CN110943952B - Method and device for detecting amplitude modulation signal - Google Patents
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Abstract
The disclosure provides a method and a device for detecting an amplitude modulation signal, and belongs to the field of signal detection. The method comprises the following steps: sampling a signal to be detected in a current sampling period to obtain sampling data, wherein the sampling data comprises N sampling points; performing Discrete Fast Fourier Transform (DFFT) on the sampling data to obtain a first sequence X (k); determining the offset of the frequency of the signal to be detected to the Fourier reference frequency based on the first sequence; correcting the sampling data based on the offset to obtain a second sequence; determining the signal-to-noise ratio of the signal to be detected based on the second sequence; and determining whether the signal to be detected in the current sampling period is an amplitude-modulated signal or not based on the signal-to-noise ratio. The method and the device can improve the accuracy of amplitude modulation signal detection.
Description
Technical Field
The present disclosure relates to the field of signal detection, and in particular, to a method and an apparatus for detecting an amplitude-modulated signal.
Background
Amplitude modulation is a modulation method in which the amplitude of a carrier wave is changed according to the change law of a desired transmission signal, but the frequency is kept constant. The amplitude-modulated carrier signal is an amplitude-modulated signal.
When the amplitude modulation signal is received, the amplitude modulation signal needs to be detected. In the related art, a method for detecting an amplitude-modulated signal includes: converting a signal to be detected from a time domain to a frequency domain through Fourier transform, calculating the signal-to-noise ratio of the signal to be detected based on the signal to be detected in the frequency domain, and detecting whether the signal to be detected is an amplitude-modulated signal based on the signal-to-noise ratio.
In implementing the present disclosure, the inventors found that the related art has at least the following problems: when the frequency of the amplitude-modulated signal shifts the Fourier reference frequency, the signal-to-noise ratio obtained by calculation is inaccurate, and the detection accuracy is reduced.
Disclosure of Invention
The embodiment of the disclosure provides a method and a device for detecting an amplitude modulation signal, which can improve the accuracy of detection. The technical scheme is as follows:
in one aspect, a method for detecting an amplitude-modulated signal is provided, where the method includes:
sampling a signal to be detected in a current sampling period to obtain sampling data, wherein the sampling data comprises N sampling points;
performing Discrete Fast Fourier Transform (DFFT) on the sampling data to obtain a first sequence X (k);
determining the offset of the frequency of the signal to be detected to the Fourier reference frequency based on the first sequence;
correcting the sampling data based on the offset to obtain a second sequence;
determining the signal-to-noise ratio of the signal to be detected based on the second sequence;
and determining whether the signal to be detected in the current sampling period is an amplitude-modulated signal or not based on the signal-to-noise ratio.
Illustratively, the determining an offset between the frequency of the signal under test and a fourier frequency based on the first sequence includes:
determining a maximum-sequence value in the first sequence and two sequence values adjacent to the maximum-sequence value;
and determining the offset of the frequency of the signal to be detected to the Fourier reference frequency based on the maximum sequence value and two sequence values adjacent to the maximum sequence value.
Illustratively, determining an offset of the frequency of the signal under test from a fourier reference frequency based on the maximum-sequence value and two sequence values adjacent to the maximum-sequence value comprises:
the offset of the frequency of the signal under test to the fourier reference frequency is calculated according to the following formula,
wherein the number of DFFT conversion points is m, 2 m N, m is greater than or equal to k is greater than or equal to 1, Δ f is the offset, f s For the sampling frequency, X (k) max ) Is the maximum sequence value of the first sequence, X (k) max +1) and X (k) max -1) are sequence values adjacent to the maximum sequence value in the first sequence, respectively, real is a complex number real calculation.
Illustratively, the correcting the sample data based on the offset to obtain a second sequence includes:
the sampled data is corrected according to the following formula,
wherein, x (t) is the sampling data, x' (t) is the second sequence, e is a natural constant, j is an imaginary unit, and t has a value range of 1-N.
Illustratively, the determining the signal-to-noise ratio of the signal to be measured based on the second sequence includes:
performing DFFT on the second sequence to obtain a third sequence;
determining a maximum sequence value for the third sequence;
and determining the signal-to-noise ratio of the signal to be detected based on the maximum sequence value in the third sequence.
