JP5322227B2 - Optical orthogonal frequency division multiplexing communication apparatus and communication method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical orthogonal frequency division multiplexing communication device that increases communication speed as compared with a prior art. <P>SOLUTION: The optical orthogonal frequency division multiplexing communication device transmits an optical signal including a plurality of first subcarriers obtained by modulating continuous light and a plurality of second subcarriers. Multilevel modulation having a modulation level higher than the second subcarrier can be used for the first subcarrier. The maximum frequency difference between the continuous light and the plurality of first subcarriers is smaller than the minimum frequency difference between the continuous light and the plurality of second subcarriers. The plurality of first subcarriers are obtained by modulating the continuous light by a first baseband signal converted and output by a first digital/analog conversion means. The plurality of second subcarriers are obtained by modulating the continuous light by a second baseband signal converted and output by a second digital/analog conversion means. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a technology for increasing the capacity of an optical communication system using orthogonal frequency division multiplexing modulation.

  Orthogonal frequency division multiplexing (OFDM) modulation is a method of transmitting transmission data in parallel using a plurality of subcarriers. Since the symbol rate of each subcarrier is relatively low, it is resistant to intersymbol interference, and digital terrestrial broadcasting In addition, it has already been used in a wireless local area network (LAN) system, and its application to an optical communication system is also being studied.

  FIG. 7 shows the configuration of a transmission side apparatus of an optical OFDM communication system according to the prior art. The baseband processing unit in FIG. 7 maps transmission data to each subcarrier, performs discrete Fourier inverse transform processing, adds a cyclic prefix, etc., and then shows amplitudes at discrete sample points on the time axis. Outputs digital baseband signals. Since the discrete Fourier inverse transform processing normally outputs a complex value, the digital baseband signal includes a real part or in-phase component (denoted as I) signal and an imaginary part or quadrature component signal (denoted as Q). ).

  The in-phase and quadrature digital baseband signals are each converted to an analog baseband signal by a digital-to-analog converter (DAC), and used in the optical modulator to modulate continuous light generated by the light source.

  An operating band is defined in the DAC, and subcarriers for OFDM modulation are usually selected so as to be within this operating band. On the other hand, even if it is outside the DAC operating band, a configuration that uses subcarriers that are higher than the DAC operating band by utilizing the fact that the required signal-to-noise ratio can be ensured by reducing the multivalue level is cited. It is described in Document 1. As shown schematically in FIG. 8, the optical spectrum of the optical signal transmitted by the device described in the cited document 1 has a portion indicated by the reference numeral 92 within the DAC operating band and a level lower than that of the portion 92. 92 and portions 93 that are outside the operating band of the DAC. The subcarrier of the portion 93 can only be applied with a multi-level modulation lower than that of the subcarrier of the portion 92 within the DAC operating band, but the configuration described in the cited reference 1 adds the subcarrier of the portion 93. To achieve higher speed.

Brendon J.M. C. Schmidt, et al. , "100 Gbit / s Transmission using Single-Band Direct-Detection Optical OFDM", OFC / NFOEC 2009, PDPC3, 2009

  However, the configuration described in the cited document 1 uses a region where the amplitude characteristic of the DAC decreases, and in reality, the number of subcarriers that can be additionally used cannot be increased so much. In addition, it is necessary to make the applicable multilevel of modulation considerably low.

  Therefore, an object of the present invention is to provide an optical OFDM communication apparatus capable of increasing the communication speed as compared with the prior art, that is, capable of increasing the capacity.

According to the communication device of the present invention,
An optical orthogonal frequency division multiplexing communication apparatus that transmits an optical signal having a plurality of first subcarriers and a plurality of second subcarriers obtained by modulating continuous light, the first subcarrier being Can use higher-level modulation than the second subcarrier, and the maximum value of the frequency difference between the continuous light and the plurality of first subcarriers is the continuous light and the plurality of second subcarriers. The plurality of first subcarriers modulate the continuous light by a first baseband signal that is converted into an analog signal by the first digital-analog conversion means and is smaller than a minimum frequency difference with the subcarrier. The plurality of second subcarriers were obtained by modulating the continuous light with the second baseband signal converted into an analog signal by the second digital / analog conversion means and output. To be things And features.

