JP4908483B2 - Signal transmitting apparatus and signal transmitting method - Google Patents

Description

  The present invention relates to a signal transmission apparatus and signal transmission method for a single carrier signal.

Conventionally, in a wireless transmission device in a communication system using a single carrier, a broadband signal is modulated and transmitted as it is (see, for example, Non-Patent Document 1).
D. Falconer, SL Ariyavisitakul, A. Benyamin-Seeyar, and B. Eidson, “Frequency domain equalization for single-carrier broadband wireless systems,” IEEE Commun. Mag., Vol. 40, no. 4, pp. 58-66 , Apr. 2002.

In recent years, it has been studied to use a single carrier in broadband transmission such as optical communication.
However, since the signal processing is performed collectively in the conventional technology, the processing speed of the modulation circuit, inverse Fourier transform, GI (guard interval) insertion circuit, D / A (digital / analog) converter, frequency conversion circuit The data rate was limited by the operating speed, and it was not possible to perform processing faster than that in real time.
Therefore, it is conceivable to divide the transmission band into a plurality of channels and generate a modulation signal using a plurality of fast Fourier transformers and inverse fast Fourier transformers. Interference with other channels will occur, leading to degradation of transmission quality. Further, in order to avoid interference, it is necessary to sufficiently separate the channel frequency intervals, and the frequency utilization efficiency is lowered.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a signal transmission apparatus and method capable of high-speed broadband transmission in real time using a single carrier.

The signal transmission device of the present invention includes a multi-wavelength light source, an optical demultiplexing unit that demultiplexes a plurality of optical carriers output from the multi-wavelength light source into a set wavelength band, and each of which receives an input serial signal. A plurality of single carrier signal generation units that convert a plurality of parallel signals corresponding to the channels and output a combined signal obtained by synthesizing the signals of the respective channels; and a corresponding single carrier signal generation unit provided for each wavelength band. A plurality of optical modulators that modulate the light in the wavelength band with the combined signal and output as optical signals, and an optical multiplexing unit that combines the optical signals modulated by the optical modulators corresponding to the wavelength bands possess the door, the single-carrier signal generating unit includes a serial-parallel converter for converting an input signal into a plurality of parallel signals, each corresponding to the channel, the plurality of parallel signals On the other hand, a plurality of processing units that generate signals of channels corresponding to itself, and a combining unit that generates signals by combining the signals of the respective channels generated by the plurality of processing units, Each processing unit modulates each parallel signal into a channel corresponding to itself, a Fourier transform unit that performs a Fourier transform on the signal modulated by the input signal modulation unit, and a Fourier transform by the Fourier transform unit A zero insertion unit that inserts a frequency component of 0 into a frequency outside the band necessary for signal transmission, or a filtering unit that superimposes a transfer function of a band limitation filter, , The inverse frequency transform that performs inverse Fourier transform on the signal in which the zero frequency component is inserted by the zero insertion unit or the signal on which the transfer function of the band limiting filter is superimposed. A Rie transform unit, a digital / analog conversion unit that converts a signal subjected to inverse Fourier transform by the inverse Fourier transform unit into an analog signal synchronized with other processing units, and an analog signal converted by the digital / analog conversion unit A frequency conversion unit that converts the frequency of the signal so that the center frequency of the frequency band of the signal is the center frequency of the frequency band of the channel corresponding to the processing unit, and the signal frequency-converted by the frequency conversion unit A band pass filter that extracts a signal in a frequency band used by a channel corresponding to the processing unit, and the synthesizing unit generates the signal by synthesizing the signals extracted by the band pass filter. It is characterized by.

  The signal transmission device according to the present invention is characterized in that each of the plurality of processing units further includes a guard interval insertion unit that inserts a guard interval into a signal that has been subjected to inverse Fourier transform by the inverse Fourier transform unit.

  The signal transmission device according to the present invention is characterized in that each of the plurality of processing units further includes a smoothing unit that performs a smoothing process at a joint between Fourier transform blocks of the signal in which the guard interval is inserted by the guard interval insertion unit. To do.

  In the signal transmission device of the present invention, the optical modulator is an intensity modulator.

  The signal transmission apparatus according to the present invention is characterized in that the optical modulator is an optical quadrature modulator.

