Equalization device, optical transmission system, and equalization method

Abstract

When reducing the difference in transmission signal quality between the channels, a penalty is incurred for the less noisy channels. Accordingly, an equalization device according to an exemplary aspect of the present invention includes processing means for performing a process associated with a signal propagating through each of a plurality of channels using a transfer function having coefficients, and coefficient generating means for generating coefficients based on channel quality information for each of the plurality of channels.

Description

Technical Field

[0001] The present invention relates to an equalization device, an optical transmission system, and an equalization method, and particularly to an equalization device, an optical transmission system, and an equalization method used in a wavelength division multiplexing system.

Background Art

[0002] In order to meet the requirement of higher communication capacity in optical fiber transmission, technological development has led to the development of multiplexing technologies related to resources from multiple perspectives such as wavelength division multiplexing (WDM) and space division multiplexing (SDM).

[0003] When multiplexing technology is applied, signals are transmitted simultaneously in multiple channels, for example, in multiple cores within a multi-core fiber (MCF) in SDM. In particular, for a non-coupled MCF, the difference in Q factor (Q factor) between channels occurs according to the individual losses and gains in each core and other multi-channel components. Furthermore, the difference in Q value is further increased due to the noise figure and gain control of erbium-doped fiber amplifiers (EDFAs) in long-distance transmission systems such as undersea transmission. The aforementioned difference in Q value has become a bottleneck for the overall transmission capacity. Therefore, it is required to equalize the difference in Q value between channels in multiplex transmission.

[0004] Patent Document 1 (PTL1) describes a transmitter that can eliminate the difference in Q value between channels in SDM. The data of two channels are equally separated and mixed by a 2×2 matrix on the transmitter side. Then, the received signal is restored by the inverse matrix of the 2×2 matrix. Therefore, each restored signal receives an average channel noise. As a result, the difference in Q value between the two channels is equalized.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The related transmitter disclosed in Patent Document 1 can reduce the difference in transmission signal quality due to the difference between two channels to a specific level. However, the related transmitter imposes a penalty on a channel that is originally less noisy. This is because the transfer matrix used in the related transmitter is designed to equally mix the signals of the two channels regardless of the channel state. Therefore, a penalty is imposed on a channel that is originally less noisy, resulting in an unnecessary degradation of the performance of the entire multi-transmission system during this equalization procedure.

[0007] An exemplary object of the present invention is to provide an equalization device, an optical transmission system, and an equalization method that solve the above-mentioned problem of imposing a penalty on a channel with less noise when reducing the difference in transmission signal quality between channels.

Means for Solving the Problems

[0008] An equalization device according to an exemplary aspect of the present invention includes processing means for executing a process associated with a signal propagating through each of a plurality of channels using a transfer function having coefficients, and coefficient generation means for generating coefficients based on channel quality information for each of the plurality of channels.

[0009] An optical transmission system according to an exemplary aspect of the present invention includes transmission processing means for receiving an input of data transmitted through a plurality of channels and converting the data into a signal using a first transfer matrix having coefficients so as to give more signal power to a channel having a lower channel quality, reception processing means for receiving an input of the signal after propagation through the plurality of channels and restoring the propagated signal to data using a second transfer matrix that is the inverse matrix of the first transfer matrix, and coefficient generation means for generating coefficients based on channel quality information for each of the plurality of channels.

[0010] An equalization method according to an exemplary embodiment of the present invention includes performing a process associated with a signal propagating through each of a plurality of channels using a transfer function having coefficients, and generating the coefficients based on channel quality information for each of the plurality of channels. [Advantages of the Invention]

[0011] An exemplary advantage according to the present invention is that it is possible to equalize the difference in transmission signal quality between channels with a minimum penalty. [Brief Description of the Drawings]

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

[0013] Embodiments of the present invention will be described below with reference to the drawings. The direction of the arrows in the drawings indicates an example of the direction and does not limit the direction of the signal between the blocks. [First Embodiment]

[0014] FIG. 1 is a block diagram showing the configuration of an equalization device according to a first embodiment of the present invention. The equalization device 100 includes a processing unit (processing means) 110 and a coefficient generation unit (coefficient generation means) 120.

