AD conversion units 23r-1 and 23r-2.

[0107] The AD conversion units 23r-1 and 23r-2 generate digital received signals by converting the electrical analog signals output by the optical / electrical conversion units 22r-1 and 22r-2 connected to them into digital signals, and output the generated digital received signals to the main signal demodulation units 24r-1 and 24r-2 connected to them. The AD conversion units 23r-1 and 23r-2 output the generated digital received signals to the control information detection unit 211r and control information extraction units 212r-1 and 212r-2 of the control information demodulation unit 210r.

[0108] The control information detection unit 211r receives the time-division multiplexed digital received signals output by the AD conversion units 23r-1 and 23r-2, and detects the positions of the control information 45-1, 45-2, ..., 45-Nt contained in the signal light 50 shown in Figure 6 from the received digital received signals based on the specific frequency of the known pilot tone signal.

[0109] One method for detecting the positions of the control information 45-1, 45-2, ..., 45-Nt is for the control information detector 211r to detect positions where power is concentrated at a specific frequency in the digital received signal as insertion positions for the control information 45-1, 45-2, ..., 45-Nt. The positions where power is concentrated are, for example, positions where the signal power of a specific frequency in the digital received signal is calculated and the calculated signal power exceeds a predetermined threshold, or positions where the signal power exceeding the predetermined threshold is the maximum. The control information detector 211r outputs the detected positions as timing information to the control information extractors 212r-1 and 212r-2.

[0110] Based on the timing information output by the control information detection unit 211r, each of the control information extraction units 212r-1, 212r-2 detects a section containing control information 45-1, 45-2, ..., 45-Nt from the digital received signals output by the AD conversion units 23r-1, 23r-2 connected to each of them, and outputs the signal of the detected section to the differential decoding unit 213r.

[0111] The differential decoding unit 213r performs differential decoding processing using the signals output by the control information extraction units 212r-1 and 212r-2, generates a differentially decoded signal, and outputs the generated differentially decoded signal to the transmission mode candidate receiving unit 201r. For example, if the output signals of the control information extraction units 212r-1 and 212r-2 in the n-th frame are Rx(n,k) and Ry(n,k), respectively, the differentially decoded signal Z(n) is expressed by the following equation (2).

[0112]

number

[0113] However, in formula (2), * " denotes a complex conjugate. "K" denotes the length of the digital received signal stored in each buffer of the control information extraction units 212r-1 and 212r-2, where K>k≧0.

[0114] The transmission mode candidate receiver 201r receives the differentially decoded signal output by the differential decoder 213r, demodulates the received differentially decoded signal, and acquires the transmission mode candidate information of the transmitting side of the optical transmitter 1t from the differentially decoded signal. Here, if the differentially decoded signal in the n-th frame is Z(n), the determination result P(n) is expressed by the following equation (3). However, in equation (3), P th (>0) is the decision threshold.

[0115]

number

[0116] The modulation / demodulation techniques performed by the control information modulator 18t, the control information demodulator 210r, and the transmission mode candidate receiver 201r do not depend on the modulation method. Therefore, even in a communication environment in which the transmission mode has not been determined and the optical receiver 2r cannot identify the modulation method of the main signal of the signal light transmitted by the optical transmitter 1t, it is possible to transmit the transmission mode candidate information on the transmitting side of the optical transmitter 1t.

[0117] The transmission mode candidate receiver 201r outputs the acquired transmitting-side transmission mode candidate information of the optical transmitter 1t to the transmission mode selector 203r. Upon acquiring the transmitting-side transmission mode candidate information of the optical transmitter 1t, the transmission mode candidate receiver 201r outputs a receiving-side transmission mode candidate information transmission instruction signal for transmitting the receiving-side transmission mode candidate information to the transmission mode candidate transmitter 202r.

[0118] (Processing of step SR2 of optical receiving device 2r) When the transmission mode candidate transmitter 202r receives a receiving-side transmission mode candidate information transmission instruction signal from the transmission mode candidate receiver 201r, it generates receiving-side transmission mode candidate information including all transmission mode numbers stored in the "Transmission Mode" field of the receiving-side transmission mode information table 2001r stored in the transmission mode information storage unit 200r. The transmission mode candidate transmitter 202r transmits the generated receiving-side transmission mode candidate information to the transmission mode candidate transmitter 101r of the optical transmitter 1r in the receiving-side system R.

[0119] The transmission mode candidate transmitter 202r transmits the generated receiving-side transmission mode candidate information to the transmission mode candidate transmitter 101r of the optical transmitter 1r, and then outputs a signal quality detection instruction signal for detecting the signal quality to the signal quality detector 204r. Upon receiving the signal quality detection instruction signal, the signal quality detector 204r sets a flag to "ON."

[0120] The transmission mode candidate transmitter 101r of the optical transmitter 1r performs the same processing as that performed by the transmission mode candidate transmitter 101t of the optical transmitter 1t in the transmitting system T in step ST1 when the transmission mode candidate transmitter 101t superimposed the transmitting side transmission mode candidate information on a pilot tone signal and transmitted it in step ST1. That is, the transmission mode candidate transmitter 101r of the optical transmitter 1r superimposes the receiving side transmission mode candidate information of the optical receiving device 2r on a pilot tone signal and transmits it to the optical receiving device 2t via the optical transmission path 3.

[0121] (Processing of step SR3 of optical receiving device 2r) The transmission mode selection unit 203r of the optical receiving device 2r in the receiving system R extracts transmission mode numbers that are common to all transmission mode numbers stored in the "Transmission Mode" item of the receiving side transmission mode information table 2001r stored in the transmission mode information storage unit 200r and the transmitting side transmission mode candidate information of the optical transmitting device 1t received from the transmission mode candidate receiving unit 201r. The transmission mode selection unit 203r selects the transmission mode number with the highest priority from the extracted common transmission mode numbers.

[0122] The transmission mode information common to the transmitting side transmission mode information table 1001t shown in Fig. 8 and the receiving side transmission mode information table 2001r shown in Fig. 11 is "mode 1," "mode 5," "mode 9," and "mode 13." In this case, assuming that the first priority is given to the modulation method multi-level and the second priority is given to the baud rate, the transmission mode selection unit 203r selects "mode 13," which includes the modulation method of 16QAM with the highest multi-level, from among "mode 1," "mode 5," "mode 9," and "mode 13."

[0123] The transmission mode selection unit 203r writes and stores the selected transmission mode number, "mode 13," in an internal storage area. The transmission mode selection unit 203r reads transmission mode information corresponding to the selected transmission mode number, "mode 13," from the receiving-side transmission mode information table 2001r in the transmission mode information storage unit 200r. The transmission mode selection unit 203r reads "16QAM," which is information indicating the modulation method in the "modulation method" field, "32 GBaud," the baud rate value in the "baud rate" field, and "RS+LDPC," which is information indicating the error correction coding method in the "error correction code type" field, from the read transmission mode information.

[0124] The transmission mode selection unit 203r generates a modulation method signal including the read information "16QAM" indicating the modulation method and outputs it to the main signal demodulation units 24r-1 and 24r-2. The transmission mode selection unit 203r generates a baud rate control signal including the read baud rate value "32GBaud" and outputs it to the clock control unit 27r. The transmission mode selection unit 203r outputs an error correction code designation signal including the read information "RS+LDPC" indicating the error correction coding method to the error correction decoding unit 25r.

[0125] As a result, the transmission mode selected by the transmission mode selection unit 203r, i.e., the main signal demodulation units 24r-1 and 24r-2 perform demodulation using the 16QAM modulation method, the clock of the optical receiving device 2r set by the clock control unit 27r operates at a clock frequency that sets the baud rate to "32 GBaud", and the error correction decoding unit 25r performs error correction decoding using the "RS+LDPC" method.

[0126] (Processing of step ST2 of optical transmitter 1t) The transmission mode candidate receiver 201t of the optical receiving device 2t in the transmitting-side system T performs processing similar to that performed by the transmission mode candidate receiver 201r of the optical receiving device 2r in the receiving-side system R described above when receiving the pilot tone signal on which the transmitting-side transmission mode candidate information is superimposed and acquiring the transmitting-side transmission mode candidate information in step SR1. That is, the transmission mode candidate receiver 201t of the optical receiving device 2t in the transmitting-side system T receives the pilot tone signal transmitted by the optical transmitting device 1r and acquires the receiving-side transmission mode candidate information of the optical receiving device 2r superimposed on the pilot tone signal.

[0127] The transmission mode candidate receiver 201t of the optical receiving device 2t in the transmitting system T transmits the acquired receiving-side transmission mode candidate information for the optical receiving device 2r to the transmission mode candidate receiver 102t of the optical transmitting device 1t. The transmission mode candidate receiver 102t of the optical transmitting device 1t receives the receiving-side transmission mode candidate information for the optical receiving device 2r. The transmission mode candidate receiver 102t of the optical transmitting device 1t outputs the received receiving-side transmission mode candidate information for the optical receiving device 2r in the receiving-side system R to the transmission mode selector 103t.

[0128] (Processing of step ST3 of optical transmitter 1t) The transmission mode selection unit 103t extracts a transmission mode number that is common to all transmission mode numbers stored in the “Transmission Mode” item of the transmission side transmission mode information table 1001t stored in the transmission mode information storage unit 100t and the reception side transmission mode candidate information of the optical receiving device 2r received from the transmission mode candidate receiving unit 102t.

[0129] The transmission mode selection unit 103t selects the transmission mode number with the highest priority from the extracted common transmission mode numbers. As described above, the priority used as a basis for selection by the transmission mode selection unit 103t is the same as the priority of the transmission mode selection unit 203r of the optical receiving device 2r. Therefore, in step SR3, the transmission mode selection unit 103t selects the transmission mode number "mode 13," which is the same as the transmission mode number selected by the transmission mode selection unit 203r of the optical receiving device 2r. The transmission mode selection unit 103t writes and stores the selected transmission mode number, "mode 13," in an internal storage area.

[0130] The transmission mode selection unit 103t reads out transmission mode information corresponding to the selected transmission mode number "mode 13" from the transmitting-side transmission mode information table 1001t in the transmission mode information storage unit 100t. The transmission mode selection unit 103t reads out, from the read-out transmission mode information, information indicating the modulation method "16QAM" in the "modulation method" field, the baud rate value "32GBaud" in the "baud rate" field, and information indicating the error correction coding method "RS+LDPC" in the "error correction code type" field. The transmission mode selection unit 103t generates a modulation method signal including the read-out information indicating the modulation method "16QAM" and outputs it to the main signal modulation units 13t-1 and 13t-2. The transmission mode selection unit 103t generates a baud rate control signal including the read-out baud rate value "32GBaud" and outputs it to the clock control unit 17t. The transmission mode selection unit 103t outputs an error correction code designation signal including the read information "RS+LDPC" indicating the error correction coding method to the error correction coding unit 12t.

