JP2010045571A - Method and apparatus for orthogonal frequency division multiplexing communication - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve transmission quality in a method for orthogonal frequency division multiplexing communication. <P>SOLUTION: The apparatus for orthogonal frequency division multiplexing communication that conveys data signals to receiver sides 308-312 from transmitter sides 301-306 and 313 through an optical transmission line 307 includes: a modulation mode determination circuit 313 to determine a modulation method for frequency channels and polarization channels respectively according to the reception status of each of the frequency channels of the polarization channels on the receiver side; modulation circuits 302-1 and 302-2 to modulate for each of the frequency channels of the polarization channels by the modulation method that is determined by the modulation mode determination circuit 313; and amplitude control circuits 303-1 and 303-2 to multiply a prescribed factor for each of the frequency channels of the polarization channels according to the reception status of each of the frequency channels of the polarization channels on the receiver side. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical orthogonal frequency division multiplexing communication method and apparatus in an optical transmission system using orthogonal frequency division multiplexing modulation / demodulation technology.

  A 100 Gb / s class ultra-high-speed optical signal has a problem that the transmission distance is significantly limited by the influence of chromatic dispersion (CD) and polarization mode dispersion (PMD). For this reason, conventionally, it has been necessary to use a highly accurate dispersion compensation technique or to increase the number of regenerative repeaters using high-cost optical / electrical / optical converters. In addition, since the occupied bandwidth of the optical signal widens with an increase in the bit rate, a reduction in frequency utilization efficiency during wavelength division multiplexing (WDM) transmission becomes a problem. In order to solve this problem, research and development of an OFDM (Orthogonal Frequency Division Multiplexing) system has been advanced. In the optical OFDM system, the data of the same channel is divided and transmitted to multiple orthogonal subcarriers with low transmission speed, and the influence of chromatic dispersion and polarization mode dispersion can be reduced, and the transmission distance can be extended. Can do. Furthermore, the occupied band per wavelength multiplexing channel can be narrowed, and the frequency utilization efficiency can be improved.

  Here, with reference to FIG. 7, the technology that is the background of the present invention will be described. FIG. 7 is a configuration example of an orthogonal frequency division multiplex communication apparatus that realizes a high communication speed by an orthogonal frequency division multiplex system through an optical transmission line. Reference numeral 901 is a serial / parallel conversion circuit, 902 is a modulation circuit, 903 is an IFFT (Inverse Fast Fourier Transform) circuit, 904 is an electrical / optical conversion circuit, 905 is an optical transmission line, and 906 is an optical / electrical conversion circuit. 907 is an FFT (Fast Fourier Transform) circuit, 908 is a demodulation circuit, and 909 is a parallel / serial conversion circuit. Here, the circuits 901 to 904 constitute a transmitter, and the circuits 906 to 909 constitute a receiver.

  The data signal to be transmitted is input to the serial / parallel conversion circuit 901, divided into the number of frequency channels, and input to the modulation circuit 902. The modulation circuit 902 performs modulation by a predetermined modulation method common to each frequency channel, and outputs the result to the IFFT circuit 903. The IFFT circuit 903 converts each frequency component signal into a time-series transmission signal, adds a training signal and inserts a guard interval signal, and then outputs the signal to the electrical / optical conversion circuit 904. The electrical / optical conversion circuit 904 converts an electrical signal into an optical signal and transmits the optical signal to the receiver via the optical transmission path 905.

  In the receiver, the received optical signal is converted by the optical / electrical conversion circuit 906 and output to the FFT circuit 907. The FFT circuit 907 detects the head position of the signal, performs Fourier transform at a position excluding the guard interval signal, converts it to frequency domain information, and outputs the information to the demodulation circuit 908. The demodulation circuit 908 demodulates the obtained signal for each frequency channel using the channel information obtained from the training signal, and outputs it to the parallel / serial conversion circuit 909. The parallel-serial conversion circuit 909 can perform parallel-serial conversion on the input signal to obtain transmitted data.

