Inertial navigation close-coupled correction method and system based on time-sharing cooperative underwater acoustic beacon

Abstract

The application belongs to the technical field of deep sea navigation and positioning, and provides an inertial navigation close-coupled correction method and system based on time-sharing cooperative underwater acoustic beacons, which is characterized in that, during the navigation process of an AUV, a pure inertial navigation mode is adopted before the arrival of acoustic auxiliary information, inertial navigation is solved based on collected IMU data and depth sensor data, and the navigation state of the AUV containing accumulated errors is obtained; after the arrival of the acoustic auxiliary information, a combined navigation mode is switched to for solving, acoustic information is broadcasted by time-sharing cooperation of beacons at different positions, the horizontal distance between the AUV and each beacon is solved, and a vertical coordinate constraint is applied; the measured distance and the navigation state of the AUV containing accumulated errors are fused by a close-coupled filtering algorithm, the accumulated errors in the navigation state of the AUV are corrected, and the corrected positioning result of the AUV is obtained. Long-time navigation and high-precision underwater positioning of the AUV are realized.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of deep sea navigation and positioning, and particularly relates to an inertial navigation tightly coupled correction method and system based on time-sharing cooperative underwater acoustic beacon. BACKGROUND

[0002] The statements in this section merely provide background information related to the present application and do not necessarily constitute prior art.

[0003] With the rapid increase in the task demand of ocean science research, resource exploration and environmental monitoring, autonomous underwater vehicles (AUVs) have become the key technical equipment for performing the above tasks due to their high autonomy, high efficiency and the advantage of replacing humans to enter dangerous or remote waters. Among them, the navigation and positioning accuracy of AUV is one of the core elements to determine the success of AUV task, and the cumulative navigation error not only may lead to task failure, but also may seriously reduce the quality and effectiveness of the collected data. Therefore, in order to ensure that AUV can efficiently and reliably perform tasks for a long time, a robust and reliable underwater navigation and positioning system is a prerequisite.

[0004] Due to the strong attenuation effect of electromagnetic waves in seawater, global navigation satellite system (GNSS) cannot be directly used for underwater vehicles, making underwater navigation and positioning face special challenges. At present, underwater navigation and positioning systems can be mainly divided into three categories: autonomous navigation systems based on intrinsic sensors, positioning systems based on acoustics and navigation systems based on geophysical matching. Autonomous navigation systems based on intrinsic sensors (such as strapdown inertial navigation system or Doppler log) have autonomy, but the former has error accumulation problem and often needs to rely on high-cost external acoustic auxiliary means for correction or regularly float to obtain GNSS signal for correction, and has high power consumption; the performance of the latter highly depends on the relative distance between the vehicle and the seabed / water layer, and significantly decreases in deep sea or far bottom environment. The positioning systems based on acoustics (such as long baseline and short baseline system) have high accuracy, but have the disadvantages of complex deployment, high cost, poor concealment, etc. The navigation systems based on geophysical matching (such as terrain matching and geomagnetic matching) have strong dependence on prior map, limited application scope and high equipment cost. Overall, the existing underwater navigation and positioning schemes are difficult to balance between system cost, deployment convenience, operational concealment, long-time performance and navigation accuracy. This contradiction seriously restricts the operational efficiency of AUV in deep sea exploration, large-scale resource exploration and other long-time and large-scale tasks.

[0005] In recent years, acoustic information-assisted inertial navigation has come into the research spotlight. Among them, inertial navigation schemes based on single beacons have attracted attention due to their ability to simplify system deployment. However, this scheme has an inherent drawback of insufficient observability: the ranging information of a single beacon cannot uniquely determine the global position of the vehicle, resulting in limited ability to correct for accumulated errors in inertial navigation. Summary of the Invention

[0006] To address at least one of the technical problems mentioned above, this invention provides an inertial navigation tightly coupled correction method and system based on time-division cooperative underwater acoustic beacons. Without increasing system cost, complexity, or power consumption, this invention overcomes the shortcomings of "multiple beacons emitting high-frequency sound (leading to high power consumption and signal conflict)" and "insufficient observability of a single beacon (leading to low accuracy)" through innovative beacon operating modes and information fusion mechanisms, thereby achieving long-endurance, high-precision underwater positioning for AUVs.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A first aspect of the present invention provides an inertial navigation tightly coupled correction method based on time-division cooperative underwater acoustic beacons, comprising the following steps:

[0009] The AUV receives broadcast acoustic signals simultaneously emitted by each stationary beacon, performs initial position calculation, and obtains the initial position of the AUV.

