JP3767690B2 - Diversity receiver - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a diversity receiver that receives a broadcast signal modulated (OFDM modulation) by an orthogonal frequency division multiplexing system.
[0002]
[Prior art]
One OFDM transmission symbol period of an OFDM-modulated broadcast signal includes an effective symbol period and a guard interval period. The effective symbol period is a signal period necessary for data transmission. The guard interval is for preventing inter-symbol interference such as multipath, and is obtained by cyclically copying the last predetermined period length portion of the effective symbol interval to the beginning of the effective symbol interval.
[0003]
Diversity receivers that receive OFDM-modulated broadcast signals such as digital terrestrial television broadcast signals are known. A conventional diversity receiver of this type has been proposed by the applicant (Japanese Patent Application No. 2000-380005 ).
[0004]
This diversity receiver uses a variable attenuator to attenuate received signals from multiple antennas, combines the attenuated outputs, and demodulates the combined output into a baseband signal. When the attenuation level of one variable attenuator in the variable attenuator is switched during the period corresponding to the guard interval interval based on the signal level, and the received signal level rises due to the switching of the attenuation amount, it corresponds to the guard interval interval thereafter. The amount of attenuation of the one variable attenuator is changed stepwise at a timing according to the period.
[0005]
[Problems to be solved by the invention]
However, even if the attenuation amount of the variable attenuator is controlled as described above, since the received signal level includes a noise component, the OFDM modulation is performed under the reception condition where the received signal level is low and the C / N is bad. If the received signal level of the signal is low and there is an antenna with almost no noise component output from the low noise amplifier, the amount of attenuation of the variable attenuator of that system is set to 0 and signals from other antennas are sent to the low noise amplifier. When the signal is combined with the amplified signal, the power of the noise component is added to increase the received signal level, and the diversity control circuit determines that the reception condition is good. However, the C / N actually deteriorates. There was a problem of end.
[0006]
On the other hand, since the attenuation amount of the variable attenuator is controlled, there is a problem that the frequency correction of the baseband signal as the detection output cannot be performed correctly for a certain period.
[0007]
An object of the present invention is to provide a stable diversity receiver by improving the reliability of substantial selection of antennas.
[0008]
[Means for Solving the Problems]
A diversity receiver according to the present invention is a diversity receiver including a plurality of antennas for receiving an OFDM-modulated signal in which one symbol period includes an effective symbol period and a guard interval period,
Variable attenuation means for attenuating received signals from a plurality of antennas, respectively;
Demodulating means for synthesizing the output from the variable attenuating means, demodulating the synthesized output, and
An attenuation amount control means for changing the attenuation amount of the variable attenuation means during a period corresponding to the guard interval section of the baseband signal obtained by the demodulation means;
When the attenuation amount of the variable attenuation means is suddenly changed from the maximum value to the minimum value, or when it is suddenly changed from the minimum value to the maximum value, the frequency of the received OFDM modulated wave and the frequency of the transmitted OFDM modulated wave are received in response to the correlation output And an automatic frequency control means for holding an automatic frequency correction signal for correcting a deviation from the value immediately before the sudden change of the attenuation amount for a predetermined period.
[0009]
A diversity receiver according to the present invention is a diversity receiver including a plurality of antennas for receiving an OFDM-modulated signal in which one symbol period includes an effective symbol period and a guard interval period,
Variable attenuation means for attenuating received signals from a plurality of antennas, respectively;
Demodulating means for synthesizing the output from the variable attenuating means, demodulating the synthesized output, and
Correlation detecting means for detecting a correlation in a period corresponding to the guard interval section of the baseband signal obtained by the demodulating means;
Attenuation amount control means for changing the attenuation amount of the variable attenuation means during the period corresponding to the guard interval section based on whether or not the peak level of the correlation output in the period corresponding to the guard interval section has increased.
When the attenuation amount of the variable attenuation means is suddenly changed from the maximum value to the minimum value, or when it is suddenly changed from the minimum value to the maximum value, the frequency of the received OFDM modulated wave and the frequency of the transmitted OFDM modulated wave are received in response to the correlation output And an automatic frequency control means for holding an automatic frequency correction signal for correcting a deviation from the value immediately before the sudden change of the attenuation amount for a predetermined period.
