JP2008278363A - Digital broadcast reception device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a digital broadcast reception device improved in precision of equalization. <P>SOLUTION: A propagation path estimation unit 30 is provided with a signal adjustment unit 35 between a time mask 18 and an FFT 19. The signal adjustment unit 35 cuts a signal of impulse response in a time domain outputted from the time mask 18, the signal which is lower than a prescribed threshold level. The signal adjustment unit 35 is provided to cut and suppress an unnecessary noise component, and then an error is suppressed during Fourier transformation by the FFT 19 from the signal in the time domain to a signal in a frequency domain. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a digital broadcast receiving apparatus, and more specifically, equalization that compensates for distortion caused by multipath in a received signal of an orthogonal frequency division multiplexing (OFDM) transmission method in demodulation of digital terrestrial broadcasting. Regarding the circuit.

  In recent years, OFDM transmission systems have attracted attention in digital audio broadcasting for mobile terminals and terrestrial digital television broadcasting.

  This OFDM transmission method is a method in which a large number of orthogonal carriers (hereinafter also referred to as carriers) are modulated with digital data to be transmitted, and these modulated waves are multiplexed and transmitted.

  In terrestrial digital broadcasting, multipath generally exists, and the frequency characteristics of the received signal are distorted by this multipath. Therefore, it is important to reduce the influence of this multipath. Yes.

  For this reason, in the OFDM transmission system, a signal obtained by copying a part of a signal to be originally transmitted is added as a guard interval. By setting this guard interval, it is possible to effectively remove the influence of distortion due to multipath.

  Further, in the OFDM transmission method using the QAM modulation method for the modulation method of each carrier, when distortion due to multipath occurs, the amplitude and phase of each carrier differ from the amplitude and phase on the transmission side. For this reason, in the receiving apparatus, it is necessary to equalize (correct) the signal affected by the distortion due to multipath so that they are equal.

  In the OFDM transmission system, the receiving side performs FFT (Fast Fourier Transform) processing and performs demodulation, so that pilot signals are scattered in the transmission signal, and the amplitude and phase of the pilot signal are monitored on the receiving side. The propagation path characteristic is estimated, and the received signal is equalized based on the estimated propagation path characteristic.

FIG. 14 is a block diagram showing a general configuration of a conventional digital broadcast receiving apparatus.
This figure shows a portion of the overall configuration of the digital broadcast receiving apparatus that performs propagation path characteristic estimation and performs equalization of the OFDM received signal after FFT demodulation.

  Referring to FIG. 14, specifically, an OFDM signal received via an antenna is supplied to an FFT circuit (not shown) as a baseband OFDM signal. The FFT circuit performs FFT processing on the input baseband OFDM signal and demodulates the OFDM signal.

  The pilot signal extraction unit 25 extracts a known pilot signal inserted in the carrier wave separately from the data signal in accordance with a predetermined rule from the output of the FFT circuit, and sets the propagation path characteristic for the carrier wave in which the pilot signal is inserted. Based on this, it outputs to the propagation path estimation unit 10 that estimates propagation path characteristics of the data signal for all carriers.

  The propagation path estimation unit 10 estimates the propagation path characteristic for the data signal from the amplitude and phase fluctuations received by the pilot signal, and outputs the result to the equalization unit 6.

  The equalization unit 6 receives the estimated channel characteristic from the channel estimation unit 10 and equalizes (corrects) the signal input from the FFT circuit to remove a distortion component with respect to the channel characteristic.

  The equalization unit 6 divides the demodulated signal input from the FFT circuit by the amplitude and phase supplied as the estimated propagation path characteristics, and removes distortion components with respect to the propagation path characteristics.

  For example, when the amplitude of the carrier wave input from the FFT circuit is ½ of the original amplitude, ½ is supplied as the amplitude information that is the estimated propagation path characteristic. Therefore, when the equalization unit 6 divides the amplitude of the signal input to the FFT circuit by the amplitude information, the original signal having the amplitude of 1 (= (1/2) / (1/2)) can be obtained. it can. Similarly, the signal of the original phase can be obtained by performing a complex operation on the phase.

FIG. 15 is a schematic block diagram illustrating the configuration of the propagation path estimation unit 10.
Referring to FIG. 15, propagation path estimation unit 10 includes an interpolation filter 16, an inverse fast Fourier transform unit (IFFT) 17, a time mask 18, and a fast Fourier transform unit (FFT) 19.

Here, the propagation path characteristic estimation method will be described.
FIG. 16 is a diagram for explaining the arrangement of pilot signals (SP) in terrestrial digital broadcasting.

  As shown in FIG. 16, pilot carrier signals (pilot signals) are inserted in the frequency direction of one OFDM symbol at a ratio of one to twelve carriers (carriers). Further, in the time direction, the pilot carrier signal insertion position is shifted by three carriers for each OFDM symbol. The pilot signal having such an arrangement is also referred to as a scattered pilot signal, and is indicated by using a code SP.

  This pilot signal is extracted by the pilot signal extraction unit 25, and pilot points are interpolated by the interpolation filter 16 of the propagation path estimation unit 10.

FIG. 17 is a diagram for explaining pilot points subjected to interpolation processing in the interpolation filter 16.
As shown in FIG. 17, in the interpolation filter 16, the extracted pilot points are interpolated to estimate the propagation path characteristics.

  Specifically, by dividing the pilot signal generated on the receiver side from the pilot signal of the extracted pilot point, the estimated value of the propagation path characteristic of the carrier at the pilot point, that is, the propagation path characteristic for the carrier into which the pilot signal is inserted It is possible to calculate an estimated value.

