JP3798596B2 - Signal detection device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
Since the present invention performs automatic reception or the like in a wireless communication receiver, it automatically determines the appearance and disappearance of a signal and easily measures the signal level (CN ratio representing the ratio of signal level to noise level). The present invention relates to a signal detection device that displays the information.
[0002]
[Prior art]
Generally, a radio communication receiver has an AGC (automatic gain control) function in order to obtain a wide input signal level range (so-called dynamic range). This AGC function makes the amplitude level constant at the output of the receiver by decreasing the gain for strong input signals and increasing the gain for weak input signals.
[0003]
Specifically, the AGC circuit having the AGC function detects the voltage output from the intermediate frequency amplifier circuit to obtain an AGC voltage corresponding to the input signal level, and uses this AGC voltage as a high frequency or intermediate frequency amplifier circuit. By feedback, the gain of the high frequency or intermediate frequency amplifier circuit is automatically adjusted, and the amplitude level of the output of the receiver is made constant.
[0004]
For this reason, at the output of the receiver, the amplitude level is kept almost constant by the AGC function, even when there is no signal or when there is a signal, so that the signal level changes due to the change in the signal level at the output point of the receiver. It was difficult to determine the appearance or disappearance.
[0005]
For this reason, in general, the AGC voltage that is internal information of the receiver, the squelch signal, and the like are used to determine the appearance or disappearance of the signal and the input level.
[0006]
[Problems to be solved by the invention]
However, since such control signals such as AGC voltage and squelch signal are signals inside the receiver, the control signal may not exist originally, and even if the control signal exists, it cannot be output to the outside. In some cases. Alternatively, interface conditions often do not match, and it has been difficult to determine the appearance of a signal using these.
[0007]
The object of the present invention has been made in view of the above circumstances, and the appearance of a signal or the appearance of a signal based on an intermediate frequency output (hereinafter, abbreviated as IF output) of a wireless communication receiver regardless of the presence or absence of the AGC function. An object of the present invention is to provide a signal detection device that can detect the extinction or the presence / absence and can easily measure the CN ratio of a signal.
[0008]
[Means for Solving the Problems]
In order to achieve the object, the present invention has the following configuration. The signal detection device of the present invention converts an input signal into an intermediate frequency signal and outputs the intermediate frequency signal through an intermediate frequency passband filter, and changes the frequency of the intermediate frequency signal from the receiver. In response, a frequency discriminating means for obtaining a demodulated signal, a fast Fourier transform means for obtaining a fast Fourier transform output by performing a fast Fourier transform process on the demodulated signal from the frequency discriminating means, and a high speed obtained by the fast Fourier transform means The measurement means for measuring the noise level of a specific frequency point group among the noise levels of each frequency in the Fourier transform output, and whether the noise level measured by this measurement means is a positive value or a negative value Signal judging means for judging the appearance or disappearance of the signal.
[0009]
According to the present invention, when the fast Fourier transform means performs a fast Fourier transform process on the demodulated signal from the frequency discrimination means and outputs a fast Fourier transform output, the measuring means obtains the fast Fourier transform obtained by the fast Fourier transform means. The noise level of a specific frequency point group within the noise level of each frequency in the conversion output is measured, and the signal determination unit appears based on whether the noise level measured by the measurement unit is a positive value or a negative value. Or determine disappearance. That is, the appearance or disappearance of a signal can be determined based on the value of the noise level regardless of the presence or absence of the AGC function.
[0010]
In addition, using the noise level of a specific frequency point group within the noise level of each frequency in the output of the fast Fourier transform from the fast Fourier transform means , input by the difference between the noise level at the time of no signal and the noise level of the unmodulated carrier It is characterized by comprising level display means for measuring the intensity of the received signal and displaying the level of the intensity of the input signal. Thereby, the CN ratio of the signal can also be easily measured.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of a signal detection apparatus according to the present invention will be described below.
[0012]
(First embodiment)
The signal detection device can detect the appearance or disappearance of the signal based on the IF output from the receiver or the sound output after product detection, and easily measures the CN ratio of the signal. Note that the IF output or the sound output after detection may be a digital output or an analog output. Here, a case where digital signal processing is performed after converting an analog IF output into a digital signal will be described as a general example.
