JP3776825B2 - 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 period called a guard interval. 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 present applicant (Japanese Patent Application No. 2002-023678).
[0004]
This diversity receiver uses a variable attenuator to attenuate received signals from a plurality of antennas, combines the attenuated outputs, and demodulates the combined output into a baseband signal. Guard diversity (also simply referred to as correlation) Detect and switch the attenuation amount of one variable attenuator in the variable attenuator during the period corresponding to the guard interval interval based on the correlation output level. The attenuation amount of the one variable attenuator is changed stepwise at a timing according to a period corresponding to the interval section.
[0005]
Such diversity receiver B is configured as shown in FIG. In the diversity receiver B, the RF signals received by the antennas 1, 2, 3, and 4 are amplified by the low noise amplifiers 5, 6, 7, and 8, respectively, and then respectively changed by the 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.
[0006]
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.
[0007]
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.
[0008]
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 transmitted 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 from the integrated value, 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. Send it out.
[0009]
The diversity receiver B includes a diversity control circuit 25. The correlation output CORR and timing signal (FFT-WINDOW) output from the guard correlator 20 are supplied to the diversity control circuit 25, and the correlation output CORR and timing signal (FFT-WINDOW) are supplied. ), The diversity control circuit 25 sends the attenuation control signals CONT1, CONT2, CONT3, and CONT4 for controlling the attenuation of the variable attenuators 9, 10, 11, and 12 to the variable attenuators 9, 10, 11, and 12, respectively. Thus, the amount of attenuation of the variable attenuators 9, 10, 11, and 12 is controlled so that the output level of the mixer 13, that is, the combined received signal level becomes higher.
[0010]
The operation of the diversity control circuit 25 will be described with reference to the timing charts shown in FIGS. 4 and 5, taking the attenuation control signal CONT1 as an example.
[0011]
Here, in the diversity receiver B, 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.
[0012]
In the diversity control circuit 25, the correlation output CORR is used to determine whether or not the reception condition is improved. In the diversity control circuit 25, the amount of attenuation of the variable attenuators 9, 10, 11, and 12 is changed during a period when the timing signal (FFT-WINDOW) is at a low potential, that is, a period corresponding to the interval of the guard interval.
[0013]
In FIG. 4, in order to prevent the input of the mixer 13 from being lost, at least one of the attenuation amounts in the variable attenuators 10, 11, and 12 is set to 0, and the attenuation amount control signal CONT1 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 at a low potential (see FIG. 4A) ( 4 (b)), the attenuation of the variable attenuator 9 is set to zero.
[0014]
As a result, the signal received by the antenna 1 is also input to the tuner 14 after being synthesized by the mixer 13. At this time, in FIG. 4, 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. 4C). 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.
[0015]
The initial state of the receiver is the same as in the case of FIG. 4, but the level of the attenuation control signal CONT1 is maximized in the interval where the timing signal (FFT-WINDOW) is low as in FIG. When the level of the correlation output CORR is lowered by setting the attenuation amount of the variable attenuator 9 to 0, the output signal level of the mixer 13 is lowered by combining the signals received by the antenna 1 in the mixer 13. Then, since it is considered that the peak level of the correlation output CORR has decreased and the reception condition has been deteriorated, the level of the attenuation control signal CONT1 is subsequently determined at the timing when the timing signal (FFT-WINDOW) becomes a high potential. Return information to a minimum.
[0016]
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 section is higher than the peak level of the correlation output in the period corresponding to the previous guard interval section, the period corresponding to the next guard interval section 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.
[0017]
As described above, 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, the correlation output is output in the next guard interval period. When the peak level of CORR is lower than the peak level of the correlation output in the period corresponding to the previous guard interval section, it corresponds to the guard interval section that follows when the attenuation amount of the variable attenuator 9 is set to zero. From the period, the attenuation amount of the variable attenuator 9 is maximized, that is, restored to the original. Thus, it is possible to set the attenuation amount so that it can be received stably.
[0018]
Even in the case of FIG. 5, at least one of the variable attenuators 10, 11, and 12 has an attenuation of 0. 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. 5A) ( 5 (b)), the attenuation of the variable attenuator 9 is maximized.
