Ultra-short baseline positioning method based on timestamp-based two-way precise time delay measurement

Abstract

This invention discloses an ultra-short baseline (USBR) positioning method based on timestamp-based two-way precise time delay measurement. It estimates the time delays on both sides of the USBR by combining timestamp information with cross-correlation and utilizing the time reference chip's time information acquisition function. The approximate distance between the underwater work unit and the surface USBR platform is obtained by calculating the time delay using the timestamp sent by the platform and the time reference chip on the underwater work unit. The underwater work unit can send its current time information when emitting acoustic signals as a timestamp to the surface platform to obtain more accurate data, thereby estimating the motion state of the underwater device and improving underwater acoustic positioning. This invention's USBR positioning method effectively improves the positioning accuracy of USBR systems.

Description

Technical Field

[0001] This invention relates to the field of marine surveying technology, and in particular to an ultra-short baseline positioning method based on timestamp-based two-way precise time delay measurement. Background Technology

[0002] Ultra-short baseline (USLB) positioning systems are widely used in underwater positioning due to their small size, light weight, and portability. Their positioning principle utilizes the phase difference (or time delay difference) between the underwater response signal arriving at the receiving unit, combined with the propagation delay between the underwater target and the USLB array, to calculate the data and achieve positioning. A sound source at a certain depth above the sea surface emits a sound signal downwards at a certain angle. When an underwater target is detected, the target reflects the sound signal back to the receiver. Then, based on the signal propagation delay and sound velocity profile, the distance from the target to the sound source is obtained, and combined with the angle information, the precise location of the target is obtained. However, traditional USLB positioning systems also have some shortcomings.

[0003] On the one hand, existing traditional USMR (Ultra-Short Baseline) underwater work units cannot obtain accurate one-sided propagation delays, thus failing to determine their distance from the surface platform and limiting certain underwater operations. On the other hand, existing USMR systems use half of the propagation delay as the slant range and positioning parameters when calculating positioning on the surface platform. However, underwater work devices move a certain distance during underwater operations, meaning the propagation delay parameters calculated by the surface platform are not truly accurate, impacting the positioning accuracy of the USMR system. Summary of the Invention

[0004] To overcome the aforementioned problems in the prior art, this invention proposes an ultra-short baseline positioning method based on timestamp-based two-way precise time delay measurement.

[0005] The technical solution adopted by this invention to solve its technical problem is: an ultra-short baseline positioning method based on timestamp-based two-way precise time delay measurement, comprising the following steps:

[0006] Step 1: The deck unit receives the pre-group code of the underwater acoustic transponder from the control terminal. The dedicated signal processor calculates and generates the corresponding response synchronization sequence and information sequence, and sends the positioning command to the acoustic transducer array.

[0007] Step 2: After receiving the encoded sequence and positioning command, the acoustic transducer array starts the transmitting module to send a wake-up signal and a modulated signal carrying timestamp information at fixed intervals, and at the same time turns on the receiving module.

[0008] Step 3: The underwater acoustic transponders in the same group within the area are awakened by the wake-up signal. After confirmation, they receive the timestamp information and calculate the one-sided propagation delay through their own calculations. Then, they calculate the approximate distance between themselves and the surface unit, transmit the spread spectrum signal, and transmit the modulated signal carrying the timestamp information in conjunction with the time reference chip.

[0009] Step 4: After receiving the response signal, the acoustic transducer array samples and transmits it to a dedicated signal processor to complete the signal synchronization and demodulation to obtain the corresponding timestamp information, and calculate the time delay and phase information of each channel.

[0010] Step 5: The deck unit combines GPS, compass and sonic profiler data to calculate the geographic coordinates of each underwater acoustic transponder in the group, and performs a certain motion trajectory estimation based on the underwater working unit in motion state to complete the precise positioning.

