JP7169209B2 - Receiving device and receiving method - Google Patents

Description

The present invention relates to a receiving device and receiving method.

According to Non-Patent Document 1, since FM broadcasting is non-linear modulation, it is extremely difficult to remove distortion after FM detection, and it is necessary to provide an adaptive digital filter in the intermediate frequency stage that preserves linearity. Also, as a reference signal necessary for controlling the adaptive digital filter, a known signal such as a synchronizing signal or a VITS signal can be used in television broadcasting, but there is no such known signal in FM broadcasting. However, since the envelope of the FM signal, which should be essentially constant, fluctuates due to multipath distortion, it is described that adaptive control is possible by utilizing this property.

Thus, it is possible to remove the multipath distortion due to the applied digital filter in the intermediate frequency stage preserving the linearity of the multipath distortion of the FM broadcast signal. However, no reference signal exists in the FM broadcast signal to control the adaptive digital filter. Instead, according to Non-Patent Document 1, the adaptive digital filter is controlled using variations in the envelope of the FM broadcast signal.

Multipath cancellation is performed by optimizing FIR (Finite Impulse Response) filter coefficients am and bm (: integers from -N to N). The coefficients am and bm can be calculated if the delay time and amplitude in each multipath are known. However, the envelope waveform is not directly indicative of either of these. However, since it is known that the envelope does not fluctuate and remains constant when there is no multipath, the values of the coefficients am and bm are adjusted to minimize the variation of the envelope without knowing the delay time and amplitude. Multipath distortion of FM broadcast signals can be removed by optimizing with a filter. The optimization is described as updating the coefficients am, bm by the maximum slope method.

Also, the technique disclosed in Patent Document 1 is a multipath analysis method using an FM stereo pilot signal. By using such a technique, it is possible to determine which of the direct wave and the delayed wave is stronger. However, only the magnitude relationship between the direct wave and the delayed wave is known, and the delay time is not known. This is a method of analyzing the components around the pilot signal (19 kHz) generated upon demodulation.

It is also possible to replace the multipath cancellation evaluation value (envelope variation) described in Non-Patent Document 1 with that calculated from the demodulated pilot signal (and its surroundings) as in Patent Document 1. be.

Mochizuki et al., "A System for Automatic Removal of FM Multipath Distortion Using an Adaptive Digital Filter", Journal of the Institute of Television Engineers of Japan, Vol. 39 (1985), No. 3, p. 228-234

JP 2011-239239 A

By the way, the adaptive digital filter of Non-Patent Document 1 only adjusts the values of the coefficients am and bm so that the variation of the envelope curve is minimized, and does not necessarily correctly remove the multipath distortion. . Since the adjustment of the coefficients am and bm is performed without knowing both the delay time and the amplitude (problem A), the envelope variation is minimized using coefficients that do not correspond to the actual delay time and amplitude. In some cases, the sound quality at the time of demodulation is further distorted contrary to the purpose.

Since the original purpose of multipath cancellation is to remove distortion from a transmission signal (a signal obtained by modulating image, sound, etc.), an envelope that does not reflect the content of the transmission signal is applied to the optimization of the coefficients am and bm. It is not appropriate to use lines as evaluation values. This is because there is no way to directly evaluate the distortion of the transmission signal due to multipath (problem B).

In the technique disclosed in Patent Document 1, multipath cancellation is linear processing in the signal of the intermediate frequency stage, but in order to extract the output DU ratio (Desired to Undesired signal ratio) as an evaluation value, nonlinear It is necessary to perform FM demodulation (FM detection or PM detection), which is processing. It is difficult to optimize coefficients while evaluating the effect of linear processing on the results of nonlinear processing (problem C). That is, since the method of changing the evaluation value with respect to the change of the coefficient becomes complicated, there is a possibility that the coefficient updating method such as the maximum slope method will not converge and diverge or oscillate.

An object of the present invention is to solve such problems, and to provide a receiving apparatus and a receiving method capable of stably canceling multipaths of broadcast signals.