  Then, by performing interpolation in the frequency direction for the carrier wave in which the pilot signal is not inserted, the propagation path characteristic of the data signal in all the carriers (carriers) can be estimated from the estimated value of the propagation path characteristic with respect to the pilot signal. Is possible.

  The interpolating process is performed by an interpolating means composed of IFFT 17, time mask 18 and FFT 19.

  Since the interpolation means can obtain the estimated value of the propagation path characteristic of the data signal in all the carriers (carriers) from the estimated value of the propagation path characteristic with respect to the carrier wave into which the pilot signal has been inserted, Can be removed.

  Note that a method for estimating the propagation path characteristic of a signal input from the FFT circuit in the OFDM transmission system and removing a distortion component with respect to the propagation path characteristic is a well-known technique described in Non-Patent Document 1. Therefore, detailed description is omitted.

  On the other hand, if an error occurs in the estimation result of the propagation path characteristic of the data signal from the propagation path estimation unit 10, the equalization accuracy decreases.

  FIG. 15 shows a case where a time mask 18 is provided between the IFFT 17 and the FFT 19 as means for removing the error of the propagation path characteristic estimation result from the interpolation filter 16. The IFFT 17 converts the estimated propagation path characteristic from the interpolation filter 16 into a time domain impulse response signal.

  In the time mask 18, components having a certain delay or more are masked to zero. That is, in the time mask 19, noise is removed by masking a long delay component for which no signal is normally assumed to 0.

  Here, the range of the time mask is determined in advance to the expected delay time of the signal (for example, about the guard interval length). This is because if the signal length is further shortened, not only the noise component but also a signal component with a long delay due to multipath or the like will be removed.

Then, an I component and a Q component, which are estimated propagation path characteristics from which errors have been removed from the FFT 19, are output to the equalization unit 6 and the above equalization processing is executed. In Patent Document 1, as an example, a method for controlling the bandwidth of an interpolation filter and processing only a minimum necessary pilot signal is shown, thereby reducing the influence of noise components in unnecessary bands.
Japanese Patent Laid-Open No. 11-239115 Makoto Itami, “Family OFDM technology”: Ohmsha, November 15, 2005, p66-82

  However, the receiver itself has a certain amount of heat during operation, for example, and the estimated value in the propagation path estimator is affected by the influence of noise components such as thermal noise caused by irregular thermal motion of electrons in the circuit resistor. There is a possibility of receiving.

  FIG. 18 is a diagram for explaining the IFFT output after the time mask that has passed through the time mask 18.

  As shown in FIG. 18, a long delay noise component having a certain delay or more can be removed by the time mask 18, but the noise component exists in every time component, so that the noise component generated in the desired signal peripheral region Cannot be removed.

  Therefore, if the signal of the noise component remains, an error may occur in the estimation result of the propagation path characteristics in the propagation path estimation unit, and the accuracy of equalization is deteriorated particularly in a reception environment with a low signal-to-noise power ratio. there's a possibility that.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide a digital broadcast receiving apparatus capable of improving the accuracy of equalization.

  The digital broadcast receiving apparatus according to the present invention is capable of receiving a reception signal of an orthogonal frequency division division transmission system using carriers having N carriers with different frequencies from the 0th to the (N-1) th frequency. A broadcast receiving apparatus that receives a first-phase Fourier transform unit that receives an in-phase signal and a quadrature-axis signal after quadrature detection and performs a Fourier transform process, and a propagation path characteristic that estimates a signal from the first Fourier transform unit. An equalization means based on the signal, an extraction means for extracting a known pilot signal for estimating a propagation path characteristic from the signal from the first Fourier transform means, and an equalization from the pilot signal extracted by the extraction means A propagation path estimating means for outputting the estimated propagation path characteristics to the means. The propagation path estimation means interpolates the pilot signal extracted by the extraction means and estimates the propagation path characteristics for the carrier in which the pilot signal is inserted, and the pilot signal from the interpolation filter means is inserted. Interpolating means for estimating and outputting the propagation path characteristics of a carrier having N carriers by interpolating the propagation path characteristics for a carrier to which no pilot signal is inserted from the estimation of propagation path characteristics for a carrier wave. The interpolation means includes an inverse Fourier transform means for inverse Fourier transforming the output signal of the interpolation filter means, a time mask for removing a signal delayed by a predetermined time or more with respect to the signal level of the impulse response obtained by the inverse Fourier transform means, The time-masked signal has signal adjusting means for cutting a signal below a predetermined threshold level, and second Fourier transform means for Fourier-transforming the signal from the signal adjusting means.

  Preferably, the propagation path estimation means is provided between the interpolation filter means and the interpolation means, and divides the frequency band of the carrier number N from the 0th to the (N−1) th carrier into a plurality of sections. Then, it further includes band dividing means for outputting an estimated value of the propagation path characteristic for the carrier wave in which the pilot signal for each section is inserted to the interpolation means.

  In particular, the interpolation means performs processing using the propagation path estimation value of the carrier wave included in the corresponding section and the propagation path estimation value of the carrier wave in a predetermined range included in the section adjacent to the corresponding section.

  In particular, the interpolation means includes an effective data extracting unit, and the effective data extracting unit processes the propagation path estimated value of the carrier wave included in the corresponding segment as the effective interval for the result processed for each segment, and corresponds to the result. A propagation path estimated value of a carrier wave in a predetermined range included in a section adjacent to the section is processed as an invalid section.

