JPH0347022B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a radio interference detection method, and more particularly to a radio interference detection method for detecting the amount of radio interference by detecting an amplitude component appearing due to radio interference in a radio device using FM waves.

When using a multi-channel mobile communication system such as a car phone system or a mobile phone system, accurate voice information cannot be transmitted if the call quality deteriorates due to radio wave interference. Under such circumstances, it is desirable to avoid radio wave interference by channel switching, but in order to perform the channel switching, etc., it is desirable to accurately measure the amount of radio wave interference in advance.

In the conventional radio wave interference method, the amplitude component detection voltage is sampled, and the power product of the main wave and the interference wave is calculated from the change in the detected power (the square of the detected voltage) over a minute period through arithmetic processing, and at the same time, the detected average power is calculated. The power sum of the main wave and the interference wave is calculated from the above, and the ratio between the main wave power and the interference power, that is, the amount of radio wave interference, is calculated through arithmetic processing. This is explained in detail in the high-capacity mobile communication system unveiled at the NTT International Symposium held in 1983.

In this radio wave interference detection method, first, the principle of generation of amplitude fluctuation components due to radio wave interference will be explained with reference to FIG.

In FIG. 1, the reference symbol D〓 indicates the FM desired wave vector, the reference symbol U〓 indicates the FM interference wave vector, and the reference symbol R〓 indicates the FM received wave vector.

As is clear from Fig. 1, if the frequencies of the desired wave D〓 and the interference wave U〓 are slightly different, the amplitude of the composite wave R〓 will change quickly with the frequency difference between the desired wave D〓 and the interference wave U〓. The amplitude fluctuates depending on the In other words, it is subjected to amplitude modulation, and an amplitude modulation component is generated. Therefore, by measuring the amount of amplitude fluctuation, it is possible to obtain the radio wave interference ratio (D〓/U〓). For reference, FIG. 2 shows an example of the relationship between the amplitude fluctuation width and the radio wave interference ratio (D〓/U〓).

On the other hand, in an FM receiver, the FM-AM conversion characteristic of the intermediate frequency filter allows the FM modulation signal to pass through, thereby generating an amplitude component. This is especially true when the passing signal frequency deviates from the center frequency of the intermediate frequency filter, causing FM-AM conversion to become noticeable.

In other words, to explain in detail, in an FM receiver, the passband characteristics of a frequency band limiting filter such as an intermediate frequency filter are not flat, and especially for filters with flat delay time characteristics, the passband characteristics are approximately square. have characteristics. Therefore, the FM modulated wave is amplitude-converted by the frequency band limiting filter. For this reason, in the radio wave interference detection method that measures the amount of amplitude fluctuation to determine the amount of radio wave interference, a problem arises in that the measurement error becomes noticeable.

The present invention has been made in order to overcome the above-mentioned disadvantages, and it is possible to detect an FM signal from an amplitude component detection signal.
It is an object of the present invention to provide a radio wave interference detection method that can accurately detect the amount of radio wave interference via an amplitude component detection signal by removing the signal component due to AM conversion. Furthermore, in the case of sampling, the purpose is to provide a radio wave interference detection method that can remove the error caused by the signal component due to FM-AM conversion from the sampling output and thereby accurately detect the amount of radio wave interference. do.

In order to achieve the above object, the present invention provides a radio interference detection method for detecting the amount of radio interference by detecting an amplitude fluctuation component caused by radio interference in an FM radio, in which the output of an intermediate frequency filter is passed through a limiter. After that, FM demodulation is performed, and a signal obtained by squaring the FM demodulated signal is added to a signal obtained by detecting the output of the intermediate frequency filter with a logarithmic detector, and an amplitude fluctuation component of the added output is detected. This feature is characterized in that the influence of the FM-AM conversion characteristics of the intermediate frequency filter is removed.