The above method can obtain high characteristics when the same signal-to-interference and noise ratio (SINR) is almost equal in all frequency channels. However, in practice, frequency channels (= subcarriers) that reduce the signal-to-interference and noise ratio occur due to device characteristics, propagation characteristics of optical transmission lines such as chromatic dispersion, polarization mode dispersion, and nonlinear optical effects, and filter characteristics. An error that occurs in this frequency channel will degrade the overall characteristics.For example, Non-Patent Document 1 reports that there are channels with a high error rate due to the frequency characteristics of the transmitter, which degrades the overall characteristics. Has been.
Brendon JC Schmidt, et al., “Experimental Demonstrations of 20 Gbit / s Direct-Detection Optica1 OFDM and 12 Git / s with a colorless transmitter,” Optical Society of America, 2007, OFC2007, PDP18

  As described with reference to FIG. 7, when the orthogonal frequency division multiplexing technique is applied to the optical transmission system, there is a difference in transmission characteristics depending on the frequency channel, and this difference in characteristics deteriorates the overall transmission quality. was there,

  The present invention has been made in view of such circumstances, and is intended to improve transmission quality in an optical orthogonal frequency division multiplexing communication method and apparatus, and more specifically, transmission quality of a frequency channel. The purpose of the present invention is to provide an optical orthogonal frequency division multiplex communication method and apparatus that can control transmission power for frequency channels in advance and determine a modulation scheme for each frequency channel to achieve improved transmission quality. is there.

  In order to solve the above-mentioned problem, an invention according to claim 1 is an orthogonal frequency division multiplex communication method for transmitting a data signal from a transmitter side to a receiver side via an optical transmission line, wherein the transmitter includes: A serial-parallel conversion step for performing serial-parallel conversion on the transmitted data signal and distributing the signal, and a plurality of frequencies according to the reception state of each frequency channel on the receiver side based on the converted parallel signal A modulation signal generating step for generating a modulation signal for the channel, a conversion step for converting the generated modulation signal for the multiple frequency channels into time-series transmission data by inverse Fourier transform, and amplifying the transmission power of the time-series transmission data And an electrical / optical conversion step for converting the amplified transmission data into an optical signal.

  According to a second aspect of the present invention, in the modulation signal generation step, the modulation method is changed for each frequency channel or the modulation signal is changed for each frequency channel according to the reception state of each frequency channel on the receiver side. It is characterized by controlling at least one of multiplying a predetermined coefficient.

  The invention according to claim 3 is an orthogonal frequency division multiplex communication method for transmitting a data signal from a transmitter side to a receiver side via two polarization channels of an optical transmission line, wherein the transmitter includes: A serial / parallel conversion step that performs serial / parallel conversion on the data signal to be transmitted and distributes the signal, and according to the reception state of each frequency channel of each polarization channel on the receiver side based on the converted parallel signal Modulation signal generation step for generating a modulation signal of a plurality of frequency channels for each polarization channel, and the generated modulation signal of the plurality of frequency channels for each polarization channel is converted into time-series transmission data by inverse Fourier transform. The conversion step, the amplifier step for amplifying the transmission power of the time-series transmission data, and the transmission data for the two polarizations And performing the electro-optical conversion step of converting the optical signal in a wave channel.

  According to a fourth aspect of the present invention, in the modulation signal generation step, a modulation scheme is changed for each frequency channel according to a reception state of each frequency channel of each polarization channel on the receiver side, or the frequency channel It is characterized in that at least one control of multiplying a modulated signal by a predetermined coefficient for each time is performed.

  The invention according to claim 5 is an orthogonal frequency division multiplex communication method for transmitting a data signal from a transmitter side to a receiver side via an optical transmission line, wherein the transmitter converts the data signal to be transmitted. A serial / parallel conversion step for performing serial / parallel conversion to distribute signals, a modulation signal generating step for generating a modulation signal of a plurality of frequency channels based on the converted parallel signal, and a generated modulation signal of a plurality of frequency channels Converting to time-series transmission data by inverse Fourier transform, amplifier step for amplifying transmission power of the time-series transmission data, and electrical / optical conversion step for converting the amplified transmission data into an optical signal In the modulation signal generation step, the frequency is changed according to the reception state of each frequency channel on the receiver side. It is characterized in that at least one of the modulation method is changed every several channels, or the amplifier step performs amplification with a frequency characteristic corresponding to the reception state of each frequency channel on the receiver side. And

