JP2012085059A - Optical signal generation device and generation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical signal generation device and method, in an OFDM modulated optical signal, capable of generating an optical signal which will not deteriorate a neighboring subcarrier even when one subcarrier is removed.SOLUTION: The optical signal generation device separates input data into parallel data for demodulation and generates a symbol data sequence. Even channels and odd channels in the symbol data sequence are converted by reverse fast Fourier transformation, and band limitation of the frequency widths of signals of the converted even channels and odd channels are implemented, and signals of the even channels and the odd channels are combined.

Description

  The present invention relates to an optical signal generation apparatus and generation method for orthogonal frequency division multiplexing (OFDM) modulation, and more particularly, to an optical signal for orthogonal frequency division multiplexing modulation suitable for use in an optical add / drop multiplexer (OADM). The present invention relates to a signal generation device and a generation method.

  OFDM modulation is a method of transmitting transmission data in parallel using a plurality of subcarriers (Non-Patent Document 1), and is resistant to intersymbol interference because the symbol rate of each subcarrier is relatively low. It is already used in broadcasting and wireless LAN (Local Area Network) systems, and its application to optical communication systems is also being studied.

  FIG. 1 shows an outline of an optical signal generation apparatus using OFDM modulation. Input data is first separated into N pieces of parallel data within the subcarrier mapping, and each is modulated by QPSK, 8-QAM, etc., to generate a symbol data string. This symbol data string is converted by inverse fast Fourier transform (IFFT), and sample values of N OFDM symbols are generated. The obtained sample values are converted in series, and then converted into a continuous signal by D / A conversion to generate a complex baseband OFDM signal. The optical modulator modulates the continuous light output from the light source with the real part of the complex baseband OFDM signal to generate optical OFDM signal light.

  FIG. 2 shows the frequency characteristics of the OFDM signal. In OFDM modulation, data is transmitted on a number of subcarriers. The frequency interval between the subcarriers is 1 / T (T: symbol length), and the subcarriers have overlapping bands on the frequency axis. However, by utilizing the orthogonal relationship between subcarriers, it is possible to correctly extract data symbols for modulating subcarriers.

  FIG. 3 shows through and drop of a WDM (Wavelength Division Multiplexing) signal in the optical add / drop multiplexer. The optical add / drop device passes or drops a WDM signal from an optical signal obtained by multiplexing WDM signals independently generated by a plurality of transmitters by a multiplexer.

Makoto Itami, “Intuitive OFDM Technology”, Ohmsha, 2005

  However, in the case of a plurality of OFDM-modulated subcarriers, as shown in FIG. 2, the subcarriers have mutually overlapping bands on the frequency axis. Therefore, as shown in FIG. 4, when one subcarrier is removed by the optical add / drop multiplexer, due to the characteristics of the optical filter of the optical add / drop multiplexer, a part of the band of the subcarrier adjacent to the subcarrier to be removed is also simultaneously It will be removed. Therefore, there arises a problem that adjacent subcarriers deteriorate.

  Accordingly, an object of the present invention is to provide an optical signal generation apparatus and a generation method for generating an optical signal in which adjacent subcarriers are not degraded even when one subcarrier is removed from an OFDM modulated optical signal. .

  In order to achieve the above object, an optical signal generation apparatus according to the present invention divides input data into parallel data and modulates it, generates a symbol data string, and divides the symbol data string into a plurality of parts. First conversion means for converting the symbol data string by inverse fast Fourier transform, means for band-limiting the frequency widths of the plurality of signals converted by the first conversion means, and the plurality of band-limited Means for multiplexing the individual signals.

  In order to achieve the above object, an optical signal generation apparatus according to the present invention separates and modulates input data into parallel data to generate a symbol data string, and reverses the even channel and odd channel of the symbol data string. A first transforming means for transforming by Fourier transform; a means for band-limiting the frequency widths of the even channel and odd channel signals converted by the first transforming means; and the band-limited even channel and odd channel. Means for multiplexing the signals.

  In order to achieve the above object, an optical signal generation device according to the present invention divides input data into parallel data and modulates it to generate a symbol data string, and divides the symbol data string into subcarriers. A first conversion means for converting the symbol data sequence obtained by inverse fast Fourier transform, a means for band-limiting the frequency width of the number of subcarriers converted by the first conversion means, and the band Means for multiplexing signals for the limited number of subcarriers.

  The band limiting means preferably limits the frequency width of the signal of the outermost subcarrier to ½.

  In order to achieve the above object, an optical signal generation device according to the present invention divides input data into parallel data and modulates it to generate a symbol data string, and divides the symbol data string into subcarriers. A first conversion means for converting the converted symbol data string by inverse fast Fourier transform, and the signals converted by the first conversion means are divided into a first group and a second group, Means for band-limiting the frequency width of the signal, and means for multiplexing the band-limited first group signal and second group signal.

