JP2003318855A - Diversity receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a diversity receiver for taking stable and sufficient effects by enhancing reliability of antenna selection at an initial state such as power application. <P>SOLUTION: Reception signals from antennas 1 to 4 that receive OFDM (orthogonal frequency division multiplexing) modulated signals are attenuated by variable attenuators 9 to 12, correlation of base band I, Q signals obtained by performing orthogonally crossed wave detection of combined output of them in a guard interval period is detected by a guard correlational device 20, a lock detection signal is generated from generation timing of guard correlational output to be continuously generated, an antenna with a high reception signal level is selected at the initial state under control of a diversity control circuit 22, attenuation quantity of a variable attenuator corresponding to the antenna is controlled as minimum and the attenuation quantity of a variable attenuation means corresponding to an antenna which is not selected is changed in the guard interval section on the basis of whether or not a peak level of the correlational output in the guard interval section is increased from when the lock detection signal is supplied. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diversity receiver that receives a broadcast signal modulated (OFDM modulated) by an orthogonal frequency division multiplexing system.

[0002]

2. Description of the Related Art 1OFD of OFDM modulated broadcast signal
The M transmission symbol period is composed of an effective symbol section and a section called a guard interval. The effective symbol period is a signal period required for data transmission. The guard interval is for preventing intersymbol interference such as multipath, and is a cyclic copy of the last predetermined period length portion of the effective symbol section to the beginning of the effective symbol section.

Diversity receivers for receiving OFDM modulated broadcast signals such as digital terrestrial television broadcast signals are known. A conventional diversity receiver of this type is proposed by the applicant (Japanese Patent Application No. 2002-023678).

In this diversity receiver, the signals received by a plurality of antennas are attenuated by variable attenuators, the attenuated outputs are combined, and the combined output is demodulated into a baseband signal. Note)), the attenuation amount of one variable attenuator in the variable attenuator is switched in the period corresponding to the guard interval section based on the level of the correlation output, and when the reception signal level is increased by switching the attenuation amount, Thereafter, the attenuation amount of the one variable attenuator is changed stepwise at a timing matched with the period corresponding to the guard interval section.

The diversity receiver B is constructed as shown in FIG. In the diversity receiver B, the RF signals received by the antennas 1, 2, 3, 4 are amplified by the low noise amplifiers 5, 6, 7, 8 respectively, and then the variable attenuators 9, 10, 11, 12 are respectively amplified. Attenuator mixer 1
3 and synthesizes the output of the mixer 13 into the tuner 14
Supply to.

The tuner 14, which has received the combined output from the mixer 13, amplifies the combined output, frequency-converts it, and limits the band to convert it into an intermediate-frequency signal. The intermediate frequency signal output from the tuner 14 is an AD converter 15
To a digital signal, and the converted digital signal is supplied to the quadrature detector 16 for quadrature detection,
Convert to baseband I and Q signals.

The baseband I and Q signals output from the quadrature detector 16 are supplied to the effective symbol extraction circuit 17, and based on the timing signal (FFT-WINDOW) indicating the effective symbol section output from the timing reproduction circuit 21, In the effective symbol extraction circuit 17, only the signal in the period corresponding to the effective symbol is fetched from the baseband I and Q signals, and the signal in the period corresponding to the effective symbol section is F.
The data is supplied to the FT circuit 18, FFT processing is performed in the FFT circuit 18 to demodulate the OFDM modulated signal to separate into information for each carrier, and the information is supplied to the demapper circuit 19 to be demapped and transmitted as demodulated data.

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 validated. The product of the delayed baseband I and Q signals delayed by the time width of the symbol period is integrated over the time width of the guard interval period, and the integration is sequentially performed for each sample period for A / D conversion in the A / D converter 15. By performing the shift, the correlation output is obtained from the integrated value, the correlation output is supplied to the timing reproduction 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 obtained.
To the effective symbol extraction circuit 17.

The diversity receiver B is provided with a diversity control circuit 25, and the correlation output CORR and timing signal (FFT-WI) output from the guard correlator 20.
NDOW is supplied to the diversity control circuit 25, and the correlation output CORR and the timing signal (FFT-WIN) are supplied.
Attenuation amount control signals CONT1, CONT2, CONT3, CON for controlling the attenuation amount of the variable attenuators 9, 10, 11, 12 from the diversity control circuit 25 based on DOW).
T4 is sent to the variable attenuators 9, 10, 11 and 12, respectively, so that the output level of the mixer 13, that is, the combined reception signal level becomes high.
The attenuation amount of 1 and 12 is controlled.

