JP2008312186A - Multipath delay estimation unit for ofdm receiver, ofdm receiver, and digital broadcast receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multipath delay estimation unit for estimating delays in multipaths with a simple constitution and a short processing time. <P>SOLUTION: The multipath delay estimation unit includes a delay means for respectively delaying in-phase axis signal and quadrature axis signal obtained after orthogonal detection by an effective symbol period, a correlation calculation means for calculating the respective correlation values of the in-phase axis signal and quadrature axis signal obtained after orthogonal detection and the in-phase axis signal and quadrature axis signal delayed by the delay means, a moving average means for continuously calculating average values of a guard period widths of the respective correlation values calculated by the correlation calculation means, a calculation means for calculating the sum of the squares or the absolute values of the moving averages calculated for respective correlation values by the moving average means, and a delay estimation means for estimating the delays in multipaths based on the sum of the squares or of absolute values obtained by the calculation means. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a multipath delay amount estimating apparatus, an OFDM receiving apparatus, and a digital broadcast receiving apparatus for an OFDM receiving apparatus.

  In recent years, orthogonal frequency division multiplexing (OFDM) transmission systems have attracted attention in digital audio broadcasting for mobiles and terrestrial digital television broadcasting.

  In this OFDM transmission method, on the transmitting side, digital data to be transmitted is modulated by a number of subcarriers (hereinafter referred to as subcarriers) orthogonal to each other, and converted from a frequency domain to a time domain signal by IFFT (Inverse Fourier Transform) processing. This is a transmission system that converts the signal from the time domain to the frequency domain by FFT (Fourier transform) processing on the receiving side. This method has a feature that when the number of subcarriers used is as large as several hundred to several thousand, the symbol period of each modulated wave becomes extremely long, so that it is hardly affected by multipath interference.

  In order to reduce the effects of multipath, in the OFDM method, a pilot signal with a known amplitude and phase is placed at a predetermined position on the frequency axis and time axis on the transmission side, and the pilot signal is extracted on the reception side. Then, the channel characteristics of the extracted pilot signal are estimated, and the amplitude and phase of the data signal are equalized based on the estimation result.

In Japanese Patent Laid-Open No. 2003-32217, an extracted pilot signal is subjected to IFFT processing to estimate a delay profile, and the estimated value is subjected to FFT processing to estimate channel characteristics and equalization is performed. However, with this circuit configuration, it is possible to estimate the transmission path with high accuracy, but the IFFT process and the FFT process are performed to estimate the delay profile and the transmission path characteristic, so that the circuit scale becomes extremely large. There are drawbacks. In addition, since IFFT processing and FFT processing are performed by fetching the received signal into the memory buffer in symbol units, the calculation result for the received signal causes a delay of several symbols, which is not suitable for real-time processing. It is a simple configuration.
Japanese Patent Laid-Open No. 2003-32217 JP 2005-286636 A

  An object of the present invention is to provide a multipath delay amount estimation device in a digital broadcast receiver for an OFDM receiver capable of estimating a multipath delay amount with a simple configuration and a short processing time.

  In addition, the present invention can estimate a multipath delay amount with a simple configuration and a short processing time, and can control an interpolation filter used for interpolation of transmission path characteristics according to the multipath delay amount. An object of the present invention is to provide an OFDM receiver and a digital broadcast receiver that can be used.

  According to the first aspect of the present invention, there is provided a multipath delay estimation apparatus for an OFDM receiver that receives an OFDM modulated signal having an effective symbol period and a guard period having a waveform that matches a part of the effective symbol period. Delay means for delaying each in-phase axis signal and quadrature axis signal after detection by an effective symbol period, in-phase axis signal and quadrature axis signal after quadrature detection, and in-phase axis signal and quadrature axis after being delayed by the delay means Correlation calculation means for calculating a correlation value with a signal, moving average means for continuously calculating an average value of guard period widths of the correlation values for each correlation value calculated by the correlation means, and moving average means Calculation means for calculating the sum of squares or absolute value of the moving average calculated for each correlation value, and the sum of squares or absolute values obtained by the calculation means Based on the value sum, characterized in that a delay amount estimating means for estimating a delay amount of multipath.

  According to a second aspect of the present invention, in the multipath delay amount estimation apparatus for the OFDM receiver according to the first aspect, the delay amount estimation means has a sum of squares or an absolute value sum obtained by the calculation means. A period length exceeding the threshold is calculated, and a multipath delay amount is estimated based on the obtained period length.