Illustratively, the determining whether the signal to be measured in the current sampling period is an amplitude-modulated signal based on the signal-to-noise ratio includes:
when the signal-to-noise ratio is larger than a first threshold value, determining that the signal to be detected in the current sampling period is an amplitude-modulated signal;
when the signal-to-noise ratio is smaller than a second threshold value, determining that the signal to be detected in the current sampling period is not an amplitude-modulated signal, wherein the first threshold value is larger than the second threshold value;
when the signal-to-noise ratio is between the first threshold and the second threshold, determining whether the signal to be measured sampled in the last sampling period is an amplitude-modulated signal,
and when the signal to be detected sampled in the last sampling period is not the amplitude modulation signal, determining that the signal to be detected in the current sampling period is not the amplitude modulation signal.
In another aspect, there is provided an apparatus for detecting an amplitude-modulated signal, including:
the sampling module is used for sampling a signal to be detected in the current sampling period to obtain sampling data, and the sampling data comprises N sampling points;
a transformation module, configured to perform DFFT on the sample data to obtain a first sequence x (k);
a first determining module, configured to determine, based on the first sequence, an offset of a frequency of the signal to be measured to a fourier reference frequency;
the correction module is used for correcting the sampling data based on the offset to obtain a second sequence;
a second determining module, configured to determine a signal-to-noise ratio of the signal to be detected based on the second sequence;
and the third determining module is used for determining whether the signal to be detected in the current sampling period is an amplitude-modulated signal or not based on the signal-to-noise ratio.
Illustratively, the first determining module is configured to,
determining a maximum-sequence value in the first sequence and two sequence values adjacent to the maximum-sequence value;
and determining the offset of the frequency of the signal to be detected to the Fourier reference frequency based on the maximum sequence value and two sequence values adjacent to the maximum sequence value.
Illustratively, the first determining module is configured to,
the offset of the frequency of the signal under test to the fourier reference frequency is calculated according to the following formula,
where Δ f is the offset, f s For the sampling frequency, X (k) max ) Is the maximum sequence value, X (k) max +1) and X (k) max -1) two sequence values adjacent to the maximum sequence value, respectively, real being a complex real part operation.
Illustratively, the correction module is configured to,
the sampled data is corrected according to the following formula,
wherein the number of transform points of the DFFT is m, 2 m N, m is more than or equal to k is more than or equal to 1, x (t) is the sampling data, x' (t) is the second sequence, e is a natural constant, j is an imaginary unit, and t has a value range of 1-N.
The technical scheme provided by the embodiment of the disclosure has the following beneficial effects: carrying out Fourier transformation on the sampling data of the signal to be detected, estimating the offset of the frequency of the signal to be detected to the Fourier reference frequency, correcting the sampling data of the signal to be detected based on the offset to eliminate the offset to obtain a de-frequency offset signal, estimating the signal-to-noise ratio of the de-frequency offset signal, and finally detecting whether an amplitude modulation signal exists based on the signal-to-noise ratio; because the signal-to-noise ratio is obtained based on the de-frequency offset signal, the accuracy of the signal-to-noise ratio is higher, the accuracy of the final detection result is higher, and a better detection result can be obtained under the condition of low signal-to-noise ratio.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present disclosure, and it is obvious for those skilled in the art to obtain other drawings based on the drawings without creative efforts.
Fig. 1 is a flowchart of a method for detecting an amplitude-modulated signal according to an embodiment of the present disclosure;
FIG. 2 is a graph comparing the results of an un-de-frequency Fourier transform and a de-frequency Fourier transform provided by embodiments of the present disclosure;
FIG. 3 is a statistical graph of signal-to-noise ratio estimates for undeviated signals provided by embodiments of the present disclosure;
FIG. 4 is a signal-to-noise ratio estimation statistical graph of a de-frequency offset signal provided by an embodiment of the disclosure;
fig. 5 is a block diagram of a detection apparatus for an amplitude-modulated signal according to an embodiment of the present disclosure.
Detailed Description
To make the objects, technical solutions and advantages of the present disclosure more apparent, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings.
Fig. 1 is a flowchart of a method for detecting an amplitude-modulated signal according to an embodiment of the disclosure. Referring to fig. 1, the flow of the method for detecting an amplitude-modulated signal includes the following steps.
