A method for automatic frequency selection of underwater acoustic 2FSK based on transducer and channel characteristics

Abstract

This invention discloses an automatic frequency selection method for underwater acoustic 2FSK based on transducer and channel characteristics, including: S1, inputting the transducer transmit response (TVR). dB (f) and receiver sensitivity RS dB (f) Generate candidate frequency set F; S2, Calculate the equivalent gain GT of the transducer link. dB (f)=TVR dB (f)+RS dB (f), and interpolate to the candidate frequency point GT dB (f i S3, obtain the effective signal-to-noise ratio (SNR) at each frequency point. dB (f i ) and amplitude ratio A(f i ) / A(f ref S4. Generate a set of candidate frequency pairs P={(f0,f1)|f1>f0}; S5. Set the symbol timing and receive correlation window, and construct the received signal model r(t); S6. Set the channel conditions: multipath parameter {a k ,τ k ,φ k} and relative velocity v rel S7. Perform Monte Carlo simulation for each frequency pair and operating condition to estimate the bit error rate (BER). S8. Traverse all frequency pairs to form a BER matrix cloud map. Based on the bright spots in the cloud map, output the optimal candidate frequency pair. Compared to traditional fixed-frequency step selection, this invention can capture discretely distributed low-BER "bright spot" frequency pairs under low signal-to-noise ratio (SNR) and multipath / Doppler conditions, significantly improving underwater acoustic communication performance under low SNR.

Description

Technical Field

[0001] This invention belongs to the field of underwater acoustic signal processing, and in particular to an automatic frequency selection method for underwater acoustic 2FSK based on transducer and channel characteristics. Background Technology

[0002] Underwater acoustic 2FSK is widely used in underwater acoustic engineering fields such as release devices due to its simplicity and robustness. However, the transducer's transmit response and receive sensitivity vary significantly with frequency, resulting in large differences in equivalent link gain and effective signal-to-noise ratio at different frequencies. Under finite symbol durations, the basis functions at different frequencies are not completely orthogonal, and frequencies that are too close together can lead to enhanced cross-correlation and increased correlation of decision statistics, resulting in a sudden increase in the bit error rate. At the same time, multipath and Doppler effects introduce frequency shift mismatch and energy leakage, causing the bit error rate to exhibit a strongly non-uniform distribution in the frequency pair plane. Therefore, fixed large-interval step frequency selection is prone to missing discrete "bright spot" frequency pairs with low bit error rates or misselecting high bit error rate stripe regions, making it difficult to guarantee reliable communication under low signal-to-noise ratio conditions. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention proposes an automatic frequency selection method for underwater acoustic communication using binary frequency shift keying (2FSK). This method only requires inputting the transducer transmit response curve and receive sensitivity curve, and combining selectable channel multipath parameters (delay / amplitude / phase), Doppler parameters (relative velocity), and symbol guard intervals. It can automatically construct a set of candidate frequency pairs and calculate the bit error rate (BER) matrix using Monte Carlo simulation, thereby outputting the optimal 2FSK frequency pair and candidate set.

[0004] The technical solution of this invention is as follows:

[0005] An automatic frequency selection method for underwater acoustic 2FSK based on transducer and channel characteristics includes the following steps:

[0006] S1, Input transducer transmit response (TVR) dB (f) and receiver sensitivity RS dB (f), or the equivalent Sa / M curve, setting the working frequency band and scan step Δf step Generate a candidate frequency point set F;

[0007] S2, Calculate the equivalent gain GT of the transducer link. dB (f)=TVR dB (f)+RS dB (f), and interpolate to the candidate frequency point GT dB (f i );

[0008] S3, Set reference frequency point f ref and reference signal-to-noise ratio (SNR) ref，dB(f) According to the SNR mapping relationship, the effective signal-to-noise ratio (SNR) of each frequency point is obtained. dB (f i ) and amplitude ratio A(f i ) / A(f ref );

[0009] S4. Generate a candidate frequency point pair set P={(f0,f1)|f1>f0};