[0131] As a result, the transmission mode selected by the transmission mode selection unit 103t, i.e., the main signal modulation units 13t-1 and 13t-2 perform modulation using the 16QAM modulation method, the clock of the optical transmission device 1t set by the clock control unit 17t operates at a clock frequency that sets the baud rate to "32 GBaud", and the error correction coding unit 12t performs error correction coding using the "RS+LDPC" method.

[0132] (Processing of step ST4 of optical transmitter 1t) The signal transmitter 110t of the optical transmitter 1t in the transmitting system T generates a main signal. Specifically, in the signal transmitter 110t, the framing unit 11t captures a client signal, writes the captured client signal into the payload section 42 of an OTN frame 40, writes information used for monitoring into the overhead section 41, and outputs the frame to the error correction encoder 12t. The error correction encoder 12t generates an error correction code by encoding the signal frame output by the framing unit 11t using the "RS+LDPC" error correction coding scheme indicated by the error correction code designation signal received from the transmission mode selector 103t. The error correction encoder 12t writes the generated error correction code into the error correction encoder 43 of the OTN frame 40 and outputs the OTN frame 40 to the main signal modulators 13t-1 and 13t-2.

[0133] The primary signal modulation units 13t-1 and 13t-2 each modulate the primary signal for X polarization and the primary signal for Y polarization output from the error correction coding unit 12t, respectively, using the modulation method "16QAM" indicated by the modulation method signal received from the transmission mode selection unit 103t. The primary signal modulation units 13t-1 and 13t-2 generate transmission symbol sequences through modulation and output the generated transmission symbol sequences to the multiplexing units 14t-1 and 14t-2 that connect them. The multiplexing units 14t-1 and 14t-2 time-division multiplex the transmission symbol sequence of the primary signal with control information. The electrical-to-optical conversion units 15t-1 and 15t-2 convert the electrical signals output from the multiplexing units 14t-1 and 14t-2 into optical signals, and the polarization multiplexing unit 16t polarization-multiplexes the optical signals and sends them to the optical transmission path 3.

[0134] (Processing of step SR4 of the optical receiving device 2r) The polarization separation unit 21r of the optical receiving device 2r of the receiving system R receives the signal light including the main signal transmitted via the optical transmission line 3. The polarization separation unit 21r performs polarization separation on the received signal light in the optical domain to separate it into two orthogonal X-polarized and Y-polarized waves, and outputs the separated X-polarized and Y-polarized waves to the optical-electrical conversion units 22r-1 and 22r-2. Each of the optical-electrical conversion units 22r-1 and 22r-2 takes in the X-polarized and Y-polarized signal lights output by the polarization separation unit 21r, converts them into electrical analog signals, and outputs the converted electrical analog signals to the corresponding AD conversion units 23r-1 and 23r-2.

[0135] The AD conversion units 23r-1 and 23r-2 convert the electrical analog signals output by the optical-electrical conversion units 22r-1 and 22r-2 connected to them into digital signals to generate digital received signals. The AD conversion units 23r-1 and 23r-2 output the generated digital received signals to the main signal demodulation units 24r-1 and 24r-2 connected to them. The AD conversion units 23r-1 and 23r-2 also output the generated digital received signals to the control information detection unit 211r and control information extraction units 212r-1 and 212-r-2 of the control information demodulation unit 210r.

[0136] Here, because the flag is "ON," signal quality detection unit 204r uses the pilot tone signal to detect signal quality, for example, the S / N ratio obtained from the strength of a specific frequency of the digital received signal. Signal quality detection unit 204r outputs information indicating the detected signal quality, i.e., the detected S / N ratio value, to signal quality determination unit 205r and sets the flag to "OFF."

[0137] (Processing of steps SR5, SR6, and SR7 of the optical receiving device 2r) The signal quality determination unit 205r of the optical receiving device 2r determines whether the signal quality is acceptable based on the information indicating the signal quality detected by the signal quality detection unit 204r and a predetermined threshold (step SR5). For example, if the information indicating the signal quality is an SNR, the signal quality determination unit 205r determines that the signal quality is acceptable if the SNR value is equal to or greater than the threshold (step SR5, Yes). If the signal quality determination unit 205r determines that the signal quality is acceptable, it transmits a notification signal of acceptable signal quality to the optical transmitting device 1r and outputs the notification signal of acceptable signal quality to the transmission mode selection unit 203r (step SR6).

[0138] On the other hand, if the SNR value is less than the threshold, the signal quality determining unit 205r determines that the signal quality is unacceptable (step SR5, No). If the signal quality determining unit 205r determines that the signal quality is unacceptable, it transmits a notification signal of signal quality unacceptable notification to the optical transmitting device 1r and outputs the notification signal of signal quality unacceptable notification to the transmission mode selecting unit 203r (step SR7).

[0139] When the transmission mode selection unit 203r of the optical receiving device 2r receives a notification signal indicating that the signal quality is acceptable from the signal quality judgment unit 205r, it determines the transmission mode information selected at that time as the transmission mode information to be used in operation, and terminates the processing.

[0140] On the other hand, when the transmission mode selection unit 203r of the optical receiving device 2r receives a notification signal indicating that the signal quality is unacceptable from the signal quality judgment unit 205r, the transmission mode selection unit 203r performs the processes from step SR3 onwards. In step SR3, the transmission mode selection unit 203r selects "mode 9" from the common transmission mode information, which is the transmission mode number of the transmission mode information with the next highest priority after the transmission mode information selected at that time.

[0141] (Processing of steps ST5 and ST6 of the optical transmitter 1t) The transmission mode selection unit 103t of the optical transmitting device 1t receives a notification signal from the signal quality determination unit 205r of the optical receiving device 2r (step ST5). Specifically, the transmission mode selection unit 103t of the optical transmitting device 1t receives the notification signal that is output from the signal quality determination unit 205r of the optical receiving device 2r and transmitted inline from the optical transmitting device 1r of the receiving system R to the optical receiving device 2t. The transmission mode selection unit 103t determines whether the received notification signal is a signal quality acceptable notification (step ST6). If the transmission mode selection unit 103t determines that the received notification signal is a signal quality acceptable notification (step ST6, Yes), it establishes the transmission mode information selected at that time as the transmission mode information to be used in operation, and ends the process.

[0142] On the other hand, if the received communication signal is not a signal quality acceptable notification, i.e., a signal quality unacceptable notification (step ST6, No), the transmission mode selection unit 103t of the optical transmitting device 1t performs processing from step ST3 onwards, and in step ST3 selects from the common transmission mode information the transmission mode number of the transmission mode information with the next highest priority after the transmission mode information selected at that time, "mode 9".

[0143] According to the configuration of the first embodiment, in the optical transmission system S, the transmission mode selectors 103t and 203r select transmission mode information in descending order of priority from among a plurality of pieces of transmission mode information, which are combinations of a plurality of parameters related to transmission performance and are common to the transmission performance of the optical transmitting device 1t and the optical receiving device 2r. The signal transmitting unit 110t of the optical transmitting device 1t modulates a signal based on the transmission mode information selected by the transmission mode selecting unit 103t and transmits the modulated signal via the optical transmission path 3. The signal receiving unit 220r of the optical receiving device 2r receives a signal transmitted via the optical transmission path 3 and demodulates the received signal based on the transmission mode information selected by the transmission mode selecting unit 203r. The signal quality detecting unit 204r of the optical receiving device 2r detects the signal quality of the signal received by the signal receiving unit 220r. The signal quality determining unit 205r of the optical receiving device 2r determines whether the signal quality of the signal is acceptable based on the information indicating the signal quality detected by the signal quality detecting unit 204r. If the signal quality determination unit 205r determines that the signal quality of the signal is not acceptable, the transmission mode selection units 103t and 203r select the transmission mode information with the next highest priority.

[0144] As a result, the optical transmitter 1t of the sending system T and the optical receiver 2r of the receiving system R can select transmission mode information with high priority and good signal quality from the multiple transmission mode information they share, and start operation in the transmission mode indicated by the selected transmission mode information. As mentioned above, with the increasing functionality of digital signal processing (DSP) for optical transmission, the number of modulation methods has increased and baud rates have become variable, resulting in various variations in the frequency band occupied by different transmission modes. Furthermore, the addition of parameters such as error correction code types has led to a diversification of transmission modes. In this way, the optical transmission system S is able to select the optimal transmission mode from a variety of transmission modes.

[0145] In other words, in the configuration of the first embodiment, the optical transmitting device 1t transmits a list of transmission mode numbers indicating its own transmission mode information to the optical receiving device 2r in response to a user operation or upon startup. When the optical receiving device 2r receives the list of transmission mode numbers from the optical transmitting device 1t, it transmits the list of transmission mode numbers indicating its own transmission mode information to the optical transmitting device 1t, thereby exchanging their respective lists of transmission mode numbers indicating their respective transmission mode information. After the exchange is complete, the optical transmitting device 1t and the optical receiving device 2r select, from among the common transmission modes, a transmission mode with a higher modulation level, a higher baud rate, and an error correction code type that is compatible between the transmitting and receiving devices, provided that signal quality is satisfied. This processing flow is a so-called autonegotiation processing procedure, and in the first embodiment, this procedure enables link establishment in the optimal transmission mode.

[0146] Furthermore, in the configuration of the first embodiment described above, when transmitting transmission mode candidate information for the optical transmitting device 1t from the optical transmitting device 1t in the transmitting system T to the optical receiving device 2r in the receiving system R, and when transmitting reception side transmission mode candidate information for the optical receiving device 2r from the optical transmitting device 1r in the receiving system R to the optical receiving device 2t in the transmitting system T, a pilot tone signal is used, which allows transmission and reception even when the modulation method cannot be identified. Therefore, even if preprocessing such as determining the modulation method in advance on the transmitting and receiving sides is not performed, for example, when devices other than the optical transmitting device 1t are activated, it is possible to start the processing shown in Fig. 14 when the optical transmitting device 1t is activated.