In order to solve the above problems, the present invention provides a receiver for receiving a broadcast signal including a signal with known characteristics, comprising: a receiver for receiving the broadcast signal; transforming means for transforming a signal having a known characteristic obtained by a linear filter into an intensity-modulated signal; specifying means for specifying multipath based on the modulated signal obtained by the transforming means; and processing means for executing processing for suppressing fading including the multipath based on the above.
With such a configuration, it is possible to stably cancel the multipath of the broadcast signal.

Also, the present invention is characterized in that the transforming means executes filtering having an inverse characteristic of a frequency characteristic of a signal with known characteristics included in the broadcast signal.
According to such a configuration, it is possible to accurately identify the delayed wave based on the difference between the peaks of the direct wave and the delayed wave.

Also, the present invention is characterized in that the broadcast signal is an FM broadcast signal and the signal with known characteristics is a pilot signal.
According to such a configuration, it is possible to reliably suppress fading including multipath of the FM broadcast signal based on the pilot signal whose characteristics are known.

The present invention further comprises second conversion means for converting the intensity-modulated signal converted by the conversion means to generate a null for a peak of the intensity-modulated signal when there is no multipath, The identification means identifies the multipath based on the conversion result of the second conversion means.
According to such a configuration, it is possible to identify the delayed wave even when the delayed wave exists close to the direct wave.

Further, according to the present invention, the second transforming means performs a Hilbert transform on the intensity-modulated signal transformed by the transforming means, and the identifying means performs the multipath transform based on the transformation result of the second transforming means. characterized by specifying
According to such a configuration, it is possible to reliably identify the delayed wave even when the delayed wave exists close to the direct wave.

Also, the present invention is characterized in that the identification means obtains maximum and minimum values at each time of the results obtained by the second conversion means, and identifies the multipath based on the difference value between them. do.
According to such a configuration, it is possible to reliably identify the delayed wave based on the difference value.

Further, the present invention is characterized in that the identifying means identifies a downwardly convex inflection point in the difference value between the maximum value and the minimum value as the position where the multipath exists.
According to such a configuration, it is possible to reliably identify the delayed wave by identifying the downwardly convex inflection point.

Further, the present invention provides a receiving method for a receiving device that receives a broadcast signal including a signal with known characteristics, comprising: a receiving step of receiving the broadcast signal; A conversion step of converting a characteristic signal into an intensity-modulated signal by a linear filter, a specifying step of specifying a multipath based on the modulated signal obtained in the converting step, and based on the specifying result in the specifying step, and a processing step of executing processing for suppressing fading including the multipath.
According to such a method, it is possible to stably cancel the multipath of the broadcast signal.

According to the present invention, it is possible to provide a receiving apparatus and a receiving method capable of stably canceling multipaths of broadcast signals.

It is a figure which shows the structural example of the receiving apparatus which concerns on 1st Embodiment of this invention. FIG. 4 is a diagram showing signal waveforms when A=0 in Equation (2); Fig. 3 shows the time domain signal shown in Fig. 2 in the frequency and phase domains; 2 is a diagram showing an example of characteristics of a pulse conversion unit shown in FIG. 1; FIG. FIG. 5 is a diagram showing frequency characteristics and phase characteristics of a signal when five frequencies are extracted from the signal shown in FIG. 2 and supplied to a pulse converter having the characteristics shown in FIG. 4; 5 is a diagram showing waveforms of a plurality of signals after conversion when five frequencies are extracted from the signal shown in FIG. 2 and supplied to a pulse converter having the characteristics shown in FIG. 4; FIG. FIG. 7 is a diagram showing waveforms obtained from absolute values obtained from the real part and the imaginary part shown in FIG. FIG. 4 is a diagram showing amplitude characteristics and phase characteristics when the center frequency is 77.5 MHz, the intensity ratio between the direct signal and the delayed signal is 1:0.5, and the delay time is 20 μsec. 9 is a diagram showing amplitude characteristics and phase characteristics of a conversion filter for converting the signal shown in FIG. 8 into an impulse-like signal; FIG. 9. It is a figure which shows the processing result which processed the signal shown in FIG. 8 by the conversion filter which has the amplitude characteristic and phase characteristic which are shown in FIG. FIG. 5 is a diagram showing a configuration example of a receiving device according to a second embodiment of the present invention; FIG. 10 is a diagram showing an output signal when an FM broadcast signal containing a delay wave A and a delay wave B as multipaths with respect to a direct wave is supplied to a pulse converter. It is a figure which shows the output signal of a Hilbert transform part. It is a figure for demonstrating the process after a Hilbert transform part. FIG. 10 is a diagram showing a configuration example of a receiver according to a modified embodiment of the present invention;

Next, embodiments of the present invention will be described.

