A method for designing acoustic Doppler velocity measurement waveform

Abstract

An acoustic Doppler velocity measurement waveform design method relates to the field of underwater acoustic navigation technology. The existing method can only perform simple waveform design for velocity measurement accuracy, and cannot dynamically adjust the velocity measurement waveform, which leads to the problem of poor velocity measurement performance. This application fixes the number of transmission cycles for different depths and speed conditions fed back in real time, and determines the number of code elements according to the depth information. The waveform design criterion min(NAEx) is used to determine the number of code elements. a ) The transmission coding is optimized with the help of a sequential quadratic programming algorithm; then, a periodically changing phase is superimposed on the signals of two of the beams according to the speed information, and finally the optimized transmission signal is used for speed measurement. The method of this application can dynamically adjust the speed measurement waveform according to different depths and speed conditions, improve the speed measurement precision and accuracy, and thus improve the navigation performance in different environments.

Description

Technical Field

[0001] The invention relates to the technical field of underwater acoustic navigation, in particular to a method for designing an acoustic Doppler velocity measurement waveform. Background Art

[0002] Acoustic Doppler velocity measurement relies on extracting the Doppler information of the scattered echo signal to measure the velocity. The typical algorithm used is the pulse pair algorithm, which adopts the Janus four-beam configuration. It is characterized by excellent velocity measurement performance and is an important part of the modern ship navigation system. Waveform design optimizes the transmission signal through the constructed design criteria or design methods, which is an effective means to improve the velocity measurement performance.

[0003] With the improvement of navigation needs, new requirements are put forward for acoustic speed measurement performance. In actual application, there are many factors that affect speed measurement performance, such as the self-noise and environmental noise of the solution that affect the speed measurement accuracy, as well as the system parameters, sidelobe coupling, attitude parameters, etc. that affect the speed measurement accuracy, and the degree of influence is different under different depths and speed conditions. Traditional methods can only perform simple waveform design for speed measurement accuracy, and cannot dynamically adjust the speed measurement waveform, which leads to poor speed measurement performance. The indicators for evaluating speed measurement performance can be divided into speed measurement accuracy and speed measurement accuracy. Summary of the invention

[0004] The purpose of the present invention is to propose an acoustic Doppler velocity measurement waveform design method to solve the problem that the existing method can only perform simple waveform design for velocity measurement accuracy and cannot dynamically adjust the velocity measurement waveform, which leads to poor velocity measurement performance.

[0005] The technical solution adopted by the present invention to solve the above technical problems is:

[0006] An acoustic Doppler velocity measurement waveform design method comprises the following steps:

[0007] Step 1: Obtain the real-time depth h and speed information f of the carrier d ;

[0008] Step 2: The total duration T' of the transmitted signal is obtained according to the depth information of the carrier, and then one fifth of the total duration T' is used as the length of the single-cycle transmitted signal, and combined with the transmitted signal bandwidth B, the number of coding bits N is obtained;

[0009] Step 3: Take the N-bit two-phase code as the optimization initial value, take the code symbol as the optimization variable, and use the design criteria and the sequential quadratic programming algorithm to obtain the coding optimization result, and obtain the optimized Janus four-beam transmission signal s(t). The design criteria are:

[0010] min(NAEχ a )

[0011] Among them, NAEχ a is the normalized ambiguity function average energy of the baseband transmission signal;

[0012] Step 4: Determine the phase change value θ of the transmitted signal based on the obtained speed information:

[0013] Step 5: Select a configuration mode, and select two beam transmission signals from the optimized Janus four-beam transmission signal according to the configuration mode, and then obtain the optimized signal s1(t). The specific steps are as follows:

[0014] If the X-type configuration is selected, the two beam transmission signals closest to the bow of the carrier are selected from the optimized Janus four-beam transmission signals. Then, the two beam transmission signals closest to the bow of the carrier are periodically superimposed according to the obtained transmission signal phase change value θ to obtain the optimized signal s1(t). The other two beam transmission signals remain unchanged to obtain the four-beam optimized signal, thus completing the waveform design.