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.

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 amount control signal CONT1 is a signal for controlling the attenuation amount of the variable attenuator 9. When the level of the attenuation amount control signal CONT1 is the maximum, the attenuation amount is controlled to 0, and the level of the attenuation amount control signal CONT1 is the minimum. In this case, the amount of attenuation becomes maximum. The case of the attenuation amount control signals CONT2, 3, 4 is the same as that of the attenuation amount control signal CONT1.

In the diversity control circuit 25, the correlation output CORR is used to judge whether or not the reception condition is improved. In the diversity control circuit 25, the attenuation amounts of the variable attenuators 9, 10, 11, 12 are changed during the period when the timing signal (FFT-WINDOW) is low potential, that is, during the period corresponding to the interval of the guard interval.

In FIG. 4, in order to prevent the input of the mixer 13 from disappearing, at least one or more of the variable attenuators 10, 11 and 12 are set to 0, and the attenuation is set as an initial state. The level of the control signal CONT1 is minimum, that is, the attenuation amount of the variable attenuator 9 is maximum. Here, in order to evaluate the signal received by the antenna 1,
In the section where the timing signal (FFT-WINDOW) becomes low potential (see FIG. 4A), the attenuation control signal CONT1
Of the variable attenuator 9 is maximized (see FIG. 4B).
The attenuation of is set to 0.

As a result, the signal received by the antenna 1 is also combined by the mixer 13 and input to the tuner 14. At this time, in FIG. 4, the peak level of the correlation output CORR is higher than that of the previous correlation output CORR. It also shows the case where the temperature also rises (see FIG. 4 (c)).
In this case, if the mixer 13 combines the signals received by the antenna 1 and combines them, the output level of the mixer 13 increases, and it is determined that the reception condition is improved. 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) becomes high potential, and thereafter, as shown by the arrow in FIG. The level of the attenuation amount control signal CONT1 is increased stepwise until the maximum level in a section where FFT-WINDOW) is at a low potential.

The initial state of the receiver is the same as in the case of FIG. 4, but the timing signal (FFT-W is the same as in FIG. 4B).
(INDOW) becomes a low potential, the attenuation control signal C
When the level of the correlation output CORR is lowered by maximizing the level of the ONT 1 and setting the attenuation amount of the variable attenuator 9 to 0, the signal received by the antenna 1 is mixed with the mixer 1
It is considered that the output signal level of the mixer 13 is lowered due to the combination in 3, and the peak level of the correlation output CORR is lowered, and it is determined that the reception condition is deteriorated. Therefore, the timing signal (FFT-WINDOW
W) becomes a high potential, the attenuation control signal CON
The level information of T1 is returned to the minimum.

As shown in FIG. 4, 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, When the peak level of the correlation output CORR in the period corresponding to the next guard interval section is higher than the peak level of the correlation output in the period corresponding to the preceding guard interval section, it corresponds to the next guard interval section. The maximum amount of attenuation of the variable attenuator 9 is achieved during the period corresponding to the guard interval section following that period, that is, the original amount is restored, and the attenuation amount of the variable attenuator 9 is sequentially reduced to 0 during the period corresponding to the subsequent guard interval section. It will be reduced stepwise.
This makes it possible to set the amount of attenuation that can be stably received.

Further, as described above, the attenuation amount of the variable attenuator 9 is set to 0 during 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 C during the next guard interval period
When the peak level of the ORR is lower than the peak level of the correlation output in the period corresponding to the preceding guard interval section, it corresponds to the subsequent guard interval section when the attenuation amount of the variable attenuator 9 is set to 0. The amount of attenuation of the variable attenuator 9 is maximized from the period, that is, the original amount is restored. This makes it possible to set the amount of attenuation that can be stably received.

In the case of FIG. 5 as well, the variable attenuators 10, 11, 1 are used.
Among the two, at least one or more have the attenuation amount of 0, and the level of the attenuation amount control signal CONT1 is maximum, that is, the attenuation amount of the variable attenuator 9 is 0 in the initial state. Here, in order to evaluate the signal received by the antenna 1, the attenuation control signal C is applied in a section where the timing signal (FFT-WINDOW) is at a low potential (see FIG. 5A).
The level of ONT1 is minimized (see FIG. 5B), and the attenuation amount of the variable attenuator 9 is maximized.

