JPH03253124A - Diversity system receiver - Google Patents

Abstract

PURPOSE:To secure stable receiving quality in any vehicle traveling state by selecting a synthesized diversity system or a selective diversity system in accordance with changing speed in the intensity change of an electric field. CONSTITUTION:A part of the output of an intermediate frequency amplifier is sent to a level detector 44 and a switch 33 is switched in accordance with the signal level. Namely, when the signal level of the amplifier 35 is less than a prescribed value, i.e., when phase variation frequency based upon fading is less than the prescrived value, the switch 33 is switched to the side of a mixer 27 and operation based upon the synthesized diversity system is executed, and when the frequency is more than the prescribed value, the switch 33 is switched to the mixer 28 side and operation based upon the selective diversity system is executed. Consequently, a modulated wave can be reproduced up to its lower limit frequency range and the stable receiving quality can be secured even in the traveling of the vehicle.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to anti-fading technology in mobile communications such as vehicles, and more particularly to spatial diversity technology using in-phase threats.

[Prior art]

Regarding the diversity method, for example, "Radio Engineering Handbook" published by Ohm Publishing, pp. 19-53 to 19-55.
” and other various books.

FIG. 6 is a block diagram of an example of a conventional combining diversity receiving apparatus. This conventional example is an example of a device that receives FM broadcasting with two branches (diversity method using two antennas).

In FIG. 6, two antennas 1 and 2 are.

They are provided in such a positional relationship that the distance between them is λ/4 or more. Then, the signals received by the antenna 1.2 are selectively amplified by a high-frequency amplifier 3.4, where only desired signals are selectively amplified, and then guided to a frequency mixer 5.6.

In the frequency mixer 5.6, the signal from the local oscillator 7.8 and the signal from the high frequency amplifier 3.4 are mixed and converted into an intermediate frequency signal which is the difference frequency of each. Next, after being amplified by an intermediate frequency amplifier 9.10, the output signals of the intermediate frequency amplifier 9.10 are combined in a combiner 1. The output of this synthesizer 11 is given to a detector 12, and the original modulated signal is demodulated.

Further, a part of the signal converted to the intermediate frequency is sent to the phase comparator 13, and output pulses corresponding to each phase difference are obtained. This pulse signal is smoothed by a filter 14, and the phase of the local oscillator 7 is controlled by this smoothed signal.

Among the above configurations, frequency mixer 5. Intermediate frequency amplifier 9
, a phase-locked loop consisting of a phase comparator 13, a filter 14 and a local oscillator 7.
op), the signal received by antenna 1 is transmitted to antenna 2.
Since the phase is shifted so that it is in the same phase as the signal received by the combiner 13, both signals are always combined in the same phase in the combiner 13. Therefore, in the above-mentioned receiving apparatus using the combining diversity method, there is an advantage that not only a combining gain can be obtained, but also more stable reception quality can be ensured in a fading environment such as in mobile communication.

There is also a receiving apparatus that uses a selective diversity method (or referred to as a switching diversity method) that selectively switches received signals from two antennas separated by a quarter wavelength or more. Although this method is slightly inferior to the above-described combined diversity method in terms of gain and stability, it has the advantage of a simpler configuration.

[Problem to be solved by the invention]

The frequency modulation band of FM broadcasting is 20 Hz to 75 kHz, and the lower limit frequency is 20 Hz, so if the cutoff frequency of the low-pass filter 14 is set to 20 Hz or higher, it becomes impossible to demodulate the low frequency range of the modulated wave.

Therefore, it is necessary to set the above cutoff frequency to 20 Hz or less.

However, in the synthetic diversity method, it is assumed that the control system can follow the phase change, but if the above cutoff frequency is set to less than 20Hz,
The control system will be unable to follow sudden changes in electric field strength exceeding . When the vehicle is running, the minimum 1/
Due to the phenomenon that the received electric field drops at interference points that occur at an interval of two wavelengths, the electric field strength changes every time the vehicle travels approximately 1.5 m, so as the vehicle speed increases, the frequency of change in the electric field strength exceeds 20 Hz (approximately (20 Hz at 1108 k/h), it becomes difficult to ensure stable reception quality in a running vehicle.

