JPH0328101B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a radio wave interference detection method, and more particularly, to a radio wave interference detection method for detecting the amount of radio wave interference using an amplitude component appearing due to radio wave 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 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 (square of the detected voltage) over a minute period through arithmetic processing.At the same time, the detected average power is The power sum of the main wave and the interference wave is determined from the above, and the ratio between the main wave power and the interference power, that is, the amount of radio wave interference, is determined 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, reference numeral D indicates the FM desired wave vector, reference numeral U indicates the FM interference wave vector, and reference numeral R indicates the FM received wave composite vector.

As is clear from Figure 1, when the frequencies of the desired wave D and the interfering wave U are slightly different, the amplitude of the composite wave R changes as quickly as the frequency difference between the desired wave D and the interfering wave U. . That is, the signal is subjected to amplitude modulation, and an amplitude modulation component is generated. Therefore, by measuring the amount of amplitude fluctuation, it is possible to determine the radio wave interference ratio (D/U). FIG. 2 is a diagram showing the relationship between the amplitude fluctuation width and the radio wave interference ratio (D/U).

On the other hand, in an FM receiver, an amplitude component is generated by passing an FM modulated signal due to the FM-AM conversion characteristics of an intermediate frequency filter. In this case, in particular, the passing signal frequency deviates from the center frequency of the intermediate frequency filter, causing FM-AM
The transformation is noticeable.

In other words, to explain in detail, in an FM receiver, the passband characteristic of a frequency band limiting filter consisting of an intermediate frequency filter etc. is not flat, and especially for a filter with a flat delay time characteristic, the passband characteristic is approximately a square characteristic. has. 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 it gives a measurement error.

The present invention has been made to overcome the above-mentioned disadvantages, and the present invention is based on the first radio interference power ratio obtained from the amplitude component assuming that the amplitude component appears only due to radio interference, and the FM-AM obtained from the FM demodulated wave. It is an object of the present invention to provide a radio wave interference detection method that can obtain a radio wave interference power ratio in which an error due to FM modulation is reduced by a difference from a radio wave interference error power ratio due to conversion.

Note that the radio wave interference power ratio herein refers to the ratio of interference wave power to desired wave power.

In order to achieve the above object, the present invention is a radio wave interference detection method that utilizes the appearance of an amplitude component due to radio wave interference in an FM radio, and which detects the amplitude fluctuation component due to radio wave interference and the amplitude fluctuation occurring within the receiver. A first radio interference power ratio determined as the sum of the components is determined, a radio interference error power ratio due to FM-AM conversion generated within the FM radio is determined based on the FM demodulated wave, and a radio interference error power ratio is determined from the first radio interference power ratio. The present invention is characterized in that a value obtained by subtracting the radio wave interference error power ratio is determined and used as the radio wave interference power ratio.

In this way, the radio wave interference error power ratio is subtracted from the first radio wave interference power ratio that includes an error, and the amount of radio wave interference can be detected with high accuracy.

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, and in FIG. 3, reference numeral 10 indicates an FM antenna.
The output side of the FM antenna 10 is connected to an FM receiver 12, particularly to a tuner section. Substantially,
The FM receiver 12 includes a frequency conversion circuit 14 connected to the output side of the antenna 10, an intermediate frequency filter 16 connected to the output side of the frequency conversion circuit 14, and an output side of the filter 16 connected in parallel. limiter amplifier 18 and logarithmic detector 2
0 and an FM demodulator 22.

In this case, the output side of the FM demodulator 22 has FM−
When the AM conversion equivalent circuit 24 is connected, this
The output side of the FM-AM conversion equivalent circuit 24 is connected to a high-pass filter 26. The output side of the high-pass filter 26 is connected to one input terminal of a subtraction circuit 30 via a power detection circuit 28.

Next, the output side of the logarithmic detector 20 is connected to a high-pass filter 32, and the output side is further connected to the other input terminal of the subtraction circuit 30 via a power detection circuit 34.

The apparatus for carrying out the radio wave interference detection method according to the present invention is basically constructed as described above, and its operation and effects will be explained next.

First, 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 supplied to a limiter amplifier 18 via an intermediate frequency filter 16, and is amplified under amplitude limitation. As mentioned above, the intermediate frequency signal amplified with amplitude limitation is supplied to the FM demodulator 22.
Demodulates FM. On the other hand, the intermediate frequency signal that has passed through the intermediate frequency filter 16 is supplied to a logarithmic detector 20 and subjected to logarithmic detection.

