JP2010087744A - Reception device, reception method, and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To exactly detect presence or absence of interference by using a signal after FFT. <P>SOLUTION: In a detection part 121 of analog broadcast interference, the presence or absence of interference by analog broadcast wave is detected by utilizing that frequency characteristics such as a video carrier of the analog broadcast have periodical peaks. When a channel of an OFDM signal which is received now is hindered by the analog broadcast wave, components of each carrier of the analog broadcast wave are detected as noise to a subcarrier with the same frequency. Since the frequency characteristics such as the video carrier of the analog broadcast have the periodical peaks, when the frequency characteristics of power of the noise by each subcarrier are detected in a form so as to have the periodical peaks, that shows that the channel is hindered by the analog broadcast wave. The present invention is applicable to a reception device of broadcast wave of an OFDM system. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a receiving device, a receiving method, and a program, and more particularly to a receiving device, a receiving method, and a program that can accurately detect the presence or absence of interference using a signal after FFT.

  As a modulation method for terrestrial digital broadcasting, a modulation method called an orthogonal frequency division multiplexing (OFDM) method is used.

  In the OFDM scheme, a number of orthogonal subcarriers are provided in the transmission band. Data is assigned to the amplitude and phase of each subcarrier, and digital modulation is performed by PSK (Phase Shift Keying) or QAM (Quadrature Amplitude Modulation).

  Since the OFDM system divides the entire transmission band by a large number of subcarriers, the band per subcarrier wave is narrowed and the transmission speed is slow, but the total transmission speed is the same as the conventional modulation system. Have.

  In the OFDM scheme, data is allocated to a plurality of subcarriers, and therefore modulation can be performed by IFFT (Inverse Fast Fourier Transform) calculation that performs inverse Fourier transform. Further, the demodulation of the OFDM signal obtained as a result of the modulation can be performed by FFT (Fast Fourier Transform) calculation that performs Fourier transform.

  Therefore, a transmitter that transmits an OFDM signal can be configured using a circuit that performs an IFFT operation, and a receiver that receives an OFDM signal can be configured using a circuit that performs an FFT operation.

  Due to the above characteristics, the OFDM system is often applied to terrestrial digital broadcasting that is strongly affected by multipath interference. Examples of terrestrial digital broadcasting standards that employ the OFDM scheme include DVB-T (Digital Video Broadcasting-Terrestrial), ISDB-T (Integrated Services Digital Broadcasting-Terrestrial), and ISDB-TSB.

  FIG. 1 is a diagram illustrating OFDM symbols.

  In the OFDM system, signal transmission is performed in units called OFDM symbols.

  As shown in FIG. 1, one OFDM symbol is composed of an effective symbol that is a signal interval in which IFFT is performed at the time of transmission, and a guard interval (hereinafter referred to as GI) in which a waveform of the latter half of the effective symbol is copied.

  The GI is inserted at a position before the valid symbol on the time axis. In the OFDM system, it is possible to prevent interference between OFDM symbols that occurs in a multipath environment by inserting a GI.

  When the effective symbol length of the OFDM symbol, that is, the effective symbol length that does not include the guard interval is Tu [seconds], and the interval between subcarriers is Fc [Hz], the relationship of the formula Fc = 1 / Tu Holds.

  A plurality of such OFDM symbols are collected to form one OFDM transmission frame. For example, in the ISDB-T standard, one OFDM transmission frame is formed from 204 OFDM symbols. The pilot signal insertion position is determined based on the unit of the OFDM transmission frame.

  In the OFDM system that uses the QAM modulation system as the modulation system for each subcarrier, the amplitude and phase of each subcarrier are different from those at the time of transmission and at the time of reception due to the influence of multipath, etc. during transmission. It will be different. Therefore, on the receiving side, it is necessary to equalize the signal so that the amplitude and phase of the received signal are equal to those transmitted.

  In the OFDM scheme, a known signal having a predetermined amplitude and a predetermined phase is inserted discretely as a pilot signal in a transmission symbol on the transmission side, and a transmission path is based on the amplitude and phase of the pilot signal on the reception side. Thus, the received signal is equalized. The pilot signal used for calculating the transmission path characteristics in this way is called a scattered pilot signal (hereinafter referred to as SP signal).

  FIG. 2 is a diagram showing an arrangement pattern in the OFDM symbol of the SP signal adopted in the DVB-T standard or the ISDB-T standard.

  The horizontal axis in FIG. 2 represents a subcarrier number that identifies a subcarrier of the OFDM signal, and the vertical axis represents an OFDM symbol number that identifies an OFDM symbol of the OFDM signal. The subcarrier number corresponds to the frequency, and the OFDM symbol number corresponds to the time.

  A white circle in FIG. 2 represents symbol data transmitted by each subcarrier, and a black circle represents an SP signal. As shown in FIG. 2, in the ISDB-T standard, SP signals are arranged for every four OFDM symbols in the time direction, and are arranged for every twelve subcarriers in the frequency direction.

  FIG. 3 is a block diagram illustrating a configuration example of a conventional OFDM receiver.

  The antenna 101 receives a broadcast wave of an OFDM signal transmitted from a transmitter of a broadcast station (not shown), converts the broadcast wave into an RF (Radio Frequency) signal, and outputs it to the tuner 102.

  The tuner 102 includes a calculation unit 102a and a local oscillator 102b. The arithmetic unit 102 a multiplies the RF signal from the antenna 101 by the signal from the local oscillator 102 b to frequency-convert the RF signal into an IF (Intermediate Frequency) signal, and outputs the IF signal to the BPF 103.

  The local oscillator 102b oscillates a sine wave signal having a predetermined frequency and outputs it to the arithmetic unit 102a.

  A BPF (Band Pass Filter) 103 filters the IF signal from the tuner 102 and outputs it to the A / D conversion unit 104.

  The A / D converter 104 performs A / D conversion on the IF signal from the BPF 103 and outputs a digital IF signal obtained as a result to the quadrature demodulator 105.