Therefore, in the conventional combined diversity receiving apparatus as described above, there is a problem in that if an attempt is made to reproduce the modulated wave up to the lower limit frequency range, it becomes difficult to ensure stable reception quality while the vehicle is running.

The present invention was made to solve the problems of the conventional technology as described above, and is capable of reproducing modulated waves up to the lower limit frequency range, ensuring stable reception quality even when the vehicle is running. The purpose of the present invention is to provide a diversity receiving device that can perform the following functions.

[Means to solve the problem]

In order to achieve the above object, the present invention is configured as described in the claims.

That is, in the present invention, if the rate of change in the electric field strength that changes with the movement of the moving object or the moving speed of the moving object is less than a predetermined value, the composite diversity method is selected, and if the speed is equal to or greater than the predetermined value, the combined diversity method is selected. is configured to include means for selecting a selection diversity method and forming a receiving system.

In the above configuration, the predetermined value for comparing the change speed of the electric field strength is, for example, a value of about 17 to 20 frequency, and the predetermined value for comparing the moving speed of the moving object is, for example, 92.
The value is approximately 1.08 m/h.

Further, in another configuration of the present invention, the receiving system of the combining diversity method and the receiving system of the selective diversity method are independently provided, and the rate of change of the intensity change of the electric field strength that changes with the movement of the mobile object is If the value is less than the first predetermined value, the combined diversity receiving system is selected, and if the value is greater than or equal to the first predetermined value but less than the second predetermined value, the S/N ratio is selected from the outputs of the receiving systems of both methods. Select the higher one, and select the second one above.
If the value is greater than a predetermined value, the configuration is provided with means for selecting a receiving system using the selection diversity method.

Note that in the above configuration, for example, the first predetermined value is 1.
7 Hz, and the second predetermined value is 20 Hz.

With the above configuration, in the present invention,
The combination diversity method is selected in the range that the control can follow, and the selective diversity method is selected in the range that the control cannot follow, so the optimal method is always selected and the low-pass filter cutoff Since the frequency can be set to a low value, it is possible to reproduce up to the lower limit frequency range of the modulated wave.

[Embodiments of the invention]

FIG. 1 is a block diagram of one embodiment of the present invention.

In FIG. 1, the signals received by antennas 21 and 22 are amplified to the required signal level by high frequency broadband amplifiers 23 and 24, and then the signals received by antenna 21 are divided into two signal systems by a divider 25. Ru. Note that, as will be explained later in the second embodiment, it is also possible to add a method of comparing the S/N ratio and controlling the switching timing at the same time.

Next, the two outputs of the divider 25 are transferred to a frequency mixer 27.2.
8, and the output of the high frequency wideband amplifier 24 is sent to a frequency mixer 30 and local oscillators 31 and 32, respectively.
is mixed with the signal from the IF and converted to an intermediate frequency IF.

The output of the frequency mixer 27.28 is then output to the switch 33.
Either one is selected by the intermediate frequency amplifier 35.
The signal is sufficiently amplified at , further passes through a switch 37 , and then sent to a combiner 40 . In addition, the frequency mixer 30
The output of is sufficiently amplified in an intermediate frequency amplifier 36, further passes through a switch 38, and then sent to a combiner 40.

The signals from each antenna sent to the combiner 40 as described above are combined by the combiner 40. The modulated signal is then demodulated by the detector 41 and output.

Furthermore, the signal phases of some of the outputs of the intermediate frequency amplifiers 35 and 36 are compared in a phase comparator 42, and an error signal is output in the form of a pulse waveform.

The above error signal is then applied to the voltage-frequency control input terminal of the local oscillator 31 via a low-pass filter 43 having a cutoff frequency of 17 Hz.

Further, a part of the output of the intermediate frequency amplifier 35 is sent to a level detector 44 for detecting the signal level, and the switch 33 is switched in accordance with the signal level. That is, when the signal level of the intermediate frequency amplifier 35 is lower than a predetermined value, for example, when the phase fluctuation frequency due to fading corresponds to less than a predetermined value (for example, 20 Hz) as described later, the switch 33 is switched to the mixer 27 side. If the value is equal to or greater than the predetermined value, the mixer 28 is switched to the mixer 28 side and operates in the selective diversity mode.