[0019]
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. 5 shows a case where the peak level of the correlation output CORR is increased (see FIG. 5C). 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. 5B), and thereafter, as indicated by an arrow in FIG. 5, the timing of the attenuation control signal CONT1 in the interval where the timing signal (FFT-WINDOW) is low potential. The level is changed stepwise until the level becomes minimum (see FIG. 5B).
[0020]
The initial state of the receiver is the same as in the case of FIG. 5, but the level of the attenuation control signal CONT1 is minimized in the interval in which the timing signal (FFT-WINDOW) is low as in FIG. When the level of the correlation output CORR is reduced by maximizing the attenuation amount of the variable attenuator 9, the level of the output signal of the mixer 13 is increased by combining the signals received by the antenna 1 in the mixer 13. Since it is considered that the peak level of the correlation output CORR has decreased and the reception condition has deteriorated, the level of the attenuation control signal CONT1 is set at the timing when the timing signal (FFT-WINDOW) becomes a high potential. Return to maximum.
[0021]
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 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.
[0022]
As described above, 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, it corresponds to the next guard interval section. When the peak level of the correlation output CORR in the selected period is lower than the peak level of the correlation output in the period corresponding to the previous guard interval, the guard that continues when the attenuation of the variable attenuator 9 is maximized The attenuation amount of the variable attenuator 9 is set to 0 from the period corresponding to the interval period, that is, restored to the original. Thus, it is possible to set the attenuation amount so that it can be received stably.
[0023]
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. As a result, stable diversity reception can be performed.
[0024]
[Problems to be solved by the invention]
However, as described above, even if the attenuation level of the variable attenuator is controlled for each OFDM symbol so as to keep the reception level always high, the antenna selected in the state where the reception status is uncertain, such as immediately after power-on, The output from the predetermined antenna is selected, and the attenuation amount of the variable attenuator is controlled. However, when the antenna is an antenna that hardly catches radio waves, there is a problem that the diversity operation is not effective.
[0025]
An object of the present invention is to provide a diversity receiver that improves the reliability of antenna selection in an initial state such as power-on, and exhibits a stable and sufficient effect.
[0026]
[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;
A demodulator that synthesizes the output from the variable attenuator, demodulates and outputs the combined output, and detects a correlation in a period corresponding to the guard interval section of the baseband signal obtained by the demodulator and subsequently generates a guard Correlation detecting means for outputting a lock detection signal when the interval of the guard interval determined from the generation timing of the correlation output is a value based on the transmission mode;
A received signal level detecting means for detecting a received signal level;
In the initial state, an antenna having a high reception signal level is selected based on the detection output from the reception signal level detection means, and the attenuation amount of the variable attenuation means corresponding to the selected antenna is controlled to the minimum attenuation amount, and is not selected. Based on whether the peak level of the correlation output has increased during the period corresponding to the guard interval section from when the lock detection signal was supplied An attenuation amount control means for changing the attenuation amount of the variable attenuation means corresponding to the antenna not selected during the period corresponding to the guard interval section;
It is provided with.
[0027]
According to the diversity receiver of the present invention, an antenna having a high reception signal level is selected based on the detection output from the reception signal level detection means in the initial state, and the attenuation amount of the variable attenuation means corresponding to the selected antenna is The minimum attenuation is controlled, and the attenuation of the variable attenuation means corresponding to the unselected antenna is controlled to the maximum attenuation. Therefore, an antenna that does not capture radio waves is not selected as a predetermined antenna as in the prior art. For this reason, the situation where the diversity operation is not effective is eliminated. Further, since the output of the selected antenna is transmitted without being attenuated, the lock detection signal is transmitted quickly, and demodulation is performed at an early stage.
