JPS5837733B2 - wireless receiving device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a radio receiving device using a variable directional antenna suitable for mobile radio communications.

In mobile radio communications, deterioration of communication quality, such as instantaneous communication interruptions due to fading caused by multipath wave interference, has become a major problem.

As a method to effectively reduce this kind of fading,
A directional diversity reception system with a threshold has been considered, which uses a variable directional antenna and controls its directivity according to the received output.

Compared to the well-known diversity reception method that utilizes diversity effects due to differences in space, frequency, polarization, etc., this power method is economical because it requires only one receiving system after the antenna.

In addition, in this method, the outputs of multiple antennas are combined via variable phase shifters and variable attenuators to operate as one variable directional antenna, so two antennas and one
This method is advantageous in terms of quick response and improved communication quality compared to a switching diversity reception method with a threshold value that uses one receiver and switches to another antenna when the reception output drops below a threshold value.

In other words, in the switching diversity method with a threshold, fading is averaged and reception is performed in order to prevent the switch from fluttering and becoming unable to receive when the reception output of both antennas drops below the threshold. It is necessary to take measures such as operating the switch according to the average value of the signal, or maintaining the same state for a certain period of time after switching, even if the reception output decreases, and as a result, the effect of improving fast fading can be improved. It gets lost.

Furthermore, there are fatal drawbacks such as instantaneous signal interruptions that occur during operation of the switching device, and noise generation due to discontinuous changes in signal amplitude and phase accompanying switching.

When a variable directional antenna is used, the directivity can be changed electrically and continuously, so this problem is fundamentally solved.

However, even this method has the following practical problems.

In other words, in order to continuously change the directivity of the variable directional antenna as described above, it is desirable to be able to continuously change the amount of phase shift and the amount of attenuation using a variable phase shifter and a variable attenuator. .

Among these, a continuously variable variable attenuator can be easily obtained, but a variable phase shifter with a continuously variable phase shift amount for VHF and UHF bands used in mobile radio communications is very expensive.

Therefore, in cases where economic efficiency is extremely important, such as in mobile radio communications, it is necessary to use an expensive switching phase shifter in which the amount of phase shift can be discontinuously switched in several steps.

However, when such a switching phase shifter is used, noise is likely to occur due to discontinuous changes in phase shift for switching, resulting in deterioration of reception quality.

This invention improves the control means of a variable directional antenna having a switching phase shifter whose phase shift amount can be switched discontinuously and a variable attenuator whose attenuation amount is continuously variable, and by changing the phase shift amount of the switching phase shifter. An object of the present invention is to provide a radio receiving device that prevents the occurrence of noise at times and enables stable and good reception.

The present invention will be explained in detail below with reference to Examples.

FIG. 1 shows the structure of a radio receiving apparatus according to an embodiment of the present invention.

In this figure, reference numeral 10 denotes a variable directional antenna, which includes a plurality of (two in this example) antenna elements 11, 12, and a phase shifter and a variable attenuator for switching the respective outputs of these antenna elements 11, 12 as appropriate. It consists of electronic circuit parts that are combined in series.

That is, the antenna elements 11, 12 are horizontally polarized dipole elements in this example and are arranged orthogonally to each other.

The output of antenna element 11 is applied directly to switched phase shifter 14 , and the output of antenna element 12 is applied via fixed phase shifter 13 to switched phase shifter 15 .

The fixed phase shifter 13 has a constant phase shift amount of, for example, π/2,
Further, the switching phase shifters 14 and 15 can discontinuously switch the amount of phase shift into two stages, for example, O and π, by external electrical control, and both of them are composed of a delay line, a surface elastic element, a semiconductor element, etc. This can be easily realized using .

Note that the fixed phase shifter 13 may be included in the switching phase shifter 15.

The outputs of the switching phase shifters 14 and 15 are connected to variable attenuators 16, respectively.
．． Added to 17.

The variable attenuators 16 and 1γ are attenuators that are continuously variable between the attenuation amount ωdB and O dB by external electrical control, and are made by an electronic circuit using a semiconductor such as a PIN diode FET as a variable resistance element, for example. configured.