  The orthogonal demodulation unit 105 performs orthogonal demodulation on the IF signal from the A / D conversion unit 104 using a carrier having a predetermined frequency, and outputs a baseband OFDM signal.

  Hereinafter, the baseband OFDM signal before the FFT operation is referred to as an OFDM time domain signal. As a result of orthogonal demodulation, the OFDM time domain signal becomes a complex signal including a real axis component (I channel signal) and an imaginary axis component (Q channel signal). The OFDM time domain signal output from the orthogonal demodulation unit 105 is supplied to the offset correction unit 106.

  The offset correction unit 106 corrects various deviations for the OFDM time domain signal from the orthogonal demodulation unit 105. For example, the sampling offset in the A / D conversion unit 104 (correction of sampling timing deviation) or the carrier frequency offset in the orthogonal demodulation unit 105 (correction of deviation from the carrier frequency used in the transmission apparatus) ) Is performed.

  The OFDM time domain signal processed by the offset correction unit 106 is supplied to the interference cancellation unit 107.

  The interference cancellation unit 107 appropriately performs a filtering process for canceling an analog broadcast wave component existing in the same channel as an interference wave according to the detection result by the analog broadcast interference detection unit 109. From the analog broadcast interference detection unit 109, the detection result of the presence or absence of interference by the analog broadcast wave is supplied to the channel of the currently received OFDM signal.

  In the filtering process, a gain that attenuates a signal in a range corresponding to a band in which an analog broadcast wave signal exists is applied to the OFDM time domain signal. The interference cancellation unit 107 outputs the OFDM time domain signal obtained by performing the filtering process to the FFT unit 108.

  The FFT unit 108 sets an FFT interval, which is a signal interval for performing FFT, according to a symbol synchronization signal supplied from a symbol timing recovery circuit (not shown), and converts the OFDM time domain signal of the FFT interval to the OFDM time from the interference cancellation unit 107. Extract from region signal.

  The FFT unit 108 performs an FFT operation on the extracted FFT section signal. By the FFT operation on the OFDM time domain signal, data transmitted on the subcarrier, that is, an OFDM signal representing a transmission symbol on the IQ constellation is obtained.

  An OFDM signal obtained by FFT calculation on an OFDM time domain signal is a frequency domain signal. Hereinafter, the OFDM signal after the FFT operation is appropriately referred to as an OFDM frequency domain signal. The OFDM frequency domain signal is supplied to an analog broadcast interference detection unit 109, a transmission path characteristic estimation unit 110, and a transmission path distortion correction unit 111.

  The analog broadcast interference detection unit 109 detects the presence or absence of interference due to the analog broadcast wave existing in the same channel using the OFDM frequency domain signal, and outputs the detection result to the interference cancellation unit 107.

  Transmission path characteristic estimation section 110 estimates the transmission path characteristics for each subcarrier using the pilot signal arranged as shown in FIG. 2 in the OFDM frequency domain signal from FFT section 108. The transmission path characteristic estimation unit 110 outputs a transmission path estimation value, which is data representing the estimated transmission path characteristics, to the transmission path distortion correction unit 111 and a CSI (Channel State Information) generation unit 112.

  Further, transmission path characteristic estimation section 110 estimates the noise power for each subcarrier based on the transmission path characteristics, and outputs the estimated value to CSI generation section 112.

  The transmission path distortion correction unit 111 divides the OFDM frequency domain signal from the FFT unit 108 by the transmission path estimation value from the transmission path characteristic estimation unit 110, so that the amplitude and phase of the OFDM frequency domain signal received on the transmission path are obtained. Correct distortion. The transmission path distortion correction unit 111 outputs the OFDM frequency domain signal whose distortion has been corrected to the error correction unit 113 as an equalized signal.

  The CSI generation unit 112 generates information representing the signal quality for each subcarrier using the transmission path characteristics and noise power for each subcarrier, and outputs the information to the error correction unit 113. As information representing the signal quality for each subcarrier, for example, an SNR (Signal to Noise Ratio) for each subcarrier is generated.

  The error correction unit 113 performs deinterleaving processing on the equalized signal supplied from the transmission path distortion correction unit 111, and further performs processing such as denpuncture, Viterbi decoding, spread signal removal, and RS decoding. The contents of these processes are switched according to the signal quality obtained by the CSI generating unit 112. The error correction unit 113 outputs data obtained by performing various processes as decoded data to the subsequent stage.

  Here, a description will be given of co-channel interference caused by analog broadcast waves for digital broadcasting.

  FIG. 4 is a diagram showing the relationship between digital broadcasting frequency and NTSC (National Television System Committee) analog broadcasting frequency in Japan.

  The horizontal axis in FIG. 4 represents frequency, and the vertical axis represents signal power. As shown in FIG. 4, a bandwidth of 6 MHz is allocated to one channel of digital broadcasting.

  As shown in FIG. 4, the subcarrier at the lower end of the OFDM signal (subcarrier with subcarrier number 0) exists at a position 5/14 [MHz] from the frequency at the lower end of the channel. The upper end subcarrier (the subcarrier having the largest subcarrier number) exists at a position of 1/14 [MHz] from the upper end frequency of the channel.

  That is, the OFDM signal indicated by a rectangular wave in FIG. 4 represents a collection of subcarriers. In the range indicated by the rectangular wave in FIG. 4, OFDM subcarriers exist at intervals of about 1 kHz. The same applies to the other drawings.

  On the other hand, video, color, and audio carriers of analog broadcasting exist at positions of 1.25 [MHz], 4.83 [MHz], and 5.75 [MHz], respectively, from the frequency at the lower end of the channel.

  In the case of this example, since an analog broadcast video signal or the like with high power exists in a form superimposed on the subcarrier of the OFDM signal, it is detected that there is an interference due to the analog broadcast wave.