  According to a third aspect of the present invention, in the multipath delay amount estimation apparatus for the OFDM receiver according to the first aspect, the delay amount estimation means has a predetermined sum of squares or absolute value sum obtained by the calculation means. Period length calculation means for calculating a period length exceeding the threshold, determination means for determining whether or not a fading state is present, and correction of the period length calculated by the period length calculation means when it is determined that the fading state is detected When it is determined that the state is not the correction unit and the fading state, the multipath delay amount is estimated based on the period length calculated by the period length calculation unit, and when it is determined that the state is the fading state, the correction is performed. An estimation means for estimating a multipath delay amount based on the period length corrected by the means is provided.

  According to a fourth aspect of the present invention, in the multipath delay amount estimating apparatus for an OFDM receiving apparatus according to the third aspect, the discriminating means has a difference value between symbols having a period length calculated by the period length calculating means. It is characterized in that it is determined whether or not it is in a fading state depending on whether or not it is larger than a predetermined value.

  According to a fifth aspect of the present invention, in the multipath delay estimation apparatus for an OFDM receiver according to the third aspect, the determination means is a symbol of the maximum value of the sum of squares or the sum of absolute values calculated by the calculation means. It is characterized in that it is determined whether or not it is in a fading state depending on whether or not the difference value between them is larger than a predetermined value.

  According to a sixth aspect of the present invention, in the multipath delay amount estimating apparatus for an OFDM receiving apparatus according to the third aspect, the discriminating means is Doppler based on a pilot signal extracted by an equalizing unit of the OFDM receiving apparatus. It is characterized in that the frequency is estimated and whether or not the fading state is determined based on whether or not the estimated Doppler frequency is larger than a predetermined value.

  According to a seventh aspect of the present invention, there is provided an OFDM receiver that receives an OFDM modulated signal having an effective symbol period and a guard period having a waveform that matches a part of the effective symbol period. Delay means for delaying each axis signal by an effective symbol period, and the correlation value between the in-phase signal and quadrature axis signal after quadrature detection and the in-phase signal and quadrature axis signal delayed by the delay means, respectively. Correlation calculating means, moving average means for continuously calculating the average value of the guard period width of the correlation value for each correlation value calculated by the correlation means, calculated for each correlation value by the moving average means A computing means for calculating a square sum or an absolute value sum of a moving average, a FO for converting the in-phase axis signal and the quadrature axis signal after the quadrature detection into a frequency domain signal. E) means for equalizing the frequency domain signal obtained by the Fourier transform means, and the equalizer means a pilot signal from the frequency domain signal obtained by the Fourier transform means. Extraction means for extracting data, transmission path characteristic estimation means for estimating the transmission path characteristics of the data carrier using the pilot signal extracted by the extraction means and the interpolation filter, and frequency domain signals obtained by the Fourier transform means Division means for dividing by the transmission path characteristic estimated by the characteristic estimation means, and filter characteristic control means for controlling the characteristic of the interpolation filter based on the sum of squares or the sum of absolute values calculated by the arithmetic means. It is characterized by.

  According to an eighth aspect of the present invention, there is provided an OFDM receiving apparatus that receives an OFDM modulated signal having an effective symbol period and a guard period having a waveform that matches a part of the effective symbol period. Delay means for delaying each axis signal by an effective symbol period, and the correlation value between the in-phase signal and quadrature axis signal after quadrature detection and the in-phase signal and quadrature axis signal delayed by the delay means, respectively. Correlation calculating means, moving average means for continuously calculating the average value of the guard period width of the correlation value for each correlation value calculated by the correlation means, calculated for each correlation value by the moving average means Multipath delay amount based on the arithmetic means for calculating the square sum or absolute value sum of the moving average, and the square sum or absolute value sum obtained by the arithmetic means Delay amount estimating means for estimating, Fourier transform means for converting the in-phase signal and quadrature axis signal after quadrature detection into a signal in the frequency domain, and equalization for equalizing the frequency domain signal obtained by the Fourier transform means Means for extracting a pilot signal from the frequency domain signal obtained by the Fourier transform means, and using the pilot signal extracted by the extraction means and an interpolation filter, Estimated by the transmission path characteristic estimation means for estimating the transmission path characteristics, the division means for dividing the frequency domain signal obtained by the Fourier transform means by the transmission path characteristics estimated by the transmission path characteristic estimation means, and the delay amount estimation means A filter characteristic control for controlling the characteristic of the interpolation filter based on the multipath delay amount. Characterized in that it comprises a means.