  The first group is preferably an outermost subcarrier signal.

  The band limiting unit includes a second conversion unit that converts a plurality of signals converted by the first conversion unit by a fast Fourier transform, and a plurality of signals converted by the second conversion unit. It is also preferable to include means for band limiting the frequency width of the signal and third conversion means for converting the plurality of band limited signals by inverse fast Fourier transform.

  Further, the band limiting means preferably limits the frequency width of the signal to ½.

  To achieve the above object, an optical signal generation method according to the present invention includes a step of separating input data into parallel data and modulating the data to generate a symbol data string, and dividing the symbol data string into a plurality of parts. A first conversion step of converting the symbol data string by inverse fast Fourier transform; a step of band-limiting the frequency widths of the plurality of signals converted in the first conversion step; Combining the plurality of signals.

  The present invention provides an optical signal that does not deteriorate adjacent subcarriers even if one subcarrier is removed by an optical add / drop multiplexer. Furthermore, an optical signal that reduces interference with an adjacent WDM channel in WDM communication and an optical signal that can combine signals of different symbol lengths are also provided.

1 shows an outline of an optical signal generation apparatus using OFDM modulation. The frequency characteristic of an OFDM signal is shown. The through and drop of the WDM signal in the optical add / drop multiplexer are shown. The drop in the optical add / drop multiplexer of the OFDM-modulated subcarrier is shown. 1 shows an overview of an optical signal generation device according to a first embodiment of the present invention. The signal on the frequency axis of the odd-numbered channel and the even-numbered channel after IFFT is shown. The frequency-axis signals of the odd-numbered channel and the even-numbered channel that are band-limited by the time-axis filter are shown. The signal on the frequency axis of the combined signal is shown. The drop in the optical add / drop multiplexer of the subcarrier in the optical signal produced | generated by the optical signal production | generation apparatus of this invention is shown. The outline | summary of the optical signal generation apparatus of the 2nd Embodiment of this invention is shown. The frequency axis signals of a signal A modulated with a symbol length T and a signal B modulated with a symbol length 2T are shown. The signal which remove | eliminated two subcarriers from the signal output from the optical signal generation apparatus of this invention is shown. The signal which inserted the subcarrier of the signal B in the vacant frequency band is shown. The outline | summary of the optical signal generation apparatus of the 3rd Embodiment of this invention is shown. The outline | summary of the optical signal generation apparatus of the 4th Embodiment of this invention is shown. The state where the subcarrier outside the adjacent WDM channel interferes is shown. Only the outer subcarriers are band-limited signals. The state where the subcarrier outside the adjacent WDM channel is not interfering is shown.

  The best mode for carrying out the present invention will be described in detail below with reference to the drawings. FIG. 5 shows an outline of the optical signal generation device according to the first embodiment of the present invention. The optical signal generation device 1 includes a subcarrier mapping 11, two IFFTs 12 (inverse fast Fourier transform), two time axis filters 13, a multiplexer 14, a DA converter 15, and an optical modulator 16.

  The subcarrier mapping 11 divides input data into N pieces of parallel data and modulates each of the input data with QPSK, 8-QAM, etc. to generate a symbol data string. The symbol data string is separated into odd-numbered channels and even-numbered channels and output to the upper IFFT 12 and the lower IFFT 12, respectively.

  IFFT 12 converts the odd-numbered channel and the even-numbered channel of the symbol data string from a signal on the frequency axis to a signal on the time axis, respectively. FIG. 6 shows signals on the frequency axis of the odd channel and the even channel after IFFT. FIG. 6A shows an odd channel signal, and FIG. 6B shows an even channel signal. Each channel has a subcarrier frequency width of 2 / T.

  Next, the band limitation of the channel is performed by the time axis filter 13. In the case of a signal sampled with a symbol length T, the subcarrier frequency width can be band limited to 1 / T without loss of information according to the sampling theorem. Therefore, the time axis filter 13 limits the input subcarrier frequency width to half. FIG. 7 shows the frequency axis signals of the odd-numbered channel and the even-numbered channel subjected to band limitation by the time-axis filter. FIG. 7A shows an odd channel signal, and FIG. 7B shows an even channel signal. Each channel has a subcarrier frequency width of 1 / T. Note that an FIR filter and an IIR filter can be used as the time axis filter 13.

  Next, the odd channel and even channel signal data output from the two time axis filters 13 are combined by the multiplexer 14. After this signal data is converted into serial data, the DA converter 15 converts it into a continuous signal to generate a complex baseband OFDM signal. The optical modulator 16 modulates the continuous light input from the light source with the real part of the complex baseband OFDM signal to generate optical OFDM signal light.