  The invention according to claim 6 is an orthogonal frequency division multiplex communication method for transmitting a data signal from a transmitter side to a receiver side via two polarization channels of an optical transmission line, wherein the transmitter includes: A serial / parallel conversion step that performs serial / parallel conversion on the transmitted data signal and distributes the signal, and a modulation signal generation step that generates a modulation signal of a plurality of frequency channels for each polarization channel based on the converted parallel signal. A conversion step for converting the generated modulation signals of the plurality of frequency channels for each polarization channel into time-series transmission data by inverse Fourier transform; and an amplifier step for amplifying the transmission power of the time-series transmission data; And the electrical / optical conversion step of converting the transmission data for the two polarizations into optical signals in the corresponding polarization channels, the modulation In the signal generation step, the modulation scheme is changed for each frequency channel according to the reception state of each frequency channel of each polarization channel on the receiver side, or each polarization on the receiver side in the amplifier step It is characterized in that at least one of the amplification is performed by giving a frequency characteristic corresponding to the reception state of each frequency channel of the channel.

  The invention according to claim 7 is an orthogonal frequency division multiplex communication apparatus for transmitting a data signal from a transmitter side to a receiver side via an optical transmission line, wherein the transmitter is connected to each receiver side. A modulation mode determination circuit that determines the modulation method for each frequency channel and polarization channel according to the reception state of each frequency channel of the polarization channel, and serial / parallel conversion of the transmitted data signal to perform signal distribution A modulation circuit that performs modulation for each frequency channel of each polarization channel according to the modulation method determined by the modulation mode determination circuit based on a signal input from the serial / parallel conversion circuit; An inverse Fourier transform circuit that obtains time-series transmission data by inverse Fourier transform based on the modulation signal modulated by the modulation circuit; An amplifier circuit that amplifies a signal level of time-series transmission data and outputs the amplified signal level to an electrical / optical conversion circuit, and an electrical / optical conversion circuit that converts the signal input from the amplifier circuit into an optical signal of each polarization channel. It is characterized by having.

  The invention according to claim 8 is an orthogonal frequency division multiplex communication apparatus for transmitting a data signal from a transmitter side to a receiver side via an optical transmission line, wherein the transmitter is configured to transmit each data signal at the receiver side. A modulation mode determination circuit that determines the modulation method for each frequency channel and polarization channel according to the reception state of each frequency channel of the polarization channel, and serial / parallel conversion of the transmitted data signal to perform signal distribution A modulation circuit that performs modulation for each frequency channel of each polarization channel according to the modulation method determined by the modulation mode determination circuit based on a signal input from the serial / parallel conversion circuit; For the modulation signal output from the modulation circuit, depending on the reception state of each frequency channel of each polarization channel on the receiver side, An amplitude control circuit that multiplies a predetermined coefficient for each frequency channel of the wave channel, an inverse Fourier transform circuit that converts an output signal of the amplitude control circuit into time-series transmission data by inverse Fourier transform, and the time-series transmission data The signal level is amplified with a frequency characteristic corresponding to the reception state of each frequency channel of each polarization channel on the receiver side, and is output from the amplifier circuit to the electrical / optical conversion circuit. And an electrical / optical conversion circuit that converts the converted signal into an optical signal of each polarization channel.

  According to the present invention, it is possible to pre-emphasize the transmission output of a frequency channel having relatively low transmission characteristics or change the modulation method in optical communication using an orthogonal frequency division multiplexing system. The signal-to-noise ratio can be improved and the transmission efficiency can be improved. Thereby, it is possible to improve the characteristics of the transmission system in which the characteristics of the specific frequency channel have deteriorated the overall characteristics, that is, it is possible to reduce the deterioration of the communication quality due to the frequency channel or the polarization channel having a low transmission characteristic.

  Hereinafter, various embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a first embodiment of an optical orthogonal frequency division multiplexing communication apparatus according to the present invention, which realizes a high communication speed by an orthogonal frequency division multiplexing system through an optical transmission line. Reference numeral 101 is a serial / parallel conversion circuit, 102 is a modulation circuit, 103 is an amplitude control circuit, 104 is an IFFT circuit, 105 is an amplifier circuit, 106 is an electrical / optical conversion circuit, 107 is an optical transmission line, and 108 is an optical / electrical conversion circuit Reference numeral 109 denotes a filter, 110 denotes an FFT circuit, 111 denotes a demodulation circuit, and 112 denotes a parallel / serial conversion circuit. Here, the circuits 101 to 106 constitute a transmitter, and the circuits 108 to 112 constitute a receiver.