The logarithmic detection output from the logarithmic detector 20 is supplied to a power detection circuit (square-law detection circuit) 34 via a high-pass filter 32 to perform square-law detection.

Further, the output of the FM demodulator 22 is supplied to an FM-AM conversion equivalent circuit 24, and a high-pass filter 26
supplied to The output of the high-pass filter 26 is supplied to a power detection circuit (square law detection circuit) 28.
The wave is multiplied. Next, the output of the power detection circuit 34 is supplied to the subtraction circuit 30 and the power detection circuit 28 is output from the power detection circuit 34.
The output of will be subtracted.

Next, the operation of one embodiment of the present invention configured as described above will be explained.

The amplitude characteristic of the intermediate frequency filter 16 described above has an FM conversion characteristic of a square characteristic as indicated by reference numeral a in FIG.
In FIG. 4, the amplitude detection characteristics of
It has the characteristics shown in . Furthermore, the FM demodulator 22 has demodulation characteristics indicated by reference numeral b in FIG.
In FIG. 4, it is indicated by reference numeral d.

Therefore, the waveform of the intermediate frequency signal _n (t) outputted from the frequency conversion circuit 14 now becomes as shown in FIG. , is off by 1KHz. In FIG. 4, an intermediate frequency signal _n (t) having a waveform indicated by reference numeral e is generated by the intermediate frequency filter 16.
The waveform of the converted signal R(t), which is converted by the FM-AM conversion characteristic, is shown in FIG.
It becomes as shown in f. The signal R(t) is subjected to amplitude detection by a logarithmic detector 20, and the waveform of the output signal L(t) of the logarithmic detector 20 is as shown in g in FIG.

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

L(t)=a・R(t)≒−a′ [ _n (t)− ₀ ] ² …
(1) Here, a and a' are positive proportionality constants, and ₀ is the center frequency of the passband of the intermediate frequency filter 16.

On the other hand, the intermediate frequency signal _n (t) hardly changes as a frequency modulated 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. This FM demodulated output AF(t) has a waveform indicated by reference numeral h in FIG. Then, the FM demodulated output AF(t) is converted by an FM-AM conversion equivalent circuit 24. Said FM-
The characteristic of the AM conversion equivalent circuit 24 is a square characteristic,
The output SQ(t) of the FM-AM conversion equivalent circuit 24 is: SQ(t) = b [AF(t)] ² = b'[ _n (t) - ₀ ] ²
...(2), and the waveform becomes as shown in (1) in Fig. 4. Here, b and b' are proportionality constants.

Therefore, assuming a′=b′, let L(t) and SQ(t)
If they are added together, the addition result will be zero, but if a slight phase difference occurs depending on the circuit conditions, complete erasure will not be obtained.

Therefore, as in this example, it is sufficient to set a'=b', perform power detection (square detection) on the alternating current components of L(t) and SQ(t), and obtain the difference. You can get a good amount of erasure.

This will be explained below.

When the desired wave D and the interference wave U are supplied to the antenna 10, D=dsin(ω ₀ t+φd(t)) …(3) U=usin {(ω ₀ +Δω)t+φu(t)} …(4) Here where d and u are proportional constants, and d>u>0 ω ₀ is the desired wave angular frequency Δω is the angular frequency difference between the desired wave and the interference wave φd (t) is the phase modulation signal of the desired wave φu (t) is the interference It is a wave phase modulation signal, and the vector R of the composite wave R is R=D+U=γ(t) sin {ω ₀ (t) + φ(t)}
…(5) Here, r(t)=√ ² + ² +2 {+(
)}
…(6) φ(t)=sin ^-1 usin {Δω(t)+φ _o (t)}/γ
(t) +φd(t)...(7) _φo (t)=φu(t)−φd(t)...(8).

Here, when looking at d》u, r(t)≒d[1+u/dcos {Δωt+φ _o (t)}]
…(9) φ(t)≒u/dsin {Δωt+φ _o (t)}+φd(t)
...(10) Therefore, amplitude fluctuation proportional to u/d and phase modulation interference proportional to u/d occur due to interference.

The input FM signal _o (t) subjected to interference becomes _o (t)=dφ(t)/dt+ ₁ (11).

Here, ₁ is the frequency of the carrier wave.