[0010] S5. Set symbol timing: transmission duration T and guard interval G, and set the reception window T. _symbol Construct the received signal model r(t);

[0011] S6. Set channel conditions: Multipath parameter {a k ,τ k ,φ k} and relative velocity v rel (α≈v) rel / c);

[0012] S7. For each frequency pair and operating condition, generate a random bit sequence. Perform sequential operations on each symbol to obtain a decision bit sequence, and calculate the bit error N. err And estimate the bit error rate (BER);

[0013] S8. Traverse all frequency point pairs to form a BER matrix cloud map. Based on the highlights in the cloud map, output the optimal candidate frequency point pair.

[0014] Preferably, in step S7, a random bit sequence of length N is generated in the Monte Carlo simulation. For each symbol, multipath / Doppler channeling, noise addition, I / Q correlation, and energy decision are performed sequentially to obtain the decision bit sequence. Error indicator function Total number of error codes N err And estimate the bit error rate (BER).

[0015] Preferably, step S7 includes:

[0016] S71. For each frequency pair and operating condition: generate a length of N. bit The random bit sequence b[n] is synthesized bit by bit into a 2FSK waveform (b=0 transmits f0, b=1 transmits f1), the transmission duration of each bit signal is T, and the guard interval is G;

[0017] S72. The signal is processed by multipath and Doppler effects to obtain r(t), and Gaussian noise is added to make the reference frequency f... ref The signal-to-noise ratio at point SNR is ref,dB The remaining frequency points are mapped using GT.

[0018] S73. Perform I / Q correlation on the candidate frequency points and calculate the energy E(f) = I. 2 +Q 2 The decision bit is obtained by comparing E(f1) and E(f0).

[0019] S74. Use the error indicator function e[n] to count the total number of bit errors N. err And estimate the bit error rate (BER).

[0020] Furthermore, in step S73, within the observation window T of each symbol... _symbol Within this process, the received signal r(t) is correlated with orthogonal basis functions to obtain in-phase and quadrature components:

[0021] ,

[0022] Where I(f) is the in-phase component, Q(f) is the quadrature component, and T _symbol Let r(t) be the observation window, f be the received signal, and t be the frequency.

[0023] And construct the energy decision statistics for the corresponding frequency points:

[0024] ,

[0025] Where E(f) is the energy at the corresponding frequency point, and I(f) is the energy at the corresponding frequency point. 2 Let Q(f) be the projected energy of the in-phase branch. 2 The projected energy of the orthogonal branch;

[0026] For binary FSK, the receiver makes an incoherent decision by comparing the energy of two candidate frequency points:

[0027] ,

[0028] Where b[n]∈{0,1} is the transmitted bit, For the decision bit, E n (f1) represents the energy statistic of the frequency point f1 corresponding to the nth symbol, E n (f0) represents the energy statistics of the frequency point f0 corresponding to the nth symbol.

[0029] Furthermore, in step S74, the total number of bit errors N err for:

[0030] ,

[0031] Where N is the total number of code elements, n is the nth code element, and e[n] is the error indicator function, representing whether the nth code element is an error;

[0032] The estimated bit error rate (BER) is:

[0033] , ,

[0034] in, For bit error rate, This is the bit error rate as a percentage.

[0035] Preferably, in step S2, the equivalent gain of the transducer link and the equivalent gain of its normalized link are defined as follows:

[0036] GT dB (f)=TVR dB (f)+RS dB (f),

[0037] ,

[0038] Among them, GT dB (f) represents the link equivalent gain, determined by the transducer sensitivity and transmit response curve, TVR dB (f) is the transmit response, RS dB (f) represents the receiving sensitivity. For the equivalent gain of the normalized link, max(GT) dB (f) represents the maximum value of the link equivalent gain.