[0147] Note that, as a premise of the processing shown in Fig. 14, the same transmission mode is selected between the optical receiving device 2t and the optical transmitting device 1r, which are in another opposing relationship, but this premise is not essential. In order to enable the present invention to be applied even when the uplink and downlink transmission modes are different, the optical transmitting device 1r and the optical receiving device 2t perform the processing of Fig. 14 in parallel with the optical transmitting device 1t and the optical receiving device 2r performing the processing of Fig. 14. As a result, in parallel with the processing of selecting the optimal transmission mode by the optical transmitting device 1t and the optical receiving device 2r, the processing of selecting the optimal transmission mode can also be performed between the optical transmitting device 1r and the optical receiving device 2t.

[0148] In this case, the connection relationship between the optical transmitting device 1t and the optical receiving device 2t in the transmitting system T is as shown in FIG. 15. In FIG. 13, which shows a configuration in which the selection of a transmission mode has already been completed between the optical receiving device 2t and the optical transmitting device 1r, the differential decoding unit 213t of the optical receiving device 2t outputs only a differentially decoded signal including "receiving-side transmission mode candidate information of the optical receiving device 2r." In contrast, when the processing shown in FIG. 14 is performed in parallel in the optical transmitting device 1r and the optical receiving device 2t, the differential decoding unit 213t of the optical receiving device 2t also outputs a differentially decoded signal including "transmitting-side transmission mode candidate information of the optical transmitting device 1r." Therefore, the transmission mode candidate receiving unit 201t of the control unit 20t in the optical receiving device 2t needs to branch processing based on the content of the information included in the differentially decoded signal output by the differential decoding unit 213t.

[0149] When the transmission mode candidate receiver 201t demodulates the differentially decoded signal output by the differential decoder 213t and acquires "transmission mode candidate information on the transmitting side of the optical transmitting device 1r," it outputs the acquired information to the transmission mode selector 203t. On the other hand, when the transmission mode candidate receiver 201t demodulates the differentially decoded signal output by the differential decoder 213t and acquires "reception side transmission mode candidate information on the optical receiving device 2r," it outputs the acquired information to the transmission mode candidate receiver 102t of the optical transmitting device 1t.

[0150] In addition, the transmission mode candidate transmitter 202t of the optical receiving device 2t transmits the "receiving side transmission mode candidate information of the optical receiving device 2t" to the transmission mode candidate transmitter 101t of the optical transmitting device 1t, as shown in FIG. 15, in order to transmit the information to the optical transmitting device 1r of the receiving side system R.

[0151] The connection relationship between the optical receiving device 2r and the optical transmitting device 1r in the receiving-side system R is as shown in FIG. 16. In FIG. 12, which shows a configuration in which the selection of a transmission mode has already been completed between the optical receiving device 2t and the optical transmitting device 1r, the differential decoding unit 213r in the optical receiving device 2r outputs only a differentially decoded signal including "transmission-side transmission mode candidate information of the optical transmitting device 1t." In contrast, when the processing shown in FIG. 14 is performed in parallel between the optical transmitting device 1r and the optical receiving device 2t, the differential decoding unit 213r in the optical receiving device 2r also outputs a differentially decoded signal including "reception-side transmission mode candidate information of the optical receiving device 2t." Therefore, the transmission mode candidate receiving unit 201r in the control unit 20r needs to branch processing based on the content of the information included in the differentially decoded signal output by the differential decoding unit 213r.

[0152] When the transmission mode candidate receiver 201r demodulates the differentially decoded signal output by the differential decoder 213r and acquires "transmission mode candidate information on the transmitting side of the optical transmitting device 1t," it outputs the acquired information to the transmission mode selector 203r. On the other hand, when the transmission mode candidate receiver 201r demodulates the differentially decoded signal output by the differential decoder 213r and acquires "reception side transmission mode candidate information on the optical receiving device 2t," it outputs the acquired information to the transmission mode candidate receiver 102r of the optical transmitting device 1r.

[0153] As described above, the processing shown in FIG. 14 needs to be performed in parallel between the optical transmitter 1t and the optical receiver 2r and between the optical transmitter 1r and the optical receiver 2t when the transmission modes of each are different. In contrast, for example, when the optical transmitter 1t and the optical receiver 2t of the transmitting system T are integrated and the types of transmission modes that can be transmitted are the same, and when the optical receiver 2r and the optical transmitter 1r of the receiving system R are integrated and the types of transmission modes that can be transmitted are the same, the processing shown in FIG. 14 does not need to be performed in parallel. This is because the optimal transmission modes between the optical transmitter 1t and the optical receiver 2r and between the optical transmitter 1r and the optical receiver 2t can be simultaneously selected by the processing shown in FIG. 14 performed by the optical transmitter 1t of the transmitting system T and the optical receiver 2r of the receiving system R. However, this assumes that there is no significant difference in the transmission quality of the path from the transmitting system T to the receiving system R on the optical transmission path 3 and the path from the receiving system R to the transmitting system T. This is because if the transmission quality of the path from the receiving system R to the transmitting system T is significantly inferior to the transmission quality of the path from the transmitting system T to the receiving system R, there is a possibility that transmission from the optical transmitting device 1r to the optical receiving device 2t cannot be performed normally in the transmission mode selected by the optical transmitting device 1t and the optical receiving device 2r. Note that after the processing of step SR6 in the optical receiving device 2r of the receiving system R shown in FIG. 14, the optical transmitting device 1r of the receiving system R may transmit a response signal indicating that the transmission mode selection processing has been completed in the finally selected transmission mode, and if the response signal is successfully received by the optical receiving device 2t of the transmitting system T, the system may transition to a normal operating state. Here, "transmission quality" refers to the OSNR when the receiving system R receives a signal.

[0154] (Another configuration example of the first embodiment) In the optical transmission system S of the first embodiment, the optical transmitting device 1t of the sending system T may be replaced with the optical transmitting device 1ta shown in Figure 17, and the optical receiving device 2r of the receiving system R may be replaced with the optical receiving device 2ra shown in Figure 18.

[0155] In the optical transmission device 1ta shown in Fig. 17, the same components as those in the optical transmission device 1t are assigned the same reference numerals, and the following description will focus on the differences. The optical transmission device 1ta does not include the control information modulation unit 18t and multiplexing units 14t-1 and 14t-2 that are included in the optical transmission device 1t. The optical transmission device 1ta includes a framing unit 11ta instead of the framing unit 11t, and a control unit 10ta instead of the control unit 10t. The control unit 10ta includes a transmission mode candidate transmission unit 101ta instead of the transmission mode candidate transmission unit 101t.

[0156] In FIG. 17, a configuration including the framing unit 11ta, the error correction coding unit 12t, the main signal modulation units 13t-1 and 13t-2, the electrical-to-optical conversion units 15t-1 and 15t-2, the polarization multiplexing unit 16t, and the clock control unit 17t is referred to as a signal transmission unit 110ta.

[0157] The overhead section 41 of the OTN frame 40 shown in FIG. 3 has two RES (Reserved) fields, denoted by reference numerals 410 and 411. The RES 410 and 411 are reserved fields to be used for future standardization. The transmission mode candidate transmitter 101ta outputs transmission-side transmission mode candidate information of the optical transmitter 1ta to be transmitted to the optical receiving device 2ra to the framing section 11ta. When the framing section 11ta forms the OTN frame 40 and writes information used for monitoring in the overhead section 41, the framing section 11ta writes the transmission-side transmission mode candidate information of the optical transmitter 1ta output by the transmission mode candidate transmitter 101ta into the RES 410 and 411 fields. As a result, the transmission-side transmission mode candidate information of the optical transmitter 1ta is transmitted to the optical receiving device 2ra as part of the main signal via the optical transmission path 3.

[0158] In the optical receiving device 2ra shown in Fig. 18, the same components as those in the optical receiving device 2r are assigned the same reference numerals, and the following describes the differences. The optical receiving device 2ra does not include the control information demodulation unit 210r that the optical receiving device 2r includes. The optical receiving device 2ra includes a deframing unit 26ra instead of the deframing unit 26r, and a control unit 20ra instead of the control unit 20r. The control unit 20ra includes a transmission mode candidate receiving unit 201ra instead of the transmission mode candidate receiving unit 201r.

[0159] In FIG. 18, the configuration including the polarization separation unit 21r, the optical-electrical conversion units 22r-1 and 22r-2, the AD conversion units 23r-1 and 23r-2, the main signal demodulation units 24r-1 and 24r-2, the error correction decoding unit 25r, the deframing unit 26ra, and the clock control unit 27r is referred to as the signal receiving unit 220ra.

[0160] The deframing unit 26ra receives the error-corrected OTN frame 40 output by the error correction decoding unit 25r, reads the client signal from the payload section 42 of the OTN frame 40, and outputs the read client signal to an IP device connected to the optical receiving device 2r. The deframing unit 26ra also reads out the sending-side transmission mode candidate information of the optical transmitting device 1ta written in the RES 410 and 411 fields of the overhead section 41 of the OTN frame 40.

[0161] The deframing unit 26ra outputs the read transmission mode candidate information of the optical transmitting device 1ta to the transmission mode candidate receiving unit 201ra, which allows the transmission mode candidate receiving unit 201ra of the optical receiving device 2ra to acquire the transmission mode candidate information of the optical transmitting device 1ta transmitted by the optical transmitting device 1ta.

[0162] The transmission mode candidate receiver 201ra outputs the acquired transmitting side transmission mode candidate information to the transmission mode selector 203r. Upon acquiring the transmitting side transmission mode candidate information, the transmission mode candidate receiver 201ra outputs a receiving side transmission mode candidate information transmission instruction signal to the transmission mode candidate transmitter 202r, which transmits the receiving side transmission mode candidate information.

[0163] As described above, when transmitting information using the RES 410 and 411 fields of the OTN frame 40, unlike when using a pilot tone signal, if the receiving side cannot recognize the modulation method of the transmitting side, the receiving side cannot demodulate the signal and obtain the information. Therefore, in the optical transmitting device 1ta and the optical receiving device 2ra, it is necessary to predetermine an initial value of the transmission mode that is automatically set at startup. For example, the transmission mode with the lowest transmission mode number, "Mode 1," having the lowest multi-level and baud rate, is predetermined as the initial value. The optical transmitting device 1ta transmits a main signal modulated based on the initial transmission mode "Mode 1" to the optical receiving device 2ra, and the optical receiving device 2ra can demodulate the received main signal based on the initial transmission mode "Mode 1" to obtain the information.