According to another embodiment of the communication device of the present invention,
The resolution of the first digital / analog conversion means is preferably higher than the resolution of the second digital / analog conversion means.

According to another embodiment of the communication device of the present invention,
A light source that generates continuous light, a branching unit that branches the continuous light generated by the light source, a first light modulation unit that modulates continuous light from the branching unit using a first baseband signal, and a second baseband It is also preferable to include a second light modulating unit that modulates the continuous light from the branching unit with a signal, and a coupling unit that combines the first light modulating unit and the optical signal output from the second light modulating unit. .

Furthermore, according to another embodiment of the communication device of the present invention,
The first baseband signal is composed of two baseband signals, the second baseband signal is composed of two baseband signals, and the first digital-analog conversion means outputs each baseband signal. The second digital-to-analog conversion means includes two digital-to-analog converters for outputting each baseband signal, and the first light modulation means has the first base Optical quadrature amplitude modulation is performed using two baseband signals of the band signal, and the second optical modulation means performs optical quadrature amplitude modulation using the two baseband signals of the second baseband signal. Is also preferable.

Furthermore, according to another embodiment of the communication device of the present invention,
A light source that generates continuous light; an adder that adds the first baseband signal and the second baseband signal; and an optical modulator that modulates the continuous light using an output signal of the adder. preferable.

Furthermore, according to another embodiment of the communication device of the present invention,
The first baseband signal is composed of two baseband signals, the second baseband signal is composed of two baseband signals, and the first digital-analog conversion means outputs each baseband signal. The second digital-to-analog converter includes two digital-to-analog converters that output each baseband signal, and the adding means includes one of the first baseband signals. A first adder that adds one baseband signal of the second baseband signal and the second baseband signal, and the other of the first baseband signal and the other of the second baseband signal. And a second adder for adding the baseband signal, and the optical modulation means converts the optical quadrature amplitude change by the output signal of the first adder and the output signal of the second adder. It is also preferable that perform.

Furthermore, according to another embodiment of the communication device of the present invention,
It is also preferable to synchronize the symbol timing of the first baseband signal and the symbol timing of the second baseband signal.

According to the communication method of the present invention,
A first conversion step for digital-to-analog conversion of a first digital baseband signal subjected to orthogonal frequency division multiplexing modulation into a first analog baseband signal; and a second digital base subjected to orthogonal frequency division multiplexing modulation A second conversion step for digital-to-analog conversion of the band signal into a second analog baseband signal; and the continuous light is modulated with the first analog baseband signal and the second analog baseband signal and transmitted. An optical orthogonal frequency division multiplex communication method including a transmission step, wherein a plurality of first subcarriers corresponding to a first digital baseband signal are modulated by a plurality of second digital baseband signals. A multi-level higher than the multi-level of the modulation of the second sub-carrier is used, and the maximum value of the frequencies of the plurality of first sub-carriers is Wherein the smaller than the minimum value of the frequency of the second subcarrier.

According to another embodiment of the communication method according to the invention,
The operation band of the digital / analog converter used in the first conversion step is wider than the frequency band of the plurality of first subcarriers, and the operation band of the digital / analog converter used in the second conversion step is plural. It is also preferable that the frequency band is wider than the frequency band of the second subcarrier.

According to another embodiment of the communication method according to the present invention,
The transmitting step modulates the continuous light with a first analog baseband signal and outputs a first optical modulated signal; and modulates the continuous light with a second analog baseband signal. It is also preferable to include a second modulation step for outputting the second optical modulation signal and a step for combining the first optical modulation signal and the second optical modulation signal.

