WO2013128783A1 - デジタル信号処理装置、受信装置、及び信号送受信システム - Google Patents
デジタル信号処理装置、受信装置、及び信号送受信システム Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
- H04L27/2649—Demodulators
- H04L27/26524—Fast Fourier transform [FFT] or discrete Fourier transform [DFT] demodulators in combination with other circuits for demodulation
- H04L27/26526—Fast Fourier transform [FFT] or discrete Fourier transform [DFT] demodulators in combination with other circuits for demodulation with inverse FFT [IFFT] or inverse DFT [IDFT] demodulators, e.g. standard single-carrier frequency-division multiple access [SC-FDMA] receiver or DFT spread orthogonal frequency division multiplexing [DFT-SOFDM]
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H17/00—Networks using digital techniques
- H03H17/02—Frequency selective networks
- H03H17/0211—Frequency selective networks using specific transformation algorithms, e.g. WALSH functions, Fermat transforms, Mersenne transforms, polynomial transforms, Hilbert transforms
- H03H17/0213—Frequency domain filters using Fourier transforms
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H21/00—Adaptive networks
- H03H21/0012—Digital adaptive filters
- H03H21/0025—Particular filtering methods
- H03H21/0027—Particular filtering methods filtering in the frequency domain
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/06—Receivers
- H04B1/10—Means associated with receiver for limiting or suppressing noise or interference
- H04B1/1027—Means associated with receiver for limiting or suppressing noise or interference assessing signal quality or detecting noise/interference for the received signal
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/06—Receivers
- H04B1/10—Means associated with receiver for limiting or suppressing noise or interference
- H04B1/12—Neutralising, balancing, or compensation arrangements
- H04B1/123—Neutralising, balancing, or compensation arrangements using adaptive balancing or compensation means
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L23/00—Apparatus or local circuits for systems other than those covered by groups H04L15/00 - H04L21/00
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/10—Frequency-modulated carrier systems, i.e. using frequency-shift keying
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H21/00—Adaptive networks
- H03H21/0012—Digital adaptive filters
- H03H2021/0085—Applications
- H03H2021/0092—Equalization, i.e. inverse modeling
Definitions
- the present invention relates to a digital signal processing device, a receiving device, and a signal transmission / reception system for processing a digital signal.
- Digital signals are transmitted and received in optical communication and wireless communication.
- waveform distortion compensation is often performed on digital signals using a digital filter (see, for example, Patent Document 1 and Non-Patent Document 1).
- Patent Document 2 describes the following technology. First, the digital signal is Fourier transformed. Next, waveform equalization processing in the frequency domain is performed on the result of the Fourier transform using a digital filter. Next, the result of the waveform equalization process is inverse Fourier transformed to generate a digital signal.
- Non-Patent Document 2 chromatic dispersion compensation is performed by controlling a FDE (frequency-domain equalization) circuit, which is difficult to control, by switching filter coefficients semi-fixedly using a lookup table (LUT). The method of performing is disclosed.
- FDE frequency-domain equalization
- An object of the present invention is to provide a digital signal processing device, a receiving device, and a signal transmission / reception system that can reduce the processing required for setting the coefficients of the filter means.
- Fourier transform means for generating a frequency domain signal that is a frequency axis signal by Fourier transforming a digital signal; Filter means for equalizing the frequency domain signal in the frequency domain using N first coefficients; An inverse Fourier transform means for returning the frequency domain signal processed by the filter means to the digital signal; first coefficient setting means for setting the N first coefficients using m (where N> m) second coefficients;
- a digital signal processing apparatus is provided.
- digital signal acquisition means for acquiring a digital signal
- Digital signal processing means for processing the digital signal
- the digital signal processing means includes Fourier transform means for generating a frequency domain signal that is a frequency axis signal by Fourier transforming the digital signal; Filter means for equalizing the frequency domain signal in the frequency domain using N first coefficients; An inverse Fourier transform means for returning the frequency domain signal processed by the filter means to the digital signal; first coefficient setting means for setting the N first coefficients using m (where N> m) second coefficients; Is provided.
- a transmission means for transmitting a digital signal receives the digital signal;
- Receiving means for receiving the digital signal includes Digital signal acquisition means for acquiring the digital signal;
- the digital signal processing means includes Fourier transform means for generating a frequency domain signal that is a frequency axis signal by Fourier transforming the digital signal;
- Filter means for equalizing the frequency domain signal in the frequency domain using N first coefficients;
- An inverse Fourier transform means for returning the frequency domain signal processed by the filter means to the digital signal;
- first coefficient setting means for setting the N first coefficients using m (where N> m) second coefficients;
- a signal transmission / reception system is provided.
- FIG. 1 shows the structure of the digital processing apparatus which concerns on 1st Embodiment. It is a figure for demonstrating in detail an example of a digital filter. It is a figure for demonstrating the process which a 1st coefficient setting part performs. It is a figure for demonstrating the 1st example of the process which a 1st coefficient setting part performs. It is a figure for demonstrating the 2nd example of the process which a 1st coefficient setting part performs. It is a figure for demonstrating the 3rd example of the process which a 1st coefficient setting part performs. It is a figure for demonstrating the 4th example of the process which a 1st coefficient setting part performs.