[0164] Furthermore, when transmitting information using the RES 410 and 411 fields of the OTN frame 40, power does not concentrate on a specific frequency, as occurs when a pilot tone signal is used. Therefore, the signal quality detector 204r cannot detect the signal quality based on the SNR obtained from the signal strength of a specific frequency or the strength itself. Therefore, in this other configuration example, the signal quality detector 204r detects, for example, the bit error rate (BER) obtained by the error correction decoder 25r as information indicating signal quality. Alternatively, a configuration similar to that of the optical transmitter 1t shown in FIG. 2 or the optical receiver 2r shown in FIG. 9, which uses a pilot tone signal, can be used to detect the OSNR obtained from the pilot tone signal as information indicating signal quality, and the RES 410 and 411 fields of the OTN frame 40 can be used to transmit transmission mode information.

[0165] In the optical transmission system S of FIG. 1, if the optical transmitter 1t of the transmitting system T is replaced with the optical transmitter 1ta shown in FIG. 17 and the optical receiver 2r of the receiving system R is replaced with the optical receiver 2ra shown in FIG. 18, information is transmitted from the other opposing optical transmitter 1r to the optical receiver 2t using a pilot tone signal. Therefore, a configuration is achieved in which transmission and reception using the RES 410 and 411 fields of the OTN frame 40 and transmission and reception using the pilot tone signal are used together. Conversely, in the configuration of FIG. 1, the optical transmitter 1t and the optical receiver 2r may remain configured to use the pilot tone signal, while the other opposing optical transmitter 1r and the optical receiver 2t may be configured to use the RES 410 and 411 fields of the OTN frame 40.

[0166] 1, the optical receiving device 2t of the transmitting system T and the optical transmitting device 1r of the receiving system R may be replaced with devices having the configuration of the optical receiving device 2ra and the optical transmitting device 1ta that transmit and receive transmission mode candidate information on the transmitting and receiving sides using the above-mentioned OTN frame 40. With this configuration, transmission and reception of transmission mode candidate information on the transmitting and receiving sides between the optical transmitting device 1ta and the optical receiving device 2ra and between the optical transmitting device 1ra and the optical receiving device 2ta are all performed using the RES 410 and 411 fields of the OTN frame 40.

[0167] Alternatively, an optical transmitter having both the configuration of the optical transmitter 1t and the configuration of the optical transmitter 1ta and an optical receiver having both the configuration of the optical receiver 2r and the configuration of the optical receiver 2ra may be applied. This configuration improves reliability by enabling the transmission of transmitting-side transmission mode candidate information and receiving-side transmission mode candidate information using two systems: a pilot tone signal and the RES 410 and 411 fields of the OTN frame 40. In addition to improving reliability, it also enables flexible implementations, such as using a pilot tone signal to detect OSNR as information indicating signal quality and using the RES 410 and 411 fields of the OTN frame 40 to transmit transmission mode information.

[0168] In the configuration of the first embodiment described above, the signal quality judgment unit 205r of the optical receiving device 2r transmits a notification signal inline to the transmission mode selection unit 103t of the optical transmitting device 1t, but the configuration of the present invention is not limited to this embodiment. The notification signal may also be transmitted from the optical receiving device 2r to the optical transmitting device 1t using the optical transmitting device 1r of the receiving system R and the optical receiving device 2t of the transmitting system T.

[0169] (Second embodiment) 19 is a block diagram showing the configuration of an optical transmission system Sb according to the second embodiment. In the second embodiment, the same components as those in the first embodiment are assigned the same reference numerals, and only the different components will be described below. The optical transmission system Sb includes an optical transmitter 1b, an optical receiver 2b, an optical transmission path 3b, and a control device 6. The optical transmission path 3b has an optical fiber 300 and transmits the signal light output from the optical transmitter 1b to the optical receiver 2b. The control device 6 and the optical transmitter 1b, and the control device 6 and the optical receiver 2b are connected by a communication line such as a dedicated line or the Internet network.

[0170] The control device 6 is, for example, a device equipped with an SDN (Software Defined Networking) controller or a conventional operating system, and includes a transmission mode selection unit 60, a transmission mode information storage unit 61, and a signal quality determination unit 205r. The transmission mode information storage unit 61 may store in advance, for example, a transmitting side transmission mode information table 1001t shown in Fig. 8 and a receiving side transmission mode information table 2001r shown in Fig. 11, or may collect information from either the optical transmitting device 1b or the optical receiving device 2b.

[0171] The transmission mode selection unit 60 extracts transmission mode numbers that are common to the transmitting side transmission mode information table 1001t and the receiving side transmission mode information table 2001r stored in the transmission mode information storage unit 61. The transmission mode selection unit 60 then selects the transmission mode number with the highest priority from among the extracted common transmission mode numbers. As in the first embodiment, the priority is determined in advance, and for example, a transmission mode number that corresponds to transmission mode information that includes a modulation method with a higher degree of multi-value and a higher baud rate has a higher priority.

[0172] The transmission mode selection unit 60 also has an internal storage area, and writes and stores the selected transmission mode number in the internal storage area. The transmission mode selection unit 60 also generates a transmission mode designation signal including the selected transmission mode number and transmits the generated transmission mode designation signal to the optical transmitting device 1b and the optical receiving device 2b. When the transmission mode selection unit 60 receives a notification signal from the signal quality determination unit 205r and the notification included in the notification signal is a signal quality unacceptable notification, the transmission mode selection unit 60 refers to the internal storage area and selects the transmission mode number of the transmission mode information with the next highest priority than the transmission mode information selected at that time. In the second embodiment, the notification signal from the signal quality determination unit 205r is output to the transmission mode selection unit 60.

[0173] The optical transmitter 1b includes a signal transmitter 110b and a control unit 10b. The signal transmitter 110b is connected to an optical transmission line 3b, and has a configuration in which, for example, the framing unit 11ta in the configuration of the signal transmitter 110ta shown in FIG. 17 is replaced with the framing unit 11t in FIG.

[0174] The control unit 10b includes a transmission mode receiving unit 120 and a transmission mode information storage unit 100b. The transmission mode information storage unit 100b stores in advance the transmitting-side transmission mode information table 1001t shown in Fig. 8. The transmission mode receiving unit 120 receives a transmission mode designation signal transmitted by the transmission mode selecting unit 60 of the control device 6, and reads out the transmission mode information of the transmission mode number contained in the transmission mode designation signal from the transmitting-side transmission mode information table 1001t of the transmission mode information storage unit 100b. Based on the read transmission mode information, the transmission mode receiving unit 120 outputs a modulation method signal to the main signal modulating units 13t-1 and 13t-2 of the signal transmitting unit 110b, outputs an error correction code designation signal to the error correction coding unit 12t, and outputs a baud rate control signal to the clock control unit 17t.

[0175] The optical receiving device 2b includes a signal receiving unit 220b and a control unit 20b. The signal receiving unit 220b is connected to the optical transmission line 3b and has the configuration of the signal receiving unit 220r of the optical receiving device 2r shown in FIG.

[0176] The control unit 20b includes a transmission mode receiving unit 230, a transmission mode information storage unit 200b, and a signal quality detection unit 204b. The transmission mode information storage unit 200b stores in advance the receiving-side transmission mode information table 2001r shown in FIG. 11. The transmission mode receiving unit 230 receives a transmission mode designation signal transmitted by the transmission mode selection unit 60 of the control device 6, and reads out the transmission mode information corresponding to the transmission mode number contained in the transmission mode designation signal from the receiving-side transmission mode information table 2001r in the transmission mode information storage unit 200b. Based on the read transmission mode information, the transmission mode receiving unit 230 outputs a modulation scheme signal to the main signal demodulation units 24r-1 and 24r-2 of the signal receiving unit 220b, outputs an error correction code designation signal to the error correction decoding unit 25r, and outputs a baud rate control signal to the clock control unit 27r.

[0177] The signal quality detection unit 204b detects the signal quality and outputs information indicating the detected signal quality to the signal quality determination unit 205r.

[0178] The signal quality detector 204b detects, for example, the OSNR detected from the control information using a pilot tone signal as information indicating the signal quality. Alternatively, the bit error rate (BER) obtained by the error correction decoder 25r may be used as information indicating the signal quality. Like the signal quality detector 204r, the signal quality detector 204b may use information obtained from a measuring instrument such as an OTDR, an optical spectrum analyzer, or a power meter as a signal quality detection method.

[0179] (Transmission mode selection process in the second embodiment) FIG. 20 is a flowchart showing the flow of a transmission mode selection process by the optical transmission system Sb of the second embodiment, and the dashed arrows indicate the transmission and reception of information between the optical transmitter 1b, the control device 6, and the optical receiver 2b.

[0180] The transmission mode selection unit 60 of the control device 6 starts processing in response to an operation by a user, or when the control device 6 is started up or when the optical transmitting device and the optical receiving device are connected. The transmission mode selection unit 60 reads out a transmitting side transmission mode information table 1001t and a receiving side transmission mode information table 2001r from the transmission mode information storage unit 61 (step SCb1).

[0181] The transmission mode selection unit 60 extracts common transmission mode numbers from the read transmitting side transmission mode information table 1001t and receiving side transmission mode information table 2001r. The transmission mode selection unit 60 selects the transmission mode number with the highest priority from the extracted common transmission mode numbers, and writes and stores the selected transmission mode number in an internal storage area (step SCb2).

[0182] The transmission mode selector 60 generates a transmission mode designation signal including the selected transmission mode number and outputs the generated transmission mode designation signal to the optical transmitter 1b and the optical receiver 2b (step SCb3). The transmission mode receiver 120 of the optical transmitter 1b receives the transmission mode designation signal transmitted by the transmission mode selector 60 of the control device 6 (step STb1).

[0183] The transmission mode receiver 120 of the optical transmitter 1b reads out transmission mode information corresponding to the transmission mode number included in the received transmission mode designation signal from the transmission-side transmission mode information table 1001t in the transmission mode information storage unit 100b. Based on the read out transmission mode information, the transmission mode receiver 230 outputs a modulation scheme signal to the main signal modulators 13t-1 and 13t-2 of the signal transmitter 110b, outputs an error correction code designation signal to the error correction encoder 12t, and outputs a baud rate control signal to the clock controller 17t to set the transmission mode (step STb2). The signal transmitter 110b of the optical transmitter 1b transmits the main signal (step STb3).