[0011] In the above-described two-way precise time delay measurement method based on timestamps, the wake-up signal detection method in step 3 is as follows: the time-domain expression of the detected signal energy is:

[0012] Where D(Y) represents the value of the decision variable, N represents the number of signal samples during detection, and n represents the number of sampling points; Y(n) = W(n) represents the sampled value of noise in the channel; when the energy value of the detected signal is greater than D(Y), the detected signal is the wake-up signal.

[0013] In the aforementioned ultra-short baseline positioning method based on timestamp-based two-way precise time delay measurement, after the underwater acoustic transponder is woken up in step 3, the transponder demodulates the received timestamp signal to obtain the time information of the acoustic signal transmitted on the water, and subtracts it from the value obtained by its own time reference chip to obtain the precise propagation delay t of the preceding stage. a The approximate distance between the underwater acoustic transponder and the surface platform is measured based on the current sound speed for underwater operations.

[0014] The above-mentioned ultra-short baseline positioning method based on timestamp-based two-way precise time delay measurement, specifically includes the geographic coordinate calculation process for each underwater acoustic transponder in step 5:

[0015] Step 5.1: Calculate the direction angles α and β, and the incident angle θ of the sound wave in the direction of the acoustic transducer array;

[0016] Step 5.2: After the surface operating platform receives the timestamp sent by the underwater acoustic transponder, the transmission time t of the acoustic signal sent by the underwater acoustic transponder is obtained. down And based on its current signal reception time t up The difference yields the precise propagation delay t. b =t up -t down , used for calculating vocal correction parameters;

[0017] Step 5.3: Divide the sound velocity profile into N layers at equal intervals from the vertical depth of the water surface to the underwater acoustic transponder, with each layer having the same spacing, and treat the change in sound velocity as a linear change;

[0018] Step 5.4, based on the layered sound ray tracking in Step 5.3, the sound ray propagates in the i-th layer and ends at point r in that layer. According to the propagation law of sound speed, let C and θ represent the speed and direction of the sound ray when the sound wave is received by the array, respectively, and let z represent the depth. Then, the gradient g of the sound speed change in the j-th layer is... j The calculation formula can be expressed as:

[0019] g j =(C j+1 -C j ) / (z j+1 -z j )

[0020] The length of the arc segment that the beam traverses in the j-th layer is ΔS. i =R i (θ i+1 -θ i The vertical displacement Δ of the j-th layer of sound ray zj Horizontal displacement Δx j and propagation time t j for:

[0021]

[0022] Among them, t j R represents the propagation time of the sound ray in the j-th layer, j = 1, 2, 3, ..., i-1, where i represents the last layer of sound ray propagation. j This represents the radius of curvature corresponding to the j-th layer of sound path;

[0023] Step 5.5: Sum the propagation times within each layer and add them to the propagation delay t. b For comparison, the layer where the time limit is exceeded is considered as the i-th layer, and the remaining time is... Calculate the residual vertical displacement Δz corresponding to the sound ray. r Remaining horizontal displacement Δx r and remaining propagation time t r for:

[0024]

[0025] Among them, R i This represents the radius of curvature corresponding to the i-th layer of sound path. p represents the Snell constant; θ r θ represents the angle of incidence of the final sound ray. iG represents the angle of incidence of the i-th layer of sound. i This represents the gradient of the sound velocity within the i-th layer.

[0026] Step 5.6: Divide the entire water column into N layers. The total horizontal distance x and vertical distance z of the sound ray are respectively:

[0027]

[0028]

[0029] Step 5.7, the angle γ between the projection of the sound ray onto the plane and the horizontal x-axis is:

[0030]

[0031] The angle λ with the y-axis is 90° - γ

[0032] Where α and β are direction angles;

[0033] Step 5.8: Based on the horizontal displacement of the sound ray, the position of the underwater acoustic transponder when emitting the sound signal is obtained as (xcosγ, xcosλ, z).

