JP7067552B2 - Optical transmitters, communication systems, transmission frequency control methods and programs - Google Patents

Description

(Description of related applications)
The present invention is based on the priority claim of Japanese patent application: Japanese Patent Application No. 2017-09737 (filed on May 16, 2017), and all the contents of the application are incorporated in this document by citation. It shall be.
The present invention relates to an optical transmitter, a communication system, a transmission frequency control method and a program.

For example, in large-capacity backbone optical communications such as 100 Gb / s (Giga bits per second), multi-level modulation methods such as QPSK (Quadrature Phase Shift Keying) and 16QAM (Quadrature Amplitude Modulation) have been put into practical use by adopting the digital coherent method. Is being done. Currently, research and development of high-order multi-level modulation methods such as 32QAM / 64QAM are being actively carried out with the aim of further increasing the capacity.

Furthermore, in parallel with the increase in capacity due to such multi-values, advanced signal band narrowing technology is used to increase the channel spacing during Wavelength-Division Multiplexing (WDM) transmission, and per optical fiber. Approaches to improve transmission capacity are also emphasized. As advanced signal bandwidth narrowing technology, Nyquist transmission method, which can narrow the signal spectrum compared to NRZ (Non-Return to Zero) transmission, and Super Nyquist transmission, which has a narrower bandwidth than the signal baud rate. There is.

In an optical transmission system of 1 Tbps (Tera bits per second) or more, a subcarrier multiplex communication method that realizes transmission of 1 Tbps or more by wavelength-multiplexing a plurality of subcarriers is considered to be promising in consideration of feasibility. In the subcarrier multiplex communication method, the closer the intervals between the subcarriers, the higher the frequency utilization efficiency. Therefore, how to narrow the subcarrier multiplex interval becomes a big technical issue.

Generally, a light source used for communication has a temporal fluctuation (fluctuation) in its frequency. Therefore, if the subcarrier multiplex interval is made too close, the signal quality is deteriorated due to the overlap of the modulated light on the frequency axis due to the frequency fluctuation (crosstalk between subcarriers). The simplest countermeasure against such a phenomenon is, for example, a method of providing a guard band that keeps the interval between subcarriers about the width of the frequency fluctuation. However, this method widens the subcarrier multiplex interval.

As a further problem caused by frequency fluctuations, signal quality deterioration due to signal band narrowing due to passing through a wavelength selective switch (WSS) in a ROADM (Re-configurable Optical Add / Drop Multiplexer) system. There is.

As a countermeasure against the problem caused by the frequency fluctuation, in Non-Patent Document 1, a frequency dither (also simply referred to as "dither") is applied to the subcarrier, and an error signal such as a Q value is always used. , A method of continuing to compensate for frequency fluctuations is disclosed.

Takahiro Kodama, 4 others, "Examination for generalization of subcarrier-linked optical frequency control", 2016 IEICE Communication Society Conference, B-10-43, September 2016

The following is an analysis of related techniques.

In the method disclosed in Non-Patent Document 1,
(a) As the number of control steps increases in proportion to the number of subcarriers, the control structure itself becomes complicated and the control time becomes longer.
(b) Deterioration of signal quality due to crosstalk between subcarriers due to dither application is unavoidable, and control accuracy deteriorates.
There is a problem.

The present invention has been made in view of the above problems, and a main object thereof is an optical transmission device, a communication system, and a transmission that enable high-speed and high-precision transmission frequency control in a subcarrier multiplex communication system. The purpose is to provide a frequency control method and a storage medium.

According to one aspect of the present invention, it is an optical transmission device that allocates transmission information to a plurality of subcarriers having different frequencies and multiplexes the transmission information, and is transmitted from an optical reception device that receives a signal from the optical transmission device. The frequency control means includes a means for receiving the received reception quality information and a frequency control means for controlling the transmission frequency of each of the plurality of subcarriers based on the reception quality information, and the frequency control means is a plurality of subcarriers. An optical transmission device that performs the dither control by dividing into two groups is provided.

According to another aspect of the present invention, an optical transmission device that allocates transmission information to a plurality of subcarriers having different frequencies and multiplexes the transmission information, and an optical signal transmitted from the optical transmission device via a transmission line. An optical communication system including an optical receiving device that receives, acquires the quality of a received signal of each subcarrier, generates reception quality information, and transmits the reception quality information to the optical transmitting device is provided. The optical transmission device includes means for receiving reception quality information transmitted from the optical reception device, and frequency control means for dither controlling the transmission frequency of each of the plurality of subcarriers based on the reception quality information. The frequency control means performs the dither control by dividing the subcarrier into a plurality of groups.