Furthermore, the present invention provides a radio wave interference detection device that detects the amount of radio wave interference by detecting an amplitude fluctuation component caused by radio wave interference in an FM radio, comprising: a frequency conversion circuit that converts the frequency of radio waves received from an antenna; an intermediate frequency filter that filters the output signal of the frequency conversion circuit; a logarithmic detector that detects the output signal of the intermediate frequency filter; and a limiter amplifier that controls the amplitude; and an FM that demodulates the output signal of the limiter amplifier.
a demodulator, a squaring circuit that squares the output signal of the FM demodulator, an addition circuit that adds the output signal of the logarithmic detector and the output signal of the squaring circuit, and a filter that filters the output signal of the addition circuit. The present invention is characterized by comprising a bypass filter (HPF) that generates a wave, and a level detector that detects the HPF output signal.

As a result, the FM-AM
The amplitude fluctuation component caused by the conversion is canceled out and no longer exists, and the amplitude fluctuation component of the addition output is caused by radio wave interference, resulting in the effect of reducing the radio wave interference detection error due to FM-AM conversion.

Next, the radio wave interference detection method according to the present invention will be described in detail below with reference to the accompanying drawings, citing preferred embodiments in relation to the apparatus that implements the method.

FIG. 3 is a block circuit diagram for implementing the radio wave interference detection method according to the present invention. In the figure, reference number 10 indicates an FM antenna, and the output side of this FM antenna 10 is an FM receiver 12, in particular, Connected to the tuner section. Substantially, this FM receiver 12 includes a frequency conversion circuit 14 connected to the output side of the FM antenna 10, and this frequency conversion circuit 1.
An intermediate frequency filter 16 connected to the output side of 4
and a limiter amplifier 18 and a logarithmic detector 2 connected in parallel to the output side of the intermediate frequency filter 16.
0, and an FM demodulator 22 connected to the output side of the limiter amplifier 18. Logarithmic detector 20
In this case, the output side of is connected to one input terminal of the adder circuit 24, while the output side of the squaring circuit 26 connected to the FM demodulator 22 is connected to the other input terminal of the adder circuit 24. do. The output side of the adder circuit 24 is connected to a high pass filter 28.
It is connected to the level detector 30 via.

In the above configuration, the output from the antenna 10 is supplied to the frequency conversion circuit 14 and converted into an intermediate frequency signal. The intermediate frequency signal converted by the frequency conversion circuit 14 is sent to a limiter amplifier 18.
The intermediate frequency signal supplied to the logarithmic detector 20 and whose amplitude is limited by the limiter amplifier 18 is
The signal is supplied to the FM demodulator 22 for FM demodulation. FM
The demodulated output signal of the demodulator 22 is supplied to a squaring circuit 26 and squared, and the output of the squaring circuit 26 and the output signal of the logarithmic detector 20 are further supplied to an adding circuit 24 and added. The addition output of the addition circuit 24 is sent to the level detector 3 via a high-pass filter 28.
0, and the output of the high-pass filter 28 is detected.

The amplitude characteristic of the intermediate frequency filter 16 mentioned above has a square characteristic as indicated by reference numeral a in FIG. 4, while the FM demodulation characteristic of the FM demodulator 22 has a This is indicated by the symbol b. Further, the amplitude detection characteristic of the logarithmic detector 20 is as shown by reference numeral c in FIG. 4, and the input/output characteristic of the square circuit 26 is
In the figure, it is indicated by reference numeral d.

Therefore, the waveform of the intermediate frequency signal f _n (t) now output from the frequency conversion circuit 14 is as shown in FIG. For example, it is off by 1KHz. An intermediate frequency signal f _n (t) having a waveform indicated by reference numeral e in FIG.
The converted signal R(t), which is converted according to the FM-AM conversion characteristic, becomes as indicated by reference numeral f in FIG. In FIG. 4, the output indicated by reference numeral f is subjected to amplitude detection by a logarithmic detector 20. Output signal L(t) of the logarithmic detector 20
The waveform of is indicated by reference numeral g in FIG.

Therefore, the output L(t) of the logarithmic detector 20 is expressed by the following equation.

