JP6139322B2 - Optical transmitter and optical receiver - Google Patents

Description

  The present invention relates to an optical communication system that performs communication using an optical signal including a plurality of subcarriers.

  Patent Document 1 proposes an optical OFDM communication system in which orthogonal frequency division multiplexing (OFDM) is applied to an optical communication system. In the optical OFDM communication system, the transmission rate can be flexibly changed by changing the number of subcarriers, the symbol rate, and the modulation multi-level for each subcarrier, and therefore, it is expected as a communication method for an elastic optical network.

JP 2012-186673 A

  In optical OFDM communication, it is considered that the optical transmission apparatus adjusts the transmission rate by changing the modulation scheme of subcarriers. This is because, for example, when one of a plurality of optical transmission lines set between two stations becomes a failure, the failed optical transmission line is recovered until the failed transmission line is restored. This is necessary when the remaining traffic is shared by the remaining optical transmission line. Note that the signal-to-noise ratio is degraded by increasing the modulation multi-level. However, since the transmission characteristics of optical fibers are extremely stable, unlike radio, the maximum value of the modulation multilevel that does not cause quality degradation is measured in advance for each subcarrier, and the modulation multivalue of each subcarrier is determined. By changing the degree below this maximum value, deterioration of transmission quality can be prevented.

  The optical receiving apparatus needs to know the modulation scheme of each subcarrier in order to demodulate the OFDM-modulated optical signal (optical OFDM signal) received from the optical transmitting apparatus. If the optical transmission device always uses the same modulation method without changing the modulation method of each subcarrier, the modulation method of each subcarrier may be set in the optical reception device in advance. However, when the optical transmission apparatus changes the modulation scheme of the subcarrier as necessary, the optical reception apparatus needs to recognize this change. For example, it may be possible to notify the optical receiver of the modulation scheme of the subcarrier via the control network, but it is difficult to synchronize the timing of the change.

  The present invention provides an optical transmission apparatus that notifies an optical reception apparatus of a change in subcarrier modulation scheme, and an optical reception apparatus that communicates with the optical transmission apparatus.

According to an aspect of the present invention, there is provided an optical transmission apparatus that transmits an optical signal having a plurality of subcarriers each including a plurality of symbols, the plurality of symbols of the plurality of subcarriers for transmitting data. A data symbol associated with one or more data symbols, and including a notification symbol for notifying a modulation scheme of the associated data symbol; Determining means for determining the modulation method, and a value indicating the modulation method determined by the determining means in the notification symbol, and according to the modulation method determined by the determining means, data is associated with the notification symbol. comprising a modulation means for modulating the sub-carrier so as to convey in use symbols, wherein the notification symbol, each of the plurality of sub-carriers Arranged periodically,
The data symbol related to the notification symbol is the same subcarrier as the notification symbol, and is arranged one temporally after the notification symbol and the notification symbol in the same subcarrier as the notification symbol. The data symbol is arranged between the notification symbol and the notification symbol .

According to an aspect of the present invention, there is provided an optical receiver that receives an optical signal having a plurality of subcarriers each including a plurality of symbols, the plurality of symbols of the plurality of subcarriers for transmitting data. A notification symbol for notifying a data symbol and one or more of the data symbols, and notifying a modulation scheme of the associated data symbol; Determining means for determining the modulation scheme of the data symbol related to the data, and demodulating means for demodulating the data symbol related to the notification symbol according to the modulation scheme determined by the determination means , The modulation method is characterized in that a modulation method that can be used for a data symbol can be designated by one symbol .

  The optical receiver can be effectively notified of the change of the subcarrier modulation scheme.

1 is a schematic configuration diagram of an optical transmission device according to an embodiment. FIG. 1 is a schematic configuration diagram of an optical receiver according to an embodiment. FIG. 1 is a schematic configuration diagram of an optical OFDM signal transmitted by an optical transmission device according to an embodiment. FIG. 1 is a schematic configuration diagram of an optical OFDM signal transmitted by an optical transmission device according to an embodiment. FIG.

  Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings. In the following drawings, components that are not necessary for the description of the embodiments are omitted from the drawings. Further, although the embodiment will be described using optical OFDM communication, the present invention is not limited to OFDM, and can be applied to an optical communication system including a plurality of subcarriers.

  FIG. 3 is an explanatory diagram of an optical OFDM signal transmitted by the optical transmission apparatus in the present embodiment. The optical OFDM signal in FIG. 3 uses eight subcarriers # 1 to # 8 and constitutes one frame with seven symbols # 1 to # 7. The number of subcarriers to be used Alternatively, the number of symbols constituting one frame is arbitrary. Each square in FIG. 3 represents one symbol of one subcarrier, and the shaded square represents a notification symbol for notifying the modulation scheme. In addition, a rectangle in which a number of 4, 8, 16 or 64 is written is a data symbol for carrying data, and a number of 4, 8, 16 or 64 is a symbol of QPSK, 8QAM, It shows that the data is modulated by 16QAM and 64QAM.

  In this embodiment, the notification symbol provided at the head of each frame indicates the modulation scheme of each data symbol of the same frame of the same subcarrier. For example, in FIG. 3, the notification symbol for subcarrier # 1 in frame # 1 indicates 8QAM, and the notification symbol for subcarrier # 1 in frame # 2 indicates 16QAM. Note that the modulation scheme of the notification symbol itself is fixed, and the modulation scheme can carry the number of types of modulation schemes that can be used for data symbols in one symbol. For example, in this embodiment, since four types of modulation schemes of QPSK, 8QAM, 16QAM, and 64QAM are used for data symbols, QPSK that can carry four values with one symbol is used. For example, the value 00 is QPSK, the value 01 is 8QAM, the value 10 is 16QAM, and the value 11 is 64QAM. Note that 8QAM, 16QAM, and 64QAM, which can carry four values as the number of modulation schemes used for data symbols in one symbol, can also be used as modulation schemes for notification symbols.

  The optical receiving apparatus of this embodiment demodulates the data symbol of the frame by demodulating the notification symbol at the head of the frame and determining the modulation method of the data symbol of the frame. In FIG. 3, for the sake of simplicity, only a modulation system notification symbol and a data symbol for carrying data are included in the frame. However, in practice, a training symbol or the like is predetermined at a predetermined position. It is inserted with the modulation method.

  With the above configuration, the optical transmission device can freely change the modulation method used for the data symbols without negotiating the modulation method used with the optical reception device in advance. In the present embodiment, four types of modulation schemes of QPSK, 8QAM, 16QAM, and 64QAM can be applied to each subcarrier. However, it is possible to limit the modulation schemes that can be used in units of subcarriers. For example, when the transmission characteristics of the frequency corresponding to subcarrier # 8 in FIG. 3 are not good, in order to maintain transmission quality, 64QAM is not used for subcarrier # 8, and the modulation with a multilevel number of 16 or less is performed. There can be a restriction that only the method is used. Further, in the present embodiment, the notification symbol is the same as the notification symbol and the data symbol between the notification symbol and the notification symbol that is the same subcarrier as the notification symbol in time. The modulation method was shown. However, the notification symbol can also be configured to indicate the modulation scheme of the data symbol from the notification symbol one time after the notification symbol to the next notification symbol. In other words, it is a data symbol that is the same subcarrier as the notification symbol and that is temporally later than the notification symbol, and the relationship between the notification symbol and the optical transmission device is the same. .

  FIG. 4 is an explanatory diagram of another embodiment of an optical OFDM signal transmitted by the optical transmission apparatus. In the configuration of FIG. 3, notification symbols are periodically provided in the time direction, and each notification symbol indicates a modulation method of data symbols up to a notification symbol at the next time position of the same subcarrier. In the embodiment of FIG. 4, one subcarrier has only a notification symbol, and each notification symbol indicates the modulation scheme of all subcarrier symbols different from the notification symbol at the next time position. Yes. For example, the notification symbols from time positions # 1 to # 3 in frame # 1 in FIG. 4 indicate 8QAM, and the notification symbols from time position # 4 in frame # 1 to time position # 3 in frame # 2 indicate 16QAM. From the symbol at time position # 4 in frame # 2 to the notification symbol at time position # 2 in frame # 3 indicates 64QAM. In the configuration of FIG. 4, each notification symbol indicates the modulation method of all data symbols at the next time position, but indicates the modulation method of data symbols at the same time position. Alternatively, it may indicate a modulation method of data symbols at time positions two or more after. With the above configuration, the optical transmission apparatus can freely change the modulation system of the data symbols without negotiating the modulation system to be used with the optical reception apparatus in advance.