According to still another aspect of the present invention, there is a transmission frequency control method for an optical transmitter that allocates transmission information to a plurality of subcarriers having different frequencies and multiplexes and transmits the signal from the optical transmitter. Based on the reception quality information transmitted from the optical receiver to be received, the transmission frequency of each of the plurality of subcarriers is dither controlled, and at that time, the dither control is performed by dividing the subcarriers into a plurality of groups. A transmission frequency control method to be performed is provided.

According to still another aspect of the present invention, a signal from the optical transmitter is sent to a processor that performs digital signal processing in an optical transmitter that allocates transmission information to a plurality of subcarriers having different frequencies and multiplexes the transmission information. This is a process of controlling the transmission frequency of each of the plurality of subcarriers based on the reception quality information transmitted from the optical receiver that receives the signal, and by dividing the subcarriers into multiple groups. A program for executing the process of performing digital control is provided.

According to the present invention, a computer-readable recording medium (for example, RAM (Random Access Memory), ROM (Read Only Memory), or EEPROM (Electrically Erasable and Programmable ROM)) or other semiconductor storage or HDD that stores the above program. (Hard Disk Drive), CD (Compact Disc), DVD (Digital Versatile Disc) and other non-transitory computer readable recording media are provided.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to increase the speed and accuracy of transmission frequency control in the subcarrier multiplex communication system.

It is a figure explaining the optical communication system of the 1st and 2nd Embodiment of this invention. It is a figure which illustrates the structure of the optical transmission apparatus of 1st Embodiment of this invention. It is a figure which illustrates the structure of the optical receiver of the 1st Embodiment of this invention. It is a figure explaining the transmission frequency control in an exemplary embodiment of this invention. It is a figure explaining the transmission frequency control in 1st Embodiment of this invention. It is a figure explaining the transmission frequency control in 1st Embodiment of this invention. It is a figure explaining the transmission frequency control in 1st Embodiment of this invention. It is a figure explaining the 2nd Embodiment of this invention. It is a figure explaining the transmission frequency control in 2nd Embodiment of this invention. It is a figure explaining the 3rd Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[Embodiment 1]
FIG. 1 is a diagram schematically illustrating an optical communication system according to an exemplary first embodiment of the present invention. The optical communication system of the first embodiment includes an optical transmission device 10, an optical reception device 20, and a transmission line (optical transmission line) 30. The optical transmitting device 10 and the optical receiving device 20 are connected to each other via a transmission line 30.

The outline of the subcarrier frequency control in the first embodiment will be described. The optical transmission device 10 outputs a transmission optical signal to the transmission line 30 based on the input transmission data. The optical transmission device 10 transmits an optical signal multiplexed by the subcarrier multiplex transmission method. That is, the optical transmission device 10 allocates input data to a plurality of frequency channels (subcarriers) and multiplexes and transmits signals assigned to the plurality of frequency channels (subcarriers).

The optical receiving device 20 receives the optical signal transmitted from the optical transmitting device 10 via the transmission line 30, separates it into reception signals of each subchannel, acquires reception data, and further receives reception quality of each subchannel. Is calculated, and the reception quality information of each sub-channel is notified to the optical transmission device 10 via the transmission line 30.

The optical transmission device 10 controls the frequency of the subcarrier of the transmission signal based on the received reception quality information. The reception quality information may be a Q value indicating the quality of the optical signal, a bit error rate (BER), or the like. That is, the optical transmission device 10 dither controls the transmission frequencies of the plurality of subcarriers by using the reception quality information. The optical transmitter 10 repeatedly divides the subcarrier into a plurality of groups in order to control the dither of the transmission frequency.

FIG. 2 is a diagram illustrating an example of the configuration of the optical transmission device 10 of FIG. The optical transmission device 10 includes a quality information receiving unit 11, a subcarrier frequency control unit 12, n transmission signal generation units 13 (n is a subcarrier multiplexing number), n subcarrier generation units 14, and n optical modulation units. A unit 15 and a wavelength division multiplexing unit 16 are provided. The outline of each part will be described below.

The quality information receiving unit 11 receives the reception quality information transmitted from the optical receiving device 20. The reception quality information is transmitted as an optical signal from the optical reception device 20, and the quality information reception unit 11 includes an optical modulation unit (not shown), demodulates the reception quality information, and takes out an electric signal of the reception quality information.

The subcarrier frequency control unit 12 controls the frequency of the subcarrier based on the reception quality information received by the quality information receiving unit 11. That is, the subcarrier frequency control unit 12 generates a signal for dither control of the transmission frequency so as to apply a dither biased according to the reception quality information, and a signal for dither control of the transmission frequency at the time of transmission frequency control. Is notified to the transmission signal generation unit 13. The subcarrier frequency control unit 12 performs frequency control in parallel and synchronously with a plurality of (n) subcarriers.