[0184] The transmission mode receiving unit 230 of the optical receiving device 2b receives the transmission mode designation signal transmitted by the transmission mode selecting unit 60 of the control device 6 (step SRb1). There may be a slight time difference between the timing of receiving the transmission mode designation signal by the optical transmitting device 1b in step STb1 and the timing of receiving the transmission mode designation signal in step SRb1 due to the difference in the distance between the control device 6 and the optical transmitting device 1b and the distance between the control device 6 and the optical receiving device 2b.

[0185] Similarly, the transmission mode receiver 230 of the optical receiver 2b reads out transmission mode information corresponding to the transmission mode number included in the received transmission mode designation signal from the receiving-side transmission mode information table 2001r in the transmission mode information storage unit 200b. Based on the read-out transmission mode information, the transmission mode receiver 230 outputs a modulation scheme signal to the main signal demodulators 24r-1 and 24r-2 of the signal receiver 220b, outputs an error correction code designation signal to the error correction decoder 25r, and outputs a baud rate control signal to the clock controller 27r to set the transmission mode (step SRb2).

[0186] The signal receiving unit 220b of the optical receiving device 2b receives the main signal transmitted through the optical transmission line 3. The signal quality detecting unit 204b of the optical receiving device 2b detects the signal quality of the main signal (step SRb3). Here, it is assumed that the signal quality detecting unit 204b detects the BER as information indicating the signal quality. The signal quality detecting unit 204b transmits information indicating the detected signal quality to the signal quality determining unit 205r of the control device 6 (step SRb4).

[0187] The signal quality determination unit 205r of the control device 6 receives information indicating the signal quality from the signal quality detection unit 204b (step SCb4). The signal quality determination unit 205r determines whether the signal quality is acceptable based on the information indicating the signal quality and a predetermined threshold (step SCb5).

[0188] If the BER value detected by the signal quality detection unit 204b is less than the threshold, the signal quality determination unit 205r determines that the signal quality is acceptable (step SCb5, Yes). If the signal quality determination unit 205r determines that the signal quality is acceptable, it outputs a notification signal for notifying that the signal quality is acceptable to the transmission mode selection unit 60. The transmission mode selection unit 60 determines the transmission mode information selected at that time as the transmission mode information to be used in operation, and ends the process.

[0189] On the other hand, if the BER value detected by the signal quality detection unit 204b is equal to or greater than the threshold, the signal quality judgment unit 205r judges the signal quality to be unacceptable (step SCb5, No). If the signal quality judgment unit 205r judges the signal quality to be unacceptable, it outputs a signal quality unacceptable notification signal to the transmission mode selection unit 60. When the transmission mode selection unit 60 receives the signal quality unacceptable notification signal from the signal quality judgment unit 205r, it performs the processes from step SCb2 onwards. In step SCb2, the transmission mode selection unit 60 selects from the common transmission mode information the transmission mode number of the transmission mode information with the next highest priority after the transmission mode information selected at that time, and in step SCb3 generates a transmission mode designation signal including the selected transmission mode number and transmits it to the optical transmitting device 1b and the optical receiving device 2b.

[0190] According to the configuration of the second embodiment, the transmission mode selector 60c of the control device 6 of the optical transmission system Sb selects transmission mode information in descending order of priority from among a plurality of pieces of transmission mode information, which are combinations of a plurality of parameters related to transmission performance and are common to the transmission performance of the optical transmitter 1b and the optical receiver 2b. The signal transmitter 110b of the optical transmitter 1b modulates a signal based on the transmission mode information selected by the transmission mode selector 60 and transmits the modulated signal via the optical transmission path 3b. The signal receiver 220b of the optical receiver 2b receives the signal transmitted through the optical transmission path 3b and demodulates the received signal based on the transmission mode information selected by the transmission mode selector 60. The signal quality detector 204b of the optical receiver 2b detects the signal quality of the signal received by the signal receiver 220b. The signal quality determiner 205r of the control device 6 determines whether the signal quality of the signal is acceptable based on the information indicating the signal quality detected by the signal quality detector 204b. If the signal quality determination unit 205r determines that the signal quality of the signal is not acceptable, the transmission mode selection unit 60 selects the transmission mode information with the next highest priority.

[0191] As a result, the control device 6 can select transmission mode information with high priority and good signal quality from among the multiple pieces of transmission mode information shared by the optical transmitting device 1b and the optical receiving device 2b.The control device 6 can then cause the optical transmitting device 1b and the optical receiving device 2b to operate in the transmission mode indicated by the selected transmission mode information.In other words, the optical transmission system Sb can select the optimal transmission mode from among transmission modes determined by a combination of various parameters related to multiple transmission performances.

[0192] In other words, in the configuration of the second embodiment, the control device 6 selects a transmission mode with a higher multi-value modulation method, a higher baud rate, and an error correction code type that is consistent between the transmitter and receiver from among multiple transmission modes that both the optical transmitter 1b and the optical receiver 2b have, thereby making it possible to establish a link in the optimal transmission mode.

[0193] Furthermore, in the configuration of the second embodiment, the control device 6 selects transmission mode information and transmits a transmission mode designation signal including the transmission mode number of the selected transmission mode information to the optical transmitting device 1b and the optical receiving device 2. Therefore, even if the optical receiving device 2b cannot recognize the modulation method of the optical transmitting device 1b, it is possible to perform the processing shown in Fig. 20 without performing pre-processing such as determining the modulation method on the transmitting and receiving sides in advance.

[0194] (Third embodiment) 21 is a block diagram showing the configuration of an optical transmission system Sc according to the third embodiment. In the third embodiment, the same components as those in the first and second embodiments are assigned the same reference numerals, and only the different components will be described below. The optical transmission system Sc includes an optical transmitter 1c, an optical receiver 2c, an optical transmission path 3c, a control device 6c, and a management device 7. The management device 7 and the control device 6c, the control device 6c and the optical transmitter 1c, and the control device 6c and the optical receiver 2c are connected by a communication line such as a dedicated line or the Internet.

[0195] The optical transmitting device 1c includes a signal transmitting unit 110b and a control unit 10c. The control unit 10c includes a transmission mode receiving unit 120, a transmission mode information storage unit 100b, and an information accumulation unit 150. The information accumulation unit 150 has an internal nonvolatile storage area, and may sequentially write and accumulate information about the optical transmitting device 1c, such as information about physical characteristic parameters obtained in time series, such as the transmitted light level, received light level, center frequency, and wavelength shift of an optical signal transmitted and received through an optical interface of the optical transmitting device 1c, into the internal storage area, or may monitor the information about the physical characteristic parameters when needed.

[0196] The optical receiving device 2c includes a signal receiving unit 220b and a control unit 20c. The control unit 20c includes a transmission mode receiving unit 230, a transmission mode information storage unit 200b, a signal quality detection unit 204c, and an information accumulation unit 250. The information accumulation unit 250 has an internal non-volatile storage area, and sequentially writes and accumulates information about the optical receiving device 2c, such as the transmission light level, reception light level, center frequency, wavelength shift, and other time-series physical characteristic parameter information of optical signals transmitted and received through the optical interface of the optical receiving device 2c, into the internal storage area.

[0197] The signal quality detector 204c detects the OSNR detected from the control information using the pilot tone signal as information indicating the signal quality, and outputs the information indicating the detected signal quality to the signal quality determiner 205c of the control device 6c. Like the signal quality detector 204r, the signal quality detector 204c may use information obtained from a measuring instrument such as an OTDR, an optical spectrum analyzer, or a power meter as a signal quality detection method.

[0198] The optical transmission path 3c includes optical fibers 300-T and 300-R, WSS (Wavelength Selective Switches) 301-T and 301-R, and optical amplifiers 302-T, 302-C, and 302-R, and transmits the signal light sent from the optical transmitter 1c to the optical receiver 2c.

[0199] WSS301-T, 301-R are wavelength selective switches, and may sequentially write and store information on physical characteristic parameters obtained in time series, such as the center frequency of the signal light for which wavelength selection is being performed, filter bandwidth, filter order, insertion loss, and polarization dependent loss (hereinafter also referred to as PDL (Polarization Dependent Loss)), in an internal non-volatile memory area, or may monitor the information on the physical characteristic parameters when necessary.

[0200] Optical amplifiers 302-T, 302-C, and 302-R are amplifiers that amplify signal light, and may sequentially write and store information on physical property parameters obtained in time series, such as the input power level, output power level, gain, and noise figure (hereinafter referred to as "NF" (Noise Figure)) of the signal light being amplified, in an internal non-volatile storage area, or may monitor the information on the physical property parameters when necessary.

[0201] The control device 6c is a device that includes an SDN controller and a conventional operating system, similar to the control device 6, and includes an information collection unit 62, a transmission mode selection unit 60c, and a signal quality determination unit 205c. The information collection unit 62 is connected via communication lines to the transmission mode information storage unit 100b, information accumulation unit 150, WSSs 301-T and 301-R, optical amplifiers 302-T, 302-C, and 302-R of the optical transmitting device 1c, and the transmission mode information storage unit 200b and information accumulation unit 250 of the optical receiving device 2c.

[0202] In addition, the information collection unit 62 reads information on physical property parameters from the internal memory area of ​​the information storage unit 150 of the optical transmitting device 1c, the internal memory area of ​​the information storage unit 250 of the optical receiving device 2c, the internal memory area of ​​the WSSs 301-T and 301-R, and the internal memory area of ​​the optical amplifiers 302-T, 302-C, and 302-R, and writes and stores the read physical property parameters in the transmission design information memory unit 71 of the management device 7. The information collecting unit 62 can also read information on physical property parameters related to the optical transmission line obtained by digital signal processing, and write and store the information in the transmission design information storage unit 71 of the management device 7. The physical property parameters related to the optical transmission line obtained by digital signal processing include chromatic dispersion, polarization mode dispersion, polarization dependent loss, nonlinear coefficient, etc. These physical property parameters can also be used to perform transmission design of an optical path to be set in an optical transmission line connecting certain points.

[0203] The information collecting unit 62 also reads out information from the transmission mode information storage unit 100b of the optical transmitting device 1c and the transmission mode information storage unit 200b of the optical receiving device 2c, respectively, stored in the transmitting side transmission mode information table 1001t and the receiving side transmission mode information table 2001r. The information collecting unit 62 also writes and stores the read information from the transmitting side transmission mode information table 1001t and the receiving side transmission mode information table 2001r in the transmission design information storage unit 71 of the management device 7.