  In particular, the interpolation means further includes an information output unit for setting a threshold level for the signal adjustment means. The information output unit adjusts the threshold level when processing at least one of the plurality of sections.

  Preferably, the propagation path estimation means further includes extrapolation means provided between the interpolation filter means and the interpolation means. The interpolation filter means interpolates the pilot signals inserted at predetermined intervals into the 0th to (N−1) th carrier number N carriers extracted by the extraction means, and the pilot signals are inserted. Estimate the propagation path characteristics for a given carrier. The extrapolation means is 0th relative to the first end region close to the 0th carrier outside the frequency band of the 0th to (N-1) th carrier N frequency carriers. To the (N-1) th carrier wave number N, extrapolate the estimated value of the propagation path characteristic for the first carrier wave in which the pilot signal extracted by the extracting means is inserted, and outside the frequency band The estimated value of the propagation path characteristic for the last carrier in which the pilot signal extracted by the extraction unit is inserted is extrapolated to the second end region close to the (N−1) th carrier.

  The digital broadcast receiving apparatus according to the present invention includes unnecessary noise included in the estimated value of the propagation path characteristic that cannot be removed by the time mask by providing a signal adjustment unit that cuts a signal below a predetermined threshold level. By suppressing the components, equalization accuracy can be improved.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same reference numerals indicate the same or corresponding parts.

[Embodiment 1]
FIG. 1 is a schematic block diagram showing an overall configuration of a digital broadcast receiving apparatus according to Embodiment 1 of the present invention.

  Referring to FIG. 1, in digital broadcast receiving apparatus 1000, an RF signal received from an antenna (not shown) is selected by tuner 100 and provided to OFDM demodulator 102. The tuner 100 down-converts the RF input signal from the antenna to an intermediate frequency (IF frequency), receives a predetermined band limitation, converts the signal into an analog OFDM signal, and outputs the analog OFDM signal to the OFDM demodulation unit 102.

  The demodulated signal from the OFDM demodulator 102 is supplied to a transport stream decoder (hereinafter also referred to as a TS decoder) 104 and is supplied to the MPEG decoder 110. That is, the TS decoder 104 extracts data streams such as video and audio from the transport stream data.

  The MPEG decoding unit 110 receives the data stream supplied from the TS decoder 104 and converts it into a video signal and an audio signal by using a random access memory (hereinafter also referred to as RAM) 112 as a buffer for temporarily storing data. To do.

  The digital broadcast receiving apparatus 1000 further stores the internal storage device 148 for receiving and storing the signal from the TS decoder 104 via the data bus BS1 and the internal storage device 148 via the data bus BS1. An arithmetic processing unit 144 for performing predetermined processing on the data and outputting it, a ROM 140 for recording a program in the arithmetic processing of the arithmetic processing unit 144, and a memory area for operation of the arithmetic processing unit 144 A RAM 142 to be provided and a high-speed digital interface 146 for performing data input / output between the data bus BS1 and the outside are provided.

  When the arithmetic processing unit 144 performs a predetermined process on the data stored in the built-in storage device 148 according to an instruction from the outside, the processed data is transferred from the on-screen display processing unit 130 to the combiner. 160.2.

  The synthesizer 160.2 synthesizes the output from the MPEG decoding unit 110 and the output from the on-screen display processing unit 130, and then gives them to the video output terminal 164. The output from the video output terminal 164 is given to the display unit 1004.

  Further, the digital broadcast receiving apparatus 1000 receives data obtained as a result of processing by the arithmetic processing unit 144 based on data stored in the built-in storage device 148, and outputs sound effects and the like for the video output from the display unit 1004. Generates an audio signal by receiving the additional sound generator 120 to be generated and given to the synthesizer 160.1 and the data processed by the arithmetic processing unit 144 based on the data stored in the built-in storage device 148 The PCM decoder 122 is provided to the combiner 160.1.

  The synthesizer 160.1 receives the output from the MPEG decoding unit 110 and the outputs from the additional sound generator 120 and the PCM decoder 122, and gives a synthesis result to the audio output terminal 162. The audio signal supplied to the audio output terminal 162 is output from the audio output unit 1002 as an audio signal.

  The digital broadcast receiving apparatus 1000 may include a modem 150 for exchanging data with the outside and an IC card interface 152 for receiving information from the IC card as necessary.

Via the high-speed digital interface 146, for example, an external storage device 180 such as an HDD device for a home server, a remote control (or a keyboard or the like) as the external input device 182 and the data bus BS1 are connected.

  The digital broadcast receiving apparatus 1000 may have a configuration integrated with a display unit 1004 that receives video output and displays it on a display, or an audio output unit 1002 such as a speaker that receives audio output signals and outputs audio. .

FIG. 2 is a block diagram showing a configuration of OFDM demodulation section 102 in FIG.
Referring to FIG. 2, OFDM demodulation section 102 includes A / D circuit 2, Hilbert transform section 3, carrier synchronization section 4, FFT circuit 5, equalization section 6, symbol synchronization section 7, and clock. Synchronizer 8, pilot signal extractor 25, propagation path estimator 30, frequency deinterleaver 11, time deinterleaver 12, demapping 13, bit deinterleaver 14, Viterbi decoder 15, byte demultiplexer Interleave 16, TS reproduction unit 17, and RS decoding unit 18 are included.

  As described with reference to FIG. 1, the analog OFDM signal from the tuner 100 is input to the analog-digital conversion circuit 2 (also referred to as A / D circuit 2), and converts the analog OFDM signal into a digital signal.