The transmission signal generation unit 13 provided corresponding to each subcarrier applies a dither to the transmission signal and transmits the transmission signal based on the control signal (the signal that dither controls the transmission frequency) notified from the subcarrier frequency control unit 12. A signal is generated, and the generated transmission signal (transmission signal to which a dither is applied) is supplied to the optical modulation unit 15. In FIG. 2, the transmission data 1 to n input to the transmission signal generation unit 13 are, for example, error-corrected and coded for the information to be transmitted, and mapped to symbols according to a modulation method such as QPSK or 16/32 / 64AQAM. It may be a signal.

Each optical modulation unit 15 outputs a subcarrier (optical signal) generated by a corresponding subcarrier generation unit 14 (a light source having a wavelength corresponding to each subcarrier (not shown)) from the transmission signal generation unit 13. An optical signal modulated by a transmission signal (a transmission signal to which a dither is applied) is output.

The wavelength division multiplexing unit 16 (optical coupler) generates a transmission signal by wavelength division multiplexing of the signals modulated by the optical modulation unit 15 corresponding to each subcarrier.

The optical receiving device 20 is arbitrary as long as it is configured to receive the optical signal from the transmission line 30, detect the quality of the received signal, and notify the optical transmitting device 10 of the reception quality information of each subcarrier. It may be the configuration of. FIG. 3 is a diagram illustrating an example of the configuration of the optical receiver 20 of FIG. 1 and corresponds to the configuration of the optical transmitter 10 of FIG. Referring to FIG. 3, the optical receiver 20 includes a wavelength separation unit 21, n optical demodulation units 22, n subcarrier generation units 23, n received signal quality detection units 24, and a quality information transmission unit. It has 25. The outline of each part will be described below.

The wavelength separation unit 21 (optical demultiplexer) includes a wavelength separation filter or the like, and wavelength-separates the received transmission signal and supplies it to the optical demodulation unit 22. The optical demodulation unit 22 demodulates the subcarriers from the subcarrier generation unit 23 (light source having a wavelength corresponding to each subcarrier) from the received optical signal, extracts the received signal, converts it into an electric signal, and outputs the received data. .. The reception signal quality detection unit 24 detects the Q value and BER as the reception quality of each subcarrier from the received data. The quality information transmission unit 25 transmits the reception quality information of each subcarrier detected by the reception signal quality detection unit 24 to the optical transmission device 10. The quality information transmission unit 25 transmits reception quality information as an optical signal to the optical transmission device 10, and the optical transmission device 10 modulates the reception quality information with an optical modulation unit (not shown) and converts it into an electric signal to convert it into an electrical signal. 11 may be supplied.

Next, the frequency control by the subcarrier frequency control unit 12 in the first embodiment will be described with reference to an example in which the subcarrier multiply perfect number is 8 (n = 8 in FIG. 2). FIG. 4 is a diagram illustrating a frequency control method when the subcarrier multiply perfect number is 8. In FIGS. 4A to 4D, the horizontal axis is the frequency f (frequency of the optical signal), and the frequency spectrum (power spectrum, amplitude spectrum, etc.) of the optical signal in which each subcarrier is modulated by the transmission signal is schematically. Is illustrated in. When the subcarrier multiply perfect number is 8, the following four steps 1 to 4 are optimized as the transmission frequency control (dither control) by the subcarrier frequency control unit 12 of FIG.

<Step 1>
As shown in FIG. 4A, in step 1, all subcarriers (SC0 to SC7) are grouped together, and dither is given to the entire group in common.

That is, a dither is given to one group (SC0 to SC7) in common, and the center frequency fc of all the subcarriers (SC0 to SC7) is moved to the center of the signal band narrowed by passing through ROADM (Fig.). 5 (a)), improve the overall reception quality.

In the example of FIG. 5B, the center frequencies fc of all the subcarriers (SC0 to SC7) of the group are not moved to the center of the signal band narrowed by passing through ROADM or the like. Since the center frequency fc is higher than the center of the signal band narrowed by passing through ROADM or the like, the reception quality of the subcarrier SC7 is deteriorated.

Further, in the example of FIG. 5C, since the center frequency fc of all the subcarriers (SC0 to SC7) is lower than the center of the signal band narrowed by the passage of ROADM or the like, the subcarrier SC0 receives the signal. Quality has deteriorated.

