JPH0746221A - Digital demodulator - Google Patents

Abstract

PURPOSE:To obtain the digital demodulator with a small circuit scale demodulating an orthogonal frequency multiplex signal. CONSTITUTION:A DFT circuit is a 2N, 1204-input discrete Fourier transformation circuit comprising a component such as a digital signal processor(DSP), applies discrete Fourier transformation to a digital signal inputted from a serial/ parallel conversion circuit 119 to demodulate the signal. An orthogonal frequency multiplex signal is inputted to a real number part input (Re) of the discrete Fourier transformation circuit 121 and a fixed value such as 0 is always inputted to an imaginary number part input (Im). Parallel/serial conversion circuits 122, 123 convert the conversion result received from the DFT circuit 121 into a serial signal, buffer memories 124, 125 executes processing such as elimination of a guard interval as to the received conversion result, and select only significant parts in the result of conversion to output as I and Q channel signals.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital demodulator for receiving and demodulating a quadrature frequency modulated signal.

[0002]

2. Description of the Related Art When transmitting a digital signal, a method of phase-modulating and amplitude-modulating a carrier signal of a single frequency based on the digital signal is generally used. As such a modulation method, phase modulation (PSK) that changes only the phase and quadrature modulation (QAM) that changes both the phase and the amplitude are often used. As in the above-described modulation methods, conventionally, a carrier signal of a single frequency is modulated so as to have an occupied bandwidth that fits within a transmission band. On the other hand, recently, as a new modulation method, a modulation method called an orthogonal frequency multiplexing method (OFDM) has been proposed.

In this orthogonal frequency multiplexing system, a plurality of orthogonal carrier signals are generated within a transmission band, the transmission band is divided, and each carrier signal is subjected to phase modulation (PSK) or quadrature modulation (QAM) with a digital signal. It is a modulation method. 1 because the transmission band is divided by multiple carrier signals
Since the band per carrier signal becomes narrower, the modulation speed per carrier signal becomes slower. However, when the transmission band is the same, the total transmission speed obtained as a result of modulating a plurality of carrier signals is the same as that of the conventional modulation. In this method, a large number of carrier signals are transmitted in parallel, so the speed per symbol becomes slower.Therefore, in a transmission line with so-called multipath interference, the delay time of the multipath interference wave relative to the time length of the symbol is delayed. Can be reduced. Therefore, this method is less susceptible to multipath interference, and due to this feature, particular attention is paid to the transmission of digital signals by terrestrial waves.

Here, it is necessary to perform discrete Fourier transform and discrete inverse Fourier transform at high speed in the signal processing of the orthogonal multiple frequency multiplex system. However, due to recent advances in semiconductor technology, semiconductor elements capable of executing discrete Fourier transform and discrete inverse Fourier transform by hardware processing, which have been difficult in the past, have been supplied. Therefore, it is possible to easily perform the modulation of the orthogonal frequency multiplexing system using such an element or demodulate the signal modulated by this modulation system. Such progress in semiconductor technology is also one of the reasons why the orthogonal frequency multiplexing method is drawing attention.

A general orthogonal frequency multiplexing system will be described below. The characteristic of the orthogonal frequency multiplexing system is that a carrier signal is generated by dividing a transmission channel (transmission band) into orthogonal bands for each predetermined bandwidth, and the modulated signal is a digital signal having a low data rate such that the modulated signal can be accommodated in each bandwidth. However, instead of modulating each carrier signal with a digital signal, all carrier signals are collectively modulated by discrete inverse Fourier transform (IDFT).