  According to a ninth aspect of the present invention, in the OFDM receiver according to the eighth aspect, the delay amount estimating means calculates a period length in which the sum of squares or the sum of absolute values obtained by the calculating means exceeds a predetermined threshold value. The multipath delay amount is estimated based on the obtained period length.

  According to a tenth aspect of the present invention, in the digital broadcast receiving apparatus, the OFDM receiving apparatus according to the seventh to ninth aspects is provided.

  According to the present invention, it is possible to estimate a multipath delay amount with a simple configuration and a short processing time.

  In addition, the present invention can estimate a multipath delay amount with a simple configuration and a short processing time, and can control an interpolation filter used for interpolation of transmission path characteristics according to the multipath delay amount. become able to.

  Embodiments of the present invention will be described below with reference to the drawings.

[1] Terrestrial Digital Broadcast Receiver FIG. 1 shows an electrical configuration of a digital broadcast receiver capable of receiving terrestrial digital broadcast.

  An RF (Radio Frequency) signal modulated by an OFDM (Orthogonal Frequency Division Multiplex) modulation method is input to the tuner unit 72 via the antenna 70. The RF signal input to the tuner unit 72 is subjected to processing such as amplification, filtering, and frequency conversion, and then sent to the OFDM demodulation unit 100 as a baseband (Low-IF) signal.

  The OFDM demodulator 100 includes an A / D converter 30, a Hilbert converter 31, a first carrier synchronization unit 32, an FFT unit (Fourier transform) 33, an equalization unit 34, a symbol synchronization unit 35, and a second carrier synchronization unit 36. And a clock synchronization unit 37. The A / D conversion unit 30, the Hilbert conversion unit 31, and the first carrier synchronization unit 32 form an orthogonal detection unit.

  The analog baseband signal (analog OFDM signal) output from the tuner unit 72 is converted into a digital OFDM signal by the A / D conversion unit 30. The OFDM signal obtained by the A / D converter 30 is sent to the Hilbert converter 31. The Hilbert transform unit 31 generates a quadrature axis signal (Q axis signal) that is 90 degrees out of phase from the input in-phase axis signal (I axis signal). As a result, a complex OFDM signal composed of the I-axis signal and the Q-axis signal is generated.

  The complex OFDM signal generated by the Hilbert transform unit 31 is sent to the first carrier synchronization unit 32. The first carrier synchronization unit 32 corrects a frequency error smaller than the subcarrier frequency interval from the correlation signal (moving average value) obtained by the symbol synchronization unit 35 described later, and is obtained by the second carrier synchronization unit 36 described later. The frequency error of the subcarrier frequency interval is corrected. The I-axis signal and the Q-axis signal output from the first carrier synchronization unit 32 become the I-axis signal and the Q-axis signal after quadrature detection.

  The FFT unit 33 converts a time domain signal into a frequency domain signal. The equalizing unit 34 obtains transmission path characteristics from the pilot signal, estimates the transmission path characteristics of the data carrier using an interpolation filter, and performs equalization by dividing the data signal by the estimated transmission path characteristics of the data carrier.

  By the way, in an actual transmission path environment, there are multipaths, and different delay times occur for each path with respect to the direct wave (main wave). The delay time of each path varies depending on mobile reception, and the amount of variation varies depending on the moving speed. Therefore, in order to improve the estimation accuracy of the transmission path characteristics at the time of mobile reception, it is preferable to use a filter having characteristics adapted to the delay time variation (multipath delay) as the interpolation filter. In this embodiment, the characteristics of the interpolation filter can be controlled according to the multipath delay amount.

  In the OFDM signal, a part of the effective symbol period is copied as a guard period and connected to the effective symbol period to form one symbol. The symbol synchronization unit 35 calculates symbol synchronization from the correlation between a signal delayed for a period corresponding to an effective symbol period and a signal that is not delayed.

  The second carrier synchronization unit 36 calculates the frequency error of the subcarrier frequency interval from the pilot signal included in the output signal of the FFT unit 33, and outputs the calculated frequency error to the first carrier synchronization unit 32. The clock synchronization unit 37 calculates clock synchronization from the symbol synchronization timing error signal obtained by the symbol synchronization unit 35, and controls the sampling frequency of the A / D conversion unit 30.