<Step 2>
As shown in FIG. 4B, in step 2, the subcarriers (SC0 to SC7) are divided into two groups (divided into two), a subcarrier (SC0 to SC3) and a subcarrier (SC4 to SC7). .. These two groups are referred to as "G2,0" and "G2,1" for convenience.

The groups G2, 0 and G2, 1 give the dither of the same phase (the same polarity) in each group, but the dither given to the adjacent groups G2, 0, G2, 1 has the opposite phase (the opposite polarity). When group G2,0 (SC0 to SC3) is given a positive dither (indicated by an arrow indicating an increasing direction of the frequency f in FIG. 4), G2, 1 (SC4 to SC7) is given a negative electrode (frequency in FIG. 4). When the dither of (indicated by the arrow in the decreasing direction of f) is given and the dither of the negative electrode is given to the group G2, 0 (SC0 to SC3), the dither of the positive electrode is given to G2, 1 (SC4 to SC7). Δf2 ⁰ is the frequency difference (difference between each center frequency) between G2, ₁ (SC4 to SC7) and G2,0 (SC0 to SC3).

That is, as shown in FIG. 6B, the subcarriers (SC0 to SC3) belonging to G2 and 0 are given parallel (same polarity) dither, but the subcarriers belonging to G2 and 1 (SC4 to SC7) are given. ) Is parallel and the dither opposite to G2,0 (opposite polarity) is added.

By giving dither in this way, the frequency difference Δf20 between the ^two groups G2, ₀ and G2, 1 is optimized without affecting the center frequency fc of the subcarriers (SC0 to SC7). , It is possible to adjust so that the subcarrier spacing does not become too wide while eliminating the influence of crosstalk (overlap on the frequency axis) between SC3 and SC4. FIG. 6 (c) gives dithers having opposite polarities to the subcarriers belonging to G2 and 0 (SC0 to SC3) and the subcarriers belonging to G2 and 1 (SC4 to SC7), and as a result, the subcarrier SC3−. It is a figure schematically explaining the example that the crosstalk between SC4 occurs and the reception quality deteriorates.

<Step 3>
As shown in FIG. 4 (c), in step 3, the groups G2, 0 and G2, 1 are further divided into two, and the subcarriers are further divided into four groups. These groups are referred to as "G3,0" to "G3,3" for convenience. As in step 2, the two groups of G3, 0 and G3, 1 and the two groups of G3, 2 and G3, 3 each have the same phase dither in the same group as shown in FIG. 7 (b). Give, and give dither of opposite phase in adjacent groups.

By this operation, the frequency difference Δf 30 of the groups G3, ₀ , G3, 1 and the frequency difference Δf ³ ₁ of the groups G3, 2, G3, ³ are optimized in parallel between the subcarriers SC1 and SC2. , And the effect of crosstalk between the subcarriers SC5-SC6 can be eliminated, and the subcarrier spacing can be adjusted so as not to be excessively widened.

Note that FIG. 7 (b) shows how the frequency difference Δf ³ ₁ (see FIG. 4 (c)) between the adjacent groups G3, 2, and G3, 3 is too narrow, and crosstalk occurs between the subcarriers SC5 and SC6. It is shown schematically. In the example of FIG. 7B, for G3, 0 and G3, 1 (adjacent group) obtained by dividing the groups G2 and 0 into two, the subcarriers of G3 and 0 on the low frequency side have a negative electrode property, and G3 on the high frequency side. For G3,2 and G3,3 (adjacent groups) in which the subcarriers of 1 are given positive dither and the groups G2 and 1 are divided into two, the subcarriers of G3 and 2 on the low frequency side have positive and high frequency sides. Negative dither is given to the subcarriers of G3 and G3. In this example, crosstalk occurs between the subcarrier SC5 at the end of G3 and 2 and the subcarrier SC6 at the end of adjacent G3 and 3 (see “Reception quality deterioration” in FIG. 7B). .. Further, FIG. 7 (c) schematically shows a state in which the frequency difference Δf ³⁰ (see FIG. 4 (c)) of the adjacent groups G3, ₀ , G3, 1 is too narrow and crosstalk occurs between the subcarriers SC1 to SC2. Is shown. In the example of FIG. 7 (c), for G3, 0 and G3, 1 (adjacent group) obtained by dividing the groups G2 and 0 into two, the subcarriers of G3 and 0 on the low frequency side have a positive electrode property, and G3 on the high frequency side. Negative dither is given to the subcarrier of 1, and for G3,2 and G3,3 (adjacent group) in which groups G2 and 1 are divided into two, the subcarriers of G3 and 2 on the low frequency side have negative and high frequency sides. The positive dither is given to the subcarriers of G3 and G3. Crosstalk occurs between the subcarrier SC1 at the end of G3 and 0 and the subcarrier SC2 at the end of the adjacent G3 and 1 (see “Reception quality deterioration” in FIG. 7 (c)). When giving positive dither to the subcarriers of the low frequency side group and giving negative dither to the subcarriers of the high frequency side group among the adjacent groups, crosstalk will occur if the frequency difference between the groups is narrow. It occurs and the reception quality deteriorates. In addition, when negative dither is given to the subcarriers of the low frequency side group and positive dither is given to the subcarriers of the high frequency side group among the adjacent groups, it is said that the frequency difference between the groups is wide. The carrier spacing may be too wide.