Further, a part of the outputs of the intermediate frequency amplifiers 35 and 36 are given to a level comparator 45, and the level comparator 45 operates a switch 37 and 38 to select the larger one of the outputs of the intermediate frequency amplifiers. Switch to operate in selection diversity mode. However, when the switch 33 is switched to the mixer 27 side and operates in the composite diversity mode, the switches 37 and 38 are both controlled to be fixed on.

Next, the effect will be explained.

A case where FM broadcasting is received using the configuration in the first @ as described above will be explained.

The carrier wave frequency band of FM broadcasting in our country is 76-9.
The range is 0MHz, and the frequency band of the modulated wave is 20H.
z~75kHz is used. If you try to receive this while moving in a vehicle, etc., the received electric field will drop at interference points that occur at intervals of a minimum of 172 wavelengths, resulting in S/N and distortion degradation due to fading every time the vehicle travels approximately 1.5 m. There are problems such as occurrence of

As a simple method to solve this problem, a selective diversity receiving device has been put into practical use, which selectively switches the received signals of two antennas separated by more than 1/4 wavelength.
Furthermore, the above-mentioned combined diversity receiving apparatus, which is advantageous in terms of gain and stability, is also being used. Note that, since the synthetic diversity receiving device uses a method of controlling the phase of the signal, it is a prerequisite that the control system can follow the phase change accompanying the movement of the vehicle.

However, in FM broadcasting, transmission information is superimposed on the frequency (phase) component of the carrier wave, so when the phase fluctuation frequency component due to fading falls within the modulation frequency band, the low-pass filter 43 in FIG. 1 separates the two. becomes difficult.

The phase fluctuation frequency due to the above fading becomes 20 when the traveling speed is approximately 108 + a/h, so it is set to a value lower than the lower limit of the modulation frequency of 20 Hz (in Figure 1, a low-pass filter with a stop of 17 is used). In order for the vehicle to run at a speed of less than approximately 108 km/h (108 km/h). If this speed is exceeded, the combined diversity method will no longer be able to provide sufficient control.

In addition, the cutoff frequency of the low-pass filter is 20Hz.
If the control system were to be able to track the vehicle at high speeds, it would be possible to cope with even higher speed driving, but at the cost of this, it would become impossible to demodulate the low frequency range of the modulation frequency.

In order to deal with the above problem, in this embodiment, a change in signal level is detected, and this phase fluctuation frequency is 20Hz.
If the number exceeds a certain level, the composition diversity method is switched to the selection diversity method.

The signal level detector 44 is also a frequency counter for detecting this phase fluctuation frequency. and switch 33
is a switch for switching between the composite diversity method and the selection diversity method, and switches 37 and 38
is the antenna 21.22 in the selection diversity method.
This is for selectively switching each receiving system.

Note that the details of the timing of the above switching will be described later.

With the above configuration, when the period of signal level fluctuation is long, the combined diversity method with higher gain and more stability is used, and when the period of signal level fluctuation is short and the control cannot follow, the selective diversity method that allows high-speed switching is used. By using this method, the advantages of both methods can be taken advantage of, and better reception conditions can be ensured under any driving conditions.

Next, the timing of switching between the combination and selection diversity methods as described above will be explained with reference to FIG.

In FIG. 2, the electric field strength of the radio waves received by the antenna 21 is shown as (a), and the electric field strength of the radio waves received by the antenna 22 is shown as (b).

First, when the switch 33 is switched to the combining diversity side, that is, the mixer 7 side, and the switches 37 and 38 are both fixed in the on state to operate in the combining diversity method, the output S/N ratio is the second A in figure (c)
As shown by the characteristic line, the phase fluctuation frequency deteriorates as the phase fluctuation frequency becomes higher, starting from 17 Hz. This is because the phase control cannot follow the phase fluctuation frequency exceeding 17 Hz.

In the above state, if the switch 33 is switched to the selection diversity side, that is, the mixer 8 side, and the switches 37 and 38 are set to the selection diversity method in which the level detector 44 selectively switches to the one with the larger output, As shown by characteristic line B in FIG. 2(c), the output S/N ratio can maintain a relatively stable S/N ratio even though the S/N ratio fluctuates to some extent.