[0013]
FIG. 1 is a block diagram showing the configuration of the signal detection apparatus according to the first embodiment. The signal detection apparatus shown in FIG. 1 includes a receiver 11, an A / D converter 13, a fast Fourier transform processing unit (hereinafter abbreviated as an FFT processing unit) 15, a level determination unit 17, and a level meter 19. Configured.
[0014]
The receiver 11 generates a local oscillator 111 that generates a local oscillation frequency signal, and a signal input from the antenna 1 by the local oscillation frequency signal from the local oscillator 111 is an intermediate frequency signal (hereinafter abbreviated as an IF signal). The frequency converter 112 to be converted, the IF filter 113 as an intermediate frequency pass band filter for passing only the intermediate frequency band (IF band) to the IF signal from the frequency converter 112, and the IF filter 113 And an IF amplifier 114 for amplifying the IF signal to a predetermined level. The frequency of the intermediate frequency signal is a difference frequency between the frequency of the input signal and the frequency of the local oscillation frequency signal.
[0015]
The A / D converter 13 converts the IF signal from the receiver 11 into a digital signal and outputs the digital IF signal to the FFT processing unit 15. The FFT processing unit 15 performs a fast Fourier transform process on the digital IF signal from the A / D converter 13, and levels the fast Fourier transform output (hereinafter abbreviated as FFT output) obtained by frequency analysis of the digital IF signal. The result is output to the determination unit 17.
[0016]
The level determination unit 17 corresponds to the signal determination unit of the present invention, and determines the appearance or disappearance of the input signal based on the value of each spectrum data in the IF passband in the FFT output from the FFT processing unit 15. The level meter 19 corresponds to the level display means of the present invention, measures the intensity of the input signal based on the value of the spectrum data in the IF passband in the FFT output from the FFT processing unit 15, and receives the input signal Displays the level of intensity.
[0017]
Next, the operation of the signal detection apparatus configured as described above will be described. First, the IF signal from the receiver 11 is converted into a discrete digital signal having a certain sample rate by the A / D converter 13. This digital signal is converted into a digital IF signal that is converted to a sample rate convenient for processing a predetermined bandwidth as required. Here, for example, the IF signal from the receiver 11 is converted into an orthogonal baseband signal.
[0018]
Further, the digital IF signal (orthogonal baseband signal) output from the A / D converter 13 is subjected to FFT processing by the FFT processing unit 15, and spectrum data is obtained at the FFT output.
[0019]
By the way, when spectrum data is observed within a certain band, generally, a modulation signal has a certain signal bandwidth, and therefore, a large level difference (in terms of frequency amplitude characteristics) does not occur within that band. However, the spectrum energy outside the signal band generally decreases rapidly.
[0020]
Further, the frequency characteristics of the IF output or audio output of the receiver 11 are generally determined by the characteristics of the IF filter 114 in the receiver 11. In the no-signal state, noise components (external noise and internal thermal noise) input to the receiver are amplified and output. Generally, the noise components have a flat frequency characteristic. Therefore, a noise spectrum determined by the frequency amplitude characteristic of the IF filter 114 is obtained.
[0021]
For this reason, in the no-signal state, as shown in FIG. 2, when attention is paid to the IF pass band BW1 (frequency f ₁ to frequency f ₂ ) of the IF filter 114, the amplitude characteristic is substantially flat. level difference between the maximum value _{P 1} and the minimum value _{P 2} is small.
[0022]
Next, when a signal having a certain bandwidth is input to the IF filter 114, as shown in FIG. 3, the level P3 and the signal band within the signal band BW2 (frequency f3 to frequency f4) occupied by the signal are shown. There is a large level difference between the level P4 in the IF passband BW1 other than BW2.