[0015] The processing unit 110 is configured to execute a process associated with a signal using a transfer function having coefficients. The signal propagates through each of a plurality of channels. The coefficient generation unit 120 is configured to generate coefficients based on channel quality information for each of the plurality of channels.

[0016] According to the equalization device 100 of the present embodiment, since the process associated with the signal is executed based on the channel quality information for each of the plurality of channels, it is possible to equalize the difference in transmission signal quality between channels with a minimum penalty.

[0017] As shown in FIG. 2, the processing unit 110 may include a transmission processing unit (transmission processing means) 111. The transmission processing unit 111 receives an input of data transmitted through a plurality of channels and converts the data into a signal using a first transfer matrix as a transfer function so as to give more signal power to channels having lower channel quality.

[0018] In addition, the processing unit 110 may include a reception processing unit (reception processing means) 112. The reception processing unit 112 receives an input of a signal after propagation through a plurality of channels and restores the propagated signal to data using a second transfer matrix as a transfer function. The second transfer matrix is the inverse matrix of the first transfer matrix.

[0019] The transfer function may include a square matrix having the same number of columns as the number of a plurality of channels. The square matrix is expressed as a product for each component of a coefficient matrix and an orthogonal matrix. The coefficient generation unit 120 is configured to determine the matrix components of the coefficient matrix.

[0020] Channel quality information includes, for each of a plurality of channels, one of a noise power level, a signal-to-noise ratio (SNR), and a bit error rate (BER).

[0021] The plurality of channels are different cores of a multi-core fiber (MCF) through which a signal propagates. Alternatively, the plurality of channels are different wavelengths in wavelength division multiplexing through which a signal propagates.

[0022] Next, an equalization method according to this embodiment will be described.

[0023] In the equalization method, first, a process associated with a signal is performed using a transfer function having coefficients. The signal propagates through each of a plurality of channels. The coefficients are generated based on channel quality information for each of the plurality of channels.

[0024] Performing the process associated with the signal may include receiving an input of data transmitted through a plurality of channels and converting the data into a signal using a first transfer matrix as a transfer function so as to give more signal power to channels having lower channel quality.

[0025] Performing the process associated with the signal may also include receiving an input of the signal after propagation through a plurality of channels and restoring the propagated signal to data using a second transfer matrix as a transfer function. The second transfer matrix is the inverse matrix of the first transfer matrix.

[0026] In the equalization method, the transfer function may include a square matrix having the same number of columns as the number of a plurality of channels. The square matrix is represented as a product of each component of a coefficient matrix and an orthogonal matrix.

[0027] In the equalization method, channel quality information includes, for each of a plurality of channels, one of a noise power level, a signal-to-noise ratio (SNR), and a bit error rate (BER).

[0028] As described above, according to the equalization apparatus 100 and the equalization method of the present embodiment, it is possible to equalize the difference in transmission signal quality between channels with a minimum penalty. [Second Embodiment]

[0029] Next, a second embodiment of the present invention will be described.

[0030] FIG. 3 is a block diagram showing an optical transmission system 1000 according to a second embodiment of the present invention. The optical transmission system 1000 includes a transmission processing unit (transmission processing means) 1100, a reception processing unit (reception processing means) 1200, and a coefficient generation unit (coefficient generation means) 1300.

[0031] The transmission processing unit 1100 is configured to receive an input of data transmitted through a plurality of channels and convert the data into a signal using a first transfer matrix having coefficients so as to give more signal power to channels having lower channel quality. The reception processing unit 1200 is configured to receive an input of a signal after propagation through a plurality of channels and restore the propagated signal to data using a second transfer matrix that is the inverse matrix of the first transfer matrix. The coefficient generation unit 1300 is configured to generate coefficients based on channel quality information for each of the plurality of channels.

[0032] The optical transmission system 1000 further includes a transmitter (transmission means) 1400, a receiver (reception means) 1500, and a channel monitor (channel monitoring means) 1600.

[0033] The transmitter 1400 is configured to perform an electro-optical modulation process on the signal. The receiver 1500 is configured to perform an opto-electrical demodulation process on the propagated signal. The channel monitor 1600 is configured to acquire channel quality information from the receiver 1500. In this case, the coefficient generation unit 1300 acquires channel quality information from the channel monitor 1600.