L(t)=a・R(t)≒−a′ [f _n (t)−f ₀ ] ² …(1) Here, a, a′ are positive proportionality constants, and f ₀ is the intermediate frequency filter. This is the center frequency of the passband.

On the other hand, the intermediate frequency signal f _n (t) hardly changes as a frequency signal by passing through the intermediate frequency filter 16, is amplitude limited by the limiter amplifier 18, and is FM demodulated by the FM demodulator 22. be done. The demodulated output AF(t) of this FM demodulator 22 is indicated by reference numeral h in FIG. Then, the demodulated output AF(t) is squared by a squaring circuit 26, and the output SQ(t) of this squaring circuit 26 is
In FIG. 4, it is indicated by reference numeral i.

In this case, the output SQ(t) of the square circuit 26 is expressed by the following equation.

SQ(t)=b[AF(t)] ² =b'[ _fn (t) _-f0 ] ² ...(2) Here, b and b' indicate positive proportionality constants.

Next, in the adder circuit 24, the output L(t) of the logarithmic detector 20 in equation (1) and the output SQ(t) of the squarer circuit 26 in equation (2) are added as voltages as a'=b'. be done.

Therefore, in the addition circuit 24, the AM fluctuation caused by passing through the intermediate frequency filter 16 is canceled out.

On the other hand, in the case of interference between the desired wave D〓 and the interference wave U〓, D〓＝dsinω ₀ t …(3) U〓＝usinω ₁ t …(4) d and u are proportional constants, and ω ₀ and ω ₁ are Each wave of hope
These are the angular velocity of D〓 and the angular velocity of the disturbance wave U〓. Here, it is assumed that d>u.

As a result, the combined received wave R〓 is R〓=D〓+U〓=dsinω ₀ t+usinω ₁ t =r(t)sin[ω ₀ t+φ(t)] …(5) Here, r(t)=√ ² + ² + 2 _o ...(6) φ(t)=sin ^-1 usinω _o t/r(t)...(7) ω _o =ω ₁ −ω ₀ ...(8)

Now, if d>>u, then r(t)≒d(1+u/dcosω _o t) …(9) φ(t)≒u/dsinω _o t …(10), and the phase shift signal φ(t) is Frequency shift signal f _o (t)
, then f _o (t)=dφ(t)/dt≒uω _o /dcosω _o t…(11).

The detection output L _o (t) obtained by detecting the amplitude fluctuation component Y(t) by the logarithmic detector 20 is L _o (t)≈Ku/dcosω _o t (12).

Therefore, the detected output L _o (t) is supplied to the adder circuit 24 and added to the output of the squaring circuit 26 which squares the FM demodulated output, and is detected by the level detector 30 through the high-pass filter 28. Level detected.

By the way, the frequency-shifted signal f _o (t) is
In the FM signal, as in the case of the intermediate frequency signal f _n (t), an amplitude fluctuation component is generated by FM-AM conversion by the intermediate frequency filter 16. However, as in the case of the intermediate frequency signal described above, the FM demodulated signal is
By adding the output of the square circuit 26 and the output of the logarithmic detector 20 by the adding circuit 24, the generated amplitude fluctuation component is removed.

Therefore, the output of the level detector 30 becomes a voltage approximately proportional to u/d, and the output is proportional to the level ratio of the desired wave D〓 and the interference wave U〓, that is, the amplitude from which the signal component due to FM-AM conversion is removed. A component voltage (interference amount detection voltage) is obtained.

Note that the high-pass filter 28 removes amplitude fluctuation components due to fading that occurs in mobile communications.

FIG. 5 is an example showing measured values comparing interference detection characteristics with a case where the squaring circuit 26 shown in FIG. 3 is not used. This figure shows the radio wave interference ratio (D〓/U〓)
The relationship between the interference amount detection voltage and the interference amount detection voltage is shown with respect to changes in the FM modulation amount.

