Underwater sound quaternary frequency shift keying signal carrier frequency estimation method

Abstract

The invention discloses an underwater acoustic quaternary frequency shift keying signal carrier frequency estimation method, which comprises the following steps of: performing periodogram method power spectrum estimation on an underwater acoustic signal which is identified as quaternary frequency shift keying, and finding four frequency points with the strongest energy; the first frequency point, the second frequency point, the third frequency point and the fourth frequency point are sorted from small to large, and the difference values of the adjacent frequency points after sorting are calculated as the first difference value, the second difference value and the third difference value. The underwater acoustic quaternary frequency shift keying signal carrier frequency estimation method provided by the invention is established on the basis that an identified communication signal is a quaternary frequency shift keying signal, so that the carrier frequency estimation method provided by the invention only aims at the condition that the power spectrum frequency does not decline or declines by one in a periodogram method; when two or more frequencies are lost, the signal can be directly identified as other signals and cannot enter the process, so that the effects of minimum calculation amount, simplest implementation and highest estimation precision are achieved.

Description

Technical Field

[0001] This invention belongs to the field of marine oil engineering technology, and particularly relates to a method for estimating the carrier frequency of a quaternary frequency shift keying signal in underwater acoustics. Background Technology

[0002] Underwater acoustic communication signal reconnaissance technology mainly includes four aspects: blind detection of underwater acoustic communication signals, identification of modulation schemes, carrier frequency estimation, and jamming. Carrier frequency estimation, as the third step in underwater acoustic communication reconnaissance, estimates the carrier frequency of the intercepted signal after its modulation scheme has been identified. It is also a prerequisite for the fourth step: precise jamming. Only when the carrier frequency is accurately estimated can reliable information be provided to commanders, enabling precise jamming of enemy underwater acoustic communication equipment and disabling its communication capabilities.

[0003] Unlike wireless channels, due to the complexity of underwater acoustic channels, the intercepted underwater acoustic quaternary frequency shift keying (QPSK) signals often experience frequency-selective fading. This makes it difficult to estimate the carrier frequency of underwater acoustic QPSK signals. Traditional methods for estimating the carrier frequency of QPSK signals perform poorly in underwater acoustic channels, resulting in low accuracy of the estimated frequency.

[0004] Therefore, it is urgent to design a carrier frequency estimation method for underwater acoustic quaternary frequency shift keying signals to solve the problems mentioned above. Summary of the Invention

[0005] To address the technical problem mentioned in the background art that the traditional quaternary frequency shift keying signal carrier frequency estimation method performs poorly in underwater acoustic channels and has low accuracy in estimating the frequency results, this paper provides an underwater acoustic quaternary frequency shift keying signal carrier frequency estimation method to solve the problems existing in the background art.

[0006] To achieve the above objectives, the specific technical solution of the underwater acoustic quaternary frequency shift keying signal carrier frequency estimation method of the present invention is as follows: A method for estimating the carrier frequency of a quaternary frequency shift keying (QPSK) signal in underwater acoustics is proposed. This method involves estimating the power spectrum of an underwater acoustic signal identified as QPSK using a periodogram method to find the four frequency points with the strongest energy. Sort the frequencies in ascending order as first frequency point, second frequency point, third frequency point, and fourth frequency point. Calculate the difference between adjacent frequency points after sorting as the first difference, second difference, and third difference.

[0007] Furthermore, if the values ​​of the first difference, the second difference, and the third difference are approximately related, then the carrier frequency estimation result is (first frequency point + second frequency point + third frequency point + fourth frequency point) / 4.

[0008] Furthermore, if the values ​​of the first difference, the second difference, and the third difference do not have an approximate relationship, then find the three frequency points with the strongest power spectrum energy in the periodogram method, and sort the first frequency point, the second frequency point, and the third frequency point in ascending order. Calculate the difference between adjacent frequency points after sorting, where the larger difference is set as the first difference and the smaller difference is set as the second difference.