  FIG. 5 is a diagram showing a conventional detection method for the presence or absence of interference by analog broadcast waves.

  Focusing on the subcarriers of the OFDM frequency domain signal after FFT corresponding to the analog broadcast video, color, and audio carriers as shown in the shaded portion of FIG. Methods for measuring are known. When the measured power exceeds the threshold value, it is detected that there is an interference by the analog broadcast wave.

  Detection based on power can also be achieved by extracting a signal in a part of a frequency band through a band pass filter to the OFDM time domain signal instead of the OFDM frequency domain signal after FFT and measuring the power.

2005-31570 publication

  The cancellation of the interference wave component exhibits the effect when there is actually an interference due to the analog broadcast wave to improve the reception performance.

  However, if the interference wave component is canceled when there is no interference, the OFDM frequency domain signal which is not actually disturbed is attenuated, so that the reception performance deteriorates.

  For this reason, accurately detecting the presence or absence of interference by analog broadcast waves is an important factor in determining the performance of the receiver.

  As described above, as a method for detecting the presence or absence of interference, a method of measuring and detecting the power of subcarriers using an OFDM frequency domain signal after FFT is known. There's a problem.

  The first is that it is detected that there is an interference, and once filtering processing for canceling the interference wave component is turned on, the presence or absence of the interference cannot be accurately detected thereafter.

  This is because the interference cancellation unit 107 that performs the filtering process is in a part that handles the signal in the time domain, and when the filtering process is turned on, the block after the interference cancellation unit 107 cannot detect the interference wave component.

  Secondly, strong power may be detected in the frequency band of analog broadcast signals by chance, depending on the multipath situation in the transmission path, even though there is actually no interference from analog broadcast waves. Is. If strong power is detected in such a frequency band, it is erroneously determined that there is interference from analog broadcast waves.

  Even if the first problem can be solved by the above-mentioned method of measuring the power of the signal extracted through the band pass filter to the OFDM time domain signal instead of the OFDM frequency domain signal after the FFT, the second problem is After all it cannot be solved.

  The present invention has been made in view of such circumstances, and makes it possible to accurately detect the presence or absence of interference using a signal after FFT.

  A receiving apparatus according to one aspect of the present invention is based on FFT means for performing FFT on an OFDM time domain signal of a predetermined channel, and a pilot signal included in the OFDM frequency domain signal obtained by performing the FFT. Estimating means for estimating the transmission path characteristics of all subcarriers and estimating the noise power for each subcarrier based on the transmission path characteristics; and the noise power for each subcarrier estimated by the estimating means in the subcarrier direction. Detecting means for detecting presence / absence of an interfering wave for the predetermined channel based on a noise power for each subcarrier so as to detect that there is an interfering wave when it has a periodic peak.

  A removal means for removing the interference wave component for the predetermined channel included in the OFDM time domain signal to be subjected to FFT when the detection means detects that there is an interference wave for the predetermined channel; Can be provided.

  The interference wave is an analog broadcast wave, and the removal means includes a filter that attenuates a signal component in a range corresponding to a frequency band of at least one of an analog broadcast video carrier, color carrier, and audio carrier. By applying the signal to the OFDM time domain signal, the interference wave component can be removed.

  Generating means for generating a sine wave signal of a predetermined frequency, multiplying means for multiplying the signal generated by the generating means, and a signal representing noise power for each subcarrier estimated by the estimating means; Integration means for integrating the multiplication result of the multiplication means can be further provided. In this case, the detection means may determine that the noise power for each subcarrier has a periodic peak in the subcarrier direction when the integration result by the integration means exceeds a preset threshold value. it can.

  The generating means generates a sine wave signal having the same frequency as a horizontal synchronizing frequency in analog broadcasting, and the integrating means is for subcarriers in a band including a frequency at which the power of the analog video broadcast carrier is maximized. The multiplication result of the multiplication means is integrated to obtain a first integration result, and the multiplication result of the multiplication means for the subcarrier in the band including the frequency at which the power of the color carrier of the analog broadcast is maximized is integrated. Then, the second integration result can be obtained, and the detection means can compare the threshold value with the result obtained by subtracting the second integration result from the first integration result.

  The generating means generates a sine wave signal having a frequency twice as high as a horizontal synchronizing frequency in analog broadcasting, and the integrating means has a frequency at which the power of the analog broadcast video carrier is maximum and the power of the color carrier. It is possible to integrate the multiplication results by the multiplication means for the subcarriers in the band including the maximum frequency.

  The generating means can generate a sine wave having a frequency that is an integral multiple of a horizontal synchronizing frequency in analog broadcasting.

  A reception method or program according to one aspect of the present invention performs FFT on an OFDM time-domain signal of a predetermined channel, and based on a pilot signal included in an OFDM frequency-domain signal obtained by performing the FFT, If the noise power for each subcarrier has a periodic peak in the subcarrier direction, the interference wave is Detecting the presence / absence of an interfering wave with respect to the predetermined channel based on the power of noise for each subcarrier so as to detect it as being present.

  In one aspect of the present invention, an FFT time domain signal of a predetermined channel is subjected to FFT, and all subcarriers are based on a pilot signal included in the OFDM frequency domain signal obtained by performing the FFT. Transmission path characteristics are estimated, and noise power for each subcarrier is estimated based on the transmission path characteristics. In addition, the presence or absence of an interfering wave for the predetermined channel is detected as the noise for each subcarrier so as to detect that there is an interfering wave when the estimated noise power for each subcarrier has a periodic peak in the subcarrier direction. It is detected based on the power of.

  According to the present invention, it is possible to accurately detect the presence or absence of interference using a signal after FFT.

[Configuration example of receiver]
FIG. 6 is a diagram illustrating a configuration example of an OFDM receiving apparatus according to an embodiment of the present invention.

  6, the same reference numerals are given to the same components as those in FIG. 3. The overlapping description will be omitted as appropriate.