[0010]
A diversity receiver according to the present invention is a diversity receiver including a plurality of antennas for receiving an OFDM-modulated signal in which one symbol period includes an effective symbol period and a guard interval period,
Variable attenuation means for attenuating received signals from a plurality of antennas, respectively;
Demodulating means for synthesizing the output from the variable attenuating means, demodulating the synthesized output, and
Correlation detecting means for detecting a correlation in a period corresponding to the guard interval section of the baseband signal obtained by the demodulating means;
Power detection means for detecting power in a period corresponding to the guard interval section of the baseband signal obtained by the demodulation means;
Attenuation amount control means for changing the attenuation amount of the variable attenuation means during the period corresponding to the guard interval section, based on whether or not the peak level of the power output in the period corresponding to the guard interval section has increased.
When the attenuation amount of the variable attenuation means is suddenly changed from the maximum value to the minimum value, or when it is suddenly changed from the minimum value to the maximum value, the frequency of the received OFDM modulated wave and the frequency of the transmitted OFDM modulated wave are received in response to the correlation output And an automatic frequency control means for holding an automatic frequency correction signal for correcting a deviation from the value immediately before the sudden change of the attenuation amount for a predetermined period.
[0011]
According to the diversity receiver of the present invention, since the automatic frequency correction signal is held at a value immediately before the sudden change of the attenuation amount for a predetermined period, stable diversity without adversely affecting the automatic frequency control. Control is possible.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a diversity receiver according to the present invention will be described according to an embodiment.
[0013]
A diversity receiver A according to an embodiment of the present invention is configured as shown in FIG.
[0014]
In diversity receiver A, the RF signals received by antennas 1, 2, 3, and 4 are amplified by low-noise amplifiers 5, 6, 7, and 8, respectively, and then variable attenuators 9, 10, 11, and 12, respectively. After attenuation, the signal is input to the mixer 13 and synthesized, and the output of the mixer 13 is supplied to the tuner 14.
[0015]
The tuner 14 that has received the combined output output from the mixer 13 performs amplification, frequency conversion, and band limitation to convert the combined output into an intermediate frequency signal. The intermediate frequency signal output from the tuner 14 is supplied to the AD converter 15 to be converted into a digital signal, and the converted digital signal is supplied to the quadrature detector 16 to perform quadrature detection. Convert to signal.
[0016]
The baseband I and Q signals output from the quadrature detector 16 are supplied to the effective symbol extraction circuit 17, and effective symbol extraction is performed based on the timing signal (FFT-WINDOW) indicating the effective symbol period output from the timing recovery circuit 21. In the circuit 17, only a signal in a period corresponding to an effective symbol is taken from the baseband I and Q signals, a signal in a period corresponding to an effective symbol period is supplied to the FFT circuit 18, and FFT processing is performed in the FFT circuit 18 to perform OFDM. The modulated signal is demodulated and separated into information for each carrier, supplied to the demapper circuit 19 and demapped to be sent as demodulated data.
[0017]
On the other hand, the baseband I and Q signals output from the quadrature detector 16 are supplied to the guard correlator 20, and the input baseband I and Q signals of the guard correlator 20 and the baseband I and Q signals are used in the effective symbol period. The product of the delayed baseband I and Q signals delayed by the time width is integrated over the time width of the guard interval period, and the integration is performed by sequentially shifting the sample periods for A / D conversion in the A / D converter 15. Thus, the correlation output is obtained, the correlation output is supplied to the timing recovery circuit 21, the timing of the OFDM symbol is obtained from the peak position of the correlation output, and the timing signal (FFT-WINDOW) is sent to the effective symbol extraction circuit 17.
[0018]
Further, the correlation output CORR and the timing signal (FFT-WINDOW) output from the guard correlator 20 are supplied to the diversity control circuit 22, and are variable from the diversity control circuit 22 based on the correlation output CORR and the timing signal (FFT-WINDOW). Attenuation control signals CONT1, CONT2, CONT3, and CONT4 for controlling the attenuation of the attenuators 9, 10, 11, and 12 are sent to the variable attenuators 9, 10, 11, and 12, respectively. That is, the attenuation amount of the variable attenuators 9, 10, 11, and 12 is controlled so that the combined received signal level becomes high.