[0204] The transmission mode selection unit 60c selects the transmission mode number with the highest priority from a transmission mode candidate list containing multiple pieces of transmission mode information provided by the management device 7. As in the first and second embodiments, the priority is determined in advance, and for example, a transmission mode number corresponding to transmission mode information containing a modulation method with a higher degree of multi-value and a higher baud rate has a higher priority.

[0205] The transmission mode selection unit 60c also has an internal storage area, and writes and stores the selected transmission mode number in the internal storage area. The transmission mode selection unit 60c also generates a transmission mode designation signal including the selected transmission mode number and transmits the generated transmission mode designation signal to the optical transmitting device 1c and the optical receiving device 2c. When the transmission mode selection unit 60c receives a notification signal from the signal quality determination unit 205c, if the notification included in the notification signal is a signal quality unacceptable notification, the transmission mode selection unit 60c refers to the internal storage area and selects from the transmission mode candidate list the transmission mode number of the transmission mode information with the next highest priority than the transmission mode information selected at that time.

[0206] The signal quality determination unit 205c receives the OSNR value transmitted by the management device 7 and sets the received OSNR value as a threshold value. Furthermore, the signal quality determination unit 205c determines whether the signal quality is acceptable based on the threshold value and the information indicating the signal quality received from the signal quality detection unit 204c.

[0207] Furthermore, if the signal quality determination unit 205c determines that the signal quality is acceptable, it outputs a notification signal of signal quality acceptable to the transmission mode selection unit 60c. Furthermore, if the signal quality determination unit 205c determines that the signal quality is unacceptable, it outputs a notification signal of signal quality unacceptable to the transmission mode selection unit 60c.

[0208] The management device 7 includes a transmission design information storage unit 71 and a transmission design processing unit 72. As described above, the transmission design information storage unit 71 stores the physical characteristic parameters of the optical transmitting device 1c, the optical receiving device 2c, the WSSs 301-T and 301-R, and the optical amplifiers 302-T, 302-C, and 302-R written by the information collecting unit 62, the information in the transmitting-side transmission mode information table 1001t, and the information in the receiving-side transmission mode information table 2001r.

[0209] The transmission design processing unit 72 performs transmission design processing for the entire network based on the level diagram between the optical transmitting device 1c and the optical receiving device 2c, based on the physical characteristic parameters stored in the transmission design information storage unit 71, the information in the transmitting side transmission mode information table 1001t, and the information in the receiving side transmission mode information table 2001r.

[0210] Furthermore, as a result of the transmission design processing, the transmission design processing unit 72 calculates the transmission quality between the optical transmitting device 1c and the optical receiving device 2c, and selects multiple pieces of transmission mode information as candidates based on the calculated transmission quality. The transmission design processing unit 72 also generates a transmission mode candidate list including the selected multiple pieces of transmission mode information, and outputs the generated transmission mode candidate list to the transmission mode selection unit 60c of the control device 6c. As a result of the transmission design processing, the transmission design processing unit 72 also calculates an OSNR that is acceptable as signal quality when the optical receiving device 2c receives the signal light transmitted by the optical transmitting device 1c. The transmission design processing unit 72 also transmits the calculated OSNR value to the signal quality determination unit 205c.

[0211] (Processing of the management device in the third embodiment) Fig. 22 is a flowchart showing the flow of processing by the management device 7 of the third embodiment. Before the processing of the flowchart shown in Fig. 22 is performed, it is assumed that information on the physical characteristic parameters of the WSSs 301-T and 301-R, the optical amplifiers 302-T, 302-C, and 302-R, the optical transmitting device 1c, and the optical receiving device 2c has already been written into the transmission design information storage unit 71 by the information collecting unit 62 of the control device 6c. It is also assumed that information on the transmitting side transmission mode information table 1001t and information on the receiving side transmission mode information table 2001r has already been written into the transmission design information storage unit 71 by the information collecting unit 62 of the control device 6c.

[0212] The transmission design processing unit 72 of the management device 7 extracts common transmission mode information from the information in the transmitting side transmission mode information table 1001t and the information in the receiving side transmission mode information table 2001r stored in the transmission design information storage unit 71. For each piece of extracted transmission mode information, the transmission design processing unit 72 performs transmission design processing based on the physical property parameters stored in the transmission design information storage unit 71, and calculates the transmission quality for each piece of transmission mode information (step SMc1).

[0213] When performing transmission design processing based on the physical characteristic parameters stored in the transmission design information storage unit 71, the transmission design processing unit 72 calculates the OSNR when the optical receiving device 2c receives the signal light transmitted by the optical transmitting device 1c (step SMc2).

[0214] Based on the calculated transmission quality, the transmission design processing unit 72 selects a predetermined number of transmission mode information as candidates, for example, in descending order of transmission quality, and generates a transmission mode candidate list including the selected transmission mode information (step SMc3).

[0215] The transmission design processing unit 72 transmits the generated transmission mode candidate list to the transmission mode selection unit 60c of the control device 6c, and transmits the calculated OSNR value to the signal quality determination unit 205c (step SMc4).

[0216] (Transmission mode selection process in the third embodiment) FIG. 23 is a flowchart showing the flow of a transmission mode selection process by the optical transmission system Sc of the third embodiment, and the dashed arrows indicate the transmission and reception of information between the optical transmitter 1c, the control device 6c, and the optical receiver 2c.

[0217] 22, the transmission design processing unit 72 of the management device 7 transmits the generated transmission mode candidate list to the transmission mode selection unit 60c of the control device 6c, and transmits the calculated OSNR value to the signal quality determination unit 205c. The transmission mode selection unit 60c of the control device 6c receives the transmission mode candidate list. The signal quality determination unit 205c of the control device 6c receives the OSNR value (step SCc1).

[0218] The transmission mode selection unit 60c selects the transmission mode number of the transmission mode information with the highest priority from the transmission mode candidate list, and writes and stores the selected transmission mode number in an internal storage area (step SCc2).

[0219] The transmission mode selection unit 60c generates a transmission mode designation signal including the selected transmission mode number, and outputs the generated transmission mode designation signal to the optical sending device 1c and the optical receiving device 2c (step SCc3).

[0220] In steps STc1 to STc3 in the optical transmitting device 1c, the same processes as steps STb1 to STb3 in the optical transmitting device 1b of the second embodiment shown in Fig. 20 are performed. In addition, in steps SRc1 to SRc2 in the optical receiving device 2c, the same processes as steps SRb1 to SRb2 in the optical receiving device 2b of the second embodiment shown in Fig. 20 are performed.

[0221] The signal receiving unit 220b of the optical receiving device 2c receives the main signal transmitted through the optical transmission line 3c. The signal quality detecting unit 204c of the optical receiving device 2c detects the OSNR of the main signal (step SRb3). The signal quality detecting unit 204c transmits the detected OSNR value to the signal quality determining unit 205c of the control device 6c (step SRc4).

[0222] The signal quality determination unit 205c of the control device 6c receives the OSNR value from the signal quality detection unit 204c (step SCc4). The signal quality determination unit 205c uses the OSNR value received from the transmission design processing unit 72 of the management device 7 in step SCc1 as a threshold, and determines whether the signal quality is acceptable based on the threshold and the OSNR value received from the signal quality detection unit 204c (step SCb5).

[0223] For example, if the OSNR value detected by the signal quality detector 204c is equal to or greater than a threshold, the signal quality determiner 205c determines that the signal quality is acceptable (step SCc5, Yes). If the signal quality determiner 205c determines that the signal quality is acceptable, it outputs a notification signal for notifying that the signal quality is acceptable to the transmission mode selector 60c. The transmission mode selector 60c determines the transmission mode information selected at that time as the transmission mode information to be used in operation, and ends the process.

[0224] On the other hand, if the OSNR value is less than the threshold, the signal quality determiner 205c determines that the signal quality is unacceptable (step SCc5, No). If the signal quality determiner 205c determines that the signal quality is unacceptable, it outputs a signal quality unacceptable notification signal to the transmission mode selector 60c. When the transmission mode selector 60c receives the signal quality unacceptable notification signal from the signal quality determiner 205c, it performs the processes from step SCc2 onwards. In step SCc2, the transmission mode selector 60c selects from the transmission mode candidate list the transmission mode number of the transmission mode information with the next highest priority after the transmission mode information selected at that time, and in step SCc3 generates a transmission mode designation signal including the selected transmission mode number and transmits it to the optical transmitter 1c and the optical receiver 2c.

[0225] According to the configuration of the third embodiment, in the management device 7 of the optical transmission system Sc, the transmission design processing unit 72 calculates the transmission quality for each of a plurality of pieces of transmission mode information common to the transmission performance of the optical transmitting device 1c and the optical receiving device 2c based on the physical characteristic parameters stored in the transmission design information storage unit 71. The transmission design processing unit 72 generates a transmission mode candidate list including a plurality of pieces of transmission mode information to be selected based on the calculated transmission quality, and transmits the generated transmission mode candidate list to the transmission mode selection unit 60c of the control device 6c. This enables the transmission mode selection unit 60c of the third embodiment to select an optimal transmission mode that has high transmission quality, high priority, and a large OSNR value, as determined by a transmission design based on the physical characteristic parameters of the various modules provided in the optical transmission line 3c, the optical transmitting device 1c, and the optical receiving device 2c.

[0226] (Fourth embodiment) 24 is a block diagram showing the configuration of an optical transmission system Sd according to a fourth embodiment. In the fourth embodiment, the same components as those in the first to third embodiments are assigned the same reference numerals, and only the different components will be described below. The optical transmission system Sd includes an optical transmitter 1c, an optical receiver 2c, an optical transmission path 3c, a control device 6c, and a management device 7d. The management device 7d and the control device 6c, the control device 6c and the optical transmitter 1c, and the control device 6c and the optical receiver 2c are connected by a communication line such as a dedicated line or the Internet.

[0227] The management device 7d includes a transmission design information storage unit 71, a transmission design processing unit 72d, a network design processing unit 74, and a network design information storage unit 73.

[0228] The transmission design processing unit 72d performs transmission design processing in the same way as the transmission design processing unit 72 to generate a transmission mode candidate list. The transmission design processing unit 72d outputs the generated transmission mode candidate list to the network design processing unit 74. Similarly to the transmission design processing unit 72, the transmission design processing unit 72d also calculates an OSNR that is acceptable as signal quality when receiving the signal light transmitted by the optical transmitting device 1c. The transmission design processing unit 72d transmits the calculated OSNR value to the network design processing unit 74. The network design information storage unit 73 stores in advance topology information, node information, path information, etc. of the optical transmission line 3. Information such as topology information, node information, and path information of the network of the optical transmission line 3 may be collected using the information collection unit 62b of the control device 6c. This makes it possible to collect network information including the optical frequency utilization efficiency at any time.