[0039] Preferably, in step S3, the frequency point with the maximum link gain is taken as the reference frequency point, and the equivalent signal-to-noise ratio of different frequency points is:

[0040] ,

[0041] Among them, SNR dB (f) represents the signal-to-noise ratio (SNR) at frequency point f. ref，dB (f) is the reference frequency f ref Signal-to-noise ratio at the location. The equivalent gain of the normalized link;

[0042] The equivalent amplitude ratios at different frequencies are:

[0043] .

[0044] Where A(f) is the amplitude at each frequency point, A(f) ref () is the amplitude of the reference frequency point.

[0045] Preferably, in step S4, certain constraints are set as follows:

[0046] f1-f0|≥Δf min and frequency band avoidance,

[0047] Where f1 is the first carrier frequency of 2FSK, f0 is the second carrier frequency of 2FSK, and Δf min This is the minimum interval between two carrier frequencies; if the interval is too small, the bit error rate will increase.

[0048] Preferably, in step S5, T is set as the transmission duration (signal duration), G is set as the guard interval, and the reception-related window T is set. _symbol The window can be T or T+G; therefore, the time-domain signal form is:

[0049] ,

[0050] Where A is the amplitude, b is the binary bits to be transmitted, t is the time, and f is the amplitude. b s represents the carrier frequency corresponding to the current bit. b (t) represents the 2FSK transmit time-domain waveform corresponding to bit b;

[0051] Considering multipath delay, the received signal model is as follows:

[0052] ,

[0053] Where r(t) is the received signal, n(t) is the channel Gaussian noise, t is time, K is the total number of multipath paths, k is the sequence number of the k-th multipath path, and a k Let τ be the attenuation coefficient of the k-th multipath path. k Let φ be the propagation delay of the k-th multipath path. k Add a random phase to the k-th multipath path.

[0054] Preferably, in step S5, it is assumed that the relative speed of transmission and reception is v. rel Then the Doppler frequency shift is:

[0055] ,

[0056] Where α is the scaling factor of the Doppler scale, v rel The relative velocity is f(1+α), and f(1+α) represents the Doppler frequency shift.

[0057] The beneficial effects of this invention are as follows: Compared with traditional fixed frequency step selection, this invention can capture low BER "bright spot" frequency pairs that are discretely distributed under low signal-to-noise ratio and multipath / Doppler conditions, which significantly improves the underwater acoustic communication performance under low signal-to-noise ratio conditions. Attached Figure Description

[0058] Figure 1 This is a flowchart illustrating the workflow of an underwater acoustic 2FSK automatic frequency selection method based on transducer and channel characteristics according to the present invention.

[0059] Figure 2This is a graph showing the transmit voltage response and sensitivity of a communication transducer according to an embodiment of the present invention.

[0060] Figure 3 This is a normalized link equivalent gain curve of the transducer in an embodiment of the present invention;

[0061] Figure 4 This is a time-domain signal model diagram with guard interval according to an embodiment of the present invention;

[0062] Figure 5 This is an embodiment of the invention - 25dB@f ref Bit error rate contour plot under signal-to-noise ratio. Detailed Implementation

[0063] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0064] I. Technical Terminology:

[0065] 1. 2FSK Modulation: Binary Frequency Shift Keying (2FSK) is a modulation method that uses the switching of the carrier frequency between two discrete frequency points f0 and f1 to represent binary information. The receiver typically makes decisions through correlation / matched filtering or energy statistics based on I / Q projection, thus eliminating the need for precise carrier phase recovery. In underwater acoustic communication, due to the significant frequency selectivity, multipath delay spread, and Doppler shift and time scale scaling caused by the relative motion of the platform, 2FSK, with its frequency discrimination mechanism and incoherent energy detection, can effectively reduce the dependence on phase consistency and amplitude stability, thus exhibiting good robustness in environments with strong multipath and fluctuating fading. Furthermore, its implementation structure is relatively simple, with low computational and synchronization requirements, making it easy to implement in low-power, low-complexity underwater nodes or control links. It also achieves acceptable bit error rate performance even under low signal-to-noise ratio conditions, and is therefore often used in underwater acoustic command control, status feedback, and low-speed, high-reliability data transmission scenarios.