  In the example of FIG. 6, an analog broadcast interference detection unit 121 is provided instead of the analog broadcast interference detection unit 109 of FIG.

  As will be described in detail later, the analog broadcast interference detection unit 121 detects the presence or absence of interference due to analog broadcast waves using the fact that the frequency characteristics of analog broadcast video carriers and the like have periodic peaks.

  The antenna 101 receives the broadcast wave of the OFDM signal, converts it to an RF signal, and outputs it to the tuner 102.

  The arithmetic unit 102 a of the tuner 102 multiplies the RF signal from the antenna 101 by the signal from the local oscillator 102 b to frequency-convert the RF signal into an IF signal, and outputs the IF signal to the BPF 103.

  The BPF 103 filters the IF signal from the tuner 102 and outputs it to the A / D conversion unit 104.

  The A / D conversion unit 104 performs A / D conversion on the IF signal from the BPF 103 and outputs the digital IF signal to the quadrature demodulation unit 105.

  Orthogonal demodulation section 105 performs orthogonal demodulation on the IF signal from A / D conversion section 104 and outputs an OFDM time domain signal, which is a baseband OFDM signal, to offset correction section 106.

  The offset correction unit 106 corrects various shifts for the OFDM time domain signal from the quadrature demodulation unit 105 and outputs the OFDM time domain signal corrected for the shift to the interference cancellation unit 107.

  The interference cancellation unit 107 appropriately performs a filtering process for canceling the component of the analog broadcast wave as the interference wave according to the detection result by the analog broadcast interference detection unit 121, and converts the OFDM time domain signal of the processing result to the FFT unit It outputs to 108.

  FIG. 7 is a diagram illustrating an example of gain characteristics of the interference cancellation filter used for the filtering process by the interference cancellation unit 107.

  As shown in FIG. 7, the interference cancellation filter is a filter having a gain characteristic that attenuates or removes an OFDM time domain signal corresponding to a frequency band in which video, color, and audio carriers exist.

In the example of FIG. 7, the power of the analog broadcast video carrier takes a maximum value at the frequency f ₂ and becomes almost zero at the frequencies f ₁ and f ₃ before and after that. As will be described later, although it is close to 0, the spectrum of the analog broadcast video carrier also appears near the frequency band of the color carrier.

In order to attenuate or remove the video carrier component having such frequency characteristics, the gain characteristic of the interference cancellation filter takes 0 at the frequency f ₂ and passes all signals in the vicinity of the frequencies f ₁ and f ₃ before and after that. It will be something to let you.

In the example of FIG. 7, the color carrier power of the analog broadcast takes a maximum value at the frequency f ₁₂ and becomes almost zero at the frequencies f ₁₁ and f ₁₃ before and after that.

In order to attenuate or remove the color carrier component having such frequency characteristics, the gain characteristic of the interference cancellation filter takes 0 at the frequency f ₁₂ and passes all signals in the vicinity of the frequencies f ₁₁ and f ₁₃ before and after that. It will be something to let you.

The power of the analog broadcast audio carrier takes a maximum value at the frequency f ₂₂ and becomes almost zero at the frequencies f ₂₁ and f ₂₃ before and after that.

In order to attenuate or remove the sound carrier component having such frequency characteristics, the gain characteristic of the interference cancellation filter takes zero at the frequency f ₂₂ and passes all signals in the vicinity of the frequencies f ₂₁ and f ₂₃ before and after that. It will be something to let you.

  When it is detected that there is interference due to the analog broadcast wave, the interference cancellation unit 107 performs filtering processing by applying an interference cancellation filter having such gain characteristics to the OFDM time domain signal.

  The interference cancellation filter is not of a gain characteristic as shown in FIG. 7, and can be appropriately changed according to required performance.

  For example, a signal in a range corresponding to at least one of the three analog broadcast carriers is attenuated or removed, such as a filter that removes only a signal in a range corresponding to the frequency band of the video carrier. It is also possible to use a filter.

  Returning to the description of FIG. 6, the interference cancellation unit 107 does not perform the filtering process when the analog broadcast interference detection unit 121 detects that there is no interference due to the analog broadcast wave. The interference cancellation unit 107 outputs the OFDM time domain signal supplied from the offset correction unit 106 to the FFT unit 108 as it is.

  The detection result of the presence or absence of the interference by the analog broadcast by the analog broadcast interference detection unit 121 is repeatedly supplied at a predetermined timing.

  Even if the interference cancellation unit 107 detects that there is an interference and turns the filtering process once, the interference cancellation unit 107 turns the filtering process OFF when the subsequent detection result indicates that there is no interference.

  Thus, ON / OFF of the filtering process using the interference cancellation filter is switched according to the detection result by the analog broadcast interference detection unit 121.

  The FFT unit 108 sets an FFT interval according to the symbol synchronization signal, and performs an FFT operation on the OFDM time domain signal in the FFT interval. The FFT unit 108 outputs the OFDM frequency domain signal obtained by performing the FFT operation to the transmission channel characteristic estimation unit 110 and the transmission channel distortion correction unit 111.

  Transmission path characteristic estimation section 110 estimates transmission path characteristics for each subcarrier based on the SP signal included in the OFDM frequency domain signal from FFT section 108, and generates a transmission path estimated value from transmission path distortion correction section 111 and CSI generation. Output to the unit 112.

  Further, the transmission path characteristic estimation unit 110 estimates the noise power for each subcarrier based on the transmission path characteristics, and sends the estimated noise power value for each subcarrier to the CSI generation unit 112 and the analog broadcast interference detection unit 121. Output.

  The transmission path distortion correction unit 111 corrects the amplitude and phase distortion that the OFDM frequency domain signal from the FFT unit 108 receives on the transmission path, and outputs an equalized signal to the error correction unit 113.

  The CSI generation unit 112 generates information representing the signal quality for each subcarrier using the transmission path characteristics and noise power for each subcarrier, and outputs the information to the error correction unit 113.