The number of transform points of DFFT can be m, 2 m More than N, m is more than or equal to k and more than or equal to 1. Preferably, m may satisfy 2 m Minimum value of N.
And 103, determining the offset of the frequency of the signal to be measured to the Fourier reference frequency based on the first sequence.
The first sequence is the estimated frequency spectrum of the signal under test, and the fourier reference frequency refers to the frequency resolution of the DFFT.
And step 104, correcting the sampling data based on the offset to obtain a second sequence.
And 105, determining the signal-to-noise ratio of the signal to be detected based on the second sequence.
And step 106, determining whether the signal to be detected in the current sampling period is an amplitude-modulated signal or not based on the signal-to-noise ratio.
In the embodiment of the disclosure, the Fourier transform is performed on the sampling data of the signal to be detected, the offset of the frequency of the signal to be detected to the Fourier reference frequency is estimated, then the sampling data of the signal to be detected is corrected based on the offset to eliminate the offset, a frequency offset removal signal is obtained, then the signal-to-noise ratio of the frequency offset removal signal is estimated, and finally whether an amplitude modulation signal exists is detected based on the signal-to-noise ratio; because the signal-to-noise ratio is obtained based on the de-frequency offset signal, the accuracy of the signal-to-noise ratio is higher, the accuracy of the final detection result is higher, a better detection result can be obtained under the condition of low signal-to-noise ratio, and in addition, the complexity of the whole calculation process is lower, and the method is easy to realize.
In an exemplary scenario, the signal to be detected is a broadcast signal sent by a sending end, and a receiving end collects the broadcast signal in real time and detects whether the broadcast signal is an amplitude-modulated signal. The transmitting end includes but is not limited to a broadcast station, and the receiving end may include but is not limited to a radio, and the above steps are described in detail below with reference to the exemplary scenario.
In step 101, the receiving end buffers the received broadcast signal and periodically processes the buffered data according to a fixed length. The fixed length may include 2048(N) samples of data (sample points).
Step 102-step 103 enable the estimation of the carrier frequency offset.
In step 102, DFFT is performed on 2048 sample data or m consecutive sample points in 2048 sample data, and the transform result is a first sequence x (k), as shown by line a in fig. 2. When the transform point number of DFFT is 2048, the first sequence x (k) also includes 2048 points.
Step 103 may include the following steps.
Step 103a, the maximum sequence value in the first sequence and two sequence values adjacent to the maximum sequence value are determined.
And 103b, determining the offset of the frequency of the signal to be detected to the Fourier reference frequency based on the maximum sequence value and two sequence values adjacent to the maximum sequence value.
In step 103b, the offset of the frequency of the signal to be measured from the fourier reference frequency can be calculated according to the following formula (1).
Where Δ f is the offset, f s For the sampling frequency, X (k) max ) Is the maximum sequence value in the first sequence, X (k) max +1) and X (k) max -1) are sequence values adjacent to the maximum sequence value in the first sequence, respectively, real is a complex number real calculation.
Step 104 achieves a de-skewing of the carrier frequency. In step 104, the sample data may be corrected according to the following formula (2).
Wherein x (t) is sampling data, x' (t) is a second sequence, e is a natural constant, j is an imaginary unit, and t is a value range of 1-2048 (N).
In step 104, 2048 sampling points in the sampling data are updated by formula (2), so as to obtain 2048 sampling point correction values after frequency offset removal, and a second sequence is formed.
Step 105 achieves the signal-to-noise ratio estimation. Step 105 may include the following steps.
And 105a, performing DFFT on the second sequence to obtain a third sequence.
Illustratively, the number of transform points for DFFT may be m.
The 2048 sample point correction values in the second sequence obtained above are subjected to fourier transform, and the transform result is a third sequence, as shown by line B in fig. 2.
And 105b, determining the maximum sequence value in the third sequence.
And 105c, determining the Signal-to-Noise Ratio (SNR) of the Signal to be detected based on the maximum sequence value in the third sequence.
In step 105b, the SNR of the signal to be measured can be determined according to the following formula (3).
Wherein X '(t) is a third sequence, X' (t) max ) Is the maximum sequence value in X' (t).