  The data signal to be transmitted is input to the serial / parallel conversion circuit 101, serial / parallel converted to correspond to the number of frequency channels (= subcarriers), the signal is distributed, and input to the modulation circuit 102. The The modulation circuit 102 modulates each frequency channel (= subcarrier) with each data converted in parallel by a predetermined modulation method, and outputs it to the amplitude control circuit 103. The amplitude control circuit 103 multiplies the modulation signal of each frequency channel by a correction coefficient according to the reception state of each frequency channel, adjusts the output level, and outputs to the IFFT circuit 104. That is, based on the parallel signal converted by the modulation circuit 102 and the amplitude control circuit 103, a modulation signal of a plurality of frequency channels is generated according to the reception state of each frequency channel on the receiver side. The IFFT circuit 104 converts the frequency component signal into a time-series transmission signal (= transmission data), adds a predetermined training signal and inserts a guard interval signal, and then outputs the signal to the amplifier circuit 105. . The transmission power output from the IFFT circuit 104 is amplified by the amplifier circuit 105 and output to the electrical / optical conversion circuit 106. The electrical / optical conversion circuit 106 converts an electrical signal into an optical signal, and transmits the optical signal to the receiver via the optical transmission path 107.

  In the receiver, the received optical signal is converted by the optical / electrical conversion circuit 108 and output to the FFT circuit 110 via the filter 109. The FFT circuit 110 detects the head position of the signal, performs Fourier transform at a position excluding the guard interval signal, converts it to frequency domain information, and outputs the information to the demodulation circuit 111. The demodulation circuit 111 demodulates the obtained signal for each frequency channel using the channel information obtained from the training signal, and outputs it to the parallel / serial conversion circuit 112. The parallel-serial conversion circuit can perform parallel-serial conversion on the input signal to obtain transmitted data.

  In the present embodiment, the amplitude control circuit 103 in the transmitter determines a correction coefficient from information on each frequency channel obtained in advance by the receiver. Information on each frequency channel can be obtained by performing feedback from the receiver to the transmitter. The correction coefficient is determined so that the signal-to-noise ratio or the error rate is the same for each frequency channel from the information on the signal-to-interference noise ratio in each frequency channel or the parameter correlated with the signal-to-noise ratio.

  An example of the correction coefficient will be described with reference to FIGS. FIG. 3 shows reception characteristics before correction by a correction coefficient. The received power levels of 128 frequency channels when OFDM transmission is performed using 128 subcarriers using a frequency band of 1.25 GHz. Represents. It can be seen that the received power of the frequency channel varies depending on the characteristics of the transmitter and receiver and the transmission path. In this way, if the communication quality obtained on the transmission path is different for each frequency channel, the result of the frequency channel with poor communication quality degrades the overall characteristics.

  Next, an example of the characteristic improvement method using the correction coefficient according to the present invention will be described. FIG. 4 is a diagram showing the level control value of each frequency channel obtained based on the reception level of each frequency channel shown in FIG. The level control value shown in FIG. 4 is obtained by taking the reciprocal of the result of fitting the obtained reception level of each frequency channel with a cubic function by the least square method. The filter function is set to 2.3e-2 · S + 6.7e-4 · S ^ 2 + 6.0e-6 · S ^ 3 [dB], where S is a frequency channel number. When the amplitude control circuit 103 multiplies the transmission signal by using the level control value shown in FIG. 4 as a correction coefficient for multiplying by each frequency channel (= subcarrier), the reception signal becomes as shown in FIG. It can be seen that the extreme difference of has been improved. The dispersion value in dB is improved from 1.39 dB to 0.14 dB.

  Next, another embodiment of the present invention will be described with reference to FIG. FIG. 2 shows a second embodiment of the optical orthogonal frequency division multiplexing communication apparatus according to the present invention, which realizes a high communication speed by an orthogonal frequency division multiplexing system through an optical transmission line. Reference numeral 201 is a serial / parallel conversion circuit, 202-1 and 202-2 are modulation circuits, 203-1 and 203-2 are amplitude control circuits, 204-1 and 204-2 are IFFT circuits, and 205-1 and 205-2. Is an amplifier circuit, 206 is an electrical / optical conversion circuit, 207 is an optical transmission line, 208 is an optical / electrical conversion circuit, 209-1 and 209-2 are filters, 210-1 and 210-2 are FFT circuits, and 211 is demodulated A circuit 212 is a parallel / serial conversion circuit. Here, the circuits 201 to 206 constitute a transmitter, and the circuits 208 to 212 constitute a receiver.