  The error correction unit 113 performs various processes such as a deinterleaving process on the equalized signal supplied from the transmission path distortion correction unit 111, and outputs decoded data to the subsequent stage.

  The analog broadcast interference detection unit 121 determines whether or not the noise power for each subcarrier estimated by the transmission path characteristic estimation unit 110 has a periodic peak in the subcarrier direction. In the case, it is determined that there is interference by analog broadcast waves.

  That is, when the channel of the currently received OFDM signal is disturbed by an analog broadcast wave, each carrier component of the analog broadcast wave is detected as noise for subcarriers of the same frequency in the transmission path characteristic estimation unit 110. (Presumed.

  As will be described later, the frequency characteristics of analog broadcast video carriers have periodic peaks, so the noise power for each subcarrier is detected in a form that has periodic peaks in the subcarrier direction. This means that the receiver is disturbed by an analog broadcast wave.

  In the NTSC system, not only the video carrier but also the frequency characteristics of the color carrier have periodic peaks. Therefore, it is possible to detect the presence or absence of interference by analog broadcast waves using both the video carrier and the color carrier.

  FIG. 8 is an enlarged view showing the vicinity of the peak of an analog broadcast video carrier and color carrier.

As shown in the upper left side of FIG. 8, the range of the video carrier delimited by a dotted line centered on the frequency f ₂ where the power is maximum is shown in an enlarged manner as shown in the lower left side of FIG.

Further, when the range of a certain color carrier centered on the frequency f _{12 at} which the power is maximum as shown in the upper right side of FIG. 8 is enlarged, it becomes as shown in the lower right side of FIG.

That is, the image carrier is indicated by the spectrum of the frequency f _H interval, represented by the same spectrum as the frequency f _H interval also color carrier. The frequency f _H is 15.734 [kHz] which is the horizontal synchronization frequency of the analog broadcast signal.

In FIG. 8, the spectrum of the color carrier is shown with a color. The spectra S _{V1 to} S _V6 appearing between the color carrier spectra shown with colors are the spectrum of the video carrier that spreads while decreasing with increasing distance from the frequency f ₂ .

  As described above, the frequency characteristics of the analog broadcast video carrier and color carrier have periodic peaks. When there is an interference due to an analog broadcast wave, the shape of the frequency characteristic of the noise power of each subcarrier estimated by the transmission path characteristic estimation unit 110 is the frequency characteristic of each carrier of the analog broadcast as shown in the lower part of FIG. It becomes the same shape as the shape.

  In the case of ISDB-T MODE3, assuming that the frequency interval of subcarriers is about 0.992 kHz and the horizontal synchronization frequency of analog broadcasting is about 15.734 kHz, every 16 subcarriers is larger than that subcarrier. It will be detected that there is noise.

When the filtering process using the interference cancellation filter is turned ON, the noise power of subcarriers near the frequencies f ₂ and f ₁₂ is reduced, but the periodicity is maintained.

  Therefore, it is possible to detect the presence or absence of an analog broadcast wave interference from the filtered signal.

  The filtering process is turned ON / OFF after the filtering process is turned ON so that the filtering process continues to be turned ON when the disturbance continues and the filtering process is turned OFF when the disturbance disappears. Can also be switched.

  FIG. 9 is a block diagram illustrating a configuration example of the analog broadcast interference detection unit 121 of FIG.

  As shown in FIG. 9, the analog broadcast interference detection unit 121 includes a sine wave generation unit 131, a multiplication unit 132, a control unit 133, an integration unit 134, and a comparison unit 135.

  A signal representing the noise power for each subcarrier output from transmission path characteristic estimation section 110 is input to multiplication section 132. Hereinafter, the noise power of the k-th subcarrier in the order of subcarrier numbers is N [k].

The sine wave generation unit 131 generates a sine wave signal represented by the following equation (1) according to the subcarrier number, and outputs it to the multiplication unit 132. f _H is the horizontal synchronization frequency of analog broadcasting, and Tu is the effective symbol length.

The multiplier 132 multiplies the signal representing the noise power of each subcarrier supplied from the transmission path characteristic estimator 110 by the sine wave signal generated by the sine wave generator 131, and the multiplication result is an integrator 134. Output to. The output of the multiplier 132 is expressed by the following equation (2).

  The control unit 133 outputs signals indicating the integration start position and end position to the integration unit 134.

  As an output of the control unit 133, Vstart shown in FIG. 9 represents a video signal start position, and Vend represents a video signal end position. Cstart represents the color signal start position, and Cend represents the color signal end position.

  In the integration unit 134, a section from the position represented by Vstart to the position represented by Vend is defined as a section for video signal detection, and a signal representing the noise power of each subcarrier in the section and a sine wave signal, The multiplication result of is integrated.

  Further, in the integration unit 134, a section from the position represented by Cstart to the position represented by Cend is used as a color signal detection section, and a signal representing the noise power of each subcarrier in the section and a sine wave The multiplication result with the signal is integrated.

  FIG. 10 is a diagram illustrating an example of an integration interval.

The horizontal axis in FIG. 10 represents the subcarrier number. As shown in FIG. 10, for example, when Kmax is the maximum subcarrier number, the section from the position of the subcarrier with the 0th subcarrier number to the position of the (Kmax / 2-1) th subcarrier is the video signal detection. It becomes a section for business. The video signal detection section is a band including a frequency f ₂ that is a frequency at which the power of the video carrier is maximized.

A section from the position of the (Kmax / 2) -th subcarrier to the position of the Cmax-th subcarrier is a color signal detection section. Cmax is the frequency f ₁₂ the power of the color carrier becomes maximum, the center of the frequency f ₂₂ the power of the sound carrier is maximized. The color signal detection section is a band including a frequency f ₁₂ that is a frequency at which the power of the color carrier is maximized.

  The control unit 133 outputs signals representing the start position and end position of the video signal detection section and the color signal detection section to the integration section 134.