As a result, the signals received by the antenna 1 are attenuated, combined by the mixer 13 and input to the tuner 14. As a result, in FIG. 5, the correlation output C
The case where the peak level of the ORR is increased is shown (see FIG. 5C). In this case, it is determined that if the signal received by the antenna 1 is attenuated, the level of the correlation output CORR rises and the reception condition becomes better, and then the timing signal (FFT-WINDOW) becomes high potential once. The level of the attenuation control signal CONT1 is returned to the maximum level (see FIG. 5B), and thereafter, as indicated by the arrow in FIG. 5, the timing control signal (FFT-WINDOW) is changed to the low potential section during the low control. The levels are changed stepwise until the level becomes minimum (see FIG. 5B).

The initial state of the receiver is the same as in the case of FIG. 5, but the timing signal (FFT-W) is the same as in FIG.
(INDOW) becomes a low potential, the attenuation control signal C
When the level of the correlation output CORR is lowered by minimizing the level of the ONT 1 and maximizing the attenuation amount of the variable attenuator 9, the mixer 13 mixes the signals received by the antenna 1 to mix the signals. It is considered that the level of the output signal of 13 has decreased and the peak level of the correlation output CORR has decreased, and it is determined that the reception conditions have deteriorated. Therefore, the timing signal (FFT-WINDOW)
The attenuation control signal CONT1
Return the level to maximum.

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 in the case shown in FIG. When the peak level of the correlation output CORR in the next guard interval period is higher than the peak level of the correlation output in the period corresponding to the preceding guard interval section, the peak level of the correlation output CORR follows the period corresponding to the next guard interval section. The attenuation amount of the variable attenuator 9 is set to 0 in the period corresponding to the guard interval section,
That is, the variable amount is restored to the original value, and the attenuation amount of the variable attenuator 9 is increased stepwise to the maximum in the period corresponding to the subsequent guard interval section. This makes it possible to set the amount of attenuation that can be stably received.

As described above, 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, the next guard interval When the peak level of the correlation output CORR in the period corresponding to the section is lower than the peak level of the correlation output in the period corresponding to the preceding guard interval section, when the attenuation amount 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 guard interval section following, that is, the original amount is restored. This makes it possible to set the amount of attenuation that can be stably received.

In this way, the variable attenuators 9, 10 and 1 are maintained with the attenuation amount of one or more variable attenuators maintained at zero.
The attenuation amounts of 1 and 12 are sequentially controlled to control the signal level input to the tuner 14 to be maximum. As a result, stable diversity reception can be performed.

[0024]

However, even if the amount of attenuation of the variable attenuator is controlled for each OFDM symbol as described above to keep the reception level high,
The antenna to be selected is predetermined when the reception situation is uncertain immediately after the power is turned on, and the attenuation amount of the variable attenuator is controlled by selecting the output from the predetermined antenna. However, if the antenna is an antenna that hardly catches radio waves, there is a problem that the diversity operation does not exhibit its effect.

An object of the present invention is to provide a diversity receiver which improves the reliability of antenna selection in the initial state such as power-on and is stable and has a sufficient effect.

[0026]

A diversity receiver of the present invention is a diversity receiver having a plurality of antennas for receiving an OFDM-modulated signal in which one symbol period includes an effective symbol section and a guard interval section. Therefore, the variable attenuating means for attenuating the received signals from the plurality of antennas, the demodulating means for synthesizing the outputs from the variable attenuating means and demodulating the synthesized output, and the baseband signal obtained by the demodulating means Correlation detecting means for detecting the correlation of the period corresponding to the guard interval section of the above and outputting the lock detection signal when the interval of the guard interval obtained from the generation timing of the guard correlation output which occurs subsequently becomes a value based on the transmission mode. And a reception signal level detection means for detecting the reception signal level, and a reception signal level in the initial state. An antenna with a high received signal level is selected based on the detection output from the level detection means, the attenuation amount of the variable attenuation means corresponding to the selected antenna is controlled to the minimum attenuation amount, and the variable amount corresponding to the antenna not selected is changed. By controlling the attenuation amount of the attenuating means to the maximum attenuation amount, the guard interval interval is determined based on whether the peak level of the correlation output in the period corresponding to the guard interval interval from when the lock detection signal is supplied increases. Attenuation amount control means for changing the attenuation amount of the variable attenuation means corresponding to the unselected antenna during the corresponding period.