[0009] Furthermore, if the value of the first difference is approximately equal to twice the value of the second difference, then interpolation is performed at the center of the first difference. The frequency corresponding to the interpolation position is the fourth frequency. The carrier frequency estimation result is (first frequency point + second frequency point + third frequency point + fourth frequency point) / 4.

[0010] Furthermore, if the first difference and the second difference are not approximately twice the original value, then based on empirical values, the first power within the frequency band of the minimum value of the first, second, and third frequency points minus 1.5 times the second difference, and the second power within the frequency band of the minimum value of the first, second, and third frequency points minus 0.5 times the second difference, are compared with the second power within the frequency band of the maximum value of the first, second, and third frequency points plus 0.5 times the second difference, and the second power within the frequency band of the maximum value of the first, second, and third frequency points plus 1.5 times the second difference.

[0011] Furthermore, if the first power is greater than the second power, the minimum value of the first frequency point, the second frequency point, and the third frequency point minus the second difference is taken as the fourth frequency point. Then the carrier frequency estimation result is (first frequency point + second frequency point + third frequency point + fourth frequency point) / 4.

[0012] Furthermore, if the first power is less than the second power, the maximum value of the first frequency point, the second frequency point, and the third frequency point plus the second difference is taken as the fourth frequency point. Then the carrier frequency estimation result is (first frequency point + second frequency point + third frequency point + fourth frequency point) / 4.

[0013] The underwater acoustic quaternary frequency shift keying signal carrier frequency estimation method of the present invention has the following advantages: (1) The carrier frequency estimation method of the present invention is based on the fact that the communication signal has been identified as a quaternary frequency shift keying signal. Therefore, the carrier frequency estimation method proposed in this invention is only for the case where the power spectrum frequency of the periodogram method has not faded or has faded by one frequency. When two or more frequencies are missing, the signal will be directly identified as other signals and will not enter this process.

[0014] (2) In the underwater acoustic channel, the proposed underwater acoustic quaternary frequency shift keying signal carrier frequency estimation method has the least amount of computation, the simplest implementation, and the highest estimation accuracy compared with the traditional quaternary frequency shift keying signal carrier frequency estimation method. Attached Figure Description

[0015] Figure 1This is a flowchart of the underwater acoustic quaternary frequency shift keying signal carrier frequency estimation method of the present invention; Figure 2 This is a simulation comparison of the performance of the underwater acoustic quaternary frequency shift keying signal carrier frequency estimation method of the present invention with that of the traditional method; Figure 3 A schematic diagram illustrating several possible scenarios of frequency point loss caused by frequency-selective fading in the underwater acoustic channel at -7dB. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] Those skilled in the art will understand that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of the invention and form different embodiments. For example, in the claims, any of the claimed embodiments can be used in any combination.

[0018] The following is a reference to the appendix. Figure 1 To be continued Figure 3 The present invention describes a method for estimating the carrier frequency of a quaternary frequency shift keying signal in underwater acoustics.

[0019] like Figure 1 As shown, the underwater acoustic quaternary frequency shift keying signal carrier frequency estimation method of the present invention performs periodogram power spectrum estimation on the underwater acoustic signal identified as quaternary frequency shift keying, finds the four frequency points with the strongest energy, and sorts them in ascending order as the first frequency point, the second frequency point, the third frequency point, and the fourth frequency point. The difference between adjacent frequency points after sorting is calculated as the first difference, the second difference, and the third difference.

[0020] The first frequency point is denoted as frequency point 1, the second frequency point as frequency point 2, the third frequency point as frequency point 3, and the fourth frequency point as frequency point 4; the first difference is denoted as difference 1, the second difference as difference 2, and the third difference as difference 3.

[0021] As a preferred embodiment, the present invention defines the frequency offset of quaternary frequency shift keying carrier frequency estimation. for: in This is an estimate of the quaternary frequency shift keying carrier frequency. This is the actual value of the quaternary frequency shift keying carrier frequency.

[0022] In an underwater acoustic channel, the carrier frequency estimation frequency offset of the classical quaternary frequency shift keying method and the method of this patent are compared as a function of the signal-to-noise ratio. Figure 2 As shown.