[0015] If a cross configuration is selected, the beam in the bow direction of the carrier and any one of the left and right beams are selected from the optimized Janus four-beam transmission signal. Then, the selected two-beam transmission signals are periodically superimposed according to the obtained transmission signal phase change value θ to obtain the optimized signal s1(t). The transmission signals of the other two beams remain unchanged to obtain the four-beam optimized signal, thus completing the waveform design.

[0016] Furthermore, the method further includes step six, specifically:

[0017] Step 6: Use the four-beam optimized signal obtained in step 5 as the transmitting signal, and use the pulse pair algorithm to solve the velocity. When solving the selected two beams, subtract θ from the phase of the correlation function in the pulse pair algorithm to perform phase compensation.

[0018] Furthermore, the specific steps of step one are: measuring the real-time depth and speed information of the carrier by transmitting a traditional two-phase coded signal.

[0019] Furthermore, the total duration T' of the transmitted signal is expressed as:

[0020]

[0021] Where c is the speed of sound and k is 0.25.

[0022] Furthermore, the number of encoding bits N is expressed as:

[0023]

[0024] Where B is the transmit signal bandwidth.

[0025] Furthermore, the normalized ambiguity function average energy NAEχ of the baseband signal a It is expressed as:

[0026]

[0027] Among them, χ a (τ,f) is the ambiguity function of the baseband transmission signal, T is the length of a single cycle of the transmission signal, max(Δf d ) is the maximum Doppler frequency difference between different scattering points within the beam footprint.

[0028] Furthermore, the maximum Doppler frequency difference max(Δf d ) is expressed as:

[0029]

[0030] Among them, θ is the beam width, v is the real-time axial velocity under the array system, f0 is the signal center frequency, and α is the angle between the transmitting beam and the horizontal plane.

[0031] Further, the transmission signal phase change value θ is expressed as:

[0032] θ=π-4πf d T.

[0033] Further, the optimized signal s(t) is expressed as:

[0034]

[0035] Where a(t) is the optimized Janus four-beam single-period baseband transmission signal.

[0036] Furthermore, the optimized signal s1(t) is expressed as:

[0037]

[0038] The beneficial effects of the present invention are:

[0039] This application fixes the number of transmission cycles for different depths and speed conditions of real-time feedback, and determines the number of symbols according to the depth information, and uses the waveform design criterion min(NAEx a ) The transmission coding is optimized with the help of a sequential quadratic programming algorithm; then, a periodically changing phase is superimposed on the signals of two of the beams according to the speed information, and finally the optimized transmission signal is used for speed measurement. The method of this application can dynamically adjust the speed measurement waveform according to different depths and speed conditions, improve the speed measurement precision and accuracy, and thus improve the navigation performance in different environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is the overall flow chart of this application. DETAILED DESCRIPTION

[0041] It should be particularly noted that, in the absence of conflict, the various embodiments disclosed in this application can be combined with each other.

[0042] Specific implementation method 1: refer to Figure 1 Specifically describing this embodiment, a method for designing an acoustic Doppler velocity measurement waveform described in this embodiment includes the following steps:

[0043] Step 1: Obtain the real-time depth h and speed information f of the carrier d ;

[0044] Step 2: The total duration T' of the transmitted signal is obtained according to the depth information of the carrier, and then one fifth of the total duration T' is used as the length of the single-cycle transmitted signal, and combined with the transmitted signal bandwidth B, the number of coding bits N is obtained;

[0045] Step 3: Take the N-bit two-phase code as the optimization initial value, take the code symbol as the optimization variable, and use the design criteria and the sequential quadratic programming algorithm to obtain the coding optimization result, and obtain the optimized Janus four-beam transmission signal s(t). The design criteria are:

[0046] min(NAEχ a )

[0047] Among them, NAEχ a is the normalized ambiguity function average energy of the baseband transmission signal;

[0048] Step 4: Determine the phase change value θ of the transmitted signal based on the obtained speed information:

[0049] Step 5: Select a configuration mode, and select two beam transmission signals from the optimized Janus four-beam transmission signal according to the configuration mode, and then obtain the optimized signal s1(t). The specific steps are as follows:

[0050] If the X-type configuration is selected, the two beam transmission signals closest to the bow of the carrier are selected from the optimized Janus four-beam transmission signals. Then, the two beam transmission signals closest to the bow of the carrier are periodically superimposed according to the obtained transmission signal phase change value θ to obtain the optimized signal s1(t). The other two beam transmission signals remain unchanged to obtain the four-beam optimized signal, thus completing the waveform design.

[0051] If a cross configuration is selected, the beam in the bow direction of the carrier and any one of the left and right beams are selected from the optimized Janus four-beam transmission signal. Then, the selected two-beam transmission signals are periodically superimposed according to the obtained transmission signal phase change value θ to obtain the optimized signal s1(t). The transmission signals of the other two beams remain unchanged to obtain the four-beam optimized signal, thus completing the waveform design.

[0052] Specific implementation method 2: This implementation method is a further description of the specific implementation method 1. The difference between this implementation method and the specific implementation method 1 is that the method further includes step 6, which is specifically:

[0053] Step 6: Use the four-beam optimized signal obtained in step 5 as the transmitting signal, and use the pulse pair algorithm to solve the velocity. When solving the selected two beams, subtract θ from the phase of the correlation function in the pulse pair algorithm to perform phase compensation.

[0054] Specific implementation method three: This implementation method is a further explanation of specific implementation method two. The difference between this implementation method and specific implementation method two is that the specific steps of step one are: measuring the real-time depth and speed information of the carrier by transmitting a traditional two-phase coded signal.

[0055] Specific implementation mode 4: This implementation mode is a further description of specific implementation mode 3. The difference between this implementation mode and specific implementation mode 3 is that the total duration T' of the transmitted signal is expressed as:

[0056]

[0057] Wherein, c is the speed of sound, and k=0.25.

[0058] Specific implementation mode 5: This implementation mode is a further description of specific implementation mode 4. The difference between this implementation mode and specific implementation mode 4 is that the number of encoding bits N is expressed as:

[0059]

[0060] Where B is the transmit signal bandwidth.

[0061] Specific implementation method 6: This implementation method is a further description of the specific implementation method 5. The difference between this implementation method and the specific implementation method 5 is that the normalized ambiguity function average energy NAEx of the baseband signal a It is expressed as:

[0062]

[0063] Among them, χ a (τ,f) is the ambiguity function of the baseband transmission signal, T is the length of a single cycle of the transmission signal, max(Δfd ) is the maximum Doppler frequency difference between different scattering points within the beam footprint.

[0064] Specific implementation method 7: This implementation method is a further explanation of specific implementation method 6. The difference between this implementation method and specific implementation method 6 is that the maximum Doppler frequency difference max (Δf d ) is expressed as:

[0065]

[0066] Among them, θ is the beam width, v is the real-time axial velocity under the array system, f0 is the signal center frequency, and α is the angle between the transmitting beam and the horizontal plane.

[0067] Specific implementation eight: This implementation is a further description of specific implementation seven. The difference between this implementation and specific implementation seven is that the phase change value θ of the transmission signal is expressed as:

[0068] θ=π-4πf d T.

[0069] Specific implementation method 9: This implementation method is a further description of specific implementation method 8. The difference between this implementation method and specific implementation method 8 is that the optimization signal s1(t) is expressed as:

[0070]

[0071] Where a(t) is the optimized Janus four-beam single-period baseband transmission signal.