  In the present embodiment, unlike the first embodiment described with reference to FIG. 1, the modulation circuits 202-1 and 202-2, the amplitude control circuits 203-1 and 203-2, and the IFFT circuits 204-1 and 204 -2, amplifier circuits 205-1 and 205-2, filters 209-1 and 209-2, and FFT circuits 210-1 and 210-2 are provided separately in two systems. Each system is provided so as to correspond to polarization components (polarization channel; X polarization component, Y polarization component) that are orthogonal to each other in each frequency channel.

  The data signal to be transmitted is input to the serial / parallel conversion circuit 201. The serial / parallel conversion circuit 201 branches the input signal in parallel so that it can be modulated in accordance with a modulation scheme determined in advance by the modulation circuits 202-1 and 202-2. Output to 202-2. The modulation circuits 202-1 and 202-2 perform modulation by a predetermined modulation method, and output to the amplitude control circuits 203-1 and 203-2. The amplitude control circuits 203-1 and 203-2 multiply the modulation signal of each frequency channel by a predetermined correction coefficient, adjust the output level, and output to the IFFT circuits 204-1 and 204-2. The IFFT circuits 204-1 and 204-2 convert the frequency component signal into a time-series transmission signal, add the training signal and insert the guard interval signal, and then connect the amplifier circuits 205-1 and 205-2. To the electrical / optical conversion circuit 206. The electrical / optical conversion circuit 206 converts the electrical signal representing the transmission data for two polarizations into an optical signal through the corresponding polarization channel, and transmits the optical signal to the receiver via the optical transmission path 207.

  In the receiver, the received optical signal corresponding to the two polarization components is converted into an electrical signal by the optical / electrical conversion circuit 208, and is passed through the filters 209-1 and 209-2, and the FFT circuits 210-1 and 210- Output to 2. The FFT circuits 210-1 and 210-2 detect the head position of the signal, perform Fourier transform at a position excluding the guard interval signal, convert it to frequency domain information, and output to the demodulation circuit 211. The demodulation circuit 211 can demodulate the obtained signal for each frequency channel using the channel information obtained from the training signal and output the signal to the parallel-serial conversion circuit 212 to obtain the transmitted data. .

  As in the first embodiment described with reference to FIG. 1, the amplitude control circuits 203-1 and 203-2 calculate correction coefficients from information on each frequency channel of each polarization channel obtained in advance by the receiver. To decide. Information on each frequency channel can be obtained by a test transmission by the apparatus installer or by feedback from the receiver to the transmitter.

  Instead of using the amplitude control circuit 103 or 203-1 and 203-2 in the first and second embodiments described above, each polarization channel on the receiver side is connected to the amplifier circuit 105 or 205-1 and 205-2. It is also possible to give the same frequency characteristic as the correction coefficient corresponding to the reception state of each frequency channel, and to reduce the variation in the transmission quality of the frequency channel.

  In addition, since the correction coefficient having a large width leads to an increase in the PAPR (peak-to-average power ratio) of the transmission signal, it is possible to limit the correction coefficient correction width. For example, the correction coefficient in FIG. 4 increases the power by about 4.6 dB at maximum, but if the correction width is set to 3 dB and the function of the correction coefficient is multiplied by 3 / 4.6, a correction coefficient with a maximum correction width of 3 dB can be obtained. .

  Next, still another embodiment of the present invention will be described with reference to FIG. FIG. 6 shows a third embodiment of an optical orthogonal frequency division multiplexing communication apparatus according to the present invention, which realizes a high communication speed by an orthogonal frequency division multiplexing method through an optical transmission line. The difference from the second embodiment is that a modulation mode determination circuit 313 is provided.

  Reference numeral 301 is a serial / parallel conversion circuit, 302-1 and 302-2 are modulation circuits, 303-1 and 303-2 are amplitude control circuits, 304-1 and 304-2 are IFFT circuits, 305-1 and 305-2 Is an amplifier circuit, 306 is an electrical / optical conversion circuit, 307 is an optical transmission line, 308 is an optical / electrical conversion circuit, 309-1 and 309-2 are filters, 310-1 and 310-2 are FFT circuits, and 311 is demodulated 312 is a parallel / serial conversion circuit, and 313 is a modulation mode determination circuit. Here, the circuits 301 to 306 and the circuit 313 constitute a transmitter, and the circuits 308 to 312 constitute a receiver. However, the modulation mode determination circuit 313 may be provided separately from the receiver side or the transceiver.

