JPH10233721A - Diversity reception device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device where an optimum reception state can be obtained even if received electric field is strong or weak and antenna switch noise is reduced by adding hysteresis to an antenna switch comparison means when a threshold is larger than a prescribed value. SOLUTION: An analog switch 13 is turned on/off by the output of a hysteresis switch comparator 14. The hysteresis switch comparator 14 compares the output voltage of a non-inversion amplifier 9 with hysteresis switch reference voltage 15 and outputs Low when the output voltage of the non-inversion amplifier 9 is not less than hysteresis switch reference voltage 15. At that time, the analog switch 13 is turned off. While the analog switch 13 is turned off, an antenna switch comparator 10 comes to have hysteresis and the switching of the antenna is not executed unless the present value of received electric field voltage 7 excessively drops compared to a case when the analog switch 13 is turned on. Consequently, the switching of the antenna in the electric field fluctuation of a small scale is restricted when the reception level is comparatively high.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiving apparatus for performing diversity by switching antennas used for mobile radio communication and the like, and more particularly to a receiving apparatus capable of selecting an appropriate receiving state while suppressing generation of noise due to antenna switching. It was done.

[0002]

2. Description of the Related Art As a fading countermeasure technique in wireless communication, a diversity reception method for selecting a system having a better reception state from a plurality of reception systems is known. A receiver that performs this diversity has multiple receivers,
A device that performs “selection diversity” for always selecting a receiver in the best reception state; and a device that is configured with a plurality of antennas and one receiver and performs “antenna switching diversity” for switching antennas under appropriate conditions. There is. The former has good reception quality but requires a large-scale device. On the other hand, the latter has lower reception quality than the former, but is easy to reduce the size of the device, and is suitable for mobile communication mobile terminals and the like.

[0003] A conventional receiver for performing antenna switching diversity includes a plurality of antennas 29, 30 as shown in FIG.
And an antenna switch 31 for switching the receiving antenna
An RF unit 32 for performing amplification and frequency conversion of a received signal;
A demodulation unit 33 that demodulates the received signal and outputs an audio signal and a received electric field voltage, an audio unit 34 that emits audio based on the demodulated audio signal, and a received electric field voltage output from the demodulation unit 33. A comparator that compares with a reference comparison voltage 37 and outputs a switch signal to the antenna switch 31 based on the comparison result
36 and.

In this device, an antenna switch 31
The signal received from the antenna 29 or 30 selected by
After being amplified and frequency-converted by the RF unit 32, it is input to the demodulation unit 33. The demodulation unit 33 demodulates the received signal, outputs the audio signal to the audio unit 34, and outputs the received electric field voltage 35 to the comparator 36.

The comparator 36 compares the received electric field voltage 35 with a reference comparison voltage 37 (threshold). For example, assume that the antenna 29 has been selected as the receiving antenna. When the received electric field decreases due to fading, the received electric field voltage output
35 goes down. When the received electric field voltage output 35 falls below the threshold, the output of the comparator 36 becomes Hi. In response, the antenna changeover switch 31 sets the antenna as a receiving antenna.
Select 30.

As described above, in the antenna switching diversity, when the reception level is equal to or lower than the threshold value, the reception quality is improved by switching the antenna.

However, in the antenna switching diversity, since the reception state can be observed only with the selected antenna, it is not known what the reception state will be after the antenna switching. If the reception level of the switched antenna is below the threshold, the antenna is switched back to the original antenna,
When the reception levels of both antennas are equal to or lower than the threshold, the antenna switching is repeated at high speed. In this state (hunting state), an unreceivable state may continue due to noise generated due to switching.

If the threshold is lowered to avoid this, the effect of the diversity of the angle cannot be obtained.