The signal transmission method of the present invention is a signal transmission method by a signal transmission device that transmits a single carrier signal, and a process in which a multi-wavelength light source outputs a plurality of optical carriers, and an optical demultiplexing unit is output from the multi-wavelength light source. The optical demultiplexing process of demultiplexing a plurality of optical carriers into a set wavelength band, and each of a plurality of single carrier signal generation units converts an input serial signal into a parallel signal corresponding to a channel, and a combined signal And a single-carrier signal generation process, and an optical modulator is provided for each wavelength band, and the optical signal is modulated by the optical modulator using the combined signal from the corresponding single-carrier signal generation unit. a light modulation step of outputting as, optical multiplexing unit possess an optical multiplexing step of multiplexing the optical signal the modulated for each light modulator corresponding to each of the wavelength bands, the The single carrier signal generation process includes a serial / parallel conversion process in which the serial / parallel conversion unit converts an input signal into a plurality of parallel signals, and each of the plurality of processing units corresponds to a channel. a plurality of process for generating the signal of the corresponding channel to the combining unit is closed and a synthetic process of generating a synthesized to signal a signal of each channel generated by said plurality of processing units, said plurality of Each processing process includes an input signal modulation process in which the input signal modulation unit modulates each parallel signal into a channel corresponding to itself, and a Fourier transform process in which the Fourier transform unit performs a Fourier transform on the signal modulated by the input signal modulation process. And the zero insertion unit performs band limitation of the signal on which the Fourier transform is performed by the Fourier transform unit, for signal transmission. A zero insertion process for inserting a zero frequency component into a frequency outside the required band, or a filtering process in which the filtering unit superimposes the transfer function of the band limiting filter, and the inverse Fourier transform unit generates a zero frequency component by the zero insertion unit. An inverse Fourier transform process for performing an inverse Fourier transform on the inserted signal or a signal on which a transfer function of a band limiting filter is superimposed, and a signal obtained by performing an inverse Fourier transform on the digital analog converter by the inverse Fourier transform unit, A digital-analog conversion process for converting into an analog signal synchronized with another processing unit, and a signal whose frequency conversion unit has converted into an analog signal by the digital-analog conversion unit, the center frequency of the frequency band of the signal is the processing unit Frequency conversion process to convert the frequency to the center frequency of the frequency band of the channel corresponding to
And a band-pass filter process for extracting a signal in a frequency band used by a channel corresponding to the processing unit from a signal whose frequency is converted by the frequency conversion unit. The unit synthesizes the signals extracted by the bandpass filter to generate the signal .

  As described above, by inserting a frequency component of 0 to a frequency outside the frequency band of the signal subjected to Fourier transform, a steep bandpass filter that is difficult to realize with only a conventional analog filter is realized, and the channel Interference from the outside of the band divided every time can be removed, and real-time and high-quality broadband transmission can be realized by frequency-converting and synthesizing each channel from which this interference has been removed. Moreover, since zero insertion, guard interval insertion, and smoothing processing are performed in parallel for each channel, it is possible to operate with a slow clock.

Further, according to the present invention, according to the present invention, as a further effect of using a multi-wavelength light source, a plurality of wavelength bands can be used, and a single carrier signal generation unit is provided for each wavelength band. Corresponding to this, it is possible to increase the bandwidth for transmitting single carrier light, increase the transmission capacity of the optical fiber, and enable real-time and high-quality broadband transmission.
In addition, according to the present invention, since light of a plurality of wavelength bands is generated from the same multi-wavelength light source, it is possible to easily match the phases of the optical signals without overlapping the bands of the optical signals. Thus, high-quality broadband transmission can be realized.

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

<First Embodiment>
FIG. 1 is a block diagram showing a configuration of a signal transmission apparatus according to the first embodiment of the present invention. In the figure, a signal transmission apparatus includes a signal generation circuit 100 that modulates binary data into an output signal of a wideband frequency, a multiwavelength light source 101 that generates a plurality of optical carriers at fixed frequency intervals, and a multiwavelength light source 101. An optical demultiplexer 102 that demultiplexes the emitted optical carrier of wavelength λi (i = 1 to n) for each wavelength band, and a single carrier signal that is an electrical signal corresponding to optical carrier λi, to optical carrier λi. The optical modulator 103-i (i = 1 to n) that superimposes and outputs an optical signal and the optical path length difference between the single carrier signals modulated by the optical modulators 103-i (i = 1 to n) are corrected. The phase adjustment unit 104-i (i = 1 to n) and the optical multiplexing unit 105 that multiplexes the optical signals whose optical path length difference is corrected by each phase adjustment unit 104-i. The signal generation circuit 100 includes single carrier signal generation circuits 100-i (i = 1 to n) corresponding to the optical modulators 103-i (i = 1 to n).

  The optical carrier group generated by the multi-wavelength light source 101 is synchronized with high accuracy in each phase, and after being demultiplexed and modulated to each frequency, the phase of each carrier is highly accurate even after being combined. Since synchronization is maintained, the phase noise between blocks is low, and a broadband single carrier signal can be generated. Conventionally, in order to synthesize a high-speed single carrier signal due to factors such as the operation speed of a single carrier signal generation circuit (single carrier signal generation unit), a D / A (digital / analog) converter, and the operating speed of an amplifier. It was necessary to increase the number of light carriers generated by a multi-wavelength light source. In this embodiment, since the single carrier signal generation circuit 100-i performs multiplexing by an electric circuit, the number of wavelengths generated by a multi-wavelength light source can be suppressed as compared with the prior art, and the S / N ratio of the transmission single carrier signal is good. Can be made.

  Below, the structural example of the multiwavelength light source 101 is demonstrated. The multi-wavelength light source 101 can be configured as shown in (1) to (5) below.

(1) Configuration using an intensity modulator;
A Mach-Zehnder type optical modulator is used as the multi-wavelength light source 101, and sine wave drive is performed with a minimum bias point. An optical carrier s output from the Mach-Zehnder type modulator, where fc is the frequency of light output from the light source and input to the Mach-Zehnder type optical modulator, and Δf is the frequency of the sine wave that drives the Mach-Zehnder type modulator. (T) is like an optical signal in the wavelength band shown in the following equation. That is, the light with the frequency fc output from the light source is modulated into sidebands fc + Δf and fc−Δf around the frequency fc.
s (t) = cos (2πfct) × cos (2πΔft)
= Cos (2π (fc + Δf) t) + cos (2π (fc−Δf) t)

(2) Configuration using a phase modulator;
A light phase modulator is used as the multi-wavelength light source 101, and the phase modulator is driven in a sine wave. When the frequency of the light source is fc and the driving frequency of the phase modulator is Δf, the phase modulator can generate three carriers of frequencies fc, fc + Δf, and fc−Δf. Also, by changing the modulation index (in the phase modulation, the ratio between the modulation frequency and the frequency deviation (input frequency)), n optical carriers can be generated around the frequency fc.