- FIG. 1 is a diagram illustrating a configuration of a digital processing apparatus 100 according to the first embodiment.
- the digital processing apparatus 100 has a digital filter 110.
- the digital filter 110 includes a Fourier transform unit 111, an inverse Fourier transform unit 112, a filter unit 113, and a first coefficient setting unit 114.
- the Fourier transform unit 111 generates a frequency domain signal which is a frequency axis signal by performing a Fourier transform on the time axis digital signal.
- the filter unit 113 equalizes the frequency domain signal in the frequency domain using the N first coefficients.
- the inverse Fourier transform unit 112 performs inverse Fourier transform on the frequency domain signal processed by the filter unit 113 to return it to a time-axis digital signal.
- the Fourier transform unit 111, the inverse Fourier transform unit 112, and the filter unit 113 compensate for waveform distortion included in the digital signal by equalization processing in the frequency domain (that is, frequency-domain equalization (FDE)).
- the first coefficient setting unit 114 sets N first coefficients used by the filter unit 113 using m (where N> m) second coefficients.
- the digital signal input to the digital filter 110 is a signal received by the receiving device in, for example, optical communication or wireless communication.
- the Fourier transform unit 111 is, for example, a size N Fourier transform circuit.
- the Fourier transform processing performed by the Fourier transform unit 111 is DFT (discrete Fourier transform) or FFT (fast Fourier transform).
- DFT discrete Fourier transform
- FFT fast Fourier transform
- IDFT Inverse discrete Fourier transform
- the inverse Fourier transform unit 112 performs IFFT (Inverse fast Fourier transform) processing.
- FIG. 2 is a diagram for explaining an example of the digital filter 110 in detail.
- the digital filter 110 is, for example, an FDE (Fre1uency-domain equalization) filter.
- the Fourier transform unit 111 is a Fourier transform circuit of size N, and converts an input time-axis digital signal into N frequency-axis digital signals.
- the converted digital signal has a constant frequency of ⁇ s .
- ⁇ s 2 ⁇ f s / N
- f s is the sampling frequency.
- the filter unit 113 performs a process of multiplying each of the N frequency axis digital signals by the first coefficient H x (0 ⁇ x ⁇ N ⁇ 1).
- the first coefficient is set for each of the N digital signals. Therefore, the first coefficient setting unit 114 sets N first coefficients for the filter unit 113.
- the N digital signals after being multiplied by the first coefficient are returned to the time-axis digital signals by the inverse Fourier transform unit 112.
- the first coefficient and the second coefficient are, for example, coefficients set for each frequency, but are not limited thereto.
- the interval of at least some (or all) second coefficients is wider than the interval of the first coefficient on the frequency axis.
- the first coefficient setting unit 114 sets an approximation function that approximates the first coefficient using the frequency as a variable, using m second coefficients. Then, the first coefficient setting unit 114 sets the first coefficient based on this approximate function.
- the approximation function setting process and the first coefficient setting process described above are performed by hardware (LSI (Large Scale Integration) circuit or FPGA (field programmable gate array)), software (CPU (Central Processing Unit or microcomputer) or PC (Personal Computer)) or the like. These processes may be performed partly by software and the rest by hardware.
- LSI Large Scale Integration
- FPGA field programmable gate array
- CPU Central Processing Unit or microcomputer
- PC Personal Computer
- FIG. 3 is a diagram for explaining processing performed by the first coefficient setting unit 114.
- the first coefficient setting unit 114 sets N digital signals H x (0 ⁇ x ⁇ N ⁇ 1) using m second coefficients h y (0 ⁇ y ⁇ m ⁇ 1).
- the first coefficient setting unit 114 includes, for example, an LSI circuit that receives m second coefficients hy as inputs and outputs N first coefficients Hx as outputs. There are several examples of this circuit.
- FIG. 4 is a diagram for explaining a first example of processing performed by the first coefficient setting unit 114.
- the first coefficient setting unit 114 includes an FIR (finite impulse response) filter transfer characteristic calculation circuit as shown in FIG.
- the FIR filter transfer characteristic calculation circuit performs calculation processing according to a transfer function represented by the following expression (1).
- FIG. 4B shows an example of the transfer function represented by the equation (1).
- First coefficient setting unit 114 by using such a function, sets a first coefficient H x in the desired omega.
- FIG. 5 is a diagram for explaining a second example of processing performed by the first coefficient setting unit 114.
- the first coefficient setting unit 114 has a segmented transfer characteristic calculation circuit as shown in FIG.
- the segmented transfer characteristic calculation circuit performs processing according to the following idea.
- the frequency axis (0 to (N ⁇ 1) ⁇ s) is divided into m segments.
- the width of each segment is an integral multiple of ⁇ s and may be equal to each other or at least partially different.