[0023]
For this reason, the level determination unit 17 measures, for example, the level difference between the maximum value P3 and the minimum value P4 in the IF passband, determines whether or not the measured level difference is greater than or equal to a certain threshold value, and the difference value Is greater than or equal to the threshold value, it is determined that a signal has appeared, and if the difference value is less than the threshold value, it is determined that the signal has disappeared. That is, the appearance or disappearance of a signal can be determined. Also, the presence or absence of a signal can be determined.
[0024]
Further, the level difference information measured by the level determination unit 17 represents signal intensity information, and this signal intensity information corresponds to the C / N ratio of the signal. For this reason, the level meter 19 displays the level difference information measured by the level determination unit 17 as a level, whereby the C / N ratio of the signal can be measured.
[0025]
Further, the input digital IF signal is subjected to FFT processing at fixed time intervals to obtain each FFT output, signal intensity information in the IF passband at each FFT output is obtained, and an average value of the obtained plurality of signal intensity information is obtained. It is also possible to determine the appearance of a signal using this average value.
[0026]
As described above, according to the signal detection apparatus of the first embodiment, the IF signal from the receiver 11 is subjected to the FFT process, and the signal input based on the value of each spectrum data in the IF passband in the FFT output is obtained. Appearance or disappearance is determined, the intensity of the input signal is measured based on the value of the spectrum data in the IF pass band, and the intensity of the input signal is displayed as a level. Appearance or disappearance can be detected, and the C / N ratio of the signal can be easily measured.
[0027]
In addition, as far as determination of the appearance of a signal is concerned, the signal bandwidth may be narrower or wider than the IF pass bandwidth, and if there is a certain level difference in the spectrum shape within the signal band, the signal appearance Can be detected.
[0028]
(Second Embodiment)
Next, a second embodiment of the signal detection apparatus according to the present invention will be described. FIG. 4 is a block diagram showing the configuration of the signal detection apparatus according to the second embodiment. The signal detection device shown in FIG. 4 is characterized in that a frequency discriminator 21 is added between the A / D converter 13 and the FFT processing unit 15 with respect to the configuration of the signal detection device shown in FIG.
[0029]
The frequency discriminator (discriminator) 21 corresponds to the frequency discriminating means of the present invention, and is FM demodulated by changing the amplitude according to the frequency change of the digital IF signal from the A / D converter 13. A signal (corresponding to the input signal) is output.
[0030]
The FFT processing unit 15 performs fast Fourier transform processing on the FM demodulated signal obtained by the frequency discriminator 21, and outputs an FFT output obtained by frequency analysis of the FM demodulated signal to the level determining unit 17.
[0031]
The level determination unit 17 measures the level in a specific band on the spectrum of the FFT output from the FFT processing unit 15 and determines the appearance or disappearance of the input signal based on the measured level value. The level meter 19 measures the strength of the input signal based on the level value measured by the level determination unit 17 and displays the level of the strength of the input signal.
[0032]
In addition, the other structure of the signal detection apparatus of 2nd Embodiment shown in FIG. 4 is the same structure as the structure of the signal detection apparatus of 1st Embodiment, and attaches | subjects the same code | symbol to the same part And
[0033]
Next, the operation of the signal detection apparatus of the second embodiment configured as described above will be described. First, the frequency discriminator 21 obtains an FM demodulated signal whose amplitude is changed according to the frequency change of the digital IF signal from the A / D converter 13.
[0034]
Next, the FFT processing unit 15 performs FFT processing on the FM demodulated signal from the frequency discriminator 21 to obtain an FFT output. FIG. 5 shows the obtained FFT output, that is, the FM demodulation output noise level for each frequency.
[0035]
In the FM demodulated output, so-called triangular noise in which the nozzle level increases with the frequency according to C / N is obtained when an unmodulated carrier is input. As shown in FIG. 5, in the case of an unmodulated carrier (C / N = 60 dBHz) and an unmodulated carrier (C / N = 80 dBHz), the nozzle level increases with the frequency according to C / N. Recognize. When there is no signal (C / N = 0 dBHz), the noise level can be obtained with a substantially flat frequency characteristic as shown in FIG.