[0034] As shown in FIG. 3, the transmission processing unit 1100 is arranged on the transmitter side in a typical optical fiber transmission system. The reception processing unit 1200 and the channel monitor 1600 are arranged on the receiver side. For example, the coefficient generation unit 1300 may also be arranged on the receiver side. The feedback path 1700 is configured to connect the coefficient generation unit 1300 to the transmission processing unit 1100 and the reception processing unit 1200.

[0035] Next, the operation of the optical transmission system 1000 will be described.

[0036] The transmission processing unit 1100 is configured to process the input data A and the input data B by a predetermined operation. In the transmission processing unit 1100, the transfer matrix (the first transfer matrix) is used to process the input data A and the input data B. Next, the output processed data is the signal C and the signal D. The relationship between the input data and the output data of the transmission processing unit 1100 is represented by Equation (1). It should be noted that the data A and the data B are symbols modulated in a general modulation format such as QPSK (quadrature phase shift keying), 16QAM (quadrature amplitude modulation), and 64QAM.

Equation

Equation

[0037] To show an essential explanation of this transfer matrix, the transfer matrix is configured in such a form that it separates a plurality of input data A and input data B into two parts at a specific ratio and mixes them to form output processing data C and D. The specific ratio is determined by the coefficient generation unit 1300 using the channel quality information from the channel monitor 1600.

[0038] Note that Equation (2) represents an example of a transfer matrix with coefficients. Another exemplary transfer matrix is represented by Equation (3).

Number

[0039] Any other matrix configured as the product of components of a coefficient matrix and an orthogonal matrix can be used as the transfer matrix. The schematic form is represented by Equation (4).

Number

[0040] That is, the first transfer matrix includes a square matrix having the same number of columns as the number of a plurality of channels. The square matrix is represented as the product of components of a coefficient matrix and an orthogonal matrix. In this case, the coefficient generation unit 1300 is configured to determine the matrix components of the coefficient matrix.

[0041] The output of the transmission processing unit 1100 is connected to transmitters 1 and 2. Transmitters 1 and 2 are configured to perform necessary operations on the input signals such as electro - optical modulation and amplification to make the input signals suitable for transmission through channels 1 and 2. The signals output from transmitters 1 and 2 are transmitted through channels 1 and 2.

[0042] Receivers 1 and 2 are configured to receive signals and convert optical signals into electrical signals. The reception processing unit 1200 receives the outputs of receivers 1 and 2. In the reception processing unit 1200, the inverse matrix of the transfer matrix in the transmission processing unit 1100 is used to restore the mixed data C and D to the original data A and B. The details of this operation inside the reception processing unit 1200 are represented by Equation (5).

Equation

[0043] The channel monitor 1600 is configured to acquire channel quality information from receivers 1 and 2. In this embodiment, the channel quality information is indicated by the noise power that can be measured by receivers 1 and 2. The noise power measured in channel 1 is represented by N1. The noise power measured in channel 2 is represented by N2. The coefficient generation unit 1300 generates coefficients for the transfer matrix and the inverse transfer matrix using the following Equations (6) and (7).

Equation

Equation

[0044] In this embodiment, the channel quality information can also be indicated by the signal-to-noise ratio (SNR) on the receiver side. The SNR measured in channel 1 is represented by SNR1. The SNR measured in channel 2 is represented by SNR2. Next, the coefficient generation unit 1300 generates coefficients for the transfer matrix and the inverse transfer matrix using the following Equations (8) and (9).

Equation

Equation

[0045] Note that the above-described configurations of the channel monitor 1600 and the coefficient generation unit 1300 are examples of this embodiment. The channel quality information is not limited to the noise power level and the SNR. The channel quality information includes a bit error rate (BER) or a Q value. The Q value is defined as the minimum SNR required to obtain a specific BER for a given signal. Any other information indicating the difference in channel quality between channels may be included in the channel quality information of this embodiment. In addition, any other method of obtaining the channel quality information and any other indicator indicating the channel quality information may be included in this embodiment.

[0046] By using an equalization device including a transmission processing unit 1100, a reception processing unit 1200, and a coefficient generation unit 1300, more signal power is allocated to a channel having a higher noise power. As a result, the SNR of the transmission signal can be equalized in both channels.