(A) Description of Configuration of First Embodiment of the Present Invention FIG. 1 is a diagram showing a configuration example of a receiver 10 according to the first embodiment of the present invention. The receiver 10 according to the first embodiment of the present invention receives, for example, an FM broadcast signal and outputs it to a demodulator (not shown), or to an upconverter or transmission device.

The receiving device 10 includes an antenna 11, a filter section 12, a level adjustment section 13, an A/D (Analog to Digital) conversion section 14, frequency mixing sections 15-1 and 15-2, filter sections 16-1 and 16-2, It has a local oscillator 17 , a π/2 phase shifter 18 , a corrector 19 , a quadrature modulator 20 , a frequency converter 21 , a local oscillator 22 , a pulse converter 23 and a coefficient generator 24 .

Here, the antenna 11 converts an FM broadcast signal transmitted from a broadcasting station (not shown) into an electric signal and outputs the electric signal.

The filter unit 12 passes an FM broadcast signal of a desired frequency from the received signal output from the antenna 11 and attenuates and outputs other signals.

The level adjustment unit 13 amplifies or attenuates the received signal output from the filter unit 12 to adjust the signal level and outputs the signal.

The A/D converter 14 converts the FM broadcast signal output from the level adjuster 13 into a digital signal and outputs the digital signal.

The frequency mixer 15-1 mixes ( multiplication), frequency-converts the broadcast signal, and outputs it. The frequency mixer 15-2 mixes (multiplies) the local oscillation signal supplied from the local oscillator 17 and the FM broadcast signal supplied from the A/D converter 14, converts the frequency of the broadcast signal, and outputs the result. do.

Filter section 16-1 subtracts unnecessary components from the signal output from frequency mixing section 15-1 and outputs the resulting signal. Filter section 16-2 subtracts unnecessary components from the signal output from frequency mixing section 15-2 and outputs the resulting signal.

The local oscillation unit 17 generates and outputs a local oscillation signal for frequency-converting the FM broadcast signal.

The π/2 phase shifter 18 shifts the phase of the local oscillation signal supplied from the local oscillator 17 by π/2 and outputs the resultant signal.

The correction unit 19 has a plurality of delay circuits and constant multiple circuits, performs adaptive digital filtering on the digital signals supplied from the filter units 16-1 and 16-2, and outputs the result.

The quadrature modulation unit 20 quadrature-modulates the signal that has been subjected to the adaptive digital filtering process by the correction unit 19 and outputs the modulated signal. Instead of the quadrature modulation section 20, a transmission signal demodulation section for demodulating the FM broadcast signal may be provided.

The frequency conversion section 21 frequency-converts the signal output from the correction section 19 using the local oscillation signal output from the local oscillation section 22 and outputs the resultant signal.

The pulse conversion section 23 performs pulse conversion processing on the signal output from the frequency conversion section 21 and outputs the result.

The coefficient generation unit 24 generates and outputs coefficients for the constant multiplier circuit of the correction unit 19 based on the signal supplied from the pulse conversion unit 23 .

(B) Description of the operation of the first embodiment of the present invention Next, the operation of the first embodiment of the present invention will be described. Below, after explaining the principle of operation of the first embodiment, the detailed operation of the first embodiment will be explained.

In the first embodiment of the present invention, an FM-modulated signal having a signal pattern with known characteristics, such as a pilot signal for FM stereo broadcasting, is converted into a pulse-like intensity-modulated waveform by linear processing. A case where the center frequency of the carrier wave is converted to 200 kHz and the pilot signal is 19 kHz (the case shown in FIG. 2) will be described below.