[0028]
Further, according to the diversity receiver of the present invention, based on whether or not the peak level of the correlation output in the period corresponding to the guard interval period has increased since the lock detection signal was supplied, During the corresponding period, the attenuation amount of the variable attenuation means corresponding to the unselected antenna is changed and controlled by the attenuation amount control means. However, the attenuation amount update control is performed in symbol period units. The update control is performed because the lock detection signal is input, so that the symbol period length is fixed, the attenuation of the variable attenuation means corresponding to the selected antenna is controlled to the minimum attenuation, In addition, since the attenuation amount of the output from the unselected antenna is changed in the guard interval section, the diversity operation works quickly, and the diversity effect can be sufficiently exhibited.
[0029]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a diversity receiver according to the present invention will be described according to an embodiment.
[0030]
FIG. 1 is a block diagram showing a configuration of a diversity receiver according to an embodiment of the present invention. In order to avoid duplicated description with diversity receiver B shown in FIG. 3, an embodiment of the present invention is applied. In the diversity receiver A, the same components as those in the diversity receiver B are denoted by the same reference numerals, and description thereof is omitted.
[0031]
The diversity receiver A includes antennas 1, 2, 3, 4, low noise amplifiers 5, 6, 7, 8, variable attenuators 9, 10, 11, 12, mixer 13, tuner 14, AD converter 15, orthogonal A detector 16, an effective symbol extraction circuit 17, an FFT circuit 18, a demapper 19, a guard correlator 20, and a timing recovery circuit 21 are provided, which operate in the same manner as in the diversity receiver B.
[0032]
Furthermore, the diversity receiver A includes a diversity control circuit 22 instead of the diversity control circuit 25. The received signal level information detected from the tuner 14, the lock detection signal and correlation output CORR output from the guard correlator 20, and the timing signal (FFT-WINDOW) output from the timing recovery circuit 21 are supplied to the diversity control circuit 22, Searches for the antenna with the highest reception level based on the received signal level information in the initial state such as when the power is turned on, maintains the attenuation of the searched antenna output to the minimum, and from when the lock detection signal is output Based on the correlation output CORR and the timing signal (FFT-WINDOW), the attenuation level of the output from the antenna other than the selected antenna is controlled so as to increase the output level of the mixer 13, that is, the synthesized received signal level. The antenna diversity operation is performed.
[0033]
Here, for the received signal level information, for example, an AGC voltage in the tuner 14 can be used. Further, the interval of the guard interval is obtained from the generation timing of the subsequently generated guard correlation output, and the interval is determined as the transmission mode (modes 1, 2, and 3 in ISDB-T, 2k mode in DVB-T). , 8k mode transmission mode), the lock detection signal is output from the guard correlator 20.
[0034]
Next, the operation of the diversity control circuit 22 will be described with reference to the timing chart shown in FIG.
[0035]
Immediately after the power is turned on, the attenuation amounts of the variable attenuators 9 to 12 are sequentially minimized, and the received signal level information at that time is checked by the diversity control circuit 22. 2A shows the amount of attenuation of the variable attenuator 9, FIG. 2B shows the amount of attenuation of the variable attenuator 10, FIG. 2C shows the amount of attenuation of the variable attenuator 11, and FIG. Represents the amount of attenuation of the variable attenuator 12, respectively. FIG. 2E shows received signal level information. In FIG. 2, instead of the attenuation amount control signals CONT1 to CONT4 of the variable attenuators 9 to 12, the attenuation amounts of the variable attenuators 9 to 12 are shown.
[0036]
In FIG. 2, when the attenuation amount of the variable attenuator 9 to the variable attenuator 12 is sequentially minimized, for example, in the period α in which the attenuation amount of the variable attenuator 10 is minimized, the variable attenuators 9, 11, The received signal level information indicates a higher level than when the attenuation of 12 is minimized. Accordingly, at the time β when the attenuation of the variable attenuator 9 to the variable attenuator 12 is sequentially minimized, the attenuation of the variable attenuator 10 is kept to a minimum, and the attenuation of the variable attenuators 9, 11 and 12 is reduced. The received signal from the antenna 2 is substantially selected by keeping the quantity maximum.
[0037]
In this state, it waits for the lock detection signal to be input, and from the time γ when the lock detection signal is input to the diversity control circuit 22 in FIG. 2, the correlation output CORR and the timing are illustrated as illustrated in FIGS. Attenuation change control is performed based on the signal (FFT-WINDOW).