(3) Configuration using an intensity modulator and a phase modulator;
FIG. 2 shows an example in which the multi-wavelength light source 101 is configured using an intensity modulator and a phase modulator. In the figure, an intensity modulator (IM) 12 such as an optical Mach-Zehnder optical modulator is driven by a sine wave having a frequency Δf, and modulates light from a light source 11 to generate two optical carriers. The phase modulator (PM) 13 phase-modulates the two optical carriers output from the intensity modulator 12 with the frequency Δf, and generates three carriers from each optical carrier. As shown in (2), by adjusting the modulation index, n optical carriers can be generated around the frequency fc.

(4) Configuration using highly nonlinear fiber;
FIG. 3 shows an example in which the multi-wavelength light source 101 is configured using a highly nonlinear fiber. In the figure, an optical carrier from a mode-locked laser 16 that oscillates simultaneously at a plurality of wavelengths is amplified by an optical amplifier 17 to generate self-phase modulation that is a nonlinear optical effect in a highly nonlinear fiber 18. Then, more light carriers are generated using the light of a plurality of wavelengths output from the mode-locked laser 16 as seed light.

(5) Configuration using a phase modulator and a dispersion medium;
FIG. 4 shows an example in which the multi-wavelength light source 101 is composed of a phase modulator and a dispersion medium.
In the figure, a phase modulator 22 performs phase modulation on an optical carrier from a light source 21 by a sine wave having a frequency Δf, and a dispersion adding unit 23 disperses the optical carrier output from the phase modulator 22 by a dispersion medium. In addition, the phase modulator 25 modulates the optical carrier output from the dispersion adding unit 23 with the sine wave of the frequency Δf whose phase is adjusted by the phase shifter 24.

Next, the configuration of the single carrier signal generation circuit 100-i (i = 1 to n) shown in FIG. 1 will be described with reference to FIG. In the following description, the multi-wavelength light source 101 has the configuration (3) described above.
In FIG. 5, an S / P (serial parallel) conversion circuit 110 converts a binary data input signal input to each single carrier signal generation circuit 100-i in the signal generation circuit 100 into a parallel signal, and converts the modulation circuit 111. Output to -k (k = 1 to m).

  Each of the modulation circuits 111-k (k = 1 to m) corresponds to a channel of a single carrier signal, and modulates a signal input from the S / P conversion circuit 110 for each channel by a predetermined modulation method. Note that each of the modulation circuits 111-k (k = 1 to m) corresponds to a channel of a single carrier signal, and a signal input from the S / P conversion circuit 110 is converted into a channel by a predetermined single carrier modulation method. Modulate every time. Hereinafter, the channels corresponding to the respective modulation circuits 111-k are referred to as channels k.

The Fourier transform circuit 112-k (k = 1 to m) performs Fourier transform on the signal modulated by the modulation circuit 111-k. The 0 insertion circuit 113-k (k = 1 to m) has a frequency of “0” in a frequency band outside the signal transmission frequency band of the signal subjected to Fourier transform by the Fourier transform circuit 112-k (k = 1 to m). Insert ingredients. The 0 insertion circuit 113-k (k = 1 to m) is a frequency band outside the signal transmission frequency band of the signal subjected to the Fourier transform by the Fourier transform circuit 112-k (k = 1 to m). The frequency component of “0” is inserted into the frequency band adjacent to the signal transmission frequency band.
Further, by using a band limiting filter such as a root Nyquist filter instead of the 0 insertion circuit 113-k (k = 1 to m), interference between adjacent channels can be reduced.

  The inverse Fourier transform circuit 114-k (k = 1 to m) performs inverse Fourier transform on the signal in which the zero frequency component is inserted by the zero insertion circuit 113-k. The GI (guard interval) insertion circuit 115-k (k = 1 to m) inserts a guard interval into the signal subjected to inverse Fourier transform by the inverse Fourier transform circuit 114-k. Depending on the configuration of the receiver, the GI insertion circuit 115-k can be omitted. The smoothing circuit 116-k (k = 1 to m) applies smoothing by digital signal processing to the joints between the Fourier transform blocks. The D / A conversion circuit 117-k (k = 1 to m) converts the digital signal into a synchronized analog signal using the clock by the common clock 21. The common clock 121 also outputs the clock to the intensity modulator 12 and the phase modulator 13 in the multi-wavelength light source 101, and is synchronized.

  The frequency conversion circuit 118-k (k = 1 to m) converts the frequency of the analog signal using the oscillation signal from the local oscillator 122. The local oscillator 122 also outputs the transmission signal to the intensity modulator 12 and the phase modulator 13 in the multi-wavelength light source 101 to synchronize. At this time, the center frequency in the frequency band of the analog signal output from the D / A conversion circuit 117-k (hereinafter, the center frequency in the frequency band is referred to as “the center frequency of the frequency band”) depends on the channel. Frequency conversion is performed so that the center frequency of the used frequency band is obtained. The BPF 119-k (k = 1 to m) extracts a frequency band signal used by the channel from the frequency-converted signal. The synthesis circuit 120 synthesizes the channels k output from the BPFs 119-k (k = 1 to m), generates a baseband signal of a single carrier signal, and outputs it as an output A.