FIG. 3 shows the time domain signal shown in FIG. 2 in the frequency and phase domains. More specifically, FIG. 3(A) shows the signal in the frequency domain and FIG. 3(B) shows the signal in the phase domain. As shown in FIG. 3A, in the frequency domain, five peaks are observed at 162 kHz, 181 kHz, 200 kHz, 219 kHz, and 238 kHz centered at 200 kHz.

FIG. 4 is a diagram showing an example of the characteristics of the pulse converter 23 shown in FIG. More specifically, FIG. 4A shows amplitude characteristics of the pulse converter 23, and FIG. 4B shows phase characteristics. In the amplitude characteristic shown in FIG. 4A, the amplitude of the 162 kHz component is amplified by 34 dB, and in the phase characteristic shown in FIG. 4B, the phase is shifted by -97 degrees. Further, in the amplitude characteristic shown in FIG. 4A, the amplitude of the 181 kHz component is amplified by 14 dB, and in the phase characteristic shown in FIG. 4B, the phase is shifted by 76 degrees.

FIG. 5 shows five frequencies (five frequencies shown in FIG. 3A) extracted from the signal shown in FIG. 5(A)) and phase characteristics (FIG. 5(B)) of the signal. The frequency specification and phase characteristics of the signal output from the pulse converter 23 are flat as shown in FIG.

FIG. 6 shows five frequencies (five frequencies shown in FIG. 3A) extracted from the signal shown in FIG. shows the waveform of a complex signal of The horizontal axis of FIG. 6 indicates time (msec), and the vertical axis indicates amplitude. A solid line indicates the real part, and a dashed line indicates the imaginary part.

FIG. 7 shows waveforms obtained from the absolute values of the real and imaginary parts shown in FIG. The horizontal axis of FIG. 7 indicates time (msec), and the vertical axis indicates amplitude. As shown in FIG. 7, the time waveform after the conversion is an impulse waveform with a period of 1/19 kHz≈52.6 μsec, and has resolution on the time axis. That is, the pulse conversion unit 23 performs the filtering process with the characteristics shown in FIG. 4 on the time domain signal shown in FIG. 2 so that the signal becomes flat in the frequency domain. As a result, in the time domain, an impulse waveform is obtained as shown in FIG.

FIG. 8 shows the amplitude characteristics when the center frequency is 77.5 MHz, the intensity ratio between the direct signal and the delayed signal is 1:0.5, and the delay time is 20 μsec (equivalent to 6 km) (FIG. 8(A)). and phase characteristics (FIG. 8B).

9A and 9B are graphs showing amplitude characteristics (FIG. 9A) and phase characteristics (FIG. 9B) of the pulse converter 23 for converting the signals shown in FIG. 8 into impulse signals. Note that in FIG. 9A, circles indicate conversion strengths, and squares indicate approximation characteristics. In addition, in FIG. 9B, circles indicate conversion phases, and squares indicate approximation characteristics.

FIG. 10 shows the result of processing the signal shown in FIG. 8 by the pulse converter 23 having the amplitude characteristics and phase characteristics shown in FIG. When an FM broadcast signal has multipaths and such a signal is processed by the pulse converter 23 having the characteristics shown in FIG. 9, peaks of the direct wave and the delayed wave are generated as shown in FIG. Therefore, the delay time and amplitude (intensity) of the delayed wave can be obtained from these peaks.

By obtaining the amplitude and delay time of the delayed signal in this manner and setting the characteristics of the corrector 19 based on the obtained information, multipath can be reliably suppressed.

Next, detailed operation of the first embodiment of the present invention will be described. Antenna 11 receives an FM broadcast signal transmitted from an FM broadcast station or an FM relay station (not shown), converts it into an electric signal, and outputs the electric signal.

The filter unit 12 passes a signal in a predetermined frequency band from the received signal supplied from the antenna 11, and attenuates and outputs other signals. The level adjustment unit 13 amplifies or attenuates the signal supplied from the filter unit 12 so as to adjust the signal level to a desired level and outputs the signal.

