JPH1022892A - Diversity receiver using synthesizing system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a diversity receiver using a synthesizing system in which the reception state does not deteriorate, even if signals having a phase shifted from each other are synthesized. SOLUTION: Radio waves, received from antennas 1 and 4, are amplified at high frequency receiving parts 2 and 5 respectively to be performed on frequency conversion, so that intermediate frequency signals are obtained. Their level values are detected at level detecting circuits 3 and 6 respectively, and thus detected level values are compared at a comparator circuit 7. Then either signal having a smaller level is attenuated by a variable attenuator 8 or 9.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diversity receiver employing a combining system in wireless transmission.

[0002]

2. Description of the Related Art A combining system in a diversity receiver is a system in which a plurality of received signals are combined to compensate for lost information to obtain more information. In this combining method, when there is a large level difference between a plurality of received signals, an optimal ratio combining method is known in which a low-level signal is attenuated by a gain control circuit or the like and the signal-to-noise ratio of the combined signal is maximized. As a further improved system, as described in Japanese Utility Model Laid-Open No. 57-98060, when the level difference is larger than a specified value, the low-level signal is further attenuated and the signal pair is reduced. A method for avoiding the deterioration of the noise ratio is also known.

[0003]

In the diversity receiver of the conventional combining system described above, one or more other signals whose levels are close to the maximum level signal are present among a plurality of received signals, and When there is a delay time difference between the maximum level signal and those signals, the synthesized signal has a frequency point synthesized in the normal phase and a frequency synthesized in the opposite phase due to the phase shift of the carrier due to the delay time difference. A point is created, and the level after synthesis increases at frequency points synthesized in normal phase, but the signals cancel each other out at frequency points synthesized in opposite phase, and the level after synthesis becomes smaller than before synthesis. Therefore, there is a problem that peaks and valleys of the level occur in the reception band, and more information is lost than when no combining is performed.

[0004] It is an object of the present invention to provide a diversity receiver of a combining system that avoids deterioration of the reception state even when receiving and combining a plurality of radio waves whose levels are close and whose phases are shifted.

[0005]

SUMMARY OF THE INVENTION To achieve the above object, a diversity receiver of the combining system according to the present invention comprises means for detecting the levels of a plurality of received signals to be combined, and means for detecting the maximum level of the received signal. A level difference between the other received signals is detected, and the received signal whose level difference is within a specified value is attenuated.

According to an embodiment of the present invention, the level of the received signal is detected using an average power.

According to another embodiment of the present invention, the level of the received signal is detected using peak power.

According to another embodiment of the present invention, the level of the received signal is detected by extracting a specific frequency band.

According to another embodiment of the present invention, the specific frequency band is a video carrier of a television transmission / reception system.

According to another embodiment of the present invention, the specific frequency band is a color subcarrier of a television transmission / reception system.

Also, the diversity receiver of the synthesizing system of the present invention comprises a plurality of antennas for receiving radio waves, a plurality of high-frequency receivers for amplifying radio waves received by the respective antennas and converting the frequencies into intermediate frequency signals, A plurality of level detection circuits for detecting the level of each of the intermediate frequency signals, a plurality of variable attenuators for attenuating the intermediate frequency signal output from each of the high frequency receiving units, and other intermediate circuits for the maximum level of the intermediate frequency signal A comparison circuit that detects a level difference between frequency signals and activates a variable attenuator for an intermediate frequency signal whose level difference is within a specified value; a combining circuit that combines outputs of the respective variable attenuators; and an output of the combining circuit. And a demodulation circuit for demodulating the signal.

According to the present invention, among a plurality of received signals, there is at least one other signal whose level is close to the maximum level signal, and a delay time difference between the maximum level signal and those signals. Even in such a case, the magnitude of the peaks and valleys of the level occurring in the reception band is reduced by attenuating the reception signal whose level difference with respect to the maximum level reception signal is within a specified value.

Therefore, it is possible to avoid the deterioration of the reception state and reduce the information to be lost.

FIG. 4 is a diagram showing an example of the waveform of a combined wave in a diversity receiver of the combining method. This example is a waveform example when two signals having a rectangular frequency amplitude characteristic are combined with a phase shift and a level difference. As described above, the peak and valley levels are determined by the level difference between the two signals to be synthesized, and the period is determined by the phase relationship between the two signals due to the delay time difference. For example, when two received signals are combined, if the levels of the two signals are equal, the peak of the level is twice that of each signal, and the attenuation of the valley of the level is infinite. The period is the reciprocal of the delay time difference. For example, when there is a time difference of 1 μS between the received signals to be combined, peaks and valleys occur every 1 MHz. In the diversity receiver of the combining method of the present invention, when the level difference between a plurality of signals to be combined is small, signals other than the maximum level are attenuated, and the peaks and valleys of the level are reduced. For example, when combining two signals, if the level difference between the two signals is 3 dB, the depth of the valley of the level is 1 to the maximum level signal before the combination.
If the level difference is reduced to within 1 dB and the level difference is set to 6 dB, the depth of the level valley is reduced to within 6 dB.