Furthermore, according to another embodiment of the communication method according to the present invention,
The first digital baseband signal is composed of a first in-phase digital signal and a first quadrature digital signal, and the first conversion step converts the first in-phase digital signal and the first quadrature digital signal respectively. , A first in-phase analog signal and a first quadrature analog signal, wherein the second digital baseband signal is composed of a second in-phase digital signal and a second quadrature digital signal, The conversion step converts the second in-phase digital signal and the second quadrature digital signal into a second in-phase analog signal and a second quadrature analog signal, respectively. The first modulation step includes: The in-phase analog signal and the first quadrature analog signal are used to perform quadrature amplitude modulation on the continuous light, and the second modulation step includes the second in-phase analog signal and the second quadrature analog signal. In quadrature analog signal, it is also preferable that the one in which the continuous light to quadrature amplitude modulation.

Furthermore, according to another embodiment of the communication method according to the present invention,
The transmission step includes an addition step of adding the first analog baseband signal and the second analog baseband signal to output an addition signal, and a modulation step of modulating the continuous light with the addition signal. It is also preferable.

Furthermore, according to another embodiment of the communication method according to the present invention,
The first digital baseband signal is composed of a first in-phase digital signal and a first quadrature digital signal, and the first conversion step converts the first in-phase digital signal and the first quadrature digital signal respectively. , A first in-phase analog signal and a first quadrature analog signal, wherein the second digital baseband signal is composed of a second in-phase digital signal and a second quadrature digital signal, The conversion step converts the second in-phase digital signal and the second quadrature digital signal into a second in-phase analog signal and a second quadrature analog signal, respectively, and the addition step includes the first in-phase analog signal. The first quadrature analog signal is output by adding the analog signal and any one of the second in-phase analog signal and the second quadrature analog signal to output the first sum signal. The other signal of the second in-phase analog signal and the second quadrature analog signal is added to output a second addition signal, and the modulation step is performed by the first addition signal and the second addition signal. It is also preferable that the light is subjected to quadrature amplitude modulation.

  While performing the digital / analog conversion processing within the operation band of the digital / analog conversion means, the transmission rate can be made higher than that of the prior art.

It is a block diagram of 1st Embodiment of the optical OFDM communication apparatus by this invention. It is a block diagram of 2nd Embodiment of the optical OFDM communication apparatus by this invention. It is a figure which shows the schematic optical spectrum in 1st Embodiment. It is a figure which shows the schematic optical spectrum in 2nd Embodiment. It is a figure which shows the example of the outline of a spectrum at the time of using DAC which is high resolution | decomposability with a narrow band, and the applicable modulation system. It is a figure which shows the example of the outline of a spectrum at the time of using DAC which is a wide band and low resolution, and the applicable modulation system. It is a figure which shows the structure of the transmission side apparatus of the optical OFDM communication system by a prior art. It is a figure which shows the outline of the optical spectrum of the optical signal which the apparatus of the cited reference 1 transmits.

  EMBODIMENT OF THE INVENTION The form for implementing this invention is demonstrated in detail below using drawing. FIG. 1 is a configuration diagram of a first embodiment of an optical OFDM communication apparatus according to the present invention. As shown in FIG. 1, the apparatus includes a light source 1, baseband processing units 2 and 3, digital-to-analog converters (DACs) 21, 22, 31 and 32, a branching unit 41, a coupling unit 42, Optical modulators 51 and 52 are provided.

  The light source 1 generates continuous light and outputs the continuous light to the branching unit 41. The branching unit 41 branches the continuous light and outputs the continuous light to the optical modulator 51 and the optical modulator 52, respectively. The baseband processing units 2 and 3 map transmission data to each subcarrier, perform discrete Fourier inverse transform processing, add a cyclic prefix, etc., and then indicate the amplitude at discrete sample points on the time axis Outputs digital baseband signals. Note that the time samples output by the discrete Fourier inverse transform process are complex numbers, and the baseband processing units 2 and 3 usually have a real part digital baseband signal (in-phase: expressed as I) and an imaginary part digital signal. Each baseband signal (orthogonal: Q) is output. That is, the digital baseband signal is composed of two signals of an in-phase component and a quadrature component.

  The DAC 21 converts the in-phase digital baseband signal from the baseband processing unit 2 into an in-phase analog baseband signal, and the DAC 22 converts the quadrature digital baseband signal from the baseband processing unit 2 into a quadrature analog baseband signal. The DAC 31 converts the in-phase digital baseband signal from the baseband processing unit 3 into an in-phase analog baseband signal, and the DAC 32 converts the quadrature digital baseband signal from the baseband processing unit 3 to quadrature analog・ Convert to baseband signal.