The A/D converter 14 samples the signal output from the level adjuster 13 at a predetermined cycle (for example, 2 MHz), converts it into a digital signal, and outputs it. The frequency mixing unit 15-1 mixes the digital signal supplied from the A/D conversion unit 14 and the signal supplied from the π/2 phase shift unit 18, which is obtained by shifting the phase of the local oscillation signal by π/2. (Multiply) and output. The frequency mixer 15-2 mixes (multiplies) the digital signal supplied from the A/D converter 14 and the local oscillation signal supplied from the local oscillator 17, and outputs the result.

The frequency mixing unit 15-1 mixes the digital signal output from the A/D conversion unit 14 with the local oscillation signal whose phase is shifted by 90 degrees supplied from the π/2 phase shift unit 18, Generates and outputs an intermediate frequency signal. If the frequency f _C of the carrier wave of the FM broadcast signal is 85.1 MHz and the frequency f _L of the local oscillation signal is 84.9 MHz, the frequency f _IF of the intermediate frequency signal is 200 kHz (85.1 MHz-84.1 MHz). becomes. The frequencies described above are only examples, and it is needless to say that frequencies other than these may be set.

The frequency mixer 15-2 mixes the digital signal output from the A/D converter 14 with the local oscillation signal supplied from the local oscillator 17 to generate and output an intermediate frequency signal. Assuming that the frequency f _C of the carrier wave of the FM broadcast signal is 85.1 MHz and the frequency f _L of the local oscillation signal is 84.1 MHz, the frequency f _IF of the intermediate frequency signal is 200 kHz (85.1 MHz-84.1 MHz). becomes. The frequencies described above are only examples, and it is needless to say that frequencies other than these may be set.

The correction unit 19 is configured by an FIR (Finite Impulse Response) filter having a plurality of delay circuits and constant multiple circuits. The constant of the constant multiplier circuit is set by the coefficient generator 24 . The correction unit 19 performs filter processing on the digital signals supplied from the filter units 16-1 and 16-2, thereby suppressing multipath components included in the FM broadcast signal and outputting the signal.

More specifically, the frequency conversion section 21 multiplies the output signal from the correction section 19 by the local oscillation signal supplied from the local oscillation section 22, converts the frequency, and outputs the result. Note that the frequency f _L0 (=ω _L0 /2π) of the local oscillation signal output from the local oscillator 22 can be set, for example, so that the frequency after frequency conversion is 200 kHz. Of course, other frequencies may be set.

The pulse conversion section 23 subjects the output signal from the frequency conversion section 21 to the above-described pulse conversion processing. More specifically, the pilot signal included in the FM broadcast signal is subjected to pulse conversion processing, which is linear conversion processing as shown in FIG. 9, for example. Then, the obtained result is output to the coefficient generator 24 .

The coefficient generating unit 24 receives the output signal from the pulse transforming unit 23, refers to this signal, identifies the multipath component, and suppresses the identified multipath component. Set the constants of the constant multiplier circuits.

More specifically, the coefficient generation unit 24 performs absolute value calculation processing on the real part and the imaginary part, which are the calculation results supplied from the pulse conversion unit 23, to obtain, for example, as shown in FIG. Get the output waveform.

Next, the coefficient generator 24 obtains the intensity of the delayed wave based on the amplitude ratio of the direct wave component and the delayed wave component included in the time waveform shown in FIG. At the same time, the delay time of the delayed wave is obtained based on the time difference between the direct wave component and the delayed wave component. For example, in the example of FIG. 10, the amplitude of the delayed wave is approximately half that of the direct wave, and the delay time is required to be 20 μsec.

Next, the coefficient generation unit 24 sets the constants of the constant circuit of the correction unit 19 so as to suppress the component corresponding to the delay wave. More specifically, constants are set so as to implement filtering that attenuates the amplitude and phase of the delayed wave. As a result, the delayed wave component shown in FIG. 10 is attenuated.

Since the output signal of the correction unit 19 is input to the pulse conversion unit 23, the delay wave component shown in FIG. 10 is reliably suppressed by repeating the processing described above.

The signal output from the correction unit 19 and having the delayed wave suppressed is supplied to, for example, an FM demodulation unit (not shown) in the case of a receiving apparatus. In the case of a repeater, for example, it is supplied to an up-converter or a transmission device (not shown).