[0066] Underwater acoustic 2FSK is widely used due to its simplicity and robustness. In engineering practice, a fixed-step frequency selection (e.g., selecting a frequency every 0.5kHz) is often used to configure the 2FSK frequency. Taking the OCEANS series release from the French company iXBlue as an example, its carrier frequency is 8-16kHz, with a carrier frequency selected at 0.5kHz intervals. All its carrier frequencies are shown in Table 1:

[0067] Table 1. All carrier frequencies of the OCEANNS series releasers from iXBlue (France)

[0068] Since multiple releases need to use different carrier frequencies to distinguish equipment batches and serial numbers, as shown in the table above, the carrier frequency pairs selectable for this series of 2FSK releases are:

[0069] ,

[0070] However, since the response and sensitivity of underwater acoustic transducers are not flat in the 8-16kHz range, and their resonant frequency is about 12kHz, the response and sensitivity of the transducer at frequencies far from the resonant frequency, such as 8kHz and 16kHz, are much lower than at the resonant frequency. This means that when frequencies far from the resonant frequency are selected as 2FSK frequency pairs, the received signal-to-noise ratio will be much lower than that at the resonant frequency, and the communication performance will deteriorate sharply.

[0071] Based on this, the present invention provides a simple and efficient automatic frequency selection method: the user only needs to provide the transducer transmit response and receive sensitivity curves (or equivalent sound source level / transmit voltage response and receive sensitivity), and set the reference signal-to-noise ratio and optional operating parameters (multipath, relative velocity, Doppler, etc.), and the system can automatically generate candidate frequency point pairs and perform Monte Carlo simulation, output BER cloud map and optimal 2FSK frequency point pairs.

[0072] Specifically, an embodiment of the present invention provides an automatic frequency selection method for underwater acoustic 2FSK based on transducer and channel characteristics, such as... Figure 1 As shown, it includes the following steps:

[0073] (1) Input transducer transmit response (TVR) dB (f) and receiver sensitivity RS dB (f) (or equivalent Sa / M curve), set the operating frequency band and frequency scan step Δf step Generate a candidate frequency point set F.

[0074] (2) Calculate the link equivalent gain GT dB (f)=TVR dB (f)+RS dB (f), and interpolate to the candidate frequency points to obtain GT dB (f i Set the reference signal-to-noise ratio (SNR). ref,dB With reference frequency f ref .

[0075] (3) Obtain the effective signal-to-noise ratio (SNR) at each frequency point according to the SNR mapping relationship. dB (f i ) and amplitude ratio A(f i ) / A(f ref ).

[0076] (4) Generate a set of candidate frequency point pairs P={(f0,f1)|f1>f0}, and apply constraints (such as |f1-f0|≥Δf). min (Frequency band avoidance).

[0077] (5) Set symbol timing: transmission duration T (20 ms) and guard interval G (80 ms), and set the reception window T. _symbol (T or T+G can be selected).

[0078] (6) Set channel operating conditions: Set multipath parameters {a k ,τ k ,φ k}, and relative velocity v rel , satisfying α≈v rel / c, where c is the wave number.

[0079] (7) For each frequency pair and operating condition: generate a length of N bit The random bit sequence b[n] is synthesized bit by bit into a 2FSK waveform (b=0 transmits f0, b=1 transmits f1), the transmission duration of each bit signal is T, and the guard interval is G.

[0080] (8) The signal is multipath-guided and Doppler-assisted to obtain r(t), and Gaussian noise is added to make the reference frequency f ref The signal-to-noise ratio is SNR ref,dB The remaining frequency points are mapped using GT.

[0081] (9) Perform I / Q correlation on the candidate frequency points and calculate the energy E(f)=I 2 +Q 2 The decision bit is obtained by comparing E(f1) and E(f0).