- the second coefficient indicates the boundary value of each segment.
- the boundary values of these segments are connected by an approximate function (for example, linear approximation), and the first coefficient is calculated using this approximate function.
- the segment boundary frequencies of a certain segment are k 1 ⁇ s and k 2 ⁇ s (k 1 ⁇ k 2 ), and the transfer characteristic values at the boundary frequencies are Hk 1 and Hk 2 , respectively.
- the value of the transfer characteristic at the frequency k ⁇ s (k 1 ⁇ k ⁇ k 2 ) is calculated as ⁇ (k 2 ⁇ k) Hk 1 + (k ⁇ k 1 ) Hk 2 ⁇ as an internal dividing point calculation by linear approximation. / (K 2 ⁇ k 1 ).
- FIG. 6 is a diagram for explaining a third example of the process performed by the first coefficient setting unit 114.
- the first coefficient setting unit 114 has a polynomial recent transfer characteristic calculation circuit as shown in FIG.
- the polynomial near-time transfer characteristic calculation circuit performs calculation processing according to a transfer function represented by the following equation (2).
- a x (0 ⁇ x ⁇ m ⁇ 1) is the second coefficient.
- FIG. 6B shows an example of the transfer function represented by Expression (2).
- First coefficient setting unit 114 by using such a function, sets a first coefficient H x in the desired omega.
- FIG. 7 is a diagram for describing a fourth example of processing performed by the first coefficient setting unit 114.
- the first coefficient setting unit 114 stores a coefficient set including m third coefficients corresponding to each of the m second coefficients for each of the N first coefficients.
- the first coefficient setting unit 114 reads out a coefficient set of the third coefficient corresponding to the first coefficient for each first coefficient.
- the first coefficient setting unit 114 calculates the first coefficient by multiplying each read third coefficient by the second coefficient corresponding to the third coefficient.
- the first coefficient setting unit 114 stores a fixed value to be used as a substitute for z ⁇ m (k) in the above equation (1) as the third coefficient. This fixed value is updated as appropriate.
- N first coefficients used by the filter unit 113 can be set using m (where N> m) second coefficients. For this reason, the arithmetic processing required for the coefficient setting of the filter unit 113 is reduced. For this reason, the speed of the digital processing apparatus 100 can be increased, and the communication speed can be increased accordingly. In addition, the circuit scale of the digital processing apparatus 100 can be reduced.
- FIG. 8 is a diagram illustrating a configuration of the digital processing apparatus 100 according to the second embodiment.
- the digital processing apparatus 100 according to the present embodiment has the same configuration as that of the digital processing apparatus 100 according to the first embodiment except that a fixed filter coefficient setting unit 116 and a multiplication unit 115 are included.
- the fixed filter coefficient setting unit 116 stores a fixed value of the first coefficient.
- the multiplier 115 multiplies the first coefficient set by the first coefficient setting unit 114 and the first coefficient stored in the fixed filter coefficient setting unit 116, and outputs the value to the filter unit 113.
- the same effect as that of the first embodiment can be obtained. Further, by correcting the first coefficient stored in the fixed filter coefficient setting unit 116 with the first coefficient calculated by the first coefficient setting unit 114, the value of the first coefficient can be easily set to an appropriate value. Can do.
- FIG. 9 is a diagram illustrating a configuration of a digital processing apparatus 100 according to the third embodiment.
- the digital processing apparatus 100 according to the present embodiment is the first implementation except that it includes an initial value setting unit 117, a digital signal processing unit 120, an error signal generation unit 130, and a second coefficient setting unit 140.
- the configuration is the same as that of the digital processing apparatus 100 according to the embodiment.
- the initial value setting unit 117 stores an initial value of the first coefficient used by the first coefficient setting unit 114.
- the first coefficient is updated as the second coefficient input from the second coefficient setting unit 140 changes.
- the digital signal processing unit 120 is, for example, a DSP (digital signal processor) and processes the digital signal output from the digital filter 110.
- the digital signal processing unit 120 performs digital signal processing necessary for signal reception, such as clock recovery, demodulation processing, and error correction.
- the error signal generation unit 130 detects an error of the digital signal output from the digital filter 110 and generates an error signal indicating the detected error.
- the error signal generator 130 calculates an error signal according to the waveform equalization (compensation) algorithm in the digital filter 110.
- the waveform equalization (compensation) algorithm for example, a CMA (constantCmodulus algorithm), LMS (least mean squares) algorithm, RLS (recursive least squares) algorithm, or the like can be used.
- the error signal generation unit 130 obtains an error between the reference signal (fixed value, training signal, identification determination (DD) signal, etc.) and the digital signal output from the digital filter 110 and equalizes each waveform (compensation). ) Perform error signal calculation according to the algorithm.
- the second coefficient setting unit 140 receives the error signal generated by the error signal generation unit 130, and sets m second coefficients based on the received error signal. For example, the second coefficient setting unit 140 sets m second coefficients by the local search method. The m second coefficients set by the second coefficient setting unit 140 are output to the first coefficient setting unit 114.