  In addition, the control unit 133 outputs a signal instructing to update the detection result output to the interference cancellation unit 107 to the comparison unit 135.

The integrating unit 134 integrates the multiplication result supplied from the multiplying unit 132 according to the following equation (3).

  The first term of Expression (3) represents the integration result for the video signal detection section, and the second term represents the integration result for the color signal detection section.

  As described with reference to FIG. 8, the spectrum of the color carrier is inserted in the center of the spectrum of the video carrier.

  In order to finally increase the total value of the integration results for the video signal detection section and the integration results for the color signal detection section, the color signal detection section is originally targeted. When integrating, it is necessary to change the phase of the sine wave by π [rad].

  If the phase of the sine wave is not changed, the integration result value gradually increases as the calculation proceeds when the video signal detection section is targeted, but the calculation proceeds after the target is switched to the color signal detection section. As a result, the value of the integration result gradually decreases.

  Therefore, in order to perform the same calculation as changing the phase of the sine wave, in the above equation (3), the color signal detection interval is calculated from the integration result of the first term for the video signal detection interval. The integration result of the target second term is subtracted.

  The integration unit 134 outputs the calculation result of the above equation (3) to the comparison unit 135.

  The comparison unit 135 obtains the amplitude or power of the signal representing the calculation result by the integration unit 134 and compares it with a predetermined threshold set in advance.

  If the amplitude or power of the calculation result by the integration unit 134 exceeds the threshold, the comparison unit 135 determines that there is interference by the analog broadcast wave, and if it does not exceed the threshold, there is no interference by the analog broadcast wave Judge as.

  The comparison unit 135 outputs the determination result to the interference cancellation unit 107 as a detection result of the presence or absence of the interference by the analog broadcast wave.

  The detection result by the comparison unit 135 is updated, for example, every predetermined time based on information supplied from the control unit 133.

[Receiver operation]
With reference to the flowchart of FIG. 11, the reception process of the OFDM receiver having the above configuration will be described.

  The processing of each step is not only performed in numerical order, but may be performed in parallel with the processing of other steps as appropriate.

  In step S1, the calculation unit 102a of the tuner 102 converts the frequency of the RF signal into an IF signal.

  In step S <b> 2, the BPF 103 filters the IF signal from the tuner 102.

  In step S <b> 3, the A / D conversion unit 104 A / D converts the IF signal from the BPF 103.

  In step S4, the orthogonal demodulator 105 orthogonally demodulates the IF signal from the A / D converter 104 and outputs an OFDM time domain signal.

  In step S5, the offset correction unit 106 corrects various deviations for the OFDM time domain signal.

  In step S <b> 6, the interference cancellation unit 107 determines whether or not there is interference due to the analog broadcast wave based on the detection result by the analog broadcast interference detection unit 121.

  When it is determined in step S6 that interference due to the analog broadcast wave is detected, in step S7, the interference cancellation unit 107 performs a filtering process for canceling the component of the analog broadcast wave as the interference wave.

  On the other hand, if it is determined in step S6 that there is no interference from the analog broadcast wave, the process in step S7 is skipped. The OFDM time domain signal output from the offset correction unit 106 is supplied as it is to the FFT unit 108 via the interference cancellation unit 107.

  In step S8, the FFT unit 108 performs an FFT operation on the OFDM time domain signal in the FFT interval, and outputs an OFDM frequency domain signal.

  In step S9, transmission path characteristic estimation section 110 estimates transmission path characteristics for all subcarriers based on the SP signal included in the OFDM time domain signal.

  In step S10, the transmission path characteristic estimation unit 110 estimates the noise power for each subcarrier based on the transmission path characteristics.

  In step S11, the transmission path distortion correction unit 111 corrects the amplitude and phase distortion that the OFDM frequency domain signal has received on the transmission path based on the transmission path estimation value.

  In step S12, as described above, the analog broadcast interference detection unit 121 determines whether there is interference due to the analog broadcast wave based on whether the noise power for each subcarrier has a periodic peak in the subcarrier direction. Is detected and the detection result is output.

  In step S13, the CSI generating unit 112 generates information representing the signal quality for each subcarrier.

  In step S14, the error correction unit 113 outputs decoded data obtained by performing various processes on the equalized signal, and ends the process.

  The above processing is repeated while the OFDM signal of a predetermined channel is being received.

  As described above, since detection is performed based on the periodicity of noise power with respect to each subcarrier, it is possible to accurately detect the presence or absence of interference by analog broadcast waves regardless of the multipath situation.

  That is, when detecting the presence or absence of interference based on the power of the OFDM frequency domain signal, a signal with strong power appears in the same frequency band as the carrier of analog broadcasting depending on the multipath situation, and false detection may occur. There is no need to be affected by such erroneous detection.

  Also, it is possible to detect the presence or absence of an analog broadcast wave interference from the signal after the filtering process, and it is possible to switch the filtering process ON / OFF even after the filtering process is turned ON.

  In the above, the presence / absence of interference is detected based on the integration result for the video signal detection section and the integration result for the color signal detection section, but the integration result for one section It may be detected based on the above.

  Note that an analog broadcast audio carrier is FM-modulated, and its frequency characteristic does not appear in a form having a periodic peak, and therefore cannot be used to detect the presence or absence of an analog broadcast wave disturbance.

<Modification>
FIG. 12 is a block diagram illustrating another configuration example of the analog broadcast interference detection unit 121.

  Of the configurations in FIG. 12, configurations corresponding to the configurations in FIG. 9 are denoted with the same reference numerals. The overlapping description will be omitted as appropriate.

  In the example of FIG. 12, a sine wave having a frequency twice that of the sine wave generated by the sine wave generation unit 131 of FIG. 9 is used as the sine wave multiplied by the noise power of each subcarrier.

The sine wave generation unit 131 generates a sine wave signal represented by the following equation (4) according to the subcarrier number, and outputs it to the multiplication unit 132.