  Next, the OFDM signal converted into the digital signal is converted into an I signal which is an in-phase detection axis signal (real axis component signal) and a Q signal which is a quadrature detection axis signal (imaginary axis component signal) by the Hilbert transform unit 3. A complex OFDM signal is generated.

The complex OFDM signal generated by the Hilbert transform unit 3 is sent to the carrier synchronization unit 4.
The carrier synchronization unit 4 corrects the carrier frequency error of the carrier interval between the transmission carrier frequency and the reception carrier frequency based on the correlation signal output from the symbol synchronization unit 7.

  The symbol synchronization unit 7 uses the formation of one symbol by copying a part of the effective symbol period, which is a characteristic of the OFDM signal, as a guard interval period. Symbol synchronization is calculated based on the correlation value.

  In addition, the symbol synchronization unit 7 outputs a correlation signal based on the correlation value to the carrier synchronization unit 4 in order to correct a frequency error within the carrier frequency.

  The clock synchronization unit 8 calculates clock synchronization from the symbol synchronization timing shift obtained by the symbol synchronization unit 7 and controls the sampling frequency of the A / D circuit 2.

  The FFT 5 performs a fast Fourier transform process on the complex OFDM signal, and converts the signal from the time axis domain to the frequency axis domain.

  The pilot signal extraction unit 25 extracts a pilot signal from the output of the FFT 5 and outputs the pilot signal to the propagation path estimation unit 30 that estimates propagation path characteristics from the pilot signal.

  The propagation path estimation unit 30 estimates propagation path characteristics from the amplitude and phase fluctuations received by the pilot signal, and outputs the result to the equalization unit 6.

  The equalization unit 6 receives the estimated channel characteristic from the channel estimation unit 30 and equalizes (corrects) the signal input from the FFT 5 to remove a distortion component with respect to the channel characteristic.

  As described above, the equalization unit 6 divides the demodulated data signal input from the FFT circuit by the amplitude and phase supplied as the estimated propagation path characteristics, and removes distortion components for the propagation path characteristics. And output to the frequency deinterleave 11.

  The frequency deinterleave 11 performs a process of returning the frequency interleave performed to compensate for the loss of a signal of a specific frequency due to the reflection of radio waves.

  The output of the frequency deinterleave 11 is given to the time deinterleave 12, and the time deinterleave 12 performs a process for restoring the time interleave applied for anti-fading and the like.

  The real-axis component signal (I signal) and imaginary-axis component signal (Q signal) subjected to time deinterleaving are 2 bits (in the case of QPSK), 4 bits (in the case of 16QAM) or 6 bits in the demapping 13. Respectively (in the case of 64QAM).

  Bit deinterleaving 21 cancels bit interleaving performed for the purpose of increasing error correction on the demapped signal.

The Viterbi decoding unit 15 performs error correction using the convolutional code performed on the transmission side.
The byte deinterleave 16 cancels the byte interleave performed for the purpose of increasing error correction in the same manner as the bit interleave for the signal subjected to Viterbi decoding. Then, the TS reproduction unit 17 reconstructs data according to the transport stream format, and the RS decoding unit 18 decodes the Reed-Solomon encoded data on the transmission side. The RS decoding unit 18 outputs a Reed-Solomon decoded result to a TS decoder (not shown).

  The error-corrected signal is output after the compressed signal is expanded in an MPEG decoding unit (not shown), converted into an analog video and an analog audio signal by digital / analog conversion.

FIG. 3 is a schematic block diagram of propagation path estimation unit 30 according to the first embodiment of the present invention.
Referring to FIG. 3, propagation path estimation unit 30 according to the first embodiment of the present invention includes an interpolation filter 16, an IFFT 17, a time mask 18, a signal adjustment unit 35, and an FFT 19.

  The propagation path estimation unit 30 according to the first embodiment of the present invention is different from the propagation path estimation unit 10 described in FIG. 15 in that a signal adjustment unit 35 is further provided between the time mask 18 and the FFT 19. . The other portions are the same as those in FIG. 15, and therefore detailed description thereof will not be repeated.

  As described above, the equalization processing is the same as described above, and in the first embodiment of the present invention, a method for mainly suppressing errors in the channel distortion generated in the OFDM signal in the channel estimation unit. explain.

  Here, the signal adjustment unit 35 further cuts a signal having a predetermined threshold level or less from the time domain impulse response signal output from the time mask 18. The threshold level can be input from the outside, and in this example, the data can be stored in advance in the ROM 140 as an example, and read from the ROM 140 and set.

  FIG. 4 is a diagram for explaining a case where the signal adjustment unit 35 cuts a signal below a predetermined threshold level.

  As shown in FIG. 4, a case where a predetermined threshold level is set for the impulse response which is an IFFT output after passing through the time mask 18 is shown. The signal adjustment unit 35 cuts the signal below the threshold level and outputs it to the FFT 19.

  FIG. 5 is a diagram for explaining a case where the signal adjustment unit 35 cuts a signal below a predetermined threshold level.

  As shown in FIG. 5, it is possible to further suppress unnecessary noise components caused by thermal noise or the like by cutting signals below a predetermined threshold level.

  As described above, in FIG. 18, the long delay noise component having a certain delay or more can be removed by the time mask 18, but the noise component is present in every time component and thus occurs in a desired signal peripheral region. Noise components cannot be removed.