According to the diversity receiver of the present invention,
An antenna with a high received signal level is selected based on the detection output from the received signal level detection means in the initial state,
The attenuation amount of the variable attenuation means corresponding to the selected antenna is controlled to the minimum attenuation amount, and the attenuation amount of the variable attenuation means corresponding to the unselected antenna is controlled to the maximum attenuation amount. Therefore, an antenna that does not capture radio waves will not be selected as a predetermined antenna as in the past. Therefore, the diversity operation does not become ineffective. Further, since the output of the selected antenna is sent without being attenuated, the lock detection signal is sent quickly, and demodulation is performed early.

Further, according to the diversity receiver of the present invention, the guard output is then determined 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. During the period corresponding to the interval section, the attenuation amount of the variable attenuation unit corresponding to the unselected antenna is changed and controlled by the attenuation amount control unit. However, this update control of the attenuation amount is performed in symbol period units. The update control is performed because the lock detection signal is input and the symbol period length is fixed, and the attenuation amount of the variable attenuating unit corresponding to the selected antenna is controlled to the minimum attenuation amount. Moreover, since the attenuation amount of the output from the antenna that is not selected is changed in the guard interval section, the diversity operation operates promptly, and the diversity effect can be sufficiently exhibited.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION A diversity receiver according to the present invention will be described below with reference to an embodiment.

FIG. 1 is a block diagram showing a configuration of a diversity receiver according to an embodiment of the present invention, and FIG.
In order to avoid redundant description with the diversity receiver B shown in FIG. 2, in the diversity receiver A according to the embodiment of the present invention, the same components as those of the diversity receiver B are designated by the same reference numerals, and The description is omitted.

The diversity receiver A has an antenna 1,
2, 3, 4, low noise amplifiers 5, 6, 7, 8, variable attenuators 9, 10, 11, 12, mixer 13, tuner 14, A
D converter 15, quadrature detector 16, effective symbol extraction circuit 17, FFT circuit 18, demapper 19, guard correlator 2
0, a timing recovery circuit 21 is provided, which operates in the same manner as in the diversity receiver B.

Furthermore, the diversity receiver A is provided with a diversity control circuit 22 instead of the diversity control circuit 25. The received signal level information detected by the tuner 14, the lock detection signal and the correlation output CORR output from the guard correlator 20, the timing signal (FFT) output from the timing recovery circuit 21.
-WINDOW) is supplied to the diversity control circuit 22, and the antenna with the highest reception level is searched based on the reception signal level information in the initial state such as when the power is turned on.
The attenuation of the searched antenna output is kept to a minimum, and from the time when the lock detection signal is output, the output of the antenna other than the selected antenna is attenuated based on the correlation output CORR and the timing signal (FFT-WINDOW). The antenna diversity operation is performed so that the output level of the mixer 13, that is, the combined received signal level becomes high by controlling the amount of change.

Here, as the received signal level information, for example, the AGC voltage in the tuner 14 can be used. Also, the interval of the guard interval is obtained from the generation timing of the guard correlation output that occurs subsequently, and the interval is the transmission mode (modes 1, 2 and 3 in the case of ISDB-T, 2k mode in the case of DVB-T). , 8k mode transmission mode), a lock detection signal is output from the guard correlator 20.

Next, the operation of the diversity control circuit 22 will be described with reference to the timing chart shown in FIG.

Immediately after the power is turned on, the attenuation amounts of the variable attenuators 9 to 12 are sequentially minimized, and the diversity control circuit 22 checks the received signal level information at that time.
2A shows the attenuation of the variable attenuator 9, FIG. 2B shows the attenuation of the variable attenuator 10, and FIG. 2C shows the variable attenuator 11.
2 (d) shows the attenuation amount of the variable attenuator 12, respectively. FIG. 2E shows the received signal level information. In FIG. 2, the variable attenuators 9-1
The attenuation amounts of the variable attenuators 9 to 12 are shown in place of the attenuation amount control signals CONT1 to CONT4 of 2.

In FIG. 2, when the attenuation amounts of the variable attenuator 9 to the variable attenuator 12 are sequentially minimized, for example,
In the period α in which the attenuation amount of the variable attenuator 10 is minimized,
The received signal level information shows a higher level than when the attenuation amounts of the variable attenuators 9, 11, 12 are minimized. Therefore, at the time point β when the attenuation amounts of the variable attenuator 9 to the variable attenuator 12 are sequentially minimized, the attenuation amount of the variable attenuator 10 is maintained at the minimum and the attenuation amounts of the variable attenuators 9, 11, and 12 are reduced. The received signal from the antenna 2 is substantially selected by keeping the quantity at a maximum.

