CN113965224A - DFT signal detection method suitable for frequency hopping system - Google Patents
DFT signal detection method suitable for frequency hopping system Download PDFInfo
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Abstract
The invention discloses a DFT signal detection method suitable for a frequency hopping system, and relates to the field of satellite communication signal detection. The invention finds out the difference between the existing signal and the non-signal by taking measures such as DFT operation, sub-band segmentation, power calculation, sequencing and the like on the frequency hopping signal in a certain bandwidth, judges whether the signal-to-noise ratio of the received signal is greater than a fixed threshold or not by calculating the signal-to-noise ratio, and finally realizes the signal detection function of the frequency hopping system. The method has the survivability and robustness of the frequency hopping system, and is suitable for signal detection of the frequency hopping communication system.
Description
Technical Field
The invention relates to the field of satellite communication, in particular to a DFT signal detection method suitable for a frequency hopping system.
Background
In satellite communication, signal detection is an important technique for determining the presence or absence of a signal. The research of the frequency hopping signal detection technology is developed internationally, and the main methods include an autocorrelation detection method, an energy detection method, a maximum likelihood detection method and the like, which all need to know one or more signal parameters in advance and cannot realize blind detection.
The domestic scholars have also made research on this direction. Some algorithm preprocessing processes are large in calculation amount, and some algorithms need prior information such as signal characteristic parameters and communication environments. In some algorithms, detection is realized by means of time-frequency analysis, but the setting of the threshold value is not easy to select, and the setting size of the threshold directly influences the detection result.
Disclosure of Invention
In view of the above-mentioned drawbacks in the background art, the present invention provides a DFT signal detection method suitable for a frequency hopping system, which is a signal detection method capable of operating before frequency hopping synchronization.
The purpose of the invention is realized as follows:
a DFT signal detection method suitable for a frequency hopping system comprises the following steps:
(1) receiving an AD signal and carrying out frequency conversion to a zero intermediate frequency signal;
(2) sampling zero intermediate frequency signals at a sampling rate fs1To detect bandwidth Bdetec2 times of the sequence, and the sequence after sampling is y (n);
(3) carrying out N-point discrete Fourier transform on the sampled sequence y (N) to obtain a frequency spectrum Y (k); n is the integral multiple of the number of sampling points of each jump;
(4) dividing the frequency spectrum after discrete Fourier transform into M sub-bands, wherein each sub-band has a bandwidth of (f)s1/M)Hz；
(5) Calculating power P of each sub-band1、P2、...Pi，…PMAnd sorting according to the sequence of the power from large to small;
(6) taking the maximum power value as the signal power and storing;
(7) removing the maximum part of power, removing the minimum part of power, averaging the residual middle section signal power to be used as the bottom noise power, and storing;
(8) repeating the steps (1) to (7) Z times, sorting the stored Z signal powers from large to small, and taking the average value of the first 10% power values as the final estimated value P of the signal powers(ii) a Averaging the stored Z background noise powers to obtain a final background noise estimated value N0(ii) a Calculating Ps/N0；
(9) Calculating P when the input signal is pure noise according to the modes of the steps (1) to (8)sIs denoted by Psn；
(10) Will Psn/N0As a threshold, if Ps/N0>Psn/N0If so, the signal is judged to be present,otherwise, the signal is judged to be no signal.
Further, in the step (1), the frequency conversion is a zero intermediate frequency signal, which means that any section of fixed frequency in the whole frequency hopping bandwidth is selected, and the frequency conversion is performed by taking a central frequency point of the section of frequency as a reference; and obtaining a signal after frequency conversion, namely the zero intermediate frequency signal.
Further, in step (4), the bandwidth of the subband is the lowest symbol rate RminI.e. M ═ fs1/Rmin。
Further, the number of times of repetition Z in step (8) is according to the frequency hopping bandwidth BhAnd a sampling rate fs1To determine that the value of Z satisfies Z fs1/Bh>100。
Compared with the background technology, the invention has the following advantages:
1. the invention is very suitable for signal detection of a frequency hopping system, and does not need to carry out frequency hopping synchronization in advance. Compared with other signal detection methods which require working at fixed frequency points, the method is not influenced by the change of frequency hopping frequency points.