  The transmitted data signal is input to the serial / parallel conversion circuit 301. The serial / parallel conversion circuit 301 branches the input signal in parallel and outputs it to the modulation circuits 302-1 and 302-2. The modulation circuits 302-1 and 302-2 perform modulation for each polarization channel and each frequency channel in accordance with the modulation method designated by the modulation mode determination circuit 313, and output the modulated signals to the amplitude control circuits 303-1 and 303-2. Similar to the first and second embodiments, the amplitude control circuits 303-1 and 303-2 convert the modulation signal of each frequency channel according to the reception state of each frequency channel of each polarization channel on the receiver side. Multiply by a predetermined correction coefficient, adjust the output level, and output to IFFT circuits 303-1 and 303-2. The IFFT circuits 303-1 and 303-2 convert the frequency component signal into a time-series transmission signal, add a training signal and insert a guard interval signal, and then connect the amplifier circuits 305-1 and 305-2. To the electrical / optical conversion circuit 306. The electrical / optical conversion circuit 306 converts the electrical signal representing the transmission data for two polarizations into an optical signal through the corresponding polarization channel, and transmits the optical signal to the receiver via the optical transmission path 307.

  In the receiver, the received optical signal corresponding to the two polarization components is converted into an electrical signal by the optical / electrical conversion circuit 308, and is passed through the filters 309-1 and 309-2, and the FFT circuits 310-1 and 310- Output to 2. The FFT circuits 310-1 and 310-2 detect the head position of the signal, perform Fourier transform at a position excluding the guard interval signal, convert it to frequency domain information, and output to the demodulation circuit 311. The demodulation circuit 311 can demodulate the obtained signal for each frequency channel using the channel information obtained from the training signal, and can output to the parallel / serial conversion circuit 312 to obtain the transmitted data. .

  The modulation mode determination circuit 313 in this embodiment determines a modulation scheme for each frequency channel and polarization channel according to the reception state of each frequency channel of each polarization channel on the receiver side. If there is an amplitude attenuation that cannot be covered by the amplitude control circuits 303-1 and 303-2, it has a function of selecting the modulation code of the channel as a receivable modulation code. For example, if the OFDM signal uses a QPSK (4-phase phase modulation) code, the channel that cannot secure the S / N (signal-to-noise ratio) required for QPSK is changed to BPSK (2-phase phase modulation). is there. Conversely, a channel with good characteristics may have a function of changing to a higher-density modulation code such as 8PSK or 16QAM (16-value quadrature amplitude modulation).

  Also, the control when generating modulation signals of multiple frequency channels according to the reception state of each frequency channel on the receiver side by the modulation circuits 302-1 and 302-2 and the amplitude control circuits 303-1 and 303-2 is Both can be performed simultaneously, or only one can be performed. That is, the frequency of each polarization channel is determined by the modulation circuits 302-1 and 302-2 and the amplitude control circuits 303-1 and 303-2 according to the reception state of each frequency channel of each polarization channel on the receiver side. It is possible to control at least one of changing the modulation method for each channel or multiplying the modulation signal by a predetermined coefficient for each frequency channel of each polarization channel.

  Also, in the third embodiment, instead of using the amplitude control circuits 303-1 and 303-2 as described above, each frequency channel of each polarization channel on the receiver side is added to the amplifier circuits 305-1 and 305-2. By giving the same frequency characteristic as the correction coefficient according to the reception state, variation in transmission quality of the frequency channel can be reduced. That is, in this case, the modulation circuit 302-1 and 302-2 and the amplifier circuits 305-1 and 305-2 change the modulation method for each frequency channel according to the reception state of each frequency channel on the receiver side. Alternatively, it is possible to control at least one of performing amplification with a frequency characteristic corresponding to the reception state of each frequency channel on the receiver side.

  As described above, in the transmitter according to each embodiment of the present invention, the transmission output for each frequency channel is controlled in advance according to the transmission quality of each frequency channel, and the modulation format is changed to the frequency channel according to the transmission quality. I try to select every one. For example, for frequency channels where the received S / N is relatively low or below the reception limit, pre-emphasis the transmission output, and for example, a QPSK code is a frequency channel where the received S / N is insufficient Has improved the reception S / N of a specific channel by changing the modulation code to the BPSK code. This produces an effect of improving the characteristics of the transmission system in which the characteristics of the specific frequency channel have deteriorated the overall characteristics. That is, according to the present invention, in optical communication using the orthogonal frequency division multiplexing method, it is possible to reduce deterioration in communication quality due to frequency channels and polarization channels having low transmission characteristics.