[0034] The above-described ultra-short baseline positioning method based on timestamp-based two-way precise time delay measurement, specifically includes step 5.1:

[0035] Step 5.1.1: Establish a spatial coordinate system and determine the coordinates of the underwater acoustic transponder and acoustic transducer;

[0036] Step 5.1.2: Calculate the x-axis direction angle α and the y-axis direction angle β based on the location of the underwater acoustic transponder and the time delay difference of the received sound waves;

[0037] Step 5.1.3: Calculate the angle along the z-axis, i.e., the cosine of the grazing angle, based on the x-axis direction angle α and the y-axis direction angle β.

[0038] Step 5.1.4: Calculate the incident angle of the sound wave in the direction of the acoustic transducer array.

[0039] The beneficial effects of this invention are that it uses timestamp information combined with cross-correlation and the time reference chip to estimate the time delay on both sides. The approximate distance between the underwater operation unit and the surface ultra-short baseline platform is obtained by calculating the time delay using the timestamp sent by the platform and the time reference chip on the underwater operation unit. The underwater operation unit can send the current time information when it transmits its acoustic signal to the surface platform in the form of a timestamp to obtain more accurate data, thereby estimating the motion state of the underwater device and thus improving underwater acoustic positioning. Attached Figure Description

[0040] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0041] Figure 1 This is a schematic diagram of the ultra-short baseline positioning of the present invention;

[0042] Figure 2 This is a flowchart of the energy detection process of the present invention;

[0043] Figure 3 This is a schematic diagram of the beam length in the i-th layer arc segment according to an embodiment of the present invention;

[0044] Figure 4 This is a flowchart illustrating the internal working process of the underwater acoustic transponder of the present invention. Detailed Implementation

[0045] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0046] This embodiment discloses an ultra-short baseline positioning method based on timestamp-based two-way precise time delay measurement, including the following steps:

[0047] Step 1: The deck unit receives the pre-group code of the underwater acoustic transponder from the control terminal. The dedicated signal processor calculates and generates the corresponding response synchronization sequence and information sequence, and sends the positioning command to the acoustic transducer array.

[0048] Step 2: After receiving the encoded sequence and positioning command, the acoustic transducer array starts the transmitting module to send a wake-up signal and a modulated signal carrying timestamp information at fixed intervals, and at the same time turns on the receiving module.

[0049] Step 3: The underwater acoustic transponders in the same group within the area are awakened by the wake-up signal. After confirmation, they receive the timestamp information and calculate the one-sided propagation delay through their own calculations. Then, they calculate the approximate distance between themselves and the surface unit, transmit the spread spectrum signal, and transmit the modulated signal carrying the timestamp information in conjunction with the time reference chip.

[0050] Currently, common wake-up signal detection methods include energy detection, matched filtering detection, and cyclic statistics detection. Energy detection and matched filtering detection are widely used in underwater acoustic communication. Energy detection is the most widely used method because it does not require prior knowledge of the signal. It determines whether a preset threshold is exceeded by calculating the energy in the time or frequency domain over a period of time, making it simple and easy to implement.

[0051]

[0052] As shown in Equation 1, in the energy detection model, X(n) and W(n) represent the sampled values ​​of signal and noise in the channel, respectively, and n represents the number of sampling points. The total energy value of signal and noise must be greater than the energy value of noise only, as shown in Equation 2.

[0053] ε[(X(n)+W(n)) 2 ]=ε[X 2 (n)]+ε[W 2 (n)]>ε[W 2 (n)] (2)

[0054] Therefore, according to the energy detection formula, the time-domain expression of the detected signal energy is Formula 3:

[0055]

[0056] By comparing the signal with a preset threshold, it can be determined whether the detected signal within the sampling time is channel noise or a wake-up signal. Energy detection methods are suitable for determining any form of signal energy, but to improve detection accuracy, the underwater acoustic transponder uses frequency domain energy detection. It detects the total signal energy in a preset frequency band using a Fast Fourier Transform (FFT). The detection block diagram is shown below. Figure 2 As shown.