FIG. 5 is a diagram showing the relationship between the peak and valley levels of the synthesized wave and the level difference between the two signals to be synthesized. From this figure, it can be seen that, if the level difference between the two signals to be combined is increased, the peak and valley levels of the combined wave are reduced. Therefore, if the two signals to be combined have a level difference equal to or more than a certain value, the peak and valley levels of the combined wave can be reduced.

[0016]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of a diversity receiver of a combining system according to a first embodiment of the present invention.

The diversity receiver of the synthesis system according to the present embodiment includes antennas 1 and 4 for receiving radio waves, and a high-frequency receiver 2 for amplifying radio waves received by the antennas 1 and 4 and converting the frequency into an intermediate frequency signal. And level detection circuits 3 and 6 for detecting the level of the intermediate frequency signal output from the high frequency receiving units 2 and 5 and obtaining the level value of the DC signal according to the magnitude of the intermediate frequency signal, and attenuation thereof. Variable attenuators 8 and 9 for attenuating the intermediate frequency signals output from the high frequency receiving units 2 and 5 according to the amount, and detecting the level difference between the intermediate frequency signal having the maximum level and the other intermediate frequency signals, and defining the level difference. A comparing circuit 7 for activating a variable attenuator for an intermediate frequency signal within a value, a combining circuit 10 for combining outputs of the variable attenuators 8 and 9, and a demodulating circuit for demodulating a signal combined by the combining circuit 10 Consisting of 1 Metropolitan.

Next, the operation of this embodiment will be described with reference to FIG. The radio wave received by the antenna 1 is amplified and frequency-converted to an intermediate frequency by the high-frequency receiving unit 2, and the output intermediate frequency signal is input to the variable attenuator 8 and the level detection circuit 3. The level detection circuit 3 detects the level of the input intermediate frequency signal, and the level value is input to the comparison circuit 7. Methods of detecting this level include a method of detecting a peak value and a method of detecting an average value. For example, in order to avoid the occurrence of a trough of a composite wave in the frequency band of a video carrier signal in a standard color television transmission / reception system such as NTSC, it is more accurate to control the attenuation by detecting a peak value. In the case where there is no fading with large frequency selectivity in each received signal and the level fluctuation of the entire receiving band has a gradual frequency characteristic, etc., the attenuation can be determined by detecting the average value. The level can be determined more accurately by performing the control.

The antenna 4, the high-frequency receiver 5, and the level detection circuit 6 perform the same operation, and input the level value of the intermediate frequency signal output from the level detection circuit 6 to the comparison circuit 7. At this time, it is assumed that the high-frequency receiving unit 2 and the high-frequency receiving unit 5 have the same gain. The comparison circuit 7 compares the input level values of the level detection circuit 3 and the level detection circuit 6. If the level value of the level detection circuit 3 is smaller, the variable attenuator 8 outputs the level value of the level detection circuit 6. If is smaller, a signal for attenuation is output to the variable attenuator 9. The amount of attenuation at this time is obtained by calculating a value such that the output difference between the variable attenuators 8 and 9 is equal to or greater than a specified value according to the level difference between the two signals. The comparison circuit 7 is composed of, for example, a differential input circuit. In this case, the magnitude of the two input signals is determined by the sign of the output signal of the differential input amplifier, and the level difference is the absolute value of the output signal. Becomes The variable attenuator 8 or the variable attenuator 9 attenuates the input intermediate frequency signal by the signal of the comparison circuit 7 and outputs the signal to the synthesis circuit 10. The combining circuit 10 combines the inputs from the variable attenuators 8 and 9 and outputs the result to the demodulation circuit 11. Demodulation circuit 11 demodulates the signal to obtain an output signal.

FIG. 2 is a block diagram of a diversity receiver of a combining system according to a second embodiment of the present invention.

In this embodiment, there are three signals to be synthesized. The antenna 12, the high-frequency receiver 13, the level detection circuit 14, and the variable attenuator 15 perform the same operations as those of the first embodiment having the same names. The comparison circuit 16 determines the level of the signal with the maximum level signal when the level difference between the remaining two signals and the maximum level signal is equal to or less than a specified value without attenuating the maximum level signal among the three signals. The respective attenuation amounts such that the difference is equal to or greater than a specified value are output to the variable attenuators 8, 9, and 15. The comparison circuit 16 is composed of, for example, three differential input amplifiers. In this case, the maximum level signal can be specified by a combination of the positive and negative output signals of the differential input amplifier. It is obtained by the absolute value of the voltage of the output signal of the dynamic input amplifier. The variable attenuators 8, 9, and 15 attenuate the respective input signals by the attenuation obtained from the level comparison circuit 16 and output the signals to the synthesis circuit 17. The combining circuit 17 combines these inputs and outputs the combined data to the demodulation circuit 11. Demodulation circuit 11 demodulates the signal to obtain an output signal.