  The optical modulator 51 performs optical quadrature amplitude modulation on the continuous light input from the branching unit 41 with the in-phase analog baseband signal from the DAC 21 and the quadrature analog baseband signal from the DAC 22, and outputs an optical OFDM signal. More specifically, for example, the continuous light is bifurcated, one of the continuous lights is amplitude-modulated with the in-phase analog baseband signal from the DAC 21, and the other continuous light is orthogonal analog baseband from the DAC 22. Amplitude modulation by the signal and phase shift of π / 2 are performed, and then both optical signals are combined to output an optical OFDM signal. Similarly, the optical modulator 52 performs optical quadrature amplitude modulation on the continuous light input from the branching unit 41 with the in-phase analog baseband signal from the DAC 31 and the quadrature analog baseband signal from the DAC 32, and converts the optical OFDM signal into an optical OFDM signal. The combining unit 42 combines the optical OFDM signal from the optical modulator 51 and the optical OFDM signal from the optical modulator 52 and outputs the combined signal to the optical transmission line.

  The operating band of the DAC and the effective bit resolution are in a trade-off relationship. That is, when a DAC with a wide operating band is used, the effective bit resolution is lowered, and when a DAC with a high effective bit resolution is used, the operating band is narrowed. In general, the operating band is a frequency at which the output is reduced by 3 dB from the peak.

  5 and 6 are diagrams for explaining a difference in OFDM modulation due to a difference in DAC operation band. FIG. 5 shows a case where a DAC having a narrower operation band than that in FIG. 6 is used. It is assumed that the OFDM symbol rate is constant. When a DAC with a narrow operating band is used, as shown in FIG. 5A, the bandwidth of the OFDM signal is narrowed and the number of usable subcarriers is reduced, but the effective bit resolution is high, so The steps become finer, so that it is possible to use high multilevel modulation as shown in FIG. 5 (b). On the other hand, when a DAC with a wide operating band is used, as shown in FIG. 6A, the bandwidth of the OFDM signal is widened. Therefore, the number of subcarriers that can be used as compared with the case of FIG. Although the effective bit resolution is reduced, the step of the amplitude that can be expressed becomes coarser. Therefore, as shown in FIG. 6 (b), the low multi-level modulation is used as compared with the case of FIG. Will have to.

  In the present invention, the DAC 21 and the DAC 22 use a DAC having a narrower operating band than the DAC 31 and the DAC 32 but having a high effective bit resolution. In addition, the modulation multilevel applied to each subcarrier in the baseband processing unit 2 is set higher than the modulation multilevel applied to each subcarrier in the baseband processing unit 3. When the present invention is applied to a communication system in which the modulation multilevel can be changed in the transmission path state, the baseband processing unit 3 selects the highest modulation multilevel that can be selected by the baseband processing unit 2. Make it higher than the highest possible multi-level modulation. For example, assuming that the operating band of the DAC 21 and the DAC 23 is A (Hz) and the operating band of the DACs 31 and 32 is B (Hz) wider than A (Hz), the modulation processing in the baseband processing unit 2 starts from −a (Hz). The subcarriers in the band of a (Hz), where | a | <| A |, are modulated by a high multilevel modulation method.

  On the other hand, the modulation processing in the baseband processing unit 3 is performed from −b (Hz) to b (Hz), where subcarriers in the band | a | <| b | <| B | Modulation is performed by a modulation method having a lower multilevel than that used in the baseband processing unit 2. However, in the present embodiment, the baseband processing unit 3 uses subcarriers in the band of −b |> | c |> | a |, where −c (Hz) to c (Hz). First, subcarriers in the band from -c (Hz) to c (Hz) are always subjected to inverse discrete Fourier transform, assuming that the origin of the complex plane is input.