  The signal equalized by the equalization unit 34 is sent to the error correction unit 74. After performing the demapping, the error correction unit 74 performs processes such as deinterleaving, Viterbi decoding, Reed-Solomon decoding, and outputs an MPEG-TS signal. The decoder unit 76 decodes the audio signal and the video signal from the MPEG-TS signal. The audio signal obtained by the decoder unit 76 is reproduced and output by the speaker 78, and the video signal obtained by the decoder unit 76 is reproduced and output by a monitor (not shown).

[2] Symbol synchronization unit 35

  FIG. 2 shows a configuration of the symbol synchronization unit 35. FIG. 3 shows signals of respective parts in FIG.

  The time-domain OFDM signals (I-axis signal and Q-axis signal) from which the frequency error has been removed by the first carrier synchronization unit 32 are sent to the delay memory 50 and to the correlator 52. The delay memory 50 delays the OFDM signal from the first carrier synchronization unit 32 by a period corresponding to the effective symbol period, and outputs the delayed signal to the correlator 52.

  The correlator 52 calculates a correlation value between the OFDM signal from the first carrier synchronization unit 32 and the OFDM signal delayed by the delay memory 50 by a period corresponding to the effective symbol period, and outputs the correlation value to the moving average calculation unit 54 . Since the time-domain OFDM signal is a signal obtained by copying the latter half of the effective symbol period to the guard period, the correlation of the guard period part is high as shown in FIG. Becomes a low signal. The correlator 52 calculates a correlation value for each I-axis signal and Q-axis signal, but only one of them is shown in FIG.

  The moving average calculator 54 continuously calculates an average (moving average) of guard period widths for each of the correlation value of the I-axis signal and the correlation value of the Q-axis signal calculated by the correlator 52. FIG. 3D shows the moving average for the correlation value of the I-axis signal calculated by the moving average calculation unit 54 and the moving average for the correlation value of the Q-axis signal. The calculated moving average is sent to the first carrier synchronization unit 32 and also sent to the square sum calculation unit 56.

  The sum-of-squares calculation unit 56 calculates the sum of the square of the moving average with respect to the correlation value of the I-axis signal and the square of the moving average with respect to the correlation value of the Q-axis signal, and uses the calculation result as the peak position detection unit 58 and the delay estimation. To the unit 62. FIG. 3E shows an output signal of the square sum calculation unit 56. In particular, FIG. 3E shows an output signal of the sum-of-squares calculation unit 56 when there is no multipath. Instead of the square sum calculator 56, an absolute value sum calculator that calculates the sum of absolute values of the moving average for the correlation value of the I-axis signal and the moving average for the correlation value of the Q-axis signal may be used.

  The peak position detection unit 58 detects the peak position of the output signal of the sum of squares calculation unit 56, calculates the interval y between peaks (see (e) of FIG. 3), and outputs it to the timing error calculation unit 60. . Further, the peak position detection unit 58 obtains a symbol delimiter and outputs a signal (symbol pulse) that is a start timing of each circuit.

  The timing error calculation unit 60 calculates an error between a period between peaks and a predetermined symbol period length as a timing error, and outputs the timing error to the clock synchronization unit 37.

  The delay estimation unit 62 calculates a period x (see (e) of FIG. 3) in which the output signal of the square sum calculation unit 56 exceeds a predetermined threshold value α, and from the difference between the calculated x and the predetermined reference value a, Estimate multipath delay. The reference value a is set to a length of a period in which the output signal of the sum of squares calculation unit 56 exceeds a predetermined threshold when there is no multipath.

  FIG. 4 shows signals of the respective units in the symbol synchronization unit 35 when a signal having multipath is received.

  Here, consider a multipath consisting of two waves, a main wave and a sub wave. The received wave is originally a wave in which the main wave and the sub-wave are combined, but in order to make the explanation easier to understand, in FIG. 4, for some signals, the signal for the main wave and the signal for the sub-wave are separated. As shown.

  In general, when a multipath exists, a subwave has a longer transmission distance to reach the receiving device than a main wave. Further, as shown in (a) of FIG. 4, the side wave arrives at the receiving apparatus later than the main wave and has a low level.

  The correlation values of the main wave and the sub wave are as shown in FIG. Further, the sum of squares of the moving average of the correlation value of the main signal I signal and the moving average of the correlation value of the Q signal and the square of the moving average of the correlation value of the I signal of the subwave and the moving average of the correlation value of the Q signal. The sum is as shown in FIG.