2. The invention can adapt to the detection of mixed signals with various rates and can work under the condition of low signal-to-noise ratio.
3. The DFT (discrete Fourier transform) method and the power statistical method adopted by the invention are suitable for FPGA realization and convenient for engineering application.
Drawings
FIG. 1 is a flow chart of the method of the present invention.
Detailed Description
The invention is described in further detail below with reference to the figures and the detailed description.
A DFT signal detection method suitable for a frequency hopping system comprises the following steps:
(1) receiving an AD signal and carrying out frequency conversion to a zero intermediate frequency signal; the frequency conversion is a zero intermediate frequency signal, which means that any section of fixed frequency in the whole frequency hopping bandwidth is selected, the frequency conversion is carried out by taking the central frequency point of the section of frequency as a reference, and the signal obtained after the frequency conversion is the zero intermediate frequency signal.
(2) Sampling zero IF signal (where "signal" may be noise only) and samplingSample rate fs1And detection bandwidth Bdetec2 times equal, and the sampled sequence is represented by y (n);
(3) carrying out N-point DFT on the sampled sequence y (N) to obtain a frequency spectrum Y (k); the value of N can be determined according to the number of sampling points of each jump, and the value of N is generally integral multiple of the number of sampling points of each jump;
(4) dividing the frequency spectrum after DFT into M sub-bands, wherein each sub-band has a bandwidth of (f)s1/M) Hz; wherein the bandwidth of the sub-band can be based on the lowest symbol rate RminAlternatively, they may be equal to each other. Thus, the value of M is then equal to the sampling rate fs1And RminThe ratio of (a) to (b).
(5) Calculating power P of each sub-band1、P2、…Pi，…PMAnd sorting according to the sequence of the power from large to small;
(6) taking the maximum power value as the signal power and storing;
(7) and removing the maximum part of power, removing the minimum part of power, averaging the residual intermediate section signal power, taking the average as the background noise power, and storing. Generally, the middle section with more stable power after sorting is selected, that is, the average value of a plurality of sub-bands with the centered power is taken as the background noise power.
(8) Repeating the steps (1) to (7) Z times, sorting the stored Z signal powers from large to small, and taking the average value of the first k power values as a final signal power estimated value Ps(ii) a Averaging the stored Z background noise powers to obtain a final background noise estimated value N0(ii) a Calculating Ps/N0。
Wherein, the value of the repetition times Z generally needs to be according to the frequency hopping bandwidth BhAnd a sampling rate fs1To meet the random distribution of frequency hopping points, the repetition times Z should be large enough, generally Z fs1/BhThe value of (A) is greater than 100.
(9) Calculating P when the input signal is pure noise according to the modes of the steps (1) to (8)sIs denoted by Psn；
(10) Will Psn/N0As a reference value (P)sn/N0Substantially constant, obtainable by simulation), Psn/N0I.e. a threshold, if Ps/N0>Psn/N0If not, the signal is judged to be present, otherwise, the signal is judged to be absent.
The DFT signal detection method suitable for the frequency hopping system is completed.
The following is a more specific example:
referring to fig. 1, a DFT signal detection method for a frequency hopping system includes the following steps:
(1) frequency conversion
The lowest point of the frequency hopping frequency point can be selected as a central frequency point for frequency conversion, and at the moment, the frequency band of the signal detection work is the lowest section in the frequency hopping bandwidth.
(2) Sampling
The zero intermediate frequency "signal" (which may also contain no signal, only noise) is sampled. If the hopping bandwidth is 400MHz, Bdetec8MHz, sample rate fs1Is 16 MHz. Selecting a signal in the lowest section of a frequency hopping bandwidth and in the range of 0-8MHz, and extracting the power of a frequency hopping signal; sampling the signals which are converted into zero intermediate frequency according to 16 MHz;
(3) 8192 point DFT operation is carried out on the sampled signals;
(4) dividing the frequency spectrum after DFT into 128 sub-bands;
(5) calculating power P of each sub-band1、P2、…Pi，…PMAnd sorting according to the sequence of the power from large to small;
(6) taking the maximum power value as the signal power and storing;
(7) removing 8 sub-bands with the largest power from the 128 sub-bands, removing the 8 sub-bands with the smallest power, averaging the power of the rest sub-bands, taking the average as the background noise, and storing the average;
(8) repeating the steps (1) to (7)4000 times, sorting the stored 4000 signal powers from large to small, and taking the average value of the first 10 power values as a final signal power estimated value Ps(ii) a Averaging the 4000 stored background noise powers to obtain a final estimated background noise value N0(ii) a Calculating Ps/N0；
(9) Calculating P when the input signal is pure noise according to the steps (1) to (8)sIs denoted by Psn；
(10) Will Psn/N0As a reference value (S)m1/N0Substantially constant, obtainable by simulation), if Ps/N0>Psn/N0If not, the signal is judged to be present, otherwise, the signal is judged to be absent.