The multiplier 132 multiplies the signal representing the noise power of each subcarrier supplied from the transmission path characteristic estimator 110 by the sine wave signal generated by the sine wave generator 131, and the multiplication result is an integrator 134. Output to. The output of the multiplier 132 is expressed by the following equation (5).

  The control unit 133 outputs signals indicating the integration start position and end position to the integration unit 134.

  As an output of the control unit 133, start shown in FIG. 12 represents the start position of integration, and end represents the end position of integration.

  FIG. 13 is a diagram illustrating an example of an integration interval.

The horizontal axis in FIG. 13 represents the subcarrier number. As shown in FIG. 13, for example, the interval from the position of the subcarrier with the 0th subcarrier number to the position of the subcarrier with the Cmax number is the integration period. The integration interval is a band including a frequency f ₂ that is a frequency at which the power of the video carrier is maximum and a frequency f ₁₂ that is a frequency at which the power of the color carrier is maximum.

The integrating unit 134 integrates the multiplication result supplied from the multiplying unit 132 according to the following equation (6).

  As described with reference to FIG. 8, the spectrum of the color carrier is inserted in the center of the spectrum of the video carrier. However, since a sine wave having a frequency twice the horizontal synchronization frequency is used, the case of FIG. In contrast, it is not necessary to perform integration by changing the sign for each target section.

  The comparison unit 135 obtains the amplitude or power of a signal representing the integration result by the integration unit 134 and compares it with a threshold value.

  When the amplitude or power of the integration result by the integration unit 134 exceeds the threshold, the comparison unit 135 determines that there is interference due to the analog broadcast wave, and when it does not exceed the threshold, there is no interference due to the analog broadcast wave Judge as.

<Other variations>
In the above description, the case where the analog broadcasting system is the NTSC system has been described. However, the presence or absence of interference by analog broadcasting of other systems such as the PAL system and the SECAM system can be detected in the same manner. In other words, if there is an interference wave whose frequency characteristic has a periodic peak, the presence or absence of the interference can be detected.

  FIG. 14 is an enlarged view showing the vicinity of the peak of a video carrier and a color carrier of PAL analog broadcasting.

As shown in the upper left side of FIG. 14, the range of the video carrier delimited by a dotted line centered on the frequency f _{2 at} which the power is maximum is shown in an enlarged manner as shown in the lower left side of FIG. The video carrier is represented by a spectrum with a frequency f _H interval.

Further, as shown in the upper right side of FIG. 14, an enlarged range of a certain color carrier centered on the frequency f ₁₂ where the power is maximum becomes as shown on the lower right side of FIG. 14. The color carrier includes a V signal and a U signal, and one spectrum of the V signal and one spectrum of the U signal are inserted between each spectrum of the video carrier.

The interval between the spectrum of the video carrier and the spectrum of the V signal of the color carrier is only the frequency f _H / 4 as shown in the lower part of FIG.

  For example, by using a sine wave obtained by quadrupling the frequency of the sine wave used in the analog broadcast interference detection unit 121 in FIG. 9, the presence or absence of interference due to the analog broadcast wave based on the periodicity of the noise power of each subcarrier. Can be detected.

  As described above, a sine wave having a frequency obtained by multiplying the frequency of the sine wave used in the analog broadcast interference detection unit 121 in FIG. 9 by an integer is used in accordance with the peak period appearing in the frequency characteristics of the interference wave to be detected. Is also possible.

  The presence or absence of interference is detected based on whether the frequency characteristic of the noise power for each subcarrier has the same frequency periodicity as the horizontal synchronization frequency, but it is not the horizontal synchronization frequency but the same frequency as the vertical synchronization frequency. It may be detected based on whether it has the periodicity.

  The OFDM receiver of FIG. 6 may be provided with a tuner for analog broadcasting.

  In this case, when the analog broadcast tuner receives the same channel as the channel received by the tuner 102 and the analog broadcast can be received, it is determined that there is interference from the analog broadcast wave.

<About noise estimation>
Here, an example of noise power estimation for each subcarrier by the transmission path characteristic estimation unit 110 will be described.

The data after the FFT is expressed as the following formula (7). Here, Y represents an FFT output, X represents a transmission symbol, H represents a transmission path characteristic, and N represents noise. Further, m represents a symbol number, and k represents a carrier number.

In Equation (7), if X _{m, k} is an SP signal, this value is known. In the case of ISDB-T _, the value of X _{m, k} is +4/3 or -4/3.

If the estimated value of the transmission line characteristic H is used for this, the estimated value of the instantaneous noise term can be obtained by the calculation of the following equation (8). “˜” indicates that the value to which it is added is an estimated value.

  When the estimated value of the transmission path characteristic is ideal, the first term of Expression (8) is 0, and the noise itself can be obtained.

What is desired to be used for detection of the presence or absence of interference by analog broadcasting is the power of noise. For each carrier with an SP signal, an estimated value of noise is obtained every time the SP signal arrives, the instantaneous noise power is calculated by squaring, and averaged in the time direction by filtering. The noise power P is expressed by the following equation (9).

  The value of P is updated at the timing when the SP signal arrives, and the previous P value is held when it is not the timing when the SP signal arrives. This makes it possible to obtain an estimated value of noise power for every three subcarriers into which the SP signal is inserted.

  Similar to the estimation of transmission path characteristics, the noise power estimation value for all subcarriers can be obtained by performing interpolation processing in the frequency direction for the noise power estimation value.

  The series of processes described above can be executed by hardware or can be executed by software. When a series of processing is executed by software, a program constituting the software is installed from a program recording medium into a computer incorporated in dedicated hardware or a general-purpose personal computer.

  FIG. 15 is a block diagram illustrating a configuration example of hardware of a computer that executes the above-described series of processing by a program.

  A CPU (Central Processing Unit) 201, a ROM (Read Only Memory) 202, and a RAM (Random Access Memory) 203 are connected to each other by a bus 204.