  The sum of squares actually obtained by the sum-of-squares calculation unit 56 is a combination of the sum of squares for the main wave and the sum of squares for the sub-waves, as shown as a composite wave in FIG. Therefore, the period x (see (e) of FIG. 4) in which the output signal of the sum of squares calculation unit 56 exceeds the predetermined threshold value α is always larger than the reference value a, so that the multipath is calculated from the difference value (x−a). Can be estimated.

  The threshold value α used in the delay estimation unit 62 may be set from the outside, or may be determined from the peak value of the output signal of the square sum calculation unit 56. When the threshold value α is determined from the peak value of the output signal of the sum-of-squares calculation unit 56, the level of the received signal can be tracked. Therefore, the delay amount can be estimated more accurately than when set from the outside. Is possible.

[3] Equalizer 34

  FIG. 5 shows the configuration of the equalization unit 34.

  The SP extraction unit 10 extracts SP (scattered pilot) which is a pilot signal from the output of the FFT unit 33. The filter coefficient ROM 16 holds a plurality of filter coefficients corresponding to the multipath delay amount. The interpolation filter selection unit 14 selects an appropriate filter coefficient from the filter coefficients stored in the filter coefficient ROM 16 based on the multipath delay amount estimated by the symbol synchronization unit 35, and outputs the filter coefficient to the transmission path estimation unit 12. To do.

  The transmission path estimation unit 12 adds the SP amplitude and phase extracted by the SP extraction unit 10 and the known amplitude and phase of the SP to the interpolation filter generated based on the filter coefficient selected by the interpolation filter selection unit 14. The transmission channel characteristic CSI of the data carrier is estimated by inputting the transmission channel characteristic CSI (Channel State Information) of the SP calculated from The division unit 18 performs equalization by dividing the output signal of the FFT unit 33 by the transmission path characteristic estimated by the transmission path estimation unit 12.

  For example, when switching two types of filter coefficients according to the multipath delay amount, when the multipath delay amount estimated by the symbol synchronization unit 35 is larger than a predetermined threshold, the interpolation filter selection unit 14 delays the received signal. It is determined that a multipath signal having a large amount is included, and a filter coefficient suitable for a case where the delay amount is large is selected from the filter coefficient ROM 16 and output to the transmission path estimation unit 12. Thereby, the estimation accuracy of the transmission path characteristics is improved, and the equalization performance is improved.

  On the other hand, when the multipath delay amount estimated by the symbol synchronization unit 35 is equal to or less than a predetermined threshold, the interpolation filter selection unit 14 determines whether the received signal includes a multipath signal with a small delay amount, A filter coefficient suitable for the case where the delay amount is small is selected from the filter coefficient ROM 16 and output to the transmission path estimation unit 12. Thereby, the estimation accuracy of the transmission path characteristics is improved, and the equalization performance is improved. It should be noted that by classifying the multipath delay amount into three or more types, three or more types of filter coefficients may be selected according to the multipath delay amount.

  As described above, it is possible to improve the equalization performance by selecting an interpolation filter used for estimating the transmission path characteristics having characteristics suitable for the multipath delay amount.

  According to the above embodiment, the multipath delay amount can be estimated without mounting a large circuit such as IFFT. In addition, since the multipath delay amount is estimated without performing IFFT calculation, the processing time is short, delay amount estimation suitable for real-time control can be performed, and the characteristics of the interpolation filter used for estimating the transmission path characteristics can be The equalization performance can be improved by controlling according to the delay amount.

[4] Modification of delay estimation unit 62 in symbol synchronization unit 35

  The delay estimation unit 62 in the symbol synchronization unit 35 of FIG. 2 includes a period x (see (e) of FIG. 4) and a reference in which the output signal of the sum of squares calculation unit 56 (the sum of squares of the correlation signal) exceeds a predetermined threshold α. The multipath delay amount is estimated based on the difference value (x−a) from the value a.

  By the way, in an actual environment, multipaths with a small time difference often occur, but multipaths with a large time difference rarely occur. However, even if a multipath with a large time difference does not occur, if fading occurs due to a multipath with a small time difference, the period x during which the output signal of the sum of squares calculation unit 56 exceeds a predetermined threshold value α may become large. Fading refers to a phenomenon that affects the strength of the radio wave level due to interference between the wavelengths of radio waves that arrive with a time difference.