[0072] Specific implementation method ten: This implementation method is a further description of specific implementation method nine. The difference between this implementation method and specific implementation method nine is that the optimization signal s1(t) is expressed as:

[0073]

[0074] Example:

[0075] A method for designing an acoustic Doppler velocity measurement waveform, the method specifically comprising the following steps:

[0076] Step 1: Obtain the real-time depth and speed information of the carrier;

[0077] Step 2: Optimize the transmission signal based on the real-time depth and speed information using a waveform design method that improves speed measurement accuracy;

[0078] Step 3: Optimize the transmission signal based on the real-time speed information using a waveform design method that improves speed measurement accuracy;

[0079] Step 4: Transmit the optimized signal to measure the speed and compensate the result.

[0080] Furthermore, in step 1, the real-time depth and speed information of the carrier are measured by transmitting a conventional two-phase coded signal, where the depth information is represented by h and the speed information is represented by f. d .

[0081] Furthermore, the specific process of step 2 is as follows:

[0082] Step 2.1: Get the total duration of the transmitted signal based on the obtained depth information:

[0083]

[0084] Where T' is the total transmission time, h is the depth information, c is the speed of sound, and k = 0.25;

[0085] Step 2.2: Take one fifth of the total duration T' as the length of the single-cycle transmission signal, and then get the number of coding bits N:

[0086]

[0087] Where B is the transmission signal bandwidth;

[0088] Step 2.3, using N-bit two-phase coding as the optimization initial value, the optimization variable is the coding symbol, and the coding optimization result is obtained by using the sequential quadratic programming algorithm through the design criteria, that is, the optimization of the Janus four-beam transmission signal is completed. The Janus four-beam transmission signal is generally a 45° Janus four-beam transmission signal.

[0089] The design criteria are:

[0090] min(NAEχ a )

[0091] Defining NAEχ a is the normalized ambiguity function average energy of the baseband transmission signal, expressed as:

[0092]

[0093] where χ a (τ,f) is the baseband signal ambiguity function, T is the length of a single cycle of the transmitted signal, max(Δf d ) is the maximum Doppler frequency difference between different scattering points within the beam footprint.

[0094] Furthermore, the maximum Doppler frequency difference max(Δf d ) is expressed as:

[0095]

[0096] Among them, θ is the beam width, v is the real-time axial velocity under the array system, f0 is the signal center frequency, and α is the angle between the transmitting beam and the horizontal plane.

[0097] Furthermore, the specific process of step 3 is as follows:

[0098] Step 3.1: Determine the phase change value of the transmitted signal based on the obtained speed information:

[0099] θ=π-4πf d T

[0100] Step 3.2: According to the optimized 45° Janus four-beam transmission signal, select the two beam transmission signals closest to the bow of the carrier on both sides, and then periodically superimpose the two beam transmission signals according to the obtained phase change value to obtain the optimized signal:

[0101]

[0102] Where a(t) is the baseband transmission signal obtained by optimization in step 2; that is, the waveform design is completed

[0103] Furthermore, the specific process of step 4 is as follows:

[0104] Use the optimized signal as the transmitting signal and use the pulse algorithm to solve the speed to get

[0105] The pulse pair algorithm is used to resolve the velocity, and the phase result is subtracted from θ to perform phase compensation.

[0106] The pulse pair algorithm is used to solve the velocity, and the phase result is compensated by subtracting θ. This sentence should be changed to: The pulse pair algorithm is used to solve the velocity, and the phase of the correlation function in the pulse pair algorithm needs to be compensated by subtracting θ.

[0107] It should be noted that the specific implementation is only an explanation and description of the technical solution of the present invention, and cannot be used to limit the scope of protection of the rights. Any partial changes made according to the claims and description of the present invention should still fall within the scope of protection of the present invention.