[0229] The network design processing unit 74 receives the transmission mode candidate list and the OSNR value output by the transmission design processing unit 72. The network design processing unit 74 performs accommodation design processing to determine an optical path that improves optical frequency utilization efficiency for each piece of transmission mode information included in the transmission mode candidate list, using information stored in the network design information storage unit 73. Optical frequency utilization efficiency refers to the efficient use of limited optical frequency resources, and represents, for example, the ratio of frequencies allocated to a certain signal. The network design processing unit 74 also adds information indicating priority to each piece of transmission mode information included in the transmission mode candidate list, based on the optical frequency utilization efficiency for each piece of transmission mode information obtained as a result of the accommodation design processing. The network design processing unit 74 then outputs the transmission mode candidate list, to which the information indicating priority has been added, to the transmission mode selection unit 60c.

[0230] Furthermore, the network design processing unit 74 outputs the OSNR value output by the transmission design processing unit 72 to the signal quality determining unit 205c.

[0231] (Processing of the management device in the fourth embodiment) Fig. 25 is a flowchart showing the flow of processing by the management device 7d of the fourth embodiment. Before the processing of the flowchart shown in Fig. 25 is performed, the information collector 62 of the control device 6c has already written information on the physical characteristic parameters of the WSSs 301-T and 301-R, the optical amplifiers 302-T, 302-C, and 302-R, the optical transmitter 1c, and the optical receiver 2c into the transmission design information storage unit 71. In addition, the information collector 62 of the control device 6c has already written information from a transmitting-side transmission mode information table 1001t and information from a receiving-side transmission mode information table 2001r into the transmission design information storage unit 71.

[0232] The transmission design processing unit 72d of the management device 7d extracts common transmission mode information from the information in the transmitting side transmission mode information table 1001t and the information in the receiving side transmission mode information table 2001r. The transmission design processing unit 72d performs transmission design processing based on the physical property parameters stored in the transmission design information storage unit 71, and calculates the transmission quality for each of the extracted transmission mode information (step SMd1).

[0233] Based on the calculated transmission quality, the transmission design processing unit 72d selects a predetermined number of transmission mode information as candidates, for example, in descending order of transmission quality, generates a transmission mode candidate list including the selected transmission mode information, and outputs the generated transmission mode candidate list to the network design processing unit 74 (step SMd2).

[0234] The transmission design processing unit 72d calculates the OSNR when the optical receiving device 2c receives the signal light transmitted by the optical transmitting device 1c (step SMd3) when performing transmission design processing based on the physical characteristic parameters stored in the transmission design information storage unit 71. The transmission design processing unit 72d outputs the calculated OSNR value to the network design processing unit 74.

[0235] The network design processing unit 74 receives the transmission mode candidate list and the OSNR value output by the transmission design processing unit 72d. For each piece of transmission mode information included in the received transmission mode candidate list, the network design processing unit 74 performs accommodation design processing to determine an optical path that improves optical frequency utilization efficiency, using information stored in the network design information storage unit 73. Based on the optical frequency utilization efficiency for each piece of transmission mode information obtained as a result of the accommodation design processing, the network design processing unit 74 adds information indicating priority to the transmission mode information so that the transmission mode information with the highest optical frequency utilization efficiency has the highest priority (step SMd4).

[0236] The network design processing unit 74 outputs the generated transmission mode candidate list to the transmission mode selection unit 60c. The network design processing unit 74 outputs the OSNR calculated by the transmission design processing unit 72 to the signal quality determination unit 205c (step SMd5).

[0237] The transmission mode selection process of the fourth embodiment is the same as that of the third embodiment shown in FIG. 23, except that the process of step SCc2 by the control device 6c in the fourth embodiment is replaced with the process described below. That is, in the fourth embodiment, information indicating priority is added to the transmission mode information included in the transmission mode candidate list. Therefore, in the first process of step SCc2, the transmission mode selector 60c selects the transmission mode number corresponding to the transmission mode information with the highest priority in accordance with the priority information added to the transmission mode information included in the transmission mode candidate list. The transmission mode selector 60c writes and stores the selected transmission mode number in an internal storage area. In the second and subsequent processes of step SCc2, the transmission mode selector 60c selects the transmission mode number with the second highest priority in the transmission mode candidate list after the transmission mode number stored in the internal storage area, and writes and stores the selected transmission mode number in the internal storage area.

[0238] According to the configuration of the fourth embodiment, in the management device 7d of the optical transmission system Sd, the network design processing unit 74 calculates information indicating priority for each piece of transmission mode information included in the transmission mode candidate list generated by the transmission design processing unit 72d, based on the information stored in the network design information storage unit 73. The transmission mode selection unit 60c of the control device 6c selects transmission mode information in descending order of priority according to the information indicating priority calculated by the network design processing unit 74.

[0239] (Fifth embodiment) 26 is a block diagram showing the configuration of an optical transmission system Se according to a fifth embodiment. In the fifth embodiment, the same components as those in the first to fourth embodiments are assigned the same reference numerals, and only the different components will be described below. The optical transmission system Se includes an optical transmitter 1c, an optical receiver 2c, an optical transmission path 3c, and a control device 6e. The control device 6e and the optical transmitter 1c, and the control device 6e and the optical receiver 2c are connected by a communication line such as a dedicated line or the Internet.

[0240] The fifth embodiment differs from the third embodiment in that the control device 6e includes an information collection unit 62e instead of the information collection unit 62, and further includes a transmission design information storage unit 71e and a transmission design processing unit 72e, and the optical transmission system Se does not include a management device 7.

[0241] The information collection unit 62e is connected via communication lines to the transmission mode information storage unit 100b of the optical transmitting device 1c, the information accumulation unit 150, WSSs 301-T and 301-R, the optical amplifiers 302-T, 302-C and 302-R, the transmission mode information storage unit 200b of the optical receiving device 2c and the information accumulation unit 250.

[0242] In addition, the information collection unit 62e reads information on physical property parameters from the internal storage area of ​​the information storage unit 150 of the optical transmitting device 1c, the internal storage area of ​​the information storage unit 250 of the optical receiving device 2c, the internal storage area of ​​the WSSs 301-T and 301-R, and the internal storage area of ​​the optical amplifiers 302-T, 302-C, and 302-R, and writes and stores the read physical property parameters in the transmission design information storage unit 71e. The information collecting unit 62e can also read information on physical property parameters related to the optical transmission line obtained by digital signal processing, and write and store the information in the transmission design information storage unit 71e. The physical property parameters related to the optical transmission line obtained by digital signal processing include chromatic dispersion, polarization mode dispersion, polarization dependent loss, nonlinear coefficient, etc. These physical property parameters can also be used to perform transmission design of an optical path to be set in an optical transmission line connecting certain points.

[0243] The information collecting unit 62e also reads out information stored in the transmitting side transmission mode information table 1001t and the receiving side transmission mode information table 2001r from the transmission mode information storage unit 100b of the optical transmitting device 1c and the transmission mode information storage unit 200b of the optical receiving device 2c, respectively. The information collecting unit 62e also writes and stores the read information stored in the transmitting side transmission mode information table 1001t and the receiving side transmission mode information table 2001r in the transmission design information storage unit 71e.

[0244] The transmission design information storage unit 71e stores the physical characteristic parameters of the optical transmitting device 1c, the optical receiving device 2c, the WSSs 301-T and 301-R, and the optical amplifiers 302-T, 302-C, and 302-R written by the information collection unit 62e, the information of the transmitting side transmission mode information table 1001t, and the information of the receiving side transmission mode information table 2001r.

[0245] The transmission design processing unit 72e performs transmission design processing for the entire network based on the level diagram between the optical transmitting device 1c and the optical receiving device 2c, based on the physical characteristic parameters stored in the transmission design information storage unit 71e, the information in the transmitting side transmission mode information table 1001t, and the information in the receiving side transmission mode information table 2001r.

[0246] Furthermore, the transmission design processing unit 72e calculates the transmission quality between the optical transmitting device 1c and the optical receiving device 2c as a result of the transmission design processing, and selects multiple pieces of transmission mode information as candidates based on the calculated transmission quality. The transmission design processing unit 72e also generates a transmission mode candidate list including the selected multiple pieces of transmission mode information, and outputs the generated transmission mode candidate list to the transmission mode selecting unit 60c. Furthermore, as a result of the transmission design processing, the transmission design processing unit 72e calculates an OSNR that is acceptable as signal quality when the optical receiving device 2c receives the signal light transmitted by the optical transmitting device 1c. The transmission design processing unit 72e also outputs the calculated OSNR value to the signal quality determining unit 205c.

[0247] As described above, the control device 6e in the fifth embodiment includes the transmission design information storage unit 71e and the transmission design processing unit 72e, thereby executing the processing shown in FIG.

[0248] The configuration of the fifth embodiment described above enables transmission design without using a management device, which improves operability by making it easier to apply to data center interconnects that connect data centers point-to-point.

[0249] (Sixth embodiment) 27 is a block diagram showing the configuration of an optical transmission system Sf according to a sixth embodiment. In the sixth embodiment, the same components as those in the first to fifth embodiments are assigned the same reference numerals, and only the different components will be described below. The optical transmission system Sf includes an optical transmitter 1c, an optical receiver 2f, an optical transmission path 3c, and a control device 6f. The control device 6f and the optical transmitter 1c, and the control device 6f and the optical receiver 2f are connected by a communication line such as a dedicated line or the Internet network.

[0250] The sixth embodiment differs from the fifth embodiment in that the control device 6e further includes a signal quality detection unit 204f, and the optical receiving device 2f includes a signal receiving unit 220f instead of the signal receiving unit 220b, and does not include the signal quality detection unit 204c.

[0251] The signal receiving unit 220f receives the main signal transmitted through the optical transmission line 3c. The signal receiving unit 220f demodulates the received main signal based on the transmission mode information selected by the transmission mode selecting unit 60c. The signal receiving unit 220f outputs the demodulated main signal to the signal quality detecting unit 204f of the control device 6f.

[0252] The signal quality detector 204f uses the pilot tone signal to detect the OSNR from the main signal output from the signal receiver 220f as information indicating the signal quality, and outputs the detected information indicating the signal quality to the signal quality determiner 205c. Like the signal quality detector 204r, the signal quality detector 204f may use information obtained from a measuring instrument such as an OTDR, an optical spectrum analyzer, or a power meter as a signal quality detection method.