When these three signals are combined, when two signals that are not the maximum level signals are in phase, the peaks and valleys of the level when the three signals are combined as they are are compared with the case where the two signals are combined. growing. Therefore, even if two signals other than the maximum level signal are attenuated by 6 dB or more with respect to the maximum level signal, the depth of the valley of the level after the combination is 11 dB with respect to the level of the maximum level signal before the combination.

FIG. 3 is a block diagram of a diversity receiver of a combining system according to a third embodiment of the present invention.

In this embodiment, band-pass filters 18 and 19 are added between the high-frequency receiving section 2 and the level detecting circuit 3 and between the high-frequency receiving section 5 and the level detecting circuit 6, respectively, in the first embodiment. It is. The pass bands of the band-pass filters 18 and 19 are equal to each other, and are set according to important signal bands used by the receiver, such as a video carrier and a color sub-carrier of a color television transmission / reception system. .

In the first and second embodiments, when the signal to be synthesized is frequency-selectively attenuated, the average power or the peak power of the entire band is detected to generate a level difference between the signals. Even if they are combined, the valley of the level cannot be suppressed below a certain value. In this embodiment, even when the signal to be synthesized is subjected to frequency-selective attenuation, the valley of the signal generated in the band is adjusted by matching the pass band of the band-pass filters 18 and 19 with the band of the signal to be protected. Level can be reduced.

[0027]

As described above, the present invention has the following effects. (1) According to the first to third or seventh aspects of the present invention, it is possible to avoid deterioration of the reception state even when receiving a plurality of radio waves whose level differences are close and whose phases are shifted. (2) According to the inventions of claims 4 to 6, it is possible to avoid a drop in signal level due to synthesis in a frequency band in which important signals are transmitted.

[Brief description of the drawings]

FIG. 1 is a block diagram of a combining diversity receiver according to a first embodiment of the present invention.

FIG. 2 is a block diagram of a combining diversity receiver according to a second embodiment of the present invention.

FIG. 3 is a block diagram of a diversity receiver of a combining scheme according to a third embodiment of the present invention.

FIG. 4 is a diagram illustrating an example of a waveform of a combined wave in a diversity receiver of the combining method.

FIG. 5 is a diagram illustrating a relationship between a peak level and a valley level of a combined wave and a level difference in the diversity receiver of the combining method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Antenna 2 High frequency reception part 3 Level detection circuit 4 Antenna 5 High frequency reception part 6 Level detection circuit 7 Comparison circuit 8 Variable attenuator 9 Variable attenuator 10 Synthesis circuit 11 Demodulation circuit 12 Antenna 13 High frequency reception part 14 Level detection circuit 15 Variable attenuation Instrument 16 Comparison circuit 17 Synthesis circuit 18 Band-pass filter 19 Band-pass filter

Claims (7)

[Claims] In a diversity receiver of a combining system, means for detecting a level of a plurality of received signals to be combined and a level difference of another received signal with respect to a received signal having a maximum level are detected. A diversity receiver of a combining system having means for attenuating a received signal within a specified value. 2. The diversity receiver according to claim 1, wherein the level of the received signal is detected using an average power. 3. The diversity receiver according to claim 1, wherein the level of the received signal is detected using peak power. 4. The diversity receiver according to claim 1, wherein a level of the received signal is detected by extracting a specific frequency band. 5. The diversity receiver according to claim 4, wherein the specific frequency band is a video carrier of a television transmission / reception system. 6. The diversity receiver according to claim 4, wherein the specific frequency band is a chrominance subcarrier in a television transmission / reception system. 7. A plurality of antennas for receiving radio waves, a plurality of high-frequency receivers for amplifying radio waves received by each of the antennas and converting the frequency into an intermediate frequency signal, and a plurality of levels for detecting the level of each of the intermediate frequency signals A level detection circuit, a plurality of variable attenuators for attenuating the intermediate frequency signal output from each of the high-frequency receiving units, and detects the level difference between the intermediate frequency signal of the maximum level and other intermediate frequency signals, A comparison circuit that activates a variable attenuator for an intermediate frequency signal whose difference is within a specified value, a combining circuit that combines outputs of the respective variable attenuators, and a demodulation circuit that demodulates an output of the combining circuit. Diversity receiver.