  An input / output interface 205 is further connected to the bus 204. To the input / output interface 205, an input unit 206 such as a keyboard and a mouse and an output unit 207 such as a display and a speaker are connected. The bus 204 is connected to a storage unit 208 made up of a hard disk, a non-volatile memory, etc., a communication unit 209 made up of a network interface, etc., and a drive 210 that drives the removable media 211.

  In the computer configured as described above, for example, the CPU 201 loads the program stored in the storage unit 208 to the RAM 203 via the input / output interface 205 and the bus 204 and executes it, thereby executing the above-described series of processing. Is done.

  The program executed by the CPU 201 is recorded in the removable medium 211 or provided via a wired or wireless transmission medium such as a local area network, the Internet, or digital broadcasting, and is installed in the storage unit 208.

  The program executed by the computer may be a program that is processed in time series in the order described in this specification, or in parallel or at a necessary timing such as when a call is made. It may be a program for processing.

  The embodiments of the present invention are not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present invention.

It is a figure which shows an OFDM symbol. It is a figure which shows the arrangement pattern in the OFDM symbol of SP signal. It is a block diagram which shows the structural example of the conventional OFDM receiver. It is a figure which shows the relationship between the frequency of digital broadcasting, and the frequency of NTSC system analog broadcasting. It is a figure shown about the conventional detection method about the presence or absence of the interference by an analog broadcast wave. It is a figure which shows the structural example of the OFDM receiver which concerns on one Embodiment of this invention. It is a figure which shows the example of the gain characteristic of an interference cancellation filter. It is a figure which expands and shows the peak vicinity of the image carrier and color carrier of analog broadcasting. It is a block diagram which shows the structural example of the analog broadcast interference detection part of FIG. It is a figure which shows the example of the area of integration. It is a flowchart explaining the reception process of an OFDM receiver. It is a block diagram which shows the other structural example of the analog broadcast interference detection part of FIG. It is a figure which shows the example of the area of integration. It is a figure which expands and shows the peak vicinity of the video carrier and color carrier of PAL system analog broadcasting. It is a block diagram which shows the structural example of the hardware of a computer.

Explanation of symbols

  107 interference cancellation unit, 108 FFT unit, 110 transmission path characteristic estimation unit, 111 transmission path distortion correction unit, 121 analog broadcast interference detection unit, 131 sine wave generation unit, 132 multiplication unit, 133 control unit, 134 integration unit, 135 comparison Part

Claims (9)

FFT means for performing FFT on an OFDM time domain signal of a predetermined channel;
Estimate the channel characteristics of all subcarriers based on the pilot signal included in the OFDM frequency domain signal obtained by performing the FFT, and estimate the noise power for each subcarrier based on the channel characteristics Means,
The presence / absence of an interfering wave for the predetermined channel is detected for each subcarrier so as to detect that there is an interfering wave when the noise power for each subcarrier estimated by the estimating means has a periodic peak in the subcarrier direction. And a detecting means for detecting based on the power of noise. A removal means for removing an interference wave component for the predetermined channel included in the OFDM time domain signal to be subjected to FFT when the detection means detects that there is an interference wave for the predetermined channel; The receiving device according to claim 1. The jamming wave is an analog broadcast wave,
The removing unit applies a filter that attenuates a signal component in a range corresponding to a frequency band of at least one of an analog broadcast video carrier, a color carrier, and an audio carrier to the OFDM time domain signal to be subjected to FFT. The receiving apparatus according to claim 2, wherein a component of an interference wave is removed by. Generating means for generating a sine wave signal of a predetermined frequency;
Multiplying means for multiplying the signal generated by the generating means by a signal representing the power of noise for each subcarrier estimated by the estimating means;
Integrating means for integrating the multiplication result of the multiplication means;
The detection means determines that the noise power for each subcarrier has a periodic peak in the subcarrier direction when the integration result by the integration means exceeds a preset threshold value. Receiver device. The generating means generates a sine wave signal having the same frequency as the horizontal synchronization frequency in analog broadcasting,
The integration means integrates the multiplication results of the multiplication means for subcarriers in a band including the frequency at which the power of the analog broadcast video carrier is maximized to obtain a first integration result, and the analog broadcast color carrier A second integration result is obtained by integrating the multiplication results by the multiplication means for subcarriers in the band including the frequency at which the power of
The receiving device according to claim 4, wherein the detection unit compares a threshold value with a result obtained by subtracting the second integration result from the first integration result. The generation means generates a sine wave signal having a frequency twice the horizontal synchronization frequency in analog broadcasting,
5. The integration means integrates the multiplication result by the multiplication means for subcarriers in a band including a frequency at which the power of analog broadcast video carrier is maximum and a frequency at which color carrier power is maximum. Receiver. The receiving device according to claim 4, wherein the generation unit generates a sine wave having a frequency that is an integral multiple of a horizontal synchronization frequency in analog broadcasting. Perform FFT on the OFDM time domain signal of a given channel,
Estimate the channel characteristics of all subcarriers based on the pilot signal included in the OFDM frequency domain signal obtained by performing the FFT, estimate the noise power for each subcarrier based on the channel characteristics,
The presence / absence of an interfering wave for the predetermined channel is used as the noise power for each subcarrier so that it is detected as an interfering wave when the estimated noise power for each subcarrier has a periodic peak in the subcarrier direction. Receiving method including detecting based on. Perform FFT on the OFDM time domain signal of a given channel,
Estimate the channel characteristics of all subcarriers based on the pilot signal included in the OFDM frequency domain signal obtained by performing the FFT, estimate the noise power for each subcarrier based on the channel characteristics,
The presence / absence of an interfering wave for the predetermined channel is used as the noise power for each subcarrier so that it is detected that there is an interfering wave when the estimated noise power for each subcarrier has a periodic peak in the subcarrier direction. A program that causes a computer to execute a process including a step of detecting based on the program.

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