[0010] During navigation, when no acoustic assistance information is received, the AUV adopts a pure inertial navigation mode, taking the AUV's initial position as the starting point of the calculation, and combining the collected IMU data and depth sensor data to perform inertial navigation calculation, thereby obtaining the inertial navigation error ellipse that represents the prior probability distribution of the predicted value of the current error state.

[0011] Upon receiving acoustic assistance information, the system switches to integrated navigation mode for calculation. Multiple stationary beacons broadcast acoustic signals in turn according to a preset period. Based on the received acoustic signal from the current stationary beacon, the system calculates the three-dimensional spatial position between the AUV and the beacon. Combined with depth information, a strong constraint is formed on the vertical coordinates of the AUV, resulting in a two-dimensional distance constraint circle representing the observation likelihood function. The inertial navigation error ellipse and the distance constraint circle are filtered and fused to calculate the updated optimal position and probability distribution boundary.

[0012] Furthermore, the method also includes: deploying at least three stationary beacons according to a preset scheme to ensure that the AUV operating area is within the acoustic coverage of multiple beacons, wherein the preset scheme is to deploy multiple stationary beacons in a configuration with an optimized geometric accuracy factor.

[0013] Furthermore, the specific mechanism for multiple stationary beacons to broadcast acoustic signals in turn is as follows: a broadcast period T is set, and the three beacons broadcast sequentially in a loop at the set broadcast period T. At the beginning time t0, beacon 1 broadcasts, while beacons 2 and 3 are in receiving or sleep mode; at time t1 = t0 + T, beacon 2 broadcasts, while beacons 1 and 3 are in receiving or sleep mode; at time t2 = t0 + 2T, beacon 3 broadcasts, while beacons 1 and 2 are in receiving or sleep mode; at time t3 = t0 + 3T, the loop returns to beacon 1 broadcasting, and the loop continues in sequence.

[0014] Furthermore, based on the received acoustic signal from the currently stationary beacon, the three-dimensional spatial position between the AUV and the beacon is calculated, including: calculating the spatial slant distance between the AUV and the beacon based on the signal propagation time. This spatial slant distance defines a sphere with the beacon as its center and the slant distance as its radius, on which the AUV should be located.

[0015] Furthermore, by combining depth information to form a strong constraint on the vertical coordinates of the AUV, a two-dimensional distance constraint circle characterizing the observation likelihood function is obtained, including:

[0016] The AUV must simultaneously lie on the horizontal plane corresponding to its current depth, which intersects the sphere. The projection of the intersection line onto the horizontal plane is a two-dimensional horizontal distance constraint circle, the center of which is the horizontal projection coordinate of the beacon. The radius is the horizontal distance R calculated based on the slope distance and depth difference.

[0017] Furthermore, the process of filtering and fusing the inertial navigation error ellipse and the range constraint circle to calculate the updated optimal position and probability distribution boundary includes:

[0018] The expected observations are calculated based on the current error state predictions. A first-order Taylor expansion is then performed on the expected observations at the current error state predictions to obtain the observation matrix.

[0019] The Kalman gain is calculated by combining the covariance matrix of the observation noise, the prediction uncertainty, and the observation matrix.

[0020] Based on Kalman gain, observation information is incorporated into prior estimation to obtain posterior probability distribution and orthogram. The mean of the posterior probability distribution is the updated optimal location estimate, and the covariance is the new probability distribution boundary.

[0021] A second aspect of the present invention provides an inertial navigation tightly coupled correction system based on time-division cooperative underwater acoustic beacons, comprising:

[0022] The initial position determination module is used to receive the broadcast acoustic signals emitted simultaneously by each stationary beacon, perform initial position calculation, and obtain the initial position of the AUV.

[0023] The cumulative error acquisition module is used by the AUV in pure inertial navigation mode during navigation when no acoustic assistance information is received. It takes the initial position of the AUV as the starting point of the calculation, combines the collected IMU data and depth sensor data to perform inertial navigation calculation, and obtains the inertial navigation error ellipse that represents the prior probability distribution of the predicted value of the current error state.