[0057] In step 3, after the underwater acoustic transponder is woken up, it demodulates the received timestamp signal to obtain the time information of the acoustic signal transmitted on the water, and subtracts the value obtained from its own time reference chip to obtain the precise propagation delay t. a The approximate distance between the underwater acoustic transponder and the surface platform is measured based on the current sound speed for underwater operations.

[0058] Step 4: After receiving the response signal, the acoustic transducer array samples and transmits it to a dedicated signal processor to complete the signal synchronization and demodulation to obtain the corresponding timestamp information, and calculate the time delay and phase information of each channel.

[0059] Step 5: The deck unit combines GPS, compass and sonic profiler data to calculate the geographic coordinates of each underwater acoustic transponder in the group, and performs a certain motion trajectory estimation based on the underwater working unit in motion state to complete the precise positioning.

[0060] The specific process of location calculation includes the following steps:

[0061] Step 5.1: Calculate the direction angles α and β, and the incident angle θ of the sound wave in the direction of the acoustic transducer array;

[0062] Ultra-short baseline positioning, such as Figure 1As shown, in this embodiment, acoustic transducers 1 and 2 are used as the x-axis, acoustic transducers 3 and 4 are used as the y-axis, and the center point of the line connecting them is used as the origin O, thus establishing a spatial coordinate system. The coordinates of the underwater acoustic transponder P are (x, y, z), the coordinates of acoustic transducer 1 are (d / 2, 0, 0), the coordinates of acoustic transducer 3 are (-d / 2, 0, 0), the coordinates of acoustic transducer 2 are (0, -d / 2, 0), and the coordinates of acoustic transducer 4 are (0, d / 2, 0).

[0063] Assume the time delay difference between acoustic transducer 1 and acoustic transducer 3 in receiving sound waves is The time delay difference between acoustic transducers 2 and 4 in receiving sound waves is If the target is far from the acoustic transducer array, according to the far-field plane wave assumption, we can obtain:

[0064]

[0065] By substituting the time delays between the base arrays calculated on the water, the magnitudes of α and β can be obtained, and from this, the angle in the Z direction, i.e., the grazing angle, can be derived. This allows us to obtain the incident angle of the sound wave in the direction of the array. Furthermore, by performing sound ray correction based on the sound velocity profile, this invention provides a more accurate propagation delay for sound ray correction.

[0066] Step 5.2: After the surface operating platform receives the timestamp sent by the underwater acoustic transponder, the transmission time t of the acoustic signal sent by the underwater acoustic transponder is obtained. down And based on its current signal reception time t up The difference yields the precise propagation delay t. b =t up -t down , used for calculating vocal correction parameters;

[0067] Step 5.3: Divide the sound velocity profile into N layers at equal intervals from the vertical depth of the water surface to the underwater acoustic transponder, with each layer having the same spacing, and treat the change in sound velocity as a linear change;

[0068] Step 5.4, based on the layered sound ray tracking in Step 5.3, the sound ray propagates in the i-th layer and ends at point r in that layer. According to the propagation law of sound speed, let C and θ represent the speed and direction of the sound ray when the sound wave is received by the array, respectively, and let z represent the depth. Then, the gradient g of the sound speed change in the j-th layer is... j The calculation formula can be expressed as:

[0069] g j =(C j+1 -C j ) / (z j+1 -z j )

[0070] The propagation direction and speed of sound waves satisfy Snell's law. Under the condition of a constant gradient change in sound speed, the actual propagation trajectory of the beam in the i-th layer is a continuous path corresponding to a certain radius of curvature R. i arc segment, p is Snell's constant. The sound velocity function of the ray tracking algorithm uses the Harmonic average sound velocity. It is assumed that the sound velocity has a constant gradient g within the i-th layer. i Changes, within its layer (z∈[z i , z i+1 The sound speed function C) i (z) is represented as:

[0071] C i (z)=C i +g i (z)(zz i )

[0072] The propagation time of sound in the i-th layer is:

[0073]

[0074] C i Substituting (z) and integrating, we get...