Further, in step 3 of FIG. 4C, the groups G2, 0 (parent group of G3, 0, G3, 1) and G2, 1 (parent group of G3, 2, G3, 3) are also out of phase (opposite polarity). ) Is given a dither. At this time, since dithers having the same phase (same polarity) are applied to the groups G3, 1 and G3, 2 (see the arrows above G3, 1 and G3, 2 in FIG. 4C), FIG. 4 The frequency difference between the subcarriers SC3-SC4 optimized in step 2 of (b) is maintained in step 3. Therefore, in step 3, the reception quality does not deteriorate due to crosstalk between the subcarriers SC3 and SC4. By doing so, it becomes possible to eliminate the interdependence in step 2 and step 3 and perform completely independent optimization of the frequency difference between the subcarriers.

<Step 4>
As shown in FIG. 4D, in step 4, the groups G3, 0 to G3, 3 are each divided into two halves. In this step 4, there are eight groups, and one subcarrier belongs to each group. By applying dither so that the subcarriers SC0 and SC1, SC2 and SC3, SC4 and SC5, and SC6 and SC7 are in opposite phases, the respective subcarrier sets ((SC0, SC1), (SC2, SC3). ), (SC4, SC5), (SC6, SC7)) (Δf ⁴⁰ , Δf ⁴¹ , _Δf ⁴² _{, Δf 4 3} ⁾ _{are optimized} .

Furthermore, at this time,
-Groups G3, 0 and G3, 1 in FIG. 4C also have opposite phases.
-Groups G3, 2 and G3, 3 in FIG. 4C also have opposite phases.
-Dither is given so that the groups G2, 0 and G2, 1 in FIG. 4B are also out of phase. (In FIG. 4D, the subcarriers SC1 and SC2 are given the same phase (same polarity) dither, the subcarriers SC3 and SC4 are given the same phase (same polarity) dither, and the subcarriers SC5 and SC6 are given the same phase (same polarity) dither. The dither of (same polarity) gives. The frequency difference between the subcarriers SC1 and SC2, between SC3 and SC4, and between SC5 and SC6 optimized in step 3 of FIG. 4C is maintained in step 4. In step 4, it is possible to avoid deterioration of reception quality due to crosstalk between the subcarriers SC1 and SC2, between SC3 and SC4, and between SC5 and SC6.

By doing so, in the adjustment of the frequency interval between the subcarriers in step 4 of FIG. 4 (d), as in step 3 of FIG. 4 (c), steps 2 and 4 (c) of FIG. 4 (a). ) Can be implemented completely independently by eliminating the interdependence with the adjustment in step 3.

In the subcarrier frequency control unit 12 of FIG. 2, the above four steps (steps 1 to 4) are repeatedly performed as the transmission frequency control.

<Embodiment 2>
Next, as an exemplary second embodiment of the present invention, an example of a control flow in the case where the subcarrier multiple number n is general will be described. In the optical communication system of the second embodiment, the configuration of the optical transmitter and the optical receiver is the same as that of the first embodiment. FIG. 8 is a diagram illustrating a control flow by the subcarrier frequency control unit 12 (FIG. 2) in the second embodiment.

In step S101, first, indexing is performed for each subcarrier. Indexing is numbered, for example, from the low frequency side to the high frequency side in order from 0. Then, a Gray code is assigned to each index.
g [i] = Gray (i) (i = 0,…, n-1)

Finally, 0 is assigned to the loop variable k of the dither control loop (step S102), and the initialization is completed.

After the initialization is completed, the dither control loop is started. In the dither control loop, for example, when the kth bit from the most significant bit (Most Significant Bit: MSB) is 0 in each subcarrier, dither in the same phase as the subcarrier SC0 is applied (step S104). If it is 1, a dither having a phase opposite to that of the subcarrier SC0 is applied (step S105). However, when k = 0, dither of the same phase is applied to all the subcarriers SC0 to SC7.