The input FM signal _o (t) is passed through the intermediate frequency filter 16
Through the FM-AM conversion, a normalized amplitude component of 1-a _o { _o (t)- ₀ } ² (12) is generated. Note that in this case, _ao is a positive proportionality constant. Therefore, the amplitude component
R _o (t) is R _o (t)≒d[1+u/dcos {Δωt+φ _o (t)}−a
_o { _o (t) − ₀ } ² ] …(13).

As a result, the logarithmic detection output L _o (t) obtained by detecting the amplitude fluctuation component R o (t) by the logarithmic detector 20 is as follows: L _o (t)≒k[u/dcos {Δωt+φ _{o (} t)} −a _o [{ _o (t) − ₀ } ² − c]] (14) is obtained.

Here, c={ _o ()- ₀ } ² , and k is a positive proportionality constant.

The intermediate frequency signal _o (t) is passed through the intermediate frequency filter 1
6. FM demodulator 22 via limiter amplifier 18
FM demodulation is performed to obtain an FM demodulated wave AF _o (t).

On the other hand, from the logarithmic detection output L _o (t), low frequency components due to fading are removed by the high pass filter 32, and interference and
Ripple power detection is performed by FM-AM conversion, and the output P _o is: P _o = _o () ² ≒ k ² [u ² /2d ² + a _o ² [{ _o () − ₀ } ⁴ − c ² 〕】…(
15) is obtained.

Furthermore, the FM demodulated wave is applied to the FM-AM equivalent circuit 24, the high-pass filter 26 removes the DC component, and the power detection circuit 28 performs power detection, and the output P _c is P _c = b "[{ _o () - ₀ } ² - c] ² = b" [{ _o (t) - ₀ } ⁴ - c ² ]...(16) is obtained. Here, b″ is a positive proportionality constant.

The output P _c of the power detection circuit 28 is subtracted from the output P _o of the power detection circuit 34 by the subtraction circuit 30, and the interference amount detection voltage output is obtained from the following equation. That is, P _o −P _c ≒ku ² /2d ₂ =k/2(u/d) ₂ (17) where b″=k ² a _o ² .

As is clear from equation (17) above, the interference amount detection voltage output is a voltage proportional to the square of u/d, so it is easy to determine the amount of radio wave interference from this, and the amount of interference is determined by FM modulation. Errors due to the signal have been removed.

Figure 5 shows the relationship between the radio wave interference ratio (D/U) and the interference detection voltage when using the method of the present invention.
It shows the relationship between the change in the amount of FM modulation and the change in the case where the present invention is not used and the actually measured value.

When the method of the present invention is not used, the FM modulation changes from no modulation to maximum modulation (±2.5 kHz deviation), so in FIG. 5, the range B indicated by the downward diagonal line is varied. On the other hand, in the case of the method of the present invention, the fluctuation is about the range A indicated by the diagonal line upward to the right in FIG. 5, and the detection accuracy of the amount of radio wave interference is improved.

In addition, as mentioned above, in the present invention, the logarithmic detection output and
The logarithmic detection output and
It is also possible to sample the FM demodulated output synchronously or asynchronously and calculate the amount of interference by digital calculation processing using a microprocessor or the like.

As explained above, according to the present invention, in a radio wave interference detection method that utilizes the fact that an amplified component appears due to radio wave interference, the FM generated in an FM radio is determined from the first radio wave interference power ratio obtained from the amplitude component.
-The error caused by AM conversion is calculated from the FM demodulated wave as a radio wave interference error power ratio and is subtracted. Therefore,
Errors caused by the FM modulation signal can be removed, and the amount of radio wave interference can be detected with higher accuracy.

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 the drawing]

Fig. 1 is an explanatory diagram of 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 block diagram showing the configuration of an embodiment of the present invention. , FIG. 4, and FIG. 5 are waveform charts and diagrams 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...FM-AM conversion equivalent circuit, 2
6...High pass filter, 28...Power detection circuit, 3
0... Subtraction circuit, 32... High pass filter, 34...
Power detection circuit.

Claims (1)

[Claims] 1 A radio wave interference detection method that utilizes the fact that an amplitude component appears due to radio wave interference in an FM radio, and the first radio wave interference power is determined as the sum of the amplitude fluctuation component due to radio wave interference and the amplitude fluctuation component generated within the receiver. Find the ratio and calculate the above based on the FM demodulated wave.
A radio wave interference error power ratio due to FM-AM conversion generated within an FM radio device is determined, and a value obtained by subtracting the radio wave interference error power ratio from the first radio wave interference power ratio is determined to be the radio wave interference power ratio. Radio wave interference detection method.