[0024] The coupling correction module is used to switch to the integrated navigation mode for calculation when acoustic auxiliary information is received. Multiple stationary beacons broadcast acoustic signals in turn according to a preset period. Based on the acoustic signal of the current stationary beacon, the three-dimensional spatial position between the AUV and the beacon is calculated. Combined with depth information, a strong constraint is formed on the vertical coordinate of the AUV to obtain a two-dimensional distance constraint circle representing the observation likelihood function. The inertial navigation error ellipse and the distance constraint circle are filtered and fused to calculate the updated optimal position and probability distribution boundary.

[0025] A third aspect of the present invention provides a computer-readable storage medium.

[0026] A computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps in the inertial navigation tightly coupled correction method based on time-division cooperative underwater acoustic beacons as described above.

[0027] A fourth aspect of the present invention provides a computer device.

[0028] A computer device includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the steps in the inertial navigation tight coupling correction method based on time-division cooperative underwater acoustic beacons as described above.

[0029] Compared with the prior art, the beneficial effects of the present invention are:

[0030] 1. High positioning accuracy and good long-term stability are mainly attributed to the technical features of "enhanced observability" and "tightly coupled fusion mechanism." Time-division co-emitting beacons provide observation information from different directions, fundamentally solving the problem of insufficient observability in single-beacon systems, enabling the filter to fully estimate and correct the accumulated error of the inertial navigation system. Compared with the optimal single-beacon scheme, the root mean square error of this invention is reduced by 79.8%.

[0031] 2. Low power consumption, an advantage directly stemming from the "time-sharing coordination mechanism" technology. Compared to traditional long-baseline systems that require all beacons to operate frequently or simultaneously, this solution reduces the signal transmission frequency of each beacon from the second level to the minute level, significantly reducing its average power consumption and fundamentally ensuring long-endurance.

[0032] 3. Flexible deployment, strong anti-interference capability, wide coverage, and low overall cost are advantages directly stemming from the "time-sharing coordination mechanism." This mechanism avoids signal collisions between beacons at the protocol level, reducing the risk of multipath interference. Compared to traditional long-baseline deployment schemes, the coverage area for the same number of beacons increases by approximately 60%-70%, significantly reducing the total cost of ownership for equipment procurement, deployment, and recovery maintenance, while maintaining high deployment flexibility.

[0033] Advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0034] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0035] Figure 1 This is a flowchart of the inertial navigation tight coupling correction method based on time-division cooperative underwater acoustic beacons provided in an embodiment of the present invention;

[0036] Figure 2 This is a beacon network distribution and vehicle trajectory diagram provided in an embodiment of the present invention;

[0037] Figure 3 This is a scene diagram based on time-division cooperative underwater acoustic beacons provided in an embodiment of the present invention;

[0038] Figure 4 This is a schematic diagram of the distance-assisted inertial navigation principle provided in an embodiment of the present invention;

[0039] Figure 5 This is a graph showing the trend of radial positioning error over time under different assisted navigation schemes provided in the embodiments of the present invention;

[0040] Figure 6 This is an architecture diagram of an inertial navigation tightly coupled correction system based on time-division cooperative underwater acoustic beacons provided in an embodiment of the present invention. Detailed Implementation

[0041] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0042] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0043] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0044] Traditional long-baseline navigation and positioning schemes typically require three or more beacons to emit signals synchronously at high frequencies (several seconds to tens of seconds), resulting in high system power consumption and limited continuous operating time. This invention proposes an optimization strategy: using only three stationary beacons and extending their emission intervals to several minutes or even tens of minutes, through a time-sharing cooperative working mechanism, significantly improving the observability and correction capabilities of the navigation system while ensuring extremely low system power consumption. Specifically, this is reflected in the following aspects:

[0045] First, innovative beacon operating mode: A rotating broadcasting network consisting of three stationary beacons is established, employing a time-sharing asynchronous broadcasting mechanism. At any given time, only one beacon is broadcasting, while the others are in low-power sleep mode. The broadcasting cycle of a single beacon is 12-30 minutes, thus reducing system power consumption.

[0046] Second, the observability enhancement design: by providing sparse acoustic ranging information from different directions through three spatially distributed beacons, the problem of insufficient observability of the single-beacon-assisted inertial navigation system is solved, and multi-directional constraint correction of the cumulative error of the inertial navigation is achieved.

[0047] Third, the tightly coupled fusion mechanism: the acoustic ranging information and the inertial navigation data are directly tightly coupled to make full use of the original observation information and improve the system robustness in scenarios with low signal-to-noise ratio or partial signal loss.