Therefore, as mentioned above, when a square circuit is provided, the interference amount voltage will only fluctuate within the range displayed with respect to the radio wave interference ratio, and when the radio wave interference ratio starts to deteriorate at around 15 dB, the FM An interference amount detection voltage that is almost unaffected by the amount of modulation can be obtained.

On the other hand, when the square circuit is not used, the interference amount voltage fluctuates within the combined range of the display area shown by the diagonal line A that crosses the radio wave interference ratio and the display area shown by the simple diagonal line B, The range of variation is large. Therefore, even when there is no radio wave interference, an interference amount detection voltage equivalent to the amount of radio wave interference of 15 dB without modulation may be generated, and the detection error is extremely large.

As explained above, in the present invention, the output obtained by logarithmically detecting the intermediate frequency signal of the FM receiver 12
Since the amplitude fluctuation component is canceled by processing the squared FM demodulated output, the FM demodulated output and the logarithmic detection output are sampled simultaneously, and the former is squared and then added to the logarithmic detection output. Even in the case of processing, the amplitude fluctuation component due to FM-AM conversion is removed, making it possible to accurately measure the amount of radio wave interference.

As explained above, according to the present invention, by adding a signal obtained by squaring the FM demodulated signal to the amplitude component detection signal caused by radio wave interference, the amplitude fluctuation component caused by FM-AM conversion is removed, and the FM modulation amount is The amount of radio wave interference can be accurately determined without being influenced by Therefore, in a multi-channel mobile communication system such as a car telephone system, it is possible to ensure high call quality by appropriate transmission power control and channel switching by detecting the amount of radio wave interference. Furthermore, since it is possible to reduce the interval between identical frequency repetition zones in the cellular system, there is also the advantage that frequencies can be used effectively.

Although the present invention has been described above with reference to preferred embodiments, the present invention is not limited to these embodiments, and various improvements and changes in design can be made without departing from the gist of the present invention. Of course.

[Brief explanation of drawings]

Fig. 1 is a diagram for explaining the generation of amplitude modulation components due to radio wave interference, Fig. 2 is a diagram showing the relationship between the amplitude fluctuation width and the radio wave interference ratio, and Fig. 3 is a diagram showing the configuration of an embodiment of the present invention. 4 is a waveform diagram for explaining the operation of an embodiment of the present invention, and FIG. 5 is a diagram for explaining the operation of an embodiment of the present invention. 10... Antenna, 12... FM receiver, 14... Frequency conversion circuit, 16... Intermediate frequency filter, 18...
Limiter amplifier, 20...logarithmic detector, 22...FM
Demodulator, 24... Addition circuit, 26... Square circuit, 28
...High pass filter, 30...Level detector.

Claims (1)

[Claims] 1. In a radio interference detection method for detecting the amount of radio interference by detecting an amplitude fluctuation component caused by radio interference in an FM radio, the output of an intermediate frequency filter is passed through a limiter and then FM demodulated. , by adding the signal obtained by squaring the FM demodulated signal and the signal obtained by detecting the output of the intermediate frequency filter with a logarithmic detector, and detecting the amplitude fluctuation component of the added output, the intermediate frequency A radio wave interference detection method characterized by removing the influence of the FM-AM conversion characteristics of a filter. 2. A radio interference detection device that detects the amount of radio interference by detecting an amplitude fluctuation component caused by radio interference in an FM radio, comprising: a frequency conversion circuit that converts the frequency of radio waves received from an antenna; and an output of the frequency conversion circuit. an intermediate frequency filter that filters a signal; a logarithmic detector that detects the output signal of the intermediate frequency filter; and a limiter amplifier that controls the amplitude; and an FM that demodulates the output signal of the limiter amplifier.
a demodulator, a squaring circuit that squares the output signal of the FM demodulator, an addition circuit that adds the output signal of the logarithmic detector and the output signal of the squaring circuit, and a filter that filters the output signal of the addition circuit. 1. A radio wave interference detection device comprising: a bypass filter (HPF) that generates a wave; and a level detector that detects the HPF output signal.