[0019]
In this way, with the attenuation of one or more variable attenuators maintained at 0, the attenuation of the variable attenuators 9, 10, 11 and 12 is sequentially controlled to change the signal level input to the tuner 14. Control to keep maximum.
[0020]
The correlation output CORR is also supplied to an automatic frequency control circuit (AFC circuit) 24 that performs an integral filter operation, the correlation output CORR is filtered by an integration filter, and the output from the AFC circuit 24 based on the correlation output CORR is controlled by the oscillation frequency. The signal is supplied as a signal to the numerically controlled oscillator of the quadrature detector 16 to correct the deviation between the frequency of the received OFDM modulated wave and the frequency of the transmitted OFDM modulated wave.
[0021]
Here, the AFC circuit 24 utilizes the fact that the phase of the peak of the correlation output output from the guard correlator 20 corresponds to the difference between the frequency of the received OFDM modulated wave and the frequency of the transmitted OFDM modulated wave. is there.
[0022]
The AFC circuit 24 includes an amplifier 26 for determining a loop gain, an adder 25 for adding the output of the amplifier 26 and the correlation output CORR, a switch means 29 for selectively turning on and off the added output, and an output of the switch means 29 for one symbol. The delay circuit 27 includes a delay filter 27 that delays the period and outputs the delayed output to the amplifier 26, and an integration filter that selectively switches on and off the input terminal and the output terminal of the delay circuit 27. The input of the delay circuit 27 is oscillated. It is sent to the quadrature detector 16 as a frequency control signal.
[0023]
The switch means 29 controls the switch means 29 to be in an OFF state and the switch means 30 to be in an ON state for a period of two symbols from the time of output of a control signal that suddenly changes the attenuation amount of the variable attenuator to the minimum or maximum from the diversity control circuit 22. To hold the output from the 2-symbol period integration filter.
[0024]
First, the operation of the diversity control circuit 22 will be described with reference to timing charts shown in FIGS. 2, 3, 4, and 5, taking the attenuation control signal CONT1 as an example.
[0025]
In diversity receiver A, the timing signal (FFT-WINDOW) indicates a period corresponding to the effective symbol period when the potential is high, and indicates a period corresponding to the guard interval period when the potential is low. The attenuation control signal CONT1 is a signal for controlling the attenuation of the variable attenuator 9. When the level of the attenuation control signal CONT1 is the maximum, the attenuation is controlled to 0, and the level of the attenuation control signal CONT1 is the minimum. In this case, the attenuation is maximized. The case of the attenuation control signal CONT2, 3, 4 is the same as that of the attenuation control signal CONT1.
[0026]
Here, the diversity control circuit 22 uses the correlation output CORR to determine whether or not the reception condition is improved. The diversity control circuit 22 changes the attenuation amount of the variable attenuators 9, 10, 11, and 12 during a period when the timing signal (FFT-WINDOW) is at a low potential, that is, during a period corresponding to the guard interval.
[0027]
In FIG. 2, in order not to lose the input of the mixer 13, at least one attenuation amount is set to 0 in the variable attenuators 10, 11, and 12, and the attenuation amount control signal CONT <b> 1 is set as an initial state. Is the minimum, that is, the amount of attenuation of the variable attenuator 9 is the maximum. Here, in order to evaluate the signal received by the antenna 1, the level of the attenuation control signal CONT1 is maximized in a section where the timing signal (FFT-WINDOW) is low (see FIG. 2A) ( 2), the attenuation of the variable attenuator 9 is set to zero.
[0028]
As a result, the signal received by the antenna 1 is also input to the tuner 14 after being synthesized by the mixer 13, and at this time, in FIG. 2, the peak level of the correlation output CORR is higher than the peak level of the previous correlation output CORR. The case is shown (see FIG. 2C). In this case, it is determined that if the signal received by the antenna 1 is combined by the mixer 13, the output level of the mixer 13 is increased, and the reception condition is determined to be better. In order to avoid the change, the level of the attenuation control signal CONT1 is once returned to the minimum at the timing when the timing signal (FFT-WINDOW) subsequently becomes a high potential, and thereafter, as shown by the arrow in FIG. The level of the attenuation control signal CONT1 is increased stepwise in a stepwise manner in the interval where the FFT-WINDOW is low.
