JP6912406B2 - Modulation method determination device and optical communication system - Google Patents

Description

The present invention relates to a technique for determining a modulation method of an optical communication system.

Various modulation methods have been proposed to approach the Shannon limit. Patent Document 1 discloses a multidimensional modulation method in which signal points arranged on a two-dimensional plane are extended into a multidimensional space.

S. Ishimura, et. al. , "Multi-dimensional permutation modulation aiming at both high spectral efficiency and high power efficiency", OFC2014, M3A. 2

As described above, various modulation methods have been proposed, but the optimum modulation method for achieving a predetermined transmission speed differs depending on the optical communication system.

The present invention provides a technique for determining a modulation method according to an optical communication system.

According to one aspect of the present invention, a plurality of modulation method determining devices used in an optical communication system have a target transmission speed and a target error rate by using a filter means that simulates the frequency response characteristics of the optical communication system. A determination means for determining the signal-to-noise ratio of each of the modulation methods of the above , and a selection means for selecting one modulation method from the candidate modulation methods having the signal-to-noise ratio of a predetermined value or less. The frequency utilization efficiency of the candidate modulation method is obtained, and up to a graph showing the relationship between the signal-to-noise ratio and the upper limit of the frequency utilization efficiency, the method is performed from the coordinates showing the frequency utilization efficiency and the signal-to-noise ratio of the candidate modulation method. A line is drawn and the candidate modulation method corresponding to the shortest coordinate of the normal line is selected as the one modulation method .

According to the present invention, it is possible to determine the modulation method according to the optical communication system.

The block diagram of the determination apparatus by one Embodiment. The block diagram of the simulated part by one Embodiment. The figure which shows the relationship between the signal-to-noise ratio and the error rate by one Embodiment. The figure which shows the relationship between the signal-to-noise ratio and frequency efficiency by one Embodiment. The block diagram of the optical communication system by one Embodiment.

Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings. The following embodiments are examples, and the present invention is not limited to the contents of the embodiments. Further, in each of the following figures, components that are not necessary for the description of the embodiment will be omitted from the drawings.

FIG. 1 is a configuration diagram of a modulation method determination device according to the present embodiment. The modulation method determination device determines the modulation method used in the optical communication system. The holding unit 10 holds a plurality of candidate modulation methods. The modulation scheme is distinguished by the number of coordinates representing one or more bits in the complex plane, the coordinate position of each coordinate, and the dimension. Further, in the present embodiment, since the target transmission speed is determined, the symbol speed (baud rate) is uniquely determined for each modulation method depending on the modulation method and the target transmission speed. Therefore, in the present embodiment, the modulation method is specified by the number of coordinates representing the bits in the complex plane, the coordinate position of each coordinate, the dimension, and the symbol velocity. The holding unit 10 selects one modulation method from the holding modulation methods, and notifies the simulation unit 20 of the selected modulation method. The simulation unit 20 performs simulation by the modulation method notified from the holding unit 10 to obtain the relationship between the signal-to-noise ratio (SNR) and the error rate (BER: bit error rate) of the modulation method. The simulation unit 20 simulates all the modulation methods held by the holding unit 10 to obtain the relationship between the SNR and the BER for each modulation method. FIG. 3 shows the relationship between the SNR and the BER of the two modulation methods.

FIG. 2 is a configuration diagram of the simulated unit 20. The filter unit 23 is configured to have the same frequency response characteristics as the frequency response characteristics of the optical communication system whose modulation method is to be determined. Here, the frequency response characteristic of the optical communication system is the frequency response characteristic from the optical modulator in the optical transmitter to the optical demodulation unit of the optical receiver. This frequency response characteristic is, for example, an optical component such as an optical modulator used in an optical transmitter, an optical demodulator used in an optical receiver, and an optical amplifier between the optical modulator and the optical demodulator. Calculated according to the characteristics. The BER measurement unit 21 outputs data of a predetermined pseudo-random bit string. The modulation unit 22 is configured to generate and output a signal according to the modulation method notified from the holding unit 10 based on the data output by the BER measurement unit 21. This signal is filtered by the filter unit 23 based on the frequency response characteristics of the optical communication system whose modulation method is to be determined. The SNR adjusting unit 24 adds noise to the signal output by the filter unit 23 so that the SNR of the signal received by the demodulation unit 25 based on the instruction from the setting unit 26 becomes the SNR instructed by the setting unit 26. The demodulation unit 25 demodulates the signal output by the SNR adjustment unit 24 according to the modulation method notified from the holding unit 10, and outputs the demodulation result to the BER measurement unit 21. The BER measurement unit 21 determines the BER based on the data output to the modulation unit 22 and the demodulation result received from the demodulation unit 25, and outputs the BER to the setting unit 26. As a result, the BER for a certain SNR is determined. When the setting unit 26 receives the BER from the BER measuring unit 21, the setting unit 26 changes the SNR notified to the SNR adjusting unit 24. By determining the BER for each SNR in this way, the setting unit 26 acquires the relationship between the SNR of the modulation method notified from the holding unit 10 and the BER. Then, the setting unit 26 outputs the relationship between the SNR of the modulation method notified from the holding unit 10 and the BER to the characteristic determination unit 30. The simulation unit 20 simulates an optical communication system for which a modulation method is determined, and can be realized by, for example, a processor that executes a predetermined program. That is, the modulation unit 22 and the demodulation unit 25 do not need to use an optical modulator or an optical demodulator that is actually used in the optical communication system for which the modulation method is determined.