  The embodiment of the present invention is not limited to the above-described one. For example, the modulation mode determination circuit of the third embodiment is combined with the first embodiment, or the signal waveform smoothing in each unit is newly performed. Changes such as adding a configuration for performing filtering can be made as appropriate.

1 is a block diagram illustrating a configuration example of an orthogonal frequency division multiplexing optical transmission apparatus (system) as a first embodiment of the present invention. It is a block diagram which shows the structural example of the orthogonal frequency division multiplexing optical transmission apparatus (system) as the 2nd Embodiment of this invention. It is a figure which shows the received signal level for every frequency channel before the amplitude correction of a transmission signal. It is a figure which shows an example of the amplitude correction coefficient (level control value) of the transmission signal for every frequency channel calculated | required based on the characteristic of FIG. FIG. 5 is a diagram illustrating a received signal level for each frequency channel when amplitude correction of a transmission signal is performed using the correction coefficient of FIG. 4. It is a block diagram which shows the structural example of the orthogonal frequency division multiplexing optical transmission apparatus (system) as the 3rd Embodiment of this invention. It is a block diagram which shows the orthogonal frequency division multiplexing optical transmission system in the background art of this invention.

Explanation of symbols

101, 201, 301 Serial-parallel conversion circuit
102, 202-1, 202-2, 302-1, 302-2 Modulation circuit
103, 203-1, 203-2, 303-1, 303-2 Amplitude control circuit
104, 204-1, 204-2, 304-1, 304-2 IFFT circuit
105, 205-1, 205-2, 305-1, 305-2 Amplifier circuit
106, 206, 306 Electrical / optical conversion circuit
107, 207, 307 Optical transmission line
108, 208, 308 Photoelectric conversion circuit
109, 209-1, 209-2, 309-1, 309-2 filter
110, 210-1, 210-2, 310-1, 310-2 FFT circuit
111, 211, 311 Demodulator
112, 212, 312 Parallel-serial conversion circuit
313 Mode decision circuit

Claims (8)