FIG. 9 shows that by adding dither in this way, it is possible to control the subcarrier frequency by the step division described in the first embodiment. Note that FIG. 9 shows the control by the Gray code according to a specific example when n = 8.

9 (a) to 9 (d) show the gray code assigned to each of the subcarriers SC0 to SC7, and step S103 in each loop of the dither control loop corresponding to k = 0 to 3 in FIG. The bits referenced by are shown in bold. In FIG. 9B, the subcarriers (SC0, SC1, SC2, SC3) (groups G2, 1) in which the first bit from the MSB of the gray code assigned to each SC0 to SC7 is 0 are assigned to the subcarrier SC0. A dither having the same phase is applied, and a dither having a phase opposite to that of the subcarrier SC0 is applied to the subcarriers (SC4, SC5, SC6, SC7) (groups G2, 1) in which the first bit is 1. In FIG. 9 (c), the subcarriers (SC0, SC1) and (SC6, SC7) (groups G3, 0, G3, 3) in which the second bit from the MSB of the gray code is 0 are in phase with the subcarrier SC0. A dither is applied, and a dither having a phase opposite to that of the subcarrier SC0 is applied to the subcarriers (SC2, SC3) and (SC4, SC5) (groups G3, 1, G3, 2) in which the second bit is 1. In FIG. 9D, a dither having the same phase as the subcarrier SC0 is applied to the subcarriers (SC0, SC3, SC4, SC7) in which the third bit from the MSB of the Gray code is 0, and the third bit is 1. A dither in the opposite phase to the subcarrier SC0 is applied to the subcarriers (SC1, SC2, SC5, SC6).

After performing dither control for a certain period of time in each loop, k is counted up by one (k = k + 1 in step S107), and the process proceeds to the next control step S103.

In the dither control loop, k is counted up, and when k reaches [log_2 n] (Yes in step S106), the process proceeds to step S102, and k = 0 to enter the next dither control loop. In the k = [log_2 n] + 1st control, the final control step (k = [log_2 8] + 1 = 4, step 4 in FIG. 9D) is reached. Note that [x] is a ceiling function and represents the smallest integer not smaller than x with respect to the real number x.

Thus, according to the second embodiment, by using the Gray code, it is possible to execute control of [log_2 n] + 1 step per loop for any n. Besides using Gray code, there are many ways to achieve dichotomy. That is, the present invention is not limited to the configuration of dividing into two by using the Gray code, and it goes without saying that a method other than the Gray code may be used.

According to the second embodiment, it is possible to maintain the frequencies of all the subcarriers so as to maximize the reception quality.

When applied in general when the number of carriers is n, the number of control steps is [log_2 n] + 1. This number of steps is smaller than the number of steps n shown in Non-Patent Document 1, and the control loop can be rotated in a short time. Further, since the interdependence in each control step can be completely eliminated, highly accurate control becomes possible.

FIG. 10 shows, as another embodiment of the present invention, the digital signal processing of the subcarrier frequency control unit 12 and the transmission signal generation unit 13 of the optical transmission device 10 of FIG. 2 is implemented by a processor such as a digital signal processor (DSP). It is a figure exemplifying the configuration. Referring to FIG. 10, the optical transmitter 10 includes a processor (DSP (Digital Signal Processor)) 101, for example, RAM (Random Access Memory), ROM (Read Only Memory), EEPROM (Electrically Erasable and Programmable ROM), HDD (Hard). It includes a storage device 102 including at least one of Disk Drive) and a communication device 103. The communication device 103 can correspond to the quality information receiving unit 11, the subcarrier generation unit 14, and the optical modulation unit 15 of FIG. A program for realizing the processing of the subcarrier frequency control unit 12 and the transmission signal generation unit 13 of the embodiment is stored in the storage device 102, and the processor 101 reads and executes the program to carry out the above-described implementation. The optical transmission device 10 of the form may be realized.

The disclosure of Non-Patent Document 1 shall be incorporated into this document by citation. Within the framework of the entire disclosure (including the scope of claims) of the present invention, it is possible to change or adjust the embodiments or examples based on the basic technical idea thereof. Further, various combinations or selections of various disclosure elements (including each element of each claim, each element of each embodiment, each element of each drawing, etc.) are possible within the scope of the claims of the present invention. .. That is, it goes without saying that the present invention includes all disclosure including claims, various modifications and modifications that can be made by those skilled in the art in accordance with the technical idea.

The above-described embodiment is added, for example, as follows (but not limited to the following).