The DFT signal detection method suitable for the frequency hopping system is completed.
In a word, the invention finds out the difference between the existing signal and the non-signal by taking measures such as DFT operation, sub-band segmentation, power calculation, sequencing and the like on the frequency hopping signal in a certain bandwidth, judges whether the signal-to-noise ratio of the received signal is greater than a fixed threshold by calculating the signal-to-noise ratio, and finally realizes the signal detection function of the frequency hopping system. The method has the survivability and the robustness of a frequency hopping system, and is particularly suitable for signal detection of the frequency hopping communication system.
The above description is only one specific embodiment of the present invention, but the scope of the present invention is not limited thereto. Any equivalent replacement or change made by the technical solution of the present invention and the inventive concept thereof by those skilled in the art should be covered within the protection scope of the present invention.
Claims (4)
1. A DFT signal detection method suitable for a frequency hopping system is characterized by comprising the following steps:
(1) receiving an AD signal and carrying out frequency conversion to a zero intermediate frequency signal;
(2) sampling zero intermediate frequency signals at a sampling rate fs1To detect bandwidth Bdetec2 times of the sequence, and the sequence after sampling is y (n);
(3) carrying out N-point discrete Fourier transform on the sampled sequence y (N) to obtain a frequency spectrum Y (k); n is the integral multiple of the number of sampling points of each jump;
(4) dividing the frequency spectrum after discrete Fourier transform into M sub-bands, wherein each sub-band has a bandwidth of (f)s1/M)Hz；
(5) Calculating power P of each sub-band1、P2、...Pi，…PMAnd sorting according to the sequence of the power from large to small;
(6) taking the maximum power value as the signal power and storing;
(7) removing the maximum part of power, removing the minimum part of power, averaging the residual middle section signal power to be used as the bottom noise power, and storing;
(8) repeating the steps (1) to (7) Z times, sorting the stored Z signal powers from large to small, and taking the average value of the first 10% power values as the final estimated value P of the signal powers(ii) a Averaging the stored Z background noise powers to obtain a final background noise estimated value N0(ii) a Calculating Ps/N0；
(9) Calculating P when the input signal is pure noise according to the modes of the steps (1) to (8)sIs denoted by Psn；
(10) Will Psn/N0As a threshold, if Ps/N0>Psn/N0If not, the signal is judged to be present, otherwise, the signal is judged to be absent.
2. The DFT signal detection method as recited in claim 1, wherein the DFT signal detection method comprises the steps of: in the step (1), the frequency conversion is a zero intermediate frequency signal, which means that any section of fixed frequency in the whole frequency hopping bandwidth is selected, and the frequency conversion is carried out by taking the central frequency point of the section of frequency as a reference; and obtaining a signal after frequency conversion, namely the zero intermediate frequency signal.
3. The DFT signal detection method as recited in claim 1, wherein the DFT signal detection method comprises the steps of: in step (4), the bandwidth of the sub-band is the lowest symbol rate RminI.e. M ═ fs1/Rmin。
4. The DFT signal detection method as recited in claim 1, wherein the DFT signal detection method comprises the steps of: the repetition times Z in the step (8) are according to the frequency hopping bandwidth BhAnd a sampling rate fs1To determine that the value of Z satisfies Z fs1/Bh>100。
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| CN114844527A (en) * | 2022-04-18 | 2022-08-02 | 中国电子科技集团公司第五十四研究所 | Signal capturing method suitable for broadband anti-interference system |
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| CN112187316A (en) * | 2020-10-09 | 2021-01-05 | 中国人民解放军空军研究院战略预警研究所 | Signal processing method, signal processing device, receiver and storage medium |
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