[0047] On the receiver side, the transmission mixed signal is restored to the original data A and B. Since the channel noise power information is acquired by the channel monitor 1600, the transfer matrix represented by Equation (4) having the coefficients determined by the coefficient generation unit 1300 can be shown to minimize the added noise. As a result, according to the above-described equalization device of this embodiment, the difference in signal quality between different channels can be reduced with a minimum penalty.

[0048] Note also that the configuration of the optical transmission system of this embodiment can be scaled to a multi-transmission system having more than two channels. FIG. 4 shows the configuration of an optical transmission system 1001 as an example of a three-channel configuration. The most different point in this configuration is the transfer matrix having coefficients inside the transmission processing unit 1100 and the reception processing unit 1200. The transfer matrix configured to process three-channel data is represented by Equation (10).

Equation

[0049] In a general case, for an N-channel transmission system where N is an arbitrary natural number, the transfer matrix configured to process N-channel data is represented by Equation (11).

Equation

[0050] As an example, when a complex Hadamard matrix is used as the orthogonal matrix of Equation 11, the transformation matrix is represented by Equation (12). F N represents an example of a complex Hadamard matrix in the form of a Fourier matrix.

Equation

[0051] Note that the orthogonal matrix used in the transfer matrix of this embodiment is not limited to the above example. Any other orthogonal matrix such as a discrete Fourier transform (DFT) matrix can be used to form a transfer matrix composed of the product of each component of the coefficient matrix and the orthogonal matrix.

[0052] Note that the coefficient generation unit 1300 is not limited to being arranged on the receiver side. According to a practical arrangement, as shown in FIG. 5, the coefficient generation unit 1300 can be arranged on the transmitter side. The channel monitor 1600 acquires channel information on the receiver side. Then, the channel information is given to the coefficient generation unit 1300 through the feedback path 1. The coefficient generation unit 1300 generates optimization coefficients for the transfer matrix and the inverse transfer matrix. The coefficients for the inverse transfer matrix on the receiver side are given through the feedback path 2.

[0053] Next, an operation method of the optical transmission system 1000 according to the present embodiment will be described. FIG. 6 shows a flowchart for explaining the operation method of the optical transmission system 1000 according to the present embodiment.

[0054] In the operation method of the optical transmission system 1000, first, channel quality information is acquired (step S10). The channel quality information is the aforementioned SNR, noise power, or any other information indicating channel quality information. The channel quality information is acquired by the channel monitor 1600.

[0055] Next, the coefficients are updated (step S20). Note that all default coefficients are set to 1, which means that equalization is disabled at the start. This process is executed to accurately monitor the channel quality information. When the channel quality information is acquired, the coefficient generation unit 1300 generates optimization coefficients for the transfer matrix and the inverse transfer matrix.

[0056] The transfer matrix in the transmission processing unit 1100 and the inverse transfer matrix in the reception processing unit 1200 are updated using the updated coefficients acquired from the coefficient generation unit 1300 through the feedback path (step S30). After the transfer matrix and the inverse transfer matrix are updated, the process proceeds to S10 so that the optical transmission system 1000 is repeatedly equalized. Even when the characteristics of the channel quality change due to other factors such as physical shape deformation or temperature change, the operation method can stably maintain advantageous effects.

[0057] As an example, the plurality of channels shown in FIGS. 3, 4, and 5 described in the foregoing embodiment are different cores in a multi-core fiber (MCF) through which signals propagate. Crosstalk, and thus the noise of each channel, varies depending on the shape of the fiber. For this reason, the equalization device is determined as described in the foregoing embodiment in order to eliminate the difference in channel performance with a minimum penalty.

[0058] As an alternative example, the plurality of channels shown in FIGS. 3, 4, and 5 described in the foregoing embodiment are different wavelengths in wavelength division multiplexing (WDM) through which signals propagate. Since the noise depends on the wavelength characteristics that vary according to different wavelengths, the noise of each channel is different. Therefore, the equalization device is determined as described in the foregoing embodiment in order to eliminate the difference in channel performance with a minimum penalty.