The configuration of a modulator for performing orthogonal frequency multiplex modulation will be described below with reference to FIG. FIG. 3 is a diagram showing the configuration of a conventional orthogonal frequency multiplexing modulator 80. The orthogonal frequency multiplex modulator 80 includes serial / parallel conversion circuits 803 and 804 and a discrete inverse Fourier transform circuit (IDF).
T) 805, parallel / serial conversion circuit (P / S) 8
06, 806, buffer memory (BM) 808, 80
9, D / A conversion circuits (D / A) 810, 811, low-pass filters (LPF) 812, 813, multiplication circuit 81
4, 815, local oscillator 816, 90 ° phase shift circuit (H)
817, adder circuit 818, band pass filter (BP
F) 819, an RF converter 820, and a transmission antenna 821. Also, the I channel signal 80
The 1 and Q channel signals 802 are digital signals to be respectively transmitted by orthogonal frequency multiplex modulation, and the transmission signal 822 is a radio wave generated by the processing by the orthogonal frequency multiplex modulation device 80 and transmitted from the transmission antenna 821. It is a signal.

The operation of the orthogonal frequency multiplexing modulator 80 will be described below. In the I-channel signal 801 and the Q-channel signal 802, in the transmission format of the orthogonal frequency multiplex signal, a signalless symbol (synchronization symbol) used for establishing synchronization of the clock signal and the DFT time window signal on the receiving side is inserted. Transmission data. The I channel signal 801 and the Q channel signal 802 are input to serial / parallel conversion circuits 803 and 804, respectively. Serial / parallel conversion circuits 803 and 804
Is an I channel signal 801 and a Q channel signal 802.
To serial / parallel conversion to generate these parallel data and input them to the discrete inverse Fourier transform circuit 805. The discrete inverse Fourier transform circuit 805 transforms the parallel I-channel signal 801 and the Q-channel signal 802 into a signal in the time domain by performing a discrete inverse Fourier transform (IDFT).

The two parallel time domain signals obtained in the discrete inverse Fourier transform circuit 805 are respectively:
The parallel / serial conversion circuits 806 and 807 convert the signals into serial signals temporally, and further, the buffer memory 80
A so-called guard interval is added by 8, 809 and input to D / A conversion circuits 810, 811. These signals with guard intervals added are D / A
The signals are converted into analog signals by the conversion circuits 810 and 811, and input to the low pass filters 812 and 813. These signals, converted to analog format signals,
Filtered by the low-pass filters 812 and 813 to remove the aliasing signal component, the multiplication circuit 814,
815 is input.

The signals from which the aliasing signal components have been removed are carrier signals output from the local oscillator 816 by the multiplying circuits 814 and 815, respectively, and this carrier signal is phase shifted by 90 ° by the 90 ° phase shift circuit 817. It is multiplied with the carrier wave signal. The respective carrier signals modulated by the multiplication circuits 814 and 815 are added by the addition circuit 818.
Are added and combined. The signals combined by the adder circuit 818 are limited to a predetermined bandwidth by the bandpass filter 819 and input to the RF converter 820. The signal band-limited by the adder circuit 818 is RF
The frequency is converted into a desired frequency by the converter 820, and is output as a transmission signal 822 from the transmission antenna 821. As described above, the I-channel signal 801 and the Q-channel signal 802 have the non-signal portions corresponding to the synchronization symbols inserted in advance, so that the orthogonal frequency multiplex modulator 80 transmitted from the orthogonal frequency multiplex modulator 80.
In the orthogonal frequency division multiplexed signal generated by, there is a synchronization symbol for every predetermined symbol.

The configuration and operation of a conventional orthogonal frequency multiplex demodulator 85 for receiving and demodulating a signal modulated by the orthogonal frequency multiplex system will be described below with reference to FIG. FIG. 4 is a diagram showing a configuration of a conventional orthogonal frequency multiplex demodulator 85. The orthogonal frequency multiplex demodulator 85 includes a receiving antenna 851, a tuner (Tu) 852, and a multiplication circuit 85.
3, 854, local oscillator 855, 90 ° phase shift circuit 85
6, low-pass filters 857 and 858, A / D conversion circuits 861 and 862, serial / parallel conversion circuit 859,
860, a discrete Fourier transform circuit (DFT) 863, parallel / serial converter circuits 864 and 865, buffer memories 866 and 867, a carrier signal reproduction circuit 868, and a clock reproduction circuit (BTR) 869.