A target value of BER is set in the characteristic determination unit 30. For example, the dotted line in FIG. 3 indicates the target BER. From FIG. 3, in the modulation method 50, the target BER SNR is A (dB), and in the modulation method 51, the target BER SNR is B (dB). The characteristic determination unit 30 determines the relationship between the target BER SNR and the frequency efficiency (SE) for each modulation method. SE is a value obtained by dividing the bit rate by the occupied bandwidth and the number of dimensions of the signal determined by the modulation method. FIG. 4 shows the values of SNR and SE, which are the target BERs, as coordinates 61 to 64 for each of the four modulation methods. FIG. 4 also shows Shannon Limit 60. The Shannon limit 60 is the limit value of SE at each SNR. Note that C (dB) in FIG. 4 is a design SNR value in the optical receiver of the optical transmission system whose modulation method is to be determined. The characteristic determination unit 30 excludes a modulation method in which the SNR as the target BER is higher than C (dB) which is the design SNR value, and selects a modulation method in which the SNR as the target BER is C (dB) or less which is the design SNR value. Use the candidate modulation method. Then, the characteristic determination unit 30 determines the relationship between the SNR and the SE for the candidate modulation method.

As shown in FIG. 4, the characteristic determination unit 30 draws a normal line from the coordinates 61 to 64 corresponding to each modulation method to the Shannon limit 60, and obtains the coordinates 65 to 68 on the Shannon limit 60, respectively. Then, the characteristic determination unit 30 sets the length of the normal line connecting the coordinates 61 and the coordinates 65, the length of the normal line connecting the coordinates 62 and the coordinates 66, the length of the normal line connecting the coordinates 63 and the coordinates 67, and the coordinates 64. Find the length of the normal line connecting the coordinates 68. Finally, the characteristic determination unit 30 outputs the modulation method corresponding to the coordinates having the shortest normal length up to the Shannon limit 60 among the coordinates 61 to 64 as the modulation method of the optical communication system to be determined. For example, in FIG. 4, the modulation method for the coordinates 62 is output as the modulation method of the optical communication system to be determined.

Here, the reason for determining the modulation method having the shortest normal length will be described. For example, the modulation scheme corresponding to coordinate 64 can achieve the target BER with the lowest SNR, but the SE is the lowest of the four modulation schemes. On the other hand, the modulation method corresponding to the coordinate 61 has the highest SE among the four modulation methods, but has the highest SNR required to achieve the target BER. That is, the margin (noise margin) with respect to the design SNR value of the optical communication system to be determined is the smallest, and it is vulnerable to noise. In this embodiment, both the noise margin and the SE are taken into consideration, and therefore the modulation method having the shortest normal length is selected. With this configuration, it is possible to select the optimum modulation method in consideration of both the noise margin and SE. Further, the modulation method is selected in consideration of the frequency response characteristics of the optical communication system to be determined, not the theoretical values of SNR and BER determined by the modulation method. That is, it is possible to select a modulation method suitable for an actual optical communication system by reflecting that the deterioration of the signal waveform caused by the frequency response characteristic differs depending on the symbol speed uniquely determined for each modulation method.