[0029]
In the case of FIG. 3, the initial state of the receiver is the same as that of FIG. 2, but the attenuation amount control signal CONT1 is a period (see FIG. 3A) in which the timing signal (FFT-WINDOW) is at a low potential. In this case, the level of the correlation output CORR is lowered (see FIG. 3C) by maximizing the level of (see FIG. 3B) and setting the attenuation amount of the variable attenuator 13 to zero.
[0030]
In this case, it is considered that the signal received by the antenna 1 is combined in the mixer 13, the level of the output signal of the mixer 13 is lowered, and the peak level of the correlation output CORR is lowered. Since it is determined that the deterioration has occurred, the level of the attenuation control signal CONT1 is returned to the minimum at the timing when the timing signal (FFT-WINDOW) subsequently becomes high (see FIG. 3B).
[0031]
When the attenuation amount of the variable attenuator 9 is set to 0 in the period corresponding to the guard interval section in the state where the attenuation amount of the variable attenuator 9 is maximum as in the case shown in FIG. When the peak level of the correlation output CORR in the period corresponding to the interval interval is higher than the peak level of the correlation output in the period corresponding to the previous guard interval interval, the period corresponding to the next guard interval interval The amount of attenuation of the variable attenuator 9 is maximized during the period corresponding to the subsequent guard interval section, that is, restored to the original, and the amount of attenuation of the variable attenuator 9 is sequentially reduced to 0 in the period corresponding to the subsequent guard interval section. Decrease. Thus, it is possible to set the attenuation amount so that it can be received stably.
[0032]
When the attenuation amount of the variable attenuator 9 is set to 0 in the period corresponding to the guard interval section in the state where the attenuation amount of the variable attenuator 9 is maximum as shown in FIG. When the peak level of the correlation output CORR is lower than the peak level of the correlation output in the period corresponding to the previous guard interval period during the guard interval period, the attenuation amount of the variable attenuator 9 is set to zero. The attenuation amount of the variable attenuator 9 is maximized from the period corresponding to the subsequent guard interval section, that is, restored to the original. Thus, it is possible to set the attenuation amount so that it can be received stably.
[0033]
Even in the case of FIG. 4, at least one of the variable attenuators 10, 11, and 12 has an attenuation of 0, and in the initial state, the level of the attenuation control signal CONT 1 is maximum, that is, the variable attenuator 9. The amount of attenuation is zero. Here, in order to evaluate the signal received by the antenna 1, the level of the attenuation control signal CONT1 is minimized in a section where the timing signal (FFT-WINDOW) is low (see FIG. 4A) ( 4 (b)), the attenuation of the variable attenuator 9 is maximized.
[0034]
As a result, the signal received by the antenna 1 is attenuated, synthesized by the mixer 13 and input to the tuner 14. As a result, FIG. 4 shows a case where the peak level of the correlation output CORR is increased (see FIG. 4C). In this case, if the signal received by the antenna 1 is attenuated, it is determined that the level of the correlation output CORR increases and the reception condition is improved, and then the timing signal (FFT-WINDOW) is once set at a timing when the potential becomes high. The level of the attenuation control signal CONT1 is returned to the maximum level (see FIG. 4B), and thereafter, as indicated by an arrow in FIG. 4, the timing of the attenuation control signal CONT1 is decreased in a section where the timing signal (FFT-WINDOW) is at a low potential. The level is changed stepwise until the level becomes minimum (see FIG. 4B).
[0035]
In the case of FIG. 5, the initial state is the same as that of FIG. 4, but the level of the attenuation control signal CONT1 is minimized in the interval where the timing signal (FFT-WINDOW) is low (see FIG. 5A). (Refer to FIG. 5B), and the peak level of the correlation output CORR is lowered by maximizing the attenuation amount of the variable attenuator 9 (see FIG. 5C). In this case, it is considered that the signal received by the antenna 1 is combined in the mixer 13, the level of the output signal of the mixer 13 is reduced, and the peak level of the correlation output CORR is reduced. Since it is determined that the deterioration has occurred, the level of the attenuation control signal CONT1 is returned to the maximum at the timing when the timing signal (FFT-WINDOW) becomes a high potential (see FIG. 5B).