As described above, according to the first embodiment of the present invention, it is possible to reliably suppress multipath by extracting a signal reflecting a demodulated signal and detecting a delayed wave. In addition, since the evaluation signal is generated by linear processing by the pulse conversion unit 23 without FM demodulation (nonlinear processing), it is possible to stabilize the update feedback of the constant multiplier circuit.

(C) Description of Configuration of Second Embodiment of the Present Invention FIG. 11 is a diagram showing a configuration example of the receiver 10 according to the second embodiment of the present invention. In FIG. 11, parts corresponding to those in FIG. 1 are denoted by the same reference numerals, and descriptions thereof are omitted.

11, frequency converter 25, local oscillator 26, pulse converter 27, Hilbert transformer 28, and delay unit 29 are newly added, and frequency converter 21 and local oscillator 22 are newly added in FIG. , the pulse conversion unit 23 and the coefficient generation unit 24 are replaced with a frequency conversion unit 31 , a local oscillation unit 32 , a pulse conversion unit 33 and a coefficient generation unit 34 . The configuration other than these is the same as in FIG.

Here, the frequency conversion unit 31 frequency-converts the I ₂ and Q ₂ signals output from the correction unit 19 using the local oscillation signal supplied from the local oscillation unit 32, and outputs them as I ₂ ′ and Q ₂ ′ signals. do.

The local oscillation section 32 generates and outputs a local oscillation signal of a predetermined frequency.

The pulse converter 33 applies pulse conversion to the I ₂ ′ and Q ₂ ′ signals output from the frequency converter 31 and outputs the I ₃ ′ and Q ₃ ′ signals.

The frequency conversion unit 25 frequency-converts the I ₁ and Q ₁ signals supplied from the filter units 16-1 and 16-2 by the local oscillation signal supplied from the local oscillation unit 26, and converts the signals into I ₁ ′ and Q ₁ ′. output as a signal. The local oscillation section 26 generates and outputs a local oscillation signal.

The pulse conversion section 27 subjects the I ₁ ' and Q ₁ ' signals supplied from the frequency conversion section 25 to pulse conversion in the same manner as the pulse conversion section 23 and outputs the resulting signals as I ₄ ' and Q ₄ ' signals.

The Hilbert transform unit 28 applies a Hilbert transform to the I ₄ ′ and Q ₄ ′ signals output from the pulse transform unit 27, shifts the phase components of the signals by 90 degrees, and converts I ₄ ″ and Q ₄ . ” is output.

The delay unit 29 applies a predetermined delay to the I ₄ ′ and Q ₄ ′ signals output from the pulse conversion unit 27 and outputs the delayed signals.

The coefficient generator 34 generates the I ₃ ′ and Q ₃ ′ signals supplied from the pulse transform unit 33 , the I ₄ ″ and Q ₄ ″ signals supplied from the Hilbert transform unit 28 , and the signal supplied from the delay unit 29 . , the constant of the constant multiplier circuit included in the correction unit 19 is set.

(D) Description of Operation of Second Embodiment of the Present Invention Next, operation of the second embodiment of the present invention will be described. In the following, after the general operation of the second embodiment is explained, the detailed operation will be explained.

FIG. 12 shows an output signal when an FM broadcast signal containing delayed waves A and B as multipaths with respect to direct waves is supplied to the pulse converter 33 . The impulse response of the pilot signal period is superimposed on the basis of the arrival time of the direct wave. Here, FIG. 12A shows the real part (I ₃ ') component output from the pulse conversion unit 33, and FIG. 12B shows the imaginary part (Q ₃ ') component output from the pulse conversion unit 33. , and FIG. 12(C) shows the amplitude (|I ₃ '+Q ₃ '|) component output from the pulse converter 33 . Here, || indicates an absolute value. As shown in FIG. 12(C), for the direct wave B, a unimodal peak is observed because it is temporally separated from the direct wave. However, since the delay wave A has a small temporal difference from the direct wave and has a small amplitude, it is buried in the base of the peak of the direct wave and cannot be recognized as a peak. In addition, if there is a slight fluctuation in the time difference between the direct wave and the delayed wave in a multipath environment, the waveform after impulse conversion will also change in various ways due to the effect of frequency conversion by the local frequency. Therefore, in FIG. 12, there is a set of multiple curves.