[0048] Fourth, dynamic mode switching: The AUV automatically switches between "pure inertial navigation mode" and "integrated navigation mode" based on the availability of acoustic signals to ensure positioning continuity and accuracy.

[0049] Example 1

[0050] like Figure 1 As shown, this embodiment provides inertial navigation tight coupling correction based on time-division cooperative underwater acoustic beacons, including the following steps:

[0051] Step 1: Deploy at least three stationary beacons according to the preset deployment plan to ensure that the AUV operating area is within the acoustic coverage of multiple beacons, and at the same time obtain the absolute coordinates of each stationary beacon;

[0052] In this embodiment, taking three stationary beacons as an example, the deployment scheme to ensure that the AUV operating area is within the acoustic coverage of the three beacons is as follows: the three beacons are arranged in a configuration with optimized geometrical dilution precision (GDOP).

[0053] Preferably, the beacon is arranged in an equilateral triangle configuration with a side length of 5000m. For example, beacon 1 coordinates: (0,0) / / unit: meters, beacon 2 coordinates: (2500,4330) / / vertex of the equilateral triangle, beacon 3 coordinates: (5000,0); the vehicle trajectory is simulated in a zigzag pattern, such as... Figure 2 As shown.

[0054] In this embodiment, the absolute coordinates of each stationary beacon can be obtained using GNSS+acoustic calibration technology, which accurately obtains the absolute coordinates of the three beacons; the calibration error is <3m.

[0055] Furthermore, the three stationary beacons are time-synchronized with the AUV with an error of ≤1ms.

[0056] Step 2: AUV initial alignment: Receive the broadcast acoustic signals emitted simultaneously by each beacon and calculate the initial position of the AUV, which will be used as the starting point for subsequent pure inertial navigation mode calculations.

[0057] In this embodiment, each beacon simultaneously emits broadcast acoustic signals at a set time interval, for example, at intervals of 4-8 seconds;

[0058] Specifically, after obtaining the acoustic signals from the three beacons, a long baseline model is established to calculate the horizontal geometric position, and the initial position of the AUV is calculated by combining the depth sensor data.

[0059] Step 3: Dynamic navigation operation: During the flight, before the arrival of acoustic assistance information, the AUV adopts pure inertial navigation mode. Based on the collected IMU data and depth sensor data, inertial navigation calculation is performed to obtain the AUV's real-time position, velocity, and attitude. At the same time, according to the inertial navigation error model, the system model input is provided for the calculation of the combined navigation mode.

[0060] In this embodiment, in pure inertial navigation mode, the positioning error accumulates over time, and the error range is represented by an "inertial navigation error ellipse." The inertial navigation error ellipse is a visualization of the prior probability distribution of the predicted value of the current error state; its mathematical expression is a method for calculating position using inertial navigation. The mean is given by the prediction error covariance matrix. A two-dimensional Gaussian distribution describing uncertainty. The "ellipse" is the isoprobability density line of this Gaussian distribution (e.g., the 95% confidence interval), whose size, shape, and direction are determined by... The eigenvalues ​​and eigenvectors determine this. The definition is based on the uncertainty propagation of the inertial sensor error model and the dynamic model during the state transition process.

[0061] Step 4: After the acoustic auxiliary information arrives, switch to the integrated navigation mode for calculation, receive the acoustic signal of the current broadcast beacon, and calculate the horizontal distance between the AUV and the beacon using the propagation time information contained in the acoustic signal. The ranging information provided by the three beacons from different spatial directions in turn, combined with the absolute coordinates of the three stationary beacons, constitutes a multi-directional absolute geometric constraint in the time series, which is continuously coupled to the filter to enhance the observability of the system state.

[0062] In this embodiment, when beacons at different locations broadcast acoustic information in a time-division coordinated manner, the beacons are scheduled to emit sound in turn according to a preset period, such as... Figure 3 As shown, by using three stationary beacons to emit sound in turn at a long period of minutes, while ensuring low power consumption, the observability of the single-beacon-assisted inertial navigation system is effectively enhanced by utilizing acoustic information from different spatial directions, thereby achieving robust correction of the cumulative error of the inertial navigation system.

[0063] The specific broadcasting mechanism is as follows: The broadcasting period is set to T, and the start time is t0. At time t0, beacon 1 starts broadcasting, while beacons 2 and 3 switch to receiving mode. At time t1 = t0 + T, beacon 2 starts broadcasting, and beacons 1 and 3 switch to receiving mode. At time t2 = t0 + 2T, beacon 3 starts broadcasting, and beacons 1 and 2 switch to receiving mode. When time t3 = t0 + 3T is reached, a new period begins, and beacon 1 starts broadcasting again. Through this mechanism, the AUV can sequentially receive acoustic signals from different beacons during navigation, and combine this with inertial navigation data to achieve continuous high-precision positioning.