- the first coefficient setting unit 114 includes the FIR filter transfer characteristic calculation circuit shown in FIG.
- the update value h ′ x (t) is calculated.
- ⁇ is a step size parameter
- conj (•) represents a complex conjugate of (•).
- the second coefficient setting unit 140 repeats the process using Expression (3). Thereby, even if the input to the digital filter 110 fluctuates in time, the first coefficient setting unit 114 can update the first coefficient following the fluctuation.
- FIG. 10 is a diagram illustrating a first example of the configuration of the second coefficient setting unit 140.
- the second coefficient setting unit 140 includes a gradient information calculation unit 141 and a second coefficient update unit 143.
- the gradient information calculation unit 141 generates gradient information indicating the rate of change of the second coefficient.
- the gradient information is, for example, information indicated by the second term on the right side of equation (3). Specifically, the gradient information is calculated according to the following equation (4).
- the second coefficient update unit 143 updates the second coefficient using the gradient information calculated by the gradient information calculation unit 141.
- the second coefficient updating unit 143 performs processing according to, for example, a steepest descent method using CMA, LMS, RLS, or a conjugate gradient method.
- FIG. 11 is a diagram for explaining a second example of the configuration of the second coefficient setting unit 140.
- the second coefficient setting unit 140 includes an error comparison unit 142 and a second coefficient update unit 143.
- the second coefficient updating unit 143 changes the second coefficient by the first minute amount in the vicinity of the second coefficients h 0 to h m ⁇ 1 at time t (h 0 + ⁇ h1 0 to h m ⁇ 1 + ⁇ h1 m ⁇ 1 ).
- the second coefficient updating unit 143 changes the second coefficient by a second minute amount in the vicinity of the second coefficients h 0 to h m ⁇ 1 (h 0 + ⁇ h2 0 to h m ⁇ 1 + ⁇ h2 m ⁇ 1 ).
- the error comparison unit 142 compares the error signal e 1 when the first minute change is made with the error signal e 2 when the second minute change is made.
- the second coefficient updating unit 143 uses the comparison result in the error comparison unit 142 to sequentially change the second coefficient update amounts ⁇ h 0 to ⁇ h m ⁇ 1 in a direction in which the error signal difference decreases.
- the error comparison unit 142 can use a local search method such as a hill-climbing method, a successive improvement method, or a neighborhood search method.
- FIG. 12 is a diagram for explaining a third example of the configuration of the second coefficient setting unit 140.
- the second coefficient setting unit 140 updates the second coefficient by sequential updating.
- the second coefficient setting unit 140 uses m error signals e (t) to e (t + m ⁇ 1) as second coefficients, and uses this second coefficient to block signal.
- the first coefficient is calculated by processing.
- the second coefficient setting unit 140 includes a Fourier transform unit 144, a gradient information calculation unit 145, and a second coefficient update unit 143.
- the Fourier transform unit 144 performs Fourier transform on m pieces of error information e (t + X) (0 ⁇ X ⁇ m ⁇ 1), which is time axis information, and generates a frequency axis signal Ex (0 ⁇ X ⁇ m ⁇ 1). Generate.
- the gradient information calculation unit 145 performs the same processing as the processing performed on the second coefficient by the gradient information calculation unit 141 on the frequency axis signal Ex (0 ⁇ X ⁇ m ⁇ 1), so that the frequency information Generate gradient information of the error in the region.
- the second coefficient updating unit 143 sets the second coefficient (described as H x (0 ⁇ X ⁇ m ⁇ 1) in the example shown in the drawing) using the gradient information generated by the gradient information calculation unit 145. Then, the first coefficient setting unit 114 sets the first coefficient, for example, by the method described with reference to FIG.
- the Fourier transform unit 144 may be omitted.
- the second coefficient setting unit 140 performs block signal processing in the time domain, as in the examples illustrated in FIGS.
- the second coefficient setting unit 140 sets the second coefficient using the error signal generated by the error signal generation unit 130. For this reason, even if the input to the digital filter 110 fluctuates with time, the first coefficient setting unit 114 can update the first coefficient following the fluctuation.
- FIG. 13 is a diagram illustrating a configuration of a signal transmission / reception system according to the third embodiment.
- the signal transmission / reception system shown in the figure includes a transmitter 10 and a reception device 30.
- the transmission device 10 generates a digital signal and transmits it to the reception device 30.
- a transmission medium 20 exists between the transmission device 10 and the reception device 30.
- the transmission medium 20 is, for example, an optical fiber.
- the transmission medium 20 is a space.
- the receiving device 30 includes a digital processing device 100 and a front end unit 200.
- the digital processing apparatus 100 has the configuration shown in any of the first to third embodiments, for example. In the example shown in this figure, the digital processing apparatus 100 has the same configuration as that of the third embodiment.
- the front end unit 200 receives a signal transmitted from the transmission device 10.