[0036]
When the attenuation amount of the variable attenuator 9 is maximized in the period corresponding to the guard interval section when the attenuation amount of the variable attenuator 9 is 0 as shown in FIG. When the peak level of the correlation output CORR is higher than the peak level of the correlation output in the period corresponding to the previous guard interval section in the interval period, the guard interval section following the period corresponding to the next guard interval section The attenuation amount of the variable attenuator 9 is set to 0 during the period corresponding to, that is, restored to the original, and the attenuation amount of the variable attenuator 9 is sequentially increased to the maximum stepwise in the period corresponding to the subsequent guard interval period. . Thus, it is possible to set the attenuation amount so that it can be received stably.
[0037]
When the attenuation amount of the variable attenuator 9 is maximized in the period corresponding to the guard interval section in the state where the attenuation amount of the variable attenuator 9 is 0 as shown in FIG. When the peak level of the correlation output CORR in the period corresponding to the guard interval interval of the current time is lower than the peak level of the correlation output in the period corresponding to the preceding guard interval interval, the attenuation amount of the variable attenuator 9 is maximized. The attenuation amount of the variable attenuator 9 is set to 0, that is, restored from the period corresponding to the guard interval interval that follows. Thus, it is possible to set the attenuation amount so that it can be received stably.
[0038]
In this way, with the attenuation of one or more variable attenuators maintained at 0, the attenuation of the variable attenuators 9, 10, 11 and 12 is sequentially controlled to change the signal level input to the tuner 14. Control to keep maximum.
[0039]
As described above, the attenuation amount of the variable attenuator is controlled so that the peak level of the correlation output CORR is referred to when detecting the signal level, so that it is less affected by the noise component and stable diversity reception can be performed.
[0040]
Next, the operation of the AFC circuit 24 will be described based on the timing chart of FIG. FIG. 6A shows a timing signal (FFT-WINDOW), in which the low potential interval indicates a period corresponding to the guard interval interval, and the high potential interval indicates a period corresponding to the effective symbol interval.
[0041]
In the example of FIG. 6, under the control of the diversity control circuit 22, the amount of attenuation in the variable attenuator 9 is controlled from the maximum value to 0 in the nth guard interval section (see FIG. 6B). Is maintained at 0 in the illustrated section (see FIG. 6C), and the attenuation in the variable attenuators 11 and 12 is maintained at the maximum in the illustrated section (see FIG. 6D and FIG. 6). (See (e)) The attenuation of one or more variable attenuators is maintained at zero.
[0042]
FIG. 6 (f) schematically shows baseband I and Q signals output from the quadrature detector 16. In FIG. 6 (f), the shaded portions with solid lines and the shaded portions with broken lines are shown in FIG. 6 (a). Corresponds to the guard interval section. FIG. 6 (g) schematically shows baseband I and Q signals delayed by an effective symbol period in order to obtain a guard correlation in the guard correlator 20, and in FIG. 6 (g), a solid hatched portion and a dashed hatched portion. Corresponds to the guard interval section, and the solid hatched line corresponds to the hatched portion of the solid line in FIG. However, the correlation output CORR output from the guard correlator 20 is copied as the guard interval by copying the last predetermined length portion of the effective symbol period to the beginning of the effective symbol period, and as shown in FIG. Become.
[0043]
As is apparent from FIG. 6 (h), the correlation output CORR is also adversely affected during the period including the period in which the amount of attenuation of the variable attenuator 9 is controlled from the maximum value to 0 by the guard correlator 20. . If AFC is performed based on the peak of the correlation output CORR that has been affected by this adverse effect, the AFC is also adversely affected and the accuracy of the AFC is reduced.