As mentioned above, if the fluctuations in the electric field strength of the radio waves received by the two antennas 21 and 22 have such a characteristic that the peaks of one match the troughs of the other, as shown in Figure 2, the phase fluctuation By switching from the synthetic diversity method to the selective diversity method when the frequency exceeds 17 to 18, deterioration of the S/N ratio can be prevented.

However, depending on the phase and level characteristics of the radio waves received by the two antennas 21 and 22, the S/N ratio (A The variation deterioration of the S/N ratio (characteristic B indicated by the broken line) in the selection diversity method may be relatively large.

Therefore, there may be cases where it is not possible to simply switch between the two diversity systems using one phase variation frequency.

FIG. 3 is a block diagram of a second embodiment of the present invention that addresses the above problem. In addition, in FIG. 3, the same reference numerals as in FIG. 1 indicate the same parts.

The configuration of this embodiment differs from the embodiment shown in FIG. 1 in that the combined diversity receiving system and the selective diversity receiving system are made independent, and an intermediate frequency amplifier 52 is provided accordingly. /N detector 53.54,
A comparator 55 for comparing the S/N ratios of the two S/N detectors, and a switch controller 56 for controlling the switch 50.51 based on the outputs of the comparator 55 and the level comparator 44. It has been added.

In this embodiment, the signal levels of the intermediate frequency amplifiers 52 and 36 are compared by a level comparator 45, and depending on the result, the signal levels of the intermediate frequency amplifiers 52 and 36 are compared, and the switch
By controlling 0, a selective diversity receiving system is constructed in which the receiving system on the antenna side with high signal strength is selectively switched.

Also, a local oscillator 31, a mixer 27, an intermediate frequency amplifier 3
5. Using the output signal of the intermediate frequency amplifier 36 as the reference frequency of the phase-locked loop composed of the phase comparator 42 and the low-pass filter 43, the two antennas 21 and 22
A circuit portion that makes the signals received by the receiver in phase and combines them with the combiner 40 constitutes a receiving system of the combining diversity system.

Further, the magnitude of the S/N ratio of the output of the selective diversity receiving system, that is, the output of the switch 50, and the S/N ratio of the output of the combining diversity receiving system, that is, the output of the combiner 40 are determined.
The magnitude of the N ratio is detected by S/N detectors 53 and 54, respectively, and the magnitudes of both are compared by a comparator 55. Then, the switch 51 is controlled via the switch controller 56 according to the output of the comparator 55 and the level detector 44, and when the phase fluctuation frequency is less than about 17 Hz, the composite diversity method is selected, and when the phase fluctuation frequency is less than about 17 Hz and about 20 Hz.
If the frequency is less than about 20 Hz, the diversity method with the higher S/N ratio is selected, and if the frequency is about 20 Hz or more, the selective diversity method is selected.

With the above configuration, high reception quality can always be maintained regardless of the traveling speed of the vehicle.

In this embodiment, the cut-off frequency of the low-pass filter 43 is set to 17, and the case is completely switched to the selective diversity method at frequencies above 20 Hz. It goes without saying that the effects of the present invention can be maximized by optimizing as appropriate.

Next, FIG. 4 is a block diagram of a third embodiment of the present invention. In FIG. 4, numeral 46 is a vehicle speed detector for detecting the running speed of the vehicle, and the same reference numerals as in FIG. 1 indicate the same components.

In this embodiment, the switches 33, 37, and 38 are switched by a signal from the vehicle speed detector 46 to switch between the combined diversity method and the selective diversity method.

As described above, fading due to vehicle travel occurs every time the vehicle travels approximately 1.5 m due to the phenomenon that the received electric field drops at interference points that occur at intervals of at least 1/2 wavelength. Regarding the relationship between the phase fluctuation frequency due to this fading and the vehicle speed, one frequency of 17 Hz corresponds to a vehicle speed of approximately 92 km/h, and one frequency of 20 Hz corresponds to a vehicle speed of approximately 1108 km/h. Therefore, if the system is configured to switch between the combined diversity system and the selective diversity system when the vehicle speed reaches a value of about 92 to 1108 k/h, the same effect as the embodiment shown in FIG. 1 can be obtained.

In particular, normal vehicles have a function that issues a signal to call attention when the speed limit is exceeded, for example at a speed of about 105 to 1108 k+/h, so this signal can be directly activated by pressing the switch 33, 37, or 38. If used as a control signal for switching, it is possible to easily and reliably switch between the combined diversity method and the selection diversity method.