[0036]
Next, the level determination unit 17 measures the level at a specific frequency point group (for example, near DC) in the FFT output obtained by the FFT processing unit 15. For example, by measuring the level N ₁ (about 25 dB) at the frequency f ₀ when no signal, measures the non-modulated carrier (C / N = 60dBHz) at level N ₂ at a frequency _{f 0} (approximately -40 dB), unmodulated carrier When (C / N = 80 dBHz), the level N ₃ (about −60 dB) at the frequency f ₀ is measured. In this case, when the level is a positive value, it can be determined that the signal has appeared, and when the level is a negative value, it can be determined that the signal has disappeared. Therefore, the appearance of a signal can be determined based on the level value.
[0037]
Note that when waiting for a signal of a specific known modulation method, the characteristics of the FM demodulated output can be predicted in advance, and therefore, a method of detecting only the target signal by performing correlation processing with a known pattern or the like with the FFT output is used. May be.
[0038]
It is also possible to obtain a level difference between the average values of each spectrum data of the FFT output and determine the appearance of a signal based on this level difference.
[0039]
Further, the level meter 19 measures the intensity of the input signal based on the level value measured by the level determination unit 17 and displays the intensity of the input signal as a level. This will be described with reference to the example shown in FIG. The level difference between the level N ₁ at the time of no signal (about 25 dB) and the level N ₂ (about −40 dB) of the unmodulated carrier (C / N = 60 dBHz) is 65 dB, which is a substantially C / N ratio. Further, the level difference between the level N ₁ at the time of no signal (about 25 dB) and the level N ₃ (about −60 dB) of the unmodulated carrier (C / N = 80 dBHz) is 85 dB, which is substantially the C / N ratio. Therefore, the C / N ratio can be displayed by displaying the level difference with the level meter 19.
[0040]
In addition, the determination of the appearance of a signal by FFT processing after passing through the frequency discriminator 21 is a concept similar to the noise squelch that has been generally used conventionally, but by using spectrum information of the FFT output. There is a feature that the degree of freedom is increased in that a spectrum used for determination can be selectively selected according to a desired signal.
[0041]
【The invention's effect】
As described above in detail, according to the present invention, it is possible to detect the appearance or disappearance of a signal based on the IF output of a wireless communication receiver regardless of the presence or absence of the AGC function, and to easily measure the CN ratio of the signal. It is possible to provide a signal detection device capable of performing the above.
[Brief description of the drawings]
FIG. 1 is a configuration block diagram of a signal detection apparatus according to a first embodiment.
FIG. 2 is a diagram showing a spectrum when there is no signal.
FIG. 3 is a diagram illustrating a spectrum when a signal is input.
FIG. 4 is a configuration block diagram of a signal detection apparatus according to a second embodiment.
FIG. 5 is a diagram showing an FM demodulated output noise level with respect to frequency when a frequency discriminator is used.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Antenna 11 Receiver 13 A / D converter 15 FFT processing part 17 Level judgment part 19 Level meter 21 Frequency discriminator 111 Local oscillator 112 Frequency converter 113 IF filter 114 IF amplifier

Claims (2)

A receiver that converts an input signal into an intermediate frequency signal and outputs the intermediate frequency signal through an intermediate frequency passband filter;
A frequency discriminating means for obtaining a demodulated signal in accordance with the frequency change of the intermediate frequency signal from the receiver;
Fast Fourier transform means that performs fast Fourier transform processing on the demodulated signal from the frequency discrimination means to obtain a fast Fourier transform output;
Measuring means for measuring the noise level of a specific frequency point group within the noise level of each frequency in the fast Fourier transform output obtained by the fast Fourier transform means;
Signal judging means for judging the appearance or disappearance of the input signal depending on whether the noise level measured by the measuring means is a positive value or a negative value ;
A signal detection apparatus comprising: The difference between the noise level at the time of no signal and the noise level of the non-modulated carrier by using the noise level of a specific frequency point group among the noise levels of each frequency in the output of the fast Fourier transform from the fast Fourier transform means. measuring the intensity of the input signal, the signal detecting apparatus according to claim 1, further comprising a level display means strength for the level display of the input signal.

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