In this state, waiting 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, as shown in FIG. 4 and FIG. The attenuation amount change control is performed based on the CORR and the timing signal (FFT-WINDOW).

From the time point γ, that is, the time point when the lock detection signal is generated, substantially normal demodulation is performed,
Correlation output CORR and timing signal (FFT-WI
Based on NDOW), change control of the attenuation amount of the variable attenuators other than the variable attenuator 10 is performed. In FIG. 2, the correlation output CORR and the timing signal (FFT-WINDOW
The case where the attenuation amount of the variable attenuator 9 is controlled based on W) is shown, and the period during which the attenuation amount is changed and controlled is indicated by δ.

However, when the lock detection signal is not output, the timing signal (FFT-WINDOW)
The high potential period of is not the effective symbol period and is when the demodulation is not normally performed. When the lock detection signal is output, the timing signal (FFT-WINDOW
The high potential period of W) is an effective symbol period, and is when the demodulation is normally performed.

As described above, since the change of the attenuation amount of the variable attenuator based on the correlation output CORR and the timing signal (FFT-WINDOW) is performed in the unit of symbol period, when the symbol period length is not fixed, that is, the lock is performed. When the detection 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.

However, in the diversity receiver A, instead of selecting a predetermined antenna in the initial state, the antenna having the maximum received signal level is substantially selected and its output is not attenuated. Since the lock detection signal is sent out quickly, demodulation is performed early, and the output from the antenna not selected since the lock detection signal was output is changed by the variable attenuator. Therefore, the diversity operation is promptly activated, and the diversity effect can be sufficiently exerted.

Further, in the above example, the diversity receiver A shows an example in which the antenna is selected immediately after the power is turned on. However, in addition to immediately after the power is turned on, the antenna immediately after the switching of the receiving channel or the lock detection signal is received. The antenna selection may be performed immediately after the disappearance.

Furthermore, in the diversity receiver A, the attenuation amount of the variable attenuator 9 to the variable attenuator 12 is sequentially minimized, and the received signal level information at that time is checked, so that one antenna is substantially realized. Although the case of selecting is illustrated, a plurality of antennas, for example, two antennas may be substantially selected. In this case, the combination that maximizes the reception level information may be obtained by minimizing the attenuation amount of the combination of the two variable attenuators.

In the diversity receiver A,
Although the AGC voltage of the tuner 14 is used as the received signal level information, the amplitude of the output signal of the AD converter 15 or the amplitude of the signal in the demodulator may be used.

[0045]

As described above, according to the diversity receiver of the present invention, the reliability of substantial selection of the antenna is improved, and stable diversity reception can be performed.

[Brief description of 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 chart for explaining the operation of the diversity receiver according to the embodiment of the present invention.

FIG. 3 is a block diagram showing the configuration of a proposed diversity receiver.

FIG. 4 is a timing chart for explaining the operation of the diversity receiver shown in FIG.

5 is a timing diagram for explaining the operation of the diversity receiver shown in FIG.

[Explanation of symbols]

9-12 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)

[Claims] 1. A diversity receiver having a plurality of antennas for receiving an OFDM-modulated signal in which one symbol period includes an effective symbol section and a guard interval section, each receiving signal from each of the plurality of antennas. The variable attenuating means for attenuating, the demodulating means for synthesizing the outputs from the variable attenuating means, demodulating and outputting the synthesized output, and the correlation of the period corresponding to the guard interval section of the baseband signal obtained by the demodulating means are detected. And a correlation detection means for outputting a lock detection signal when the interval of the guard interval obtained from the generation timing of the guard correlation output that occurs subsequently and a value based on the transmission mode, and a reception signal level detection for detecting the reception signal level And the received signal based on the detection output from the received signal level detecting means in the initial state. Select a high level antenna, control the amount of attenuation of the variable attenuator corresponding to the selected antenna to the minimum amount of attenuation, and set the amount of attenuation of the variable attenuator corresponding to the antenna not selected to the maximum amount of attenuation. Based on whether or not the peak level of the correlation output in the period corresponding to the guard interval section from the time of controlling and supplying the lock detection signal is increased, the unselected antenna is provided in the period corresponding to the guard interval section. Damping amount control means for changing the damping amount of the variable damping means corresponding to
A diversity receiver characterized by having. 2. The diversity receiver according to claim 1, wherein an antenna having a high received signal level is selected by sequentially controlling the attenuation amount of the variable attenuation means corresponding to each antenna to the minimum attenuation amount from the initial state. A diversity receiver, which is performed based on the detection level of the received signal level detecting means at that time.