(Appendix 1)
An optical transmitter that allocates transmission information to multiple subcarriers with different frequencies and multiplexes and transmits it.
A means for receiving reception quality information transmitted from an optical receiving device for receiving a signal from the optical transmitting device, and a means for receiving the reception quality information.
A frequency control means that dither controls the transmission frequency of each of the plurality of subcarriers based on the reception quality information.
Equipped with
The frequency control means is an optical transmission device characterized in that the dither control is performed by dividing the subcarrier into a plurality of groups.

(Appendix 2)
The optical transmission device according to Appendix 1, wherein the frequency control means applies dither so that the polarities of the divided adjacent groups conflict with each other when the group is divided into two.

(Appendix 3)
The frequency control means is
The dither control is divided into a plurality of steps and executed.
In each step, the subcarriers are divided into a plurality of groups, the subcarriers belonging to the same group after the division are given dither in the same phase, and the adjacent groups are given dither in the opposite phase. The optical transmitter according to Appendix 1 or 2.

(Appendix 4)
The frequency control means assigns a Gray code to the index of each subcarrier.
The optical transmission according to any one of Supplementary note 1 to 3, wherein each step of the dither control determines the phase of the dither applied to each of the subcarriers based on the corresponding bit value of the Gray code. Device.

(Appendix 5)
An optical transmitter that allocates transmission information to multiple subcarriers with different frequencies and multiplexes and transmits it.
An optical receiver that receives an optical signal transmitted from the optical transmitter via a transmission line, acquires the quality of the received signal of each subcarrier, generates reception quality information, and transmits the optical signal to the optical transmitter.
Equipped with
The optical transmitter is
A means for receiving reception quality information transmitted from the optical receiver, and
A frequency control means that dither controls the transmission frequency of each of the plurality of subcarriers based on the reception quality information.
Equipped with
The frequency control means is a communication system characterized in that the dither control is performed by dividing the subcarrier into a plurality of groups.

(Appendix 6)
The communication system according to Appendix 5, wherein the frequency control means applies dither so that the polarities of the divided adjacent groups conflict with each other when the group is divided into two.

(Appendix 7)
The frequency control means is
The dither control is divided into a plurality of steps and executed.
In each step, the subcarriers are divided into a plurality of groups, the subcarriers belonging to the same group after the division are given dither in the same phase, and the adjacent groups are given dither in the opposite phase. The communication system according to Appendix 5 or 6.

(Appendix 8)
The frequency control means assigns a Gray code to the index of each subcarrier.
The communication system according to any one of Supplementary note 5 to 7, wherein each step of the dither control determines the phase of the dither given to each of the subcarriers based on the corresponding bit value of the Gray code. ..

(Appendix 9)
It is a transmission frequency control method using an optical transmitter that allocates transmission information to multiple subcarriers with different frequencies and multiplexes and transmits it.
Based on the reception quality information transmitted from the optical receiver that receives the signal from the optical transmitter, the transmission frequency of each of the plurality of subcarriers is dither controlled, and at that time, the subcarriers are divided into a plurality of groups. A transmission frequency control method characterized in that dither control is performed by performing division.

(Appendix 10)
The transmission frequency control method according to Appendix 9, wherein dithering is applied so that the polarities of the divided adjacent subcarrier groups conflict with each other when the group is divided into two.

(Appendix 11)
The dither control is divided into a plurality of steps and executed.
In each step, the subcarriers are divided into a plurality of groups, dither of the same phase is applied to the subcarriers belonging to the same group after the division, and dither of the opposite phase is given to the adjacent groups. The transmission frequency control method according to Appendix 9 or 10.

(Appendix 12)
Assign a gray code to the index of each subcarrier,
The transmission frequency according to any one of Supplementary note 9 to 11, wherein each step of the dither control determines the phase of the dither applied to each of the subcarriers based on the corresponding bit value of the Gray code. Control method.

(Appendix 13)
To a processor that performs digital signal processing in an optical transmitter that allocates transmission information to multiple subcarriers with different frequencies and multiplexes and transmits it.
It is a process of dithering and controlling the transmission frequency of each of the plurality of subcarriers based on the reception quality information transmitted from the optical receiver that receives the signal from the optical transmitter, to a plurality of groups of the subcarriers. A program that executes the process of performing the dither control by performing dither division.

(Appendix 14)
The program according to Appendix 13, wherein the process for performing dither control is to apply dither so that the polarities of the divided adjacent subcarrier groups conflict with each other when the group is divided into two.

(Appendix 15)
The process of performing the dither control is executed by dividing the dither control into a plurality of steps.
In each step, the subcarriers are divided into a plurality of groups, dither of the same phase is applied to the subcarriers belonging to the same group after the division, and dither of the opposite phase is given to the adjacent groups. The program according to Appendix 13 or 14.