Step 106 enables detection of amplitude modulated signals. In the related art, after the signal-to-noise ratio is determined, the presence of the amplitude modulated signal is typically obtained by comparing the signal-to-noise ratio with a threshold value. The signal-to-noise ratio is compared with a single threshold value, and the situation that random jump is unstable can occur in a judgment result under a critical condition. In order to solve the problem, the embodiment of the present disclosure sets two threshold values, and performs detection on the amplitude modulation signal of the current period by combining the determination result of the previous period. Illustratively, step 106 may include the following steps.
Step 106a, comparing the signal-to-noise ratio with a first threshold value and comparing the signal-to-noise ratio with a second threshold value.
And step 106b, determining whether the signal to be detected in the current sampling period is an amplitude-modulated signal or not based on the comparison result.
In step 106b, when the signal-to-noise ratio is greater than the first threshold, determining that the signal to be detected in the current sampling period is an amplitude-modulated signal; and when the signal-to-noise ratio is smaller than a second threshold value, determining that the signal to be detected in the current sampling period is not an amplitude-modulated signal, wherein the first threshold value is larger than the second threshold value. When the signal-to-noise ratio is between the first threshold and the second threshold, determining whether the signal to be detected sampled in the last sampling period is an amplitude modulation signal, when the signal to be detected sampled in the last sampling period is the amplitude modulation signal, determining that the signal to be detected in the current sampling period is the amplitude modulation signal, and when the signal to be detected sampled in the last sampling period is not the amplitude modulation signal, determining that the signal to be detected in the current sampling period is not the amplitude modulation signal. Wherein the initial time (first sampling period) considers that the last period has no amplitude modulation signal.
In step 106, the obtained signal-to-noise ratio is input into a hysteresis comparator to judge the current state of the signal to be measured. A first threshold value and a second threshold value are set in the hysteresis comparator. Illustratively, the first threshold may be-3 and the second threshold may be-6. Referring to table 1 below, it is assumed that the signal-to-noise ratio is less than-6, the amplitude modulation signal does not exist, if the signal-to-noise ratio is greater than-3, the amplitude modulation signal exists, and if the signal-to-noise ratio is between-6 and-3, whether the amplitude modulation signal exists according to the state of the last sampling period is determined. During the initial first sampling period, the last sampling period may be considered to be free of amplitude modulated signals.
TABLE 1
When the signal-to-noise ratio of the amplitude-modulated signal carrier is in a critical interval of-6 to-3 dB, the hysteresis comparator can obviously improve the stability of a judgment result.
In the next sampling period of the current period, the above step 101-106 is repeated, so as to complete the monitoring and determination of the continuous amplitude modulation signal.
In this embodiment, a simulation tool is used to simulate the performance of the method provided by the embodiment of the present disclosure, in a-3 dB gaussian white noise channel, a signal of 132.8Hz is sampled with a sampling frequency of 6K, a signal-to-noise ratio of the sampled result is calculated after 2048-point DFFT is performed, 500 times of signal-to-noise ratio estimation calculation are performed, and the direct estimation of the signal-to-noise ratio and the estimation statistics after frequency offset removal are respectively shown in fig. 3 and fig. 4. It can be seen that the snr estimation without removing the frequency offset in fig. 3 is about-5.42 dB, which is far from the actual situation, and the snr estimation after removing the frequency offset in fig. 4 is about-3 dB, which is in line with the actual situation. Therefore, the de-frequency deviation obviously improves the estimation precision of the signal-to-noise ratio.
Fig. 5 is a block diagram of a detection apparatus for an amplitude-modulated signal according to an embodiment of the present disclosure. Referring to fig. 5, the apparatus 50 for detecting an amplitude-modulated signal includes: a sampling module 501, a transformation module 502, a first determination module 503, a correction module 504, a second determination module 505, and a third determination module 506.
The sampling module 501 is configured to sample a signal to be detected in a current sampling period to obtain sampling data, where the sampling data includes N sampling points.
A transform module 502, configured to perform DFFT on the sampled data to obtain a first sequence x (k).
A first determining module 503, configured to determine, based on the first sequence, an offset of the frequency of the signal to be measured from the fourier reference frequency.
And a correcting module 504, configured to correct the sample data based on the offset to obtain a second sequence.