  By providing the signal adjustment unit 35 according to the first embodiment, unnecessary noise components generated in a desired signal peripheral region are also cut and suppressed, so that an error in the estimated value of the propagation path characteristic output from the FFT 19 is reduced. Since it can be suppressed, equalization accuracy can be improved even in a reception environment with a low signal-to-noise power ratio.

[Embodiment 2]
In the first embodiment, the method of suppressing the noise component generated by the influence of thermal noise or the like by the signal adjusting unit 35 has been described.

  On the other hand, as described above, the propagation path estimation unit inserts the pilot signal in the frequency direction based on IFFT processing and FFT processing based on the estimated value of propagation path characteristics for the carrier into which the pilot signal is inserted in the OFDM transmission band. In the above description, the propagation characteristics of all carrier waves are estimated by executing interpolation processing of estimated values of propagation characteristics of non-carrier waves. However, depending on the IFFT processing and the FFT window section to be subjected to FFT processing, The estimate may cause an error at the end of the OFDM transmission band.

FIG. 6 is a diagram for explaining an FFT window section in the OFDM transmission band.
Referring to FIG. 6, here, a case where the FFT window section is wider than the OFDM transmission band is shown. And the estimated value of the propagation path characteristic estimated based on the pilot signal in the OFDM transmission band is shown. The vertical axis is the power spectrum, and the horizontal axis is the frequency. In this case, the OFDM transmission band is set as an effective section, and the portion outside the band is set as an invalid section and is filled with zeros.

  For example, in mode 3 of the Japanese terrestrial digital television transmission system (ISDB-T transmission system), the number of OFDM carriers is Nc = 5617, and the number of FFT processing points (FFT window section) is N. = 8192, the zero-filled section, which is an invalid section outside the band of the OFDM signal, increases to 2575 points.

  Further, when the noise component is removed by the time mask 18 and the signal adjustment unit 35, only a signal component having a predetermined level or higher mainly in the vicinity of time 0 remains on the time axis, and not only the noise component but also a signal having a low signal level is left. Ingredients may be cut.

  FIG. 7 is a diagram when IFFT processing, time mask processing, signal adjustment processing, and FFT processing are performed on the estimated channel characteristic values of FIG. 6 to return to the original waveforms.

  Referring to FIG. 7, here, it is shown that the estimated value of the propagation path characteristic after the FFT processing is smaller than the original size at the end of the OFDM transmission band.

  As shown in FIG. 7, when the FFT window section is wide with respect to the OFDM transmission band, the invalid section outside the band is a zero-filled section, and the signal component is cut by time mask processing and signal adjustment processing. Since it is set to 0, there is a possibility that a change in a discontinuous portion becomes dull and an error is likely to occur at the end of the OFDM transmission band.

  In the second embodiment of the present invention, a method for suppressing an error occurring at the end of the OFDM transmission band as described above will be described.

FIG. 8 is a schematic block diagram of propagation path estimation unit 30 # according to the second embodiment of the present invention.
Referring to FIG. 8, propagation path estimation unit 30 # according to the second embodiment of the present invention can be replaced with propagation path estimation unit 30 described in FIG. 3, and is further inserted between interpolation filter 16 and IFFT 17. An extrapolation portion 36 is provided. The other portions are the same as those in FIG. 3, and therefore detailed description thereof will not be repeated.

  Here, the extrapolation unit 36 performs an extrapolation process on the frequency-domain OFDM signal output from the interpolation filter 16.

FIG. 9 is a diagram for explaining extrapolation processing in the extrapolation unit 36.
Referring to FIG. 9, here, a case where the FFT window section is wider than the OFDM transmission band is shown. Specifically, the case where the total number of carriers in the OFDM transmission band is N and the FFT window section is M (> N) points is shown. Then, the propagation path estimated by the carrier into which the pilot signal is inserted in the OFDM transmission bands of the 0th to (N−1) th carriers H [0] to H [N−1] which are OFDM carriers. The estimated value of the characteristic is shown. The vertical axis is the power spectrum, and the horizontal axis is the frequency.

  Specifically, the estimated value of the propagation path characteristic estimated from the pilot signals inserted with respect to the interpolated 0th, 3rd and 6th carriers H [0], H [3], H [6]. It is shown. Here, (N−1) is a multiple of 3.

  The extrapolation unit 36 extrapolates a part of the invalid section where there is no carrier, which is a band outside the frequency band of all carriers of the number N of carriers in the OFDM transmission band, using the estimated value of the propagation path characteristic. Execute. Specifically, a predetermined range extrapolation is performed using an estimated value of the propagation path characteristic of the carrier H [0] with respect to a band outside the frequency band close to the first carrier H [0] where the pilot signal is inserted. Perform the process.

  In addition, the estimated value of the propagation path characteristic of the carrier wave H [N-1] is used for a band outside the frequency band near the last carrier wave H [N-1] in which the pilot signal is inserted. The process to insert is performed.

  In this example, a predetermined range extrapolation is performed with an estimated value of the propagation path characteristic of the 0th carrier H [0] for the left region with respect to the OFDM transmission band (frequency band) where there is no carrier. The right region is extrapolated by a predetermined range with the estimated value of the propagation path characteristic of the [N−1] -th carrier H [N−1]. Here, it is desirable that the predetermined range is appropriately set in accordance with the range of the FFT window section. If the area of the invalid section where no carrier exists is small, the 0th carrier wave for the entire area of the invalid section is small. You may extrapolate with the estimated value of the propagation path characteristic of H [0] or the estimated value of the propagation path characteristic of the [N−1] -th carrier H [N−1].