[0059] As described above, according to the optical transmission system 1000 and the operation method of the optical transmission system 1000 of the present embodiment, it is possible to equalize the difference in the transmission signal quality between channels with a minimum penalty.

[0060] All or part of the embodiments disclosed above may be described as follows in the appended claims, but are not limited thereto.

[0061] (Appended Claim 1) An equalization device comprising: processing means for executing a process associated with a signal propagating through each of a plurality of channels using a transfer function having coefficients; and coefficient generation means for generating the coefficients based on channel quality information regarding each of the plurality of channels.

[0062] (Appended Claim 2) The equalization device according to Appended Claim 1, wherein the processing means includes transmission processing means, and the transmission processing means is configured to receive an input of data transmitted through the plurality of channels and convert the data into the signal using a first transfer matrix as the transfer function so as to give more signal power to a channel having a lower channel quality.

[0063] (Appendix 3) The processing means includes reception processing means, and the reception processing means is configured to receive the input of the signal after propagation through the plurality of channels and restore the propagated signal to the data using a second transfer matrix as the transfer function, where the second transfer matrix is the inverse matrix of the first transfer matrix. The equalization device according to Appendix 2.

[0064] (Appendix 4) The transfer function includes a square matrix having the same number of columns as the number of the plurality of channels, and the square matrix is represented as the product of each component of a coefficient matrix and an orthogonal matrix. The equalization device according to any one of Appendix 1, 2, and 3.

[0065] (Appendix 5) The coefficient generation means is configured to determine the matrix components of the coefficient matrix. The equalization device according to Appendix 4.

[0066] (Appendix 6) The channel quality information includes, for each of the plurality of channels, one of a noise power level, a signal-to-noise ratio, and a bit error rate. The equalization device according to any one of Appendix 1, 2, 3, 4, and 5.

[0067] (Appendix 7) The plurality of channels are different cores in the multi-core fiber through which the signal propagates. The equalization device according to any one of Appendix 1, 2, 3, 4, 5, and 6.

[0068] (Appendix 8) The plurality of channels are different wavelengths in the wavelength division multiplexing through which the signal propagates. The equalization device according to any one of Appendix 1, 2, 3, 4, 5, and 6.

[0069] (Appendix 9) Transmission processing means for receiving an input of data transmitted through a plurality of channels and converting the data into a signal using a first transfer matrix having a coefficient so as to give more signal power to a channel having a lower channel quality; receiving processing means for receiving an input of the signal after propagation through the plurality of channels and restoring the propagated signal to the data using a second transfer matrix which is the inverse matrix of the first transfer matrix; and coefficient generation means for generating the coefficient based on channel quality information regarding each of the plurality of channels. An optical transmission system comprising the same.

[0070] (Appendix 10) Further comprising transmission means for performing an electro-optical modulation process on the signal, reception means for performing an optical-electrical demodulation process on the signal after propagation, and channel monitoring means for acquiring the channel quality information from the reception means, wherein the coefficient generation means acquires the channel quality information from the channel monitoring means. The optical transmission system according to Appendix 9.

[0071] (Appendix 11) The first transfer matrix includes a square matrix having the same number of columns as the number of the plurality of channels, and the square matrix is expressed as a product of components of a coefficient matrix and an orthogonal matrix. The optical transmission system according to Appendix 9 or 10.

[0072] (Appendix 12) The coefficient generation means is configured to determine matrix components of the coefficient matrix. The optical transmission system according to Appendix 11.

[0073] (Appendix 13) The channel quality information includes, for each of the plurality of channels, one of a noise power level, a signal-to-noise ratio, and a bit error rate. The optical transmission system according to any one of Appendices 9, 10, 11, and 12.

[0074] (Appendix 14) The plurality of channels are different cores of a multi-core fiber through which the signal propagates. The optical transmission system according to any one of Appendices 9, 10, 11, 12, and 13.

[0075] (Appendix 15) The plurality of channels are different wavelengths in wavelength division multiplexing through which the signal propagates, and the optical transmission system according to any one of Appendices 9, 10, 11, 12, and 13.

[0076] (Appendix 16) Executing a process associated with a signal using a transfer function having coefficients, wherein the signal propagates through each of a plurality of channels, and generating the coefficients based on channel quality information for each of the plurality of channels. An equalization method including the above.