Japanese Patent Application Laid-Open No. 8-84104 discloses a diversity receiver configured to change a threshold value in response to a change in reception level in order to improve such a point. In this receiver, there are provided a received signal average level calculating means for obtaining an average value of the reception level, and a threshold value calculating means for obtaining a threshold value by multiplying the obtained average value of the reception level by a fixed ratio. Compare with the reception level,
When the reception level falls below the threshold, the antenna is switched.

In this receiver, the threshold value is compared with a fixed value, and when the threshold value falls below the fixed value, that is, when the reception level is extremely low, the switching of the antenna is stopped.

[0011]

However, in the conventional diversity receiving apparatus which changes the threshold value in accordance with the transition of the reception level, even if the reception level is relatively high and the S / N is good, When the reception level is lower than the threshold value obtained from the average value of the reception levels, the switching of the antenna is performed, so that there is a problem that the switching noise frequently occurs in the reception signal due to the discontinuity of the phase.

The present invention has been made to solve the above-mentioned conventional problems, and it is possible to obtain an optimum reception state regardless of whether the reception electric field is strong or weak, and to reduce the reception quality due to antenna switching noise. It is an object of the present invention to provide a diversity receiving apparatus that can suppress the diversity.

[0013]

Therefore, in the diversity receiving apparatus according to the present invention, threshold setting means for setting a threshold value which continuously changes based on the average value of the reception level, and the set threshold value and the reception level are set. An antenna switching comparing means for comparing and controlling the selection of the antenna switching switch and a hysteresis adding means for adding hysteresis to the antenna switching comparing means when the threshold value is larger than a predetermined value are provided.

For this reason, when the reception level is relatively high, hysteresis is added to the antenna switching comparison means, so that switching of the antenna is not performed with a small-scale electric field fluctuation. As a result, the frequency of occurrence of switching noise is reduced.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention comprises a plurality of antennas, an antenna changeover switch for selecting these antennas, and a detecting means for detecting a reception level of a reception signal. In a diversity receiving apparatus that performs diversity, a threshold setting unit that sets a threshold that continuously changes based on an average value of a reception level, and compares the set threshold with the reception level to control selection of an antenna switch. An antenna switching comparing means and a hysteresis adding means for adding hysteresis to the antenna switching comparing means when the threshold value is larger than a predetermined value are provided.If the reception level is relatively high, a small hysteresis is added. Switching of antennas due to electric field fluctuation of a scale is limited, and the frequency of switching noise is reduced.

An embodiment of the present invention will be described below with reference to FIGS.

As shown in FIG. 1, the diversity receiving apparatus according to the embodiment of the present invention includes a plurality of antennas 1 and 2, an antenna switch 3 for switching a receiving antenna, and an RF section for amplifying a received signal and performing frequency conversion. 4, a demodulation unit 5 that demodulates a received signal to output a voice signal and a received electric field voltage 7, a voice unit 6 that emits voice based on the demodulated voice signal, and a voice output from the demodulation unit 5. An integrator 8 for averaging the received electric field voltage 7, a non-inverting amplifier 9 for amplifying the output of the integrator 8 to an appropriate level, and a hysteresis switching comparator for comparing the output voltage of the non-inverting amplifier 9 with a reference voltage 15
14 and a resistor 11 for lowering the output voltage of the non-inverting amplifier 9
And a receiving field voltage 7 output from the demodulation unit 5 and an output of the resistor 11, and based on the comparison result, an antenna switching comparator for outputting a switching signal to the antenna switching switch 3.
10, a resistor 12 that cooperates with a resistor 11 to determine the amount of hysteresis of the antenna switching comparator 10, and an analog that turns on and off a feedback loop of the antenna switching comparator 10 based on the output of the hysteresis switching comparator 14. A switch 13 is provided.

In this device, the antenna changeover switch 3
Is received from the antenna 1 or 2 selected by
After being amplified and frequency-converted by the RF unit 4, it is input to the demodulation unit 5. The demodulation unit 5 demodulates the received signal, outputs the audio signal to the audio unit 6, and outputs the received electric field voltage 7 to the integrator 8 and the antenna switching comparator 10.