[0253] The configuration of the sixth embodiment described above eliminates the need to provide multiple signal quality detectors for each optical receiving device 2f; instead, it is sufficient to provide one signal quality detector in the control device 6f. This allows for a reduction in overall system costs when the number of optical receiving devices 2f increases. Furthermore, the raw data received by the signal receiving unit 220f can be transferred directly to the control device 6f for advanced analysis using machine learning with a deep neural network, thereby improving functionality.

[0254] As described above, the increasing functionality of DSPs for optical transmission has led to an increase in the number of modulation methods and variable baud rates, resulting in various frequency bands occupied by different transmission modes. Furthermore, as advances in optical technology expand optically transparent areas that eliminate electrical relays, network topologies have become more complex, evolving from point-to-point to ring and mesh. The transmission mode selector 60c of the fourth embodiment performs accommodation design processing to improve optical frequency utilization efficiency and streamline frequency resources throughout the network, in addition to considering transmission design. The transmission mode selector 60c then prioritizes transmission mode information and selects transmission modes in descending order of priority. This makes it possible to select an optimal transmission mode that offers high transmission quality, high optical frequency utilization efficiency, and a high OSNR value.

[0255] In the first to sixth embodiments described above, the transmission mode information is a combination of the modulation method, the baud rate, and the type of error correction code. However, any parameter related to transmission performance may be used, and may include, for example, a parameter such as the number of carriers.

[0256] Furthermore, when a new error correction technique is developed, the new error correction technique may be added as a parameter to the error correction code type of the transmission mode information so that it can be selected.

[0257] In the configuration of the first embodiment described above, only the transmission mode number is included in the transmission mode candidate information on the transmitting side and the transmission mode candidate information on the receiving side, but the configuration of the present invention is not limited to this embodiment. The transmission mode information itself may also be included in the transmission mode candidate information on the transmitting side and the transmission mode candidate information on the receiving side.

[0258] In the second to sixth embodiments, the transmission mode selectors 60 and 60c transmit a transmission mode designation signal including a transmission mode number. However, the transmission mode designation signal may include transmission mode information. This eliminates the need for the optical transmitters 1b and 1c to include a transmission mode information storage unit 100b, and similarly, the optical receivers 2b, 2c, and 2f to include a transmission mode information storage unit 200b. Instead, in the third to sixth embodiments, the information in the transmitting-side transmission mode information table 1001t stored in the transmission mode information storage unit 100b and the information in the receiving-side transmission mode information table 2001r stored in the transmission mode information storage unit 200b are stored in advance in the transmission design information storage unit 71.

[0259] In the first embodiment, the transmission mode information storage unit 100t is configured to store the transmitting-side transmission mode information table 1001t in advance, but the configuration of the present invention is not limited to this embodiment. For example, the control unit 10t may be provided with a write processing unit that writes information into the transmission mode information storage unit 100t in response to a user operation, and the write processing unit may write the transmitting-side transmission mode information table 1001t into the transmission mode information storage unit 100t in response to the user operation. Furthermore, when the write processing unit finishes writing the transmitting-side transmission mode information table 1001t, it may transmit a start instruction signal to the transmission mode candidate sending unit 101t to start the processing of step ST1 shown in FIG. 14, thereby starting the processing of FIG. 14.

[0260] Furthermore, in the above first to sixth embodiments, an example was shown in which the OTN frame 40 of the ITU-T G.709 recommendation shown in FIG. 3 is used, but other frames having a reserved field may also be applied.

[0261] In addition, in the above first to fourth embodiments, the signal quality detection unit 204r is provided inside the optical receiving devices 2r and 2ra, and the signal quality detection units 204t, 204b, and 204c are provided inside the optical receiving devices 2t, 2b, and 2c, but they may also be configured to be provided in external devices such as measuring instruments.

[0262] Furthermore, in the third and sixth embodiments, the OSNR is used to determine the signal quality, but the BER may also be used.

[0263] In addition, in the third and fourth embodiments, the transmission design processing unit 72 or the network design processing unit 74 calculates the OSNR as a threshold value. However, instead of calculating the OSNR, a predetermined threshold value may be provided to the signal quality determination unit 205c.

[0264] Furthermore, in the above third and fourth embodiments, the interfaces between the management devices 7, 7d and the control device 6c, the interface between the control device 6c and the optical transmitting device 1c, the interface between the control device 6c and the optical receiving device 2c, and the interfaces between the control device 6c and the various modules of the optical transmission path 3c, i.e., WSS301-T, 301-R, optical amplifiers 302-T, 302-C, 302-R, are assumed to use API (Application Programming Interface), but may also be conventional interfaces such as TL-1 (Transaction Language 1).

[0265] Furthermore, in the configurations of the first to sixth embodiments described above, the signal quality determination units 205r and 205c perform determination processing using a threshold. Furthermore, the control information detection unit 211r and the transmission mode candidate reception unit 201r also perform determination processing using a threshold. In these determination processing, the determination processing of "exceeds the threshold," "below the threshold," "greater than the threshold," and "below the threshold" are merely examples, and may be replaced with determination processing of "greater than the threshold," "below the threshold," "exceeds the threshold," and "below the threshold," respectively, depending on the type of information indicating the signal quality to be determined and how the threshold is defined.

[0266] In the above first to fourth embodiments, the signal quality detectors 204r, 204b, and 204c may detect bit error information obtained from the error correction decoders 25r and 220b as the signal quality. In the first and second embodiments, the transmission mode candidate information may be included in the control information.

[0267] In the first to sixth embodiments described above, when selecting the highest-priority transmission mode number from among the common transmission mode numbers, the transmission mode selection units 103t, 203t, 60, and 60c select a candidate that maximizes the transmission capacity. However, a transmission mode number that results in low power consumption or high optical frequency utilization efficiency may be selected as a high-priority transmission mode number. In this configuration, the transmission mode selection units 103t, 203t, 60, and 60c first select a candidate transmission mode number for the transmission capacity required between the transmitter and receiver from among the common transmission mode numbers. The transmission capacity required between the transmitter and receiver may be set in advance. For example, if the transmission capacity required between the transmitter and receiver is 200 G, the transmission mode numbers for a transmission capacity of 200 G are four: "mode 7," "mode 8," "mode 13," and "mode 14." The transmission mode selection unit 103t, the transmission mode selection unit 203t, the transmission mode selection unit 60, and the transmission mode selection unit 60c select a transmission mode that reduces power consumption or improves optical frequency utilization efficiency from among the selected candidates for the transmission capacity required between the transmitter and the receiver. The transmission mode that reduces power consumption or improves optical frequency utilization efficiency may be set in advance by any combination of modulation method, baud rate, and error correction code type.

[0268] In the first to sixth embodiments, the functional units having the name "storage unit", i.e., the transmission mode information storage units 100t, 100r, 200r, 200t, 100b, 200b, 61, the transmission design information storage unit 71, and the network design information storage unit 73, are non-volatile storage areas. Furthermore, among the functional units included in the control information modulation unit 18t and the control information demodulation unit 210r of the first embodiment and the control units 10t, 10r, 20r, 20t, 10ta, 20ra, 10b, 20b, 10c, and 20c of the first to fourth embodiments, the functional units other than the functional units having the name "storage unit" may be functional units configured by, for example, executing a program in a processor such as a CPU (Central Processing Unit).

[0269] Therefore, the control information modulator 18t and the control information demodulator 210r in the above-described embodiment, and the functional units designated as "control units" in the first to fourth embodiments, i.e., the control units 10t, 10r, 20r, 20t, 10ta, 20ra, 10b, 20b, 10c, and 20c, may be implemented by a computer. In this case, a program for implementing this function may be recorded on a computer-readable recording medium, and the program recorded on the recording medium may be loaded into a computer system and executed. Note that the term "computer system" herein includes hardware such as an OS and peripheral devices. Furthermore, the term "computer-readable recording medium" refers to portable media such as flexible disks, optical magnetic disks, ROMs, and CD-ROMs, as well as storage devices such as hard disks built into a computer system. Furthermore, the term "computer-readable recording medium" may also include devices that dynamically store programs for a short period of time, such as communication lines when transmitting programs via networks such as the Internet or telephone lines, or devices that store programs for a fixed period of time, such as volatile memory within the computer systems that serve as the server or client in such cases. Furthermore, the above program may be one that realizes part of the above-mentioned functions, or may be one that can realize the above-mentioned functions in combination with a program already recorded in a computer system, or may be one that is realized using a programmable logic device such as an FPGA (Field Programmable Gate Array).

[0270] Although an embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs within the scope of the gist of the present invention. [Industrial Applicability]

[0271] As DSPs become more sophisticated, they have a variety of transmission modes, and this technology enables selection of the optimal transmission mode by considering not only the modulation method but also various parameters such as baud rate, error correction code type, and number of carriers. [Explanation of symbols]

[0272] 1t, 1r...optical transmitting device, 2r, 2t...optical receiving device, 3...optical transmission path, 4T, 4R...multiplexing unit, 9...communication line, T...transmitting system, R...receiving system, S...optical transmission system, 300...optical fiber

Claims

1. a transmission mode candidate transmitter that transmits transmission mode candidate information including transmission mode information that is a combination of a plurality of parameters related to the transmission performance of the own device to a transmission device to be communicated with; a transmission mode candidate receiving unit that receives transmission mode candidate information including the transmission mode information of the transmission device to be communicated with; a transmission mode selection unit that selects transmission mode information to be used for communication from a plurality of pieces of transmission mode information that are common between the transmission mode candidate information of the own device and the transmission mode candidate information of the communication target transmission device; a signal transmitting / receiving unit that transmits and receives signals based on the selected transmission mode information; Equipped with The transmission mode selection unit selects candidate transmission mode information that is a candidate for the transmission capacity required between the transmitter and the receiver from among the plurality of pieces of common transmission mode information, and selects, from the selected candidate transmission mode information, transmission mode information that reduces power consumption or transmission mode information that improves optical frequency utilization efficiency in order of priority.

2. the transmission mode selection unit selects the transmission mode information that reduces the power consumption or the transmission mode information that improves the optical frequency utilization efficiency based on any combination of a modulation method, a baud rate, and an error correction code type related to the transmission performance of the device itself; The transmitting / receiving device according to claim 1 .

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