  In the fading state, the output signal of the square sum calculation unit 56 varies as shown in FIG. For this reason, the period x during which the output signal of the square sum calculation unit 56 exceeds the predetermined threshold value α also varies. In FIG. 6, the waveform wo indicates the output signal of the square sum calculation unit 56 when there is no fading, the waveform wb indicates the output signal of the square sum calculation unit 56 when the received wave becomes strong due to fading, and the waveform ws. The output signal of the sum-of-squares calculation part 56 when a received wave becomes weak by fading is shown. The periods during which the output signal of the square sum calculation unit 56 exceeds the predetermined threshold α are xo, xb, and xs, respectively. The magnitude relationship is xb> xo> xs.

  In this modification, it is determined whether or not it is in the fading state, and when it is determined that it is in the fading state, the period x in which the output signal of the square sum calculation unit 56 exceeds the predetermined threshold value α is corrected. Yes. Specifically, when it is determined that the state is a fading state, x is corrected by subtracting a predetermined offset value offset from a period x in which the output signal of the sum of squares calculation unit 56 exceeds a predetermined threshold value α. Yes. That is, it is prevented that the delay amount of multipath is estimated to be larger than the actual due to fading. Also in this modification, instead of the square sum calculation unit 56, an absolute value sum calculation unit that calculates the absolute value sum of the moving average for the correlation value of the I-axis signal and the moving average for the correlation value of the Q-axis signal is provided. It may be used.

  When it is determined that the current state is the fading state, the threshold value α is corrected by adding a predetermined offset value offset to the threshold value α, and the output signal of the square sum calculation unit 56 is set to a predetermined value using the corrected threshold value α. A period x exceeding the threshold value α may be calculated.

  In the following, three types of modifications with different fading state detection methods will be described.

[4-1] Modification 1

  FIG. 7 shows the configuration of Modification 1 of the delay estimation unit in the symbol synchronization unit 35.

  The delay estimation unit 62A includes a period length calculation unit 81, a fading state detection unit 82, a period length correction unit 83, and a delay amount estimation unit 84.

  The period length calculation unit 81 calculates a period x in which the output signal (see FIGS. 3 and 4) of the square sum calculation unit 56 (see FIG. 2) exceeds a predetermined threshold value α. The period x calculated by the period length calculation unit 81 is given to the fading state detection unit 82 and to the period length correction unit 83.

  The fading state detection unit 82 calculates an absolute value Δ of a difference between the previously calculated period x and the currently calculated period x (difference of x between symbols), and whether the calculated Δ is greater than a predetermined value d. Whether or not it is in a fading state is determined. That is, when the absolute value Δ of the difference between the previously calculated period x and the currently calculated period x is greater than d, it is determined that the state is fading, and when Δ is equal to or less than d, the fading state is not established. Is determined. The determination result by the fading state detection unit 82 is given to the period length correction unit 83.

  When the determination result by the fading state detection unit 82 indicates that the fading state is not in the fading state, the period length correction unit 83 gives the period x calculated by the period length calculation unit 81 to the delay amount estimation unit 84 as it is. On the other hand, when the determination result by the fading state detection unit 82 indicates that it is in the fading state, the period length correction unit 83 subtracts a predetermined offset value offset from the period x calculated by the period length calculation unit 81. As a result, x is corrected, and the corrected x is supplied to the delay amount estimation unit 84.

  The delay amount estimation unit 84 estimates a multipath delay amount based on a difference (x−a) between x given by the period length correction unit 83 and a predetermined reference value a. The multipath delay amount estimated by the delay amount estimation unit 84 is provided to the equalization unit 34 (see FIG. 5).

[4-2] Modification 2

  FIG. 8 shows a configuration of a second modification of the delay estimation unit in the symbol synchronization unit 35. 8, the same components as those in FIG. 7 are denoted by the same reference numerals, and the description thereof is omitted.

  In this delay estimation unit 62B, the fading state detection method by the fading state detection unit 82A is different from the delay estimation unit 62A of FIG. The fading state detection unit 82A determines whether or not it is in the fading state based on the output signal (see FIGS. 3 and 4) of the square sum calculation unit 56 (see FIG. 2).

  Specifically, fading state detection unit 82A calculates the maximum value max of the output signal (sum of squares of correlation signals) of square sum calculation unit 56 for each symbol. Then, the absolute value Δm of the difference between the maximum value max calculated last time and the maximum value max calculated this time (max difference between symbols) is calculated, and the fading state is determined depending on whether the calculated Δm is larger than a predetermined value dm. It is determined whether or not. That is, when the absolute value Δm of the difference between the maximum value max calculated last time and the maximum value max calculated this time is larger than dm, it is determined that the state is fading, and when Δm is less than dm, the fading state is determined. It is determined that it is not. The determination result by the fading state detection unit 82A is given to the period length correction unit 83.