Although the above embodiments have been described with reference to the case where FM broadcasting is received, it goes without saying that the present invention is not limited to this and can be used as is for TV broadcasting, mobile radio communication, and the like.

Moreover, although the explanation has been given using a vehicle as an example of a moving object, it goes without saying that the present invention can be similarly applied not only to automobiles and railway vehicles but also to other moving objects such as aircraft, forvercraft, ships, and the like.

In the above description, the case where the present invention is mainly applied to audio reception such as FM broadcasting has been explained. For radio wave types with relatively narrow occupied bandwidth, such as voice transmission,
Switching for modulated waves is based on the fact that audio is a continuous analog signal and that if switching is performed as fast as it is when switching the diversity method, harsh noise such as switching noise will become inaudible. The timing is not a particular problem.

However, in the case of a signal that has a wide occupied bandwidth and includes a synchronization signal, such as a TV broadcast wave, disturbances in the received image can be minimized by selecting the timing.

For example, as shown in FIG. 5, the period after the equivalent pulse on the back porch of the vertical synchronization pulse within the vertical retrace period of the video signal, that is, 7H to 20H (H It is preferable to perform the switching operation during one horizontal opening period).

〔Effect of the invention〕

As explained above, according to the present invention, the composite diversity method is selected in the range that the control can follow, and the selective diversity method is selected in the range that the control cannot follow, thereby increasing the gain of the composite diversity method. It is possible to take advantage of both the high speed of selection diversity and the high speed of selection diversity, ensuring stable reception quality under any vehicle driving condition.Moreover, the cutoff frequency of the -pass filter is set to a low value. Therefore, an excellent effect can be obtained in that it is possible to reproduce up to the lower limit frequency range of the modulated wave.

Furthermore, in the embodiment shown in Fig. 3, the optimal method can always be selected even in the phase fluctuation frequency range where the superiority of the synthetic diversity method and the selective diversity method changes depending on the situation, and the reception quality is improved as much as possible. I can do it.

In addition, in the embodiment shown in Fig. 4, it is possible to easily switch between both types using a speed warning signal provided in a normal vehicle, and the configuration can be simplified. There are advantages.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a first embodiment of the present invention, FIG. 2 is a waveform diagram showing switching timing between two diversity methods, and FIG. 3 is a block diagram of a second embodiment of the present invention.
FIG. 4 is a block diagram of a third embodiment of the present invention, FIG. 5 is a waveform diagram showing switching timing in a video signal, and FIG. 6 is a block diagram of an example of a conventional device. <Explanation of symbols> 21.22...Antenna 23.24...High frequency wideband amplifier 25...Distributor 27.28.30...Mixer 31.32...Local oscillator 33... Switches 35, 36...Intermediate frequency amplifier 37, 38...Switch 40...Synthesizer 41...Detector 42...Phase comparator 43...Low pass filter 44...Level detector 45 ... Level comparator 46 ... Vehicle speed detector 50.51 ... Switch 52 ... Intermediate frequency amplifier 53.54-8 / N detector 55 ... Comparator 56 ... Switch controller

Claims (1)

[Claims] 1. A combining diversity method in which received signals from a plurality of antennas provided at a distance in space above a moving object are combined in the same phase, and among the received signals from the plurality of antennas, means for forming a reception system by selecting one of the two methods, a selection diversity method for selecting the higher level of If the rate of change of the intensity change or the moving speed of the moving object is less than a predetermined value, select the above composite diversity method,
A diversity method receiving device, characterized in that the diversity method receiving device selects the selection diversity method when the value is equal to or greater than the predetermined value. 2. A receiving system using a combining diversity method that combines the received signals from multiple antennas installed at a distance in the space above the mobile object in the same phase, and the high level of the received signals from the multiple antennas. A receiving system of the selective diversity method is selected, and a receiving system of the combining diversity method is selected when the rate of change in the electric field strength that changes with the movement of the mobile object is less than the first predetermined value. , if the value is greater than or equal to the first predetermined value but less than the second predetermined value, select the one with the higher S/N ratio among the outputs of both of the above receiving systems, and if it is greater than or equal to the second predetermined value, A diversity method receiving device comprising: means for selecting a receiving system of the selective diversity method.