Further, in FIG. 4, an RF input signal 850
Is an orthogonal frequency multiplex signal (transmission signal 822) generated by the orthogonal frequency multiplex modulator 80 and having a synchronization symbol inserted in addition to the data to be transmitted and transmitted. The I channel signal 871 and the Q channel signal 872 are
Is a signal in digital format obtained as a result of demodulation of the orthogonal frequency multiplex demodulator 85 by the orthogonal frequency multiplex demodulator 85.

The operation of the orthogonal frequency multiplex demodulator 85 will be described below. The RF signal input 850 is the receiving antenna 851.
It is captured by and input to the tuner 852. Tuner 8
At 52, the RF input signal 850 is frequency-converted into a signal in the intermediate frequency band, amplified, and input to the multiplication circuits 853 and 854. The output signals of the local oscillator 855 and the signal obtained by shifting the output signal of the local oscillator 855 by 90 ° by the 90 ° phase shift circuit 856 are input to the multiplication circuits 853 and 854, respectively. -Na 852
Is multiplied by the output signal of 1 to convert the intermediate frequency band signal output from the tuner 852 into a baseband signal. Unwanted harmonic components of these baseband signals are removed by low-pass filters 857 and 858, respectively, and are input to A / D conversion circuits 859 and 860.

The baseband signals from which unnecessary harmonic components have been removed are converted into digital signals by A / D conversion circuits 859 and 860, respectively, and are further paralleled by serial / parallel conversion circuits 861 and 862. The signal is converted into a signal of the format and is input to the discrete Fourier transform circuit 863. These signals converted into digital format signals are subjected to discrete Fourier transform (DFT) by the discrete Fourier transform circuit 863 and further converted into serial (serial) format signals by the parallel / serial conversion circuits 864 and 865. And buffer memory 866, 8
It is input to 67.

These signals converted into serial format signals are processed by buffer memories 866 and 867 such as removal of guard intervals added at the time of modulation,
It is output as an I channel signal 871 and a Q channel signal 872 in digital form. The local oscillator 855 is
DF by parallel / serial conversion circuits 864 and 865
Based on the signal after the T processing,
For example, the carrier signal is reproduced under the control of the Costas loop. The clock recovery circuit 869 receives the clock signal C based on the output signals of the low pass filters 857 and 858.
Generate K and DFT time window signals. These clock signals CK define the operation of signal processing in the discrete Fourier transform circuit 863 and the like. Further, the discrete Fourier transform circuit 863 cuts out the received signal to be the target of the discrete Fourier transform based on the DFT time window signal.

[0015]

In the conventional circuit, first, the received orthogonal frequency multiplexed signal is converted into two baseband signals by orthogonal reproduction carrier signals, so-called cos signal and sin signal, and these baseband signals are further converted. The signal is demodulated by performing similar processing in circuits of two systems. Therefore, it is necessary to have two systems of circuits that perform similar processing on two baseband signals, which causes a problem that the circuit scale becomes large. The present invention has been made in view of the above-mentioned problems of the prior art, and an object of the present invention is to provide a digital demodulation device for demodulating an orthogonal frequency multiplexed signal having a small circuit scale.

[0016]

In order to achieve the above-mentioned object, the digital demodulating device of the present invention has at least 2 units.
A means for processing an input signal having a predetermined type relationship, and having an orthogonal frequency multiplex signal and a demodulation means for converting a predetermined eigenvalue as the input signal from a time domain to a frequency domain to obtain a demodulated signal. Is characterized by. Further preferably, the transform from the time domain to the frequency domain is a Fourier transform. Further preferably, the input signal of the demodulation means is of two types, that is, a real part of an input of a Fourier transform and an imaginary part of an input of a Fourier transform, and the demodulation means outputs the orthogonal frequency multiplexed signal. One of the real number part and the imaginary number part of the input signal is used, and the fixed value is subjected to Fourier transform as the other of the input signal. Further preferably, the demodulation means further comprises a selection means for selecting only a predetermined significant portion of the demodulated signal.