[0044]
When the attenuation of the variable attenuator 9 is controlled from the maximum value to 0 during the nth guard interval period, the period that adversely affects AFC is near the beginning of the nth symbol period and the (n + 1) th symbol period. Near the head, that is, a period including the period in which the attenuation amount of the variable attenuator 9 is controlled from the maximum value to 0 is included in the time width to be integrated by the guard correlator 20, and this is the period a and the period b in FIG. This is the section indicated by.
[0045]
Therefore, from the time of signal generation that the attenuation amount of the variable attenuator 9 output from the diversity control circuit 22 is changed from the maximum value to 0, the influence of the attenuation amount of the variable attenuator 9 being changed from the maximum value to 0 is eliminated. During the period, that is, the period from when the attenuation amount of the variable attenuator 9 is changed from the maximum value to 0 until the end of the 2OFDM transmission symbol period (period c in FIG. 6 (h)), the switch means 29 is turned off, and the switch means 30 Is turned on by the output from the diversity control circuit 22.
[0046]
As a result, during this period, the sum output of the correlation output CORR output from the guard correlator 20 and the output of the amplifier 26 is not used for AFC, but the output delayed by the delay unit 27, that is, the variable attenuator 9's output. When the attenuation amount is changed from the maximum value to 0, AFC is performed by the output held in the correlation output CORR, and adverse effects such as deterioration of AFC accuracy are avoided.
[0047]
Although the case where the attenuation amount of the variable attenuator 9 is changed from the maximum value to 0 has been illustrated, the same applies when the attenuation amount of the variable attenuator 9 is changed from 0 to the maximum value, and the variable attenuators 10, 11, 12 are the same. The same applies to the case of. Further, when the attenuation is controlled stepwise as shown in FIG. 2 and FIG. 4, since the change of the attenuation corresponding to each step of the staircase is small, the diversity control circuit 22 switches to the AFC circuit 24. The control signal for controlling 29 and 30 is not output.
[0048]
As described above, when using the diversity receiver A, the period until the influence of the attenuation of the variable attenuator 9 from the maximum value to 0 is eliminated, that is, the attenuation of the variable attenuator 9 is changed from the maximum value to 0. An automatic frequency correction signal for correcting the deviation between the frequency of the received OFDM modulated wave and the frequency of the transmitted OFDM modulated wave by receiving the correlation output during the period from the start of the 2 OFDM transmission symbol period to immediately before the sudden change of the attenuation amount Therefore, stable diversity reception can be performed without adversely affecting the AFC operation.
[0049]
In the above, the diversity control circuit is configured such that the switch means 29 is in the off state and the switch means 30 is in the on state during the period from when the attenuation amount of the variable attenuator 9 is changed from the maximum value to 0 until the end of the 2OFDM transmission symbol period. Although the case where the control is performed by the output from 22 has been described, the switch means 29 is turned off during the period from when the attenuation amount of the variable attenuator 9 is changed from the maximum value to 0 until the end of one OFDM transmission symbol period. Even if the control is performed by the output from the diversity control circuit 22 in the ON state, the above-described adverse effects are almost alleviated.
[0050]
Further, in the diversity receiver A, the baseband I and Q signals output from the quadrature detector 16 while the control of the AFC circuit 24 by the correlation output CORR from the correlation detector 20 and the output from the diversity control circuit 22 remain unchanged. In response to this, a power detector for detecting the power in the period corresponding to the guard interval section of the baseband signal is newly provided, and diversity control is performed on the power signal RX-POWER detected by the power detector instead of the correlation output CORR. The attenuation control signals CONT1, 2, 3, and 4 may be generated based on the power signal RX-POWER supplied by the circuit 22, and in this case, as in the case of the diversity receiver A. The effect of can be obtained.
[0051]
【The invention's effect】
As described above, according to the diversity receiver according to the present invention, the reliability of substantial antenna selection can be improved and stable diversity reception can be performed without adversely affecting the AFC operation.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a diversity receiver according to an embodiment of the present invention.
FIG. 2 is a timing diagram for explaining the operation of the diversity receiver according to the embodiment of the present invention.
FIG. 3 is a timing diagram for explaining the operation of the diversity receiver according to the embodiment of the present invention.
FIG. 4 is a timing diagram for explaining the operation of the diversity receiver according to the embodiment of the present invention.