[0075] t i =(1 / g i )ln(C i+1 / C i ).

[0076] like Figure 3 As shown, the arc length traversed by the beam in the j-th layer is ΔS. i =R i (θ i+1 -θ i The vertical displacement Δz of the j-th layer of sound ray j Horizontal displacement Δx j and propagation time t j for:

[0077]

[0078] Among them, t j R represents the propagation time of the sound ray in the j-th layer, j = 1, 2, 3, ..., i-1, where i represents the last layer of sound ray propagation. j This represents the radius of curvature corresponding to the j-th layer of sound path;

[0079] Step 5.5: Sum the propagation times within each layer and add them to the propagation delay t. b For comparison, the layer where the time limit is exceeded is considered as the i-th layer, and the remaining time is... Calculate the residual vertical displacement Δz corresponding to the sound ray.r Remaining horizontal displacement Δx r and remaining propagation time t r for:

[0080]

[0081] Among them, R i This represents the radius of curvature corresponding to the i-th layer of sound path. p represents the Snell constant; θ r θ represents the angle of incidence of the final sound ray. i G represents the angle of incidence of the i-th layer of sound. i This represents the gradient of the sound velocity within the i-th layer.

[0082] Step 5.6: Divide the entire water column into N layers. The total horizontal distance x and vertical distance z of the sound ray are respectively:

[0083]

[0084]

[0085] Step 5.7, the angle γ between the projection of the sound ray onto the plane and the horizontal x-axis is:

[0086]

[0087] The angle λ with the y-axis is 90° - γ

[0088] Where α and β are direction angles;

[0089] Step 5.8: Based on the horizontal displacement of the sound ray, the position of the underwater acoustic transponder when emitting the sound signal is obtained as (xcosγ, xcosλ, z).

[0090] The above embodiments are merely exemplary embodiments of the present invention and are not intended to limit the present invention. The scope of protection of the present invention is defined by the claims. Those skilled in the art can make various modifications or equivalent substitutions to the present invention within its spirit and scope of protection, and such modifications or equivalent substitutions should also be considered to fall within the scope of protection of the present invention.

Claims

1. A method for ultra-short baseline positioning based on time-stamped two-way precise time delay measurement, characterized in that, It comprises the following steps: Step 1, the deck unit inputs the water acoustic transponder pre-grouping code from the control terminal, and a special signal processor calculates corresponding response synchronization sequence and information sequence, and sends a positioning instruction to the acoustic transducer array; Step 2, after the acoustic transducer array receives the coded sequence and the positioning instruction, the transmitting module is started to send the wake-up signal and the modulated signal carrying the time stamp information at a fixed interval, and the receiving module is started at the same time; Step 3, the water acoustic transponders in the same group in the region are awakened by the wake-up signal, receive the time stamp information after confirmation, and obtain the approximate distance between the water acoustic transponder and the water unit through self-solution after calculating the one-way propagation time delay, and then transmit the spread spectrum signal and the modulated signal carrying the time stamp information combined with the time reference chip; Step 4, after the acoustic transducer array receives the response signal, the signal is sampled and transmitted to the special signal processor, the corresponding time stamp information is obtained through synchronization and demodulation of the signal, and the time delay and phase information of each channel are calculated; Step 5, the deck unit calculates the geographic coordinates of each water acoustic transponder in the group combined with the GPS, compass and sound velocity profiler data information, and performs certain motion state trajectory estimation based on the underwater operating unit in the motion state to complete the accurate positioning.

2. The time-stamp based ultra-short baseline positioning method under double- trip precision time delay measurement according to claim 1, characterized in that, The wake-up signal detection method in step 3 is that the time domain expression of the detected signal energy is: Wherein, D(Y) represents the decision variable value, N represents the sampling number of the signal at the time of detection, n represents the sampling point number; Y(n)=W(n) represents the sampling value of the noise in the channel; when the detected signal energy value is greater than D(Y), the detected signal is the wake-up signal.