[0038]
Substantially normal demodulation is performed from the time point γ, that is, the time point when the lock detection signal is generated, and the attenuation of the variable attenuators other than the variable attenuator 10 is based on the correlation output CORR and the timing signal (FFT-WINDOW). Quantity change control is performed. FIG. 2 shows a case where the amount of attenuation of the variable attenuator 9 is controlled based on the correlation output CORR and the timing signal (FFT-WINDOW), and a period during which the amount of attenuation is controlled to change is indicated by δ.
[0039]
However, when the lock detection signal is not output, the high potential period of the timing signal (FFT-WINDOW) is not an effective symbol period, and is not demodulated normally. When the lock detection signal is output, the high potential period of the timing signal (FFT-WINDOW) is an effective symbol period and demodulation is performed normally.
[0040]
As described above, since the attenuation of the variable attenuator based on the correlation output CORR and the timing signal (FFT-WINDOW) is changed on a symbol period basis, when the symbol period length is not fixed, that is, the lock detection signal is When the signal is not output, the control for changing the attenuation amount of the variable attenuator cannot be performed, and the diversity effect cannot be exhibited.
[0041]
However, diversity receiver A does not select a predetermined antenna in the initial state, but rather selects an antenna having the maximum received signal level and transmits the output without attenuation. The lock detection signal is sent out quickly, demodulation is performed at an early stage, and the output from the antenna not selected from when the lock detection signal is output is changed by the variable attenuator. For this reason, the diversity operation is quickly performed, and the diversity effect can be sufficiently exhibited.
[0042]
In the above-described example, the diversity receiver A shows an example in which the antenna is selected immediately after the power is turned on, but in addition to immediately after the power is turned on, immediately after switching the reception channel or immediately after the lock detection signal disappears. Alternatively, the antenna may be selected.
[0043]
Furthermore, in the diversity receiver A, the attenuation amount of the variable attenuator 9 to the variable attenuator 12 is sequentially minimized, and one antenna is substantially selected by checking the received signal level information at that time. However, a plurality of antennas, for example, two antennas may be substantially selected. In this case, a combination that maximizes the reception level information may be obtained by minimizing the attenuation for the combination of the two variable attenuators.
[0044]
In the diversity receiver A, the AGC voltage of the tuner 14 is used as reception signal level information. However, the amplitude of the output signal of the AD converter 15 or the amplitude of the signal in the demodulator may be used.
[0045]
【The invention's effect】
As described above, according to the diversity receiver according to the present invention, the reliability of substantial antenna selection is improved, and stable diversity reception can be performed.
[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 block diagram showing a configuration of a proposed diversity receiver.
4 is a timing diagram for explaining the operation of the diversity receiver shown in FIG. 3; FIG.
FIG. 5 is a timing chart for explaining the operation of the diversity receiver shown in FIG. 3;
[Explanation of symbols]
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

Claims (2)

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
When the correlation of the period corresponding to the guard interval section of the baseband signal obtained by the demodulating means is detected, and the interval of the guard interval obtained from the timing of generation of the guard correlation output generated subsequently becomes a value based on the transmission mode Correlation detection means for outputting a lock detection signal;
A received signal level detecting means for detecting a received signal level;
In the initial state, an antenna having a high reception signal level is selected based on the detection output from the reception signal level detection means, and the attenuation amount of the variable attenuation means corresponding to the selected antenna is controlled to the minimum attenuation amount, and is not selected. Based on whether the peak level of the correlation output has increased during the period corresponding to the guard interval section from when the lock detection signal was supplied An attenuation amount control means for changing the attenuation amount of the variable attenuation means corresponding to the antenna not selected during the period corresponding to the guard interval section;
A diversity receiver comprising: 2. The diversity receiver according to claim 1, wherein selection of an antenna having a high received signal level is performed when the attenuation amount of the variable attenuation means corresponding to each antenna is sequentially controlled to the minimum attenuation amount from the initial state. A diversity receiver which is performed based on a detection level of a detection means.

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