(Appendix 16)
In the process of performing dither control, a gray code is assigned to the index of each subcarrier, and the gray code is assigned.
The program according to any one of Supplementary note 13 to 15, wherein each step of the dither control determines the phase of the dither to be applied to each of the subcarriers based on the corresponding bit value of the Gray code.

10 Optical transmitter 11 Quality information receiver 12 Subcarrier frequency control unit 13 Transmission signal generator 14 Subcarrier generator 15 Optical modulation unit 16 Wavelength division multiplexing 20 Optical receiver 21 Wavelength separator 22 Optical demodulator 23 Subcarrier generator 24 Received signal quality detector 25 Quality information transmitter 30 Optical communication path 101 Processor 102 Storage device 103 Communication device

Claims (8)

An optical transmitter that allocates transmission information to multiple subcarriers with different frequencies and multiplexes and transmits it.
A means for receiving reception quality information transmitted from an optical receiving device for receiving a signal from the optical transmitting device, and a means for receiving the reception quality information.
Based on the reception quality information, a frequency control means for performing dither control for applying dither to each transmission frequency of the plurality of subcarriers, and
Equipped with
The frequency control means divides the dither control into a plurality of steps and executes the dither control.
In the first step, the plurality of subcarriers are given a common dither as one group, and the dither is given.
In each step after the second step, for each group immediately before the dither division in the step, a plurality of subcarriers belonging to the group are divided into two, and the subcarriers belonging to one group after the dither division are the first. The subcarriers belonging to the other group after the dithering are given a second dither having the opposite polarity to the first dither.
An optical transmitter comprising repeating the steps after the second step until the number of subcarriers included in the bisected group becomes one . The optical transmission device according to claim 1, wherein the frequency control means applies dither so that the polarities of the adjacent groups divided into two are opposite to each other when the group is divided into two. The frequency control means assigns a Gray code to the index of each subcarrier.
The optical transmission device according to claim 1 or 2 , wherein in each step of the dither control, the phase of the dither to be applied to each of the subcarriers is determined based on the corresponding bit value of the Gray code. An optical transmitter that allocates transmission information to multiple subcarriers with different frequencies and multiplexes and transmits it.
An optical receiver that receives an optical signal transmitted from the optical transmitter via a transmission line, acquires the quality of the received signal of each subcarrier, generates reception quality information, and transmits the optical signal to the optical transmitter.
Equipped with
The optical transmitter is
A means for receiving reception quality information transmitted from the optical receiver, and
Based on the reception quality information, a frequency control means for performing dither control for applying dither to each transmission frequency of the plurality of subcarriers, and
Equipped with
The frequency control means divides the dither control into a plurality of steps and executes the dither control.
In the first step, the plurality of subcarriers are given a common dither as one group, and the dither is given.
In each step after the second step, for each group immediately before the dither division in the step, a plurality of subcarriers belonging to the group are divided into two, and the subcarriers belonging to one group after the dither division are the first. The subcarriers belonging to the other group after the dithering are given a second dither having the opposite polarity to the first dither.
A communication system characterized in that the steps after the second step are repeated until the number of subcarriers included in the bisected group becomes one . The communication system according to claim 4 , wherein the frequency control means applies dither so that the polarities of the adjacent groups divided into two are opposite to each other when the group is divided into two. It is a transmission frequency control method using an optical transmitter that allocates transmission information to multiple subcarriers with different frequencies and multiplexes and transmits it.
Based on the reception quality information transmitted from the optical receiver that receives the signal from the optical transmitter, dither control is performed to apply dither to each transmission frequency of the plurality of subcarriers, and at that time, the subcarriers are subjected to dither control. The dither control is performed by dividing the group into two groups.
At the time of dividing the group into two,
A transmission frequency control method characterized in that dithers of the same phase are given to subcarriers belonging to the same group after being divided into two, and dithers are given so that the polarities of adjacent groups conflict with each other . To a processor that performs digital signal processing in an optical transmitter that allocates transmission information to multiple subcarriers with different frequencies and multiplexes and transmits it.
It is a process of performing dither control for giving dither to each transmission frequency of the plurality of subcarriers based on the reception quality information transmitted from the optical receiver that receives the signal from the optical transmitter. It is a program that executes the process of performing the dither control by performing the dither division that divides the carrier group into two groups.
At the time of dividing the group into two,
A program that grants dither of the same phase to subcarriers belonging to the same group after division into two, and executes the process of dithering so that the polarities of adjacent groups conflict with each other . A storage medium that stores the program according to claim 7 .

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