[0017]

The received orthogonal frequency multiplexed signal is converted into a baseband signal by a single reproduction carrier signal, and the baseband signal is input to either the imaginary number input or the real number input of the discrete Fourier transform circuit. Then, a fixed value is input to the other inputs, a discrete Fourier transform is performed, and demodulation is performed. In addition, of the results of the discrete Fourier transform, only the significant ones are selected as the demodulation output.

[0018]

EXAMPLES Prior to the description of the examples, orthogonal frequency multiplexing (O
The FDM) signal will be described using mathematical expressions. The quadrature frequency multiplex signal is a multi-level modulation such as a general 64QAM, which performs amplitude modulation and phase modulation of a single carrier signal to transmit information within a predetermined band, while a plurality of carrier signals are respectively transmitted.
This is a modulation method in which information is transmitted within a predetermined band by modulating at a lower information rate (bit rate) than a modulation method using a single carrier signal. When the number of carrier signals of the orthogonal frequency multiplexed signal is N and each carrier signal is QAM-modulated, the m-th symbol f of the orthogonal frequency multiplexed signal
_m (t) is represented by the following equation.

[0019]

[Equation 1]

In Expression 1, Δφ _mn is a term for correcting the phase rotation of the symbol due to the guard interval described later, and is represented by the following expression.

[0021]

[Equation 2]

From Equations 1 and 2, the orthogonal frequency multiplexed signal is formulated by the following equation.

[0023]

[Equation 3]

The power spectrum of the orthogonal frequency multiplex signal will be formulated below. The Fourier integral of the m-th symbol f _m (t) in the time width T ′ of the m-th symbol represented by Expression 1 is represented by the following expression.

[0025]

[Equation 4]

From Equation 4, the energy spectrum in this section is as expressed by the following equation.

[0027]

[Equation 5]

In the second term of Equation 5,

[0029]

[Equation 6]

[Mathematical formula-see original document] is the correlation function of the modulated waves of the m-th and k-th carrier signals, and assuming that there is no correlation in the information, equation 6 becomes 0. Therefore, the equation 3 is transformed into the following equation.

[0031]

[Equation 7]

Hereinafter, SSB in the orthogonal frequency multiplexing system
The generation of signals will be described. If the Hilbert transform of the signal g (t) is represented by g ′ (t), then the upper side signal (USB) S _u (t) and the lower side signal (USB) S
_l (t) is represented by the following equations, respectively.

[0033]

[Equation 8]

[0034]

[Equation 9]

In the Hilbert transform, g ′ (t) is
It is defined by the following formula.

[0036]

[Equation 10]

That is, the Hilbert transform is an output signal when a signal is input to a filter whose impulse response function h (t) is as in the following equation.

[0038]

[Equation 11]

When the Fourier transform of the impulse response function h (t) is H (ω), the following equation is obtained.

[0040]

[Equation 12]

Such a filter is usually called a Hilbert filter. Next, consider the Fourier transform F (ω) of the signal f (t) in which the spectrum exists only in the positive frequency region as shown in FIG. FIG. 1 is a diagram illustrating a signal spectrum. In FIG. 1, (A) is a signal F (ω) having a spectrum only in the positive frequency region,
(B) is an even function signal F _e (ω) when F (ω) shown in (A) is decomposed, and (C) is an odd function F when F (ω) shown in (A) is decomposed. Indicates _o (ω). This Fourier transform F (ω) can be decomposed into two functions shown in FIGS. 1 (B) and 1 (C). That is, the Fourier transform F (ω) is expressed by the following equation.

[0042]

[Equation 13]

The even function F _e (ω) and the odd function F _o (ω) shown in FIG. 1 are defined by the following equations.

[0044]

[Equation 14]

[0045]

[Equation 15]

The even function F _e (ω) and the odd function F _o (ω) shown in FIG. 1 have the following relationship.