In the second embodiment, the pulse transforming section 27 generates an output as shown in FIG. The Hilbert transform unit 28 performs Hilbert transform, which is a type of linear transform, on the signal output from the pulse transform unit 27 and outputs the result.

FIG. 13 is a diagram showing the output signal of the Hilbert transform section 28. As shown in FIG. More specifically, FIG. 13A shows the real part (I ₄ ″) output from the Hilbert transform unit 28, and FIG. 13B shows the imaginary part (Q ₄ ″) output from the Hilbert transform 28. ) component, and FIG. 13C shows the amplitude (|I ₄ ″+Q ₄ ″|) component output from the Hilbert transform unit 28 .

As shown in FIG. 13(C), the amplitude of the signal after being subjected to the Hilbert transform by the Hilbert transform unit 28 is constricted at the positions where the direct waves or the delayed waves A and B are present. The time when this constriction occurs corresponds to the arrival time of each signal. Also, the height of the constriction on the vertical axis reflects the magnitude of the interference. In FIG. 13C, delayed wave A is most affected by interference.

The I ₄ ″ and Q ₄ ″ signals output from the Hilbert transform unit 28 are supplied to the coefficient generation unit 34 . The coefficient generation unit 34 obtains the maximum and minimum values of the I ₄ ″ and Q ₄ ″ signals supplied from the Hilbert transform unit 28 and calculates the difference between them. Further, the maximum values of the delayed I ₄ ′ and Q ₄ ′ signals supplied from the delay unit 29 are obtained, and the maximum and minimum values of the I ₄ ″ and Q ₄ ″ signals are obtained near the obtained maximum values. A portion where the difference value is a downwardly convex inflection point is specified as a delayed wave.

FIG. 14 is a diagram for explaining the processing after the Hilbert transform unit 28. As shown in FIG. A curve C1 shown in FIG. 14A shows the maximum values of the I ₄ ″ and Q ₄ ″ signals supplied from the Hilbert transform unit 28 at _each time. It shows the minimum value of the Q ₄ ″ signal at each time.

A curve C3 shown in FIG. 14B is a curve showing a difference value between the curve C1 representing the maximum value shown in FIG. 14A and the curve C2 representing the minimum value. This curve C3 has a downwardly convex bend at the positions of the direct wave and the delayed wave.

In the coefficient generator 34, near the maximum values of the I ₄ ′ and Q ₄ ′ signals supplied from the delay unit 29, a downwardly convex curve C3, which is the difference between the maximum and minimum values obtained by the above calculation, is generated. The position of the inflection point is estimated as the position of the direct wave and the reflected wave. As a result, the positions of the direct wave, the delayed wave A, and the delayed wave B can be correctly estimated as indicated by the curve C4 shown in FIG. 14(C).

Since the delayed wave B is delayed from the delayed wave A, the interference with the delayed wave A is small. Therefore, in the delayed wave B, the curve C3, which is the difference value between the maximum value and the minimum value, does not clearly bend. In such cases, a bend in curve C1 with maximum values may be used. As a more specific procedure, the downwardly convex bends of the curve C1 and the curve C3 are compared and the clearer one is adopted. As a method for quantitatively comparing the downwardly convex bends, when the curve C1 and the curve C3 are differentiated second-order with respect to time, the larger positive value may be adopted as the clear bend. good.

The coefficient generating unit 34 generates the direct wave and the delayed wave specified by the above method based on the signals supplied from the Hilbert transform unit 28 and the delay unit 29, and the signal supplied from the pulse transform unit 33 (first embodiment and signal obtained by a similar method), the constants of the multiple constant multiplier circuits included in the correction unit 19 are set. This makes it possible to reliably suppress delayed waves.

As described above, according to the second embodiment of the present invention, delayed waves are specified by referring to the result of the Hilbert transform by the Hilbert transform unit 28. Even if it exists, it is possible to reliably identify the delayed wave and suppress the delayed wave.

(E) Description of Modified Embodiments The above-described embodiments are examples, and needless to say, the present invention is not limited to the above-described cases. For example, in each of the above embodiments, multipath signals of FM broadcast signals are suppressed, but the present invention is not limited to FM broadcast signals.