The output of the variable attenuator 16.17 is sent to the sensor modulator 18.
19, the signals are combined into a single signal by a combining circuit 21.

Sensing modulators 18 and 19 are sensing signal generators 2
The amplitude of the input signal is modulated, that is, periodically changed by a minute amount by the signal from
Even if the amount of phase shift of 5 and the amount of attenuation of variable attenuators 16 and 17 are constant, they periodically change by a minute amount.

The output of the combining circuit 21, which is the output of the variable directional antenna 10, is input to the receiver 22, and a desired signal is selected as a received signal and demodulated.

A part of the received signal output of this receiver 22 is applied to a control circuit 25 via a level detector 23 and a phase comparator 24.

Here, the level detector 23 detects whether the received signal level of the receiver 22 is below a threshold value, and sends a control command to the control circuit 25 when it becomes below a specified value.

First, the phase comparator 24 compares the phase of the modulated component by the sensing modulators 18 and 19 in the received signal of the receiver 22 with the phase of the sensing signal from the sensing signal generator 20, and outputs the received signal of the receiver 22. It determines the transition direction of the directivity in which the level increases, and sends an output signal corresponding to the determined transition direction to the control circuit 25.

As a result, the control circuit 2 is constructed mainly of logic circuits.
5, when a control command is given from the level detector 23,
The directivity is changed by appropriately controlling the phase shift amounts of the switching phase shifters 14 and 15 and the attenuation amounts of the variable attenuators 16 and 17 so that the directivity of the antenna 10 transitions in the transition direction determined by the phase comparator 24. control.

In the apparatus configured as described above, when receiving multipath waves arriving at the antenna 10 with the antenna 10 set to a certain directivity, if these multipath waves interfere and cancel each other out, the receiver The received signal level at 22 will drop and cause deep fading.

However, in this case, the level detector 23 detects that the received signal level is below the threshold, and based on this, the control circuit 25 automatically controls the directivity of the antenna 10. The multipath waves automatically escape from the state of cancellation due to interference, the received signal level increases, and fading is improved.

The principle by which fading is improved by changing the directivity of the antenna 10 will be described below.

In mobile radio communications, many multipath waves arrive at the receiving antenna due to reflections from surrounding buildings, and the received electric field is given by the vector sum of these waves.

If this is represented in a vector diagram, it will look like the solid line in Fig. 2, and the composite vector IE of the multipath waves IE1, IE2, ...
The magnitude of gives the received electric field strength.

When the size of this IE becomes small as shown in the figure, deep fading will occur.

In such a case, a vector diagram for changing the amplitude of the IE1 wave to IE1/, for example, becomes as shown by a dotted line, and the composite vector Ig becomes larger, improving fading.

In this case, a similar effect can be obtained by changing the phase of IE.

That is, fading can be improved by appropriately changing the amplitude or phase directivity characteristics of the antenna.

When this principle is applied to the device shown in FIG. 1, it becomes as follows.

The multipath waves as described above arrive at the antenna elements 11 and 12, respectively, and the combined output is the vector sum of these multipath waves.

The outputs of the antenna elements 11 and 12 are changed in phase and amplitude by the fixed phase shifter 13, the switching phase shifters 14 and 15, and the variable attenuators 16 and 17, respectively, and then synthesized by the combination circuit 21. Therefore, the outputs of the branches of the antenna elements 11 and 12 (inputs of the combination circuit 21) are expressed as l R+ , I R
2, the received signal is expressed as its vector sum IR as shown in FIGS. 3 and 4.

The fact that the multipath waves cancel each other out and cause deep fading means that lRt and lR2 cancel each other out and the combined vector IR becomes smaller.

Here, for example, by increasing the amount of attenuation of the variable attenuator 11 on the branch of the antenna element 12, as shown in FIG.
If the amplitude of 2 is changed as shown in IR2', the combined vector becomes IR', which eliminates the cancellation state and improves fading.

In addition, the switching phase shifter 1 also located on the branch of the antenna element 12
Even if the phase shift amount of 5 is changed and the phase of IR2 is changed by π to -IR2 as shown in FIG. 4, the resultant vector becomes lR' and fading is similarly improved.