- the front end unit 200 converts the signal into a signal that can be processed by the digital processing apparatus 100.
- FIG. 14 is a diagram illustrating the configuration of the receiving device 30 in detail.
- the front end unit 200 includes a front end circuit 201 and a complex signal generation unit 208.
- the front-end circuit 201 generates four-channel signals Ix, Qx, Iy, and Qy using the signal received from the transmission device 10 and the reference signal LO.
- j is an imaginary unit.
- the digital processing apparatus 100 has two digital filters 110.
- the processing performed by the two digital filters 110 is as shown in the first to third embodiments.
- the receiving device 30 includes two signal quality determination units 132.
- the first signal quality determination unit 132 determines the signal quality of the output E xout (t) of the first digital filter 110. Specifically, the first signal quality determination unit 132 generates a waveform distortion signal indicating the waveform distortion based on the waveform distortion of the output E xout (t). The generated waveform distortion signal is input to the error signal generation unit 130.
- the second signal quality determination unit 132 determines the signal quality of the output E yout (t) of the second digital filter 110. Specifically, the second signal quality determination unit 132 generates a waveform distortion signal indicating the waveform distortion based on the waveform distortion of the output E yout (t). The generated waveform distortion signal is input to the error signal generation unit 130.
- the error signal generation unit 130 generates two types of error signals based on the two waveform distortion signals.
- the second coefficient setting unit 140 sets a second coefficient for each of x and y based on each of the two types of error signals.
- the first coefficient setting unit 114 sets the first coefficient for each of x and y.
- the error signal generation unit 130 sets an error signal using the waveform distortion signal generated by the signal quality determination unit 132. For this reason, when the error signal generation unit 130, the second coefficient setting unit 140, and the first coefficient setting unit 114 are incorporated into the receiving apparatus 30 that already has the signal quality determination unit 132, a new error signal is generated. There is no need to add a detection circuit to the digital processing apparatus 100.
- FIG. 15 is a diagram illustrating a configuration of a reception device 30 used in the signal transmission / reception system according to the fifth embodiment.
- the signal transmission / reception system according to the present embodiment has the same configuration as the signal transmission / reception system according to the fourth embodiment, except for the configuration of the reception device 30.
- the receiving device 30 according to the present embodiment has the same configuration as the receiving device 30 according to the fourth embodiment, except that an error correcting unit 134 is provided instead of the signal quality determining unit 132.
- the error correction unit 134 corrects errors in the digital signal output from the digital signal processing unit 120. Further, the error correction unit 134 outputs error correction information indicating the correction content of the digital signal to the error signal generation unit 130.
- the error signal generation unit 130 generates an error signal based on the error correction signal.
- the error signal generation unit 130 sets an error signal using the error correction information generated by the error correction unit 134. Therefore, when the error signal generation unit 130, the second coefficient setting unit 140, and the first coefficient setting unit 114 are incorporated into the receiving device 30 that already has the error correction unit 134, detection for newly generating an error signal There is no need to add circuitry to the digital processing device 100.
- the signal transmission / reception system according to the present embodiment has the same configuration as the signal transmission / reception system according to the fifth embodiment, except that the signal transmission / reception system uses a digital coherent technology to transmit / receive a signal. That is, in this embodiment, the signal is transmitted by optical communication.
- the optical signal is subjected to multilevel modulation using a polarization multiplexing method, QAM (quadrature amplitude modulation), or the like.
- FIG. 16 is a diagram illustrating a configuration of a reception device 30 used in the signal transmission / reception system according to the sixth embodiment.
- the digital signal processing unit 120 is not shown.
- the receiving device 30 includes a front end unit 200 and a digital processing device 100.
- the front end unit 200 includes an optical hybrid 202, a photoelectric conversion unit 204, an AD (Analog-Digital) conversion unit 206, and a complex signal generation unit 208.
- the optical hybrid 202 receives signal light from the transmission path and local light from the local light source.
- the optical hybrid 202 causes the optical signal and local light to interfere with each other with a phase difference of 0 to generate a first optical signal (I x ), and causes the optical signal and local light to interfere with each other with a phase difference of ⁇ / 2 to generate the second light.
- a signal (Q x ) is generated.
- the optical hybrid 202 generates a third optical signal (I y ) by causing the optical signal and local light to interfere with each other with a phase difference of 0, and causes the optical signal and local light to interfere with each other with a phase difference of ⁇ / 2.
- An optical signal (Q y ) is generated.
- the first optical signal and the second optical signal form a set of signals
- the third optical signal and the fourth optical signal also form a set of signals.
- the photoelectric conversion unit 204 photoelectrically converts the four optical signals (output light) generated by the optical hybrid 202 to generate four analog signals.
- the AD conversion unit 206 converts each of the four analog signals generated by the photoelectric conversion unit 204 into digital signals.
- the digital processing apparatus 100 includes a band compensation coefficient setting unit 118 and a chromatic dispersion compensation coefficient setting unit 119.