[0064] This is represented as: at time t0: beacon 1 broadcasts acoustic signals, beacon 2 / 3 are in sleep (or receive mode);

[0065] At time t1 = t0 + T: Beacon 2 broadcasts acoustic signals, Beacon 1 / 3 goes into sleep mode;

[0066] At time t2 = t0 + 2T: Beacon 3 broadcasts acoustic signals, Beacon 1 / 2 goes into sleep mode;

[0067] At time t3 = t0 + 3T: the broadcast loops back to beacon 1, forming a periodic alternating sound.

[0068] When an AUV receives an acoustic signal from a beacon, the specific processing steps are as follows:

[0069] Step 401: Calculate the spatial slant distance between the AUV and the beacon based on the signal propagation time;

[0070] In this embodiment, in the three-dimensional positioning model, the spatial slant range defines a sphere with the beacon as the center and the slant range as the radius, and the AUV should be located on this sphere;

[0071] Step 402: Combining depth information, a strong constraint is formed on the vertical coordinates of the AUV to obtain a two-dimensional horizontal distance constraint circle;

[0072] In this embodiment, by combining the real-time, high-precision depth information provided by the depth gauge, a strong constraint can be formed on the vertical coordinates of the AUV. That is, the AUV must be simultaneously located on the horizontal plane corresponding to its current depth. This horizontal plane intersects with the aforementioned spherical surface, and the projection of the intersection line onto the horizontal plane is a two-dimensional horizontal distance constraint circle, the center of which is the horizontal projection coordinate of the beacon. The radius is the horizontal distance R calculated from the slope distance and depth difference. Therefore, the three-dimensional positioning problem is simplified to positioning within a two-dimensional plane.

[0073] This "dimensionality reduction constraint" method not only reduces the dimension of state estimation from three dimensions to two dimensions, significantly reducing the computational complexity of the filter, but also effectively avoids the interference of inertial navigation vertical channel errors on horizontal positioning by introducing independent and accurate depth information.

[0074] In a probabilistic sense, this "distance constraint circle" is not an ideal geometric circle, but rather defines an observation likelihood function: the true location of the AUV is most likely to appear near the beacon with a radius R, and its uncertainty is described by the variance of the observation noise.

[0075] Step 403: By using extended Kalman filtering, the inertial navigation error ellipse, which represents the prior probability distribution of the current error state prediction value, and the distance constraint circle, which represents the observation likelihood function, are fused to calculate the updated optimal position and the new probability distribution boundary.

[0076] Specifically, the steps include the following:

[0077] Filter fusion is the core of integrated navigation algorithms. Essentially, it's the update process within the Extended Kalman Filter (EKF), aiming to achieve optimal fusion of prediction and observation information based on a probabilistic framework. Through EKF, the "inertial navigation error ellipse" (prior probability distribution) and the "range constraint circle" (observation likelihood), representing prediction uncertainty, are fused to calculate the mean of the posterior probability distribution. (i.e., the updated optimal error estimate) and covariance (i.e., the new probability distribution boundary), its geometric representation is as follows: Figure 4 As shown. The specific fusion steps are as follows:

[0078] Step 4031: Observation Prediction and Linearization: Predict values ​​based on the current error state Calculate the expected observations (predicted distance). , Let the geometric distance function be the AUV's predicted location to the beacon, and let the predicted distance be... exist A first-order Taylor expansion is performed to obtain the observation matrix (Jacobi matrix), thereby achieving local linearization of the nonlinear observation equation. The observation matrix is ​​expressed as:

[0079]

[0080] Step 4032: Combine the covariance matrix of the observation noise Forecast uncertainty and observation matrix Calculate the Kalman gain;

[0081] Kalman gain This is the key matrix that determines the weights between prior estimates and observed values, and its calculation formula is: ;

[0082] Step 4033: Based on Kalman gain, incorporate the observation information into the prior estimate to obtain the uncertainty of the posterior error state estimate and the updated state estimate;

[0083] The position update formula for the AUV is as follows:

[0084] ,

[0085] The uncertainty (i.e., error covariance) of the updated state estimate is:

[0086] ,

[0087] in, For optimal state estimation using the extended Kalman filter, The measured value is the horizontal distance. The updated covariance matrix is ​​used to estimate the uncertainty.