  The Fourier transform circuit 112-k (k = 1 to m) can use Fast Fourier Transform (FFT) when discrete Fourier transform is used as Fourier transform. The inverse Fourier transform circuit 114-k (k = 1 to m) can use inverse fast Fourier transform (IFFT: Inverse FFT) when inverse discrete Fourier transform is used as inverse Fourier transform. is there. Thus, by using the fast Fourier transform for the Fourier transform circuit 112-k (k = 1 to m) and by using the inverse fast Fourier transform for the inverse Fourier transform circuit 114-k (k = 1 to m). The calculation load and calculation time for each channel are further reduced.

Next, FIG. 6 is a diagram illustrating a configuration example of the optical modulator 103-i (i = 1 to n) illustrated in FIG. As shown in FIG. 6, a Mach-Zehnder type modulator is used for each of the optical modulators 103-i (i = 1 to n) in this embodiment, and the corresponding single carrier signal generation circuit 100-i ( The output A from i = 1 to n) is input. As a result, the optical modulator 103-i is an optical single of DSB (double sideband) centered on the wavelength band λi (i = 1 to n) demultiplexed by the optical demultiplexing unit 102, that is, the optical carrier of the frequency fc. Generate a carrier signal. When driving the optical modulator 103-i, if the bias point is set to half of the half-wave voltage ( _Vπ ), the optical carrier remains, and if the bias point is set to the NULL point, the optical carrier can be suppressed. .

Next, signal processing by the single carrier signal generation circuit described above will be described.
First, the S / P conversion circuit 110 converts the binary signal input to the signal generation circuit 1 from a serial signal to a parallel signal having a predetermined data length, and outputs it to the modulation circuit 111-k (k = 1 to m). Output. Next, the modulation circuit 111-k (k = 1 to m) has a predetermined modulation scheme, for example, 16QAM (Quadrature Amplitude Modulation), 64QAM, QPSK (Quadrature Phase Shift Keying). The data input from the S / P conversion circuit 110 is modulated by a single carrier modulation method such as the above, mapped to a channel, and output to the Fourier transform circuit 112-k (k = 1 to m).

  Specifically, the modulation circuit 111-k (k = 1 to m) in the single carrier signal generation circuit 100-i has an in-phase component (I component) and a quadrature component (Q component) for each channel assigned to data. A signal consisting of Note that no signal can be assigned to any channel i. In addition, it is possible not to assign a signal to an adjacent frequency band outside the channel k.

  In the above description, the S / P conversion circuit 110 converts, for example, serial signal data transmitted through the channel k (k = 1 to m) from serial signals into parallel signals having a predetermined data length. To the corresponding modulation circuit 111-k (k = 1 to m).

  Next, the Fourier transform circuit 112-k (k = 1 to m) performs Fourier transform on the signal modulated by the modulation circuit 111-k, and outputs the result to the 0 insertion circuit 113-k (k = 1 to m). .

  Next, the 0 insertion circuit 113-k (k = 1 to m) is outside the signal transmission frequency band of the signal subjected to the Fourier transform by the Fourier transform circuit 112-k (k = 1 to m) and adjacent thereto. A frequency component of 0 is inserted into the frequency band and output to the inverse Fourier transform circuit 114-k.

  FIG. 7 is a diagram illustrating the output of the 0 insertion circuit 113-k when no signal is assigned to the frequency band corresponding to the outside of the channel k. In FIG. 7, 0 is inserted in the frequency band (λi) outside the transmission symbol of the channel k from the modulation circuit 111-k input through the Fourier transform circuit 112-k. Further, by designating 0 for all channels in advance and outputting a signal to the corresponding channel by the modulation circuit 111-k, the same effect can be obtained without going through the 0 insertion circuit 113-k. . Here, by using a band limiting filter such as a root Nyquist filter instead of the 0 insertion circuit 113-k, interference with an adjacent channel can be reduced.

  Next, the inverse Fourier transform circuit 114-k (k = 1 to m) performs inverse Fourier transform on the data input from the 0 insertion circuit 113-k, thereby converting the transmission signal mapped in the frequency domain into the time domain. To a single carrier signal. Thereby, in the channel k, the inverse Fourier transform circuit 114-k operates the inverse Fourier transform on the signal series in which 0 is inserted.

  Here, modulation is performed by the Fourier transform circuit 112-k (k = 1 to m), the 0 insertion circuit 113-k (k = 1 to m), and the inverse Fourier transform circuit 114-k (k = 1 to m). When the signal modulated by the circuit 111-k (k = 1 to m) is viewed in the frequency domain, the frequency “0” is inserted outside the signal transmission frequency band in the frequency domain. Become. This has the effect of reducing interference between channels in the frequency domain.

Next, the GI (guard interval) input circuit 115-k (k = 1 to m) inserts a guard interval into the signal input from the inverse Fourier transform 114-k (k = 1 to m). .
FIG. 8 is a diagram illustrating a guard interval insertion method in the GI insertion circuit 115-k. The guard interval 115-k adds the same signal as a part of the second half of one Fourier transform block, which is an original single carrier signal, to the first half of the Fourier transform block as a guard interval.