3. The time-stamp based ultra-short baseline positioning method under double- trip precision time delay measurement according to claim 1, characterized in that, After the underwater acoustic transponder is woken up in step 3, the underwater acoustic transponder demodulates the received timestamp signal to obtain time information when the acoustic signal is transmitted on water, and obtains the precise propagation time delay t by subtracting the value obtained by the time reference chip itself a , and calculates the approximate distance between the underwater acoustic transponder and the platform on water according to the current sound speed for underwater operation.

4. The timestamp-based ultra-short baseline positioning method under double- trip precision time delay measurement according to claim 1, characterized in that, The geographic coordinate calculation process of each water acoustic transponder in step 5 specifically comprises: Step 5.1, calculate the direction angles α, β and the incident angle θ of the sound wave in the direction of the acoustic transducer array; Step 5.2, after the waterborne platform receives the time stamp sent from the acoustic transponder, the sending time t of the acoustic transponder sending the acoustic signal is obtained down And according to the current received signal time t up The difference is obtained b = t up -t down , used for parameter calculation of the acoustic line correction algorithm; Step 5.3, divide the vertical depth from the water surface to the water acoustic transponder into N layers with equal intervals on the sound velocity profile, and the sound velocity change is regarded as linear change; Step 5.4, based on the layered sound ray tracking in Step 5.3, the sound ray propagates in the i-th layer and ends at point r in that layer. According to the propagation law of sound speed, let C and θ represent the speed and direction of the sound ray when the sound wave is received by the array, respectively, and let z represent the depth. Then, the gradient g of the sound speed change in the j-th layer is... j The calculation formula can be expressed as: g j = (C j+1 -C j ) / (z j+1 -z j ) The length of the arc segment experienced by the beam at the jth layer is ΔS j = R j ( sin θ j+1 - θ j ), the vertical displacement Δz j , horizontal displacement Δx j and propagation time t j of the jth layer acoustic ray are given by: wherein t j represents the propagation time of the sound ray in the jth layer, j = 1, 2, 3,..., i-1, i represents the last layer of sound ray propagation, R j represents the radius of curvature corresponding to the jth layer sound ray path; Step 5.5, add the propagation time within each layer, and the propagation delay t b Compare, and consider the layer where the excess time occurs as the ith layer, and the remaining time Calculate the remaining vertical displacement Δz corresponding to the sound ray r , the remaining horizontal displacement Δx r and the remaining propagation time t r are: wherein R i represents the radius of curvature corresponding to the i-th layer sound ray path, p represents the Snell constant; θ r represents the angle of incidence of the final sound ray, θ i represents the angle of incidence of the i-th layer sound ray, g i represents the variation gradient of the sound velocity within the i-th layer, Step 5.6, divide the whole water column into N layers, and the total sound line horizontal distance x and vertical distance z are respectively: Step 5.7, the angle γ between the projection of the sound line in the plane and the horizontal x axis direction is: And the angle λ between the projection of the sound line in the plane and the y axis direction is 90°-γ Wherein, α, β are direction angles; Step 5.8, according to the horizontal displacement of the sound line, the position of the water acoustic transponder when the sound signal is transmitted is (xcosγ, xcosλ, z).

5. The method of claim 4, wherein, The step 5.1 specifically comprises: Step 5.1.1, establish a space coordinate system to clearly define the coordinates of the water acoustic transponder and the acoustic transducer; Step 5.1.2, calculate the x-axis direction angle α and the y-axis direction angle β according to the position of the water acoustic transponder and the time delay of the received sound wave; Step 5.1.3, the angle of z-axis direction, i.e. the grazing angle cosine value, is calculated according to the direction angle a of x-axis and the direction angle β of y-axis, i.e. Step 5.1.4, calculating the angle of incidence of the acoustic wave in the direction of the acoustic transducer array

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