And a second determining module 505, configured to determine a signal-to-noise ratio of the signal to be measured based on the second sequence.
A third determining module 506, configured to determine whether the signal to be measured in the current sampling period is an amplitude-modulated signal based on the signal-to-noise ratio.
The number of transform points of DFFT is m, 2 m ＞N，m≥k≥1。
Illustratively, the first determining module 503 is configured to determine a maximum-sequence value in the first sequence, and two sequence values adjacent to the maximum-sequence value; and determining the offset of the frequency of the signal to be detected to the Fourier reference frequency based on the maximum sequence value and two sequence values adjacent to the maximum sequence value.
Illustratively, the first determining module 503 is configured to calculate an offset of the frequency of the signal to be measured from the fourier reference frequency according to the foregoing formula (1).
Illustratively, the correction module 504 is configured to correct the sampled data according to the foregoing formula (2).
The apparatus for detecting an amplitude-modulated signal may be applied to a receiving end (e.g., a receiving end receiving a broadcast signal), and in terms of hardware implementation, the apparatus for detecting an amplitude-modulated signal may be implemented by a computing device including a processor and a memory.
In the embodiment of the disclosure, the Fourier transform is performed on the sampling data of the signal to be detected, the offset of the frequency of the signal to be detected to the Fourier reference frequency is estimated, then the sampling data of the signal to be detected is corrected based on the offset to eliminate the offset, a frequency offset removal signal is obtained, then the signal-to-noise ratio of the frequency offset removal signal is estimated, and finally whether an amplitude modulation signal exists is detected based on the signal-to-noise ratio; because the signal-to-noise ratio is obtained based on the de-frequency offset signal, the accuracy of the signal-to-noise ratio is higher, the accuracy of the final detection result is higher, a better detection result can be obtained under the condition of low signal-to-noise ratio, and in addition, the complexity of the whole calculation process is lower, and the method is easy to realize.
It should be noted that: in the foregoing embodiment, when detecting an amplitude-modulated signal, the apparatus for detecting an amplitude-modulated signal provided in the foregoing embodiment is only illustrated by dividing the functional modules, and in practical applications, the functions may be distributed by different functional modules according to needs, that is, the internal structure of the apparatus is divided into different functional modules to complete all or part of the functions described above. In addition, the detection apparatus for amplitude-modulated signals and the detection method for amplitude-modulated signals provided by the above embodiments belong to the same concept, and specific implementation processes thereof are detailed in the method embodiments and are not described herein again.
It will be understood by those skilled in the art that all or part of the steps for implementing the above embodiments may be implemented by hardware, or may be implemented by a program instructing relevant hardware, where the program may be stored in a computer-readable storage medium, and the above-mentioned storage medium may be a read-only memory, a magnetic disk or an optical disk, etc.
The above description is intended to be exemplary only and not to limit the present disclosure, and any modification, equivalent replacement, or improvement made without departing from the spirit and scope of the present disclosure is to be considered as the same as the present disclosure.
Claims (8)
1. A method for detecting an amplitude modulated signal, the method comprising:
sampling a signal to be detected in a current sampling period to obtain sampling data, wherein the sampling data comprises N sampling points;
for the sampling dataPerforming Discrete Fast Fourier Transform (DFFT) to obtain a first sequence
；
Determining the offset of the frequency of the signal to be measured to the Fourier reference frequency based on the first sequence;
correcting the sampling data based on the offset to obtain a second sequence;
performing DFFT on the second sequence to obtain a third sequence;
determining a maximum sequence value in the third sequence;
determining the signal-to-noise ratio of the signal to be detected based on the maximum sequence value in the third sequence;
when the signal-to-noise ratio is larger than a first threshold value, determining that the signal to be detected in the current sampling period is an amplitude-modulated signal;
when the signal-to-noise ratio is smaller than a second threshold value, determining that the signal to be detected in the current sampling period is not an amplitude-modulated signal, wherein the first threshold value is larger than the second threshold value;
when the signal-to-noise ratio is between the first threshold and the second threshold, determining whether the signal to be measured sampled in the last sampling period is an amplitude-modulated signal,
and when the signal to be detected sampled in the last sampling period is not the amplitude modulation signal, determining that the signal to be detected in the current sampling period is not the amplitude modulation signal.