Next, the smoothing circuit 116-k (k = 1 to m) performs smoothing by digital signal processing on the joint between the Fourier transform blocks of the signal input from the GI insertion circuit 115-k, and performs D / A The data is output to the conversion circuit 117-k.
FIG. 9 is a diagram illustrating a smoothing process in the smoothing circuit 116-k. If the Fourier transform blocks are simply arranged continuously, the signal becomes discontinuous between the Fourier transform blocks. Therefore, the smoothing circuit 116-k performs processing so that the joints between the Fourier transform blocks change smoothly, and removes the presence of steep frequency components.

  Next, the D / A conversion circuit 117-k (k = 1 to m) uses a clock based on the common clock 121 and converts the digital signal input from the smoothing circuit 116-k to another D / A conversion circuit 117-. k is converted into an analog signal synchronized with that of k and output to the frequency conversion circuit 118-k. The frequency conversion circuit 118-k (k = 1 to m) uses the oscillation signal from the local oscillator 122 to change the frequency band of the analog signal of the channel k input from the D / A conversion circuit 117-k to the frequency band. The frequency is converted to fk and output to BPF 119-k. The center frequency of the frequency band fk matches the center frequency of the frequency band used by the channel k. That is, the frequency conversion circuit 118-k has the center frequency of the frequency band of the input analog signal set to the channel k. The frequency is converted so as to be the center frequency of the frequency band.

  FIG. 10 is a diagram illustrating frequency conversion in the frequency conversion circuit 118-1. In FIG. 10, the frequency conversion circuit 118-1 frequency-converts the signal output from the D / A conversion circuit 117-1 into the frequency band f1. The frequency bands f1 to fm are continuous so that a part of the frequency band fk (a part or all of the frequency band δfk described later) overlaps with the adjacent frequency bands f (k−1) and f (k + 1). It is a frequency band.

Next, the BPF 119-k (k = 1 to m) extracts a signal of the frequency band Δfk corresponding to the frequency band of the channel k from the frequency-converted signal of the frequency band fk. At this time, the frequency band Δfk A signal for the frequency band δfk adjacent to is also extracted.
FIG. 11 is a diagram showing processing in the BPF 119-1. In FIG. 11, the BPF 119-1 extracts a signal of the frequency band Δf1 from the signal of the frequency band f1, but the BPF 119-1 extracts a frequency adjacent to the frequency band Δf1 when extracting the frequency band Δf1. The signal in the band δf1 is extracted at the same time. However, since the outer portion of the frequency band Δf1 corresponds to the frequency portion in which 0 insertion is performed by the 0 insertion circuit 113-1, a steep BPF (δf1 is close to 0) difficult to achieve with only a conventional analog filter is used. Without using it, it is possible to remove interference from outside the frequency band of the channel k and drop the operation clock of the inverse Fourier transform.

Next, the synthesis circuit 120 synthesizes the channels k (k = 1 to m) output from the BPFs 119-k (k = 1 to m), generates an output A, and outputs the output A.
FIG. 12 is a diagram illustrating the output A output from the synthesis circuit 120. As shown in FIG. 12, the synthesizing circuit 120 synthesizes the channels 1 to m of the frequency bands f1 to fm output from the BPF 119-k (k = 1 to m), respectively, and generates an electrical ultra-wideband single carrier. An output A that is a signal is generated.

Next, when a Mach-Zehnder type modulator is used for the optical modulator 103-i (i = 1 to n), the output A of the corresponding signal generation circuit 100-i (i = 1 to n) is input. Then, a DSB optical single carrier signal is generated around the optical carrier having the frequency fc in the frequency band λi output from the optical demultiplexing unit 102.
FIG. 13 is a diagram illustrating a spectrum of an optical single carrier signal output from the optical modulator 103-i. As shown in FIG. 13, the optical single carrier signal output from the optical modulator 103-i has sidebands corresponding to the frequency fk (k = 1 to m) in both bands around the optical carrier frequency fc. A belt is made. When the intensity modulator 4 is driven, when the bias point is set to half of the half-wave voltage ( _Vπ ), the optical carrier remains, and when the bias point is set to the NULL point, the optical carrier can be suppressed.

As described above, in DSB, the same single carrier signal is generated in both bands around the frequency fc, but in order to increase the use efficiency of the band, as shown in FIG. 14, the optical modulator 103-i (i = 1 to n), optical BPFs (band pass filters) 106-i (i = 1 to n) are provided, and the single carrier signal output from the optical modulator 103-i is transmitted by the optical BPF 106-i. SSB (single sideband) may be used.
FIG. 15 is a diagram illustrating a spectrum of a single carrier signal output from the optical BPF 106-i. As shown in FIG. 15, in the single carrier signal output from the optical BPF 106-i, the side waves appearing in both bands around the optical carrier frequency fc in the optical single carrier signal output from the optical modulator 103-i. Only one of the bands is taken out.
Although not shown, if an optical quadrature modulator is used as the optical modulator 103-i, the output B is used as the Ich drive signal, and the Hilbert transform of the output A is used as the Qch drive signal, so that the optical BPF is not used. Can be converted to SSB.