[0082] (10) Statistical analysis of bit error N using the bit error indicator function. err The BER (Bit Error Rate) is calculated, and all frequency pairs are traversed to form a BER matrix cloud map. The optimal candidate frequency pair is output based on the horizontal and vertical coordinates corresponding to the bright spots in the cloud map.

[0083] Specifically, the transducer's transmit response (TVR) dB and receiver sensitivity curve MS dB This is a curve describing how the transmitting and receiving performance of a hydrophone changes with frequency. For example... Figure 2 As shown, the transmit response and sensitivity curves of a certain communication transducer are known, where: Transmit Response (TVR) dB and receiver sensitivity MS dBThese values ​​respectively characterize the transducer's ability to convert electrical energy into acoustic energy and incident sound pressure into electrical signals; a higher value generally indicates a higher transmitting sound source level and a stronger receiving output at the corresponding frequency. For a typical resonant underwater acoustic transducer, the peak values ​​of the transmitting response and receiving sensitivity usually appear near the resonant frequency and are located at roughly the same position. It should be noted that within the effective operating bandwidth of underwater acoustic communication, the two frequency response curves often exhibit significant fluctuations (significant frequency selectivity), which directly leads to large differences in the link equivalent gain and effective signal-to-noise ratio at different carrier frequencies.

[0084] Based on this, the link equivalent gain of the transducer and its normalized link equivalent gain are defined as follows:

[0085] ,

[0086] ,

[0087] The obtained transducer normalized link equivalent gain curve is as follows: Figure 3 As shown.

[0088] In this link, the equivalent signal-to-noise ratio at different frequencies can be written as:

[0089] ,

[0090] Taking the frequency point with the maximum link gain as the reference frequency point, the equivalent amplitude at different frequency points is:

[0091] ,

[0092] Let T be the signal duration and G be the guard interval, then the time-domain signal form is:

[0093] ,

[0094] The established time-domain signal model with guard interval, such as Figure 4 As shown.

[0095] Considering multipath delay, the received signal model can be written as:

[0096] ,

[0097] Assume the relative speed of transmission and reception is v rel The Doppler frequency shift is:

[0098] .

[0099] Therefore, the decision and bit error rate estimation for candidate frequency points f0 and f1 can be expressed as follows:

[0100] Within the observation window T_symbol of each symbol, the received signal r(t) is correlated with orthogonal basis functions to obtain in-phase and quadrature components:

[0101] ,

[0102] Where I(f) is the in-phase component (the integral value of the received signal projected onto a cosine orthogonal basis at frequency f), Q(f) is the quadrature component (the integral value of the received signal projected onto a sine orthogonal basis at frequency f), and T _symbol Let r(t) be the observation window, f be the received signal, and t be the frequency.

[0103] And construct the energy decision statistics for the corresponding frequency points:

[0104] ,

[0105] Where E(f) represents energy, and I(f) represents... 2 Let Q(f) be the projected energy of the in-phase branch. 2 This represents the projected energy of the orthogonal branch.

[0106] For binary FSK, the receiver makes an incoherent decision by comparing the energy of two candidate frequency points:

[0107] ,

[0108] Where b[n]∈{0,1} is the transmitted bit, For the decision bit, E n (f1) represents the energy statistic of the frequency point f1 corresponding to the nth symbol, E n (f0) represents the energy statistics of the frequency point f0 corresponding to the nth symbol.

[0109] Generate a random bit sequence of length N in a Monte Carlo simulation. For each symbol, the following steps are performed sequentially: "channel effect (multipath / Doppler) + noise addition + I / Q correlation + energy decision" to obtain... And with an error indicator function:

[0110] ,

[0111] Count the total number of bit errors and estimate the bit error rate:

[0112] ,

[0113] Where N is the total number of code elements, n is the nth code element, and e[n] is the error indicator function, representing whether the nth code element is an error;

[0114] , ,

[0115] in, For bit error rate, Bit error rate expressed as a percentage;

[0116] After obtaining the bit error rate of all candidate frequency points f0 and f1 using 2FSK encoding, a BER matrix cloud map is formed.