[0088] After fusing observational information, the uncertainty of the estimate is reduced, and a new, smaller "error ellipse" is defined as the prior uncertainty of the prediction step at the next time step.

[0089] As beacons broadcast in turn, the AUV-end navigation subsystem uses the ranging information provided by beacons at different spatial locations to periodically apply constraints from different directions, completing an omnidirectional correction every 3T cycle. This achieves continuous high-precision correction of the accumulated errors of the inertial navigation system, ensuring stable and reliable navigation and positioning during long-endurance travel.

[0090] In the above process, the acoustic information broadcast by the three beacons in a time-division coordinated manner is used to improve navigation and positioning accuracy while maintaining low power consumption. Based on the inertial navigation accuracy and working area range of the AUV, the beacon broadcast signal frequency and beacon spacing are reasonably arranged to achieve the optimal balance between positioning accuracy and system power consumption.

[0091] Figure 5 The left and right sub-graphs are used to compare and show how the radial positioning error changes over time under different assisted navigation schemes. Figure 5 (a) shows the error trend over the entire time period (0–7000 seconds). Figure 5 Image (b) shows a detailed magnification of a local time period (4000–7000 seconds), demonstrating the significant advantages of the time-sharing cooperative beacon scheme in error control. The results show that the time-sharing cooperative beacon-assisted INS, through multi-beacon alternating observation and tight coupling fusion, significantly suppresses the accumulation of inertial navigation errors, improves the long-term accuracy and stability of the system, and verifies the effectiveness and reliability of this invention in complex underwater environments.

[0092] Table 1 compares the positioning performance of different navigation systems in underwater environments, as shown below:

[0093] Table 1. Comparison of Positioning Performance of Different Navigation Systems in Underwater Environment

[0094]

[0095] Compared with the optimal single beacon scheme, the solution of this invention has the following advantages:

[0096] 1. Positioning accuracy is significantly improved: the root mean square error is reduced by 79.8% (from 414.95m to 83.93m);

[0097] 2. Enhanced system stability: The maximum error decreased from 1047.71m to 359.48m, indicating that the system has better error boundary control capability;

[0098] 3. Fundamental improvement in observability: By providing observation information from different directions in turn through three beacons, the system's observability is improved from insufficient to sufficient.

[0099] Example 2

[0100] like Figure 6 The diagram shows the overall architecture of a tightly coupled inertial navigation correction system based on time-division cooperative underwater acoustic beacons, including a beacon network subsystem and an AUV-end navigation subsystem, which are connected via acoustic broadcast signals.

[0101] Among them, the beacon network subsystem, as an external reference source, is the key to the system's low power consumption and high accuracy, and includes three stationary beacons;

[0102] In this embodiment, the three stationary beacons are deployed according to the optimized positioning geometric precision factor (GDOP) and their positions are precisely calibrated.

[0103] The beacon has two operating modes: initialization and alternating beeping.

[0104] In initialization mode, all three beacons can emit signals simultaneously for high-precision initial alignment of the AUV. In alternating emission mode, a time-division coordinating mechanism is employed, with the three beacons emitting acoustic ranging signals in a preset sequence, ensuring that only one beacon is broadcasting at any given time, while the others are in low-power receiving or sleep mode. This "working" The extremely low duty cycle mode of "long sleep" fundamentally reduces system power consumption and the probability of channel collisions, which is the core design for achieving long battery life. In addition, the beacon can be in receive mode during non-broadcast periods, further supporting extended functions such as network status monitoring and time synchronization, enhancing the system's flexibility and maintainability.

[0105] The AUV-side navigation subsystem, as the core processing unit, adopts a three-layer architecture to achieve multi-source information fusion and high-precision positioning, including a data acquisition layer, an information processing layer, an algorithm layer, and a decision layer. The data acquisition layer integrates an IMU, a hydrophone, and a depth sensor. The information processing layer calculates the acoustic information as the distance between the beacon and the AUV. The algorithm and decision layers automatically switch algorithm modes based on the availability of acoustic signals to achieve high-precision navigation and positioning.

[0106] The data acquisition layer includes an inertial measurement unit, a depth sensor, and a hydrophone array.

[0107] In this embodiment, the inertial measurement unit adopts an optical fiber IMU with a sampling rate of 200Hz, a gyroscope zero-bias stability of 0.027° / h, and an accelerometer zero-bias stability of 15mGal.