- the band compensation coefficient setting unit 118 stores a coefficient for compensating for chromatic dispersion caused by the front end unit 200.
- the coefficient stored in the chromatic dispersion compensation coefficient setting unit 119 and the coefficient stored in the band compensation coefficient setting unit 118 are multiplied by the first coefficient set by the first coefficient setting unit 114. Then, the first coefficient after multiplication is output to the digital filter 110.
- the information stored in the band compensation coefficient setting unit 118 and the chromatic dispersion compensation coefficient setting unit 119 is a semi-fixed value, and is updated manually, for example, as necessary.
- the digital processing apparatus 100 may further include a storage unit that stores a coefficient for performing skew compensation and a storage unit that stores a coefficient for performing IQ imbalance compensation. The coefficients stored in these storage units are also multiplied by the first coefficient set by the first coefficient setting unit 114.
- FIG. 17 is a diagram showing a configuration of the digital filter 110 shown in FIG.
- the Fourier transform unit 111, the inverse Fourier transform unit 112, and the filter unit 113 are provided for each of the two digital signals.
- the two Fourier transform units 111, the inverse Fourier transform unit 112, and the filter unit 113 constitute a butterfly circuit.
- FIG. 18 is a diagram illustrating an example of the configuration of the second coefficient setting unit 140 and the first coefficient setting unit 114 in the present embodiment.
- the second coefficient setting unit 140 performs the processing described with reference to FIG.
- the second coefficient setting unit 140 includes a gradient information calculation unit 141 and a second coefficient update unit 143.
- the gradient information calculation unit 141 calculates gradient information for each of the four signals Ix, Qx, Iy, and Qy.
- the second coefficient updating unit 143 sets the second coefficient for each of the four signals Ix, Qx, Iy, and Qy.
- the first coefficient setting unit 114 sets the first coefficient for each of the four signals Ix, Qx, Iy, and Qy.
- the same effect as in the fifth embodiment can be obtained. Further, in the receiving apparatus used for digital coherent, it is possible to reduce the arithmetic processing required for setting the coefficient of the digital filter 110.
- the signal transmission / reception system according to the present embodiment has the same configuration as that of the signal transmission / reception system according to the fifth embodiment except that the signal transmission / reception system is a system that transmits and receives signals by wireless communication.
- FIG. 19 is a diagram illustrating a configuration of the receiving device 30 according to the present embodiment.
- the receiving device 30 includes an antenna 300, a front end unit 400, a digital processing device 100, a first coefficient setting unit 114, a digital signal processing unit 120, an error signal generation unit 130, and a second coefficient setting unit 140.
- the configurations of the digital processing device 100, the first coefficient setting unit 114, the digital signal processing unit 120, the error signal generation unit 130, and the second coefficient setting unit 140 are the same as those in any of the second to sixth embodiments described above. is there.
- the antenna 300 receives a signal transmitted wirelessly.
- the front end unit 400 processes the signal received by the antenna 300 and outputs the processed digital signal to the digital processing device 100.
- FIG. 20 is a diagram illustrating a functional configuration of the front end unit 400.
- the front end unit 400 includes a filter 402, a low noise amplifier 404, a mixer 406, a reference signal source 407, a filter 408, a variable gain amplifier 410, and an AD conversion unit 412.
- the filter 402 removes a frequency component that becomes noise from the signal received by the antenna 300.
- the low noise amplifier 404 amplifies the analog signal output from the filter 402.
- the mixer 406 multiplies the reference signal generated by the reference signal source 407 on the analog signal output by the low noise amplifier 404.
- the filter 408 removes a frequency component that becomes noise from the analog signal output from the mixer 406.
- the variable gain amplifier 410 amplifies the analog signal output from the filter 408.
- the AD conversion unit 412 converts the analog signal output from the variable gain amplifier 410 into a digital signal.
- the front end unit 400 may not include at least one (including all cases) of the filter 402, the low noise amplifier 404, the mixer 406, the reference signal source 407, the filter 408, and the variable gain amplifier 410. .
- the signal received by the antenna 300 is directly converted into a digital signal by the AD conversion unit 412.
- the signal transmission / reception system according to the present embodiment has the same configuration as that of the signal transmission / reception system according to the seventh embodiment, except that wireless communication is performed using a MIMO (Multiple Input Multiple Output) scheme.
- MIMO Multiple Input Multiple Output
- FIG. 21 is a diagram illustrating a configuration of the receiving device 30 according to the eighth embodiment.
- the receiving apparatus 30 includes a plurality of sets of an antenna 300, a front end unit 400, a complex signal generation unit 208, and a digital filter 110.
- the front end unit 400 extracts a real number component (I n ) and an imaginary number component (Q n ) from the analog signal received by the antenna 300, and AD-converts each.
- the processing after the complex signal generation unit 208 is the same as the processing described with reference to FIGS.