[0117] like Figure 5 As shown, after obtaining the bit error rate (BER) of all candidate frequency points f0 and f1 using 2FSK encoding through the above steps, a BER matrix contour map is formed. The brightest point in the BER contour map is output according to the BER from smallest to largest, and its horizontal and vertical coordinates represent the optimal candidate frequency point pair. Even at -25dB@f ref At a signal-to-noise ratio of 5%, the BRE cloud map still shows "bright spots" with a regular distribution and a bit error rate of less than 5%. The horizontal and vertical axes represent the optimal candidate 2FSK carrier frequency point pairs. However, the conventional method of selecting 2FSK frequency points every 0.5 kHz results in a sharp deterioration in bit error rate performance (e.g., a bit error rate of nearly 50% at 11.5 kHz). It is evident that the 2FSK frequency selection method proposed in this invention can greatly improve the performance of underwater acoustic communication under low signal-to-noise ratio conditions.

[0118] It should be noted that the above embodiments are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Equivalent modifications made based on the above embodiments are all within the scope of protection of the present invention.

Claims

1. An automatic frequency selection method for underwater acoustic 2FSK based on transducer and channel characteristics, characterized in that, The steps include the following: S1, Input transducer transmit response (TVR) dB (f) and receiver sensitivity RS dB (f), or the equivalent Sa / M curve, setting the working frequency band and scan step Δf step Generate a candidate frequency point set F; S2, Calculate the equivalent gain GT of the transducer link. dB (f)=TVR dB (f)+RS dB (f), and interpolate to the candidate frequency point GT dB (f i ); S3, Set reference frequency point f ref and reference signal-to-noise ratio (SNR) ref，dB (f) yields the effective signal-to-noise ratio (SNR) at each frequency point. dB (f i ) and amplitude ratio A(f i ) / A(f ref ); S4. Generate a candidate frequency point pair set P={(f0,f1)|f1>f0}; S5. Set symbol timing: transmission duration T and guard interval G, and set the reception window T. _symbol Construct the received signal model r(t); S6. Set channel conditions: Multipath parameter {a k ,τ k ,φ k } and relative velocity v rel ; S7. For each frequency pair and operating condition, generate a random bit sequence. Perform sequential operations on each symbol to obtain a decision bit sequence, and calculate the bit error N. err And estimate the bit error rate (BER); S8. Traverse all frequency point pairs to form a BER matrix cloud map. Based on the highlights in the cloud map, output the optimal candidate frequency point pair.

2. The underwater acoustic 2FSK automatic frequency selection method based on transducer and channel characteristics according to claim 1, characterized in that: In step S7, a random bit sequence of length N is generated in the Monte Carlo simulation. For each symbol, multipath / Doppler channeling, noise addition, I / Q correlation, and energy decision are performed sequentially to obtain the decision bit sequence. Error indicator function Total number of error codes N err And estimate the bit error rate (BER).

3. The underwater acoustic 2FSK automatic frequency selection method based on transducer and channel characteristics according to claim 2, characterized in that: Step S7 includes: S71. For each frequency pair and operating condition: generate a length of N. bit The random bit sequence b[n] is synthesized bit by bit into a 2FSK waveform, with the transmission duration of each bit signal being T and the guard interval being G; S72. The signal is processed by multipath and Doppler effects to obtain r(t), and Gaussian noise is added to make the reference frequency f... ref The signal-to-noise ratio at point SNR is ref,dB The remaining frequency points are mapped using GT. S73. Perform I / Q correlation on the candidate frequency points and calculate the energy E(f) = I. 2 +Q 2 The decision bit is obtained by comparing E(f1) and E(f0). S74. Use the error indicator function e[n] to count the total number of bit errors N. err And estimate the bit error rate (BER).