  As an example, the case where the carrier wave H [N−1] is the last carrier wave of a multiple of 3 in which the pilot signal is inserted has been described, but the carrier wave H [N−1] is a carrier wave into which the pilot signal is not inserted. In this case, extrapolation processing is performed using the estimated value of the propagation path characteristic of the last carrier wave in which the pilot signal extracted by the pilot signal extraction means 25 is inserted. Similarly, the case where the carrier wave H [0] is the first carrier wave into which the pilot signal is inserted has been described. However, when the carrier wave H [0] is not the carrier wave into which the pilot signal is inserted, the pilot signal is transmitted. Extrapolation processing can be performed using the estimated value of the propagation path characteristic of the first carrier wave into which the pilot signal extracted by the extraction means 25 is inserted.

  FIG. 10 is a diagram when IFFT processing and FFT processing are performed on the signal waveform of FIG. 9.

  As shown in FIG. 10, even when the FFT window section is wide with respect to the OFDM transmission band, the presence of the carrier at the end of the OFDM transmission band (frequency band) by performing extrapolation processing by the extrapolation unit 36 An estimated value of the propagation path characteristic is given in a predetermined area where IFFT and FFT processing are performed. In other words, because the location where the signal waveform changes discontinuously shifts outside the OFDM transmission band, continuity at the end of the OFDM transmission band is maintained by IFFT and FFT processing, and the amplitude at the end of the band is larger than the original size. Also, it is possible to suppress a small value. That is, an error according to IFFT and FFT processing can be suppressed. Note that a region surrounded by a dotted line indicates a region used as an effective interval in estimation of propagation path characteristics.

  By this method, it is possible to suppress the error at the band edge by extrapolating the estimated value of the propagation path characteristic of the carrier wave at the predetermined range and the OFDM transmission band edge. Thereby, it is possible to improve the equalization accuracy by reducing the error of the estimated value of the propagation path characteristic at the end of the OFDM transmission band.

[Modification 1 of Embodiment 2]
In the first modification of the second embodiment of the present invention, a method of suppressing an error in the estimated value of the propagation path characteristic at the end of the OFDM transmission band by another method will be described.

  FIG. 11 is a diagram illustrating a schematic block of transmission path estimation unit 30a according to the first modification of the second embodiment of the present invention.

  Referring to FIG. 11, transmission path estimation unit 30a according to the first modification of the second embodiment of the present invention includes an interpolation filter 16, a band division unit 37, an IFFT 17a, a time mask 18, and a signal adjustment unit 35. , FFT 19 a, valid data extraction unit 39, and information output unit 38.

  Compared with the propagation path estimation unit 30 described in FIG. 3, the propagation path estimation unit 30a according to the first modification of the second embodiment of the present invention includes a band division unit 37, an effective data extraction unit 39, and an information output unit. The difference is that 38 is further provided. Further, IFFT 17 and FFT 19 that execute IFFT processing and FFT processing for M point are respectively replaced with IFFT 17 a and FFT 19 a that execute IFFT processing and FFT processing for M # point, respectively.

  Specifically, a band dividing unit 37 is provided between the interpolation filter 36 and the IFFT 17a. The band dividing unit 37 divides the OFDM transmission band into a plurality of sections and outputs the divided sections to the IFFT 17a for each section.

  The valid data extraction unit 39 extracts valid data from the result of processing in the FFT 19 a for each section and outputs it to the equalization unit 6.

The information output unit 38 outputs a threshold level to the signal adjustment unit 35.
FIG. 12 is a diagram for explaining the band division in the band dividing unit 37.

  Referring to FIG. 12, here, a case where the OFDM transmission band is divided by the division number D is shown. An FFT window section is set corresponding to the divided OFDM transmission band. Specifically, the case where the total number of carriers of the OFDM signal is N and the FFT window section is M # (> N / D) points is shown. The interpolation filter 16 outputs an estimated value of the propagation path characteristic for the carrier wave into which the interpolated pilot signal is inserted in the OFDM transmission band with the total number of carriers N. Then, as described above, the estimated value of the propagation path characteristic of the data signal for each section in the OFDM transmission band of the total number of carriers N is output by the interpolation means configured by IFFT 17a, time mask 18, signal adjustment unit 35, and FFT 19. Is done.

  It is possible to narrow the invalid section of the FFT window section corresponding to the OFDM transmission band divided by the method. As a result, the signal waveform detected by IFFT and FFT processing in each divided OFDM transmission band is narrowed in the invalid section, so that the amplitude of the transmission band end portion is larger than the original size at the transmission band end portion. It is possible to suppress a small value. That is, an error at the end of the transmission band according to IFFT and FFT processing can be suppressed.

  Also, in this example, an estimation error is likely to occur similarly in the vicinity of the boundary of the divided OFDM transmission band, that is, in the boundary area of the section. In this example, only the divided OFDM transmission band that is the corresponding section is subjected to IFFT. Instead of executing the FFT process, the estimated value of the propagation path characteristic of the carrier wave included in the section adjacent to the corresponding section area is also included in the FFT window section.

  Thereby, the continuity of the signal is maintained in the boundary region of the section, and an error in the estimated value of the propagation path characteristic in the boundary region of the section can be suppressed.

  As for the obtained results, the valid data extraction unit 39 processes the corresponding section area as a valid section, and processes the portion including the carrier of the section adjacent to the corresponding section as an invalid section.