  FIG. 8 shows a signal on the frequency axis of the combined signal. Since the frequency is limited by the filter, the interval between the subcarriers is 1 / T, and the subcarriers have no overlapping bands on the frequency axis.

  FIG. 9 shows a drop of the subcarrier in the optical add / drop multiplexer in the optical signal generated by the optical signal generator of the present invention. Since the subcarrier bands of this optical signal do not overlap, as shown in FIG. 9, even if one subcarrier is removed by the optical add / drop multiplexer, the subcarrier bands adjacent to the subcarrier to be removed are simultaneously removed. There is nothing. Therefore, the adjacent subcarrier does not deteriorate.

  FIG. 10 shows an outline of an optical signal generation apparatus according to the second embodiment of the present invention. The optical signal generation apparatus 1 includes a subcarrier mapping 11, two IFFTs 12 (inverse fast Fourier transform), two FFTs 17 (fast Fourier transforms), two frequency axis filters 18, two IFFTs 19, and a multiplexer 14, DA It is composed of a converter 15 and an optical modulator 16.

  As in the first embodiment, the subcarrier mapping 11 divides input data into N pieces of parallel data, and modulates each of the input data with QPSK, 8-QAM, or the like to generate a symbol data string. The symbol data string is separated into odd-numbered channels and even-numbered channels and output to the upper IFFT 12 and the lower IFFT 12, respectively.

  IFFT 12 converts the odd-numbered channel and the even-numbered channel of the symbol data string from a signal on the frequency axis to a signal on the time axis, respectively. Next, the FFT 17 returns the symbol data strings of the odd-numbered channel and the even-numbered channel from the signal on the time axis to the signal on the frequency axis. The signals on the frequency axes of the odd-numbered channel and the even-numbered channel returned by the FFT 17 are the same as those in the first embodiment and are shown in FIG.

  Next, the frequency axis filter 18 limits the frequency of the channel. As in the case of the first embodiment, the frequency axis filter 18 limits the input subcarrier frequency width to half. The odd-numbered channel and even-numbered-channel frequency-axis signals subjected to frequency restriction by the frequency-axis filter 18 are the same as those in the first embodiment and are shown in FIG.

  Next, the IFFT 19 converts the signal on the frequency axis into the signal on the time axis again, and the multiplexer 14 multiplexes the signal data of the odd and even channels. After this signal data is converted into serial data, the DA converter 15 converts it into a continuous signal to generate a complex baseband OFDM signal. The optical modulator 16 modulates the continuous light input from the light source with the real part of the complex baseband OFDM signal to generate optical OFDM signal light.

  Also in the case of the second embodiment, the signal on the frequency axis of the combined signal is a signal as shown in FIG. 8, and the subcarriers have no overlapping bands on the frequency axis. Therefore, as in the first embodiment, as shown in FIG. 9, it is possible to remove one subcarrier by the optical add / drop multiplexer without deteriorating adjacent subcarriers.

  The application example of the 1st Embodiment of this invention and the 2nd optical signal generation apparatus is shown. Signals modulated with different symbol lengths cannot be combined because the subcarrier frequency interval is different. FIG. 11 shows signals on the frequency axis of a signal A modulated with a symbol length T and a signal B modulated with a symbol length 2T. The subcarrier frequency interval of signal A is 1 / T, and the subcarrier frequency interval of signal B is 1 / 2T, and cannot be multiplexed as it is.

  However, when the signal A is output from the optical signal generation apparatus of the present invention, the subcarrier frequency interval of the signal A is 1 / 2T. FIG. 12 shows a signal obtained by removing two subcarriers from this signal by an optical add / drop multiplexer. A subcarrier from which a portion surrounded by a dotted line is removed is shown. In this case, as shown in FIG. 13, the subcarrier of signal B can be inserted into the free frequency band and multiplexed. This is the subcarrier of signal B in which the two subcarriers in FIG. 13 are inserted.

  FIG. 14 shows an outline of an optical signal generation device according to the third embodiment of the present invention. The optical signal generation device 1 includes a subcarrier mapping 11, a plurality of IFFTs 12, a plurality of time axis filters 13, a multiplexer 14, a DA converter 15, and an optical modulator 16. The number of IFFTs 12 and time axis filters 13 is the same as the number of subcarriers.

  The basic operation of this embodiment is the same as that of the first embodiment, but the symbol data sequence output from the subcarrier mapping 11 is output for each subcarrier (4 in FIG. 14). Further, the limit width of the time axis filter 13 can give different band limits for each subcarrier. That is, since the time axis filter 13 does not limit the band, it can be variably performed until the band is limited to half.