[0077] (Appendix 17) The execution of the process associated with the signal includes receiving an input of data transmitted through the plurality of channels, and converting the data into the signal using a first transfer matrix as the transfer function so as to give more signal power to channels having lower channel quality. The equalization method according to Appendix 16.

[0078] (Appendix 18) The execution of the process associated with the signal includes receiving an input of the signal after propagation through the plurality of channels, and restoring the propagated signal to the data using a second transfer matrix as the transfer function, wherein the second transfer matrix is the inverse matrix of the first transfer matrix. The equalization method according to Appendix 17.

[0079] (Appendix 19) The transfer function includes a square matrix having the same number of columns as the number of the plurality of channels, and the square matrix is expressed as a product of components of a coefficient matrix and an orthogonal matrix. The equalization method according to any one of Appendices 16, 17, and 18.

[0080] (Appendix 20) The channel quality information includes, for each of the plurality of channels, one of a noise power level, a signal-to-noise ratio, and a bit error rate. The equalization method according to any one of Appendices 16, 17, 18, and 19.

[0081] The present invention has been described above with reference to the embodiments (and examples), but the present invention is not limited to the above embodiments (and examples). Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.

Description of Reference Numerals

[0082] 100 Equalizer 110 Processing Unit 111 Transmission Processing Unit 112 Reception Processing Unit 120 Coefficient Generation Unit 1000 Optical Transmission System 1100 Transmission Processing Unit 1200 Reception Processing Unit 1300 Coefficient Generation Unit 1400 Transmitter 1500 Receiver 1600 Channel Monitor 1700 Feedback Path

Claims

1. Processing means for executing a process associated with signals propagating through each of a plurality of channels using a transfer function having coefficients; Coefficient generation means for generating the coefficients based on channel quality information regarding each of the plurality of channels; Comprising: The coefficients generated by the coefficient generation means are coefficients that give more signal power to channels having lower channel quality; The processing means includes transmission processing means; The transmission processing means receives an input of data transmitted through the plurality of channels and converts the data into the signals so as to give more signal power to channels having lower channel quality using a first transfer matrix as the transfer function, an equalization device.

2. The processing means includes reception processing means; The reception processing means receives an input of the signals after propagation through the plurality of channels and restores the propagated signals to the data using a second transfer matrix as the transfer function; The second transfer matrix is the inverse matrix of the first transfer matrix; The equalization device according to Claim 1.

3. The transfer function includes a square matrix having the same number of columns as the number of the plurality of channels; The square matrix is represented as a product of components of a coefficient matrix and an orthogonal matrix; The equalization device according to Claim 1 or 2.

4. The coefficient generation means determines matrix components of the coefficient matrix; The equalization device according to Claim 3.

5. The channel quality information includes, for each of the plurality of channels, one of a noise power level, a signal-to-noise ratio, and a bit error rate; The equalization device according to any one of Claims 1, 2, 3, and 4.

6. The plurality of channels are different cores of a multi-core fiber through which the signals propagate; The equalization device according to any one of Claims 1, 2, 3, 4, and 5.

7. The plurality of channels are different wavelengths in wavelength division multiplexing through which the signals propagate; The equalization device according to any one of Claims 1, 2, 3, 4, and 5.

8. Transmission processing means for receiving an input of data transmitted through a plurality of channels and converting the data into signals so as to give more signal power to channels having lower channel quality using a first transfer matrix having coefficients that give more signal power to channels having lower channel quality; Receiving the input of the signal after propagation through the plurality of channels, and using a second transfer matrix that is the inverse matrix of the first transfer matrix to restore the propagated signal to the data; a reception processing means; A coefficient generation means for generating the coefficient based on channel quality information regarding each of the plurality of channels. An optical transmission system comprising: **Claim 9** Executing a process associated with a signal propagating through each of a plurality of channels using a transfer function having coefficients, An equalization method for generating the coefficients based on channel quality information regarding each of the plurality of channels, The coefficients being coefficients that give more signal power to channels having lower channel quality, Receiving an input of data transmitted through the plurality of channels, and using the transfer function having the coefficients to convert the data into the signal so as to give more signal power to channels having lower channel quality, An equalization method.

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