  Referring to FIG. 11 again, the OFDM transmission band divided by the band dividing unit 37 is processed for each division. Specifically, the processing from IFFT 17a to FFT 19a shown in FIG. 11 is repeated for the number of divisions (D times).

  Then, the valid data extraction unit 39 receives the result processed for each of the above sections, extracts the valid section based on the valid section and the invalid section, and outputs it as valid data.

  As a result, it is possible to improve the equalization accuracy by reducing the error of the estimated value of the propagation path characteristic at the transmission band end.

  In addition, since the OFDM transmission band is divided into a plurality of sections, the threshold level in the signal adjusting unit 35 can be set according to each section.

  In this example, an information output unit 38 is provided for this purpose, and the information output unit 38 outputs a threshold level to the signal adjustment unit 35 corresponding to each section. Although not shown, it is assumed that the information output unit 38 has a memory 40 that stores a threshold level in advance.

  For example, it is possible to set a threshold level for suppressing noise components in the signal adjustment unit 35 for each segment by dividing the segment into segments.

  Specifically, in terrestrial digital broadcasting, it is divided into 13 segments, and the central one segment is used as a partial reception layer, and the modulation method may differ from the other 12 segments. For example, one segment is modulated by a QPSK modulation scheme, and the other 12 segments are modulated by a 64QAM modulation scheme. Since the tolerance of the signal to the noise component differs depending on the modulation method, it is desirable that the optimum threshold level be a different value according to the modulation method.

  Therefore, for example, when the OFDM transmission band is divided and processed in segments, the information output unit 38 grasps the layer of the segment currently being processed, and in the case of the partial reception layer (1 segment reception) The threshold level can be set to a different value in other cases (12-segment reception).

  For example, since the band dividing unit 37 outputs each segment (each segment) to the IFFT 17a, the segment information is output from the band dividing unit 37 to the information output unit 38. It is possible to switch the threshold level between the case of segment reception) and the other case (12 segment reception). For example, as the segment information, when the partial reception layer (1 segment reception) is output from the band dividing unit 37 to the IFFT 17a, an “H” level signal indicating the processing of the partial reception layer (1 segment reception) is output to the information output unit 38. Can be realized by receiving the signal and operating it.

  The reception quality as a whole can be further improved by switching the threshold level for suppressing the noise component by the above method.

  Further, the circuit division of the IFFT 17a and the FFT 19a can be reduced by being divided and processed for each section by the band dividing unit 37.

[Modification 2 of Embodiment 2]
FIG. 13 is a diagram illustrating a schematic block of transmission path estimation unit 30b according to the second modification of the second embodiment of the present invention.

  Referring to FIG. 13, transmission path estimation unit 30b according to the second modification of the second embodiment of the present invention further includes extrapolation unit 36 as interpolation filter 16, as compared with transmission path estimation unit 30a in FIG. The difference is that it is provided with the band dividing unit 37. Since the other points are the same, detailed description thereof will not be repeated.

  As described above, the extrapolation unit 36 performs the above-described extrapolation process on the estimated value of the propagation path characteristic for the pilot signal in the OFDM transmission band output from the interpolation filter 16.

  In the scheme according to the first modification of the second embodiment, the OFDM transmission band is divided into a plurality of sections, so that the invalid section of the FFT window section corresponding to each section is narrowed, and transmission is performed at the end of each section. A method for suppressing an error occurring in the amplitude of the band edge portion has been described. Similarly, an estimation error is likely to occur in the vicinity of the boundary of the divided OFDM transmission band, that is, in the boundary area of the section. Therefore, the value of the carrier included in the section adjacent to the corresponding section area is included in the FFT window section and processed. The method was explained.

  On the other hand, when the OFDM transmission band is divided into a plurality of divisions, the divisions located at both ends of the division are divided corresponding to the divisions at both ends as described above because the invalid section is adjacent to the zero value area. At the end of the OFDM transmission band, the amplitude at the end of the band may be smaller than the original size.

  Therefore, by performing the extrapolation process using the extrapolation unit 36 as described above, the error of the estimated value of the propagation path characteristic is further suppressed even at the end of the divided OFDM transmission band corresponding to the segments at both ends. It is possible. Thereby, it is possible to further reduce the error of the propagation path estimation value at the band edge and improve the equalization accuracy. That is, high propagation path estimation accuracy can be maintained, and reception quality can be further improved.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is a schematic block diagram which shows the whole structure of the digital broadcast receiver according to Embodiment 1 of this invention. FIG. 2 is a block diagram showing a configuration of an OFDM demodulator 102 in FIG. 1. It is a schematic block diagram of the propagation path estimation part 30 according to Embodiment 1 of this invention. It is a figure explaining the case where the signal adjustment part 35 cuts the signal below a predetermined threshold level. It is a figure explaining the case where the signal below a predetermined threshold level is cut by the signal adjustment part 35. FIG. It is a figure explaining the window area of FFT in an OFDM transmission band. It is a figure at the time of performing IFFT processing and FFT processing with respect to the signal waveform of FIG. 6, and returning to the original waveform. It is a schematic block diagram of the propagation path estimation part 30 # according to Embodiment 2 of this invention. It is a figure explaining the extrapolation process in the extrapolation part. FIG. 10 is a diagram when IFFT processing and FFT processing are performed on the signal waveform of FIG. 9. It is a figure explaining the schematic block of the transmission-line estimation part 30a according to the modification 1 of Embodiment 2 of this invention. It is a figure explaining the band division | segmentation in the band division part 37. FIG. It is a figure explaining the schematic block of the transmission-line estimation part 30b according to the modification 2 of Embodiment 2 of this invention. It is a block diagram which shows the general structure of the conventional digital broadcast receiver. 3 is a schematic block diagram illustrating a configuration of a propagation path estimation unit 10. FIG. It is a figure explaining arrangement | positioning of the pilot signal (SP) in terrestrial digital broadcasting. It is a figure explaining the pilot point which performs the interpolation process in the interpolation filter 16. FIG. It is a figure explaining IFFT output after the time mask which passed the time mask.