  Therefore, the schematic optical spectrum of the optical OFDM signal output from the optical modulator 51 is, as shown in FIG. 3A, the sideband of the band 2a (Hz) centered on the optical frequency of continuous light, And an optical carrier 81 corresponding to continuous light. The schematic optical spectrum of the optical OFDM signal output from the optical modulator 52 includes a sideband of a band 2b (Hz) centering on the optical frequency of continuous light, as shown in FIG. And an optical carrier 82 corresponding to continuous light. However, since the baseband processing unit 3 does not use subcarriers in the band from −c (Hz) to c (Hz), the signal is within the range of the band 2c centered on the optical frequency of continuous light. Does not exist. Although the optical carrier 81 and the optical carrier 82 are ideally the same signal, it is preferable to suppress one of the optical carriers in order to avoid the influence due to the difference in processing paths. The optical carrier 82 is suppressed. Therefore, the coupling unit 42 includes a sideband 71 modulated at a high multilevel, a sideband 72 modulated at a low multilevel, and an optical carrier 81, as schematically shown in FIG. The included optical signal is transmitted to the optical transmission line.

  With the above configuration, it is possible to increase the transmission rate while performing digital / analog conversion processing within the operating band of the DAC. Note that the apparatus that receives the optical signal shown in FIG. 3C facing the optical OFDM communication apparatus according to the present invention, for example, separates the sideband 71 and the sideband 72 separately after branching the received signal. Demodulate after digital conversion.

  In the embodiment described above, the unused band 2c (Hz) in the baseband processing unit 3 is made wider than the used band 2a (Hz) in the baseband processing unit 2, as shown in FIG. A guard band of | c−a | (Hz) is provided between the waveband 71 and the sideband 72. However, a synchronization signal is supplied from a synchronization signal generation unit (not shown) to the baseband processing unit 2 and the baseband processing unit 3, and symbol timings in the baseband processing unit 2 and the baseband processing unit 3, that is, symbol switching By synchronizing the positions, the guard band can be made zero. In this case, it is preferable to perform an fine adjustment of the phase timing by providing an optical phase shifter for adjusting the optical phase between the output of the optical modulator 51 or 52 and the branching unit 42.

  FIG. 2 is a configuration diagram of a second embodiment of an optical OFDM communication apparatus according to the present invention. Note that the same reference numerals are used for the same components as those in the first embodiment, and detailed description thereof is omitted. As shown in FIG. 2, the apparatus includes a light source 1, baseband processing units 2 and 3, digital-to-analog converters (DACs) 21, 22, 31 and 32, an optical modulator 5, an adder 61 and And an adder 62.

  The operating bands of the DACs 21, 22, 31, and 32 and the subcarriers used by the baseband processing units 2 and 3 in this embodiment are the same as those in the first embodiment. Therefore, the high multilevel modulation processing in the baseband processing unit 2 uses subcarriers in the band of −a (Hz) to a (Hz), and the low multilevel modulation in the baseband processing unit 3. The processing uses subcarriers excluding subcarriers in the band of -b (Hz) to b (Hz) and in the band of -c (Hz) to c (Hz). Therefore, the spectrum of the electrical signal output from the DAC 21 and the DAC 22 has a band up to a (Hz) as shown in FIG. 4A, and the spectrum of the electrical signal output from the DAC 31 and the DAC 32 is respectively As shown in FIG. 4B, it has a band from c to b (Hz).

  The adder 61 adds and outputs the in-phase analog baseband signal from the DAC 21 and the in-phase analog baseband signal from the DAC 31, and the adder 62 outputs the quadrature analog baseband signal from the DAC 22 and the quadrature from the DAC 32. Add analog baseband signals and output. Therefore, the spectrums of the electrical signals output from the adder 61 and the adder 62 are as shown in FIG.

  The optical modulator 5 is the same as the optical modulators 51 and 52, and performs optical quadrature amplitude modulation on the continuous light input from the light source 1 using the electrical signal from the adder 61 and the electrical signal from the adder 62. Outputs an optical OFDM signal. Therefore, the optical modulator 5 outputs the same signal as that of the coupling unit 42 of the first embodiment, as shown in FIG.