[0047]

[Equation 16]

Here, the even function F _e (ω) and the odd function F
The inverse Fourier transform of _o (ω) is obtained, and each of them is a function f _e
(T), and, when a function f _o (t), which are expressed by the following equation.

[0049]

[Equation 17]

[0050]

[Equation 18]

However, in equations 17 and 18, R (ω)
And X (ω) are the real part and the imaginary part of F (ω), respectively, and the following relationship holds with the Fourier transform F (ω).

[0052]

[Formula 19]

Therefore, the function f _e (t) is a real function,
Function f _o (t) is found to be imaginary function.

In Equation 18, consider the inverse Fourier transform of sgnω.

[0055]

[Equation 20]

That is, the following equation holds.

[0057]

[Equation 21]

[0058]

[Equation 22]

[0059]

[Equation 23]

Therefore, the following equation is obtained from the equation 16 and the equations 21 to 23 by using the superposition integral theorem.

[0061]

[Equation 24]

[0062]

[Equation 25]

From equations 24 and 25, it is understood that the function f _e (t) and the function f _o (t) are in the relationship of Hilbert transform.

From the equations 17 and 18, the function f _e (t)
Is a real function, and the function f _o (t) is an imaginary function. Therefore, in order to convert the orthogonal frequency signal into SSB, the following processing is performed. First, it is assumed that there is only a positive side (negative side) frequency component and a negative side (positive side) frequency component is 0, that is, a function F (ω). Next, the time function f _e (t) + jf is obtained by performing the inverse Fourier integration of the function F (ω).
_{Get o} (t). Next, the upper wave SSB signal is changed to S
_{Suppose u} (t) and the lower sideband SSB signal are S _l (t), the following equation is calculated to obtain the SSB signal.

Examples of the present invention will be described below. First,
The principle of the digital demodulator of the present invention will be described. The orthogonal frequency multiplexed signal input to the digital demodulator of the present invention is a real-time function. Therefore, in the spectrum of the orthogonal frequency-multiplexed signal, the amplitude becomes even symmetry and the phase becomes odd symmetry in the upper and lower bands of the carrier signal.

Here, a discrete Fourier transform circuit (DFT circuit) is input to the orthogonal frequency multiplex signal, which is a real-time function, at the input of the real part of this transform circuit to perform a discrete Fourier transform (DFT). It is possible to obtain a signal in which the amplitude is even symmetric and the phase is odd symmetric in the upper and lower bands of the carrier signal. Of this DFT result,
Since the transmission data can be output if one of the upper and lower signals (positive and negative frequencies) of the carrier signal is known, only the significant frequency component of the first half or the second half of the DFT output is extracted and used as the demodulation output. be able to. When this quadrature frequency multiplexed signal is input to the imaginary part input of the DFT circuit, the real part output of the DFT circuit becomes even symmetry at the positive and negative frequencies, and the imaginary part output is different by 180 degrees at the positive and negative frequencies unlike the above case. Phase difference occurs. However, also in this case, only the significant frequency components of the first half or the second half of the DFT output can be extracted and used as the demodulation output.

The digital demodulating device of the present invention is used for demodulating digital image data modulated by, for example, an orthogonal frequency multiplexing system. FIG. 2 is a diagram showing the configuration of the orthogonal frequency multiplex demodulator 18 of the present invention. In FIG. 2, a reception antenna 101 captures a reception signal that is orthogonal frequency-multiplexed by an orthogonal frequency multiplexing modulator 80 shown as a conventional technique and is transmitted as a radio wave signal. The tuner 102 has a receiving antenna 101.
The received signal captured by is converted into a predetermined intermediate frequency band, amplified, and input to the demodulator. The multiplication circuit 111
The received signal of the intermediate frequency band input from the tuner 102 and the output signal of the local oscillator (LO) 113 are multiplied and input to the low pass filter (LFP) 115. The low-pass filter 115 passes a component having a frequency equal to or lower than a predetermined high cutoff frequency in the output signal of the multiplication circuit 111, removes an unnecessary frequency component, and inputs the component to the analog / digital conversion circuit (A / D) 117.