Explanation of symbols

  2 A / D circuit, 3 Hilbert transform unit, 4 carrier synchronization unit, 5 FFT circuit, 6 equalization unit, 7 symbol synchronization unit, 8 clock synchronization unit, 11 frequency deinterleave, 12 time deinterleave, 13 demapping, 14 Bit deinterleave, 15 Viterbi decoding unit, 16 byte deinterleaving, 17 TS playback unit, 18 RS decoding unit, 16 interpolation filter, 17 IFFT, 18 time mask, 19 FFT, 25 pilot signal extraction unit, 30, 30a, 30b propagation Path estimation unit, 35 signal adjustment unit, 40 memory, 100 tuner, 102 OFDM demodulation unit, 104 TS decoder, 110 MPEG decoding unit, 112, 142 RAM, 120 additional sound generator, 122 PCM decoder, 130 on-screen display processing unit 150 Audio output unit modem, 152 IC card interface, 160.1, 160.2 synthesizer, 144 arithmetic processing unit, 146 high-speed digital interface, 148 built-in storage device, 164 video output terminal, 180 external storage device, 182 external input device, 1000 Digital broadcast receiver, 1002 Audio output unit, 1004 Display unit.

Claims (6)

A digital broadcast receiving apparatus capable of receiving a reception signal of an orthogonal frequency division division transmission scheme using carriers of N number of carriers having different frequencies from the 0th to the (N-1) th frequency,
First Fourier transform means for receiving the in-phase axis signal and the quadrature axis signal after quadrature detection and performing Fourier transform;
Equalizing means for equalizing the signal from the first Fourier transform means based on the estimated propagation path characteristics;
Extraction means for extracting a known pilot signal for estimating a propagation path characteristic from the signal from the first Fourier transform means;
Propagation path estimation means for outputting the estimated propagation path characteristics to the equalization means from the pilot signal extracted by the extraction means,
The propagation path estimation means includes
Interpolation filter means for estimating a propagation path characteristic for a carrier wave into which the pilot signal is inserted by performing interpolation processing on the pilot signal extracted by the extraction means;
From the estimation of the propagation path characteristic for the carrier in which the pilot signal is inserted from the interpolation filter means, the propagation path characteristic for the carrier in which the pilot signal is not inserted is interpolated to estimate the propagation path characteristic of the carrier having N carriers. And interpolating means for outputting,
The interpolating means includes
Inverse Fourier transform means for inverse Fourier transforming the output signal of the interpolation filter means;
A time mask for removing a signal delayed by a predetermined time or more with respect to the signal level of the impulse response obtained by the inverse Fourier transform means;
Signal adjusting means for cutting a signal below a predetermined threshold level for the time masked signal;
A digital broadcast receiving apparatus comprising: second Fourier transform means for Fourier transforming a signal from the signal adjustment means.   The propagation path estimation means is provided between the interpolation filter means and the interpolation means, and divides the frequency band of the carrier number N from the 0th to the (N−1) th carrier into a plurality of sections. 2. The digital broadcast receiving apparatus according to claim 1, further comprising: a band dividing unit that divides and outputs an estimated value of a propagation path characteristic with respect to a carrier wave into which the pilot signal is inserted for each section to the interpolation unit.   The interpolation means performs processing using an estimated value of propagation path characteristics of a carrier wave included in a corresponding section and an estimated value of propagation path characteristics of a carrier wave in a predetermined range included in a section adjacent to the corresponding section. Item 3. The digital broadcast receiver according to Item 2. The interpolation means includes an effective data extraction unit,
The effective data extraction unit processes the estimated value of the propagation path characteristic of the carrier wave included in the corresponding section as the effective section for the result processed for each section, and the predetermined data included in the section adjacent to the corresponding section 4. The digital broadcast receiving apparatus according to claim 3, wherein an estimated value of propagation path characteristics of a carrier wave in a range is processed as an invalid section. The interpolation means further includes an information output unit for setting a threshold level for the signal adjustment means,
5. The digital broadcast receiving apparatus according to claim 2, wherein the information output unit adjusts a threshold level when processing at least one of the plurality of sections. The propagation path estimation means further includes extrapolation means provided between the interpolation filter means and the interpolation means,
The interpolation filter means interpolates the pilot signals inserted at predetermined intervals into the 0th to (N−1) th carrier number N carriers extracted by the extraction means to perform the pilot processing. Estimate the propagation path characteristics for the carrier into which the signal is inserted,
The extrapolation means is for the first end region close to the 0th carrier outside the frequency band of the 0th to (N−1) th carrier number N of the carrier, Extrapolating the estimated value of the propagation path characteristic for the first carrier in which the pilot signal extracted by the extraction means is inserted among the 0th to (N−1) th carriers of N number of carriers, Propagation path characteristics of the last carrier in which the pilot signal extracted by the extraction means is inserted with respect to the second end region close to the (N−1) -th carrier outside the frequency band. The digital broadcast receiving apparatus according to claim 1, wherein the estimated value is extrapolated.

Images