FIG. 5 is a timing diagram for explaining the operation of the diversity receiver according to the embodiment of the present invention.
FIG. 6 is a timing diagram for explaining the operation of the diversity receiver according to the embodiment of the present invention.
[Explanation of symbols]
A Diversity receiver 9 to 12 Variable attenuator 13 Mixer 14 Tuner 15 AD converter 16 Quadrature detector 17 Effective symbol extraction circuit 18 FFT circuit 20 Guard correlator 21 Timing recovery circuit 22 Diversity control circuit 24 AFC circuit 25 Adder 27 Delay devices 29 and 30 Switching means

Claims (5)

A diversity receiver having a plurality of antennas for receiving an OFDM-modulated signal in which one symbol period includes an effective symbol period and a guard interval period,
Variable attenuation means for attenuating received signals from a plurality of antennas, respectively;
Demodulating means for synthesizing the output from the variable attenuating means, demodulating the synthesized output, and
An attenuation amount control means for changing the attenuation amount of the variable attenuation means during a period corresponding to the guard interval section of the baseband signal obtained by the demodulation means;
When the attenuation amount of the variable attenuation means is suddenly changed from the maximum value to the minimum value, or when it is suddenly changed from the minimum value to the maximum value, the frequency of the received OFDM modulated wave and the frequency of the transmitted OFDM modulated wave are received in response to the correlation output A diversity receiver comprising: automatic frequency control means for holding an automatic frequency correction signal for correcting a deviation from a value immediately before a sudden change in attenuation for a predetermined period. A diversity receiver having a plurality of antennas for receiving an OFDM-modulated signal in which one symbol period includes an effective symbol period and a guard interval period,
Variable attenuation means for attenuating received signals from a plurality of antennas, respectively;
Demodulating means for synthesizing the output from the variable attenuating means, demodulating the synthesized output, and
Correlation detecting means for detecting a correlation in a period corresponding to the guard interval section of the baseband signal obtained by the demodulating means;
Attenuation amount control means for changing the attenuation amount of the variable attenuation means during the period corresponding to the guard interval section based on whether or not the peak level of the correlation output in the period corresponding to the guard interval section has increased.
When the attenuation amount of the variable attenuation means is suddenly changed from the maximum value to the minimum value, or when it is suddenly changed from the minimum value to the maximum value, the frequency of the received OFDM modulated wave and the frequency of the transmitted OFDM modulated wave are received in response to the correlation output A diversity receiver comprising: automatic frequency control means for holding an automatic frequency correction signal for correcting a deviation from a value immediately before a sudden change in attenuation for a predetermined period. A diversity receiver having a plurality of antennas for receiving an OFDM-modulated signal in which one symbol period includes an effective symbol period and a guard interval period,
Variable attenuation means for attenuating received signals from a plurality of antennas, respectively;
Demodulating means for synthesizing the output from the variable attenuating means, demodulating the synthesized output, and
Correlation detecting means for detecting a correlation in a period corresponding to the guard interval section of the baseband signal obtained by the demodulating means;
Power detection means for detecting power in a period corresponding to the guard interval section of the baseband signal obtained by the demodulation means;
Attenuation amount control means for changing the attenuation amount of the variable attenuation means during the period corresponding to the guard interval section, based on whether or not the peak level of the power output in the period corresponding to the guard interval section has increased.
When the attenuation amount of the variable attenuation means is suddenly changed from the maximum value to the minimum value, or when it is suddenly changed from the minimum value to the maximum value, the frequency of the received OFDM modulated wave and the frequency of the transmitted OFDM modulated wave are received in response to the correlation output A diversity receiver comprising: automatic frequency control means for holding an automatic frequency correction signal for correcting a deviation from a value immediately before a sudden change in attenuation for a predetermined period. 4. The diversity receiver according to claim 1, wherein the automatic frequency control means is an integration filter having a correlation output as an input. 4. The diversity receiver according to claim 1, wherein the period during which the automatic frequency correction output is held at a value immediately before the sudden change of the attenuation amount is at least one symbol from when the attenuation amount is suddenly changed. A diversity receiver characterized by a period.

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