  When an absolute value sum calculation unit that calculates a sum of absolute values of the moving average for the correlation value of the I-axis signal and the moving average for the correlation value of the Q-axis signal is used instead of the square sum calculation unit 56, the fading state detection is performed. The unit 82A calculates the maximum value max of the output signal (the absolute value sum of the correlation signal) of the absolute value sum calculation unit for each symbol. Then, the absolute value Δm of the difference between the maximum value max calculated last time and the maximum value max calculated this time (max difference between symbols) is calculated, and the fading state is determined depending on whether the calculated Δm is larger than a predetermined value dm. It is determined whether or not.

[4-3] Modification 3

  FIG. 9 shows a configuration of a third modification of the delay estimation unit in the symbol synchronization unit 35. 9, the same components as those in FIG. 7 are denoted by the same reference numerals, and the description thereof is omitted.

  In the delay estimation unit 62C, a determination signal indicating whether or not the fading state is obtained from an external unit other than the delay estimation unit 62C is given to the period length correction unit 83.

  As an external means, the Doppler frequency is estimated based on the SP (scattered pilot) extracted by the equalizing unit 34, and when the estimated Doppler frequency is greater than a predetermined value, it is determined that the fading state is present and estimated. A means for determining that the state is not a fading state when the Doppler frequency is equal to or lower than a predetermined value is used.

It is a block diagram which shows the electrical constitution of the digital broadcasting receiver which can receive terrestrial digital broadcasting. 3 is a block diagram showing a configuration of a symbol synchronization unit 35. FIG. FIG. 3 is a time chart showing signals at various parts in FIG. 2 when there is no multipath. FIG. FIG. 3 is a time chart showing signals at various parts in FIG. 2 when a multipath exists. FIG. 3 is a block diagram showing a configuration of an equalization unit 34. FIG. It is a wave form diagram for demonstrating that the output signal of the square sum calculation part 56 fluctuates in a fading state. FIG. 10 is a block diagram showing a configuration of Modification 1 of the delay estimation unit in the symbol synchronization unit 35. 11 is a block diagram showing a configuration of a second modification of the delay estimation unit in the symbol synchronization unit 35. FIG. 12 is a block diagram showing a configuration of a third modification of the delay estimation unit in the symbol synchronization unit 35. FIG.

Explanation of symbols

30 A / D conversion unit 31 Hilbert conversion unit 32 First carrier synchronization unit 33 FFT unit (Fourier transform unit)
34 equalization unit 35 symbol synchronization unit 36 second carrier synchronization unit 37 clock synchronization unit 50 delay memory 52 correlator 54 moving average calculation unit 56 sum of squares calculation unit 62, 62A, 62B, 62C delay estimation unit 10 SP extraction unit 12 transmission Path estimation unit 14 Interpolation filter selection unit 16 Filter coefficient ROM
18 division unit 81 period length calculation unit 82, 82A fading state detection unit 83 period length correction unit 84 delay amount estimation unit 100 OFDM demodulation unit

Claims (10)