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Abstract
Description
N個の第1係数を用いて、前記周波数領域信号を周波数領域で等化するフィルタ手段と、
前記フィルタ手段で処理された前記周波数領域信号を前記デジタル信号に戻す逆フーリエ変換手段と、
m個(ただしN>m)の第2係数を用いて、前記N個の第1係数を設定する第1係数設定手段と、
を備えるデジタル信号処理装置が提供される。
前記デジタル信号を処理するデジタル信号処理手段と、
を備え、
前記デジタル信号処理手段は、
前記デジタル信号をフーリエ変換して周波数軸の信号である周波数領域信号を生成するフーリエ変換手段と、
N個の第1係数を用いて、前記周波数領域信号を周波数領域で等化するフィルタ手段と、
前記フィルタ手段で処理された前記周波数領域信号を前記デジタル信号に戻す逆フーリエ変換手段と、
m個(ただしN>m)の第2係数を用いて、前記N個の第1係数を設定する第1係数設定手段と、
を備える受信装置が提供される。
前記デジタル信号を受信する受信手段と、
を備え、
前記受信手段は、
前記デジタル信号を取得するデジタル信号取得手段と、
前記デジタル信号を処理するデジタル信号処理手段と、
を備え、
前記デジタル信号処理手段は、
前記デジタル信号をフーリエ変換して周波数軸の信号である周波数領域信号を生成するフーリエ変換手段と、
N個の第1係数を用いて、前記周波数領域信号を周波数領域で等化するフィルタ手段と、
前記フィルタ手段で処理された前記周波数領域信号を前記デジタル信号に戻す逆フーリエ変換手段と、
m個(ただしN>m)の第2係数を用いて、前記N個の第1係数を設定する第1係数設定手段と、
を備える信号送受信システムが提供される。
図1は、第1の実施形態に係るデジタル処理装置100の構成を示す図である。デジタル処理装置100は、デジタルフィルタ110を有している。デジタルフィルタ110は、フーリエ変換部111、逆フーリエ変換部112、フィルタ部113、及び第1係数設定部114を有している。フーリエ変換部111は、時間軸のデジタル信号をフーリエ変換して周波数軸の信号である周波数領域信号を生成する。フィルタ部113は、N個の第1係数を用いて、周波数領域信号を周波数領域で等化する。逆フーリエ変換部112は、フィルタ部113が処理した周波数領域信号を逆フーリエ変換して、時間軸のデジタル信号に戻す。すなわちフーリエ変換部111、逆フーリエ変換部112、及びフィルタ部113は、デジタル信号に含まれる波形歪を、周波数領域における等化処理(すなわちFDE(frequency-domain equalization))で、補償する。第1係数設定部114は、m個(ただしN>m)の第2係数を用いて、フィルタ部113が用いるN個の第1係数を設定する。
図8は、第2の実施形態に係るデジタル処理装置100の構成を示す図である。本実施形態に係るデジタル処理装置100は、固定フィルタ係数設定部116及び乗算部115を有している点を除いて、第1の実施形態に係るデジタル処理装置100と同様の構成である。
図9は、第3の実施形態に係るデジタル処理装置100の構成を示す図である。本実施形態に係るデジタル処理装置100は、初期値設定部117、デジタル信号処理部120、誤差信号生成部130、及び第2係数設定部140を有している点を除いて、第1の実施形態に係るデジタル処理装置100と同様の構成である。
図13は、第3の実施形態に係る信号送受信システムの構成を示す図である。本図に示す信号送受信システムは、送信機10及び受信装置30を有している。送信装置10は、デジタル信号を生成して受信装置30に送信する。送信装置10と受信装置30の間には、伝送媒質20が存在している。送信装置10と受信装置30の間の通信が有線で行われる場合、伝送媒質20は、例えば光ファイバである。また送信装置10と受信装置30の間の通信が無線で行われる場合、伝送媒質20は空間である。
図15は、第5の実施形態に係る信号送受信システムで用いられる受信装置30の構成を示す図である。本実施形態に係る信号送受信システムは、受信装置30の構成を除いて、第4の実施形態に係る信号送受信システムと同様の構成である。
本実施形態に係る信号送受信システムは、デジタルコヒーレント技術を用いて、信号を送受信するシステムである点を除いて、第5の実施形態に係る信号送受信システムと同様の構成である。すなわち本実施形態において、信号は、光通信によって送信される。光信号は、偏波多重方式やQAM(quadrature amplitude modulation)などを用いて、多値変調されている。
本実施形態に係る信号送受信システムは、無線通信により信号を送受信するシステムである点を除いて、第5の実施形態に係る信号送受信システムと同様の構成である。
本実施形態に係る信号送受信システムは、MIMO(Multiple Input Multiple Output)方式で無線通信する点を除いて、第7の実施形態に係る信号送受信システムと同様の構成である。
Claims (14)