  FIG. 15 shows an outline of an optical signal generation device according to the fourth embodiment of the present invention. The optical signal generation device 1 includes a subcarrier mapping 11, a plurality of IFFTs 12, a plurality of time axis filters 13, a multiplexer 14, a DA converter 15, and an optical modulator 16. Note that the number of IFFTs 12 is the same as the number of subcarriers. However, the number of time axis filters 13 is smaller than the number of subcarriers.

  In the case of this embodiment, the subcarriers are band-limited (top and bottom in FIG. 15) and non-band-limited groups (two in FIG. 15) and are not band-limited. In the configuration, the time axis filter 13 is not set. In the case of this configuration, the time axis filter 13 can be reduced.

  In the third embodiment and the fourth embodiment, the time axis filter 13 can be replaced with the FFT 17, the frequency axis filter 18, and the IFFT 19 as in the second embodiment.

  The application example of the optical signal generation apparatus of the 3rd Embodiment and 4th Embodiment of this invention is shown. In wavelength division multiplexing (WDM) communication, interference with adjacent WDM channels can be reduced by using this optical signal generation device.

  Since adjacent WDM channels do not have an orthogonal relationship, interference occurs when bands overlap. FIG. 16 shows a state where subcarriers outside the adjacent WDM channel interfere with each other. In order to reduce this interference, only the outer subcarrier is band-limited using the optical signal generation apparatus of the present invention. FIG. 17 shows a signal in which only the outer subcarrier is band-limited. In this case, as shown in FIG. 18, the adjacent WDM channel does not overlap the band, and interference is reduced.

  Moreover, all the embodiments described above are illustrative of the present invention and are not intended to limit the present invention, and the present invention can be implemented in other various modifications and changes. Therefore, the scope of the present invention is defined only by the claims and their equivalents.

1 Optical signal generator 11 Subcarrier mapping 12 IFFT
13 Time axis filter 14 Multiplexer 15 DA converter 16 Optical modulator 17 FFT
18 Frequency axis filter 19 IFFT

Claims (9)

Means for separating and modulating input data into parallel data and generating a symbol data sequence;
A first converting means for dividing the symbol data string into a plurality of parts, and transforming the divided symbol data string by inverse fast Fourier transform;
Means for band-limiting the frequency widths of the plurality of signals converted by the first conversion means;
Means for multiplexing the plurality of band-limited signals;
An optical signal generation device comprising: Means for separating and modulating input data into parallel data and generating a symbol data sequence;
First conversion means for converting the even channel and the odd channel of the symbol data string by inverse fast Fourier transform;
Means for band-limiting the frequency widths of the even channel and odd channel signals converted by the first conversion unit;
Means for combining the band-limited even channel and odd channel signals;
An optical signal generation device comprising: Means for separating and modulating input data into parallel data and generating a symbol data sequence;
Dividing the symbol data string into subcarriers, and converting the divided symbol data string by inverse fast Fourier transform;
Means for band limiting the frequency width of the signal for the number of subcarriers converted by the first conversion means;
Means for multiplexing signals corresponding to the number of subcarriers limited in bandwidth;
An optical signal generation device comprising:   4. The optical signal generation apparatus according to claim 3, wherein the band limiting unit limits the frequency width of the signal of the outermost subcarrier to ½. Means for separating and modulating input data into parallel data and generating a symbol data sequence;
Dividing the symbol data string into subcarriers, and converting the divided symbol data string by inverse fast Fourier transform;
Means for dividing the signals converted by the first conversion means into a first group and a second group, and band-limiting the frequency width of the signals of the first group;
Means for combining the band-limited first group of signals and the second group of signals;
An optical signal generation device comprising:   The optical signal generation apparatus according to claim 5, wherein the first group is an outermost subcarrier signal. The band limiting means includes
Second conversion means for converting a plurality of signals converted by the first conversion means by fast Fourier transform;
Means for band-limiting the frequency widths of the plurality of signals converted by the second conversion means;
The optical signal generation device according to claim 1, further comprising: a third conversion unit configured to convert the plurality of band-limited signals by inverse fast Fourier transform. .   The optical signal generation apparatus according to claim 1, wherein the band limiting unit limits a frequency width of the signal to ½. Separating input data into parallel data and modulating them to generate a symbol data sequence;
A first conversion step of dividing the symbol data string into a plurality of parts, and transforming the divided symbol data string by an inverse fast Fourier transform;
Band-limiting the frequency widths of the plurality of signals converted in the first conversion step;
Combining the plurality of band-limited signals;
An optical signal generation method comprising:

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