In the multipath delay estimation device for an OFDM receiver that receives an OFDM modulated signal having an effective symbol period and a guard period having a waveform that matches a part of the effective symbol period,
Delay means for delaying the in-phase signal and the quadrature axis signal after quadrature detection by an effective symbol period;
Correlation calculation means for calculating correlation values between the in-phase axis signal and the quadrature axis signal after the quadrature detection, and the in-phase axis signal and the quadrature axis signal after being delayed by the delay means,
For each correlation value calculated by the correlation means, a moving average means for continuously calculating an average value of guard period widths of the correlation values;
Based on the arithmetic means for calculating the sum of squares or absolute values of the moving averages calculated for each correlation value by the moving average means, and the multipath delay amount based on the sum of squares or absolute values obtained by the arithmetic means. A delay amount estimating means for estimating,
A multipath delay amount estimation apparatus for an OFDM receiver characterized by comprising: The delay amount estimation means calculates a length of a period in which the sum of squares or sum of absolute values obtained by the computing means exceeds a predetermined threshold, and estimates the amount of delay of the multipath based on the obtained period length. The multipath delay amount estimation apparatus for an OFDM reception apparatus according to claim 1. The delay amount estimating means includes
A period length calculating means for calculating a period length in which the sum of squares or the sum of absolute values obtained by the calculating means exceeds a predetermined threshold;
A discriminating means for discriminating whether or not a fading state;
When it is determined that it is in the fading state, the correction means for correcting the period length calculated by the period length calculation means, and when it is determined that it is not in the fading state, it is set to the period length calculated by the period length calculation means. An estimation unit that estimates a multipath delay amount based on the period length corrected by the correction unit when the multipath delay amount is determined based on the period length corrected by the correction unit;
The multipath delay amount estimation apparatus for an OFDM receiver according to claim 1, comprising: The determination means determines whether or not a fading state is present depending on whether or not a difference value between symbols having a period length calculated by the period length calculation means is larger than a predetermined value. Item 4. The multipath delay amount estimation apparatus for an OFDM receiver according to Item 3. The discriminating means discriminates whether or not it is in a fading state depending on whether or not a difference value between symbols of the maximum value of the square sum or absolute value sum calculated by the arithmetic means is larger than a predetermined value. The multipath delay amount estimating apparatus for an OFDM receiving apparatus according to claim 3, wherein: The discriminating means estimates a Doppler frequency based on a pilot signal extracted by an equalization unit of the OFDM receiver, and discriminates whether or not a fading state is present depending on whether or not the estimated Doppler frequency is greater than a predetermined value. The multipath delay amount estimating apparatus for an OFDM receiving apparatus according to claim 3, wherein: In an OFDM receiver that receives an OFDM modulated signal having an effective symbol period and a guard period having a waveform that matches a part of the effective symbol period,
Delay means for delaying the in-phase signal and the quadrature axis signal after quadrature detection by an effective symbol period;
Correlation calculation means for calculating correlation values between the in-phase axis signal and the quadrature axis signal after the quadrature detection, and the in-phase axis signal and the quadrature axis signal after being delayed by the delay means,
For each correlation value calculated by the correlation means, a moving average means for continuously calculating an average value of guard period widths of the correlation values;
A computing means for calculating a square sum or absolute value sum of the moving averages calculated for each correlation value by the moving average means;
Fourier transform means for converting the in-phase signal and quadrature axis signal after the quadrature detection into a frequency domain signal, and an equalization means for equalizing the frequency domain signal obtained by the Fourier transform means,
The equalization means estimates a transmission path characteristic of a data carrier using an extraction means for extracting a pilot signal from a frequency domain signal obtained by the Fourier transform means, and a pilot signal extracted by the extraction means and an interpolation filter. Transmission path characteristic estimation means, division means for dividing the frequency domain signal obtained by the Fourier transform means by transmission path characteristics estimated by the transmission path characteristic estimation means, and sum of squares or absolute value calculated by the calculation means An OFDM receiver comprising: filter characteristic control means for controlling the characteristic of the interpolation filter based on the above. In an OFDM receiver that receives an OFDM modulated signal having an effective symbol period and a guard period having a waveform that matches a part of the effective symbol period,
Delay means for delaying the in-phase signal and the quadrature axis signal after quadrature detection by an effective symbol period;
Correlation calculation means for calculating correlation values between the in-phase axis signal and the quadrature axis signal after the quadrature detection, and the in-phase axis signal and the quadrature axis signal after being delayed by the delay means,
For each correlation value calculated by the correlation means, a moving average means for continuously calculating an average value of guard period widths of the correlation values;
A computing means for calculating a square sum or absolute value sum of the moving averages calculated for each correlation value by the moving average means;
A delay amount estimating means for estimating a multipath delay amount based on the sum of squares or the sum of absolute values obtained by the computing means;
Fourier transform means for converting the in-phase signal and quadrature axis signal after the quadrature detection into a frequency domain signal, and an equalization means for equalizing the frequency domain signal obtained by the Fourier transform means,
The equalization means estimates a transmission path characteristic of a data carrier using an extraction means for extracting a pilot signal from a frequency domain signal obtained by the Fourier transform means, and a pilot signal extracted by the extraction means and an interpolation filter. Transmission path characteristic estimation means, division means for dividing the frequency domain signal obtained by the Fourier transform means by transmission path characteristics estimated by the transmission path characteristic estimation means, and multipath delay estimated by the delay amount estimation means An OFDM receiving apparatus comprising: filter characteristic control means for controlling the characteristic of the interpolation filter based on a quantity. The delay amount estimation means calculates a length of a period in which the sum of squares or sum of absolute values obtained by the computing means exceeds a predetermined threshold, and estimates the amount of delay of the multipath based on the obtained period length. The OFDM receiver according to claim 7. A digital broadcast receiver comprising the OFDM receiver according to claim 7.

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