As mentioned above, changing the amount of phase shift of the switching phase shifter 15 and the amount of attenuation of the variable attenuator 17 means changing the directivity of the antenna 10, but in FIG. Since there is a phase shifter 14 and a variable attenuator 16,
By changing these combinations, it is possible to change the directivity state in many different ways.

FIG. 5 shows the respective branches of antenna elements 11 and 12 as A,
8 shows combinations of eight states of signal amplitude and phase in branches A and B, and the directivity of the antenna 10 in each state, where B is the amplitude and phase of the signal in branches A and B.

In this figure, the directivity diagrams in states ■, ■, ■, and ■ indicate the directivity of the turnstile antenna, and the arrows indicate the direction of phase rotation.

Also, the diagrams of directivity in states ■, ■, ■, and ■ show the directivity of the dipole antenna.

As shown in the state transition diagram in Figure 6, these states change in the direction of ■→■→■→...■→■→... and ■→
Transition is possible in any of the directions ■→■→...■→■→....

In this case, there is no jumping from one state to another state.

As is clear from FIG. 5, there are eight combinations of amplitude and phase of the signals of branches A and H, but the directivity of states ■ to ■ is the same as that of states ■ to ■. In the end, a total of four types of directivity can be realized.

All of these four types of directivity may be used as appropriate for actual reception, but only two specific types of directivity may be used selectively, and the other directivity may be passed through during the transition process. It's okay.

In that case, the two directivities are in their respective states, i.e. the second
It is desirable to select one with a small fading correlation coefficient so that the probability that the received signal levels both take a low value in the states of the solid line and the dotted line in FIGS.

According to experiments, the fading correlation coefficient between ■ and ■ and between ■ and ■ is extremely small, so it is better to use one of these combinations and simply pass the other states through the transition process. .

Figure 7 shows an example of actual measurement of fading when receiving data with a single antenna in mobile radio communication in an urban area. The correlation coefficient when receiving is approximately 0.5, and the correlation coefficient is approximately 0.2 when receiving with a dipole antenna where the directions of maximum reception amplitude are orthogonal, which is the state of ■ and ■. It was confirmed that the combination of the two also had a significant directional directional effect.

This shows that fading can be effectively improved by directional diversity reception with a threshold.

In order to experimentally confirm this fading improvement effect,
FIG. 8 shows the results of directional diversity reception with a threshold using the configuration of the present invention.

This figure compares the cumulative probability distribution of the received signal level when receiving with a single antenna element and when performing directional diversity reception with a threshold according to the present invention.

The dotted line is the theoretical value of Rayleigh aging, and the actual measured value (indicated by a circle) when receiving with a single antenna element approximately follows the Rayleigh quotient.

The solid line is the theoretical value in the case of directional diversity reception with a threshold value, and the actual measured value (marked with an x) matches this value extremely well.

From this, it can be seen that according to the present invention, fading can be improved by more than 10 dB.

Note that even in the case of directional diversity reception with a threshold according to this embodiment, the received signal level in the directivity actually used for reception (in the above example, ■ and ■ or ■ and ■) both fall below the threshold. When this happens, fluctuations will occur as in the case of conventional switching diversity reception with a threshold value.

However, as shown in Figure 5, the directivity is transitioned by continuously changing the amplitude in a sine or cosine manner, and the frequency of the sinusoidal change in the received signal level due to this change is shifted outside the received signal band. If set to , this fluttering will not cause noise.

Therefore, unlike switching diversity reception with a threshold, the improvement effect on fast fading will not be reduced by countermeasures against flapping, and since there is no restriction in principle on the directivity transition speed, the improvement effect on fast fading will not be reduced. I can fully demonstrate my abilities.

By the way, as shown in FIG.
When changing the directivity of the antenna 10 by changing the amount of phase shift, noise generation due to the change in the amount of phase shift becomes a problem.