An orthogonal frequency division multiplex communication method for transmitting a data signal from a transmitter side to a receiver side via an optical transmission line,
The transmitter is
A serial / parallel conversion step that performs serial / parallel conversion on the data signal to be transmitted and distributes the signal;
Based on the converted parallel signal, a modulation signal generation step of generating a modulation signal of a plurality of frequency channels according to the reception state of each frequency channel on the receiver side;
A conversion step of converting the generated modulated signals of the multiple frequency channels into time-series transmission data by inverse Fourier transform;
An amplifier step for amplifying the transmission power of the time-series transmission data;
An orthogonal frequency division multiplexing communication method comprising: performing an electrical / optical conversion step of converting the amplified transmission data into an optical signal. In the modulation signal generation step,
According to the reception state of each frequency channel on the receiver side, at least one of control of changing a modulation method for each frequency channel or multiplying a modulation signal by a predetermined coefficient for each frequency channel is performed. The orthogonal frequency division multiplexing communication method according to claim 1, wherein the orthogonal frequency division multiplexing communication method is performed. An orthogonal frequency division multiplex communication method for transmitting a data signal from a transmitter side to a receiver side via two polarization channels of an optical transmission line,
The transmitter is
A serial / parallel conversion step that performs serial / parallel conversion on the data signal to be transmitted and distributes the signal;
Based on the converted parallel signal, a modulation signal generation step of generating a modulation signal of a plurality of frequency channels for each polarization channel according to the reception state of each frequency channel of each polarization channel on the receiver side;
A conversion step of converting the generated modulation signal of the multi-frequency channel for each polarization channel into time-series transmission data by inverse Fourier transform,
An amplifier step for amplifying the transmission power of the time-series transmission data;
An orthogonal frequency division multiplex communication method comprising: performing an electrical / optical conversion step of converting the transmission data for the two polarizations into an optical signal through a corresponding polarization channel. In the modulation signal generation step, the modulation scheme is changed for each frequency channel or predetermined for each modulation signal according to the reception state of each frequency channel of each polarization channel on the receiver side. 4. The orthogonal frequency division multiplex communication method according to claim 3, wherein at least one of the multiplication is performed. An orthogonal frequency division multiplex communication method for transmitting a data signal from a transmitter side to a receiver side via an optical transmission line,
The transmitter is
A serial / parallel conversion step that performs serial / parallel conversion on the data signal to be transmitted and distributes the signal;
A modulation signal generating step for generating a modulation signal of a plurality of frequency channels based on the converted parallel signal;
A conversion step of converting the generated modulated signals of the multiple frequency channels into time-series transmission data by inverse Fourier transform;
An amplifier step for amplifying the transmission power of the time-series transmission data;
When performing the electrical / optical conversion step of converting the amplified transmission data into an optical signal,
In the modulation signal generation step, the modulation method is changed for each frequency channel according to the reception state of each frequency channel on the receiver side, or the reception state of each frequency channel on the receiver side in the amplifier step An orthogonal frequency division multiplex communication method characterized in that at least one of the amplification is performed with a frequency characteristic corresponding to the frequency. An orthogonal frequency division multiplex communication method for transmitting a data signal from a transmitter side to a receiver side via two polarization channels of an optical transmission line,
The transmitter is
A serial / parallel conversion step that performs serial / parallel conversion on the data signal to be transmitted and distributes the signal;
A modulation signal generation step for generating a modulation signal of a plurality of frequency channels for each polarization channel based on the converted parallel signal;
A conversion step of converting the generated modulation signal of the multi-frequency channel for each polarization channel into time-series transmission data by inverse Fourier transform,
An amplifier step for amplifying the transmission power of the time-series transmission data;
When performing the electrical / optical conversion step of converting the transmission data for the two polarizations into an optical signal in the corresponding polarization channel,
In the modulation signal generation step, depending on the reception state of each frequency channel of each polarization channel on the receiver side, the modulation scheme is changed for each frequency channel, or each step on the receiver side in the amplifier step An orthogonal frequency division multiplex communication method characterized by controlling at least one of amplification by giving a frequency characteristic corresponding to a reception state of each frequency channel of a polarization channel. An orthogonal frequency division multiplex communication apparatus that transmits a data signal from a transmitter side to a receiver side via an optical transmission line,
A modulation mode determining circuit for determining a modulation scheme for each frequency channel and polarization channel according to a reception state of each frequency channel of each polarization channel on the receiver side of the transmitter;
A serial / parallel conversion circuit that performs serial / parallel conversion on the transmitted data signal and distributes the signal;
A modulation circuit that performs modulation for each frequency channel of each polarization channel based on the signal input from the serial / parallel conversion circuit, according to the modulation method determined by the modulation mode determination circuit;
Amplitude control for multiplying a modulation signal output from the modulation circuit by a predetermined coefficient for each frequency channel of each polarization channel according to the reception state of each frequency channel of each polarization channel on the receiver side Circuit,
An inverse Fourier transform circuit that converts the output signal of the amplitude control circuit into time-series transmission data by inverse Fourier transform;
An amplifier circuit that amplifies the signal level of the time-series transmission data and outputs the amplified signal level to the electrical / optical conversion circuit;
An orthogonal frequency division multiplex communication apparatus comprising: an electrical / optical conversion circuit that converts a signal input from the amplifier circuit into an optical signal of each polarization channel. An orthogonal frequency division multiplex communication apparatus that transmits a data signal from a transmitter side to a receiver side via an optical transmission line,
A modulation mode determining circuit for determining a modulation scheme for each frequency channel and polarization channel according to a reception state of each frequency channel of each polarization channel on the receiver side of the transmitter;
A serial / parallel conversion circuit that performs serial / parallel conversion on the transmitted data signal and distributes the signal;
A modulation circuit that performs modulation for each frequency channel of each polarization channel based on the signal input from the serial / parallel conversion circuit, according to the modulation method determined by the modulation mode determination circuit;
An inverse Fourier transform circuit that obtains time-series transmission data by an inverse Fourier transform based on the modulation signal modulated by the modulation circuit;
An amplifier circuit that amplifies the signal level of the time-series transmission data with frequency characteristics corresponding to the reception state of each frequency channel of each polarization channel on the receiver side, and outputs the amplified signal to the electrical / optical conversion circuit; ,
An orthogonal frequency division multiplex communication apparatus comprising: an electrical / optical conversion circuit that converts a signal input from the amplifier circuit into an optical signal of each polarization channel.

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