Claims

1. A method for designing an acoustic Doppler velocity measurement waveform, characterized in that The following steps are involved: Step 1: Obtain the real-time depth h and speed information f of the carrier d ; Step 2: The total duration T' of the transmitted signal is obtained according to the depth information of the carrier, and then one fifth of the total duration T' is used as the length of the single-cycle transmitted signal, and combined with the transmitted signal bandwidth B, the number of coding bits N is obtained; Step 3: Take the N-bit two-phase code as the optimization initial value, take the code symbol as the optimization variable, and use the design criteria and the sequential quadratic programming algorithm to obtain the coding optimization result, and obtain the optimized Janus four-beam transmission signal s(t). The design criteria are: min(NAEχ a ) Among them, NAEχ a is the normalized ambiguity function average energy of the baseband transmission signal; Step 4: Determine the phase change value θ of the transmitted signal based on the obtained speed information: Step 5: Select a configuration mode, and select two beam transmission signals from the optimized Janus four-beam transmission signal according to the configuration mode, and then obtain the optimized signal s1(t). The specific steps are as follows: If the X-type configuration is selected, the two beam transmission signals closest to the bow of the carrier are selected from the optimized Janus four-beam transmission signals. Then, the two beam transmission signals closest to the bow of the carrier are periodically superimposed according to the obtained transmission signal phase change value θ to obtain the optimized signal s1(t). The other two beam transmission signals remain unchanged to obtain the four-beam optimized signal, thus completing the waveform design. If a cross configuration is selected, the beam in the bow direction of the carrier and any one of the left and right beams are selected from the optimized Janus four-beam transmission signal. Then, the selected two-beam transmission signals are periodically superimposed according to the obtained transmission signal phase change value θ to obtain the optimized signal s1(t). The transmission signals of the other two beams remain unchanged to obtain the four-beam optimized signal, thus completing the waveform design.

2. The method for designing an acoustic Doppler velocity measurement waveform according to claim 1, characterized in that The method further comprises step six, specifically: Step 6: Use the four-beam optimized signal obtained in step 5 as the transmitting signal, and use the pulse pair algorithm to solve the velocity. When solving the selected two beams, subtract θ from the phase of the correlation function in the pulse pair algorithm to perform phase compensation.

3. The method for designing an acoustic Doppler velocity measurement waveform according to claim 2, characterized in that The specific steps of step one are: measuring the real-time depth and speed information of the carrier by transmitting a traditional two-phase coded signal.

4. The method for designing an acoustic Doppler velocity measurement waveform according to claim 3, characterized in that The total duration T' of the transmitted signal is expressed as: Where c is the speed of sound and k is 0.

25.

5. The method for designing an acoustic Doppler velocity measurement waveform according to claim 4, characterized in that The number of encoding bits N is expressed as: Where B is the transmit signal bandwidth.

6. The method for designing an acoustic Doppler velocity measurement waveform according to claim 5, characterized in that The normalized ambiguity function average energy NAEχ of the baseband transmission signal a It is expressed as: Among them, χ a (τ,f) is the ambiguity function of the baseband transmission signal, T is the length of a single cycle of the transmission signal, max(Δf d ) is the maximum Doppler frequency difference between different scattering points within the beam footprint.

7. The method for designing an acoustic Doppler velocity measurement waveform according to claim 6, characterized in that The maximum Doppler frequency difference max(Δf d ) is expressed as: Among them, θ is the beam width, v is the real-time axial velocity under the array system, f0 is the signal center frequency, and α is the angle between the transmitting beam and the horizontal plane.

8. The method for designing an acoustic Doppler velocity measurement waveform according to claim 7, characterized in that The phase change value θ of the transmission signal is expressed as: θ=π-4πf d T.

9. The method for designing an acoustic Doppler velocity measurement waveform according to claim 8, characterized in that The optimized signal s(t) is expressed as: Where a(t) is the optimized Janus four-beam single-period baseband transmission signal.

10. The method for designing an acoustic Doppler velocity measurement waveform according to claim 9, characterized in that The optimized signal s1(t) is expressed as:

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