The analog / digital conversion circuit 117 is
Each of the analog signals input from the low-pass filter 115 is converted into a digital signal. The serial / parallel conversion circuit (S / P) 119 converts a serial (serial) format digital signal input from the analog / digital conversion circuit 117 into a parallel (parallel) format signal, and inputs the real part of the DFT circuit 121. (R
Enter in e). The DFT circuit 121 is composed of, for example, a digital signal processor (DSP) 2
A discrete Fourier transform circuit having N, 1204 inputs,
The digital signal input from the serial / parallel conversion circuit 119 is converted from the time domain to the frequency domain (discrete Fourier transform (DFT)) and input to the parallel / serial conversion circuits (P / S) 122 and 123. DFT circuit 1
The conversion performed at 21 is shown by the following equation.

[0069]

[Equation 26]

Among the inputs of the discrete Fourier transform circuit 121, the output signal of the serial / parallel conversion circuit 119 is input to the real part input (Re), and a fixed value, for example, 0 is input to the imaginary part input (Im). Is always entered. Here, the relationship between the input to the discrete Fourier transform circuit 121 and the converted output of the discrete Fourier transform circuit 121 will be described. When the received data is input to the real number input of the discrete Fourier transform circuit 121 and the numerical value 0 is input to the imaginary number input, the output of the discrete Fourier transform circuit 121 is the temporal center of the output signal. Is even symmetric to. On the contrary, when the received data is input to the imaginary number input of the discrete Fourier transform circuit 121 and the numerical value 0 is input to the real number input, the output of the discrete Fourier transform circuit 121 is the time of the output signal. It is oddly symmetric with respect to the center. That is, in any of the above cases, the output signal of the discrete Fourier transform circuit 121 includes the same information in the first half and the second half of the output signal, and by selecting and outputting only the first half or the second half, It is possible to demodulate an orthogonal frequency multiplexed signal.

Parallel / serial conversion circuits 122, 12
3 receives the real part and the imaginary part of the conversion result of the discrete Fourier transform circuit 121, respectively.
The parallel format digital signal input from the converter 21 is converted into a serial format signal, and the buffer memory (BM) 1
24, 125, and a synchronizing circuit (SYNC) 181.

The buffer memories 124 and 125 perform processing such as guard interval removal on the conversion results input from the parallel / serial conversion circuits 122 and 123, respectively, and select only significant portions of the conversion results. And outputs as an I channel signal and a Q channel signal. Carrier wave signal reproduction circuit (SYNC) 181
Is composed of, for example, a Costas loop circuit or the like, controls the local oscillator 113 based on the output signals of the parallel / serial conversion circuits 122 and 123 to generate a local frequency signal of a predetermined frequency, and the clock generation circuit 182.
To reproduce a carrier signal of a predetermined frequency. The local oscillator 113 is, for example, a voltage control oscillator circuit (VCO).
The local signal of a predetermined frequency is generated under the control of the synchronizing circuit 181. The local oscillator 182 is, for example, a voltage control oscillator (VCO), and generates a carrier signal of a predetermined frequency under the control of the synchronizing circuit 181.

The operation of the orthogonal frequency multiplex demodulator 18 will be described below. The tuner 102 amplifies the reception signal generated by the quadrature frequency multiplex modulation device 10 shown in the first embodiment and captured by the reception antenna 101,
The signal is converted into a signal in a predetermined intermediate frequency band and input to the multiplication circuit 111. The multiplication circuit 111 multiplies the input signal from the tuner 102 by the carrier signal generated by the local oscillator 113, converts the signal into a baseband signal, and inputs the baseband signal to the low-pass filter 115. These baseband signals are band-limited by the low pass filters 115 and 116,
Further, analog / digital conversion circuits 117 and 118
Is converted into a digital format signal by. analog/
The output signals of the digital conversion circuits 117 and 118 are converted into parallel format signals by the serial / parallel conversion circuits 119 and 120, respectively, and are input to the real part input and the imaginary part input of the DFT circuit 121, and the discrete Fourier transform is performed. To be done. The result of the discrete Fourier transform is converted into a serial format signal by the parallel / serial conversion circuits 122 and 123, the speed is converted by the calling signal generation circuit 131, the guard interval is removed, and the discrete Fourier transform circuit 121 is further added. A significant portion of the first half or the second half of the conversion result by is selected and output as demodulation output data.