Next, the phase adjustment unit 104-i (i = 1 to n) adjusts and outputs the phase of the optical single carrier signal output from the corresponding optical modulator 103-i (i = 1 to n).
Then, the optical multiplexing unit 105 synthesizes and outputs the optical single carrier signals having the same phase that are output from the phase adjustment units 104-i (i = 1 to n).
FIG. 16 shows a signal output from the optical multiplexing unit 105. As shown in FIG. 16, the optical single carrier signal output from the optical multiplexing unit 105 is an array of optical single carrier signals obtained by modulating optical carriers λi (i = 1 to n). Here, in the configuration of FIG. 14, an optical single carrier signal obtained by extracting only one of the sidebands is used. FIG. 16 shows a case where m of the frequency band fik (k = 1 to m) in which each optical carrier is modulated using λi (i = 1 to n) is “3”.

  According to the above-described embodiment, since a broadband signal can be modulated in the electrical frequency region as compared with the conventional technology, the optical carrier λi (i = 1 to 1) demultiplexed by the multi-wavelength light source 101 and the optical demultiplexing unit 102. n) and the optical modulator 103-i (i = 1 to n) corresponding to the optical carrier λi (i = 1 to n) can be modulated in a wide band with high frequency utilization efficiency.

  Note that the 0 insertion circuit 113-k (k = 1 to m) in the optical single carrier signal generation circuit 100-i has a frequency of “0” in the corresponding frequency band by the modulation circuit 111-k (k = 1 to m). Although a component is inserted, a frequency component having a value of “substantially 0” that does not affect the signal component during inverse discrete Fourier transform may be inserted.

  Note that the signal spectrum is dynamically mapped to the entire band with respect to the signal subjected to the Fourier transform by the Fourier transform circuit 112-k (k = 1 to m) in the optical single carrier signal generation circuit 100-i. Thus, it is possible to obtain the frequency diversity effect and reduce the influence of interference.

<Second Embodiment>
Next, a signal transmission apparatus according to the second embodiment of the present invention will be described. In the second embodiment, the same parts as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  FIG. 17 is a block diagram showing a configuration of a signal transmission apparatus according to the second embodiment of the present invention. In the first embodiment, the signal A, which is a broadband single electric carrier signal generated by the single carrier signal generation circuit 100-i (i = 1 to n) in the signal generation circuit 100, is converted into the optical modulator 103-i ( In this embodiment, the output channel Ich signal and the Qch signal generated by the single carrier generation circuit 100a-i in the signal generation circuit 100a are used as the optical orthogonal modulator 107-i. The point of output to (i = 1 to n) is different.

  FIG. 18 is a block diagram showing a configuration of the signal generation circuit 100a of the present embodiment. In the figure, in the digital signal processing unit up to the smoothing circuit 116-k (k = 1 to m), the single carrier signal generation circuit 100-i (i = i = i) in the signal generation circuit 100 of the first embodiment shown in FIG. Similar to the configuration of 1 to n), calculation is performed using complex signals. Therefore, the D / A conversion circuits 117a-k (k = 1 to m) of the present embodiment output analog complex signals (Ich, Qch). As a result, the Ich signal and the Qch signal of output A shown in FIG. 13 are output from the synthesis circuit 120a.

  FIG. 19 is a block diagram showing another configuration of the signal generation circuit 100a of the present embodiment. In the figure, the digital signal processing section up to the GI insertion circuit 115-k (k = 1 to m) is the same as the configuration of the signal generation circuit 100 of the first embodiment shown in FIG. The smoothing circuits 116a-k (k = 1 to m) perform the same processing as in the first embodiment, but the output to the D / A conversion circuit is divided into Ich and Qch, and Ich is The D / A conversion circuit 117b-k (k = 1 to m) and Qch are output to the D / A conversion circuit 117c-k (k = 1 to m). Then, the D / A conversion circuit 117b-k, the frequency conversion circuit 118b-k, the BPF 119b-k, and the synthesis circuit 120b are the I / D conversion circuit 117c-k, the frequency conversion circuit 118c-k, the BPF 119c-k, and the synthesis. The circuit 120c performs the same processing on Qch as the D / A conversion circuit 117-k, the frequency conversion circuit 118-k, the BPF 119-k, and the synthesis circuit 120 described in the first embodiment. In this way, by processing the subsequent circuits from the smoothing circuits 116a-k separately for Ich and Qch, the number of clocks of the D / A conversion circuit can be reduced.

  FIG. 20 is a diagram illustrating a configuration of the optical orthogonal modulation unit 107-i (i = 1 to n). As shown in FIG. 20, the optical quadrature modulation unit 107-i (i = 1 to n) has Mach-Zehnder type modulators arranged in parallel, and each of them is a single carrier signal generation circuit 100a-i (in the signal generation circuit 100a). Ich drive signal and Qch drive signal output from i = 1 to n) are input. Then, by applying a phase shift π / 2 to one branch to which the Qch signal is input, it is possible to modulate the light sin (Qch) and cos (Ich) waves.

  FIG. 21 is a diagram illustrating a spectrum of an optical single carrier signal output from the optical orthogonal modulation unit 107-i (i = 1 to n). The optical quadrature modulator 107-i (i = 1 to n) is driven by the Ich signal and Qch signal of the output A output from the single carrier signal generation circuit 100a-i (i = 1 to n). As shown in the spectrum transition shown in FIG. 21, a broadband optical single carrier signal centered on the frequency fc of the light source can be generated. At this time, if the bias point of the optical orthogonal modulator 107-i is set to a NULL point, the optical carrier can be suppressed. In the case of this configuration, the band utilization efficiency is increased as compared with the configuration using the intensity modulator.