The integrator 8 averages the received electric field voltage 7 output from the demodulation unit 5, and the non-inverting amplifier 9 amplifies the averaged received electric field voltage to an appropriate level. The output of the non-inverting amplifier 9 is input to the + side of the antenna switching comparator 10 after the voltage is dropped by the resistor 11.

The current reception electric field voltage 7 output from the demodulator 5 is input to the minus side of the antenna switching comparator 10.
When the analog switch 13 is on, a part of the output of the antenna switching comparator 10 is fed back via the analog switch 13 and the resistor 12, and is input to the + side of the antenna switching comparator 10.

The analog switch 13 is turned on / off by the output of the hysteresis switching comparator 14. The hysteresis switching comparator 14 compares the output voltage of the non-inverting amplifier 9 with a reference voltage (hysteresis switching reference voltage) 15 and outputs the hysteresis switching reference voltage.
If it is 15 or more, Low is output. At this time, the analog switch 13 is closed. The hysteresis switching comparator 14 outputs High when the output voltage of the non-inverting amplifier 9 is equal to or lower than the hysteresis switching reference voltage 15. At this time, the analog switch 13 is opened.

When the analog switch 13 is open, the antenna switching comparator 10 sets the average value of the received electric field voltage output from the non-inverting amplifier 9 and dropped by the resistor 11 as a reference comparison voltage (threshold). The value is compared with the current reception electric field voltage 7. Then, when the current value of the reception electric field voltage 7 falls below the threshold value, the output is set to High. In response, the antenna switch 3 switches the receiving antenna.

On the other hand, when the analog switch 13 is closed, a part of the output of the antenna switching comparator 10 is fed back via the analog switch 13 and the resistor 12, and is input to the + side of the antenna switching comparator 10. Therefore, the output of the antenna switching comparator 10 does not become High unless the current reception electric field voltage 7 further decreases as compared with when the analog switch 13 is open.

That is, when the analog switch 13 is closed, the antenna switching comparator 10 has a hysteresis, and the current value of the received electric field voltage 7 is further reduced than when the analog switch 13 is open. Otherwise, antenna switching will not be performed. The magnitude of this hysteresis is determined by the values of the resistors 11 and 12.

As described above, in this receiver, when the average value of the reception level is higher than the hysteresis switching reference voltage 15, hysteresis is added to the antenna switching. Therefore, when the reception level is relatively high, switching of the antenna due to small electric field fluctuation is limited. As a result, the number of times of antenna switching is reduced, and the occurrence of switching noise is reduced.

FIG. 3 shows the operation of the receiver under varying electric fields. 3A, a dotted line 21 indicates a received signal of the antenna 2, a dotted line 22 indicates a received signal of the antenna 1, and a solid line 24 indicates a threshold value obtained by averaging the received electric field by the integrator 8 and amplifying it to an appropriate level. ing. A solid line 25 indicates the hysteresis switching reference level 15. The bold line 23 indicates a received signal of the antenna selected by the antenna changeover switch 3. FIG. 3B shows an antenna selected by the antenna switch 3, and FIG. 3C shows whether or not hysteresis has been added in antenna switching.

When the threshold value 24 that changes according to the reception level does not exceed the hysteresis switching reference level 25, no hysteresis is added, and the antenna changeover switch 3 operates immediately when the reception level of the selected antenna falls below the threshold value 24. Switch antennas.

The threshold value 24 is the hysteresis switching reference level 25
Above, hysteresis is added, and the switching of the antenna due to small electric field fluctuation is limited. Therefore, as shown by 26 in FIG. 3A, even when the reception level of the selected antenna fluctuates near the threshold value 24, the antenna is not switched, and the frequency of switching noise is reduced.

Further, in this receiver, since the threshold value of the antenna switching comparator 10 is continuously changed according to the reception level, stable reception quality from a weak electric field to a strong electric field can be obtained. This will be described with reference to FIG.