2. The method according to claim 1, wherein said determining an offset of a frequency of said signal under test from a fourier reference frequency based on said first sequence comprises:
determining a maximum-sequence value in the first sequence, and two sequence values adjacent to the maximum-sequence value;
and determining the offset of the frequency of the signal to be detected to the Fourier reference frequency based on the maximum sequence value and two sequence values adjacent to the maximum sequence value.
3. The method according to claim 2, wherein said determining the offset of the frequency of the signal under test from the fourier reference frequency based on the maximum sequence value and two sequence values adjacent to the maximum sequence value comprises:
the offset of the frequency of the signal under test to the fourier reference frequency is calculated according to the following formula,
wherein the number of transform points of the DFFT is m,
，
Δ f is the offset, f s For the sampling frequency, X (k) max ) Is the maximum sequence value in the first sequence, X (k) max +1) and X (k) max -1) respectively sequence values adjacent to said maximum sequence value in said first sequence, real being a complex real part operation.
4. The method according to claim 3, wherein said correcting said sampled data based on said offset to obtain a second sequence comprises:
the sampled data is corrected according to the following formula,
wherein the content of the first and second substances,
for the purpose of the sampling data, it is,
and e is a natural constant, j is an imaginary number unit, and the value range of t is 1-N.
5. An apparatus for detecting an amplitude-modulated signal, comprising:
the sampling module is used for sampling a signal to be detected in the current sampling period to obtain sampling data, and the sampling data comprises N sampling points;
a transformation module for performing DFFT on the sampled data to obtain a first sequence
；
A first determining module, configured to determine, based on the first sequence, an offset of a frequency of the signal to be measured to a fourier reference frequency;
the correction module is used for correcting the sampling data based on the offset to obtain a second sequence;
a second determining module, configured to determine a signal-to-noise ratio of the signal to be detected based on the second sequence;
the third determining module is used for determining whether the signal to be detected in the current sampling period is an amplitude-modulated signal or not based on the signal-to-noise ratio;
the determining the signal-to-noise ratio of the signal to be detected based on the second sequence comprises:
performing DFFT on the second sequence to obtain a third sequence;
determining a maximum sequence value in the third sequence;
determining the signal-to-noise ratio of the signal to be detected based on the maximum sequence value in the third sequence;
the determining whether the signal to be detected in the current sampling period is an amplitude-modulated signal based on the signal-to-noise ratio includes:
when the signal-to-noise ratio is larger than a first threshold value, determining that the signal to be detected in the current sampling period is an amplitude-modulated signal;
when the signal-to-noise ratio is smaller than a second threshold value, determining that the signal to be detected in the current sampling period is not an amplitude-modulated signal, wherein the first threshold value is larger than the second threshold value;
when the signal-to-noise ratio is between the first threshold and the second threshold, determining whether the signal to be measured sampled in the last sampling period is an amplitude-modulated signal,
and when the signal to be detected sampled in the last sampling period is not the amplitude modulation signal, determining that the signal to be detected in the current sampling period is not the amplitude modulation signal.
6. The apparatus for detecting an amplitude modulated signal as claimed in claim 5, wherein the first determining module is configured to,
determining a maximum-sequence value in the first sequence and two sequence values adjacent to the maximum-sequence value;
and determining the offset of the frequency of the signal to be detected to the Fourier reference frequency based on the maximum sequence value and two sequence values adjacent to the maximum sequence value.
7. The apparatus for detecting an amplitude modulated signal as claimed in claim 6, wherein the first determining module is configured to,
the offset of the frequency of the signal under test to the fourier reference frequency is calculated according to the following formula,
wherein the number of transform points of the DFFT is m,
，
Δ f is the offset, f s For the sampling frequency, X (k) max ) Is the maximum sequence value of the first sequence, X (k) max +1) and X (k) max -1) are respectively the sequence values of the first sequence adjacent to the maximum sequence value, real is a complex number real calculation.
8. The apparatus for detecting an amplitude modulated signal as claimed in claim 7, wherein the correction module is configured to,
the sampled data is corrected according to the following formula,
wherein the content of the first and second substances,
for the purpose of the sampling data, it is,
and e is a natural constant, j is an imaginary number unit, and the value range of t is 1-N.
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