  In the above description, the optical single carrier signal is generated and transmitted. However, the single carrier signal may be transmitted wirelessly. In this case, a radio signal is generated in the D / A conversion circuits 117a-k (k = 1 to m), or the output A from the signal generation circuit 100 is placed on the carrier wave of the radio signal.

In addition, the inverse Fourier transform circuit 114-k (k = 1 to m) and the GI insertion circuit 115-k (k = 1 to m) in FIGS. 5, 18 and 19 described above are different for each channel. The number of inverse Fourier transform points and the guard interval length can also be used.
Further, the common clock 121 and local oscillator 122 in FIGS. 5, 18 and 19 are common to all channels, but different clocks and local oscillators may be used for each channel instead of being common. (In this case, it is necessary to synchronize the clock and the transmission signal by outputting them to the multi-wavelength light source 101).
Further, in the frequency conversion circuit 118-k (k = 1 to m) of FIGS. 5 and 18 and 118b-k (k = 1 to m) and 118c-k (k = 1 to m) of FIG. After frequency conversion is performed for each channel, level adjustment is made to the preset target value of power common to all channels, and the signal power of all channels is made constant so that the transmission quality of all channels is the same. You can also.

  According to the present embodiment, it is possible to realize a steep band pass filter (BFP) that is difficult to realize with only a conventional analog filter, and to remove interference from outside the band divided for each channel. By combining and frequency-converting each channel from which interference has been removed, real-time and high-quality broadband transmission using a single carrier can be realized. Moreover, since zero insertion, guard interval insertion, and smoothing processing are performed in parallel for each channel, it is possible to operate with a slow clock.

1 is a signal transmission device according to a first embodiment of the present invention. It is a block diagram which shows the structure of the multiwavelength light source 101 by the embodiment. It is a block diagram which shows the other structure of the multiwavelength light source 101 by the embodiment. It is a block diagram which shows the further another structure of the multiwavelength light source 101 by the embodiment. It is a block diagram which shows the structure of the single carrier signal generation circuit 100-i by the embodiment. It is a block diagram which shows the structure of optical modulator 103-i by the embodiment. It is a figure which shows the output of 0 insertion circuit 113-i by the embodiment. It is a figure which shows the output of GI insertion circuit 115-k by the embodiment. It is a figure which shows the output of the smoothing circuit 116-k by the embodiment. It is a figure which shows the output of the frequency converter circuit 118-k by the embodiment. It is a figure which shows the process of BPF119-k by the embodiment. It is a figure which shows the output of the synthetic | combination circuit 120 by the embodiment. It is a figure which shows the output from optical modulator 103-i by the embodiment. It is a block diagram which shows the other structure of the signal transmitter by the same embodiment. It is a figure which shows the output from optical BPF106-i by the embodiment. It is a figure which shows the output from the optical multiplexing part 105 by the embodiment. It is a signal transmission apparatus in the 2nd Embodiment of this invention. It is a block diagram which shows the structure of the signal generation circuit by the embodiment. It is a block diagram which shows the other structure of the signal generation circuit by the embodiment. It is a block diagram which shows the structure of the optical orthogonal modulator 107-i by the same embodiment. It is a figure which shows the output from the optical orthogonal modulator 107-i by the embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11, 21 ... Light source 12 ... Intensity modulator 13, 22, 25 ... Phase modulator 16 ... Mode-locked laser 17 ... Optical amplifier 18 ... Optical nonlinear fiber 23 ... Dispersion adding part 24 ... Phase shifter 100, 100a ... Signal generation circuit 100 −1 to 100-n Single carrier signal generation circuit 101 Multi-wavelength light source 102 Optical demultiplexing unit 102
103-1 to 103-n Optical modulators 104-1 to 104-n Phase adjustment unit 105 Optical multiplexing units 106-1 to 106-n Optical BPF (optical bandpass filter)
107-1 to 107-n: Optical orthogonal modulation unit 110 ... S / P conversion circuit (serial / parallel conversion unit)
111-1 to 111-m ... Fourier transform circuit (Fourier transform unit)
112-1 to 112-m ... modulation circuit (input signal modulation unit)
113-1 to 113-m ... 0 insertion circuit (zero insertion section)
114-1 to 114-m: Inverse Fourier transform circuit (inverse Fourier transform unit)
115-1 to 115-m ... GI insertion circuit (guard interval insertion section)
116-1 to 116-m, 116a-1 to 116a-m ... smoothing circuit (smoothing unit)
117-1 to 117-m, 117a-1 to 117a-m, 117b-1 to 117b-m, 117c-1 to 117c-m ... D / A conversion circuit (digital / analog conversion circuit)
118-1 to 118-m, 118b-1 to 118b-m, 118c-1 to 118c-m ... frequency conversion circuit (frequency conversion unit)
119-1 to 119 -m, 119 b-1 to 119 b -m, 119 c-1 to 119 c -m... BPF (band pass filter)
120, 120a, 120b, 120c... Synthesis circuit (synthesis unit)

Claims (6)