  With the above configuration, it is possible to increase the transmission rate while performing digital / analog conversion processing within the operating band of the DAC. As in the first embodiment, a synchronization signal is supplied from a synchronization signal generation unit (not shown) to the baseband processing unit 2 and the baseband processing unit 3, and symbol timings in the baseband processing unit 2 and the baseband processing unit 3 are set. By synchronizing, it is possible to make the guard band zero, that is, c = a. Further, the adder 61 may add the outputs of the DAC 21 and the DAC 32, and the adder 62 may add the outputs of the DAC 22 and the DAC 31.

  In the above-described embodiment, both positive and negative frequency subcarriers are used. However, for example, only a positive frequency subcarrier may be used. In this case, the spectrum of the optical signal transmitted by the optical OFDM communication apparatus according to the present invention is only the one on the higher frequency side than the optical carrier in FIGS. 3 (c) and 4 (d). Further, an unused band may be provided between the optical carrier 81 and the sideband 71. In any case, the maximum value of the frequency difference between the optical carrier 81 having the same frequency as the continuous light generated by the light source 1 and each subcarrier in the sideband 71 is the same as that in the optical carrier 81 and the sideband 72. It becomes larger than the minimum value of the frequency difference with each subcarrier. Further, the optical carrier 81 may be removed, and another optical carrier having a frequency different from that of the optical carrier 81 may be used.

  Further, in the above-described embodiment, both the baseband processing units 2 and 3 output baseband signals composed of two in-phase and quadrature signals, but only one baseband signal is output. In this case, for example, the DAC 22, the DAC 32, and the adder 62 can be omitted, and the continuous light is simply amplitude-modulated. In order to output only one baseband signal, data transmission is performed only on a positive frequency subcarrier, and data transmitted on a corresponding positive frequency subcarrier is transmitted to a negative frequency subcarrier. The inverse complex transform may be performed by inputting the conjugate complex value of the corresponding complex value.

DESCRIPTION OF SYMBOLS 1 Light source 2, 3 Baseband process part 21, 22, 31, 32 Digital-analog converter 41 Branch part 42 Coupling part 5, 51, 52 Optical modulator 61, 62 Adder 71, 72 Sideband 81, 82 Light Carrier 92, 93 Optical spectrum part

Claims (11)