FIG. 5 shows an optical communication system using the modulation method determined by the determination device. In FIG. 5, the optical transmission line 71 connecting the optical transmitter and the optical receiver is a working transmission line, and the optical transmission line 72 is a backup transmission line. As shown in the figure, the optical modulator of the optical transmitter and the optical demodulator of the optical receiver are shared by the optical transmission line 71 and the optical transmission line 72. That is, the light modulator normally transmits the modulated light to the optical transmission line 71, and does not transmit the optical signal to the optical transmission line 72. Then, the optical demodulator normally receives the modulated light from the optical transmission line 71 and demodulates it. When a failure occurs, the light modulator stops transmission to the optical transmission line 71 and transmits the modulated light to the optical transmission line 72, and the optical demodulator receives the modulated light from the optical transmission line 72. Demodulate. Further, the optical modulator and the optical demodulator are configured so that modulation and demodulation can be performed according to a modulation method instructed by a control unit (not shown), respectively.

The control unit of the optical transmitter and the optical receiver holds a modulation method used in the optical transmission line 71 determined by the determination device and a modulation method used in the optical transmission line 72, respectively. Normally, the control unit of the optical transmitter notifies the optical modulator of the modulation method used in the optical transmission line 71, and the control unit of the optical receiver informs the optical demodulator of the modulation method used in the optical transmission line 71. Notice. Then, when the failure of the optical transmission line 71 is detected, the control unit of the optical transmitter notifies the optical modulator of the modulation method used in the optical transmission line 72, and the control unit of the optical receiver informs the optical demodulator of light. Notifies the modulation method used in the transmission line 72. An optical switch that distributes the modulated light transmitted by the optical modulator to the optical transmission line 71 or the optical transmission line 72, and light that outputs the modulated light from either the optical transmission line 71 or the optical transmission line 72 to the optical demodulator. Although the switches are omitted from FIG. 5, these optical switches are also controlled by the control unit. Further, any method can be used for detecting a failure of the optical transmission line 71 and the like.

The determination device according to the present invention can be incorporated into, for example, an optical receiver. The optical receiver estimates the frequency response characteristics of the optical communication system by equalization processing at the time of demodulation. Therefore, it is possible to determine the optimum modulation method for each optical transmission line by performing the simulation described in FIG. 2 by utilizing this frequency response characteristic. The determined modulation method is notified to the optical transmitter, for example, via a network management device (not shown).

Further, in the present embodiment, the simulation unit 20 obtains the BER while changing the SNR for each modulation method. However, since the target BER is determined in advance, the SNR for setting the target BER may be obtained. When the SNR to be the target BER is determined for a certain modulation method, the processing for the modulation method is terminated and the next It is also possible to have a configuration in which processing for the modulation method is started.

The determination device according to the present invention can be realized by a program that operates the computer as the determination device. These computer programs are stored in a computer-readable storage medium or can be distributed over a network.

23: Filter unit, 20: Simulation unit, 30: Characteristic determination unit

Claims (3)

It is a modulation method determination device used in optical communication systems.
A determination means for determining the signal-to-noise ratio of each of the plurality of modulation methods, which is the target transmission speed and the target error rate, by using the filter means that simulates the frequency response characteristics of the optical communication system.
A selection means for selecting one modulation method from the candidate modulation methods in which the signal-to-noise ratio is equal to or less than a predetermined value, and
Equipped with a,
The selection means obtains the frequency utilization efficiency of the candidate modulation method, and up to a graph showing the relationship between the signal-to-noise ratio and the upper limit value of the frequency utilization efficiency, the frequency utilization efficiency of the candidate modulation method and the signal-to-noise ratio. A determination device, characterized in that a normal line is drawn from the coordinates indicating the above, and the candidate modulation method corresponding to the shortest coordinate of the normal line is selected as the one modulation method. The determination device according to claim 1, wherein the frequency response characteristic of the optical communication system is acquired from the optical receiver of the optical communication system. With an optical transmitter
With an optical receiver
A first optical transmission line connecting the optical transmitter and the optical receiver,
A second optical transmission line connecting the optical transmitter and the optical receiver,
Is a system that has
The optical transmitter and the optical receiver are determined for the first modulation method determined by the determination device according to claim 1 or 2 for the first optical transmission line and for the second optical transmission line. It has information indicating that the second modulation method is used.
When the first optical transmission line is normal, the optical transmitter and the optical receiver communicate with each other via the first optical transmission line with modulated light according to the first modulation method, and perform the first optical transmission. An optical communication system characterized in that when an obstacle occurs in a path and the second optical transmission line is normal, communication is performed via the second optical transmission line with modulated light according to the second modulation method. ..

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