  As a further embodiment, for example, a notification symbol is provided only in one specific subcarrier of the head symbol of each frame, and the modulation scheme of all data symbols in each frame is used for notification of the same frame. It is also possible to adopt a form indicated by a symbol. More generally, each notification symbol is associated with one or more data symbols, and each notification symbol indicates the modulation scheme of the associated data symbol. It is sufficient that the relationship is known between the optical transmission device and the optical reception device. The time position of the data symbol related to the notification symbol is the same as that of the notification symbol or after the notification symbol. Therefore, any number of notification symbols can be used for each frame. Furthermore, the notification symbol arrangement pattern can be repeated for each of a plurality of frames instead of for each frame. That is, for example, one notification symbol can be arranged in a plurality of frames.

  FIG. 1 is a schematic configuration diagram of an optical transmission apparatus 100 that generates the above-described optical OFDM signal. The modulation type notification unit 11 determines a modulation method for each data symbol related to one notification symbol and notifies the mapping unit 10 of the modulation method. For example, in the case of the optical OFDM signal shown in FIG. 3, the data symbol related to a certain notification symbol is the same subcarrier as the notification symbol, and is one time later than the notification symbol and the notification symbol. It is a data symbol between a certain notification symbol. For example, the modulation type notifying unit 11 modulates a data symbol related to each notification symbol based on a transmission rate input from an external management device, a transmission rate of data input to the optical transmission device 100, or the like. To decide.

  By changing the modulation scheme used by the optical transmission device 100 for each subcarrier, the transmission rate of the optical transmission device 100 changes. Data is input to the mapping unit 10 at a speed corresponding to the transmission speed of the optical transmission device 100. The mapping unit 10 distributes the input data to each subcarrier for each symbol period, and performs inverse discrete Fourier transform on the complex value corresponding to the data for each subcarrier according to the modulation scheme notified from the modulation type notification unit 11. The data is output to the (IDFT) unit 12. This process is performed on the data symbols. Further, the mapping unit 10 performs inverse discrete Fourier transform (IDFT) on the complex value corresponding to the value indicating the modulation method according to the modulation method of the notification symbol based on the value indicating the modulation method notified from the modulation type notification unit 11. To the unit 12. This process is performed on the notification symbol. As described above, the processing in the mapping unit 10 carries a value indicating the modulation scheme determined by the modulation type notification unit 11 using a notification symbol, and associates data with the notification symbol according to the modulation scheme determined by the modulation type notification unit 11. The subcarriers are modulated so as to be carried by data symbols to be transmitted.

  The IDFT unit 12 performs an inverse discrete Fourier transform on the complex value of each input subcarrier, and outputs a temporally discrete OFDM signal to the transmission unit 13. The transmitter 13 performs analog conversion on the temporally discrete OFDM signal to generate a temporally continuous OFDM signal. Then, the optical OFDM signal is generated by modulating the continuous light with the temporally continuous OFDM signal, and the generated optical OFDM signal is transmitted to the optical receiver.

  FIG. 2 is a schematic configuration diagram of an optical receiver 200 that receives an optical OFDM signal transmitted by the optical transmitter 100 of FIG. The optical receiver 20 performs photoelectric conversion of the received optical OFDM signal and converts it into a temporally continuous OFDM signal. Thereafter, the optical receiving unit 20 samples the temporally continuous OFDM signal and outputs the temporally discrete OFDM signal to the discrete Fourier transform (DFT) unit 21. The DFT unit 21 performs discrete Fourier transform on the temporally discrete OFDM signal, and outputs the complex value of each subcarrier to the demodulation unit 22 and the modulation type determination unit 23. The modulation type determination unit 23 demodulates the notification symbol modulated by the predetermined modulation method, determines the modulation method of the data symbol related thereto, and notifies the demodulation unit 22 of the determined modulation method. The demodulator 22 demodulates each data symbol according to the modulation scheme notified from the modulation type determination unit 23.