[0023] In underwater acoustic channels, the underwater acoustic quaternary frequency shift keying carrier frequency estimation method proposed in this invention has a carrier frequency estimation frequency offset of almost 0 when the signal-to-noise ratio is as low as -10dB, while the other four classic methods have a carrier frequency estimation effect with a frequency offset of more than 50Hz.

[0024] The carrier frequency estimation method proposed in this invention has excellent multipath resistance. Under the influence of underwater acoustic channels, both the accuracy of carrier frequency estimation and the minimum signal-to-noise ratio required for accurate carrier frequency estimation are superior to the four classic carrier frequency estimation methods.

[0025] This invention is primarily verified using simulation experiments, and all steps and conclusions have been verified correctly using Matlab 2020. To facilitate understanding of the technical content of this invention by those skilled in the art, the following description, in conjunction with the accompanying drawings, further illustrates the invention. Figure 3 Taking the underwater acoustic quaternary frequency shift keying signal with a carrier frequency of 11kHz and the third frequency point lost as an example, estimate the carrier frequency of the signal.

[0026] Furthermore, if the values ​​of the first difference, the second difference, and the third difference are approximately related, then the carrier frequency estimation result is (first frequency point + second frequency point + third frequency point + fourth frequency point) / 4.

[0027] If the values ​​of the first difference, the second difference, and the third difference do not have an approximate relationship, then find the three frequency points with the strongest power spectrum energy in the periodogram method, and sort the first frequency point, the second frequency point, and the third frequency point in ascending order. Calculate the difference between adjacent frequency points after sorting, and set the larger difference as the first difference and the smaller difference as the second difference.

[0028] Preferably, the power spectrum of the underwater acoustic signal identified as quaternary frequency shift keying is estimated using the periodogram method to find the four frequency points with the strongest energy, and sort them in ascending order as the first frequency point (9483Hz), the second frequency point (10512Hz), the third frequency point (12432Hz), and the fourth frequency point (12507Hz). The differences between adjacent frequency points after sorting are calculated as the first difference (1029Hz), the second difference (1920Hz), and the third difference (75Hz).

[0029] Furthermore, if the value of the first difference is approximately equal to twice the value of the second difference, then interpolation is performed at the center of the first difference. The frequency corresponding to the interpolation position is the fourth frequency. The carrier frequency estimation result is (first frequency point + second frequency point + third frequency point + fourth frequency point) / 4.

[0030] Preferably, the values ​​of the first difference (1029Hz), the second difference (1920Hz), and the third difference (75Hz) do not have an approximate relationship, and proceed to the next step.

[0031] If the values ​​of the first difference, the second difference, and the third difference do not have an approximate relationship, then find the three frequency points with the strongest power spectrum energy in the periodogram method, and sort them in ascending order: the first frequency point (9483Hz), the second frequency point (10512Hz), and the third frequency point (12507Hz). Calculate the difference between adjacent frequency points after sorting, and set the larger difference as the first difference (1995Hz) and the smaller difference as the second difference (1029Hz).

[0032] The value of the first difference is approximately twice the value of the second difference. Interpolation is performed at the center of the first difference, and the frequency corresponding to the interpolation position is the fourth frequency (11509.5Hz). The estimated carrier frequency is (9483+10512+12507+11509.5) / 4=11002.9Hz, which deviates from the true value of the signal carrier frequency of 11000Hz by only 2.9Hz.

[0033] Furthermore, such as Figure 1 As shown, if the first difference and the second difference are not approximately twice the value, then based on experience, the first power within the frequency band is calculated as follows: the minimum value of the first frequency point, the second frequency point, and the third frequency point minus 1.5 times the second difference, and the second power within the frequency band is calculated as follows: the minimum value of the first frequency point, the second frequency point, and the third frequency point minus 0.5 times the second difference, and the second power within the frequency band is calculated as follows: the maximum value of the first frequency point, the second frequency point, and the third frequency point plus 0.5 times the second difference, and the second power within the frequency band is calculated as follows: the maximum value of the first frequency point, the second frequency point, and the third frequency point plus 1.5 times the second difference, and these values ​​are compared.