Further, in the first embodiment, the output signal of the correction unit 19 is quadrature-demodulated and input to the pulse conversion unit 23, but the input signal of the correction unit 19 is quadrature-demodulated and input to the pulse conversion unit 23. can be

Further, in the second embodiment, the pulse conversion unit 33 and the like are provided, but the frequency conversion unit 31, the local oscillation unit 32, and the pulse conversion unit 33 are excluded, and the output signals of the Hilbert conversion unit 28 and the delay unit 29 are The coefficient generator 34 may operate based on. Further, in the second embodiment, the input signal of the correction unit 19 is frequency-converted and input to the pulse conversion unit 33 , but the output signal of the correction unit 19 is frequency-converted and input to the pulse conversion unit 27 . can be

Further, in each of the above embodiments, the pulse conversion units 23 and 33, the Hilbert conversion unit 28, the delay unit 29, and the like are realized by digital circuits, but they may be realized by analog circuits. good. Also, it may be realized by using a digital circuit and an analog circuit together.

Further, in the first embodiment shown in FIG. 1, the A/D conversion section 14 is arranged after the level adjustment section 13, but as shown in FIG. A/D converters 14-1 and 14-2 may be arranged in the latter stage. Also, in the second embodiment shown in FIG. 11, similarly to FIG. good.

10 Receiving Device 11 Antenna 12 Filter Section 13 Level Adjustment Section 14-1, 14-2 A/D Conversion Section 15-1, 15-2 Frequency Mixing Section 16-1, 16-2 Filter Section 17 Local Oscillation Section 18 π/ 2 phase shift section 19 correction section 20 quadrature modulation section 21 frequency conversion section 22 local oscillation section 23 pulse conversion section 24 coefficient generation section 25 frequency conversion section 26 local oscillation section 27 pulse conversion section 28 Hilbert conversion section 29 delay section 31 frequency conversion section 32 Local oscillator 33 Pulse converter 34 Coefficient generator

Claims (8)

In a receiver that receives a broadcast signal containing a signal with known characteristics,
receiving means for receiving the broadcast signal;
converting means for converting a signal of known characteristics included in the broadcast signal received by the receiving means into an intensity-modulated signal using a linear filter;
identifying means for identifying a multipath based on the modulated signal obtained by the converting means;
processing means for executing processing for suppressing fading including the multipath based on the result of identification by the identification means;
A receiving device characterized by comprising: 2. The receiving apparatus according to claim 1, wherein said converting means performs filtering having an inverse characteristic of a frequency characteristic of a signal of known characteristic included in said broadcast signal. 2. The receiving apparatus according to claim 1, wherein said broadcast signal is an FM broadcast signal and said signal of known characteristics is a pilot signal. further comprising second conversion means for converting the intensity-modulated signal converted by the conversion means so as to generate a null for a peak of the intensity-modulated signal in the absence of the multipath;
The identification means identifies the multipath based on the conversion result of the second conversion means.
4. The receiving apparatus according to any one of claims 1 to 3, characterized by: The second conversion means performs a Hilbert transform on the intensity-modulated signal converted by the conversion means,
The identification means identifies the multipath based on the conversion result of the second conversion means.
5. The receiving apparatus according to claim 4, characterized by: 6. A method according to claim 5, wherein said identifying means obtains the maximum and minimum values of the results obtained by said second transforming means at each time, and identifies said multipath based on the difference between these values. receiver. 7. The receiving apparatus according to claim 6, wherein said identifying means identifies a downwardly convex inflection point in a difference value between a maximum value and a minimum value as a position where said multipath exists. In a receiving method for a receiving device that receives a broadcast signal containing a signal with known characteristics,
a receiving step of receiving the broadcast signal;
a converting step of converting a signal of known characteristics included in the broadcast signal received in the receiving step into an intensity-modulated signal using a linear filter;
an identification step of identifying multipaths based on the modulated signal obtained in the conversion step;
a processing step of executing processing for suppressing fading including the multipath based on the identification result in the identification step;
A receiving method for a receiving device, comprising:

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