Claims (7)

An optical transmitter that transmits an optical signal having a plurality of subcarriers each including a plurality of symbols,
The plurality of symbols of the plurality of subcarriers include a data symbol for transmitting data and one or more data symbols, and a notification symbol for reporting a modulation scheme of the related data symbol. Including
The optical transmitter is
Determining means for determining a modulation method of a data symbol related to the notification symbol;
A value indicating the modulation scheme determined by the determining means is carried by the notification symbol, and a subcarrier is transmitted so that data is carried by a data symbol related to the notification symbol according to the modulation scheme determined by the determining means. Modulation means for modulating;
Equipped with a,
The notification symbol is periodically arranged on each of the plurality of subcarriers,
The data symbol related to the notification symbol is the same subcarrier as the notification symbol, and is arranged one temporally after the notification symbol and the notification symbol in the same subcarrier as the notification symbol. An optical transmitter characterized in that it is a data symbol arranged between the notification symbol . An optical transmitter that transmits an optical signal having a plurality of subcarriers each including a plurality of symbols,
The plurality of symbols of the plurality of subcarriers include a data symbol for transmitting data and one or more data symbols, and a notification symbol for reporting a modulation scheme of the related data symbol. Including
The optical transmitter is
Determining means for determining a modulation method of a data symbol related to the notification symbol;
A value indicating the modulation scheme determined by the determining means is carried by the notification symbol, and a subcarrier is transmitted so that data is carried by a data symbol related to the notification symbol according to the modulation scheme determined by the determining means. Modulation means for modulating;
Equipped with a,
The notification symbol is periodically arranged on one of the plurality of subcarriers,
The data symbol related to the notification symbol is a data symbol of a subcarrier different from the notification symbol at the same symbol position in time as the notification symbol or a time later than the notification symbol. An optical transmitter characterized by being a data symbol of a subcarrier different from the notification symbol at a symbol position . Modulation scheme notification symbols, optical transmission apparatus according to claim 1 or 2, characterized in that it can specify the modulation schemes available for data symbols in one symbol. An optical transmitter that transmits an optical signal having a plurality of subcarriers each including a plurality of symbols,
The plurality of symbols of the plurality of subcarriers include a data symbol for transmitting data and one or more data symbols, and a notification symbol for reporting a modulation scheme of the related data symbol. Including
The optical transmitter is
Determining means for determining a modulation method of a data symbol related to the notification symbol;
A value indicating the modulation scheme determined by the determining means is carried by a notification symbol, and the subcarrier is modulated according to the modulation scheme determined by the determining means so that data is carried by a data symbol related to the notification symbol. Modulation means to
Equipped with a,
The optical transmitter according to claim 1, wherein the modulation method of the notification symbol can specify a modulation method that can be used as a data symbol by one symbol . The optical transmission apparatus according to claim 4 , wherein the notification symbol is periodically arranged on at least one subcarrier. An optical receiver that receives an optical signal having a plurality of subcarriers each including a plurality of symbols,
The plurality of symbols of the plurality of subcarriers is a data symbol for transmitting data and a notification symbol for notifying one or more of the data symbols and reporting a modulation scheme of the related data symbols Including
The optical receiver is
A determination means for determining a modulation scheme of a data symbol related to the notification symbol from the notification symbol;
Demodulating means for demodulating a data symbol related to the notification symbol according to the modulation scheme determined by the determining means;
Equipped with a,
The optical receiver according to claim 1, wherein the modulation method of the notification symbol can specify a modulation method that can be used for a data symbol by one symbol . The optical receiver according to claim 6, wherein the notification symbols are periodically arranged on at least one subcarrier.

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