In the orthogonal frequency multiplex demodulator 18 of the present invention shown in FIG. 2, the orthogonal frequency modulated signal is input to the real part input of the discrete Fourier transform circuit 121, and the fixed value is input to the imaginary part input. However, conversely to this configuration, a fixed value is input to the real part input of the discrete Fourier transform circuit 121 and an orthogonal frequency multiplex signal is input to the imaginary part input. The result of can be obtained. In addition to the above-described embodiment, the digital demodulating device of the present invention can have various configurations like the above-mentioned modification.

[0075]

As described above, according to the present invention, the baseband signal is not input to the real part input and the imaginary part input at the same time, but the baseband signal is input to one of the real part input and the imaginary part input. Enter. Therefore, it is possible to omit one of the so-called sin system circuit and the cos system circuit that processes two orthogonal baseband signals as shown in the related art. In particular, it is possible to greatly reduce the number of multiplication circuits of the discrete Fourier transform circuit. Therefore, a circuit for processing the baseband signal of one system can realize a function equivalent to that of the digital demodulator shown as the conventional technique, and the circuit scale can be significantly reduced. Therefore, in particular, the digital demodulation device of the present invention is a device that demodulates an orthogonal frequency multiplex signal used in a place where the radio field intensity is relatively strong, and in the case where downsizing and cost reduction of the device are required. It is valid.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a signal spectrum,
(A) is a signal F (ω) in which the spectrum exists only in the positive frequency region, and (B) is an even function signal F _e (ω) obtained by decomposing F (ω) shown in (A), (C ) Indicates an odd function F _o (ω) when F (ω) shown in (A) is decomposed.

FIG. 2 is a diagram showing a configuration of an orthogonal frequency multiplex demodulator of the present invention.

FIG. 3 is a diagram showing a configuration of a conventional orthogonal frequency multiplexing modulator.

FIG. 4 is a diagram showing a configuration of a conventional orthogonal frequency multiplex demodulator.

[Explanation of symbols]

18 ... Orthogonal frequency multiplex demodulator, 101 ... Receiving antenna, 102 ... Tuner, 111 ... Multiplication circuit, 113 ... Local oscillator, 115 ... Low-pass filter, 117 ... Analog / Digital conversion circuit, 119 ... Serial / parallel conversion circuit, 121
... Discrete Fourier transform circuit, 122,123 ...
Parallel / serial conversion circuit, 124, 125 ... Buffer memory, 181, Synchronous circuit, 182 ... Clock generation circuit

Claims (4)

[Claims] 1. A means for processing an input signal having at least two kinds of predetermined relations, which is an orthogonal frequency multiplex signal,
And a digital demodulation device comprising demodulation means for converting a predetermined eigenvalue as the input signal from a time domain to a frequency domain to obtain a demodulated signal. 2. The transformation from the time domain to the frequency domain is
The digital demodulation device according to claim 1, wherein the digital demodulation device is a Fourier transform. 3. The demodulation means has two kinds of input signals, a real part of a Fourier transform input and an imaginary part of a Fourier transform input, and the demodulation means outputs the orthogonal frequency multiplexed signal. 3. The digital demodulator according to claim 2, wherein one of a real part and an imaginary part of an input signal is used, and the fixed value is subjected to Fourier transform as the other of the input signal. 4. The digital demodulating device according to claim 1, wherein the demodulating means further comprises a selecting means for selecting only a predetermined significant portion of the demodulated signal.