[0108] The depth sensor is pressure-based, with a measurement accuracy of ≤0.1mFS, ensuring precise vertical constraint.

[0109] The ranging accuracy of the hydrophone array is 2m;

[0110] Before the arrival of acoustic assistance information, a pure inertial navigation mode is used for calculation, and autonomous inertial navigation is performed based on fiber optic inertial navigation and depth gauge data. The output results are continuous but have accumulated errors. When relying solely on inertial navigation, the positioning error accumulates over time, and its uncertainty range is represented by an inertial navigation error ellipse. After the arrival of acoustic assistance information, the calculation is switched to a combined navigation mode. First, the hydrophone is used to receive and calculate the acoustic distance information, forming a distance constraint circle on a two-dimensional plane with the beacon as the center and the measured distance as the radius. Combined with the precise constraint of the vertical channel by the depth sensor, the three-dimensional positioning problem is simplified to two dimensions. Then, through the extended Kalman filter algorithm, the horizontal distance constraint circle intersects with the inertial navigation error ellipse, jointly defining the probability distribution boundary of the AUV's position, thereby achieving effective correction of the accumulated inertial navigation error.

[0111] Multiple beacons provide ranging information in turn, applying constraints from different directions multiple times, which significantly improves the accuracy and reliability of error correction.

[0112] Multiple beacons that emit sound in turn provide distance observations from different spatial directions, which helps to overcome the lack of observability in single-beacon-assisted inertial navigation systems, enabling the filter to fully observe and correct the inertial navigation. At the same time, the tightly coupled algorithm directly fuses the original ranging information and inertial navigation data. Compared with the loosely coupled method of solving the position first and then fusing, it can make fuller use of the observation information and is more robust when the signal is partially lost or the signal-to-noise ratio is low.

[0113] It should be noted that the specific implementation of the inertial navigation tight coupling correction system based on time-division cooperative underwater acoustic beacon in this embodiment of the invention is similar to the specific implementation of the inertial navigation tight coupling correction method based on time-division cooperative underwater acoustic beacon in this embodiment of the invention. For details, please refer to the description in the method section. In order to reduce redundancy, it will not be repeated here.

[0114] Example 3

[0115] This embodiment provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the steps in the inertial navigation tight coupling correction method based on time-division cooperative underwater acoustic beacons as described above.

[0116] Example 4

[0117] This embodiment provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the steps in the inertial navigation tight coupling correction method based on time-division cooperative underwater acoustic beacons as described above.

[0118] Example 5

[0119] This embodiment provides a program product, which is a computer program product, including a computer program. When the computer program is executed by a processor, it implements the steps in the inertial navigation tight coupling correction method based on time-division cooperative underwater acoustic beacons as described above.

[0120] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of hardware embodiments, software embodiments, or embodiments combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage and optical storage) containing computer-usable program code.

[0121] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0122] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0123] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0124] Those skilled in the art will understand that all or part of the processes in the above embodiments can be implemented by a computer program instructing related hardware. The program can be stored in a computer-readable storage medium, and when executed, it can include the processes of the embodiments of the above methods. The storage medium can be a magnetic disk, optical disk, read-only memory (ROM), or random access memory (RAM), etc.