An optical orthogonal frequency division multiplexing communication device that transmits an optical signal having a plurality of first subcarriers and a plurality of second subcarriers obtained by modulating continuous light,
The first subcarrier can use a higher degree of modulation than the second subcarrier,
The maximum value of the frequency difference between the continuous light and the plurality of first subcarriers is smaller than the minimum value of the frequency difference between the continuous light and the plurality of second subcarriers,
The plurality of first subcarriers are obtained by modulating the continuous light with a first baseband signal that is converted into an analog signal by the first digital-analog conversion means and output,
A plurality of second subcarriers state, and are not the second digital-to-analog converter is obtained by modulating the continuous light by the second baseband signal output into an analog signal,
The resolution of the first digital / analog conversion means is higher than the resolution of the second digital / analog conversion means,
Optical orthogonal frequency division multiplexing communication device. A light source that generates continuous light;
A branching means for branching the continuous light generated by the light source;
First light modulating means for modulating continuous light from the branching means with a first baseband signal;
Second light modulating means for modulating continuous light from the branching means with a second baseband signal;
Coupling means for coupling optical signals output from the first light modulation means and the second light modulation means;
The optical orthogonal frequency division multiplexing communication apparatus according to claim 1, comprising: The first baseband signal is composed of two baseband signals,
The second baseband signal is composed of two baseband signals,
The first digital-to-analog conversion means includes two digital-to-analog converters that output each baseband signal,
The second digital-to-analog conversion means includes two digital-to-analog converters that output each baseband signal,
The first light modulation means performs optical quadrature amplitude modulation using two baseband signals of the first baseband signal,
The second light modulation means performs optical quadrature amplitude modulation using two baseband signals of the second baseband signal.
The optical orthogonal frequency division multiplexing communication apparatus according to claim 2 . A light source that generates continuous light;
Adding means for adding the first baseband signal and the second baseband signal;
Light modulating means for modulating the continuous light by the output signal of the adding means;
The optical orthogonal frequency division multiplexing communication apparatus according to claim 1, comprising: The first baseband signal is composed of two baseband signals,
The second baseband signal is composed of two baseband signals,
The first digital-to-analog conversion means includes two digital-to-analog converters that output each baseband signal,
The second digital-to-analog conversion means includes two digital-to-analog converters that output each baseband signal,
The adding means includes a first adder for adding one baseband signal of the first baseband signal and one baseband signal of the second baseband signal, and the other base of the first baseband signal. A second adder for adding the band signal and the other baseband signal of the second baseband signal;
The optical modulation means performs optical quadrature amplitude modulation using the output signal of the first adder and the output signal of the second adder.
The optical orthogonal frequency division multiplex communication apparatus according to claim 4 . Synchronizing the symbol timing of the first baseband signal and the symbol timing of the second baseband signal;
The optical orthogonal frequency division multiplexing communication apparatus according to any one of claims 1 to 5. A first conversion step of digital-to-analog conversion of the first digital baseband signal subjected to orthogonal frequency division multiplexing modulation into a first analog baseband signal;
A second conversion step of digital-to-analog conversion of the second digital baseband signal subjected to orthogonal frequency division multiplexing modulation into a second analog baseband signal;
A transmission step of modulating and transmitting continuous light with a first analog baseband signal and a second analog baseband signal;
An optical orthogonal frequency division multiplex communication method including:
The modulation of the plurality of first subcarriers corresponding to the first digital baseband signal has a higher multi-level than the modulation of the plurality of second subcarriers corresponding to the second digital baseband signal. Use value degree,
Maximum value of the frequency of the plurality of first sub-carriers, rather smaller than the minimum value of the frequency of the plurality of second sub-carrier,
The operation band of the digital / analog converter used in the first conversion step is wider than the frequency band of the plurality of first subcarriers, and the operation band of the digital / analog converter used in the second conversion step is plural. Wider than the frequency band of the second subcarrier of
Communication method. The sending step is
A first modulation step of modulating the continuous light with a first analog baseband signal and outputting a first light modulation signal;
A second modulation step of modulating the continuous light with a second analog baseband signal and outputting a second light modulation signal;
Combining the first light modulation signal and the second light modulation signal;
The communication method according to claim 7 , further comprising: The first digital baseband signal is composed of a first in-phase digital signal and a first quadrature digital signal, and the first conversion step converts the first in-phase digital signal and the first quadrature digital signal respectively. , Converting to a first in-phase analog signal and a first quadrature analog signal,
The second digital baseband signal is composed of a second in-phase digital signal and a second quadrature digital signal, and the second conversion step converts the second in-phase digital signal and the second quadrature digital signal, respectively. , To convert to a second in-phase analog signal and a second quadrature analog signal,
The first modulation step is to perform quadrature amplitude modulation of the continuous light with a first in-phase analog signal and a first quadrature analog signal,
In the second modulation step, the continuous light is subjected to quadrature amplitude modulation with a second in-phase analog signal and a second quadrature analog signal.
The communication method according to claim 8 . The sending step is
An adding step of adding the first analog baseband signal and the second analog baseband signal to output an added signal;
A modulation step of modulating the continuous light with an addition signal;
The communication method according to claim 7 , further comprising: The first digital baseband signal is composed of a first in-phase digital signal and a first quadrature digital signal, and the first conversion step converts the first in-phase digital signal and the first quadrature digital signal respectively. , Converting to a first in-phase analog signal and a first quadrature analog signal,
The second digital baseband signal is composed of a second in-phase digital signal and a second quadrature digital signal, and the second conversion step converts the second in-phase digital signal and the second quadrature digital signal, respectively. , To convert to a second in-phase analog signal and a second quadrature analog signal,
In the adding step, the first in-phase analog signal, one of the second in-phase analog signal and the second quadrature analog signal are added to output a first sum signal, and the first quadrature analog signal And adding the other signal of the second in-phase analog signal and the second quadrature analog signal to output a second addition signal,
The modulation step is to perform quadrature amplitude modulation on the continuous light with the first addition signal and the second addition signal.
The communication method according to claim 1 0.

Images