4. The underwater acoustic 2FSK automatic frequency selection method based on transducer and channel characteristics according to claim 3, characterized in that: In step S73, the observation window T for each symbol _symbol Within this process, the received signal r(t) is correlated with orthogonal basis functions to obtain in-phase and quadrature components: ， Where I(f) is the in-phase component, Q(f) is the quadrature component, and T _symbol Let r(t) be the observation window, f be the received signal, and t be the frequency. And construct the energy decision statistics for the corresponding frequency points: ， Where E(f) is the energy at the corresponding frequency point, and I(f) is the energy at the corresponding frequency point. 2 Let Q(f) be the projected energy of the in-phase branch. 2 The projected energy of the orthogonal branch; For binary FSK, the receiver makes an incoherent decision by comparing the energy of two candidate frequency points: ， Where b[n]∈{0,1} is the transmitted bit, For the decision bit, E n (f1) represents the energy statistic of the frequency point f1 corresponding to the nth symbol, E n (f0) represents the energy statistics of the frequency point f0 corresponding to the nth symbol.

5. The underwater acoustic 2FSK automatic frequency selection method based on transducer and channel characteristics according to claim 1, characterized in that: In step S74, the total number of bit errors N err for: ， Where N is the total number of code elements, n is the nth code element, and e[n] is the error indicator function; The estimated bit error rate (BER) is: ， ， in, For bit error rate, This is the bit error rate as a percentage.

6. The underwater acoustic 2FSK automatic frequency selection method based on transducer and channel characteristics according to claim 1, characterized in that: In step S2, the equivalent gain of the transducer link and the equivalent gain of its normalized link are defined as follows: GT dB (f)=TVR dB (f)+RS dB (f), ， Among them, GT dB (f) represents the link equivalent gain, determined by the transducer sensitivity and transmit response curve, TVR dB (f) is the transmit response, RS dB (f) represents the receiving sensitivity. For the equivalent gain of the normalized link, max(GT) dB (f) represents the maximum value of the link equivalent gain.

7. The underwater acoustic 2FSK automatic frequency selection method based on transducer and channel characteristics according to claim 1, characterized in that: In step S3, the frequency point with the maximum link gain is taken as the reference frequency point, and the equivalent signal-to-noise ratio of different frequency points is: ， Among them, SNR dB (f) represents the signal-to-noise ratio (SNR) at frequency point f. ref，dB (f) is the reference frequency f ref Signal-to-noise ratio at the location. The equivalent gain of the normalized link; The equivalent amplitude ratios at different frequencies are: ， Where A(f) is the amplitude at each frequency point, A(f) ref () is the amplitude of the reference frequency point.

8. The underwater acoustic 2FSK automatic frequency selection method based on transducer and channel characteristics according to claim 1, characterized in that: In step S4, a certain constraint is set as follows: f1-f0|≥Δf min and frequency band avoidance, Where f1 is the first carrier frequency of 2FSK, f0 is the second carrier frequency of 2FSK, and Δf min This represents the minimum interval between two carrier frequencies.

9. The underwater acoustic 2FSK automatic frequency selection method based on transducer and channel characteristics according to claim 1, characterized in that: In step S5, the time-domain signal takes the following form: ， Where A is the amplitude, b is the binary bits to be transmitted, t is the time, and f is the amplitude. b s represents the carrier frequency corresponding to the current bit. b (t) represents the 2FSK transmit time-domain waveform corresponding to bit b; Considering multipath delay, the received signal model is as follows: ， Where r(t) is the received signal, n(t) is the channel Gaussian noise, t is time, K is the total number of multipath paths, k is the sequence number of the k-th multipath path, and a k Let τ be the attenuation coefficient of the k-th multipath path. k Let φ be the propagation delay of the k-th multipath path. k Add a random phase to the k-th multipath path.

10. The underwater acoustic 2FSK automatic frequency selection method based on transducer and channel characteristics according to claim 1, characterized in that: In step S5, it is assumed that the relative speed of transmission and reception is v. rel Then the Doppler frequency shift is: ， Where α is the scaling factor of the Doppler scale, v rel The relative velocity is f(1+α), and f(1+α) represents the Doppler frequency shift.

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