- デジタル信号をフーリエ変換して周波数軸の信号である周波数領域信号を生成するフーリエ変換手段と、
N個の第1係数を用いて、前記周波数領域信号を周波数領域で等化するフィルタ手段と、
前記フィルタ手段で処理された前記周波数領域信号を前記デジタル信号に戻す逆フーリエ変換手段と、
m個(ただしN>m)の第2係数を用いて、前記N個の第1係数を設定する第1係数設定手段と、
を備えるデジタル信号処理装置。 - 請求項1に記載のデジタル信号処理装置において、
前記第1係数及び第2係数は周波数別に設定された係数であり、
周波数軸上において、前記第2係数の間隔の少なくとも一つは、前記第1係数の間隔よりも広く、
前記第1係数設定手段は、前記周波数を変数としていて前記第1係数を近似する近似関数を、前記m個の第2係数を用いて設定し、前記近似関数に基づいて前記第1係数を設定するデジタル信号処理装置。 - 請求項1に記載のデジタル信号処理装置において、
前記第1係数設定手段は、前記m個の第2係数を入力として前記N個の第1係数を出力とする回路を有するデジタル信号処理装置。 - 請求項3に記載のデジタル信号処理装置において、
前記回路は、FIR(finite impulse response)フィルタ伝達特性演算回路、セグメント分け伝達特性演算回路、又は多項式近時伝達特性演算回路であるデジタル信号処理装置。 - 請求項1に記載のデジタル信号処理装置において、
前記第1係数設定手段は、
前記m個の第2係数それぞれに対応したm個の第3係数からなる係数セットを、前記N個の第1係数別に記憶しており、
前記第1係数別に、当該第1係数に対応する前記係数セットに含まれる前記m個の第3係数それぞれを、当該第3係数に対応する前記第2係数に乗ずることにより、当該第1係数を算出するデジタル信号処理装置。 - 請求項1~5のいずれか一項に記載のデジタル信号処理装置において、
前記逆フーリエ変換手段が生成した前記デジタル信号の誤差を示す誤差信号を受信し、前記誤差信号に基づいて、前記m個の第2係数を設定する第2係数設定手段を備えるデジタル信号処理装置。 - 請求項6に記載のデジタル信号処理装置において、
前記逆フーリエ変換手段が生成した前記デジタル信号と参照信号の差に基づいて、前記誤差信号を生成する誤差信号生成手段を備えるデジタル信号処理装置。 - 請求項6に記載のデジタル信号処理装置において、
前記逆フーリエ変換手段が生成した前記デジタル信号の誤りを訂正したことを示す誤り訂正情報から、前記誤差信号を生成する誤差信号生成手段を備えるデジタル信号処理装置。 - 請求項6に記載のデジタル信号処理装置において、
前記逆フーリエ変換手段が生成した前記デジタル信号の波形ゆがみに基づいて、前記誤差信号を生成する誤差信号生成手段を備えるデジタル信号処理装置。 - 請求項6~9のいずれか一項に記載のデジタル信号処理装置において、
前記第2係数設定手段は、局所探索法により前記m個の第2係数を設定するデジタル信号処理装置。 - 請求項1~10のいずれか一項に記載のデジタル信号処理装置において、
複数の前記デジタル信号が入力され、
前記複数のデジタル信号別に、前記フーリエ変換手段、前記フィルタ手段、及び前記逆フーリエ変換手段を有しており、
前記複数の前記フーリエ変換手段、前記フィルタ手段、及び前記逆フーリエ変換手段は、バタフライ回路であるデジタル信号処理装置。 - デジタル信号を取得するデジタル信号取得手段と、
前記デジタル信号を処理するデジタル信号処理手段と、
を備え、
前記デジタル信号処理手段は、
前記デジタル信号をフーリエ変換して周波数軸の信号である周波数領域信号を生成するフーリエ変換手段と、
N個の第1係数を用いて、前記周波数領域信号を周波数領域で等化するフィルタ手段と、
前記フィルタ手段で処理された前記周波数領域信号を前記デジタル信号に戻す逆フーリエ変換手段と、
m個(ただしN>m)の第2係数を用いて、前記N個の第1係数を設定する第1係数設定手段と、
を備える受信装置。 - 請求項12に記載の受信装置において、
光信号を光電変換してアナログ信号を生成する光電変換手段をさらに備え、
前記デジタル信号取得手段は、前記アナログ信号を前記デジタル信号に変換することにより、前記デジタル信号を取得する受信装置。 - デジタル信号を送信する送信手段と、
前記デジタル信号を受信する受信手段と、
を備え、
前記受信手段は、
前記デジタル信号を取得するデジタル信号取得手段と、
前記デジタル信号を処理するデジタル信号処理手段と、
を備え、
前記デジタル信号処理手段は、
前記デジタル信号をフーリエ変換して周波数軸の信号である周波数領域信号を生成するフーリエ変換手段と、
N個の第1係数を用いて、前記周波数領域信号を周波数領域で等化するフィルタ手段と、
前記フィルタ手段で処理された前記周波数領域信号を前記デジタル信号に戻す逆フーリエ変換手段と、
m個(ただしN>m)の第2係数を用いて、前記N個の第1係数を設定する第1係数設定手段と、
を備える信号送受信システム。
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