[0034] The first power is denoted as P1, and the second power is denoted as P2.

[0035] If the first power is greater than the second power, the minimum value of the first frequency point, the second frequency point, and the third frequency point minus the second difference is taken as the fourth frequency point. Then the carrier frequency estimation result is (first frequency point + second frequency point + third frequency point + fourth frequency point) / 4.

[0036] If the first power is less than the second power, the maximum value of the first frequency point, the second frequency point, and the third frequency point plus the second difference is taken as the fourth frequency point. Then the carrier frequency estimation result is (first frequency point + second frequency point + third frequency point + fourth frequency point) / 4.

[0037] Based on the underwater acoustic quaternary frequency shift keying signal carrier frequency estimation method, the proposed underwater acoustic quaternary frequency shift keying signal carrier frequency estimation method has the least computational complexity, the simplest implementation, and the highest estimation accuracy compared to the traditional quaternary frequency shift keying signal carrier frequency estimation method in underwater acoustic channels.

[0038] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for estimating the carrier frequency of an underwater acoustic quaternary frequency shift keying signal, characterized in that, Power spectrum estimation of underwater acoustic signals identified as quaternary frequency shift keying was performed using the periodogram method to find the four frequency points with the strongest energy. Sort the frequencies in ascending order as first frequency point, second frequency point, third frequency point, and fourth frequency point. Calculate the difference between adjacent frequency points after sorting as the first difference, second difference, and third difference.

2. The underwater acoustic quaternary frequency shift keying signal carrier frequency estimation method according to claim 1, characterized in that, If the values ​​of the first difference, the second difference, and the third difference are approximately related, then the carrier frequency estimation result is (first frequency point + second frequency point + third frequency point + fourth frequency point) / 4.

3. The underwater acoustic quaternary frequency shift keying signal carrier frequency estimation method according to claim 1, characterized in that, If the values ​​of the first difference, the second difference, and the third difference do not have an approximate relationship, then find the three frequency points with the strongest power spectrum energy in the periodogram method, and sort the first frequency point, the second frequency point, and the third frequency point in ascending order. Calculate the difference between adjacent frequency points after sorting, and set the larger difference as the first difference and the smaller difference as the second difference.

4. The underwater acoustic quaternary frequency shift keying signal carrier frequency estimation method according to claim 1, characterized in that, If the value of the first difference is approximately equal to twice the value of the second difference, then interpolation is performed at the center of the first difference. The frequency corresponding to the interpolation position is the fourth frequency. The carrier frequency estimation result is (first frequency point + second frequency point + third frequency point + fourth frequency point) / 4.

5. The underwater acoustic quaternary frequency shift keying signal carrier frequency estimation method according to claim 1, characterized in that, If the first difference and the second difference are not approximately twice the value, then based on experience, the first power within the frequency band is calculated as follows: the minimum value of the first frequency point, the second frequency point, and the third frequency point minus 1.5 times the second difference, and the second power within the same frequency band is calculated as follows: the maximum value of the first frequency point, the second frequency point, and the third frequency point plus 0.5 times the second difference, and the second power within the same frequency band is calculated as follows: the maximum value of the first frequency point, the second frequency point, and the third frequency point plus 1.5 times the second difference.

6. The method for estimating the carrier frequency of a quaternary frequency shift keying signal for underwater acoustics according to claim 5, characterized in that, If the first power is greater than the second power, the minimum value of the first frequency point, the second frequency point, and the third frequency point minus the second difference is taken as the fourth frequency point. Then the carrier frequency estimation result is (first frequency point + second frequency point + third frequency point + fourth frequency point) / 4.

7. The underwater acoustic quaternary frequency shift keying signal carrier frequency estimation method according to claim 5, characterized in that, If the first power is less than the second power, the maximum value of the first frequency point, the second frequency point, and the third frequency point plus the second difference is taken as the fourth frequency point. Then the carrier frequency estimation result is (first frequency point + second frequency point + third frequency point + fourth frequency point) / 4.

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