[0125] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A tightly coupled inertial navigation correction method based on time-division cooperative underwater acoustic beacons, characterized in that, include: The AUV receives broadcast acoustic signals simultaneously emitted by each stationary beacon, performs initial position calculation, and obtains the initial position of the AUV. During navigation, when no acoustic assistance information is received, the AUV adopts a pure inertial navigation mode, taking the AUV's initial position as the starting point of the calculation, and combining the collected IMU data and depth sensor data to perform inertial navigation calculation, thereby obtaining the inertial navigation error ellipse that represents the prior probability distribution of the predicted value of the current error state. Upon receiving acoustic assistance information, the system switches to integrated navigation mode for calculation. Multiple stationary beacons broadcast acoustic signals in turn according to a preset period. Based on the received acoustic signal from the current stationary beacon, the system calculates the three-dimensional spatial position between the AUV and the beacon. Combined with depth information, a strong constraint is formed on the vertical coordinates of the AUV, resulting in a two-dimensional distance constraint circle characterizing the observation likelihood function. The inertial navigation error ellipse and the distance constraint circle are filtered and fused to calculate the updated optimal position and probability distribution boundary. The specific mechanism for multiple stationary beacons to broadcast acoustic signals in turn is as follows: A broadcast period T is set, and the three beacons broadcast sequentially in a loop at the set broadcast period T. At the beginning time t0, beacon 1 broadcasts, while beacons 2 and 3 are in receiving or sleep mode; at time t1 = t0 + T, beacon 2 broadcasts, while beacons 1 and 3 are in receiving or sleep mode; at time t2 = t0 + 2T, beacon 3 broadcasts, while beacons 1 and 2 are in receiving or sleep mode; at time t3 = t0 + 3T, the loop returns to beacon 1, and the loop continues in this manner. Based on the received acoustic signal from the current stationary beacon, calculate the three-dimensional spatial position between the AUV and the beacon, including: calculating the spatial slant distance between the AUV and the beacon based on the signal propagation time. The spatial slant distance defines a sphere with the beacon as the center and the slant distance as the radius, and the AUV should be located on this sphere. The process of filtering and fusing the inertial navigation error ellipse and the range constraint circle to calculate the updated optimal position and probability distribution boundary includes: The expected observations are calculated based on the current error state predictions. A first-order Taylor expansion is then performed on the expected observations at the current error state predictions to obtain the observation matrix. The Kalman gain is calculated by combining the covariance matrix of the observation noise, the prediction uncertainty, and the observation matrix. Based on Kalman gain, observation information is incorporated into prior estimation to obtain posterior probability distribution and orthogram. The mean of the posterior probability distribution is the updated optimal location estimate, and the covariance is the new probability distribution boundary.

2. The inertial navigation tight coupling correction method based on time-division cooperative underwater acoustic beacons as described in claim 1, characterized in that, The method further includes: deploying at least three stationary beacons according to a preset scheme to ensure that the AUV operating area is within the acoustic coverage of multiple beacons, wherein the preset scheme is to deploy multiple stationary beacons in a configuration with an optimized geometric accuracy factor.

3. The inertial navigation tight coupling correction method based on time-division cooperative underwater acoustic beacons as described in claim 1, characterized in that, The combination of depth information creates a strong constraint on the vertical coordinates of the AUV, resulting in a two-dimensional distance constraint circle characterizing the observation likelihood function, including: The AUV must simultaneously lie on the horizontal plane corresponding to its current depth, which intersects the sphere. The projection of the intersection line onto the horizontal plane is a two-dimensional horizontal distance constraint circle, the center of which is the horizontal projection coordinate of the beacon. The radius is the horizontal distance R calculated based on the slope distance and depth difference.

4. An inertial navigation tightly coupled correction system based on time-division cooperative underwater acoustic beacons, characterized in that, The method for implementing the inertial navigation tight coupling correction method based on time-division cooperative underwater acoustic beacons as described in any one of claims 1-3 includes: The initial position determination module is used to receive the broadcast acoustic signals emitted simultaneously by each stationary beacon, perform initial position calculation, and obtain the initial position of the AUV. The cumulative error acquisition module is used by the AUV in pure inertial navigation mode during navigation when no acoustic assistance information is received. It takes the initial position of the AUV as the starting point of the calculation, combines the collected IMU data and depth sensor data to perform inertial navigation calculation, and obtains the inertial navigation error ellipse that represents the prior probability distribution of the predicted value of the current error state. The coupling correction module is used to switch to the integrated navigation mode for calculation when acoustic auxiliary information is received. Multiple stationary beacons broadcast acoustic signals in turn according to a preset period. Based on the acoustic signal of the current stationary beacon, the three-dimensional spatial position between the AUV and the beacon is calculated. Combined with depth information, a strong constraint is formed on the vertical coordinate of the AUV to obtain a two-dimensional distance constraint circle representing the observation likelihood function. The inertial navigation error ellipse and the distance constraint circle are filtered and fused to calculate the updated optimal position and probability distribution boundary.

5. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the steps in the inertial navigation tight coupling correction method based on time-division cooperative underwater acoustic beacons as described in any one of claims 1-3.

6. A computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the steps in the inertial navigation tight coupling correction method based on time-division cooperative underwater acoustic beacons as described in any one of claims 1-3.

7. A program product, said program product being a computer program product, comprising a computer program, characterized in that, When the computer program is executed by the processor, it implements the steps in the inertial navigation tight coupling correction method based on time-division cooperative underwater acoustic beacons as described in any one of claims 1-3.

Images