FIG. 2 shows how the probability of the reception level dropping below a certain level when antenna switching diversity or selection diversity is performed under Rayleigh fading is calculated. It is illustrated. The horizontal axis of FIG. 2 represents the relative value of the reception level when the average reception level at a certain time is 0 dB. The vertical axis represents the cumulative probability corresponding to the reception level on the horizontal axis, that is, the probability that the reception level is equal to or less than the value of the reception level on the horizontal axis.

Here, the line 16 indicates the cumulative probability when diversity reception is not performed. From this line 16, when diversity reception is not performed, the probability that the reception level will be -40 dB or less of the average reception level is 0.007%.
It can be seen that the probability of being -30 dB or less is about 0.07%.

A line 17 indicates the cumulative probability when two antennas are used and the threshold value is fixed at -10 dB from the average reception level to perform antenna switching diversity reception. Similarly, the line 18 shows the cumulative probability when the threshold is fixed at −15 dB from the average reception level and the threshold is fixed at −20 dB from the average reception level, and the antenna switching diversity reception is performed. I have.

A line 20 indicates the cumulative probability when the selection diversity is performed using two receivers.
In the case of selection diversity, the probability that the reception level will be -40 dB or less of the average reception level is 0.0000005.
%, And the probability of becoming -30 dB or less is 0.0
It is as small as 0005%.

As is clear from this figure, in the antenna switching diversity, the cumulative probability becomes equal to the selection diversity at each threshold value, and the cumulative probability becomes worse as the difference from the threshold value increases.

Therefore, when the threshold value is continuously changed according to the average reception level as in the receiving apparatus of the present invention, it is possible to obtain the same stable reception quality from the weak electric field to the strong electric field as the same as the selection diversity. Can be.

Although the output of the integrator 8 is amplified by the non-inverting amplifier 9 in this receiving apparatus, the output of the integrator 8 may be attenuated using an attenuator depending on the set level of the threshold. .

[0037]

As is apparent from the above description, in the diversity receiving apparatus of the present invention, when the average receiving level is low and the receiving state is poor, the transmission of information in the radio communication is prioritized. When the level falls below the threshold, the antenna is switched immediately,
When the average reception level is relatively large and the S / N ratio is good, hysteresis is provided for antenna switching to limit frequent antenna switching. Therefore, the frequency of occurrence of the switching noise is reduced, and the reception quality can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a diversity receiving apparatus according to an embodiment of the present invention;

FIG. 2 is a diagram illustrating a relationship between a reception level and a cumulative probability in order to explain an operation of the receiving apparatus according to the embodiment;

FIG. 3 is a diagram illustrating an antenna switching operation in the receiving device of the embodiment;

FIG. 4 is a block diagram illustrating a configuration of a conventional receiving apparatus that performs antenna switching diversity.

[Explanation of symbols]

 1, 2, 29, 30 Receiving antenna 3, 31 Antenna changeover switch 4, 32 RF circuit 5, 33 Demodulation circuit 6, 34 Audio circuit 7, 35 Received electric field voltage output 8 Integrator 9 Non-inverting amplifier 10, 36 Antenna switching comparison 11 and 12 Resistance 13 Analog switch 14 Hysteresis switching comparator 15 Hysteresis switching reference voltage 37 Antenna switching comparison voltage

Claims (1)

[Claims] 1. A diversity receiving apparatus comprising: a plurality of antennas; an antenna changeover switch for selecting these antennas; and a detecting means for detecting a reception level of a reception signal, wherein the diversity reception apparatus performs antenna switching diversity. Threshold setting means for setting a threshold that continuously changes based on the threshold value; antenna switching comparison means for controlling selection of the antenna changeover switch by comparing the set threshold value with a reception level; and the threshold value is larger than a predetermined value. And a hysteresis adding means for adding hysteresis to the antenna switching comparing means.