A multi-wavelength light source;
An optical demultiplexing unit for demultiplexing a plurality of optical carriers output from the multi-wavelength light source into a set wavelength band;
Each of the plurality of single carrier signal generation units for converting the input serial signal into a plurality of parallel signals corresponding to the channels and outputting a combined signal obtained by combining the signals of the respective channels,
A plurality of optical modulators that are provided for each wavelength band and modulate the light of the wavelength band by a combined signal from a corresponding single carrier signal generation unit and output as an optical signal;
Possess the optical multiplexing section for multiplexing the optical signal the modulated for each light modulator corresponding to each of the wavelength bands,
The single carrier signal generator is
A serial-parallel converter that converts an input signal into a plurality of parallel signals;
A plurality of processing units each corresponding to a channel and generating a signal of a channel corresponding to the plurality of parallel signals,
A synthesizing unit that synthesizes the signals of the respective channels generated by the plurality of processing units to generate a signal;
With
Each of the plurality of processing units is
An input signal modulator that modulates each parallel signal to a channel corresponding to the parallel signal;
A Fourier transform unit for performing a Fourier transform on the signal modulated by the input signal modulation unit;
The signal subjected to Fourier transform by the Fourier transform unit is subjected to band limitation of the signal, and a zero insertion unit for inserting a zero frequency component into a frequency outside the band necessary for signal transmission, or transmission of a band limiting filter A filtering unit for superimposing functions;
An inverse Fourier transform unit that performs an inverse Fourier transform on a signal in which a zero frequency component is inserted by the zero insertion unit, or a signal on which a transfer function of a band limiting filter is superimposed;
A digital-analog converter that converts the signal that has been subjected to the inverse Fourier transform by the inverse Fourier transform unit into an analog signal that is synchronized with another processing unit;
A frequency converter that converts the frequency of the signal converted into an analog signal by the digital analog converter so that the center frequency of the frequency band of the signal is the center frequency of the frequency band of the channel corresponding to the processing unit;
A band-pass filter that extracts a signal of a frequency band used by a channel corresponding to the processing unit from the signal frequency-converted by the frequency conversion unit;
The synthesizing unit generates the signal by synthesizing the signals extracted by the bandpass filter;
A signal transmission apparatus characterized by that. Each of the plurality of processing units is
A guard interval insertion unit that inserts a guard interval into the signal that has been inverse Fourier transformed by the inverse Fourier transform unit;
The signal transmission device according to claim 1 . Each of the plurality of processing units is
A smoothing unit that performs a smoothing process at a joint between Fourier transform blocks of the signal in which the guard interval is inserted by the guard interval insertion unit;
The signal transmission apparatus according to claim 2 .   The signal transmission device according to claim 1, wherein the optical modulator is an optical intensity modulator.   The signal transmission device according to claim 1, wherein the optical modulator is an optical quadrature modulator. A signal transmission method by a signal transmission device that transmits a single carrier signal,
A process in which a multi-wavelength light source outputs a plurality of optical carriers;
An optical demultiplexing process in which an optical demultiplexing unit demultiplexes a plurality of optical carriers output from the multi-wavelength light source into a set wavelength band;
Each of a plurality of single carrier signal generation units converts an input serial signal into a parallel signal corresponding to a channel, and outputs a combined signal, a single carrier signal generation process,
An optical modulator is provided for each wavelength band, and an optical modulation process in which light in the wavelength band is modulated by the optical modulator by a combined signal from a corresponding single carrier signal generation unit and output as an optical signal;
Possess the optical multiplexing step of multiplexing the optical signal the modulated for each light modulator optical multiplexing unit corresponding to each of the wavelength bands,
The single carrier signal generation process includes:
A serial-parallel conversion process in which the serial-parallel converter converts the input signal into a plurality of parallel signals;
Each of a plurality of processing units corresponds to a channel, and a plurality of processing steps for generating a signal of a channel corresponding to the plurality of parallel signals,
A synthesizing process in which a synthesizing unit generates a signal by synthesizing the signals of the respective channels generated by the plurality of processing units;
I have a,
Each of the plurality of processing steps is
An input signal modulation process in which the input signal modulation unit modulates each parallel signal to a channel corresponding to itself,
A Fourier transform process in which a Fourier transform unit performs a Fourier transform on the signal modulated by the input signal modulation process;
A zero insertion process in which a zero insertion unit inserts a frequency component of 0 into a frequency outside a band necessary for signal transmission, which performs band limitation of the signal on which the Fourier transform is performed by the Fourier transform unit, or filtering A filtering process in which the part superimposes the transfer function of the band limiting filter;
An inverse Fourier transform process in which an inverse Fourier transform unit performs an inverse Fourier transform on a signal in which a zero frequency component is inserted by the zero insertion unit, or a signal on which a transfer function of a band limiting filter is superimposed;
A digital-analog conversion process in which the digital-analog conversion unit converts the signal subjected to the inverse Fourier transform by the inverse Fourier transform unit into an analog signal synchronized with another processing unit;
Frequency at which the frequency conversion unit converts the signal converted into the analog signal by the digital analog conversion unit so that the center frequency of the frequency band of the signal is the center frequency of the frequency band of the channel corresponding to the processing unit The conversion process,
A bandpass filter process of extracting a signal of a frequency band used by a channel corresponding to the processing unit from a signal whose bandpass filter is frequency-converted by the frequency conversion unit;
With
In the synthesis process, the synthesis unit synthesizes the signals extracted by the bandpass filter to generate the signal.
A signal transmission method characterized by the above.

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