This invention eliminates the generation of such noise by controlling the switching of the amount of phase shift of the switching phase shifters 14 and 15 while making the attenuation amount of the variable attenuators 16 and 17 connected in series sufficiently large. This is to prevent

That is, as shown in FIG. 5, for example, in branch A, the phase is
That is, when the phase shift amount of the switching phase shifter 14 switches from O to π or from π to 0, the amplitude becomes O, that is, the attenuation amount of the variable attenuator 16.

Also for branch B, the phase is from star to phantom or 22? When the phase shifter 15 switches from O to 1, that is, when the phase amount of the switching phase shifter 15 switches from O to π or from π to O, the amplitude is 0, that is, the attenuation amount of the variable attenuator 11.

Therefore, in principle, no noise is generated due to switching of the amount of phase shift of the switching phase shifters 14 and 15.

As described above, according to the present invention, an inexpensive switching phase shifter capable of discontinuously switching the phase shift amount is used as a variable phase shifter in a variable directional antenna, and noise is reduced when changing the phase shift amount. Fading can be improved without occurrence of fading, and even in digital communication where code errors caused by noise are a problem, there is an advantage that stable and good reception with as few code errors as possible can be performed.

In the example, two sets of horizontally polarized dipole elements were used as antenna elements in such a way that the signals of each branch A and H changed in the combination of phase and amplitude shown in FIG. By changing the combination, and also by changing the arrangement of both antenna elements, it is possible to create dipole antennas in which the maximum amplitude direction of directivity differs by 45 degrees from that in Figure 5, or single antennas with maximum amplitude values in opposite directions. Various directivity such as directivity can be combined.

Of course, various types of directivity can be similarly achieved for polarized waves other than horizontally polarized waves.

The present invention is also applicable to cases where the number of antenna elements is three or more.

Further, in the embodiment, each antenna element branch has been described as a diversity branch having a directional diversity effect, but the present invention can be similarly applied to other types of diversity branches such as ordinary space diversity and polarization diversity.

In these cases as well, the signals from the branches of each antenna element are used in a suitably combined state, resulting in a variable directivity antenna in a broad sense.

Further, in the embodiment, sensing modulators 18 and 19, a sensing signal generator 20, and a phase comparator 24 are provided, so that the control circuit 25 detects the directivity transition direction of the antenna 10 in the direction in which the received signal level always increases, that is, in the transition process. Although the direction is set in a direction that does not involve a decrease in the signal level, the fading improvement effect can still be ensured even if the direction of transition force is defined in one direction without using such a method.

This is because the reduction in the received signal level during the directionality transition process does not always occur, and even if it does occur, it is only for a very short time, so the degree of fading improvement is reduced by specifying the transition direction as one direction. This is because the directionality is extremely small, and if economic efficiency is more important, the directivity transition direction can be specified to be one direction.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of a radio receiving device according to an embodiment of the present invention, FIG. 2 is a vector diagram showing the principle of improving fading due to multipath waves, and FIGS. 3 and 4 are the same diagrams. FIG. 5 is a vector diagram showing the principle of improving fading according to the embodiment. FIG. Figure 6 is a state transition diagram of the above directionality,
FIG. 7 is a diagram showing an example of fading during reception of mobile radio communication using a single antenna, and FIG. 8 is a diagram showing an actual measurement example of the fading improvement effect according to the present invention. 10...Variable directional antenna, 11, 12...
...Antenna element, 14, 15...Switching phase shifter, 16,17...Variable phase shifter, 21...
...combination circuit, 22...receiver, 23...
... Level detector, 25 ... Control circuit.

Claims (1)

[Claims] 1. A variable directional antenna that connects a plurality of antenna element outputs in series through a switching phase shifter whose phase shift amount can be switched discontinuously and a variable attenuator whose attenuation amount is continuously variable;
A receiver that receives a signal via this antenna, and a directivity of the antenna by appropriately controlling the phase shift amount of the switching phase shifter and the attenuation amount of the variable attenuator according to the received signal level of this receiver. and a control circuit for changing the amount of attenuation of the variable attenuator, the control circuit being configured to control the amount of phase shift of the switching phase shifter in a state where the amount of attenuation of the variable attenuator is sufficiently large. Wireless receiving device.